Poly (meth) acrylic acid (salt)-based water-absorbent resin and absorbent article

Abstract

Provided are: a water-absorbent resin which reduces the amount of liquid reflux in an absorbent article provided with the water-absorbent resin and a water-permeable base material and which has excellent liquid retention properties; and an absorbent article which has excellent liquid diffusivity. The problem is solved by using: a poly (meth) acrylic acid (salt)-based water-absorbent resin having a resistance to intrusion between fibers of a water-permeable base material of 60 wt% or more; and an absorbent article as follows. The absorbent article comprises, in this order, a liquid-impermeable lower gasket, an absorbent body comprising a water-absorbent resin and a water-permeable base material, and a liquid-permeable upper gasket. The water-absorbent resin is a poly (meth) acrylic acid (salt) water-absorbent resin having a resistance to intrusion between fibers of the water-permeable base material of 60 wt% or more.

Description

Technical Field

[0001] This invention relates to a water-absorbing resin and an absorbent article. More specifically, this invention relates to a poly(meth)acrylate (salt)-based water-absorbing resin and an absorbent article comprising an absorbent body containing the poly(meth)acrylate (salt)-based water-absorbing resin. Background Technology

[0002] In recent years, from the perspective of bodily fluid absorption, absorbent resins have been widely used as absorbent agents in sanitary materials such as diapers, sanitary napkins, and incontinence pads. Examples of such absorbent resins include, for instance, hydrolysates of starch-acrylonitrile graft copolymers, neutralized starch-acrylic acid graft polymers, saponified vinyl acetate-acrylate copolymers, and crosslinked polymers of partially neutralized (meth)acrylic acid polymers. Among these, poly(meth)acrylic acid (salt)-based absorbent resins, which use (meth)acrylic acid and / or its salts as monomers as the main component, are the most widely produced industrially from the perspective of absorbency.

[0003] As parameters reflecting the desired properties of the poly(meth)acrylate (salt)-based absorbent resin, various parameters are known, including unpressurized absorbent ratio (CRC), pressurized absorbent ratio (AAP), absorption rate (FSR / vortex), unpressurized flowability, pressurized flowability, impact resistance, urine resistance, flowability, gel strength, colorfastness, and particle size. Furthermore, even for the same parameter, such as unpressurized absorbent ratio, various methods for measuring the parameter have been proposed from different perspectives. Regarding absorbent resins developed with these various properties in mind, even if these various properties (e.g., "unpressurized absorbent ratio (CRC)" and "pressurized absorbent ratio (AAP)") are controlled, the following problem remains: when used in absorbents such as diapers for practical application, it is difficult to say that the resin has achieved its full performance.

[0004] When absorbents used in diapers and the like are put into practical use, it is undoubtedly necessary to improve the absorbency of the absorbent resin to enhance its performance, thereby increasing the absorbency of the diaper. In addition, it is also possible to reduce the liquid backflow of the absorbent by improving the diffusion and liquid permeability of the diaper (Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 2015-107488 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] However, even with the aforementioned improved absorbent resins that enhance liquid permeability, when used in absorbent articles such as diapers that incorporate both absorbent resins and permeable substrates, there is still a possibility that the absorbed liquid is not sufficiently distributed throughout the entire absorbent article, leading to increased liquid backflow. Therefore, from the perspective of liquid retention, there is still room for improvement. Furthermore, even with absorbent resins and permeable substrates that enhance liquid permeability as described above, there is still a possibility that the absorbed liquid is not sufficiently distributed throughout the entire absorbent article. Therefore, from the perspective of liquid diffusion, there is still room for improvement.

[0010] One objective of this invention is to provide an absorbent resin that reduces liquid backflow and exhibits excellent liquid retention in absorbent articles comprising an absorbent resin and a permeable substrate. Another objective of this invention is to provide an absorbent article with excellent liquid diffusion properties.

[0011] Solution for solving the problem

[0012] The poly(meth)acrylate (salt)-based water-absorbing resin of one embodiment of the present invention has a resistance to interfiber intrusion of a water-permeable substrate of 60% by weight or more, as determined by the steps (1) to (3) below:

[0013] (1) On the bottom surface of a polystyrene cuboid box with a base of 6cm × 9cm and a depth of 1cm (measured by the inner surface of the box), use double-sided tape to fix a cut piece of non-woven fabric measuring 6cm × 9cm.

[0014] Here, the nonwoven fabric has a thickness of 3 mm and a unit area weight of 41 g / m². 2 Furthermore, the hot-air nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate has a fiber diameter of 0.18 mm for polyethylene and 0.27 mm for polyethylene terephthalate.

[0015] (2) Distribute 1.0g of water-absorbing resin evenly over the entire surface of the nonwoven fabric, and invert the nonwoven fabric with the water-absorbing resin distributed thereon and the box together on a tray with a bottom area larger than the box to recover the water-absorbing resin that has fallen onto the tray.

[0016] (3) Calculate the interfiber intrusion resistance of the permeable substrate according to the following formula (1).

[0017] Resistance to intrusion between fibers of a permeable substrate [wt%] = weight of recycled absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 Equation (1).

[0018] Additionally, one embodiment of the absorbent article of the present invention comprises, in sequence, an impermeable lower gasket, an absorbent comprising a water-absorbing resin and a water-permeable substrate, and a water-permeable upper gasket.

[0019] The water-absorbing resin is a poly(meth)acrylate (salt)-based water-absorbing resin, and,

[0020] The water-absorbing resin, as determined by steps (1) to (3) below, has a resistance to inter-fiber intrusion of the water-permeable substrate of 60% by weight or more.

[0021] (1) On the bottom surface of a polystyrene cuboid box with a base of 6cm × 9cm and a depth of 1cm (measured by the inner surface of the box), use double-sided tape to fix a cut piece of non-woven fabric measuring 6cm × 9cm.

[0022] Here, the nonwoven fabric has a thickness of 3 mm and a unit area weight of 41 g / m². 2 Furthermore, the hot-air nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate has a fiber diameter of 0.18 mm for polyethylene and 0.27 mm for polyethylene terephthalate.

[0023] (2) Distribute 1.0g of water-absorbing resin evenly over the entire surface of the nonwoven fabric, and invert the nonwoven fabric with the water-absorbing resin distributed thereon and the box together on a tray with a bottom area larger than the box to recover the water-absorbing resin that has fallen onto the tray.

[0024] (3) Calculate the interfiber intrusion resistance of the permeable substrate according to the following formula (1).

[0025] Resistance to intrusion between fibers of a permeable substrate [wt%] = weight of recycled absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 Equation (1).

[0026] Invention Effects

[0027] According to one aspect of the present invention, a water-absorbing resin that reduces liquid backflow and exhibits excellent liquid retention properties in absorbent articles comprising a water-absorbing resin and a water-permeable substrate can be provided. Furthermore, according to one aspect of the present invention, an absorbent article with excellent liquid diffusion properties can be provided. Attached Figure Description

[0028] Figure 1 1001 is a diagram showing the absorbent sheet used for evaluating liquid reflux flow rate in the embodiment, 1002 is a view of the absorbent sheet from directly above, and 1003 is a cross-sectional view of the absorbent sheet.

[0029] Figure 21003 is a diagram showing an absorbent article used for evaluating the liquid diffusivity in the embodiments, 1004 is a view of the absorbent article viewed from directly above, and 1005 is a cross-sectional view of the absorbent article.

[0030] Figure 3 This is a schematic diagram of a roller crushing device used in the crushing process of one embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram illustrating a pair of rollers in a roller crushing device used in a crushing process according to one embodiment of the present invention. 2001 is a pair of rollers with grooves provided on the surfaces of both rollers, and 2002 is a pair of rollers with grooves provided on the surface of one roller and no grooves provided on the surface of the other roller. Detailed Implementation

[0032] The invention will now be described with reference to the preferred mode. Unless otherwise specified, the terminology used herein should be understood to have the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, this specification (including definitions) shall prevail. The invention is not limited to the embodiments described below, and various modifications may be made within the scope of the claims.

[0033] [1] Definition of the term (1-1) "Water-absorbing resin"

[0034] In this invention, "water-absorbing resin" refers to a water-swellable and water-insoluble polymeric gelling agent, which is a substance that meets the following physical properties. That is, it refers to a polymeric gelling agent that, as "water-swellable," has a CRC of 5 g / g or more as specified in ERT441.2-02, and, as "water-insoluble," has an Ext of 50% by weight or less as specified in ERT470.2-02.

[0035] The absorbent resin can be designed according to its intended use and is not particularly limited. It is preferably a hydrophilic crosslinked polymer formed by crosslinking and polymerizing unsaturated monomers having carboxyl groups. Furthermore, the absorbent resin is not limited to a composition where all components (100% by weight) are polymers; it can also be an absorbent resin composition containing additives, etc., within the range satisfying the aforementioned physical properties (CRC, Ext). In addition, the absorbent resin in this invention is not limited to the final product; it sometimes refers to intermediates in the manufacturing process of absorbent resins (e.g., polymerized hydrogel-like crosslinked polymers, dried polymers, absorbent resins before surface crosslinking, absorbent resins after surface crosslinking, absorbent resins after granulation, etc.), and is collectively referred to as "absorbent resin" along with the absorbent resin composition. It should be noted that the shape of the absorbent resin is not particularly limited; examples include sheet-like, fibrous, film-like, and granular forms. In this invention, granular absorbent resins are preferred.

[0036] (1-2) "Poly(meth)acrylate (salt) based water-absorbing resin"

[0037] In this invention, "poly(meth)acrylate (salt)-based water-absorbing resin" refers to a water-absorbing resin that arbitrarily contains grafted components and whose main component is a structural unit derived from (meth)acrylate and / or its salts (hereinafter referred to as "(meth)acrylate (salt)"). The poly(meth)acrylate (salt)-based water-absorbing resin is a water-absorbing resin that preferably contains 50-100 mol%, more preferably 70-100 mol%, further preferably 90-100 mol%, and particularly preferably substantially 100 mol% of (meth)acrylate (salt) relative to all monomers used in the polymerization (excluding crosslinking agents).

[0038] (1-3) "EDANA" and "ERT"

[0039] "EDANA" is the abbreviation for the European Disposables and Nonwovens Association, and "ERT" is the abbreviation for the EDANA Recommended Test Methods, a European standard (essentially a global standard). In this invention, unless otherwise specified, the physical properties of the absorbent resin are determined according to the original ERT (2002 revision / public literature).

[0040] (1-4) "Permeable substrate"

[0041] In this invention, "permeable substrate" refers to a component in the absorbent body used in absorbent articles such as diapers that has the function of allowing the liquid to pass through and / or diffuse and is in direct contact with the absorbent resin. Specifically, examples include hydrophilic fibers (such as pulp fibers), fiber stacks of hydrophilic fibers, hydrophilic nonwoven fabrics containing hydrophilic fibers as constituent fibers, and nonwoven fabrics containing synthetic fibers as constituent fibers.

[0042] (1-5) Other

[0043] In this specification, the range "X~Y" means "above X and below Y". In this specification, "weight" and "mass", "weight%" and "mass%", and "parts by weight" and "parts by mass" are treated as synonyms. In this specification, unless otherwise specified, "ppm" means "mass ppm". In this specification, "~acid (salt)" means "~acid and / or its salt", and "(meth)acryloyl" means "acryloyl and / or methacryloyl". In this specification, the unit of volume "liter" is sometimes written as "l" or "L".

[0044] [2] Resistance of water-absorbing resin (2-1) to interfiber intrusion of water-permeable substrate

[0045] The inventors conducted research focusing on the liquid diffusion properties of the absorbent. They discovered that, in addition to the inherent liquid permeability of the absorbent resin itself, in absorbent articles comprising an absorbent resin and a permeable substrate, the absorbent resin penetrates into the interfibers of the permeable substrate, causing fiber blockage. This prevents the full utilization of the permeable substrate's internal liquid permeability, leading to a decrease in the overall absorbency of the absorbent article and resulting in liquid backflow. This led to the completion of the present invention. The "resistance to penetration between fibers of the permeable substrate" in this invention is a novel physical property value used to evaluate the difficulty of the absorbent resin penetrating into the interfibers of the permeable substrate in an absorbent article. Specifically, it is a value measured by the measurement method described in the examples. In one embodiment of the present invention, the resistance of the absorbent resin to penetration between fibers of the permeable substrate is 60% by weight or more, preferably 65% ​​by weight or more, more preferably 70% by weight or more, and even more preferably 75% by weight or more. A water-absorbing resin with a fiber-to-fiber intrusion resistance of 60% or more to a water-permeable substrate has the following advantages: it is less likely to cause fiber clogging in the water-permeable substrate in absorbent articles, thus exhibiting excellent water absorption performance and reducing liquid backflow. There is no particular upper limit to the fiber-to-fiber intrusion resistance to the water-permeable substrate, but it is 99% or less, preferably 95% or less, and more preferably 90% or less.

