Granular water absorbent

Abstract

[Subject] Provide: A particulate water absorbent that can significantly reduce liquid reflux when the particulate water absorbent is in a swollen state, even if the particulate water absorbent is subjected to external pressure. [Solution] A particulate water absorbent having a surface-crosslinked polyacrylic acid (salt)-based water-absorbing resin as a main component, the particulate water absorbent satisfying the following formula (1). AAP (2.06 kPa) + RCAP (2.06 kPa) ≥ 0.58 × CRC + 55.6 (1) (In formula (1), AAP (2.06 kPa) represents the water absorption rate (g / g) under a pressure of 2.06 kPa, RCAP (2.06 kPa) represents the water absorption rate (g / g) after swelling and under pressure, and CRC represents the water absorption rate (g / g) without pressure).

Description

Technical Field

[0001] The present invention relates to a particulate water-absorbing agent which has little liquid backflow even under pressure after absorbing liquid. Background Art

[0002] Super absorbent polymer (SAP) is a water-swellable and water-insoluble polymer gelling agent. Granular absorbents with super absorbent resin as the main component are used in various absorbent articles such as diapers, sanitary napkins, incontinence products for adults, soil water-retaining agents for agriculture, forestry and horticulture, and industrial waterproofing agents. As raw materials for such super absorbent resins, various monomers and hydrophilic polymers have been proposed, but from the perspective of performance and cost, polyacrylic acid (salt)-based super absorbent resins using acrylic acid and / or its salts as monomers are the most commonly used.

[0003] With the high performance of diapers, the main purpose of particulate water absorbents, a variety of functions (physical properties) are required for particulate water absorbents. Specific examples of the physical properties of particulate water absorbents are not limited to simply high water absorption rate, and gel strength, water-soluble components, water absorption rate, water absorption rate under pressure, liquid permeability, particle size distribution, urine resistance, antibacterial properties, impact resistance (damage resistance), powder fluidity, deodorization, coloring resistance (whiteness), low dust, etc. can also be listed. Among these, there is a so-called "backflow" physical property of releasing liquid again from the particulate water absorbent toward the introduction direction of the absorbed liquid. Backflow can cause discomfort to the user due to the liquid contacting the skin, so reducing backflow is a very important topic in the field of water-absorbent resins (for example, Patent Document 1).

[0004] It should be noted that Patent Document 2 is another related prior art.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-213911

[0008] Patent Document 2: International Publication No. 97 / 003114 Summary of the invention

[0009] However, it is not necessary to replace absorbent articles such as diapers every time after urine or other liquids are discharged from them. Usually, absorbent articles are discharged multiple times. The granular absorbent that absorbs the liquid will be in a swollen state. Therefore, users sometimes use absorbent articles with granular absorbents in a swollen state. In this way, when the granular absorbent is in a swollen state, it is necessary to improve the liquid retention capacity of the absorbent body and reduce the liquid reflux even when pressure is applied from the outside due to daily actions, especially in a state of bearing body weight (such as supine state, sitting down, etc.), thereby reducing skin inflammation and other troubles, and users can use absorbent articles comfortably for a long time. In the past, attention was only paid to "how to absorb liquid under load", which is usually expressed by the absorption rate under pressure (AAP), and no attention was paid to how much liquid can be retained in the swollen state after absorbing liquid even when bearing a load. It can be considered that there is still room for improvement.

[0010] Therefore, an object of the present invention is to provide a particulate water absorbing agent that can significantly reduce liquid reflux even when the particulate water absorbing agent is subjected to pressure from the outside when the particulate water absorbing agent is in a swollen state.

[0011] The above-mentioned problems are solved by a particulate water absorbing agent comprising, as a main component, a surface-crosslinked polyacrylic acid (salt)-based water absorbing resin, the particulate water absorbing agent satisfying the following formula (1).

[0012] AAP(2.06kPa)+RCAP(2.06kPa)≥0.58×CRC+55.6 (1)

[0013] (In formula (1), AAP (2.06 kPa) represents the water absorption rate (g / g) under a pressure of 2.06 kPa, RCAP (2.06 kPa) represents the water absorption rate (g / g) after swelling and under pressure, and CRC represents the water absorption rate (g / g) without pressure). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram showing an apparatus for measuring gel permeation rate (GPR).

[0015] Figure 2 This is a graph showing AAP (2.06 kPa) + RCAP (2.06 kPa) [g / g] (vertical axis) plotted against CRC [g / g] (horizontal axis) in each example and comparative example. The straight line represents AAP (2.06 kPa) + RCAP (2.06 kPa) = 0.58 × CRC + 55.6. DETAILED DESCRIPTION

[0016] Below, the present invention is described while showing the best mode. For the entirety of this specification, as long as it is not specifically mentioned, the expression in the singular should be understood to also include the concept of its plural form. Therefore, as long as it is not specifically mentioned, it should be understood that the article in the singular (such as "a", "an", "the" in English, etc.) also includes the concept of its plural form. In addition, as long as it is not specifically mentioned, the terms used in this specification should be understood to be used according to the meaning commonly used in the field. Therefore, as long as it is not defined separately, all professional terms and scientific and technical terms used in this specification have the same meaning as the meaning commonly understood by technicians in the field to which the present invention belongs. In the event of a conflict, this specification (including definitions) takes precedence. The present invention is not limited to the following embodiments, and various changes can be made within the scope of the claims.

[0017] [1] Definition of terms

[0018] (1-1) "Water-absorbent resin"

[0019] The "water-absorbent resin" in the present invention refers to a water-swellable and water-insoluble polymer cross-linked body that satisfies the following physical properties. That is, it refers to a polymer cross-linked body that satisfies the physical property of CRC of 5 g / g or more specified in ERT441.2-02 as "water-swellability" and the physical property of Ext of 50 wt% or less specified in ERT470.2-02 as "water-insolubility".

[0020] The water-absorbent resin can be appropriately designed according to its application and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking and polymerizing an unsaturated monomer having a carboxyl group. In addition, it is not limited to the form of a polymer in total amount (100 wt%), and may be a water-absorbent resin composition containing additives and the like within the range satisfying the above-mentioned physical properties (CRC, Ext).

[0021] Furthermore, the water-absorbent resin in the present invention is not limited to the final product, and sometimes refers to the intermediate in the production process of the water-absorbent resin (for example, a hydrogel cross-linked polymer after polymerization, a dried polymer after drying, a water-absorbent resin powder before surface cross-linking, etc.), and all of them are collectively referred to as "water-absorbent resin". It should be noted that the shape of the water-absorbent resin includes sheet, fiber, film, granule, gel, etc., and the water-absorbent resin of the present invention is mainly in granule (powder).

[0022] (1-2) “Granular water absorbent”

[0023] In this specification, the water absorbent contains a water absorbent resin as a main component. In this specification, a granular water absorbent refers to a granular (also known as a powdered) water absorbent (containing water absorbent resin particles as a main component), and both a single granular water absorbent and a plurality of granular water absorbents are referred to as granular water absorbents. "Granular" means having a particle form, and particles refer to small granular objects with a measurable size and in a solid or liquid state (JIS Industrial Terminology Dictionary 4th edition, page 2002). It should be noted that in this specification, a granular water absorbent is sometimes referred to as a water absorbent.

[0024] It should be noted that the aqueous liquid is not limited to water, and may be urine, blood, sweat, feces, waste liquid, moisture, steam, ice, a mixture of water and an organic solvent and / or an inorganic solvent, rainwater, groundwater, etc., and is not particularly limited as long as it contains water. Preferred examples include urine, menstrual blood, sweat, and other body fluids.

[0025] The granular water absorbent of the present invention can be suitably used as a sanitary material for absorbing aqueous liquids. The granular water absorbent of the present invention has a surface-crosslinked polyacrylic acid (salt)-based water-absorbing resin (particles) (hereinafter also referred to as a polyacrylic acid (salt)-based water-absorbing resin) as a main component. In other words, in the granular water absorbent, the content of the surface-crosslinked polyacrylic acid (salt)-based water-absorbing resin is preferably 60 to 100% by weight, 70 to 100% by weight, 80 to 100% by weight, 90 to 100% by weight. In addition, the granular water absorbent optionally contains additives such as other water-absorbing resin particles, water, and / or water-insoluble inorganic particles, water-soluble compounds containing polyvalent metal cations. The suitable water content of the granular water absorbent is 0.2 to 30% by weight. That is, the water-absorbing resin composition formed by integrating these components also belongs to the category of the granular water absorbent.

[0026] It should be noted that the upper limit of the polyacrylic acid (salt)-based water-absorbing resin in the water-absorbing agent is 99% by weight, further 97% by weight, and particularly about 95% by weight, and it is preferred that water and the additives described later (water-insoluble inorganic particles, water-soluble compounds containing polyvalent metal cations) are also included.

[0027] In addition, the particulate water-absorbing agent of the present invention has a polyacrylic acid (salt) water-absorbing resin as a main component, and the particulate water-absorbing agent may contain other water-absorbing resins. Examples of other water-absorbing resins include polysulfonic acid (salt) water-absorbing resins, maleic anhydride (salt) water-absorbing resins, polyacrylamide water-absorbing resins, polyvinyl alcohol water-absorbing resins, polyethylene oxide water-absorbing resins, polyaspartic acid (salt) water-absorbing resins, polyglutamic acid (salt) water-absorbing resins, polyalginic acid (salt) water-absorbing resins, starch water-absorbing resins, and cellulose resins.

[0028] (1-3) “Polyacrylic acid (salt)” and “Polyacrylic acid (salt)-based water-absorbent resin”

[0029] The "polyacrylic acid (salt)" in the present invention refers to polyacrylic acid and / or its salt. In addition, the polyacrylic acid (salt)-based water-absorbing resin refers to a resin that contains acrylic acid and / or its salt (hereinafter referred to as "acrylic acid (salt)") as a repeating unit as a main component, and is preferably a polyacrylic acid (salt) that is internally crosslinked by a graft component and is surface-crosslinked.

[0030] The polyacrylic acid (salt)-based water-absorbing resin is preferably in a granular form (also known as a powder form) among the granular water-absorbing agents.

[0031] It should be noted that the above-mentioned "main component" means that the amount (content) of acrylic acid (salt) is usually 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably substantially 100 mol%, relative to the total amount of monomers (excluding internal crosslinking agents) used in the polymerization.

[0032] (1-4) “EDANA” and “ERT”

[0033] "EDANA" is the abbreviation of European Disposables and Nonwovens Associations, and "ERT" is the abbreviation of EDANA Recommended Test Methods, which is a European standard (basically a world standard). In the present invention, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the ERT original (revised in 2002 / known document).

[0034] (1-5) "PSD" (ERT420.2-02)

[0035] “PSD” is an abbreviation for particle size distribution, and refers to the particle size distribution of a particulate water-absorbing agent or a water-absorbing resin measured by sieving.

[0036] The weight-average particle diameter (D50) and the logarithmic standard deviation (σζ) of the particle size distribution were measured by the same method as in “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution” described in U.S. Patent No. 7,638,570.

[0037] (1-6) Others

[0038] In this specification, "X to Y" indicating a range means "above X and below Y". In addition, unless otherwise noted, the unit of weight "t (ton)" means "metric ton" and "ppm" means "ppm by weight" or "ppm by mass". Furthermore, "weight" and "mass", "parts by weight" and "parts by mass", and "weight %" and "mass %" are respectively regarded as synonyms. In addition, "acid (salt)" means "acid and / or its salt", and "(meth)acryloyl" means "acryloyl and / or methacryloyl".

[0039] In addition, “liter” may be abbreviated as “1” or “L”, and “weight %” may be abbreviated as “wt %.” Furthermore, when measuring trace components, the detection limit is hereinafter expressed as ND (Non Detected).

[0040] 〔2〕Granular water absorbent

[0041] The particulate water absorbing agent of the present invention contains a surface-crosslinked polyacrylic acid (salt)-based water absorbing resin as a main component, and the particulate water absorbing agent satisfies the formula (1).

[0042] The particulate water absorbing agent of the present invention can significantly reduce liquid reflux even when pressure is applied to the particulate water absorbing agent from the outside when the particulate water absorbing agent is in a swollen state.

[0043] Hereinafter, a value obtained by using AAP (2.06 kPa) + RCAP (2.06 kPa) is also referred to as a value (A), and a value obtained by using 0.58×CRC + 55.6 is also referred to as a value (B).

[0044] When the particulate water absorbing agent does not satisfy the formula (1), that is, when value (A) < value (B), the amount of liquid reflux becomes significantly larger after the particulate water absorbing agent absorbs water and swells.

[0045] The value (A) is the sum of AAP (2.06 kPa) and RCAP (2.06 kPa). "AAP" is the abbreviation of Absorption Against Pressure, which refers to the water absorption rate of a particulate water absorbent under pressure. "RCAP" is the abbreviation of Retention Capacity Against Pressure, which refers to the water absorption rate of a particulate water absorbent under pressure when it swells. In addition, "CRC" is the abbreviation of Centrifuge Retention Capacity, which refers to the water absorption rate of a particulate water absorbent or a water-absorbent resin under no pressure (sometimes also referred to as "water absorption rate"). Generally, the water absorption rate decreases under pressure, so in the same particulate water absorbent, AAP (2.06 kPa) [g / g] <CRC(2.06kPa)[g / g]。

[0046] When assuming the actual use of water-absorbent articles, various usage conditions can be imagined, such as urination under the condition of bearing body weight, swelling without pressurization during urination and pressurization with movement, etc. In the process of trying to solve the problem of "the amount of reflux after swelling of the particulate water-absorbing agent after absorption of water is reduced", the present inventors found that "liquid retention capacity" (the amount of absorption obtained by adding the amount of liquid retained in the gaps between the water-absorbent resin particles (including primary particles and / or secondary particles formed by aggregation of primary particles) to the water-absorbent resin particles themselves) is important in various situations, and focused on AAP (2.06 kPa) and RCAP (2.06 kPa) among various physical properties of the particulate water-absorbing agent.

[0047] Here, regarding the subject of the present application that "when the particulate water absorbent is in a swollen state, even if pressure is applied to the particulate water absorbent from the outside, the liquid reflux can be significantly reduced", it can be considered that the subject can be solved if the RCAP is high. However, in the course of research by the present inventors, it has been clarified that for the liquid reflux in the swollen state, it is not sufficient to only consider the water absorption ratio under pressure during swelling, that is, RCAP. For example, the fact that the RCAP of Comparative Example 1-5 described later is higher than that of Example 1-8, but the liquid reflux of the particulate water absorbent during swelling is significantly reduced can also be understood. In addition, the present inventors found that the sum of AAP (2.06 kPa) + RCAP (2.06 kPa) and CRC are important factors related to the liquid reflux of the particulate water absorbent during swelling, and further found that the new particulate water absorbent satisfying formula (1) can significantly suppress the liquid reflux of the particulate water absorbent during swelling.

[0048] It should be noted that the "backflow" (sometimes also referred to as the reflux amount, Re-Wet) generally used as a physical property evaluation of a water-absorbent resin is an evaluation of an absorbent sheet (absorbent body) obtained by laminating an absorbent layer containing a water-absorbent resin (water-absorbent agent) and pulp, etc., with a nonwoven fabric, etc., and is not an evaluation of the water-absorbent resin (water-absorbent agent) itself. In addition, in the aforementioned Re-Wet evaluation, it cannot be said that the water-absorbent resin contained in the absorbent body is in a saturated state (after absorbing liquid on the surface of the absorbent body multiple times at intervals of 30 minutes, the backflow is evaluated under a load), and the subject of this application, that is, the liquid retention capacity of the particulate water-absorbent agent in a "swollen state" under a further pressurized state is not evaluated.

[0049] Furthermore, the particulate water absorbing agent more preferably satisfies the following formula (2).

[0050] AAP(2.06kPa)+RCAP(2.06kPa)≥0.58×CRC+56.0 (2)

[0051] The particulate water-absorbing agent that satisfies the above formula (2) has excellent liquid retention capacity when a swollen absorbent body is pressurized.

[0052] In particular, when the CRC of the particulate water-absorbing agent is less than 37.0 g / g, it is more preferable to satisfy the above formula (2).

[0053] Furthermore, the particulate water absorbing agent more preferably satisfies the following formula (3).

[0054] AAP(2.06kPa)+RCAP(2.06kPa)≥0.58×CRC+56.5 (3)

[0055] The particulate water-absorbing agent that satisfies the above formula (3) has excellent liquid retention capacity when a swollen absorbent body is pressurized.

[0056] In particular, when the CRC of the particulate water-absorbing agent is less than 37.0 g / g, it is more preferable to satisfy the above formula (3).

[0057] The value (A) is not particularly limited, but is preferably greater than 76.0 g / g. That is, the particulate water absorbing agent preferably satisfies the following formula (A).

[0058] AAP(2.06kPa)+RCAP(2.06kPa)>76.0 (A)

[0059] By setting the value (A) to be greater than 76.0 g / g, it is easier to further reduce the liquid reflux after swelling of the particulate water absorbing agent. The upper limit of the value (A) is not particularly limited, but is usually 90.0 g / g or less, and may be 85.0 g / g or less.

[0060] It should be noted that when calculating formulas (1) to (3) and formula (A), AAP (2.06 kPa), RCAP (2.06 kPa) and CRC use measured values ​​up to the first decimal place, and when calculating value (A), value (B), and the right side of formulas (2) and (3), the values ​​calculated using the above measured values ​​are rounded to the second decimal place and the values ​​up to the first decimal place are used.

[0061] (2-1) CRC (centrifuge holding capacity) (ERT441.2-02)

[0062] “CRC” is an abbreviation of Centrifuge Retention Capacity, and refers to the water absorption ratio of a particulate water-absorbing agent or a water-absorbing resin under no pressure (sometimes also referred to as “water absorption ratio”).

[0063] Specifically, it refers to the water absorption ratio (unit: g / g) after placing 0.2 g of a particulate water-absorbing agent or a water-absorbing resin into a nonwoven bag, immersing the bag in a significantly excessive 0.9 wt % sodium chloride aqueous solution for 30 minutes to allow the bag to swell freely, and then draining the water using a centrifuge (250 G).

