Water-absorbing agent composition containing water-absorbing resin as a main component and method for producing the same

Abstract

This invention provides a method for manufacturing a water-absorbing agent composition. This method, in manufacturing the water-absorbing agent composition using a water-absorbing resin with a large specific surface area, can suppress particle segregation caused by transport and improve particle flowability while maintaining its water-absorbing properties. The manufacturing method of this invention includes: a step of mixing a water-soluble flowability enhancer into the water-absorbing resin under specific conditions during or after a surface crosslinking step. The method for manufacturing the water-absorbing agent composition satisfies all of the following (a) to (d): (a) The specific surface area of ​​the water-absorbing resin is 25 m². 2 (a) When the above-mentioned water-soluble flowability improver is mixed into the water-absorbing resin, the form of the above-mentioned water-soluble flowability improver is an aqueous solution of 0.01% by mass or more and 20% by mass or less; (b) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the average droplet diameter of the above-mentioned aqueous solution is 10 μm or more and 1 mm or less; (d) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the mixing power index is 70000 or more.

Description

Technical Field

[0001] This invention relates to a water-absorbing agent composition with water-absorbing resin as the main component and a method for manufacturing the same. Background Technology

[0002] In sanitary materials such as disposable diapers, sanitary napkins, and incontinence pads, absorbent polymer compositions using absorbent resins are widely used for absorbing bodily fluids. Cross-linked polyacrylic acid derivatives are known as such absorbent resins. While these absorbent polymer compositions naturally exhibit excellent absorbency properties, including absorption rates under both pressure and no pressure, hygiene considerations and the stable operation of their manufacturing equipment must also be taken into account when applying them to sanitary materials.

[0003] Furthermore, in addition to the required absorption rate under no pressure and the absorption rate under pressure, the required water absorption speed has also increased as a physical property requirement for water-absorbing resins. Therefore, in recent years, water-absorbing resins with increased specific surface area to accelerate water absorption have been disclosed (Patent Documents 1-7). In addition, water-absorbing resins with a large specific surface area for absorbing blood have also been disclosed (Patent Document 8).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 97 / 03114

[0007] Patent Document 2: Japanese Patent Application Publication No. 10-057805

[0008] Patent Document 3: European Patent Application Publication No. 0872491

[0009] Patent Document 4: European Patent Application Publication No. 0937739

[0010] Patent Document 5: International Publication No. 99 / 03577

[0011] Patent Document 6: International Publication No. 2013 / 018571

[0012] Patent Document 7: International Publication No. 2016 / 111223

[0013] Patent Document 8: International Publication No. 02 / 085959

[0014] Patent Document 9: International Publication No. 2005 / 075070

[0015] Patent Document 10: International Publication No. 2008 / 120742

[0016] Patent Document 11: International Publication No. 2019 / 098244

[0017] Patent Document 12: International Publication No. 2018 / 062539 Summary of the Invention

[0018] In recent years, water-absorbing resins with large specific surface areas have been proposed to accelerate water absorption. One method to increase the specific surface area is to specifically increase the surface texture of the water-absorbing resin (Patent Documents 1-7). However, increasing the surface texture leads to increased jamming between water-absorbing resin particles at the uneven portions, resulting in decreased powder flowability. Therefore, the inventors investigated the use of surfactants (water-soluble polymers) described in Patent Documents 9-12 to improve the powder flowability of water-absorbing resins with increased specific surface areas and texture. However, during their research, they discovered a problem: when water-absorbing resin (water-absorbing agent composition) containing a surfactant (water-soluble flowability enhancer) is fed through a feeder, particle size segregation occurs in the fed water-absorbing resin (water-absorbing agent composition). Furthermore, the water-absorbing properties of the water-absorbing resin (water-soluble flowability enhancer) sometimes decrease when a surfactant (water-soluble flowability enhancer) is added. Therefore, there is a need for a technology that can not only solve the flowability problems during transport as described above, but also maintain the absorbent properties of the water-absorbing resin (water-absorbing agent composition) while using surfactants (water-soluble flowability improvers).

[0019] Therefore, the object of the present invention is to provide a technique for suppressing particle size segregation caused by transport and improving particle flowability while maintaining the absorbent properties of a water-absorbing agent composition (water-absorbing resin) manufactured using a water-absorbing resin with a large specific surface area.

[0020] The inventors conducted in-depth research to solve the aforementioned technical problems. As a result, they discovered that by adding a specific water-soluble flowability enhancer to the water-absorbing resin under specific conditions during the manufacturing process of the water-absorbing composition, specifically during the surface crosslinking process or in a process following the surface crosslinking process, the aforementioned technical problems can be solved, thus completing the present invention.

[0021] The present invention, which can solve the above-mentioned technical problems, has the following structure.

[0022] That is, one aspect of the present invention is as follows. [1] A method for manufacturing a water-absorbing composition, wherein the water-absorbing composition is mainly composed of a water-absorbing resin, the manufacturing method comprising: a monomer aqueous solution preparation step, a polymerization step, a gel pulverization step, a drying step, a pulverization step, a grading step, and a surface crosslinking step, wherein in or after the surface crosslinking step, a step is included in the water-absorbing resin of a water-soluble flowability enhancer having a mixed mass-average molecular weight of 200 or more and 50,000 or less relative to the mass of the water-absorbing resin, wherein the manufacturing method of the water-absorbing composition satisfies all of the following (a) to (d): (a) the specific surface area of ​​the water-absorbing resin is 25 m². 2 (a) When the above-mentioned water-soluble flowability improver is mixed into the water-absorbing resin, the form of the above-mentioned water-soluble flowability improver is an aqueous solution of 0.01% by mass or more and 20% by mass or less; (b) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the average droplet diameter of the above-mentioned aqueous solution is 10 μm or more and 1 mm or less; (d) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the mixing power index defined by the following (Formula 1) is 70000 or more.

[0023] [Formula 1]

[0024]

[0025] [2] In the manufacturing method described in [1] above, it is preferable that the dynamic friction coefficient of the particles with a particle size of 300 μm or more and less than 600 μm in the water-absorbent resin after adding the above-mentioned water-soluble flowability improver is 0.80 or less;

[0026] [3] In the manufacturing method described in [1] or [2] above, it is preferred that the water-soluble flowability improver is selected from one or more of nonionic substances, zwitterionic substances, anionic substances and cationic substances;

[0027] [4] In the manufacturing method described in [3] above, preferably, the nonionic substance is selected from polyols, modified polyols with hydroxyl groups, side-chain and / or terminal polyether modified polysiloxanes, and epoxy alkyl adducts of higher aliphatic amines; the zwitterionic substance is selected from alkyl betaine and alkyl amine oxides; the anionic substance is selected from alkyl sulfate salts, sulfate salts, sulfonates, dicarboxylate salts, alkylamine diacetates, phosphate salts of higher alcohol epoxy alkyl adducts, and carboxylates of higher alcohol epoxy alkyl adducts; the cationic substance is selected from ammonium salts;

[0028] [5] In any of the manufacturing methods described in [1] to [4] above, it is preferable that the water-soluble flowability improver comprises at least one selected from nonionic substances;

[0029] [6] In any of the manufacturing methods described in [1] to [5] above, it is preferable that the water-soluble flowability improver comprises at least one selected from nonionic substances having a polyalkylene glycol chain in the molecule;

[0030] [7] In any of the manufacturing methods described in [1] to [6] above, it is preferable that the water-soluble flowability improver contains at least one selected from polyols and polyol hydroxyl modifiers;

[0031] [8] In any of the manufacturing methods described in [1] to [7] above, it is preferable that the pH of the aqueous solution is 4.5 or higher;

[0032] [9] In any of the manufacturing methods described in [1] to [8] above, it is preferable that the water-absorbing resin and the water-absorbing agent composition each contain 50% by mass or more of particles with a particle size of 300 μm or more and less than 600 μm, and the reduction rate of the dynamic friction coefficient calculated by the following (Formula 2) is 10% or more.

[0033] [Formula 2]

[0034]

[0035] In Formula 2, A: the dynamic friction coefficient of the absorbent resin particles with a particle size of 300 μm or more and less than 600 μm before the addition of the water-soluble flowability improver; B: the dynamic friction coefficient of the absorbent composition particles with a particle size of 300 μm or more and less than 600 μm after the addition of the water-soluble flowability improver.

[0036]

[10] In any of the manufacturing methods described in [1] to [9] above, it is preferable to include a step of further adding polyalkylene glycol between at least one step selected from the preparation step of the monomer aqueous solution, the polymerization step and the gel pulverization step, and / or between each of the above steps;

[0037]

[11] In the manufacturing method described in

[10] above, it is preferable that the polyalkylene glycol is polyethylene glycol with a mass-average molecular weight of 3000 or less;

[0038]

[12] In the manufacturing method described in

[10] or

[11] above, it is preferable that the amount of the polyalkylene glycol added is 0.01% by mass or more and 0.25% by mass or less relative to the total mass of the monomer contained in the monomer aqueous solution.

[0039] In addition, another aspect of the present invention is as follows.

[0040]

[13] A water-absorbing composition having a water-absorbing resin as the main component, the water-absorbing composition comprising a water-soluble flowability enhancer, and satisfying all of the following (1) to (5): (1) The specific surface area of ​​the above-mentioned water-absorbing composition is 25 m². 2 / kg or more; (2) the surface tension of the above-mentioned absorbent composition is 56mN / m or more; (3) the flow rate of the above-mentioned absorbent composition is 10.0g / s or more; (4) the mass proportion of particles with a particle size of 300μm or more and less than 600μm in the above-mentioned absorbent composition is 50% by mass or more; (5) the coefficient of kinetic friction of particles with a particle size of 300μm or more and less than 600μm in the above-mentioned absorbent composition is 0.80 or less;

[0041]

[14] In the absorbent composition described in

[13] above, it is preferable that the Vortex (absorption rate) of the absorbent composition is 50 seconds or less;

[0042]

[15] In the absorbent composition described in

[13] or

[14] above, it is preferable that the SFC (salt water flow induction) of the absorbent composition is 1 × 10⁻⁶. -7 cm 3 • sec / g or higher;

[0043]

[16] In any of the above

[13] to

[15] water-absorbing compositions, it is preferred that the D50 (mass-average particle size) of the water-absorbing composition is 250 μm or more and less than 550 μm, and the mass proportion of particles with a particle size of less than 150 μm in the water-absorbing composition is 3% by mass or less.

[0044]

[17] In any of the above-mentioned

[13] to

[16] absorbent compositions, it is preferred that the absorbent composition has an AAP (absorption rate under pressure) of 20 g / g or more.

[0045] In addition, another aspect of the present invention is as follows.

[0046]

[18] An absorbent comprising a water-absorbing composition according to any one of

[13] to

[17] above;

[0047]

[19] In the absorbent described in

[18] above, it is preferable that the weight per unit area of ​​the pulp is 300 g / m³. 2 the following;

[0048]

[20] In the absorbent described in

[18] or

[19] above, it is preferable that the weight per unit area of ​​the absorbent composition is 450 g / m². 2 the following.

[0049] In addition, another aspect of the present invention is as follows.

[0050]

[21] An absorbent article comprising an absorbent body according to any one of

[18] to

[20] above;

[0051]

[22] In the absorbent articles described above

[21] , it is preferred that the absorbent articles do not contain pulp. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the measuring section of a rheometer used to measure the coefficient of kinetic friction. Figure 1 In the text, 1 represents a dish (containing part), 2 represents a parallel plate, and 3 represents a water-absorbing agent composition.

[0053] Figure 2 This is a schematic diagram of the electromagnetic feeder drive unit 4 used in the feeding test. Figure 2 In the diagram, 4 represents the electromagnetic feeder drive unit, and 5 represents the slot. Detailed Implementation

[0054] One aspect of the present invention is a method for manufacturing a water-absorbing agent composition, wherein the water-absorbing agent composition is mainly composed of a water-absorbing resin, and the manufacturing method includes: a monomer aqueous solution preparation step, a polymerization step, a gel pulverization step, a drying step, a pulverization step, a grading step, and a surface crosslinking step, wherein, in or after the above-mentioned surface crosslinking step, a step is included in which a water-soluble flowability enhancer with a mixed quality average molecular weight of 200 or more and 50,000 or less relative to the mass of the water-absorbing resin is added to the water-absorbing resin, and the water-absorbing agent composition satisfies all of the following (a) to (d): (a) the specific surface area of ​​the water-absorbing resin is 25 m². 2 (a) When the above-mentioned water-soluble flowability improver is mixed into the water-absorbing resin, the form of the above-mentioned water-soluble flowability improver is an aqueous solution of 0.01% by mass or more and 20% by mass or less; (b) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the average droplet diameter of the above-mentioned aqueous solution is 10 μm or more and 1 mm or less; (d) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the mixing power index defined by the above-mentioned (Formula 1) is 70000 or more.

[0055] [Formula 3]

[0056]

[0057] It should be noted that, in this specification, the method for manufacturing the absorbent composition having such a structure is also referred to as "the manufacturing method of the present invention" or "the method of the present invention". Furthermore, in this specification, "the absorbent composition manufactured by the method of the present invention" is also referred to as "the absorbent composition of the present invention".

[0058] The inventors have studied the technical problems of absorbent compositions (absorbent resins) generated during the continuous production of sanitary materials such as disposable diapers, and found that, compared with the past, there is a tendency for the supply (transportability) of the absorbent composition to decrease. Therefore, in the process of conducting research to solve this problem, the inventors believe that the aforementioned decrease in supplyability may be due to the use of absorbent resins with a large specific surface area.

[0059] From a sustainability perspective, existing sanitary materials are trending towards thinner / lighter designs, requiring absorbent resins to have the highest possible water absorption rate. Therefore, to address this requirement, techniques have been proposed to obtain absorbent resins with high water absorption rates by increasing their specific surface area. On the other hand, as mentioned above, techniques for adding surfactants (water-soluble polymers) have been proposed to improve the supply (transportability) of such absorbent resins with large specific surface areas (Patent Documents 9-12). However, the inventors have discovered the following problem: even when surfactants (water-soluble flowability improvers) are added to improve the flowability of the powder (absorbent resin), it is sometimes difficult to continuously and stably supply the absorbent resin. More specifically, it has been found that even when surfactants (water-soluble flowability improvers) are added to absorbent resins with large specific surface areas, particle size segregation occurs in the transported absorbent resin (absorbent composition).

[0060] Therefore, the inventors conducted in-depth research and discovered a correlation between the continuous and stable supply of a water-absorbing resin with a large specific surface area and the coefficient of kinetic friction of the water-absorbing agent composition. They repeatedly studied techniques for controlling the coefficient of kinetic friction. The results showed that, in order to accurately control the coefficient of kinetic friction of the water-absorbing agent composition, it is crucial to control the type and form of the added water-soluble flowability enhancer and the conditions under which it is added, thus completing this invention.

[0061] In the manufacturing method of the present invention, a water-soluble flowability improver (sometimes referred to simply as "flowability improver" in this specification) is added to the absorbent resin in the form of an aqueous solution. Furthermore, when adding the aqueous solution of the flowability improver, mixing and stirring are performed such that the "mixing force index" specified in the above-mentioned (Formula 1) reaches a specific value or higher. In the manufacturing method of the present invention, the stirring speed (circumferential speed), mixing time, and average droplet diameter of the aqueous solution of the flowability improver are not controlled individually; instead, the mixing force index specified in the above-mentioned (Formula 1) is comprehensively controlled to reach a specific value or higher, thereby enabling the flowability improver to be uniformly added to the absorbent resin with a large specific surface area. As a result, the coefficient of kinetic friction of the absorbent composition decreases uniformly and without deviation between particle sizes; therefore, the flowability of the absorbent composition becomes uniform between particle sizes, suppressing particle size segregation after transport as described above.

[0062] Furthermore, according to the manufacturing method of the present invention, as described above, the flowability improver is thoroughly mixed with the water-absorbing resin, so even if the amount of flowability improver added is small, a sufficient flowability improvement effect can be obtained. Therefore, the decrease in water-absorbing properties caused by the addition of the flowability improver can be suppressed, and good water-absorbing properties can be maintained.

[0063] It should be noted that, according to the manufacturing method of the present invention, an aqueous solution of a flowability improver can be uniformly added to a water-absorbing resin with a large specific surface area. That is, the flowability improver is not unevenly added to particles with fine particle size and large specific surface area (particles with a particle size less than 300 μm), and the kinetic friction coefficient of more than half of the particles in the water-absorbing resin (particles with a particle size of 300 μm or more but less than 600 μm) can be significantly reduced. In other words, significantly reducing the kinetic friction coefficient of particles with a particle size of 300 μm or more but less than 600 μm means uniformly improving the flowability of all particles.

[0064] Therefore, according to the manufacturing method of the present invention, a water-absorbing agent composition with a high water absorption rate and a low coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm can be provided. That is, a water-absorbing agent composition with a high water absorption rate and uniformly improved flowability of all particles of the water-absorbing resin can be provided. Therefore, by uniformly improving flowability, the problem of particle size segregation after conveying the water-absorbing agent composition through a feeder can be solved. It should be noted that the mechanism described is speculative and does not limit the technical scope of the present invention.

[0065] The following describes in detail the method for manufacturing the absorbent composition of the present invention. However, the scope of the present invention is not limited to these descriptions. For situations other than those described below, appropriate modifications and implementations may be made without prejudice to the spirit of the present invention. Specifically, the present invention is not limited to the following embodiments. Various modifications can be made within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of the present invention.

[0066] Throughout this specification, unless otherwise specified, singular expressions should be understood to include their plural forms as well. Therefore, unless otherwise specified, articles in the singular form (e.g., "a," "an," "the," etc. in the English context) should be understood to include their plural forms as well. Furthermore, unless otherwise specified, the terminology used in this specification should be understood to be used in the sense commonly understood in the art. Therefore, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, this specification (including definitions) shall prevail.

[0067] [1] Definition of terminology

[0068] [1-1] Composition of water-absorbing resin and water-absorbing agent

[0069] In this specification, "water-absorbing resin" refers to a water-swellable and water-insoluble polymeric gelling agent, generally in powder form. In addition, "water-swellable" means that the CRC (absorption ratio without pressure) specified in NWSP 241.0.R2 (19) is 5 g / g or more, and "water-insoluble" means that the Ext (soluble content) specified in NWSP 270.0.R2 (19) is 50% by mass or less.

[0070] The aforementioned "water-absorbing resin" is preferably a hydrophilic crosslinked polymer formed by crosslinking and polymerizing unsaturated monomers with carboxyl groups, but it is not required that its total amount, i.e., 100% by mass, is a crosslinked polymer. It may also contain additives within the range that meets the aforementioned properties such as CRC and Ext.

[0071] In addition, the term "hygroscopic resin" sometimes refers to "a polymer that is cross-linked only internally (i.e., a polymer in which the cross-linking density is substantially the same internally and on the surface)" or "a polymer that is cross-linked internally and on the surface (i.e., a polymer in which the cross-linking density on the surface is higher than that on the internal surface)".

[0072] In this specification, the terms "polymers with internal crosslinking only" and "polymers with internal and surface crosslinking" are essentially the same and are both described as "hygroscopic resins." However, when it is necessary to clearly distinguish whether or not surface crosslinking is involved, since the "polymers with internal crosslinking only" are applied before surface crosslinking, they are described as "hygroscopic resins before surface crosslinking," and since the "polymers with internal and surface crosslinking" are applied after surface crosslinking, they are described as "hygroscopic resins after surface crosslinking." It should be noted that "before surface crosslinking" means "before the addition of a surface crosslinking agent" or "although after the addition of a surface crosslinking agent, but before the start of the heat-based crosslinking reaction."

[0073] In addition, the term "absorbent resin" sometimes refers only to the resin component, but it can also include additives and other components besides the resin.

[0074] In this specification, "water-absorbing composition" refers to a composition comprising the aforementioned "water-absorbing resin" and "flow-enhancing agent". The aforementioned "water-absorbing composition" includes both a state where the water-absorbing resin composition comprising the flow-enhancing agent can be shipped as a final product as is, and a state where the water-absorbing resin composition comprising the flow-enhancing agent has undergone further arbitrary treatment.

[0075] The aforementioned "water-absorbing agent composition" contains a water-absorbing resin as a main component. The term "main component" refers to a water-absorbing resin having a mass ratio of 50% or more relative to the total mass of the water-absorbing agent composition when the total mass of the water-absorbing agent composition is set to 100% by mass. The lower limit of the mass ratio of the water-absorbing resin relative to the total mass of the aforementioned water-absorbing agent composition can be 60% or more by mass, 70% or more by mass, 80% or more by mass, or 90% or more by mass. Furthermore, the upper limit is 100% or less by mass, which can be less than 100% by mass or less than 99% by mass. Additionally, the aforementioned "water-absorbing agent composition" may contain water and trace components other than water as components other than the water-absorbing resin and the flowability improver (other components). In one embodiment, the water-absorbing resin contained in the water-absorbing composition may be 50% or more and 100% or less by mass, 60% or more and less than 100% by mass, 70% or more and less than 100% by mass, 80% or more and less than 100% by mass, or 90% or more and 99% or less by mass.

[0076] [1-2] Polyacrylic acid (salt) based water-absorbing resin

[0077] In this specification, "polyacrylic acid (salt) based water-absorbing resin" refers to a water-absorbing resin made from acrylic acid and / or its salts (hereinafter referred to as "acrylic acid (salt)"). That is, "polyacrylic acid (salt) based water-absorbing resin" is a polymer having structural units derived from acrylic acid (salt), and a polymer having grafted components as any component. Specifically, relative to the portion of the monomers participating in the polymerization reaction, excluding the internal crosslinking agent, the polyacrylic acid (salt) based water-absorbing resin is a polymer containing preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, preferably 100 mol% or less, and more preferably substantially 100 mol% of acrylic acid (salt).

[0078] [1-3] "EDANA" and "NWSP"

[0079] "EDANA" is the abbreviation for the European Disposables and Nonwovens Association. Furthermore, "NWSP" is short for Non-Woven Standard Procedure, representing the world standard testing method for absorbent compositions or resins provided by EDANA. In this invention, unless otherwise specified, the physical properties of absorbent compositions or resins are determined according to the original NWSP (2019 revised edition). It should be noted that, unless otherwise mentioned, the testing methods in the following examples are followed in this specification.

[0080] [1-4]CRC (NWSP 241.0.R2(19))

[0081] "CRC" is short for Centrifuge Retention Capacity, which refers to the water absorption ratio of a water-absorbing agent composition or water-absorbing resin under no pressure. Specific measurement methods and conditions are detailed in the examples.

[0082] [1-5]Ext (NWSP 270.0.R2(19))

[0083] "Ext" is short for Extractables, referring to the amount of water-soluble components in a water-absorbing composition or resin. Specifically, it refers to the amount of polymer dissolved (in mass%) after adding 1.0 g of the water-absorbing composition or resin to 200 ml of a 0.9% (w / w) sodium chloride aqueous solution and stirring at 250 rpm for 1 hour or 16 hours. The amount of dissolved polymer is determined using pH titration. The stirring time is recorded when reporting the results.

[0084] [1-6]AAP (NWSP 242.0.R2(19))

[0085] "AAP" is short for Absorption Against Pressure, which refers to the water absorption ratio of a water-absorbing agent composition or water-absorbing resin under pressure. Specific measurement methods and conditions are detailed in the examples.

[0086] [1-7] Specific surface area

[0087] In this specification, "specific surface area" refers to the surface area per unit mass of the water-absorbing agent composition or water-absorbing resin (unit: m²). 2 / kg), the details of the determination conditions are described in the examples.

[0088] [1-8] Other

[0089] In this specification, "A and / or B" and "A and / or B" refer to A, B, and combinations thereof. Furthermore, "~acid (salt)" means "~acid and / or its salt," and the term "(meth)acryloyl" means "propylene and / or methpropylene." Therefore, for example, the term "(meth)acrylic acid" includes acrylic acid and methacrylic acid, and combinations thereof. Furthermore, unless otherwise specified, concentration, %, and ppm represent mass concentration, mass %, and mass ppm, respectively, and ratios, unless otherwise specified, are mass ratios. Furthermore, unless otherwise specified, operations and determinations of physical properties are performed at room temperature (23±2℃) and relative humidity 35±5%RH.

[0090] [2] Method for manufacturing water-absorbing agent composition

[0091] The absorbent composition obtained by the manufacturing method of the present invention comprises an absorbent resin as a main component and also comprises a flowability improver. The absorbent resin is not particularly limited as long as it has the characteristics described in [1-1] above, but is preferably a polyacrylic acid (salt) based absorbent resin. That is, one embodiment of the present invention provides a method for manufacturing an absorbent resin composition (absorbent composition) comprising a polyacrylic acid (salt) based absorbent resin and a flowability improver. Hereinafter, the manufacturing method of the above-described absorbent composition will be described in detail.

[0092] In one embodiment, the manufacturing method of the present invention includes: a monomer aqueous solution preparation step, a polymerization step, a gel pulverization step, a drying step, a post-drying pulverization step, a classification step, a surface crosslinking step, and a flowability improver aqueous solution addition step, wherein the flowability improver aqueous solution addition step is performed during or after the surface crosslinking step. In a preferred embodiment, the manufacturing method of the present invention sequentially includes: a monomer aqueous solution preparation step, a polymerization step, a gel pulverization step, a drying step, a post-drying pulverization step, a classification step, a surface crosslinking step, and a flowability improver aqueous solution addition step. In addition to the above steps, the manufacturing method of the present invention may further include, as needed: an additive addition step, a cooling step, a rewetting step, a micronization granulation step, a conveying step, a storage step, a packaging step, and a preservation step. The following describes each step.

[0093] [2-1] Preparation process of monomer aqueous solution

[0094] This process involves preparing an aqueous solution of monomers, preferably unsaturated monomers, more preferably unsaturated monomers having carboxyl groups, and even more preferably monomers containing acrylic acid (salt) as a main component, which is a raw material for the absorbent resin. The aqueous monomer solution preferably contains one or more polymerizable internal crosslinking agents. The term "main component" refers to a component whose acrylic acid (salt) content, excluding the internal crosslinking agent, is 50 mol% or more relative to the monomer supplied for the polymerization reaction. The lower limit of the acrylic acid (salt) content relative to the monomer supplied for the polymerization reaction (excluding the internal crosslinking agent) is preferably 70 mol% or more, more preferably 90 mol% or more. Furthermore, the upper limit is 100 mol% or less, and can be 99 mol% or less, or 95 mol% or less. It should be noted that the preferred range of the acrylic acid (salt) content can be set as a range defined by any combination selected from the above upper and lower limits. A monomer slurry can also be used within a range that does not affect the absorbent properties of the absorbent composition obtained as the final product, but for convenience, an aqueous monomer solution is described in this specification.

[0095] (Acrylic acid (salt))

[0096] In this invention, from the viewpoint of the physical properties of the absorbent composition or the absorbent resin, it is preferable to use known acrylic acid (salt) as a monomer (hereinafter sometimes referred to as "polymerizable monomer"). Known acrylic acid contains trace amounts of polymerization inhibitors, impurities, etc. As the polymerization inhibitor, methoxyphenols are preferred, and p-methoxyphenols are more preferred. From the viewpoint of the polymerizability of acrylic acid, the color of the absorbent composition or the absorbent resin, etc., the lower limit of the concentration of the polymerization inhibitor in the acrylic acid, on a mass basis, is preferably 10 ppm or more, more preferably 20 ppm or more. On the other hand, the upper limit is preferably 200 ppm or less, more preferably 160 ppm or less, and even more preferably 100 ppm or less. It should be noted that the preferred range of the concentration of the polymerization inhibitor in the acrylic acid can be set as a range defined by any combination selected from the above upper and lower limits.

[0097] In addition to organic compounds such as acetic acid, propionic acid, and furfural, the compounds described in U.S. Patent Application Publication No. 2008 / 0161512 can be listed as impurities. Furthermore, as acrylates, salts obtained by neutralizing the aforementioned acrylic acid with the following basic compounds can be listed. The acrylates can be commercially available acrylates or salts obtained by neutralizing acrylic acid.

[0098] (Alkaline compounds)

[0099] In this invention, "alkaline compound" refers to a compound that exhibits alkalinity. Specifically, sodium hydroxide and the like are considered alkaline compounds. It should be noted that commercially available sodium hydroxide, at the ppm level (mass basis), contains heavy metals such as zinc, lead, and iron, and can strictly be described as a composition. In this invention, such compositions are also considered to be included within the scope of alkaline compounds.

