Particulate water absorbent, absorbent body comprising said particulate

Abstract

The present invention provides a particulate water absorbent which can be used for manufacturing a sanitary product that can further reduce the backflow of an absorbed liquid in actual use. A swelling gel obtained by bringing the particulate water absorbent into contact with a 0.9% sodium chloride aqueous solution for 10 minutes has a water absorbency of more than 50 g / g when left to stand for 1 minute without pressure, and a water absorbency of more than 41.5 g / g when left to stand for 1 minute at a pressure of 4.83 kPa.

Description

Technical Field

[0001] This invention relates to a granular absorbent, an absorbent containing the granular absorbent, and a sanitary product containing the absorbent. Background Technology

[0002] Superabsorbent polymers (SAPs) are polymeric gelling agents with both water-swellable and water-insoluble properties. Granular absorbent agents with SAPs as the main component are used in a variety of absorbent products, including diapers, sanitary napkins, and incontinence products for adults; soil conditioners for agriculture, forestry, and horticulture; and industrial waterproofing agents. Many monomers and hydrophilic polymers have been proposed as raw materials for these superabsorbent polymers. From a performance and cost perspective, the most commonly used superabsorbent polymers are polyacrylic acid (salt) based superabsorbent polymers that use acrylic acid and / or its salts as monomers.

[0003] With the increasing demand for high-performance granular absorbents, primarily used in disposable diapers, numerous functional (physical property) requirements have been placed on them. Among these many functions is the ability to maintain excellent liquid retention even under external pressure while in a swollen state, thus reducing backflow.

[0004] Absorbent products such as diapers are not changed every time urine or other absorbent liquids are expelled; they are typically emptied multiple times. The absorbent granules that have absorbed the liquid become swollen. Therefore, users sometimes use absorbent products with swollen granules. This requires the granules to have the following properties: when in a swollen state, they should maintain excellent liquid retention regardless of the wearer's daily movements, especially under external pressure such as body weight pressing on the absorbent, reducing backflow. Examples of body weight pressing on the absorbent include lying down and sitting.

[0005] As a granular superabsorbent possessing the aforementioned function, for example, there is the granular superabsorbent described in Patent Document 1. Patent Document 1 discloses a granular superabsorbent whose water absorption ratio under pressure of 2.06 kPa (AAP(2.06 kPa), water absorption ratio without pressure (CRC), and water absorption ratio under pressure after swelling (RCAP(2.06 kPa)) have a specific relationship. Here, RCAP(2.06 kPa) represents the weight change of the granular superabsorbent before and after immersing it in a 0.9% by weight sodium chloride aqueous solution for 1 hour to form a swollen gel, and then placing it under a 2.06 kPa load for 1 minute, i.e., the water absorption ratio.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2021 / 201177 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] However, especially in the actual use of hygiene products such as adult diapers, the granular absorbent contained in these products needs to absorb large amounts of urine and other fluids without pressure, within a shorter time than the immersion time (1 hour) measured in the RCAP (2.06 kPa) test. Furthermore, it is believed that in the actual use of these hygiene products, the swollen granular absorbent will remain in a swelled state under no pressure, or be subjected to pressures exceeding 2.06 kPa, depending on the user's movements.

[0011] Therefore, the RCAP (2.06 kPa) cannot be considered a parameter corresponding to the actual conditions under which the sanitary product is used. Thus, for the sanitary product containing granular absorbent as described in Patent Document 1, there is room for improvement in reducing the backflow of absorbed liquid during actual use.

[0012] The technical problem of the present invention has been addressed in view of the aforementioned problem points, and its object is to provide a granular absorbent that can be used to manufacture sanitary products that can further reduce the backflow of absorbed liquid during actual use.

[0013] Solution for solving the problem

[0014] The inventors discovered two novel parameters corresponding to the actual use conditions of the aforementioned sanitary products, and found that granular absorbents with these parameters within a specific range could solve the aforementioned technical problem, thus conceiving this invention. The parameters are corresponding to the following two absorbency ratios: the absorbency ratio of a swollen gel obtained by swelling the granular absorbent in a short time when held without pressure, and the absorbency ratio of the swollen gel when held under high pressure.

[0015] That is, one aspect of the present invention relates to a granular water-absorbing agent, wherein the granular water-absorbing agent is mainly composed of a polyacrylic acid (salt) based water-absorbing resin formed by surface cross-linking, and the granular water-absorbing agent satisfies the following formula (A) and the following formula (B).

[0016] SRC(NP) > 50.0 g / g(A)

[0017] SRC (4.83 kPa) > 41.5 g / g (B)

[0018] Here, the SRC(NP) is determined by a method comprising the following steps (a) to (c):

[0019] (a) The granular absorbent (WO) [g] is contacted with a 0.9% sodium chloride aqueous solution (hereinafter referred to as the "test solution") for 10 minutes without applying a load to obtain a swollen gel;

[0020] (b) Separate the swollen gel obtained in step (a) from the test solution;

[0021] (c) Determine the weight (W1) [g] of the swollen gel separated in step (b), and calculate the SRC (NP) of the granular absorbent based on the following formula (1);

[0022] SRC(NP)[g / g]=W1 / W0(1)

[0023] The SRC (4.83 kPa) was determined by replacing step (c) with steps (c') to (e') described later in the method comprising steps (a) to (c).

[0024] (c') Apply a load of 4.83 kPa to the swollen gel separated in step (b) for 1 minute;

[0025] (d') Remove the exudate that has seeped from the swollen gel through step (c');

[0026] (e') The weight (W2) [g] of the swollen gel obtained in step (d') is determined, and the SRC (4.83 kPa) is calculated based on the following formula (2);

[0027] SRC(4.83kPa)[g / g]=W2 / W0(2).

[0028] Invention Effects

[0029] The granular absorbent of one embodiment of the present invention will achieve the following effect: it can be used to manufacture sanitary products that can further reduce the backflow of absorbed liquid during actual use. Detailed Implementation

[0030] The invention will now be described with reference to the preferred mode. Throughout this specification, unless otherwise specified, the singular form should be understood to include the concept of its plural form. Therefore, unless otherwise specified, articles in the singular form (e.g., "a," "an," "the," etc. in English) should be understood to include the concept of their plural forms. Furthermore, unless otherwise specified, the terminology used in this specification should be understood to be used in accordance with its common meaning in the art. Therefore, unless otherwise defined, all technical and technical terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, this specification (including definitions) shall prevail. The invention is not limited to the embodiments described below, and various modifications may be made within the scope of the claims.

[0031] [1] Definition of terms

[0032] (1-1) "Water-absorbing resin"

[0033] In this invention, "water-absorbing resin" refers to a polymeric cross-linked polymer that swells into an insoluble gel after absorbing liquid, possessing both "swellability" and "insolubility," and satisfying the following physical properties. Specifically, it refers to a polymeric cross-linked polymer that, as having "water-swellability," satisfies the property of a CRC of 5 g / g or more as specified in ERT441.2-02, and, as having "water insolubility," satisfies the property of an Ext of 50% by weight or less as specified in ERT470.2-02.

[0034] The absorbent resin can be appropriately designed according to its application and is not particularly limited. It is preferably a hydrophilic crosslinked polymer obtained by crosslinking and polymerizing unsaturated monomers having carboxyl groups. Furthermore, it is not limited to a polymer in total amount (100% by weight), and may also be an absorbent resin composition containing additives, etc., within the range of satisfying the aforementioned physical properties (CRC, Ext).

[0035] Furthermore, the water-absorbing resin in one embodiment of the present invention is not limited to the final product, and sometimes also refers to intermediates in the water-absorbing resin manufacturing process (e.g., the polymerized hydrogel-like crosslinked polymer and the dried polymer, as well as the water-absorbing resin powder before surface crosslinking, etc.). In this specification, all of these are included and collectively referred to as "water-absorbing resin". In addition, as for the shape of water-absorbing resin, flakes, fibers, films, granules, gels, etc. can be listed, but the water-absorbing resin in one embodiment of the present invention is mainly in the form of granules (powder).

[0036] (1-2) "Granular water absorbent"

[0037] In this specification, the desiccant contains a water-absorbing resin as its main component. In this specification, granular desiccant refers to a granular (also known as powdered) desiccant (containing water-absorbing resin particles as its main component), whether it is a single granular desiccant or multiple granular desiccants. "Granular" means having a granular form; particles refer to small solid or liquid particles of measurable size (JIS Industrial Terminology Dictionary, 4th Edition, p. 2002). Additionally, in this specification, granular desiccant is sometimes simply referred to as desiccant.

[0038] In this specification, the aqueous liquid is not limited to water, but can also be urine, blood, sweat, feces, waste liquid, moisture, vapor, ice, mixtures of water with organic and / or inorganic solvents, rainwater, groundwater, etc., as long as it contains water, there are no particular limitations. Urine, menstrual blood, sweat, and other bodily fluids are preferably included as the aqueous liquid.

[0039] A granular absorbent according to one embodiment of the present invention is suitable for use as a sanitary material for absorbing aqueous liquids. The granular absorbent is primarily composed of a surface-crosslinked polyacrylic acid (salt)-based absorbent resin (granules) (hereinafter also simply referred to as polyacrylic acid (salt)-based absorbent resin). In other words, the granular absorbent preferably contains 60-100% by weight, 70-100% by weight, 80-100% by weight, or 90-100% by weight of surface-crosslinked polyacrylic acid (salt)-based absorbent resin. Furthermore, the granular absorbent may optionally contain one or more materials selected from the group consisting of other absorbent resin particles, water, and additives. The additives may be inorganic colloidal particles, water-insoluble inorganic particles, water-soluble compounds containing polyvalent metal cations, etc. The preferred water content of the granular absorbent is 0.2-30% by weight. That is, absorbent resin compositions formed by integrating these components also fall within the scope of the granular absorbent.

[0040] In addition, the content of polyacrylic acid (salt) based water-absorbing resin in the water-absorbing agent is at most 99% by weight, and in particular should be about 95% by weight, 90% by weight, or 85% by weight. It preferably also contains water and / or additives described later (inorganic colloidal particles, water-insoluble inorganic particles, water-soluble compounds containing polyvalent metal cations).

[0041] Furthermore, in one embodiment of the present invention, the granular absorbent is mainly composed of polyacrylic acid (salt) based absorbent resin, but may also contain other absorbent resins. Examples of such other absorbent resins include: polysulfonic acid (salt) based absorbent resin, maleic anhydride (salt) based absorbent resin, polyacrylamide based absorbent resin, polyvinyl alcohol based absorbent resin, polyethylene oxide based absorbent resin, polyaspartic acid (salt) based absorbent resin, polyglutamic acid (salt) based absorbent resin, polyalgic acid (salt) based absorbent resin, starch based absorbent resin, and cellulose based resin. The other absorbent resins may be one or more.

[0042] (1-3) "Polyacrylic acid (salt)" and "Polyacrylic acid (salt) based water-absorbing resin"

[0043] In one embodiment of the present invention, "polyacrylic acid (salt)" refers to polyacrylic acid and / or its salts. Furthermore, "polyacrylic acid (salt)-based water-absorbing resin" as the main component is a polyacrylic acid (salt) crosslinked polymer containing structural units derived from acrylic acid and / or its salts (hereinafter referred to as "acrylic acid (salt)") as repeating units and having an internal crosslinking structure. The polyacrylic acid (salt)-based water-absorbing resin is preferably surface-crosslinked.

[0044] The polyacrylic acid (salt) based water-absorbing resin is preferably in granular form (also known as powder) in the granular water-absorbing agent.

[0045] Additionally, the term "main component" refers to the amount (content) of acrylate (salt) relative to all monomers used in polymerization (excluding internal crosslinking agents), which is typically 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably substantially 100 mol%.

[0046] (1-4) "EDANA" and "ERT"

[0047] "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 / publicly available literature).

[0048] (1-4-1) "CRC" (ERT441.2-02)

[0049] "CRC" is short for Centrifuge Retention Capacity, which refers to the water absorption ratio of granular desiccant or desiccant resin without pressure (sometimes also called "water absorption ratio").

[0050] Specifically, this refers to: after filling 0.2g of granular water absorbent or water-absorbing resin into a non-woven fabric bag, immersing it in a large amount of excess 0.9% by weight sodium chloride aqueous solution for 30 minutes to allow it to swell freely, and then using a centrifuge (250G) to measure the water absorption ratio (unit: g / g) after draining.

[0051] (1-4-2) "PSD" (ERT420.2-02)

[0052] "PSD" is short for Particle Size Distribution, which refers to the particle size distribution of granular water-absorbing agents or water-absorbing resins as determined by sieve grading.

[0053] In addition, the weight-average particle size (D50) and the logarithmic standard deviation of particle size distribution (σζ) were determined by the same method as described in U.S. Patent No. 7,638,570, “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution”.

[0054] (1-5) Other

[0055] In this specification, the range “X~Y” means “above X and below Y”. Furthermore, unless otherwise specified, “t (ton)” as a unit of weight means “metric ton”, and “ppm” means “weight ppm” or “mass ppm”. Moreover, “weight” and “mass,” “parts by weight” and “parts by mass,” and “weight%” and “mass%” are considered synonyms. Additionally, “~acid (salt)” means “~acid and / or its salt,” and “(meth)acryloyl” means “acryloyl and / or methacryloyl.”

[0056] Furthermore, for convenience, "liter" is sometimes written as "l" or "L", and "weight %" is written as "wt%". Moreover, when determining trace components, the limit of detection is expressed as ND (Non Detected).

[0057] [2] Granular water absorbent

[0058] One embodiment of the granular water-absorbing agent of the present invention (hereinafter referred to as "the granular water-absorbing agent of the present invention") is a granular water-absorbing agent with polyacrylic acid (salt) based water-absorbing resin formed by surface crosslinking as the main component, which satisfies the following formula (A) and the following formula (B).

[0059] SRC(NP) > 50.0 g / g(A)

[0060] SRC (4.83 kPa) > 41.5 g / g (B)

[0061] Here, the SRC(NP) is determined by a method comprising the following steps (a) to (c):

[0062] (a) The granular absorbent (WO) [g] is contacted with a 0.9% sodium chloride aqueous solution (hereinafter referred to as the "test solution") for 10 minutes without applying a load to obtain a swollen gel;

[0063] (b) Separate the swollen gel obtained in step (a) from the test solution;

[0064] (c) Determine the weight (W1) [g] of the swollen gel separated in step (b), and calculate the SRC (NP) of the granular absorbent based on the following formula (1);

[0065] SRC(NP)[g / g]=W1 / W0(1)

[0066] The SRC (4.83 kPa) was determined by replacing step (c) with steps (c') to (e') described later in the method comprising steps (a) to (c).

[0067] (c') Apply a load of 4.83 kPa to the swollen gel separated in step (b) for 1 minute;

[0068] (d') Remove the exudate that has seeped from the swollen gel through step (c');

[0069] (e') The weight (W2) [g] of the swollen gel obtained in step (d') is determined, and the SRC (4.83 kPa) is calculated based on the following formula (2);

[0070] SRC(4.83kPa)[g / g]=W2 / W0(2)

[0071] The SRC(NP) is a parameter representing the amount of liquid retained in the granular superabsorbent after it has absorbed and swelled in liquid for a short period of time, and then retained under no pressure. Additionally, "SRC(NP)" is an abbreviation for Short-time Retention Capacity (No Pressure). Furthermore, the SRC (4.83 kPa) is a parameter representing the amount of liquid retained in the granular superabsorbent after it has absorbed and swelled in liquid for a short period of time, and then retained under high pressure.