[0064] The CRC (centrifuge retention capacity) of the particulate water absorbent of the present invention is preferably 30 g / g or more, more preferably 31 g / g or more, further preferably 32 g / g or more, and further preferably 33 g / g or more. By making the CRC to be 30 g / g or more, the absorption amount becomes appropriate, and the performance as an absorbent of sanitary products such as paper diapers can be ensured. In addition, the CRC (centrifuge retention capacity) of the particulate water absorbent is preferably 70 g / g or less, more preferably 60 g / g or less, further preferably 50 g / g or less, and particularly preferably 40 g / g or less. By making the CRC to be 70 g / g or less, the speed of absorbing body fluids such as urine and blood is maintained, and therefore, it is also suitable for paper diapers of high water absorption speed type. It should be noted that the CRC can be controlled according to the type and amount of the internal crosslinking agent.

[0065] (2-2) Absorption under pressure (AAP) (ERT442.2-02)

[0066] "AAP" is the abbreviation of Absorption Against Pressure, which refers to the water absorption ratio of a particulate water-absorbing agent or a water-absorbing resin under pressure.

[0067] Specifically, AAP (2.06 kPa) means that 0.9 g of a particulate water-absorbing agent or a water-absorbing resin is placed in a significantly excessive amount of a 0.9 wt % sodium chloride aqueous solution at 2.06 kPa (21 g / cm2 Water absorption ratio (unit: g / g) after swelling for 1 hour under a load of 4.83 kPa (49 g / cm 2 In this case, it is recorded as AAP (4.83 kPa).

[0068] In addition, ERT442.2-02 also expresses it as Absorption Under Pressure, but the content is essentially the same.

[0069] The AAP (2.06 kPa) of the particulate water-absorbing agent of the present invention is preferably 20 g / g or more, more preferably 24 g / g or more, further preferably 26 g / g or more, further preferably 28 g / g or more, particularly preferably 29 g / g or more, and most preferably 30 g / g or more. There is no particular limitation on the upper limit, but it is preferably 40 g / g or less. By satisfying the above conditions, the AAP (2.06 kPa) is high to a certain extent, so it is easy to satisfy the conditions of formula (1). In addition, the diaper manufactured using the particulate water-absorbing agent has excellent ability to absorb urine from pulp, can reduce the amount of reflux, and can inhibit skin inflammation and urine leakage. It should be noted that, if referring to the examples and comparative examples described later, it can be understood that there is no correlation between high AAP (2.06 kPa) and satisfying formula (1).

[0070] In addition, the AAP (4.83 kPa) of the particulate water-absorbing agent of the present invention is preferably 10 g / g or more, more preferably 13 g / g or more, further preferably 17 g / g or more, and particularly preferably 20 g / g or more. There is no particular limitation on the upper limit, but it is preferably 30 g / g or less. By satisfying the above conditions, the paper diaper manufactured using the particulate water-absorbing agent has excellent ability to absorb urine from pulp, can reduce the amount of reflux, and can inhibit skin inflammation and urine leakage. It should be noted that AAP can be controlled by the type and amount of the surface cross-linking agent.

[0071] (2-3) Retention Capacity Against Pressure (RCAP)

[0072] "RCAP" is the abbreviation of Retention Capacity Against Pressure, which refers to the water absorption ratio of a granular water absorbent when it is swollen and under pressure.

[0073] The RCAP test can be measured using the barrel, piston and weight used in the Gel Bed Permeability test described in the specification of U.S. Patent No. 8269060. Figure 1 The device shown in .

[0074] Before the test is carried out, the total weight of the barrel, piston and weight is measured and the value is set as Wa [g]. About 0.9 g of the test sample is measured and evenly spread on the bottom of the barrel. It is immersed in the test solution (0.9 wt % sodium chloride aqueous solution) for 60 minutes to make the sample swell without applying a limiting load. After 60 minutes, the sample in the barrel is loaded with a piston and a weight (total weight of about 596 g), the barrel is lifted up from the test solution, and placed on a JIS standard sieve with a mesh of 2000 μm, and the liquid is controlled for about 1 minute. After the liquid is controlled, the water droplets attached to the lower part of the barrel are removed with Kimwipes (S-200 manufactured by NIPPON PAPER CRECIA) and the like, and the weight is measured, and the obtained value is set as Wb [g]. It should be noted that the removal of water droplets attached to the lower part of the barrel by Kimwipes is performed as follows: the water contained in the swollen gel layer in the barrel is not removed, but only the water attached to the outside of the barrel is removed, and the wiping is performed within 0.5 seconds without the pressure applied by the Kimwipes. RCAP is calculated using the following formula (4).

[0075] [Number 1]

[0076]

[0077] The RCAP (2.06 kPa) of the particulate water-absorbing agent of the present invention is preferably 18 g / g or more, more preferably 24 g / g or more, further preferably 30 g / g or more, particularly preferably 40 g / g or more, and most preferably 43 g / g or more. There is no particular limitation on the upper limit, but it is preferably 60 g / g or less. By satisfying the above conditions, the RCAP (2.06 kPa) is high to a certain extent, so it is easy to satisfy the conditions of formula (1). In addition, the diaper manufactured using the particulate water-absorbing agent has excellent ability to absorb urine from pulp, can reduce the amount of reflux, and can inhibit skin inflammation and urine leakage. It should be noted that, if referring to the embodiments and comparative examples described later, it can be understood that the high RCAP (2.06 kPa) has no correlation with satisfying formula (1).

[0078] RCAP (2.06 kPa) can be controlled by controlling the production method of the water-absorbent resin, for example, the mixing time of additives (such as water-insoluble inorganic particles), and the content of soluble components.

[0079] (2-3) Gel Permeation Rate (GPR)

[0080] In this specification, the "liquid permeability" of a particulate water-absorbing agent refers to the fluidity of a liquid passing between swollen gel particles under a load. As this index, the gel permeation rate (GPR) can be used. The GPR of the particulate water-absorbing agent is measured by referring to the saline flow conductivity (SFC) test described in the specification of U.S. Patent No. 5,849,405, changing the measurement conditions and performing the following steps.

[0081] As a device for measuring, use Figure 1 The device 400 shown in FIG. The device 400 is generally composed of a container 410 and a tank 420. A cell 411 (with an inner diameter of 6 cm) is provided in the container 410, and a swollen gel 414 (a substance obtained by making a particulate water absorbent absorb water) can be stored inside the cell 411, and a liquid 423 can be introduced. In addition, by fitting a piston 412 into the cell 411, pressure can be applied to the swollen gel 414. Metal meshes 413a and 413b (a metal mesh made of No. 400 stainless steel with a mesh size of 38 μm) are laid on the bottom surface of the cell 411 and the bottom surface of the piston 412, so that the swollen gel 414 (and the particulate water absorbent) cannot pass through. Here, a 0.90 mass % sodium chloride aqueous solution is used as the liquid 423. The tank 420 stores the liquid 423 inside. The liquid 423 is introduced into the cell 411 through an L-shaped tube 422 with a stopcock. In addition, a glass tube 421 is inserted into the tank 420, and the interior of the glass tube 421 is filled with air. As a result, the lower end of the glass tube 421 can be made equal to the liquid level in the box 411. That is, while the liquid level of the liquid 423 in the tank 420 is located above the lower end of the glass tube 421, the liquid level in the box 411 can be kept constant. In this measurement, the height difference between the lower liquid level of the liquid 423 in the tank 420 (i.e., the lower end of the glass tube 421) and the bottom surface of the swollen gel 414 is set to 4 cm. In other words, according to the device 400, the liquid 423 of a predetermined hydrostatic pressure can be introduced into the box 411. The hole 415 is opened in the piston 412, so that the liquid 423 flows in the hole 415, and then also flows in the swollen gel 414 layer, and flows out to the outside of the box 411. The container 410 is placed on a stainless steel metal mesh 431 that does not hinder the passage of the liquid 423. Therefore, the liquid 423 flowing out of the box 411 is finally collected by the collection container 432. In addition, the amount of the liquid 423 collected by the collection container 432 can be weighed by the upper plate balance 433.

[0082] The specific method for measuring the gel permeation rate (GPR) is as follows: It should be noted that the following operations were performed at room temperature (20 to 25°C).

[0083] (1) A particulate water-absorbing agent (0.900 g) is uniformly placed in the box 411 .

[0084] (2) The particulate water-absorbing agent was allowed to absorb liquid (0.90 mass % sodium chloride aqueous solution) for 60 minutes without applying pressure to prepare a swollen gel 414 .

[0085] (3) A piston is placed on the swollen gel 414 to create a pressurized state of 0.3 psi (2.06 kPa).

[0086] (4) While maintaining the hydrostatic pressure at 3923 dyne / cm 2 While maintaining a constant value, liquid 423 is introduced into box 411 to allow the swollen gel 414 layer to pass through the liquid.

[0087] (5) The amount of liquid 423 flowing through the swollen gel 414 layer is recorded at 5-second intervals for 3 minutes. In other words, the flow rate of liquid 423 flowing through the swollen gel 414 layer is measured. The measurement is performed using a top plate balance 433 and a computer (not shown).

[0088] (6) The flow rates from 1 minute to 3 minutes after the start of the flow of the liquid 423 were averaged to calculate the gel permeation rate (GPR) [g / min].

[0089] The gel permeation rate (GPR) of the particulate water absorbent of the present invention is preferably 20 g / min or more. By setting the gel permeation rate (GPR) to be 20 g / min or more, the liquid diffusivity when the particulate water absorbent is used in an absorbent is excellent. The gel permeation rate (GPR) of the particulate water absorbent is more preferably 22 g / min or more, further preferably 24 g / min or more, and particularly preferably 26 g / min or more. There is no particular limitation on the upper limit, but it is preferably 300 g / min or less, and more preferably 150 g / min or less.

[0090] The gel permeation rate (GPR) can be controlled by controlling, for example, the amount of internal crosslinking, the amount of surface crosslinking, the time of the surface crosslinking reaction, etc. of the water-absorbent resin.

[0091] (2-4) Moisture absorption and agglomeration rate

[0092] The "hygroscopic fluidity" in the present invention is an index for evaluating the fluidity of the particulate water absorbent in the form of agglomerates, cakes or powders when the particulate water absorbent is left for 1 hour under the conditions of an air temperature of 25°C and a relative humidity of 90%RH, and can be judged by the hygroscopic caking rate. The calculation method of the hygroscopic caking rate is described in detail in the Examples. In short, the particulate water absorbent is placed on a sieve and classified, and the weight of the particulate water absorbent remaining on the sieve (W1 [g]) and the weight of the particulate water absorbent passing through the sieve (W2 [g]) are measured, and the hygroscopic fluidity is calculated according to the following formula.

[0093] Moisture absorption and caking rate [weight %] = {W1 / (W1+W2)}×100.

[0094] The details of the measurement method are as described in the Examples.

[0095] The moisture absorption agglomeration rate of the particulate water-absorbing agent of the present invention is usually 50% by weight or less, preferably 40% by weight or less, more preferably 30% by weight or less, further preferably 20% by weight or less, further preferably 10% by weight or less, and most preferably 0% by weight. The moisture absorption agglomeration rate of the particulate water-absorbing agent of the present invention may be 0 to 50% by weight, 0 to 40% by weight, 0 to 30% by weight, 0 to 20% by weight, or 0 to 10% by weight. By making the moisture absorption agglomeration rate 40% by weight or less, the particulate water-absorbing agent has good handling properties even in a humid environment, and the possibility of problems such as aggregation and clogging in the conveying piping of the manufacturing equipment and failure to uniformly mix with the hydrophilic fiber when manufacturing a thin absorbent for sanitary materials is reduced. Therefore, by satisfying the above conditions, when the particulate water-absorbing agent and the fiber substrate are used to make an absorbent, adhesion to the device can be reduced.

[0096] The moisture absorption caking rate can be controlled by the type of agent added to improve fluidity during moisture absorption or the amount of agent added.

[0097] (2-5) Flow Rate (ERT450.2-02)

[0098] Flow rate refers to the powder fluidity of the particulate water-absorbing agent.

[0099] Specifically, 100 g of the particulate water absorbing agent was placed in a funnel having a baffle at the bottom, the baffle was opened, and the time from the start of the flow to the end of the flow was measured to calculate the flow amount of the particulate water absorbing agent per unit time as the flow rate.

[0100] The flow rate of the particulate water absorbent of the present invention is preferably 8.5 g / s or more. When the flow rate is less than 8.5 g / s, the fluidity of the particulate water absorbent is low, and thus, the following problems may occur: it is difficult to supply the particulate water absorbent to the hopper, it is difficult to transport the particulate water absorbent using a feeder, and it is difficult to uniformly mix with hydrophilic fibers when manufacturing an absorbent for sanitary materials.

[0101] (2-6) Dust volume

[0102] The dust amount of the granular water absorbing agent of the present invention is preferably 400 mg / kg or less relative to the water absorbing agent. By making the dust amount of the water absorbing agent below the above upper limit, the dust is sufficiently reduced, and the handling property of the water absorbing agent is excellent. The dust amount of the water absorbing agent is more preferably 300 mg / kg or less relative to the water absorbing agent, further preferably 250 mg / kg or less, and particularly preferably 200 mg / kg or less. This value is ideal for a water absorbing agent of 0 mg / kg. Considering the productivity in actual use and on an industrial scale, the lower limit is usually 10 mg / kg or more relative to the water absorbing agent, and may be 15 mg / kg or more, or may be 20 mg / kg or more.

[0103] The dust amount of the particulate water-absorbing agent was calculated using the method described in Examples.

[0104] (2-7) Surface tension

[0105] Surface tension refers to the work (free energy) required to increase the surface area of ​​a solid or liquid expressed in the form of per unit area. The surface tension mentioned in this application refers to the surface tension of an aqueous solution when a particulate water absorbent is dispersed in a 0.90 mass % sodium chloride aqueous solution. It should be noted that the surface tension of the water absorbent is measured according to the following steps. That is, 50 ml of physiological saline adjusted to 20°C is added to a fully cleaned 100 ml beaker, and the surface tension of the physiological saline is first measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). Next, a fully cleaned 25 mm long fluororesin rotor and 0.5 g of particulate water absorbent are added to the beaker containing the physiological saline adjusted to 20°C and the surface tension measured, and stirred at 500 rpm for 4 minutes. Stirring was stopped after 4 minutes, and after the water-containing particulate water absorbent was precipitated, the same operation was performed again to measure the surface tension of the supernatant. It should be noted that in the present invention, a plate method using a platinum plate was adopted, and the plate was thoroughly cleaned with deionized water and heated and cleaned with a gas burner before each measurement.

[0106] The surface tension of the particulate water-absorbing agent of the present invention is preferably 65 [mN / m] or more, more preferably 66 [mN / m] or more, 68 [mN / m] or more, 70 [mN / m] or more, 71 [mN / m] or more, and 72 [mN / m] or more. By making the surface tension satisfy the above conditions, the amount of backflow in the disposable diaper can be further reduced. The upper limit is usually 75 [mN / m] is sufficient.

[0107] (2-8) Particle shape

[0108] The particle shape of the water-absorbent resin (powder) is preferably an irregularly broken shape. Here, the irregularly broken shape refers to broken particles with an irregular shape. Compared with spherical particles obtained by reverse suspension polymerization and gas phase polymerization, the irregularly broken shape is not fixed in shape, so it has excellent mixing properties with hydrophilic fibers such as pulp, and the liquid diffusivity achieved by the gaps between particles is high, so it is preferred. The particulate water absorbent described in one embodiment of the present invention is preferably a crushed product in aqueous solution polymerization. The irregularly broken shape is obtained by crushing a gel or a dried product (preferably a dried product) of a cross-linked polymer obtained by aqueous solution polymerization. On the other hand, in the case of not undergoing a crushing process, representatively, spherical particles or granulated products of spherical particles obtained by reverse suspension polymerization, droplet polymerization such as spraying and polymerizing the polymerization monomer, etc. are not irregularly broken. In an embodiment of the present invention, if the shape of the particulate water absorbent is an irregularly broken shape, the water absorption rate and RCAP are excellent compared to substances with a high average roundness (such as spherical substances). In the embodiment of the present invention, the average circularity of the particulate water-absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.

[0109] The calculation method of the average circularity is as follows. Randomly select more than 100 particulate water absorbents, use an electron microscope (Keyence Corporation, VE-9800) (magnification 50 times) to photograph each particulate water absorbent, obtain an image of the particulate water absorbent, and use the attached image analysis software to calculate the circumference and area of ​​each particle. The circularity of each particle is calculated using the following formula.

[0110] [Mathematical formula 2]

[0111] Roundness = 4 × π × area / (circumference) 2

[0112] The average of the obtained values ​​was calculated as the average circularity.

[0113] (2-9) Water-insoluble inorganic particles / water-soluble compounds containing polyvalent metal cations

[0114] The particulate water-absorbing agent of the present invention preferably further contains at least one selected from the group consisting of water-insoluble inorganic particles and water-soluble polyvalent metal cation-containing compounds.

[0115] The granular water absorbent can improve the hygroscopic fluidity of the granular water absorbent by including water-insoluble inorganic particles. In addition, the absorption capacity of the absorbent article can be increased by adding water-insoluble inorganic particles. Furthermore, the water-absorbent resin particles (composition) sometimes lose fluidity when manufacturing absorbent articles due to storage after manufacturing. By mixing water-insoluble inorganic particles with the water-absorbent resin particles (composition) that have lost fluidity, the water-absorbent resin particles (composition) are suitably formed into an absorbent body, thereby maintaining the performance while restoring the fluidity of the water-absorbent resin particles (composition), thereby improving productivity. Here, hygroscopic fluidity refers to the fluidity of the granular water absorbent when stored under high humidity conditions, and the granular water absorbent containing the water-absorbent resin usually has its fluidity reduced due to moisture absorption. It should be noted that, in order to improve the hygroscopic fluidity of the particulate water-absorbing agent, water-insoluble inorganic particles have been added so far. However, when the water-insoluble inorganic particles are simply added and mixed, the relationship of formula (1) cannot be satisfied, and the amount of liquid reflux under pressure of the particulate water-absorbing agent in a swollen state increases (see the comparative example described later). On the other hand, by improving the conditions for adding / mixing the water-insoluble inorganic particles (e.g., mixing time), etc., the particulate water-absorbing agent can satisfy the relationship of formula (1), and the liquid reflux under pressure of the particulate water-absorbing agent in a swollen state can be significantly suppressed.