[0100] Specific examples of the aforementioned alkaline compounds include alkali metal carbonates, bicarbonates, alkali metal hydroxides, ammonia, and organic amines. Among these, strongly alkaline compounds are selected from the viewpoint of the absorbent properties of the absorbent composition or the absorbent resin. Therefore, hydroxides of alkali metals such as sodium, potassium, and lithium are preferred, and sodium hydroxide is more preferred. It should be noted that, from an operability viewpoint, the alkaline compound is preferably prepared as an aqueous solution.

[0101] (Neutralization)

[0102] When using the salt obtained by neutralizing acrylic acid as the aforementioned acrylate, neutralization can be performed before, during, or after polymerization, or at multiple times or locations. Furthermore, from the viewpoint of production efficiency of the water-absorbing composition or the water-absorbing resin, continuous neutralization is preferred.

[0103] When acrylic acid (salt) is used in this invention, the lower limit of the neutralization rate relative to the acid groups of the monomer is preferably 10 mol% or more, more preferably 40 mol% or more, further preferably 50 mol% or more, and particularly preferably 60 mol% or more. On the other hand, the upper limit of the neutralization rate is preferably 90 mol% or less, more preferably 85 mol% or less, further preferably 80 mol% or less, and particularly preferably 75 mol% or less. It should be noted that the preferred range of the above-mentioned neutralization rate can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. By setting it to the range of the neutralization rate, it is easier to suppress the decrease in the water absorption performance of the water-absorbing agent composition or the water-absorbing resin.

[0104] It should be noted that the above-mentioned neutralization rate range applies to any neutralization occurring before, during, or after polymerization. Furthermore, it applies not only to the acid groups of the water-absorbing resin but also to the acid groups of the water-absorbing composition used in the final product.

[0105] (Other monomers)

[0106] In this invention, monomers other than acrylic acid (salt) (hereinafter referred to as "other monomers") may be used in combination with acrylic acid (salt) as needed. Specifically, examples of the aforementioned other monomers include: maleic acid, maleic anhydride, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluenesulfonic acid, vinyl toluenesulfonic acid, styrene sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, 2-(meth)acryloyl ethanesulfonic acid, 2-(meth)acryloyl propanesulfonic acid, 2-hydroxyethyl(meth)acryloyl phosphate, and other anionic unsaturated monomers and their salts; unsaturated monomers containing thiol groups; unsaturated monomers containing phenolic hydroxyl groups; unsaturated monomers containing amide groups such as (meth)acrylamide, N-ethyl(meth)acrylamide, and N,N-dimethyl(meth)acrylamide; and unsaturated monomers containing amino groups such as N,N-dimethylaminoethyl(meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, and N,N-dimethylaminopropyl(meth)acrylamide. Furthermore, the other monomers include water-soluble or hydrophobic unsaturated monomers. When using the other monomers, their amount used relative to the monomers other than the internal crosslinking agent is preferably 30 mol% or less, more preferably 10 mol% or less (lower limit 0 mol%), and even more preferably 5 mol% or less.

[0107] (Internal cross-linking agent)

[0108] In a preferred manufacturing method of the present invention, an internal crosslinking agent is used. Specifically, examples of internal crosslinking agents include: N,N'-methylenebis(meth)acrylamide, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerol tri(meth)acrylate, ethoxylated modified glycerol tri(meth)acrylate, glycerol acrylate methacrylate, ethoxylated modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkane, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, polyethyleneimine, and glycidyl methacrylate. These internal crosslinking agents can be used alone or in combination with two or more. Considering reactivity and other factors, one or more internal crosslinking agents can be selected from these agents. Furthermore, from the viewpoint of the water-absorbing properties of the absorbent composition or the absorbent resin, it is preferable to select an internal crosslinking agent having two or more polymerizable unsaturated groups; more preferably, an internal crosslinking agent that exhibits pyrolytic properties at the drying temperature described later; and even more preferably, an internal crosslinking agent having a (poly)alkylene glycol structure and having two or more polymerizable unsaturated groups.

[0109] Specifically, allyl and (meth)acrylate groups can be listed as polymerizable unsaturated groups. (Meth)acrylate groups are preferred. Furthermore, polyethylene glycol can be listed as an internal crosslinking agent having a (poly)alkylene glycol structure. It should be noted that the number of alkylene glycol units (hereinafter sometimes referred to as "n") is preferably 1 or more, more preferably 6 or more, preferably 100 or less, more preferably 50 or less, further preferably 20 or less, and particularly preferably 10 or less.

[0110] Examples of internal crosslinking agents having the aforementioned polymerizable unsaturated groups and (poly)alkylene glycol structures include (poly)ethylene glycol di(meth)acrylate and (poly)propylene glycol di(meth)acrylate.

[0111] The lower limit of the amount of the aforementioned internal crosslinking agent used is preferably 0.0001 mol% or more, more preferably 0.001 mol% or more, and even more preferably 0.01 mol% or more, relative to the monomer excluding the internal crosslinking agent. The upper limit is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 1 mol% or less. It should be noted that the preferred range for the amount of the aforementioned internal crosslinking agent can be set as a range defined by any combination selected from the above upper and lower limits. By setting the amount used within the aforementioned range, it is easier to obtain a water-absorbing agent composition or water-absorbing resin with the desired water absorption properties (e.g., suppressing the increase of water-soluble components and the decrease of absorption rate).

[0112] The aforementioned internal crosslinking agent is preferably added in advance during the preparation of the monomer aqueous solution, in which case the polymerization reaction and the crosslinking reaction occur simultaneously. Alternatively, the polymerization reaction can be initiated without adding an internal crosslinking agent, and the crosslinking reaction can be carried out by adding the internal crosslinking agent during or after the polymerization reaction. Furthermore, these methods can be used in combination. Additionally, it can be configured as a self-crosslinking reaction without the use of an internal crosslinking agent.

[0113] (Substances added to the monomer aqueous solution)

[0114] From the viewpoint of improving the physical properties of the absorbent composition or the absorbent resin, the following substances may be added to the monomer aqueous solution at any of the following points: during the preparation of the monomer aqueous solution, during the polymerization and crosslinking reactions, or after the polymerization and crosslinking reactions. Specifically, such substances include: hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol (hereinafter sometimes referred to as "PVA"), polyacrylic acid (salt), and crosslinks of polyacrylic acid (salt); compounds such as carbonates, azo compounds, foaming agents that generate various bubbles, surfactants, chelating agents, and chain transfer agents. It should be noted that the surfactants and other substances added to the monomer aqueous solution are not added for the purpose of improving the flowability of the absorbent composition.

[0115] The upper limit of the amount of the hydrophilic polymer added, relative to the monomer aqueous solution, is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less. On the other hand, the lower limit is preferably 0% by mass, more preferably more than 0% by mass. Furthermore, the upper limit of the amount of the compound added, relative to the monomer aqueous solution, is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. On the other hand, the lower limit is preferably 0% by mass or more, more preferably more than 0% by mass. It should be noted that the preferred ranges for the amounts of the hydrophilic polymer and the compound can be set as ranges defined by any combination selected from the above upper and lower limits.

[0116] If a water-soluble resin or a water-absorbing resin is used as the aforementioned hydrophilic polymer, grafted polymers or water-absorbing resin compositions such as starch-acrylate (salt) copolymers and PVA-acrylate (salt) copolymers can be obtained. These grafted polymers or water-absorbing resin compositions are also included within the scope of polyacrylate (salt)-based water-absorbing resins of the present invention.

[0117] (Concentration of monomeric components)

[0118] According to the purpose, each of the above-mentioned substances and components (hereinafter referred to as "monomer components") is selected, and their respective amounts are specified in a manner that satisfies the above-mentioned range and mixed with each other to prepare a monomer aqueous solution. It should be noted that, in this invention, in addition to preparing the monomer into an aqueous solution, a mixed solution of water and a hydrophilic solvent can also be prepared, and such a form is also referred to as a monomer aqueous solution.

[0119] Furthermore, from the viewpoint of the physical properties of the absorbent composition or the absorbent resin, the lower limit of the total concentration of the monomer components is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. On the other hand, the upper limit is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. It should be noted that the preferred range of the total concentration of the monomer components can be set as a range defined by any combination selected from the above upper and lower limits. It should be noted that the concentration of the monomer components is calculated according to the following (Formula I).

[0120] The concentration (mass%) of the monomer component = {(mass of the monomer component) / (mass of the monomer aqueous solution)} × 100…… (Formula I)

[0121] In the above (Formula I), the "mass of monomer aqueous solution" does not include the mass of grafted components, water-absorbing resin, and hydrophobic organic solvents in reverse suspension polymerization.

[0122] (polyalkylene glycol)

[0123] Polyalkylene glycols can be added during the preparation of the monomer aqueous solution. It should be noted that polyalkylene glycols can also be added as an internal crosslinking agent during the preparation of the monomer aqueous solution. Furthermore, polyalkylene glycols can be added during the polymerization and / or gel pulverization processes detailed below. That is, in one embodiment, the method for manufacturing the absorbent composition of the present invention preferably includes a step of further adding polyalkylene glycols between at least one step selected from the monomer aqueous solution preparation step, the polymerization step, and the gel pulverization step, and / or between each of the above steps (monomer aqueous solution preparation step, polymerization step, and gel pulverization step).

[0124] It should be noted that the polyalkylene glycol added here is not intended to improve the flowability of the superabsorbent polymer. That is, the polyalkylene glycol added in at least one step selected from the preparation of the monomer aqueous solution, the polymerization step, and the gel pulverization step, and / or in each of the above steps, is not included in the flowability improver of this invention. Generally, to improve the flowability of superabsorbent polymers, from the viewpoint of surface modification, it is necessary to form a coating on the surface of the superabsorbent polymer particles. However, when added in the above-mentioned steps, i.e., in steps that allow the polyalkylene glycol to be uniformly distributed within the superabsorbent polymer, almost no polyalkylene glycol is present on the surface of the superabsorbent polymer particles, and the desired flowability improvement effect cannot be obtained.

[0125] Here, polyalkylene glycol can be added in any one of the monomer aqueous solution preparation step, the polymerization step, and the gel pulverization step, or in any two steps, or in all steps. Furthermore, polyalkylene glycol can be added between the monomer aqueous solution preparation step and the polymerization step, between the polymerization step and the gel pulverization step, or between both; it can be added not only between these steps but also within the aforementioned steps. It should be noted that when polyalkylene glycol is added in multiple steps or between steps, the amount of polyalkylene glycol added in each step or between steps can be the same or different. Preferably, the addition of polyalkylene glycol is carried out in the monomer aqueous solution preparation step. That is, in one embodiment, it is preferred that the method for manufacturing the water-absorbing composition of the present invention includes a step of further adding polyalkylene glycol in the monomer aqueous solution preparation step.

[0126] As the above-mentioned polyalkylene glycols, polyalkylene glycols having the structure shown in the following general formula (1) can be listed.

[0127] H-(OR) n -OH(1)

[0128] In general formula (1), R is an alkylene group having 2 to 4 carbon atoms, which can be linear or branched. Furthermore, n is the average number of moles of oxyalkylene (-OR-) added, preferably 4 to 70, more preferably 4 to 50, and even more preferably 6 to 15.

[0129] In general formula (1), the alkylene groups (-OR-) in a molecule can be the same or different. More specifically, examples of the aforementioned polyalkylene glycols include: polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol copolymer, polyethylene glycol-polypropylene glycol-polybutane glycol copolymer, etc. These polyalkylene glycols can be used alone or in combination of two or more.

[0130] The upper limit of the mass-average molecular weight of the aforementioned polyalkylene glycol is preferably 3000 or less. The lower limit of the mass-average molecular weight of the aforementioned polyalkylene glycol is preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more. Furthermore, the mass-average molecular weight is more preferably 2500 or less, even more preferably 2400 or less, and particularly preferably 2300 or less. By setting the mass-average molecular weight of the polyalkylene glycol within the above range, the water absorption performance of the surface-crosslinked water-absorbing resin is improved. Here, the mass-average molecular weight of the polyalkylene glycol is a value determined by gel permeation chromatography.

[0131] Polyalkylene glycols having the above-mentioned mass-average molecular weight can be water-soluble. It should be noted that the definition of the term "water-soluble" is as described below. By making the polyalkylene glycol water-soluble, when added in at least any one of the steps selected from the preparation of the monomer aqueous solution, the polymerization step, and the gel pulverization step, or between these three steps, the addition can be more uniform. As a result, a water-absorbing resin uniformly containing polyalkylene glycol can be obtained. Furthermore, as a result, the water absorption properties of the surface-crosslinked water-absorbing resin are improved. It should be noted that the polyalkylene glycol added in at least one of the steps selected from the preparation of the monomer aqueous solution, the polymerization step, and the gel pulverization step, or between these three steps, is not equivalent to the flowability improver described above.

[0132] In a preferred embodiment, the polyalkylene glycol may be polyethylene glycol with a mass-average molecular weight of 3000 or less. In another embodiment, the polyalkylene glycol may be polyethylene glycol with a mass-average molecular weight of 200 or more and 3000 or less. More preferably, the mass-average molecular weight of the polyethylene glycol is 300 or more and 2500 or less, even more preferably 400 or more and 2400 or less, and particularly preferably 400 or more and 2300 or less.

[0133] The amount of polyalkylene glycol added is preferably 0.01% by mass or more and 0.25% by mass or less, relative to the total mass of monomers contained in the aqueous monomer solution. Here, the total mass of monomers contained in the aqueous monomer solution refers to the total mass of monomers excluding the internal crosslinking agent. The lower limit of the amount of polyalkylene glycol added is more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more. On the other hand, the upper limit is more preferably 0.23% by mass or less, even more preferably 0.20% by mass or less, and particularly preferably 0.18% by mass or less. When two or more polyalkylene glycols are added, the above-mentioned amount refers to their total amount. It should be noted that the preferred range of the amount of polyalkylene glycol added can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the amount of polyalkylene glycol added can, for example, be 0.02% by mass or more and 0.23% by mass or less, 0.02% by mass or more and 0.20% by mass or less, or 0.03% by mass or more and 0.18% by mass or less. Furthermore, when the aforementioned polyalkylene glycol is added in multiple processes, i.e., in at least one process selected from the monomer aqueous solution preparation process, polymerization process, and gel pulverization process, and / or between the aforementioned processes (monomer aqueous solution preparation process, polymerization process, and gel pulverization process), the amount added is preferably added such that the total amount of the aforementioned polyalkylene glycol added in each process falls within the aforementioned range. By setting the amount of polyalkylene glycol added within the aforementioned range, the water absorption performance of the surface-crosslinked water-absorbing resin is improved.

[0134] As the aforementioned polyalkylene glycols, two or more polyalkylene glycols can be used. Furthermore, when using one or more polyalkylene glycols, polyalkylene glycols having various mass-average molecular weights can be used in combination for each polyalkylene glycol.

[0135] [2-2] Polymerization process

[0136] This process involves polymerizing the monomer aqueous solution obtained in the above monomer aqueous solution preparation process, which contains a monomer with acrylic acid (salt) as the main component and one or more polymerizable internal crosslinking agents, to obtain a hydrogel.

[0137] (Polymerization initiator)

[0138] In this process, a polymerization initiator is preferably used. Examples of polymerization initiators include pyrolytic polymerization initiators, photodegradable polymerization initiators, and redox polymerization initiators that also incorporate a reducing agent that promotes the decomposition of these polymerization initiators. Specifically, examples of free radical polymerization initiators include sodium persulfate, potassium persulfate, ammonium persulfate, tert-butyl hydroperoxide, hydrogen peroxide, and 2,2'-azobis(2-amidinylpropane) dihydrochloride. Considering the polymerization method, one or more of these polymerization initiators can be selected. Furthermore, from the viewpoint of the operability of the polymerization initiator and the physical properties of the absorbent composition or absorbent resin, peroxides or azo compounds are preferred as polymerization initiators, peroxides are more preferred, and persulfates are even more preferred. In addition, when using an oxidizing free radical polymerization initiator, redox polymerization can be carried out using a reducing agent such as sodium sulfite, sodium bisulfite, ferrous sulfate, or L-ascorbic acid.

[0139] The lower limit of the amount of the polymerization initiator used relative to the monomer excluding the internal crosslinking agent is preferably 0.001 mol% or more, more preferably 0.01 mol% or more. On the other hand, the upper limit is preferably 1 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.1 mol% or less. Furthermore, the lower limit of the amount of the reducing agent used relative to the monomer excluding the internal crosslinking agent is preferably 0.0001 mol% or more, more preferably 0.0005 mol% or more. On the other hand, the upper limit is preferably 0.02 mol% or less, more preferably 0.015 mol% or less. It should be noted that the preferred ranges for the amounts of the polymerization initiator and the reducing agent can be set to a range defined by any combination selected from the above upper and lower limits. By setting the amounts within the aforementioned ranges, it is easier to obtain a water-absorbing composition or water-absorbing resin with the desired water-absorbing properties.

[0140] Furthermore, in this invention, the above-mentioned polymerization reaction can also be initiated by irradiation with active energy rays such as radiation, electron beams, or ultraviolet rays. Additionally, irradiation with active energy rays and the above-mentioned polymerization initiator can be used in combination.

[0141] (Aggregation method)

[0142] Examples of polymerization methods applicable to this invention include aqueous solution polymerization, reverse suspension polymerization, spray polymerization, droplet polymerization, bulk polymerization, and precipitation polymerization. From the viewpoint of ease of polymerization control and the water absorption properties of the superabsorbent composition or superabsorbent resin, aqueous solution polymerization or reverse suspension polymerization is preferred, aqueous solution polymerization is more preferred, and continuous aqueous solution polymerization is even more preferred. Reverse suspension polymerization is described in International Publication No. 2007 / 004529, International Publication No. 2012 / 023433, etc. Furthermore, examples of continuous aqueous solution polymerization include continuous belt polymerization described in U.S. Patent No. 4,893,999, U.S. Patent No. 6,906,159, U.S. Patent No. 7,091,253, U.S. Patent No. 7,741,400, U.S. Patent No. 8,519,212, and Japanese Patent Application Publication No. 2005-36,100, or continuous kneader polymerization described in U.S. Patent No. 6,987,151, etc.

[0143] Preferred methods for the aforementioned continuous aqueous solution polymerization include high-temperature initiation polymerization, high-concentration polymerization, and foaming polymerization. "High-temperature initiation polymerization" refers to a polymerization method in which the temperature of the monomer aqueous solution during polymerization initiation is preferably 30°C or higher, more preferably 35°C or higher, further preferably 40°C or higher, and particularly preferably 50°C or higher, with the upper limit temperature set at the boiling point of the monomer aqueous solution. "High-concentration polymerization" refers to a polymerization method in which the monomer concentration during polymerization initiation is preferably 30% by mass or higher, more preferably 35% by mass or higher, further preferably 40% by mass or higher, and particularly preferably 42% by mass or higher, with the upper limit concentration set at the saturation concentration of the monomer aqueous solution. Furthermore, "foaming polymerization" refers to a polymerization method in which the aforementioned monomer aqueous solution containing a foaming agent or bubbles is polymerized. It should be noted that these polymerization methods can be implemented individually or in combination of two or more.

[0144] The above-described foaming polymerization is one of the methods for increasing the specific surface area of ​​the water-absorbing agent composition or the water-absorbing resin, and is one of the preferred methods. Examples of methods for dispersing bubbles in the foaming polymerization include: (I) a method of dispersing gas dissolved in the monomer aqueous solution as bubbles by decreasing solubility; (II) a method of dispersing gas as bubbles by introducing gas from the outside; (III) a method of foaming by adding a foaming agent to the monomer aqueous solution; etc. Furthermore, the above-described dispersion methods can be used in combination depending on the water-absorbing properties of the water-absorbing agent composition or the water-absorbing resin.

[0145] The gases dissolved in the monomer aqueous solution mentioned above (I) can be listed as oxygen used to stabilize the monomer, nitrogen, carbon dioxide, ozone, etc., which are inert gases, and their mixtures.

[0146] In the case of the method described above (II) where a gas is introduced from the outside and dispersed in the form of bubbles, the gas can specifically include: oxygen, air, nitrogen, carbon dioxide, ozone, and mixtures thereof. Among these, from the viewpoints of polymerizability and cost, inert gases such as nitrogen and carbon dioxide are preferred, and nitrogen is more preferred.

[0147] In the case of the method described in (III) above, where a foaming agent is added to an aqueous monomer solution to cause foaming, the foaming agent can specifically include: azo compounds, organic or inorganic carbonate solutions, dispersions, or powders with a particle size of 0.1 μm or more and 1000 μm or less, preferably carbonates or bicarbonates such as sodium carbonate, ammonium carbonate, and magnesium carbonate. In the aqueous monomer solution containing the aforementioned foaming agent or bubbles, a surfactant can be used to stably maintain the bubbles.

[0148] In the methods (I) to (III) disclosed as methods for dispersing bubbles in the aforementioned foaming polymerization, surfactants may be used in conjunction. Examples of surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, fluorinated surfactants, and organometallic surfactants. Specifically, surfactants described in International Publication No. 97 / 017397 and US Patent No. 6107358 may be cited.

[0149] It should be noted that the surfactants used in the methods (I) to (III) above cannot achieve the desired improvement in the flowability of the absorbent resin as described in this specification. From a surface modification perspective, it is necessary to form a coating on the surface of the absorbent resin particles to improve their flowability. However, when a surfactant is added during the polymerization process—that is, during a process that allows the surfactant to be uniformly distributed within the absorbent resin—there is almost no surfactant on the surface of the absorbent resin particles, making it impossible to achieve the desired improvement in flowability.

[0150] The above-described polymerization methods can be carried out in an air environment, but from the viewpoint of the color of the water-absorbing agent composition or the water-absorbing resin, it is preferable to carry out the polymerization in an environment with inert gases such as nitrogen or argon, and more preferably in an environment with an oxygen concentration of 1% by volume or less. It should be noted that, regarding the dissolved oxygen in the monomer aqueous solution, it is also preferable to use an inert gas to fully replace it, and more preferably to ensure that the dissolved oxygen content is less than 1 mg / L beforehand.

[0151] The formation of a foamed hydrogel, water-absorbing resin, or water-absorbing agent composition through foaming polymerization results in a faster water absorption rate for the water-absorbing agent composition or resin. Furthermore, it facilitates the immobilization of the water-absorbing agent composition into an absorbent article, making it preferable. It should be noted that the foamed shape can be confirmed by observing the pores on the particle surface under an electron microscope. Furthermore, examples of pore size include pores with a diameter of 1 μm or more and 100 μm or less. The lower limit for the number of pores in each particle of water-absorbing agent composition or water-absorbing resin is preferably 1 or more, more preferably 10 or more. On the other hand, the upper limit is preferably 10,000 or less, more preferably 1,000 or less. It should be noted that the preferred range for the number of pores can be set as a range defined by any combination selected from the above upper and lower limits. The pores can be controlled by the foaming polymerization described above. From the perspective of increasing the specific surface area of ​​the water-absorbing agent composition or water-absorbing resin, the foaming polymerization is a preferred technique.

[0152] [2-3] Gel pulverization process

[0153] This step involves gel pulverizing the hydrogel obtained in the polymerization step described above to obtain particulate hydrogel (hereinafter referred to as "particulate hydrogel"). It should be noted that, to distinguish it from the "pulverization" in the pulverization step described below, the pulverization in this step is referred to as "gel pulverization." The aforementioned "gel pulverization" refers to using a gel pulverizer such as a kneader, meat grinder, or shredder to adjust the hydrogel to a specified size.

[0154] Regarding the implementation methods and operating conditions for gel pulverization, the contents described in Japanese Patent No. 5989913 or Japanese Patent No. 6067126 are preferably applied in this invention. It should be noted that when the polymerization method is kneading polymerization, the polymerization step and the gel pulverization step are performed simultaneously. Furthermore, when particulate hydrogels are obtained through polymerization steps such as reverse suspension polymerization, spray polymerization, or droplet polymerization, the gel pulverization step is considered to be performed simultaneously with the polymerization step. Moreover, the gel pulverization step can yield irregularly fragmented water-absorbing agent compositions and water-absorbing resins.

[0155] The particle size of the finely granulated hydrogel obtained through the gel pulverization process is preferably 0.05 mm or more and 10 mm or less. When the particle size of the hydrogel is 0.05 mm or more, the physical properties of the resulting water-absorbing agent composition or water-absorbing resin become better. Furthermore, when the particle size of the hydrogel is 10 mm or less, the hydrogel can be dried efficiently.

[0156] Furthermore, the lower limit of the D50 (mass-average particle size) of the above-mentioned particulate hydrogel is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 140 μm or more. On the other hand, the upper limit is preferably 2000 μm or less, more preferably 1500 μm or less, and even more preferably 1000 μm or less. It should be noted that the preferred range of the D50 of the above-mentioned particulate hydrogel can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. For example, controlling the D50 (mass-average particle size) of the above-mentioned particulate hydrogel within the above-mentioned preferred range by the method described in (B) below is one of the methods to increase the specific surface area of ​​the water-absorbing agent composition or the water-absorbing resin, and is one of the preferred solutions.

[0157] As for the PSD (particle size distribution) of the aforementioned particulate hydrogel, the σζ (logarithmic standard deviation), which represents the narrowness of its particle size distribution, is preferably 0.2 or higher. On the other hand, its upper limit is preferably 1.5 or lower, more preferably 1.3 or lower, and even more preferably 1.2 or lower. It should be noted that the preferred range of the above-mentioned σζ (logarithmic standard deviation of particle size distribution) can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. The smaller the value of the above-mentioned σζ (logarithmic standard deviation of particle size distribution), the more uniform the particle size, which has the advantage of being able to dry more uniformly. However, in order to set the σζ (logarithmic standard deviation of particle size distribution) to be less than 0.2, special operations such as particle size control during polymerization before gel pulverization and classification of particulate hydrogels after gel pulverization are required, which is practically difficult to implement from the point of view of productivity and cost.

[0158] In this invention, it is ideal to control one or more of the following methods: (A) foaming polymerization of monomer aqueous solution, (B) pulverization and granulation of particulate hydrogel or its dried polymer, and (C) micron powder recycling, so that the specific surface area of ​​the water-absorbing resin is 25 m². 2 / kg or more.

[0159] As a foaming polymerization of the above-mentioned monomer aqueous solution, for example, by employing a foaming polymerization method, the specific surface area of ​​the water-absorbing resin can be increased to 25 m². 2The foam polymerization method, with a volume of / kg or more, includes: foaming by gelling dissolved gases in a monomer aqueous solution during high-temperature, short-time polymerization, sealing them within the system; or foaming polymerization in which a surfactant and a monomer aqueous solution coexist, i.e., the foaming polymerization method described in Japanese Patent No. 5647625 (specifically, for example, a method of generating bubbles in a monomer aqueous solution by decreasing the solubility of dissolved gases in the monomer aqueous solution in the presence of a surfactant); foaming polymerization method in which gas is introduced from the outside into the monomer aqueous solution and dispersed in the form of bubbles for polymerization; and foaming polymerization method in which a foaming agent is added to the monomer aqueous solution to cause foaming for polymerization, etc. Therefore, the water-absorbing resin is also preferably obtained by foaming polymerization of an unsaturated monomer aqueous solution.

[0160] Furthermore, as for the pulverization and granulation of the above-mentioned (B) particulate hydrogel or its dried polymer, for example, by using the gel pulverization method described in Japanese Patent No. 5989913, Japanese Patent No. 6067126, and International Publication No. 2016 / 204302 as the gel pulverization step, and further drying, the specific surface area of ​​the water-absorbing resin can be increased to 25 m². 2 / kg or more. Furthermore, by appropriately controlling the mold aperture, number of holes, mold thickness, amount of warm water added, and screw shaft speed of a gel pulverizer such as a meat grinder, a water-absorbing resin with a desired specific surface area can also be obtained. It should be noted that the above-described granulation can be performed on the hydrogel during polymerization, or on the micronized product of the polymerized hydrogel while drying, or on the dried micronized product using water and / or organic or inorganic binders. Therefore, granules of the hydrogel containing the water-absorbing resin or its dried product are preferred.

[0161] Furthermore, as for the recycling of the aforementioned (C) micro-powder, for example, by recovering the micro-powder of the water-absorbing resin that has passed through a sieve with a mesh size of 150 μm during the polymerization process, gel pulverization process, and drying process, or by granulating and recycling the micro-powder, the specific surface area of ​​the water-absorbing resin can be increased to 25 m². 2 / kg or more. Therefore, the micronized recycled product containing the water-absorbing resin is also preferred. The methods (A) to (C) above can be carried out individually or in combination.

