Granular absorbent, absorbent containing the absorbent, and absorbent articles using the absorbent.

Abstract

[Problem] To provide a granular absorbent that can produce an absorbent with excellent liquid absorption rate and reduced backflow. [Solution] A granular absorbent, characterized in that it is a granular absorbent with poly(meth)acrylate (salt)-based absorbent resin particles as the main component, the granular absorbent comprising: connecting pores, which are spaces communicating with the outside; and independent air bubbles, which are closed spaces not communicating with the outside, wherein the total volume fraction of the connecting pores is 10% by volume or more, and the total volume fraction of the independent air bubbles is 0.5% by volume or less.

Description

Technical Field

[0001] This invention relates to a granular absorbent with poly(meth)acrylate (salt) based absorbent resin particles as the main component, an absorbent containing the absorbent, and an absorbent article using the absorbent. Background Technology

[0002] Superabsorbent polymers (SAPs) are water-swellable and water-insoluble polymeric gelling agents. Granular absorbent agents with SAPs as the main component are used in various absorbent products, including diapers, sanitary napkins, adult incontinence products, soil conditioners for agriculture and horticulture, and industrial waterproofing agents. Various monomers and hydrophilic polymers have been proposed as raw materials for these superabsorbent polymers, but from a performance and cost perspective, poly(meth)acrylic acid (salt)-based superabsorbent polymers using (meth)acrylic acid and / or its salts as monomers are the most commonly used.

[0003] With the increasing demand for high-performance granular absorbents, primarily used in diapers, a variety of functional requirements (physical properties) are being placed on them. Specific examples of the physical properties of granular absorbents include absorption rate, absorbency ratio, absorbency ratio under pressure, liquid permeability, backflow, gel strength, water solubility, particle size distribution, urine resistance, antibacterial properties, impact resistance (damage resistance), powder flowability, deodorization, colorfastness (whiteness), and low dust content.

[0004] Taking disposable diapers as an example, improvements are needed to address leakage and skin inflammation as particulate absorbents (absorbent resins). For instance, if urine is difficult to absorb into the diaper, or if absorption by particulate absorbents is slow, leakage and skin inflammation are likely to occur. Therefore, it is believed that improving the absorbency of particulate absorbents and increasing their absorption speed will reduce diaper backflow and absorption time, thereby reducing leakage and skin inflammation.

[0005] For example, in order to improve the absorbency and water absorption rate of granular water-absorbing agents, a technique for improving the particle shape of water-absorbing resins has been proposed. Patent Document 1 discloses that water-absorbing resins obtained by foaming polymerization, which have open bubbles (spaces communicating with the outside) and closed bubbles (independent bubbles) (spaces not communicating with the outside), have excellent liquid permeability and water absorption rate.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2013 / 002387 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] However, while absorbents made using absorbent resins obtained through the technology described in Patent Document 1 achieve the effect of reducing reflux, they have the following problems: in the case of high-concentration liquids (e.g., menstrual blood) or absorbents without pulp, the effect may not be sufficient in terms of liquid absorption rate and reflux.

[0011] Therefore, the present invention aims to provide a particulate absorbent that can produce an absorbent with excellent liquid absorption rate and reduced backflow.

[0012] In addition, another object of the present invention is to provide an absorbent that has a superior absorption rate of liquid compared to the past and reduces backflow.

[0013] Solution for solving the problem

[0014] The inventors conducted in-depth research in view of the above-mentioned problems. As a result, they discovered a granular absorbent with poly(meth)acrylate (salt) based absorbent resin particles as the main component. The granular absorbent comprises: interconnecting pores, which are spaces communicating with the outside; and independent air bubbles, which are closed spaces not communicating with the outside. The total volume fraction of the interconnecting pores is 10% by volume or more, and the total volume fraction of the independent air bubbles is 0.5% by volume or less. This solves the above-mentioned problems, thus completing the present invention.

[0015] The effects of the invention

[0016] According to the present invention, a particulate desiccant is provided that enables the production of an absorbent with excellent liquid inhalation rate and reduced backflow. That is, according to the present invention, a particulate desiccant is provided that imparts excellent liquid inhalation rate and backflow within an absorbent. Attached Figure Description

[0017] Figure 1 A front view schematic diagram illustrating the voids (connecting pores and independent air bubbles) formed in a granular absorbent according to one embodiment of the present invention.

[0018] Figure 2A A partially cut-out side view showing an example of a gel crushing apparatus (meat grinder / screw extruder) used in the manufacturing method of an embodiment of the present invention.

[0019] Figure 2B For illustrative purposes only Figure 2A A diagram of a support installed on the extrusion port in a gel pulverizing device.

[0020] Figure 3This is a partially cut-out side view showing an example of a gel pulverizing apparatus (multi-shaft mixer) used in the manufacturing method of an embodiment of the present invention.

[0021] Figure 4 for Figure 3 An enlarged view of the gel crushing device (view of the central part of the main body from above).

[0022] Figure 5 A diagram illustrating the classification of gel granulation devices with extrusion action and porous plates.

[0023] Figure 6 A diagram illustrating the extrusion section of a gel granulation device.

[0024] Figure 7 A schematic diagram illustrating the structure of a gel granulation device (a screw-type front extrusion device with a spherical (dome-shaped) mold) according to one embodiment is provided.

[0025] Figure 8 This is a partially cut-out side view showing an example of a drying apparatus (rotary heating apparatus with heating tubes) used in the manufacturing method according to an embodiment of the present invention.

[0026] Figure 9 This is a schematic diagram showing the cross-section of an absorber obtained by cutting it along the width direction in the absorber according to the first embodiment of the present invention.

[0027] Figure 10 To indicate along Figure 9 A schematic diagram of the cross-section of line AA.

[0028] Figure 11 This is a schematic diagram illustrating other embodiments of the voids in the absorber of the first embodiment of the present invention.

[0029] Figure 12 To indicate along Figure 9 A schematic diagram of the cross-section of line AA, illustrating other embodiments of the gap.

[0030] Figure 13 To indicate along Figure 9 A schematic diagram of the cross-section of line AA, illustrating other embodiments of the gap.

[0031] Figure 14 To indicate along Figure 9 A schematic diagram of the cross-section of line AA, illustrating other embodiments of the gap.

[0032] Figure 15This is a schematic diagram showing the cross-section of an absorber obtained by cutting it along the width direction in the absorber according to the second embodiment of the present invention.

[0033] Figure 16 The diagram shown is a schematic diagram illustrating another embodiment of the absorber in the second embodiment of the present invention, and is a cross-section of the absorber obtained by cutting along the width direction.

[0034] Figure 17 This is a schematic diagram showing a cross-section of an absorber according to one embodiment of the present invention.

[0035] Figure 18 This is an evaluation device used to determine the aspiration time and reflux rate of a liquid.

[0036] Figure 19 A graph illustrating the relationship between the interconnected pores and individual air bubbles in the absorbent resin particles produced in the examples and comparative examples.

[0037] Figure 20 Top and front views of the liquid injection cylinder used for evaluating the return flow rate.

[0038] Figure 21 The diagram illustrates a scenario where a liquid injection cylinder is placed on the absorber used in the embodiments of this application during reflux flow evaluation. It is a schematic diagram viewed from the length direction of the absorber and a schematic diagram viewed from the width direction of the absorber.

[0039] Figure 22 A front view showing a scenario where a funnel is used to add an aqueous sodium chloride solution from a liquid injection cylinder to an absorber during reflux flow evaluation.

[0040] Figure 23 This is a schematic diagram illustrating a scenario where a liquid injection tube is placed on the absorber used in an embodiment of this application during reflux flow evaluation. Detailed Implementation

[0041] The invention will now be described with reference to the preferred mode. Throughout this specification, unless otherwise specified, the singular form should be understood to also include the concept of its plural form. Therefore, unless otherwise specified, articles in the singular form (e.g., "a," "an," "the," etc. in English) should also be understood to include the concept of their plural forms. Furthermore, unless otherwise specified, the terminology used in this specification should be understood to be used according to its common meaning in the art. Therefore, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, this specification (including definitions) takes precedence. The invention is not limited to the embodiments described below, and various modifications can be made within the scope of the claims.

[0042] [1] Definition of terminology

[0043] [1-1] "Water-absorbing resin"

[0044] In this invention, "water-absorbing resin" refers to a water-swellable and water-insoluble polymeric gelling agent that meets the following physical properties. Specifically, in this specification, "water-absorbing resin" refers to a polymeric gelling agent with a CRC (centrifuge retention capacity) (water swelling) of 5 g / g or more as specified in NWSP 241.0.R2(15) and an Ext (water-soluble component) of 50% by mass or less as specified in NWSP 270.0.R2(15). It should be noted that "NWSP" will be explained later.

[0045] The aforementioned water-absorbing resin can be designed according to its use and purpose, and is not particularly limited. It is preferably a hydrophilic crosslinked polymer formed by crosslinking and polymerizing unsaturated monomers with carboxyl groups. In addition, it is not limited to the form of a crosslinked polymer in total amount. As long as the above-mentioned physical properties (CRC, Ext) meet the above-mentioned numerical range, it can also be a composition containing additives, etc.

[0046] The "water-absorbing resin" in this invention can be formed by surface crosslinking (also known as post-crosslinking, secondary crosslinking) or without surface crosslinking. Surface crosslinking is preferred. It should be noted that in this specification, "water-absorbing resin particles" (sometimes also called "water-absorbing resin powder") refers to powdered water-absorbing resin, preferably water-absorbing resin adjusted to a specified solid content (moisture content) and particle size (particle diameter). In addition, water-absorbing resin particles that have undergone a specified surface crosslinking treatment are sometimes also referred to as "surface-crosslinked (post-crosslinked) water-absorbing resin particles" or "granular water absorbent (water absorbent)".

[0047] [1-2] "Poly(meth)acrylate (salt) based water-absorbing resin"

[0048] In this invention, "poly(meth)acrylate (salt)" refers to poly(meth)acrylate and / or its salts, and "poly(meth)acrylate (salt)-based superabsorbent resin" refers to a crosslinked polymer that contains, in the form of repeating units, a structure derived from (meth)acrylate and / or its salts (hereinafter also referred to as "(meth)acrylate (salt)") as the main component and a structure derived from an internal crosslinking agent as any component. Preferably, the poly(meth)acrylate (salt)-based superabsorbent resin is a crosslinked polymer containing a structure derived from (meth)acrylate (salt) as a repeating unit, having an internal crosslinking structure, and having undergone surface crosslinking.

[0049] The term "main component" refers to the amount (content) of (meth)acrylate (salt) relative to the total monomers used in the polymerization (excluding crosslinking agents), which is preferably 50 mol% to 100 mol%, more preferably 70 mol% to 100 mol%, further preferably 90 mol% to 100 mol%, and particularly preferably substantially 100 mol%.

[0050] Here, "poly(meth)acrylate (salt)" may be unneutralized, but is preferably partially or completely neutralized poly(meth)acrylate (salt), more preferably a monovalent salt, further preferably an alkali metal salt or ammonium salt, even more preferably an alkali metal salt, and particularly preferably a sodium salt.

[0051] Poly(meth)acrylate (salt) based water-absorbing resin is in granular form (also known as: powder) in granular water-absorbing agents. In this specification, the granular poly(meth)acrylate (salt) based water-absorbing resin is referred to as "poly(meth)acrylate (salt) based water-absorbing resin granules", but it is sometimes simply referred to as "poly(meth)acrylate (salt) based water-absorbing resin".

[0052] [1-3] "Granular water absorbent"

[0053] In this specification, the desiccant contains poly(meth)acrylate (salt) based desiccant particles as its main component. In this specification, granular desiccant refers to a granular (also known as powder) desiccant, whether it is a single granular desiccant or multiple granular desiccant particles. "Granular" means having a granular form; a particle refers to a small, measurable object that is solid or liquid (JIS Industrial Terminology Dictionary, 4th Edition, p. 2002). It should be noted that in this specification, granular desiccant is sometimes simply referred to as desiccant.

[0054] It should be noted that aqueous liquids are not limited to water, but can include urine, blood, sweat, feces, waste liquid, moisture, vapor, ice, mixtures of water with organic and / or inorganic solvents, rainwater, groundwater, etc., as long as they contain water, there are no particular limitations. Preferred examples include bodily fluids such as urine, menstrual blood, and sweat.

[0055] The granular absorbent of the present invention is suitable for use as a sanitary material for absorbing aqueous liquids. The granular absorbent of the present invention uses poly(meth)acrylate (salt)-based absorbent resin particles as the main component. In other words, in the granular absorbent, the poly(meth)acrylate (salt)-based absorbent resin particles preferably comprise 60-100% by mass, 70-100% by mass, 80-100% by mass, or 90-100% by mass. Furthermore, the granular absorbent optionally includes other absorbent resin particles, water, and / or water-insoluble inorganic particles as additives. The suitable water content of the granular absorbent is 0.2-30% by mass. That is, absorbent resin compositions formed by integrating these components also fall under the category of granular absorbents. Furthermore, the granular absorbent used in this invention preferably exhibits excellent handling properties under high humidity conditions (specifically, the granular absorbent fluidity (absorption clumping rate) described in WO2017 / 170605 is preferably 30% or less, more preferably 20% or less, further preferably 10% or less, and most preferably 5% or less).

[0056] It should be noted that the upper limit of the poly(meth)acrylate (salt)-based water-absorbing resin particles in the water-absorbing agent is 99% by mass, further 97% by mass, and particularly about 95% by mass, and preferably further contains water and / or the additives (water-insoluble inorganic particles) described later.

[0057] Furthermore, in the granular water-absorbing agent of the present invention, poly(meth)acrylate (salt) based water-absorbing resin particles are used as the main component, but the granular water-absorbing agent may contain other water-absorbing resins. Examples of other water-absorbing resins include polysulfonic acid (salt) based water-absorbing resins, maleic anhydride (salt) based water-absorbing resins, polyacrylamide based water-absorbing resins, polyvinyl alcohol based water-absorbing resins, polyethylene oxide based water-absorbing resins, polyaspartic acid (salt) based water-absorbing resins, polyglutamic acid (salt) based water-absorbing resins, polyalgic acid (salt) based water-absorbing resins, starch based water-absorbing resins, and cellulose based resins.

[0058] [1-4] "Absorbent"

[0059] In this invention, "absorbent" refers to a structure having a first substrate with a liquid-absorbing surface formed on its surface for direct liquid absorption, and an absorbent layer disposed on the back side of the first substrate. The absorbent layer is formed by loading and / or sandwiching particulate absorbent (water-absorbing resin) onto one or more substrates and / or fibers (preferably hydrophilic fibers). In addition to particulate absorbent, the absorbent layer may also contain fibrous materials such as hydrophilic fibers. Furthermore, when the absorbent layer contains both particulate absorbent and hydrophilic fibers, examples of the absorbent structure include a structure formed by uniformly mixing particulate absorbent and hydrophilic fibers, and / or a structure formed by sandwiching particulate absorbent between layers of hydrophilic fibers. It should be noted that the absorbent structure can be integrated by further sandwiching the absorbent layer containing particulate absorbent and hydrophilic fibers with nonwoven fabric, tissue paper, etc., but is not limited to these illustrated structures. Furthermore, an absorbent layer obtained by directly fixing granular absorbent to sheet-like substrates such as nonwoven fabrics and thin cotton paper and then composites them (i.e., an absorbent layer containing granular absorbent and sheet-like substrate) without hydrophilic fibers can also be used as the absorbent of the present invention.

[0060] [1-5] Definition of evaluation methods

[0061] "NWSP" stands for "Non-Woven Standard Procedures-Edition 2015." EDANA (European Disposables and Nonwovens Association) and INDA (Association of the Nonwoven Fabrics Industry) are a unified evaluation method for nonwoven fabrics and their products, jointly issued by the United States and Europe, and describe the standard method for determining the properties of absorbent resins. Unless otherwise specified, the physical properties of absorbent resins in this invention are determined according to "Non-Woven Standard Procedures-Edition 2015." For evaluation methods not described in NWSP, the methods and conditions described in the examples are used for determination.

[0062] [1-5-1] "CRC" (NWSP 241.0.R2(15))

[0063] "CRC" is short for Centrifuge Retention Capacity, which refers to the water absorption ratio (sometimes called "water absorption ratio") of granular superabsorbent polymers (hygroscopic resins) under no pressure. Specifically, it refers to the water absorption ratio (unit: g / g) after immersing 0.2g of granular superabsorbent polymer (hygroscopic resin) in a nonwoven bag, allowing it to freely swell in a significantly excess 0.9% (w / w) sodium chloride aqueous solution for 30 minutes, and then centrifuging (250G) to remove water for 3 minutes. It should be noted that for hydrogels after polymerization and / or gel pulverization, 0.4g of hydrogel is used, the measurement time is changed to 24 hours, and solids content correction is performed to determine the CRC.

[0064] [1-5-2] "PSD" (NWSP 220.0.R2(15))

[0065] "PSD" is short for Particle Size Distribution, which refers to the particle size distribution of granular superabsorbent polymers (water-absorbing resins) determined by sieve grading. It should be noted that the mass-average particle size (D50) and the logarithmic standard deviation (σζ) of the particle size distribution are determined using a vibratory classifier (power supply 60 Hz) in the same manner as described in paragraphs 27-28 (3) of US Patent No. 7,638,570, regarding mass-average particle size (D50) and the logarithmic standard deviation of particle size distribution.

[0066] [1-5-3] "AAP" (NWSP 242.0.R2(15))

[0067] "AAP" is short for Absorption Against Pressure, which refers to the water absorption ratio of granular water absorbent (water-absorbing resin) under pressure.

[0068] Specifically, AAP 0.3 psi (2.06 kPa) refers to: 0.9 g of granular desiccant or desiccant resin relative to a significant excess of 0.9 wt% sodium chloride aqueous solution at 2.06 kPa (21 g / cm³). 2 The water absorption ratio (in g / g) after swelling for 1 hour under a load of 0.3 psi. It should be noted that sometimes the load condition is changed to 4.83 kPa (49 g / cm³). 2 The absorbance was measured at 0.7 psi. In this case, it is recorded as AAP (4.83 kPa). In this invention, the absorbance ratio (unit: g / g) is measured using AAP 0.3 psi (2.06 kPa) under the conditions described in the examples.

[0069] [1-5-4] "Moisture Content" (NWSP 230.0.R2(15))

[0070] "Moisture Content" refers to the moisture content defined by the loss on drying of the granular water-absorbing agent (water-absorbing resin). Specifically, it refers to the value (unit: mass%) calculated from the loss on drying of 4.0 g of granular water-absorbing agent (water-absorbing resin) at 105°C for 3 hours. It should be noted that in this invention, for the dried granular water-absorbing agent (water-absorbing resin), the loss on drying is defined by 1.0 g of granular water-absorbing agent (water-absorbing resin) at 180°C for 3 hours; for the hydrogel before drying, the loss on drying is defined by 2.0 g of hydrogel at 180°C for 24 hours.

[0071] [1-6] Others

[0072] In this specification, the range “X~Y” means “above X and below Y”. Furthermore, unless otherwise specified, the unit of mass “t (ton)” means “Metric ton”, and “ppm” means “mass ppm” or “weight ppm”. Moreover, “mass” and “weight”, “parts by mass” and “parts by weight”, and “mass%” and “weight%” are treated as synonyms. Additionally, “~acid (salt)” means “~acid and / or its salt”, and “(meth)acrylic acid” means “acrylic acid and / or methacrylic acid”.

[0073] Additionally, for convenience, "liter" is sometimes written as "l" or "L", and "weight %" is written as "wt%". Furthermore, in cases of determining trace components, the detection limit is expressed as ND (Not Detected).

[0074] [2] "Granular water absorbent"

[0075] [2-1] Connecting holes and independent air bubbles

[0076] The granular absorbent of the present invention is a granular absorbent with poly(meth)acrylate (salt)-based absorbent resin particles as the main component. The granular absorbent contains interconnected pores and independent air bubbles, wherein the total volume fraction of interconnected pores is 10% by volume or more, and the total volume fraction of independent air bubbles is 0.5% by volume or less. The poly(meth)acrylate (salt)-based absorbent resin particles are as described in [1-2]. Hereinafter, the poly(meth)acrylate (salt)-based absorbent resin particles contained in the granular absorbent are sometimes simply referred to as "absorbent resin particles".

[0077] In this invention, "connecting hole" (also called "Cavity") refers to, for example, Figure 1As shown as a connecting hole 1a, a cavity (exposed on the surface of the granular absorbent 1) is a space (cavity) formed in the granular absorbent 1 that connects to the outside of the granular absorbent 1. That is, a "connecting hole" is a space (cavity) existing in the granular absorbent that communicates with the outside. This cavity also includes depressions, grooves, etc., formed on the surface of the granular absorbent 1. Specifically, a connecting hole refers to a hole, through-hole, depression, groove, etc., that can be identified on the surface of the granular absorbent 1 when three-dimensional image data is acquired using a microfocus X-ray CT system (inspeXio SMX-100CT / manufactured by Shimadzu Corporation) under the following conditions, and when the three-dimensional image data is analyzed using high-speed three-dimensional analysis software (TRI / 3D-VOL-FCS64 / RATOC Systems Engineering, Inc.) under the conditions described in the embodiment.

[0078] In this invention, "independent air bubble" (also called "Void") refers to, for example, Figure 1 As shown as an independent bubble 1b, an independent bubble is a void (existing inside the granular absorbent 1) that is not connected to the outside of the granular absorbent 1 and exists within the void formed in the granular absorbent 1. That is, an "independent bubble" is a closed space (void) existing in the granular absorbent that is not connected to the outside. Specifically, an independent bubble refers to a void such as a bubble that can be identified inside the granular absorbent 1 when three-dimensional image data is acquired using a microfocus X-ray CT system (inspeXio SMX-100CT / manufactured by Shimadzu Corporation) under the following conditions and analyzed using high-speed three-dimensional analysis software (TRI / 3D-VOL-FCS64 / RATOC Systems Engineering, Inc.) under the conditions described in the examples.

[0079] It should be noted that in the granular water-absorbing agent of the present invention, the particles containing interconnected pores and independent air bubbles are mainly water-absorbing resin particles, but other particles contained in the granular water-absorbing agent may further contain interconnected pores and independent air bubbles. In the granular water-absorbing agent (among all the components constituting the granular water-absorbing agent), as a whole, interconnected pores and independent air bubbles occupy a defined volume range, thereby exerting the effect of the present invention. In addition, in the embodiments described later, the total volume fraction of interconnected pores and the total volume fraction of independent air bubbles are measured using the granular water-absorbing agent, but in the method for measuring the total volume fraction of interconnected pores and the total volume fraction of independent air bubbles of the present invention, whether only water-absorbing resin particles are used as the measurement object or the granular water-absorbing agent is used as the measurement object, the values ​​of the total volume fraction of interconnected pores and the total volume fraction of independent air bubbles remain almost unchanged.

[0080] In the embodiments of this application, granular absorbents were prepared with and without additives (DTPA or EDTMP as chelating agents, tricalcium phosphate, hydrotalcite or silica particles as inorganic microparticles, and sodium sulfite as an inorganic reducing agent) relative to the absorbent resin particles. For example, when comparing Examples 1-1 and 1-11, the presence or absence of additives differed in the granular absorbents, but the total volume fraction of interconnected pores and the total volume fraction of independent bubbles remained unchanged. This is believed to be because the resolution of X-ray CT measurements is 10 μm (showing a resolution of 10 μm due to a voxel size of 0.01 mm / voxel), and the size of the inorganic microparticles is less than that; the chelating agents and inorganic reducing agents are usually added in the form of aqueous solutions, thus integrating with the absorbent resin particles; and the amount of additives added is also less than 1% relative to the absorbent resin particles; therefore, the total volume fraction of interconnected pores and the total volume fraction of independent bubbles do not change regardless of whether additives are added.

[0081] The following description of interconnected pores and independent air bubbles is based on the interconnected pores and independent air bubbles of granular water-absorbing agents, but the same understanding applies to water-absorbing resin particles.

[0082] "Total volume fraction of interconnected pores" refers to the ratio of the total volume of interconnected pores in the granular absorbent to the total volume of the granular absorbent, specifically calculated using the method described in the following embodiments. "Total volume fraction of independent air bubbles" refers to the ratio of the total volume of independent air bubbles in the granular absorbent to the total volume of the granular absorbent, specifically calculated using the method described in the following embodiments.

[0083] Regarding the granular superabsorbent of this embodiment, the total volume fraction of interconnected pores is 10% or more, and the total volume fraction of independent bubbles is 0.5% or less, resulting in excellent liquid absorption rate and reduced backflow. In other words, the granular superabsorbent of this embodiment can rapidly absorb liquid with minimal backflow after absorption. When the total volume fraction of interconnected pores in the granular superabsorbent is less than 10% by volume, the absorption rate of high-viscosity liquids by the granular superabsorbent decreases, and the backflow rate significantly increases (Comparative Examples 1-7). When the total volume fraction of independent bubbles in the granular superabsorbent exceeds 0.5% by volume, the liquid absorption rate and backflow rate in the granular superabsorbent significantly increase (Comparative Examples 1-1 to 1-9).

[0084] Considering the practical use of absorbent articles containing granular absorbents, various usage scenarios are envisioned, such as urination occurring while under body weight, swelling during urination without pressure but with pressure due to movement, or absorption of blood, etc. The inventors have discovered that in the subject of "an absorbent body (granular absorbent) capable of rapidly absorbing liquid with minimal backflow after absorption," the shape of the granular absorbent (absorbent resin particles), i.e., the ratio of the interconnecting pores to the individual air bubbles in the granular absorbent (absorbent resin particles), is important, and they focus on the total volume fraction of the interconnecting pores and the total volume fraction of the individual air bubbles in the granular absorbent (absorbent resin particles).

[0085] Particulate absorbents (absorbent resin particles) with a large total volume fraction of interconnected pores tend to have a larger specific surface area. Since the total volume fraction of interconnected pores cannot be fully evaluated solely by measuring specific surface area, the volume of the concave portions on the particle surface is also evaluated. When the total volume fraction of interconnected pores reaches 10% by volume or more, the rate at which the absorbent resin particles themselves absorb liquid increases through capillary action. Furthermore, the gaps between the gel particles during the swelling of the absorbent resin particles also increase, resulting in an increase in the amount of liquid retained in the interconnected pore volume portion of the gel particles and in the gaps between the gel particles. As a result, the absorbency of the particulate absorbent (absorbent resin particles) is improved, and the liquid absorption rate is increased. Therefore, the particulate absorbent of the present invention exhibits excellent liquid absorption rate even when used in absorbents with a low ratio of fibrous materials such as pulp, and in absorbent articles such as thin diapers containing such absorbents. For granular superabsorbent polymers (water-absorbing resin particles) with a total volume fraction of independent air bubbles of 0.5% or less, when the granular superabsorbent polymers (water-absorbing resin particles) absorb liquid, there is no obstruction to liquid absorption caused by independent air bubbles. Therefore, the absorbency of the granular superabsorbent polymers (water-absorbing resin particles) is improved, and the liquid absorption rate is increased. In addition, the situation where absorbed liquid enters the independent air bubbles is reduced, and the liquid is more easily absorbed by the superabsorbent resin itself. As a result, the situation where absorbed liquid returns is reduced, and the backflow rate is reduced. Therefore, it can be considered that by setting the ratio of interconnected pores and independent air bubbles in the granular superabsorbent polymers (water-absorbing resin particles) within a specified range, it is possible to achieve the effect of rapid liquid absorption and low backflow rate after absorption.

[0086] In one embodiment, the total volume fraction of the interconnected pores in the granular superabsorbent (water-absorbing resin particles) is preferably more than 10% by volume, more preferably 11% by volume or more, further preferably 12% by volume or more, particularly preferably 13% by volume or more, and most preferably 14% by volume or more. Regarding the upper limit of the total volume fraction of the interconnected pores in the granular superabsorbent (water-absorbing resin particles), if the total volume fraction of the interconnected pores in the granular superabsorbent (water-absorbing resin particles) is too large, the mechanical strength of the granular superabsorbent (water-absorbing resin particles) itself and the swollen gel will be significantly reduced. Therefore, it is preferably 40% by volume or less, more preferably 35% by volume or less, further preferably 30% by volume or less, and particularly preferably 25% by volume or less. In one embodiment, the total volume fraction of independent air bubbles in the granular superabsorbent (water-absorbing resin particles) is preferably 0.5% by volume or less, more preferably 0.4% by volume or less, and further preferably 0.3% by volume or less. The lower limit of the total volume fraction of independent air bubbles in the granular superabsorbent (water-absorbing resin particles) is not particularly limited, but is preferably 0.01% by volume or more.

[0087] It should be noted that in this invention, "able to quickly absorb liquid and with low reflux after absorption" refers to the evaluation of the absorbent body (absorbent sheet) obtained by laminating an absorbent layer containing granular absorbent, pulp, etc., using nonwoven fabric or the like, and not the evaluation of the granular absorbent itself. Furthermore, in the reflux evaluation, the granular absorbent (water-absorbing resin particles) contained in the absorbent body is not limited to a saturated state.

[0088] Furthermore, the evaluation methods for "liquid absorption rate" and "re-wet flow rate" in this invention differ from those commonly used for evaluating the physical properties of granular absorbents (absorbent resin particles), which typically involve measuring the absorption rate (or absorption time or "absorption speed") and "re-wet flow rate" (sometimes also called backflow or re-wet). In conventional evaluation methods, an absorbent body made of granular absorbent (absorbent resin particles) is placed on a flat surface, and the absorption rate (i.e., "absorption rate") and re-wet flow rate are measured for the absorbent body placed on the flat surface. In this invention, the absorption time (liquid absorption rate) and re-wet flow rate are measured for an absorbent body arranged in a U-shape. That is, the evaluation is performed under conditions simulating actual use as a hygiene product such as a diaper or sanitary pad. It should be noted that in this specification, the liquid absorption rate is expressed as liquid absorption time [seconds]. Additionally, the liquid used in measuring the liquid absorption rate and re-wet flow rate in this invention is a high-viscosity solution (e.g., a solution with a viscosity of 5 mPa·s at 23°C). In this specification, the liquid absorption rate and reflux rate calculated using a U-shaped evaluation with a high-viscosity solution (based on an evaluation of an absorber configured in a U-shape) are referred to as "spot absorption." Excellent spot absorption means a high liquid absorption rate and a low reflux rate. In this specification, the time for absorbing the liquid using a 0.9% sodium chloride aqueous solution at 23°C on an absorber configured on a platform is referred to as "absorption rate," and the time for absorbing the liquid using a high-viscosity solution on an absorber configured in a U-shape is referred to as "liquid absorption rate." The "liquid absorption rate" is sometimes simply referred to as "absorption rate" as an evaluation of the physical properties of a typical absorber.

[0089] When liquid is locally introduced into a portion of the absorbent, the introduced liquid is gradually absorbed while diffusing on the surface and inside the absorbent. Therefore, the rate of liquid absorption into the absorbent is related to both osmosis-based absorption (longitudinal / thickness direction) and diffusion-based absorption (lateral / surface direction). On the other hand, by making the absorbent U-shaped, liquid diffusion is restricted, thus it is presumed that osmosis-based absorption becomes the main absorption pathway. That is, by using a U-shaped evaluation, the evaluation is conducted under conditions where liquid absorption into the absorbent caused by diffusion due to the liquid's own weight and the suppression of liquid backflow are limited, allowing for a more significant evaluation of the water absorption performance (liquid absorption rate, backflow rate) of particulate desiccant present in the thickness direction.

[0090] Furthermore, a high-viscosity solution is used in the evaluation of this invention. Typically, an aqueous solution of approximately 0.5% by mass, such as physiological saline or artificial urine, is used to evaluate the absorption performance of absorbents, with a viscosity of approximately 1 mPa·s at 23°C. This invention uses a high-viscosity solution, resulting in a low diffusion rate due to its own weight. Therefore, compared to physiological saline or artificial urine, the liquid introduced into the absorbent is less likely to diffuse along the lateral / planar direction of the absorbent, leading to localized liquid retention at the location where the liquid was introduced. Therefore, it is believed that the absorbent evaluation of this invention can more significantly evaluate the absorption performance of the absorbent.