[0072] The granular absorbent of the present invention satisfies formulas (A) and (B). Therefore, the granular absorbent of the present invention can absorb a large amount of liquid in a short time, and exhibits excellent liquid retention in both the swollen state under no pressure and under high pressure. This excellent liquid retention in both the swollen state and under no pressure is a necessary characteristic for further reducing backflow in the actual use of the sanitary product. This is consistent with the description in the "Problems to be Solved by the Invention" section. Therefore, the granular absorbent of the present invention can be used to manufacture sanitary products that further reduce backflow of absorbed liquid during actual use.

[0073] Additionally, in step (a), the granular absorbent WO[g] is brought into contact with a 0.9% sodium chloride aqueous solution (hereinafter referred to as the "test solution") adjusted to 23±1°C for 10 minutes without applying a load. Here, typically, the absorbency of a granular absorbent under load is limited. Therefore, "bringing into contact for 10 minutes without applying a load" means bringing the granular absorbent into contact with a large amount of excess test solution without limiting its absorbency under load, and maintaining the granular absorbent in a state where it can fully absorb the test solution for 10 minutes, allowing it to swell freely. "Contact" means bringing the granular absorbent into contact with the test solution to a state where it can absorb the test solution. Here, the granular absorbent and the test solution can also be brought into contact through liquid-permeable components such as nonwoven fabrics and metal mesh. Therefore, in step (a), the amount of test solution and the shape and size of the measuring device can be adjusted appropriately to avoid insufficient test solution used within the 10 minutes, which would hinder the free swelling of the granular absorbent.

[0074] There are no particular limitations on the container used to perform step (a), and for example, a barrel equipped with a piston can be cited. Preferably, the bottom surface of the barrel is fitted with a metal mesh that prevents the permeable particulate absorbent and swelling gel described later from passing through, while allowing the test solution and exudate described later to flow in or out. For example, the barrel and piston used in the gel bed permeability test described in U.S. Patent Publication No. 8269060 can be used as the container.

[0075] There are no particular limitations on the specific method for implementing step (a). For example, when using a barrel equipped with the piston, methods including the steps shown in (a1) to (a3) ​​below can be listed as examples of such methods.

[0076] (a1) First, measure the total weight of the barrel and the piston, and set this value as W. a [g] process.

[0077] (a2) Following step (a1), approximately 0.9 g of the granular absorbent sample to be tested is measured and evenly distributed on the bottom surface of the barrel. Here, the accurate weight of the sample is weighed beforehand and denoted as W0[g].

[0078] (a3) Following step (a2), the barrel is immersed in a large excess of 0.9% sodium chloride aqueous solution as the test solution, and the uniformly dispersed sample is brought into contact with the test solution for 10 minutes to obtain a swollen gel. Here, in step (a3), the sample absorbs the test solution and swells without being subjected to a load, ultimately obtaining a swollen gel.

[0079] The shape and size of the measuring device are not limited. From the viewpoint of improving the accuracy of the SRC (NP) and SRC (4.83 kPa) measurements, the device used in this measurement is preferably 19–40 cm² in size. 2 A circular barrel. Furthermore, the weight per unit area of ​​the granular absorbent used in this determination is preferably 250–350 g / m². 2 As an example, the barrel and piston used in the gel bed permeability test described in U.S. Patent Publication No. 8269060 are used as the measuring device, and the amount of particulate absorbent used in the test is preferably 0.9 g.

[0080] In step (b), the swollen gel obtained in step (a) is separated from the test solution. That is, this means ending the contact between the particulate absorbent and the test solution in step (a); and removing the test solution (hereinafter also referred to as "residual water") that was not absorbed by the hydrogel particles and remained between the hydrogel particles of the swollen gel obtained in step (a). The method for removing the residual water is not particularly limited. Examples of such methods include: lifting the swollen gel obtained in step (a) from a large amount of excess test solution, placing it on a sieve to stand, and performing dehydration. The dehydration time is preferably about 1 minute. Furthermore, dehydration continues until the residual liquid is removed from the hydrogel particles. The "residual water removed state" means that no water droplets fall from the measuring device within 5 seconds.

[0081] In addition, when removing residual water, the surrounding environment is usually preferably at room temperature (20-25°C) and normal pressure (1 atmosphere) to match the usage environment of diapers and other sanitary products.

[0082] In step (b), to ensure uniform thickness of the swollen gel, it is preferable to lift the swollen gel from the test solution while a piston or similar device is placed on it. Furthermore, it is preferable to directly remove the liquid from the swollen gel while the piston or similar device is placed on it. From the viewpoint of ensuring uniform thickness of the swollen gel without excessively loading it, the load on the piston is preferably 0.22–0.28 kPa, more preferably 0.24–0.26 kPa, and particularly preferably 0.25 kPa.

[0083] In step (c), the weight of the swollen gel separated in step (b), i.e., the swollen gel separated from the test solution, is determined. There is no particular limitation on the method for determining the weight of the swollen gel; a commercially available weighing meter can be used. Alternatively, steps (a) to (c) can be performed with the granular absorbent and the swollen gel placed in a container consisting of a barrel and a piston, etc. In this case, the weight of the container can be determined beforehand, and the total weight of the container and the swollen gel can be measured. The weight of the swollen gel can then be calculated by subtracting the weight of the container from the total weight. Furthermore, if the test solution adheres to the container in the form of water droplets, the water droplets should be removed, for example, using wiping paper, before measuring the weight.

[0084] In step (c), the weight W0 [g] of the granular absorbent before swelling obtained in step (a) and the weight W1 [g] of the swollen gel obtained in step (c) are used, and the value of SRC(NP) is calculated based on the following formula (1).

[0085] SRC(NP)[g / g]=W1 / W0(1).

[0086] In step (c'), a load of 4.83 kPa is applied to the swollen gel separated in step (b), i.e., the swollen gel separated from the test solution, for 1 minute. Furthermore, similar to step (b), to match the usage environment of hygiene products such as diapers, the ambient environment when applying the load to the swollen gel is generally preferably room temperature (20–25°C) and normal pressure (1 atmosphere). The load can be applied, for example, by placing a piston on the swollen gel uniformly distributed on the bottom surface of a barrel, and placing a weight capable of applying a 4.83 kPa load to the swollen gel on the piston. Hereinafter, by applying the load, some of the liquid absorbed by the swollen gel in step (b) will seep out from the swollen gel. This seeped liquid will be referred to as "exudate".

[0087] In step (d'), the exudate that has seeped from the swollen gel obtained in step (c') is removed. That is, after applying a load of 4.83 kPa for 1 minute, the exudate that has seeped from the swollen gel is removed. The method for removing the exudate is not particularly limited, and methods that perform steps (i) and (ii) below can be listed as examples.

[0088] (i) A piston is placed on a metal mesh uniformly distributed on the bottom of the barrel, and a load of 4.83 kPa is applied to the piston. Under this condition, the piston is placed on a sieve for liquid removal.

[0089] (ii) Use a pipette to remove the exudate that has seeped onto the piston.

[0090] In step (e'), the weight of the swollen gel obtained in step (d'), i.e., the swollen gel after removing the exudate, is measured. There is no particular limitation on the method for measuring the weight of the swollen gel; a commercially available weighing instrument can be used. Alternatively, steps (a), (b), and (c') through (e') can be performed while the granular absorbent and the swollen gel are placed in a container consisting of a barrel, piston, and weights. In this case, the weight of the container can be measured beforehand, and the total weight of the container and the swollen gel can be measured. The weight of the swollen gel can then be calculated by subtracting the weight of the container from this total weight. Furthermore, if the test solution and the exudate adhere to the container in the form of water droplets, the water droplets remaining on the container can be removed, for example, using wiping paper, before measuring the weight.

[0091] In step (e'), the weight W0 [g] of the granular absorbent before swelling obtained in step (a) and the weight W2 [g] of the swollen gel obtained in step (e') are used, and the value of SRC (4.83 kPa) is calculated based on the following formula (2).

[0092] SRC(4.83kPa)[g / g]=W2 / W0(2).

[0093] Furthermore, the term "reflow" typically used for evaluating the physical properties of absorbent resins refers to the evaluation of absorbent sheets (absorbent bodies) obtained by laminating an absorbent layer containing absorbent resin (absorbent agent) and pulp with a nonwoven fabric or similar material, rather than the evaluation of the absorbent resin (absorbent agent) itself. Additionally, "reflow" is sometimes also referred to as re-wet or reflux rate.

[0094] (2-1)SRC(NP)

[0095] The method for determining the SRC(NP) is not particularly limited as long as it includes steps (a) to (e). The SRC(NP) can be determined, for example, by the method described in the embodiments of this application.

[0096] The lower limit of the SRC(NP) is a value exceeding 50.0 g / g, preferably exceeding 54.0 g / g, more preferably exceeding 56.0 g / g, even more preferably exceeding 58.0 g / g, and particularly preferably exceeding 59.0 g / g. The upper limit of the SRC(NP) is not particularly limited and is typically below 70.0 g / g. The SRC(NP) of the granular absorbent of the present invention exceeds the preferred lower limit value, thus enabling it to absorb a larger amount of liquid in a shorter time, and, in a swollen state, to adequately retain this large amount of liquid without pressure. Ultimately, the sanitary product containing the granular absorbent of the present invention can further reduce the backflow of absorbed liquid during actual use.

[0097] (2-2)SRC(4.83kPa)

[0098] The method for measuring the SRC (4.83 kPa) is not particularly limited as long as it includes steps (a), (b), and (c') to (e'). The SRC (4.83 kPa) can be measured, for example, by the method described in the embodiments of this application.

[0099] The lower limit of the SRC (4.83 kPa) is a value exceeding 41.5 g / g, preferably exceeding 42.0 g / g, more preferably exceeding 42.5 g / g, and particularly preferably 43.0 g / g. The upper limit of the SRC (4.83 kPa) is not particularly limited and is typically below 50.0 g / g. The SRC (4.83 kPa) of the granular absorbent of the present invention exceeds the preferred lower limit, thus enabling it to absorb a larger amount of liquid in a shorter time, and effectively retaining this large amount of liquid when held at a high pressure of 4.83 kPa in a swollen state. Ultimately, the sanitary product containing the granular absorbent of the present invention can further reduce the backflow of absorbed liquid during actual use.

[0100] (2-3) CRC (Centrifuge Hold-up Capacity) (ERT441.2-02)

[0101] "CRC" is short for Centrifuge Retention Capacity, which refers to the water absorption ratio of granular desiccant or desiccant resin without pressure (sometimes also called "water absorption ratio").

[0102] Specifically, this refers to: after filling 0.2g of granular water absorbent or water-absorbing resin into a non-woven fabric bag, immersing it in a large amount of excess 0.9% by weight sodium chloride aqueous solution for 30 minutes to allow it to swell freely, and then using a centrifuge (250G) to measure the water absorption ratio (unit: g / g) after draining.

[0103] The lower limit of the CRC (centrifuge retention capacity) of the granular absorbent of the present invention is preferably 35 g / g or more, more preferably 36 g / g or more, even more preferably 38 g / g or more, even more preferably 39 g / g or more, particularly preferably 40 g / g or more, and even more particularly preferably 41 g / g or more. With a CRC of 35 g / g or more, the absorption capacity of the granular absorbent becomes appropriate, ensuring its performance as an absorbent in sanitary products such as diapers. Furthermore, the upper limit of the CRC (centrifuge retention capacity) of the granular absorbent of the present invention is preferably 70 g / g or less, more preferably 60 g / g or less. If the CRC exceeds 70 g / g, gel blockage is likely to occur when the granular absorbent swells. Therefore, with the CRC within an appropriate range, the granular absorbent is also suitable for high-absorbency diapers and the like. Additionally, the CRC can be controlled according to the type and / or amount of the internal cross-linking agent.

[0104] (2-4) Water absorption rate (Vortex method)

[0105] The absorbency rate (vortex method) of the granular absorbent of the present invention is preferably 40 seconds or less, more preferably 38 seconds or less, even more preferably 35 seconds or less, particularly preferably 33 seconds or less, and even more particularly preferably 31 seconds or less. By increasing SRC (NP) and SEC (4.83 kPa) to the above ranges and further controlling the absorbency rate (vortex method) within the above ranges, the absorption capacity in a short time is further increased, thereby improving the performance when used in sanitary products such as diapers.

[0106] (2-5) Surface tension (STR)

[0107] Surface tension is a physical quantity that represents the work (free energy) required to increase the surface area of ​​a solid and / or liquid, expressed per unit area. The surface tension described in this application refers to the surface tension of an aqueous solution when a particulate absorbent is dispersed in a 0.90% by mass sodium chloride aqueous solution. Furthermore, the surface tension is measured using the following steps: 50 ml of physiological saline adjusted to 20°C and a 25 mm long fluoropolymer rotor, thoroughly cleaned, are added to a 100 ml beaker. The surface tension of the physiological saline is then measured using a surface tension meter (KRUSS K11 automatic surface tension meter), confirming a value of 71–75 [mN / m]. Next, 0.5 g of the particulate absorbent is added to the beaker containing the physiological saline adjusted to 20°C and the measured surface tension, and the mixture is stirred at 500 rpm for 4 minutes. After 4 minutes, stirring is stopped, and after the aqueous particulate absorbent settles, the same procedure is repeated to measure the surface tension of the supernatant. In another embodiment of the present invention, a plate method using platinum plates is employed. The plates are thoroughly cleaned with deionized water before each measurement and then heated and cleaned with a gas burner before use.

[0108] The surface tension of the granular absorbent of the present invention is preferably 66 mN / m or more, more preferably 68 mN / m or more, even more preferably 70 mN / m or more, even more preferably 71 mN / m or more, and particularly preferably 72 mN / m or more. By satisfying the aforementioned conditions through surface tension, the backflow rate in the sanitary products such as diapers can be further reduced. An upper limit of 75 mN / m is generally sufficient.

[0109] (2-6) Particle shape

[0110] The particle shape of the water-absorbing resin (powder) is preferably irregular and broken. Here, irregular and broken means particles in a broken state with an irregular shape. Irregularly broken particles are preferred over spherical particles obtained by reverse suspension polymerization or gas-phase polymerization for the following reasons (i) to (iii).

[0111] (i) Irregularly broken particles have a large surface area and a large contact area with the liquid, resulting in excellent absorption rate.

[0112] (ii) The irregular, broken particles have an unfixed shape, so gaps are easily formed between the particles, and the absorption capacity increases due to the liquid retention capacity brought about by the gaps between the particles.

[0113] (iii) The irregular, broken particles have an unfixed shape, thus exhibiting excellent mixability with hydrophilic fibers such as pulp, and high liquid diffusion due to the gaps between particles.

[0114] In one embodiment of the present invention, the granular superabsorbent is preferably a pulverized product from aqueous solution polymerization. Irregularly broken particles are obtained by pulverizing a gel or dried product (preferably dried product) of a crosslinked polymer obtained through aqueous solution polymerization. Alternatively, without a pulverization process, representative methods include droplet polymerization, such as reverse suspension polymerization or polymerization by spraying polymeric monomers, to obtain spherical particles or granulated spherical particles, which are not irregularly broken. When the granular superabsorbent has an irregularly broken shape, it exhibits superior physical properties, selected from the group consisting of absorption rate, SRC (NP), and SRC (4.83 kPa), compared to granular superabsorbents with high average roundness (e.g., spherical granular superabsorbents). In one embodiment of the present invention, the average roundness of the granular superabsorbent is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.

[0115] Average roundness can be calculated, for example, by the following method.

[0116] • Randomly select more than 100 granular absorbent particles and photograph each particle using an electron microscope (VE-9800, Keyence Corporation, 50x magnification). Obtain images of the granular absorbent particles and use the accompanying image analysis software to calculate the perimeter and area of ​​each particle. Then, using the area and perimeter, calculate the roundness using the following formula: Roundness = 4 × π × Area / (Perimeter) 2 The roundness of each particle is determined, and the average value of the obtained values ​​is calculated as the average roundness.