[0162] It should be noted that this increases the specific surface area of ​​the water-absorbing resin to 25m². 2Methods using particles larger than / kg also contain a large amount of small particles. However, these methods often contain a large amount of small particles, particularly micro-powder that passes through a sieve with a mesh size of 150 μm. As a result, the resulting absorbent composition is prone to gelation blockage, and its liquid absorption and flow properties under pressure decrease, making it undesirable. Therefore, when adjusting the specific surface area using the micro-powder, methods (B) and / or (C) described above are preferred. In this invention, it is preferable to pay close attention to adjusting the particle size distribution and implement the adjustment method described later.

[0163] The methods for determining the D50 (mass-average particle size) and σζ (logarithmic standard deviation of particle size distribution) of the above-mentioned particulate hydrogels are performed by referring to the methods described in paragraphs 0257 to 0270 of International Publication No. 2016 / 111223.

[0164] [2-4] Drying process

[0165] This process involves drying the hydrogel and / or particulate hydrogel obtained in the above-described polymerization and / or gel pulverization processes to a desired solid content to obtain a dried polymer. The solid content of this dried polymer is determined based on the mass change when 1 g of the water-absorbing resin is heated at 180°C for 3 hours. The lower limit of the solid content of the dried polymer is preferably 80% by mass or more, more preferably 85% by mass or more, further preferably 90% by mass or more, and particularly preferably 92% by mass or more. On the other hand, the upper limit is preferably 99% by mass or less, more preferably 98% by mass or less, and further preferably 97% by mass or less. It should be noted that the preferred range of the solid content of the dried polymer can be defined as a range determined by any combination of the above-described upper and lower limits.

[0166] Specifically, drying methods for the aforementioned hydrogels and / or particulate hydrogels include: heating drying, hot air drying, vacuum drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, drying based on azeotropic dehydration with hydrophobic organic solvents, and high-humidity drying using high-temperature steam. From the viewpoint of drying efficiency, hot air drying is preferred, and belt drying, which involves hot air drying over a ventilation belt, is more preferred.

[0167] From the viewpoint of the color tone and drying efficiency of the absorbent composition or absorbent resin, the lower limit of the drying temperature in the above-mentioned hot air drying is preferably 100°C or higher, more preferably 150°C or higher. On the other hand, the upper limit is preferably 300°C or lower, more preferably 200°C or lower. It should be noted that the preferred range of the above-mentioned drying temperature can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. It should be noted that the drying temperature in hot air drying is defined by the temperature of the hot air. In addition, regarding the drying conditions other than the above-mentioned drying temperature, such as the hot air velocity and drying time, they can be appropriately set according to the water content, total mass and target solid composition of the particulate hydrogel supplied for drying. When performing belt drying, the conditions described in International Publication Nos. 2006 / 100300, 2011 / 025012, 2011 / 025013, and 2011 / 111657 can be appropriately applied.

[0168] The lower limit of the drying time of the present invention is preferably 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. On the other hand, the upper limit is preferably 10 hours or less, more preferably 3 hours or less, and even more preferably 1 hour or less. It should be noted that the preferred range of the above-mentioned drying time can be set to a range defined by any combination selected from the above-mentioned upper and lower limits. By setting the drying temperature and drying time within the above-mentioned range, the physical properties of the obtained water-absorbing agent composition can be set to a desired range. In addition, the physical properties of the water-absorbing resin as an intermediate product can also be set to a desired range. Furthermore, when drying is carried out by hot air drying, the lower limit of the hot air velocity is preferably 0.5 m / s or more. On the other hand, the upper limit is preferably 3.0 m / s or less, more preferably 2.0 m / s or less. The preferred range of the above-mentioned hot air velocity can be set to a range defined by any combination selected from the above-mentioned upper and lower limits. It should be noted that for other drying conditions, appropriate settings can be made according to the water content and total mass of the particulate hydrogel being dried and the target solid composition.

[0169] [2-5] Crushing process, grading process

[0170] The pulverizing process involves pulverizing the dried polymer obtained from the aforementioned drying process. By pulverizing after drying, an irregularly broken, water-absorbing resin can be obtained. Furthermore, the grading process involves classifying the pulverized dried polymer from the aforementioned pulverizing process and producing it into a particle size within a desired range. Through this process, a water-absorbing resin before surface crosslinking can be obtained.

[0171] Specifically, the pulverizers used in the above-mentioned pulverizing process can include high-speed rotary pulverizers such as roller mills, hammer mills, screw mills, and pin mills, vibratory mills, knuckle-type pulverizers, and cylindrical mixers. From the viewpoint of pulverizing efficiency, roller mills are preferred. Furthermore, multiple pulverizers can be used in combination.

[0172] As methods for particle size adjustment in the above-mentioned grading process, examples include sieve grading using a JIS standard sieve (JIS Z8801-1 (2000)) and air classifying. Among these, sieve grading is preferred from the viewpoint of grading efficiency. It should be noted that particle size adjustment of the water-absorbing agent composition or water-absorbing resin is not limited to the pulverizing process or grading process, but can also be implemented in the polymerization process, especially reverse suspension polymerization, droplet polymerization, or other processes such as granulation process or micron powder recovery process.

[0173] The proportion of particles with a particle size of less than 150 μm (hereinafter referred to as "particles less than 150 μm") in the water-absorbing resin before surface crosslinking after grading is preferably 3% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2% by mass or less. Furthermore, in continuous commercial production, from the viewpoint of production efficiency, it is sometimes very difficult to achieve a proportion of particles less than 150 μm of 0% by mass. Therefore, the proportion of particles less than 150 μm is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. It should be noted that, in this specification, "particles with a particle size of less than 150 μm" refers to particles that have passed through a sieve with a mesh size of 150 μm after grading using the same method as the grading method in the evaluation method for the coefficient of kinetic friction of the embodiments.

[0174] Furthermore, (ii) the lower limit of D50 (mass-average particle size) is preferably 250 μm or more, more preferably 300 μm or more, and even more preferably 330 μm or more. On the other hand, its upper limit is preferably less than 550 μm, more preferably less than 500 μm, and even more preferably less than 450 μm. It should be noted that the preferred range of D50 (mass-average particle size) can be set as a range defined by any combination selected from the above upper and lower limits.

[0175] Furthermore, (iii) the particle size distribution of the water-absorbing resin before surface crosslinking is more preferably within the range of (ii) above, with D50 (mass-average particle size) being within the range of (ii) above, and the proportion of particles smaller than 150 μm being within the range of (i) above.

[0176] Furthermore, (iv) the lower limit of σζ (logarithmic standard deviation of particle size distribution) is preferably 0.20 or more, more preferably 0.25 or more, and even more preferably 0.27 or more. On the other hand, its upper limit is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.35 or less. It should be noted that the preferred range of σζ (logarithmic standard deviation of particle size distribution) can be set as a range defined by any combination selected from the above upper and lower limits. The smaller the value of σζ (logarithmic standard deviation of particle size distribution), the more uniform the particle size, which has the advantage of reducing particle segregation. However, excessively reducing the σζ (logarithmic standard deviation of particle size distribution) requires repeated crushing and classification to remove coarse and fine particles, which may be disadvantageous from the point of view of productivity and cost.

[0177] The aforementioned particle size, i.e., (i) to (iv) above, applies not only to the water-absorbing resin before surface crosslinking but also to the water-absorbing resin and water-absorbing agent composition after surface crosslinking. Therefore, it is preferable to perform the surface crosslinking treatment, i.e., the surface crosslinking process, in a way that maintains the particle size within the aforementioned range adjusted in the water-absorbing resin before surface crosslinking, and more preferably, to perform particle size adjustment by setting a granulation process after the surface crosslinking process. Furthermore, it is possible to arbitrarily select and combine the above (i) and (iv), (ii) and (iv), and (iii) and (iv) above, in which case the preferred ranges can be arbitrarily combined.

[0178] [2-6] Surface crosslinking process

[0179] This process involves further setting a high-crosslinking-density portion on the surface layer of the absorbent resin obtained before surface crosslinking, as described in the preceding processes. It includes a mixing process and a heat treatment process. In the surface crosslinking process, free radical crosslinking, surface polymerization, and a crosslinking reaction with a surface crosslinking agent occur on the surface of the absorbent resin before the surface crosslinking process, resulting in a surface-crosslinked absorbent resin. In the manufacturing method of this invention, an aqueous solution of a flowability improver can be added during the surface crosslinking process. Thus, when a flowability improver is added during the surface crosslinking process, the absorbent resin obtained after the surface crosslinking process contains the flowability improver. Therefore, in this case, the "absorbent composition" can be the absorbent resin after the surface crosslinking process.

[0180] [2-6-1] Mixing process

[0181] This process involves mixing a solution containing a surface crosslinking agent (hereinafter referred to as "surface crosslinking agent solution") with a water-absorbing resin before surface crosslinking in a mixing apparatus to obtain a humidified mixture. In cases where an aqueous solution of a flowability improver is added during the surface crosslinking process, it is preferable to add the aforementioned aqueous solution in this process. It should be noted that the preferred conditions in this case are as described later in [2-9].

[0182] (Surface crosslinking agent)

[0183] In this invention, a surface crosslinking agent is preferably used during surface crosslinking. Specifically, examples of such surface crosslinking agents include: polyol compounds, amino alcohol compounds, alkylene carbonate compounds, oxazolidinone compounds, oxetane compounds, and epoxy compounds. It is preferable to use at least one surface crosslinking agent selected from these. Furthermore, organic surface crosslinking agents capable of forming ester bonds with carboxyl groups are preferred. Examples of surface crosslinking agents that form ester bonds (preferably dehydrated ester bonds) with the functional groups of polyacrylic acid (salt)-based water-absorbing resins, such as carboxyl groups, include surface crosslinking agents with intramolecular hydroxyl groups, such as polyol compounds or amino alcohol compounds; alkylene carbonate compounds; oxazolidinone compounds; oxetane compounds; and epoxy compounds that generate hydroxyl groups through ring-opening.

[0184] More specifically, the following can be listed as surface crosslinking agents: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, 1,3-propanediol, 1-methyl-1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerol, polyglycerol, 2-buten-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanemethanol, 1,2-cyclohexanediol, 1,2- Cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylidene-oxypropylene block copolymer, pentaerythritol, mesoerythritol, D-sorbitol, sorbitol and other polyol compounds; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidyl ether and other epoxy compounds; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polyamide polyamine and other polyamine compounds, and their derivatives. Inorganic or organic salts, such as aziridine salts; polyisocyanate compounds such as 2,4-toluene diisocyanate and hexamethylene diisocyanate; halogenated epoxy compounds such as epichlorohydrin, epibromopropane, and α-methylepoxychloropropane; polyoxazoline compounds such as 1,2-ethylidene bisoxazoline; oxazolidinone compounds such as N-acyloxazolidinone and 2-oxazolidinone; 1,3-dioxolane-2-one, 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 ... Alkyl carbonate compounds such as pentane-2-one, 4-hydroxymethyl-1,3-dioxane-2-one, 1,3-dioxane-2-one, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, and 1,3-dioxane-heptane-2-one; cyclic urea compounds; oxetane compounds such as oxetane, 2-methyloxetane, 3-methyl-3-hydroxymethyloxetane, and 3-ethyl-3-hydroxymethyloxetane; amino alcohol compounds such as ethanolamine; and polyvalent metal compounds such as hydroxides or chlorides of zinc, calcium, magnesium, aluminum, iron, and zirconium.

[0185] Among these surface crosslinking agents, at least one is preferably selected from the group consisting of polyol compounds, epoxy compounds, polyamine compounds and their salts, oxetane compounds, and alkylene carbonate compounds. More preferably, the surface crosslinking agent is selected from one or more of the group consisting of polyol compounds with 3 or more and 6 or fewer carbon atoms and containing 2 or more and 3 or fewer hydroxyl groups, epoxy compounds with 6 or more and 12 or fewer carbon atoms, alkylene carbonate compounds with 3 or more and 5 or fewer carbon atoms, and oxetane compounds with 3 or more and 10 or fewer carbon atoms. Furthermore, considering its reactivity and the heating temperature in the heat treatment process, one or more surface crosslinking agents can be used. It should be noted that the surface crosslinking process can be performed more than twice to achieve the desired effect. In this case, subsequent processes can be performed using the same surface crosslinking agent as the first, or different surface crosslinking agents can be used.

[0186] The lower limit of the amount of the surface crosslinking agent used is preferably 0.01 parts by mass or more, relative to 100 parts by mass of the absorbent resin before surface crosslinking. On the other hand, the upper limit is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the absorbent resin before surface crosslinking. It should be noted that the preferred range of the amount of the surface crosslinking agent used can be set as a range defined by any combination selected from the above upper and lower limits. By setting the amount of the surface crosslinking agent within the aforementioned range, an optimal crosslinking structure can be formed on the surface layer of the absorbent resin before surface crosslinking, further facilitating the acquisition of a absorbent resin and absorbent agent composition with high physical properties. It should be noted that the amount used when using multiple surface crosslinking agents is their total amount.

[0187] The aforementioned surface crosslinking agent is preferably added to the aforementioned absorbent resin in a solution state, and more preferably added to the absorbent resin before surface crosslinking in the form of an aqueous solution. Therefore, when a flowability improver is added in the surface crosslinking process, it is preferable to further include the flowability improver in the aqueous solution of the surface crosslinking agent. When the surface crosslinking agent is added in the form of an aqueous solution, the lower limit of the amount of water used relative to 100 parts by weight of the absorbent resin before surface crosslinking is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more. On the other hand, the upper limit of the amount of water used relative to 100 parts by weight of the absorbent resin before surface crosslinking is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and even more preferably 10 parts by weight or less. It should be noted that the preferred range of the amount of water used can be set to a range defined by any combination selected from the above upper and lower limits. By setting the amount of water used to the range described above, the processability of the surface crosslinking agent solution is further improved, and the surface crosslinking agent can be easily and uniformly mixed with the absorbent resin before surface crosslinking.

[0188] Furthermore, the lower limit of the concentration of the surface crosslinking agent in the above-mentioned surface crosslinking agent solution is preferably 0.1% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. On the other hand, the upper limit is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. It should be noted that the preferred range of the concentration of the surface crosslinking agent can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. By setting the concentration of the surface crosslinking agent within the above-mentioned range, an optimal crosslinking structure can be formed on the surface layer of the water-absorbing resin before surface crosslinking with a high specific surface area, thereby improving physical properties such as water absorption performance.

[0189] Alternatively, the hydrophilic organic solvent can be used in combination with the water described above to prepare the surface crosslinking agent solution as needed. In this case, the amount of hydrophilic organic solvent used is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the absorbent resin before surface crosslinking. Specifically, examples of the hydrophilic organic solvent include: lower alcohols such as methanol; ketones such as acetone; ethers such as dioxane; amides such as N,N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; and polyols such as ethylene glycol. However, while these hydrophilic organic solvents function as mixing aids to uniformly disperse the surface crosslinking agent on the surface of the absorbent resin, from a commercial point of view, they lead to increased costs. Therefore, even when used, it is preferable to limit the amount used to the minimum possible.

[0190] (Mixed methods, mixed conditions)

[0191] As a method for mixing the water-absorbing resin prior to surface crosslinking with the surface crosslinking agent solution, the following methods can be listed: A surface crosslinking agent solution is prepared in advance, and the water-absorbing resin prior to surface crosslinking is preferably sprayed or dripped into the solution, more preferably sprayed in a mist, thereby mixing. When a flowability improver is added in the surface crosslinking process, the surface crosslinking agent solution preferably further contains the flowability improver. It should be noted that the preferred conditions in this case are as described in [2-9] below.

[0192] As the mixing apparatus for performing the above-mentioned mixing, a mixing apparatus having the torque required to uniformly and reliably mix the water-absorbing resin and the surface crosslinking agent before surface crosslinking is preferred. The mixing apparatus is preferably a high-speed stirring mixer, more preferably a high-speed stirring continuous mixer. It should be noted that the lower limit of the rotational speed of the high-speed stirring mixer is preferably 100 rpm or more, more preferably 300 rpm or more. On the other hand, its upper limit is preferably 10,000 rpm or less, more preferably 2,000 rpm or less. It should be noted that the preferred range of the rotational speed of the high-speed stirring mixer can be set to a range defined by any combination selected from the above upper and lower limits.

[0193] From the viewpoint of miscibility with the surface crosslinking agent solution and cohesiveness of the humidified mixture, the lower limit of the temperature of the water-absorbing resin supplied to this process before surface crosslinking is preferably 25°C or higher, more preferably 35°C or higher. On the other hand, the upper limit is preferably 80°C or lower, more preferably 70°C or lower, and even more preferably 60°C or lower. Furthermore, the lower limit of the mixing time is preferably 1 second or higher, more preferably 5 seconds or higher. On the other hand, the upper limit is preferably 1 hour or lower, more preferably 10 minutes or lower. It should be noted that the preferred ranges of the temperature of the water-absorbing resin before surface crosslinking and the mixing time can be set as a range defined by any combination selected from the above-mentioned upper and lower limits.

[0194] [2-6-2] Heat treatment process

[0195] This step involves applying heat to the humidified mixture obtained from the above mixing process to induce a cross-linking reaction on the surface of the absorbent resin before surface cross-linking. The heat treatment of the humidified mixture can be performed by heating it in a static state or by using a dynamic force such as stirring in a flowing state. Considering the need for uniform heating of the humidified mixture as a whole, heating under stirring is preferred. Specifically, heat treatment apparatus for performing the above heat treatment includes paddle dryers, multi-finned dryers, and tower dryers.

[0196] The lower limit of the heating temperature in this process is preferably 80°C or higher, more preferably 90°C or higher. On the other hand, the upper limit is preferably 250°C or lower, more preferably 230°C or lower. It should be noted that the preferred range of the heating temperature can be defined as a range determined by any combination of the above upper and lower limits.

[0197] Furthermore, the heating time in this process is preferably 5 minutes or more, more preferably 7 minutes or more. On the other hand, this upper limit is preferably 1.5 hours or less, more preferably 1 hour or less. It should be noted that the preferred range of the above heating time can be set as a range defined by any combination selected from the above upper and lower limits.

[0198] It is preferable to improve the water absorption properties of the obtained water-absorbing agent composition or the surface-crosslinked water-absorbing resin by controlling the above heating temperature and heating time within the above range.

[0199] [2-7] Cooling process

[0200] After the heat treatment (heat treatment step) in the above-mentioned surface crosslinking process, a cooling step can be performed as needed. That is, the cooling step is an optional step set as needed after the heat treatment step in the above-mentioned surface crosslinking process. This step is to forcibly cool the water-absorbing resin after the surface crosslinking has ended the above-mentioned heat treatment step to a specified temperature, so as to quickly end the surface crosslinking reaction.

[0201] The cooling of the surface-crosslinked absorbent resin described above can be performed under static conditions or under flowing conditions using dynamic methods such as stirring. Considering the need for uniform cooling of the entire absorbent resin, cooling under stirring is preferred. From this perspective, cooling devices for performing this cooling include paddle dryers, multi-finned dryers, and tower dryers. It should be noted that these cooling devices can also adopt the same specifications as the heat treatment equipment used in the heat treatment process. This is because by changing the heat medium of the heat treatment equipment to a cold medium, it can be used as a cooling device.

[0202] The cooling temperature in this process can be appropriately set based on the heating temperature in the heat treatment process, the water-absorbing agent composition, or the water-absorbing properties of the surface-crosslinked water-absorbing resin. Specifically, the temperature of the surface-crosslinked water-absorbing resin is preferably below 150°C, more preferably below 100°C, further preferably below 90°C, and particularly preferably below 80°C. On the other hand, the lower limit is preferably above 20°C, more preferably above 30°C.

[0203] In the manufacturing method of the present invention, an aqueous solution of a flowability improver is added to the water-absorbing resin during or after the surface crosslinking process. At this time, the water absorption rate of the water-absorbing resin with a high specific surface area is faster than that of existing products, making it difficult to uniformly coat the aqueous solution of the flowability improver between particles. Furthermore, the water absorption rate of the water-absorbing resin is also affected by temperature; therefore, if the aqueous solution of the flowability improver is added to a water-absorbing resin at an excessively high temperature and mixed, some of the water-absorbing resin may absorb the aqueous solution of the flowability improver. This results in the surface of the water-absorbing resin becoming adhesive, easily generating coarse aggregates, and potentially reducing the uniformity of the mixture. Therefore, especially considering the miscibility of the water-absorbing resin with a high specific surface area and the aqueous solution of the flowability improver, it is preferable to control the temperature of the surface-crosslinked water-absorbing resin within the aforementioned range when adding the aqueous solution of the flowability improver. By controlling the temperature within the above-mentioned range, an aqueous solution of mixed flowability improver can be uniformly added to the water-absorbing resin, which easily reduces the dynamic friction coefficient of particles with a particle size of 300 μm or more but less than 600 μm in the water-absorbing resin.

[0204] The shape of the surface-crosslinked superabsorbent resin can be any of the following: spherical, granular, agglomerated, or irregularly fragmented. Considering the water absorption rate of the superabsorbent resin, an irregularly fragmented shape is preferred. Furthermore, if the superabsorbent resin is broken up after surface crosslinking, the surface crosslinking effect is reduced; therefore, the shape of the superabsorbent resin before and after surface crosslinking is preferably irregularly fragmented. Specifically, considering the irregularly fragmented shape of the superabsorbent resin in the surface crosslinking process, or the effect of adding the aqueous solution of the flowability improver, it is preferable that the shape of the superabsorbent resin is also irregularly fragmented when the aqueous solution of the flowability improver is added in the mixing process. Irregularly fragmented superabsorbent resin can be obtained by pulverizing hydrogels or dry polymers.

[0205] The proportion of water-absorbing resin particles with a particle size of less than 150 μm (hereinafter referred to as "particles less than 150 μm") in the surface-crosslinked water-absorbing resin is preferably less than 3% by mass. Particles less than 150 μm have a significantly increased specific surface area compared to particles larger than 150 μm, thus resulting in faster absorption of aqueous liquids. Therefore, when there are many particles less than 150 μm (e.g., a mass percentage of 3% or more), these particles preferentially absorb the aqueous solution of the flowability improver. Consequently, when the aqueous solution of the flowability improver is added, it may be difficult to uniformly mix into the surface-crosslinked water-absorbing resin, or coarse particles formed by the aggregation of particles less than 150 μm may be generated. Therefore, the proportion of water-absorbing resin particles less than 150 μm in the water-absorbing resin before the addition of the aqueous solution of the flowability improver is preferably less than 3% by mass.

[0206] Particles smaller than 150 μm can be appropriately adjusted using the same particle size adjustment method as described in the grading process above. Furthermore, the preferred method for the surface-crosslinked water-absorbing resin can be found in the descriptions of (i) to (iv) in the section “[2-5] Crushing Process, Grading Process” above. “(i) the proportion of particles smaller than 150 μm,” “(ii) D50 (mass-average particle size),” “(iii) the proportion of D50 (mass-average particle size) and particles smaller than 150 μm,” “(iv) σζ (logarithmic standard deviation of particle size distribution),” and their combinations and preferred ranges are as described above. In particular, if (iv) σζ (logarithmic standard deviation of particle size distribution) is within the desired range described above, the deviation in specific surface area between particles is small, the absorption rate and deviation of the aqueous liquid are also small, and it is easy to mix uniformly when an aqueous solution containing a flowability improver is added, which is therefore preferred.

[0207] [2-8] Additives and their addition processes

[0208] In this invention, additives other than flow improvers (hereinafter also referred to as "additives") can be added to any one or more of the water-absorbing resin before surface crosslinking and after surface crosslinking. In other words, the water-absorbing agent composition may contain additives in addition to the water-absorbing resin and the flow improver.

[0209] [2-8-1] Additives

[0210] The additives used in this invention, other than flowability improvers, include flowability improvers or similar additives, other additives, etc., and one or more of them can be used.

[0211] (Liquid permeability improver or its components)

[0212] As a flowability enhancer used in this invention, an additive that has the function of improving the saline flow induction (hereinafter referred to as "SFC") and gel bed permeability under load or no load (hereinafter referred to as "GBP") of the water-absorbing composition or water-absorbing resin can be used, for example, at least one compound selected from polyvalent metal salts, cationic polymers (excluding the flowability enhancers described in detail below), and inorganic microparticles can be used, and two or more can be used in combination as needed.

[0213] These additives may also be used for other purposes besides improving liquid permeability, such as acting as anti-caking agents under moisture absorption or as adhesives for water-absorbing resins. It should be noted that when added for other purposes, they are referred to as conjugate agents. The amount of the aforementioned liquid permeability improvers or conjugate agents added is appropriately set according to the selected compound. It should be noted that not only when using these additives alone, but also when using two or more in combination, the appropriate range of their respective addition amounts can be appropriately selected within the ranges described below.

[0214] The above-mentioned "SFC" is short for Saline Flow Conductivity, which is the flow permeability of a 0.69% by mass sodium chloride aqueous solution relative to the water-absorbing agent composition or water-absorbing resin under a load of 2.07 kPa.

[0215] Furthermore, the aforementioned "GBP" is an abbreviation for Gel Bed Permeability, which is the permeability of a 0.9% by mass sodium chloride aqueous solution relative to the absorbent composition or absorbent resin under load or free swelling, and is a value determined according to the GBP test method described in International Publication No. 2005 / 016393.

[0216] (Polyvalent metal salts)

[0217] When using a polyvalent metal salt, the polyvalent metal cation of the polyvalent metal salt is preferably divalent or higher, more preferably trivalent or higher, and most preferably tetravalent or lower. Furthermore, aluminum, zirconium, etc., can be listed as usable polyvalent metals. Therefore, aluminum lactate, zirconium lactate, aluminum sulfate, zirconium sulfate, etc., can be listed as polyvalent inorganic salts usable in this process. Among these, from the viewpoint of improving the effect of SFC, aluminum lactate or aluminum sulfate is more preferred, and aluminum sulfate is even more preferred. The amount of the above-mentioned polyvalent metal salt added is preferably 0 moles or more and less than 3.6 × 10⁻⁶ moles per 1 g of absorbent resin. -5 moles, more preferably 0 moles or more and less than 1.4 × 10⁻⁶ moles. -5 The mole, more preferably 0 moles or more and less than 1.0 × 10⁻⁶. -5 Moore.

[0218] (Catonic polymer)

[0219] When using cationic polymers, the substances described in U.S. Patent No. 7,098,284 can be listed as cationic polymers. Among these, ethyleneamine polymers are more preferred from the viewpoint of improving the effects of SFC and GBP. Furthermore, the mass-average molecular weight of the cationic polymer is preferably 5,000 or more and 1,000,000 or less.

[0220] The lower limit of the amount of the cationic polymer added relative to 100 parts by weight of the absorbent resin is preferably 0 parts by weight or more, more preferably more than 0 parts by weight. On the other hand, the upper limit of the amount added relative to 100 parts by weight of the absorbent resin is preferably less than 2.5 parts by weight, more preferably less than 2.0 parts by weight, and even more preferably less than 1.0 parts by weight. It should be noted that the preferred range of the amount of the cationic polymer added can be set as a range defined by any combination selected from the above upper and lower limits.

[0221] (Inorganic particles)

[0222] When using inorganic particulate matter, substances described in U.S. Patent No. 7,638,570 can be cited as examples of inorganic particulate matter. Among these, silicon dioxide is preferred from the viewpoint of improving the effects of SFC and GBP.

[0223] When the primary particle size of the inorganic microparticles is less than 20 nm, the lower limit of the amount of the inorganic microparticles added relative to 100 parts by weight of the water-absorbing resin is preferably 0 parts by weight or more, more preferably more than 0 parts by weight. On the other hand, relative to 100 parts by weight of the water-absorbing resin, the upper limit is preferably less than 1.2 parts by weight, more preferably less than 1.0 parts by weight, and even more preferably less than 0.5 parts by weight. Furthermore, when the primary particle size of the inorganic microparticles is 20 nm or more, the lower limit of the amount of the inorganic microparticles added relative to 100 parts by weight of the water-absorbing resin is preferably 0 parts by weight or more, more preferably more than 0 parts by weight. On the other hand, relative to 100 parts by weight of the water-absorbing resin, the upper limit is preferably less than 2.0 parts by weight, more preferably less than 1.5 parts by weight, and even more preferably less than 1.0 parts by weight. It should be noted that the preferred range of the amount of inorganic microparticles added can be set as a range defined by any combination selected from the above upper and lower limits.