[0091] [2-2] CRC (Centrifuge Retention Capacity)

[0092] The CRC of the granular absorbent of the present invention is preferably 25 g / g or more, more preferably 30 g / g or more, further preferably 32 g / g or more, and even more preferably 33 g / g or more. With a CRC of 25 g / g or more, the absorption capacity becomes appropriate, ensuring the performance of the absorbent as a sanitary product such as a diaper. Furthermore, the CRC of the granular absorbent of the present invention is preferably 70 g / g or less, more preferably 60 g / g or less, further more preferably 50 g / g or less, and particularly preferably 40 g / g or less. With a CRC of 70 g / g or less, the absorption rate of bodily fluids such as urine and blood is maintained, thus making it suitable for use in high-absorbency diapers and the like. It should be noted that the CRC can be controlled by the type and amount of the internal crosslinking agent. It should also be noted that the CRC of the absorbent resin particles contained in the granular absorbent of the present invention is preferably within the same numerical range as that of the granular absorbent.

[0093] [2-3] Absorption Ratio under Pressure (AAP)

[0094] The AAP (Acid-Adjusted Pressure) of the granular absorbent of the present invention at 0.3 psi (2.06 kPa) is preferably 20 g / g or more, more preferably 24 g / g or more, further preferably 26 g / g or more, even more preferably 28 g / g or more, particularly preferably 29 g / g or more, and most preferably 30 g / g or more. There is no particular limitation on the upper limit, but it is preferably 40 g / g or less. The effects of the present invention are further enhanced by using an AAP of 0.3 psi (2.06 kPa) within the above range. Furthermore, diapers manufactured using the granular absorbent with an AAP of 0.3 psi (2.06 kPa) within the above range exhibit excellent urine absorption capacity from the pulp, reducing backflow and thus inhibiting skin inflammation and leakage. It should be noted that the AAP can be controlled by adjusting the particle size, changing the surface crosslinking agent, etc. It should also be noted that the AAP of 0.3 psi (2.06 kPa) in the absorbent resin particles contained in the granular absorbent of the present invention is preferably within the same numerical range as that of the granular absorbent.

[0095] [2-4] Moisture content and solid content

[0096] The moisture content of the granular water-absorbing agent of the present invention is preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 6% by mass or more, particularly preferably 7% by mass or more, and most preferably 8% by mass or more. The upper limit of the moisture content of the granular water-absorbing agent is preferably 15% by mass or less, more preferably 14% by mass or less, further preferably 13% by mass or less, and particularly preferably 12% by mass or less. By setting the moisture content within the above range, a water-absorbing agent with excellent powder properties (e.g., flowability, transportability, damage resistance, etc.) can be obtained. Furthermore, the solid content of the granular water-absorbing agent of the present invention is preferably 85% by mass to 99% by mass, more preferably 86% by mass to 95% by mass, further preferably 87% by mass to 94% by mass, particularly preferably 88% by mass to 93% by mass, and most preferably 88% by mass to 92% by mass. It should be noted that the moisture content and solid content of the water-absorbing resin particles contained in the granular water-absorbing agent of the present invention are also preferably within the same numerical range as those of the granular water-absorbing agent.

[0097] [2-5] Particle size

[0098] The mass-average particle size (D50) of the granular superabsorbent of the present invention is preferably 200 μm or more, more preferably 200 μm to 600 μm, further preferably 230 μm to 550 μm, and particularly preferably 250 μm to 500 μm. Furthermore, the proportion of particles with a particle size of less than 106 μm in the granular superabsorbent is preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 6% by mass or less. Additionally, the proportion of particles with a particle size of more than 850 μm in the granular superabsorbent is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 1% by mass or less. The granular superabsorbent preferably contains 90% by mass or more, more preferably 95% by mass or more, further preferably 97% by mass or more, and particularly preferably 99% by mass or more of particles with a particle size of 106 μm to 850 μm. Ideally, the granular superabsorbent contains 100% by mass of particles with a particle size of 106 μm to 850 μm. The granular absorbent of the present invention preferably contains 30% by mass or more, more preferably 35% by mass or more, further preferably 36% by mass or more, and particularly preferably 37% by mass or more of particles with a particle size of 250 μm to 425 μm. There is no particular upper limit to the proportion of particles with a particle size of 250 μm to 425 μm in the granular absorbent. In practice, as an embodiment, it can be 90% by mass or less, 85% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, or 65% by mass or less. By using the above-mentioned range of particles with a particle size of 250 μm to 425 μm, the effects of the present invention are further enhanced. The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and further preferably 0.27 to 0.35. It should be noted that the particle size of the absorbent resin particles contained in the granular absorbent of the present invention is also preferably within the same numerical range as that of the granular absorbent.

[0099] [2-6] Absorption time of high viscosity liquid

[0100] The high-viscosity liquid absorption time refers to the absorption time of a superabsorbent resin when a high-viscosity liquid is used instead of physiological saline. The high-viscosity liquid absorption time is determined according to the standard described in JISK 7224-1996 "Explanation of the Test Method for Water Absorption Rate of Superabsorbent Resins", except that the physiological saline used is replaced with a high-viscosity test liquid prepared by the method shown in the examples.

[0101] The absorption time of the high-viscosity liquid by the granular water absorbent of the present invention is preferably 140 seconds or less, more preferably 135 seconds or less, further preferably 130 seconds or less, even more preferably 120 seconds or less, particularly preferably 110 seconds or less, and most preferably 100 seconds or less. There is no particular limitation on the lower limit, but it is preferably 5 seconds or more, more preferably 10 seconds or more.

[0102] By achieving the absorption time of high-viscosity liquids within the aforementioned range, a specified amount of liquid can be absorbed in a short time. When used in absorbent materials such as diapers, the user experiences less skin wetness, reducing discomfort and leakage. It should be noted that the absorption time of high-viscosity liquids in the absorbent resin particles contained in the granular absorbent of this invention is preferably within the same numerical range as that of the granular absorbent itself.

[0103] [2-7] Water-insoluble inorganic particles

[0104] The granular absorbent of the present invention preferably further comprises water-insoluble inorganic particles.

[0105] By including water-insoluble inorganic particles in granular absorbents, the hygroscopic flowability of the granular absorbents can be improved. Furthermore, by adding water-insoluble inorganic particles, the absorbency of absorbent articles can be increased. Moreover, absorbent resin particles (compositions) sometimes lose their flowability during the manufacture of absorbent articles due to post-manufacturing storage. By mixing these lost-flow absorbent resin particles (compositions) with water-insoluble inorganic particles and appropriately shaping the absorbent body, the flowability of the absorbent resin particles (compositions) is restored while maintaining its performance, thereby increasing productivity. Here, hygroscopic flowability refers to the flowability of granular absorbents when stored under high humidity conditions; granular absorbents containing absorbent resins typically experience reduced flowability due to moisture absorption.

[0106] Examples of water-insoluble inorganic particles include multi-metallic compounds such as hydrotalcite, silica (silica), aluminum hydroxide, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, metal phosphates (e.g., calcium phosphate, barium phosphate, aluminum phosphate, tricalcium phosphate), metal borates (e.g., titanium borate, aluminum borate, iron borate, magnesium borate, manganese borate, calcium borate), silicic acid or its salts, clay, diatomaceous earth, zeolite, bentonite, kaolin, activated clay, etc. From the perspective of significantly achieving the effects of the present invention, the water-insoluble inorganic particles preferably contain at least one selected from multi-metallic compounds, silica, aluminum hydroxide, talc, and tricalcium phosphate, and more preferably contain at least one selected from hydrotalcite, silica, aluminum hydroxide, and tricalcium phosphate.

[0107] [3] Method for manufacturing granular water absorbent

[0108] The method for manufacturing the granular absorbent of the present invention includes a polymerization step, a drying step, and a surface crosslinking step. Preferably, the manufacturing method further includes a gel pulverization step concurrent with the polymerization step or a gel pulverization step after the polymerization step, a gel granulation step before the drying step, a cooling step, a pulverization step of the dried material, and a classification step before the surface crosslinking step, and includes an additive addition step after the surface crosslinking step. In addition, it may include a monomer aqueous solution preparation step, a separation step, a step of adding various additives, a micron removal step, and a micron recovery step. Furthermore, various known steps may be included depending on the purpose. The manufacturing steps of the granular absorbent of the present invention are shown below [3-1] to [3-11].

[0109] [3-1] Preparation process of monomer aqueous solution

[0110] This step involves preparing an aqueous solution (hereinafter referred to as "monomer aqueous solution") containing a monomer (e.g., (meth)acrylate (salt)) as the main component. It should be noted that a monomer slurry can also be used, provided it does not reduce the water absorption properties of the resulting absorbent resin; however, for convenience, an aqueous monomer aqueous solution is described in this project.

[0111] In addition, the term "main component" refers to the amount (content) of (meth)acrylate (salt) relative to the total amount of monomers (excluding internal crosslinking agents) supplied for the polymerization reaction of the absorbent resin, which is typically 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more (up to 100 mol%).

[0112] (Meth)acrylic acid

[0113] In this invention, from the viewpoint of the physical properties and productivity of the obtained granular water absorbent, (meth)acrylic acid and / or its salts (hereinafter referred to as "(meth)acrylic acid (salt)") are used as monomers.

[0114] The aforementioned "(meth)acrylic acid" can be any known (meth)acrylic acid. As a polymerization inhibitor, it is preferable to contain methoxyphenols, more preferably p-methoxyphenols. From the viewpoint of the polymerizability of acrylic acid and the color of the particulate water-absorbing agent, it is preferable to contain 200 ppm or less, more preferably 10 to 160 ppm, and even more preferably 20 to 100 ppm. Furthermore, for impurities in (meth)acrylic acid, the compounds described in U.S. Patent Application Publication No. 2008 / 0161512 are also used in this invention.

[0115] Furthermore, the aforementioned "(meth)acrylate" is a substance obtained by neutralizing the aforementioned (meth)acrylic acid with the alkaline composition described below. In this invention, a neutralized salt obtained by neutralizing part or all of the carboxyl groups contained in (meth)acrylic acid can be used as a monomer. For example, as a (meth)acrylate, a salt with a monovalent cation is preferred, more preferably at least one selected from alkali metal salts, ammonium salts, and amine salts, further preferably an alkali metal salt, even more preferably at least one selected from sodium salts, lithium salts, and potassium salts, and particularly preferably a sodium salt. As a (meth)acrylate, a commercially available (meth)acrylate (e.g., sodium (meth)acrylate) can be used, or a salt obtained by neutralization in a granular desiccant manufacturing plant.

[0116] (Alkaline composition)

[0117] In this invention, "alkaline composition" refers to a composition containing an alkaline compound, such as commercially available sodium hydroxide aqueous solution, which is an alkaline composition.

[0118] Specifically, examples of alkaline compounds include alkali metal carbonates or bicarbonates, alkali metal hydroxides, ammonia, and organic amines. From the viewpoint of the physical properties of the resulting granular desiccant, strong alkalinity is desirable. That is, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are preferred, with sodium hydroxide being more preferred.

[0119] (Neutralization)

[0120] As neutralization in this invention, either neutralization of (meth)acrylic acid (before polymerization) or neutralization of the hydrogel-like crosslinked polymer obtained by crosslinking (meth)acrylic acid (after polymerization) (hereinafter referred to as "post-neutralization") can be selected, or a combination thereof can be used. In addition, these neutralizations can be continuous or intermittent, without particular limitation, but continuous neutralization is preferred from the viewpoint of production efficiency, etc.

[0121] It should be noted that the conditions for neutralization, such as the apparatus, neutralization temperature, and residence time, are also applied in this invention as described in International Patent Publication No. 2009 / 123197 and U.S. Patent Application Publication No. 2008 / 0194863.

[0122] Regarding the neutralization rate in this invention, relative to the acid groups of the monomer, it is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, further preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol%. When the neutralization rate is less than 10 mol%, the water absorption ratio is sometimes significantly reduced. On the other hand, when the neutralization rate exceeds 90 mol%, it is sometimes impossible to obtain a water-absorbing resin with a high water absorption ratio under pressure.

[0123] The above neutralization rate also applies to post-neutralization cases. Furthermore, the above neutralization rate also applies to the neutralization rate of the granular superabsorbent as the final product. It should be noted that a neutralization rate of 75 mol% refers to a mixture of 25 mol% (meth)acrylic acid and 75 mol% (meth)acrylate. This mixture is sometimes also referred to as a partially neutralized (meth)acrylic acid compound.

[0124] (Other monomers)

[0125] In this invention, "other monomers" refers to monomers other than the (meth)acrylate (salt) mentioned above. Other monomers can be used in combination with acrylic acid (salt) to manufacture granular water absorbents.

[0126] Other monomers mentioned above include water-soluble or hydrophobic unsaturated monomers. Specifically, compounds described in U.S. Patent Application Publication No. 2005 / 0215734 (excluding (meth)acrylic acid) are also used in this invention.

[0127] (Internal crosslinking agent)

[0128] As the internal crosslinking agent used in this invention, the compounds described in U.S. Patent No. 6,241,928 are also applied. One or more of these compounds are selected from among them, taking into account reactivity. In this invention, considering water absorption properties, it is preferable to perform surface treatment on the crosslinked body using the internal crosslinking agent.

[0129] Furthermore, from the viewpoint of the water absorption properties of the obtained water-absorbing resin, etc., as an internal crosslinking agent, it is preferable to use a compound having two or more polymerizable unsaturated groups, more preferably a compound that has thermal decomposability at the following drying temperature, and even more preferably a compound having two or more polymerizable unsaturated groups containing (poly)alkylene glycol structural units.

[0130] As the aforementioned polymerizable unsaturated groups, allyl and (meth)acrylate groups are preferred, and (meth)acrylate groups are more preferred. Furthermore, as the aforementioned (poly)alkylene glycol structural unit, polyethylene glycol is preferred, and the number of n is preferably 1 to 100, more preferably 6 to 50.

[0131] Therefore, in this invention, (poly)alkylene glycol di(meth)acrylate or (poly)alkylene glycol tri(meth)acrylate is preferred, and (poly)ethylene glycol di(meth)acrylate is more preferred.

[0132] The amount of the aforementioned internal crosslinking agent relative to the monomer as a whole is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%. By setting the amount within the above range, a desired water-absorbing resin can be obtained. It should be noted that if the amount is too small, there is a concern that the resulting hydrogel-like crosslinked polymer may have insufficient strength, leading to problems with workability; if the amount is too large, there is a tendency for the water absorption ratio to decrease.

[0133] In this invention, the preferred method is to pre-add a predetermined amount of internal crosslinking agent to the monomer aqueous solution and carry out the crosslinking reaction simultaneously with polymerization. Alternatively, other methods include: adding an internal crosslinking agent during or after polymerization to perform post-crosslinking; using a free radical polymerization initiator for free radical crosslinking; and using radiation crosslinking with active energy rays such as electron beams or ultraviolet light. Furthermore, these methods can be combined.

[0134] (Other substances added to the monomer aqueous solution)

[0135] In this invention, from the viewpoint of improving the physical properties of the obtained water-absorbing resin, the following substances may also be added during the preparation of the monomer aqueous solution.

[0136] Specifically, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), and polyacrylic acid (salt) crosslinkers can be added in an amount preferably 50% by weight or less, more preferably 20% by weight or less, further preferably 10% by weight or less, and particularly preferably 5% by weight or less (lower limit 0% by weight) in the monomer aqueous solution. Alternatively, carbonates, azo compounds, foaming agents such as bubbles, surfactants, chelating agents such as diethylenetriaminepentaacetic acid (salt) and ethylenediaminetetramethylenephosphonic acid (salt), hydroxycarboxylic acid compounds such as lactic acid (salt), and chain transfer agents can be added in an amount preferably 5% by weight or less, more preferably 1% by weight or less, and further preferably 0.5% by weight or less (lower limit 0% by weight) in the monomer aqueous solution.

[0137] Furthermore, the aforementioned substances can be added not only in the monomer aqueous solution, but also during the polymerization process, or in combination.

[0138] It should be noted that when water-soluble resins or water-absorbing resins are used as hydrophilic polymers, grafted polymers or water-absorbing resin compositions (e.g., starch-acrylic polymers, PVA-acrylic polymers, etc.) can be obtained. These polymers and water-absorbing resin compositions also fall within the scope of this invention.

[0139] (Concentration of monomeric components)

[0140] In this process, the above-mentioned substances are added when preparing the monomer aqueous solution. The concentration of the monomer component in the monomer aqueous solution is not particularly limited, but from the viewpoint of the physical properties of the water-absorbing resin, it is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, and even more preferably 30 to 70% by weight.

[0141] In addition, when using aqueous solution polymerization or reverse suspension polymerization, solvents other than water can be used in combination as needed. In this case, there are no particular restrictions on the type of solvent.

[0142] It should be noted that the “concentration of monomer components” mentioned above refers to the value obtained by the following (Formula i). The weight of the monomer aqueous solution does not include the weight of the grafted components, the hydrophobic resin, or the hydrophobic solvent in the reverse suspension polymerization.

[0143] (Concentration of monomer component (wt%)) = (Weight of monomer component) / (Weight of monomer aqueous solution) × 100 (Equation i).

[0144] [3-2] Polymerization process

[0145] This process involves polymerizing the aqueous solution of (meth)acrylate monomers obtained through the above-mentioned monomer aqueous solution preparation process to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").

[0146] (Polymerization initiator)

[0147] The polymerization initiator used in this invention is appropriately selected based on the polymerization method, and therefore is not particularly limited. Examples include thermally decomposable polymerization initiators, photodecomposable polymerization initiators, or redox polymerization initiators formed by combining reducing agents that promote the decomposition of these polymerization initiators. Specifically, one or more of the polymerization initiators disclosed in U.S. Patent No. 7,265,190 may be used. It should be noted that, from the viewpoint of the processability of the polymerization initiator and the physical properties of the particulate water-absorbing agent or water-absorbing resin, peroxides or azo compounds are preferred, peroxides are more preferred, and persulfates are even more preferred.

[0148] The amount of the polymerization initiator relative to the monomer is preferably 0.001 to 1 mol%, more preferably 0.001 to 0.5 mol%. Additionally, the amount of the reducing agent relative to the monomer is preferably 0.0001 to 0.02 mol%.

[0149] It should be noted that, in addition to the polymerization initiators mentioned above, polymerization reactions can also be carried out by irradiation with active energy rays such as radiation, electron beams, and ultraviolet rays, or these active energy rays can be used in combination with polymerization initiators.

[0150] (Aggregation Method)

[0151] The polymerization method used in this invention is not particularly limited. From the viewpoint of water absorption characteristics and ease of polymerization control, spray droplet polymerization, aqueous solution polymerization, and reverse suspension polymerization are preferred, aqueous solution polymerization and reverse suspension polymerization are more preferred, and aqueous solution polymerization is even more preferred. Among these, continuous aqueous solution polymerization is particularly preferred, but continuous belt polymerization and continuous kneading polymerization can also be used.

[0152] As specific polymerization methods, continuous belt polymerization is disclosed in U.S. Patent Nos. 4,893,999, 6,241,928, and 2005 / 215,734, while continuous kneading polymerization is disclosed in U.S. Patent Nos. 6,987,151 and 6,710,141, among others. By employing these continuous aqueous solution polymerization methods, the production efficiency of water-absorbing resins is improved.

[0153] Furthermore, as preferred methods for the aforementioned continuous aqueous solution polymerization, "high-temperature initiation polymerization" and "high-concentration polymerization" can be listed. "High-temperature initiation polymerization" refers to a method of initiating polymerization at a temperature preferably above 30°C, more preferably above 35°C, further preferably above 40°C, and particularly preferably above 50°C (upper limit being the boiling point). "High-concentration polymerization" refers to a method of polymerization at a monomer concentration preferably above 30% by weight, more preferably above 35% by weight, further preferably above 40% by weight, and particularly preferably above 45% by weight (upper limit being the saturation concentration). These polymerization methods can also be used in combination.

[0154] Furthermore, in this invention, polymerization can be carried out in an air atmosphere, but from the viewpoint of the color tone of the resulting water-absorbing resin, polymerization can also be carried out in an inert atmosphere such as nitrogen or argon. In this case, for example, it is preferable to control the oxygen concentration to below 1% by volume. It should be noted that the dissolved oxygen in the monomer aqueous solution is also preferably replaced beforehand with an inert gas (e.g., dissolved oxygen: less than 1 mg / L).

[0155] Furthermore, as a method of aqueous solution polymerization, the present invention can be implemented by static polymerization, in which the monomer aqueous solution is polymerized in a static state, or by stirred polymerization, in which the monomer is polymerized in a stirring device. In static polymerization, a ring-shaped belt is preferably used. The belt is preferably made of resin or rubber that does not easily allow the heat of polymerization to escape from the surface in contact with the material.

[0156] As the polymerization method used in this invention, reverse suspension polymerization can also be employed, as disclosed in International Publication Nos. 2009 / 025235, 2013 / 018571, 2016 / 182082, and 2020 / 067310. It can be either batch reverse suspension polymerization or continuous reverse suspension polymerization. From the perspective of being able to continuously implement each process and each operation between processes, and being able to achieve mass production through long-term operation, continuous reverse suspension polymerization is preferred, and liquid-phase droplet continuous polymerization is further preferred.

[0157] [3-3] Shredding process

[0158] The shredding process is an optional step performed after the polymerization step and before the gel pulverization step, whereby the hydrogel-like crosslinked polymer is cut or coarsely crushed to a size suitable for feeding into the gel pulverization apparatus. This shredding process is particularly preferred when the polymerization step is belt polymerization, resulting in sheet-like or block-like hydrogels. Therefore, in one embodiment of the present invention, the hydrogel-like crosslinked polymer obtained after the polymerization step is sheet-like, and the process further includes a shredding step where the sheet-like hydrogel-like crosslinked polymer is shredded before the gel pulverization step. The mechanism for cutting or coarsely crushing the hydrogel in the shredding process is not particularly limited; a rotary cutter, a drum cutter, a guillotine cutter, etc., can be used. The shredded size is not particularly limited as long as it is suitable for feeding into the gel pulverization apparatus described later. The preferred size of the shredded hydrogel is 1 mm to 3 μm, more preferably 5 mm to 2.5 μm, and particularly preferably 1 cm to 2 μm. It should be noted that the shredding process may be omitted if the objective of the present invention is achieved. For example, if reverse suspension polymerization is performed, a particulate hydrogel-like crosslinked polymer is obtained, so this step is not required.

[0159] [3-4] Gel pulverization process

[0160] This step is an optional step after the above polymerization, whereby the hydrogel-like crosslinked polymer obtained from the polymerization step is pulverized to form fine particles, thereby obtaining granular hydrogel-like crosslinked polymers (hereinafter referred to as "granular hydrogels"). The particle size of the granular hydrogels is adjusted to a preferred range described later, so as to obtain (surface-crosslinked) water-absorbing resin particles of the target shape and properties in high yield. It should be noted that this step may be performed more than twice in order to obtain granular hydrogels of the specified particle size. It should also be noted that the gel pulverization step may be omitted if the object of the present invention is achieved. For example, in the case of gas-phase polymerization or reverse-phase suspension polymerization, granular hydrogel-like crosslinked polymers are obtained, and therefore this step is not required.

[0161] In this invention, the type of gel pulverizing device is not particularly limited as long as the water absorption performance (liquid absorption rate and return flow) is not impaired in the gel pulverizing process. Examples of gel pulverizing devices include, for instance, intermittent or continuous double-arm kneaders, gel pulverizers with multiple rotating stirring blades, single-screw extruders, twin-screw extruders, screw extruders such as meat grinders, multi-screw mixers (kneaders) with two or more shafts, and gel pulverizers such as cutters. It should be noted that when the polymerization process is kneading polymerization, both the polymerization process and the gel pulverizing process are performed simultaneously.

[0162] In one embodiment, a meat grinder or a multi-shaft mixer with two or more shafts is preferably used in the gel pulverization process. Particularly when an aqueous gel is obtained through aqueous solution polymerization, the use of a meat grinder or a multi-shaft mixer with two or more shafts in the gel pulverization process enables the formation of fine particles. Consequently, when water-absorbing resin particles are obtained, a large number of interconnected pores can be formed as aggregates of fine particles, and independent air bubbles can be reduced. Therefore, the ratio of interconnected pores to independent air bubbles formed in the water-absorbing resin particles can be easily controlled, further enhancing the effects of the present invention. That is, in a preferred embodiment, the gel pulverization process using a meat grinder or a multi-shaft mixer with two or more shafts is performed after aqueous solution polymerization. It should be noted that, regarding gel pulverization conditions and methods other than those described above, the contents disclosed in International Publication No. 2011 / 126079 are also preferably applied in this invention.

[0163] (Gel fluidizing agent)

[0164] In this embodiment, a gel flow agent may be added before and / or during the gel pulverization process. This yields a granular hydrogel containing the gel flow agent. By adding the gel flow agent, the adhesion or bonding of hydrogel particles to each other is suppressed during the subsequent drying process, promoting the formation of interconnected pores and suppressing the formation of independent air bubbles, thereby improving the water absorption performance of the obtained water-absorbing resin. Furthermore, it also reduces the load in the subsequent pulverization process after drying, reducing the amount of fine powder generated. Moreover, when stirring drying is performed in the drying process, the particle size of the obtained granular dried polymer is close to the product particle size, thus the above-mentioned effects become significant. From the viewpoint that each particle of the obtained granular hydrogel uniformly contains the gel flow agent, it is preferable to add it during the gel pulverization process. It should be noted that, in cases where a gel pulverization process is not required, such as when reverse suspension polymerization is performed in the polymerization process, it is also preferable to add the gel flow agent to the granular hydrogel at least before the drying process.

[0165] The amount of gel flow agent added is appropriately set according to the water content of the hydrogel or granular hydrogel and the type of gel flow agent. The amount added is preferably 0.001% to 0.5% by mass, more preferably 0.01% to 0.3% by mass, and even more preferably 0.02% to 0.2% by mass relative to the solid content of the hydrogel.

[0166] Examples of such gel flow agents include anionic, cationic, nonionic, and amphoteric surfactants, as well as their low-molecular-weight or high-molecular-weight surfactants and high-molecular-weight lubricants.

[0167] (surfactant)

[0168] Specifically, surfactants used as gel flow agents include (1) nonionic surfactants such as sucrose fatty acid esters, polyglycerol fatty acid esters, dehydrated sorbitol fatty acid esters, polyoxyethylene dehydrated sorbitol fatty acid esters, polyoxyethylene glycerol fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropylene alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl glucamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkylallyl ethers. 2) Alkyl dimethylaminoacetic acid betaine, such as octyl dimethylaminoacetic acid betaine, lauryl dimethylaminoacetic acid betaine, myristyl dimethylaminoacetic acid betaine, stearyl dimethylaminoacetic acid betaine, etc.; alkyl amamidopropyl betaine, such as lauryl hydroxysulfonyl betaine, such as cocoa fatty acid amamidopropyl betaine, such as palm kernel oil fatty acid amamidopropyl betaine, such as lauryl hydroxysulfonyl betaine, such as alkyl carboxymethyl hydroxyethyl imidazoline betaine, etc.; (3) Alkyl aminodiacetic acid monosodium, lauryl aminodiacetic acid potassium, myristyl aminodiacetic acid sodium, etc.; alkyl aminodiacetic acid monoalkali metal, etc.; and (4) long-chain alkyl dimethylaminoethyl quaternary salt, etc., cationic surfactants. Among them, two or more can be used in combination.

[0169] (Polymer lubricant)

[0170] In this embodiment, the polymeric lubricants exemplified below can be added to the above-mentioned monomer aqueous solution and hydrogel within the scope of achieving the objectives of the present invention.

[0171] Specifically, examples of the aforementioned polymeric lubricants include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene / propylene copolymer, maleic anhydride-modified ethylene / propylene / diene terpolymer (EPDM), maleic anhydride-modified polybutadiene, maleic anhydride / ethylene copolymer, maleic anhydride / propylene copolymer, maleic anhydride / ethylene / propylene copolymer, maleic anhydride / butadiene copolymer, polyethylene, polypropylene, ethylene / propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene / propylene copolymer, ethylene / acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose, and polyepoxides such as polyethylene glycol. Their molecular weights (weight-average molecular weights) are preferably selected within the range of 2 million to 2 million, more preferably 4 million to 1 million. Two or more of these can be used in combination.

[0172] Furthermore, these polymeric lubricants and the aforementioned surfactants can be used in combination as gel flow agents. When using a combination of surfactants and polymeric lubricants, the total amount added is appropriately set according to the polymerization method, the composition of the monomer aqueous solution, and the water content of the hydrogel. When added to the monomer aqueous solution, the amount is set in terms of concentration relative to the monomer component; when added to the hydrogel, the amount is set in terms of its solid content; and when both are added, the amount is set in the total amount mentioned above. These gel flow agents can be reused with the dispersing agents used in reverse suspension polymerization.

[0173] The total amount of surfactant and polymeric lubricant added is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, more preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more.

[0174] (hydrogen peroxide)

[0175] In this embodiment, hydrogen peroxide can be added in a step prior to the drying step. By adding hydrogen peroxide in a step prior to the drying step, and then heating in the drying step or subsequent steps, the hydrogen peroxide can be used to break down the cross-linked structures in the absorbent resin during the heating process, thereby efficiently increasing the absorption ratio (CRC) without affecting the formation of interconnected pores and independent bubbles in the gel crushing and gel granulation steps. More specifically, it is preferable to add hydrogen peroxide to the aforementioned monomer aqueous solution before the polymerization step and / or to the hydrogel during the gel crushing step.

[0176] Regarding the amount of hydrogen peroxide added relative to the monomer aqueous solution and / or hydrogel, it should be appropriately set considering the selected polymerization conditions and the amount of hydrogen peroxide remaining before drying (ppm). For example, considering the improvement of the physical properties of the obtained water-absorbing resin, especially the absorption ratio (CRC), the total amount relative to the mass (%) of the solid component of the monomer aqueous solution or hydrogel crosslinked polymer is preferably 50 ppm (0.005 wt%) or more, more preferably 50 ppm (0.005 wt%) to 10000 ppm (1.0 wt%), and even more preferably 100 ppm (0.01 wt%) to 5000 ppm (0.5 wt%).

[0177] There are no particular limitations on the method of adding hydrogen peroxide. For ease of addition, it is preferable to use an aqueous solution containing dissolved hydrogen peroxide. The concentration of this solution is not particularly limited, but is typically around 1–40% by mass. Furthermore, the aqueous hydrogen peroxide solution may contain small amounts of hydrophilic solvents such as methanol, ethanol, n-propanol, or isopropanol. There are no particular requirements on the temperature at which hydrogen peroxide or the hydrogen peroxide solution is added; for example, a range of -10 to 100°C is acceptable, but 0 to 30°C is more preferred.

[0178] Furthermore, when hydrogen peroxide is added, the hydrogel-like crosslinked polymer and / or the dried polymer are preferably heated in a manner that maximizes a temperature exceeding 160°C during and after the drying process. This heating, using hydrogen peroxide, breaks down the crosslinking structure in the water-absorbing resin, resulting in a granular water-absorbing agent with a high absorption ratio (CRC).

[0179] (Surface tension)

[0180] Regarding the type and amount of gel flow agent, adjustments are made appropriately considering factors such as the flowability of the granular hydrogel during the gel pulverization and drying processes. Based on factors such as the reflux rate in actual use of the resulting absorbent resin absorbent article (diaper), the type and amount of gel flow agent that will not excessively reduce the surface tension of the absorbent resin in the final product are preferred. For example, the type and amount of gel flow agent are selected such that the surface tension of the absorbent resin (the surface tension of the absorbent resin dispersion in physiological saline) is preferably 55 mN / m or more, more preferably 60 mN / m or more, and even more preferably 65 mN / m or more. This surface tension is measured using the method described in WO2015 / 129917.

[0181] (Contains the percentage of solid components in the hydrogel)

[0182] The solid content (hereinafter referred to as gel solid content) of the hydrogel supplied for the gel pulverization process is preferably 25% by mass or more. From the viewpoints of inhibiting the aggregation of hydrogel particles after gel pulverization, the energy required for pulverization, drying efficiency, and absorption performance, the gel solid content is more preferably 25% to 75% by mass, further preferably 30% to 70% by mass, even more preferably 35% to 65% by mass, and particularly preferably 40% to 60% by mass.