[0046] (2-2) Shape of water-absorbing resin

[0047] In one embodiment of the present invention, the shape of the absorbent resin is preferably granular. Specifically, irregularly shaped fragments, spherical particles, rugby ball-shaped particles, aggregated particles, or granulated particles are examples. In this specification, "spherical" is not limited to a perfect sphere, but also includes approximately spherical particles with an aspect ratio of 1.0 to 1.2. Among these, aggregated particles or granulated particles are preferred from the viewpoint that they do not easily penetrate the fibers of the permeable substrate and that the water absorption rate is increased by increasing the specific surface area.

[0048] (2-3) Additives

[0049] In one embodiment of the present invention, the absorbent resin may also contain additives to exhibit various functions. Examples of additives include surfactants, compounds having phosphorus atoms, oxidizing agents, organic reducing agents, water-insoluble inorganic particles, organic powders (e.g., metal soaps), deodorants, antibacterial agents, pulp, thermoplastic fibers, etc. It should be noted that the compounds disclosed in International Patent Publication No. 2011 / 040530, "〔5〕Water-insoluble inorganic particles", can be used in the present invention as the water-insoluble inorganic particles. Among these water-insoluble inorganic particles, those containing hydrophilic particles with a high degree of hydrophilicity (expressed as the proportion of particles suspended in a colloidal state in a mixture of water / methanol = 70 / 30) as described in European Patent No. 0629411 (e.g., 70% or more) and hydrophilic particles with a low contact angle with water (e.g., less than 10°) as described in Japanese Patent No. 6837139, such as silica, when used in absorbent articles, generate moderate friction between the absorbent resin particles and the permeable substrate, thereby inhibiting the penetration of absorbent resin into the interfibers of the permeable substrate, and are therefore preferred.

[0050] From the viewpoint of imparting a moderate friction between the water-absorbing resin and the water-permeable substrate, the content of water-insoluble inorganic particles is preferably 0.01 to 5.00 parts by weight relative to 100 parts by weight of the water-absorbing resin, more preferably 0.05 to 3.00 parts by weight, even more preferably 0.10 to 1.00 parts by weight, and particularly preferably 0.20 to 0.50 parts by weight.

[0051] Compared to the particle size of the superabsorbent resin, the water-insoluble inorganic microparticles are of a very small size. The average particle size of the water-insoluble inorganic microparticles is preferably 0.01 μm to 50.00 μm, but can also be 0.10 μm to 30.00 μm or 1.00 μm to 20.00 μm. Here, the average particle size can be determined based on the characteristics of the particles using a fine-pore resistance method or a laser diffraction / scattering method.

[0052] (2-4) CRC

[0053] "CRC" is short for Centrifuge Retention Capacity, which refers to the water absorption ratio of a superabsorbent resin under no pressure. In this specification, CRC is determined according to the EDANA method (ERT441.2-02).

[0054] (2-5)FSC

[0055] "FSC" is short for Free Swell Capacity, which refers to the water absorption ratio of a water-absorbing resin under suspension without pressure. In this specification, FSC is determined according to the EDANA method (ERT440.2-02). The FSC value can be controlled by changing the type and amount of internal and surface crosslinking agents.

[0056] In one embodiment of the present invention, the FSC of the water-absorbing resin is preferably 40 g / g or more, more preferably 45 g / g or more, and even more preferably 50 g / g or more. There is no particular upper limit, but a higher FSC is preferred. From the viewpoint of good balance with other physical properties, it is preferably 80 g / g or less, more preferably 75 g / g or less, and even more preferably 70 g / g or less.

[0057] If the FSC is 40g / g or higher, the absorbency is sufficient, making it suitable for use as an absorbent in absorbent products such as diapers. Furthermore, if the FSC is 70g / g or lower, it prevents a decrease in the absorption rate of bodily fluids (such as urine and blood), making it suitable for use in high-absorbency diapers, etc.

[0058] (2-6)Ext

[0059] "Ext" is an abbreviation for extractables, referring to the amount of soluble components extracted from absorbent resins. In this specification, Ext is determined according to the EDANA method (ERT470.2-02).

[0060] (2-7)AAP

[0061] "AAP" is short for Absorption Against Pressure, which refers to the water absorption ratio of a water-absorbing resin under pressure. In this invention, AAP is determined according to the EDANA method (ERT442.2-02), except that the load condition is changed to 4.83 kPa (0.7 psi). Specifically, 0.9 g of water-absorbing resin is swollen under 4.83 kPa pressure for 1 hour using a 0.9% by mass sodium chloride aqueous solution, and then the AAP (water absorption ratio under pressure) (unit: g / g) is measured.

[0062] From the viewpoint of improving the absorbency of the water-absorbing resin when used in sanitary materials, the AAP of the absorbent resin in one embodiment of the present invention is preferably 15 g / g or more, more preferably 20 g / g or more, and even more preferably 23 g / g or more. Furthermore, there is no particular limitation on the upper limit of the AAP of the absorbent resin, but it is preferably 40 g / g or less.

[0063] (2-8) Moisture content

[0064] Regarding the "moisture content", except for changing the sample amount to 1.0g and the drying temperature to 180℃, the determination was carried out according to the EDANA method (ERT430.2-02).

[0065] (2-9) Average particle size (D50)

[0066] The mass-average particle size (D50) is determined according to the description in columns 27 and 28 of U.S. Patent No. 7,638,570, which is “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution”.

[0067] From the viewpoint of preventing the water-absorbing resin in absorbent articles from penetrating between the fibers of a permeable substrate, the mass-average particle size (D50) of the water-absorbing resin in one embodiment of the present invention is preferably 250 μm to 800 μm, more preferably 300 μm to 700 μm, further preferably 310 μm to 600 μm, and particularly preferably 320 μm to 500 μm. Furthermore, from the viewpoint of preferring fewer fine particles in absorbent articles that can penetrate between the fibers of a permeable substrate, the proportion of particles with a particle size less than 150 μm, i.e., the proportion of particles passing through a JIS standard sieve with a mesh size of 150 μm, is preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 20% by mass or less, and particularly preferably 10% by mass or less. As long as the mass-average particle size is 250 μm or more, it has the following advantages: it can reduce the penetration of water-absorbing resin in absorbent articles into the fibers of a permeable substrate, resulting in less dust and better operability. In addition, as long as the average particle size is below 800 μm, it can prevent the reduction in the absorption rate of bodily fluids (such as urine and blood), making it suitable for use in high absorbency diapers and the like.

[0068] (2-10) Bulk density

[0069] "Bulk density" was determined according to the EDANA method (ERT460.2-02).

[0070] In one embodiment of the present invention, the bulk density of the absorbent resin is preferably 0.60 g / mL to 1.00 g / mL, more preferably 0.62 g / mL to 0.90 g / mL, and even more preferably 0.64 g / mL to 0.80 g / mL. As long as the bulk density is 0.60 to 1.00 g / mL, it is possible to prevent a decrease in the absorption rate of the absorbent resin for bodily fluids (such as urine and blood), and the absorbent resin is suitable for use in high-absorbency diapers and the like.

[0071] (2-11) Water absorption rate

[0072] In this invention, the "water absorption rate" of the water-absorbing resin refers to the "water absorption rate based on the vortex method". The "water absorption rate based on the vortex method" refers to the time it takes to add 2.0 g of water-absorbing resin to 50 g of a 0.9% by mass sodium chloride aqueous solution stirred at 600 rpm using a stirring head until the stirring head is covered by the test solution.

[0073] A water-absorbing resin with excellent "absorption speed" is preferred when used as an absorbent article because it can absorb liquid immediately and reduce liquid backflow. In one embodiment of the present invention, the water absorption speed of the water-absorbing resin is preferably 50 seconds or less, more preferably 45 seconds or less, even more preferably 40 seconds or less, and further preferably 30 seconds or less. There is no particular limitation on the lower limit of the absorption speed, but it is 10 seconds or more, preferably 15 seconds or more, and further preferably 20 seconds or more. As long as the water absorption speed of the water-absorbing resin is 45 seconds or less, it can quickly absorb liquid diffused from the permeable substrate, thus exhibiting excellent liquid retention and making it suitable for high-absorption-speed diapers, etc. Furthermore, the faster the water absorption speed of the water-absorbing resin, the higher the risk of "gel blockage," where the rapidly swelling gel clogs the gaps between the water-absorbing resins, hindering liquid flow. Therefore, using a water-absorbing resin with high resistance to intrusion between the fibers of the permeable substrate has a greater advantage in avoiding a reduction in diffusion within the fibers.

[0074] [3] Method for manufacturing water-absorbing resin

[0075] The following describes a manufacturing process for a water-absorbing resin according to one embodiment of the present invention.

[0076] (3-1) Monomer aqueous solution preparation process

[0077] This step is to prepare an aqueous solution (hereinafter referred to as "monomer aqueous solution") containing (meth)acrylic acid (salt) as the main component. It should be noted that monomer slurry can also be used within the range that the water absorption performance of the obtained water-absorbing resin is not reduced, but for the sake of convenience, monomer aqueous solution is described in this section.

[0078] Furthermore, the term "main component" refers to the amount (content) of (meth)acrylate (salt) relative to all monomers (excluding internal crosslinking agents) supplied to the polymerization reaction of the absorbent resin. This amount (content) is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more (up to 100 mol%).

[0079] ((meth)acrylate (salt))

[0080] In one embodiment of the present invention, a method for manufacturing a water-absorbing resin can use (meth)acrylic acid (salt) as a monomer from the viewpoint of improving the physical properties of the obtained water-absorbing resin and increasing productivity.

[0081] As for the "(meth)acrylic acid", any known (meth)acrylic acid is acceptable. From the viewpoint of improving the polymerizability and color tone of the water-absorbing resin, it may also contain preferably 200 ppm or less, more preferably 10 ppm to 160 ppm, even more preferably 20 ppm to 100 ppm of a preferred methoxyphenol, and more preferably p-methoxyphenol as a polymerization inhibitor. Furthermore, regarding impurities in (meth)acrylic acid, compounds described in U.S. Patent Application Publication No. 2008 / 0161512 may also be used in this invention.

[0082] The "(meth)acrylate" is a neutralized product obtained by neutralizing the (meth)acrylic acid with the following alkaline composition. As this (meth)acrylate, commercially available (meth)acrylates (e.g., sodium (meth)acrylate) can be used, or (meth)acrylates obtained by neutralization in an equipment for manufacturing water-absorbing resins can be used.

[0083] (Alkaline composition)

[0084] In one embodiment of the present invention, "alkaline composition" refers to a composition containing an alkaline compound. Examples of alkaline compositions include commercially available aqueous solutions of sodium hydroxide.

[0085] Specifically, examples of alkaline compounds include alkali metal carbonates, alkali metal bicarbonates, alkali metal hydroxides, ammonia, and organic amines. Among these, from the viewpoint of improving the physical properties of the obtained absorbent resin, the alkaline compound is preferably strongly alkaline. That is, the alkaline compound is preferably an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.), and more preferably sodium hydroxide.

[0086] (Neutralization)

[0087] In one embodiment of the invention, as neutralization, 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 used in combination. These neutralization methods can be continuous or batch-based, without particular limitation, but continuous methods are preferred from the viewpoint of improving production efficiency, etc.

[0088] Regarding the neutralization apparatus, neutralization temperature, residence time, and other conditions, the conditions described in International Patent Publication No. 2009 / 123197 or U.S. Patent Application Publication No. 2008 / 0194863 may be applied.

[0089] In one embodiment of the present invention, the neutralization rate relative to the acid groups of the monomer is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, even more preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol%. When the neutralization rate is 10 mol% or more, a significant decrease in the water absorption ratio can be suppressed. On the other hand, when the neutralization rate is 90 mol% or less, a water-absorbing resin with a high water absorption ratio under pressure can be obtained.

[0090] The neutralization rate is the same whether neutralization occurs before or after polymerization. Furthermore, the neutralization rate can also be applied to the neutralization rate of the absorbent resin used in the final product. It should be noted that in this specification, "neutralization rate 75 mol%" refers to a mixture of 25 mol% (meth)acrylic acid and 75 mol% (meth)acrylate. Additionally, such a mixture of (meth)acrylic acid and (meth)acrylate is sometimes referred to as a partially neutralized (meth)acrylic acid.

[0091] (Other monomers)

[0092] In this specification, "other monomers" refers to monomers other than the (meth)acrylate (salt) described above. These other monomers can be combined with (meth)acrylate (salt) to produce water-absorbing resins.

[0093] Other monomers mentioned include, for example, water-soluble or hydrophobic unsaturated monomers. Specifically, compounds described in U.S. Patent Application Publication No. 2005 / 0215734 (except for (meth)acrylic acid) may also be used in this invention.

[0094] (Internal cross-linking agent)

[0095] Examples of internal crosslinking agents used in this invention include N,N'-methylenebis(meth)acrylamide, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerol tri(meth)acrylate, glycerol acrylate methacrylate, ethylene oxide modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, 1,4-butanediol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethyleneimine, and glycidyl methacrylate. The internal crosslinking agent can be one or more.