[0117] (2-7) Inorganic colloidal particles, water-insoluble inorganic particles, and water-soluble compounds containing polyvalent metal cations.

[0118] From the viewpoint of inhibiting adhesion between absorbent particles, the granular absorbent of one embodiment of the present invention preferably further comprises at least one selected from the group consisting of inorganic colloidal particles, water-insoluble inorganic particles, and water-soluble compounds containing polyvalent metal cations.

[0119] The granular absorbent of the present invention exhibits excellent operability in humid environments when it contains any one of inorganic colloidal particles, water-insoluble inorganic particles, and water-soluble compounds containing polyvalent metal cations. Therefore, by using this granular absorbent, problems such as aggregation and blockage in the conveying piping of manufacturing equipment and inability to mix uniformly with hydrophilic fibers are less likely to occur when manufacturing thin absorbent bodies for sanitary products. Thus, using this granular absorbent is suitable for suppressing performance degradation in sanitary products when manufacturing thin absorbent bodies containing the granular absorbent of the present invention.

[0120] By including inorganic colloidal particles in the granular absorbent, the performance of the granular absorbent can be further improved. The inorganic colloidal particles refer to inorganic particles dispersed in a dispersion medium within a colloidal solution. Specific examples of the inorganic colloidal particles include colloidal silica obtained by dispersing silica particles in water and alumina sol obtained by dispersing alumina in water. Relative to 100 parts by weight of the polyacrylic acid (salt)-based absorbent resin in the granular absorbent of the present invention, the content of the inorganic colloidal particles is preferably 0.001 to 5 parts by weight, based on solid components, and more preferably 0.01 to 1 part by weight, based on solid components.

[0121] By including water-insoluble inorganic particles in the granular absorbent, the performance of the granular absorbent can be further improved.

[0122] The water-insoluble inorganic particles are not particularly limited. Specific examples of such water-insoluble inorganic particles include silica, aluminum hydroxide, zinc oxide, talc, zeolite, hydrotalcite, and tricalcium phosphate.

[0123] The content of the water-insoluble inorganic particles is preferably 0.01% by weight or more and less than 10% by weight, and more preferably 0.1% to 5% by weight, relative to 100% by weight of the polyacrylic acid (salt)-based water-absorbing resin.

[0124] By including a water-soluble polyvalent metal cation compound in the granular absorbent of the present invention, the performance of the granular absorbent can be improved.

[0125] The water-soluble polyvalent metal cation compound refers to a compound containing divalent or higher, preferably trivalent or higher, metal cations, and is water-soluble. There is no particular limitation on the water-soluble polyvalent metal cation compound. Specific examples of such water-soluble polyvalent metal cation compounds include aluminum chloride, potassium zirconium carbonate, zirconium sulfate, aluminum sulfate, potassium aluminum sulfate, and sodium aluminum sulfate.

[0126] In this specification, "water solubility" refers to the property of being soluble (or readily soluble) in water at room temperature (20–25°C) and normal pressure (1 atmosphere), for example, indicating a solubility of 1 g or more relative to 100 ml of water at room temperature and normal pressure. Conversely, "water insoluble" refers to the property of being insoluble (or sparingly soluble) in water at room temperature (20–25°C) and normal pressure (1 atmosphere), for example, indicating a solubility of less than 1 g relative to 100 ml of water at room temperature and normal pressure. Preferably, the water insoluble property indicates a solubility of less than 0.1 g relative to 100 ml of water at room temperature and normal pressure.

[0127] Relative to 100 parts by weight of the polyacrylic acid (salt)-based absorbent resin, the content of the water-soluble polyvalent metal cation-containing compound, converted into the amount of polyvalent metal cations, is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 2 parts by weight, and even more preferably 0.01 to 1 part by weight. By maintaining the content within these ranges, the performance of the granular absorbent can be improved.

[0128] (2-8) Chelating agents

[0129] To prevent discoloration and deterioration, the granular absorbent of the present invention preferably further comprises at least one chelating agent. The chelating agent is particularly preferably at least one selected from the group consisting of organophosphorus chelating agents and aminocarboxylic acid chelating agents. Due to trace amounts of metal ions and L-ascorbic acid contained in urine, granular absorbents that have absorbed urine deteriorate over time, resulting in a decrease in liquid retention capacity and potentially causing temporarily absorbed liquid to be re-exposed from sanitary products. By including a chelating agent in the granular absorbent, backflow over time can be suppressed when used in sanitary products.

[0130] The content of the chelating agent is preferably 0 to 3 parts by weight relative to 100 parts by weight of the polyacrylic acid (salt)-based water-absorbing resin, more preferably 0.005 to 1 part by weight, and even more preferably 0.01 to 0.5 parts by weight.

[0131] Furthermore, as the chelating agent, compounds and their dosages disclosed in International Publication No. 2011 / 040530, "〔2〕 Chelating Agents", can be applied to one embodiment of the present invention.

[0132] [3] Method for manufacturing granular water absorbent

[0133] The following describes the manufacturing process (3-1) to (3-8) of a granular water absorbent according to one embodiment of the present invention.

[0134] (3-1) Preparation process of monomer aqueous solution

[0135] This step is to prepare an aqueous solution (hereinafter referred to as "monomer aqueous solution") containing acrylic acid (salt) as the main component, which is a monomer. Alternatively, a monomer slurry can be used without reducing the water absorption properties of the resulting water-absorbing resin, but for convenience, an aqueous monomer solution is described here.

[0136] Furthermore, the term "main component" refers to the amount (content) of acrylic acid (salt) relative to all monomers (excluding internal crosslinking agents) supplied to the polymerization reaction of the water-absorbing resin, which is typically 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more (up to 100 mol%).

[0137] (acrylic acid)

[0138] In one embodiment of the present invention, from the viewpoint of the physical properties and productivity of the resulting granular water absorbent, acrylic acid and / or its salts (hereinafter referred to as "acrylic acid (salt)") are used as monomers.

[0139] The "acrylic acid" may be any known acrylic acid. The "acrylic acid" only needs to contain preferably methoxyphenols (preferably less than 200 ppm, more preferably 10-160 ppm, further preferably 20-100 ppm), and more preferably p-methoxyphenols as polymerization inhibitors. The content of the polymerization inhibitor is preferred from the viewpoint of the polymerizability of acrylic acid and / or the color of the particulate absorbent. Furthermore, regarding impurities in the acrylic acid, compounds described in U.S. Patent Application Publication No. 2008 / 0161512 may also be used in one embodiment of the present invention.

[0140] Furthermore, the "acrylate" is obtained by neutralizing the acrylic acid with the following alkaline composition. This acrylate can be a commercially available acrylate (e.g., sodium acrylate), or it can be obtained by neutralizing acrylic acid in a granular absorbent manufacturing facility.

[0141] (Alkaline composition)

[0142] In one embodiment of the present invention, "alkaline composition" refers to a composition containing an alkaline compound, such as commercially available sodium hydroxide aqueous solution.

[0143] Specifically, examples of alkaline compounds include alkali metal carbonates or bicarbonates, alkali metal hydroxides, ammonia, and organic amines. From the viewpoint of the physical properties of the resulting granular desiccant, it is desirable that the alkaline compound be strongly alkaline. That is, the preferred alkaline compound is an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, or lithium hydroxide, and more preferably sodium hydroxide.

[0144] (Neutralization)

[0145] As one embodiment of the present invention, neutralization can be performed by selecting or using either neutralization of acrylic acid (before polymerization) or neutralization of the hydrogel-like crosslinked polymer obtained by crosslinking polymerization of acrylic acid (after polymerization) (hereinafter referred to as "post-neutralization"). Furthermore, these neutralizations can be continuous or batch-based, without particular limitation, but continuous neutralization is preferred from the viewpoint of production efficiency, etc.

[0146] Furthermore, the conditions described in International Patent Publication No. 2009 / 123197 or U.S. Patent Application Publication No. 2008 / 0194863, such as the apparatus for neutralization, neutralization temperature, and residence time, can also be applied to one embodiment of the present invention.

[0147] In one embodiment of the present invention, the neutralization rate relative to the acid group 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 less than 10 mol%, the water absorption ratio may sometimes decrease significantly. On the other hand, when the neutralization rate exceeds 90 mol%, it may sometimes be impossible to obtain a water-absorbing resin with a high water absorption ratio under pressure.

[0148] The neutralization rate is also applied in the case of post-neutralization. Furthermore, the neutralization rate can also be applied to the neutralization rate of the granular absorbent as the final product. Additionally, for example, "neutralization rate 75 mol%" refers to a mixture of 25 mol% acrylic acid and 75 mol% acrylate. Moreover, this mixture is sometimes referred to as partially neutralized acrylic acid.

[0149] (Other monomers)

[0150] In one embodiment of the present invention, "other monomers" refers to monomers other than the acrylic acid (salt) mentioned above, which can be combined with acrylic acid (salt) to produce granular water-absorbing agents.

[0151] Other monomers may include water-soluble or hydrophobic unsaturated monomers. Specifically, compounds described in U.S. Patent Application Publication No. 2005 / 0215734 (except for acrylic acid) may also be used in one embodiment of the present invention.

[0152] (Internal cross-linking agent)

[0153] As an internal crosslinking agent used in one embodiment of the present invention, the compound described in U.S. Patent No. 6,241,928 may also be used in one embodiment of the present invention. Considering reactivity, one or more of these compounds may be selected. Depending on the polymerization method and / or the type of polymerization initiator described later, a crosslinked polymer may be obtained without using an internal crosslinking agent, but it is preferred to use at least one internal crosslinking agent.

[0154] The amount of the internal crosslinking agent relative to the total monomer is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, even more preferably 0.001 to 0.5 mol%, even more preferably 0.005 to 0.1 mol%, and particularly preferably 0.005 to 0.05 mol%. By setting the amount within the above range, a desired water-absorbing resin can be obtained. Furthermore, if the amount is too small, the gel strength of the resulting water-absorbing resin tends to decrease, and the water-soluble component tends to increase. Conversely, if the amount is too large, the water absorption ratio of the resulting water-absorbing resin tends to decrease. Additionally, the mol% relative to the total monomer refers to the percentage of the number of moles of the internal crosslinking agent relative to the total number of moles of monomer contained in the aqueous monomer solution.

[0155] In one embodiment of the present invention, the following method is preferred: a predetermined amount of internal crosslinking agent is added to the monomer aqueous solution in advance, and the crosslinking reaction is carried out simultaneously with polymerization. Alternatively, in addition to this method, methods such as adding an internal crosslinking agent during and / 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 may also be employed. Furthermore, these methods may be used in combination.

[0156] (Other substances added to the monomer aqueous solution)

[0157] In one embodiment of the present invention, from the viewpoint of improving the physical properties of the resulting water-absorbing resin, the following substances may be added during the preparation of the monomer aqueous solution.

[0158] Examples of such substances include starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), and cross-linked polyacrylic acid (salt) polymers. This hydrophilic polymer can be added in the monomer aqueous solution, preferably at 50% by weight or less, more preferably at 20% by weight or less, further preferably at 10% by weight or less, and particularly preferably at 5% by weight or less (the lower limit is 0% by weight). Furthermore, carbonates, azo compounds, foaming agents such as bubbles, surfactants, chelating agents, α-hydroxycarboxylic acids (salts), chain transfer agents, etc., can be added in the monomer aqueous solution, preferably at 5% by weight or less, more preferably at 1% by weight or less, and further preferably at 0.5% by weight or less. The lower limit for the amount of such substances added is 0% by weight. Examples of such chelating agents include diethylenetriaminepentaacetic acid (salt), triethylenetetraminehexaacetic acid (salt), hydroxyethylenediphosphonic acid (salt), and ethylenediaminetetramethylenephosphonic acid (salt). In addition, as α-hydroxycarboxylic acid (salt), the compounds exemplified in the additive addition process described later (3-7) can also be added.

[0159] Furthermore, the substance can be in the form added to the monomer aqueous solution, or in the form added during polymerization, or in a combination of these forms.

[0160] Furthermore, when water-soluble resins or water-absorbing resins are used as hydrophilic polymers, grafted polymers or water-absorbing resin compositions (e.g., starch-acrylic polymers, PVA-acrylic polymers, etc.) can be obtained. These polymers and water-absorbing resin compositions also fall within the scope of this invention.

[0161] (Concentration of monomeric components)

[0162] 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 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.

[0163] In addition, when using aqueous solution polymerization or reverse suspension polymerization, solvents other than water can be used as needed. In this case, there are no particular restrictions on the type of solvent.

[0164] In addition, the “concentration of monomer components” refers to the value obtained by the following formula (3), and the weight of the monomer aqueous solution does not include the weight of the grafted components and the water-absorbing resin, as well as the weight of the hydrophobic solvent in the reverse suspension polymerization.

[0165] (Concentration of monomer component (weight %)) = (Weight of monomer component) / (Weight of monomer aqueous solution) × 100 Equation (3)

[0166] (3-2) Polymerization process

[0167] This process involves polymerizing the acrylic (salt) monomer aqueous solution obtained in the monomer aqueous solution preparation process to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").

[0168] (Polymerization initiator)

[0169] The polymerization initiator used in one embodiment of the present invention can be appropriately selected according to the polymerization method, and is therefore not particularly limited. Examples include thermally decomposable polymerization initiators, photodecomposable polymerization initiators, or redox polymerization initiators that incorporate 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 can be used. Furthermore, from the viewpoint of the operability of the polymerization initiator and the physical properties of the particulate superabsorbent or superabsorbent resin, peroxides or azo compounds are preferred, peroxides are more preferred, and persulfates are even more preferred.

[0170] The amount of the polymerization initiator relative to the monomer is preferably 0.001 to 1 mol%, more preferably 0.001 to 0.5 mol%. Furthermore, the amount of the reducing agent relative to the monomer is preferably 0.0001 to 0.02 mol%.

[0171] Alternatively, the polymerization initiator can be replaced by irradiation with active energy rays such as radiation, electron beams, or ultraviolet rays to carry out the polymerization reaction, or these active energy rays and the polymerization initiator can be used together.

[0172] (Aggregation Method)

[0173] The polymerization method used in this invention is not particularly limited, but from the viewpoints of water absorption characteristics and ease of polymerization control, spray droplet polymerization, aqueous solution polymerization, and reverse suspension polymerization are preferred, aqueous solution polymerization and reverse suspension polymerization are more preferred, and aqueous solution polymerization is even more preferred. Among these, continuous aqueous solution polymerization is particularly preferred. As a continuous aqueous solution polymerization, any of the following can also be used: continuous belt polymerization and continuous kneader polymerization.

[0174] Specific polymerization methods have been disclosed in U.S. Patent Nos. 4,893,999, 6,241,928, and 2005 / 215,734, and in U.S. Patent Application Publication No. 2005 / 215,734, and in U.S. Patent Nos. 6,987,151 and 6,710,141, respectively. By employing these continuous aqueous solution polymerization methods, the production efficiency of water-absorbing resins will be improved.

[0175] Furthermore, preferred methods for the continuous aqueous solution polymerization include "high-temperature initiation polymerization" and "high-concentration polymerization." "High-temperature initiation polymerization" refers to a method of initiating polymerization by setting the temperature of the monomer aqueous solution preferably to 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and particularly preferably 50°C or higher (upper limit being the boiling point). "High-concentration polymerization" refers to a method of polymerization by setting the monomer concentration preferably to 30% by weight or higher, more preferably 35% by weight or higher, even more preferably 40% by weight or higher, and particularly preferably 45% by weight or higher (upper limit being the saturation concentration). These polymerization methods can also be used in combination.