[0183] (Water content of granular hydrogels)

[0184] The water content of the particulate hydrogel (hereinafter referred to as gel water content) was determined by the measurement method described in the examples below. From the viewpoint of the flowability of the particulate hydrogel in the drying process described later, the gel water content is preferably 25% by mass or more, more preferably 30% by mass or more, further preferably 35% by mass or more, particularly preferably 40% by mass or more, and extremely preferably 43% by mass or more. Excessively high-concentration polymerization may reduce the physical properties of the water-absorbing resin. From the viewpoint of drying efficiency and absorption performance, the gel water content is preferably 75% by mass or less, more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

[0185] (Particle size of granular hydrogels)

[0186] From the viewpoint of controlling the particle size and the proportion of interconnected pores and independent air bubbles in the obtained water-absorbing resin, the weight-average particle size of the granular hydrogel obtained by the gel pulverization process (granular hydrogel before drying) is preferably 10 μm to 1000 μm, more preferably 20 μm to 800 μm, further preferably 40 μm to 500 μm, particularly preferably 50 μm to 300 μm, and most preferably 60 μm to 200 μm, calculated based on the solid content. It should be noted that the average particle size of the granular hydrogel calculated based on the solid content (average gel particle size calculated based on the solid content) can be determined by the method described in WO2016 / 204302, "Weight-average particle size (μm) calculated based on the dried content of hydrogel particles".

[0187] (Using a meat grinder to pulverize the gel)

[0188] In one embodiment, the gel pulverization process preferably uses... Figure 2A The gel pulverizer 100 (screw extruder) shown is used for grinding ( Figure 2AFor details, please refer to WO2013 / 0023187). In conventional meat grinder 100 gel pulverization, a mold (also called a "mold plate" or "porous plate") is provided at the extrusion port 16. However, when using the meat grinder 100 in the gel pulverization process of the present invention, it is preferable to perform gel pulverization without using such a mold. By not providing a mold at the extrusion port 16 of the meat grinder, the pressure applied to the gel during pulverization is mitigated, and excessive compaction of the pulverized gel particles is suppressed, thereby sufficiently maintaining the interconnected pores in the absorbent resin. In this embodiment, a support member 17 is provided at the extrusion port 16 of the meat grinder 100 instead of a mold.

[0189] Figure 2B The diagram shows one embodiment of the support member 17. The support member 17 is a component that supports the screw 13 at the extrusion port 16. Figure 2B In the support member 17 shown, region 17a is the portion through which the pulverized granular hydrogel passes, and region 17b is the portion supporting the shaft of the screw 13. Therefore, region 17b is the portion through which the shaft of the screw 13 passes, and the granular hydrogel will not pass through. The shape of the support member 17 only needs to have the minimum strength required to support the shaft of the screw 13; there are no particular limitations. Figure 2B The support member 17 shown is preferably shaped to maximize the aperture ratio (minimize the number of holes and maximize the size of each hole). The aperture ratio is defined as a value calculated with the area of ​​region 17a (the portion through which the pulverized granular hydrogel passes) as the numerator and the area of ​​the circle with the outer diameter D of the support member 17 as the denominator. It should be noted that a support member with an aperture ratio of 56% is used in the embodiments of this application.

[0190] Furthermore, regarding the grinding process using a meat grinder, it is preferable to pass the material through the meat grinder at least twice, and more preferably at least three times. In this invention, the gel grinding energy (GGE) used for gel grinding of hydrogels is preferably 60 [J / g] or less, more preferably 50 [J / g] or less, and even more preferably 40 [J / g] or less, as an upper limit. Furthermore, the lower limit is preferably 18 [J / g] or more, more preferably 20 [J / g] or more, and even more preferably 25 [J / g] or more. For example, in this invention, the gel grinding energy (GGE(1)) used for gel grinding of hydrogels is 18 to 60 [J / g], preferably 20 to 50 [J / g], and more preferably 25 to 40 [J / g]. Furthermore, the gel pulverizing energy (GGE(2)) used for gel pulverizing hydrogels is 18–60 [J / g], preferably 20–50 [J / g], and more preferably 25–40 [J / g]. By controlling GGE(1) and GGE(2) within the above ranges, gel pulverization can be performed while applying appropriate shear / compression force to the hydrogel. It should be noted that the gel pulverizing energy (GGE(1)) is defined including the energy during the idling of the gel pulverizer, and the gel pulverizing energy (GGE(2)) is defined by subtracting the energy during the idling of the gel pulverizer. In the case of performing multiple gel pulverizations, the gel pulverizing energy applied in each pulverization is totaled.

[0191] The gel pulverization energy, described in International Patent Publication No. 2011 / 126079 (corresponding to U.S. Patent Application Publication No. 2013 / 026412 and U.S. Patent Application Publication No. 2016 / 332141), refers to the mechanical energy required per unit weight (unit weight of the hydrogel-like crosslinked polymer) by the gel pulverization device when pulverizing the hydrogel-like crosslinked polymer. When the gel pulverization device is driven by three-phase alternating current, it is calculated using the following formula (a-1).

[0192] Gel pulverization energy GGE(1) [J / g]

[0193] ={3 1 / 2 ×Voltage×Current×Power Factor×Motor Efficiency} / {Weight of hydrogel fed into the gel crushing device in 1 second}···(Equation a-1).

[0194] Here, the power factor and motor efficiency are inherent values ​​of the device, varying according to the operating conditions of the gel pulverizer, and are taken as values ​​from 0 to 1. When the gel pulverizer is driven by single-phase AC power, by using formula 3 above... 1 / 2 The value is changed to 1 and calculated. In the above (Equation a-1), the unit of voltage is [V], the unit of current is [A], and the unit of mass of hydrogel is [g].

[0195] The specified gel pulverization energy GGE(2) is calculated by subtracting the energy of the gel pulverizer during idling using the following formula (a-2).

[0196]

[0197] In Equation a-2 above, the power factor and motor efficiency, like in Equation a-1, are inherent values ​​of the device that vary depending on the operating conditions of the gel pulverizing device, and are taken as values ​​from 0 to 1. In Equation a-2 above, the unit of voltage is [V], the unit of current is [A], and the unit of mass of hydrogel is [g].

[0198] As for gel pulverization using a meat grinder (screw extruder), apart from the above-mentioned die configuration (a support member 17 is used instead of a die at the extrusion port 16) and gel pulverization capacity, the conditions described in WO2013 / 0023187 can be applied in this invention.

[0199] (Gel pulverization using a multi-shaft mixer with two or more shafts)

[0200] In one embodiment, the gel pulverization process preferably uses... Figure 3 and Figure 4 The gel pulverizer shown is a multi-shaft mixer. (Example:) Figure 3 and Figure 4 As shown, in the gel pulverization process after the polymerization process, a gel pulverization device is used, which has an inlet, a main body with multiple built-in rotating shafts, and an outlet. Each rotating shaft has a pulverization mechanism. In this gel pulverization device, the hydrogel-like crosslinked polymer continuously fed into the main body from the inlet is pulverized at a temperature above 50°C using the pulverization mechanism of each rotating shaft, and continuously removed from the outlet in the form of granular hydrogel-like crosslinked polymer. That is, the hydrogel-like crosslinked polymer fed into the main body from the inlet moves from the inlet to the outlet while being kept at a temperature above 50°C, and is pulverized using the pulverization mechanism of each rotating shaft. It should be noted that, in this invention, the main body refers to the body part equipped with multiple rotating shafts and pulverization mechanisms ( Figure 3 The symbol 208), also known as a barrel, trough, shell, etc.

[0201] The aforementioned multi-shaft mixing mill can be continuous, and can be longitudinal (where the hydrogel travels vertically), transverse, or horizontal (where the hydrogel travels horizontally or left-right). Furthermore, in both longitudinal and transverse gel pulverizing devices, the inclination relative to the horizontal direction can range from 0° to 90°. For example, Figure 3In the case of the horizontal continuous pulverizing device shown, an inclination can be appropriately provided as needed. This inclination can be downward or upward from the inlet to the outlet (i.e., relative to the direction of travel of the hydrogel). Typically, the inclination angle is 0° to 10°, preferably 0° to 1°, and particularly preferably 0°.

[0202] In the aforementioned multi-shaft mixer, the hydrogel fed into the inlet is pulverized to the target particle size until it is discharged from the outlet, without applying excessive pressure to the hydrogel. Therefore, unlike conventional extruders (meat grinders), which require extrusion from a die, this multi-shaft mixer removes granular hydrogel that has been adjusted to the target particle size from the outlet. By using the aforementioned multi-shaft mixer, the pressure applied to the gel during pulverization is mitigated, preventing excessive compaction of the pulverized gel particles, thereby effectively maintaining the interconnected pores in the water-absorbing resin.

[0203] From the viewpoint of continuously pulverizing gels at temperatures above 50°C, the aforementioned multi-shaft mixer preferably includes a heating mechanism and / or a heat-insulating mechanism. There are no particular limitations on the heating and / or heat-insulating mechanisms; however, from the viewpoint of preventing the adhesion and aggregation of hydrogels and particulate hydrogels, a heating mechanism utilizing direct heat transfer based on convection and / or indirect heat transfer based on heat conduction from the heating surface (the contact surface with the hydrogel, the heat source portion) of the gel pulverizing device heated by a heat medium is preferred. More preferably, the heating mechanism is a ventilated heating type in the case of direct heat transfer and an external wall heating type in the case of indirect heat transfer.

[0204] From the viewpoint of reducing excessive load on the hydrogel, it is preferable to have a heating mechanism and / or a heat preservation mechanism on the outer surface of the main body, and more preferably a heating mechanism. Examples of such a heat preservation mechanism include covering a portion or the entire outer surface of the main body with a heat-insulating material (preferably 50% or more, more preferably 80% or more, and particularly preferably the entire outer surface). Examples of heating mechanisms include jackets using electric heating, steam heating, or heating with a heat medium. It has been found that, in order to obtain the water-absorbing resin particles with interconnected pores required in this invention, the influence of temperature changes on the adhesion and flowability of the hydrogel particles is greater than imagined within the scope of the prior art. As a result, research in this invention has revealed that the energy required for pulverizing the hydrogel and the adhesion between the pulverized gel particles vary significantly depending on the temperature. By incorporating the aforementioned heating mechanism and / or heat preservation mechanism, a multi-shaft mixer can perform the gel pulverization process within a more preferred temperature range. Furthermore, it is possible to avoid the deterioration of the gel pulverization quality caused by temperature differences such as seasons and day / night cycles. Furthermore, when the gel pulverizer is started, it can be smoothly induced to operate stably.

[0205] The type of pulverizing mechanism in each rotating shaft is not particularly limited as long as the effects of the present invention can be obtained. For example, various shapes of discs can be listed as pulverizing mechanisms that have a shearing effect on hydrogels. Discs are sometimes called chops, paddles, elements, kneaders, rotors, etc. The shape of the disc is not particularly limited, and can be appropriately selected from circular plates, elliptical shapes, approximately triangular shapes, etc. Different shapes of discs can also be used in combination, and their arrangement can be appropriately adjusted from the viewpoint of the particle size of the target particulate hydrogel and the energy required for pulverization. In addition, as a pulverizing mechanism, arms, blades, blades, cutting discs (CDs), etc., can be used in combination.

[0206] For example, when each rotating shaft has a circular or elliptical disc as a crushing mechanism, the ratio of the effective length L inside the main body to the maximum diameter D (or the diameter of the largest disc if multiple discs of different diameters are used) is defined as L / D. This L / D is preferably 5 to 40, more preferably 6 to 30, and even more preferably 6.5 to 20. It should be noted that the effective length L refers to... Figure 3 The figure shows the axial length (total length) of the main body (bucket) including the outlet, starting from the inlet.

[0207] Furthermore, the distance (interval) between the disc and the main body (bucket) sometimes varies depending on the location. When the minimum interval C is defined as the shortest distance between the outer periphery of the disc and the inner wall of the main body (bucket), the minimum interval C is preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less relative to the maximum diameter D of the disc. If it is below the upper limit mentioned above, the shear force between the bucket and the disc becomes stronger during gel pulverization, resulting in good gel pulverization efficiency. Additionally, the minimum interval C is preferably 0.2% or more, more preferably 0.5% or more, and even more preferably 1% or more relative to the maximum diameter D of the disc. If it is above the lower limit mentioned above, contact between the disc and the inner wall of the main body (bucket) is suppressed, and the ingress of metallic foreign matter due to wear is suppressed. In a suitable embodiment of the present invention, the minimum interval C is 0.2% to 20% relative to the maximum diameter D of the disc.

[0208] The rotational speeds of the multiple rotating shafts in the aforementioned multi-shaft mixing mill can be constant or non-constant, and are preferably set according to the appropriate settings of the device, preferably in the range of 1 rpm to 1000 rpm, more preferably in the range of 3 rpm to 500 rpm, and even more preferably in the range of 5 rpm to 300 rpm. Furthermore, when the rotational speeds of the rotating shafts are different, the ratio of the rotational speed of one rotating shaft to the rotational speed of another rotating shaft is typically in the range of 1 to 10, preferably in the range of 1 to 2.

[0209] Furthermore, when the multiple rotating shafts have discs as the pulverizing mechanism, the circumferential speed (V) of the discs, as defined by the following (Formula b), can be constant or non-constant, and is appropriately set according to the device. Preferably, it is 0.05 m / s to 5 m / s, more preferably 0.1 m / s to 5 m / s, even more preferably 0.15 m / s to 3 m / s, and particularly preferably 0.2 m / s to 2 m / s. Exceeding the above range, the shear force of the hydrogel becomes excessive, and the pulverized hydrogel particles experience physical property deterioration and over-consolidation, which is undesirable. Furthermore, below the above range, the throughput per unit time in the gel pulverization process decreases, which is also undesirable. Additionally, when the circumferential speeds of the discs on each rotating shaft are different, the ratio of the circumferential speed of one rotating shaft to that of another is typically in the range of 1 to 10, preferably in the range of 1 to 2.

[0210] Circular velocity (V) (m / s) = πD × n / 60 ··· (Equation b)

[0211] Here, in (Equation b), V is the circumferential speed of the disk (unit: m / s), D is the maximum diameter of the disk (unit: m), and n is the rotational speed of the disk per unit time (unit: rpm).

[0212] Furthermore, regarding the rotation direction of the multiple rotating shafts, they can be either a unidirectional type where each rotating shaft rotates in the same direction, or an antidirectional type where each rotating shaft rotates in opposite directions. A unidirectional type device offers self-cleaning properties, while an antidirectional type device offers strong shearing force. The rotation direction of each rotating shaft is appropriately selected based on its combination with the aforementioned pulverizing mechanism (disc pattern).

[0213] The aforementioned multi-shaft mixer preferably has a function of supplying water and / or steam inside the main body. By supplying water and / or steam (preferably water and steam) while performing gel pulverization, it is possible to obtain water-absorbing resin particles that sufficiently contain the desired interconnected pores. Therefore, according to one embodiment of the invention, water and / or steam are supplied to the interior of the main body during the gel pulverization process. As a mechanism for supplying water and / or steam, the gel pulverization device may have multiple inlets. The location of the water and / or steam inlets is not required, but it is preferred to be located on the inlet side containing the hydrogel. In addition, water and steam can be supplied from different inlets.

[0214] There are no particular limitations on the addition of water vapor; for example, gases such as air, dry air, and nitrogen can be mixed with water vapor and added as a mixed gas. The pressure of the added water vapor is not particularly limited, but is preferably 0.2 to 0.8 MPa. The temperature of the water and / or water vapor (including the mixed gas) is not particularly limited, but is preferably 50°C or higher, more preferably 60°C or higher, further preferably 70°C or higher, and particularly preferably 80°C or higher. From the viewpoint of suppressing excessive heating and drying of the hydrogel, it is preferably 200°C or lower, more preferably 170°C or lower, further preferably 150°C or lower, even more preferably 120°C or lower, and particularly preferably 100°C or lower. Preferably, the temperature of the water and / or water vapor supplied to the interior of the main body is 50 to 120°C. The temperature of the hydrogel and granular hydrogel in the aforementioned multi-shaft mixer can also be adjusted by utilizing the temperature and amount of water and / or water vapor (including the mixed gas) used. In this case, water vapor and / or mixed gases act as a direct heat transfer medium, heating or maintaining the temperature of the hydrogel and granular hydrogel inside the substrate to a specified temperature. It should be noted that additives such as gel flow agents, crosslinking agents, oxidizing agents, reducing agents, and polymerization initiators are mixed into the added water and / or water vapor (including mixed gases).

[0215] The amount of water and / or water vapor supplied, relative to the mass of the solid component of the hydrogel, is preferably 0.1% to 50% by mass, more preferably 0.5% to 40% by mass, and even more preferably 1% to 30% by mass.

[0216] The aforementioned multi-shaft mixer preferably has a heating mechanism and / or a heat preservation mechanism on the outer surface of the main body. A liquid heat medium such as warm water or oil can be introduced into a jacket or similar device located on the outer surface of the main body, or heated gas (hot air) can be introduced as the heat medium. These heat media function as indirect heat transfer media. From the viewpoint of heating efficiency and / or heat preservation efficiency of indirect heat transfer, the temperature of the heat medium is preferably 50°C or higher, more preferably 60°C or higher, further preferably 70°C or higher, and particularly preferably 80°C or higher. On the other hand, from the viewpoint of suppressing excessive heating and drying of the hydrogel, the temperature of the heat medium is preferably 200°C or lower, more preferably 170°C or lower, further preferably 150°C or lower, even more preferably 130°C or lower, and particularly preferably 110°C or lower. Warm water or steam is particularly preferred as the heat medium. Furthermore, the temperature of the heat medium can be a constant temperature or can be appropriately varied during the gel crushing process.

[0217] More preferably, before adding the hydrogel to the aforementioned multi-shaft mixer, the temperature of the interior (inner surface) of the main body is heated to 50°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, and even more preferably 80°C or higher. This reduces the adhesion of the hydrogel to the inner surface of the main body. Furthermore, the resulting water-absorbing resin particles contain sufficiently interconnected pores, further improving water absorption performance. That is, in the gel pulverization using the aforementioned multi-shaft mixer, before adding the hydrogel and at the start of gel pulverization, the inner surface of the main body is preferably heated to the aforementioned temperature or higher. More preferably, the inner surface of the main body, the multiple rotating shafts, and the outer surface of the pulverizing mechanism of each rotating shaft are preferably heated to the aforementioned temperature or higher. On the other hand, from the viewpoint of suppressing excessive heating and drying of the hydrogel, before adding the hydrogel to the gel pulverizing apparatus, the heating temperature of the interior (inner surface) of the main body is preferably 200°C or lower, more preferably 170°C or lower, even more preferably 150°C or lower, even more preferably 130°C or lower, and particularly preferably 110°C or lower. For example, by circulating and maintaining a heat medium inside a jacket provided on the main body, the temperature inside the main body (inner surface) can be adjusted to a desired range. From the viewpoint of maintaining the temperature above 50°C during the gel pulverization process, it is preferable that the temperature inside the main body (inner surface) is maintained within the aforementioned range during the gel pulverization process.

[0218] Here, "continuously pulverizing the hydrogel-like cross-linked polymer at temperatures above 50°C" refers to... Figure 3 The interval shown in (A), in other words, the interval from the inlet to the outlet, involves continuously pulverizing the hydrogel-like crosslinked polymer while maintaining its temperature above 50°C. For example, if the temperature T1 of the hydrogel-like crosslinked polymer fed into the inlet of the multi-shaft mixer is set to above 50°C, and the temperature of the heat medium in the jacket installed on the outside of the main body of the device is set to above 50°C, then it is possible to... Figure 3 The temperature of the hydrogel-like crosslinked polymer is maintained above 50°C in section (A), enabling continuous pulverization of the hydrogel-like crosslinked polymer at temperatures above 50°C. Furthermore, it includes situations where, for example, even if the temperature T1 of the hydrogel-like crosslinked polymer fed into the inlet of the multi-shaft mixer is below 50°C, high-temperature water and / or steam are supplied to the inlet, or the jacket heat medium temperature of the main body of the apparatus is set to a high temperature, causing the hydrogel-like crosslinked polymer to rapidly heat up, and the temperature in section (A) is set above 50°C for continuous pulverization.

[0219] The temperature for continuous pulverization of the hydrogel-like crosslinked polymer is preferably 50°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, and even more preferably 80°C or higher.

[0220] There is no particular limit to the upper limit of the temperature for continuous pulverization of the hydrogel-like crosslinked polymer. From the viewpoint of suppressing excessive heating and drying of the hydrogel, it is preferably 200°C or below, more preferably 170°C or below, even more preferably 150°C or below, even more preferably 130°C or below, and particularly preferably 110°C or below.

[0221] Figure 3 and 4 An example of a multi-shaft mixer (gel crushing device) 200 suitable for use in this invention is shown. Figure 3 A partially cut-away side view of the gel pulverizing device 200. Figure 4 This is an enlarged view of the gel pulverizing device 200 (viewed from above, showing the central part of the main body). The following uses... Figure 3 and Figure 4 This section describes the basic structure and usage of the gel pulverizing device 200.

[0222] As shown in the figure, the gel crushing device 200 includes an inlet 204, a main body 208, two rotating shafts 206, an outlet 210, a drive unit 214, and a gas inlet 216. It should be noted that the main body 208 is also called a container. Figure 1 Two rotating shafts 206 are provided along the orthogonal direction of the paper. The rotating shafts 206 extend along the length of the main body 208. One end of each rotating shaft 206 passes through the main body 208 and is connected to the drive device 214. Although not shown, in this gel pulverizing device 200, the other end of the rotating shaft 206 is rotatably supported by a bearing behind it. In other words, the rotating shaft 206 is held at both ends. However, the gel pulverizing device in the manufacturing method of the present invention is not limited to this dual-shaft support configuration; as long as the purpose of the present invention is achieved, it can also be a so-called single-shaft support structure without a bearing behind the outlet 210. The inlet 204, gas inlet 216, gel flow agent inlet 217, and outlet 210 are respectively fixed to the main body 208 and communicate with the interior of the main body 208. Figure 3 The left and right directions in the figure represent the length direction of the main body 208 and the axial direction of the rotation axis 206. Although not shown in the figure, the main body 208 has a jacket structure.

[0223] Figure 4 The figure shows a portion of the main body 208 of the gel pulverizing apparatus 200. As shown, in this gel pulverizing apparatus 200, two rotating shafts 206 are built into the main body 208. Pulverizing mechanisms 212 are respectively provided on the outer periphery of the two rotating shafts 206. That is, the pulverizing mechanisms 212 and the rotating shafts 206 are configured as separate bodies. In this embodiment, the rotating shafts 206 have multiple discs as pulverizing mechanisms 212. Figure 4 The vertical direction is the width direction of the main body 208. Figure 4 The left and right directions are the length directions of the main body 208 and the axial direction of the rotation axis 206.

[0224] In one suitable manner of performing the gel pulverizing process using the gel pulverizing apparatus 200, firstly, a heat medium is circulated in a jacket (not shown) to heat the main body 208. Then, each rotating shaft 206 is rotated using a drive device 214 (e.g., a motor). Accompanying the rotation of the rotating shafts 206, multiple discs, which serve as screws 206 and pulverizing mechanisms 212, rotate.

[0225] Next, the hydrogel is continuously added to the inlet 204. At this time, water or water vapor can be simultaneously added to the inlet 204. Alternatively, water vapor or water can be added to the gas inlet 216. The hydrogel and the main body 208 are heated using water and water vapor and maintained at a specified temperature.

[0226] The hydrogel injected into the main body 208 moves toward the discharge port 210.

[0227] The hydrogel comes into contact with the pulverizing mechanism 212 (i.e., multiple disks) within the body 208. The hydrogel is granulated by the shearing action of the rotating disks. The hydrogel is pulverized by the shearing action of the pulverizing mechanism 212 and moves toward the discharge port 210. At the discharge port 210, the granular hydrogel that has been adjusted to a specified particle size is removed.

[0228] The rotating shaft of the gel pulverizing apparatus has multiple discs. The discs can be the same or different in shape, but are preferably different. Regarding the combination of discs, for example, see patent document (Japanese Patent Application Publication No. 2005-35212), and may be appropriately modified according to the physical properties of the hydrogel and the desired size of the pulverized gel.

[0229] Examples of gel pulverizing devices (multi-shaft mixers) with this basic configuration include, for example, multi-shaft mixers (kneaders) with two or more shafts. Specifically, mixers with 2, 3, 4, or 8 shafts can be listed. From the viewpoint of production efficiency, this gel pulverizing device is suitable for continuous operation. Specifically, examples of gel crushing devices include the CKH type continuous mixer (Honda Iron Works Co., Ltd.), the TEX twin-screw extruder (Nippon Steel Works Co., Ltd.), the TEXαIII twin-screw extruder (Nippon Steel Works Co., Ltd.), the continuous kneader (CONTINUOUS KNEADER, DALTONCORPORATION), the KRC mixing reactor (KRC HYBRID REACTER, Kurimoto Iron Works Co., Ltd.), the KRC kneader (KURIMOTO-READCO CONTINUOUS KNEADER, Kurimoto Iron Works Co., Ltd.), the KEX extruder (KEXEXTRUDER, Kurimoto Iron Works Co., Ltd.), the KEXD extruder (KEXD EXTRUDER, Kurimoto Iron Works Co., Ltd.), and the twin-arm type kneading extruder (KNEADER-RUDER, moriyama). The invention includes various types of extruders, such as the TEX-SSG (Toshiba Machine Co., Ltd.), TEX-CS (Toshiba Machine Co., Ltd.), TEX-SX (Toshiba Machine Co., Ltd.), TEX-DS (Toshiba Machine Co., Ltd.), TEX-A (Toshiba Machine Co., Ltd.), TEX-B (Toshiba Machine Co., Ltd.), TEX-BS (Toshiba Machine Co., Ltd.), and the WDR series (TECHNOVEL CORPORATION) 2-spindle compounding extruders. Therefore, in a preferred embodiment of the invention, the gel pulverizing device is a continuous multi-spindle compounding machine.

[0230] Regarding the gel pulverizing energy (GGE) used for gel pulverizing hydrogels in the pulverization process using a multi-shaft mixer, the upper limit is preferably 150 [J / g] or less, more preferably 130 [J / g] or less, and even more preferably 120 [J / g] or less. The lower limit is preferably 20 [J / g] or more, more preferably 40 [J / g] or more, and even more preferably 50 [J / g] or more. For example, in this invention, the gel pulverizing energy (GGE(1)) for gel pulverizing hydrogels is 20 to 150 [J / g], preferably 40 to 130 [J / g], and even more preferably 50 to 120 [J / g]. Furthermore, the GGE(2) is 20 to 150 [J / g], preferably 40 to 130 [J / g], and even more preferably 50 to 120 [J / g]. By controlling the GGE(1) and CGE(2) within the above range, it is possible to crush the hydrogel while applying appropriate shear / compression force.

[0231] (Gel temperature)

[0232] In gel pulverization using a multi-shaft mixer, from the viewpoint of continuously pulverizing the hydrogel-like crosslinked polymer at 50°C or higher, it is preferable that the temperature T1 (hereinafter also referred to as "gel temperature T1 at the inlet" or simply "gel temperature T1") of the hydrogel-like crosslinked polymer fed into the inlet of the gel pulverizing apparatus during the gel pulverization process is 50°C or higher. This gel temperature T1 is preferably measured using a thermometer installed at the inlet. From the viewpoint of preventing the hydrogel from adhering to the apparatus after gel pulverization, this gel temperature T1 is preferably 60°C or higher; from the viewpoint of further improving the water absorption properties of the water-absorbing resin particles, it is more preferably 70°C or higher, and even more preferably 80°C or higher. From the viewpoint of suppressing excessive drying, the gel temperature T1 is preferably 130°C or lower, more preferably 110°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower. For the same reason, the gel temperature during pulverization is preferably 130°C or lower. It should be noted that, for the gel temperature T1, the gel temperature T1 can be adjusted to the desired range by keeping the hydrogel-like cross-linked polymer, whose temperature rises due to the heat of polymerization, warmed by feeding it into the gel crushing device; or by heating the obtained hydrogel-like cross-linked polymer.

[0233] From the viewpoint of suppressing the aggregation of hydrophilic gels after gel pulverization, the temperature T2 of the particulate hydrophilic gel crosslinked polymer discharged from the gel pulverization apparatus (hereinafter also referred to as "gel temperature T2 at the discharge port" or simply "gel temperature T2") is preferably 60°C to 140°C, more preferably 70°C to 130°C, even more preferably 80°C to 120°C, particularly preferably 80°C to 115°C, and most preferably 100°C to 115°C. Preferably, the temperature T2 is set within the aforementioned temperature range, and the temperature T1 is within the aforementioned temperature range. This gel temperature T2 is preferably measured using a thermometer installed at the discharge port. It should be noted that the gel temperature T2 can be adjusted to the desired range by appropriately adjusting the set temperature of the heating mechanism and / or the heat preservation mechanism of the gel pulverization apparatus, and thus the residence time of the hydrophilic gel crosslinked polymer inside the gel pulverization apparatus.

[0234] The aforementioned gel flow agent is preferably added during gel pulverization using a multi-shaft mixer. The gel flow agent can be added once or in multiple additions (two or more times), and can be added at any location within the mixer. When adding the gel flow agent in multiple additions, it is preferable to add it at different locations. In one embodiment, during pulverization using a multi-shaft mixer, the gel flow agent is added near the gel inlet of the multi-shaft mixer (e.g., Figure 3 In the middle, near the inlet 204 for dispensing the strip-shaped hydrogel and the gel outlet ( Figure 3 In the process of gel pulverizing, the gel flow agent is added separately at inlet 217. By adding the gel flow agent separately, the adhesion and fusion of the pulverized gels are inhibited. This process is used in the gel pulverizing step. Figure 3 and Figure 4 In the case of the multi-shaft mixer shown, small-diameter granular hydrogels can be obtained. By adding a gel flow agent, excessive aggregation of particles in the superabsorbent resin particles can be suppressed, and blockage of interconnecting pores can be prevented. Therefore, the variation in the ratio of interconnecting pores to independent air bubbles in the superabsorbent resin particles can be suppressed, thereby improving the effectiveness of the present invention.

[0235] [3-5] Separation process

[0236] In the case of reverse suspension polymerization in the above polymerization process, the resulting hydrophobic gel-like crosslinked polymer is separated from the hydrophobic organic solvent in the separation process. There are no particular limitations on the type and structure of the apparatus used in the separation process, as long as it does not impair the water absorption performance (liquid intake rate and reflux rate); for example, known apparatus such as filtration, sedimentation, centrifugation, and extrusion can be used. Alternatively, azeotropic dehydration can be performed by heating under normal or reduced pressure using a stirring device with impellers used in the polymerization process, thereby separating the polymer from the hydrophobic organic solvent. In batch reverse suspension polymerization, azeotropic dehydration under normal or reduced pressure is suitable.

[0237] In the case of continuous suspension polymerization, the hydrophobic gel formed during the polymerization process, along with the hydrophobic organic solvent constituting the continuous phase, is continuously discharged from the reaction apparatus. As described above, the hydrophobic organic solvent and the hydrophobic gel can be separated by known methods such as filtration, sedimentation, centrifugation, and extrusion. Furthermore, as a preferred embodiment, it is preferable to recover the hydrophobic organic solvent separated in this process and recirculate it back to the dispersion unit via piping—a recirculation process.

[0238] [3-6] Gel granulation process

[0239] In the case where reverse suspension polymerization is performed in the above polymerization process, it is preferable to granulate the hydrogel polymer separated from the hydrophobic organic solvent by the above separation process using a gel granulation device having an extrusion section and a porous plate. This yields a granulated hydrogel polymer (hereinafter referred to as granulated gel).

[0240] "Gel Granulation Device"

[0241] In this specification, "gel granulation" refers to the process of producing particles with a generally uniform shape and size by extruding a wet mass formed from granular hydrogel through the pores of a porous plate into a cylindrical shape. In other words, by using a porous plate, the hydrogel that has excessively aggregated into coarse aggregates during the solvent separation process in the preceding step is broken up, and small-diameter, single-particle hydrogel particles are brought into a moderately aggregated state. Therefore, through this process, hydrogels with a relatively uniform particle size (granulated gel) and sufficiently interconnected pores can be obtained. It should be noted that granulated gel can also include single-particle hydrogels.