[0116] Examples of the water-insoluble inorganic particles include polynary metal compounds such as hydrotalcite, silicon dioxide (silica), aluminum hydroxide, titanium dioxide, aluminum oxide, magnesium oxide, zinc oxide, talc, metal phosphates (e.g., calcium phosphates such as tricalcium phosphate, barium phosphate, aluminum phosphate), metal borates (e.g., titanium borate, aluminum borate, iron borate, magnesium borate, manganese borate, calcium borate), silicic acid or its salts, clay, diatomaceous earth, zeolite, bentonite, kaolin, activated clay, etc. Among them, from the perspective of significantly obtaining the effects of the present invention, the water-insoluble inorganic particles preferably contain at least one selected from the group consisting of polynary metal compounds, silicon dioxide, talc, and tricalcium phosphate, and more preferably contain at least one selected from the group consisting of silicon dioxide, aluminum hydroxide, and tricalcium phosphate.

[0117] The volume average particle size of the water-insoluble inorganic particles is preferably 10 μm or less, more preferably 5 μm or less, and further preferably 1 μm or less. In addition, the volume average particle size is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. By being above the above lower limit, it is possible to suppress the reduction in workability during the addition process and obtain sufficient performance. It should be noted that the volume average particle size of the water-insoluble inorganic particles can be measured using a "laser diffraction scattering method" (for example, using a particle size analyzer manufactured by Nikkiso Co., Ltd., trade name: MICROTRAC MT3000II).

[0118] The water-insoluble inorganic particles may be subjected to a surface treatment. Specific examples of the surface treatment agent used for the surface treatment include the following surface treatment agents for polyvalent metal compounds.

[0119] The above-mentioned polyvalent metal compound refers to a polyvalent metal compound containing two kinds of metal cations, divalent and trivalent, and containing a hydroxyl group.

[0120] Examples of the divalent metal cation include Mg 2+ , Fe 2+ 、Zn 2+ , Ca 2+ 、Ni 2+ 、Co 2+ , Cu 2+ From the viewpoint of heat resistance, Mg is preferred. 2+ Examples of the trivalent metal cations include Al 3+ , Fe 3+ , Mn 3+ From the viewpoint of heat resistance, Al is preferred. 3+ Therefore, a suitable embodiment of the multivalent metal compound is that the divalent metal cation is a magnesium cation and the trivalent metal cation is an aluminum cation.

[0121] The polymetallic compound preferably has the general formula (1): [M 1 2+ 1-x M 2 3+ x (OH - ) 2 ] x+ ·[(A n- ) x / n ·mH 2 O] x- (M 1 2+ Represents a divalent metal cation, M 2 3+A represents a trivalent metal cation. n- Indicates an n-valent anion, H 2 O represents water) and has a known hydrotalcite-like structure.

[0122] In addition, regarding the ratio of the divalent metal cation to the trivalent metal cation in the general formula (1), x is preferably in the range of 0.2 to 0.75, more preferably in the range of 0.25 to 0.7, and even more preferably in the range of 0.25 to 0.5. - 、F - , Cl - Br - 、NO 3 - , CO 3 2- 、SO 4 2- 、Fe(CN) 6 3- , CH 3 COO - , oxalate ion or salicylate ion, etc., preferably carbonate anion. In addition, m is a real number greater than 0, preferably 0 <m≤10。

[0123] The shape of the polymetallic compound is not particularly limited, but is preferably spherical (including powdered). In addition, the polymetallic compound is preferably of a specified particle size, and the volume average particle size is preferably 2 μm or less, more preferably 1.5 μm or less, and further preferably 1 μm or less. By making the particle size below the above upper limit, the amount added to obtain a sufficient effect will not be too much, and the possibility of damaging the water absorption performance of the resulting water absorbent is small. In addition, the volume average particle size is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. By being above the above lower limit, the decrease in workability during the addition process can be suppressed, and sufficient performance can be obtained. In addition, the average particle size of the polymetallic compound attached to the surface of the water-absorbent resin particles can be measured by a measurement method using an SEM (scanning electron microscope).

[0124] Furthermore, an organic compound may be inserted between the layers, and a surface treatment may be performed to improve the miscibility with water-absorbing resin particles and the like.

[0125] Preferred structural formulas of the polymetallic compound include Mg 6 Al 2 (OH) 16 CO 3 ·4H 2 O、Mg 4 Al 2 (OH)12 CO 3 ·3H 2 O, etc. Specifically, DHT-4H and DHT-6 manufactured by Kyowa Chemical Industry Co., Ltd. and STABIACE HT-1-NC and STABIACE HT-P manufactured by Sakai Chemical Industry Co., Ltd. are mentioned.

[0126] From the viewpoint of increasing the absorption capacity of the absorbent article and making the article excellent in the balance between the absorption capacity and the recycle amount, the content of the water-insoluble inorganic particles is 0.01 wt % or more and less than 10 wt %, preferably 0.1 to 5 wt %, based on 100 wt % of the polyacrylic acid (salt)-based water-absorbent resin.

[0127] The performance of the particulate water absorbing agent is improved by including a water-soluble compound containing a polyvalent metal cation. It should be noted that, in order to improve the moisture absorption fluidity of the particulate water absorbing agent, the addition of a water-soluble compound containing a polyvalent metal cation has been performed so far, but by improving the addition / mixing conditions (e.g., mixing time) of the water-soluble compound containing a polyvalent metal cation, instead of simply adding and mixing the water-soluble compound containing a polyvalent metal cation, the relationship of formula (1) can be satisfied, and a particulate water absorbing agent showing sufficient water absorption performance under pressure can be obtained.

[0128] The water-soluble compound containing a polyvalent metal cation refers to a compound other than a polyvalent metal compound containing a metal cation having a valence of 2 or more, preferably 3 or more. Examples of the metal cation having a valence of 3 or more include aluminum, zirconium, and titanium, preferably aluminum. Examples of the water-soluble compound containing a polyvalent metal cation include inorganic salts of polyvalent metals such as aluminum sulfate, aluminum chloride, zirconium oxychloride, ammonium zirconium carbonate, potassium zirconium carbonate, potassium zirconium carbonate, zirconium sulfate, zirconium acetate, and zirconium nitrate; polyvalent metal compounds such as organic salts of polyvalent metals such as aluminum acetate, aluminum lactate, zirconium hydroxychloride, titanium triethanolaminate, and titanium lactate. Among them, a compound containing aluminum as a polyvalent metal cation is preferred, and aluminum sulfate, potassium aluminum sulfate, and sodium aluminum sulfate are more preferred.

[0129] From the viewpoint of improving the performance of the water-absorbing agent, the content of the water-soluble polyvalent metal cation-containing compound 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, based on 100 parts by weight of the polyacrylic acid (salt)-based water-absorbing resin, in terms of the amount of the polyvalent metal cation.

[0130] The particulate water-absorbing agent of the above-described embodiment can be obtained by controlling the following production methods (a) to (c) so as to satisfy the formula (1), for example.

[0131] (Manufacturing method a)

[0132] Water-insoluble inorganic particles are added to a water-absorbent resin and the mixing time is controlled to obtain a particulate water-absorbing agent satisfying the formula (1).

[0133] The water-absorbent resin to which the water-insoluble inorganic particles are added may or may not be surface-crosslinked. In addition, the water-insoluble inorganic particles may be mixed with a water-absorbent resin composition containing the water-absorbent resin or other additives. Furthermore, when manufacturing an absorbent article, the water-absorbent resin (composition), the water-insoluble inorganic particles and the hydrophilic fiber may be mixed.

[0134] In addition, the water-absorbent resin and the water-insoluble inorganic particles are preferably dry-mixed. By dry mixing, the dust content of the obtained water-absorbing agent will be reduced, so it is preferred. The dry mixing refers to mixing in a state where there is substantially no (preferably no) liquid substance other than the water-insoluble inorganic particles and the liquid substance absorbed or retained in the water-absorbent resin. Specifically, it includes the following form: without further adding a liquid substance, the water-insoluble inorganic particles containing hygroscopic water and an organic compound retained between layers are mixed with a water-absorbent resin having a dry residue, hygroscopic water, a surface crosslinking agent added in the aforementioned surface crosslinking agent addition step, a solvent, etc.

[0135] The mixing time of the water-absorbent resin and the water-insoluble inorganic particles is not particularly limited and can be appropriately set using a mixing device. It is preferred to mix for a longer time in a manner that satisfies the above formula (1). That is, in the present invention, it is preferred to mix the water-absorbent resin and the water-insoluble inorganic particles for a longer time than the mixing time for the purpose of simply mixing the additives. Usually, for the purpose of improving productivity, the operation of the mixing device is stopped at the moment when it can be confirmed by visual inspection or conventional evaluation methods that the additives have been uniformly mixed. In addition, through this conventional mixing, the basic performance required for particulate water absorbents such as AAP and CRC is also ensured. However, the reflux amount of these particulate water absorbents under pressure when the particulate water absorbents are swollen is not sufficiently reduced. The present inventors have discovered this problem and conducted research, and as a result, they have made the following assumption: it may be because the water-insoluble inorganic particles are easy to aggregate, so they are not fully dispersed microscopically in the water-absorbing resin, and when the water-insoluble inorganic particles are added, the physical properties of the particulate water-absorbing agent are reduced, especially the reflux amount under pressure in the swollen state is increased. And it was found that: by making the mixing time when mixing the water-insoluble inorganic particles longer than the time required for normal uniform mixing, a particulate water-absorbing agent that satisfies the formula (1) can be obtained. Generally, the time required for uniform mixing is set by the previous evaluation method, etc., but the present inventors have found that the new parameter RCAP is an indicator for improving the reflux amount under pressure in the swollen state, and thus, the additional effect achieved by further extending the mixing time that was previously considered to be sufficient was first discovered. In the past, it was believed that a longer mixing time would lead to a decrease in productivity, etc., and it was not preferred, so it was not actively implemented, but in the present invention, according to the above discovery, a greater advantage can be obtained that far exceeds the disadvantages such as reduced productivity. The mixing time of the water-absorbent resin and the water-insoluble inorganic particles is, for example, 5 minutes or more, preferably 15 minutes or more, and more preferably 30 minutes or more.

[0136] The means used for mixing the water-absorbent resin and the water-insoluble inorganic particles is not particularly limited, but it is preferred to use a mixing means that provides strong stirring conditions rather than gentle stirring such as with a paddle stirring device.

[0137] The upper limit of the mixing time is not particularly limited. If the productivity and the saturation of the effect are taken into account, it is preferably less than 5 hours, more preferably less than 2 hours. In addition, as a mixing method, it is not particularly limited, preferably a method of mixing while applying vibration, a method of mixing while rotating (such as a method using a drum rocking mixer), a method of mixing based on a stirrer, air conveying, etc., which transports particles together with airflow. The stirring condition is appropriately set according to the mixing device. For example, when a drum rocking mixer is used, its rotation speed is preferably higher than 45rpm, more preferably more than 70rpm, and more preferably more than 100rpm. In addition, the mixing time required for ideal mixing varies due to various mixing methods, and the purpose of the present application can be achieved by appropriately adjusting the mixing time. Regarding the judgment of whether the purpose of the present application can be achieved, whether the physical property parameters of the present application are met can become an indicator.

[0138] (Manufacturing method b)

[0139] A water-soluble compound containing a polyvalent metal cation is added to a water-absorbent resin and the mixing time is controlled to obtain a particulate water-absorbent satisfying the formula (1).

[0140] The water-soluble polyvalent metal cation-containing compound may be directly mixed with the water-absorbent resin in the form of powder, or may be mixed in the form of a solution, particularly an aqueous solution, or may be dissolved in a surface crosslinking agent or its aqueous solution.

[0141] In addition, it can be added multiple times. In this case, for example, when adding twice, the (weight) ratio is specified as 1 / 99 to 99 / 1, preferably 10 / 90 to 90 / 10. If it exceeds these ranges, it is very similar to the same situation as adding once, lacking the effect of multiple additions, so it is not preferred.

[0142] The method of adding the water-soluble compound containing polyvalent metal cations is not particularly limited, but preferably: (1) adding at the same time as adding the surface crosslinking agent (adding in the surface crosslinking step); (2) adding after the surface crosslinking step. By adding the water-soluble compound containing polyvalent metal cations at this time, it can be present near the surface of the particles, which can improve the performance of the water absorbent. When adding after the surface crosslinking step, it can also be added together with other additives.

[0143] The water-soluble compound containing polyvalent metal cations can be added to the water-absorbent resin (powder) in a solution state dissolved in a solvent (e.g., water). When the water-soluble compound containing polyvalent metal cations is added in the form of an aqueous solution, in addition to water, a hydrophilic organic solvent (alcohol or polyglycol) and a surfactant can be used in combination to improve dispersibility, solubility, and miscibility. The amount of water used is appropriately determined depending on the type of the water-soluble compound containing polyvalent metal cations and the method of adding, and is, for example, 0 parts by weight (dry mixing) to 50 parts by weight, further 0.1 to 10 parts by weight, 0.5 to 5 parts by weight, relative to 100 parts by weight of the water-absorbent resin.

[0144] In addition, the water-soluble compound containing polyvalent metal cations can be added to the water-absorbent resin (powder) in its original form. In this case, the water-soluble compound containing polyvalent metal cations is preferably in the form of particles. The volume average particle size of the water-soluble compound containing polyvalent metal cations is preferably 10 μm or less, more preferably 5 μm or less, and further preferably 1 μm or less. In addition, the volume average particle size is preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.3 μm or more. By being above the above lower limit, the decrease in workability during the addition process can be suppressed, and sufficient performance can be obtained. It should be noted that the volume average particle size of the water-soluble compound containing polyvalent metal cations can be measured using the "laser diffraction scattering method" (for example, using a particle size analyzer manufactured by Nikkiso Co., Ltd., trade name: MICROTRAC MT3000II).

[0145] In this specification, water-soluble means a substance that is soluble (or easily soluble) in water at room temperature (23°C) and normal pressure (1 atmosphere). For example, it refers to a substance that dissolves more than 1g in 100ml of water at room temperature and normal pressure. In addition, water-insoluble means a substance that is insoluble (or poorly soluble) in water at room temperature (23°C) and normal pressure (1 atmosphere). For example, it refers to a substance that dissolves less than 1g in 100ml of water at room temperature and normal pressure, and more preferably, it dissolves less than 0.1g in 100ml of water at room temperature and normal pressure.

[0146] The mixing time of the water-absorbent resin and the water-soluble compound containing polyvalent metal cations is not particularly limited and can be appropriately set using a mixing device. It is preferred to mix for a longer time in a manner that satisfies the above formula (1). That is, in the present invention, it is preferred to mix the water-absorbent resin and the water-soluble compound containing polyvalent metal cations for a longer time than the mixing time for the purpose of simply mixing the additives. Usually, for the purpose of improving productivity, the operation of the mixing device is stopped at the moment when it can be confirmed by visual inspection or conventional evaluation methods that the additives have been uniformly mixed. In addition, through this conventional mixing, the basic performance required for particulate water absorbents such as AAP and CRC is also ensured. However, the reflux amount of these particulate water absorbents under pressure when the particulate water absorbents are swollen is not sufficiently reduced. The present inventors have discovered this problem and conducted research, and as a result, they have made the following assumption: the water-soluble compound containing polyvalent metal cations is probably insufficient in the conventional mixing method and time, and therefore it is not sufficiently dispersed microscopically in the water-absorbent resin, and when the water-soluble compound containing polyvalent metal cations is added, the physical properties of the particulate water-absorbing agent are reduced, especially the amount of reflux under pressure in the swollen state is increased. And it is found that the particulate water-absorbing agent that satisfies the formula (1) can be obtained by making the mixing time when mixing the water-soluble compound containing polyvalent metal cations longer than the time required for normal uniform mixing. Generally, the time required for uniform mixing is set by conventional evaluation methods, etc., but the present inventors have found that the new parameter RCAP is an indicator for improving the amount of reflux under pressure in the swollen state, and thus, for the first time, they have found an additional effect achieved by further extending the mixing time that was previously considered sufficient. In the past, it was believed that a longer mixing time would lead to a decrease in productivity, etc., which was not preferred, and therefore, it was not actively implemented. However, in the present invention, according to the above findings, greater advantages that far outweigh the disadvantages of reduced productivity can be obtained. The mixing time of the water-absorbent resin and the water-soluble compound containing polyvalent metal cations is, for example, more than 5 minutes, preferably more than 15 minutes, and more preferably more than 30 minutes. The upper limit of the mixing time is not particularly limited. If the productivity and the saturation of the effect are taken into account, it is preferably less than 5 hours, and more preferably less than 2 hours. In addition, as a mixing method, it is not particularly limited, and preferably a method of mixing while applying vibration, a method of mixing while rotating (such as a method using a rotary drum swing mixer), a method of mixing based on a stirrer, air conveying, etc., which conveys particles together with an air flow. The rotation speed at this time can also be the same as that of the manufacturing method a. In addition, the mixing time required for ideal mixing varies depending on the various mixing methods, and the purpose of the present application can be achieved by appropriately adjusting the mixing time. Whether the physical property parameters of the present application are met can be an indicator for determining whether the purpose of the present application can be achieved.

[0147] (Manufacturing method c)

[0148] In the manufacturing method of the particulate water-absorbing agent, there is a step of washing the water-absorbing resin with a washing liquid containing water as a main component. By washing the water-absorbing resin with a washing liquid containing water as a main component, a particulate water-absorbing agent satisfying the formula (1) can be easily obtained. The detailed mechanism is not clear, but it is considered that by washing the water-absorbing resin with a washing liquid containing water as a main component, the water-absorbing resin contains water and is in a swollen state. By washing in this state, it is possible to effectively wash away unnecessary components that may affect the water absorption performance, and it is easy to obtain a water-absorbing agent with a high RCAP.