[0176] Furthermore, in one embodiment of the present invention, polymerization may be carried out in an air atmosphere; however, from the viewpoint of the color tone of the resulting water-absorbing resin, polymerization may also be carried out in an inert gas atmosphere such as nitrogen or argon. In this case, for example, it is preferable to control the oxygen concentration to below 1% by volume. In addition, regarding the dissolved oxygen in the monomer aqueous solution, it is also preferable to pre-replace it with an inert gas (e.g., dissolved oxygen: less than 1 mg / L).

[0177] In addition, in one embodiment of the present invention, foaming polymerization can also be used, in which bubbles (especially the inert gas, etc.) are dispersed in an aqueous solution of monomers for polymerization.

[0178] (3-3) Gel pulverization process

[0179] This process involves pulverizing the hydrogel obtained in the polymerization process using a gel pulverizer such as a kneader, a screw extruder (e.g., a meat grinder), or a shredder to obtain granular hydrogel (hereinafter referred to as "granular hydrogel"). Additionally, when a kneader is used in the polymerization process, both the polymerization and gel pulverization processes are performed simultaneously. Furthermore, when gas-phase polymerization or reverse-phase suspension polymerization is used, and granular hydrogel is directly obtained during the polymerization process, the gel pulverization process may sometimes be omitted.

[0180] By controlling the gel pulverizing mechanism (kneader, etc.) and the gel pulverizing energy (GGE), which is described later as one of the gel pulverizing conditions, the SRC (NP) and SRC (4.83 kPa) of the manufactured granular superabsorbent can be controlled. In this case, the contents disclosed in International Publication No. 2011 / 126079, other than the gel pulverizing energy (GGE), can be preferably applied to one embodiment of the present invention.

[0181] (3-4) Drying process

[0182] This step involves drying the granular hydrogel obtained in the polymerization step and / or gel pulverization step to a desired resin solids composition, thereby obtaining a dried polymer. This resin solids composition can be determined based on the weight loss on drying (the change in weight when 1 g of the water-absorbing resin is heated at 180°C for 3 hours), preferably 80% by weight or more, more preferably 85-99% by weight, further preferably 90-98% by weight, and particularly preferably 92-97% by weight.

[0183] There are no particular limitations on the drying method for the particulate hydrogel, and examples include heating drying, hot air drying, vacuum drying, fluidized bed 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, from the viewpoint of drying efficiency, hot air drying is preferred, and belt drying, which involves hot air drying on a ventilation belt, is more preferred.

[0184] From the viewpoint of the color tone of the absorbent resin and drying efficiency, the drying temperature (hot air temperature) in the hot air drying process is preferably 120–250°C, more preferably 150–200°C. Furthermore, drying conditions other than the drying temperature, such as the hot air velocity and drying time, can be appropriately set based on the moisture content, total weight, and solid composition of the granular hydrogel supplied for drying. When performing belt drying, the conditions described in International Publications Nos. 2006 / 100300, 2011 / 025012, 2011 / 025013, and 2011 / 111657 can be appropriately applied.

[0185] (3-5) Crushing and Grading Processes

[0186] This process involves pulverizing the dried polymer obtained in the drying process (pulverization process) and adjusting it to a specified particle size (grading process) to obtain water-absorbing resin powder (for convenience, the powdered water-absorbing resin before surface crosslinking is referred to as "water-absorbing resin powder").

[0187] Examples of equipment used in the pulverizing process in one embodiment of the present invention include: high-speed rotary pulverizers such as roller mills, hammer mills, screw mills, and pin mills; vibratory mills; knuckle-type pulverizers; and cylindrical mixers. These can be used in combination as needed.

[0188] Furthermore, the particle size adjustment method in the grading process, as one embodiment of the present invention, is not particularly limited. For example, sieve grading using a JIS standard sieve (JIS Z8801-1(2000)) and air classification can be cited. In addition, the particle size adjustment of the water-absorbing resin is not limited to the pulverizing process and the grading process, but can be appropriately implemented in the polymerization process (especially reverse suspension polymerization and spray droplet polymerization) and other processes (e.g., granulation process and micron powder recovery process).

[0189] The weight-average particle size (D50) of the water-absorbing resin powder obtained in the aforementioned process (the water-absorbing resin powder before the surface crosslinking process, the so-called base polymer) is preferably 200–600 μm, more preferably 200–550 μm, even more preferably 250–500 μm, and particularly preferably 300–500 μm. Furthermore, the proportion of particles with a particle size less than 150 μm in the water-absorbing resin powder is preferably 10% by weight or less, more preferably 5% by weight or less, even more preferably 3% by weight or less, and particularly preferably 1% by weight or less. The proportion of particles with a particle size of 850 μm or more in the water-absorbing resin powder is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less. Moreover, as a lower limit for these particle proportions, the lower the amount, the better; ideally, it should be 0% by weight, but it can also be around 0.1% by weight. Furthermore, the logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and even more preferably 0.27 to 0.35. If the logarithmic standard deviation (σζ) of the particle size distribution is too small, the usable particle size range becomes narrower, the efficiency of the crushing and grading processes is significantly reduced, and the productivity of the absorbent resin powder decreases. Therefore, the absorbent resin powder in one embodiment of the present invention preferably meets the aforementioned particle size distribution. In addition, these particle sizes can be determined using standard sieves according to the determination methods disclosed in U.S. Patent No. 7,638,570 or EDANAERT 420.2-02.

[0190] The aforementioned particle size can be applied not only to surface-crosslinked water-absorbing resins (for convenience, sometimes referred to as "water-absorbing resin particles"), but also to granular water-absorbing agents as the final product. Therefore, in water-absorbing resin particles, it is preferable to perform surface crosslinking treatment (surface crosslinking process) in a manner that maintains the particle size within the aforementioned range, and more preferably, a granulation process is performed after the surface crosslinking process to adjust the particle size.

[0191] (3-6) Surface crosslinking process

[0192] This process involves further setting a high crosslinking density portion on the surface layer (within 10 μm of the surface of the water-absorbing resin powder) obtained through the above process. It consists of a mixing process, a heat treatment process, and a cooling process (optional).

[0193] In this surface crosslinking process, water-absorbing resin (water-absorbing resin particles) can be obtained by free radical crosslinking, surface polymerization, and crosslinking reaction with surface crosslinking agent on the surface of water-absorbing resin powder.

[0194] (Surface crosslinking agent)

[0195] The surface crosslinking agent used in one embodiment of the present invention is not particularly limited, and organic or inorganic surface crosslinking agents can be listed. From the viewpoint of the physical properties of the water-absorbing 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 U.S. Patent No. 7,183,456 can be listed. More specifically, polyol compounds, epoxy compounds, halogenated epoxy compounds, polyamine compounds or their condensates with halogenated epoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc., can be listed.

[0196] Specific examples of the aforementioned organic surface crosslinking agents include: (di, tri, tetra, poly)ethylene glycol, (di, poly)propylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, (poly)glycerol, 2-buten-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, diethanolamine or triethanolamine, pentaerythritol, sorbitol, and other polyol compounds; (poly)ethylene glycol diglycidyl ether, (di... Epoxy compounds such as poly(glycerol) glycidyl ether and glycidyl ether; oxazoline compounds such as 2-oxazolidinone, N-hydroxyethyl-2-oxazolidinone, and 1,2-ethylenebisoxazolidinone; 1,3-dioxolane-2-one (ethylene carbonate), 4-methyl-1,3-dioxolane-2-one, 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, 4-hydroxymethyl- alkyl carbonate esters such as 1,3-dioxane-2-one, 1,3-dioxane-2-one, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, and 1,3-dioxane-heptane-2-one; halogenated epoxy compounds and their polyamine adducts such as epichlorohydrin, epibromohydrin, and α-methylepicochlorohydrin (e.g., Hercules' KYMENE, a registered trademark); γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane... Silane coupling agents such as silanes; oxocyclic butane compounds such as 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol, 3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, and polyvalent oxetane compounds; and cyclic urea compounds such as 2-imidazolium ketones.

[0197] As the polyol, polyols with 2 to 8 carbon atoms are preferred, polyols with 3 to 6 carbon atoms are more preferred, and polyols with 3 to 4 carbon atoms are even more preferred. Furthermore, diols are particularly preferred as the polyol. Examples of diols include ethylene glycol, propylene glycol, 1,3-propanediol, and 1,4-butanediol. Among these, one or more polyols selected from propylene glycol (1,2-propanediol), 1,3-propanediol, and 1,4-butanediol are preferred.

[0198] Furthermore, polyglycidyl compounds are preferred as the epoxy compounds, and ethylene glycol diglycidyl ether may be used appropriately.

[0199] In addition to the aforementioned organic surface crosslinking agents, from the viewpoint of more effectively performing surface crosslinking, polyvalent cationic polymers such as polyamine polymers and / or water-soluble polyvalent metal-containing cationic compounds can also be used as ionic crosslinking agents. As described above, these water-soluble polyvalent metal-containing cationic compounds can be added to the surface crosslinking agent solution described later and mixed with the water-absorbing resin powder, or they can be added separately from the surface crosslinking agent solution and mixed with the water-absorbing resin powder.

[0200] The amount of the surface crosslinking agent (total amount when multiple agents are used) relative to 100 parts by weight of the water-absorbing resin powder is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight. Furthermore, the surface crosslinking agent is preferably added as an aqueous solution; in this case, the amount of water relative to 100 parts by weight of the water-absorbing resin powder is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight. Moreover, when a hydrophilic organic solvent is used as needed, its amount relative to 100 parts by weight of the water-absorbing resin powder is preferably 10 parts by weight or less, more preferably 5 parts by weight or less.

[0201] (Mixed Process)

[0202] This step involves mixing the water-absorbing resin powder with the surface crosslinking agent. There are no particular limitations on the mixing method for the surface crosslinking agent; the following methods can be used: a surface crosslinking agent solution is prepared in advance, and the liquid is preferably sprayed or dripped onto the water-absorbing resin powder, more preferably sprayed, for mixing.

[0203] There are no particular limitations on the apparatus used for this mixing; a high-speed stirring mixer is preferred, and a high-speed stirring continuous mixer is more preferred.

[0204] (Heat treatment process)

[0205] This process involves heating the mixture discharged from the mixing process to induce a cross-linking reaction on the surface of the water-absorbing resin powder.

[0206] There are no particular limitations on the apparatus for carrying out the crosslinking reaction, but a paddle dryer is a preferred example. The reaction temperature in the crosslinking reaction can be appropriately set according to the type of surface crosslinking agent used, preferably 50 to 300°C, and more preferably 80 to 200°C.

[0207] (Cooling process)

[0208] This step is an optional step that is set up as needed after the heat treatment step.

[0209] The cooling device is not particularly limited, but it is preferably the same as the device used in the heat treatment process, and more preferably a paddle dryer. This is because, by changing the heat medium to a refrigerant, this device can be used as a cooling device. Furthermore, in this cooling process, the water-absorbing resin particles obtained in the heat treatment process are forcibly cooled to a temperature preferably 40–80°C, more preferably 50–70°C, as needed.

[0210] (3-7) Additive addition process

[0211] This process involves adding additives such as polyvalent metal salts, cationic polymers, chelating agents, inorganic reducing agents, hydroxycarboxylic acid compounds, water-insoluble inorganic particles, inorganic colloidal particles, water-soluble compounds containing polyvalent metal cations, surfactants, and non-polymeric water-soluble compounds to the water-absorbing resin particles obtained in the surface crosslinking process. These additives can also be mixed simultaneously with the surface crosslinking agent (aqueous solution) and the water-absorbing resin powder.

[0212] (polyvalent metal salts and / or cationic polymers)

[0213] From the viewpoint of improving the water absorption rate, liquid permeability, and moisture flowability of the obtained granular water absorbent, polyvalent metal salts and / or cationic polymers can also be added to the water absorbent resin particles obtained in the surface crosslinking process.

[0214] Specifically, the compounds and their amounts disclosed in International Publication No. 2011 / 040530, “〔7〕Multivalent metal salts and / or cationic polymers”, can be applied to one embodiment of the present invention.

[0215] (chelating agent)

[0216] From the perspective of the color tone (preventing staining) and the prevention of deterioration of the obtained granular water absorbent, a chelating agent may also be added to the water absorbent resin particles obtained in the surface crosslinking process.

[0217] As the chelating agent, compounds and their dosages disclosed in International Publication No. 2011 / 040530, "〔2〕 Chelating Agents", can be applied to one embodiment of the present invention.

[0218] (Inorganic reducing agent)

[0219] From the perspectives of color tone (preventing staining), preventing deterioration, and reducing residual monomers in the obtained granular water absorbent, an inorganic reducing agent may also be added to the water absorbent resin particles obtained in the surface crosslinking process.

[0220] As the inorganic reducing agent, for example, the compounds and their dosages disclosed in International Publication No. 2011 / 040530, "〔3〕Inorganic Reducing Agents", can be applied to one embodiment of the present invention.

[0221] (α-Hydroxycarboxylic acid compounds)

[0222] From the viewpoint of the resulting granular absorbent's color (to prevent staining), α-hydroxycarboxylic acid may also be added to the absorbent resin particles obtained in the surface crosslinking process. Furthermore, "α-hydroxycarboxylic acid compound" refers to a carboxylic acid or its salt having a hydroxyl group within the molecule, specifically a hydroxycarboxylic acid having a hydroxyl group at the α-position.

[0223] As the α-hydroxycarboxylic acid compound, for example, the compound and its dosage disclosed in International Publication No. 2011 / 040530, “[6] α-hydroxycarboxylic acid compound”, can be applied to one embodiment of the present invention, and malic acid (salt) and lactic acid (salt) are particularly preferred.

[0224] (Water-insoluble inorganic particles)

[0225] From the viewpoint of improving the flowability of granular water-absorbing agents, water-insoluble inorganic particles may also be added to the water-absorbing resin particles obtained in the surface crosslinking process. Examples of such water-insoluble inorganic particles added to the water-absorbing resin particles obtained in the surface crosslinking process include those listed in columns (2-6).

[0226] (Inorganic colloidal particles)

[0227] From the viewpoint of improving the physical properties of the resulting particulate absorbent, inorganic colloidal particles may also be added to the absorbent resin particles obtained in the surface crosslinking process. Examples of such inorganic colloidal particles added to the absorbent resin particles obtained in the surface crosslinking process include those described in columns (2-6).

[0228] (Water-soluble compounds containing polyvalent metal cations)

[0229] From the viewpoint of improving the performance of the obtained granular water-absorbing agent, a water-soluble polyvalent metal cation compound may also be added to the water-absorbing resin particles obtained in the surface crosslinking process. Examples of such water-soluble polyvalent metal cation compounds include those described in columns (2-6).

[0230] (surfactant)

[0231] From the viewpoint of improving the physical properties of the resulting water-absorbing resin (e.g., water absorption rate), a surfactant may also be added to the water-absorbing resin particles obtained in the surface crosslinking process.

[0232] Examples of surfactants disclosed in International Publication No. 97 / 017397 or U.S. Patent No. 6107358 include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc.

[0233] (Non-polymer water-soluble compound)

[0234] From the viewpoint of reducing dust from the absorbent resin, a non-polymeric water-soluble compound may be added to the absorbent resin particles obtained in the surface crosslinking process. For example, compounds and their dosages disclosed in International Publication No. 2014 / 034667, "Non-polymeric Water-soluble Compounds," can be applied to one embodiment of the present invention.