[0242] The term "gel granulation apparatus having an extrusion action and a perforated plate" used in the gel granulation process is not particularly limited to any apparatus that has an extrusion action and a perforated plate (mold or screen), the extrusion action typically having an extrusion member that extrudes and supplies contents to the perforated plate, and the apparatus is capable of producing granules of a specified size by extruding material from the perforated plate.

[0243] Figure 5 The diagram illustrates the classification of gel granulation devices with an extrusion action and a perforated plate. Gel granulation devices with an extrusion action and a perforated plate are broadly classified into screw type, rotary perforated die type, and rotary blade type based on the structure of the extrusion action.

[0244] The screw-type gel granulating device 310 has a rotary-driven screw 311 (equivalent to an extrusion unit) and a die 313 (equivalent to a perforated plate) with orifices 312. The input material (refer to arrow 314) is extruded using the rotary-driven screw 311 and fed to the die 313, where it is extruded through the orifices 312 (refer to arrow 315). Depending on the direction of material extrusion, the screw-type gel granulating device 310 has a transverse extrusion mode and a front extrusion mode. In the transverse extrusion mode, as shown in the example figure, the die 313 is arranged parallel to the direction extending from the rotation axis of the screw 311, and the material is extruded in a direction intersecting the rotation axis of the screw 311. In the front extrusion mode, the die 313 is arranged orthogonally to the rotation axis of the screw 311, and the material is extruded in the direction extending from the rotation axis of the screw 311.

[0245] As a screw-type gel granulation device, screw-type front-extrusion granulators, screw-type cross-extrusion granulators, and screw-type pre-treatment combined extrusion granulators can be used. As a screw-type cross-extrusion granulator, the single-screw extruder with kneader manufactured by AKIRA Machinery Co., Ltd. can be cited. As a screw-type front-extrusion granulator, the Twin Dome Gran series manufactured by DALTON CORPORATION can be cited. As a screw-type pre-treatment combined extrusion granulator, the Multi Gran manufactured by DALTON CORPORATION can be cited.

[0246] The gel granulation device 320 in the form of a rotating porous die has a roller 321 (equivalent to an extrusion unit) and a rotating die 323 (equivalent to a porous plate) with orifices 322 formed therein and driven by rotation. The roller 321 is disposed inside the rotating die 323. The material fed between the rotating die 323 and the roller 321 (see arrow 324) is extruded from the orifices 322 of the rotating die 323 by the roller 321 (see arrow 325).

[0247] As a gel granulation device in the form of a rotating porous die, a roller-type annular die extrusion granulator can be used. An example of a roller-type annular die extrusion granulator is the Disc Pelleter manufactured by DALTON CORPORATION.

[0248] The rotary blade-type gel granulation device 330 has a rotary-driven paddle 331 (equivalent to an extrusion unit) and a cylindrical mold 333 (equivalent to a perforated plate) with orifices 332. The paddle 331 is disposed inside the cylindrical mold 333. A rotary-driven pressing blade 336 is disposed above the paddle 331. The input material (refer to arrow 334) is extruded into the cylindrical mold 333 by the rotary-driven pressing blade 336 and the paddle 331, and is extruded from the orifices 332 of the cylindrical mold 333 (refer to arrow 335).

[0249] As a rotary blade type gel granulating device, blade-type basket extruders and blade-type oscillating extruders can be used. For example, the cylindrical granulator manufactured by Freund-Turbo Corporation is a blade-type oscillating extruder. The "gel granulating device having an extrusion action section and a perforated plate" used in the gel granulation process is preferably a screw-type front extrusion granulator or a screw-type cross extrusion granulator, more preferably a screw-type front extrusion granulator.

[0250] Here, "perforated plate" refers to a component with a large number of holes used to shape particles into a specified size, corresponding to a die or screen. The shape of the perforated plate is not particularly limited and can be planar, curved, spherical (dome-shaped), etc. For example, in a screw-type front-extrusion granulator, a dome-shaped die is provided at the front end of the screw. Alternatively, in a screw-type cross-extrusion granulator, a curved screen is provided on the outer periphery of the screw. In this case, the extrusion blades are preferably spherical (i.e., their edge contours form part of a sphere). By making the die or screen spherical and the front end of the extrusion blades spherical, extrusion granulation can be easily performed even using a die with a small aperture, further increasing productivity and enabling the production of high-strength granules of any particle size. It should be noted that the term "sphere" broadly includes: the trajectory surface formed by rotating circles such as perfect circles and ellipses, the trajectory surface obtained by combining and rotating multiple circles, hemispheres, curved surfaces, hyperboloids, parabolic surfaces, and other surfaces other than planes.

[0251] Furthermore, the shape of the holes in the porous plate (mold or screen) is not particularly limited; any suitable shape can be selected, such as a circle, ellipse, hexagon, polygon, or triangle. From the viewpoint of particle strength, a circle or ellipse shape is preferred. There is also no particular limitation on the pore diameter, but it is preferably 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.8 mm or less. By keeping it below such an upper limit, the size of the obtained granulated gel can be prevented from increasing beyond what is necessary, and water-absorbing resin particles with appropriate particle size and total integral of interconnected pores can be obtained. The pore diameter is preferably 0.3 to 1.5 mm, more preferably 0.3 to 0.8 mm. If the pore diameter of the porous plate is 0.3 mm or more, efficient extrusion can be achieved during the extrusion operation. It should be noted that the above pore diameter is defined as follows: First, when the hole is not a circle, the geometric mean of the minor axis and major axis of the hole is used as the pore diameter. Furthermore, when the diameters of the holes in the perforated plate are different, the diameters of all holes are calculated, and their arithmetic mean is used as the diameter of the holes in the perforated plate. Moreover, when the diameter of the perforated plate changes (the diameter changes in the thickness direction of the perforated plate) in the region from the extrusion action side to the opposite side, the value in which the diameter reaches its minimum is used.

[0252] There is no particular limitation on the thickness of the perforated plate (mold or screen). Regarding the characteristics of the gel granulation apparatus, when the pore size is small, extrusion granulation can sometimes become difficult if the thickness of the perforated plate is not reduced. Therefore, the thickness of the perforated plate (mold or screen) is preferably about 0.1 to 5 times the pore diameter, more preferably 0.2 to 3 times the pore diameter, and even more preferably 0.5 to 2 times the pore diameter. When the thickness of the perforated plate (mold or screen) is less than 5 times the pore diameter, it can prevent increased resistance in the perforated portion, allowing for smooth extrusion granulation. On the other hand, when the thickness of the perforated plate is 0.1 times or more the pore diameter, it can prevent a decrease in granulation strength.

[0253] Figure 6 This diagram schematically illustrates the extrusion section of the gel granulation apparatus. The symbol "CL" in the diagram represents the gap between the perforated plate 343 (die or screen) and the extrusion action 341 in the gel granulation apparatus 340. In the example shown, the extrusion action 341 is composed of a screw. If the extrusion action 341 has extrusion blades, the gap CL is the distance from the edge of the extrusion blades to the back surface of the perforated plate 343 of the gel granulation apparatus 340. Additionally, the symbol "d" in the diagram represents the aperture of the holes 342 in the perforated plate 343. It should be noted that the hollow arrow 344 in the diagram indicates the extrusion direction of the gel.

[0254] The gap CL between the perforated plate 343 (die or screen) and the extrusion action 341 in the gel granulation apparatus 340 (when the extrusion action 341 has extrusion blades, the distance from the edge of the extrusion blade to the back surface of the perforated plate 343 of the gel granulation apparatus 340) is preferably 0.1 to 10.0 mm. More preferably, when the pore diameter d of the perforated plate 343 is 0.3 to 1.5 mm, the gap CL between the perforated plate 343 (die or screen) and the extrusion action 341 in the gel granulation apparatus 340 (when the extrusion action 341 has extrusion blades, the distance from the edge of the extrusion blade to the back surface of the perforated plate 343 of the gel granulation apparatus 340) is preferably 0.1 mm to 10.0 mm. When the gap is 0.1 mm or more, it can prevent damage to the perforated plate 343 and a shortened lifespan due to the perforated plate 343 being too close to the screw 341. On the other hand, when the aforementioned gap is 10.0 mm or less, it can prevent the following situation: due to the increased pressure during the extrusion operation, the primary particles of the hydrogel become excessively compacted, causing the interconnecting pores in the aggregate to collapse and reducing the total volume fraction of the interconnecting pores. Here, for example, in the case of a screw-type front-extrusion granulator, there is a straight screw as the extrusion action part, and the space between the straight screw and the die is called the pressure equalization part. The thickness of the pressure equalization part is equivalent to the "gap (interval) between the perforated plate (die or screen) and the extrusion action part". In addition, in the case of a cross-extrusion granulator, the die is arranged around the straight screw, and the distance between the die and the straight screw is equivalent to the interval. It should be noted that the length (distance) of the aforementioned gap is the shortest length (distance) of the gap between the perforated plate and the extrusion action part.

[0255] It should be noted that, in the case of a rotating blade type (blade-type basket extruder and blade-type oscillating extruder), the distance from the edge of the rotating blade to the back of the perforated plate is called the gap CL between the perforated plate and the extrusion action, and is preferably within the same numerical range as that of the extruder. In the case of a rotating perforated die type (roller-type annular die extruder), this gap is essentially 0, and therefore it is not limited to this.

[0256] Figure 7This is a schematic diagram illustrating the structure of a screw-type front-extrusion granulator with a spherical (dome-shaped) die, as described above. In this screw-type front-extrusion granulator 400, the feed screw 420, which serves as the extrusion action unit, is connected to a drive unit (not shown) via a gear mechanism within a gearbox 410 and is housed inside a screw box 430. Furthermore, a feed hopper 440 for feeding raw materials is provided at the top of the screw box 430, and a spherical die 450 is mounted at the front of the screw box 430. The front end of the feed screw 420 is spherical, and one or more spherical extrusion blades 460 are provided at this spherical front end 420a. The outline of the edge 460a of the spherical extrusion blade 460 is designed to follow the shape of the spherical back surface 450a of the spherical die 450, and is formed in a spiral shape on the surface of the spherical front end 420a. Therefore, an evenly spaced interval is formed throughout the entire surface between the rotation trajectory of the edge 460a of the spherical extrusion blade 460 and the aforementioned spherical back surface 450a.

[0257] (Contains hydrogel temperature)

[0258] There is no particular limitation on the lower limit of the temperature of the hydrogel placed in the granulation device, but from the viewpoint of granulation efficiency and suppressing damage to the hydrogel, it is preferably 60°C or higher, more preferably 70°C, and even more preferably 80°C or higher. There is no particular limitation on the upper limit of the temperature of the hydrogel when it is placed in the granulation device, and it is usually below 100°C.

[0259] In this gel granulation process, the aforementioned gel flow agent may also be added.

[0260] The gel flow agent can be added in the gel granulation process as described above. However, in the case of reverse suspension polymerization, other methods of addition include adding it to the aqueous gel separated from the hydrophobic organic solvent in the separation process, adding it to the granulated gel before the drying process, and adding it to the monomer aqueous solution in the monomer aqueous solution preparation process. Additionally, it can be added repeatedly with surfactants and polymeric additives used as dispersing aids in the dispersion process.

[0261] The total amount of surfactants and polymeric lubricants, which are used as gel flow agents, added relative to the solid component of the gel fed into the gel granulator is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, more preferably 0.01% by mass or more, and particularly preferably 0.05% by mass or more.

[0262] [3-7] Drying process

[0263] This process involves drying the granular hydrogel obtained through the polymerization process and / or gel pulverization process, and the granulated gel obtained through the gel granulation process, to a desired resin solids composition to obtain a dried polymer. This resin solids composition is determined based on the loss on drying (the weight change when 1 g of the water-absorbing resin is heated at 180°C for 3 hours), and is preferably 80% by weight or more, more preferably 85-99% by weight, further preferably 90-98% by weight, and particularly preferably 92-97% by weight.

[0264] There are no particular limitations on the drying method for the aforementioned particulate hydrogels, and examples include, for instance, heating drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, rotary dryer drying, drying based on azeotropic dehydration with hydrophobic organic solvents, and high-humidity drying using high-temperature steam. From the viewpoint of drying efficiency, hot air drying is preferred, and belt drying (ventilated belt dryer) is more preferred, where hot air is dried over a ventilated belt.

[0265] From the viewpoint of the color of the absorbent resin and drying efficiency, the drying temperature (hot air temperature) in the above-mentioned hot air drying process is preferably 120-250°C, more preferably 150-200°C. It should be noted that drying conditions other than the drying temperature, such as hot air velocity and drying time, can be appropriately set according to the water content, total weight, and target resin solids content of the granular hydrogel to be dried. When performing belt drying, the conditions described in International Publications Nos. 2006 / 100300, 2011 / 025012, 2011 / 025013, and 2011 / 111657 can be appropriately applied. Belt drying yields granular absorbents with an appropriate ratio of interconnected pores and independent air bubbles in the dried absorbent resin.

[0266] In one embodiment, a heating device is used as a drying apparatus in the drying process. This heating device includes: a rotating container that contains and rotates a particulate hydrogel; and a plurality of heating tubes located inside the rotating container, extending axially therein, and rotating together with the rotating container. In this specification, a heating device having this configuration is sometimes referred to as a "rotary heating device" or a "rotary heating device with heating tubes." More preferably, the heating device further includes other heating mechanisms on the outer peripheral surface of its rotating container. In this heating device, the particulate hydrogel contained in the rotating container is stirred by the rotation of the container and heated through contact with the plurality of heating tubes or through heat conduction from the heating tubes. The inner surface of the rotating container is also heated by radiant heat from the plurality of heating tubes, etc., and, as needed, the particulate hydrogel is further heated using the heating mechanisms located on the outer peripheral surface of the rotating container. In this heating device, other stirring mechanisms such as stirring blades are also used as needed. However, the granular hydrogel mainly flows within the container through the rotation of the rotating container holding the granular hydrogel and the action of multiple heating tubes rotating together with the container. Therefore, mechanical and thermal damage to the granular hydrogel being dried is minimal. This suppresses the generation of fine powder and the deterioration of physical properties during the drying process. Furthermore, this heating device performs drying through indirect heat transfer from the heating tubes, thus offering the following advantages: there is no scattering of the dried material as in hot air drying (ventilated belt dryers, ventilated heated rotary kilns), and no need for large-scale waste gas treatment. In addition, since the drying material is mainly circulated through the rotation of the rotating container, this heating device offers the following advantages: unlike continuous stirred dryers that use stirring blades or other stirring methods, stirring adhesive granular hydrogels does not require a large amount of energy, thus avoiding the reduction of the physical properties of the absorbent resin after drying (e.g., reduced water absorption capacity, increased soluble components), the generation of fine powder, and aggregation during drying.

[0267] During the drying process, the generation of fine powder is suppressed by using a rotary heating device, and the clogging of the connecting holes during the drying process is also suppressed. Therefore, using a rotary heating device in the drying process is an example of a suitable implementation. This allows for the production of water-absorbing resin particles with an appropriate ratio of connecting holes to independent air bubbles, thereby improving the effectiveness of the present invention.

[0268] In one embodiment, the absorbent resin particles of the present invention are subjected to multiple gel pulverization processes in a meat grinder without molds during the gel pulverization process, and a rotary heating device is used in the drying process. This prevents the pulverized gel particles from agglomerating, thus reducing the likelihood of clogging the interconnecting pores. Furthermore, it enables the formation of numerous interconnecting pores in the form of fine particle aggregates within the absorbent resin particles, while also reducing independent air bubbles, thereby further enhancing the effectiveness of the present invention.

[0269] In one embodiment, the superabsorbent resin particles of the present invention are processed using a multi-shaft mixer in the gel pulverization step and a rotary heating device in the drying step. This allows for the formation of numerous interconnected pores in the superabsorbent resin particles as aggregates of fine particles, while reducing independent air bubbles, further enhancing the effectiveness of the present invention. Specifically, in a preferred embodiment, after polymerization of the aqueous solution, a gel pulverization step using a multi-shaft mixer with two or more shafts is performed, followed by a drying step using a rotary heating device.

[0270] As a heating device used in this embodiment, an example is a rotary dryer with a steam pipe. Specific examples include steam pipe dryers (manufactured by Kurimoto Iron Works Co., Ltd.), steam pipe dryers (manufactured by Ube Industries, Ltd.), steam pipe dryers (manufactured by Tsukishima Machinery Co., Ltd.), and steam pipe dryers (manufactured by Mitsui Shipbuilding Co., Ltd.).

[0271] Figure 8 An example of a rotary heating device 502 with a heating element is shown. The following uses... Figure 8 The basic structure of the heating device 502 will be explained below. Regarding the method of using the rotary heating device with heating tube and the drying and surface treatment processes using the rotary heating device with heating tube, the conditions described in WO2018 / 092863 are also applied in this invention.

[0272] Figure 8 As shown in the figure, the heating device 502 has a main body 504, an input and output section 506, and a steam inlet / outlet section 508. The main body 504 has a rotating container 510, multiple heating tubes 512, a first gear 514, and a second gear 516. The rotating container 510 is generally cylindrical. Figure 8 The left and right directions in the figure represent the axial direction of the rotating container 510.

[0273] The rotating container 510 houses a plurality of heating tubes 512. Each heating tube 512 extends axially along the rotating container 510 and passes through both ends of the rotating container 510. As will be described later, none of the plurality of heating tubes 512 contacts the inner circumferential surface of the rotating container 510 in the axial direction.

[0274] The first gear 514 is fixed to the outer circumferential surface of the rotating container 510. The second gear 516 meshes with the first gear 514.

[0275] The object to be dried and heated is fed into the inlet and outlet opening 506, and the object to be processed is removed. It should be noted that when adding a surface crosslinking agent solution to the particulate hydrogel during the drying process, it can be added by spraying through the inlet and outlet opening 506.

[0276] The steam inlet / outlet 508 has a steam inlet 544 and a discharge outlet 546. The steam inlet 544 is connected to a plurality of heating tubes 512. The discharge outlet 546 is also connected to a plurality of heating tubes 512.

[0277] To perform the drying process using the heating device 502, steam is introduced into the heating tube 512 from the steam inlet 544. This steam is used to raise the temperature inside the rotating container 510. A portion of the steam is cooled due to heat exchange. The cooled steam becomes water and is discharged from the outlet 546. Steam is continuously introduced from the steam inlet 544 in a manner that compensates for the steam that becomes water and is discharged, thereby controlling the temperature inside the rotating container 510.

[0278] Gas is introduced into the rotating container 510. The rotating container 510 is filled with gas. Excess gas is discharged from the rotating container 510.

[0279] The second gear 516 is rotated by a drive mechanism (e.g., a motor) not shown. The rotation of the second gear 516 causes the first gear 514 to rotate, which in turn causes the rotating container 510 to rotate. Along with the rotating container 510, multiple heating tubes 512 also rotate. Although not shown, a seal disconnects the rotating container 510 from the steam inlet / outlet 508, so even if the rotating container 510 rotates, the steam inlet / outlet 508 will not rotate.

[0280] [3-8] Crushing process and grading process

[0281] This process involves pulverizing the dried polymer obtained through the above-mentioned drying process (pulverization process) and adjusting it to a specified particle size (grading process) to obtain a water-absorbing resin (for convenience, the powdered water-absorbing resin before surface crosslinking is referred to as "water-absorbing resin").

[0282] Examples of machines used in the pulverizing process of this invention include high-speed rotary pulverizers such as roller mills, hammer mills, screw mills, and pin mills; vibratory mills, knuckle-type pulverizers, and cylindrical agitators, which can be combined as needed.

[0283] Furthermore, the particle size adjustment method in the grading process of this invention is not particularly limited, and examples include sieving and air classifying using a JIS standard sieve (JIS Z8801-1(2000)). It should be noted that the particle size adjustment of the water-absorbing resin is not limited to the above-mentioned pulverizing and grading processes, and can be appropriately implemented using polymerization processes (especially reverse suspension polymerization and spray droplet polymerization) and other processes (such as granulation processes and micron powder recovery processes).

[0284] Regarding the water-absorbing resin obtained through the above process (the water-absorbing resin before the surface crosslinking process, the so-called base polymer), the weight-average particle size (D50) is preferably 200-600 μm, more preferably 200-550 μm, and even more preferably 250-500 μm. Furthermore, the proportion of particles with a particle size less than 106 μm is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1% by weight or less; the proportion of particles with a particle size of 850 μm or more is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less. It should be noted that, as a lower limit value for the proportion of these particles, the lower the value, the more preferred it is, ideally 0% by weight, but can be around 0.1% by weight. Furthermore, the logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20-0.50, more preferably 0.25-0.40, and even more preferably 0.27-0.35. It should be noted that these particle sizes can be determined using standard sieves according to the determination method disclosed in US Patent No. 7,638,570, EDANA ERT420.2-02.

[0285] The aforementioned particle size can be applied not only to surface-crosslinked water-absorbing resins (hereinafter, for convenience, sometimes referred to as "water-absorbing resin particles" or "water-absorbing resin powder"), but also to granular water-absorbing agents as the final product. Therefore, it is preferable to perform surface crosslinking treatment (surface crosslinking process) in a manner that maintains the particle size within the aforementioned range in the water-absorbing resin particles, and more preferably, to perform particle size adjustment by setting a granulation process during and after the surface crosslinking process.

[0286] [3-9] Surface crosslinking process

[0287] This process involves further creating a highly crosslinked portion on the surface layer (a portion within 10 μm of the surface of the absorbent resin particles) obtained through the above process. It consists of a mixing process, a heat treatment process, and a cooling process (optional).

[0288] In this surface crosslinking process, water-absorbing resin (water-absorbing resin particles) is obtained by free radical crosslinking, surface polymerization, and crosslinking reaction with surface crosslinking agent on the surface of the water-absorbing resin particles.

[0289] (Surface crosslinking agent)

[0290] The surface crosslinking agent used in this invention is not particularly limited, and can be either organic or inorganic. From the viewpoint of the physical properties of the absorbent resin and the processability of the surface crosslinking agent, an organic surface crosslinking agent that reacts with a carboxyl group is preferred. Examples include one or more surface crosslinking agents disclosed in, for instance, U.S. Patent 7,183,456. More specifically, examples include polyol compounds, epoxy compounds, halogenated epoxy compounds, polyamine compounds or their condensates with halogenated epoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds (e.g., ethylene carbonate), cyclic urea compounds, etc.

[0291] Specific examples of organic surface crosslinking agents include (di, tri, tetra, poly)ethylene glycol, (di, poly)propylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, (poly)glycerol, 2-buten-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, diethanolamine or triethanolamine, pentaerythritol, sorbitol, and other polyol compounds; ethylene glycol diglycidyl ether, (poly)ethylene glycol diglycidyl ether... Epoxy compounds such as oil ethers, (di-, poly)glycerol polyglycidyl ethers, and glycidyl ether; oxazoline compounds such as 2-oxazolidinone, N-hydroxyethyl-2-oxazolidinone, and 1,2-ethylenebisoxazolidinone; 1,3-dioxolane-2-one (ethylene carbonate), 4-methyl-1,3-dioxolane-2-one, 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, and 4-hydroxymethyl Alkyl carbonate esters such as 1,3-dioxane-2-one, 1,3-dioxane-2-one, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, and 1,3-dioxane-heptane-2-one; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepicochlorohydrin, and their polyamine adducts (e.g., KYMENE manufactured by Hercules; a registered trademark); γ-glycidoxypropyltrimethoxysilane, γ-aminopropyl... Silane coupling agents such as triethoxysilane; oxocyclic butane compounds such as 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol, 3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, and polyoxetane compounds; and cyclic urea compounds such as 2-imidazolidineone.

[0292] As for the aforementioned polyols, polyols with 2 to 8 carbon atoms are preferred, polyols with 3 to 6 carbon atoms are more preferred, and polyols with 3 to 4 carbon atoms are even more preferred. Furthermore, diols are preferred, and examples include ethylene glycol, propylene glycol, 1,3-propanediol, and 1,4-butanediol, with polyols selected from propylene glycol (1,2-propanediol), 1,3-propanediol, and 1,4-butanediol being more preferred.

[0293] In addition, polyglycidyl compounds are preferred as epoxy compounds, and ethylene glycol diglycidyl ether is suitable.

[0294] Based on the above-mentioned organic surface crosslinking agents, from the viewpoint of more effectively carrying out surface crosslinking, as an ionic surface crosslinking agent, polyamine polymers and other multivalent cationic polymers can be used in combination.

[0295] The amount of the surface crosslinking agent (total amount when multiple agents are used) is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, relative to 100 parts by weight of the water-absorbing resin particles. Furthermore, the surface crosslinking agent is preferably added in the form of an aqueous solution. In this case, the amount of water is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of the water-absorbing resin particles. Moreover, if a hydrophilic organic solvent is used as needed, its amount is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, relative to 100 parts by weight of the water-absorbing resin particles.

[0296] (Mixed Process)

[0297] This process involves mixing the absorbent resin particles with the aforementioned surface crosslinking agent. There are no particular limitations on the mixing method for the surface crosslinking agent; examples include: preparing a surface crosslinking agent solution beforehand, preferably spraying or dripping the liquid onto the absorbent resin, more preferably spraying the liquid, and then mixing.

[0298] The apparatus for performing this mixing is not particularly limited, but a high-speed stirring mixer is preferred, and a high-speed stirring continuous mixer is even more preferred. When reverse-phase suspension polymerization is used in the polymerization process, a surface crosslinking agent may be added during the separation process when the organic solvent is distilled off or azeotropically dehydrated, so that surface crosslinking occurs simultaneously with solvent separation.

[0299] (Heat treatment process)

[0300] This process involves applying heat to the mixture discharged from the above mixing process, causing a cross-linking reaction on the surface of the water-absorbing resin particles.

[0301] There are no particular limitations on the apparatus for carrying out the crosslinking reaction, but a paddle dryer is a preferred example. The reaction temperature in the crosslinking reaction is appropriately set according to the type of surface crosslinking agent used, preferably 50 to 300°C, more preferably 100 to 200°C.

[0302] (Cooling process)

[0303] This step is an optional step that is set up as needed after the above-mentioned heat treatment step.

[0304] The cooling device is not particularly limited, but it is preferably the same as the device used in the heat treatment process, and more preferably a paddle dryer. This is because by changing the heat medium to a refrigerant, it can be used as a cooling device. It should be noted that the water-absorbing resin particles obtained by the above-described heat treatment process are preferably forcibly cooled to 40-80°C, and more preferably to 50-70°C, as needed in this cooling process.

[0305] [3-10] Additive addition process

[0306] This process involves adding additives such as polyvalent metal salts, cationic polymers, chelating agents, inorganic reducing agents, hydroxycarboxylic acid compounds, water-insoluble inorganic particles, surfactants, and non-polymeric water-soluble compounds to the absorbent resin particles obtained through the surface crosslinking process described above. As mentioned above, the additives and the aforementioned surface crosslinking agent (aqueous solution) can also be mixed simultaneously with the absorbent resin particles.

[0307] (polyvalent metal salts and / or cationic polymers)

[0308] From the viewpoint of improving the liquid permeability and moisture flowability of the obtained water-absorbing resin, polyvalent metal salts and / or cationic polymers can be added.

[0309] Specifically, the compounds and their amounts disclosed in International Publication No. 2011 / 040530, “〔7〕Multivalent metal salts and / or cationic polymers”, are used as the above-mentioned polyvalent metal salts and / or cationic polymers.

[0310] (chelating agent)

[0311] From the perspective of the color tone (anti-staining) and anti-deterioration of the obtained water-absorbing resin, chelating agents can be added.

[0312] Specifically, the chelating agent described above is the compound and its dosage disclosed in International Publication No. 2011 / 040530, "〔2〕 Chelating Agent".

[0313] (Inorganic reducing agent)

[0314] From the perspectives of improving the color (anti-staining), resistance to degradation, and reducing residual monomers of the resulting water-absorbing resin, inorganic reducing agents can be added.

[0315] Specifically, the inorganic reducing agent described above is the compound and its dosage disclosed in International Publication No. 2011 / 040530, "〔3〕Inorganic Reducing Agent".

[0316] (α-Hydroxycarboxylic acid compounds)

[0317] From the perspective of the resulting absorbent resin's color tone (anti-staining properties), α-hydroxycarboxylic acids can be added. It should be noted that "α-hydroxycarboxylic acid compound" refers to a carboxylic acid or its salt that has a hydroxyl group within the molecule, specifically a hydroxycarboxylic acid with a hydroxyl group at the α-position.

[0318] Specifically, the compounds and their amounts disclosed in International Publication No. 2011 / 040530, “〔6〕α-hydroxycarboxylic acid compounds”, are used in this invention.

[0319] (Water-insoluble inorganic particles)

[0320] From the viewpoint of improving the flowability of absorbent resin particles, water-insoluble inorganic particles can be added. Specifically, the water-insoluble inorganic particles described in section [2-7] above can be listed.

[0321] (surfactant)

[0322] From the perspective of improving the physical properties of the resulting water-absorbing resin (such as water absorption speed), surfactants can be added.

[0323] Specifically, surfactants disclosed in International Publication No. 97 / 017397 and US Patent No. 6107358 can be listed as examples, namely, nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc.

[0324] (Non-polymer water-soluble compound)

[0325] From the viewpoint of reducing dust from absorbent resins, non-polymeric water-soluble compounds can be added. In this invention, the compounds and their dosages disclosed in International Publication No. 2014 / 034667, "Non-polymeric Water-soluble Compounds," are applied.

[0326] In this invention, in order to add various functions to the absorbent resin, additives other than those mentioned above may also be added. Specifically, examples of such additives include compounds containing phosphorus atoms, oxidizing agents, organic reducing agents, organic powders such as metal soaps, deodorizing agents, antibacterial agents, pulp, thermoplastic fibers, etc.

[0327] The amount of this additive can be appropriately determined according to its application, and therefore is not particularly limited. It is preferably 3 parts by weight or less, more preferably 1 part by weight or less, relative to 100 parts by weight of the water-absorbing resin. In addition, this additive may also be added in a process different from the above-described process.

[0328] [3-11] Other processes

[0329] In addition to the above-mentioned processes, this invention may include granulation, sizing, micron powder removal, and micron powder reuse processes as needed. Furthermore, it may include one or more of the following processes: transportation, storage, packaging, and preservation. It should be noted that the "sizing process" includes: micron powder removal during and after the surface cross-linking process; and a process of grading and pulverizing when the absorbent resin aggregates to a size exceeding the desired size. Furthermore, the "micron powder reuse process," in addition to directly adding micron powder as in this invention, also includes: forming large hydrogels and adding them in any step of the absorbent resin manufacturing process.

[0330] [4] Uses of granular water absorbents

[0331] The granular absorbent of the present invention can be used for purposes of water absorption and is widely used as an absorbent. It can also be used as an absorbent article containing the absorbent. In particular, the granular absorbent of the present invention reduces backflow under pressure; therefore, it can be suitably used as an absorbent in absorbent articles for use by humans or animals to absorb bodily fluids such as urine and blood (hereinafter referred to as "wearable absorbent"). It can also be suitably used as an absorbent in absorbent articles suitable for placement on an object (e.g., floor, bed sheet, etc.) to absorb bodily fluids such as urine and blood from humans or animals (hereinafter referred to as "placement absorbent"). Examples of wearable absorbents include, for example, disposable diapers, incontinence pads, and sanitary napkins; examples of placement absorbents include, for example, pet pads, waterproof nursing sheets, and makeshift toilets for disaster relief. Examples of other absorbent articles include, for example, cat litter, drip absorbent materials, food preservation materials, and anti-condensation sheets. Other applications of this water-absorbing resin include soil moisture retention agents, seedling sheets, seed coating materials, disposable heat packs, cooling headscarves, cold insulators, medical waste liquid solidifying agents, residual soil solidifying materials, waterproof waste liquid gelling agents, absorbent sandbags, patch materials, thickeners for cosmetics, waterproofing materials for communication cables, gaskets and sealants, slow-release agents for fertilizers, various slow-release agents (space bactericides, fragrances, etc.), wound dressings, anti-condensation building materials, and oil moisture removal agents. Furthermore, the granular water-absorbing agent of this invention can also be used as a coating, adhesive, anti-blocking agent, light diffusing agent, matting agent, additive for decorative panels, additive for artificial marble, and additive for colorants, where it absorbs water / swells and is mixed into resins and substrates.