[0224] (Other additives)

[0225] Other additives include, specifically, chelating agents, inorganic reducing agents, aromatic substances, organic reducing agents, hydroxycarboxylic acid compounds, compounds containing phosphorus atoms, oxidizing agents, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, thermoplastic fibers, etc. One or more of these other additives may be used. Among them, chelating agents are preferred, and amino polycarboxylic acids or amino polyphosphoric acids are more preferred. Specifically, examples of chelating agents include those described in Japanese Patent Application Publication No. 11-060975, International Publication No. 2007 / 004529, International Publication No. 2011 / 126079, International Publication No. 2012 / 023433, Japanese Patent Application Publication No. 2009-509722, Japanese Patent Application Publication No. 2005-097519, Japanese Patent Application Publication No. 2011-074401, Japanese Patent Application Publication No. 2013-076073, Japanese Patent Application Publication No. 2013-213083, Japanese Patent Application Publication No. 59-105448, Japanese Patent Application Publication No. 60-158861, Japanese Patent Application Publication No. 11-241030, and Japanese Patent Application Publication No. 2-41155.

[0226] Other additives, especially chelating agents, are preferably added or contained in the range of 0.001% by mass or more and 1% by mass relative to the monomer or water-absorbing resin.

[0227] [2-8-2] Additive addition process

[0228] The additives described above can be added before, during, or in the middle of at least one of the steps selected from the preparation step of the monomer aqueous solution, the polymerization step, the gel pulverization step, the drying step, the pulverization step, the classification step, and the surface crosslinking step. That is, in one embodiment of the manufacturing method of the present invention, in addition to the steps of preparing the monomer aqueous solution, the polymerization step, the gel pulverization step, the drying step, the pulverization step, the classification step, the surface crosslinking step, and the addition step of the fluidity improver aqueous solution, an additive addition step may also be included. Preferably, the additives are added before, after, or in the middle of any step following the polymerization step.

[0229] When the above-mentioned additive is added to the absorbent resin, if the additive is a liquid or a solution of an aqueous medium such as water, it is preferable to spray the liquid or solution onto the absorbent resin in a mist form and apply sufficient torque to ensure that the absorbent resin and the additive are mixed uniformly and reliably. On the other hand, if the above-mentioned additive is in the form of a powder or other solid, it can be dry-mixed with the absorbent resin, or an aqueous liquid such as water can be used as a binder.

[0230] Specifically, the apparatus used in the above-mentioned mixing process can include stirring mixers, cylindrical mixers, double-walled conical mixers, V-type mixers, belt mixers, screw mixers, flow-type rotary mixers, air-flow mixers, double-arm kneaders, internal mixers, pulverizing kneaders, rotary mixers, and screw extruders. When using a stirring mixer, its rotational speed is preferably 5 rpm or more, more preferably 10 rpm or more, preferably 10,000 rpm or less, and more preferably 2,000 rpm or less.

[0231] [2-9] Aqueous solution of flowability improver and its addition process

[0232] This step involves adding a flowability improver in the form of an aqueous solution to a water-absorbing resin with a high specific surface area obtained through the aforementioned steps. This process is performed during or after the surface crosslinking step. Here, "performed after the surface crosslinking step" includes not only adding the aqueous solution after the surface crosslinking step, but also adding the aqueous solution of the flowability improver in any step performed after the surface crosslinking step (e.g., cooling step, rewetting step, micronization step, etc.). According to one embodiment of the invention, by performing this step under specific conditions, particle size segregation due to transport in a water-absorbing agent composition with a high specific surface area can be suppressed, further improving the flowability of the powder. Furthermore, the water-absorbing properties of the resulting water-absorbing agent composition are maintained well. Furthermore, according to another embodiment of the invention, a water-absorbing agent composition with a high specific surface area and a reduced coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm by more than 10% can be obtained.

[0233] One aspect of the present invention is a method for manufacturing a water-absorbing agent composition, wherein the water-absorbing agent composition is mainly composed of a water-absorbing resin, and the manufacturing method includes: a monomer aqueous solution preparation step, a polymerization step, a gel pulverization step, a drying step, a pulverization step, a grading step, and a surface crosslinking step, wherein, in or after the above-mentioned surface crosslinking step, a step is included in which a water-soluble flowability enhancer with a mixed quality average molecular weight of 200 or more and 50,000 or less relative to the mass of the water-absorbing resin is added to the water-absorbing resin, and the water-absorbing agent composition satisfies all of the following (a) to (d): (a) the specific surface area of ​​the water-absorbing resin is 25 m². 2(a) When the above-mentioned water-soluble flowability improver is mixed into the water-absorbing resin, the form of the above-mentioned water-soluble flowability improver is an aqueous solution of 0.01% by mass or more and 20% by mass or less; (b) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the average droplet diameter of the above-mentioned aqueous solution is 10 μm or more and 1 mm or less; (d) When the above-mentioned aqueous solution is added to / mixed into the water-absorbing resin, the mixing power index defined by the following (Formula 1) is 70000 or more.

[0234] [Formula 4]

[0235]

[0236] [2-9-1] Water-absorbing resin

[0237] In one embodiment of the present invention, an aqueous solution of a mixed flowability improver is added to the water-absorbing resin. In this case, the water-absorbing resin can be either a water-absorbing resin before surface crosslinking or a water-absorbing resin after surface crosslinking, but is preferably a water-absorbing resin after surface crosslinking. That is, the water-absorbing resin to which the flowability improver is added can be a water-absorbing resin obtained through the above-described surface crosslinking process (a water-absorbing resin that has undergone surface crosslinking). Furthermore, the lower limit of the specific surface area of ​​this water-absorbing resin is 25 m². 2 / kg or more. If the specific surface area of ​​the water-absorbing resin is less than 25m². 2 If the surface area is less than 1 / kg, a water-absorbing composition with sufficient vortex cannot be obtained. The specific surface area of ​​the water-absorbing resin used to manufacture the water-absorbing composition can be set according to the desired specific surface area of ​​the water-absorbing composition. A higher specific surface area of ​​the water-absorbing resin is preferred, preferably 26m². 2 / kg or more, preferably 27m 2 / kg or more, further preferably 28m 2 / kg or more, with 29m being a more preferred option. 2 / kg or more, and more preferably 30m 2 / kg or more, with 35m being particularly preferred 2 / kg or more, the optimal value is 36m 2 / kg or more. On the other hand, its upper limit is preferably 60m. 2 / kg or less, preferably 55m 2 / kg or less. It should be noted that the preferred range of the specific surface area can be set as a range defined by any combination selected from the above upper and lower limits. Therefore, the specific surface area of ​​the water-absorbing resin can, for example, be 25m². 2 / kg or more and 60m 2 For weights below / kg, 26m can be used. 2 / kg or more and 60m2 For weights below / kg, 27m can be used. 2 / kg or more and 60m 2 For weights below / kg, 28m can be used. 2 / kg or more and 60m 2 For weights below / kg, 29m can be used. 2 / kg or more and 60m 2 For weights below / kg, 30m can be used. 2 / kg or more and 55m 2 For weights below / kg, 35m can be used. 2 / kg or more and 55m 2 For weights below / kg, 36m can be used. 2 / kg or more and 55m 2 / kg or less.

[0238] When a flowability improver is added to an aqueous solution, the physical properties of the water-absorbing resin preferably satisfy the properties disclosed in the above-mentioned "[2-5] pulverizing process, grading process", for example, the above-mentioned (i) to (iv) can be applied. In particular, it is more preferable that the particle size distribution of the water-absorbing resin is that the D50 (weight-average particle size) is within the range of the above-mentioned (ii), and the proportion of particles smaller than 150 μm is within the range of the above-mentioned (i).

[0239] The manufacturing method of the present invention preferably satisfies the following condition in addition to (a) to (d) above: (e) the coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent resin after adding the above-mentioned water-soluble flowability improver is 0.80 or less. The coefficient of kinetic friction can be measured as the coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition, for example, being 0.10 or more and 0.80 or less, preferably 0.30 or more and 0.79 or less, more preferably 0.50 or more and 0.78 or less, further preferably 0.60 or more and 0.77 or less, particularly preferably 0.60 or more and 0.76 or less, and most preferably 0.60 or more and 0.73 or less. Furthermore, the detailed measurement conditions for the coefficient of kinetic friction of the particles with a particle size of 300 μm or more and less than 600 μm are described in the examples.

[0240] [2-9-2] Flowability improver

[0241] In the manufacturing method of this invention, a flowability improver (an aqueous solution) is added to the absorbent resin under specific conditions. In this specification, "flowability improver" refers to a water-soluble component that, by adding the reagent, improves the flowability (reduces the coefficient of kinetic friction) of the absorbent composition (absorbent resin). "Water-soluble" means dissolving at least 0.1g in 100g of water at 25°C. It should be noted that the amount of the flowability improver dissolved in 100g of water at 25°C is preferably at least 1g, more preferably at least 5g. Furthermore, the flowability improver is another expression for "water-soluble polymer" in the basic application of this application, and has the same meaning. In addition, in this specification, "water-soluble polymer" in the basic application of this application is referred to as "water-soluble flowability improver" or simply "flowability improver".

[0242] The lower limit of the mass-average molecular weight of the flowability improver is 200 or more, preferably 220 or more, more preferably 250 or more, and even more preferably 300 or more. If the mass-average molecular weight of the flowability improver is less than 200, it cannot impart sufficient sliding properties to the absorbent resin, making it difficult to achieve the effect of improving the flowability of the absorbent composition during delivery. Furthermore, the upper limit of the mass-average molecular weight of the flowability improver is 50,000 or less, preferably 40,000 or less, more preferably 30,000 or less, even more preferably 20,000 or less, particularly preferably 10,000 or less, and most preferably 5,000 or less. If the mass-average molecular weight of the flowability improver exceeds 50,000, the viscosity of the flowability improver itself becomes high, making it difficult to add it uniformly to the absorbent resin. It should be noted that the preferred range of the mass-average molecular weight of the flowability improver can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the mass-average molecular weight of the flowability improver can be, for example, 200 or more and 50,000 or less, 220 or more and 40,000 or less, 220 or more and 30,000 or less, 250 or more and 20,000 or less, 300 or more and 10,000 or less, or 300 or more and 5,000 or less.

[0243] Furthermore, by using a flowability enhancer with a mass-average molecular weight within the aforementioned range, the coefficient of kinetic friction of particles with a diameter of 300 μm or more but less than 600 μm can be significantly reduced. It should be noted that the mass-average molecular weight of the flowability enhancer is determined, for example, by gel permeation chromatography (GPC) using polyethylene glycol as a standard. It should also be noted that in this specification, when referring to the molecular weight of a flowability enhancer with a defined structure (e.g., a flowability enhancer with a lower molecular weight), it is also collectively referred to as "mass-average molecular weight." The molecular weight of such a flowability enhancer may not be determined by GPC as described above, but rather calculated from its chemical formula.

[0244] According to a preferred embodiment of the present invention, the water-soluble flowability improver can be one or more selected from nonionic substances, zwitterionic substances, anionic substances, and cationic substances. In one embodiment, the nonionic substance is selected from (a) polyols, (b) modified polyols with hydroxyl groups, (c) side-chain and / or terminal polyether modified polysiloxanes, and (d) epoxy alkyl adducts of higher aliphatic amines; the zwitterionic substance is selected from (e) alkyl betaine and (f) alkyl amine oxides; the anionic substance is selected from (g) alkyl sulfate salts, (h) sulfate salts of higher alcohol epoxy alkyl adducts, (i) sulfonates, (j) dicarboxylate salts, (k) alkylamine diacetates, (l) phosphate salts of higher alcohol epoxy alkyl adducts, and (m) carboxylates of higher alcohol epoxy alkyl adducts; and the cationic substance is selected from (n) ammonium salts. With this configuration, the desired effects of the present invention can be achieved efficiently.

[0245] (a) Polyols

[0246] According to a preferred embodiment of the present invention, "polyols" refer to compounds having multiple hydroxyl groups. Specifically, examples include polyalkylene glycols such as polyethylene glycol and polypropylene glycol, as well as block copolymers or random copolymers of polyethylene glycol and polypropylene glycol. Here, the number of carbon atoms in the alkylene units of the repeating units in the polyalkylene glycol is preferably C1 to C6, more preferably C2 to C4, and particularly preferably C2 to C3. (In this specification, a number is sometimes added after "C" to indicate the number of carbon atoms. For example, if the number of carbon atoms is 1, it is sometimes expressed as C1; if the number of carbon atoms is 10, it is sometimes expressed as C10). With this configuration, the coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm can be significantly reduced.

[0247] It should be noted that polyalkylene glycols, such as block copolymers or random copolymers of polyethylene glycol and polypropylene glycol, are readily available from the market. For example, the following products are preferably shown as examples.

[0248] Made by ADEKA Co., Ltd.

[0249] • Pluronic (registered trademark, hereinafter the same) series

[0250] Pluronic L-34, Pluronic L-44, Pluronic L-64, Pluronic P-84, Pluronic P-85, Pluronic P-103, Pluronic F-68, Pluronic F-88, Pluronic F-108, Pluronic 17R-3, Pluronic 17R-4, Pluronic TR-704, Pluronic TR-913R.

[0251] Made by NOF Co., Ltd.

[0252] Pronon (registered trademark, same below) #104, Pronon#204, Pronon#208, Unireave 70DP-600B, Unireave 70DP-950B.

[0253] Daiichi Kogyo Pharmaceutical Co., Ltd.

[0254] Epan (registered trademark, same below) 450, Epan 485, Epan 680, Epan 740, Epan 750, Epan 785, Epan U-103, Epan U-105, Epan U-108.

[0255] (b) Modified polyols containing hydroxyl groups

[0256] According to a preferred embodiment of the present invention, "modified polyol hydroxyl groups" refers to compounds in which one or more hydroxyl groups of a polyol have been modified by ester and / or ether. It should be noted that the modification by ester and / or ether is preferably carried out through a hydrocarbon group. The hydrocarbon group preferably has C1 to C30 carbon atoms, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms is less than C30, the hydrophobicity will not become excessive, and the surface tension can be well maintained.

[0257] Furthermore, the aforementioned hydrocarbon groups are not limited to straight chains; they can also be branched or cyclic saturated hydrocarbon groups and / or unsaturated hydrocarbon groups, phenyl groups, alkylphenyl groups, and other aromatic hydrocarbon groups. Moreover, the aforementioned hydrocarbon groups can possess reactive functional groups such as hydroxyl, amino, and glycidyl groups.

[0258] According to a preferred embodiment of the present invention, as modifiers of the hydroxyl groups of the polyols described in (b) above, examples include (b-1) glycidyl-modified polyols, (b-2) alkylene oxide adducts of higher alcohols, or (b-3) alkylene oxide adducts of polyol fatty acid esters. (b-1) may be a compound in which at least one end of a (poly)alkylene glycol is modified with a glycidyl group. (b-2) may be a compound in which a single end of a (poly)alkylene glycol is modified with a substituent having a hydrocarbon group of C1 to C30. (b-3) may be a compound in which an alkylene oxide is added to at least one hydroxyl group of a polyol, and at least one hydroxyl group of a polyol is modified with a substituent having a hydrocarbon group of C1 to C30 via an ester bond. It should be noted that the polyol in (b-3) may be glycerol, pentaerythritol, sorbitol, sorbitan anhydride, or sugars. This configuration can significantly reduce the coefficient of kinetic friction for particles with a diameter of 300 μm or larger but less than 600 μm.

[0259] (b-1) Glycidyl-modified polyols

[0260] Glycidyl-modified polyols are compounds formed by modifying at least one of the ends of (poly)alkylene glycols with a glycidyl group. Specifically, examples include: water-soluble (poly)alkylene glycol diglycidyl ethers such as diethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether; polypropylene glycol diglycidyl ether; hexanediol diglycidyl ether; glycerol polyglycidyl ether; trimethylolpropane polyglycidyl ether; pentaerythritol polyglycidyl ether; diglycerol polyglycidyl ether; polyglycerol polyglycidyl ether; sorbitol polyglycidyl ether; and other water-soluble polyglycidyl ethers of polyols.

[0261] Glycidyl modified polyols are readily available from the market, and the following products are preferred examples.

[0262] ·Made by Nagase ChemteX Co., Ltd.

[0263] Denacol (registered trademark, the same below) EX-145, Denacol EX-171, Denacol EX-211, Denacol EX-212, Denacol EX-252, Denacol EX-810, Denacol EX-811, Denacol EX-850, Denacol EX-851, Denacol EX-821, Denacol EX-830, Denacol EX-832, Denacol EX-841, Denacol EX-861, Denacol EX-911, Denacol EX-941, Denacol EX-920, Denacol EX-931, Denacol EX-313, Denacol EX-314, Denacol EX-321, Denac EX-521, Denacol EX-612, Denacol EX-614, Denacol EX-614B.

[0264] (b-2) Epoxide adducts of higher alcohols

[0265] The alkylene oxide adduct of a higher alcohol can be a compound formed by modifying the single end of a (poly)alkylene glycol with a substituent having a hydrocarbon group having a C1 to C30 (preferably C6 to C30) group. In one embodiment, the alkylene oxide adduct of a higher alcohol is preferably a compound represented by the following general formula (Chemical Formula 1).

[0266] [Chemical Formula 1]

[0267]

[0268] In the above formula (Chemical Formula 1), R is a hydrocarbon group with 1 to 30 carbon atoms (preferably C6 to C30). The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained. Furthermore, the hydrocarbon group is preferably a straight-chain or branched saturated hydrocarbon group.

[0269] In the above formula, (AO) can also be derived from C. n H 2n The repeating unit is represented by O (n is a natural number). The number of carbon atoms constituting AO (n above) is preferably C1 to C6, more preferably C1 to C3, further preferably C2 to C3, and particularly preferably C2. That is, the repeating unit (AO) in the above general formula (chemical formula 1) is particularly preferably [CH2CH2O], and the repeating unit can be a structure derived from the addition of ethylene oxide or the condensation of ethylene glycol.

[0270] In the above formula, 'a' represents the number of repeating units (AO). When 'a' is 2 or more, the number of carbon atoms constituting each repeating unit can be the same or different. That is, the alkylene oxide adduct of the higher alcohol shown in the above general formula (Chemical Formula 1) can be a polymer having the same repeating units (AO), or it can be a block polymer or a random polymer with different repeating units (AO).

[0271] In the above formula, a is preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. If the repeating unit is 1000 or less, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0272] Epoxide adducts of higher alcohols are readily available from the market, and the following products are preferably exemplified below.

[0273] Made by Kao Co., Ltd.

[0274] Polyoxyethylene lauryl ether

[0275] Emulgen (registered trademark, same below) 106 (HLB=10.5), Emulgen 108 (HLB=12.1), Emulgen 109P (HLB=13.6), Emulgen 120 (HLB=15.3), Emulgen 123P (HLB=16.9), Emulgen 130K (HLB=18.1), Emulgen 147 (HLB=16.3), Emulgen 150 (HLB=18.4).

[0276] Polyoxyalkylene polyoxypropylene alkyl ether

[0277] Emulgen MS-110 (HLB=12.7).

[0278] Polyoxyethylene cetyl ether

[0279] Emulgen 210P (HLB=10.7), Emulgen 220 (HLB=14.2).

[0280] Polyoxyethylene stearyl ether

[0281] Emulgen 320P (HLB=13.9), Emulgen 350 (HLB=17.8).

[0282] · Polyoxyethylene oil-based ether

[0283] Emulgen 408 (HLB=10.0), Emulgen 409PV (HLB=12.0), Emulgen 420 (HLB=13.6), Emulgen 430 (HLB=16.2).

[0284] Polyoxyethylene myristyl ether

[0285] Emulgen 4085 (HLB=18.9).

[0286] Polyoxyethylene octyl dodecyl ether

[0287] Emulgen 2020G-HA (HLB=13.0), Emulgen 2025G (HLB=15.7).

[0288] Made by NOF Co., Ltd.

[0289] Polyoxyethylene isodecanyl ether

[0290] Nonion ID-203 (HLB=12.5), Nonion ID-209 (HLB=14.3).

[0291] Polyoxyethylene-2-ethylhexyl ether

[0292] Nonion EH-204 (HLB=11.5), Nonion EH-208 (HLB=14.6).

[0293] Made by Japan Emulsifier Co., Ltd.

[0294] Polyoxyethylene nonylphenyl ether

[0295] Newcol (registered trademark, same below) 560 (HLB=10.9), Newcol 564 (HLB=12.3), Newcol 565 (HLB=13.3), Newcol 566 (HLB=14.1), Newcol 568 (HLB=15.2), Newcol 504 (HLB=16.0), Newcol 506 (HLB=17.2), Newcol 509 (HLB=18.0), Newcol 516 (HLB=18.8).

[0296] (b-3) Epoxyalkane adducts of polyol fatty acid esters

[0297] The ethylene oxide adduct of a polyol fatty acid ester can be a compound formed by adding an ethylene oxide to at least one of the hydroxyl groups of the polyol, and by modifying at least one of the hydroxyl groups of the polyol with a substituent having a hydrocarbon group having a C1 to C30 via an ester bond. Examples of such polyols include glycerol, pentaerythritol, sorbitol, sorbitan anhydride, and sugars.

[0298] Preferably, alkyl oxide adducts of glycerol fatty acid monoesters and alkyl oxide adducts of sorbitan fatty acid monoesters are included. In one embodiment, the alkyl oxide adduct of glycerol fatty acid monoesters is preferably a compound represented by the following general formula (Chemical Formula 2). Furthermore, the alkyl oxide adduct of sorbitan fatty acid monoesters includes structural isomers. Therefore, in one embodiment, the alkyl oxide adduct of sorbitan fatty acid monoesters can be a compound represented by the following general formula (Chemical Formula 3) or (Chemical Formula 4).

[0299] [Chemical Formula 2]

[0300]

[0301] In the above formula (Chemical Formula 2), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the above-mentioned hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the above-mentioned hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0302] In the above formula, (A1O) and (A2O) can also be derived from C. n H 2n The repeating unit is represented by O (n is a natural number). The number of carbon atoms constituting A1O and A2O (n above) is preferably C1 to C6, more preferably C1 to C3, further preferably C2 to C3, and particularly preferably C2. That is, the repeating unit (A1O or A2O) in the above general formula (chemical formula 2) is particularly preferably [CH2CH2O], and the repeating unit can be a structure derived from the addition of ethylene oxide or the condensation of ethylene glycol.

[0303] In the above formula, a and b represent the number of repeating units (A1O and A2O), respectively. When a or b is 2 or more, the number of carbon atoms constituting each repeating unit can be the same or different. Furthermore, in A1O and A2O, the number of carbon atoms constituting A1 and the number of carbon atoms constituting A2 can be the same or different. That is, the epoxide portion contained in the above general formula (Chemical Formula 2) can be a polymer having the same repeating units (A1O or A2O), or it can be a block polymer or a random polymer with different repeating units (A1O or A2O).

[0304] In the above formula, the sum of a and b (a+b) is preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. a and b can be different or the same. If the sum of a+b is less than 1000, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0305] [Chemical Formula 3]

[0306]

[0307] [Chemical Formula 4]

[0308]

[0309] In the above formulas (Chemical Formulas 3 and 4), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained. In addition, the hydrocarbon group is preferably a straight-chain or branched saturated hydrocarbon group.

[0310] In the above formula, (A1O), (A2O), and (A3O) can also be derived from C. n H 2nThe repeating unit is represented by O (n is a natural number). The number of carbon atoms (n) constituting A1O, A2O, and A3O respectively is preferably C1 to C6, more preferably C1 to C3, further preferably C2 to C3, and particularly preferably C2. That is, the repeating unit (A1O, A2O, or A3O) in the above general formula (Chemical Formula 3) and (Chemical Formula 4) is particularly preferably [CH2CH2O], and the repeating unit can be a structure derived from the addition of ethylene oxide or the condensation of ethylene glycol.

[0311] In the above formulas, a to c represent the number of repeating units (A1O, A2O, and A3O), respectively. When a, b, or c is 2 or more, the number of carbon atoms constituting each repeating unit can be the same or different. Furthermore, in A1O, A2O, and A3O, the number of carbon atoms constituting A1, A2, and A3 can be the same or different. That is, the epoxide portion contained in the above general formulas (Chemical Formula 3) and (Chemical Formula 4) can be a polymer having the same repeating units (A1O, A2O, or A3O), or it can be a block polymer or a random polymer with different repeating units (A1O, A2O, or A3O).

[0312] In the above formula, the total of a to c (a+b+c) is preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. a, b, and c can be different or the same. If the total of a+b+c is less than 1000, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0313] Epoxyalkyl adducts of polyol fatty acid esters are readily available from the market, for example, the following products are preferably shown as examples.

[0314] Made by Kao Co., Ltd.

[0315] Polyoxyethylene sorbitan monolaurate

[0316] Rheodol (registered trademark, same below) TW-L120 (HLB=16.7), Rheodol TW-L106 (HLB=13.3), Rheodol Super TW-L120.

[0317] Polyoxyethylene sorbitan monopalmitate

[0318] Rheodol TW-P120 (HLB=15.6).

[0319] Polyoxyethylene sorbitan monostearate

[0320] Rheodol TW-S120V (HLB=14.9).

[0321] Polyoxyethylene sorbitan tristearate

[0322] Rheodol TW-S320V (HLB=10.5).

[0323] Polyoxyethylene sorbitan monooleate

[0324] Rheodol TW-O120V (HLB=15.0), Rheodol TW-O106V (HLB=10.0).

[0325] Polyoxyethylene sorbitan trioleate

[0326] Rheodol TW-O320V (HLB=11.0).

[0327] Made by NOF Co., Ltd.

[0328] Polyoxyethylene coconut oil fatty acid glycerides

[0329] Unigly (registered trademark, same below) MK-207 (HLB=13.0), Unigly MK-230 (HLB=17.4).

[0330] (c) Side-chain and / or terminal polyether modified polysiloxane

[0331] According to a preferred embodiment of the present invention, "side-chain and / or terminal polyether-modified polysiloxane" refers to a compound in which the side chains and / or terminals of a polysiloxane are modified with polyether. The polyether modification site of the polysiloxane is not particularly limited and can be any of the following: the side chain of the polysiloxane, both ends of the polysiloxane, a single end of the polysiloxane, or both the side chain and both ends of the polysiloxane. The polyether modifying group includes polyoxyethylene, polyoxypropylene, or a polyether modifying group having both polyoxyethylene and polyoxypropylene. With this configuration, the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm can be significantly reduced.

[0332] Polyether-modified polysiloxanes are readily available from the market, and the following products are preferred examples.

[0333] Shin-Etsu Chemical Industry Co., Ltd.

[0334] KF-351A (HLB=12), KF-353 (HLB=10), KF-354L (HLB=16), KF-355A (HLB=12), KF-615A (HLB=10), KF-640 (HLB=14), KF-642 (HLB=12), KF-643 (HLB=14), KF-6011 (HLB=12).

[0335] Made by Dow Corning Toray Co., Ltd.

[0336] FZ-77 (HLB=11), L-7604 (HLB=11).

[0337] (d) Epoxide adducts of higher aliphatic amines

[0338] According to a preferred embodiment of the present invention, "epoxide adduct of higher aliphatic amines" refers to a compound formed by adding an epoxide to two hydrogen atoms on the nitrogen atom of a primary amine having a C1 to C30 hydrocarbon group. With this configuration, the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm can be significantly reduced.

[0339] In one embodiment, the alkyl oxide adduct of the higher aliphatic amine is preferably a compound represented by the following general formula (Chemical Formula 5).

[0340] [Chemical Formula 5]

[0341]

[0342] In the above formula (Chemical Formula 5), ​​R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained.

[0343] In the above formula, (A1O) and (A2O) can also be derived from C. n H 2nThe repeating unit is represented by O (n is a natural number). The number of carbon atoms constituting A1O and A2O (n above) is preferably C1 to C6, more preferably C1 to C3, further preferably C2 to C3, and particularly preferably C2. That is, the repeating unit (A1O or A2O) in the above general formula (Chemical Formula 5) is particularly preferably [CH2CH2O], and the repeating unit can be a structure derived from the addition of ethylene oxide or the condensation of ethylene glycol.

[0344] In the above formula, a and b represent the number of repeating units (A1O and A2O), respectively. When a or b is 2 or more, the number of carbon atoms constituting each repeating unit can be the same or different. Furthermore, in A1O and A2O, the number of carbon atoms constituting A1 and the number of carbon atoms constituting A2 can be the same or different. That is, the epoxide portion contained in the above general formula (Chemical Formula 5) can be a polymer having the same repeating units (A1O or A2O), or it can be a block polymer or a random polymer with different repeating units (A1O or A2O).

[0345] In the above formula, the sum of a and b (a+b) is preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. a and b can be different or the same. If the sum of a+b is less than 1000, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0346] Epoxide adducts of higher aliphatic amines are readily available from the market, and the following products are preferably exemplified below.

[0347] Made by NOF Co., Ltd.