[0235] In one embodiment of the present invention, in order to add various functions to the absorbent resin, additives other than the above-mentioned additives may be added to the absorbent resin particles obtained in the surface crosslinking process. Examples of such additives include compounds having phosphorus atoms, oxidants, organic reducing agents, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, and thermoplastic fibers.

[0236] The amount of this additive can be appropriately determined according to its application, and therefore is not particularly limited. The amount is preferably 3 parts by weight or less, more preferably 1 part by weight or less, relative to 100 parts by weight of the water-absorbing resin. Furthermore, this additive may also be added in a process different from the process described above.

[0237] (3-8) Other processes

[0238] In one embodiment of the present invention, in addition to the above-described steps, a granulation step, a sizing step, a micron powder removal step, and a micron powder recycling step may be provided as needed. Furthermore, one or more of the following steps may be included: a transportation step, a storage step, a packaging step, and a preservation step. Additionally, the "sizing step" includes: a micron powder removal step after the surface cross-linking step, and a step of classifying and pulverizing the superabsorbent resin when it aggregates and exceeds a desired size. Furthermore, the "micron powder recycling step," in addition to the direct addition of micron powder as in the present invention, also includes the following step: forming a large hydrogel and adding it to any step of the superabsorbent resin manufacturing process.

[0239] (3-9) Control methods for SRC (NP) and SRC (4.83 kPa)

[0240] By employing the control method described below in the manufacturing processes (3-1) to (3-8), the SRC (NP) and SRC (4.83 kPa) of the manufactured granular water-absorbing agent can be controlled within a preferred range. Therefore, the granular water-absorbing agent of the present invention can be appropriately manufactured.

[0241] As a control method, for example, the gel pulverization described in the "(3-3) Gel Pulverization Step" section can be performed under specific conditions. Specifically, the gel pulverization can be performed by controlling the gel pulverization energy (GGE) to preferably 15–40 J / g, more preferably 20–40 J / g, further preferably 20–35 J / g, and particularly preferably 25–35 J / g. By performing the gel pulverization in this way, the gel pulverization can be performed while applying appropriate shear and compressive forces to the hydrogel. Ultimately, the particle shape and particle size distribution of the hydrogel can be controlled, and the SRC (NP) and SRC (4.83 kPa) of the manufactured granular water absorbent can be controlled within the preferred range.

[0242] Here, in one embodiment of the present invention, "gel grinding energy" refers to the unit energy required by the gel grinding device when grinding hydrogels, i.e., the mechanical energy per unit mass of hydrogel. The energy for heating and cooling the outer casing, as well as the energy of the water and steam to be introduced, are not included in the gel grinding energy. In addition, "gel grinding energy" is abbreviated as "GGE" according to its English expression "Gel Grinding Energy".

[0243] When the gel crusher is driven by three-phase AC power, GGE is calculated by the following formula (6).

[0244]

[0245] The "power factor" and "motor efficiency" are inherent values ​​of the device that vary depending on the operating conditions of the gel pulverizer, and are values ​​between 0 and 1. These values ​​can be obtained by consulting the device manufacturer, etc. Furthermore, when the gel pulverizer is driven by single-phase AC power, the GGE can be adjusted by using the power factor in equation (6). Change the value to "1" for calculation. Additionally, the unit for voltage is [V], the unit for current is [A], and the unit for the mass of hydrogel is [g / s].

[0246] The "power factor" and "motor efficiency" in the GGE are values ​​taken during gel crushing. Sometimes the current value is small under no-load conditions, so the values ​​of the power factor and motor efficiency under no-load conditions are approximately defined according to Equation (6). The "mass of hydrous gel fed into the gel crusher within 1 second" [g / s] in Equation (6) refers to, for example, the value converted to [g / s] when the hydrous gel is continuously fed using a metering feeder. However, as will be discussed later, sometimes the hydrous gel contains recycled granulated gel.

[0247] Furthermore, the mechanical energy applied to the hydrogel is crucial in this invention. Therefore, the "current" value in equation (6) is preferably the current value obtained by subtracting the current value of the gel pulverizing device under no-load conditions from the current value during gel pulverization to calculate the aforementioned gel pulverization energy. Especially when gel pulverization is performed using multiple devices, the total no-load current values ​​become larger. Therefore, a suitable method for calculating the "current" value in equation (6) is to use the value obtained by subtracting the no-load current value from the current value during gel pulverization to calculate the GGE.

[0248] In this invention, during the gel pulverization process, a high GGE of 15 J / g or more is applied to pulverize the hydrogel. Following this gel pulverization process, the drying and pulverization / grading processes are performed to obtain hydroabsorbent resin particles. The CRC of these particles is preferably 50–70 g / g, more preferably 50–65 g / g, further preferably 51–63 g / g, and particularly preferably 52–62 g / g. However, when applying a high GGE of 15 J / g or more to pulverize the hydrogel, and then performing the drying and pulverization / grading processes after the gel pulverization process to obtain hydroabsorbent resin particles, controlling the CRC within the appropriate range is very difficult. The reasons for this are explained below.

[0249] To improve the CRC of the superabsorbent resin particles, the hydrogel obtained in the polymerization process must be a low-crosslinked gel with a relatively low crosslinking density. Such a low-crosslinked gel is difficult to pulverize using high GGE (above 15 J / g). Therefore, for such a low-crosslinked gel, it is difficult to apply appropriate shear and compressive forces to control the SRC (NP) and SRC (4.83 kPa) within the preferred range.

[0250] Regarding this problem, the inventors conducted repeated and in-depth research, resulting in a reduction in the discharge rate of hydrogels from the pulverizer compared to previous methods. Methods for reducing hydrogel discharge rate include installing a weir at the pulverizer outlet, narrowing the pulverizer outlet, and adjusting the perforated plate at the pulverizer outlet. Consequently, even when the hydrogel supplied to the pulverizer is a low-crosslinked gel, energy can be easily applied to it, thereby applying appropriate shear and compressive forces. Ultimately, the SRC (NP) and SRC (4.83 kPa) were improved.

[0251] In addition, if a screw extruder or multiple screw extruders are used to perform gel pulverization after the kneader polymerizes the gel, the total energy consumed in each device is taken as the gel pulverization energy (GGE).

[0252] Furthermore, as a control method, besides the method of performing gel pulverization under the specific conditions, other methods include, for example, forming the absorbent resin particles into a foamed shape, and reducing the monomer concentration in the monomer aqueous solution during the polymerization process. By forming the foamed shape, the surface area of ​​the absorbent resin particles can be increased, thereby improving the liquid retention capacity of the granular absorbent. Furthermore, by employing a method of reducing the monomer concentration during polymerization, the performance of the granular absorbent can be improved. Ultimately, the SRC (NP) and SRC (4.83 kPa) of the manufactured granular absorbent can be controlled within the preferred range.

[0253] [4] Uses of granular water absorbents

[0254] The granular absorbent of the present invention can be used for purposes of absorbing water and can be widely used as an absorbent. Furthermore, the granular absorbent of the present invention can be used in absorbent articles containing this absorbent. In particular, because the granular absorbent of the present invention reduces backflow under pressure, it is especially suitable for use in absorbent articles for human use in the absorption of bodily fluids such as urine and blood.

[0255] That is, a preferred embodiment of the present invention is an absorbent comprising the granular absorbent described above. Furthermore, another preferred embodiment of the present invention is a sanitary article comprising the absorbent. Since the absorbent comprises the granular absorbent of the present invention, the sanitary article comprising this absorbent can further reduce backflow of absorbed liquid during actual use.

[0256] Examples of absorbent materials include those formed primarily of granular absorbent and a fibrous substrate (e.g., hydrophilic fibers). The content (core concentration) of the granular absorbent is preferably 10–100% by weight, more preferably 15–90% by weight, particularly preferably 20–80% by weight, and most preferably 25–80% by weight, relative to the total weight of the granular absorbent and hydrophilic fibers in the absorbent. The higher the core concentration in the absorbent, the more the absorbency of the absorbent and the sanitary product containing it is affected by the absorbency of the granular absorbent contained in the absorbent and the sanitary product. Furthermore, the granular absorbent contained in the absorbent and the sanitary product is the granular absorbent used in the manufacture of the absorbent and the sanitary product. Such absorbents are formed, for example, by mixing or layering a fibrous substrate such as hydrophilic fibers with the granular absorbent. Examples of fiber substrates used include: hydrophilic fibers such as pulverized wood pulp, cotton linters, cross-linked cellulose fibers, rayon, cotton, wool, acetate, and vinylon. These fiber substrates are preferably formed by air-laid web formation.

[0257] In addition, the absorbent can also be a (pulp-free) absorbent sheet made by fixing absorbent resin between two sheets (e.g., nonwoven fabric).

[0258] Furthermore, the absorbent article comprises the absorbent body, a liquid-permeable surface sheet, and a liquid-impermeable back sheet. The absorbent article is manufactured by sandwiching the absorbent body (absorbent core) between the liquid-permeable surface sheet and the liquid-impermeable back sheet. Then, as needed, by adding elastic members, diffusion layers, adhesive tapes, etc., absorbent articles such as adult diapers and sanitary napkins can be obtained. Additionally, at this time, the absorbent core is, for example, compressed to a density of 0.06–0.50 g / cm³. 3 Weight per unit area: 0.01–0.20 g / cm³ 2 The scope of ].

[0259] One embodiment of the present invention may include the inventions shown in [1] to [8] below.

[0260] [1] A granular absorbent, wherein the granular absorbent is mainly composed of a polyacrylic acid (salt) based absorbent resin formed by surface cross-linking, and

[0261] The granular absorbent satisfies the following formula (A) and the following formula (B).

[0262] SRC(NP) > 50.0 g / g(A)

[0263] SRC (4.83 kPa) > 41.5 g / g (B)

[0264] Here, the SRC(NP) is determined by a method comprising the following steps (a) to (c):

[0265] (a) The granular absorbent (WO) [g] is contacted with a 0.9% sodium chloride aqueous solution (hereinafter referred to as the "test solution") for 10 minutes without applying a load to obtain a swollen gel;

[0266] (b) Separate the swollen gel obtained in step (a) from the test solution;

[0267] (c) Determine the weight (W1) [g] of the swollen gel separated in step (b), and calculate the SRC (NP) of the granular absorbent based on the following formula (1);

[0268] SRC(NP)[g / g]=W1 / W0(1)

[0269] The SRC (4.83 kPa) is determined by performing the following method: in a method including steps (a) to (c), step (c) is replaced by steps (c') to (e') described later.

[0270] (c') Apply a load of 4.83 kPa to the swollen gel separated in step (b) for 1 minute;

[0271] (d') Remove the exudate that has seeped from the swollen gel through step (c');

[0272] (e') The weight (W2) [g] of the swollen gel obtained in step (d') is determined, and the SRC (4.83 kPa) is calculated based on the following formula (2);

[0273] SRC(4.83kPa)[g / g]=W2 / W0(2).

[0274] [2] According to the granular water absorbent of [1], wherein the SRC (4.83 kPa) value in the formula (B) is >42 g / g.

[0275] [3] According to the granular absorbent of [1] or [2], wherein the SRC(NP) value in the formula (A) is >54.

[0276] [4] The granular absorbent according to any one of [1] to [3], wherein the water absorption rate (vortex method) of the granular absorbent is less than 40 seconds.

[0277] [5] The granular absorbent according to any one of [1] to [4], wherein the surface tension (STR) of the granular absorbent is 66 mN / m or more.

[0278] [6] The granular absorbent according to any one of [1] to [5], wherein the centrifugal retention capacity (CRC) of the granular absorbent is 35 g / g or more.

[0279] [7] According to the granular absorbent of [6], wherein the centrifugal retention capacity (CRC) of the granular absorbent is 40 g / g or more.

[0280] [8] The granular absorbent according to any one of [1] to [7], wherein the granular absorbent further comprises one or more selected from the group consisting of inorganic colloidal particles, water-insoluble inorganic particles and water-soluble compounds containing polyvalent metal cations.

[0281] [9] An absorbent comprising a particulate absorbent according to any one of [1] to [8].

[0282]

[10] A sanitary article comprising an absorbent according to [9].

[0283] Example

[0284] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. In addition, unless otherwise specified, the operation in the following examples is carried out at room temperature (20-25°C) and relative humidity 45-55%RH.

[0285] In addition, unless otherwise noted, the electrical equipment used in the examples, comparative examples and reference examples (including the determination of the physical properties of particulate water absorbents) uses a 200V or 100V power supply.

[0286] (a) Method for determining SRC(NP)

[0287] The SRC(NP) determination is performed using the barrel and piston described in U.S. Patent Publication No. 8269060 for the Gel Bed Permeability test. Additionally, a 400-mesh metal mesh is mounted on the bottom of the barrel, which allows for the absorption or drainage of the test solution and exudate without leakage of the granular absorbent and swollen gel described later.

[0288] First, the combined weight of the barrel and the piston used to measure the SRC(NP) is determined and set as W. a[g]. Next, approximately 0.9g of the granular absorbent sample to be tested was measured and evenly distributed on the bottom surface of the barrel. Here, the accurate weight of the sample is set as W0[g]. Next, the barrel was immersed in a large excess of 0.9% sodium chloride aqueous solution, which had been adjusted to 23±1°C, as the test solution. The evenly distributed sample was then brought into contact with the test solution for 10 minutes, allowing the sample to absorb the test solution and swell without applying a load, thus obtaining a swollen gel.

[0289] Next, a piston (approximately 72g) is placed on the swollen gel in the barrel, and the barrel is lifted from the test solution. The barrel, lifted from the test solution, is placed on a JIS standard sieve with a mesh size of 2000μm. Here, when the barrel is lifted from the test solution and placed on the JIS standard sieve, the solution present in the barrel that the swollen gel failed to retain, i.e., the residual liquid, is removed from the bottom of the barrel. In other words, the residual liquid that the swollen gel failed to retain is removed.

[0290] The barrel was left to stand on the JIS standard sieve for 1 minute to remove residual water from the swollen gel particles. In other words, from the start of the dehydration process, i.e., the moment the barrel was placed on the JIS standard sieve, after 1 minute, the barrel reached a state where no water droplets fell from the measuring device for 5 seconds. Then, the weight of the barrel, the swollen gel, and the piston was measured. If water droplets were present on the bottom and / or sides of the barrel at this time, they were removed using wiping paper (CRECIA S-200, Nippon Paper) before the weight was measured. The resulting weight of the barrel, the swollen gel, and the piston was set as W. b [g]. Using the aforementioned W0, W a and W b And based on the following formula (1'), the SRC(NP) of the particulate absorbent constituting the sample is calculated. Additionally, the (W) of formula (1') described later... b [g]-W a [g]), is the weight of the swollen gel after standing in step (b): W1[g]:

[0291] SRC(NP)[g / g]=(W b [g]-W a [g]) / W0[g](1').

[0292] (b) Method for determining SRC (4.83 kPa)

[0293] The SRC (4.83 kPa) was determined using the barrel, piston, and weight described in U.S. Patent Publication No. 8269060 for the Gel Bed Permeability test. Additionally, a 400-mesh metal mesh was mounted on the bottom of the barrel, which could attract or expel the test solution and exudate described later without leakage of the granular absorbent and swollen gel.

[0294] First, the total weight of the barrel, the piston, and the weight used to measure the SRC (4.83 kPa) is measured, and its value is set as W. c [g]. Next, approximately 0.9g of the granular absorbent sample to be tested was measured and evenly distributed on the bottom surface of the barrel. Here, the accurate weight of the sample is set as W0[g]. Next, the barrel was immersed in a large excess of 0.9% sodium chloride aqueous solution, which had been adjusted to 23±1°C, as the test solution. The evenly distributed sample was then brought into contact with the test solution for 10 minutes, allowing the sample to absorb the test solution and swell without applying a load, thus obtaining a swollen gel.