[0149] It should be noted that in the above-mentioned Patent Document 2 (International Publication No. 97 / 003114), washing is performed for the purpose of reducing the residual cross-linking agent, and "the mixing ratio range of water and the hydrophilic organic solvent is selected so that the mixed liquid does not cause the water-absorbent resin powder to swell", which is clearly different from the above-mentioned step of causing the water-absorbent resin powder to swell by washing with a washing liquid containing water as a main component.

[0150] As a washing method, for example, after the water-absorbent resin is swollen, washing with a washing liquid is preferably performed. As a method for swollen the water-absorbent resin, a method of using a liquid containing water as a main component and immersing the water-absorbent resin in the liquid can be cited. As for the immersion time, there is no particular limitation as long as the water-absorbent resin is sufficiently swollen, and for example, it can be 1 minute or more, or 5 minutes or more.

[0151] Water as the main component means that the cleaning liquid contains 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more, and further preferably 99% by weight or more of water, and preferably consists essentially of water.

[0152] The water preferably contains no impurities, and is preferably RO water, deionized water, distilled water, purified water, etc., and more preferably deionized water or distilled water.

[0153] As a component other than water, a hydrophilic organic solvent may be contained. As the hydrophilic organic solvent used, lower alcohols such as methanol, ethanol, propanol, isopropanol, and tert-butanol can be appropriately exemplified.

[0154] Here, the water-absorbent resin may be either water-absorbent resin powder before surface crosslinking treatment or water-absorbent resin particles after surface crosslinking. From the viewpoint of more easily obtaining a particulate water-absorbing agent satisfying formula (1), it is preferred that the water-absorbent resin powder before surface crosslinking treatment (so-called base polymer) is washed.

[0155] The washing method is not particularly limited, and the water-absorbent resin may be washed using a washing liquid in a continuous or discontinuous batch method. Examples of the washing method include a method in which the water-absorbent resin is brought into contact with the washing liquid while stirring as necessary, and then the water-absorbent resin is separated from the washing liquid by, for example, decantation or suction filtration; and a method in which a swollen hydrogel is washed by passing the washing liquid.

[0156] In addition, cleaning can be performed multiple times.

[0157] In these methods, the cleaning time (water flow time) is preferably 15 minutes to 10 hours, more preferably 30 minutes to 8 hours, and further preferably 1 to 5 hours. From the aspect of the cleaning effect, the temperature of the cleaning solution is preferably 20 to 50° C. In addition, the pressure during cleaning can be pressurized, decompressed, or normal pressure, and is usually carried out under normal pressure.

[0158] The washed water-absorbing resin (hydrogel) may be subjected to the same subsequent steps as those for the hydrogel in the method for producing a particulate water-absorbing agent [3] described below, and may be further subjected to drying, pulverization, classification and the like as necessary.

[0159] [3] Method for producing granular water-absorbing agent

[0160] The following will show the production steps (3-1) to (3-8) of the particulate water-absorbing agent according to the present invention.

[0161] (3-1) Preparation step of monomer aqueous solution

[0162] This step is a step of preparing an aqueous solution containing a monomer (e.g., acrylic acid (salt)) as a main component (hereinafter referred to as "monomer aqueous solution"). It should be noted that a slurry of the monomer may be used within a range that does not reduce the water absorption performance of the obtained water-absorbent resin, but in this section, for convenience, the monomer aqueous solution is described.

[0163] The above-mentioned "main component" means that the amount (content) of acrylic acid (salt) used is usually 50 mol% or more, preferably 70 mol% or more, more preferably 90 mol% or more (the upper limit is 100 mol%) based on the total amount of monomers (excluding the internal crosslinking agent) used in the polymerization reaction of the water-absorbent resin.

[0164] (acrylic acid)

[0165] In the present invention, acrylic acid and / or a salt thereof (hereinafter referred to as "acrylic acid (salt)") is used as a monomer from the viewpoint of physical properties and productivity of the obtained particulate water-absorbing agent.

[0166] The "acrylic acid" may be a known acrylic acid. As a polymerization inhibitor, it is preferred to contain methoxyphenols, more preferably p-methoxyphenol. From the viewpoint of the polymerizability of acrylic acid and the color tone of the particulate water-absorbing agent, it is preferred to contain 200 ppm or less, more preferably 10 to 160 ppm, and even more preferably 20 to 100 ppm. In addition, regarding impurities in acrylic acid, the compounds described in U.S. Patent Application Publication No. 2008 / 0161512 can also be applied in the present invention.

[0167] The "acrylate" is obtained by neutralizing the acrylic acid with the following alkaline composition. The acrylate may be a commercially available acrylate (eg, sodium acrylate) or may be obtained by neutralization in a particulate water-absorbing agent production facility.

[0168] (Alkaline composition)

[0169] In the present invention, the "alkaline composition" refers to a composition containing an alkaline compound, and for example, a commercially available sodium hydroxide aqueous solution is suitable.

[0170] Specifically, the alkaline compound includes alkali metal carbonates, bicarbonates, alkali metal hydroxides, ammonia, organic amines, etc. Among these, strong alkalinity is desirable from the viewpoint of the physical properties of the obtained particulate water-absorbing agent. That is, preferably, an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., more preferably sodium hydroxide.

[0171] (Neutral)

[0172] As the neutralization in the present invention, any of the neutralization of acrylic acid (before polymerization) and the neutralization of the hydrogel crosslinked polymer obtained by crosslinking and polymerizing acrylic acid (after polymerization) (hereinafter referred to as "post-neutralization") can be selected or used in combination. In addition, these neutralizations may be continuous or intermittent, and are not particularly limited. From the viewpoint of production efficiency, etc., continuous is preferred.

[0173] In addition, regarding the conditions such as the neutralization apparatus, neutralization temperature, and residence time, the conditions described in International Publication No. 2009 / 123197 and US Patent Application Publication No. 2008 / 0194863 can also be applied to the present invention.

[0174] The neutralization rate in the present invention is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, further preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol% relative to the acid groups of the monomer. When the neutralization rate is less than 10 mol%, the water absorption rate may be significantly reduced. On the other hand, when the neutralization rate exceeds 90 mol%, a water-absorbent resin having a high water absorption rate under pressure may not be obtained.

[0175] The above neutralization rate is the same in the case of post-neutralization. In addition, the above neutralization rate can also be applied to the neutralization rate of the particulate water-absorbing agent as the final product. It should be noted that the neutralization rate of 75 mol% refers to a mixture of 25 mol% of acrylic acid and 75 mol% of acrylic acid salt. In addition, this mixture is sometimes referred to as a partially neutralized acrylic acid.

[0176] (Other monomers)

[0177] In the present invention, "other monomers" refer to monomers other than the above-mentioned acrylic acid (salt), and other monomers can be used in combination with acrylic acid (salt) to produce a particulate water-absorbing agent.

[0178] Examples of the other monomers include water-soluble or hydrophobic unsaturated monomers. Specifically, the compounds described in US Patent Application Publication No. 2005 / 0215734 (excluding acrylic acid) can also be used in the present invention.

[0179] (Internal crosslinking agent)

[0180] As the internal crosslinking agent used in the present invention, the compounds described in U.S. Patent No. 6241928 can also be used in the present invention. One or more compounds can be selected from these in consideration of reactivity. In the present invention, in consideration of water absorption performance, it is preferred to surface treat the crosslinked body using the internal crosslinking agent.

[0181] From the viewpoint of the water absorption performance of the obtained water-absorbing resin, it is preferred to use a compound having two or more polymerizable unsaturated groups as the internal crosslinking agent, more preferably a compound having thermal decomposition at the drying temperature described below, and still more preferably a compound having two or more polymerizable unsaturated groups having a (poly)alkylene glycol structural unit.

[0182] As the polymerizable unsaturated group, preferably allyl group and (meth)acrylate group are mentioned, and more preferably (meth)acrylate group is mentioned. In addition, as the (poly)alkylene glycol structural unit, polyethylene glycol is preferred, and the number n is preferably 1-100, and more preferably 6-50.

[0183] Therefore, in the present invention, it is preferred to use (poly)alkylene glycol di(meth)acrylate or (poly)alkylene glycol tri(meth)acrylate, and it is more preferred to use (poly)ethylene glycol di(meth)acrylate.

[0184] The amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, relative to the total monomer. By setting the amount within the above range, the desired water-absorbent resin can be obtained. It should be noted that when the amount is too small, the gel strength tends to decrease and the water-soluble component tends to increase, and when the amount is too large, the water absorption rate tends to decrease.

[0185] In the present invention, it is preferred to use a method in which a predetermined amount of an internal crosslinking agent is added to an aqueous monomer solution in advance and a crosslinking reaction is carried out simultaneously with polymerization. On the other hand, in addition to this method, the following methods may be used: a method in which an internal crosslinking agent is added during or after polymerization to carry out post-crosslinking; a method in which a free radical polymerization initiator is used to carry out free radical crosslinking; a method in which radiation crosslinking is carried out using active energy rays such as electron beams and ultraviolet rays, etc. may be used. In addition, these methods may be used in combination.

[0186] (Other substances added to the monomer aqueous solution)

[0187] In the present invention, from the viewpoint of improving the physical properties of the obtained water-absorbing resin, the following substances may be added when preparing the aqueous monomer solution.

[0188] Specifically, hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), and polyacrylic acid (salt) crosslinked products can be added to the aqueous monomer solution in an amount of preferably 50% by weight or less, more preferably 20% by weight or less, further preferably 10% by weight or less, and particularly preferably 5% by weight or less (the lower limit is 0% by weight). Foaming agents such as carbonates, azo compounds, bubbles, surfactants, chelating agents such as diethylenetriaminepentaacetic acid (salt), ethylenediaminetetramethylenephosphonic acid (salt), and chain transfer agents can also be added to the aqueous monomer solution in an amount of preferably 5% by weight or less, more preferably 1% by weight or less, and further preferably 0.5% by weight or less (the lower limit is 0% by weight).

[0189] Furthermore, the above substances may be added not only to the aqueous monomer solution but also during the polymerization process, and these forms may be used in combination.

[0190] When a water-soluble resin or a water-absorbent resin is used as the hydrophilic polymer, a graft polymer or a water-absorbent resin composition (for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.) can be obtained. These polymers and water-absorbent resin compositions also fall within the scope of the present invention.

[0191] (Concentration of monomer component)

[0192] In this step, the various substances mentioned above are added when preparing the monomer aqueous solution. The concentration of the monomer component in the monomer aqueous solution is not particularly limited, but is preferably 10 to 80 wt %, more preferably 20 to 75 wt %, and even more preferably 30 to 70 wt % from the viewpoint of the physical properties of the water-absorbent resin.

[0193] When aqueous solution polymerization or reverse phase suspension polymerization is employed, a solvent other than water may be used in combination as necessary. In this case, the type of solvent is not particularly limited.

[0194] The “monomer component concentration” is a value obtained by the following formula (5), and the weight of the aqueous monomer solution does not include the weight of the graft component, the water-absorbing resin, and the hydrophobic solvent in the reversed phase suspension polymerization.

[0195] (Concentration of monomer component (weight %)) = (weight of monomer component) / (weight of monomer aqueous solution) × 100 Formula (5)

[0196] (3-2) Polymerization process

[0197] This step is a step of polymerizing the acrylic acid (salt)-based monomer aqueous solution obtained in the above monomer aqueous solution preparation step to obtain a hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel").

[0198] (Polymerization initiator)

[0199] The polymerization initiator used in the present invention is appropriately selected according to the polymerization form, etc., and is therefore not particularly limited. Examples thereof include a thermal decomposition type polymerization initiator, a photodecomposition type polymerization initiator, or a redox polymerization initiator obtained by combining 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. 7265190 can be used. It should be noted that, from the viewpoint of the handling property of the polymerization initiator, the physical properties of the particulate water absorbent or the water-absorbing resin, it is preferred to use a peroxide or an azo compound, more preferably a peroxide, and further preferably a persulfate.

[0200] The amount of the polymerization initiator used is preferably 0.001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the monomer. The amount of the reducing agent used is preferably 0.0001 to 0.02 mol%, based on the monomer.

[0201] In addition, instead of the above-mentioned polymerization initiator, the polymerization reaction may be carried out by irradiating active energy rays such as radiation, electron beams, and ultraviolet rays, or these active energy rays may be used in combination with the polymerization initiator.

[0202] (Aggregate form)

[0203] The polymerization form used in the present invention is not particularly limited, and from the viewpoints of water absorption characteristics and ease of polymerization control, spray droplet polymerization, aqueous solution polymerization, and reversed phase suspension polymerization are preferably listed, aqueous solution polymerization and reversed phase suspension polymerization are more preferably listed, and aqueous solution polymerization is further preferably listed. Among them, continuous aqueous solution polymerization is particularly preferred, and continuous belt polymerization and continuous kneader polymerization can be applied.

[0204] As specific polymerization forms, continuous belt polymerization is disclosed in U.S. Patent No. 4,893,999, U.S. Patent No. 6,241,928, and U.S. Patent Application Publication No. 2005 / 215734, and continuous kneader polymerization is disclosed in U.S. Patent No. 6,987,151 and U.S. Patent No. 6,710,141. By adopting these continuous aqueous solution polymerizations, the production efficiency of the water-absorbent resin is improved.

[0205] In addition, as preferred forms of the above-mentioned continuous aqueous solution polymerization, "high temperature initiated polymerization" and "high concentration polymerization" can be listed. "High temperature initiated polymerization" means a form in which polymerization is initiated at a temperature of preferably 30°C or higher, more preferably 35°C or higher, further preferably 40°C or higher, and particularly preferably 50°C or higher (the upper limit is the boiling point) of the monomer aqueous solution, and "high concentration polymerization" means a form in which polymerization is carried out under conditions where the monomer concentration is preferably 30% by weight or higher, more preferably 35% by weight or higher, further preferably 40% by weight or higher, and particularly preferably 45% by weight or higher (the upper limit is the saturated concentration). These polymerization forms may also be used in combination.

[0206] In the present invention, polymerization can be carried out in an air atmosphere, but from the viewpoint of the color tone of the obtained water-absorbing resin, polymerization can be carried out in an atmosphere of an inert gas such as nitrogen or argon. In this case, for example, the oxygen concentration is preferably controlled to be 1% by volume or less. It should be noted that the dissolved oxygen in the aqueous monomer solution is also preferably replaced with an inert gas in advance (for example, dissolved oxygen: less than 1 mg / l).

[0207] In the present invention, foaming polymerization may be performed by dispersing bubbles (particularly the above-mentioned inert gas and the like) in an aqueous monomer solution to perform polymerization.

[0208] In addition, in the present invention, the solid content concentration can be increased during polymerization. As an indicator of such an increase in solid content concentration, the solid content increase degree is defined by the following formula (6). It should be noted that the increase in the solid content concentration is preferably 1% by weight or more, and more preferably 2% by weight or more. (Solid content increase degree (weight %)) = (solid content concentration (weight %) of the hydrogel after polymerization) - (solid content concentration (weight %) of the monomer aqueous solution) Formula (6).

[0209] The solid content concentration of the aqueous monomer solution refers to the value calculated using the following formula (7), and the components in the polymerization system refer to the aqueous monomer solution and the grafted components, the water-absorbing resin, and other solid substances (such as water-insoluble particles, etc.), excluding the hydrophobic solvent in the reverse suspension polymerization.

[0210] (Solid content of monomer aqueous solution (weight %)) = ((weight of monomer component + graft component + water-absorbent resin + other solid matter)) / (weight of components in polymerization system) × 100 Formula (7).

[0211] In addition, as the form of aqueous solution polymerization, the present invention can be implemented by using a stationary polymerization method in which a monomer aqueous solution is polymerized in a stationary state, a stirring polymerization method in which polymerization is performed in a stirring device, etc. In the stationary polymerization method, an endless belt is preferably used. The belt is preferably a resin or rubber belt from which polymerization heat is not easily dissipated from the material contact surface.

[0212] (3-3) Gel crushing step

[0213] This step is a step of obtaining a granular hydrogel (hereinafter referred to as "granular hydrogel") by gel-crushing the hydrogel obtained in the above-mentioned polymerization step using a screw extruder such as a kneader, a meat grinder, or a gel-crushing machine such as a cutting mill. It should be noted that when the above-mentioned polymerization step is kneader polymerization, the polymerization step and the gel-crushing step may be carried out simultaneously. In addition, when a granular hydrogel is directly obtained during the polymerization process such as gas phase polymerization or reverse phase suspension polymerization, the gel-crushing step may not be carried out.

[0214] Regarding the gel grinding conditions and forms other than those described above, the contents disclosed in International Publication No. 2011 / 126079 are preferably applied in the present invention.

[0215] (3-4) Drying process

[0216] This step is a step of drying the particulate hydrogel obtained in the above-mentioned polymerization step and / or gel pulverization step to a desired resin solid content to obtain a dry polymer. The resin solid content is determined from the loss on drying (weight change when 1 g of the water-absorbent resin is heated at 180° C. for 3 hours) and is preferably 80% by weight or more, more preferably 85 to 99% by weight, further preferably 90 to 98% by weight, and particularly preferably 92 to 97% by weight.

[0217] The drying method of the particulate hydrogel is not particularly limited, and examples thereof include heating drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum drying, drying by azeotropic dehydration with a hydrophobic organic solvent, high humidity drying using high temperature steam, etc. Among them, hot air drying is preferred from the viewpoint of drying efficiency, and belt drying in which hot air drying is performed on a ventilation belt is more preferred.

[0218] The drying temperature (hot air temperature) in the hot air drying is preferably 120 to 250° C., more preferably 150 to 200° C., from the viewpoint of the color tone of the water-absorbent resin and the drying efficiency. The drying conditions other than the drying temperature, such as the hot air velocity and the drying time, may be appropriately set according to the water content and the total weight of the particulate hydrogel to be dried and the target resin solid content. When belt drying is performed, the conditions described in International Publication No. 2006 / 100300, International Publication No. 2011 / 025012, International Publication No. 2011 / 025013, International Publication No. 2011 / 111657, etc. may be appropriately applied.