[0096] From the viewpoint of improving the water absorption performance of the obtained water-absorbing resin, the internal crosslinking agent is preferably a compound having two or more polymeric unsaturated groups, more preferably a compound having two or more polymeric unsaturated groups that is thermally decomposable at the drying temperature described later, and even more preferably a compound having two or more polymeric unsaturated groups that has a (poly)alkylene glycol structural unit.

[0097] As the polymerizable unsaturated group, allyl and (meth)acrylate groups are preferably included. Among them, (meth)acrylate groups are more preferred from the viewpoint of improving water absorption performance. As the (poly)alkylene glycol structural unit, polyethylene glycol is preferred from the viewpoint of improving water absorption performance. The number of n in the (poly)alkylene glycol structural unit is preferably 1 to 100, more preferably 6 to 50.

[0098] The amount of the 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 using this amount within the specified range, the desired water-absorbing resin can be obtained. It should be noted that when the amount is 0.0001 mol% or more, there is a tendency for the gel strength to increase and the water-soluble component to decrease; when the amount is 10 mol% or less, there is a tendency for the water absorption ratio to increase, which is therefore preferred.

[0099] In one embodiment of the present invention, the method of adding the internal crosslinking agent is not particularly limited. Examples include: adding the internal crosslinking agent to the monomer aqueous solution beforehand to induce a crosslinking reaction during polymerization; adding the internal crosslinking agent during or after polymerization for post-crosslinking; using a free radical polymerization initiator for free radical crosslinking; and using active energy rays such as electron beams or ultraviolet light for radiation crosslinking. Among these, from the viewpoint of improving reactivity, the method of adding the internal crosslinking agent to the monomer aqueous solution beforehand to induce a crosslinking reaction during polymerization is preferred. These methods can be used in combination without impairing the effects of the present invention. (Other substances added to the monomer aqueous solution)

[0100] In one embodiment of the present invention, from the viewpoint of improving the physical properties of the obtained water-absorbing resin, the following substances may be added when preparing the monomer aqueous solution.

[0101] Specifically, relative to all monomers used in the polymerization (excluding crosslinking agents), hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, poly(meth)acrylate (salt), and poly(meth)acrylate (salt) crosslinkers may be added, 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 (with a lower limit of 0% by weight).

[0102] In addition, relative to all monomers used in the polymerization (excluding crosslinking agents), carbonates, azo compounds, foaming agents such as bubbles, surfactants, chelating agents, chain transfer agents, etc., can be added, preferably less than 5% by weight, more preferably less than 1% by weight, and even more preferably less than 0.5% by weight (the lower limit is 0% by weight).

[0103] The substance can be added to the monomer aqueous solution or added during polymerization. Regarding the method of addition, various methods can be used in combination without impairing the effectiveness of the invention.

[0104] It should be noted that when using water-soluble resins or water-absorbing resins 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 the water-absorbing resins of this invention.

[0105] (Concentration of monomeric components)

[0106] In this process, the aforementioned 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 improving the physical properties of the water-absorbing resin, it is preferably 10-80% by weight, more preferably 20-75% by weight, and even more preferably 30-70% by weight.

[0107] In the case of aqueous solution polymerization or reverse suspension polymerization, solvents other than water may be used as needed. In this case, there is no particular limitation on the type of solvent.

[0108] In this specification, the “concentration of monomer components” refers to the value obtained by the following formula (2), and the weight of the monomer aqueous solution does not include the grafting components of hydrophilic polymers (such as starch), the micronized water-absorbing resin produced in the manufacturing process for reuse, and the weight of the hydrophobic solvent in the reverse suspension polymerization.

[0109] Concentration of monomer component (weight %) = {(weight of monomer component) / (weight of monomer aqueous solution)} × 100 ··· Equation (2).

[0110] (3-2) Polymerization process

[0111] This process involves polymerizing the monomer aqueous solution obtained in the monomer aqueous solution preparation process to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").

[0112] (Polymerization initiator)

[0113] In one embodiment of the present invention, the polymerization initiator used is selected according to the polymerization method, etc., and is therefore not particularly limited. Examples include thermally decomposable polymerization initiators, photodecomposable polymerization initiators, or redox polymerization initiators that use a reducing agent that promotes 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 improving the operability of the polymerization initiator and the physical properties of the water-absorbing resin, peroxides or azo compounds are preferred, peroxides are more preferred, and persulfates are even more preferred.

[0114] The amount of the polymerization initiator is preferably 0.001 to 1 mol% relative to all monomers used in the polymerization (excluding the crosslinking agent), more preferably 0.001 to 0.5 mol%. Furthermore, the amount of the reducing agent is preferably 0.0001 to 0.02 mol% relative to all monomers used in the polymerization (excluding the crosslinking agent).

[0115] It should be noted that active energy rays such as radiation, electron beams, and ultraviolet rays can be used instead of the polymerization initiator to carry out the polymerization reaction, or these active energy rays and the polymerization initiator can be used together.

[0116] (Aggregation Method)

[0117] The polymerization method used in one embodiment of the present invention is not particularly limited, and examples include aqueous solution polymerization, reverse suspension polymerization, droplet polymerization, bulk polymerization, and precipitation polymerization. Among these, aqueous solution polymerization or reverse suspension polymerization is preferred from the viewpoint of ensuring good water absorption properties and improving the ease of polymerization control.

[0118] (3-3) Gel pulverization process

[0119] This process involves pulverizing the hydrogel obtained in the polymerization process using a gel pulverizer (such as a kneader, a screw extruder or meat grinder, or a shredder) to obtain granular hydrogel (hereinafter referred to as "granular hydrogel"). It should be noted that when the polymerization process is kneader polymerization, the polymerization process and the gel pulverization process are performed simultaneously. In cases such as droplet polymerization or reverse suspension polymerization, where granular hydrogel is directly obtained during polymerization, this gel pulverization process may sometimes be omitted.

[0120] Regarding gel pulverization conditions and methods other than those described above, the contents disclosed in International Publication No. 2011 / 126079 are preferably applied to this invention.

[0121] (3-4) Drying process

[0122] This step involves drying the granular hydrogel obtained in the polymerization step and / or gel pulverization step to the desired resin solids content to obtain a dried polymer. This resin solids content is determined based on the weight loss on drying (the weight change when 1 g of 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, and even more preferably 90-98% by weight.

[0123] There are no particular limitations on the drying method for the granular hydrogel, and examples include heating drying, hot air drying, vacuum drying, fluidized bed drying, stirred drying, infrared drying, microwave drying, drum dryer drying, drying by azeotropic dehydration with a hydrophobic organic solvent, and high-humidity drying using high-temperature steam. Among these, stirred drying is preferred from the viewpoint of improving drying efficiency and shape retention.

[0124] (3-5) Crushing process

[0125] The pulverization process is a process of pulverizing the granular dried polymer obtained by the drying process, or the granules or aggregates obtained by the granulation process described later, or their dried products (dried granules), and adjusting them to the desired particle size and particle shape.

[0126] In one embodiment of the invention, it is important to precisely control the pulverizing conditions in the pulverizing process following the formation of granules or aggregates of primary particles of the water-absorbing resin. In this specification, the pulverizing process following the formation of granules or aggregates of primary particles of the water-absorbing resin refers, for example, to the pulverizing process following the formation of granules or aggregates in the granulation process described later, and preferably to the pulverizing process of dried granules obtained by further drying after the formation of granules or aggregates in the granulation process described later.

[0127] For example, in the case of aqueous solution polymerization, a method for manufacturing a water-absorbing resin according to one embodiment of the present invention may include multiple pulverization steps, such as: a pulverization step of pulverizing a dried polymer, wherein the dried polymer is obtained by drying the granular hydrogel obtained in the polymerization step and / or gel pulverization step; and a pulverization step of pulverizing a dried granule, wherein the dried granule is obtained by pulverizing the granular water-absorbing resin obtained by the former to obtain microparticles, and the microparticles are granulated / dried in a granulation step.

[0128] In addition, in the case of reverse suspension polymerization, the method for manufacturing the water-absorbing resin according to one embodiment of the present invention may include, for example, a pulverizing step of pulverizing dried granules, which are obtained by drying an aggregate of primary particles obtained by multi-stage reverse suspension polymerization, adding an agglomerating agent to the gel of the polymerized primary particles, etc.

[0129] (Grinding device)

[0130] Various pulverizing devices can be listed as the pulverizing apparatus used in this process. In one embodiment of the present invention, a specific roller pulverizing device is preferred because it is easy to adjust the granular dried polymer or dried granules to the most suitable shape. As such a specific roller pulverizing device, for example, a roller pulverizing device consisting of two paired rollers, with a groove (longitudinal groove) extending parallel to the direction of roller rotation provided on the surface of at least one of the rollers. By passing the granular dried polymer or dried granules through the gap between the pair of rollers provided in this specific roller pulverizing device, the granular dried polymer or dried granules are compressed, sheared, or compacted between the rollers, thereby pulverizing the granular dried polymer or dried granules. Examples of such specific roller pulverizing devices include, for example, a roller granulator (manufactured by NIPPON GRANULATOR Co., Ltd.), a roller granulator (manufactured by Kurimoto Tekko Co., Ltd.), and a GRAN-U-LIZER (manufactured by MPE Corporation). By using this specific roller crushing device, the generation of particles that expose flat surfaces after crushing can be suppressed in the resulting pulverized material. Particles with exposed flat surfaces tend to easily slide into and penetrate the fibers of the permeable substrate in absorbent articles, so it is preferable to suppress the generation of such particles.

[0131] On the other hand, among the pair of rollers, rollers without grooves on the surfaces of both rollers, or rollers with grooves but which have grooves that extend perpendicularly to the direction of roller rotation, will produce a large number of smooth surfaces on the surface of the crushed absorbent resin, and are therefore not preferred.

[0132] Here, the pulverizing device used in the pulverizing process before the formation of granules or aggregates of primary particles of the water-absorbing resin, such as the aforementioned pulverizing process performed before granulation, which pulverizes the dried polymer obtained by drying the granular hydrogel obtained in the polymerization process and / or gel pulverizing process, is not particularly limited. It can be a pulverizing device other than the specific roller pulverizing device, but it is more preferable to select the specific roller pulverizing device (e.g., roller granulator).

[0133] A schematic diagram of the specific roller milling device used in the pulverizing process according to one embodiment of the present invention is shown below. Figure 3 .like Figure 3As shown, the roller mill 200 includes: a pipe 201 for supplying granular dry polymer or dry granules to the device 200; an inlet 202 for supplying the dry polymer or dry granules into the device 200; and a pair of rollers 203 for crushing the supplied dry polymer or dry granules. These components are arranged in this order in a top-to-bottom direction. It should be noted that the "top-to-bottom direction" is not limited to the vertical direction and may also include the concept of an inclined direction. The pair of rollers 203 consists of two rollers 203a and 203b. It should be noted that in the roller mill 200, it is sufficient to have at least one pair (two rollers), for example, two or more pairs (four or more rollers) may be arranged side by side in the vertical direction. For example, when the two pairs of rollers are arranged side by side in the vertical direction, the dry polymer or dry granules are crushed between the upper pair of rollers and then further crushed between the lower pair of rollers.

[0134] The dried polymer or dried granules 20a fed between the rollers 203 pass between rollers 203a and 203b of the pair of rollers 203, becoming pulverized dried polymer or dried granules, i.e., water-absorbing resin 20b. It should be noted that, although not shown, the roller pulverizing device 200 may also have a feeder for quantitative supply between the inlet 202 and the pair of rollers 203.

[0135] The specific roller milling apparatus described herein has grooves (undulating patterns) on the surface of at least one of a pair of rollers. In this specification, "groove" refers to the irregularities on the roller surface; in one embodiment of the invention, it refers to a shape in which the grooves are arranged in a stripe pattern. Multiple grooves are arranged side-by-side in the roller width direction (the direction of the roller's rotation axis). That is, in the roller milling apparatus, multiple grooves (longitudinal grooves) extending parallel to the roller rotation direction are arranged side-by-side on the surface of at least one of a pair of rollers in the roller width direction. Therefore, irregularities (concave and convex portions) are formed on the roller surface, extending parallel to the roller rotation direction. Consequently, the gap between the pair of rollers does not substantially change due to the rotation of the rollers at any position in the roller width direction. Since the gap between the rollers remains constant at any position in the roller width direction, appropriate force can be applied to the dried polymer or dried granules passing between the rollers, presumably resulting in a uniform particle size distribution of the pulverized material. It should be noted that in this specification, "gap between rollers" refers to the distance between a pair of opposing rollers.

[0136] In a preferred embodiment of the manufacturing method of the present invention, grooves are respectively provided on the two roller surfaces of a pair of rollers. It is considered that, in this case, by interlocking the corresponding concave and convex surfaces of the two rollers, the gap between the rollers can be kept constant at any position in the roller width direction, thereby enabling the application of a constant force to the dried material to be pulverized. Therefore, it is presumed that, particularly in the pulverization of primary particle aggregates or granules of the dried material, the resulting pulverized material is more likely to have a uniform particle size, and pulverized material with a narrower particle size distribution can be obtained. The pair of rollers can be of the same shape (groove shape, diameter) or different shapes, but it is preferred to use rollers of the same shape (including symmetrical relationships).