[0295] Next, a piston (approximately 72g) is placed on the swollen gel in the barrel, and the barrel is lifted from the test solution. The barrel, lifted from the test solution, is placed on a JIS standard sieve with a mesh size of 2000μm. Here, when the barrel is lifted from the test solution and placed on the JIS standard sieve, the solution present in the barrel that the swollen gel failed to retain, i.e., the residual liquid, is removed from the bottom of the barrel. In other words, the residual liquid that the swollen gel failed to retain is removed.

[0296] The barrel is left to stand on the JIS standard sieve for 1 minute to remove residual water from the swollen gel particles. In other words, from the start of the dehydration process, i.e., the moment the barrel is placed on the JIS standard sieve, after 1 minute, no water droplets fall from the measuring device for 5 seconds. Then, the weight (approximately 1316 g) is applied to the piston. At this time, the load applied to the swollen gel is 4.83 kPa. Through this operation, the solution that could be held between the swollen gel particles before pressurization seeps out. A portion of the seeped solution, i.e., the exudate, seeps to the lower part of the swollen gel, i.e., the bottom surface of the barrel, and is dehydrated from this bottom surface. On the other hand, the residual portion of the exudate accumulates on the upper side of the swollen gel, i.e., the upper part of the piston. After the weight is placed on the piston for 1 minute, the seepage of the exudate stops and becomes stable, so the residual portion of the exudate accumulated on the upper part of the piston is quickly removed using a pipette. As described above, after removing the exudate from the swollen gel, the weights of the barrel, piston, weight, and swollen gel are measured. If water droplets are present on the bottom and / or sides of the barrel, these droplets are removed using wiping paper (CRECIA S-200 from Nippon Paper) before measuring the weight. The resulting weights of the barrel, piston, weight, and swollen gel are denoted as W. d [g]. Using the aforementioned W0, W c and W d And based on the following equation (2'), the SRC (4.83 kPa) of the particulate absorbent constituting the sample was calculated. Additionally, the (W) of equation (2') described later... d [g]-W c [g]), is the weight of the swollen gel after removing the exudate in step (d'): W2[g]:

[0297] SRC(4.83kPa)[g / g]=(W d [g]-W c [g]) / W0[g](2').

[0298] (c) Methods for determining CRC

[0299] According to the EDANA method (ERT441.2-02), the centrifuge retention capacity (water absorption ratio without pressure, CRC) of granular water absorbents or water-absorbing resins was determined.

[0300] (d) Particle size distribution (particle size distribution, weight-average particle size (D50), logarithmic standard deviation of particle size distribution (σζ))

[0301] According to “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution” described in columns 27 and 28 of U.S. Patent No. 7638570, the particle size distribution (particle size distribution, weight-average particle size (D50), and logarithmic standard deviation of particle size distribution (σζ)) of granular water absorbents or water-absorbing resins were determined.

[0302] (e) Method for determining water absorption rate (eddy current method)

[0303] To 1000 parts by weight of a pre-prepared 0.90 wt% sodium chloride aqueous solution, add 0.02 parts by weight of Edible Blue No. 1 (as a food additive), and adjust the liquid temperature to 30°C. Measure 50 ml of the blue-colored 0.90 wt% sodium chloride aqueous solution into a 100 ml beaker, and stir at 600 rpm using a cylindrical stirrer (40 mm long, 8 mm wide). During this stirring period, add 2.00 g of granular absorbent, and measure the water absorption time (seconds). Regarding the endpoint, according to the standard described in JISK 7224-1996 "Explanation of the Test Method for Water Absorption Rate of Superabsorbent Resins," the water absorption rate (seconds) is measured as the time from when the absorbent absorbs physiological saline until the test solution covers the stirrer tip.

[0304] (f) Methods for measuring surface tension (STR)

[0305] 50 ml of physiological saline, adjusted to 20°C, and a 25 mm long fluoropolymer rotor, thoroughly cleaned, were added to a 100 ml beaker. First, the surface tension of the physiological saline was measured using a surface tension meter (KRUSS K11 automatic surface tension meter). The measurement confirmed that the surface tension value was in the range of 71–75 [mN / m].

[0306] Next, 0.5 g of granular absorbent was added to a beaker containing physiological saline that had been adjusted to 20°C for surface tension measurement, and the mixture was stirred at 500 rpm for 4 minutes. After 4 minutes, stirring was stopped, and after the aqueous granular absorbent settled, the same procedure as for measuring the surface tension of physiological saline alone was performed to measure the surface tension of the supernatant. Furthermore, in this embodiment, a platinum plate method was used. The plates were thoroughly cleaned with deionized water and heated with a gas burner before each measurement.

[0307] (g) Method for determining the absorption capacity of absorbents

[0308] <The Creation of Absorber A>

[0309] Two 2.8g sheets of absorbent cotton (8cm x 16cm cut cotton manufactured by Kawamoto Sangyo Co., Ltd.) are evenly torn along the surface of an 80mm x 160mm piece of absorbent cotton. Next, absorbent paper is cut into 200mm x 200mm pieces, and an 8cm x 16cm frame is placed near the center of each piece. One of the 2.8g absorbent cotton sheets is placed inside the frame, and its upper surface is smoothed using an acrylic sheet or similar material. 3g of granular absorbent is evenly distributed on this upper surface, and then the other 2.8g absorbent cotton sheet is placed on top, creating a sandwich structure. A 10kg load is then applied to the entire frame and held for 1 minute to form an absorbent core. The load and frame are then removed, and the two ends of the absorbent paper are folded back along the length of the absorbent core to wrap it. The obtained absorbent was placed inside a nonwoven bag (10cm×22cm) made of Heatron paper and the surrounding area was heat-sealed to produce absorbent A.

[0310] <Determination of Absorption Capacity of Absorbers>

[0311] Add a 0.9% sodium chloride aqueous solution to a deep tank to a depth of at least 5 cm, and adjust the liquid temperature in the tank to 25°C. Immerse absorbent A in the tank and leave it for 10 minutes without applying a load to allow absorbent A to swell. After swelling, remove the swollen absorbent A from the tank while keeping it level with the liquid surface, and place it directly on a JIS standard sieve with a diameter of 45 cm and a mesh size of 2000 μm while maintaining this level position. Next, place an acrylic plate on the portion of absorbent A with 8 cm × 16 cm of granular absorbent material on its upper surface, and place a weight (6405 g total weight of the acrylic plate) on top of it, and perform dehydration for 1 minute. Apply a pressure of 50 g / cm² to the portion of absorbent A containing the acrylic plate through the acrylic plate and the weight. 2 The weight of absorbent A after liquid removal is measured, and the difference between this weight and the pre-measured weight of absorbent A before impregnation is calculated as the "absorption amount of absorbent". The calculated values ​​are shown in Table 2.

[0312] (h) Method for determining the reflux flow rate from the absorber

[0313] <How to make absorber B>

[0314] Ethylene tape (Nitto Denko Corporation 21-100TM) was cut into 100mm x 200mm pieces, with the adhesive side facing up, and an 80mm x 160mm frame was placed on top. An 80mm x 160mm piece of degreased cotton (Kawamoto Sangyo Co., Ltd. 8cm x 16cm cut cotton) was evenly torn along the surface to create a 2.8g degreased cotton sheet, which was then placed inside the frame. Next, 1.5g of granular absorbent was evenly distributed onto the degreased cotton sheet inside the frame. The frame was removed, and a 100mm x 200mm piece of breathable nonwoven fabric was placed on top of the granular absorbent. The outer periphery of this breathable nonwoven fabric was then bonded to the ethylene tape to form absorbent body B.

[0315] <Determination of the reflux flow rate from the absorber>

[0316] 70 mL of a 0.9% sodium chloride aqueous solution was added to the center of absorber B. The sodium chloride aqueous solution was added using a liquid injection device. This device consisted of an 80 mm × 160 mm plate with a central circular hole of 20 mm inner diameter and a cylindrical section of 20 mm inner diameter and 80 mm length. The inner side of the cylinder communicated with the circular hole. The liquid injection device was positioned on the 8 cm × 16 cm portion (the center) of the upper surface of absorber B containing granular absorbent. Using a funnel at a flow rate of 7 mL / sec, the sodium chloride aqueous solution was injected into the center of absorber B through the cylinder and the circular hole. Ten minutes after the initial injection of the sodium chloride aqueous solution, 30 sheets of pre-weighed 80 mm × 80 mm filter paper were stacked and placed in the center. A 3200 g weight was applied to the entire filter paper for 1 minute. At this time, liquid seeped out from absorber B and was absorbed by the filter paper. The filter paper used was ADVANTEC model No. 2, cut from 100mm × 100mm to 80mm × 80mm. The difference between the weight of the filter paper before use and the weight of the filter paper after absorbing the liquid was calculated as the "recirculation flow from the absorber". The calculated values ​​are shown in Table 2.

[0317] [Manufacturing Example 1]

[0318] A monomer aqueous solution was prepared, consisting of 300 parts by weight of acrylic acid, 123.6 parts by weight of 48% sodium hydroxide aqueous solution, 0.44 parts by weight of polyethylene glycol diacrylate (average n number 9) (hereinafter referred to as "PEGDA-9"), 1.18 parts by weight of 31% ethylenediaminetetramethylenephosphonic acid aqueous solution, and 331.8 parts by weight of deionized water (1).

[0319] Next, the monomer aqueous solution (1), which has been heated to 41°C, is continuously supplied by a metering pump to a continuous polymerizer having a planar polymerization belt with weirs at both ends for polymerization. Before being supplied to the continuous polymerizer, 127.0 parts by weight of a 48% by weight sodium hydroxide aqueous solution is continuously mixed into the monomer aqueous solution (1) using a pipeline mixer. After mixing, the liquid temperature of the mixture of the monomer aqueous solution (1) and the 48% by weight sodium hydroxide aqueous solution rises to 80°C due to the heat of neutralization.

[0320] In the obtained monomer aqueous solution (1), 10.6 parts by weight of a 5% sodium persulfate aqueous solution were continuously mixed using a pipeline mixer to obtain a mixture. This mixture was continuously fed to the continuous polymerizer, so that the liquid depth on the polymerization belt was 10 mm. A polymerization reaction occurred on the polymerization belt to obtain a strip-shaped hydrogel (1). The polymerization time was 3 minutes. The obtained strip-shaped hydrogel (1) was continuously cut at equal intervals in the width direction relative to the direction of travel of the polymerization belt, with a cutting length of 300 mm, to obtain the hydrogel (1).

[0321] The hydrogel (1) was fed into a screw extruder for gel pulverization. The screw extruder was a meat grinder with a perforated plate at the front end having a diameter of 100 mm, a hole diameter of 4.0 mm, 207 holes, and a thickness of 10 mm, and a screw shaft outer diameter of 86 mm. With the screw shaft speed of the meat grinder set to 130 rpm, the hydrogel (1) was simultaneously supplied to the meat grinder at 4640 g / min and water vapor at 83 g / min. Thus, the hydrogel (1) was pulverized. Finally, a pulverized gel, i.e., granular hydrogel (1), was obtained. The gel pulverization energy (GGE) in the gel pulverization was 29.3 J / g.

[0322] The granular hydrogel (1) was spread on a 50-mesh metal mesh and dried with hot air at 180°C for 30 minutes to obtain dried product A (1). The dried product A (1) was pulverized using a roller mill (WML type roller mill / Inoguchi Giken Co., Ltd.) to obtain pulverized product (1). The pulverized product (1) was then sieved using a JIS sieve with mesh sizes of 850μm, 600μm, 500μm, 300μm, 150μm, and 45μm.

[0323] Finally, irregularly broken water-absorbing resin particles (1) were obtained. The physical properties of the water-absorbing resin particles (1) were determined by the method described above. Finally, the mass-average particle size (D50) of the water-absorbing resin particles (1) was 358 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.36, and the centrifuge holding capacity (CRC) was 53.4 (g / g).

[0324] [Manufacturing Example 2]

[0325] 0.36 parts by weight of polyethylene glycol diacrylate with an average n number of 4 were used instead of 0.44 parts by weight of PEGDA-9. Furthermore, 0.82 parts by weight of a 45% by weight aqueous solution of diethylenetriaminepentaacetic acid were used instead of 1.18 parts by weight of a 31% by weight aqueous solution of ethylenediaminetetramethylenephosphonic acid. Otherwise, irregularly broken hydroabsorbent resin particles were obtained by the same method as in Manufacturing Example 1. These hydroabsorbent resin particles were designated as hydroabsorbent resin particles (2). The gel pulverization energy (GGE) in the gel pulverization of Manufacturing Example 2 was 27.9 [J / g]. The physical properties of the hydroabsorbent resin particles (2) were determined by the aforementioned method. Ultimately, the mass-average particle size (D50) of the hydroabsorbent resin particles (2) was 337 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.34, and the centrifuge holding capacity (CRC) was 56.1 (g / g).

[0326] [Manufacturing Example 3]

[0327] The amount of PEGDA-9 was changed to 0.52 parts by weight. Furthermore, 1.83 parts by weight of a 1% diethylenetriaminepentaacetic acid aqueous solution was used instead of 1.18 parts by weight of a 31% ethylenediaminetetramethylenephosphonic acid aqueous solution. Furthermore, the amount of deionized water was changed to 332.9 parts by weight. Otherwise, irregularly broken water-absorbing resin particles were obtained by the same method as in Manufacturing Example 1. These water-absorbing resin particles were designated as water-absorbing resin particles (3). The gel pulverization energy (GGE) in the gel pulverization of Manufacturing Example 3 was 31.1 [J / g]. The physical properties of the water-absorbing resin particles (3) were determined by the aforementioned method. Ultimately, the mass-average particle size (D50) of the water-absorbing resin particles (3) was 346 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.35, and the centrifuge holding capacity (CRC) was 51.1 (g / g).

[0328] [Manufacturing Example 4]

[0329] The perforated plate at the front end of the screw extruder was modified to have a perforation diameter of 9.5 mm and 40 perforations. Otherwise, irregularly broken water-absorbing resin particles were obtained using the same method as in Manufacturing Example 1. These water-absorbing resin particles were designated as water-absorbing resin particles (4). The gel pulverization energy (GGE) in the gel pulverization of Manufacturing Example 4 was 8.3 [J / g]. The physical properties of the water-absorbing resin particles (4) were determined using the aforementioned method. Ultimately, the mass-average particle size (D50) of the water-absorbing resin particles (4) was 341 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.34, and the centrifuge holding capacity (CRC) was 53.7 (g / g).

[0330] [Manufacturing Example 5]

[0331] The perforated plate at the front end of the screw extruder was modified to have a perforation diameter of 9.5 mm and 40 perforations. Otherwise, irregularly broken water-absorbing resin particles were obtained using the same method as in Manufacturing Example 2. These water-absorbing resin particles were designated as water-absorbing resin particles (5). The gel pulverization energy (GGE) in the gel pulverization of Manufacturing Example 5 was 7.2 [J / g]. The physical properties of the water-absorbing resin particles (5) were determined using the aforementioned method. Ultimately, the mass-average particle size (D50) of the water-absorbing resin particles (5) was 353 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.36, and the centrifuge holding capacity (CRC) was 56.3 (g / g).

[0332] [Manufacturing Example 6]

[0333] The perforated plate at the front end of the screw extruder was modified to have a perforation diameter of 9.5 mm and 40 perforations. Otherwise, irregularly broken water-absorbing resin particles were obtained using the same method as in Manufacturing Example 3. These water-absorbing resin particles were designated as water-absorbing resin particles (6). The gel pulverization energy (GGE) in the gel pulverization of Manufacturing Example 6 was 9.8 [J / g]. The physical properties of the water-absorbing resin particles (6) were determined using the aforementioned method. Ultimately, the mass-average particle size (D50) of the water-absorbing resin particles (6) was 338 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.34, and the centrifuge holding capacity (CRC) was 50.9 (g / g).