[0219] (3-5) Crushing and Classification Process

[0220] This step is a step of pulverizing the dry polymer obtained in the above-mentioned drying step (pulverization step) and adjusting the particle size to a predetermined range (classification step) to obtain a water-absorbent resin powder (the powdery water-absorbent resin before surface cross-linking is simply referred to as "water-absorbent resin powder").

[0221] Examples of the machine used in the pulverizing step of the present invention include high-speed rotary pulverizers such as roller mills, hammer mills, screw mills, and pin mills; vibration mills, knuckle-type pulverizers, cylindrical agitators, etc., which can be used in combination as needed.

[0222] In addition, the particle size adjustment method in the classification step of the present invention is not particularly limited, and examples thereof include sieving using a JIS standard sieve (JIS Z8801-1 (2000)), air flow classification, etc. It should be noted that the particle size adjustment of the water-absorbent resin is not limited to the above-mentioned pulverization step and classification step, and can be appropriately carried out in a polymerization step (particularly reversed phase suspension polymerization, spray droplet polymerization) or other steps (for example, a granulation step, a fine powder recovery step).

[0223] The water-absorbent resin powder obtained in the above process (water-absorbent resin powder before the surface cross-linking process, so-called base polymer) has a weight average particle size (D50) of preferably 200 to 600 μm, more preferably 200 to 550 μm, and even more preferably 250 to 500 μm. In addition, the proportion of particles having a particle size of less than 150 μm is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1% by weight or less, and the proportion of particles having a particle size of 850 μm or more is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less. It should be noted that the lower limit of the proportion of these particles is preferably as small as possible in any case, and is preferably 0% by weight, and can be about 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. It should be noted that these particle sizes can be measured using a standard sieve according to the measurement methods disclosed in US Pat. No. 7,638,570 and EDANA ERT420.2-02.

[0224] The above particle size is applicable not only to the water-absorbing resin after surface crosslinking (hereinafter sometimes referred to as "water-absorbing resin particles") but also to the particulate water-absorbing agent as the final product. Therefore, it is preferred to carry out the surface crosslinking treatment (surface crosslinking step) so as to maintain the particle size in the above range in the water-absorbing resin particles, and it is more preferred to provide a particle size adjustment step during and after the surface crosslinking step.

[0225] (3-6) Surface cross-linking process

[0226] This step is a step of further providing a portion with a high crosslinking density on the surface layer (portion several tens of micrometers from the surface of the water-absorbent resin powder) of the water-absorbent resin powder obtained through the above steps, and comprises a mixing step, a heat treatment step and a cooling step (optional).

[0227] In the surface crosslinking step, surface-crosslinked water-absorbent resin (water-absorbent resin particles) is obtained by radical crosslinking, surface polymerization, a crosslinking reaction with a surface crosslinking agent, etc. at the surface of the water-absorbent resin powder.

[0228] (Surface cross-linking agent)

[0229] As the surface crosslinking agent used in the present invention, there is no particular limitation, and organic or inorganic surface crosslinking agents can be listed. Among them, from the viewpoint of the physical properties of the water-absorbent resin and the handleability of the surface crosslinking agent, an organic surface crosslinking agent that reacts with a carboxyl group is preferred. For example, one or more surface crosslinking agents disclosed in U.S. Patent No. 7183456 can be listed. More specifically, polyol compounds, epoxy compounds, halogenated epoxy compounds, polyamine compounds or condensates thereof with halogenated epoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. can be listed.

[0230] Specific examples of organic surface crosslinking agents include (di-, tri-, tetra-, poly)ethylene glycol, (di-, poly)propylene glycol, 1,3-propylene glycol, 2,2,4-trimethyl-1,3-pentanediol, (poly)glycerol, 2-butene-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-, poly)glycerol Epoxides such as polyglycidyl ether and glycidol; oxazoline compounds such as 2-oxazolidinone, N-hydroxyethyl-2-oxazolidinone and 1,2-ethylenebisoxazoline; 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-1,3-dioxolane Alkylene carbonate compounds 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-dioxepane-2-one; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin, and α-methyl epichlorohydrin, and polyamine adducts thereof (e.g., KYMENE manufactured by Hercules; registered trademark); γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, Silane coupling agents such as triethoxysilane; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol, 3-chloromethyl-3-methyloxetane, 3-chloromethyl-3-ethyloxetane, polyvalent oxetane compounds and other oxetane compounds; cyclic urea compounds such as 2-imidazolidinone, etc.

[0231] As the polyol, a polyol having 2 to 8 carbon atoms is preferred, a polyol having 3 to 6 carbon atoms is more preferred, and a polyol having 3 to 4 carbon atoms is further preferred. Furthermore, a diol is preferred, and examples thereof include ethylene glycol, propylene glycol, 1,3-propanediol, and 1,4-butanediol. A polyol selected from propylene glycol (1,2-propanediol), 1,3-propanediol, and 1,4-butanediol is preferred.

[0232] The epoxy compound is preferably a polyglycidyl compound, and ethylene glycol diglycidyl ether is preferably used.

[0233] On the basis of the above-mentioned organic surface crosslinking agent, from the viewpoint of more effectively performing surface crosslinking, as an ionic bonding surface crosslinking agent, a polyvalent cationic polymer such as a polyamine polymer and a water-soluble compound containing a polyvalent metal cation can be used in combination. As the water-soluble compound containing a polyvalent metal cation, it is as described above.

[0234] The amount of the surface crosslinking agent used (the total amount when using a plurality of types) is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the water-absorbent resin powder. In addition, the surface crosslinking agent is preferably added in the form of an aqueous solution, in which case the amount of water used is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the water-absorbent resin powder. Furthermore, when a hydrophilic organic solvent is used as necessary, the amount thereof is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, based on 100 parts by weight of the water-absorbent resin powder.

[0235] Furthermore, as described above, in the surface cross-linking step, a water-soluble compound containing a polyvalent metal cation may be added.

[0236] (Mixing process)

[0237] This step is a step of mixing the water-absorbent resin powder with the surface crosslinking agent. The method of mixing the surface crosslinking agent is not particularly limited, and examples thereof include a method of preparing a surface crosslinking agent solution in advance and spraying or dropping the liquid onto the water-absorbent resin powder, and more preferably spraying and mixing the liquid.

[0238] The apparatus for performing the mixing is not particularly limited, but preferably, a high-speed stirring type mixer is used, and more preferably, a high-speed stirring type continuous mixer is used.

[0239] (Heat treatment process)

[0240] This step is a step of applying heat to the mixture discharged from the above-mentioned mixing step to cause a cross-linking reaction on the surface of the water-absorbent resin powder.

[0241] The apparatus for carrying out the crosslinking reaction is not particularly limited, but a paddle dryer is preferably used. The reaction temperature in the crosslinking reaction is appropriately set depending on the type of the surface crosslinking agent used, and is preferably 50 to 300°C, more preferably 100 to 200°C.

[0242] (Cooling process)

[0243] This step is an optional step provided after the above-mentioned heat treatment step as needed.

[0244] The device for performing the cooling is not particularly limited, but is preferably a device of the same specifications as the device used in the heating treatment step, and more preferably a paddle dryer. This is because the heat medium can be used as a cooling device by replacing it with a refrigerant. It should be noted that the water-absorbing resin particles obtained by the above-mentioned heating treatment step are preferably forced to cool to 40 to 80° C., more preferably forced to cool to 50 to 70° C. in the cooling step as needed.

[0245] (3-7) Additive Addition Process

[0246] This step is a step of adding additives such as a water-soluble compound containing polyvalent metal cations, a polyvalent metal salt, a cationic polymer, a chelating agent, an inorganic reducing agent, a hydroxycarboxylic acid compound, water-insoluble inorganic particles, a surfactant, and a non-polymer water-soluble compound to the water-absorbent resin particles obtained by the above-mentioned surface crosslinking step. As described above, the additives and the above-mentioned surface crosslinking agent (aqueous solution) may be mixed with the water-absorbent resin powder at the same time.

[0247] (polyvalent metal salt and / or cationic polymer)

[0248] From the viewpoint of improving the water absorption rate, liquid permeability, moisture absorption fluidity, etc. of the resulting water-absorbent resin, a polyvalent metal salt and / or a cationic polymer may be added.

[0249] Specifically, the polyvalent metal salt and / or cationic polymer described in “[7] Polyvalent metal salt and / or cationic polymer” of International Publication No. 2011 / 040530 and the amount thereof used are used in the present invention.

[0250] In particular, as described above, the embodiment in which a water-soluble compound containing a polyvalent metal cation is added to the water-absorbing resin particles obtained by the surface crosslinking step is a preferred embodiment from the viewpoint of easily obtaining a particulate water-absorbing agent satisfying the formula (1).

[0251] (Chelating Agent)

[0252] A chelating agent may be added from the viewpoint of the color tone (anti-coloration) and anti-deterioration of the obtained water-absorbent resin.

[0253] Specifically, the compounds and the amounts used thereof disclosed in "[2] Chelating agent" of International Publication No. 2011 / 040530 are used as the chelating agent in the present invention.

[0254] (Inorganic reducing agent)

[0255] From the viewpoints of the color tone (anti-coloration), anti-deterioration, reduction of residual monomers, etc. of the obtained water-absorbing resin, an inorganic reducing agent may be added.

[0256] Specifically, the inorganic reducing agent described in “[3] Inorganic reducing agent” of International Publication No. 2011 / 040530 and the amount thereof used are used in the present invention.

[0257] (α-Hydroxycarboxylic acid compound)

[0258] α-Hydroxycarboxylic acid may be added from the viewpoint of the color tone (anti-coloration) of the obtained water-absorbing resin, etc. The “α-hydroxycarboxylic acid compound” refers to a carboxylic acid or a salt thereof having a hydroxyl group in the molecule, and is a hydroxycarboxylic acid having a hydroxyl group at the α position.

[0259] Specifically, the α-hydroxycarboxylic acid compound disclosed in “[6] α-hydroxycarboxylic acid compound” of International Publication No. 2011 / 040530 and the amount thereof used are applied in the present invention.

[0260] (Water-insoluble inorganic particles)

[0261] From the viewpoint of improving the fluidity of the water-absorbent resin, water-insoluble inorganic particles may be added. Specifically, the water-insoluble inorganic particles described in the above column (2-9) may be cited. As described above, from the viewpoint of easily obtaining a particulate water-absorbing agent satisfying formula (1), the form in which water-insoluble inorganic particles are added to the water-absorbent resin particles obtained by the above surface crosslinking step is a preferred form.

[0262] (Surfactant)

[0263] From the viewpoint of improving the physical properties (for example, water absorption rate) of the obtained water-absorbent resin, a surfactant may be added.

[0264] Specific examples of the surfactant include surfactants disclosed in International Publication No. 97 / 017397 and US Pat. No. 6,107,358, that is, nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.

[0265] (Non-polymer water-soluble compounds)

[0266] From the viewpoint of reducing dust of the water-absorbing resin, etc., a non-polymer water-soluble compound may be added. In the present invention, the compounds and the amounts used thereof disclosed in "Non-polymer water-soluble compound" of International Publication No. 2014 / 034667 are applied.

[0267] In the present invention, in order to add various functions to the water-absorbent resin, additives other than the above-mentioned additives may be added. Specific examples of such additives include compounds having phosphorus atoms, oxidants, organic reducing agents, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, thermoplastic fibers, and the like.

[0268] The amount of the additive used (added amount) can be appropriately determined according to its application and is not particularly limited, but is preferably 3 parts by weight or less, more preferably 1 part by weight or less, based on 100 parts by weight of the water-absorbent resin. The additive may also be added in a step different from the above step.

[0269] (3-8) Other processes

[0270] In the present invention, in addition to the above-mentioned steps, a granulation step, a granulation step, a fine powder removal step, a fine powder recycling step, etc. may be provided as needed. In addition, one or more steps of a transportation step, a storage step, a packaging step, a storage step, etc. may be further included. It should be noted that the "granulation step" includes: a fine powder removal step during and after the surface cross-linking step; a step of classifying and pulverizing when the water-absorbent resin aggregates and exceeds the desired size. In addition, in the "fine powder recycling step", in addition to the form of directly adding fine powder as in the present invention, it also includes: a step of making a large hydrogel and adding it in any step of the production process of the water-absorbent resin.

[0271] 〔4〕Application of granular water absorbent

[0272] The granular water-absorbing agent of the present invention can be used for applications for the purpose of absorbing water, and is widely used as an absorbent. In addition, it can be used as an absorbent article including the absorbent. In particular, the granular water-absorbing agent of the present invention can reduce backflow under pressure, and therefore, among absorbent articles, it can be suitably used as a sanitary article used by humans for absorbing body fluids such as urine and blood.

[0273] That is, a preferred embodiment of the present invention is an absorbent including the particulate water-absorbing agent of the above-described embodiment.

[0274] Moreover, another suitable embodiment of the present invention is a sanitary article including the absorbent body of the above-mentioned form.

[0275] As the absorbent, there can be cited an absorbent material formed by using a particulate water absorbent and a fiber substrate (e.g., hydrophilic fiber) as the main components. It is further preferred that the content (core concentration) of the particulate water absorbent in the absorbent is 20 to 100% by weight relative to the total weight of the particulate water absorbent and the hydrophilic fiber, more preferably 25 to 90% by weight, particularly preferably 30 to 80% by weight, and most preferably 40 to 80% by weight. The higher the core concentration in the absorbent, the more it will be affected by the water absorption performance of the particulate water absorbent when manufacturing the absorbent, absorbent articles, etc. This absorbent is formed by, for example, blending or sandwiching a fiber substrate such as a hydrophilic fiber with a particulate water absorbent. As the fiber substrate used, there can be cited: for example, hydrophilic fibers such as crushed wood pulp; cotton linters, cross-linked cellulose fibers, rayon, cotton, wool, acetate, vinylon, etc. These fiber substrates are preferably those formed by air-laying.

[0276] The absorbent body may be a (paste-free) water-absorbent sheet in which a water-absorbent resin is fixed between two sheets (for example, nonwoven fabrics).

[0277] In addition, the above-mentioned absorbent article refers to an absorbent article having the above-mentioned absorbent body, a liquid-permeable surface sheet and a liquid-impermeable back sheet. Regarding the above-mentioned absorbent article, an absorbent body (absorbent core) is manufactured, and the absorbent core is clamped by a liquid-permeable surface sheet and a liquid-impermeable back sheet. Thereafter, as required, by equipping elastic components, diffusion layers, adhesive tapes, etc., absorbent articles such as adult diapers and sanitary napkins are obtained. It should be noted that at this time, the above-mentioned absorbent core is compressed and formed to, for example, a density of 0.06 to 0.50 [g / cm 3 ], basis weight is 0.01~0.20[g / cm 2 ] range.

[0278] Example

[0279] The present invention is 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, in the following examples, unless otherwise specified, the operation is performed under the conditions of room temperature (20 to 25° C.) and relative humidity of 45 to 55% RH.

[0280] In addition, the electrical equipment used in Examples, Comparative Examples, and Reference Examples (including the measurement of physical properties of the particulate water-absorbing agent) used a power supply of 200 V or 100 V unless otherwise specified.

[0281] (a) Determination of Moisture Absorption Blocking Ratio (BR)

[0282] 2 g of the particulate water-absorbing agent or water-absorbing resin was evenly spread in an aluminum cup with a diameter of 52 mm, and then allowed to stand for 1 hour in a constant temperature and humidity chamber (PLATINOUS LUCIFERPL-2G; manufactured by Tabai ESPEC Co., Ltd.) at a temperature of 25° C. and a relative humidity of 90±5% RH. After 1 hour, the particulate water-absorbing agent or water-absorbing resin in the aluminum cup was gently transferred to a JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm) with a mesh size of 2000 μm (JIS 8.6 mesh), and classified for 5 seconds using a Ro-Tap type sieve shaker (manufactured by Iida Seisakusho Co., Ltd., ES-65 type sieve shaker; rotation speed 230 rpm, impact number 130 rpm) at room temperature (20 to 25° C.) and a relative humidity of 50% RH. The weight of the particulate water absorbent or water absorbent resin remaining on the JIS standard sieve (W1 [g]) and the weight of the particulate water absorbent or water absorbent resin passing through the JIS standard sieve (W2 [g]) were measured, and the hygroscopic fluidity (hygroscopic agglomeration rate) was calculated according to the following formula. It should be noted that the lower the agglomeration rate, the better the hygroscopic fluidity.

[0283] Hygroscopic fluidity (BR) [weight %] = {W1 / (W1+W2)}×100.

[0284] (b) Dust quantity determination method

[0285] The method is implemented in accordance with the descriptions of

[281] to

[282] of International Publication No. 2006 / 098271. That is, the dust amount of the particulate water absorbent is measured based on the weight gain of the dust attracted and captured by the glass fiber filter paper within a specified time under the following conditions. As a measuring device, a Heubach Dust Meter (Heubach DUSTMETER) manufactured by Heubach Engineering GmbH, Germany is used, and the measurement mode is Type II. The atmospheric temperature during the measurement is 23°C (±2°C), the relative humidity is 20 to 40% RH, and the measurement is carried out under normal pressure. The measurement method is carried out as follows.

[0286] (1) 100.00 g of a particulate water-absorbing agent as a measurement sample is placed in a rotating drum.

[0287] (2) The weight of a glass fiber filter paper having a retention particle size of 0.5 μm (JIS P3801) and a diameter of 50 mm (e.g., GLASS FIBER GC-90 manufactured by ADVANTEC or a product thereof processed to a diameter of 50 mm) is measured to the nearest 0.00001 g ([Da] g).

[0288] (3) Install a large particle separator on the drum and a filter box equipped with glass fiber filter paper.

[0289] (4) The measurement conditions of the control unit in the dust tester are set as follows, and the measurement is performed: drum rotation speed: 30 rpm, suction air volume: 4 L / min, time (measurement time): 30 minutes.

[0290] (5) After a predetermined period of time, the weight of the glass fiber filter paper is measured to the nearest 0.00001 g ([Db]).

[0291] Using the above Da and the above Db, the dust amount is calculated according to the following formula (8).

[0292] Dust amount [mg / kg] = ([Db] - [Da]) / 100 × 1,000,000 Formula (8).