[0348] Polyoxyethylene laurylamine

[0349] Nymeen (registered trademark, same below) L-207 (HLB=12.5).

[0350] · Polyoxyethylene alkyl coconut oil alkylamine

[0351] Nymeen F-215 (HLB=15.4).

[0352] · Polyoxyethylene stearylamine

[0353] Nymeen S-210 (HLB=12.5), Nymeen S-215 (HLB=14.5), Nymeen S-220 (HLB=15.4).

[0354] · Polyoxyethylene tallow alkylamine

[0355] Nymeen T2-210 (HLB=12.5), Nymeen T2-230 (HLB=16.7).

[0356] Polyoxyethylene alkylpropanediamine

[0357] Nymeen DT-208 (HLB=10.7).

[0358] Made by Kao Co., Ltd.

[0359] Amiet (registered trademark, hereinafter the same) 105A (HLB=10.8), Amiet 320 (HLB=15.4).

[0360] (e) Alkyl betaine

[0361] According to a preferred embodiment of the present invention, "alkyl betaine" refers to a compound having a cationic group and an anionic group at non-adjacent positions within the same molecule, wherein the cationic group is a secondary ammonium cation, a tertiary ammonium cation, or a quaternary ammonium cation, and at least one substituent on the secondary ammonium cation, tertiary ammonium cation, or quaternary ammonium cation is a substituent having a hydrocarbon group having a C1 to C30 structure. This configuration can significantly reduce the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm. In one embodiment, the alkyl betaine is preferably a compound represented by the following general formula (Chemical Formula 6).

[0362] [Chemical Formula 6]

[0363]

[0364] In the above formula (Chemical Formula 6), R1 is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained.

[0365] In the above formula, R2 and R3 are each independently hydrogen or a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the above-mentioned hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the above-mentioned hydrocarbon group is preferably C1 to C30, more preferably C1 to C25, and even more preferably C1 to C20. If the above-mentioned hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become too strong, and the surface tension of the water-absorbing agent composition can be well maintained. R1, R2, and R3 can be different or the same.

[0366] In the above formula, X has no special restrictions on its structure except that it contains more than 1 carbon atoms (C1).

[0367] In the above formula, the anion part (Z) can be a carboxylate (carboxylate anion), a sulfonate (sulfonic acid anion), or a phosphate (phosphate anion).

[0368] In one embodiment, the alkyl betaine, in addition to the compound shown in the above general formula (Chemical Formula 6), may also be a compound shown in the following general formula (Chemical Formula 7) (a compound having a cationic group on an imidazolium ring). For example, as a commercially available product, Amphitol (registered trademark, hereinafter the same) 20YB (manufactured by Kao Corporation) is an example.

[0369] [Chemical Formula 7]

[0370]

[0371] In the above formula (Chemical Formula 7), R1 is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is less than 30, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0372] In the above formula, R2 is hydrogen or a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C1 to C25, and even more preferably C1 to C20. If the hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained. R1 and R2 can be different or the same.

[0373] In the above formula, X has no special restrictions on its structure except that it contains more than 1 carbon atoms (C1).

[0374] In the above formula, the anion part (Z) can be a carboxylate (carboxylate anion), a sulfonate (sulfonic acid anion), or a phosphate (phosphate anion).

[0375] (f) Alkylamine oxide

[0376] According to a preferred embodiment of the present invention, "alkyl amine oxide" refers to a compound having a cationic group and an anionic group at adjacent positions within the same molecule, wherein the cationic group is a secondary ammonium cation, a tertiary ammonium cation, or a quaternary ammonium cation, and at least one substituent on the secondary ammonium cation, tertiary ammonium cation, or quaternary ammonium cation is a substituent having a hydrocarbon group having a C1 to C30 structure. With this configuration, the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm can be significantly reduced. In one embodiment, the alkyl amine oxide is preferably a compound represented by the following general formula (Chemical Formula 8).

[0377] [Chemical Formula 8]

[0378]

[0379] In the above formula (Chemical Formula 8), R1 is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0380] In the above formula, R2 and R3 are each independently hydrogen or a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the above-mentioned hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the above-mentioned hydrocarbon group is preferably C1 to C30, more preferably C1 to C25, and even more preferably C1 to C20. If the above-mentioned hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become too strong, and the surface tension of the water-absorbing agent composition can be well maintained. R1, R2, and R3 can be different or the same.

[0381] In one embodiment, the alkylamine oxide used as a flowability improver is preferably a compound in which R1 is a straight-chain saturated hydrocarbon group (alkyl) of C4 to C24, and R2 and R3 are each independently a straight-chain saturated hydrocarbon group (alkyl) of C1 to C25. Furthermore, in one embodiment, the alkylamine oxide used as a flowability improver is preferably a compound in which R1 is a straight-chain saturated hydrocarbon group (alkyl) of C6 to C22, and R2 and R3 are each independently a straight-chain saturated hydrocarbon group (alkyl) of C1 to C20.

[0382] Alkyl betaine and alkyl amine oxides are readily available from the market, and the following products are preferred examples.

[0383] Made by Kao Co., Ltd.:

[0384] Amphitol 20BS, Amphitol 24B (desalted version of 20BS), Amphitol 86B, Amphitol 20N, Amphitol 20YB, Amphitol 20AB, Amphitol 55AB, Amphitol 20HD.

[0385] Made by Daiichi Kogyo Pharmaceutical Co., Ltd.

[0386] Amogen (registered trademark, same below) SH, Amogen K, Amogen LB-C, Amogen CB-H, AmogenHB-C, Amogen AOL.

[0387] Made by ADEKA Co., Ltd.:

[0388] Adeka Amphote (registered trademark, hereinafter the same) PB-30L, Adeka Amphote AB-35L.

[0389] Made by NOF Co., Ltd.:

[0390] Nissan Anon (registered trademark, same below) BF, Nissan Anon BL, Nissan Anon B BL-SF, Nissan Anon BDF-R, Nissan Anon BDF-SF, Nissan Anon BDC-SF, Nissan Anon BDL-SF, Nissan Anon GLM-R, Unisafe (registered trademark, same below) A-LM, Unisafe A-SM, Unisafe A-LE.

[0391] Japanese emulsifier manufacturer:

[0392] Texnol (registered trademark, hereinafter the same) R2.

[0393] Made by Toho Chemical Industry Co., Ltd.

[0394] Obazolin (registered trademark, hereinafter the same) LB-SF.

[0395] Made by New Nippon Rika Co., Ltd.:

[0396] Wandamine (registered trademark, hereinafter the same) OX-300.

[0397] (g) Alkyl sulfate salt

[0398] According to a preferred embodiment of the present invention, "alkyl sulfate salt" refers to a compound having a sulfate group (-SO4-) within the same molecule. This configuration significantly reduces the coefficient of kinetic friction for particles with a diameter of 300 μm or more but less than 600 μm. In one embodiment, the alkyl sulfate salt is preferably a compound represented by the following general formula (Chemical Formula 9).

[0399] [Chemical Formula 9]

[0400]

[0401] In the above formula (Chemical Formula 9), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0402] In the above formula, M + It can be an alkali metal ion (Li + Na + K + (etc.), ammonium ions.

[0403] Alkyl sulfate salts are readily available from the market, and the following products are preferred examples.

[0404] Made by Kao Co., Ltd.:

[0405] Emal (registered trademark, same below) 2F, Latemul (registered trademark, same below) AD-25.

[0406] Made by Takemoto Oil Co., Ltd.:

[0407] Takesurf (registered trademark, hereinafter the same) A-24.

[0408] Made by NOF Co., Ltd.:

[0409] Sintrex (registered trademark, same below) EH-R, Persoft (registered trademark, same below) SK.

[0410] Made by Lion Specialty Chemicals Co., Ltd.:

[0411] Sunnol (registered trademark, hereinafter the same) LM-1130.

[0412] (h) Sulfate salts of higher alcohol epoxide adducts

[0413] According to a preferred embodiment of the present invention, "sulfate salt of higher alcohol alkylene oxide adduct" refers to a compound in which one end of a (poly)alkylene glycol is modified with a substituent having a C1-C30 hydrocarbon group, and the other end is a sulfate salt. This configuration significantly reduces the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm. In one embodiment, the sulfate salt of higher alcohol alkylene oxide adduct is preferably a compound represented by the following general formula (Chemical Formula 10).

[0414] [Chemical Formula 10]

[0415]

[0416] In the above formula (Chemical Formula 10), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained.

[0417] In the above formula, (AO) can also be derived from C. n H 2n The repeating unit is represented by O (n is a natural number). The number of carbon atoms constituting AO (n above) is preferably C1 to C6, more preferably C1 to C3, further preferably C2 to C3, and particularly preferably C2. That is, the repeating unit (AO) in the above general formula (chemical formula 10) is particularly preferably [CH2CH2O], and the repeating unit can be a structure derived from the addition of ethylene oxide or the condensation of ethylene glycol.

[0418] In the above formula, 'a' represents the number of repeating units (AO). When 'a' is 2 or more, the number of carbon atoms constituting each repeating unit can be the same or different. That is, the alkylene oxide portion contained in the above general formula (Chemical Formula 10) can be a polymer having the same repeating units (AO), or it can be a block polymer or a random polymer with different repeating units (AO).

[0419] In the above formula, a is preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. If the repeating unit is 1000 or less, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0420] In the above formula, M+ It can be an alkali metal ion (Li + Na + K + ), ammonium ions.

[0421] Sulfate salts of higher alcohol epoxide adducts are readily available from the market, and the following products are preferably exemplified below.

[0422] Made by Kao Co., Ltd.

[0423] Sodium polyoxyethylene lauryl ether sulfate

[0424] Emal 20C, Emal E-27C, Emal 270J, Emal 20CM.

[0425] Made by Japan Emulsifier Co., Ltd.

[0426] · Polyoxyethylene alkyl ether sulfate salt

[0427] Newcol 1020-SN, Newcol 2308-SF, Newcol 2320-SN, Newcol 2360-SN, Newcol1305-SN, Newcol 1330-SF, Newcol 1703-SFD, Newcol 1525-SFC.

[0428] Made by NOF Co., Ltd.

[0429] Sodium polyoxyethylene alkyl ether sulfate

[0430] Persoft EP, NISSAN TRAX (registered trademark, same below) K-40, NISSAN TRAX K-300, Persoft EF, Persoft EDO, Persoft EL, Persoft EK.

[0431] (i) sulfonates

[0432] According to a preferred embodiment of the present invention, "sulfonate" refers to a compound having a sulfonic acid group (-SO3-) within the same molecule. This configuration significantly reduces the coefficient of kinetic friction for particles with a diameter of 300 μm or more but less than 600 μm. In one embodiment, the sulfonate is preferably a compound represented by the following general formula (Chemical Formula 11).

[0433] [Chemical Formula 11]

[0434]

[0435] In the above formula (Chemical Formula 11), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0436] In the above formula, M + It can be an alkali metal ion (Li + Na + K + ), ammonium ions.

[0437] Sulfonates are readily available from the market; for example, the following products are preferred examples.

[0438] Made by Kao Co., Ltd.

[0439] Alkylbenzenesulfonic acid

[0440] Neopelex (registered trademark, hereinafter the same) GS.

[0441] Sodium dodecylbenzenesulfonate

[0442] Neopelex G-15, Neopelex G-25, Neopelex G-65.

[0443] Sodium alkylnaphthalenesulfonate

[0444] Pelex (registered trademark, hereinafter the same) NB-L.

[0445] Sodium dialkyl sulfosuccinate

[0446] Pelex OT-P, Pelex TR.

[0447] · Disodium alkyl sulfosuccinate

[0448] Pelex TA.

[0449] Sodium alkyl diphenyl ether disulfonate

[0450] Pelex SS-L, Pelex SS-H.

[0451] Sodium alkyl sulfonate

[0452] ·Latemul PS.

[0453] Made by Takemoto Oil Co., Ltd.

[0454] Sodium alkyl diphenyl ether disulfonate

[0455] Pionin A-43-D, Takesurf A-43-NQ.

[0456] (j) dicarboxylate

[0457] According to a preferred embodiment of the present invention, a "dicarboxylate" refers to a compound having two carboxyl groups (-CH3COO-) within the same molecule. It should be noted that the term "dicarboxylate" as used herein refers to compounds other than amine compounds, excluding "(k)alkylamine diacetate" described below. This configuration significantly reduces the coefficient of kinetic friction for particles with a particle size of 300 μm or more but less than 600 μm. Examples of such dicarboxylates include alkenyl succinates and acyl aspartate salts. In one embodiment, the alkenyl succinate is preferably a compound represented by the following general formula (Chemical Formula 12). Furthermore, in one embodiment, the acyl aspartate salt is preferably a compound represented by the following general formula (Chemical Formula 13).

[0458] [Chemical Formula 12]

[0459]

[0460] [Chemical Formula 13]

[0461]

[0462] In the above formulas (Chemical Formula 12) and (Chemical Formula 13), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained.

[0463] In the above formula, M + It can be an alkali metal ion (Li + Na + K +Ammonium ions. In addition, in a molecule, it can be in the form of a salt formed by two carboxylic acid groups (the form with two carboxylic acid salt parts) or in the form of a salt formed by only one carboxylic acid group (the form with one carboxylic acid salt part).

[0464] Dicarboxylate salts are readily available from the market; for example, the following products are preferred examples.

[0465] Made by Kao Co., Ltd.:

[0466] Dipotassium alkenylsuccinate

[0467] Latemul ASK.

[0468] Made by ASAHI KASEI FINECHEM Co., Ltd.:

[0469] Sodium cocoyl glutamate

[0470] Aminosurfact (registered trademark, hereinafter the same) ACDS-L.

[0471] Sodium lauroyl aspartate

[0472] AminoFoamer (registered trademark, hereinafter the same) FLDS-L.

[0473] (k) Alkylamine diacetate

[0474] According to a preferred embodiment of the present invention, "alkylamine diacetate" refers to an amine compound having a hydrocarbon group and two carboxyl groups (-CH3COO-). This configuration significantly reduces the coefficient of kinetic friction for particles with a diameter of 300 μm or more but less than 600 μm. In one embodiment, the alkylamine diacetate is preferably a compound represented by the following general formula (Chemical Formula 14).

[0475] [Chemical Formula 14]

[0476]

[0477] In the above formula (Chemical Formula 14), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained.

[0478] In the above formula, M + It can be an alkali metal ion (Li + Na + K + ), ammonium ions.

[0479] Alkylamine diacetates are readily available from the market, and the following products are preferred examples.

[0480] Made by NOF Co., Ltd.:

[0481] Sodium laurylaminodiacetate

[0482] Nissan Anon LA.

[0483] (l) Phosphate salts of higher alcohol epoxide adducts

[0484] According to a preferred embodiment of the present invention, a "phosphate salt of a higher alcohol alkylene oxide adduct" refers to a compound in which one end of a (poly)alkylene glycol is modified by a substituent of a hydrocarbon group having C1 to C30 carbon atoms, and the other end is a phosphate salt. This configuration significantly reduces the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm. In one embodiment, the phosphate salt of the higher alcohol alkylene oxide adduct is preferably a compound represented by the following general formula (Chemical Formula 15).

[0485] [Chemical Formula 15]

[0486]

[0487] In the above formula (Chemical Formula 15), R1 and R2 are each independently a hydrocarbon group with C1 to C30 carbon atoms. The hydrocarbon group with C1 to C30 carbon atoms can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the above-mentioned hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the above-mentioned hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the above-mentioned hydrocarbon group is 30 or less, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0488] In the above formula, 'a' represents the number of repeating units (CH2CH2O), preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. If the number of repeating units is 1000 or less, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0489] In the above formula, M + It can be an alkali metal ion (Li + Na + K + ), ammonium ions.

[0490] Phosphate salts of higher alcohol epoxide adducts are readily available from the market, for example, the following products are preferably shown as examples.

[0491] Made by Daiichi Kogyo Pharmaceutical Co., Ltd.

[0492] Ply Surf (registered trademark, hereinafter the same) A212C, Ply Surf A207H, Ply Surf A208S.

[0493] Made by Takemoto Oil Co., Ltd.:

[0494] Takesurf A-72TK65, Takesurf A-7004.

[0495] (m) Carboxylates of higher alcohol epoxide adducts

[0496] According to a preferred embodiment of the present invention, a "carboxylate of a higher alcohol alkyl oxide adduct" refers to a compound in which one end of a (poly)alkylene glycol is modified with a substituent having a C1-C30 hydrocarbon group, and the other end is a carboxylate. This configuration significantly reduces the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm. In one embodiment, the carboxylate of the higher alcohol alkyl oxide adduct is preferably a compound represented by the following general formula (Chemical Formula 16).

[0497] [Chemical Formula 16]

[0498]

[0499] In the above formula (Chemical Formula 16), R is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become excessive, and the surface tension of the absorbent composition can be well maintained. In addition, the hydrocarbon group is preferably a straight-chain or branched saturated hydrocarbon group.

[0500] In the above formula, (AO) can also be derived from C. n H 2n The repeating unit is represented by O (n is a natural number). The number of carbon atoms constituting AO (n above) is preferably C1 to C6, more preferably C1 to C3, further preferably C2 to C3, and particularly preferably C2. That is, the repeating unit (AO) in the above general formula (chemical formula 16) is particularly preferably [CH2CH2O], and the repeating unit can be a structure derived from the addition of ethylene oxide or the condensation of ethylene glycol.

[0501] In the above formula, 'a' represents the number of repeating units (AO). When 'a' is 2 or more, the number of carbon atoms constituting each repeating unit can be the same or different. That is, the alkylene oxide portion contained in the above general formula (Chemical Formula 16) can be a polymer having the same repeating units (AO), or it can be a block polymer or a random polymer with different repeating units (AO).

[0502] In the above formula, a is preferably 1 to 1000, more preferably 2 to 500, and even more preferably 2 to 300. If the repeating unit is 1000 or less, the viscosity will not become too high, and it can be easily and uniformly added to the water-absorbing resin.

[0503] In the above formula, M + It can be an alkali metal ion (Li + Na + K + ), ammonium ions.

[0504] In one embodiment, the carboxylate of the higher alcohol epoxide adduct, which serves as a flowability improver, is preferably a compound in which R is a straight-chain saturated hydrocarbon group (alkyl) of C4 to C24, the number of carbon atoms constituting AO is 2 to 3 (C2 to C3), a is 2 to 500, and M... + It is an alkali metal ion. Furthermore, in one embodiment, the carboxylate salt of the higher alcohol epoxide adduct, used as a flowability improver, is preferably a compound with the following structure: In the above general formula (Chemical Formula 16), R is a C6-C22 straight-chain saturated hydrocarbon group (alkyl), AO is -CH2CH2O-, a is 2-300, and M... + It is an alkali metal ion.

[0505] Carboxylates of higher alcohol epoxide adducts are readily available from the market, and the following products are preferably exemplified below.

[0506] Made by Kao Co., Ltd.

[0507] Sodium polyoxyethylene lauryl ether acetate

[0508] Kao Akypo RLM-100NV, Kao Akypo RLM-100, Kao Akypo RLM-45 NV, Kao Akypo RLM-45.

[0509] (n) ammonium salt

[0510] According to a preferred embodiment of the present invention, "ammonium salt" refers to a compound in which at least one hydrogen atom of an ammonium salt is modified by a substituent having a C1 to C30 hydrocarbon group. This configuration significantly reduces the coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm. In one embodiment, the ammonium salt is preferably a compound represented by the following general formula (Chemical Formula 17).

[0511] [Chemical Formula 17]

[0512]

[0513] In the above formula (Chemical Formula 17), R1 is a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the hydrocarbon group is preferably C1 to C30, more preferably C2 to C28, further preferably C3 to C26, particularly preferably C4 to C24, and most preferably C6 to C22. If the number of carbon atoms in the hydrocarbon group is less than 30, the hydrophobicity will not become excessive, and the surface tension of the water-absorbing agent composition can be well maintained.

[0514] In the above formula, R2, R3, and R4 are each independently hydrogen or a hydrocarbon group with 1 to 30 carbon atoms. The hydrocarbon group can be a straight-chain, branched, or cyclic saturated hydrocarbon group and / or an unsaturated hydrocarbon group, an aromatic hydrocarbon group (alkylphenyl, alkylbenzyl, etc.), or a polycyclic aromatic hydrocarbon group (naphthyl, etc.). Furthermore, the above-mentioned hydrocarbon group can have reactive functional groups such as hydroxyl, amino, and glycidyl groups, and can also have ether bonds, ester bonds, carbamate bonds, or amide bonds. The number of carbon atoms in the above-mentioned hydrocarbon group is preferably C1 to C30, more preferably C1 to C25, and even more preferably C1 to C20. If the above-mentioned hydrocarbon group has 30 or fewer carbon atoms, the hydrophobicity will not become too strong, and the surface tension of the water-absorbing agent composition can be well maintained. R1, R2, R3, and R4 can be different or the same.

[0515] In the above formula, N - Counterions to ammonium cations include, for example: halide ions, carboxylate ions (e.g., acetate ions), sulfonate ions, hydroxyl ions, and BF ions. 4- PF 6- ,ClO 4- AsF 6- 、SbF 6- wait.

[0516] Ammonium salts are readily available from the market; for example, the following products are preferred examples.

[0517] Made by Kao Co., Ltd.

[0518] Coconutamine acetate

[0519] Acetamin (registered trademark, hereinafter the same) 24.

[0520] ·Stearylamine acetate

[0521] Acetamin 86.

[0522] ·Lauryltrimethylammonium chloride

[0523] Quartamin (registered trademark, hereinafter the same) 24P.

[0524] ·Stearyltrimethylammonium chloride

[0525] Quartamin 86W.

[0526] Cetyltrimethylammonium chloride

[0527] Quartamin 60W.

[0528] Distearate dimethyl ammonium chloride

[0529] Quartamin D86P.

[0530] ·alkylbenzyldimethylammonium chloride

[0531] Sanisol (registered trademark, hereinafter the same) C, Sanisol B-50.

[0532] Made by NOF Co., Ltd.

[0533] Tetradecylamine acetate

[0534] Nissan Cation (registered trademark, hereinafter the same) MA.

[0535] Dodecyltrimethylammonium chloride

[0536] Nissan Cation BB.

[0537] ·cocoyltrimethylammonium chloride

[0538] Nissan Cation FB.

[0539] • Hexadecyltrimethylammonium chloride

[0540] Nissan Cation PB-300.

[0541] • Tallow alkyl trimethylammonium chloride

[0542] Nissan Cation ABT2-500.

[0543] ·Octadecyltrimethylammonium chloride

[0544] Nissan Cation AB, Nissan Cation AB-600.

[0545] behenyltrimethylammonium chloride

[0546] Nissan Cation VB-M Flakes, Nissan Cation VB-F.

[0547] Didecyldimethylammonium chloride

[0548] Nissan Cation 2-DB-500E.

[0549] Dioleodimethylammonium chloride

[0550] Nissan Cation 2-OLR.

[0551] ·Cocoyl dimethyl benzyl ammonium chloride

[0552] Nissan Cation F2-50R.

[0553] Tetradecyl dimethyl benzyl ammonium chloride

[0554] Nissan Cation M2-100R.

[0555] The HLB content of the aforementioned nonionic substance is preferably 11 or more, more preferably 12 or more. By ensuring that the HLB content of the nonionic substance is within the above range, it can be added in the form of an aqueous solution and can be uniformly added to the water-absorbing resin with a high specific surface area.

[0556] Here, HLB is a value calculated using the Griffin method. It should be noted that the HLB of a nonionic substance whose HLB is unknown can be determined using the following method: Emulsify an oil with the nonionic substance whose HLB is to be determined (adding a surfactant with a known HLB value if necessary), and then emulsify the same oil again with a surfactant with a known HLB value (using surfactants with the same HLB value). The HLB value obtained when the emulsions are in the same state is taken as the HLB of the nonionic substance.

[0557] In the manufacturing method of the present invention, the flowability improver added to the water-absorbing resin is preferably selected from nonionic substances, zwitterionic substances, anionic substances, and cationic substances, and more preferably from nonionic substances. That is, according to a preferred embodiment of the present invention, the water-soluble flowability improver comprises at least one selected from nonionic substances. Furthermore, the water-soluble flowability improver more preferably comprises at least one selected from nonionic substances having a polyalkylene glycol chain in the molecule. In addition, according to other preferred embodiments, the flowability improver comprises at least one selected from (a) polyols and (b) modifiers of the hydroxyl groups of polyols.

[0558] Furthermore, according to other preferred embodiments, the flowability improver comprises at least one selected from nonionic substances, zwitterionic substances, anionic substances, and cationic substances, wherein the nonionic substance is (a) a polyol or (b) a modified polyol hydroxyl group, the zwitterionic substance is (f) an alkylamine oxide, the anionic substance is (m) a carboxylate of a higher alcohol epoxide adduct, and the cationic substance is (n) an ammonium salt.

[0559] The amount of the aforementioned flowability improver added relative to the mass of the absorbent resin is greater than 0 ppm and less than 200 ppm. By setting the amount of the flowability improver within the above range, the decrease in the surface tension of the absorbent composition can be suppressed, thereby suppressing the decrease in the fixed height absorbance (FHA) of the absorbent composition at a height of 20 cm. Thus, by suppressing the decrease in FHA, the absorbency when pressure is applied to the absorbent is well maintained. It should be noted that the preferred range of FHA, etc., will be described later.

[0560] Furthermore, flowability improvers also contain substances that enhance the flowability of absorbent resin during transport using feeders, etc., i.e., improve the flowability of absorbent resin in dynamic environments, while on the other hand, they hinder the flow of absorbent resin from a stationary state. Even when using such flowability improvers, by setting the amount of flowability improver added within the aforementioned range, the effect of hindering the flow from a stationary state can be suppressed, i.e., the decrease in the flow rate of the absorbent composition can be suppressed, and the flowability in dynamic environments can be appropriately improved.

[0561] The lower limit of the amount of the aforementioned flowability improver added relative to the mass of the water-absorbing resin is preferably 1 ppm or more, more preferably 2 ppm or more, and even more preferably 3 ppm or more. Furthermore, the upper limit of the amount of the aforementioned flowability improver added relative to the mass of the water-absorbing resin is preferably 180 ppm or less, more preferably 160 ppm or less, even more preferably 150 ppm or less, and particularly preferably 80 ppm or less. It should be noted that the preferred range of the amount of the aforementioned flowability improver added can be set as a range defined by any combination selected from the aforementioned upper and lower limits. Therefore, in the manufacturing method of the present invention, the amount of the flowability improver added can, for example, be 1 ppm or more and 180 ppm or less, 2 ppm or more and 160 ppm or less, 3 ppm or more and 160 ppm or less, 3 ppm or more and 150 ppm or less, or 3 ppm or more and 80 ppm or less.

[0562] It should be noted that in the manufacturing method of the present invention, additives may be added in the process from the preparation of the monomer aqueous solution to the surface crosslinking process within the manufacturing process of the water-absorbing resin. The additives here may be components used as flowability improvers (also referred to as "water-soluble components" in this specification, the same component as the flowability improver). In this case, the water-soluble component added before the surface crosslinking process is not included in the amount of flowability improver added as described above. That is, the amount of flowability improver added as described above refers to the total amount of flowability improver added in or after the surface crosslinking process. This is because the contribution of the flowability improver added in or after the surface crosslinking process to the flowability of the water-absorbing composition (its behavior on the surface of the water-absorbing resin) is different from that of the water-soluble component added before the surface crosslinking process.

[0563] As the aforementioned flowability improver, any flowability improver having the aforementioned weight-average molecular weight can be added in the aforementioned amount; within this range, multiple flowability improvers can be used. Furthermore, when using one or more flowability improvers, multiple flowability improvers having the aforementioned weight-average molecular weight can be used in combination. It should be noted that the amount added when using multiple flowability improvers refers to their total amount.

[0564] [2-9-3] Adding and mixing processes

[0565] In the method for manufacturing the water-absorbing agent composition of the present invention, the flowability improver having the above-mentioned mass-average molecular weight is added to the water-absorbing resin at the above-mentioned addition amount in the surface crosslinking step or in a step after the surface crosslinking step. It should be noted that the addition of the flowability improver may be performed only in the surface crosslinking step, only in a step after the surface crosslinking step, or both in the surface crosslinking step and in a step after the surface crosslinking step. In one embodiment, the flowability improver addition step is preferably performed at least in a step after the surface crosslinking step (the flowability improver is added after the surface crosslinking step), and more preferably in a cooling step (the flowability improver is added in a cooling step after the surface crosslinking step). This is because if the flowability improver is added in a step after the surface crosslinking step, there is no concern that the flowability improver may be modified due to heating at high temperatures.