[0332] That is, a suitable embodiment of the present invention is an absorbent comprising the granular water-absorbing agent described above.

[0333] Another suitable embodiment of the present invention is a sanitary article comprising an absorbent as described above.

[0334] Examples of absorbent materials include absorbent materials formed by molding granular absorbent and a fibrous substrate (e.g., hydrophilic fibers) as the main components. More preferably, the content (core concentration) of the granular absorbent in the absorbent is 20-100% by weight, more preferably 25-90% by weight, particularly preferably 30-80% by weight, and most preferably 40-80% by weight relative to the total weight of the granular absorbent and hydrophilic fibers. The higher the core concentration in the absorbent, the more the absorbency of the granular absorbent will affect the manufacturing of the absorbent, absorbent articles, etc. Such absorbents are formed, for example, by blending or sandwiching a fibrous substrate such as hydrophilic fibers with granular absorbent. Examples of fibrous substrates used include, for example, hydrophilic fibers such as pulverized wood pulp, cotton linters, cross-linked cellulose fibers, rayon, cotton, wool, acetate, vinylon, etc. These fibrous substrates are preferably materials formed by air-laid web formation.

[0335] Alternatively, as an absorbent, it can be an absorbent sheet (without paste) obtained by fixing a water-absorbing resin between two sheets (e.g., nonwoven fabric).

[0336] Furthermore, the aforementioned absorbent article refers to an absorbent article comprising the aforementioned absorbent body, a liquid-permeable surface sheet, and a liquid-impermeable back sheet. Regarding the aforementioned absorbent article, an absorbent body (absorbent core) is manufactured by clamping the absorbent core with a liquid-permeable surface sheet and a liquid-impermeable back sheet. Subsequently, as needed, by equipping it with elastic members, a diffusion layer, adhesive tape, etc., absorbent articles such as adult diapers and sanitary napkins are obtained. It should be noted that, at this time, the aforementioned absorbent core is compressed to, for example, a density of 0.06–0.50 g / cm³. 3 Basis weight is 0.01~0.20 [g / cm³] 2 The scope of ].

[0337] The preferred embodiment of the absorbent comprising the granular absorbent described above will be described below.

[0338] [4-1] Wearable absorber (wearable type)

[0339] In one embodiment, an absorbent containing the particulate absorbent of the present invention can be used as an absorbent for constituting an absorbent article worn by a person or animal. In this embodiment, the absorbent is an absorbent having a first substrate and an absorbent layer, the first substrate having an absorbent surface formed on its surface side for direct liquid absorption, the absorbent layer being disposed on the back side of the first substrate, the absorbent layer containing particulate absorbent containing poly(meth)acrylate (salt) based absorbent resin particles as the main component, the particulate absorbent comprising: communicating pores, which are spaces communicating with the outside; and independent air bubbles, which are closed spaces not communicating with the outside, the total volume fraction of the communicating pores being 10% by volume or more, the total volume fraction of the independent air bubbles being 0.5% by volume or less, and the absorbent satisfying at least one of the following (a) and (b): (a) the area of ​​the absorbent layer containing the particulate absorbent is disposed with gaps that are substantially free of the particulate absorbent, the gaps being formed extending along the length direction of the absorbent; (b) the first substrate is a liquid-permeable sheet with a porosity of 95% or more.

[0340] The absorbent of this embodiment is characterized by the use of a specific granular absorbent, namely, a granular absorbent as described above. Therefore, in the absorbent of this embodiment, the granular absorbent is a granular absorbent with polyacrylic acid (salt) based absorbent resin particles as the main component, having a shape containing interconnected pores and independent air bubbles, with a total volume fraction of interconnected pores of 10% or more and a total volume fraction of independent air bubbles of 0.5% or less. Hereinafter, a granular absorbent with polyacrylic acid (salt) based absorbent resin particles as the main component, having a shape containing interconnected pores and independent air bubbles, a total volume fraction of interconnected pores of 10% or more, and a total volume fraction of independent air bubbles of 0.5% or less will sometimes be referred to as a "specific granular absorbent." The composition of the specific granular absorbent is as described above. By using a specific granular absorbent in the absorbent layer, an absorbent with a high liquid absorption rate and reduced backflow can be produced. In this embodiment, it was discovered that using a specific granular absorbent with excellent absorption performance results in a composition that exhibits even better absorption performance.

[0341] It should be noted that, in this specification, the absorption rate of the liquid is indicated by the time it takes for the absorber to absorb a specified amount of liquid; a shorter time is considered desirable. Additionally, the re-wet rate (also known as backflow or re-wet) indicates the amount of liquid absorbed by the absorber that is released due to pressure applied to the absorber; a lower re-wet rate is considered desirable.

[0342] The absorbent in this embodiment preferably contains not only a specific particulate absorbent in the absorbent layer, but also satisfies at least one of the following (a) and (b): (a) the regions in the absorbent layer containing the particulate absorbent are arranged with gaps that are substantially free of the particulate absorbent, and the gaps are formed extending along the length of the absorbent; (b) the first substrate is a liquid-permeable sheet with a porosity of 95% or more.

[0343] With the above configuration, an absorbent with high liquid absorption rate and reduced backflow can be manufactured, that is, an absorbent with significantly superior liquid absorption rate and backflow. Regarding the absorbent of this embodiment, the surface of the first substrate forms an absorbent surface that directly absorbs the liquid. In this specification, "directly" means that the liquid contacts or permeates the substrate before contacting the absorbent layer. In this method, even if a portion of the particulate absorbent contained in the absorbent layer permeates through the first substrate and moves on the first substrate, resulting in some exposure, this is not considered as the presence of an absorbent layer. It should be noted that the cause of this movement is assumed to be, for example, vibration generated during the transport and handling of the absorbent as a final product. The intentional dispersion or arrangement of particulate absorbent on the first substrate is not within the scope of this method.

[0344] In another embodiment of this invention, the surface of the first substrate is a liquid-absorbing surface that can directly absorb liquid, so no water-absorbing layer is provided on the first substrate. Therefore, the absorbent of this embodiment is an absorbent having a first substrate and a water-absorbing layer. The first substrate has a liquid-absorbing surface formed on its surface side that directly absorbs liquid. The water-absorbing layer is disposed on the back side of the first substrate. No water-absorbing layer is disposed on the surface side of the first substrate. The water-absorbing layer contains a particulate water-absorbing agent with poly(meth)acrylate (salt) based water-absorbing resin particles as the main component. The particulate water-absorbing agent contains: a connecting hole, which is a space communicating with the outside; and an independent bubble, which is a closed space not communicating with the outside. The total volume fraction of the connecting hole is 10% or more, and the total volume fraction of the independent bubble is 0.5% or less. The absorbent satisfies at least one of the following (a) and (b): (a) the area of ​​the water-absorbing layer containing the particulate water-absorbing agent is disposed with a gap that does not contain the particulate water-absorbing agent, and the gap is formed extending along the length direction of the absorbent; (b) the first substrate is a liquid-permeable sheet with a porosity of 95% or more.

[0345] The inventors discovered that in the embodiments of this application, the reflux rate of conventional absorbers was significantly higher during the measurement of reflux flow. In other words, when liquid is introduced intermittently multiple times (especially more than three times), the liquid volume reaches more than the set absorption capacity in the usual configuration, resulting in excessive "reflux". In contrast, in this embodiment, by satisfying at least one of (a) and (b), the liquid introduced from the absorbent surface is not allowed to remain on the absorbent surface (and thus, the introduced liquid is not allowed to be partially retained), and the liquid can be efficiently delivered to the lower absorbent layer that performs the water absorption function.

[0346] According to the configuration in (a), the regions of the absorbent layer containing particulate absorbent are arranged with gaps that are substantially free of particulate absorbent, and these gaps are formed extending along the length of the absorbent. Here, the gaps between the regions containing particulate absorbent can function as a flow path for liquid to be introduced from the first substrate into the absorbent layer when liquid is introduced. That is, by having a flow path, liquid introduced from the absorbent surface is not allowed to remain on the absorbent surface (and thus, the introduced liquid is not allowed to remain locally), and liquid can be efficiently delivered into the absorbent layer. Specifically, liquid (e.g., urine) in the first substrate is introduced into the entire surface and gaps of the absorbent layer. Regarding the liquid introduced into the gaps, since there is no particulate absorbent that hinders liquid permeation in the regions containing particulate absorbent, it becomes easy to diffuse. As a result of liquid diffusion, uneven liquid absorption is prevented, such as the particulate absorbent absorbing more liquid at the liquid introduction site and less liquid at the particulate absorbent site away from the liquid introduction site. Therefore, it can prevent the formation of areas where the particulate absorbent becomes saturated and swollen, in other words, areas where it cannot absorb liquid, thereby increasing the reflux rate. As a result, it is believed that the reflux rate can be reduced.

[0347] Furthermore, by shaping the gaps to extend along the length of the absorbent, even when liquid is partially introduced onto the absorbent surface, the liquid reaching the absorbent layer can easily diffuse along the surface direction. Additionally, the absorbent in this embodiment uses a specific particulate desiccant with excellent absorption properties in the absorbent layer. By providing gaps extending along the length of the absorbent in the absorbent layer containing the specific particulate desiccant, diffusion when liquid is partially introduced onto the absorbent surface is efficiently utilized. That is, the specific particulate desiccant has excellent absorption properties (liquid absorption rate), thus it can quickly absorb locally introduced liquid, but by incorporating liquid into the surrounding particulate desiccant (i.e., providing gaps extending along the length of the absorbent), the absorption properties of the surrounding particulate desiccant can also be fully utilized. Therefore, by adopting this configuration, the absorption performance of the specific particulate desiccant can be further improved.

[0348] Furthermore, for example, when a particulate absorbent swells upon absorbing liquid, the swollen particulate absorbent expands into areas considered gaps due to its increased volume, sometimes reducing the gap size. In this case, even with intermittent multiple liquid introductions, the liquid absorption capacity gradually decreases as the gap size decreases. Moreover, as the gap size decreases and liquid becomes more difficult to pass through, the particulate absorbent easily becomes locally saturated and swells. Therefore, when liquid is released from the absorbent layer, the amount flowing back to the absorbent surface of the first substrate gradually increases. Consequently, the backflowing liquid rises to the skin (contacts the skin), causing discomfort.

[0349] In contrast, it was discovered that the absorbent of this embodiment uses a specific particulate absorbent in the absorbent layer as described above, and further provides gaps extending along the length direction of the absorbent in the absorbent layer, thereby maximizing the absorption performance of the particulate absorbent and significantly reducing backflow. That is, according to this embodiment, an excellent absorbent is achieved through the specific particulate absorbent and (a) composition.

[0350] According to the composition of (b), the first substrate is a liquid-permeable sheet with a porosity of 95% or more. Here, in this specification, "porosity of the substrate" refers to the porosity of the "fiber matrix constituting the substrate", which is expressed by the following (Formula 1).

[0351] Porosity (%) = [1 - (M / (A×T×D))]×100 (Equation 1)

[0352] M: Mass of the substrate (fiber matrix) (g)

[0353] A: Area (cm²) of the substrate (fiber matrix) 2 )

[0354] T: Thickness (cm) of the substrate (fiber matrix)

[0355] D: Density of the fibers forming the substrate (fiber matrix) (g / cm³) 3 ).

[0356] In the case of a liquid-permeable sheet with a porosity of 95% or more in the first substrate, numerous pores exist within the first substrate, facilitating flow paths when liquid is introduced. Therefore, liquid introduced from the absorbent surface (the upper surface of the first substrate) is not retained on the absorbent surface (and consequently, the introduced liquid is not locally retained), allowing the liquid to be efficiently delivered to the entire surface of the absorbent layer. Specifically, this is believed to be because: when liquid passes through the first substrate, the liquid has high diffusivity in the surface direction, causing the diffused liquid (e.g., urine) to move (migrate) extensively and without omission across the entire surface of the absorbent layer. That is, when the absorbed liquid reaches the absorbent layer, the liquid diffuses in the surface direction; therefore, even if a large amount of liquid is introduced into the absorbent layer, the absorbent layer absorbs the liquid that spreads in the surface direction rather than being locally present. Thus, the absorbent layer can adequately absorb and retain liquid. Furthermore, once the liquid is absorbed by the absorbent layer, the excellent absorption properties of the specific particulate absorbent can significantly reduce the backflow of the liquid absorbed by the absorbent layer to the absorbent surface of the first substrate, thereby suppressing the backflow of liquid from rising to the skin (in contact with the skin).

[0357] Furthermore, the absorbent in this embodiment is suitable, for example, as an absorbent article (e.g., a diaper) for use by infants with small bladders who are beginning to walk, during active periods of movement such as daytime. Of course, its use is not limited to this. Additionally, the mechanisms described in this specification are not limited to the scope of protection of the claims of this application.

[0358] Hereinafter, this embodiment will be described with reference to the accompanying drawings. It should be noted that in the description of the drawings, the same symbols are used for the same elements, and repeated descriptions are omitted. Furthermore, the dimensions in the drawings are exaggerated for ease of explanation and may sometimes differ from the actual dimensions.

[0359] First implementation: "Absorber based on the structure of (a)"

[0360] The absorbent of the first embodiment of the present invention is an absorbent having a first substrate and a water-absorbing layer. The first substrate has a liquid-absorbing surface formed on its surface side for directly absorbing liquid. The water-absorbing layer is disposed on the back side of the first substrate. The water-absorbing layer contains a specific particulate water-absorbing agent. The absorbent satisfies the following: (a) the area of ​​the water-absorbing layer containing the particulate water-absorbing agent is disposed with a gap that is substantially free of the particulate water-absorbing agent. The gap is formed extending along the length direction of the absorbent.

[0361] In one embodiment, the absorbent of the first embodiment has: a first substrate; a second substrate; and an absorbent layer located between the first substrate and the second substrate. That is, in one embodiment, the absorbent further includes a second substrate, and the absorbent layer is located between the first substrate and the second substrate.

[0362] For the first implementation method, based on Figures 9-14 Please provide an explanation. Figure 9 This is a schematic diagram showing a cross-section of the absorber cut along the width direction in the absorber of the first embodiment. Figure 10 To show along Figure 9 A schematic diagram of a cross-sectional view of line AA viewed from above. Figure 11 This is a schematic diagram illustrating another way of creating a gap in the absorber of the first embodiment. Figures 12-14 To show along Figure 9 A schematic diagram of a cross-sectional view of line AA viewed from above, illustrating other embodiments of the gap. Figure 9 and Figure 11 In the diagram, the arrows indicate the direction in which the liquid to be absorbed is introduced.

[0363] like Figure 9 As shown, the absorbent 50 includes a first substrate 51, an absorbent layer 52, and a second substrate 53. The absorbent layer 52 is sandwiched between the first substrate 51 and the second substrate 53. The first substrate 51 is located on the side where the liquid to be absorbed (the liquid to be absorbed) is introduced relative to the absorbent layer 52. That is, the first substrate 51 is disposed on the liquid discharge side (e.g., the skin side in the case of a diaper). The absorbent layer 52 is disposed between the first substrate 51 and the second substrate 53.

[0364] The absorbent layer 52 contains granular absorbent agent 54. Figure 9 In the diagram, the absorbent layer 52 shows a state where particulate absorbent 54 exists between the first substrate 51 and the second substrate 53. A portion of the particulate absorbent 54 can detach from each substrate 51, 53. The particulate absorbent 54 (the region containing the particulate absorbent 54) is disposed with gaps 55 that are substantially free of particulate absorbent 54. The gaps 55 are formed between the first substrate 51 and the second substrate 53. Therefore, the absorbent "layer" is not only a continuous sheet, but can also be of any form as long as it exists between the first substrate 51 and the second substrate 53 with a certain thickness and length. For example, the absorbent layer 52 can exist intermittently between the first substrate 51 and the second substrate 53 with a certain thickness and length.

[0365] The absorbent layer 52 includes granular absorbent 54 that is in contact with (or fixed to) the first substrate 51 and granular absorbent 54 that is in contact with (or fixed to) the second substrate 53. A portion of the granular absorbent 54 may not be in contact with the substrates 51 and 53 (or may not be fixed to the substrates 51 and 53; it may detach from the substrates 51 and 53). To fix the granular absorbent 54 to the substrates 51 and 53, an adhesive may be used, for example.

[0366] A particulate absorbent 54 may be present within the first substrate 51. The particulate absorbent 54 within the first substrate 51 may be, for example, a particulate absorbent 54 that is in contact with (or fixed to) the first substrate 51, or a particulate absorbent 54 that is in contact with (or fixed to) the second substrate 53 and is detached and captured within the first substrate 51.

[0367] In this embodiment, the first substrate 51 and the particulate absorbent 54 in the absorbent layer 52 are preferably in direct contact or in contact with an adhesive, and / or the second substrate 53 and the particulate absorbent 54 in the absorbent layer 52 are preferably in direct contact or in contact with an adhesive.

[0368] The gap 55 can be partially formed in the absorbent layer, and the area containing the particulate absorbent can be disposed in part of the absorbent layer through the gap that does not substantially contain the aforementioned particulate absorbent.

[0369] Here, as Figure 10 As shown, the gap 55 is formed extending along the length direction of the absorber 50. Figure 10 In this configuration, the gap 55 is positioned at the center of both the length and width directions of the absorber 50. For example, if the absorber 50 has dimensions of 160 mm in length and 80 mm in width, the gap 55 has dimensions of 60 mm in length and 10 mm in width.

[0370] Regarding the absorbent 50 of this embodiment, no particulate absorbent 54 is dispersed or disposed in the region of the gap 55, therefore the region of the gap 55 is substantially free of particulate absorbent 54. In this region of the gap 55, additives other than particulate absorbent 54 may be contained. For example, the gap 55 can be formed by direct contact between the first substrate 51 and the second substrate 53 or by contact using an adhesive. Alternatively, the gap 55 may also be shaped such that the first substrate 51 follows the shape of the particulate absorbent 54 (the region containing the particulate absorbent 54). In this case, as... Figure 11 As shown, the first substrate 51 is shaped such that it covers the area containing the particulate absorbent 54 over the area containing the particulate absorbent 54, and at the gap 55, it is shaped to sink into the second substrate 53 along the upper side of the area containing the particulate absorbent 54. Alternatively, the second substrate 53 may also be shaped to follow the particulate absorbent 54 (the area containing the particulate absorbent 54). In this case, the second substrate 53 is shaped such that it covers the area containing the particulate absorbent 54 below the area containing the particulate absorbent 54, and at the gap 55, it is shaped to rise towards the first substrate 51 along the lower side of the area containing the particulate absorbent 54 (illustration omitted).

[0371] When the first substrate 51 and / or the second substrate 53 follow the shape of the granular absorbent 54, the area containing the granular absorbent 54 is separated by the contact between the first substrate 51 and the second substrate 53. In this embodiment, the first substrate 51 and the second substrate 53 are also in contact, but the liquid flow path is maintained, and therefore they are considered as gaps 55. The absorbent layer 52 is separated by the first substrate 51 (or, depending on the case, the first substrate 51 and the second substrate 53), so the absorbent layer 52 exists intermittently in this manner. In addition, the end of the absorbent 50 is sometimes closed by the first substrate 51 and the second substrate 53 because the end of the first substrate 51 overlaps with the end of the second substrate 53 (not shown). In this case, since the first substrate 51 (or, depending on the case, the first substrate 51 and the second substrate 53) enters the end of the absorbent layer 52, the end of the absorbent layer 52 is in a state where the absorbent layer 52 is not present.

[0372] In the absorbent 50, a gap 55 is formed by providing a region on the second substrate 53 where no particulate absorbent 54 is present. In the absorbent 50 of this embodiment, the gap 55 (i.e., the region where no particulate absorbent 54 is present) extends along the length direction of the absorbent 50. This allows it to effectively function as a liquid passage path. The shape of the gap 55 along the length direction can be, for example, straight, curved, or wavy. The location of the gap 55 is not limited as long as it is a continuous shape; from an absorbency point of view, it is preferably at the center in the width direction of the absorbent 50. The length of the gap 55 (length in the length direction) is not limited as long as it is within the range that enables the effect of this embodiment to be achieved; from an absorbency point of view, it is preferably 1 / 50 to 1 / 1, more preferably 1 / 20 to 1 / 1, and even more preferably 1 / 10 to 1 / 1, relative to the length of the absorbent 50 (length in the length direction). Furthermore, the width (length in the width direction) of the gap 55 is not limited as long as it is within the range that enables the effect of this embodiment. From the viewpoint of absorption, it is preferably 1 / 50 to 1 / 1, more preferably 1 / 20 to 1 / 1, and even more preferably 1 / 10 to 1 / 1, relative to the width (length in the width direction) of the absorber 50. Additionally, there can be one or more gaps 55. An example of the shape of the gap 55 is shown below. Figures 7-9 .

[0373] Regarding gap 55, the portion extending along the length direction can be considered as a single unit. For example, as... Figure 12 As shown in (A), the gap 55 can be formed from one end of the absorber 50 along its length to the other end. Additionally, as... Figure 12 As shown in (B) to (D), one or more gaps 55 that are orthogonal to or angularly intersecting the gaps 55 extending along the length direction can be further provided. Figure 13 As shown in (A) to (C), multiple gaps 55 extending along the length direction can be provided, and the gaps 55 can be provided intermittently. For example... Figure 14 As shown in (A) to (D), the gap 55 can be a waveform, V-shape, O-shape, or a combination thereof.

[0374] Second implementation: "Absorber based on the structure of (b)"

[0375] The absorber of the second embodiment of this embodiment is an absorber having a first substrate and a water-absorbing layer. The first substrate has a liquid-absorbing surface formed on its surface side that directly absorbs liquid. The water-absorbing layer is disposed on the back side of the first substrate. The water-absorbing layer contains a specific particulate water-absorbing agent. The absorber satisfies (b) that the first substrate is a liquid-permeable sheet with a porosity of 95% or more.

[0376] In one embodiment, the absorbent of the second embodiment has a first substrate, a second substrate, and an absorbent layer located between the first substrate and the second substrate. That is, in one embodiment, the absorbent further includes a second substrate, and the absorbent layer is located between the first substrate and the second substrate.

[0377] For the second implementation method, based on Figure 15 and Figure 16 Please provide an explanation. Figure 15 This is a schematic diagram showing a cross-section of the absorber 50 cut along the width direction in the absorber 50 of the second embodiment. Figure 16 The diagram illustrates another embodiment of the absorbent body according to the second embodiment, and is a schematic diagram showing a cross-section of the absorbent body cut along its width. In the second embodiment, it is the same as the first embodiment except that the absorbent layer 52 does not have gaps 55, the porosity of the first substrate is within a specific range, and the second substrate has a laminated structure. In the second embodiment, the components identical to those in the first embodiment are omitted. That is, Figure 15 and Figure 16 The explanations in the text can also be applied. Figures 9-14 Explanation (symbols).

[0378] like Figure 15 As shown, the absorbent 50 includes a first substrate 51, an absorbent layer 52, and a second substrate 53. The absorbent layer 52 is a structure sandwiched between the first substrate 51 and the second substrate 53. The first substrate 51 is located on the side where the liquid to be absorbed (the liquid to be absorbed) is introduced relative to the absorbent layer 52. That is, the first substrate 51 is disposed on the liquid introduction side (e.g., the skin side in the case of a diaper). The absorbent layer 52 is disposed between the first substrate 51 and the second substrate 53. The absorbent layer 52 contains particulate absorbent agent 54. Figure 15 The diagram shows the state of the absorbent layer 52 with particulate absorbent 54 between the first substrate 51 and the second substrate 53.

[0379] In the second embodiment, the first substrate 51 is a liquid-permeable sheet with a porosity of 95% or more. The first substrate 51 is preferably a liquid-permeable sheet with a porosity of 95.5% or more, more preferably 96% or more, further preferably 96.5% or more, particularly preferably 97.5% or more, and most preferably 98% or more. The porosity of the first substrate is a value calculated using the method described above. The porosity of the first substrate can be controlled by factors such as bulk density, weight per unit area, material, mesh structure, and manufacturing process conditions.

[0380] In the second embodiment, the second substrate 53 can be formed by overlapping a third substrate 53a. For example, as... Figure 16 As shown, the second substrate 53 is formed by stacking multiple (e.g., 3 layers) third substrates 53a. This allows the absorbed liquid to diffuse upon reaching the second substrate 53, increasing the liquid retention in the second substrate and thus further improving the absorption rate and reflux rate. Preferably, the third substrates 53a are stacked in 2 or more layers, more preferably in 3 or more layers. Practically, the maximum number of stacked third substrates 53a is 10 layers or less.

[0381] This embodiment is not limited to the above embodiment, and various changes can be made within the scope of the claims.

[0382] The components constituting the absorber of this embodiment will now be described in detail. It should be noted that, unless otherwise specified, the following description applies to either the first or second embodiment.

[0383] [1] First substrate

[0384] The first substrate is a liquid-permeable substrate located on the side where the liquid to be absorbed is introduced. It should be noted that the liquid to be absorbed is not limited to water, and can also be urine, blood, sweat, feces, waste liquid, moisture, steam, ice, mixtures of water with organic and / or inorganic solvents, rainwater, groundwater, etc., as long as it contains water, there are no particular limitations. Preferred examples include bodily fluids such as urine, menstrual blood, and sweat.

[0385] In the absorbent of the first embodiment of this invention, the liquid-permeable substrate used as the first substrate is not particularly limited in terms of raw materials, composition, and shape, as long as it is permeable to liquid. For example, it can be a liquid-permeable sheet (e.g., nonwoven fabric) obtained by mixing hydrophilic fibers with a heat-melting resin, adhesive, etc., and processing it into a sheet, or it can be a layered molded article obtained by compressing hydrophilic fibers without using a heat-melting resin, adhesive, etc., but only (e.g., a pulp pad). It should be noted that in this specification, the term "liquid-permeable substrate" is not particularly limited in terms of raw materials, composition, and shape, as long as it is permeable to liquid. The term "liquid-permeable sheet" is limited to those obtained by mixing hydrophilic fibers with a heat-melting resin, adhesive, etc., and processing them into a sheet. Therefore, when it is called a "liquid-permeable sheet," it is a liquid-permeable substrate that is not formed solely from hydrophilic fibers and is limited to a sheet shape.

[0386] In the absorbent of the second embodiment of this invention, regarding the liquid-permeable substrate used as the first substrate, from the viewpoint of liquid diffusion and reflux, it is preferable that it not only has high liquid permeability but also high shape retention. Therefore, the first substrate in the second embodiment is preferably a liquid-permeable sheet (e.g., a nonwoven fabric) obtained by mixing hydrophilic fibers with a heat-melting resin, adhesive, etc., and processing them into a sheet shape.

[0387] The first substrate is a liquid-permeable substrate and is located on the liquid-absorbing side, thereby fully utilizing the performance of the absorbent as the effect of this embodiment (backflow, surface leakage, etc.). Regarding the water permeability of the liquid-permeable substrate, the water permeability coefficient (JIS A1218:2009) is preferably 1×10⁻⁶. -5 The permeability is preferably 1×10 cm / s or higher. -4 cm / s or higher, more preferably 1×10 -3 speeds of cm / s or higher, with a preferred speed of 1×10⁻⁶. -2 speeds of cm / s or higher, with the optimal value being 1×10⁻⁶. -1 Speeds of cm / s or higher.

[0388] In the first embodiment, the unit area weight of the first substrate is preferably 3 to 100 g / m². 2 More preferably, 5–90 g / m 2 A further preferred value is 10–80 g / m³. 2 By using a weight per unit area of ​​the first substrate within this range, the absorption rate of the absorber is further increased, and the recirculation rate can be further reduced. In the second embodiment, the weight per unit area of ​​the first substrate 51 is preferably 3 to 100 g / m². 2 More preferably, 5–90 g / m 2 A further preferred value is 10–80 g / m³. 2With the weight per unit area of ​​the first substrate within this range, the liquid can diffuse efficiently in the first substrate, resulting in a further increase in the absorption rate of the absorber and a further reduction in the reflux rate.

[0389] In both the first and second embodiments, the thickness of the first substrate is preferably 0.01 mm or more and 10 mm or less, more preferably 0.03 mm or more and 9 mm or less, further preferably 0.05 mm or more and 8 mm or less, particularly preferably 0.07 mm or more and 7 mm or less, and most preferably 0.09 mm or more and 6 mm or less, at a RH range of 40% to 50%. By using this range of thickness for the first substrate, the distance between the liquid-absorbing surface of the first substrate and the absorbent layer and the second substrate can be sufficiently ensured, significantly reducing backflow of liquid temporarily reaching the absorbent layer and the second substrate. The thickness of the first substrate in the second embodiment is as described above.

[0390] It should be noted that the thicknesses of the first substrate, the second substrate, and the absorber in this application were measured using vernier calipers. Regarding the number of measurement points, five points were set at different locations on the sheet being measured, and each location was measured twice. The average value of the five measurements was taken. During thickness measurement, pressure was applied to the sheet being measured as little as possible.

[0391] The thickness and weight per unit area of ​​the first substrate can be controlled by the materials constituting the first substrate, the manufacturing method of the first substrate, etc., and the thickness and weight per unit area of ​​the first substrate are determined by the balance of these factors.

[0392] "Materials constituting the substrate"

[0393] Materials constituting the first substrate include, for example, paper (sanitary paper, such as tissue paper, toilet paper, and towel paper), cellulose fibers such as mechanical pulp, chemical pulp, semi-chemical pulp, and dissolving pulp derived from wood, rayon, cellulose acetate, and other artificial cellulose fibers, as well as webs, nonwoven fabrics, woven fabrics, and membranes. In the first embodiment of this invention, from the viewpoint of water permeability, the first substrate is preferably made of hydrophilic fibers such as pulp or nonwoven fabric. In the second embodiment of this invention, from the viewpoint of water permeability and shape retention, the first substrate is preferably made of nonwoven fabric.

[0394] There are no particular limitations on the hydrophilic fibers or nonwoven fabrics used. From the viewpoint of liquid permeability, softness and strength when made into absorbents, examples include polyolefin fibers such as polyethylene (PE) and polypropylene (PP), polyester fibers such as polyethylene terephthalate (PET), polypropylene terephthalate (PTT), and polyethylene naphthalate (PEN), polyamide fibers such as nylon, synthetic fibers such as rayon, cotton, silk, hemp, and pulp (cellulose fibers).

[0395] The preferred materials for nonwoven fabrics that can be used as the first substrate include rayon fibers, polyolefin fibers, polyester fibers, pulp fibers, and fibers blended therein, with polyolefin fibers being more preferred. These fibers may be subjected to hydrophilic treatment.

[0396] In addition, there are no particular limitations on the nonwoven fabric that can be used as the first substrate, and it can be obtained by any of the following methods: hot air method; air-blown web method; spunbond method; jet spraying method, etc.

[0397] It should be noted that the hot air method refers to the following processing: hot air is blown onto composite fibers such as PE / PP and PE / PET that can be thermally welded to achieve thermal welding, while simultaneously increasing the amount of air contained between the fibers, increasing volume, and reducing density. Additionally, the airflow web forming method is a method of producing nonwoven fabric by uniformly dispersing and absorbing the pulp fibers onto a metal mesh with the flow of air. Because the dispersion of pulp fibers utilizes air, it can increase volume and reduce density. By using a hot air nonwoven fabric as the first substrate, the liquid to be absorbed is easily and quickly introduced into the first substrate after contact with its absorbent surface. That is, by using a hot air nonwoven fabric as the first substrate, a first substrate with low water absorption and high liquid permeability can be produced, significantly reducing backflow in the absorbent.

[0398] In a first embodiment, the first substrate is preferably a substrate formed solely of hydrophilic fibers such as pulp, or a nonwoven fabric obtained by a hot-air method or an air-laid method (air-laid nonwoven fabric or hot-air nonwoven fabric), more preferably a hot-air nonwoven fabric. In one embodiment of the first embodiment, the first substrate comprises at least one selected from the group consisting of air-laid nonwoven fabric and pulp. In a second embodiment, the first substrate is preferably a hot-air nonwoven fabric.