[0293] (c) Surface tension measurement method

[0294] 50 ml of physiological saline adjusted to 20° C. was placed in a well-cleaned 100 ml beaker, and the surface tension of the physiological saline was first measured using a surface tension meter (K11 automatic surface tension meter manufactured by KRUSS Co., Ltd.) In this measurement, the surface tension value must be in the range of 71 to 75 [mN / m].

[0295] Next, a well-cleaned 25 mm long fluororesin rotor and 0.5 g of a particulate water absorbent or water absorbent resin are placed in a beaker containing physiological saline adjusted to 20°C and the surface tension of which is measured, and stirred at 500 rpm for 4 minutes. After 4 minutes, stirring is stopped, and after the water-containing particulate water absorbent or water absorbent resin settles, the same operation is performed again to measure the surface tension of the supernatant. It should be noted that in the present invention, a plate method using a platinum plate is adopted, and the plate is thoroughly washed with deionized water before each measurement, and is heated and cleaned using a gas burner before use.

[0296] (d) Coloration evaluation (yellowness / YI value)

[0297] The coloring of the particulate water absorbent or water absorbent resin is evaluated using a spectrophotometer SZ-Σ80 COLOR MEASURING SYSTEM manufactured by Nippon Denshoku Industries. Under the set conditions (reflection measurement / attached powder / paste sample stand (30 mm inner diameter, 12 mm height / standard round white plate No. 2 / 30 Φ projection tube for powder / paste as standard)), 5 g of the particulate water absorbent or water absorbent resin is filled into the sample stand (filling about 60% of the sample stand), and the surface color (YI value (Yellow Index)) is measured using the spectrophotometer at room temperature (20-25°C) and humidity of 50 RH%. In addition, the color of objects of other scales (L, a, b) or WB (Hunter Color) can also be measured simultaneously using the same measurement method using the same device. The larger the L / WB and the smaller the a / b, the lower the coloring and the closer to white it is in substance.

[0298] Next, 5 g of the particulate water absorbent or water absorbent resin was filled into the paste sample stand, and the paste sample stand filled with the particulate water absorbent or water absorbent resin was exposed for 14 days in a constant temperature and humidity chamber (manufactured by ESPEC, product name: small environmental tester, model: SH-641) in an atmosphere adjusted to 70±1°C and 65±1%RH. After exposure, the surface color (YI value (Yellow Index)) was measured using the spectrophotometer. The YI value is preferably 35 or less, more preferably 32 or less, further preferably 29 or less, and particularly preferably 26 or less.

[0299] (e) Paint stirrer test

[0300] 30 g of water-absorbent resin was placed in a glass container having a diameter of 6 cm and a height of 11 cm, and the container was placed in a paint shaker (No. 488 test disperser, manufactured by Toyo Seiki Seisaku-sho Co., Ltd.) The paint shaker was then shaken at 800 (cycle / min) for a predetermined time and then stopped.

[0301] [Production Example 1]

[0302] Into a 2-liter polypropylene container, 351.7 g of acrylic acid, 0.860 g of polyethylene glycol diacrylate (molecular weight 523) as an internal crosslinking agent (0.034 mol % relative to the unsaturated monomer containing a carboxyl group), 2.15 g of a 1.0 wt % aqueous solution of trisodium diethylenetriamine pentaacetate (DTPA·3Na), 149.0 g of a 48.5 wt % aqueous solution of sodium hydroxide and 336.2 g of deionized water (ion exchange water) were added and mixed to prepare a monomer aqueous solution (a').

[0303] Next, the above-mentioned monomer aqueous solution (a') was cooled while stirring. When the liquid temperature reached 40.0°C, 144.8 g of a 48.5 wt% sodium hydroxide aqueous solution adjusted to 40°C was added and mixed to prepare a monomer aqueous solution (a). At this time, the temperature of the monomer aqueous solution (a) rose to 78.2°C due to the second stage neutralization heat immediately after the preparation. Precipitates were observed immediately after the mixing of the 48.5 wt% sodium hydroxide aqueous solution began, but gradually dissolved to form a transparent uniform solution.

[0304] Next, 15.49 g of a 4.0 wt% sodium persulfate aqueous solution was added to the stirred monomer aqueous solution (a), and immediately injected into a stainless steel tray-type container (bottom surface 340×340 mm, height 25 mm, inner surface: Teflon (registered trademark) coating) in an atmosphere-open system. The time from the start of the second-stage neutralization to the injection of the monomer aqueous solution (a) into the tray-type container was set to 55 seconds, and the tray-type container was heated to a surface temperature of 40° C. using a hot plate (NEO HOTPLATE HI-1000 / Inouchi Seieido Co., Ltd.).

[0305] The above-mentioned monomer aqueous solution (a) started the polymerization reaction 60 seconds after being injected into the tray-type container. In the polymerization reaction, it expanded and foamed in all directions while generating water vapor, and then shrunk to a size slightly larger than the tray-type container. After 3 minutes from the start of the polymerization reaction, the hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") (1) was taken out. It should be noted that these series of operations were carried out in an atmosphere-open system.

[0306] The hydrogel (1) obtained in the above polymerization reaction was cut into short strips and fed to a screw extruder for gel pulverization to obtain a granular hydrogel (1). It should be noted that in the screw extruder, a porous plate with a diameter of 100 mm, a hole diameter of 11.0 mm, 40 holes, an open porosity of 62.5%, and a thickness of 10 mm was provided at the front end, and the outer diameter of the screw shaft was 86 mm.

[0307] The gel was crushed by simultaneously supplying the short strips of water-containing gel (1) and water vapor from different supply ports while the rotation speed of the screw shaft of the screw extruder was set to 130 rpm. It should be noted that the supply amount of the water-containing gel (1) was 4640 g per minute and the supply amount of water vapor was 83 g per minute.

[0308] The granular hydrogel (1) was spread on a 50-mesh metal net and dried with hot air at 190°C for 30 minutes. The dried product was pulverized with a roll mill (WML roll mill / Iguchi Giken Co., Ltd.), and then sieved with JIS standard sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, and then blended to obtain an irregularly crushed precursor water-absorbent resin (A) having a weight average particle size (D50) of 305 μm and a logarithmic standard deviation (σζ) of particle size distribution of 0.35. The centrifuge retention capacity (CRC) of the precursor water-absorbent resin (A) was 48.4 (g / g).

[0309] [Production Example 2]

[0310] Into a 2-liter polypropylene container were added 335.3 g of acrylic acid, 0.720 g of polyethylene glycol diacrylate (molecular weight 523) as an internal crosslinking agent (0.030 mol % relative to the carboxyl group-containing unsaturated monomer), 2.05 g of a 1.0 wt % aqueous solution of trisodium diethylenetriamine pentaacetate (DTPA·3Na), 142.1 g of a 48.5 wt % aqueous solution of sodium hydroxide and 367.2 g of deionized water (ion exchange water), and the mixture was mixed to prepare a monomer aqueous solution (b').

[0311] Next, the monomer aqueous solution (b') was cooled while stirring. When the liquid temperature reached 42.0°C, 138.1 g of a 48.5 wt% sodium hydroxide aqueous solution adjusted to 40°C was added and mixed to prepare a monomer aqueous solution (b). At this time, the temperature of the monomer aqueous solution (b) rose to 77.8°C due to the second stage neutralization heat immediately after the preparation. Precipitates were observed immediately after the mixing of the 48.5 wt% sodium hydroxide aqueous solution began, but gradually dissolved to form a transparent uniform solution.

[0312] Next, 14.77 g of a 4.0 wt% sodium persulfate aqueous solution was added to the stirred monomer aqueous solution (b), and immediately injected into a stainless steel tray-type container (bottom surface 340×340 mm, height 25 mm, inner surface: Teflon (registered trademark) coating) in an atmosphere-open system. The time from the start of the second-stage neutralization to the injection of the monomer aqueous solution (b) into the tray-type container was set to 55 seconds, and the tray-type container was heated to a surface temperature of 40° C. using a hot plate (NEO HOTPLATE HI-1000 / Inouchi Seieido Co., Ltd.).

[0313] The above-mentioned monomer aqueous solution (b) started the polymerization reaction 60 seconds after being injected into the tray-type container. In the polymerization reaction, it expanded and foamed in all directions while generating water vapor, and then shrunk to a size slightly larger than the tray-type container. After 3 minutes from the start of the polymerization reaction, the hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") (2) was taken out. It should be noted that these series of operations were carried out in an atmosphere-open system.

[0314] The hydrogel (2) obtained in the above polymerization reaction is cut into short strips, supplied to a screw extruder and subjected to gel pulverization to obtain a granular hydrogel (2). It should be noted that in the screw extruder, a porous plate with a diameter of 100 mm, a hole diameter of 9.5 mm, 40 holes, an open porosity of 62.5%, and a thickness of 10 mm is provided at the front end, and the outer diameter of the screw shaft is 86 mm.

[0315] The gel was crushed by simultaneously supplying the short strips of water-containing gel (2) and water vapor from different supply ports while the rotation speed of the screw shaft of the screw extruder was set to 130 rpm. It should be noted that the supply amount of the water-containing gel (2) was 4640 g per minute and the supply amount of the water vapor was 83 g per minute.

[0316] The finely divided hydrogel (2) was spread on a 50-mesh metal net and dried with hot air at 190°C for 30 minutes. The dried product was pulverized with a roll mill (WML roll mill / Iguchi Giken Co., Ltd.), and then sieved with JIS standard sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, and then blended to obtain an irregularly crushed precursor water-absorbent resin (B) having a weight average particle size (D50) of 298 μm and a logarithmic standard deviation (σζ) of particle size distribution of 0.35. The centrifuge retention capacity (CRC) of the precursor water-absorbent resin (B) was 50.1 (g / g).

[0317] (Example 1-1)

[0318] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (1) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.01 parts by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbent resin was placed in a mayonnaise bottle with a capacity of 225 mL together with silica, and mixed at 101 rpm for 30 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (1). The absorption performance of the particulate water-absorbing agent (1) is shown in Table 1. The AAP4.83 kPa of the particulate water-absorbing agent (1) was 19.4 [g / g], the GPR was 81 [g / min], and the flow rate was 10.1 [g / s].

[0319] (Example 1-2)

[0320] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propylene glycol, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (2) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.01 parts by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (2). The absorption performance of the particulate water-absorbing agent (2) is shown in Table 1.

[0321] (Example 1-3)

[0322] In Production Example 1, after sieving with JIS standard sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, the weight average particle size (D50) was adjusted to 343 μm, and the logarithmic standard deviation (σζ) of the particle size distribution was adjusted to 0.36. With respect to 100 parts by weight of the precursor water-absorbent resin (A) thus obtained, a surface crosslinking agent solution containing 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 2.0 parts by weight of deionized water was uniformly mixed, and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (3) became about 35 [g / g]. The mixture was then cooled and uniformly mixed with an aqueous solution containing 1 part by weight of deionized water, 0.03 part by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na) and 0.01 part by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) relative to 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve having a mesh size of 850 μm and 0.3 part by weight of silica (trade name: AEROSIL200, manufactured by Japan AEROSIL) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were placed in a mayonnaise bottle having a capacity of 225 mL and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (3). The absorption performance of the particulate water-absorbing agent (3) is shown in Table 1.

[0323] (Examples 1-4)

[0324] A surface crosslinking agent solution containing 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.5 parts by weight of propylene glycol and 3.5 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (4) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.05 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (4). The absorption performance of the particulate water-absorbing agent (4) is shown in Table 1.

[0325] (Examples 1-5)

[0326] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (5) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.01 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: Sipernat 22S, manufactured by EVONIK Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 45 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (5). The absorption performance of the particulate water-absorbing agent (5) is shown in Table 1.

[0327] (Examples 1-6)

[0328] A surface crosslinking agent solution containing 0.04 parts by weight of ethylene glycol diglycidyl ether, 2.8 parts by weight of propylene glycol and 4.2 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (6) became about 35 [g / g]. After cooling, the paint shaker test (shaking time: 15 minutes) was performed to give damage equivalent to the production process, and then an aqueous solution containing 1 part by weight of deionized water and 0.05 parts by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: Sipernat 22S, manufactured by EVONIK Corporation) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (6). The absorption performance of the particulate water-absorbing agent (6) is shown in Table 1.

[0329] (Examples 1-7)

[0330] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.21 parts by weight of ethylene glycol, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (7) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 0.5 parts by weight of deionized water, 0.05 parts by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na) and 0.25 parts by weight of polypropylene glycol 700 (manufactured by Kishida Chemical Co., Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: OSC C132, Oriental Silica Corporation) was mixed. During mixing, 30 g of the water-absorbent resin was put into a mayonnaise bottle with a capacity of 225 mL together with silica, and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (7). The GPR of the particulate water-absorbing agent (7) was 46 [g / min] and the dust amount was 70 [mg / kg]. In addition, the absorption performance of the particulate water-absorbing agent (7) is shown in Table 1.

[0331] (Example 1-8)

[0332] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (8) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.01 part by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 0.01 part by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) and 0.2 part by weight of polyethylene glycol 400 (trade name: XG-40A, manufactured by Nippon Shokubai Co., Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and 0.3 parts by weight of silica (trade name: OSC C132, Oriental Silica Corporation) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (8). The absorption performance of the particulate water-absorbing agent (8) is shown in Table 1.

[0333] (Example 1-9)

[0334] In Production Example 1, after sieving with JIS standard sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, the weight average particle size (D50) was adjusted to 379 μm and the logarithmic standard deviation (σζ) of the particle size distribution was adjusted to 0.38. A surface crosslinking agent solution containing 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.2 parts by weight of propylene glycol, and 2.8 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 90° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (9) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.01 part by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and mixed with 0.4 parts by weight of aluminum hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). During the mixing, 30 g of the water-absorbent resin was put into a mayonnaise bottle with a capacity of 225 mL together with the aluminum hydroxide, and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water absorbent (9). The AAP4.83 kPa of the particulate water absorbent (9) was 22.1 [g / g] and the surface tension was 72.4 mN / m. In addition, the absorption performance of the particulate water absorbent (9) is shown in Table 1.

[0335] (Examples 1-10)

[0336] A surface crosslinking agent solution containing 0.04 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 0.75 parts by weight of aluminum sulfate 14-18 hydrate was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (10) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.03 parts by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na), and 0.1 parts by weight of polyethylene glycol 600 (trade name: PEG-600, manufactured by Sanyo Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve having a mesh size of 850 μm. Furthermore, 30 g of the water-absorbent resin was placed in a mayonnaise bottle of 225 mL, and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (10). The particulate water-absorbing agent (10) had an AAP4.83 kPa of 18.5 [g / g], a moisture absorption caking rate of 0 [%], and a dust amount of 260 [mg / kg]. The absorption performance of the particulate water-absorbing agent (10) is shown in Table 1.

[0337] (Example 1-11)

[0338] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propylene glycol, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (11) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.03 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 30 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (11). The absorption performance of the particulate water-absorbing agent (11) is shown in Table 1.

[0339] (Examples 1-12)

[0340] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (12) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.1 part by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na), 0.01 part by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) and 0.2 part by weight of polyethylene glycol 1000 (trade name: PEG-1000, manufactured by Sanyo Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were put into a mayonnaise bottle with a capacity of 225 mL and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises Co., Ltd.) to obtain a particulate water absorbent (12). The GPR of the particulate water absorbent (12) was 71 [g / min] and the dust content was 150 [mg / kg]. In addition, the absorption performance of the particulate water absorbent (12) is shown in Table 1.

[0341] (Examples 1-13)

[0342] A surface crosslinking agent solution containing 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 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (13) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.03 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) and 0.1 parts by weight of polyethylene glycol 400 (trade name: XG-40A, manufactured by Nippon Shokubai Co., Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve having a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: AEROSIL200, manufactured by Nippon AEROSIL Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (13). The absorption performance of the particulate water-absorbing agent (13) is shown in Table 1.

[0343] (Examples 1-14)

[0344] A surface crosslinking agent solution containing 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.5 parts by weight of propylene glycol and 3.5 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (14) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.05 parts by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) and 0.05 parts by weight of polyethylene glycol 1000 (trade name: PEG-1000, manufactured by Sanyo Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 30 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (14). The absorption performance of the particulate water-absorbing agent (14) is shown in Table 1.

[0345] (Examples 1-15)

[0346] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (15) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.03 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) and 0.01 parts by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and 0.3 parts by weight of silica (trade name: Sipernat 22S, manufactured by EVONIK Co., Ltd.) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were put into a 225 mL mayonnaise bottle and mixed for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises Co., Ltd.) to obtain a particulate water-absorbing agent (15). The absorption performance of the particulate water-absorbing agent (15) is shown in Table 1.

[0347] (Example 1-16)

[0348] A surface crosslinking agent solution containing 0.04 parts by weight of ethylene glycol diglycidyl ether, 2.8 parts by weight of propylene glycol and 4.2 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (16) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.01 part by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: Sipernat 22S, manufactured by EVONIK Corporation) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (16). The absorption performance of the particulate water-absorbing agent (16) is shown in Table 1.

[0349] (Example 1-17)

[0350] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.21 parts by weight of ethylene glycol, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (17) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.05 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: OSC C132, Oriental Silica Corporation) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (17). The absorption performance of the particulate water-absorbing agent (17) is shown in Table 1.

[0351] (Example 1-18)

[0352] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (B), and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (18) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.01 part by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 0.001 part by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) and 0.2 part by weight of polyethylene glycol 600 (trade name: PEG-600, manufactured by Sanyo Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and 0.3 parts by weight of silica (trade name: OSC C132, Oriental Silica Corporation) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were put into a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (18). The absorption performance of the particulate water-absorbing agent (18) is shown in Table 1.

[0353] (Example 1-19)

[0354] A surface crosslinking agent solution containing 0.04 parts by weight of ethylene glycol diglycidyl ether, 4.0 parts by weight of propylene glycol, 5.8 parts by weight of deionized water, and 0.75 parts by weight of aluminum sulfate 14-18 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (A), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (19) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.05 parts by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) and 0.05 parts by weight of polypropylene glycol 700 (manufactured by Kishida Chemical Co., Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve having a mesh size of 850 μm. Furthermore, 30 g of the water-absorbent resin was placed in a mayonnaise bottle of 225 mL, and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (19). The particulate water-absorbing agent (19) had an AAP4.83 kPa of 19.5 [g / g], a GPR of 114 [g / min], and a moisture absorption caking rate of 0 [%]. The absorption performance of the particulate water-absorbing agent (19) is shown in Table 1.