[0137] For example, in one embodiment, the roller crushing device 200 has grooves (recesses and protrusions) extending parallel to the direction of roller rotation on the surfaces of two of the pair of rollers 203. That is, as... Figure 4 As shown in 2001, both of the pair of rollers 203 (rollers 203a and 203b) have a concave portion and a convex portion on their roller surfaces that extend parallel to the direction of roller rotation relative to the rotation axis A of the rollers. In this way, the convex portion configured to be provided on the roller surface of one of the pair of rollers engages with the concave portion provided on the roller surface of the other of the pair of rollers by rotation.

[0138] In another implementation, such as Figure 4 As shown in 2002, one of a pair of rollers 203 (e.g., roller 203a) has a groove on its surface that extends parallel to the direction of rotation of the roller relative to the axis of rotation A of the roller, and the other of the pair of rollers (e.g., roller 203b) has a smooth surface (smooth surface) without grooves on its surface.

[0139] Here, based on Figure 4 2001 and Figure 4 The gap between the rollers in 2002 is explained. For example... Figure 4 As shown in Figure 2001, when grooves are provided on the surfaces of the two rollers 203a and 203b, the gap d is a constant value d at any position in the roller width direction. Furthermore, as... Figure 4 As shown in Figure 2002, when a groove is provided on the surface of one roller 203a and no groove is provided on the surface of the other roller 203b, the gap d has a maximum value (dmax) and a minimum value (dmin) depending on its position in the roller width direction. Figure 4 2001 Figure 4 In any of the 2002 configurations, the grooves on the roller are formed by extending parallel to the direction of roller rotation, and therefore do not substantially change due to the rotation of the roller.

[0140] It should be noted that in longitudinal groove structures, due to manufacturing conditions of the roller, a transverse groove (a groove extending along the width direction of the roller) or a protrusion extending along the width direction of the roller may sometimes be formed in a portion of the roller. Such a groove or protrusion will result in a gap in a portion of the longitudinal groove of the roller. In this case, due to the presence of the gap in the portion formed in the longitudinal groove of the roller, a change in gap will occur at any position in the width direction of the roller. Here, "not substantially changing due to the rotation of the roller" includes "the gap does not change within a length range of 70% or more, preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more during one revolution of the roller." Therefore, even if a gap exists in a portion of the longitudinal groove of the roller, it is considered "not substantially changing due to the rotation of the roller" when the above requirement is met.

[0141] Here, in Figure 4 In the 2001 method, the gap d is the same at any position in the roll width direction; in contrast, in Figure 4 In the 2002 method, the gap d varies depending on the position of the roller in the width direction. In this invention, even if the gap d varies depending on the position of the roller in the width direction, it is acceptable as long as the gap d does not substantially change due to the rotation of the roller at any position.

[0142] It should be noted that, in Figure 4 In the rollers shown in 2001 and 2002, the grooves are arranged in a shape that extends substantially parallel (0 degrees) to the direction of roller rotation. In this specification, "substantially parallel" means that grooves inclined at less than ±1° relative to the direction of roller rotation are included in the configuration of this invention. This inclination angle relative to the direction of roller rotation can be either a positive or negative direction.

[0143] The minimum gap between the rollers, dmin, is not particularly limited, but is preferably greater than 0 and less than 3 mm. More preferably, the minimum gap between the rollers, dmin, is 0.05 mm to 3 mm; further preferably, 0.05 mm to 2.5 mm; even more preferably, 0.1 mm to 2 mm; particularly preferably, 0.1 mm to 1.5 mm; and most preferably, 0.2 mm to 1 mm. By arranging a pair of rollers within the range of the minimum gap between the rollers, dmin, the effect of reducing particles exposed on the flat surface in the pulverized material can be further enhanced. It should be noted that when the minimum gap, dmin, and the maximum gap, dmax, are the same (i.e., ...), ... Figure 4 In the case of 2001), the gap d is considered to be the minimum gap value dmin. When two or more pairs of rollers are used in the crushing process, the minimum of the minimum gap values ​​set between each roller is within the range described above.

[0144] In addition, such as Figure 4In 2002, when the gap d varies depending on the position of the roller in the width direction, the gap d at each position is calculated, and the difference between the maximum gap dmax and the minimum gap dmin is called the "gap difference". The gap difference is not particularly limited, but is preferably 0 to 0.2 mm, more preferably 0 to 0.1 mm, and even more preferably 0 to 0.05 mm.

[0145] The spacing (interval) of the grooves on the roller can be determined according to the size of the particles to be crushed. It is preferable to use a larger groove spacing when the particle size is large, and a smaller groove spacing when the particle size is small. The groove spacing is not particularly limited, but it is preferable to set the grooves at intervals of 0.1mm to 2mm, more preferably 0.2mm to 1.5mm, and even more preferably 0.3mm to 1.2mm. Here, the groove spacing p is... Figure 4 As shown in 2001, the spacing refers to the interval between the mountain portion of any groove and the mountain portion of an adjacent groove, or the interval between the valley portion of any groove and the valley portion of an adjacent groove. For example, when a circumferentially parallel surface (hereinafter referred to as a "flat portion") is provided between the mountain and valley portions of a groove, the spacing refers to the interval between the mountain portions of adjacent grooves, including the flat portion, or the interval between the valley portions of adjacent grooves. The groove spacing may vary on a single roller, but it is preferable to keep it constant over the overall width of the roller, and when grooves are provided on both of a pair of rollers, it is preferable to keep it constant over the entire pair of rollers.

[0146] The height of the groove is not particularly limited, but it is preferably set to a height of 0.1mm to 2mm, more preferably 0.2mm to 1.5mm, and even more preferably 0.3mm to 1mm. Here, the height of the groove is defined as follows: Figure 4 As shown in 2001, it refers to the height difference between the apex of the mountain part of any trough and the bottom of the valley part of the trough.

[0147] (Water-absorbing resin before the crushing process)

[0148] In one embodiment of the present invention, the dried polymer or dried granules obtained in the drying process and supplied to the pulverizing process can be directly pulverized in their entirety using a pulverizing device, preferably the specific roller pulverizing device. However, depending on the shape of the dried polymer or dried granules, they can also be supplied to other processes, such as a coarse crushing process, or further to a grading process before being pulverized using the pulverizing device. It should be noted that the "coarse crushing process" refers to the process of breaking down (dispersing) aggregated particles. Therefore, when the dried polymer or dried granules are aggregated into lumps, etc., in order to efficiently utilize the pulverizing device, preferably the specific roller pulverizing device, for pulverization, the dried polymer or dried granules can be coarsely crushed in advance.

[0149] In one embodiment of the present invention, as the particle size distribution of the dried polymer or dried granules fed into the pulverizing apparatus, preferably the specific roller pulverizing apparatus, the proportion of particles with a diameter of 850 μm or more (the proportion of particles that have not passed through a sieve with a mesh size of 850 μm) in 100% by mass of the dried polymer or dried granules is preferably at an upper limit of 50% by mass or less, more preferably at 45% by mass or less, and even more preferably at 40% by mass or less (the lower limit is 0% by mass). Furthermore, the proportion of particles with a diameter of 1400 μm or more (the proportion of particles that have not passed through a sieve with a mesh size of 1400 μm) in 100% by mass of the dried polymer or dried granules is preferably at an upper limit of 40% by mass or less, more preferably at 35% by mass or less, and even more preferably at 30% by mass or less (the lower limit is 0% by mass).

[0150] In one embodiment of the present invention, the resin solids content of the dried polymer or dried granules supplied for the pulverizing process is preferably 80-99% by mass, more preferably 90-98.8% by mass, and even more preferably 95-98.5% by mass. That is, the moisture content of the dried polymer or dried granules of the present invention is preferably 1-20% by mass, more preferably 1.2-10% by mass, and even more preferably 1.5-5% by mass. By setting the solids content ratio of the dried polymer or dried granules to the range described above, the size and hardness of the aggregates formed by the dried polymer or dried granules can be adjusted to be suitable for the size and hardness of pulverization in the pulverizing process, and the generation of particles with broken, exposed flat surfaces in the resulting pulverized material can be suppressed. Particles with exposed flat surfaces tend to easily slide into and penetrate the permeable substrate fibers in absorbent articles, and the generation of such particles is preferably suppressed. It should be noted that the method for determining the resin solids content of the dried polymer or dried granules is as described in "(3-4) Drying Process".

[0151] In one embodiment of the invention, the gap between the pair of rollers is preferably in a ratio of 1:0.3 to 1:10 to the mass-average particle size of the dried polymer or dried granules supplied to the roller mill. In this case, applying pressure suitable for breaking down the aggregates formed by the primary particles of the dried polymer or dried granules during milling can suppress the generation of particles that are broken down and exposed on a flat surface. More preferably, the gap between the pair of rollers is in a ratio of 1:0.5 to 1:5 to the mass-average particle size of the dried polymer or dried granules supplied to the roller mill is 1:0.9 to 1:3.

[0152] (3-6) Grading process

[0153] The water-absorbing resin (e.g., water-absorbing resin powder) obtained after the pulverization process is further supplied to the grading process as needed. In one embodiment of the present invention, the particle size adjustment method in the grading process is not particularly limited, and examples include sieve grading using a JIS standard sieve (JIS Z8801-1(2000)) and air classifying.

[0154] (3-7) Surface crosslinking process

[0155] The water-absorbing resin (e.g., water-absorbing resin powder) obtained through the aforementioned pulverization process (and any subsequent processes) is preferably surface-crosslinked using a surface crosslinking agent. This surface crosslinking is a treatment that creates a highly crosslinked region on the surface layer of the water-absorbing resin (from the surface of the resin to within a few tens of μm). By performing this surface crosslinking treatment, various water absorption properties can be improved. In this specification, the water-absorbing resin also includes surface-crosslinked water-absorbing resin.

[0156] (Surface crosslinking agent)

[0157] The surface crosslinking agent used in this process is not particularly limited, and examples include organic or inorganic surface crosslinking agents. From the viewpoint of improving the physical properties of the absorbent resin and the operability of the surface crosslinking agent, organic surface crosslinking agents that react with carboxyl groups are preferred. For example, one or more surface crosslinking agents disclosed in US Patent 7,183,456 can be cited. Specifically, examples include polyol compounds, epoxy compounds, halogenated epoxy compounds, polyamine compounds, condensates of polyamine compounds and halogenated epoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc.

[0158] (3-8) Granulation process

[0159] A method for manufacturing a water-absorbing resin according to one embodiment of the present invention preferably includes a granulation step for obtaining aggregates of primary particles.

[0160] For example, in the case of reverse suspension polymerization, aggregates of primary particles can be obtained through multi-stage reverse suspension polymerization and the addition of an agglomerating agent to the gel of the polymerized primary particles. Therefore, these processes can be considered granulation processes.

[0161] In the case of aqueous solution polymerization, as a granulation process, an example is adding an aqueous liquid to the microparticles of the water-absorbing resin powder, such as microparticles of the water-absorbing resin that have passed through a JIS standard sieve with a mesh size of 150 μm, and stirring and mixing them.

[0162] The average particle size of the water-absorbing resin micropowder is preferably in the range of 150 μm to 10 μm. The content of micropowder with a particle size of 150 μm or less is preferably 70% by mass or more, and more preferably 90% by mass or more, relative to the total amount of the water-absorbing resin micropowder.

[0163] Preferably, the aqueous liquid is preheated before mixing with the water-absorbing resin micropowder. The temperature at which the aqueous liquid and water-absorbing resin micropowder are mixed is typically above 40°C, preferably above 50°C, more preferably above 60°C, and even more preferably above 70°C. The upper limit of the temperature at which the aqueous liquid and water-absorbing resin micropowder are mixed is below the boiling point of the aqueous liquid. The boiling point can be adjusted in various ways, such as by adding salts or other solvents or changing the pressure (reducing or increasing pressure), but since there is no significant change at temperatures exceeding 100°C, it is generally preferred to set it below 100°C.

[0164] The amount of aqueous liquid added is preferably less than 100 parts by weight relative to 100 parts by weight of water-absorbing resin powder, more preferably less than 80 parts by weight, more preferably more than 10 parts by weight, more preferably more than 15 parts by weight, and even more preferably more than 20 parts by weight.

[0165] In one embodiment of the present invention, it is preferable to mix the heated aqueous liquid with the water-absorbing resin micropowder at high speed. In this specification, "high-speed mixing" refers to a short mixing time from the moment the aqueous liquid and the water-absorbing resin micropowder come into contact until the formation of an aqueous gel-like granule. With a short mixing time, the aqueous liquid and the micropowder can be mixed uniformly, preventing the mixture from becoming a large, monolithic gel. Furthermore, a short mixing time prevents a decrease in the performance of the water-absorbing resin, such as an increase in the water-soluble component of the resulting water-absorbing resin or a decrease in the water absorption ratio under pressure. The time from the moment the aqueous liquid and the water-absorbing resin micropowder come into contact until the formation of the aqueous gel-like granule is preferably 3 minutes or less, more preferably 1 minute or less. The addition time of the aqueous liquid is also preferably short, preferably 60 seconds or less, more preferably 30 seconds or less, and most preferably 10 seconds or less.