[0566] The aforementioned flowability improver is added in the form of an aqueous solution when added to or mixed with the absorbent resin. Therefore, in one embodiment, it is preferable to prepare an aqueous solution of the flowability improver in advance, and then add the aqueous solution to the absorbent resin. In this case, the concentration of the aqueous solution is 0.01% by mass or more and 20% by mass or less, preferably 0.02% by mass or more and 15% by mass or less, more preferably 0.05% by mass or more and 10% by mass or less, and particularly preferably 0.1% by mass or more and 3% by mass or less. By setting the concentration of the aqueous solution within the above range, the operability of the aqueous solution containing the flowability improver can be improved, and the flowability improver can be uniformly mixed into the absorbent resin.

[0567] The lower limit of the pH of the aqueous solution of the aforementioned flowability improver is preferably 4.5 or higher, more preferably 4.6 or higher, even more preferably 5.0 or higher, and particularly preferably 5.5 or higher. When the flowability improver contained in the aqueous solution of the aforementioned flowability improver is an ester compound containing a polyalkylene glycol chain, it may sometimes undergo hydrolysis due to long-term storage, exposure to high temperatures, etc. If such hydrolysis occurs, the pH of the aqueous solution of the flowability improver decreases due to the byproduct carboxylic acid. Furthermore, the hydrophobicity of the hydrolyzed flowability improver increases, thus becoming a cause of problems such as dissolution residues or precipitation leading to clogging of the spray nozzle. By controlling the lower limit of the pH of the aqueous solution of the flowability improver within the aforementioned range, the occurrence of the above-mentioned problems can be prevented, and therefore this is preferable. Furthermore, from the viewpoint of suppressing the deterioration of devices in contact with the aqueous solution and the safety of operators, the upper limit of the pH of the aqueous solution of the aforementioned flowability improver is preferably 11.0 or lower, more preferably 10.5 or lower, even more preferably 10.0 or lower, and particularly preferably 9.5 or lower. It should be noted that the preferred pH range described above can be set as a range defined by any combination of the upper and lower limits mentioned above. Therefore, the pH of the aqueous solution of the flowability improver can be, for example, 4.5 or higher and 11.0 or lower, 4.6 or higher and 10.5 or lower, 5.0 or higher and 10.0 or lower, or 5.5 or higher and 9.5 or lower.

[0568] The lower limit of the amount of the above-mentioned flowability improver aqueous solution added relative to 100 parts by weight of the water-absorbing resin is preferably 0.001 parts by weight or more, more preferably 0.002 parts by weight or more, and even more preferably 0.003 parts by weight or more. On the other hand, the upper limit is preferably 10 parts by weight or less, more preferably 9 parts by weight or less, and even more preferably 8 parts by weight or less. It should be noted that the preferred range of the amount of the above-mentioned flowability improver added can be set as a range defined by any combination of the above-mentioned upper and lower limits. By setting the amount of the above-mentioned flowability improver added to 10 parts by weight or less relative to 100 parts by weight of the water-absorbing resin, the moisture content adjustment of the water-absorbing agent composition after addition does not require a large amount of drying energy, which is advantageous in terms of production cost. In addition, the strong agglomeration of the water-absorbing resin caused by the large amount of flowability improver added can be suppressed, so there is no need for an additional process of crushing the agglomerates. Therefore, the destruction of the surface cross-linking layer caused by the additional crushing process (the already formed surface cross-linking layer is destroyed) can be suppressed, and as a result, the decrease in the absorption ratio under pressure can be suppressed.

[0569] The aqueous solution of the aforementioned flowability improver is added to the absorbent resin in droplet form and mixed. At this time, if the average droplet diameter exceeds 1 mm, the number of droplets per unit amount of the flowability improver solution decreases, thus reducing the probability of contact with the absorbent resin and preventing uniform mixing, which in turn fails to uniformly improve particle flowability. As a result, the reduction effect on the coefficient of kinetic friction of particles with a diameter of 300 μm or more but less than 600 μm is diminished. Furthermore, if the aqueous solution of the flowability improver with an average droplet diameter exceeding 1 mm is stirred and mixed with the absorbent resin having a particularly large specific surface area, coarse particles are easily agglomerated. Therefore, the upper limit of the average droplet diameter is 1 mm or less, preferably 0.9 mm (900 μm) or less, more preferably 0.8 mm (800 μm) or less, and even more preferably 0.5 mm (500 μm) or less. On the other hand, although the smaller the droplet diameter of the aqueous solution of the added flowability improver, the easier it is for the aqueous solution of the flowability improver and the water-absorbing resin to mix uniformly, the cost of making the droplets fine is too high relative to the effect obtained. Therefore, the lower limit of the above-mentioned average droplet diameter (diameter) is 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. It should be noted that the preferred range of the above-mentioned average droplet diameter can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the above-mentioned average droplet diameter can be, for example, 10 μm or more and 0.9 mm or less, 20 μm or more and 0.8 mm or less, 30 μm or more and 0.5 mm or less, or 40 μm or more and 0.5 mm or less. As a unit for adding the aqueous solution of the flowability improver in droplet form, examples include spray units such as spray nozzles with a desired nozzle diameter and straight pipes with a desired inner diameter. In addition, the average droplet diameter can be determined by photographing the addition process using a high-speed camera or similar means. It is a value determined based on the inner diameter of the droplet addition port in the spray unit and the spray pressure.

[0570] The temperature of the aqueous solution of the flowability improver, specifically the temperature of the droplets, when the aqueous solution of the flowability improver is added to the absorbent resin, is preferably 20°C or higher at the lower end and 80°C or lower at the upper end, more preferably 70°C or lower, and even more preferably 60°C or lower. It should be noted that the preferred range of the temperature (droplet temperature) of the aqueous solution of the flowability improver can be set to a range defined by any combination selected from the above upper and lower limits. Therefore, the temperature of the aqueous solution of the flowability improver is preferably 20°C or higher and 80°C or lower, more preferably 20°C or higher and 70°C or lower, and even more preferably 20°C or higher and 60°C or lower. The aqueous solution of the flowability improver adjusted to the above temperature is effective in improving the miscibility with absorbent resins with particularly high specific surface areas. If the temperature of the aqueous solution of the flowability improver is too high, the water in the aqueous solution of the flowability improver will evaporate, and the flowability improver will easily precipitate, making it difficult to mix uniformly. On the other hand, if the above temperature is too low, the solubility of the flowability improver in water will decrease, and the concentration of the aqueous solution of the flowability improver that can be produced will be low. Therefore, when adding the desired flowability improver, the amount of water added increases, which may result in the formation of a large amount of coarse particles (product clumps) in the product, which is undesirable. It should be noted that the temperature range of the aqueous solution mentioned above was determined before being affected by the temperature of the absorbent resin and the apparatus. The apparatus referred to here is one that retains the absorbent resin.

[0571] The temperature of the aqueous solution of the aforementioned flowability improver and the average droplet diameter of the aqueous solution can be controlled individually. However, the inventors investigated their relationship and found that combining them within the aforementioned preferred range is effective in improving the mixability with absorbent resins with particularly high specific surface areas. Specifically, by setting both the temperature of the aqueous solution and the average droplet diameter within the aforementioned preferred range, a significant effect can be achieved in suppressing segregation when the absorbent composition containing the flowability improver is fed into the absorbent resin via a feeder. In particular, the higher the temperature of the aqueous solution of the flowability improver added to the absorbent resin with a large specific surface area, the faster the water absorption rate. Therefore, reducing the average droplet diameter is effective as a method for more uniform mixing. Furthermore, if the temperature of the aqueous solution of the flowability improver is excessively increased, or the droplet diameter is excessively decreased, the aqueous solution of the flowability improver may volatilize and easily precipitate. Therefore, it is preferable to control them separately within the aforementioned ranges.

[0572] The apparatus (mixing device) for mixing the aqueous solution of the aforementioned flowability improver preferably has a large mixing force. Specifically, examples of such mixing devices include: cylindrical mixers, double-walled conical mixers, V-shaped mixers, belt mixers, screw mixers, rotary mixers, double-arm kneaders, internal mixers, pulverizing kneaders, rotary mixers, screw extruders, fluidized bed mixers, and airflow mixers. Furthermore, apparatus capable of mixing by stirring is more preferred; examples include high-speed stirring mixing devices and vertical rotary disc mixing devices, more preferably high-speed stirring continuous mixing devices, and even more preferably horizontal high-speed stirring continuous mixing devices or vertical high-speed stirring continuous mixing devices. Specifically, examples include: Schugi mixer (manufactured by Hosokawa Micron), turbulence enhancer (manufactured by Hosokawa Micron), Lodige mixer (manufactured by Lodige), and flow jet mixer (manufactured by Funken Powers).

[0573] Furthermore, the water absorption rate of highly surface-area absorbent resins is faster than that of existing products, making it difficult to uniformly mix trace amounts of flowability enhancers (less than 200 ppm) between particles. Therefore, the inventors conducted multiple experiments by arbitrarily varying the circumferential speed, mixing time, and average droplet diameter. The results showed that by controlling the mixing force index defined by the following formula (Equation 1) instead of individually controlling the circumferential speed, mixing time, and average droplet diameter, uniform mixing between particles of the highly surface-area absorbent resin can be achieved even when adding trace amounts of flowability enhancers (less than 200 ppm). In other words, when an aqueous solution of the aforementioned flowability enhancer is added / mixed into the absorbent resin, by setting the suitable mixing force index in the following formula (Equation 1) to a specific value or higher, the flowability of the absorbent composition can be uniformly improved, suppressing particle size segregation after transport.

[0574] [Hybrid Power Index]

[0575] In the manufacturing method of the present invention, the mixing power index when the aqueous solution of the flowability improver is added to / mixed into the water-absorbing resin is calculated according to the following (Formula 1). It should be noted that the mixing power index is a value calculated each time the flowability improver is added / mixed. For example, when the flowability improver is added / mixed in both the surface crosslinking process and the process following the surface crosslinking process, the mixing power index refers to the mixing power index in each process. In the manufacturing method of the present invention, it is preferable that either the mixing power index in the surface crosslinking process or the mixing power index in the process following the surface crosslinking process is 70,000 or more, and at least the mixing power index in the process following the surface crosslinking process is 70,000 or more.

[0576] [Formula 5]

[0577]

[0578] It should be noted that in the above (Equation 1), the circumferential speed (unit: m / s) refers to the circumferential speed of the stirring blade. Specifically, the circumferential speed (m / s) = π × stirring blade diameter (m) × rotational speed (rpm) / 60.

[0579] From the viewpoint of uniformly mixing the flowability improver among the particles of the highly surface-area absorbent resin, the lower limit of the mixing power index is 70,000 or more, preferably 80,000 or more, more preferably 90,000 or more, further preferably 100,000 or more, particularly preferably 500,000 or more, and most preferably 1,000,000 or more. On the other hand, highly surface-area absorbent resins have more surface irregularities compared to existing products, resulting in lower damage resistance. During mixing in the apparatus, surface defects easily lead to the generation of fine particles. Therefore, from the viewpoint of suppressing the generation of these particles, the upper limit of the mixing power index is preferably 6,000,000 or less, more preferably 5,000,000 or less, further preferably 4,000,000 or less, and particularly preferably 3,000,000 or less. It should be noted that the preferred range of the mixing power index can be defined as a range determined by any combination of the above-mentioned upper and lower limits. Therefore, the aforementioned mixing power index can be, for example, above 70,000 and below 6,000,000, above 80,000 and below 5,000,000, above 90,000 and below 4,000,000, above 100,000 and below 3,000,000, above 500,000 and below 3,000,000, or above 1,000,000 and below 3,000,000.

[0580] From the viewpoint of efficient mixing, the lower limit of the diameter of the stirring blades in the above-mentioned mixing device is preferably 0.01 m or more, more preferably 0.02 m or more, and even more preferably 0.03 m or more. Furthermore, from the viewpoint of the size and cost of the mixing device, the upper limit of the diameter of the stirring blades in the mixing device is preferably 10 m or less, more preferably 5 m or less, and even more preferably 3 m or less. It should be noted that the preferred range of the diameter of the stirring blades in the above-mentioned mixing device can be defined as a range determined by any combination of the above-mentioned upper and lower limits. Therefore, the diameter of the stirring blades in the mixing device is preferably 0.01 m or more and 10 m or less, more preferably 0.02 m or more and 5 m or less, and even more preferably 0.03 m or more and 3 m or less.

[0581] The lower limit of the rotational speed of the stirring mixer is preferably 5 rpm or more, more preferably 10 rpm or more, further preferably 15 rpm or more, particularly preferably 100 rpm or more, and most preferably 200 rpm or more. Furthermore, the upper limit of the rotational speed is preferably 10,000 rpm or less, more preferably 2,000 rpm or less, further preferably 1,000 rpm or less, and particularly preferably 500 rpm or less. It should be noted that the preferred range of the above-mentioned rotational speed can be defined by any combination selected from the above upper and lower limits. Therefore, the above-mentioned rotational speed can be, for example, 5 rpm or more and 10,000 rpm or less, 10 rpm or more and 2,000 rpm or less, 15 rpm or more and 1,000 rpm or less, 100 rpm or more and 500 rpm or less, or 200 rpm or more and 500 rpm or less.

[0582] The aforementioned circumferential speed (the circumferential speed of the stirring blades of the mixing device) can be a constant value or can vary midway. "Variation of circumferential speed" refers to a mixing device where the circumferential speed varies within a single device, or where two or more different circumferential speeds are used. Based on the preferred ranges of the stirring blade diameter and the rotational speed, the lower limit of the circumferential speed of the stirring blades of the mixing device is preferably 0.002 m / s or more, more preferably 0.01 m / s or more, further preferably 0.02 m / s or more, particularly preferably 0.5 m / s or more, and most preferably 1.0 m / s or more. On the other hand, the upper limit is preferably 6000 m / s or less, more preferably 600 m / s or less, further preferably 200 m / s or less, particularly preferably 100 m / s or less, and most preferably 50 m / s or less. It should be noted that the preferred range of the circumferential speed of the stirring blades of the mixing device can be set as a range defined by any combination selected from the aforementioned upper and lower limits. Therefore, the circumferential speed of the aforementioned stirring blades can be, for example, 0.002 m / s or more and 6000 m / s or less, 0.01 m / s or more and 600 m / s or less, 0.02 m / s or more and 200 m / s or less, 0.5 m / s or more and 100 m / s or less, or 1.0 m / s or more and 50 m / s or less.

[0583] Flowability improvers with a mass-average molecular weight within the aforementioned range are less likely to be incorporated into the particles of the absorbent resin compared to low molecular weight water-soluble substances. That is, by adding the flowability improver to the absorbent resin and mixing thoroughly, the flowability improver adhering to the surface of one absorbent resin particle can come into contact with the surfaces of other absorbent resin particles. As a result, the uniformity of mixing of the flowability improver within the overall absorbent resin is improved. Therefore, the "mixing time" in this specification refers to the total time for stirring and mixing the absorbent resin within one hour, starting from the point when the flowability improver comes into contact with the absorbent resin. The lower limit of the mixing time is preferably 10 seconds or more, more preferably 15 seconds or more, and even more preferably 20 seconds or more. Furthermore, the upper limit of the mixing time is preferably 60 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less. It should be noted that the preferred range of the above mixing time can be defined as a range determined by any combination of the above upper and lower limits. Therefore, the above mixing time can be, for example, more than 10 seconds and less than 60 minutes, more than 15 seconds and less than 30 minutes, or more than 20 seconds and less than 20 minutes.

[0584] For example, the mixing power index is calculated using the formula "mixing power index (unit: none) = C1 (m / s) × D1 (s) / {E1 (mm) / 1000}" when an aqueous solution of a flowability improver is added with an average droplet diameter of E1 (mm), the mixture is stirred at a circumferential speed of C1 (m / s) and a mixing time of D1 (s), and D1 is within 1 hour after the flowability improver comes into contact with the water-absorbing resin.

[0585] For example, in an aqueous solution with an average droplet diameter of E2 (mm), a flowability improver is added, and the mixture is stirred at a circumferential speed of C2 (m / s) and a mixing time of D2 (s), where D2 is the mixing power index after 1 hour and 10 minutes from the time the flowability improver comes into contact with the absorbent resin. The mixing time is considered to be up to 1 hour (3600 seconds), and it is calculated using the formula: "Mixability index (unit: none) = C2 (m / s) × 3600 (s) / {E2 (mm) / 1000}".

[0586] For example, the mixing power index is calculated by adding a flowability improver to an aqueous solution with an average droplet diameter of E3 (mm), stirring at a circumferential speed of C3 (m / s) and a mixing time of D3 (s), stirring at a circumferential speed of C4 (m / s) and a mixing time of D4 (s), where D3 and D4 are within 1 hour after the flowability improver comes into contact with the water-absorbing resin. The mixing power index (unit: none) is calculated by adding the flowability improver to an aqueous solution with an average droplet diameter of E3 (mm) and a mixing time of D3 (s) and D4 (m / s) and a mixing time of D4 ( ... and D4 (s) (s)).

[0587] For example, the mixing power index of an aqueous solution containing a flowability enhancer with an average droplet diameter of E4 (mm), after stirring and mixing at a circumferential speed of C5 (m / s) and a mixing time of D5 (s), then stirring and mixing at a circumferential speed of C6 (m / s) and a mixing time of D6 (s), and further stirring and mixing at a circumferential speed of C7 (m / s) and a mixing time of D7 (s), where D5 and D6 are within 1 hour after the flowability enhancer comes into contact with the water-absorbing resin, and D7 is after 1 hour after the flowability enhancer comes into contact with the water-absorbing resin, is calculated using the formula: "Mixability power index (unit: none) = {C5 (m / s) × D5 (s) + C6 (m / s) × D6 (s)} / {(E4 (mm) / 1000}".

[0588] It should be noted that as long as the stirring and mixing are within 1 hour after the flowability improver comes into contact with the water-absorbing resin, they can be continuous or divided into multiple stages, but it is preferable to stir immediately after the flowability improver comes into contact with the water-absorbing resin.

[0589] When the above-mentioned flowability improver is added to an aqueous solution, the aqueous solution of the flowability improver may further contain at least one of the group consisting of chelating agents, plant components, antibacterial agents, inorganic salts, and other additives, as described later. The content of the additives in this case is appropriately selected as needed, but ideally is set to be 0.001% by mass or more and 50% by mass or less of the aqueous solution of the flowability improver. As the chelating agent mentioned above, a chelating agent with high ion blocking and chelating ability for Fe and Cu is preferred. Specifically, chelating agents with a stability constant of 10 or more for Fe ions are listed, preferably 20 or more, further preferably amino polycarboxylic acids and their salts, and particularly preferably amino carboxylic acids and their salts having three or more carboxyl groups. Specifically, these polycarboxylic acids can be listed as follows: diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl ether diaminetetraacetic acid, ethylenediaminetetrapropionic acid, N-alkyl-N'-carboxymethyl aspartic acid, N-alkenyl-N'-carboxymethyl aspartic acid, and their alkali metal salts, alkaline earth metal salts, ammonium salts, or amine salts. The salts can be completely neutralized, partially neutralized, or mixtures. Diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, N-hydroxyethylethylenediaminetriacetic acid, and their salts are most preferred. Furthermore, the lower limit of the amount of the above-mentioned chelating agent used relative to 100 parts by weight of the water-absorbing resin is preferably 0.00001 parts by weight or more, more preferably 0.0001 parts by weight or more. On the other hand, the upper limit is preferably 10 parts by weight or less, more preferably 1 part by weight or less. It should be noted that the preferred range for the amount of the chelating agent used can be set as a range defined by any combination of the above upper and lower limits.

[0590] To achieve deodorizing properties, the lower limit of the amount of the aforementioned plant component used relative to 100 parts by weight of the absorbent resin is preferably 0 parts by weight or more, more preferably 0.001 parts by weight or more, and even more preferably 0.002 parts by weight or more. On the other hand, the upper limit is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, and even more preferably within the range of 3 parts by weight or less. It should be noted that the preferred range of the amount of the aforementioned plant component can be set as a range defined by any combination of the above-mentioned upper and lower limits. The plant component is preferably at least one compound selected from polyphenols, flavonoids and their derivatives, and caffeine, and even more preferably at least one compound selected from tannins, tannic acid, gallnuts, gallic acid, and gallic acid. In addition, the aforementioned antibacterial agent is a known antibacterial agent with antibacterial properties, for example, the antibacterial agent disclosed in Japanese Patent Application Publication No. 11-267500.

[0591] [2-9-4] Hardening process

[0592] The mixture of the aqueous solution of the aforementioned water-absorbing resin and the aforementioned flowability improver, obtained through the above series of operations, is preferably subjected to a hardening treatment. That is, the manufacturing method of the present invention preferably further includes a step of hardening the mixture of the water-absorbing resin and the flowability improver after mixing the aforementioned flowability improver into the aforementioned water-absorbing resin. It should be noted that "hardening" refers to the operation of eliminating the wettability of the surface of the water-absorbing resin and performing powdering. Furthermore, the "hardening treatment" is a process in which the object is hardened by controlling the temperature of the object to a predetermined hardening temperature and maintaining that temperature for a predetermined hardening time.

[0593] In one embodiment of the present invention, it is preferable to use a hot air or other airflow heat medium in the above-described curing process. Furthermore, when the above-described curing process is performed in a process following the surface crosslinking step, the lower limit of the heating temperature, such as the temperature of the heat medium or the material temperature, is preferably 40°C or higher, more preferably 50°C or higher, and the upper limit is preferably 150°C or lower, more preferably 140°C or lower, and particularly preferably 100°C or lower. Furthermore, the curing time within this temperature range is preferably 1 minute or more and 2 hours or less, more preferably 5 minutes or more and 1.5 hours or less, and particularly preferably 10 minutes or more and 1 hour or less. By setting the curing temperature and curing time within the above-described ranges, the phenomenon of the surface state of the obtained absorbent composition being wet, thereby increasing its adhesiveness, can be suppressed, making it easier to process as a powder. Furthermore, if the curing temperature is too high or the curing time is too long, it is uneconomical in terms of energy; therefore, the curing temperature and curing time are preferably within the above-described ranges. It should be noted that each of the preferred ranges for the above-described heating temperature and curing time (heating time) can be set as a range defined by any combination selected from the above-described upper and lower limits.

[0594] The addition, mixing, and subsequent curing of the aforementioned fluidity improver aqueous solution can be performed in the same apparatus or in different apparatuses. Furthermore, the timing of these series of treatments can be performed during the heat treatment step in the aforementioned surface crosslinking process, during the aforementioned cooling step, or after the cooling step. As an example of the apparatus used, the aforementioned apparatus (mixing apparatus) can be used, as long as the heat medium, such as gas, conductive heat transfer medium, etc., is adjusted to the aforementioned temperature within the apparatus. During curing, as long as the temperature and moisture content can be controlled within a specified range, stirring or standing (i.e., without stirring) can be performed. When the curing process is performed by standing, the lower limit of the thickness of the laminated absorbent resin is preferably 1 cm or more, more preferably 5 cm or more, and even more preferably 10 cm or more. On the other hand, the upper limit can be achieved by laminating and curing with a thickness preferably 100 cm or less, more preferably 80 cm or less, and even more preferably 70 cm or less. It should be noted that the preferred range of the aforementioned thickness can be defined as a range determined by any combination of the aforementioned upper and lower limits. The hardened absorbent resin can be pulverized or graded as needed to prepare an absorbent composition with a desired particle size.

[0595] [2-10] Other processes

[0596] In addition to the above-mentioned processes, this invention may include granulation, sizing, micron powder removal, micron powder recovery, micron powder reuse, iron removal, etc., as needed. Furthermore, it may further include at least one process selected from conveying, storage, packaging, and preservation processes.

[0597] [2-11] Rate of reduction in kinetic friction coefficient

[0598] According to the manufacturing method of the present invention, the coefficient of dynamic friction of the water-absorbing resin (i.e., the water-absorbing agent composition) after adding the flowability improver can be significantly reduced compared with the coefficient of dynamic friction of the water-absorbing resin before adding the flowability improver. Specifically, a method for manufacturing a water-absorbing agent composition in which the coefficient of dynamic friction is reduced by more than 10% as calculated by the following (Formula 2) can be provided.

[0599] [Formula 6]

[0600]

[0601] In equation 2,

[0602] A: The coefficient of kinetic friction of water-absorbing resin particles with a particle size of 300μm or larger and less than 600μm before the addition of flowability improver;

[0603] B: The coefficient of kinetic friction of particles with a particle size of 300 μm or more but less than 600 μm in the absorbent composition after adding a flowability improver. It should be noted that the coefficients of kinetic friction of A and B above were determined using the methods described in the examples.

[0604] It should be noted that, in this specification, "particles with a particle size of 300 μm or more but less than 600 μm" refers to particles that, after being classified using the grading method in the evaluation method for the coefficient of kinetic friction of the embodiment, pass through a sieve with a mesh size of 600 μm but remain on a sieve with a mesh size of 300 μm.

[0605] In the manufacturing method of the present invention, it is preferable that the reduction rate of the dynamic friction coefficient is 10% or more.

[0606] The lower limit of the aforementioned reduction rate of the coefficient of kinetic friction is preferably 12% or more, more preferably 15% or more, and particularly preferably 20% or more. On the other hand, the higher the upper limit, the more preferred, and there is no particular limitation; for example, it is 90% or less, preferably 70% or less, more preferably 50% or less, and even more preferably 35% or less. The preferred range of the aforementioned reduction rate of the coefficient of kinetic friction can be set as a range defined by any combination selected from the aforementioned upper and lower limits. That is, the aforementioned reduction rate of the coefficient of kinetic friction is, for example, 10% or more and 90% or less, preferably 12% or more and 90% or less, more preferably 15% or more and 90% or less, and particularly preferably 20% or more and 90% or less.

[0607] In a preferred embodiment, the absorbent resin (before adding the flowability improver) and the resulting absorbent composition each contain 50% by mass or more particles with a particle size of 300 μm or more and less than 600 μm, and the reduction rate of the coefficient of kinetic friction calculated by the above (Equation 2) can be 10% or more. It should be noted that, in this case, the preferred range of the reduction rate of the coefficient of kinetic friction is the same as that described above.

[0608] [3] Properties of the water-absorbing agent composition

[0609] The absorbent composition obtained through the above-described process is a final product ready for shipment. The manufacturing method of the present invention described above can yield an absorbent composition that satisfies (1) to (5) below. Therefore, another aspect of the present invention provides an absorbent composition that is primarily composed of an absorbent resin, contains a flowability enhancer, and satisfies all of (1) to (5) below.

[0610] (1) The specific surface area of ​​the above-mentioned absorbent composition is 25 m². 2 / kg or more.

[0611] (2) The surface tension of the above-mentioned absorbent composition is 56 mN / m or more.

[0612] (3) The flow rate of the above absorbent composition is 10.0 g / s or more.

[0613] (4) The mass percentage of particles with a particle size of 300 μm or more and less than 600 μm in the above-mentioned absorbent composition is 50% by mass or more.

[0614] (5) The kinetic friction coefficient of the particles with a particle size of 300 μm or more and less than 600 μm in the above-mentioned absorbent composition is 0.80 or less.

[0615] [3-1] Specific surface area

[0616] For the water-absorbing composition of the present invention, the lower limit of its specific surface area is set to 25m². 2 A water absorption rate of / kg or higher can achieve even better results based on the Vortex method. A higher specific surface area of ​​the water-absorbing agent composition is preferred, with 26m² being the most desirable. 2 / kg or more, preferably 27m 2 / kg or more, further preferably 28m 2 / kg or more, with 29m being a more preferred option. 2 / kg or more, and more preferably 30m 2 / kg or more, with 35m being particularly preferred 2 / kg or more, the optimal value is 36m 2 / kg or more. On the other hand, the upper limit of the specific surface area of ​​the absorbent composition is preferably 60m². 2 / kg or less, preferably 55m 2 / kg or less. It should be noted that the preferred range of the specific surface area of ​​the above-mentioned absorbent composition can be set as a range defined by any combination selected from the above upper and lower limits. Therefore, the specific surface area of ​​the absorbent composition can, for example, be 25m². 2 / kg or more and 60m 2 For weights below / kg, 26m can be used. 2 / kg or more and 60m 2 For weights below / kg, 27m can be used. 2 / kg or more and 60m 2 For weights below / kg, 28m can be used. 2 / kg or more and 60m 2 For weights below / kg, 29m can be used. 2 / kg or more and 60m 2 For weights below / kg, 30m can be used. 2 / kg or more and 55m 2 For weights below / kg, 35m can be used. 2 / kg or more and 55m 2 For weights below / kg, 36m can be used.2 / kg or more and 55m 2 / kg or less. From the perspective of accelerating water absorption, a higher specific surface area of ​​the water-absorbing agent composition is more ideal. However, if the specific surface area is too large, excessive foaming polymerization is required in the polymerization process and excessively fine gel pulverization is required in the gel pulverization process, which may result in a decrease in AAP (Absorption Rate under Pressure). On the other hand, if the specific surface area of ​​the water-absorbing agent composition is less than 25m², 2 If the ratio is less than 1 / kg, it is difficult to obtain a desiccant composition with the desired water absorption rate (Vortex), and therefore it is not preferred.