[0334] [Manufacturing Example 7]

[0335] Referring to Example 12-1 of International Publication No. 2017 / 170605, water-absorbing resin particles (7) were manufactured.

[0336] [Manufacturing Example 8]

[0337] Using Examples 1-13 of International Publication No. 2021 / 201177, water-absorbing resin particles (8) were manufactured.

[0338] [Manufacturing Example 9]

[0339] Except for the following changes, irregularly broken water-absorbing resin particles (9) were obtained by the same method as in manufacturing example 1.

[0340] The amount of PEGDA-9 was changed to 0.63 parts by weight. Furthermore, 1.83 parts by weight of a 1% diethylenetriaminepentaacetic acid aqueous solution was used instead of 1.18 parts by weight of a 31% ethylenediaminetetramethylenephosphonic acid aqueous solution. Additionally, 1.83 parts by weight of a 60% sodium lactate aqueous solution was added as a raw material for the monomer aqueous solution (1), and the amount of deionized water was changed to 328.3 parts by weight.

[0341] The gel pulverization energy (GGE) in the gel pulverization of Example 9 was 29.0 [J / g]. The physical properties of the superabsorbent resin particles (9) were determined using the method described above. The mass-average particle size (D50) of the superabsorbent resin particles (9) was 350 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.37, and the centrifuge hold-up capacity (CRC) was 53.1 (g / g).

[0342] [Manufacturing Example 10]

[0343] Except for the following changes, irregularly broken water-absorbing resin particles (10) were obtained by the same method as in manufacturing example 1.

[0344] The amount of PEGDA-9 was changed to 0.50 parts by weight. Furthermore, 1.83 parts by weight of a 1% diethylenetriaminepentaacetic acid aqueous solution was used instead of 1.18 parts by weight of a 31% ethylenediaminetetramethylenephosphonic acid aqueous solution. Additionally, 2.93 parts by weight of a 50% malic acid aqueous solution was added as a raw material for the monomer aqueous solution (1), and the amount of deionized water was changed to 327.1 parts by weight.

[0345] The gel pulverization energy (GGE) in the gel pulverization of Manufacturing Example 10 was 28.1 [J / g]. The physical properties of the superabsorbent resin particles (10) were determined using the method described above. The mass-average particle size (D50) of the superabsorbent resin particles (10) was 342 μm, the logarithmic standard deviation (σζ) of the particle size distribution was 0.36, and the centrifuge hold-up capacity (CRC) was 54.0 (g / g).

[0346] [Example 1]

[0347] The surface crosslinking agent solution was uniformly mixed into the water-absorbing resin particles (1) obtained in Manufacturing Example 1. Then, the resulting mixture was heated at 190°C for 30 minutes to obtain the water-absorbing resin (1). The surface crosslinking agent solution was a solution composed of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water relative to 100 parts by weight of the water-absorbing resin particles (1).

[0348] Then, 30g of the cooled absorbent resin (1) was placed in a glass container with a diameter of 6cm and a height of 11cm, and placed in a paint mixer (No. 488 experimental disperser, manufactured by Toyo Seiki Co., Ltd.). The paint mixer was then vibrated at 800 cycles / min for 30 minutes. Then, an EDTMP·5Na aqueous solution was uniformly mixed into the vibrated absorbent resin (1) at 100 parts by weight relative to 100 parts by weight. Furthermore, when the weight of the absorbent resin (1) was set to 100 parts by weight, the EDTMP·5Na aqueous solution was an aqueous solution composed of 1 part by weight of water and 0.01 parts by weight of sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP·5Na).

[0349] Next, an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution, relative to 100 parts by weight of the absorbent resin (1), was uniformly mixed into the absorbent resin (1) containing the EDTMP·5Na aqueous solution. Furthermore, the cationic colloidal silica aqueous solution is, under the trade name: Klebosol 30CAL25 30% aqueous solution, manufactured by AZ Electronic Material Co., Ltd. / containing aluminum cations in silica microparticles.

[0350] The resulting mixture was dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850 μm to obtain granular water absorbent (1). The physical properties of the granular water absorbent (1) were determined using the method described above. The results are shown in Table 2 below.

[0351] [Example 2]

[0352] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (2).

[0353] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.31 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water was used relative to 100 parts by weight of the water-absorbing resin particles (2). • An aqueous solution consisting of 1 part by weight of water, 0.03 parts by weight of EDTMP·5Na, and 0.05 parts by weight of sodium bisulfite was used instead of the EDTMP·5Na aqueous solution.

[0354] • A solution consisting of 1.0 parts by weight of water and 1.5 parts by weight of alumina sol aqueous solution is used instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol and 1.5 parts by weight of cationic colloidal silica aqueous solution.

[0355] Using the method described above, the physical properties of the granular water absorbent (2) were determined. The results are shown in Table 2 below. In addition, the alumina sol aqueous solution used was a product of the trade name: Alumina Sol 520-A (20.5% aqueous solution of alumina, manufactured by Nissan Chemical Co., Ltd.).

[0356] [Example 3]

[0357] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (3).

[0358] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol and 3.2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (1).

[0359] • The mixture obtained by uniformly mixing the water-absorbing resin particles (1) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0360] • Change the vibration time of the paint mixer from 30 minutes to 10 minutes.

[0361] • Use a polyethylene glycol aqueous solution consisting of 1 part by weight of water and 0.03 parts by weight of polyethylene glycol (average molecular weight 400) instead of an EDTMP·5Na aqueous solution.

[0362] • Without using an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution, the mixture of the polyethylene glycol aqueous solution and the water-absorbing resin is dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850 μm.

[0363] • After passing through a JIS standard sieve, 0.3 parts by weight of silica (trade name: Aerosil 200, manufactured by Aerosil Corporation of Japan) are then uniformly mixed.

[0364] The physical properties of the granular water absorbent (3) were determined using the method described above. The results are shown in Table 2 below.

[0365] [Example 4]

[0366] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (4).

[0367] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, 2.7 parts by weight of deionized water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate is used relative to 100 parts by weight of the water-absorbing resin particles (1).

[0368] • The mixture obtained by uniformly mixing the water-absorbing resin particles (1) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0369] • Change the vibration time of the paint mixer from 30 minutes to 10 minutes.

[0370] • Use a polyethylene glycol aqueous solution consisting of 1 part by weight of water, 0.12 parts by weight of polyethylene glycol (average molecular weight 600), and 0.03 parts by weight of sodium sulfite to replace the EDTMP·5Na aqueous solution.

[0371] Instead of using an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica, the mixture of the polyethylene glycol aqueous solution and the water-absorbing resin is dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850 μm.

[0372] Using the method described above, the physical properties of the granular water absorbent (4) were determined. The results are shown in Table 2 below.

[0373] [Example 5]

[0374] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (5).

[0375] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (1).

[0376] • Use a polyethylene glycol aqueous solution consisting of 1 part by weight of water and 0.1 part by weight of polyethylene glycol (average molecular weight 400) instead of an EDTMP·5Na aqueous solution.

[0377] • Use an aqueous solution of aluminum sulfate consisting of 1.5 parts by weight of water and 0.5 parts by weight of 14-18 hydrate of aluminum sulfate instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol and 1.5 parts by weight of cationic colloidal silica.

[0378] Using the method described above, the physical properties of the granular water absorbent (5) were determined. The results are shown in Table 2 below.

[0379] [Example 6]

[0380] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (6).

[0381] • Use the water-absorbing resin particles (2) prepared in Manufacturing Example 2 instead of the water-absorbing resin particles (1).

[0382] • Use an aqueous solution of DTPA·3Na, consisting of 2.0 parts by weight of water, 0.02 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), and 0.1 parts by weight of sodium sulfite, instead of an aqueous solution of EDTMP·5Na.

[0383] • Without using an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution, the mixture of the DTPA·3Na aqueous solution and the water-absorbing resin is dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850μm.

[0384] • After passing through a JIS standard sieve, 0.3 parts by weight of hydrotalcite (trade name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) are then uniformly mixed.

[0385] The physical properties of the granular water absorbent (6) were determined using the method described above. The results are shown in Table 2 below.

[0386] [Example 7]

[0387] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (7).

[0388] • Use the water-absorbing resin particles (2) prepared in Manufacturing Example 2 instead of the water-absorbing resin particles (1).

[0389] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol and 2.7 parts by weight of deionized water was used relative to 100 parts by weight of the water-absorbing resin particles (2).

[0390] • The mixture obtained by uniformly mixing the water-absorbing resin particles (2) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0391] • Change the vibration time of the paint mixer from 30 minutes to 10 minutes.

[0392] • Use an aqueous solution of sodium bisulfite consisting of 0.5 parts by weight of water and 0.03 parts by weight of sodium bisulfite instead of an aqueous solution of EDTMP·5Na.

[0393] • A solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of alumina sol aqueous solution is used instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution.

[0394] Using the method described above, the physical properties of the granular water absorbent (7) were determined. The results are shown in Table 2 below. In addition, the alumina sol aqueous solution used was a product of the trade name: Alumina Sol 520-A (20.5% aqueous solution of alumina, manufactured by Nissan Chemical Co., Ltd.).

[0395] [Example 8]

[0396] Except for the following aspects, the same operation as in Example 1 was performed to obtain the granular water absorbent (8).

[0397] • Use the water-absorbing resin particles (2) prepared in Manufacturing Example 2 instead of the water-absorbing resin particles (1).

[0398] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.31 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water was used relative to 100 parts by weight of the water-absorbing resin particles (2). • The vibration time of the paint agitator was changed from 30 minutes to 10 minutes.

[0399] • Without using EDTMP·5Na aqueous solution, a mixture of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol and 1.5 parts by weight of cationic colloidal silica aqueous solution and a water-absorbing resin is dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850μm.

[0400] The physical properties of the granular water absorbent (8) were determined using the method described above. The results are shown in Table 2 below.

[0401] [Example 9]

[0402] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (9).

[0403] • Use the water-absorbing resin particles (2) prepared in Manufacturing Example 2 instead of the water-absorbing resin particles (1).

[0404] • Use an aqueous solution of DTPA·3Na, consisting of 1.5 parts by weight of water and 0.01 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), instead of an aqueous solution of EDTMP·5Na.

[0405] • Use an aqueous solution of aluminum sulfate consisting of 1.5 parts by weight of water, 1.0 parts by weight of propylene glycol, and 0.5 parts by weight of 14-18 hydrate of aluminum sulfate instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica.

[0406] The physical properties of the granular water absorbent (9) were determined using the method described above. The results are shown in Table 2 below.

[0407] [Example 10]

[0408] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (10).

[0409] • Use the water-absorbing resin particles (2) prepared in Manufacturing Example 2 instead of the water-absorbing resin particles (1).

[0410] • A mixed solution consisting of 2.0 parts by weight of water, 0.01 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 0.05 parts by weight of sodium sulfite, and 0.03 parts by weight of polyethylene glycol (average molecular weight 600) was used instead of the aqueous solution of EDTMP·5Na.

[0411] • Do not use an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution. Dry the mixture of the mixed solution and the water-absorbing resin at 60°C for 1 hour, and then pass it through a JIS standard sieve with a mesh size of 850 μm.

[0412] • After passing through a JIS standard sieve, 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) are then uniformly mixed.

[0413] Using the method described above, the physical properties of the granular water absorbent (10) were determined. The results are shown in Table 2 below.

[0414] [Example 11]

[0415] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (11).

[0416] • Use the water-absorbing resin particles (3) prepared in Manufacturing Example 3 instead of the water-absorbing resin particles (1).

[0417] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 2.45 parts by weight of propylene glycol, 3.55 parts by weight of deionized water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate was used relative to 100 parts by weight of the water-absorbing resin particles (3).

[0418] • The mixture obtained by uniformly mixing the water-absorbing resin particles (3) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0419] • Change the vibration time of the paint mixer from 30 minutes to 10 minutes.

[0420] • Use an aqueous solution of DTPA·3Na, consisting of 1.5 parts by weight of water, 0.15 parts by weight of polyethylene glycol (average molecular weight 400), and 0.03 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), instead of an aqueous solution of EDTMP·5Na.

[0421] • Without using an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution, the mixture of the DTPA·3Na aqueous solution and the water-absorbing resin is dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850μm.

[0422] The physical properties of the granular water absorbent (11) were determined using the method described above. The results are shown in Table 2 below.

[0423] [Example 12]

[0424] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (12).

[0425] • Use the water-absorbing resin particles (3) prepared in Manufacturing Example 3 instead of the water-absorbing resin particles (1).

[0426] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (3).

[0427] • A mixed solution consisting of 1.5 parts by weight of water, 0.05 parts by weight of polyethylene glycol (average molecular weight 600), 0.05 parts by weight of sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP·5Na), and 0.1 parts by weight of sodium sulfite was used instead of the aqueous solution of EDTMP·5Na.

[0428] • A solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of alumina sol aqueous solution is used instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution.

[0429] The physical properties of the granular water absorbent (12) were determined using the method described above. The results are shown in Table 2 below.

[0430] [Example 13]

[0431] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (13).

[0432] • Use the water-absorbing resin particles (3) prepared in Manufacturing Example 3 instead of the water-absorbing resin particles (1).

[0433] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol and 3.2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (3).

[0434] • The mixture obtained by uniformly mixing the water-absorbing resin particles (3) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0435] • Use an aqueous solution of DTPA·3Na, consisting of 1 part by weight of water and 0.02 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), instead of an aqueous solution of EDTMP·5Na.

[0436] • Use an aqueous solution consisting of 1.0 parts by weight of water and 1.5 parts by weight of cationic colloidal silica aqueous solution instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol and 1.5 parts by weight of cationic colloidal silica aqueous solution.

[0437] The physical properties of the granular water absorbent (13) were determined using the method described above. The results are shown in Table 2 below.

[0438] [Comparative Example 1]

[0439] Using the absorbent resin particles (4) prepared in Manufacturing Example 4 instead of the absorbent resin particles (1), the same method as in Example 1 was performed to manufacture the comparative granular absorbent (1). The physical properties of the comparative granular absorbent (1) were determined using the method described above. The results are shown in Table 2 below.

[0440] [Comparative Example 2]

[0441] Using the absorbent resin particles (4) prepared in Manufacturing Example 4 instead of the absorbent resin particles (1), the same method as in Example 3 was performed to manufacture a comparative granular absorbent (2). The physical properties of the comparative granular absorbent (2) were determined using the method described above. The results are shown in Table 2 below.

[0442] [Comparative Example 3]

[0443] Using the absorbent resin particles (4) prepared in Manufacturing Example 4 instead of the absorbent resin particles (1), the same method as in Example 5 was performed to manufacture a comparative granular absorbent (3). The physical properties of the comparative granular absorbent (3) were determined using the method described above. The results are shown in Table 2 below.

[0444] [Comparative Example 4]

[0445] Using the absorbent resin particles (5) prepared in Manufacturing Example 5 instead of the absorbent resin particles (2), the same method as in Example 6 was performed to manufacture a comparative granular absorbent (4). The physical properties of the comparative granular absorbent (4) were determined using the method described above. The results are shown in Table 2 below.

[0446] [Comparative Example 5]

[0447] Using the absorbent resin particles (5) prepared in Manufacturing Example 5 instead of the absorbent resin particles (2), the same method as in Example 9 was performed to manufacture the comparative granular absorbent (5). The physical properties of the comparative granular absorbent (5) were determined using the method described above. The results are shown in Table 2 below.