[0355] (Example 1-20)

[0356] In Production Example 1, after sieving with JIS standard sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, the weight average particle size (D50) was adjusted to 379 μm, and the logarithmic standard deviation (σζ) of the particle size distribution was adjusted to 0.38. With respect to 100 parts by weight of the precursor water-absorbent resin (A) thus obtained, a surface crosslinking agent solution containing 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.2 parts by weight of propylene glycol, and 2.8 parts by weight of deionized water was uniformly mixed, and a heat treatment was performed at 90° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (20) became about 35 [g / g]. The mixture was then cooled and uniformly mixed with an aqueous solution containing 1.5 parts by weight of deionized water, 0.01 parts by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na), 0.75 parts by weight of aluminum sulfate 14-18 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 0.75 parts by weight of propylene glycol with respect to 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm. Furthermore, 30 g of the water-absorbent resin was placed in a mayonnaise bottle with a capacity of 225 mL and mixed for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbent (20). The AAP4.83 kPa of the particulate water-absorbent (20) was 22.9 [g / g]. In addition, the absorption performance of the particulate water-absorbent (20) is shown in Table 1.

[0357] (Example 1-21)

[0358] 50 parts by weight of the precursor water-absorbent resin (A) was added to a 99L plastic barrel filled with deionized water and allowed to stand for 10 minutes. After confirming the gel sedimentation, a 150μm mesh screen was covered on the plastic barrel and fixed to the plastic barrel. A hose was fixed on the screen, and deionized water was passed into the plastic barrel through the hose for 3 hours. After the water was passed, the liquid in the plastic barrel was controlled using a JIS standard sieve with a mesh of 150μm. The obtained gel was spread on a 50-mesh metal net, air-dried at 60°C for 24 hours, and then dried under reduced pressure at 60°C until the moisture content reached 7%.

[0359] The dried product was pulverized with a roll mill (WML type roll mill / Iguchi Giken Co., Ltd.), and then sieved with JIS standard sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, and then blended to obtain an irregularly crushed precursor water-absorbent resin (C) having a weight average particle size (D50) of 314 μm and a logarithmic standard deviation (σζ) of particle size distribution of 0.35. The centrifuge retention capacity (CRC) of the precursor water-absorbent resin (C) was 49.8 (g / g).

[0360] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (C), and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (21) became about 35 [g / g], thereby obtaining a particulate water-absorbent agent (21). The absorption performance of the particulate water-absorbent agent (21) is shown in Table 1.

[0361] (Comparative Example 1-1)

[0362] A comparative particulate water absorbing agent (1) was obtained by the same method as in Example 1-1 except that the mixing time of silica by the rotary mixer was set to 2 minutes. The comparative particulate water absorbing agent (1) had an AAP4.83 kPa of 18.0 [g / g], a GPR of 112 [g / min], and a flow rate of 10.1 [g / s]. The absorption performance of the comparative particulate water absorbing agent (1) is shown in Table 1.

[0363] (Comparative Example 1-2)

[0364] The comparative particulate water absorbing agent (2) was obtained in the same manner as in Example 1-2 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (2).

[0365] (Comparative Examples 1-3)

[0366] A comparative particulate water absorbing agent (3) was obtained in the same manner as in Example 1-4 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (3).

[0367] (Comparative Examples 1-4)

[0368] A comparative particulate water absorbing agent (4) was obtained in the same manner as in Example 1-5 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (4).

[0369] (Comparative Examples 1-5)

[0370] A comparative particulate water absorbing agent (5) was obtained in the same manner as in Example 1-9 except that 0.4 part by weight of aluminum hydroxide was replaced with 0.3 part by weight of silicon dioxide (trade name: OSC C132, Oriental Silica Corporation) and the mixing time by the tumble mixer was changed to 2 minutes. The absorption performance of the comparative particulate water absorbing agent (5) is shown in Table 1. The surface tension of the comparative particulate water absorbing agent (5) was 72.3 mN / m.

[0371] (Comparative Examples 1-6)

[0372] A comparative particulate water absorbing agent (6) was obtained in the same manner as in Example 1-11 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (6).

[0373] (Comparative Examples 1-7)

[0374] A comparative particulate water absorbing agent (7) was obtained in the same manner as in Example 1-12 except that the mixing time of silica by the rotary mixer was set to 2 minutes. The absorption performance of the comparative particulate water absorbing agent (7) is shown in Table 1. The GPR of the comparative particulate water absorbing agent (7) was 78 [g / min] and the dust amount was 160 [mg / kg].

[0375] (Comparative Examples 1-8)

[0376] A comparative particulate water absorbing agent (8) was obtained in the same manner as in Example 1-13 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (8).

[0377] (Comparative Examples 1-9)

[0378] A comparative particulate water absorbing agent (9) was obtained in the same manner as in Example 1-15 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (9).

[0379] (Comparative Examples 1-10)

[0380] A comparative particulate water absorbing agent (10) was obtained in the same manner as in Example 1-16 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (10).

[0381] (Comparative Example 1-11)

[0382] A comparative particulate water absorbing agent (11) was obtained in the same manner as in Example 1-17 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (11).

[0383] (Comparative Examples 1-12)

[0384] A comparative particulate water absorbing agent (12) was obtained in the same manner as in Example 1-18 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 1 shows the absorption performance of the comparative particulate water absorbing agent (12).

[0385] (Comparative Examples 1-13)

[0386] In Production Example 1, the monomer aqueous solution was adjusted so that the polyethylene glycol diacrylate as an internal crosslinking agent was 0.019 mol% relative to the carboxyl group-containing unsaturated monomer, and a precursor water-absorbent resin (D) was obtained by the same method as in Production Example 1. The centrifuge retention capacity (CRC) of the precursor water-absorbent resin (D) was 52.7 (g / g).

[0387] In Example 1-4, a comparative particulate water-absorbing agent (13) was obtained by the same method as in Example 1-4 except that the precursor water-absorbing resin (D) was used, the amount of ethylene glycol in the surface crosslinking agent solution was changed to 0.25 parts by weight, the amount of deionized water added to the water-absorbing resin was changed to 10 parts by weight, the amount of trisodium diethylenetriamine pentaacetate (DTPA·3Na) was changed to 0.01 parts by weight, the silica was changed to hydrotalcite (trade name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.), the amount of hydrotalcite mixed was changed to 0.4 parts by weight, and the mixing time by the rotary mixer was changed to 2 minutes. The absorption performance of the comparative particulate water-absorbing agent (13) is shown in Table 1.

[0388] (Comparative Examples 1-14)

[0389] In Comparative Example 1-13, except that the amount of deionized water added to the water-absorbent resin was changed to 15 parts by weight, the type of hydrotalcite (trade name: HT-1-NC, manufactured by Sakai Chemical Industry Co., Ltd.) was changed, and the amount of hydrotalcite mixed was changed to 0.2 parts by weight, a comparative particulate water-absorbing agent (14) was obtained by the method of Comparative Example 1-13. The absorption performance of the comparative particulate water-absorbing agent (14) is shown in Table 1.

[0390] [Evaluation of the amount of absorption of the absorbent body]

[0391] Absorbent bodies A and B were prepared by the method described below, and the absorption amount of the absorbent bodies was evaluated.

[0392] Method for manufacturing model absorber A

[0393] Tear 80mm×160mm absorbent cotton (for example, 8cm×16cm cut cotton made by Kawamoto Sangyo Co., Ltd.) uniformly along the surface direction to make 2 pieces of 1.6g absorbent cotton sheets. Next, cut the absorbent paper into 200mm×200mm, and place a 8cm×16cm frame near the center of the absorbent paper. Lay the absorbent cotton sheet adjusted to 1.6g in the frame, smooth the upper surface of the absorbent cotton with an acrylic plate, evenly spread 3.2g of granular absorbent from above, and then place 1.6g of absorbent cotton sheets to make a sandwich structure. Under a load of 10kg applied to the absorbent body as a whole, keep it for 1 minute to shape the absorbent body. Thereafter, remove the load and frame, and fold the two ends of the absorbent paper along the length direction of the absorbent body in a way that wraps the absorbent body. This was placed in a nonwoven bag (10 cm×22 cm) made of Heatron paper, and the periphery was heat-sealed to prepare a model absorbent body A.

[0394] Method for manufacturing model absorber B

[0395] Cut a 100 mm × 180 mm plastic tape (for example, the plastic tape 21-100TM manufactured by Nitto Denko Co., Ltd. can be used), place the adhesive surface upward, set a 80 mm × 160 mm frame in the center, and evenly spread 3.2 g of the particulate water absorbent in the frame. Remove the frame, place a spunbonded nonwoven fabric cut into a size of 100 mm × 180 mm on it, and bond it to the plastic tape. Put it in a nonwoven fabric bag (10 cm × 22 cm) made of Heatron paper, and heat seal the periphery to make a model absorbent body B.

[0396] Absorption determination method

[0397] A 0.9 wt% sodium chloride aqueous solution is placed in a deep tray so that the liquid depth reaches more than 5 cm, and the temperature is adjusted so that the liquid temperature in the tray becomes 37°C. The model absorbent is immersed in the tray and allowed to swell for 60 minutes without applying a load. During the immersion, the model absorbent B is immersed in a manner such that the plastic tape surface becomes the upper surface, and all subsequent operations are performed with the plastic tape surface as the upper surface. After swelling, the model absorbent is taken out from the tray, placed on a JIS standard sieve with a diameter of 45 cm and a mesh size of 2000 μm, and a weight of 2690 g (21 g / cm 2 ) and control the liquid for 1 minute. The weight of the model absorbent body after the control of the liquid was measured, and the difference between the weight of the model absorbent body measured in advance before the immersion was taken as the absorption amount. The results are shown in Table 1.

[0398] [Table 1-1]

[0399]

[0400] [Table 1-2]

[0401]

[0402] For the above-mentioned Examples and Comparative Examples, a graph obtained by plotting AAP (2.06 kPa) + RCAP (2.06 kPa) (vertical axis) against CRC [g / g] (horizontal axis) is Figure 2 The straight line represents AAP (2.06 kPa) + RCAP (2.06 kPa) = 0.58 x CRC + 55.6.

[0403] From the evaluation results of the absorbent in Table 1, it can be seen that the particulate water absorbing agent satisfying the formula (1), i.e., the particulate water absorbing agent of the embodiment, when used in the absorbent, has a liquid retention amount (absorption amount) greater by more than 1 g under pressure, even if the particulate water absorbing agent is in a state of absorbing liquid and swollen, compared with the comparative example. This difference in liquid retention amount is a significant difference in the art. From this result, it can be seen that the particulate water absorbing agent of the embodiment can significantly reduce liquid reflux when the particulate water absorbing agent is in a swollen state, even if the particulate water absorbing agent is subjected to pressure from the outside.

[0404] [Production Example 3]

[0405] Into a 2-liter polypropylene container were charged 351.7 g of acrylic acid, 0.910 g of polyethylene glycol diacrylate (molecular weight: 523) as an internal crosslinking agent (0.036 mol % relative to the unsaturated monomer containing a carboxyl group), 2.15 g of a 1.0 wt % aqueous solution of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 149.0 g of a 48.5 wt % aqueous solution of sodium hydroxide, 1.41 g of a 50.0 wt % aqueous solution of malic acid (DL-malic acid, 50.0% aqueous solution, manufactured by Fuso Chemical Industries, Ltd., food additive grade) (0.108 mol % of malic acid relative to the unsaturated monomer containing a carboxyl group) and 336.2 g of deionized water (ion exchange water), and the mixture was mixed to prepare a monomer aqueous solution (e').

[0406] Next, the monomer aqueous solution (e') was cooled while stirring. When the liquid temperature reached 40.0°C, 144.8 g of a 48.5 wt% sodium hydroxide aqueous solution adjusted to 40°C was added and mixed to prepare a monomer aqueous solution (e). At this time, the temperature of the monomer aqueous solution (e) rose to 77.9°C due to the second stage neutralization heat immediately after the preparation. Precipitates were observed immediately after the mixing of the 48.5 wt% sodium hydroxide aqueous solution was started, but gradually dissolved to form a transparent uniform solution.

[0407] Next, 15.49 g of a 4.0 wt% sodium persulfate aqueous solution was added to the stirred monomer aqueous solution (e), and immediately injected into a stainless steel tray-type container (bottom surface 340×340 mm, height 25 mm, inner surface: Teflon (registered trademark) coating) in an atmosphere-open system. The time from the start of the second-stage neutralization to the injection of the monomer aqueous solution (e) into the tray-type container was set to 55 seconds, and the tray-type container was heated to a surface temperature of 40° C. using a hot plate (NEO HOTPLATE HI-1000 / Inouchi Seieido Co., Ltd.).

[0408] The above-mentioned monomer aqueous solution (e) started the polymerization reaction 60 seconds after being injected into the tray-type container. In the polymerization reaction, it expanded and foamed in all directions while generating water vapor, and then shrunk to a size slightly larger than the tray-type container. After 3 minutes from the start of the polymerization reaction, the hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") (3) was taken out. It should be noted that these series of operations were carried out in an atmosphere-open system.

[0409] The hydrogel (3) obtained in the above polymerization reaction is cut into short strips, supplied to a screw extruder and subjected to gel pulverization to obtain a granular hydrogel (3). It should be noted that in the screw extruder, a porous plate with a diameter of 100 mm, a hole diameter of 11.0 mm, 40 holes, an open porosity of 62.5%, and a thickness of 10 mm is provided at the front end, and the outer diameter of the screw shaft is 86 mm.

[0410] The gel was crushed by simultaneously supplying the short strips of water-containing gel (3) and water vapor from different supply ports while the rotation speed of the screw shaft of the screw extruder was set to 130 rpm. It should be noted that the supply amount of the water-containing gel (3) was 4640 g per minute and the supply amount of the water vapor was 83 g per minute.

[0411] The granular hydrogel (3) was spread on a 50-mesh metal net and dried with hot air at 190°C for 30 minutes. The dried product was pulverized with a roll mill (WML roll mill / Iguchi Giken Co., Ltd.), and then sieved with JIS sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, and then blended to obtain an irregularly crushed precursor water-absorbent resin (E) having a weight average particle size (D50) of 303 μm and a logarithmic standard deviation (σζ) of particle size distribution of 0.36. The centrifuge retention capacity (CRC) of the precursor water-absorbent resin (E) was 50.2 (g / g).

[0412] [Production Example 4]

[0413] Into a 2-liter polypropylene container were charged 335.3 g of acrylic acid, 1.344 g of polyethylene glycol diacrylate (molecular weight: 523) as an internal crosslinking agent (0.056 mol % relative to the unsaturated monomer containing a carboxyl group), 2.05 g of a 1.0 wt % aqueous solution of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 142.1 g of a 48.5 wt % aqueous solution of sodium hydroxide, 6.706 g of a 50.0 wt % aqueous solution of malic acid (DL-malic acid, 50.0% aqueous solution, manufactured by Fuso Chemical Industries, Ltd., food additive grade) (0.537 mol % of malic acid relative to the unsaturated monomer containing a carboxyl group) and 367.2 g of deionized water (ion exchange water), and the mixture was mixed to prepare a monomer aqueous solution (f').

[0414] Next, the monomer aqueous solution (f') was cooled while stirring. When the liquid temperature reached 42.0°C, 138.1 g of a 48.5 wt% sodium hydroxide aqueous solution adjusted to 40°C was added and mixed to prepare a monomer aqueous solution (f). At this time, the temperature of the monomer aqueous solution (f) rose to 78.1°C due to the second stage neutralization heat immediately after the preparation. Precipitates were observed immediately after the mixing of the 48.5 wt% sodium hydroxide aqueous solution was started, but gradually dissolved to form a transparent uniform solution.

[0415] Next, 14.77 g of a 4.0 wt% sodium persulfate aqueous solution was added to the stirred monomer aqueous solution (f), and then immediately injected into a stainless steel tray-type container (bottom surface 340×340 mm, height 25 mm, inner surface: Teflon (registered trademark) coating) in an atmosphere-open system. It should be noted that the time from the start of the second-stage neutralization to the injection of the monomer aqueous solution (f) into the tray-type container was set to 55 seconds, and the tray-type container was heated to a surface temperature of 40° C. using a hot plate (NEO HOTPLATE HI-1000 / Inoue Seieido Co., Ltd.).

[0416] The above-mentioned monomer aqueous solution (f) started the polymerization reaction 60 seconds after being injected into the tray-type container. In the polymerization reaction, it expanded and foamed in all directions while generating water vapor, and then shrunk to a size slightly larger than the tray-type container. After 3 minutes from the start of the polymerization reaction, the hydrogel-like crosslinked polymer (hereinafter referred to as "hydrogel") (4) was taken out. It should be noted that these series of operations were carried out in an atmosphere-open system.

[0417] The hydrogel (4) obtained in the above polymerization reaction is cut into short strips, supplied to a screw extruder and subjected to gel pulverization to obtain a granular hydrogel (4). It should be noted that in the screw extruder, a porous plate with a diameter of 100 mm, a hole diameter of 9.5 mm, 40 holes, an open porosity of 62.5%, and a thickness of 10 mm is provided at the front end, and the outer diameter of the screw shaft is 86 mm.

[0418] The gel was crushed by simultaneously supplying the short strips of water-containing gel (4) and water vapor from different supply ports while the rotation speed of the screw shaft of the screw extruder was set to 130 rpm. It should be noted that the supply amount of the water-containing gel (4) was 4640 g per minute and the supply amount of the water vapor was 83 g per minute.