[0617] [3-2] Surface tension

[0618] The lower limit of the surface tension of the absorbent composition of the present invention is 56 mN / m or more, preferably 58 mN / m or more, more preferably 60 mN / m or more, and even more preferably 65 mN / m or more. The upper limit is not particularly limited, but from the viewpoint of balancing with other physical properties, it is preferably 75 mN / m or less. If the surface tension is less than 56 mN / m, the backflow of liquid when pressure is applied to the absorbent increases, therefore it is not suitable for absorbent compositions used in absorbent articles such as disposable diapers. It should be noted that the preferred range of the surface tension of the above-mentioned absorbent composition can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the surface tension of the above-mentioned absorbent composition is, for example, 56 mN / m or more and 75 mN / m or less, preferably 58 mN / m or more and 75 mN / m or less, more preferably 60 mN / m or more and 75 mN / m or less, and even more preferably 65 mN / m or more and 75 mN / m or less. The above-mentioned surface tension can be controlled by additives or the like added after surface crosslinking. Furthermore, the detailed measurement conditions for the surface tension described above are as described in the examples.

[0619] [3-3] Flow Rate

[0620] The lower limit of the flow rate of the absorbent composition of the present invention is 10.0 g / s or more. The lower limit of the flow rate is preferably 10.2 g / s or more, more preferably 10.5 g / s or more. If the flow rate is less than 10.0 g / s, the time required to supply the absorbent composition to the hopper and from the hopper to the feeder increases, which is undesirable from a production efficiency point of view. The upper limit of the flow rate is preferably 20.0 g / s or less, more preferably 15.0 g / s or less. Performing a process to make the flow rate higher than the above range may result in poor economic efficiency. It should be noted that the preferred range of the flow rate can be defined as a range determined by any combination selected from the above upper and lower limits. Therefore, the flow rate is, for example, 10.0 g / s or more and 20.0 g / s or less, preferably 10.2 g / s or more and 20.0 g / s or less, more preferably 10.5 g / s or more and 15.0 g / s or less. Furthermore, the detailed measurement conditions for the above-mentioned flow rate are as described in the example.

[0621] [3-4] Mass proportion of particles with a diameter of 300 μm or larger and less than 600 μm

[0622] The lower limit of the mass percentage of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition of the present invention is 50% by mass or more, preferably 53% by mass or more, more preferably 55% by mass or more, and even more preferably 57% by mass or more. If the above-mentioned mass percentage is 50% by mass or more, the stability of the absorbent composition conveyed by the feeder is further improved. It should be noted that, in continuous commercial production, from the viewpoint of production efficiency, it is sometimes very difficult to achieve a mass percentage of 0% by mass for both particles smaller than 300 μm and particles larger than 600 μm. Therefore, the upper limit of the mass percentage of particles with a particle size of 300 μm or more and less than 600 μm is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, particularly preferably 80% by mass or less, and most preferably 75% by mass or less. It should be noted that the preferred range of the mass percentage of particles with a particle size of 300 μm or more and less than 600 μm can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the mass proportion of particles with a diameter of 300 μm or larger and less than 600 μm is, for example, 50% by mass or larger and 95% by mass or smaller, preferably 53% by mass or larger and 90% by mass or smaller, more preferably 55% by mass or larger and 85% by mass or smaller, even more preferably 57% by mass or larger and 80% by mass or smaller, and particularly preferably 57% by mass or larger and 75% by mass or smaller. It should be noted that, according to the manufacturing method of the present invention, an aqueous solution of a flowability improver can be uniformly added to a water-absorbing resin with a large specific surface area. That is, the flowability improver is not unevenly added to particles with fine particle size and large specific surface area (particles with a particle size less than 300 μm), etc., and the kinetic friction coefficient of particles with a particle size of 300 μm or larger and less than 600 μm, which constitute more than half of the particles in the water-absorbing agent composition, can be significantly reduced. In other words, significantly reducing the kinetic friction coefficient of particles with a particle size of 300 μm or larger and less than 600 μm means uniformly improving the flowability of all particles.

[0623] [3-5] Coefficient of kinetic friction

[0624] For the absorbent composition of the present invention, the upper limit of the coefficient of kinetic friction (sometimes referred to simply as "coefficient of kinetic friction" in this specification) for particles with a particle size of 300 μm or more and less than 600 μm is 0.80 or less, preferably 0.79 or less, more preferably 0.78 or less, further preferably 0.77 or less, particularly preferably 0.76 or less, and most preferably 0.73 or less. A coefficient of kinetic friction exceeding 0.80 means that a flowability improver has been unevenly added to particles with a particle size of not more than 300 μm and less than 600 μm. That is, if the coefficient of kinetic friction exceeds 0.80, the difference in flowability between particles with a particle size of 300 μm or more and less than 600 μm and particles with a particle size of not more than 300 μm and less than 600 μm becomes large. As a result, particle size segregation of the absorbent composition occurs during conveying using a feeder, which is therefore undesirable. On the other hand, the lower limit value is, for example, 0.10 or more, preferably 0.30 or more, more preferably 0.50 or more, and even more preferably 0.60 or more. It should be noted that the preferred range of the kinetic friction coefficient of the particles 300 μm or more and less than 600 μm can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the kinetic friction coefficient of the particles 300 μm or more and less than 600 μm is, for example, 0.10 or more and 0.80 or less, preferably 0.30 or more and 0.79 or less, more preferably 0.50 or more and 0.78 or less, even more preferably 0.60 or more and 0.77 or less, particularly preferably 0.60 or more and 0.76 or less, and most preferably 0.60 or more and 0.73 or less. Furthermore, the detailed measurement conditions for the kinetic friction coefficient of the particles 300 μm or more and less than 600 μm are described in the examples.

[0625] [3-6] Preferred method

[0626] The absorbent composition of the present invention preferably satisfies all of the above-described (1) to (5) conditions, and has at least one of the preferred ranges of specific surface area, surface tension, flow rate, mass ratio of particles with a particle size of 300 μm or more and less than 600 μm, and coefficient of kinetic friction. More preferably, the absorbent composition satisfies all of the above-described (1) to (5) conditions, and at least satisfies the preferred ranges of surface tension and flow rate. More preferably, the absorbent composition satisfies all of the above-described (1) to (5) conditions, and at least satisfies the preferred ranges of surface tension, flow rate, and coefficient of kinetic friction. Particularly preferably, the absorbent composition satisfies all of the above-described (1) to (5) conditions, and at least satisfies the preferred ranges of specific surface area, surface tension, flow rate, and coefficient of kinetic friction. Most preferably, the absorbent composition satisfies all of the above-described (1) to (5) conditions, and satisfies all specific surface area, surface tension, flow rate, mass ratio of the above-described particles, and coefficient of kinetic friction.

[0627] More specifically, provided that all of the above (1) to (5) are satisfied, the surface tension of the absorbent composition of the present invention is preferably 56 mN / m or more and 75 mN / m or less, more preferably 58 mN / m or more and 75 mN / m or less, further preferably 60 mN / m or more and 75 mN / m or less, particularly preferably 65 mN / m or more and 75 mN / m or less, and the flow rate is preferably 10.0 g / s or more and 20.0 g / s or less, more preferably 10.2 g / s or more and 20.0 g / s or less, particularly preferably 10.5 g / s or more and 15.0 g / s or less. Furthermore, in addition to the above, the coefficient of kinetic friction of the absorbent composition is preferably 0.10 or higher and 0.80 or lower, more preferably 0.30 or higher and 0.79 or lower, even more preferably 0.50 or higher and 0.78 or lower, even more preferably 0.60 or higher and 0.77 or lower, particularly preferably 0.60 or higher and 0.76 or lower, and most preferably 0.60 or higher and 0.73 or lower. Furthermore, in addition to the above, the specific surface area of ​​the absorbent composition is preferably 25 m². 2 / kg or more and 60m 2 / kg or less, preferably 26m 2 / kg or more and 60m 2 / kg or less, and more preferably 27m 2 / kg or more and 60m 2 Below / kg, and more preferably 28m 2 / kg or more and 60m 2 Below / kg, more preferably 29m2 / kg or more and 60m 2 / kg or less, more preferably 30m 2 / kg or more and 55m 2 / kg or less, with 35m being particularly preferred 2 / kg or more and 55m 2 / kg or less, the optimal value is 36m 2 / kg or more and 55m 2 / kg or less. Furthermore, in addition to the above, the mass percentage of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition is preferably 50% by mass or more and 95% by mass or less, preferably 53% by mass or more and 90% by mass or less, more preferably 55% by mass or more and 85% by mass or less, even more preferably 57% by mass or more and 80% by mass or less, and particularly preferably 57% by mass or more and 75% by mass or less.

[0628] [3-7] Other physical properties of the absorbent composition

[0629] The absorbent composition of the present invention preferably further comprises at least one of the following physical properties (a) to (g) within a preferred range.

[0630] The physical properties (a) to (g) are: (a) D50 (mass-average particle size), (b) mass ratio of particles with a particle size less than 150 μm, (c) CRC (absorption rate without pressure), (d) AAP (absorption rate under pressure), (e) SFC (saline flow induction), (f) Vortex (water absorption rate), and (g) FHA (absorption value at a fixed height of 20 cm).

[0631] Furthermore, any two or more of the preferred ranges possessing the aforementioned physical properties (a) to (g) can be combined. Most preferably, the preferred ranges possessing all of (a) to (g) are included.

[0632] (a) D50 (mass-average particle size)

[0633] The lower limit of the D50 (mass-average particle size) of the absorbent composition of the present invention is preferably 250 μm or more, more preferably 300 μm or more, and even more preferably 330 μm or more. On the other hand, the upper limit is preferably less than 550 μm, more preferably less than 500 μm, and even more preferably less than 450 μm. It should be noted that the preferred range of D50 of the above-mentioned absorbent composition can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the above-mentioned D50 (mass-average particle size) is preferably 250 μm or more and less than 550 μm, more preferably 300 μm or more and less than 500 μm, and even more preferably 330 μm or more and less than 450 μm. By setting the above-mentioned D50 (mass-average particle size) within the above range, the AAP (absorption rate under pressure) and Vortex (absorption speed), which are preferred absorption characteristics, can be controlled more effectively and in a balanced manner. If the D50 (mass-average particle size) is 250 μm or more, the AAP (absorption rate under pressure), a preferred absorption characteristic, can be maintained at a good value. Conversely, if the D50 (mass-average particle size) is less than 550 μm, the Vortex (absorption rate), a preferred absorption characteristic, can be maintained at a good value. Furthermore, the particle roughness of the absorbent composition becomes less noticeable, and when used in absorbent articles such as disposable diapers and sanitary napkins, it can maintain good skin feel and wearing comfort. Detailed measurement conditions for the D50 (mass-average particle size) are described in the examples.

[0634] (b) Proportion of particles with a diameter less than 150 μm

[0635] The upper limit of the proportion of particles smaller than 150 μm in the absorbent composition of the present invention, relative to 100% by mass of the absorbent composition, is preferably 3% by mass or less, more preferably 2% by mass or less, further preferably 1% by mass or less, and particularly preferably 0% by mass. It should be noted that in continuous commercial production, it is sometimes very difficult to achieve a proportion of particles smaller than 150 μm of 0% by mass from the viewpoint of production efficiency. Therefore, its lower limit is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 0.3% by mass or more. It should be noted that the preferred range of the proportion of particles smaller than 150 μm can be set as a range defined by any combination selected from the above upper and lower limits. Therefore, the proportion of particles smaller than 150 μm is preferably 0.1% by mass or more and 3% by mass or less, more preferably 0.2% by mass or more and 2% by mass or less, and further preferably 0.3% by mass or more and 1% by mass or less. By setting the proportion of particles smaller than 150 μm within the above range, it is easier to further balance and control AAP (absorption rate under pressure) and Vortex (absorption speed). If the proportion of particles smaller than 150 μm is less than 3% by mass, not only can the AAP (Absorption Ratio under Pressure), which is the preferred absorption characteristic, be maintained at a good value, but it can also suppress the deterioration of the working environment caused by dust dispersion at the site where the absorbent composition is processed, and the handling difficulties caused by the accumulation of microparticles in the device.

[0636] Furthermore, the absorbent composition preferably satisfies a preferred range for D50 (mass-average particle size) within the aforementioned range, and also a preferred range for the proportion of particles smaller than 150 μm within the aforementioned range. By satisfying both, the aforementioned effects can be synergistically achieved. Specifically, it is preferred that the absorbent composition has a D50 (mass-average particle size) of 250 μm or more and less than 550 μm, and that the proportion of particles with a particle size smaller than 150 μm in the absorbent composition is 3% by mass or less. Furthermore, the preferred ranges for D50 (mass-average particle size) and the proportion of particles with a particle size smaller than 150 μm in the absorbent composition are as described in (a) and (b) above, respectively. It should be noted that the D50 (mass-average particle size) and the proportion of particles smaller than 150 μm in the absorbent composition were determined by the method described in the examples.

[0637] (c) CRC (Absorption Ratio without Pressure)

[0638] The lower limit of the CRC (Cycles Ratio without Pressure) of the absorbent composition of the present invention is preferably 25 g / g or more. On the other hand, the upper limit is preferably 40 g / g or less, more preferably 38 g / g or less, further preferably 35 g / g or less, particularly preferably 32 g / g or less, and most preferably 30 g / g or less. It should be noted that the preferred range of the above-mentioned CRC can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. If the above-mentioned CRC (Cycles Ratio without Pressure) is too low, the absorbency of the absorbent composition will decrease, and it may not be suitable for use as an absorbent in absorbent articles such as disposable diapers and sanitary napkins. On the other hand, if the above-mentioned CRC (Cycles Ratio without Pressure) is too high, the gel strength may become weak.

[0639] (d) AAP (Absorption Ratio under Pressure)

[0640] The lower limit of the absorbent polymer (AAP) of the absorbent composition of the present invention is preferably 20 g / g or more, more preferably 23 g / g or more, even more preferably 25 g / g or more, and particularly preferably 25.2 g / g or more. On the other hand, the upper limit is preferably 30 g / g or less, more preferably 28 g / g or less. It should be noted that the preferred range of the above-mentioned AAP can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the above-mentioned AAP is preferably 20 g / g or more and 30 g / g or less, more preferably 23 g / g or more and 30 g / g or less, even more preferably 25 g / g or more and 30 g / g or less, and particularly preferably 25.2 g / g or more and 28 g / g or less. By setting the above-mentioned AAP (absorbent polymer) within the above range, the liquid backflow when pressure is applied to the absorbent can be further reduced, thus making it a suitable absorbent resin or absorbent composition for use as an absorbent in absorbent articles such as disposable diapers and sanitary napkins.

[0641] (e) SFC (Saline Flow Inducibility)

[0642] The lower limit of the SFC (salt water flow induction) of the absorbent composition of the present invention is preferably 1 × 10⁻⁶. -7 cm 3 • sec / g or higher, more preferably 2×10 -7 cm 3 •sec / g or higher, more preferably 3×10 -7 cm 3 •sec / g or higher, more preferably 5×10 -7 cm 3 •sec / g or higher, more preferably 10×10 -7 cm 3 • sec / g or higher, more preferably 15 × 10-7 cm 3 • sec / g or higher, especially preferably 20 × 10 -7 cm 3 • sec / g or higher, with the optimal value being 25 × 10 - 7 cm 3 • sec / g or higher. A higher upper limit for SFC is preferred; there are no specific limitations, for example, it can be 50 × 10⁻⁶. -7 cm 3 • sec / g or less. It should be noted that the preferred range of the above-mentioned SFC can be defined as a range determined by any combination selected from the above upper and lower limits. Therefore, the above-mentioned SFC is preferably 1×10-1. -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less, more preferably 2×10 -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less, more preferably 3 × 10 -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less, more preferably 5 × 10 -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less, more preferably 10 × 10 -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less, more preferably 15 × 10 -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less, with 20×10⁻⁶ being particularly preferred. -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 For values ​​below sec / g, the optimal value is 25 × 10⁻⁶. -7 cm 3 • sec / g or higher and 50 × 10 -7 cm 3 • sec / g or less. For detailed measurement conditions of the above SFC, please refer to the examples.

[0643] (f) Vortex (water absorption rate)

[0644] The upper limit of the Vortex (absorption rate) of the absorbent composition of the present invention is preferably 50 seconds or less, more preferably 48 seconds or less, further preferably 46 seconds or less, particularly preferably 44 seconds or less, and most preferably 42 seconds or less. On the other hand, the lower limit is preferably more than 10 seconds, more preferably 15 seconds or more. It should be noted that the preferred range of the above-mentioned Vortex can be set as a range defined by any combination selected from the above-mentioned upper and lower limits. Therefore, the above-mentioned Vortex (absorption rate) is preferably more than 10 seconds and less than 50 seconds, more preferably more than 10 seconds and less than 48 seconds, further preferably more than 10 seconds and less than 46 seconds, particularly preferably more than 10 seconds and less than 44 seconds, and most preferably more than 15 seconds and less than 42 seconds. If the above-mentioned Vortex (absorption rate) is 50 seconds or less, the resulting absorbent composition has a fast absorption rate for bodily fluids such as urine and blood, and this absorbent composition is suitable as an absorbent for absorbent articles such as disposable diapers. It should be noted that the Vortex (water absorption rate) can be controlled by foaming polymerization, particle size distribution, etc. Detailed measurement conditions for the Vortex (water absorption rate) are described in the examples.

[0645] (g) FHA (Focused Absorption Value at a Fixed Height of 20cm)

[0646] The lower limit of the absorbent HA (fixed height absorbance value at a height of 20 cm) of the absorbent composition of the present invention is preferably 24.0 g / g or more, more preferably 24.5 g / g or more, further preferably 25.0 g / g or more, and particularly preferably 25.5 g / g or more. The upper limit is not particularly limited, but from the viewpoint of balancing with other physical properties, it is preferably 30.0 g / g or less. It should be noted that the preferred range of the above-mentioned FHA can be defined as a range determined by any combination selected from the above-mentioned upper and lower limits. When the above-mentioned FHA is 24.0 g / g or more, the absorbency when pressure is applied to the absorbent increases, thus making it suitable as an absorbent for absorbent articles such as disposable diapers. It should be noted that the above-mentioned FHA can be controlled by internal crosslinking agents, particle size, surface crosslinking agents, and / or additives added after the surface crosslinking process. Detailed measurement conditions for the above-mentioned FHA (fixed height absorbance value at a height of 20 cm) are described in the examples.

[0647] [3-8] Relationship between water-absorbing resin and water-absorbing agent composition

[0648] Relative to the total amount of the absorbent composition, the lower limit of the amount (mass ratio) of the absorbent resin contained in the absorbent composition of the present invention is preferably 80% or more, more preferably 85% or more, further preferably 90% or more, particularly preferably 95% or more by mass, more preferably 98% or more by mass, and further preferably 99% or more by mass. It should be noted that when the various additives mentioned above (flow improvers, other additives, and water added together with these additives) are included, the amount of absorbent resin contained in the absorbent composition is not 100% by mass. That is, the upper limit of the amount (mass ratio) of the absorbent resin contained in the absorbent composition of the present invention can be less than 100% by mass.

[0649] Furthermore, the shape of the absorbent composition of the present invention can be any of the following: spherical, granular, agglomerated, irregularly broken, etc., but considering the water absorption rate, an irregularly broken shape is preferred.

[0650] [4] Uses of water-absorbing agent compositions

[0651] The absorbent composition of the present invention is preferably used primarily as an absorbent body or absorbent layer (hereinafter collectively referred to as "absorbent body") in absorbent articles such as disposable diapers and sanitary napkins, and more preferably as an absorbent body in absorbent articles where a large amount is used per absorbent article. That is, another aspect of the present invention provides an absorbent body comprising the above-described absorbent composition.

[0652] The aforementioned absorbent refers to an absorbent formed by molding the absorbent composition into sheets, fibers, tubes, etc., preferably into sheets to form an absorbent layer. In addition to the absorbent composition of the present invention, absorbent materials such as pulp fibers (pulp), adhesives, nonwoven fabrics, etc., may also be used during molding. Therefore, in one embodiment, the absorbent of the present invention, in addition to the aforementioned absorbent, also contains pulp fibers (pulp). In this case, the lower limit of the amount of the absorbent composition in the absorbent (hereinafter referred to as "core concentration") is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and particularly preferably 80% by mass or more. On the other hand, its upper limit is preferably 100% by mass or less. It should be noted that the preferred range of the core concentration can be set to a range defined by any combination selected from the above upper and lower limits. By setting the core concentration within the above range, when the absorbent is used in absorbent articles, even if the absorbent composition absorbs urine and gels, a suitable space can be formed between the gel particles.

[0653] In the above-mentioned absorbent, the unit area weight of the water-absorbing agent composition is preferably 25 g / m². 2 Above and 450g / m 2 The following is more preferably 50g / m 2 Above and 400g / m2 The following is a further preferred value: 75g / m 2 Above and 350g / m 2 The following describes how, by setting the weight per unit area of ​​the absorbent composition within the above-mentioned range, urine can be effectively absorbed when the absorbent is used in absorbent articles.

[0654] In the above-mentioned absorbent, the weight per unit area of ​​absorbent material such as pulp (preferably pulp) is preferably 0 g / m³. 2 Above and 300g / m 2 The following is more preferably 0 g / m 2 Above and 250g / m 2 The following is further preferred: 0 g / m 2 Above and 200g / m 2 The following is particularly preferred: 0 g / m 2 Above and 150g / m 2 The following describes how, by setting the weight per unit area of ​​the pulp within the aforementioned range, the absorbent article can be made thinner when the absorbent is used in absorbent articles. As described above, the weight per unit area of ​​the absorbent material (preferably pulp) can be 0 g / m³. 2 That is, in one embodiment, the absorbent may not contain pulp.

[0655] As a specific example of an absorbent, one can cite an absorbent formed by cutting a strip of absorbent sheet (usually cut into rectangles approximately 10cm wide and 10cm long) between two sheets, in which an absorbent composition (absorbent resin) is fixed between the two sheets. This type of absorbency, manufactured by cutting the aforementioned strip of absorbent sheet during the diaper manufacturing process, has increasingly been used in the production of diapers (so-called SAP sheet diapers) in recent years. By purchasing or manufacturing strips of absorbent sheet, diaper manufacturers can simplify the diaper manufacturing process, thereby eliminating the use of pulp and enabling thinner diapers. The aforementioned absorbent sheet has a structure in which an absorbent composition (absorbent resin particles) is sandwiched between upper and lower sheets (especially non-woven sheets). In the manufacture of disposable diapers, after manufacturing the aforementioned long absorbent sheet, the sheet is usually cut into rectangles approximately 10cm wide and several 10cm long, and then assembled into a disposable diaper (refer to International Publication No. 2010 / 143635).

[0656] [5] Absorbent items

[0657] The absorbent composition of the present invention is suitable for absorbent articles. Specifically, another aspect of the present invention is an absorbent article comprising the above-described absorbent composition. Furthermore, another aspect of the present invention provides an absorbent article comprising the above-described absorbent body. Such absorbent articles, in addition to the absorbent body, typically also have a liquid-permeable front sheet and a liquid-impermeable back sheet. Examples of absorbent articles include disposable diapers and sanitary napkins.

[0658] In the case of absorbent articles such as disposable diapers, the disposable diaper is manufactured by sandwiching an absorbent containing the absorbent composition of the present invention between a liquid-permeable top sheet located on the side in contact with the skin when worn and a liquid-impermeable bottom sheet located on the outside when worn. It should be noted that the disposable diaper is also provided with components known to those skilled in the art, such as adhesive tape for securing the disposable diaper after wearing.

[0659] In one embodiment, the absorbent article is preferably free of pulp. That is, the absorbent article is preferably a diaper that does not contain pulp. The absorbent article may be a pulp-free diaper in which the weight per unit area of ​​the absorbent composition in the absorbent body is within the range described above.

[0660] In another embodiment, in addition to the absorbent composition, the absorbent article may also contain pulp. That is, the absorbent article may be a diaper containing pulp. The absorbent article may be a pulp-containing diaper in which the weight per unit area of ​​pulp in the absorbent body is within the range described above.

[0661] Example

[0662] The present invention is described below with reference to specific embodiments. However, the present invention is not limited to the embodiments described below, and may be implemented by appropriate modifications within the scope of the preceding and following description, all of which are included within the technical scope of the present invention. Furthermore, in the present invention, unless otherwise specifically mentioned, the methods for measuring the above-mentioned physical properties are based on the methods described in the embodiments.

[0663] The methods for determining each property in the table are described below. It should be noted that all measurements were performed at room temperature (23±2℃) and relative humidity 35±5%RH. Furthermore, in the descriptions of the methods for determining each property below, when the object of measurement is not a water-absorbing composition (e.g., particulate hydrogels, water-absorbing resins before / after surface crosslinking, etc.), replace "water-absorbing composition" with "particulate hydrogels," "water-absorbing resins before surface crosslinking," or "water-absorbing resins after surface crosslinking" in the following descriptions.

[0664] <Methods for Determining Physical Properties>

[0665] [Coefficient of kinetic friction]

[0666] The coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition of the present invention was determined by the method described below.

[0667] (Grading of water-absorbing agent compositions)

[0668] 100.0g of the absorbent composition was graded using two JIS standard sieves (THE IIDA TESTING SIEVE: diameter 16cm) with mesh sizes of 600μm and 300μm. The grading was carried out by sieving for 5 minutes using a vibratory classifier (IIDA SIEVE SHAKER, TYPE: ES-65 (speed: 60Hz 230rpm, impact number: 60Hz 130rpm), SER. No. 0501).

[0669] Through the above-described grading process, we obtained a water-absorbing agent composition with a particle size of 600 μm or more, a water-absorbing agent composition with a particle size of 300 μm or more but less than 600 μm, and a water-absorbing agent composition with a particle size of less than 300 μm.

[0670] (Determination of shear stress using a rheometer)

[0671] A rheometer (Anton Paar, MCR301) was used (see reference). Figure 1 The shear stress of the water-absorbing agent composition with a particle size of 300 μm or more and less than 600 μm obtained through the above-described grading process was measured. Hereinafter, using... Figure 1 The determination method is described in detail.

[0672] 1. Set up dish 1 (inner diameter: 52 mm, depth: 30 mm, material: aluminum, note: the inner bottom surface is sandblasted) and parallel plate 2 (diameter: 50 mm, material: aluminum, note: the plate surface is machined into a grid pattern) in the rheometer. It should be noted that dish 1 and parallel plate 2 are thoroughly cleaned and dried. Furthermore, the rheometer and dish 1 are set up in a strictly horizontal manner.

[0673] 2. Set the measurement temperature to 25℃ and the lifting position (the distance between dish 1 and parallel plate 2) to 100mm.

[0674] 3. Adjust the zero gap between dish 1 and parallel plate 2.

[0675] 4. Raise the parallel plate 2 to the lifting position set in operation 2 above, increase the distance between dish 1 and parallel plate 2 to 100 mm, and then uniformly disperse 10.0 g of the water-absorbing agent composition with a particle size of 300 μm or more and less than 600 μm obtained through the above-described grading operation in dish 1. It should be noted that after the zero-gap adjustment operation in 3. above, dish 1 and parallel plate 2 are not removed from the rheometer. That is, the operation is performed with dish 1 and parallel plate 2 in the rheometer while the water-absorbing agent composition is being dispersed in dish 1. Furthermore, if dish 1 and parallel plate 2 are temporarily removed from the rheometer by cleaning or the like, the zero-gap adjustment is performed again when they are placed back in the rheometer, and the water-absorbing agent composition is dispersed without removing dish 1 and parallel plate 2 from the rheometer.

[0676] 5. Lower the parallel plate 2 to the starting position of the measurement (the position where the parallel plate 2 contacts the above-mentioned absorbent composition dispersed in the dish 1).