[0399] [2] Second substrate

[0400] The second substrate is a liquid-permeable substrate and is located on the opposite side of the liquid-absorbing side, thereby fully utilizing the performance of the absorbent as the effect of this embodiment (backflow, surface leakage, etc.). In the absorbents of the first and second embodiments of this embodiment, the liquid-permeable substrate used as the second substrate is not particularly limited in terms of its raw materials, composition, and shape, as long as it is a liquid-permeable material. For example, it can be a liquid-permeable sheet (e.g., nonwoven fabric) obtained by mixing hydrophilic fibers with a heat-melting resin, adhesive, etc., and then processing it into a sheet shape; it can also be a layered molded material obtained by compressing hydrophilic fibers without using heat-melting resin, adhesive, etc., but simply by compressing the hydrophilic fibers (e.g., a pulp pad). Regarding the water permeability of the liquid-permeable substrate, a water permeability coefficient (JIS A1218:2009) of 1×10⁻⁶ is preferred. -5The permeability is preferably 1×10 cm / s or higher. -4 cm / s or higher, more preferably 1×10 -3 speeds of cm / s or higher, with a preferred speed of 1×10⁻⁶. -2 speeds of cm / s or higher, with the optimal value being 1×10⁻⁶. -1 Speeds of cm / s or higher.

[0401] In both the first and second embodiments, the thickness of the second substrate is preferably 0.01 mm or more and 50 mm or less, more preferably 0.05 mm or more and 45 mm or less, further preferably 0.1 mm or more and 40 mm or less, particularly preferably 0.15 mm or more and 35 mm or less, and most preferably 0.2 mm or more and 30 mm or less, at a RH of 40% to 50%. It should be noted that in the second embodiment, when the second substrate is formed by stacking multiple third substrates, the thickness of the second substrate refers to the total thickness of the multiple third substrates.

[0402] In the first embodiment, the unit area weight of the second substrate is preferably 5 to 500 g / m². 2 More preferably, it is 10–400 g / m 2 A further preferred value is 15–350 g / m³. 2 By using a second substrate with a specific area weight within this range, the absorption rate of the absorber is further increased, and the reflux rate can be further reduced. In the second embodiment, the second substrate's area weight is preferably 5 to 750 g / m². 2 More preferably, it is 10–650 g / m 2 A further preferred value is 15–550 g / m³. 2 With the weight per unit area of ​​the second substrate within this range, the liquid can diffuse efficiently in the first substrate, resulting in a further increase in the absorption rate of the absorber and a further reduction in the reflux rate.

[0403] The thickness and weight per unit area of ​​the second substrate can be controlled by the materials constituting the second substrate and the manufacturing method of the second substrate. The thickness and bulk density of the second substrate are determined by the balance of these factors.

[0404] "Materials constituting the substrate"

[0405] The material constituting the second substrate can also be the same as that of the first substrate. In both the first and second embodiments, from the viewpoint of water permeability, the second substrate is preferably made of hydrophilic fibers such as pulp and nonwoven fabric. Furthermore, the same material as the first substrate can be used as the material for the nonwoven fabric, such as rayon fibers, polyolefin fibers, polyester fibers, pulp fibers, and fibers blended thereto, with polyolefin fibers being more preferred.

[0406] Furthermore, there are no particular limitations on the nonwoven fabric that can be used as the second substrate, and it can be obtained by any of the following methods: hot air method, air-laid method, spunbond method, jet-spray method, etc. It should be noted that the jet-spray method is a method that uses high-pressure water jets to interweave fibers, and it is a method that does not use adhesives. The air-laid method involves dispersing a pulverized slurry with air, capturing it using a suction roller or screen belt to form a fabric, and then hot-pressing the surface with adhesives, thermally bonded fibers, etc.

[0407] The second substrate is preferably a substrate formed solely of hydrophilic fibers such as pulp, a substrate obtained by air-laid fabrication (air-laid nonwoven fabric), or a substrate obtained by jet-laid fabrication (jet-laid nonwoven fabric), more preferably a substrate formed solely of hydrophilic fibers such as pulp or an air-laid nonwoven fabric, and even more preferably an air-laid nonwoven fabric. In one embodiment, the second substrate comprises at least one selected from the group consisting of air-laid nonwoven fabric and pulp. By using a substrate formed solely of hydrophilic fibers such as pulp, an air-laid nonwoven fabric, or a jet-laid nonwoven fabric as the second substrate, the absorption rate in the absorbent can be increased, and the recirculation rate can be significantly reduced.

[0408] In the second embodiment, when the second substrate is formed by overlapping the third substrate, it is preferable that the second substrate is formed by overlapping the third substrate. In this case, the absorption rate in the absorber can be increased, and the reflux rate can be significantly reduced.

[0409] [3] Absorbent layer

[0410] The absorbent layer in the absorbent of this embodiment contains a specific particulate absorbent. In the first and second embodiments, the content of the particulate absorbent (preferably a specific particulate absorbent) contained in the absorbent is preferably 50 to 400 g / m³. 2 More preferably 75–380 g / m 2 A further preferred value is 100–350 g / m³. 2 .

[0411] In this embodiment, the absorbent layer may contain, in addition to a specific granular absorbent, other granular absorbents, pulp, deodorants, antibacterial agents, fragrances, various inorganic powders, pigments, dyes, absorbent fibers, oxidants, reducing agents, etc. The absorbent layer in this embodiment can be an absorbent layer formed by mixing granular absorbents with hydrophilic fibers such as pulp. In this case, the absorbent layer can be manufactured, for example, by dry mixing granular absorbents and pulverized hydrophilic fibers using a mixer or similar apparatus, forming the resulting mixture into a mesh using, for example, air forming, and then compressing it as needed. As such an absorbent layer, in... Figure 17An example is shown in the image.

[0412] Figure 17 This is a schematic diagram showing a cross-section of the absorber 50 cut along its width in the absorber 50 of the second embodiment of this invention. Additionally, Figure 17 The methods, besides the different morphology of the absorbent layer and the fact that the different morphology of the absorbent layer eliminates the need for a second substrate, are similar to... Figure 15 and Figure 16 Similarly. Figure 17 As shown, the absorbent layer 52 of the absorbent body 50 includes particulate absorbent 54 and hydrophilic fibers 56. It should be noted that the morphology of this absorbent layer also applies to the first embodiment. Therefore, in the first embodiment, the absorbent body 50 having an absorbent layer containing particulate absorbent 54 and hydrophilic fibers 56 may also omit the second substrate 53.

[0413] In one embodiment of the second embodiment, the regions containing particulate absorbent in the absorbent layer may be configured as in the first embodiment, with gaps that are substantially free of particulate absorbent, the gaps being formed extending along the length of the absorbent. Therefore, the second embodiment can also be applied in the same way. Figures 9-14 In one embodiment of the second embodiment, the regions of the absorbent layer containing particulate absorbent are arranged with gaps that are substantially free of particulate absorbent, the gaps being formed extending along the length direction of the absorbent, and the second substrate is formed by overlapping a third substrate. In this case, the absorption rate in the absorbent can be increased, and the backflow rate can be significantly reduced.

[0414] (Granular water absorbent)

[0415] The absorbent layer contains specific granular absorbent agents. It should be noted that, unless otherwise stated, when the absorbent agent is a mixture of multiple granular absorbent agents, the following description pertains to the physical properties of that mixture. That is, the physical properties of the granular absorbent agents are those of the mixture containing all the granular absorbent agents in the absorbent layer. Furthermore, regarding the physical properties of the granular absorbent agents, they can be measured by removing only the granular absorbent agents from the absorbent in a manner that prevents the mixing of cotton-like pulp or the like.

[0416] The absorbent in this embodiment contains a specific particulate absorbent in the absorbent layer. The particulate absorbent is primarily composed of polyacrylic (salt) based absorbent resin particles and has a shape containing interconnected pores and individual air bubbles. The total volume fraction of the interconnected pores is 10% by volume or more, and the total volume fraction of the individual air bubbles is 0.5% by volume or less. This specific particulate absorbent is as described above.

[0417] [4-2] Configuration-type absorber

[0418] In one embodiment, the absorbent containing the granular absorbent of the present invention is suitable for use as an absorbent article placed on an object (e.g., a bed, floor, etc.). The absorbent of this embodiment also has the same characteristics as the wearable absorbent: it uses a specific granular absorbent, namely, the granular absorbent described above. Therefore, the placement-type absorbent has an absorbent layer containing a granular absorbent with poly(meth)acrylate (salt)-based absorbent resin particles as the main component. The granular absorbent includes: connecting pores, which are spaces communicating with the outside; and independent air bubbles, which are closed spaces not communicating with the outside. The total volume fraction of the connecting pores is 10% by volume or more, and the total volume fraction of the independent air bubbles is 0.5% by volume or less. By using a specific granular absorbent in the absorbent layer, an absorbent with a high liquid absorption rate and reduced backflow can be produced. In this embodiment, it was discovered that using this specific granular absorbent with excellent absorption performance results in a configuration that exhibits even better absorption performance.

[0419] As a configuration-type absorbent, an absorbent layer containing a specific particulate absorbent can be used directly as the absorbent. In this case, the absorbent article described later can be formed by an absorbent (absorbent layer), a liquid-permeable sheet configured to cover the absorbent (absorbent layer), and a liquid-impermeable sheet configured to sandwich the absorbent (absorbent layer) together with the liquid-permeable sheet (refer to [4-3]). As the absorbent (absorbent layer), an absorbent obtained by wrapping a specific particulate absorbent with paper, tissue paper, or nonwoven fabric can be used; or an absorbent obtained by wrapping a substance made of pulp, cotton, or other materials mixed with a specific particulate absorbent with paper, tissue paper, or nonwoven fabric. The absorbent (absorbent layer) is positioned near the center of the liquid-permeable sheet and the liquid-impermeable sheet to absorb excrement such as urine from humans or animals.

[0420] In this case, the absorbent material (absorbent layer) can be grooved. The grooves can be formed by pressing the absorbent material (absorbent layer) with rollers, or by thinning the components constituting the absorbent material (granular absorbent, pulp, cotton, etc.). The grooves can be continuous or discontinuous. Alternatively, the entire surface of the absorbent material (absorbent layer) can be embossed. In this case, multiple recesses are formed on the entire surface or a portion of the absorbent material (absorbent layer). The recesses can be formed using an embossing process involving pressing the absorbent material (absorbent layer) with rollers. The shape of the recesses is not particularly limited; they can be quadrilaterals, triangles, polygons, circles, ellipses, etc. The width and depth of the grooves and recesses are not particularly limited and can be adjusted appropriately.

[0421] In one embodiment, the configured absorbent may be an absorbent having a first substrate and an absorbent layer disposed on the back side of the first substrate. That is, in one embodiment, the configured absorbent is an absorbent having a first substrate and a water-absorbing layer. The first substrate has a liquid-absorbing surface formed on its surface side for direct liquid absorption. The water-absorbing layer is disposed on the back side of the first substrate. The water-absorbing layer contains a particulate absorbent with poly(meth)acrylate (salt) based water-absorbing resin particles as the main component. The particulate absorbent includes: connecting pores, which are spaces communicating with the outside; and independent air bubbles, which are closed spaces not communicating with the outside. The total volume fraction of the connecting pores is 10% by volume or more, and the total volume fraction of the independent air bubbles is 0.5% by volume or less. The absorbent satisfies at least one of the following (a) and (b): (a) the area of ​​the water-absorbing layer containing the particulate absorbent is disposed with gaps that are substantially free of the particulate absorbent, and the gaps are formed extending along the length direction of the absorbent; (b) the first substrate is a liquid-permeable sheet with a porosity of 95% or more. In this embodiment, it is preferred that the absorbent satisfies the above (b). Furthermore, in this embodiment, more preferably, the absorbent has a first substrate, a second substrate, and an absorbent layer located between the first substrate and the second substrate. That is, in one embodiment, the absorbent further includes a second substrate, and the absorbent layer is located between the first substrate and the second substrate.

[0422] In this embodiment, the first substrate, the second substrate, and the absorbent layer can be the same as those used in the wearable absorbent described above, except for the unit area weight of the granular absorbent in the absorbent layer. As a configuration-type absorbent, it can be used with a relatively large area (e.g., 20cm x 20cm or more). In this case, the unit area weight of the granular absorbent is preferably 5 to 100 g / m². 2 .

[0423] [4-3] Absorbent materials

[0424] An absorbent article according to one embodiment of the present invention has a structure in which the absorbent body described in [4-1] and [4-2] is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. Here, the liquid-permeable sheet is located on the first substrate side, and the liquid-impermeable sheet is located on the second substrate side. That is, the absorbent article according to one embodiment of the present invention is formed by sandwiching the absorbent body of the present invention between a liquid-permeable sheet and a liquid-impermeable sheet, with the liquid-permeable sheet located on the first substrate side and the liquid-impermeable sheet located on the aforementioned second substrate side. It should be noted that the liquid-permeable sheet in the absorbent article is prepared separately from the liquid-permeable sheet used in the first substrate. Specific examples of absorbent articles include diapers, incontinence pads, sanitary napkins, pet pads, waterproof sheets for nursing care, portable toilets for disaster relief, drip pads for food, and waterproofing agents for power cables.

[0425] As both liquid-permeable and liquid-impermeable sheets, sheets known in the art of absorbent articles can be used without particular limitation. Furthermore, absorbent articles can be manufactured using known methods.

[0426] Example

[0427] The invention is illustrated in more detail by way of the following experimental examples, but the invention is not to be construed as limited to these descriptions. Experimental examples obtained by appropriately combining the technical means disclosed in the various experimental examples are also included within the scope of the invention. In the embodiments, the expressions "parts" or "%" are sometimes used, which, unless otherwise specified, indicate "parts by mass" or "% by mass". In addition, unless otherwise specified, all operations are performed at room temperature (25°C).

[0428] [Example 1-1]

[0429] (Preparation process of monomer aqueous solution)

[0430] A monomer aqueous solution was prepared by comprising 300 parts by weight of acrylic acid, 100 parts by weight of 48% sodium hydroxide aqueous solution, 0.65 parts by weight of polyethylene glycol diacrylate (average n number 9), 16.4 parts by weight of 0.1% ethylenediaminetetramethylenephosphonate pentasodium aqueous solution, and 273.2 parts by weight of deionized water.

[0431] The monomer aqueous solution, adjusted to 38°C, was continuously supplied using a metering pump, and then further mixed via pipeline to continuously mix 150.6 parts by mass of a 48% sodium hydroxide aqueous solution. It should be noted that at this point, the temperature of the monomer aqueous solution rises to 87°C due to the heat of neutralization.

[0432] (Polymerization process of monomer aqueous solution)

[0433] Subsequently, 14.6 parts by mass of a 4% sodium persulfate aqueous solution were continuously mixed via pipeline mixing and then continuously fed into a continuous polymerizer having a planar polymerization belt with weirs at both ends, with a thickness of 10 mm. Polymerization was then carried out continuously for 3 minutes to obtain a strip-shaped hydrogel crosslinked polymer (1-1a). The obtained strip-shaped hydrogel (1-1a) was continuously cut at equal intervals along the width direction relative to the direction of travel of the polymerization belt to obtain strip-shaped hydrogels with a cut length of 300 mm (1-1b).

[0434] (The crushing process containing hydrogels)

[0435] The obtained strip-shaped hydrogel (1-1b) was fed into a screw extruder and subjected to gel pulverization. The screw extruder used was a support member with an outer diameter of 86 mm for the screw shaft and a diameter of 100 mm and a thickness of 10 mm at the front end (extrusion port) (see reference). Figure 2B )of Figure 2A The meat grinder 100 shown performs gel pulverization (first gel pulverization) while simultaneously supplying warm water at 80°C, steam, and a 10% by mass aqueous solution of lauryl dimethylaminoacetic acid betaine to the hydrogel (1-1b). It should be noted that the warm water at 80°C is supplied in a manner where, relative to the solid composition of the hydrogel (1-1b), the warm water is 1% by mass, the steam is 1% by mass, and the lauryl dimethylaminoacetic acid betaine is 0.05% by mass as an active ingredient. Next, similarly, while supplying warm water, steam, and the lauryl dimethylaminoacetic acid betaine aqueous solution, the pulverized gel obtained through the first gel pulverization is further pulverized (second gel pulverization). Next, similarly, while supplying warm water, steam, and the lauryl dimethylaminoacetic acid betaine aqueous solution, the pulverized gel obtained through the second gel pulverization is further pulverized (third gel pulverization). Next, while supplying warm water, steam, and an aqueous solution of lauryl dimethylaminoacetic acid betaine, the pulverized gel obtained by the third gel pulverization was further pulverized (fourth gel pulverization). It should be noted that the first, second, third, and fourth gel pulverizations were all carried out at a screw shaft speed of 65 rpm. GGE(2) was calculated as the sum of the first, second, third, and fourth gel pulverizations, which was 35 J / g.

[0436] The obtained granular hydrogel (1-1c) had a solid content of 49% by mass (water content of 51% by mass) and an average gel particle size of 135 μm based on the solid content.

[0437] (Drying process for granular hydrogels)

[0438] The obtained granular hydrogel (1-1c) was dried using a hot air dryer. The dryer was equipped with a cage (30cm × 20cm at the bottom) formed by a wire mesh with a 1.2mm opening. 500g of the granular hydrogel (1-1c) was spread in a roughly uniform manner on the bottom surface of the cage, and hot air at 190°C was blown from below for 30 minutes to obtain the dried product (1-1A').

[0439] (Pulverization and grading of dried materials)

[0440] The cooled, dried material (1-1A') was fed into a roller mill and pulverized, and then classified using JIS standard sieves with 850 μm and 150 μm openings. The component that passed through the 850 μm sieve but did not pass through the 150 μm sieve was collected to obtain the water-absorbing resin (1-1A).

[0441] (Surface crosslinking process of water-absorbing resin)

[0442] Next, a surface crosslinking agent solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was sprayed onto 100 parts by weight of the water-absorbing resin (1-1A) and mixed. The mixture was then heated at 200°C for 30 minutes to obtain surface-crosslinked water-absorbing resin particles (1-1B).

[0443] (The process of adding additives)

[0444] Add 10 parts by weight of 0.1% sodium pentasodium ethylenediaminetetramethylenephosphonate aqueous solution as a chelating agent to 100 parts by weight of surface-crosslinked water-absorbing resin particles (1-1B), and mix for 1 minute.

[0445] Next, after placing it in a hot air dryer at 60°C for 30 minutes, it is passed through a metal wire mesh with an 850μm opening, and 0.5 parts by weight of tricalcium phosphate is mixed in. The mixing is done by placing 30g of surface-crosslinked water-absorbing resin particles (1B) together with tricalcium phosphate into a 225ml mayonnaise bottle, and vibrating it for 3 minutes using a paint stirrer to obtain granular water-absorbing agent (EX-1-1).

[0446] [Examples 1-2]

[0447] (Preparation process of monomer aqueous solution)

[0448] The monomer aqueous solution was prepared by replacing the sodium pentasodium ethylenediaminetetramethylenephosphonate with sodium trisodium diethylenetriaminepentaacetate, otherwise following the same procedure as in Example 1-1.

[0449] (Polymerization process of monomer aqueous solution)

[0450] The same procedure as in Example 1-1 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-2b).

[0451] (The crushing process containing hydrogels)

[0452] The same procedure as in Example 1 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-2c).

[0453] (Drying process for granular hydrogels)

[0454] The same procedure as in Example 1-1 (drying process of particulate hydrogel) was followed to obtain the dried product (1-2A').

[0455] (Pulverization and grading of dried materials)

[0456] The same procedure as in Example 1-1 (crushing and grading of the dried material) was followed to obtain the water-absorbing resin (1-2A).

[0457] (Surface crosslinking process of water-absorbing resin)

[0458] Relative to 100 parts by weight of the obtained absorbent resin (1-2A), a surface crosslinking agent solution formed by 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was spray-mixed using a continuous high-speed stirred dryer (TURBULIZER, manufactured by Hosokawa Micron) to obtain a humidified material (1-2B').

[0459] The obtained humidifier (1-2B') is used with a device Figure 8 The drying apparatus shown (a rotary heating apparatus with heating tubes) performs the heating treatment. The dryer has a cylindrical rotating container (35L volume) with 10 heating tubes extending along the rotation axis inside.

[0460] First, steam at a gauge pressure of 1.8 MPa (temperature 210°C) is introduced into each heating tube of the rotary heating device to preheat the inner surface of the rotating container to over 180°C. Then, the outer wall of the rotating container is fully heated by trace heating. Next, 4.0 kg of humidifying agent (1-2B') is added to the dryer, and the rotating container is rotated to achieve a Froude number Fr 0.07 for 30 minutes of heating treatment. After the heating treatment, the absorbent resin removed from the dryer is cooled to below 80°C to obtain surface-crosslinked absorbent resin particles (1-2B).

[0461] (The process of adding additives)

[0462] By replacing pentasodium ethylenediaminetetramethylenephosphonate with trisodium diethylenetriaminepentaacetate and replacing 0.5 parts by weight of tricalcium phosphate with 0.2 parts by weight of hydrotalcite (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.), the same procedure as in Example 1-1 (additive addition process) was performed to obtain granular water absorbent (EX-1-2).

[0463] [Examples 1-3]

[0464] (Preparation process of monomer aqueous solution)

[0465] Prepare monomer aqueous solutions by operating in the same manner as in Examples 1-2 (preparation steps of monomer aqueous solutions).

[0466] (Polymerization process of monomer aqueous solution)

[0467] The same procedure as in Example 1-1 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-3b).

[0468] (The crushing process containing hydrogels)

[0469] The same procedure as in Example 1-1 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-3c).

[0470] (Drying process for granular hydrogels)

[0471] The obtained particulate hydrogel (1-3c) was used with... Figure 8 Drying was performed using a basic drying apparatus (a rotary heating apparatus with heating tubes). This apparatus has a cylindrical rotating container (35L volume) with 10 heating tubes extending along the rotation axis. First, water vapor at 2.7 MPa (temperature 228.1°C) is introduced into each heating tube to preheat the interior of the rotating container (as specified by a contact thermometer) to over 200°C. Then, the outer wall of the rotating container is also fully heated by tracing. Next, 4.0 kg of 95°C granular hydrogel (1-3c) is added, and the rotating container is rotated to achieve a Froude number Fr 0.07. Carrier air at 140°C is supplied to the rotating container at a rate of 65 L / h, and drying is performed for 40 minutes. After drying, the solid content of the dried material (1-3A') collected at the outlet is 98.5% by mass.

[0472] (Pulverization and grading of dried materials)

[0473] Next, the dried material (1-3A') discharged from the outlet of the heating device is forcibly cooled to below 80°C with cold air, and then the cooled material is fed to a single-stage roller mill (pulverizer) for pulverization. The components that pass through an 850μm sieve but do not pass through a 150μm sieve are collected to obtain the water-absorbing resin (1-3A).

[0474] (Surface crosslinking process of water-absorbing resin particles)

[0475] Spray 100 parts by weight of the obtained water-absorbing resin (1-3A) with a surface crosslinking agent solution containing 0.2% by weight of ethylene glycol diglycidyl ether and 3% by weight of water, and heat at 150°C for 30 minutes to obtain surface-crosslinked water-absorbing resin particles (1-3B).

[0476] (The process of adding additives)

[0477] In Example 1-1 (additive addition step), ethylenediaminetetramethylenephosphonate pentasodium was replaced with diethylenetriaminepentaacetic acid trisodium, and 0.3 parts by weight of hydrophobic silica (AEROSIL R-972, manufactured by AEROSIL Corporation of Japan) was used instead of 0.5 parts by weight of tricalcium phosphate. Otherwise, the operation was the same as in Example 1-1 to obtain granular water absorbent (EX-1-3).

[0478] [Examples 1-4]

[0479] (Preparation process of monomer aqueous solution)

[0480] Prepare the monomer aqueous solution by operating in the same manner as in Example 1-1 (preparation process of monomer aqueous solution).

[0481] (Polymerization process of monomer aqueous solution)

[0482] The same procedure as in Example 1-1 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-4b).

[0483] (The crushing process containing hydrogels)

[0484] The same procedure as in Example 1-1 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-4c).

[0485] (Drying and surface crosslinking process of granular hydrogels)

[0486] After 10 minutes of adding granular hydrogels (1-4c) at 95°C to the drying apparatus of Examples 1-3, a nozzle was inserted into the drying apparatus to spray a surface crosslinking agent solution containing 0.16% by mass ethylene glycol diglycidyl ether and 2% by mass water relative to the solid components of the granular hydrogels (1-4c) during the drying process. Otherwise, the operation was the same as that of Experimental Example 3 (drying process of granular hydrogels) to obtain surface-crosslinked water-absorbing resin particles (1-4B).

[0487] (The process of adding additives)

[0488] In Example 1-1 (additive addition step), 0.6 parts by weight of hydrotalcite was mixed in place of 0.5 parts by weight of tricalcium phosphate. Otherwise, the same procedure as in Example 1-1 was followed to obtain a granular water absorbent (EX'-1-4).

[0489] (Grinding and grading processes)

[0490] The obtained granular water-absorbing agent (EX'-1-4) was fed into a single-stage roller mill (pulverizer) and pulverized, and classified using JIS standard sieves with 850 μm and 150 μm openings. The components that passed through the 850 μm sieve but did not pass through the 150 μm sieve were collected to obtain the granular water-absorbing agent (EX-1-4).

[0491] [Examples 1-5]

[0492] (Preparation process of monomer aqueous solution)

[0493] The monomer aqueous solution was prepared by changing polyethylene glycol diacrylate (average n number 9) to 1.19 parts by mass, changing ethylenediaminetetramethylenephosphonate pentasodium to diethylenetriaminepentaacetic acid trisodium, and adding 3.1 parts by mass of a 60% by mass sodium lactate aqueous solution. Otherwise, the operation was the same as in Example 1-1.

[0494] (Polymerization process of monomer aqueous solution)

[0495] The same procedure as in Example 1-1 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-5b).

[0496] (The crushing process containing hydrogels)

[0497] The obtained strip-shaped hydrogel (1-5b) is fed into a screw extruder and subjected to gel pulverization. The screw extruder uses a support member with an outer diameter of 86 mm for the screw shaft and a diameter of 100 mm and a thickness of 10 mm at the front end (extrusion port) (see reference). Figure 2B )of Figure 2AThe meat grinder 100 shown performs gel pulverization (first gel pulverization) while simultaneously supplying warm water at 80°C, steam, a 10% by mass aqueous solution of lauryl dimethylaminoacetic acid betaine, and a 5% by mass aqueous solution of hydrogen peroxide with the hydrogel (1-5b). It should be noted that the warm water at 80°C is 1% by mass, the steam is 1% by mass, the lauryl dimethylaminoacetic acid betaine is 0.05% by mass (based on active ingredient), and the hydrogen peroxide is 0.09% by mass (based on active ingredient) relative to the solid composition of the hydrogel (1-5b). Next, the pulverized gel obtained by the first gel pulverization is further pulverized (second gel pulverization) while similarly supplying warm water, steam, the lauryl dimethylaminoacetic acid betaine aqueous solution, and the hydrogen peroxide aqueous solution. Next, while supplying warm water, steam, an aqueous solution of lauryl dimethylaminoacetic acid betaine, and an aqueous solution of hydrogen peroxide, the pulverized gel obtained by the second gel pulverization was further pulverized (third gel pulverization). Next, while supplying warm water, steam, an aqueous solution of lauryl dimethylaminoacetic acid betaine, and an aqueous solution of hydrogen peroxide, the pulverized gel obtained by the third gel pulverization was further pulverized (fourth gel pulverization). It should be noted that the first, second, third, and fourth gel pulverizations were all carried out at a screw shaft speed of 65 rpm. GGE(2) is calculated as the sum of the first, second, third, and fourth gel pulverizations, which is 32 J / g.

[0498] The obtained particulate hydrogel (1-5c) had a solid content of 48.0% by mass (water content of 52.0% by mass) and an average gel particle size of 149 μm based on the solid content.

[0499] (Drying and surface crosslinking process of granular hydrogels)

[0500] The same procedure as in Examples 1-4 (drying and surface crosslinking of particulate hydrogels) was followed to obtain surface-crosslinked water-absorbing resin particles (1-5B).

[0501] (The process of adding additives)

[0502] Add an aqueous solution consisting of 10 parts by weight of a 0.1% by weight solution of trisodium diethylenetriaminepentaacetate and 0.1 parts by weight of sodium sulfite to 100 parts by weight of surface-crosslinked water-absorbing resin particles (1-5B) while stirring, and mix for 1 minute.

[0503] Next, after placing it in a hot air dryer at 60°C for 30 minutes, it is passed through a metal wire mesh with an 850μm opening, and 0.3 parts by weight of tricalcium phosphate is mixed in. The mixing is done by placing 30g of surface-crosslinked water-absorbing resin particles (5B) together with tricalcium phosphate into a 225ml mayonnaise bottle, and vibrating it for 3 minutes using a paint stirrer to obtain granular water-absorbing agent (EX'-1-5).

[0504] (Grinding and grading processes)

[0505] The obtained granular water-absorbing agent (EX'-5) was fed into a single-stage roller mill (pulverizer) and pulverized, and classified using JIS standard sieves with 850 μm and 106 μm openings. The components that passed through the 850 μm sieve but did not pass through the 106 μm sieve were collected to obtain granular water-absorbing agent (EX-1-5).

[0506] [Examples 1-6]

[0507] (Preparation process of monomer aqueous solution)

[0508] A monomer aqueous solution was prepared by comprising 300 parts by weight of acrylic acid, 100 parts by weight of 48% sodium hydroxide aqueous solution, 0.65 parts by weight of polyethylene glycol diacrylate (average n number 9), 16.4 parts by weight of 0.1% trisodium diethylenetriaminepentaacetate aqueous solution, and 273.2 parts by weight of deionized water.

[0509] The monomer aqueous solution, adjusted to 38°C, was continuously supplied using a metering pump, and then further mixed via pipeline to continuously mix 150.6 parts by mass of a 48% sodium hydroxide aqueous solution. It should be noted that at this point, the temperature of the monomer aqueous solution rises to 87°C due to the heat of neutralization.

[0510] (Polymerization process of monomer aqueous solution)

[0511] Subsequently, 14.6 parts by mass of a 4% sodium persulfate aqueous solution were continuously mixed via pipeline mixing and then continuously fed into a continuous polymerizer having a planar polymerization belt with weirs at both ends, with a thickness of 10 mm. Polymerization was then carried out continuously for 3 minutes to obtain a strip-shaped hydrogel crosslinked polymer (1-6a). The obtained strip-shaped hydrogel (1-6a) was continuously cut at equal intervals along the width direction relative to the direction of travel of the polymerization belt to obtain strip-shaped hydrogels with a cut length of 300 mm (1-6b).

[0512] (The crushing process containing hydrogels)

[0513] As a gel pulverizing device, a two-shaft mixer equipped with a main body (bucket) having two rotating shafts that rotate in the same direction is used to pulverize strip-shaped hydrogels (1-6b). Each rotating shaft is mainly equipped with a circular plate-shaped disk that serves as a pulverizing mechanism. The bucket has a jacketed structure and a gas inlet that penetrates the jacket to introduce water vapor into the main body. In addition, near the outlet of the pulverized granular hydrogels (1-6c), there is a solution inlet that penetrates the jacket to introduce a gel flower into the main body.

[0514] First, a 105°C heat transfer medium is circulated inside the jacket to maintain the internal temperature of the main body (bucket) at 105°C. Then, at a speed of 50 rpm, strip-shaped hydrogels (1-6b) heated to 80°C are fed into the inlet of the 2-shaft mixer at a rate of 0.25 kg / min (one strip-shaped hydrogel (1-6b) every 2.5 seconds). Simultaneously, 90°C water and a 10% by mass aqueous solution of lauryl dimethylaminoacetic acid betaine as a gel flow agent are supplied along with the hydrogels (1-6b). A 1% by mass aqueous solution of hydrogen peroxide is then supplied from the inlet, followed by a 0.6 MPa water vapor supply from the gas inlet. The amount of 90°C water supplied is 11.8% by mass relative to the solids content of the strip-shaped hydrogels (1-6b). The amount of 0.6 MPa water vapor supplied is 9.7% by mass relative to the solids content of the strip-shaped hydrogels (1-6b). The amount of lauryl dimethylaminoacetic acid betaine added, based on the active ingredient, is 0.08% by mass relative to the solid content of the strip-shaped hydrogel (1-6b). The amount of hydrogen peroxide added, based on the active ingredient, is 0.01% by mass relative to the solid content of the strip-shaped hydrogel (1-6b). In addition, a 10% by mass aqueous solution of lauryl dimethylaminoacetic acid betaine is supplied near the outlet. The amount of lauryl dimethylaminoacetic acid betaine added, based on the active ingredient, is 0.08% by mass relative to the solid content of the strip-shaped hydrogel (1-6b). The diameter D of the disc used in gel pulverization is 50 mm, and the minimum spacing between the drum and the disc is 1 mm (2% of the disc diameter D). It should be noted that the GGE (2) during gel pulverization is 89 J / g.