[0419] The finely divided hydrogel (4) was spread on a 50-mesh metal net and dried with hot air at 190°C for 30 minutes. The dried product was pulverized with a roll mill (WML roll mill / Iguchi Giken Co., Ltd.), and then sieved with JIS sieves having mesh sizes of 850 μm, 600 μm, 500 μm, 300 μm, and 150 μm, and then blended to obtain an irregularly crushed precursor water-absorbent resin (F) having a weight average particle size (D50) of 303 μm and a logarithmic standard deviation (σζ) of the particle size distribution of 0.35. The centrifuge retention capacity (CRC) of the precursor water-absorbent resin (F) was 49.6 (g / g).

[0420] (Example 2-1)

[0421] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (E), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (22) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.05 parts by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) and 0.15 parts by weight of sodium sulfite was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: REOLOSIL QS-20, manufactured by Tokuyama Co., Ltd.) was mixed. During mixing, 30 g of the water-absorbent resin and silica were placed in a mayonnaise bottle with a capacity of 225 mL, and mixed at 101 rpm for 30 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (22). The GPR of the particulate water-absorbing agent (22) was 84 [g / min], the surface tension was 72.3 mN / m, and the YI value after coloring evaluation was 24. The absorption performance of the particulate water-absorbing agent (22) is shown in Table 2.

[0422] (Example 2-2)

[0423] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.21 parts by weight of ethylene glycol, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (E), and a heat treatment was performed at 190°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (23) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water and 0.03 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: OSC C132, Oriental Silica Corporation) was mixed. During mixing, 30 g of the water-absorbing resin and silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (23). The absorption performance of the particulate water-absorbing agent (23) is shown in Table 2.

[0424] (Example 2-3)

[0425] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 1.2 parts by weight of propylene glycol and 2.8 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (E), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (24) became about 35 [g / g]. Thereafter, the mixture was cooled, subjected to the above-mentioned paint shaker test (shaking time: 10 minutes), and damaged in accordance with the production process, and then an aqueous solution containing 1 part by weight of deionized water, 0.01 part by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na) and 0.2 part by weight of polyethylene glycol 600 (trade name: PEG-600, manufactured by Sanyo Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and 0.3 parts by weight of silica (trade name: Sipernat 22S, manufactured by EVONIK Co., Ltd.) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises Co., Ltd.) to obtain a particulate water-absorbing agent (24). The absorption performance of the particulate water-absorbing agent (24) is shown in Table 2.

[0426] (Example 2-4)

[0427] A surface crosslinking agent solution containing 0.04 parts by weight of ethylene glycol diglycidyl ether, 3.5 parts by weight of propylene glycol, 5.0 parts by weight of deionized water, and 0.75 parts by weight of aluminum sulfate 14-18 hydrate was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (E), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (25) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.01 part by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na), and 0.05 part by weight of polypropylene glycol 700 (manufactured by Kishida Chemical Co., Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve having a mesh size of 850 μm. Furthermore, 30 g of the water-absorbent resin was placed in a mayonnaise bottle of 225 mL, and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbent (25). The particulate water-absorbent (25) had an AAP4.83 kPa of 19.1 [g / g], a GPR of 79 [g / min], and a moisture absorption caking rate of 0 [%]. The absorption performance of the particulate water-absorbent (25) is shown in Table 2.

[0428] (Example 2-5)

[0429] A surface crosslinking agent solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol and 2.0 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (F), and a heat treatment was performed at 190° C. for about 30 minutes so that the CRC of the obtained water-absorbent resin (26) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.1 part by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na), 0.01 part by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) and 0.2 part by weight of polyethylene glycol 1000 (trade name: PEG-1000, manufactured by Sanyo Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm and 0.3 parts by weight of silica (trade name: OSC C132, Oriental Silica Corporation) was mixed. During the mixing, 30 g of the water-absorbent resin and the silica were put into a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (26). The absorption performance of the particulate water-absorbing agent (26) is shown in Table 2.

[0430] (Example 2-6)

[0431] A surface crosslinking agent solution containing 0.04 parts by weight of ethylene glycol diglycidyl ether, 2.8 parts by weight of propylene glycol and 4.2 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (F), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (27) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.03 parts by weight of trisodium diethylenetriamine pentaacetate (DTPA·3Na) and 0.01 parts by weight of polyoxyethylene (20) sorbitan monostearate (trade name: RHEODOL TW-S120V, manufactured by Kao Corporation) was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.3 parts by weight of silica (trade name: Sipernat 22S, manufactured by EVONIK Corporation) was mixed. During mixing, 30 g of the water-absorbent resin was placed in a mayonnaise bottle with a capacity of 225 mL together with silica, and mixed at 101 rpm for 45 minutes using a rotary drum mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (27). The flow rate of the particulate water-absorbing agent (27) was 9.4 [g / s], and the YI value after coloring evaluation was 23. The absorption performance of the particulate water-absorbing agent (27) is shown in Table 2.

[0432] (Example 2-7)

[0433] A surface crosslinking agent solution containing 0.03 parts by weight of ethylene glycol diglycidyl ether, 1.5 parts by weight of propylene glycol and 3.5 parts by weight of deionized water was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (F), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (28) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.01 part by weight of ethylenediaminetetramethylenephosphonic acid pentasodium (EDTMP·5Na) and 0.1 part by weight of sodium hydrogen sulfite was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve with a mesh size of 850 μm, and 0.4 parts by weight of aluminum hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed. During mixing, 30 g of the water-absorbing resin and aluminum hydroxide were placed in a 225 mL mayonnaise bottle and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (28). The absorption performance of the particulate water-absorbing agent (28) is shown in Table 2.

[0434] (Example 2-8)

[0435] A surface crosslinking agent solution containing 0.04 parts by weight of ethylene glycol diglycidyl ether, 2.8 parts by weight of propylene glycol, 4.2 parts by weight of deionized water, and 0.75 parts by weight of aluminum sulfate 14-18 hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was uniformly mixed with 100 parts by weight of the precursor water-absorbent resin (F), and a heat treatment was performed at 100°C for about 30 minutes so that the CRC of the obtained water-absorbent resin (29) became about 35 [g / g]. Thereafter, the mixture was cooled, and an aqueous solution containing 1 part by weight of deionized water, 0.05 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA·3Na), 0.3 parts by weight of polyethylene glycol 400 (trade name: XG-40A, manufactured by Nippon Shokubai Co., Ltd.), and 0.03 parts by weight of sodium sulfite was uniformly mixed with 100 parts by weight of the water-absorbent resin. After drying at 60°C for 1 hour, the mixture was passed through a JIS standard sieve having a mesh size of 850 μm. Furthermore, 30 g of the water-absorbent resin was placed in a mayonnaise bottle of 225 mL, and mixed at 101 rpm for 60 minutes using a rotary mixer T2F (manufactured by Shinmaru Enterprises) to obtain a particulate water-absorbing agent (29). The dust amount of the particulate water-absorbing agent (29) was 50 [mg / kg], and the YI value after coloring evaluation was 25. The absorption performance of the particulate water-absorbing agent (29) is shown in Table 2.

[0436] (Example 2-9)

[0437] The particulate water absorbing agent (30) was obtained in the same manner as in Example 2-1 except that the mixing time of silica by the tumble mixer was 15 minutes. Table 2 shows the water absorption performance of the particulate water absorbing agent (30).

[0438] (Comparative Example 2-1)

[0439] A comparative particulate water absorbing agent (15) was obtained by the same method as in Example 2-1 except that the mixing time of silica by the rotary mixer was set to 2 minutes. The GPR of the comparative particulate water absorbing agent (15) was 100 [g / min], the surface tension was 72.2 mN / m, and the YI value after coloring evaluation was 24. The absorption performance of the comparative particulate water absorbing agent (15) is shown in Table 2.

[0440] (Comparative Example 2-2)

[0441] A comparative particulate water absorbing agent (16) was obtained in the same manner as in Example 2-3 except that the mixing time of silica by the tumble mixer was changed to 2 minutes. Table 2 shows the absorption performance of the comparative particulate water absorbing agent (16).

[0442] (Comparative Example 2-3)

[0443] A comparative particulate water absorbing agent (17) was obtained in the same manner as in Example 2-5 except that the mixing time of silica by the tumble mixer was 2 minutes. Table 2 shows the absorption performance of the comparative particulate water absorbing agent (17).

[0444] (Comparative Example 2-4)

[0445] A comparative particulate water absorbing agent (18) was obtained by the same method as in Example 2-6 except that the mixing time of silica by the rotary mixer was set to 2 minutes. The flow rate of the comparative particulate water absorbing agent (18) was 9.2 [g / s], and the YI value after coloring evaluation was 23. In addition, the absorption performance of the comparative particulate water absorbing agent (18) is shown in Table 2.

[0446] (Comparative Example 2-5)

[0447] 25.5 g of granular water absorbent (irregularly crushed) obtained by removing as much pulp as possible from the absorbent of the diaper "GOO.N Pants Massara Sara Breathable Boys L Size" (purchased in 2020) manufactured by Daio Paper Co., Ltd. was filled into a polyethylene bag with a slider (the size of the inner side of the slider: 70 mm × 50 mm, thickness: 0.04 mm, capacity: 35 mL). The polyethylene bag was placed on a JIS standard sieve with a mesh size of 850 mm and an inner diameter of 200 mm. The standard sieve was fixed to a vibrating sieve machine AS200 (manufactured by Retsch) and oscillated at an amplitude of 0.3 mm for 30 minutes. At this time, the calculated value of the acceleration to which the granular water absorbent was subjected was a maximum of 2.2 G. The granular water absorbent after oscillation was used as a comparative granular water absorbent (19). The water absorption performance of the comparative granular water absorbent (19) is shown in Table 3.

[0448] (Comparative Example 2-6)

[0449] The same operation as in Comparative Example 2-5 was carried out except that the shaking time was changed to 300 minutes, thereby obtaining a comparative particulate water absorbing agent (20). Table 3 shows the water absorption performance of the comparative particulate water absorbing agent (20).

[0450] [Table 2]

[0451]

[0452] [Table 3]

[0453]

[0454] From the evaluation results of the absorbent in Table 2, it can be seen that the particulate water absorbing agent satisfying the formula (1), i.e., the particulate water absorbing agent of the embodiment, when used in the absorbent, has a liquid retention amount (absorption amount) greater by 2 g or more under pressure, even if the particulate water absorbing agent is in a state of absorbing liquid and swollen, compared with the comparative example. This difference in liquid retention amount is a significant difference in the art. From this result, it can be seen that the particulate water absorbing agent of the embodiment can significantly reduce liquid reflux when the particulate water absorbing agent is in a swollen state, even if the particulate water absorbing agent is subjected to pressure from the outside.

[0455] It should be noted that in any of the embodiments, the gel permeation rate (GPR) is greater than 20 g / min, the moisture absorption agglomeration rate is less than 40 wt %, the flow rate (Flow Rate) is greater than 8.5 g / s, the dust amount is less than 400 mg / kg, the surface tension is greater than 65 mN / m, and the water-absorbent resin powder is irregularly crushed.

[0456] This application is based on Japanese patent application No. 2020-064626 filed on March 31, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0457] Industrial Applicability

[0458] 400 devices,

[0459] 410 containers,

[0460] 411 boxes,

[0461] 412 Piston,

[0462] 413a, 413b Metal mesh,

[0463] 414 Swelling gel (substance obtained by making a granular water-absorbing agent absorb water),

[0464] 415 holes,

[0465] 420 cans,

[0466] 421 Glass tube,

[0467] 422 L-shaped tube with stopcock glass tube,

[0468] 423 Liquid,

[0469] 431 Stainless steel wire mesh,

[0470] 432 capture container,

[0471] 433 Put on the scale.

Claims

1. A particulate water-absorbing agent, comprising a surface-crosslinked polyacrylic acid (salt) water-absorbing resin as a main component, The particulate water-absorbing agent satisfies the following formula (1): AAP(2.06kPa)+RCAP(2.06kPa)≥0.58×CRC+55.6 (1) In formula (1), AAP(2.06 kPa) represents the water absorption rate (g / g) under a pressure of 2.06 kPa, RCAP(2.06 kPa) represents the water absorption rate (g / g) under a pressure of 2.06 kPa after swelling, and CRC represents the water absorption rate (g / g) under no pressure.

2. The particulate water-absorbing agent according to claim 1, which satisfies the following formula (A): AAP(2.06kPa)+RCAP(2.06kPa)>76.0(A).

3. The particulate water-absorbing agent according to claim 1 or 2, which satisfies the following formula (2): AAP(2.06kPa)+RCAP(2.06kPa)≥0.58×CRC+56.0 (2).

4. The particulate water-absorbing agent according to claim 3, wherein The CRC is less than 37 g / g.

5. The particulate water-absorbing agent according to claim 1 or 2, which satisfies the following formula (3): AAP(2.06kPa)+RCAP(2.06kPa)≥0.58×CRC+56.5 (3).

6. The particulate water-absorbing agent according to claim 5, wherein The CRC is less than 37 g / g.

7. The particulate water-absorbing agent according to claim 1 or 2, wherein The CRC is greater than 30 g / g.

8. The particulate water-absorbing agent according to claim 1 or 2, wherein The CRC is above 33 g / g.

9. The particulate water-absorbing agent according to claim 1 or 2, wherein The water absorption ratio AAP (4.83 kPa) under a pressure of 4.83 kPa is 10 g / g or more.

10. The particulate water-absorbing agent according to claim 1 or 2, wherein The water absorption ratio AAP (4.83 kPa) under a pressure of 4.83 kPa is 20 g / g or more.

11. The particulate water-absorbing agent according to claim 1 or 2, wherein The AAP (2.06 kPa) is 20 g / g or more.

12. The particulate water-absorbing agent according to claim 1 or 2, wherein The AAP (2.06 kPa) is 30 g / g or more.

13. The particulate water-absorbing agent according to claim 1 or 2, wherein The RCAP (2.06 kPa) is 18 g / g or more.

14. The particulate water-absorbing agent according to claim 1 or 2, wherein The RCAP (2.06 kPa) is 24 g / g or more.

15. The particulate water-absorbing agent according to claim 1 or 2, wherein The RCAP (2.06 kPa) is 30 g / g or more.

16. The particulate water-absorbing agent according to claim 1 or 2, wherein The RCAP (2.06 kPa) is 40 g / g or more.

17. The particulate water-absorbing agent according to claim 1 or 2, wherein The RCAP (2.06 kPa) is 43 g / g or more.

18. The particulate water-absorbing agent according to claim 1 or 2, wherein The RCAP (2.06 kPa) is 60 g / g or less.

19. The particulate water-absorbing agent according to claim 1 or 2, which has a gel permeation rate of 20 g / min or more.

20. The particulate water-absorbing agent according to claim 19, wherein The gel permeation rate is above 26 g / min.

21. The particulate water-absorbing agent according to claim 1 or 2, which has a moisture absorption agglomeration rate of 40% by weight or less.

22. The particulate water-absorbing agent according to claim 21, wherein The moisture absorption agglomeration rate is 0 to 10% by weight.

23. The particulate water-absorbing agent according to claim 1 or 2, which has a flow rate of 8.5 g / s or more.

24. The particulate water-absorbing agent according to claim 1 or 2, wherein the amount of dust is 400 mg / kg or less.

25. The particulate water-absorbing agent according to claim 24, wherein The dust amount is less than 200 mg / kg.

26. The particulate water-absorbing agent according to claim 1 or 2, which has a surface tension of 65 mN / m or more.

27. The particulate water-absorbing agent according to claim 26, wherein The surface tension is greater than 72 mN / m.

28. The particulate water-absorbing agent according to claim 1 or 2, wherein The water-absorbent resin is in irregular broken shape.

29. The particulate water-absorbing agent according to claim 1 or 2, further comprising at least one selected from the group consisting of water-insoluble inorganic particles and water-soluble polyvalent metal cation-containing compounds.

30. The particulate water-absorbing agent according to claim 29, wherein The water-insoluble inorganic particles are at least one selected from the group consisting of polymetallic compounds, silicon dioxide, talc and tricalcium phosphate.

31. The particulate water-absorbing agent according to claim 29, wherein The water-insoluble inorganic particles have a volume average particle size of 10 μm or less.

32. The particulate water-absorbing agent according to claim 29, wherein The volume average particle size of the water-insoluble inorganic particles is 1 μm or less.

33. The particulate water-absorbing agent according to claim 29, wherein The volume average particle size of the water-insoluble inorganic particles is greater than or equal to 0.05 μm.

34. The particulate water-absorbing agent according to claim 29, wherein The volume average particle size of the water-insoluble inorganic particles is greater than or equal to 0.3 μm.

35. The particulate water-absorbing agent according to claim 29, wherein The content of the water-insoluble inorganic particles is 0.01% by weight or more and less than 10% by weight based on 100% by weight of the polyacrylic acid (salt)-based water-absorbent resin.

36. The particulate water-absorbing agent according to claim 29, wherein The content of the water-insoluble inorganic particles is 0.1 to 5% by weight based on 100% by weight of the polyacrylic acid (salt)-based water-absorbent resin.

37. The particulate water-absorbing agent according to claim 29, wherein The water-soluble compound containing a polyvalent metal cation is a compound containing aluminum as a polyvalent metal cation.

38. The particulate water-absorbing agent according to claim 29, wherein The water-soluble compound containing a polyvalent metal cation is at least one selected from aluminum sulfate, potassium aluminum sulfate, and sodium aluminum sulfate.

39. The particulate water-absorbing agent according to claim 29, wherein The content of the water-soluble polyvalent metal cation-containing compound is 0.001 to 5 parts by weight in terms of polyvalent metal cation amount relative to 100 parts by weight of the polyacrylic acid (salt)-based water-absorbent resin.

40. The particulate water-absorbing agent according to claim 29, wherein The content of the water-soluble polyvalent metal cation-containing compound is 0.01 to 2 parts by weight in terms of polyvalent metal cation amount relative to 100 parts by weight of the polyacrylic acid (salt)-based water-absorbent resin.

41. The particulate water-absorbing agent according to claim 29, wherein The content of the water-soluble polyvalent metal cation-containing compound is 0.01 to 1 part by weight in terms of polyvalent metal cation amount relative to 100 parts by weight of the polyacrylic acid (salt)-based water-absorbent resin.

42. An absorbent body comprising the particulate water-absorbing agent according to any one of claims 1 to 41.

43. A sanitary article comprising the absorbent body according to claim 42.

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