[0166] The mixer used is not particularly limited as long as the high-speed mixing can be achieved. For example, a container-type mixer is preferred, especially a mechanical stirring mixer. Specifically, examples include the TURBULIZER (manufactured by Hosokawa Micron Co., Ltd.), the Loedige mixer (manufactured by Loedige Co., Ltd.), and the mortar mixer (manufactured by West Japan Experimental Machine Co., Ltd.). Both batch mixers and continuous mixers can be used. For small-volume processing, small food processing machines can also be used.

[0167] The resulting hydrogel-like granules are preferably further dried to produce dried granules with improved granulation strength. By drying the hydrogel-like granules, the microparticles are more firmly integrated, maintaining the aggregate shape of the primary particles. The drying method can be applied under the same conditions as described in (3-4). It should be noted that, here, "hydrogel-like granules" refers to either the hydrogel-like granules obtained during aqueous solution polymerization or the aggregates of primary particles obtained during reverse suspension polymerization.

[0168] A method for manufacturing a water-absorbing resin according to one embodiment of the present invention preferably includes a pulverizing step in addition to a granulation step, wherein the pulverizing step uses the specific roller pulverizing device to pulverize the water-absorbing resin obtained in the granulation step. This allows for the manufacture of a water-absorbing resin with suitable resistance to intrusion between fibers of a permeable substrate.

[0169] (3-9) Other processes

[0170] In addition to the steps described above, the method for manufacturing the water-absorbing resin according to one embodiment of the present invention may, as needed, include a water-containing (re-wetting) step, a step for adding other additives, a granulation step, and a micron powder recycling step. Furthermore, it may also include a conveying step, a storage step, a packaging step, and a preservation step.

[0171] (Rewetting process)

[0172] This process, which can be implemented arbitrarily, is a process in which at least one additive selected from the group consisting of polyvalent metal salts, cationic polymers, chelating agents, inorganic reducing agents, and α-hydroxycarboxylic acid compounds is added to the water-absorbing resin (e.g., water-absorbing resin particles) obtained in the surface crosslinking process.

[0173] The additive is preferably added to the water-absorbing resin (e.g., water-absorbing resin particles) in the form of an aqueous solution or dispersion (slurry). It should be noted that the additive can be added or mixed simultaneously with the aforementioned surface crosslinking agent solution.

[0174] Specifically, the method described in International Patent Publication No. 2015 / 053372, “(2-7) Rewetting process”, is also applied to this invention.

[0175] (Additive addition process)

[0176] In one embodiment of the method for manufacturing the absorbent resin according to the present invention, additives other than the above-mentioned additives (hereinafter referred to as "other additives") may be added to the absorbent resin to impart various functions. Specifically, examples of such other additives include surfactants, compounds having phosphorus atoms, oxidants, organic reducing agents, water-insoluble inorganic particles, organic powders (e.g., metal soaps), deodorants, antibacterial agents, pulp, thermoplastic fibers, etc. It should be noted that, regarding the water-insoluble inorganic particles, the compounds disclosed in International Patent Publication No. 2011 / 040530, "[5] Water-insoluble inorganic particles," can be applied to the present invention. By adding these water-insoluble inorganic particles, moderate friction is generated between the absorbent resin (particles) and the permeable substrate, which, in the case of absorbent articles, can inhibit the penetration of the absorbent resin into the interfibers of the permeable substrate, and is therefore preferred. Silica is particularly preferred to be added to these water-insoluble inorganic particles. Here, the water-insoluble inorganic microparticles can also be used as powdered inorganic agglomerants added in polymerization processes, or they can be added separately.

[0177] (Granulation process)

[0178] "Particle shaping" refers to the process of breaking up the loosely aggregated absorbent resin that has undergone the surface cross-linking process to adjust its particle size. It should be noted that this particle shaping process includes a micron powder removal process and a grading process following the surface cross-linking process. From the viewpoint of adjusting the particle size of the absorbent resin and obtaining stable absorbent properties, the particle shaping process is preferred.

[0179] (Micronized powder recycling process)

[0180] "Micronized powder reuse process" refers to a process in which micronized powder generated in the aforementioned processes through sieving and grading is directly supplied to any of the processes, or micronized powder is granulated and then supplied to any of the processes. From the viewpoint of reducing the production loss of water-absorbing resin, implementing the micronized powder reuse process is preferred.

[0181] [4] Uses of water-absorbing resins

[0182] The use of the absorbent resin in one embodiment of the present invention is not particularly limited, but it is preferably used as an absorbent in absorbent articles such as disposable diapers (for infants and adults), sanitary napkins, and incontinence pads. In particular, it is suitable for use as an absorbent in disposable diapers that have an absorbent resin and a permeable substrate. Other absorbent materials include, for example: soil moisture retainers, seedling sheets, seed coating materials, anti-condensation sheets, leakage absorbent materials, preservation materials, disposable heat packs, cooling headscarves, cold insulators, medical waste liquid solidifying agents, residual soil solidifying materials, waterproof waste liquid gelling agents, absorbent sandbags, disaster relief makeshift toilets, wet cloth materials, cosmetic thickeners, water-blocking materials for electrical / electronic communication cables, sealing gaskets, fertilizer slow-release agents, various slow-release agents (space disinfectants, fragrances, etc.), pet mats, cat litter, wound dressings, anti-condensation building materials, oil moisture removers, coatings, adhesives, resin additives (anti-blocking agents, light diffusing agents, matting agents, additives for decorative panels, additives for artificial marble, additives for colorants, etc.), etc.

[0183] [5] Absorbent materials

[0184] An absorbent article according to one embodiment of the present invention comprises, in sequence: a liquid-impermeable lower pad; an absorbent body comprising a poly(meth)acrylate (salt)-based absorbent resin and a water-permeable substrate having a resistance to intrusion between fibers of a water-permeable substrate of 60% or more; and a liquid-permeable upper pad.

[0185] In one embodiment of the invention, a known sheet material suitable for constituting an absorbent article can be used as the impermeable undersheet, without particular limitation. For example, a thin plastic film such as a polyethylene film can be used as the impermeable undersheet. Among the plastic films, a breathable film is more preferred to provide comfort to the user of the absorbent article.

[0186] In one embodiment of the invention, the liquid-permeable upper gasket can be any known sheet material suitable for constituting an absorbent article, without particular limitation. The liquid-permeable upper gasket is typically a nonwoven fabric, such as hot-air nonwoven fabric, dot-bonded nonwoven fabric, spunbond nonwoven fabric, spunlace nonwoven fabric, meltblown nonwoven fabric, air-laid nonwoven fabric, or a laminate of two or more nonwoven fabrics selected therefrom. Examples of laminates of two or more nonwoven fabrics include spunbond / meltblown / spunbond (SMS) nonwoven fabric and spunbond / meltblown / meltblown / spunbond (SMMS) nonwoven fabric.

[0187] The material constituting the liquid-permeable upper gasket is not particularly limited; examples include synthetic fibers such as polypropylene, polyethylene, and polyester. These materials can be used alone or in combination of two or more. Furthermore, these synthetic fibers are preferably hydrophilized using surfactants.

[0188] In one embodiment of the present invention, the absorbent comprises the absorbent resin and the permeable substrate. Examples of typical absorbent compositions include those consisting of a uniform mixture of absorbent resin particles and a permeable substrate, or those in which absorbent resin particles are sandwiched between sheet-like or layered fibrous permeable substrates. In one embodiment of the present invention, from the viewpoint of maximizing the permeability of the liquid to be absorbed within the sheet-like or layered fibrous permeable substrates, it is preferable that the absorbent resin is absent within the permeable substrate. That is, it is preferable that the absorbent resin and the permeable substrate are each formed as layers. The absorbent resin layer and the permeable substrate layer may each be formed as a single layer, or at least one may be formed as multiple layers, with the absorbent resin layer and the permeable substrate layer alternately stacked. It should be noted that in the present invention, the term "permeable substrate layer" includes both a permeable substrate layer composed of sheet-like permeable substrates and a permeable substrate layer composed of layered fibrous permeable substrates. Specifically, the preferred configurations are as follows: a permeable substrate layer composed of a sheet-like permeable substrate on which a water-absorbing resin layer is disposed; a permeable substrate layer composed of a layered fibrous permeable substrate on which a water-absorbing resin layer is disposed; a permeable substrate layer disposed on a water-absorbing resin layer; and a configuration in which a water-absorbing resin layer is sandwiched between multiple permeable substrate layers.

[0189] Nonwoven fabrics can be used as the sheet-like permeable substrate. For example, they can be hot-air nonwoven fabrics, dot-bonded nonwoven fabrics, spunbond nonwoven fabrics, spunlace nonwoven fabrics, meltblown nonwoven fabrics, air-laid nonwoven fabrics, or laminates of two or more nonwoven fabrics selected therefrom. Examples of laminates of two or more nonwoven fabrics include spunbond / meltblown / spunbond (SMS) nonwoven fabrics, spunbond / meltblown / meltblown / spunbond (SMMS) nonwoven fabrics, etc.

[0190] The material constituting the sheet-like permeable substrate is not particularly limited; examples include synthetic fibers such as polypropylene, polyethylene, and polyester. These materials can be used alone or in combination of two or more. Furthermore, these synthetic fibers are preferably hydrophilized using surfactants.

[0191] From the viewpoint of maximizing liquid diffusion, the thickness of the sheet-like permeable substrate is preferably 1 mm or more, more preferably 3 mm or more. Furthermore, from the viewpoint of suppressing the thickness of the absorbent article, the thickness of the sheet-like permeable substrate is preferably 9 mm or less, more preferably 4 mm or less.

[0192] From the viewpoint of maximizing liquid diffusion, the preferred lower limit for the weight per unit area of ​​the sheet-like permeable substrate is 30 g / m². 2The above, more preferably 40g / m 2 That's all. Additionally, the preferred upper limit is 100g / m³. 2 The following is more preferably 50g / m 2 the following.

[0193] Examples of fibrous permeable substrates include pulp fibers, cross-linked cellulose fibers, rayon, cotton, wool, acetate, and vinylon. The fibrous permeable substrate can be used alone or in combination with two or more other materials.

[0194] In the absorbent, the amount of absorbent resin used (by weight per square meter) is preferably 50–300 g / m² relative to the area where the absorbent resin is present. 2 More preferably 100-200 g / m 2 When the amount of absorbent resin used is within the aforementioned range, an absorbent article possessing both excellent liquid diffusion and high liquid absorption capacity can be produced. It should be noted that, in this invention, the "absorbent resin presence area" refers to the entire area in the absorbent body where the absorbent resin is dispersed.

[0195] In one embodiment of the present invention, the absorbent may include additives in addition to the absorbent resin and the permeable substrate. The additives may be those commonly found in absorbents of absorbent articles, and are not particularly limited. Specific examples of such additives include inorganic powders (e.g., amorphous silica), deodorants, pigments, dyes, antibacterial agents, fragrances, and binders. When the absorbent resin contains inorganic particles, the absorbent may additionally contain inorganic powder in addition to the inorganic particles in the absorbent resin. Examples of such inorganic powders include silica, zeolite, kaolin, and clay.

[0196] In addition to the above-described configuration, an absorbent article according to one embodiment of the present invention may also have a core covering at least one side of the absorbent body and three-dimensional pleats to maintain the shape of the absorbent body.

[0197] In one embodiment of the present invention, the core layer of the absorbent article can be, for example, tissue paper, particularly crepe paper, nonwoven fabric, particularly hot-air nonwoven fabric, dot-bonded nonwoven fabric, spunbond nonwoven fabric, spunlace nonwoven fabric, etc., formed from synthetic fibers such as polypropylene, polyethylene, and polyester. Furthermore, the core layer can also be a composite nonwoven fabric of these materials. Examples of such composite nonwoven fabrics include, for instance, spunbond / meltblown / spunbond (SMS nonwoven fabric) and spunbond / meltblown / meltblown / spunbond (SMMS nonwoven fabric). These core layers are preferably hydrophilized using surfactants.

[0198] In one embodiment of the present invention, the thickness of the absorbent body in the absorbent article is preferably 1 mm to 10 mm, more preferably 1 mm to 5 mm. Furthermore, in another embodiment of the present invention, the overall thickness of the absorbent article is preferably 1.2 mm to 15 mm, more preferably 1.2 mm to 10 mm.

[0199] That is, the present invention is composed of the following structure.

[0200] [1] A poly(meth)acrylate (salt) based water-absorbing resin, wherein the poly(meth)acrylate (salt) based water-absorbing resin, as determined by the steps (1) to (3) below, has a resistance to intrusion between fibers of a water-permeable substrate of 60% by weight or more:

[0201] (1) On the bottom surface of a polystyrene cuboid box with a base of 6cm × 9cm and a depth of 1cm (measured by the inner surface of the box), use double-sided tape to fix a cut piece of non-woven fabric measuring 6cm × 9cm.