[0448] [Comparative Example 6]

[0449] Using the absorbent resin particles (6) prepared in Manufacturing Example 6 instead of the absorbent resin particles (3), the same method as in Example 12 was performed to manufacture a comparative granular absorbent (6). The physical properties of the comparative granular absorbent (6) were determined using the method described above. The results are shown in Table 2 below.

[0450] [Comparative Example 7]

[0451] A comparative granular absorbent (7) was manufactured by performing the same procedures as in Example 7 of International Publication No. 2017 / 170605. The physical properties of the comparative granular absorbent (7) were determined using the described method. The results are shown in Table 2 below.

[0452] [Comparative Example 8]

[0453] A comparative granular absorbent (8) was manufactured by performing the same procedures as in Example 12-1 of International Publication No. 2017 / 170605. The physical properties of the comparative granular absorbent (8) were determined using the described method. The results are shown in Table 2 below.

[0454] [Comparative Example 9]

[0455] A comparative granular absorbent (9) was manufactured by performing the same procedures as in Examples 1-13 of International Publication No. 2021 / 201177. The physical properties of the comparative granular absorbent (9) were determined using the described method. The results are shown in Table 2 below.

[0456] [Example 14]

[0457] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (14).

[0458] • Use the water-absorbing resin particles (9) prepared in Manufacturing Example 9 instead of the water-absorbing resin particles (1).

[0459] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol and 2.7 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (9).

[0460] • The mixture obtained by uniformly mixing the water-absorbing resin particles (9) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0461] • Use an aqueous solution of DTPA·3Na, consisting of 1.5 parts by weight of water and 0.02 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), instead of an aqueous solution of EDTMP·5Na.

[0462] • An aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of alumina sol aqueous solution is used instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution.

[0463] Using the method described above, the physical properties of the granular water absorbent (14) were determined. The results are shown in Table 2 below. In addition, the alumina sol aqueous solution used was a product of the trade name: Alumina Sol 520-A (20.5% aqueous solution of alumina, manufactured by Nissan Chemical Co., Ltd.).

[0464] [Example 15]

[0465] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (15).

[0466] • Use the water-absorbing resin particles (9) prepared in Manufacturing Example 9 instead of the water-absorbing resin particles (1).

[0467] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (9).

[0468] • A mixed solution consisting of 0.5 parts by weight of water, 0.05 parts by weight of polyethylene glycol (average molecular weight 400), 0.03 parts by weight of sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP·5Na), and 0.05 parts by weight of sodium sulfite was used instead of the aqueous solution of EDTMP·5Na.

[0469] • Use an aqueous solution consisting of 1.5 parts by weight of water, 1.0 parts by weight of propylene glycol, and 0.5 parts by weight of 14-18 hydrate of aluminum sulfate instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica.

[0470] Using the method described above, the physical properties of the granular water absorbent (15) were determined. The results are shown in Table 2 below.

[0471] [Example 16]

[0472] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (16).

[0473] • Use the water-absorbing resin particles (9) prepared in Manufacturing Example 9 instead of the water-absorbing resin particles (1).

[0474] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol and 3.2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (9).

[0475] • The mixture obtained by uniformly mixing the water-absorbing resin particles (9) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0476] • Change the vibration time of the paint mixer from 30 minutes to 10 minutes.

[0477] • Use an aqueous solution consisting of 1.5 parts by weight of water, 0.07 parts by weight of sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP·5Na), and 0.1 parts by weight of sodium sulfite instead of the aqueous solution of EDTMP·5Na.

[0478] • Do not use an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution. Dry the mixture of the aqueous solution and the water-absorbing resin at 60°C for 1 hour, and then pass it through a JIS standard sieve with a mesh size of 850 μm.

[0479] • After passing through a JIS standard sieve, 0.3 parts by weight of hydrotalcite (trade name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) are then uniformly mixed.

[0480] The physical properties of the granular water absorbent (16) were determined using the method described above. The results are shown in Table 2 below.

[0481] [Example 17]

[0482] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (17).

[0483] • Use the water-absorbing resin particles (10) prepared in Manufacturing Example 10 instead of the water-absorbing resin particles (1).

[0484] • As a surface crosslinking agent solution, a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol and 3.2 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (10).

[0485] • The mixture obtained by uniformly mixing the water-absorbing resin particles (10) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0486] • Use a mixed solution consisting of 1.5 parts by weight of water, 0.03 parts by weight of polyethylene glycol (average molecular weight 600), and 0.05 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) instead of an aqueous solution of EDTMP·5Na.

[0487] • Use an aqueous solution consisting of 1.0 parts by weight of water and 1.5 parts by weight of cationic colloidal silica aqueous solution instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol and 1.5 parts by weight of cationic colloidal silica aqueous solution.

[0488] Using the method described above, the physical properties of the granular water absorbent (17) were determined. The results are shown in Table 2 below.

[0489] [Example 18]

[0490] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (18).

[0491] • Use the water-absorbing resin particles (10) prepared in Manufacturing Example 10 instead of the water-absorbing resin particles (1).

[0492] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol and 2.7 parts by weight of deionized water is used relative to 100 parts by weight of the water-absorbing resin particles (10).

[0493] • The mixture obtained by uniformly mixing the water-absorbing resin particles (10) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0494] • Change the vibration time of the paint mixer from 30 minutes to 10 minutes.

[0495] • Use a mixed solution consisting of 2 parts by weight of water, 0.25 parts by weight of polyethylene glycol (average molecular weight 400), and 0.1 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) instead of an aqueous solution of EDTMP·5Na.

[0496] • Use an aqueous solution of aluminum sulfate consisting of 1.5 parts by weight of water and 0.5 parts by weight of 14-18 hydrate of aluminum sulfate instead of an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol and 1.5 parts by weight of cationic colloidal silica.

[0497] The physical properties of the granular water absorbent (18) were determined using the method described above. The results are shown in Table 2 below.

[0498] [Example 19]

[0499] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (19).

[0500] • Use the water-absorbing resin particles (10) prepared in Manufacturing Example 10 instead of the water-absorbing resin particles (1).

[0501] • As a surface crosslinking agent solution, a solution consisting of 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, 2.7 parts by weight of deionized water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate is used relative to 100 parts by weight of the water-absorbing resin particles (10).

[0502] • The mixture obtained by uniformly mixing the water-absorbing resin particles (10) with the surface crosslinking agent is heated at 100°C for 40 minutes instead of heated at 190°C for 30 minutes.

[0503] • Use a mixed solution consisting of 2 parts by weight of water, 0.2 parts by weight of polyethylene glycol (average molecular weight 600), 0.07 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), and 0.1 parts by weight of sodium sulfite instead of the aqueous solution of EDTMP·5Na.

[0504] • Do not use an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution. Dry the mixture of the mixed solution and the water-absorbing resin at 60°C for 1 hour, and then pass it through a JIS standard sieve with a mesh size of 850 μm.

[0505] The physical properties of the granular water absorbent (19) were determined using the method described above. The results are shown in Table 2 below.

[0506] [Example 20]

[0507] Except for the following aspects, the same operation as in Example 1 was performed to obtain granular water absorbent (20).

[0508] • Use the water-absorbing resin particles (10) prepared in Manufacturing Example 10 instead of the water-absorbing resin particles (1).

[0509] • Use an aqueous solution consisting of 1 part by weight of water, 0.07 parts by weight of sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP·5Na), and 0.03 parts by weight of sodium bisulfite instead of the aqueous solution of EDTMP·5Na.

[0510] • Do not use an aqueous solution consisting of 1.0 parts by weight of water, 1.0 parts by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution. Dry the mixture of the aqueous solution and the water-absorbing resin at 60°C for 1 hour, and then pass it through a JIS standard sieve with a mesh size of 850 μm.

[0511] • After passing through a JIS standard sieve, 0.3 parts by weight of silica (trade name: Aerosil 200, manufactured by Aerosil Corporation of Japan) are then uniformly mixed.

[0512] Using the method described above, the physical properties of the granular water absorbent (20) were determined. The results are shown in Table 2 below.

[0513] [Comparative Example 10]

[0514] The surface crosslinking agent solution was uniformly mixed into the water-absorbing resin particles (6) obtained in Manufacturing Example 6. Then, the resulting mixture was heated at 190°C for 30 minutes to obtain water-absorbing resin (1). The surface crosslinking agent solution was a solution composed of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water relative to 100 parts by weight of the water-absorbing resin particles (1).

[0515] Then, 30g of the cooled absorbent resin (1) was placed in a glass container with a diameter of 6cm and a height of 11cm, and placed in a paint mixer (No. 488 experimental disperser, manufactured by Toyo Seiki Co., Ltd.). Next, the paint mixer was vibrated at 800 cycles / min for 30 minutes.

[0516] The resulting mixture was dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850 μm to obtain a comparative granular water absorbent (10). The physical properties of the comparative granular water absorbent (10) were determined using the method described above. The results are shown in Table 2 below.

[0517] [Comparative Example 11]

[0518] An aqueous solution of aluminum sulfate was uniformly mixed into the comparative granular absorbent (10) obtained in Comparative Example 10. Furthermore, when the weight of the comparative granular absorbent (10) was set to 100 parts by weight, the aqueous solution of aluminum sulfate was an aqueous solution composed of 1.5 parts by weight of water and 0.5 parts by weight of 14-18 hydrates of aluminum sulfate.

[0519] The resulting mixture was dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850 μm to obtain a comparative granular water absorbent (11). The physical properties of the comparative granular water absorbent (11) were determined using the method described above. The results are shown in Table 2 below.

[0520] [Comparative Example 12]

[0521] An aqueous solution consisting of 1 part by weight of water, 0.01 part by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) and 0.004 parts by weight of polyoxyethylene sorbitan monostearate (trade name: RHEODOL Tw-S120V, manufactured by Kao Corporation) was uniformly mixed into the comparative granular water absorbent (10) obtained in Comparative Example 10.

[0522] Next, the aluminum sulfate aqueous solution is mixed evenly. In addition, when the weight of the comparative granular water absorbent (10) is set to 100 parts by weight, the aluminum sulfate aqueous solution is an aqueous solution composed of 1.5 parts by weight of water and 0.5 parts by weight of 14-18 hydrates of aluminum sulfate.

[0523] The resulting mixture was dried at 60°C for 1 hour and then passed through a JIS standard sieve with a mesh size of 850 μm to obtain a comparative granular water absorbent (12). The physical properties of the comparative granular water absorbent (12) were determined using the method described above. The results are shown in Table 2 below.

[0524] [result]

[0525] The gel pulverizing energy (GGE) of the manufacturing conditions in Manufacturing Examples 1 to 10 and the physical properties of the water-absorbing resin particles (1) to (10) prepared in Manufacturing Examples 1 to 10 are shown in Table 1 below.

[0526] [Table 1]

[0527] Table 1

[0528]

[0529] The physical properties of the granular absorbents (1) to (20) and the comparative granular absorbents (1) to (12) manufactured in Examples 1 to 20 and Comparative Examples 1 to 12 are shown below.

[0530] [Table 2]

[0531] Table 2

[0532]

[0533] As shown in Table 2, the granular absorbents (1) to (20) manufactured in Examples 1 to 20 have an SRC (NP) exceeding 50.0 g / g and an SRC (4.83 kPa) exceeding 41.5 g / g. Therefore, the granular absorbents (1) to (20) conform to the granular absorbents of the present invention. In addition, the water absorption rate (eddy current) of the granular absorbents (1) to (20) is also excellent. On the other hand, the comparative granular absorbents (1) to (12) manufactured in Comparative Examples 1 to 12 have an SRC (NP) of 50.0 g / g or less and / or an SRC (4.83 kPa) of 41.5 or less, which do not conform to the granular absorbents of the present invention.

[0534] Furthermore, compared to the comparative granular absorbents (1) to (12), the absorbents using granular absorbents (1) to (20) have a greater absorption capacity and less backflow. In particular, regarding the backflow in the absorbent, the granular absorbents (1) to (20) are much smaller than the comparative granular absorbents (9) with a lower SRC (4.83 kPa) and the comparative granular absorbents (12) with a lower STR. Therefore, the granular absorbents (1) to (20) can absorb a large amount of 0.9% sodium chloride aqueous solution in a short time due to their high SRC (NP), and due to their high SRC (4.83 kPa), they exhibit excellent liquid retention capacity and reduced backflow even when held under high pressure after absorbing liquid.

[0535] As can be seen from the above, the granular absorbent of the present invention, in addition to having the function of absorbing a large amount of urine in a short time, also has the function of retaining liquid even when strong pressure is applied from the outside due to the user's movements after absorption. This function is particularly needed for granular absorbents used in sanitary products such as diapers for adults who urinate in large quantities each time. Ultimately, the present invention achieves the following effect: it can be used to manufacture sanitary products that have excellent liquid retention during actual use and further reduce the backflow of absorbed liquid during actual use.

[0536] Industrial availability

[0537] The granular absorbent of one embodiment of the present invention can be widely used in the field of hygiene products such as diapers.

Claims

1. A granular water-absorbing agent, wherein the granular water-absorbing agent is mainly composed of a polyacrylic acid (salt)-based water-absorbing resin formed by surface cross-linking, and The granular absorbent satisfies the following formula (A) and the following formula (B). SRC(NP) > 50.0 g / g(A) SRC (4.83 kPa) > 41.5 g / g (B) Here, the SRC(NP) is determined by a method comprising the following steps (a) to (c): (a) The granular absorbent (WO) [g] is contacted with a 0.9% sodium chloride aqueous solution for 10 minutes without applying a load to obtain a swollen gel, wherein the 0.9% sodium chloride aqueous solution is referred to below as the "test solution"; (b) Separate the swollen gel obtained in step (a) from the test solution; (c) Determine the weight (W1) [g] of the swollen gel separated in step (b), and calculate the SRC (NP) of the granular absorbent based on the following formula (1); SRC(NP)[g / g]=W1 / W0(1) The SRC (4.83 kPa) was determined by replacing step (c) with steps (c') to (e') described later in the method comprising steps (a) to (c). (c') Apply a load of 4.83 kPa to the swollen gel separated in step (b) for 1 minute; (d') Remove the exudate that has seeped from the swollen gel through step (c'); (e') The weight (W2) [g] of the swollen gel obtained in step (d') is determined, and the SRC (4.83 kPa) is calculated based on the following formula (2); SRC(4.83kPa)[g / g]=W2 / W0(2).

2. The granular absorbent according to claim 1, wherein, The SRC (4.83 kPa) value in formula (B) is >42 g / g.

3. The granular absorbent according to claim 1 or 2, wherein, The SRC(NP) value in formula (A) is >54 g / g.

4. The granular absorbent according to any one of claims 1 to 3, wherein, The granular absorbent has an absorption rate of less than 40 seconds based on the vortex method.

5. The granular absorbent according to any one of claims 1 to 4, wherein, The surface tension (STR) of the granular absorbent is above 66 mN / m.

6. The granular absorbent according to any one of claims 1 to 5, wherein, The centrifugal retention capacity (CRC) of the granular water absorbent is above 35 g / g.

7. The granular absorbent according to claim 6, wherein, The centrifugal separator retains a capacity (CRC) of 40 g / g or more for the granular absorbent.

8. The granular absorbent according to any one of claims 1 to 7, wherein, The granular absorbent further comprises one or more of the following groups: inorganic colloidal particles, water-insoluble inorganic particles, and water-soluble compounds containing polyvalent metal cations.

9. An absorbent comprising a particulate absorbent according to any one of claims 1 to 8.

10. A sanitary article comprising the absorbent according to claim 9.

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