[0515] The obtained granular hydrogels (1-6c) had a solid content of 45% by mass (water content of 55% by mass) and an average gel particle size of 132 μm based on the solid content.

[0516] (Drying process for granular hydrogels)

[0517] The obtained granular hydrogel (1-6c) was dried using a hot air dryer. The dryer was equipped with a cage (30cm × 20cm at the bottom) formed by a wire mesh with a 1.2mm opening. 500g of the granular hydrogel (1-6c) was spread in a roughly uniform manner on the bottom surface of the cage, and hot air at 190°C was blown from below for 30 minutes to obtain the dried product (1-6A').

[0518] (Pulverization and grading of dried materials)

[0519] The cooled, dried material (1-6A') was fed into a roller mill and pulverized, and then classified using JIS standard sieves with 850 μm and 150 μm openings. The component that passed through the 850 μm sieve but did not pass through the 150 μm sieve was collected to obtain the water-absorbing resin (1-6A).

[0520] (Surface crosslinking process of water-absorbing resin)

[0521] Next, a surface crosslinking agent solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was sprayed onto 100 parts by weight of the water-absorbing resin (1-6A) and mixed. The mixture was then heated at 200°C for 30 minutes to obtain surface-crosslinked water-absorbing resin particles (1-6B).

[0522] (The process of adding additives)

[0523] Add 10 parts by weight of 0.1% DTPA (trisodium diethylenetriaminepentaacetate) aqueous solution as a chelating agent to 100 parts by weight of surface-crosslinked water-absorbing resin particles (1-6B) while stirring, and mix for 1 minute.

[0524] Next, after placing it in a hot air dryer at 60°C for 30 minutes, it is passed through a metal wire mesh with an 850μm opening, and 0.5 parts by weight of tricalcium phosphate is mixed in. The mixing is done by placing 30g of surface-crosslinked water-absorbing resin particles (6B) together with tricalcium phosphate into a 225ml mayonnaise bottle, and vibrating it for 3 minutes using a paint stirrer to obtain granular water-absorbing agent (EX-1-6).

[0525] [Examples 1-7]

[0526] (Preparation process of monomer aqueous solution)

[0527] The monomer aqueous solution was prepared by replacing trisodium diethylenetriaminepentaacetate with pentasodium ethylenediaminetetramethylenephosphonate, otherwise following the same procedure as in Examples 1-6 (preparation of monomer aqueous solution).

[0528] (Polymerization process of monomer aqueous solution)

[0529] The same procedure as in Examples 1-6 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-7b).

[0530] (The crushing process containing hydrogels)

[0531] The same procedure as in Examples 1-6 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-7c).

[0532] (Drying process for granular hydrogels)

[0533] The same procedure as in Examples 1-6 (drying process of particulate hydrogels) was followed to obtain the dried product (1-7A').

[0534] (Pulverization and grading of dried materials)

[0535] The same procedure as in Examples 1-6 (crushing and grading of the dried material) was followed to obtain the water-absorbing resin (1-7A).

[0536] (Surface crosslinking process of water-absorbing resin)

[0537] Relative to 100 parts by weight of the obtained absorbent resin (1-7A), a surface crosslinking agent solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was spray-mixed using a continuous high-speed stirred dryer (TURBULIZER, Hosokawa Micron Corporation) to obtain a humidified material (1-7B').

[0538] The obtained humidifier (1-7B') is used with a device Figure 8 The drying apparatus shown (a rotary heating apparatus with heating tubes) performs the heating treatment. The dryer has a cylindrical rotating container (35L volume) with 10 heating tubes extending along the rotation axis inside.

[0539] First, steam at a gauge pressure of 1.8 MPa (temperature 210°C) is introduced into each heating tube of the rotary heating device to preheat the inner surface of the rotating container to over 180°C, and then the outer wall of the rotating container is fully heated by tracing. Next, 4.0 kg of humidifying agent (1-7B') is added to the dryer, and the rotating container is rotated to achieve a Froude number Fr 0.07 for 30 minutes of heat treatment. After heat treatment, the water-absorbing resin removed from the dryer is cooled to below 80°C to obtain surface-crosslinked water-absorbing resin particles (1-7B).

[0540] (The process of adding additives)

[0541] By replacing trisodium diethylenetriaminepentaacetate with pentasodium ethylenediaminetetramethylenephosphonate, and otherwise operating in the same manner as in Examples 1-6 (additive addition process), granular water absorbent (EX-1-7) was obtained.

[0542] [Examples 1-8]

[0543] (Preparation process of monomer aqueous solution)

[0544] The amount of polyethylene glycol diacrylate (average n number 9) was changed to 0.85 parts by mass, and 1.8 parts by mass of a 60% by mass sodium lactate aqueous solution was added. Otherwise, the same procedure as in Examples 1-6 was followed to prepare the monomer aqueous solution.

[0545] (Polymerization process of monomer aqueous solution)

[0546] The same procedure as in Examples 1-6 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-8b).

[0547] (The crushing process containing hydrogels)

[0548] The same procedure as in Examples 1-6 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-8c).

[0549] (Drying process for granular hydrogels)

[0550] The obtained particulate hydrogel (1-8c) was used with... Figure 8 Drying was performed using a basic drying apparatus (a rotary heating apparatus with heating tubes). This apparatus has a cylindrical rotating container (35L volume) with 10 heating tubes extending along the rotation axis. First, water vapor at 2.7 MPa (temperature 228.1°C) is introduced into each heating tube to preheat the interior of the rotating container (as specified by a contact thermometer) to over 200°C. Then, the outer wall of the rotating container is also fully heated by tracing. Next, 4.0 kg of 95°C granular hydrogel (1-8c) is added, and the rotating container is rotated to achieve a Froude number Fr 0.07. Carrier air at 140°C is supplied to the rotating container at a rate of 65 L / h, and drying is performed for 40 minutes. After drying, the solid content of the dried material (1-8A') collected at the outlet is 98.5% by mass.

[0551] (Pulverization and grading of dried materials)

[0552] Next, the dried material (1-8A') discharged from the outlet of the heating device is forcibly cooled to below 80°C with cold air, and then the cooled material is fed to a single-stage roller mill (pulverizer) for pulverization. The components that pass through an 850μm sieve but do not pass through a 150μm sieve are collected to obtain the water-absorbing resin (1-8A).

[0553] (Surface crosslinking process of water-absorbing resin)

[0554] Spray 100 parts by weight of the obtained water-absorbing resin (1-8A) with a surface crosslinking agent solution containing 0.2% by weight of ethylene glycol diglycidyl ether and 3% by weight of water, and heat at 150°C for 30 minutes to obtain surface-crosslinked water-absorbing resin particles (1-8B).

[0555] (The process of adding additives)

[0556] Add an aqueous solution consisting of 10 parts by weight of a mixture of 0.1% by weight of trisodium diethylenetriaminepentaacetate and 0.1 parts by weight of sodium sulfite to 100 parts by weight of surface-crosslinked water-absorbing resin particles (1-8B), while stirring, and mix for 1 minute.

[0557] Next, after placing it in a hot air dryer at 60°C for 30 minutes, it is passed through a metal wire mesh with an 850μm opening, and 0.2 parts by weight of hydrotalcite is mixed in. The mixing is done by placing 30g of surface-crosslinked water-absorbing resin particles (1-8B) together with the hydrotalcite into a 225ml mayonnaise bottle, and vibrating it for 3 minutes using a paint stirrer to obtain granular water-absorbing agent (EX-1-8).

[0558] [Examples 1-9]

[0559] (Preparation process of monomer aqueous solution)

[0560] The monomer aqueous solution was prepared by replacing trisodium diethylenetriaminepentaacetate with pentasodium ethylenediaminetetramethylenephosphonate, otherwise following the same procedure as in Examples 1-6 (preparation of monomer aqueous solution).

[0561] (Polymerization process of monomer aqueous solution)

[0562] The same procedure as in Examples 1-6 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-9b).

[0563] (The crushing process containing hydrogels)

[0564] The same procedure as in Examples 1-6 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-9c).

[0565] (Drying and surface crosslinking process of granular hydrogels)

[0566] After 10 minutes of adding granular hydrogels (1-9c) at 95°C to the drying apparatus of Examples 1-8, a nozzle was inserted into the drying apparatus to spray a surface crosslinking agent solution containing 0.16% by mass ethylene glycol diglycidyl ether and 2% by mass water relative to the solid components of the granular hydrogels (1-9c) during the drying process. Otherwise, the operation was the same as that of the drying process of granular hydrogels in Examples 1-8, to obtain surface-crosslinked water-absorbing resin particles (1-9B).

[0567] (The process of adding additives)

[0568] The trisodium diethylenetriaminepentaacetate was replaced with pentsodium ethylenediaminetetramethylenephosphonate, and the operation was otherwise the same as in Examples 1-6 (additive addition process) to obtain granular water absorbent (EX'-1-9).

[0569] (Grinding and grading processes)

[0570] The obtained granular water-absorbing agent (EX'-1-9) was fed into a single-stage roller mill (pulverizer) and pulverized, and classified using JIS standard sieves with 850 μm and 150 μm openings. The components that passed through the 850 μm sieve but did not pass through the 150 μm sieve were collected to obtain the granular water-absorbing agent (EX-1-9).

[0571] [Examples 1-10]

[0572] (Preparation process of monomer aqueous solution)

[0573] The monomer aqueous solution was prepared by changing the amount of polyethylene glycol diacrylate (average n number 9) to 0.85 parts by mass, otherwise following the same procedure as in Examples 1-6.

[0574] (Polymerization process of monomer aqueous solution)

[0575] The same procedure as in Examples 1-6 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-10b).

[0576] (The crushing process containing hydrogels)

[0577] The concentration of the supplied hydrogen peroxide aqueous solution was set to 5% by mass, and the amount of hydrogen peroxide added, based on the effective ingredient, was set to 0.1% by mass relative to the solid content of the strip-shaped hydrogel (1-10b). Otherwise, the procedure was the same as in Examples 1-6 (hydrogel pulverization process) to obtain granular hydrogels (1-10c). The obtained granular hydrogels (1-10c) had a solid content of 45.2% by mass (water content of 54.8% by mass) and an average gel particle size converted from solid content of 148 μm. The GGE (2) during gel pulverization was 75 J / g.

[0578] (Drying and surface crosslinking process of granular hydrogels)

[0579] The same procedure as in Examples 1-9 (drying and surface crosslinking of particulate hydrogels) was followed to obtain surface-crosslinked water-absorbing resin particles (1-10B).

[0580] (The process of adding additives)

[0581] The 0.5 parts by weight of tricalcium phosphate were replaced with 0.3 parts by weight of hydrotalcite, and the same procedure as in Examples 1-6 (additive addition process) was followed to obtain granular water absorbent (EX'-1-10).

[0582] (Grinding and grading processes)

[0583] The obtained granular water-absorbing agent (EX'-1-10) was fed into a single-stage roller mill (pulverizer) and pulverized, and classified using JIS standard sieves with 850 μm and 106 μm openings. The components that passed through the 850 μm sieve but did not pass through the 106 μm sieve were collected to obtain the granular water-absorbing agent (EX-1-10).

[0584] [Examples 1-11]

[0585] (Preparation process of monomer aqueous solution)

[0586] Prepare the monomer aqueous solution by operating in the same manner as in Example 1-1 (preparation process of monomer aqueous solution).

[0587] (Polymerization process of monomer aqueous solution)

[0588] The same procedure as in Example 1-1 (polymerization process of monomer aqueous solution) was followed to obtain a strip-shaped hydrogel (1-11b).

[0589] (The crushing process containing hydrogels)

[0590] The same procedure as in Example 1-1 (the pulverization process of the hydrogel) was followed to obtain granular hydrogels (1-11c).

[0591] (Drying process for granular hydrogels)

[0592] The same procedure as in Example 1-1 (drying process of particulate hydrogel) was followed to obtain the dried product (1-11A').

[0593] (Pulverization and grading of dried materials)

[0594] The same procedure as in Example 1-1 (crushing and grading of the dried material) was followed to obtain the water-absorbing resin (1-11A).

[0595] (Surface crosslinking process of water-absorbing resin)

[0596] The same procedure as in Example 1-1 (surface crosslinking process of water-absorbing resin) was followed to obtain surface-crosslinked water-absorbing resin particles (1-11B).

[0597] (The process of adding additives)

[0598] Add 10 parts by weight of deionized water while stirring, relative to 100 parts by weight of surface-crosslinked water-absorbing resin particles (1-11B), and mix for 1 minute.

[0599] Next, after placing it in a hot air dryer at 60°C for 30 minutes, it is passed through a metal wire mesh with an 850μm opening to obtain granular water absorbent (EX-1-11).

[0600] [Examples 1-12]

[0601] According to International Publication No. 2020 / 067310 Figure 1 The manufacturing process shown involves a series of steps to prepare hydrogel polymers (1-12c).

[0602] First, n-heptane, as an organic solvent, is added to the dispersion unit 12, the polymerization unit 14, the separation unit 16, and the piping (including joints) connecting them. Next, the feed pump 18 is run to begin circulating the hydrophobic organic solvent at a flow rate of 300 mL / min. It should be noted that the entire amount of the organic solvent is fed into the polymerization unit 14 via the dispersion unit 12. Additionally, the heat exchanger 20 is run to heat the circulating organic solvent to a temperature of 90°C. Next, as a dispersing aid, maleic anhydride-modified ethylene / propylene copolymer (trade name: Hi-WAX (registered trademark) 1105A / Mitsui Chemicals Co., Ltd.) is added in an amount of 0.005% by mass relative to 100% by mass of the hydrophobic organic solvent.

[0603] Acrylic acid, a 48.5% by mass aqueous solution of sodium hydroxide, and deionized water were mixed, and then polyethylene glycol diacrylate (average degree of polymerization: 9) and trisodium diethylenetriaminepentaacetate, which serve as internal crosslinking agents, were mixed to prepare a monomer solution (1-12a). Separately, sodium persulfate, which serves as a polymerization initiator, was mixed with deionized water to prepare a 6% by mass aqueous solution of sodium persulfate (1-12a').

[0604] Next, the monomer solution (1-12a) obtained through the above operation is supplied to the mixing device 10 and mixed with the sodium persulfate aqueous solution (1-12a') to prepare the monomer aqueous solution (1-12b). The monomer aqueous solution (1-12b) has a monomer concentration of 43% by mass and a neutralization rate of 75 mol%. In addition, the amount of polyethylene glycol diacrylate is 0.020 mol% relative to 100 mol% of monomer (acrylic acid), the amount of trisodium diethylenetriaminepentaacetate is 200 ppm relative to monomer (acrylic acid), and the amount of sodium persulfate is 0.1 g / mol relative to monomer (acrylic acid).

[0605] The monomer aqueous solution (1-12b) was fed into the piping of the dispersion device at a flow rate of 40 mL / min (47.2 g / min). The supplied monomer aqueous solution (1-12b) was dispersed in the hydrophobic organic solvent in droplets using the dispersion device.

[0606] Next, the dispersion obtained as described above is supplied to the polymerization apparatus 14. Droplets formed from the monomer aqueous solution (1-12b) polymerize while moving along the circulation direction of the hydrophobic organic solvent within the polymerization apparatus, which is filled with the hydrophobic organic solvent as the continuous phase. The hydrogel polymer (1-12c) obtained through the above series of operations, together with the hydrophobic organic solvent, is continuously supplied from the polymerization apparatus via a junction to the separation apparatus 16, where the hydrogel polymer (1-12c) is separated from the organic solvent.

[0607] A hydrogel polymer (1-12d') (geling temperature: 90°C) pre-mixed with an aqueous solution of lauryl dimethylaminoacetic acid betaine (3.5% by mass as a gel flow agent, with a solid content of 0.20% by mass relative to the hydrogel polymer (1-12c)) is added to a gel granulation device (Dome Gran DG-L1, orifice diameter of dome die: 0.5 mm, gap with extrusion action: 1.2 mm, manufactured by DALTON CORPORATION) and discharged from the gel granulation device to obtain granulated gel (1-12d).

[0608] Next, the obtained whole-particle gel (1-12d) was fed into a stirred dryer and dried at a jacket temperature of 200°C for 50 minutes to obtain a dried polymer (1-12A'). The dried polymer (1-12A') was classified using an 850 μm open sieve. The material that did not pass through the 850 μm open sieve was pulverized. The particles that passed through the sieve were mixed with the particles that passed through the 850 μm open sieve before pulverization. The resulting mixture was classified using a 150 μm open sieve. Thus, the fraction that passed through the 850 μm open sieve but did not pass through the 150 μm sieve was recovered to obtain the water-absorbing resin (1-12A).

[0609] Finally, relative to 100 parts by weight of the water-absorbing resin (1-12A), a surface crosslinking agent solution formed by spraying 0.015 parts by weight of ethylene glycol diglycidyl ether, 1.0 part by weight of propylene glycol and 3.0 parts by weight of deionized water is sprayed and uniformly mixed using a high-speed continuous mixer.

[0610] The resulting mixture was introduced into a heat treatment machine with the temperature adjusted to an atmosphere temperature of 195℃±2℃ and heated for 30 minutes. The powder temperature was then forcibly cooled to 60℃ to obtain surface-crosslinked water-absorbing resin particles (1-12B).

[0611] To 100 parts by weight of the aforementioned absorbent resin particles (1-12B), a mixture consisting of 0.1 parts by weight of trisodium diethylenetriaminepentaacetate and 10 parts by weight of deionized water was added dropwise and mixed thoroughly. The mixture was then allowed to stand in a hot air dryer at 60°C and passed through a JIS standard sieve with a 1000 μm opening to granulate, yielding granular absorbent (EX-1-12) with a moisture content of 10%.

[0612] [Examples 1-13]

[0613] (Preparation process of monomer aqueous solution)

[0614] Prepare the monomer aqueous solution by operating in the same manner as in Example 1-1 (preparation process of monomer aqueous solution).

[0615] (Polymerization process of monomer aqueous solution)

[0616] The same procedure as in Example 1-1 (polymerization process of monomer aqueous solution) was followed to obtain a strip-shaped hydrogel (1-13b).

[0617] (The crushing process containing hydrogels)

[0618] In Example 1-1 (the process of pulverizing hydrogel), the fourth gel pulverization was not performed, but the process was otherwise the same as in Example 1-1 (the process of pulverizing hydrogel) to obtain granular hydrogel (1-13c). GGE (2) was 25 J / g, calculated as the sum of the first, second, and third gel pulverizations.

[0619] The obtained granular hydrogel (1-13c) had a solid content of 50% by mass (water content of 50% by mass) and an average gel particle size of 321 μm based on the solid content.

[0620] (Drying and surface crosslinking process of granular hydrogels)

[0621] After 10 minutes of adding granular hydrogel (1-13c) at 95°C to the drying apparatus of Examples 1-3, a nozzle was inserted into the drying apparatus to spray an addition of a surface crosslinking agent solution containing 0.16% by mass ethylene glycol diglycidyl ether and 2% by mass water relative to the solid components of the granular hydrogel (1-13c) during the drying process. Otherwise, the operation was the same as in Examples 1-3 (drying process of granular hydrogel) to obtain surface-crosslinked water-absorbing resin particles (1-13B).

[0622] (The process of adding additives)

[0623] In Example 1-1 (additive addition step), 0.6 parts by weight of hydrotalcite were mixed in place of 0.5 parts by weight of tricalcium phosphate. Otherwise, the same procedure as in Example 1-1 was followed to obtain a granular water absorbent (EX'-1-13).

[0624] (Grinding and grading processes)

[0625] The obtained granular water-absorbing agent (EX'-1-13) was fed into a single-stage roller mill (pulverizer) and pulverized, and classified using JIS standard sieves with 850 μm and 106 μm openings. The components that passed through the 850 μm sieve but did not pass through the 106 μm sieve were collected to obtain the granular water-absorbing agent (EX-1-13).

[0626] [Examples 1-14]

[0627] (Preparation process of monomer aqueous solution)

[0628] Prepare monomer aqueous solutions by operating in the same manner as in Examples 1-6 (preparation steps of monomer aqueous solutions).

[0629] (Polymerization process of monomer aqueous solution)

[0630] The same procedure as in Examples 1-6 (polymerization process of monomer aqueous solution) was followed to obtain strip-shaped hydrogels (1-14b).

[0631] (The crushing process containing hydrogels)

[0632] In Examples 1-6 (the process of pulverizing hydrogels), the minimum interval between the barrel and the disc of the gel pulverizing apparatus was changed to 2.5 mm (5% of the disc diameter D). Otherwise, the process was the same as in Examples 1-6 (the process of pulverizing hydrogels) to obtain granular hydrogels (1-14c). It should be noted that the GGE (2) during gel pulverization was 32 J / g.

[0633] The obtained granular hydrogel (1-14c) had a solid content of 45% by mass (water content of 55% by mass) and an average gel particle size of 297 μm based on the solid content.

[0634] (Drying process for granular hydrogels)

[0635] The same procedure as in Examples 1-6 (drying process of particulate hydrogel) was followed to obtain the dried product (1-14A').

[0636] (Pulverization and grading of dried materials)

[0637] The same procedure as in Examples 1-6 (crushing and grading of the dried material) was followed to obtain the water-absorbing resin (1-14A).

[0638] (Surface crosslinking process of water-absorbing resin)

[0639] The same procedure as in Examples 1-6 (surface crosslinking process of water-absorbing resin) was followed to obtain surface-crosslinked water-absorbing resin particles (1-14B).

[0640] (The process of adding additives)

[0641] The same procedure as in Examples 1-6 (additive addition process) was followed to obtain granular water absorbent (EX-1-14).

[0642] [Comparative Example 1-1]

[0643] In Comparative Example 1-1, the "particulate water absorbent (EX-12)" disclosed in Example 12 of International Publication No. 2016 / 204302 was used as the particulate water absorbent (CE-1-1).

[0644] [Comparative Examples 1-2]

[0645] In Comparative Examples 1-2, the same procedure was followed as in Example 1 disclosed in International Application PCT / JP2020 / 047821 to obtain granular superabsorbent (CE-1-2). Specifically, as described below.

[0646] (Preparation process of monomer aqueous solution)

[0647] A monomer aqueous solution was prepared by mixing 422.0 parts by weight of acrylic acid, 173.9 parts by weight of a 48.5% by weight sodium hydroxide aqueous solution, 2.5 parts by weight of polyethylene glycol diacrylate (average molecular weight: 523), 2.6 parts by weight of a 1.0% by weight trisodium diethylenetriaminepentaacetate aqueous solution, and 403.3 parts by weight of deionized water in a 2L polypropylene container. The temperature of this monomer aqueous solution exceeded 40°C due to the heat of neutralization and heat of solution generated during the aforementioned mixing process.

[0648] (Polymerization process)

[0649] Next, the aforementioned monomer aqueous solution was stirred and cooled. When the liquid temperature reached 40°C, 178.7 parts by mass of a 48.5% sodium hydroxide aqueous solution, adjusted to 40°C, was added to the aforementioned monomer aqueous solution under open atmosphere for approximately 20 seconds and mixed (initiating the second stage of neutralization). Thus, monomer aqueous solution (1-22a) was prepared. At this time, the liquid temperature of the aforementioned monomer aqueous solution (1-22a) rose to approximately 78°C due to the heat of neutralization and heat of dissolution generated during the aforementioned mixing process. Furthermore, precipitates were observed immediately after the aforementioned sodium hydroxide aqueous solution was added to the aforementioned monomer aqueous solution, but they subsequently dissolved, and the prepared monomer aqueous solution (1-22a) became a transparent, homogeneous solution.

[0650] Then, in the stirred monomer aqueous solution (1-22a), nitrogen gas was introduced for 5 seconds using a Kinoshita-type glass ball filter (filter particle No. 4 / manufactured by Kinoshita Rika Kogyo Co., Ltd.) at a pressure of 0.1 MPa and a flow rate of 0.1 L / min. Next, 18.4 parts by mass of 4.5% sodium persulfate aqueous solution were added to the monomer aqueous solution (1-22a). Then, the monomer aqueous solution (1-22a) was immediately allowed to flow into a stainless steel urn-shaped container (bottom 340×340 mm, height 25 mm, inner surface: Teflon coating) under open atmospheric conditions. It should be noted that the time from the start of the second stage of neutralization until the aforementioned monomer aqueous solution (1-22a) flowed into the urn-shaped container was set to 65 seconds. In addition, the urn-shaped container was heated to a surface temperature of 50°C using a hot plate (NEO HOTPLATE HI-1000 / manufactured by Inouchi Moriedo Co., Ltd.).

[0651] After the aforementioned monomer aqueous solution (1-22a) is poured into the aforementioned urn-shaped container, the polymerization reaction begins within 1 minute. During this polymerization reaction, water vapor is generated and expands and foams in all directions while the monomer aqueous solution (1-22a) polymerizes. The resulting polymer then shrinks to a size slightly larger than the bottom of the urn-shaped container. Two minutes after the start of the polymerization reaction, the hydrogel (1-22b) is removed from the urn-shaped container. It should be noted that this series of operations is carried out under open atmospheric conditions.

[0652] (Gel pulverization process)

[0653] Next, the hydrogel (1-22b) obtained through the aforementioned polymerization reaction was cut into pieces with a mass of approximately 60g each, and then pulverized using a meat grinder (HL-G22SN, 6.0mm aperture / manufactured by REMACOM Corporation) to obtain granular hydrogel (1-1). The aforementioned hydrogel (1-1) was added at a rate of approximately 360g / min. Simultaneously with the addition of hydrogel (1-22b), deionized water at a temperature adjusted to 90°C was added to the meat grinder at a rate of 25g / min to pulverize the gel, resulting in granular hydrogel (1-22c).

[0654] The aforementioned particulate hydrogel (1-22c) has a D50 (mass-average particle size) of 320 μm and a σζ (logarithmic standard deviation of particle size distribution) of 0.91.

[0655] (Drying process)

[0656] Next, the aforementioned granular hydrogel (1-22c) was spread on a metal wire mesh with a 300 μm opening and placed in a hot air dryer. Then, the granular hydrogel (1-22c) was dried by circulating hot air at 190°C for 30 minutes to obtain a dried polymer (1-22A'). This dried polymer (1-22A') contained no undried material.

[0657] (Grading process)

[0658] Next, the aforementioned dried polymer (1-22A') was fed into a roller mill (WML type roller mill / manufactured by Inoguchi Giken Co., Ltd.) and pulverized. Then, it was classified using two JIS standard sieves with 710 μm and 150 μm openings. This process yielded an irregularly broken, pre-crosslinking, water-absorbing resin (1-22A) that passed through the 710 μm opening sieve but remained on the 150 μm opening sieve.

[0659] (Surface crosslinking process)

[0660] Next, relative to 100 parts by weight of the aforementioned pre-crosslinking water-absorbing resin (1-22A), a surface crosslinking agent aqueous solution consisting of 0.4 parts by weight of ethylene carbonate, 0.7 parts by weight of propylene glycol, 2.9 parts by weight of deionized water, and 0.001 parts by weight of polyoxyethylene (20) dehydrated sorbitan monostearate (manufactured by Kao Corporation) was sprayed on and uniformly mixed. The resulting mixture was then heated at 200°C for 40 minutes to perform surface crosslinking. Next, the mixture was graded using two JIS standard sieves with openings of 710 μm and 150 μm. This operation yielded a particulate water-absorbing agent (CE-1-2) that passed through the 710 μm sieve but remained on the 150 μm sieve.

[0661] [Comparative Examples 1-3]

[0662] In Comparative Examples 1-3, the same procedures were followed as in Example 1 disclosed in WO2019 / 221154 to obtain the "water-absorbing resin particles (C1)" described in Example 1 of WO2019 / 221154. These are used as particulate water-absorbing agents in this application (CE-1-3).

[0663] [Comparative Examples 1-4]

[0664] In Comparative Examples 1-4, the same procedure was followed as in Experimental Example 28 disclosed in WO2018 / 092863 to obtain the "surface-crosslinked water-absorbing resin powder (28)" described in Experimental Example 28 of WO2018 / 092863. This powder is used as a particulate water-absorbing agent in this application (CE-1-4).

[0665] [Comparative Examples 1-5]

[0666] In Comparative Examples 1-5, the same procedure was followed as in Experimental Example 18 disclosed in WO2018 / 092863 to obtain the "water-absorbing resin (18)" described in Experimental Example 18 of WO2018 / 092863. This resin is used as a particulate water-absorbing agent in this application (CE-1-5).

[0667] [Comparative Examples 1-6]

[0668] In Comparative Examples 1-6, the same procedure was followed as in Experimental Example 3 disclosed in International Application PCT / JP2021 / 034800 to obtain granular superabsorbent (CE-1-6). Specifically, as described below.

[0669] (Preparation process of monomer aqueous solution)

[0670] A monomer aqueous solution was prepared by comprising 300 parts by weight of acrylic acid, 100 parts by weight of 48% sodium hydroxide aqueous solution, 0.61 parts by weight of polyethylene glycol diacrylate (average n number 9), 16.4 parts by weight of 0.1% trisodium diethylenetriaminepentaacetate aqueous solution, and 273.2 parts by weight of deionized water.

[0671] Next, the monomer aqueous solution, adjusted to 38°C, was continuously supplied using a metering pump, and then further mixed via pipeline to continuously mix 150.6 parts by mass of a 48% sodium hydroxide aqueous solution. It should be noted that at this point, the temperature of the monomer aqueous solution rises to 87°C due to the heat of neutralization.

[0672] (Polymerization process of monomer aqueous solution)

[0673] Subsequently, 14.6 parts by mass of a 4% sodium persulfate aqueous solution were continuously mixed via pipeline mixing and then continuously fed into a continuous polymerizer having a planar polymerization belt with weirs at both ends, with a thickness of 10 mm. Polymerization was then carried out continuously for 3 minutes to obtain a strip-shaped (sheet-shaped) hydrogel crosslinked polymer (1-26a). The obtained strip-shaped hydrogel (1-26a) was cut according to the processing speed and feeding interval in the gel pulverizer described later to obtain strip-shaped hydrogels (1-26b) with a width of several cm. For example, when the processing speed of the gel pulverizer was set to 0.64 kg / min and the strip-shaped hydrogels were fed at 2.5-second intervals, the mass of each strip-shaped hydrogel was set to 0.0267 kg. It should be noted that the polymerization rate of the strip-shaped hydrogel (1-26b) was 98.5% by mass and the solids content was 53% by mass.

[0674] (The crushing process containing hydrogels)

[0675] As a gel pulverizing device, a two-shaft mixer with a main body (bucket) having two rotating shafts that rotate in the same direction is used to pulverize strip-shaped hydrogels (1-26b). Each rotating shaft is mainly equipped with a circular plate-shaped disk that serves as a pulverizing mechanism. The bucket has a jacketed structure and a gas inlet that penetrates the jacket to introduce water vapor into the main body.

[0676] First, a 105°C heat transfer medium is circulated inside the jacket to maintain the internal temperature of the main body (bucket) at 105°C. Then, at a speed of 100 rpm, strip-shaped hydrogel (1-26b) heated to 80°C is fed into the inlet of the 2-shaft mixer at a rate of 0.64 kg / min (one strip-shaped hydrogel (1-26b) every 2.5 seconds). Simultaneously with the hydrogel (1-26b), 90°C water is supplied from the inlet, followed by 0.6 MPa water vapor from the gas inlet, and then a 10% (w / w) lauryl dimethylaminoacetic acid betaine aqueous solution from the inlet. The amount of 90°C water supplied is 11.8% (w / w) of the solids content of the strip-shaped hydrogel (1-26b). The amount of 0.6 MPa water vapor supplied is 9.7% (w / w) of the solids content of the strip-shaped hydrogel (1-26b). The amount of lauryl dimethylaminoacetic acid betaine added, on a solids basis, was 0.15% by mass relative to the solids of the strip-shaped hydrogel (1-26b). The diameter D of the disc used for gel pulverization was 50 mm, and the minimum spacing between the drum and the disc was 1 mm (2% of the disc diameter D). It should be noted that the GGE (2) during gel pulverization was 125 J / g.