[0202] Here, the nonwoven fabric has a thickness of 3 mm and a unit area weight of 41 g / m². 2 Furthermore, the hot-air nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate has a fiber diameter of 0.18 mm for polyethylene and 0.27 mm for polyethylene terephthalate.

[0203] (2) Distribute 1.0g of water-absorbing resin evenly over the entire surface of the nonwoven fabric, and invert the nonwoven fabric with the water-absorbing resin distributed thereon and the box together on a tray with a bottom area larger than the box to recover the water-absorbing resin that has fallen onto the tray.

[0204] (3) Calculate the interfiber intrusion resistance of the permeable substrate according to the following formula (1).

[0205] Resistance to intrusion between fibers of a permeable substrate [wt%] = weight of recycled absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 Equation (1).

[0206] [2] The poly(meth)acrylate (salt) water-absorbing resin according to [1], wherein the water absorption rate of the poly(meth)acrylate (salt) water-absorbing resin based on the vortex method is less than 50 seconds.

[0207] [3] The poly(meth)acrylate (salt) water-absorbing resin according to [1] or [2], wherein the mass-average particle size (D50) of the poly(meth)acrylate (salt) water-absorbing resin is 250 μm to 800 μm.

[0208] [4] The poly(meth)acrylate (salt) based water-absorbing resin according to any one of [1] to [3], wherein the poly(meth)acrylate (salt) based water-absorbing resin comprises water-insoluble inorganic particles.

[0209] [5] An absorbent article comprising, in sequence, an impermeable lower gasket, an absorbent comprising a water-absorbing resin and a water-permeable substrate, and a water-permeable upper gasket, and

[0210] The water-absorbing resin is a poly(meth)acrylate (salt)-based water-absorbing resin, and,

[0211] The water-absorbing resin, as determined by steps (1) to (3) below, has a resistance to inter-fiber intrusion of the water-permeable substrate of 60% by weight or more.

[0212] (1) On the bottom surface of a polystyrene cuboid box with a base of 6cm × 9cm and a depth of 1cm (measured by the inner surface of the box), use double-sided tape to fix a cut piece of non-woven fabric measuring 6cm × 9cm.

[0213] Here, the nonwoven fabric has a thickness of 3 mm and a unit area weight of 41 g / m². 2 Furthermore, the hot-air nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate has a fiber diameter of 0.18 mm for polyethylene and 0.27 mm for polyethylene terephthalate.

[0214] (2) Distribute 1.0g of water-absorbing resin evenly over the entire surface of the nonwoven fabric, and invert the nonwoven fabric with the water-absorbing resin distributed thereon and the box together on a tray with a bottom area larger than the box to recover the water-absorbing resin that has fallen onto the tray.

[0215] (3) Calculate the interfiber intrusion resistance of the permeable substrate according to the following formula (1).

[0216] Resistance to intrusion between fibers of a permeable substrate [wt%] = weight of recycled absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 Equation (1).

[0217] [6] The absorbent article according to [5], wherein the absorbent resin absorbs water at a rate of less than 50 seconds based on the vortex method.

[0218] [7] The absorbent article according to [5] or [6], wherein the mass-average particle size (D50) of the absorbent resin is 250 μm to 800 μm.

[0219] [8] An absorbent article according to any one of [5] to [7], wherein the absorbent resin comprises water-insoluble inorganic particles.

[0220] [9] An absorbent article according to any one of [5] to [8], wherein the permeable substrate is a sheet-like permeable substrate, the sheet-like permeable substrate having a thickness of 1 mm or more and a unit area weight of 50 g / m². 2 the following.

[0221] Example

[0222] The present invention will be described in more detail below with reference to the embodiments and comparative examples shown, but the present invention is not limited to these embodiments. Embodiments obtained by combining the technical means described in the embodiments are also included within the scope of the present invention. It should be noted that the expressions "parts" or "%" are sometimes used in the embodiments, which, unless otherwise specified, represent "parts by mass" or "% by mass". Furthermore, unless otherwise specified, all operations are performed at room temperature (23°C ± 2°C) and relative humidity 40–50% RH. It should be noted that the electrical equipment used in the embodiments and comparative examples (including the determination of the physical properties of the water-absorbing resin) uses a power supply of 200V or 100V at 60Hz unless otherwise specified.

[0223] [1. Evaluation Methods]

[0224] [1-1] Free-suspension absorbency (FSC) of absorbent resins

[0225] The unpressurized suspension absorbency (FSC) of the superabsorbent resin was determined according to the EDANA method (ERT440.2-02).

[0226] Specifically, 0.2g of absorbent resin was placed into a nonwoven bag, which was then immersed in a large excess of 0.90% sodium chloride aqueous solution for 30 minutes to allow it to swell freely. The bag was then lifted and suspended for 10 minutes, and the water absorption ratio (in g / g) after water control was calculated.

[0227] [1-2] Absorbency ratio (AAP) of water-absorbing resins under pressure

[0228] The AAP (average uptake under pressure) of the superabsorbent resin was determined according to the EDANA method (ERT442.2-02). It should be noted that the load condition was changed to 4.83 kPa (0.7 psi).

[0229] [1-3] Moisture content of water-absorbing resin

[0230] The moisture content of the superabsorbent resin was determined according to the EDANA method (ERT430.2-02). It should be noted that during the determination, the mass of the sample (superabsorbent resin) was changed to 1.0 g, the drying temperature was changed to 180℃, and the drying time was changed to 3 hours.

[0231] Specifically, after adding 1.0g of the sample (water-absorbing resin) into an aluminum cup with a bottom diameter of 50mm, accurately weigh the total mass W1 (g) of the sample and the aluminum cup.

[0232] Next, with the sample placed in an aluminum cup, it was placed in an oven at an ambient temperature of 180°C. After 3 hours, the sample and aluminum cup were removed from the oven, and the total mass W2 (g) of the dried sample and aluminum cup was accurately weighed. When the mass of the sample (hygroscopic resin) used in this test is set as M (1.0 g), the moisture content (mass%) of the sample is calculated according to the following formula (3):

[0233] Moisture content (mass%) = {(W1-W2) / M}×100…Equation (3).

[0234] [1-4] Mass-average particle size (D50) of water-absorbing resins

[0235] The mass-average particle size (D50) of the superabsorbent resin was determined according to the method described in “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution” in columns 27 and 28 of U.S. Patent No. 7,638,570.

[0236] [1-5] Bulk density of water-absorbing resin

[0237] The bulk density of the superabsorbent resin was determined according to the EDANA method (ERT460.2-02). [1-6] Water absorption rate of superabsorbent resin (vortex method)

[0238] Add 0.02 parts by weight of Food Blue No. 1 (as a food additive) to 1000 parts by weight of 0.90% sodium chloride aqueous solution (physiological saline), and adjust the solution temperature to 30°C. Measure 50 ml of physiological saline into a 100 ml beaker. Using a cylindrical stirring head (40 mm long, with a diameter of 8 mm perpendicular to its length) and a magnetic stirrer, stir at 600 rpm while simultaneously adding 2.0 g of superabsorbent resin. Calculate the time until the superabsorbent resin absorbs the physiological saline and covers the stirring head as the absorption rate (in seconds).

[0239] [1-7] Resistance of absorbent resin to interfiber intrusion of permeable substrate

[0240] The "resistance to interfiber intrusion of the water-absorbing resin into the permeable substrate" is determined according to the steps shown below.

[0241] On the bottom of a polystyrene rectangular box (6cm x 9cm base, 1cm depth, both dimensions being the inner surface of the box), use double-sided tape to secure a 6cm x 9cm piece of non-woven fabric (3mm thick, 41g / m² weight per unit area) to the surface. 2 A hot-air nonwoven fabric is made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate (PET), wherein the fiber diameters of polyethylene and polypropylene are 0.18 mm, and the fiber diameter of PET is 0.27 mm. 1.0 g of absorbent resin is uniformly distributed over the entire surface of the hot-air nonwoven fabric. Next, the nonwoven fabric with the absorbent resin distributed thereon, along with its box, is placed upside down on a tray with a base area larger than the box, and the absorbent resin that has fallen onto the tray is recovered. Here, the recovered absorbent resin is the absorbent resin that has not penetrated between the fibers of the nonwoven fabric. The resistance to penetration between the fibers of the permeable substrate is calculated according to the following formula (1).

[0242] Resistance to intrusion between fibers of a permeable substrate [wt%] = weight of recycled absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 … Equation (1).

[0243] [1-8] Evaluation of liquid reflux rate of absorbent sheets

[0244] (1) Preparation of absorbent tablets

[0245] Figure 1 Image 1001 is an image of the absorber 100 viewed from directly above. Figure 1 1002 is a cross-sectional view of the absorbent sheet 100 cut in a direction perpendicular to the XY plane and parallel to the X-axis or Y-axis. In the adhesive surface of the 10cm × 11cm adhesive tape 2 (NITTO DENKO vinyl tape No. 21S), the area enclosed by four sides located 1cm inward from each of the four ends is uniformly distributed with 0.5g of absorbent resin 1. On the distributed absorbent resin, a nonwoven fabric 3 (3mm thick, with a unit area weight of 41g / m²) of the same area as the area with the distributed absorbent resin, i.e., 8cm × 9cm, is placed on top. 2A hot-air nonwoven fabric is made from a mixture of polyethylene, polypropylene, and polyethylene terephthalate (PET). The fiber diameters of polyethylene and polypropylene are 0.18 mm, and the fiber diameter of PET is 0.27 mm. 0.5 g of absorbent resin 1 is uniformly distributed across the entire surface of this hot-air nonwoven fabric, and a 10 cm × 11 cm liquid-permeable nonwoven fabric 4 (air-laid nonwoven fabric, weight per unit area 46.6 g / m²) is placed on top. 2 ), and attach it to the adhesive surfaces on all four sides to make an evaluation absorbent sheet 100.

[0246] (2) Measurement of liquid reflux rate (liquid retention)

[0247] The evaluation absorbent sheet 100, with the liquid-permeable nonwoven fabric 4 as its upper surface, is placed on a flat table. Using a syringe (syringe needle specification: 21G), 10g of a 0.9% by mass sodium chloride aqueous solution at 20°C is added to the evaluation absorbent sheet over a period of 45 seconds while the tip of the syringe is in contact with the center of the evaluation absorbent sheet 100 (first liquid addition). Ten minutes after the first liquid addition, 20g of a 0.9% by mass sodium chloride aqueous solution at 20°C is added over a period of 45 seconds following the same procedure as the first liquid addition (second liquid addition). Ten minutes after the second liquid addition, 20g of a 0.9% by mass sodium chloride aqueous solution at 20°C is added over a period of 45 seconds following the same procedure as the second liquid addition (third liquid addition). Ten minutes after the third liquid addition, 32 sheets of kitchen paper towels (manufactured by Nepia Oji Co., Ltd.) cut into 5.5cm x 5.5cm pieces with a total weight K1 (g) were placed in the center of the evaluation absorbent sheet. At the same time, a 500g weight (Φ5.5cm) was placed on top of the kitchen paper towels (load: 0.3psi). After 10 seconds of placing the kitchen paper towels and the weight, the kitchen paper towels and the weight were removed, and the total weight K2 (g) of the 32 sheets of kitchen paper towels was measured. Based on the following formula (4), the liquid return flow rate was calculated according to the amount of liquid absorbed by the kitchen paper towels.

[0248] Liquid reflux flow rate (g) = K2 - K1... Equation (4).

[0249] [1-9] Determination of thickness of nonwoven fabrics

[0250] Regarding the thickness of nonwoven fabrics, a large-scale dial thickness gauge (thickness measuring instrument) (manufactured by Ozaki Manufacturing Co., Ltd., model: JB, probe: anvil, φ50mm) was used. The upper probe of the thickness measuring instrument was brought close to a height of 2-3mm from the nonwoven fabric, and the handle was slowly released, applying as little pressure as possible to the nonwoven fabric, thus measuring the thickness of the nonwoven fabric. [1-10] Evaluation of the liquid diffusivity of absorbent materials

[0251] The absorbent articles manufactured in the examples and comparative examples described later were placed on a flat table with a liquid-permeable nonwoven fabric as the upper surface. Using a syringe (syringe needle specification: 21G), 10g of a 0.9% by mass sodium chloride aqueous solution at 20°C, colored with Blue No. 1, was added to the absorbent article over a period of 45 seconds while the tip of the syringe was in contact with the center of the absorbent article. One minute after the start of liquid addition, the maximum longitudinal and transverse lengths of the colored area of ​​the sodium chloride aqueous solution were measured to evaluate the liquid diffusion of the absorbent article. It should be noted that in this invention, "longitudinal" refers to the direction of the long side of the absorbent article, and "transverse" refers to the direction of the short side of the absorbent article.

[0252] [1-11] Determination of thickness of nonwoven fabrics and absorbents

[0253] Regarding the thickness of nonwoven fabrics and absorbents, a large-scale dial thickness gauge (thickness measuring instrument) (manufactured by Ozaki Manufacturing Co., Ltd., model: JB, probe: φ50mm on the upper and lower anvils) is used. After bringing the upper probe of the thickness measuring instrument close to a height of 2-3mm from the nonwoven fabric and absorbent, the handle is slowly released, and as little pressure as possible is applied to the nonwoven fabric and absorbent to measure the thickness of the nonwoven fabric and absorbent.

[0254] [2. Water-absorbing resin]

[0255] [2-1. Manufacturing of water-absorbing resin]

[0256] [Example 1]

[0257] In a 1L polypropylene container, 364g of acrylic acid, 2.11g of polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n=9) as an internal crosslinking agent, 22.16g of a 0.1 wt% trisodium diethylenetriaminepentaacetate aqueous solution as a chelating agent, 296g of a 48.5 wt% sodium hydroxide aqueous solution, and 330g of deionized water were added and stirred to prepare a monomer aqueous solution (1). It should be noted that the liquid temperature of the monomer aqueous solution (1) rises to approximately 80°C due to the heat of neutralization.

[0258] The monomer aqueous solution (1) was stirred continuously, and 15.8 g of 3.8 wt% sodium persulfate aqueous solution was added when the temperature of the monomer aqueous solution (1) reached 78°C. Then, the monomer aqueous solution (1) was immediately poured into a stainless steel butt-type reaction apparatus (bottom surface: 340×340 mm, height: 25 mm, inner surface: Teflon coating), and the polymerization reaction started shortly thereafter. It should be noted that a hot plate (NEOHOTPLATE HI-1000 / Made by Seieido Inouchi Co., Ltd.) was provided below the stainless steel butt-type reaction apparatus, and the temperature of the inner surface of the tank was preset to 50°C. When the polymerization reaction started, the reaction liquid (1) gelled while generating water vapor, and the generated gel expanded and contracted in all directions while foaming. This expansion and contraction was completed in about 1 minute. Then, the product was kept in the reaction apparatus for 3 minutes, thereby obtaining an aqueous gel-like crosslinked polymer (1). It should be noted that this series of operations was carried out in an open atmospheric system.

[0259] The obtained hydrogel-like crosslinked polymer (1) was gel-crushed using a meat grinder (No. 32 / manufactured by Hiraga Manufacturing Co., Ltd.) equipped with a die head with a die head aperture of 9.5 mm to obtain granular hydrogel-like crosslinked polymer (1). The gel-crushing was performed by feeding 2.4 kg / min of hydrogel-like crosslinked polymer (1) and 5.0 kg / h of water vapor into the meat grinder with the screw shaft speed of the meat grinder set to 130 rpm.

[0260] Next, the obtained granular hydrogel-like crosslinked polymer (1) was dried using a rotary dryer. Specifically, the rotary container of the rotary dryer was rotated at 75 rpm in an atmosphere at 200°C, and the granular hydrogel-like crosslinked polymer (1) was fed into the rotary dryer and dried until the moisture content was 2% by mass, thus obtaining the dried polymer (1).

[0261] Next, a roller mill (WML type roller mill / developed by Inoguchi Technology) was used as a pulverizing device to pulverize the dried polymer (1) to obtain water-absorbing resin powder (1). Here, in the roller mill, a pair of rollers were set in the first section for single-stage pulverization. It should be noted that the pair of rollers used were rollers with V-shaped grooves on the surface of each roller in a direction approximately perpendicular to the direction of roller rotation. Specifically, on the roller surface, one groove was continuously provided from one end of the roller (i.e., continuously in the direction of roller width) to the other end, and multiple grooves were arranged continuously at equal intervals throughout the circumference. The roller grooves (tooth shape of the grooves) of the pair of rollers were identical. It should be noted that the gap between the rollers refers to the distance between the two rollers.

[0262] • Roller speed: 480 / 200 rpm

[0263] • Slot spacing: 1.15mm

[0264] • Gap between rollers: 1.0mm.

[0265] The water-absorbing resin powder (1) was graded using a JIS standard sieve with a mesh size of 150 μm to obtain water-absorbing resin micro-powder (1) that passed through the sieve. Next, 30 parts by weight of the water-absorbing resin micro-powder (1) were added to a food processor. While stirring, 20 parts by weight of ion-exchanged water at 90°C was added every 5 seconds, and the mixture was stirred for another 10 seconds to obtain a hydrogel-like granule (1). Then, using the rotary dryer in the cylindrical container, the obtained hydrogel-like granule (1) was dried again under the same conditions until the moisture content was 2% by weight, resulting in dried granules (1).

[0266] The dried granules (1) were graded using a JIS standard sieve with a mesh size of 150 μm. A roller granulator (manufactured by NIPPON GRANULATOR CO.,LTD., roller size: diameter 115 mm × length 100 mm) was used as a pulverizing device to pulverize the dried granules (1) remaining on the sieve. The pulverized material was further graded using a JIS standard sieve with a mesh size of 150 μm to obtain granules in the shape of granules remaining on the sieve as water-absorbing resin particles (1). Here, in the roller granulator, a pair of rollers were set in the first section for single-stage pulverization. It should be noted that the rollers used as a pair of rollers were as follows: on the surface of each roller, a V-shaped groove (gap difference: 0) was provided in a direction parallel to the direction of roller rotation. Specifically, the grooves covered the entire circumference of the roller surface, and multiple grooves were arranged continuously from one end of the roller at equal intervals to the other end. The groove spacing (interval) of the pair of rollers was the same in each roller. In addition, the grooves in each roller were as follows Figure 4 As in 2001, the mountain portion of the groove of one roller and the valley portion of the groove of another roller are positioned in the same axial direction of the roller, and the gap between the rollers is constant.

[0267] • Roller speed: 565 / 462 rpm (inner ring)

[0268] • Height of the groove (angle of inclination of the groove): 1.0 mm (45°)

[0269] • Slot spacing: 2.0mm

[0270] • Gap between rollers: 1mm.

[0271] Next, a surface crosslinking agent solution consisting of 0.373 parts by weight of ethylene carbonate, 0.74 parts by weight of propylene glycol, and 2.52 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the water-absorbing resin particles (1), and heated at 198°C for 30 minutes. Then, the powder temperature was forcibly cooled to 60°C and passed through a JIS standard sieve with a mesh size of 850 μm to granulate the powder, thereby obtaining surface-crosslinked water-absorbing resin particles (1).

[0272] 0.3 parts by weight of particulate silica (trade name: AEROSIL (registered trademark) 200, manufactured by AEROSIL Co., Ltd., Japan) were uniformly mixed into 100 parts by weight of the surface-crosslinked water-absorbing resin particles (1) to obtain water-absorbing resin (1). The physical properties of the obtained water-absorbing resin (1) are shown in Table 1.

[0273] [Example 2]

[0274] Take 800g of n-heptane into a 2000mL four-necked separable flask equipped with a stirrer, reflux cooler, thermometer, nitrogen inlet tube and dropping funnel, add 0.88g of maleic anhydride modified ethylene-propylene copolymer (trade name: HI-WAX (registered trademark) HW2203A / manufactured by Mitsui Chemicals Co., Ltd.) as a dispersant and dissolve it, then blow in nitrogen to expel the dissolved oxygen.

[0275] In addition, a monomer aqueous solution (2) consisting of 127g sodium acrylate, 36g acrylic acid, 0.077g polyethylene glycol diacrylate (n=9), 0.008g trisodium diethylenetriaminepentaacetate and 215g deionized water was prepared in a flask, and nitrogen gas was blown in to expel the dissolved oxygen dissolved in the aqueous solution.

[0276] Next, 1.5 g of a 15% aqueous solution of sodium persulfate was added to the monomer aqueous solution (2) in the flask, and the entire amount was added to the separable flask and dispersed by stirring at 230 rpm. Then, the bath temperature was raised to 60°C to initiate the polymerization reaction. After maintaining the bath temperature at 60°C for 2 hours, the polymerization slurry was cooled to room temperature.

[0277] Then, while stirring at 1000 ppm, a dispersion obtained by pre-dispersing 0.092 g of amorphous silica (trade name: REOLOSIL (registered trademark) QS-20, manufactured by Oriental Silicas Corporation) as inorganic microparticles (powdered inorganic agglomerant) in 100 g of n-heptane was added to the polymer slurry, and then stirred for 10 minutes to mix. Then, the organic solvent was filtered off by suction filtration, and the residue was air-dried at room temperature overnight to obtain an aggregate-shaped hydrogel crosslinked polymer (2).

[0278] Next, the aqueous gel-like crosslinked polymer (2) was dried using the same cylindrical container rotary dryer as in Example 1. Specifically, the aqueous gel-like crosslinked polymer (2) was supplied to a cylindrical container rotary dryer set to the same temperature and speed as in Example 1, and dried until the moisture content reached 10% by mass, resulting in dried polymer (2).

[0279] Next, using a roller granulator (manufactured by NIPPON GRANULATOR CO.,LTD., roller size: diameter 115mm × length 100mm) as a pulverizing device, the dried polymer (2) was pulverized under the same pulverizing conditions as the pulverization of the dried granules (1) in Example 1, thereby obtaining water-absorbing resin particles (2) in the shape of aggregates.

[0280] A surface crosslinking agent solution consisting of 0.003 parts by weight of ethylene glycol diglycidyl ether, 0.385 parts by weight of ethylene carbonate, 0.644 parts by weight of propylene glycol, and 2.6 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the water-absorbing resin particles (2). After heating at 195°C for 25 minutes, the powder temperature was forcibly cooled to 60°C, thereby obtaining surface-crosslinked water-absorbing resin particles (2).

[0281] Relative to 100 parts by weight of the surface-crosslinked water-absorbing resin particles (2), 10.0 parts by weight of water were uniformly mixed and granulated by passing the mixture through a JIS standard sieve with a mesh size of 1000 μm. Then, 0.3 parts by weight of particulate silica (trade name: AEROSIL (registered trademark) 200, manufactured by AEROSIL Co., Ltd., Japan) were further uniformly mixed to obtain water-absorbing resin (2). The physical properties of the obtained water-absorbing resin (2) are shown in Table 1.

[0282] [Comparative Example 1]

[0283] For the water-absorbing resin powder (1) of Example 1, it was classified using a JIS standard sieve with a mesh size of 150 μm to obtain comparative water-absorbing resin particles (1) remaining on the sieve.

[0284] The comparative absorbent resin particles (1) were subjected to a surface crosslinking process and a silica addition process under the same conditions as in Example 1 to obtain the comparative absorbent resin (1). The physical properties of the obtained comparative absorbent resin (1) are shown in Table 1.

[0285] [Comparative Example 2]

[0286] A comparative monomer aqueous solution (2) was prepared by dissolving 2.189 g of polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n = 9) as an internal crosslinking agent in 5000 g of a 33 wt% sodium acrylate aqueous solution with a neutralization rate of 75 mol%. The comparative monomer aqueous solution (2) was then supplied to a reactor formed by covering a jacketed stainless steel double-arm kneader with two SIGMA-type blades and an internal volume of 10 L. While maintaining the reaction solution at 25°C, the system was purged with nitrogen to remove dissolved oxygen.

[0287] Next, while stirring the comparative monomer aqueous solution (2), 18.6 g of 15 wt% ammonium persulfate aqueous solution and 23.3 g of 0.1 wt% L-ascorbic acid aqueous solution were added as polymerization initiators. Polymerization started after about 1 minute. Then, polymerization was carried out at 25°C to 90°C. Forty minutes after the start of polymerization, the obtained comparative hydrogel crosslinked polymer (2) was removed. The comparative hydrogel crosslinked polymer (2) was finely divided into particles of about 5 mm.

[0288] Next, the comparative hydrogel-like crosslinked polymer (2) was dried using a rotary dryer identical to that used in Example 1. Specifically, the comparative hydrogel-like crosslinked polymer (2) was fed into a rotary dryer set to the same temperature and speed as in Example 1 and dried until the moisture content reached 2% by mass, resulting in a relatively dry polymer (2). Next, a pulverizing process was performed under the same conditions as in Example 1 to obtain a comparatively absorbent resin powder (2). The comparatively absorbent resin powder (2) was graded using a JIS standard sieve with a mesh size of 150 μm to obtain comparatively absorbent resin particles (2) remaining on the sieve.

[0289] A surface crosslinking agent solution consisting of 0.25 parts by weight of ethylene carbonate, 0.02 parts by weight of ethylene glycol diglycidyl ether, 0.41 parts by weight of propylene glycol, and 1.66 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the comparative water-absorbing resin particles (2). After heating at 165°C for 30 minutes, the powder temperature was forcibly cooled to 60°C and passed through a JIS standard sieve with a mesh size of 850 μm to granulate the powder, thereby obtaining the surface-crosslinked comparative water-absorbing resin particles (2).

[0290] The comparative absorbent resin particles (2) were subjected to a silica addition process under the same conditions as in Example 1 to obtain the comparative absorbent resin (2). The physical properties of the obtained comparative absorbent resin (2) are shown in Table 1.