[0677] The obtained particulate hydrogel (1-26c) had a solid content of 48.2% by mass (water content of 51.8% by mass) and an average gel particle size of 141 μm based on the solid content.

[0678] (Drying process for granular hydrogels)

[0679] The obtained granular hydrogel (1-26c) was dried using a hot air dryer. The dryer was equipped with a cage (30cm × 20cm at the bottom) formed by a wire mesh with a 1.2mm opening. 500g of the granular hydrogel (1-26c) was spread in a roughly uniform manner on the bottom surface of the cage, and hot air at 190°C was blown from below for 30 minutes to obtain the dried product (1-26A').

[0680] (Pulverization and grading of dried materials)

[0681] The cooled, dried material (1-26A') was fed into a roller mill and pulverized, and then classified using JIS standard sieves with 850 μm and 150 μm openings. The component that passed through the 850 μm sieve but did not pass through the 150 μm sieve was collected to obtain the water-absorbing resin (1-26A).

[0682] (Surface crosslinking process of water-absorbing resin)

[0683] Next, a surface crosslinking agent solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was sprayed onto 100 parts by weight of the water-absorbing resin (1-26A) and mixed. The mixture was then heat-treated at 200°C for 35 minutes to obtain granular water-absorbing agent (CE-1-6).

[0684] [Comparative Examples 1-7]

[0685] In Comparative Examples 1-7, the same operation was performed as in Example 12 disclosed in Japanese Patent Application Publication No. 2006-057075 to obtain the "particulate water absorbent (10)" described in Example 12 of Japanese Patent Application Publication No. 2006-057075. This is used as the particulate water absorbent in this application (CE-1-7).

[0686] [Comparative Examples 1-8]

[0687] In Comparative Examples 1-8, the same procedures were followed as in Example 1 disclosed in WO2015 / 129917 to obtain the "granular water absorbent (EX-1)" described in Example 1 of WO2015 / 129917. This is used in this application as the granular water absorbent (CE-1-8).

[0688] [Comparative Examples 1-9]

[0689] In Comparative Examples 1-9, the same procedures were followed as in Example 5 disclosed in WO2009 / 025235 to obtain the "water-absorbing resin" described in Example 5 of WO2009 / 025235. This resin is used in this application as a particulate water-absorbing agent (CE-1-9).

[0690] [Evaluation Method]

[0691] For the granular superabsorbents (EX-1-1) to (EX-1-14) obtained in Examples 1-1 to 1-14 and the granular superabsorbents (CE-1-1) to (CE-1-9) obtained in Comparative Examples 1-1 to 1-9, the following were measured: "total volume fraction of interconnected pores [volume %]", "total volume fraction of independent bubbles [volume %]", "absorption time of high viscosity liquid", "CRC", "AAP 2.06 kPa", "moisture content", and "spot absorbency". "CRC", "AAP 2.06 kPa", and "moisture content" were measured using the methods described above. The evaluation results are shown in Tables 2 and 3.

[0692] "Determination of the total volume fraction [volume %] of connected pores and the total volume fraction [volume %] of independent bubbles"

[0693] Regarding the total volume fraction of the granular superabsorbent of the present invention, the total volume fraction of interconnected pores (unit: volume%), and the total volume fraction of independent air bubbles (unit: volume%), three-dimensional image data of the granular superabsorbent was acquired using a microfocus X-ray CT system (inspeXio SMX-100CT / manufactured by Shimadzu Corporation), and the three-dimensional image data was analyzed using high-speed three-dimensional analysis software (TRI / 3D-VOL-FCS64 / RATOC Systems Engineering, Inc.), and the results were calculated using Microsoft Excel. The total volume fraction of interconnected pores and the total volume fraction of independent air bubbles were determined using granular superabsorbent with a particle size of 250 μm to 425 μm. Specifically, three-dimensional image data of granular superabsorbent with a particle size of 250 μm to 425 μm was acquired using the aforementioned microfocus X-ray CT system, analyzed using the aforementioned high-speed three-dimensional analysis software, and the results were calculated using Excel.

[0694] The specific calculation method is described below. First, the extraction method for granular absorbent with a particle size of 250μm to 425μm is described. First, JIS standard sieves (The IIDA TESTING SIEVE / manufactured by Iida Corporation, diameter: 8cm, sieve opening: 425μm / 250μm) are stacked in descending order of opening size from top to bottom, and a receiver (manufactured by Iida Corporation, diameter: 8cm) is stacked at the bottom. Next, 10.0g of granular absorbent is added to the top sieve (sieve opening: 425μm), and the lid (manufactured by Iida Corporation, diameter: 8cm) is placed on top. Then, the stacked lid, two sieves, and receiver are vibrated for 5 minutes using an IIDA SIEVE SHAKER (TYPE: ES-65, SER. No. 0632). After vibration, only the water-absorbing resin remaining on the 250 μm open sieve is extracted and used as a granular water-absorbing agent with a particle size of 250 μm to 425 μm. The above operation is carried out indoors at a temperature of 20.0 to 25.0 °C and a humidity of 35% to 50%.

[0695] In a plastic, lidded cylindrical container (approximately 1 cm inner diameter and 5 cm height), 0.3 g of thermosetting spherical microparticles (EPOSTAR MV1002 / Nippon Shokubai Co., Ltd.) was added, followed by 0.1 g of granular water-absorbing agent with a particle size of 250 μm to 425 μm. The container was shaken and / or tapped to thoroughly mix the particles, thereby uniformly dispersing the granular water-absorbing agent within the thermosetting spherical microparticles to prepare the sample. Next, double-sided tape was attached to the bottom of the cylindrical container, which was then fixed to the sample stage of the aforementioned microfocus X-ray CT system. Three-dimensional image data was acquired under the following conditions.

[0696] [Table 1]

[0697]

[0698] Using the aforementioned high-speed 3D analysis software, perform the analysis according to the following steps.

[0699] 1. From the menu bar, select Particle Measurement > 3D Particles > Particle Separation > Giant Particle Separation.

[0700] 2. In the EVC panel, select the Binarize tab and choose LW. Keep the W value unchanged from its initial value, and change the L value from its initial value to a value greater than "1" to extract the circular measurement object area. Next, apply this processing to all slice images. Set the image data extracted through this operation as (A) and save it in bin5ch(b5) ​​on the BC panel.

[0701] 3. On the EVC panel, select the Binarize tab and choose LW. Keep the W value unchanged from its initial value, and change the L value from its initial value to "37580" to extract all granular absorbent material within the measurement area. Next, apply this processing to all slice images. Set the granular image data extracted through this operation as (B) and save it in binDch(bD) on the BC panel.

[0702] 4. Based on the particle image data (B), firstly, select Ers Sml in the Binary tab of the EVC panel to remove particles smaller than 10 voxels, which are considered noise. Next, select Invert in the Binary tab of the EVC panel to invert the region where particles were extracted from and the region where particles were not extracted. Next, select Ers Sml in the Binary tab of the EVC panel to remove particles smaller than 1 voxel, which are considered noise. Next, select Labeling in the 3D tab of the EVC panel, and then select Volume and Max to extract only the region with the largest volume. Here, after confirming that LabelCount is 1, select Invert again in the Binary tab of the EVC panel to remove noise in the measurement object area and extract all particles with embedded Void (independent bubbles). Set the particle image data extracted through these operations as (C) and save it in bin2ch (b2) in the BC panel.

[0703] 5. In the LOP tab (Inter-channel logical operation processing), select "2" for Object 1 and "D" for Object 2, then select "SUB" and press Execute to subtract particle image data (B) from particle image data (C). Next, in the Binary tab of the EVC panel, select Ers Sml to remove particles smaller than 1 voxcel that are considered noise, thus extracting Void (independent bubbles). Set the particle image data extracted through these operations to (D) and save it in bin6ch (b6) on the BC panel.

[0704] 6. Based on the particle image data (C), perform two dilation operations around the 8-link selection in the 3D label on the EVC panel, followed by two erosion operations. Set the particle image data extracted through this operation as (E) and save it in bin1h(b1) on the BC panel.

[0705] 7. In the LOP tab (Inter-channel logical operation processing), select "1" for Object 1 and "2" for Object 2, then select "SUB" and press Execute to subtract the particle image data (C) from the particle image data (E). This operation extracts the Cavity (connecting holes). Set the resulting particle image data as (F) and save it in bin7ch (b7) on the BC panel.

[0706] 8. Based on the particle image data (E), select small particle extraction (do not select large particle extraction) on the large particle separation panel, and set the shrinkage ratio, repair filter size and repair Mrg Sml diameter to "0" to perform particle separation and color differentiation.

[0707] 9. On the EVC panel, select Labeling in the 3D tab, then select coordinate values ​​(loop), and set the particle size to "100" to perform particle separation. Set the particle image data extracted through these operations as (G) and save it in bin1ch(b1) on the BC panel.

[0708] 10. From the menu bar, select Particle Measurement > Void in 3D Particles > Measurement after Separation.

[0709] 11. On the measurement panel after separation, select voxcel as the unit, then select edge particle removal, and then select surface area calculation and Void (independent bubble) calculation as the measurement items. Select Binary 5ch as the measurement ROI specification to perform the calculation.

[0710] 12. Extract the data obtained through the calculations in step 10 above in the form of an Excel CSV file.

[0711] Through the above operations, the particle volume (unit: mm) of each individual particle of all granular absorbent present in the measurement area was obtained. 3 Void volume (hereinafter referred to as "independent bubble volume") (unit: mm) 3 ) and Cavity volume (hereinafter referred to as "connecting hole volume") (unit: mm) 3 The data is from [the data source]. It should be noted that the aforementioned particle volume is a value calculated for the granular absorbent in the state where the Void (independent air bubble) and Cavity (connecting pores) are embedded. Furthermore, in the aforementioned measurement area, there exists a granular absorbent containing approximately 200 to 500 particles.

[0712] (Calculation of the total volume fraction [volume %] of the connecting holes)

[0713] Next, the particle volume (in mm) of each particle was extracted from Excel. 3 Independent bubble volume (unit: mm) 3 ) and the volume of the connecting hole (unit: mm) 3 Calculate the total volume fraction [volume %] of the interconnected pores based on the data. First, calculate the volume of each particle (unit: mm). 3 Independent bubble volume (unit: mm) 3 ) and the volume of the connecting hole (unit: mm) 3 Calculate the total volume (H) of all particles by summing them up separately (unit: mm). 3 ), Total volume of independent bubbles (I) (unit: mm) 3 ) and the total volume of the connecting holes (J) (unit: mm) 3 It should be noted that the total volume of all the aforementioned particles is a value calculated in the granular absorbent with the Void (independent air bubble) and Cavity (connecting pores) embedded. Next, the total volume fraction of the connecting pores (unit: volume %), which is the average value of all granular absorbent present in the measurement area, is calculated according to the following formula (1).

[0714] Total volume fraction of connecting holes = J / (HI)×100…Equation (1)

[0715] Here,

[0716] H: Total volume of all particles (unit: mm) 3 )

[0717] I: Total volume of all individual bubbles in all particles (unit: mm)3 )

[0718] J: Total volume of the interconnected pores of all particles (unit: mm) 3 ).

[0719] (Calculation of the total volume fraction [volume %] of independent bubbles)

[0720] The total volume fraction (unit: volume%) of independent bubbles, which is the average value of all particulate desiccant present in the measurement area, is calculated according to the following formula (2).

[0721] Total volume fraction of independent bubbles = I / (HJ)×100…Equation (2)

[0722] Here,

[0723] H: Total volume of all particles (unit: mm) 3 )

[0724] I: Total volume of all individual bubbles in all particles (unit: mm) 3 )

[0725] J: Total volume of the interconnected pores of all particles (unit: mm) 3 ).

[0726] "Absorption time of high viscosity liquid"

[0727] (Preparation of high-viscosity test solution)

[0728] A test solution was prepared consisting of 792.8 parts by mass of ion-exchanged water, 7.2 parts by mass of sodium chloride, 35.6 parts by mass of sodium carbonate, 160 parts by mass of glycerol, 0.04 parts by mass of red food coloring, and 4.4 parts by mass of carboxymethyl cellulose (Aldrich, product number: C5678-500G). The viscosity of this test solution was 5 mPa·s at 23°C and 3.4 mPa·s at 37°C.

[0729] (Determination of absorption time [seconds] for high viscosity liquids)

[0730] Weigh 50g of the high-viscosity test solution, adjusted to a liquid temperature of 23℃, into a 100mL beaker. Stir at 600rpm using a cylindrical stirrer with a length of 40mm and a diameter of 8mm. During this process, add 2.00g of granular superabsorbent polymer (SAP) and measure the absorption time (in seconds). Regarding the endpoint, according to the standard described in JISK 7224-1996 "Explanation of the Test Method for Water Absorption Rate of Superabsorbent Resins," the time until the granular superabsorbent polymer absorbs the high-viscosity test solution and the test solution covers the stirrer chip is measured as the high-viscosity liquid absorption time (in seconds).

[0731] "Spot absorption" ("Liquid draw-in time and return flow")

[0732] Regarding the granular absorbent of the present invention, the following absorbent was prepared and evaluated.

[0733] (Preparation of single-layer granular absorbent tablets)

[0734] Cut a 10cm wide piece of vinyl tape (Nitto Denko Co., Ltd., Nitto Vinyl Tape No. 21-100TM) into 18cm lengths, with the adhesive side facing up. Place it on a horizontal workbench and attach a plastic frame (1cm thick) with an inner frame having a longitudinal length of 8cm and a transverse length of 16cm, and an outer frame having a longitudinal length of 10cm and a transverse length of 18cm. At this point, no wrinkles should form on the vinyl tape. Distribute 1.278g of granular absorbent evenly on the adhesive side of the vinyl tape. Then, consider the vinyl tape surface as a divided section of three sections, each 8cm long and 5.33cm wide. Distribute 0.426g of granular absorbent evenly to each section. After distribution, tilt the frame to adhere all the granular absorbent to the adhesive side of the vinyl tape. Peel the vinyl tape from the plastic frame in a manner that prevents the adhesive granules from falling off. Place the tape with the adhesive granules facing up on a horizontal laboratory table. Place a piece of nonwoven fabric cut to 10cm in length and 18cm in width (18.5g / m²) on top of the vinyl tape with the adhesive granules. 2 A spunbond nonwoven fabric is bonded using the adhesive residue of vinyl tape to obtain a single-layer sheet of granular absorbent. The four corners of the vinyl tape are then aligned and bonded to the four corners of the nonwoven fabric, ensuring the lower surface of the nonwoven fabric is in contact with the granular absorbent. A black magic pen mark is used to mark the center of the resulting granular absorbent sheet as the location for the addition funnel. Additionally, four marks are made at 27.5 mm intervals along the 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock positions to mark the placement of filter paper.

[0735] (Inhalation rate and reflux rate of test solution for monolayer granular desiccant tablets)

[0736] With the nonwoven fabric facing upwards, ensure the granular absorbent monolayer is completely aligned with the fabric. Figure 18 The evaluation device shown is set with a curved surface within its frame. It should be noted that... Figure 18The device is a container (material: transparent acrylic resin) with a semi-circular recess inside, the recess measuring 122mm in diameter × 102mm in width (61mm in depth). It is positioned so that the nonwoven fabric at the filter paper placement area does not wrinkle. Aligning with the curved surface of the evaluation device, one 180mm × 10mm silicon wafer (2mm thick) is placed along the bottom two corners of the curved surface, i.e., along the two sides of the 180mm length of the granular absorbent single-layer sheet, to prevent leakage from the sides.

[0737] A funnel is set up 1 cm above the liquid addition funnel, adjusted to allow 5g of high-viscosity test liquid to be added in 2 seconds. 5g of high-viscosity test liquid is added to the funnel. A stopwatch is started the instant the liquid initially contacts the granular absorbent monolayer, and the time taken until the liquid surface completely disappears from the granular absorbent monolayer is recorded as the liquid absorption rate (in seconds). It should be noted that a short liquid absorption rate indicates excellent liquid absorption performance. In Tables 2-4 below, the liquid absorption rate is referred to as "absorption rate".

[0738] Two minutes and 50 seconds after the initial liquid contact with the granular absorbent monolayer, the granular absorbent monolayer was removed from the evaluation device with the liquid surface facing upwards and placed on a horizontal experimental table. Three minutes after the initial liquid contact with the granular absorbent monolayer, five Φ55mm filter papers with a pre-determined total weight (W1[g]) were stacked in the center (where the filter paper was placed), and a weight (Φ50mm, weight 1035g, 5.2kPa) was applied for a 10-second load. After 10 seconds of the load being applied, the weight (W2[g]) of the five Φ55mm filter papers was measured, and the difference (W2-W1) was calculated as the reflux rate [g] of the granular absorbent monolayer.

[0739] [Table 2]

[0740]

[0741] [Table 3]

[0742]

[0743] Figure 19 The graphs were plotted by defining the x-axis as the total volume fraction of interconnected pores and the y-axis as the total volume fraction of independent air bubbles, for the granular superabsorbents of the examples and comparative examples. Figure 19 This shows the correlation between the total volume fraction of connected pores and the total volume fraction of independent bubbles. According to... Figure 19It can be seen that the granular absorbents of Examples 1-1 to 1-14, in which the total volume fraction of connected pores is 10% or more and the total volume fraction of independent bubbles is 0.5% or less, occupy the lower right region of the graph. It can be considered that the absorbent using the granular absorbent in this region exhibits excellent liquid absorption rate and recirculation. Furthermore, according to... Figure 19 It is understood that the granular water absorbents (CE-1-1) to (CE-1-9) of Comparative Examples 1-1 to 1-9 do not meet the requirements of the total volume fraction of interconnected pores and the total volume fraction of independent air bubbles in the granular water absorbent of the present invention.

[0744] [Reference Example]

[0745] To demonstrate that a particulate absorbent, using particles that pass through a sieve with a 425 μm opening but not through a 250 μm opening, meets the specified requirements for the total volume fraction of connected pores and the total volume fraction of independent bubbles as determined by X-ray CT, thereby enabling an increase in the liquid absorption rate of the absorbent and a reduction in the reflux rate, the following reference example is shown.

[0746] [Refer to Example 1-1]

[0747] The 30g of granular absorbent (EX-1-1) obtained in Example 1-1 was graded using a sieve with an opening of 850 / 425 / 250 / 106μm. First, JIS standard sieves (The IIDA TESTING SIEVE / Iida Manufacturing Co., Ltd., diameter: 15cm, sieve opening: 850μm / 425μm / 250μm / 106μm) were stacked in descending order of opening size from top to bottom, with a receiver (Iida Manufacturing Co., Ltd., diameter: 15cm) stacked at the bottom. Next, 30.0g of granular absorbent (EX-1-1) was added to the topmost sieve (sieve opening: 850μm), and the lid (Iida Manufacturing Co., Ltd., diameter: 15cm) was placed on top. Next, using an IIDA SIEVE SHAKER (TYPE: ES-65, SER. No. 0632), the overlapping lid, two sieves, and receiver were vibrated for 5 minutes. After vibration, the amount of granular superabsorbent that passed through the 850 μm sieve but not through the 425 μm sieve (fraction A) was 13.02 g (43.4% by mass). The amount of superabsorbent that passed through the 425 μm sieve but not through the 250 μm sieve (fraction B) was 11.40 g (38.0% by mass). The amount of granular superabsorbent that passed through the 250 μm sieve but not through the 106 μm sieve (fraction C) was 5.58 g (18.6% by mass).

[0748] Similarly, 30 g of the granular superabsorbent polymer (CE-1-5) obtained in Comparative Examples 1-5 was fractionated using a sieve with an opening size of 850 / 425 / 250 / 106 μm. The fraction X (12.90 g, 43.0% by mass) of granular superabsorbent polymer passed through the 850 μm sieve but not through the 425 μm sieve. The fraction Y (11.46 g, 38.2% by mass) of granular superabsorbent polymer passed through the 425 μm sieve but not through the 250 μm sieve. The fraction Z (5.64 g, 18.8% by mass) of granular superabsorbent polymer passed through the 250 μm sieve but not through the 106 μm sieve.

[0749] Fractions X, B, and Z were mixed to obtain granular absorbent (RE-1). The absorbent was evaluated using granular absorbent (RE-1), and the results showed a liquid absorption rate of 21 seconds and a reflux rate of 0.4 g.

[0750] [Refer to Examples 1-2]

[0751] Fractions A, Y, and C were mixed to obtain granular absorbent (RE-2). The absorbent was evaluated using granular absorbent (RE-2), and the results showed an absorption rate of 29 seconds and a reflux rate of 0.7 g.

[0752] As shown in Reference Examples 1-1 and 1-2 above, when using a desiccant with a total volume fraction of interconnected pores and a total volume fraction of independent bubbles determined by X-ray CT measurement of particles passing through a sieve with a 425 μm opening but not through a sieve with a 250 μm opening, the liquid absorption rate and the recirculation rate of the absorbent can be increased, thereby achieving a reduction in the liquid absorption rate and the recirculation rate of the absorbent. Specifically, Reference Example 1-1 is similar to Example 1-1, with good liquid absorption rate and recirculation rate. Reference Example 1-2 is similar to Comparative Example 1-5, with deterioration in liquid absorption rate and recirculation rate. From the above results, it can be seen that the fraction of liquid that passes through a sieve with a 425 μm opening but not through a sieve with a 250 μm opening, which preferably accounts for more than 35% by mass of the total desiccant, dominates the liquid absorption rate and recirculation rate in the absorbent evaluation.

[0753] [Table 4]

[0754]

[0755] (Reasons for the preferred X-ray CT measurement at a particle size of 425 / 250)

[0756] When using fractions larger than 425 μm for X-ray CT measurements, the number of particles that can be measured at once c...

Claims

1. A granular water absorbent, characterized in that, It is a granular water-absorbing agent with poly(meth)acrylic acid and / or poly(meth)acrylate salt-based water-absorbing resin particles as the main component. The granular absorbent comprises: interconnecting pores, which are spaces communicating with the outside; and individual air bubbles, which are closed spaces not communicating with the outside. The connecting holes are through-holes, depressions, and grooves present on the surface of the granular absorbent in three-dimensional image data obtained using a microfocus X-ray CT system. The total volume fraction of the connecting holes is 10% or more. The total volume fraction of the independent bubbles is less than 0.5% by volume. The total volume fraction of the connecting holes = J / (HI) × 100 Equation (1) Here, H: Total volume of all particles, in mm. 3 , I: Total volume of all individual bubbles in all particles, in mm. 3 , J: Total volume of the interconnected pores of all particles, in mm. 3 ; The total volume fraction of the independent bubbles = I / (HJ) × 100 Equation (2) Here, H: Total volume of all particles, in mm. 3 , I: Total volume of all individual bubbles in all particles, in mm. 3 , J: Total volume of the interconnected pores of all particles, in mm. 3 .

2. The granular water absorbent according to claim 1, wherein the CRC is 25 g / g or more, and the CRC is the water absorption ratio of the granular water absorbent under no pressure.

3. The granular superabsorbent according to claim 1 or 2, wherein the AAP0.3psi under a load of 2.06 kPa is 20 g / g or more, and the AAP is the water absorption ratio of the granular superabsorbent under pressure.

4. The granular absorbent according to claim 1 or 2 has a water content of 5% by mass or more.

5. The granular absorbent according to claim 1 or 2, wherein the absorption time of the high-viscosity liquid is less than 140 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

6. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is 11% or more.

7. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is 12% or more.

8. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is 13% or more.

9. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is 14% or more.

10. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is less than 40% by volume.

11. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is less than 35% by volume.

12. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is less than 30% by volume.

13. The granular absorbent according to claim 1, wherein, The total volume fraction of the connecting holes is less than 25% by volume.

14. The granular absorbent according to claim 1, wherein, The total volume fraction of the independent bubbles is less than 0.4% by volume.

15. The granular absorbent according to claim 1, wherein, The total volume fraction of the independent bubbles is less than 0.3% by volume.

16. The granular absorbent according to claim 1, wherein, The total volume fraction of the independent bubbles is 0.01% or more.

17. The granular absorbent according to claim 2, wherein, The CRC is above 32g / g.

18. The granular absorbent according to claim 2, wherein, The CRC is above 33g / g.

19. The granular absorbent according to claim 2, wherein, The CRC is below 70g / g.

20. The granular absorbent according to claim 2, wherein, The CRC is below 60g / g.

21. The granular absorbent according to claim 2, wherein, The CRC is below 50g / g.

22. The granular absorbent according to claim 2, wherein, The CRC is below 40g / g.

23. The granular absorbent according to claim 3, wherein, The AAP 0.3psi under a load of 2.06 kPa is above 24 g / g.

24. The granular absorbent according to claim 3, wherein, The AAP 0.3psi under a load of 2.06 kPa is above 26 g / g.

25. The granular absorbent according to claim 3, wherein, The AAP 0.3psi under a load of 2.06 kPa is above 28 g / g.

26. The granular absorbent according to claim 3, wherein, The AAP 0.3psi under a load of 2.06 kPa is above 29 g / g.

27. The granular absorbent according to claim 3, wherein, The AAP 0.3psi under a load of 2.06 kPa is above 30 g / g.

28. The granular absorbent according to claim 3, wherein, The AAP at a load of 2.06 kPa and 0.3 psi is less than 40 g / g.

29. The granular absorbent according to claim 1 or 2, wherein the moisture content is 0.2 to 30% by mass.

30. The granular absorbent according to claim 1 or 2, wherein the water content is 1% by mass or more.

31. The granular absorbent according to claim 1 or 2, wherein the water content is 6% by mass or more.

32. The granular absorbent according to claim 1 or 2, wherein the water content is 7% by mass or more.

33. The granular absorbent according to claim 1 or 2, wherein the water content is 8% by mass or more.

34. The granular absorbent according to claim 1 or 2, wherein the moisture content is less than 15% by mass.

35. The granular absorbent according to claim 1 or 2, wherein the moisture content is less than 14% by mass.

36. The granular absorbent according to claim 1 or 2, wherein the moisture content is less than 13% by mass.

37. The granular absorbent according to claim 1 or 2, wherein the water content is less than 12% by mass.

38. The granular absorbent according to claim 1 or 2, wherein, The solid content of the granular water absorbent is 85% to 99% by mass.

39. The granular absorbent according to claim 1 or 2, wherein, The solid content of the granular water absorbent is 86% to 95% by mass.

40. The granular absorbent according to claim 1 or 2, wherein, The solid content of the granular water absorbent is 87% to 94% by mass.

41. The granular absorbent according to claim 1 or 2, wherein, The solid content of the granular water absorbent is 88% to 93% by mass.

42. The granular absorbent according to claim 1 or 2, wherein, The solid content of the granular absorbent is 88% to 92% by mass.

43. The granular absorbent according to claim 1 or 2, wherein, The mass-average particle size D50 of the granular water absorbent is greater than 200 μm.

44. The granular absorbent according to claim 1 or 2, wherein, The mass-average particle size D50 of the granular water absorbent is 200μm~600μm.

45. The granular absorbent according to claim 1 or 2, wherein, The mass-average particle size D50 of the granular water absorbent is 230μm~550μm.

46. ​​The granular absorbent according to claim 1 or 2, wherein, The mass-average particle size D50 of the granular water absorbent is 250μm~500μm.

47. The granular absorbent according to claim 1 or 2, wherein, The proportion of particles with a diameter of less than 106 μm in the granular water absorbent is less than 10% by mass.

48. The granular absorbent according to claim 1 or 2, wherein, The proportion of particles with a diameter of less than 106 μm in the granular water absorbent is less than 8% by mass.

49. The granular absorbent according to claim 1 or 2, wherein, The proportion of particles with a diameter of less than 106 μm in the granular water absorbent is less than 6% by mass.

50. The granular absorbent according to claim 1 or 2, wherein, The proportion of particles with a diameter exceeding 850 μm in the granular water absorbent is less than 5% by mass.

51. The granular absorbent according to claim 1 or 2, wherein, The proportion of particles with a diameter exceeding 850 μm in the granular water absorbent is less than 3% by mass.

52. The granular absorbent according to claim 1 or 2, wherein, The proportion of particles with a diameter exceeding 850 μm in the granular water absorbent is less than 1% by mass.

53. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains more than 90% by mass particles with a particle size of 106μm to 850μm.

54. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains at least 95% by mass particles with a diameter of 106 μm to 850 μm.

55. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains at least 97% by mass particles with a diameter of 106 μm to 850 μm.

56. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains 99% by mass or more particles with a diameter of 106 μm to 850 μm.

57. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is more than 30% by mass.

58. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is 35% by mass or more.

59. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains at least 36% by mass particles with a diameter of 250 μm to 425 μm.

60. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains at least 37% by mass particles with a diameter of 250 μm to 425 μm.

61. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is less than 90% by mass.

62. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is less than 85% by mass.

63. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is less than 80% by mass.

64. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is less than 75% by mass.

65. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is less than 70% by mass.

66. The granular absorbent according to claim 1 or 2, wherein, The content of particles with a diameter of 250μm to 425μm in the granular water absorbent is less than 65% by mass.

67. The granular absorbent according to claim 1 or 2, wherein, The logarithmic standard deviation σζ of the particle size distribution of the granular water absorbent is 0.20~0.

50.

68. The granular absorbent according to claim 1 or 2, wherein, The logarithmic standard deviation σζ of the particle size distribution of the granular water absorbent is 0.27~0.

35.

69. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is less than 135 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

70. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is less than 130 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

71. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is less than 120 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

72. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is less than 110 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

73. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is less than 100 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

74. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is more than 5 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

75. The granular absorbent according to claim 1 or 2, wherein the high-viscosity liquid absorption time is more than 10 seconds, and the high-viscosity liquid is a solution with a viscosity of 5 mPa·s at 23°C.

76. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains 60-100% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate absorbent resin particles.

77. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains 70-100% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate-based absorbent resin particles.

78. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains 80-100% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate-based absorbent resin particles.

79. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains 90-100% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate-based absorbent resin particles.

80. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains less than 99% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate absorbent resin particles.

81. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains less than 97% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate absorbent resin particles.

82. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent contains less than 95% by weight of poly(meth)acrylic acid and / or poly(meth)acrylate absorbent resin particles.

83. The granular absorbent according to claim 1 or 2, wherein, In the poly(meth)acrylic acid and / or poly(meth)acrylate salt-based water-absorbing resin particles, the amount of (meth)acrylic acid and / or (meth)acrylate salt is 50 mol% to 100 mol% relative to the total monomers used in polymerization, i.e., all monomers except crosslinking agents.

84. The granular absorbent according to claim 1 or 2, wherein, In the poly(meth)acrylic acid and / or poly(meth)acrylate salt-based water-absorbing resin particles, the amount of (meth)acrylic acid and / or (meth)acrylate salt is 70 mol% to 100 mol% relative to the total monomers used in polymerization, i.e., all monomers except crosslinking agents.

85. The granular absorbent according to claim 1 or 2, wherein, In the poly(meth)acrylic acid and / or poly(meth)acrylate salt-based water-absorbing resin particles, the amount of (meth)acrylic acid and / or (meth)acrylate salt is 90 mol% to 100 mol% relative to the total monomers used in polymerization, i.e., all monomers except crosslinking agents.

86. The granular absorbent according to claim 1 or 2, wherein, The granular absorbent also contains water-insoluble inorganic particles.

87. The granular absorbent according to claim 86, wherein, The water-insoluble inorganic particles are selected from at least one of polymetallic compounds, silicon dioxide, aluminum hydroxide, talc, and tricalcium phosphate.

88. The granular absorbent according to claim 86, wherein, The water-insoluble inorganic particles are selected from at least one of hydrotalcite, silica, aluminum hydroxide, and tricalcium phosphate.

89. An absorbent body that uses the granular absorbent according to any one of claims 1 to 88.

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