[0291] [Comparative Example 3]

[0292] In the monomer aqueous solution preparation process of Example 1, acrylic acid was changed to 341g, polyethylene glycol diacrylate (molecular weight 522.66, average number of ethylene oxide units: n=9) was changed to 0.38g, 0.1% by weight of trisodium diethylenetriaminepentaacetate aqueous solution was changed to 22.16g, 48.5% by weight of sodium hydroxide aqueous solution was changed to 291g, and deionized water was changed to 263g. Apart from this, the same polymerization process, gel pulverization process, drying process, and pulverization process using a roller mill as in Example 1 were performed to obtain a comparative water-absorbing resin powder (3).

[0293] The comparative absorbent resin powder (3) was graded using a JIS standard sieve with a mesh size of 150 μm. The comparative absorbent resin micro powder (3) that passed through the sieve was then subjected to the same granulation and drying processes as in Example 1 to obtain the comparatively dry granules (3).

[0294] The relatively dry granules (3) were pulverized using a roller mill (WML type roller mill / developed by Inoguchi Technology) and further classified using a JIS standard sieve with a mesh size of 150 μm to obtain granules in the shape of granules remaining on the sieve as the relatively absorbent resin particles (3). Here, the pulverization conditions of the roller mill were the same as those for pulverizing the absorbent resin powder (1) in Example 1.

[0295] A surface crosslinking agent solution consisting of 0.018 parts by weight of ethylene glycol diglycidyl ether, 0.20 parts by weight of ethylene carbonate, 0.34 parts by weight of propylene glycol, and 1.04 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the comparative water-absorbing resin particles (3). After heating at 165°C for 30 minutes, the powder temperature was forcibly cooled to 60°C, thereby obtaining the surface-crosslinked comparative water-absorbing resin particles (3).

[0296] 0.3 parts by weight of particulate silica (trade name: AEROSIL (registered trademark) 200, manufactured by AEROSIL Co., Ltd., Japan) were uniformly mixed into 100 parts by weight of the surface-crosslinked comparative absorbent resin particles (3) to obtain comparative absorbent resin (3). The physical properties of the obtained comparative absorbent resin (3) are shown in Table 1.

[0297] [Comparative Example 4]

[0298] The same polymerization process as in Example 2 was performed. After cooling the obtained polymer slurry to room temperature, the process of adding inorganic particles and mixing the polymer slurry was not carried out. Instead, the organic solvent was filtered out by suction filtration, and the residue was air-dried at room temperature overnight to obtain a relatively hydrous gel-like crosslinked polymer (4). Then, the same drying, pulverizing, and surface crosslinking processes as in Example 2 were performed to obtain surface-crosslinked relatively absorbent resin particles (4). 10.0 parts by weight of water were uniformly mixed with 100 parts by weight of the surface-crosslinked relatively absorbent resin particles (4), and the mixture was granulated by passing it through a JIS standard sieve with a mesh size of 300 μm. Then, 0.3 parts by weight of particulate silica (trade name: AEROSIL (registered trademark) 200, manufactured by AEROSIL Co., Ltd., Japan) were uniformly mixed to obtain relatively absorbent resin (4). The physical properties of the obtained relatively absorbent resin (4) are shown in Table 1.

[0299] [Comparative Example 5]

[0300] The dried polymer (2) obtained in Example 2 was fed into a roller mill (WML type roller mill / developed by Inoguchi Technology) and pulverized under the same pulverization conditions as the pulverization of the dried granules (1) in Example 1, thereby obtaining comparative water-absorbing resin particles (5).

[0301] 100 parts by weight of the comparative absorbent resin particles (5) were subjected to surface crosslinking under the same conditions as in Example 2, and then water and silica were added under the same conditions as in Example 2 to obtain the comparative absorbent resin (5). The physical properties of the obtained comparative absorbent resin (5) are shown in Table 1.

[0302] [2-2. Evaluation results of water-absorbing resins]

[0303] [Table 1]

[0304] (Table 1)

[0305]

[0306] The comparison between the examples and comparative examples shows that the absorbent resin with an intrusion resistance of 60% by weight or more between the fibers of the permeable substrate significantly reduces the liquid return flow in the evaluation of absorbent sheets used in absorbent articles such as diapers that simulate absorbent resin and permeable substrate, i.e., it has excellent liquid retention.

[0307] [3. Absorbent materials]

[0308] [3-1. Manufacturing of absorbent materials]

[0309] [Example 3]

[0310] Figure 2 Image 1003 is an image of the absorbent object 101 viewed from directly above. Figure 2 1004 is a cross-sectional view of the absorbent article 101 cut in a direction perpendicular to the XY plane and parallel to the X-axis or Y-axis. On the adhesive surface of the 10cm × 11cm adhesive tape (NITTO DENKO vinyl tape No. 21S) cut into sheets equivalent to the impermeable gasket 5, in an area 1cm inward from each end along the long side and 2cm inward from each end along the short side—that is, a 6cm × 9cm area in the center of the adhesive tape—a 6cm × 9cm nonwoven fabric (3mm thick, 41g / m² in weight per unit area) serving as a sheet-like permeable substrate 6 is placed. 2 A hot-air nonwoven fabric was made from a mixture of polyethylene, polypropylene, and polyethylene terephthalate (PET), with polyethylene and polypropylene fibers having a diameter of 0.18 mm and PE fibers having a diameter of 0.27 mm. 1.0 g of the absorbent resin (1) obtained in Example 1 was uniformly distributed across the entire surface of this nonwoven fabric. Here, the portion with the absorbent resin (1) distributed corresponds to the absorbent body. Then, on the portion with the absorbent resin (1) distributed, a 10 cm × 11 cm liquid-permeable nonwoven fabric (air-laid nonwoven fabric, weight per unit area 46.6 g / m²) corresponding to the liquid-permeable top pad 7 was placed. 2 ), and attach it to the adhesive surfaces on the four sides to create an absorbent article (1).

[0311] [Example 4]

[0312] The absorbent article (2) was manufactured using the same method as in Example 3, except that the absorbent resin (2) obtained in Example 2 was used instead of the absorbent resin (1).

[0313] [Comparative Example 6]

[0314] The comparative absorbent resin (2) obtained in Comparative Example 2 was used instead of the absorbent resin (1), and otherwise the comparative absorbent article (1) was manufactured using the same method as in Example 3.

[0315] [Comparative Example 7]

[0316] The comparative absorbent resin (3) obtained in Comparative Example 3 was used instead of the absorbent resin (1), and otherwise the comparative absorbent article (2) was manufactured using the same method as in Example 3.

[0317] [Comparative Example 8]

[0318] The comparative absorbent resin (4) obtained in Comparative Example 4 was used instead of the absorbent resin (1), and the comparative absorbent article (3) was manufactured using the same method as in Example 3.

[0319] [Comparative Example 9]

[0320] The comparative absorbent resin (5) obtained in Comparative Example 5 was used instead of the absorbent resin (1), and otherwise the comparative absorbent article (4) was manufactured using the same method as in Example 3.

[0321] [3-2. Evaluation Results of Absorbent Substances]

[0322] The liquid diffusivity of absorbent articles (1) and (2) manufactured in Examples 3 and 4 and comparative absorbent articles (1) to (4) manufactured in Comparative Examples 6 to 9 was determined using the method described above. The results are shown in Table 2 below.

[0323] [Table 2]

[0324] (Table 2)

[0325]

[0326] The comparison between the examples and comparative examples shows that the absorbent articles manufactured in Examples 3 and 4, which contain poly(meth)acrylate (salt) based water-absorbing resin with an intrusion resistance of 60% by weight or more to the fibers of the water-permeable substrate, have a larger liquid diffusion length in both the longitudinal (long side) and transverse (short side) directions, i.e., superior liquid diffusion properties, compared to the absorbent articles manufactured in Comparative Examples 6 to 9, which contain poly(meth)acrylate (salt) based water-absorbing resin with an intrusion resistance of less than 60% by weight to the fibers of the water-permeable substrate.

[0327] Industrial availability

[0328] According to one embodiment of the present invention, a water-absorbing resin composition can provide a water-absorbing resin that reduces liquid backflow and has excellent liquid retention properties in absorbent articles comprising a water-absorbing resin and a water-permeable substrate. Therefore, it is suitable for use in hygiene materials (hygiene products) such as diapers, sanitary napkins, incontinence products for adults (incontinence pads), and pet pads.

[0329] Symbol Explanation

[0330] 1: Water-absorbing resin

[0331] 2: Adhesive tape

[0332] 3: Nonwoven fabric

[0333] 4: Liquid-permeable nonwoven fabric

[0334] 5: Lower gasket

[0335] 6: Permeable substrate

[0336] 7: Upper gasket

[0337] 20a: Dried polymer or dried granules

[0338] 20b: Powdered form of dried polymer or dried granules (hygroscopic resin powder)

[0339] 100: Absorption Tablets

[0340] 101: Absorbent Items

[0341] 200: Roller Crushing Device

[0342] 201: Piping

[0343] 202: Input Port

[0344] 203, 203a, 203b: Rollers.

Claims

1. A poly(meth)acrylate (salt) based water-absorbing resin, wherein the poly(meth)acrylate (salt) based water-absorbing resin, as determined by the steps (1) to (3) below, has a resistance to intrusion between fibers of a water-permeable substrate of 60% by weight or more: (1) On the bottom surface of a polystyrene cuboid box with a base of 6cm × 9cm and a depth of 1cm (measured by the inner surface of the box), use double-sided tape to fix a cut piece of non-woven fabric measuring 6cm × 9cm. Here, the nonwoven fabric has a thickness of 3 mm and a unit area weight of 41 g / m². 2 Furthermore, the hot-air nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate has a fiber diameter of 0.18 mm for polyethylene and 0.27 mm for polyethylene terephthalate. (2) Distribute 1.0g of water-absorbing resin evenly over the entire surface of the nonwoven fabric, and invert the nonwoven fabric with the water-absorbing resin distributed thereon and the box together on a tray with a bottom area larger than the box to recover the water-absorbing resin that has fallen onto the tray. (3) Calculate the resistance to intrusion between fibers of the permeable substrate according to the following formula (1): Resistance to intrusion between fibers of the permeable substrate [weight%] = weight of recovered absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 Formula (1).

2. The poly(meth)acrylate (salt) based water-absorbing resin according to claim 1, wherein, The poly(meth)acrylate (salt)-based water-absorbing resin absorbs water in less than 50 seconds using a vortex method.

3. The poly(meth)acrylate (salt) based water-absorbing resin according to claim 1 or 2, wherein, The mass-average particle size D50 of the poly(meth)acrylate (salt)-based water-absorbing resin is 250 μm to 800 μm.

4. The poly(meth)acrylate (salt)-based water-absorbing resin according to any one of claims 1 to 3, wherein, The poly(meth)acrylate (salt) based water-absorbing resin contains water-insoluble inorganic particles.

5. An absorbent article, said absorbent article comprising, in sequence, a liquid-impermeable lower gasket, an absorbent body comprising a water-absorbing resin and a water-permeable substrate, and a liquid-permeable upper gasket, and The water-absorbing resin is a poly(meth)acrylate (salt)-based water-absorbing resin, and, The water-absorbing resin, as determined by steps (1) to (3) below, has a resistance to inter-fiber intrusion of the water-permeable substrate of 60% by weight or more. (1) On the bottom surface of a polystyrene cuboid box with a base of 6cm × 9cm and a depth of 1cm (measured by the inner surface of the box), use double-sided tape to fix a cut piece of non-woven fabric measuring 6cm × 9cm. Here, the nonwoven fabric has a thickness of 3 mm and a unit area weight of 41 g / m². 2 Furthermore, the hot-air nonwoven fabric made of a mixture of polyethylene, polypropylene, and polyethylene terephthalate has a fiber diameter of 0.18 mm for polyethylene and 0.27 mm for polyethylene terephthalate. (2) Distribute 1.0g of water-absorbing resin evenly over the entire surface of the nonwoven fabric, and invert the nonwoven fabric with the water-absorbing resin distributed thereon and the box together on a tray with a bottom area larger than the box to recover the water-absorbing resin that has fallen onto the tray. (3) Calculate the resistance to intrusion between fibers of the permeable substrate according to the following formula (1): Resistance to intrusion between fibers of the permeable substrate [weight%] = weight of recovered absorbent resin [g] / weight of dispersed absorbent resin [g] × 100 Formula (1).

6. The absorbent article according to claim 5, wherein, The water-absorbing resin absorbs water in less than 50 seconds using a vortex method.

7. The absorbent article according to claim 5 or 6, wherein, The mass-average particle size D50 of the water-absorbing resin is 250μm to 800μm.

8. The absorbent article according to any one of claims 5 to 7, wherein, The absorbent resin contains water-insoluble inorganic particles.

9. The absorbent article according to any one of claims 5 to 8, wherein, The permeable substrate is a sheet-like permeable substrate with a thickness of 1 mm or more and a unit area weight of 50 g / m². 2 the following.

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