[0677] 6. Under the test conditions described in Table 1 below, measure the shear stress of the above-mentioned absorbent composition. It should be noted that conditions (1) to (5) described in Table 1 below are measured consecutively, and the time required from the start of condition (1) to the end of condition (5) is 1050 seconds. It should be noted that after the measurement, the parallel plate is lifted to a height of 100 mm, and the powder surface of the absorbent composition (the surface in contact with the parallel plate) is checked. At this time, if, for example, there is a partial depression on the powder surface, and part of the parallel plate cannot contact the powder surface, a re-measurement is performed. That is, only the case where the powder surface of the absorbent composition after the measurement has no depression and the bottom surface of the parallel plate can contact the powder surface is taken as the accurate measurement result.

[0678] 7. Among the shear stresses obtained in the above 6 determination, the average value of the shear stresses measured under conditions (3), (4) and (5) as described in Table 1 below, from the 41st to the 60th measurement point, shall be taken as the shear stress (unit: Pa) of the above absorbent composition under conditions (3), (4) and (5), i.e., under vertical loads of 1N, 3N and 5N.

[0679] The shear stress of the absorbent composition with a particle size of 300 μm or more and less than 600 μm obtained by the above-described grading operation in this invention under vertical loads of 1 N (condition (3)), 3 N (condition (4)) and 5 N (condition (5)) was measured twice using the same sample (absorbent composition), and the average value was taken. However, if the shear stress under 5 N (condition (5)) differed by more than 150 Pa between the two measurements, an additional measurement was performed, and the average value was calculated from the two measurements with a difference of less than 150 Pa.

[0680]

[0681] (Calculation of vertical stress)

[0682] The vertical stress (unit: Pa) of the absorbent composition under conditions (3), (4) and (5) listed in Table 1 above is calculated according to the following formula (a).

[0683] Vertical stress (Pa) = (Vertical load (N)) / (Area of ​​parallel plate (m²)) 2 ))……(Formula a)

[0684] It should be noted that the area of ​​the parallel plate in the above (equation a) is 0.0252 × π (m²). 2 ).

[0685] That is, the vertical stress of the absorbent composition with a particle size of more than 300 μm and less than 600 μm obtained by the above-mentioned grading operation under vertical loads of 1 N (condition (3)), 3 N (condition (4)) and 5 N (condition (5)) is 509 Pa, 1528 Pa and 2546 Pa.

[0686] (Calculation of the coefficient of kinetic friction)

[0687] The coefficient of dynamic friction of the water-absorbing agent composition with a particle size of 300 μm or more and less than 600 μm obtained by the above grading operation was calculated by the following method.

[0688] 1. The shear stress and vertical stress of the above-mentioned absorbent composition under vertical loads of 1N, 3N and 5N are indicated with the longitudinal axis as shear stress and the transverse axis as vertical stress.

[0689] 2. The markings of the three points are linearly approximated by a straight line passing through the origin without intercept, and the slope of the straight line is taken as the coefficient of kinetic friction of the above-mentioned absorbent composition.

[0690] It should be noted that in the above linear approximation, when the R-squared value of the approximation is less than 0.9000, the shear stress measurement using the rheometer is performed again, and only the slope of the linear approximation with an R-squared value of 0.9000 or more is used as the coefficient of kinetic friction.

[0691] [Reduction rate of kinetic friction coefficient]

[0692] The reduction rate (in %) of the kinetic friction coefficient of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition of the present invention is calculated according to the following (Formula 2).

[0693] [Formula 7]

[0694]

[0695] In equation 2,

[0696] A: The coefficient of kinetic friction of water-absorbing resin particles with a particle size of 300μm or larger and less than 600μm before the addition of flowability improver;

[0697] B: The coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition after adding a flowability improver.

[0698] After measuring the kinetic friction coefficients of A and B using the methods described above, the reduction rate of the kinetic friction coefficient was calculated using the above formula (Equation 2).

[0699] [Feed Test]

[0700] The feeding test of the water-absorbing agent composition of the present invention was conducted using an electromagnetic feeder drive unit 4 (series: MFS type small series, model: MUS-6, manufacturer: Murakami Seiki Co., Ltd.) (see reference). Figure 2 This is implemented using a controller (Series: MC type, Model: MC-2-2, Manufacturer: Murakami Seiki Co., Ltd.). The following will use... Figure 2 The experimental methods are described in detail.

[0701] 1. A slot 5 (total length: 20cm, width: 7cm, weir: 5cm, material: SUS) is provided on the electromagnetic feeder drive unit 4.

[0702] 2. Place 50.0g of the absorbent composition on tank 5, positioning it at a position 12cm to 20cm from the outlet of tank 5.

[0703] 3. Set the controller scale to 2 and start feeding.

[0704] 4. Starting from the start of feeding, sample the absorbent composition dispensed from the outlet of tank 5 between 70 and 120 seconds.

[0705] [Particle size change rate]

[0706] The particle size change rate (in %) of the absorbent composition of the present invention was calculated by the following method.

[0707] (Grading of water-absorbing agent compositions)

[0708] Two JIS standard sieves (THE IIDA TESTING SIEVE: 8cm diameter) with mesh sizes of 600μm and 300μm were used to classify 10.0g of the absorbent composition before the above-mentioned feed test and 10.0g of the absorbent composition sampled in the above-mentioned feed test, respectively. The classification was carried out by sieving for 5 minutes using a vibratory classifier (IIDA SIEVE SHAKER, TYPE: ES-65 (speed: 60Hz 230rpm, impact number: 60Hz 130rpm), SER. No. 0501).

[0709] Through the above-described grading process, the absorbent composition before the above-described feed test and the absorbent composition sampled in the above-described feed test are respectively graded into absorbent compositions with a particle size of 600 μm or more, absorbent compositions with a particle size of 300 μm or more but less than 600 μm, and absorbent compositions with a particle size of less than 300 μm.

[0710] (Calculation of particle size change rate)

[0711] For "water-absorbing composition with a particle size of 600 μm or more", "water-absorbing composition with a particle size of 300 μm or more and less than 600 μm", and "water-absorbing composition with a particle size of less than 300 μm", the particle size change rate is calculated based on the following formulas (b) to (d).

[0712] (Particle size change rate (mass%) of water-absorbing agent compositions with a particle size of 600 μm or more) = α1 - β1 ... (Formula b)

[0713] Here,

[0714] α1: The mass percentage (in mass%) of the absorbent composition having a particle size of 600 μm or more in the absorbent composition before the above-mentioned feed test.

[0715] β1: The mass percentage (in mass%) of the absorbent composition with a particle size of 600 μm or more in the absorbent composition sampled in the above feed test.

[0716] (Particle size change rate (mass%) of a water-absorbing agent composition with a particle size of 300 μm or more but less than 600 μm) = α² - β² ... (Formula c)

[0717] Here,

[0718] α2: The mass percentage (in mass%) of the superabsorbent composition having a particle size of 300 μm or more and less than 600 μm in the superabsorbent composition before the above feeding test.

[0719] β2: The mass percentage (in mass%) of the absorbent composition having a particle size of 300 μm or more and less than 600 μm in the absorbent composition sampled in the above feed test.

[0720] (Particle size change rate (mass%) of water-absorbing agent compositions with a particle size of less than 300 μm) = α³ - β³ … (Formula d)

[0721] Here,

[0722] α3: The mass percentage (in mass%) of the absorbent composition having a particle size of less than 300 μm in the absorbent composition before the above feeding test.

[0723] β3: The mass percentage (in mass%) of the absorbent composition with a particle size of less than 300 μm in the absorbent composition sampled in the above feed test.

[0724] Specific surface area

[0725] The specific surface area of ​​the absorbent composition of the present invention was determined by analyzing the three-dimensional image data of the absorbent composition obtained using a microfocused X-ray CT system (Shimadzu inspeXio SMX-100CT) using high-speed three-dimensional analysis software (TRI / 3D-VOL-FCS64, Ratoc Systems). Specifically, firstly, 1.0 g of the absorbent composition was added to a plastic cylindrical container with a lid, approximately 1 cm in inner diameter and 5 cm in height, and thoroughly mixed by agitation to ensure uniform particle size. Next, double-sided tape was attached to the bottom of the cylindrical container, and the container was fixed to the sample stage of the microfocused X-ray CT system. Three-dimensional image data was then obtained under the conditions shown in Table 2 below.

[0726]

[0727] Next, using the aforementioned high-speed 3D analysis software, perform the analysis according to the following steps.

[0728] 1. From the menu bar, select Particle Measurement > 3D Particles > Particle Separation > Giant Particle Separation.

[0729] 2. In the Binarize tab of the EVC panel, select LW, keep the W value at its initial value, and change the L value from its initial value to a value greater than 1 to extract the circular measurement object region. Next, apply this processing to all layered images. Set the image data extracted through this operation as (A).

[0730] 3. In the Binarize tab of the EVC panel, select LW, keep the W value at its initial value, and change the L value from the initial value to 37580 to extract all particles in the measurement area. Next, apply this processing to all layered images. Set the particle image data extracted through this operation as (B).

[0731] 4. Based on the particle image data (B), firstly, in the Binary tab of the EVC panel, select Ers Sml to remove particles smaller than 10 voxels, which are considered noise. Next, in the Binary tab of the EVC panel, select Invert to reverse the regions where particles were extracted and those where they were not. Then, select Ers Sml again to remove particles smaller than 10 voxels, which are considered noise. Next, in the 3D tab of the EVC panel, select Labeling, and further select Volume and Max to extract only the region with the largest volume. Finally, by selecting Invert again in the Binary tab of the EVC panel, noise is removed from the measurement area, and all particles are extracted even with embedded cavities (Voids). The particle image data extracted through these operations is set as (C). It should be noted that the cavity referred to here is a void existing inside the absorbent resin that is not in contact with the outside.

[0732] 5. In the L Op tag (inter-channel logic operation processing), after subtracting the particle image data (B) from the particle image data (C), select Ers Sml in the Binary tag on the EVC panel to remove particles with a particle size of less than 10 voxcel that are considered noise, thereby extracting the cavity.

[0733] 6. Based on the particle image data (C), select small particle extraction (do not select large particle extraction) on the large particle separation panel, and set the shrinkage ratio, repair filter size, and repair Mrg Sml Diameter to 0 to perform particle separation and color differentiation.

[0734] 7. In the 3D tab of the EVC panel, select Labeling, then select coordinate values ​​(loop), and set the particle size to 10 to perform particle separation.

[0735] 8. From the menu bar, select Particle Measurement > Void in 3D Particles > Measurement after Separation. Next, in the measurement panel after separation, select voxcel as the unit, select Remove Edge Particles, select Surface Area Calculation and Void Calculation as the measurement items, and select the image data (A) extracted through the above step 2 as the measurement ROI specification for calculation processing.

[0736] Through the above operations, the total surface area of ​​all particles in the measurement area can be calculated (unit: mm). 2 ) and apparent total volume (unit: mm) 3 ) and total volume of Void (unit: mm) 3 It should be noted that the apparent total volume refers to the total volume of all particles calculated assuming there are no void particles inside the particle. Furthermore, using the values ​​obtained through the above image analysis, the true density of the absorbent composition is set to 1.7 g / cm³. 3 Calculate the specific surface area (unit: m²) of the absorbent composition according to the following formula (e). 2 / kg).

[0737] Specific surface area = total surface area of ​​all particles / ((apparent total volume - Void total volume) × 1.7) ... (e.g.)

[0738] [ST (Surface Tension)]

[0739] The surface tension (ST) of the absorbent composition of the present invention is determined by the following method.

[0740] First, add 40 mL of a 0.9% (w / w) sodium chloride aqueous solution, adjusted to 23°C to 24°C, to a thoroughly cleaned 50 mL beaker. Measure the surface tension of the 0.9% (w / w) sodium chloride aqueous solution using a surface tension meter (KRUSS K11 automatic surface tension meter). During this measurement, the surface tension value must be within the range of 72 mN / m to 74 mN / m.

[0741] Next, after adjusting the surface tension measurement to 23°C to 24°C, a thoroughly cleaned cylindrical stir bar (25 mm long, 7 mm in cross-sectional diameter) and 0.5 g of desiccant composition were added to a beaker containing 40 mL of 0.9% sodium chloride aqueous solution. The mixture was stirred at 350 rpm for 3 minutes. After 3 minutes, stirring was stopped, and the mixture was allowed to stand for 2 minutes. After the desiccant composition had absorbed water and settled, the same procedure was repeated to measure the surface tension of the supernatant. It should be noted that this measurement used the plate method with platinum plates. The plates were thoroughly cleaned with deionized water and heated with a gas torch before each measurement.

[0742] [Flow rate]

[0743] The flow rate (in g / s) of the absorbent composition of the present invention is determined according to WSP250.3 (10). Specifically, 100.0 g of the absorbent composition is added to a funnel with a regulating valve at the bottom, the regulating valve is opened, and the time from the start of the flow to the end of the flow is measured. The amount of absorbent composition flowing down per unit time is calculated and taken as the flow rate (in g / s).

[0744] [D50 (mass-average particle size) and σζ (log-standard deviation of particle size distribution)]

[0745] The D50 (mass-average particle size) and σζ (logarithmic standard deviation of particle size distribution) of the absorbent composition of the present invention are determined according to the determination method described in paragraphs 0245-0246 of U.S. Patent No. 7,638,570.

[0746] [Vortex (water absorption rate)]

[0747] The Vortex (water absorption rate) of the absorbent composition of the present invention was determined according to JIS K 7224 (1996) following these steps: First, 0.02 parts by weight of Edible Blue No. 1 (CAS No. 3844-45-9) as a food additive was added to 1000 parts by weight of physiological saline for coloring, and the liquid temperature was adjusted to 30°C. This was used as the test solution. Next, 50 mL of the above test solution was measured into a 100 mL beaker, and a cylindrical stir bar with a length of 40 mm and a diameter of 8 mm was placed in the beaker, and stirring was started at 600 rpm. Next, 2.0 g of absorbent resin was added to the above-stirred test solution, and the time until the stir bar was covered by the test solution was measured as the water absorption rate based on the Vortex method.

[0748] [SFC (Saline Flow Inducibility)]

[0749] SFC (Saline Flow Induction) of the absorbent composition of the present invention (unit: ×10) -7 cm 3 The sec / g is determined according to the method described in U.S. Patent No. 5,669,894.

[0750] Specifically, 1.500g of the absorbent composition is uniformly placed into a container, and then the absorbent composition is immersed in artificial urine. The absorbent composition is swollen under pressure of 2.07 kPa. The artificial urine is prepared by mixing 0.25g of calcium chloride dihydrate, 2.0g of potassium chloride, 0.50g of magnesium chloride hexahydrate, 2.0g of sodium sulfate, 0.85g of ammonium dihydrogen phosphate, 0.15g of diammonium hydrogen phosphate, and 994.25g of pure water.

[0751] Sixty minutes after pressurization, the height (cm) of the swollen absorbent composition gel layer was recorded. Next, while the gel layer was pressurized at 2.07 kPa, a 0.69% (w / w) sodium chloride aqueous solution was passed through it. The room temperature was adjusted to 20°C to 25°C. Then, using a balance and a computer, the amount of saline solution passing through the gel layer was recorded at 20-second intervals, and the flow rate Fs(T) of the passing saline solution was measured. The flow rate Fs(T) was measured by dividing the increase in the mass (g) of saline solution passing through every 20 seconds by the passage time (s). The time it took for the hydrostatic pressure of the saline solution to become constant, resulting in a stable flow rate, was set as Ts. Using data measured over 10 minutes starting from Ts, the flow rate Fs(T=0) was calculated. That is, Fs(T) was plotted against time, and Fs(T=0) was calculated based on the results obtained using the least squares method. Fs(T=0) is the initial flow rate (g / s) of the saline solution through the gel layer. Then, the saline flow induction (SFC) is calculated according to the following formula (f).

[0752] SFC={Fs(T=0)×L0} / (ρ×A×ΔP)……(Formula f)

[0753] Here,

[0754] L0: Height of the gel layer (unit: cm);

[0755] ρ: Density of salt water (unit: g / cm³) 3 );

[0756] A: Cross-sectional area of ​​the gel layer (unit: cm²) 2 );

[0757] ΔP: Hydrostatic pressure applied to the gel layer (unit: dyne / cm) 2 ).

[0758] [CRC (Rate of Absorption at No Pressure)]

[0759] The CRC (Cyclic Ratio without Pressure) of the absorbent composition of the present invention was determined according to NWSP 241.0.R2 (19). Specifically, 0.2 g of the absorbent composition was placed in a nonwoven bag and immersed in a large excess of 0.9% by mass sodium chloride aqueous solution for 30 minutes to allow the absorbent composition to swell freely. Then, after dehydration using a centrifuge (250G), the CRC (Cyclic Ratio without Pressure) (unit: g / g) was determined.

[0760] [AAP (Absorption Ratio under Pressure)]

[0761] The AAP (Absorption Rate under Pressure) of the absorbent composition of the present invention was determined according to NWSP 242.0.R2 (19). Specifically, 0.9 g of the absorbent composition was subjected to a large excess of 0.9% by mass sodium chloride aqueous solution at 4.83 kPa (49 g / cm³). 2 After swelling for 1 hour under a load of 0.7 psi, the AAP (absorption rate under pressure) (unit: g / g) was measured.

[0762] [FHA (Fixed Height Absorption Value at 20cm)]

[0763] The FHA (Functional Height Absorption Value at a Height of 20 cm) of the absorbent composition of the present invention was determined according to the method described in paragraphs 0104 to 0116 of U.S. Patent Application Publication No. 2005 / 0003191.

[0764] [pH of the aqueous solution of the flowability improver]

[0765] The pH of the aqueous solution of the flowability improver of the present invention was measured using a portable pH meter D-71 manufactured by HORIBA while stirring the aqueous solution at 30 rpm.

[0766] <Manufacturing of Water-Absorbent Resins>

[0767] [Manufacturing Example 1]

[0768] (Preparation process of monomer aqueous solution)

[0769] A monomer aqueous solution (1') was prepared by adding 422.0 parts by weight of acrylic acid, 173.9 parts by weight of 48.5% sodium hydroxide aqueous solution, 2.5 parts by weight of polyethylene glycol diacrylate (average molecular weight: 523), 1.3 parts by weight of 2.0% trisodium diethylenetriaminepentaacetate aqueous solution, 0.2 parts by weight of polyethylene glycol 600 (weight average molecular weight 600, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.), and 403.1 parts by weight of deionized water to a 2L polypropylene container. The temperature of the monomer aqueous solution (1') exceeded 40°C due to the heat of neutralization and heat of solution generated during the mixing process.

[0770] (Polymerization process)

[0771] Next, while stirring the monomer aqueous solution (1'), cooling was performed. When the liquid temperature reached 40°C, 178.7 parts by mass of a 48.5% sodium hydroxide aqueous solution, adjusted to 40°C, was added to the monomer aqueous solution (1') over approximately 20 seconds under open atmospheric conditions, and mixing was initiated (the second stage of neutralization began). Thus, the monomer aqueous solution (1) was prepared. At this time, the liquid temperature of the monomer aqueous solution (1) rose to approximately 78°C due to the heat of neutralization and heat of dissolution generated during the mixing process. Furthermore, although precipitates were observed after the initial mixing of the sodium hydroxide aqueous solution into the monomer aqueous solution (1'), they gradually dissolved, resulting in a transparent and homogeneous monomer aqueous solution (1).

[0772] Next, under stirring, nitrogen gas was introduced into the monomer aqueous solution (1) for 5 seconds using a gas filter tube (TOP Corporation, particle number #4) at a pressure of 0.1 MPa and a flow rate of 0.1 L / min. Then, 18.4 parts by mass of 4.5% sodium persulfate aqueous solution were added to the nitrogen-introduced monomer aqueous solution (1). Immediately afterward, the monomer aqueous solution (1) was poured into a stainless steel trough-shaped container (bottom 340 mm × 340 mm, height 25 mm, inner surface: Teflon coating) under open atmospheric conditions. It should be noted that the time from the start of the second stage of neutralization to the pouring of the monomer aqueous solution (1) into the trough-shaped container was set to 65 seconds. Furthermore, the trough-shaped container was preheated to a surface temperature of 50°C using a heating plate (NEO HOTPLATE HI-1000 / Iinouchi Seieido Co., Ltd.) before the monomer aqueous solution (1) was poured in.

[0773] After the monomer aqueous solution (1) is introduced into the trough-shaped container, the polymerization reaction begins within 1 minute. During the polymerization reaction, the monomer aqueous solution (1) polymerizes while water vapor is generated and expands and foams in all directions. The resulting polymer then shrinks to a size slightly larger than the bottom of the trough-shaped container. Two minutes after the start of the polymerization reaction, the hydrogel (1) of the resulting polymer is removed from the trough-shaped container. It should be noted that this series of operations is carried out under open atmospheric conditions.

[0774] (Gel pulverization process)

[0775] Next, the hydrogel (1) obtained in the polymerization reaction was cut into pieces with a mass of approximately 60g each, and then pulverized using a meat grinder (HL-G22SN, plate aperture 6.0mm / manufactured by REMACOM Corporation) to obtain particulate hydrogel (1). The amount of hydrogel (1) added was approximately 360g / min, and while adding the hydrogel (1), deionized water at a temperature adjusted to 90°C was added to the meat grinder at a rate of 50g / min, and pulverization was carried out simultaneously. The D50 (mass-average particle size) of the particulate hydrogel (1) was 390μm.

[0776] (Drying process)

[0777] Next, the particulate hydrogel (1) was spread out and placed on a metal mesh with a mesh size of 300 μm, and then placed in a hot air dryer. The particulate hydrogel (1) was then dried by passing hot air at 190°C for 30 minutes to obtain a dried polymer (1). The dried polymer (1) contained no undried material.

[0778] (Grinding process, grading process)

[0779] Next, the dried polymer (1) was fed into a roller mill (WML type roller mill, manufactured by Inokuchi Giken Co., Ltd.) for pulverization, and then classified using two JIS standard sieves with mesh sizes of 710 μm and 150 μm. Through this operation, an irregularly broken, uncrosslinked, pre-crosslinking water-absorbing resin (1) was obtained, passing through the 710 μm sieve but remaining on the 150 μm sieve.

[0780] (Surface crosslinking process)

[0781] Next, relative to 100 parts by weight of the pre-crosslinked water-absorbing resin (1), an aqueous solution of a surface crosslinking agent comprising 0.2 parts by weight of 1,6-hexanediol, 0.4 parts by weight of triethylene glycol, and 3.0 parts by weight of deionized water was sprayed in a mist and mixed uniformly. The resulting mixture was then heated at 210°C for 40 minutes to perform surface crosslinking. The heated mixture was then graded using two JIS standard sieves with mesh sizes of 710 μm and 150 μm. This operation yielded a surface-crosslinked water-absorbing resin (1) that passed through a 710 μm mesh sieve but remained on a 150 μm mesh sieve.

[0782] [Manufacturing Example 2]

[0783] The water-absorbing resin (2) is manufactured under the following manufacturing conditions with reference to Reference Example 1 described in Japanese Patent No. 4926474.

[0784] (Preparation process of monomer aqueous solution)

[0785] 5.9 parts by weight of polyethylene glycol diacrylate (average molecular weight: 523) were added to 5500 parts by weight of sodium acrylate aqueous solution with a neutralization rate of 75 mol% (monomer concentration 38 mol%) and mixed to obtain monomer aqueous solution (2).

[0786] (Polymerization and gel pulverization process)

[0787] Next, the monomer aqueous solution (2) was degassed under a nitrogen atmosphere for 30 minutes.

[0788] Next, the monomer aqueous solution (2) was supplied to a reactor formed by covering a jacketed stainless steel double-arm kneader with two SIGMA-type blades and an internal volume of 10L. While maintaining the monomer aqueous solution (2) at 30°C, the system was purged with nitrogen. Then, while stirring the monomer aqueous solution (2), 2.46 parts by weight of sodium persulfate and 0.10 parts by weight of L-ascorbic acid were added, and polymerization began after about 1 minute. Then, polymerization was carried out at 30°C to 90°C, and the particulate hydrogel (2) was removed 60 minutes after the start of polymerization.

[0789] The resulting particulate hydrogel (2) was subdivided into particles with a diameter of approximately 5 mm.

[0790] (Drying process)

[0791] Next, the particulate hydrogel (2) was spread out and placed on a metal mesh with a mesh size of 300 μm, and then placed in a hot air dryer. The particulate hydrogel (2) was then dried by passing hot air at 150°C for 90 minutes to obtain a dried polymer (2). The dried polymer (2) contained no undried material.

[0792] (Grinding process, grading process)

[0793] Next, the dried polymer (2) was fed into a roller mill (WML type roller mill, manufactured by Inokuchi Giken Co., Ltd.) for pulverization, and then classified using two JIS standard sieves with mesh sizes of 850 μm and 150 μm. Through this operation, an irregularly broken, uncrosslinked, pre-crosslinking water-absorbing resin (2) was obtained, which passed through the 850 μm sieve but remained on the 150 μm sieve.

[0794] (Surface crosslinking process)

[0795] Next, relative to 100 parts by weight of the pre-crosslinked water-absorbing resin (2), an aqueous solution of a surface crosslinking agent comprising 0.03 parts by weight of ethylene glycol glycidyl ether, 0.5 parts by weight of propylene glycol, 0.3 parts by weight of 1,4-butanediol, and 3.0 parts by weight of water was sprayed in a mist and mixed uniformly. The resulting mixture was then heated at 200°C for 45 minutes to perform surface crosslinking. The heated mixture was then graded using two JIS standard sieves with mesh sizes of 850 μm and 150 μm. This operation yielded a surface-crosslinked water-absorbing resin (2) that passed through the 850 μm sieve but remained on the 150 μm sieve.

[0796] [Manufacturing Example 3]

[0797] (Preparation process of monomer aqueous solution)

[0798] A monomer aqueous solution (3') was prepared by adding 422.0 parts by weight of acrylic acid, 173.9 parts by weight of a 48.5% by weight sodium hydroxide aqueous solution, 2.3 parts by weight of polyethylene glycol diacrylate (average molecular weight: 523), 1.3 parts by weight of a 2.0% by weight trisodium diethylenetriaminepentaacetate aqueous solution, 0.2 parts by weight of polyethylene glycol 600 (weight average molecular weight 600, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.), and 403.2 parts by weight of deionized water to a 2L polypropylene container and mixing them. The temperature of the monomer aqueous solution (3') exceeded 40°C due to the heat of neutralization and heat of solution generated during the mixing process.

[0799] (Polymerization process)

[0800] Next, while stirring the monomer aqueous solution (3'), cooling was performed. When the liquid temperature reached 40°C, 178.7 parts by mass of a 48.5% sodium hydroxide aqueous solution, adjusted to 40°C, was added to the monomer aqueous solution (3') over approximately 20 seconds under open atmospheric conditions, and mixing was carried out (starting the second stage of neutralization). Thus, the monomer aqueous solution (3) was prepared. At this time, the liquid temperature of the monomer aqueous solution (1) rose to approximately 78°C due to the heat of neutralization and heat of dissolution generated during the mixing process. Furthermore, although precipitates were observed after the initial mixing of the sodium hydroxide aqueous solution into the monomer aqueous solution (3'), they gradually dissolved, resulting in a transparent and homogeneous monomer aqueous solution (3).

[0801] Next, with stirring, nitrogen gas was introduced into the monomer aqueous solution (3) for 5 seconds using a gas filter tube (TOP Corporation, particle number #4) at a pressure of 0.1 MPa and a flow rate of 0.1 L / min. Then, 18.4 parts by mass of 4.5% sodium persulfate aqueous solution were added to the nitrogen-introduced monomer aqueous solution (3). Immediately afterward, the monomer aqueous solution (3) was poured into a stainless steel trough-shaped container (bottom 340 mm × 340 mm, height 25 mm, inner surface: Teflon coating) under open atmospheric conditions. It should be noted that the time from the start of the second stage of neutralization to the pouring of the monomer aqueous solution (3) into the trough-shaped container was set to 67 seconds. Furthermore, the trough-shaped container was preheated to a surface temperature of 50°C using a heating plate (NEO HOTPLATE HI-1000 / Iinouchi Seieido Co., Ltd.) before the monomer aqueous solution (3) was poured in.

[0802] After the monomer aqueous solution (3) is poured into the trough-shaped container, the polymerization reaction begins within 1 minute. During the polymerization reaction, the monomer aqueous solution (3) polymerizes while water vapor is generated and expands and foams in all directions. The resulting polymer then shrinks to a size slightly larger than the bottom of the trough-shaped container. Two minutes after the start of the polymerization reaction, the hydrogel (3) of the resulting polymer is removed from the trough-shaped container. It should be noted that this series of operations is carried out under open atmospheric conditions.

[0803] (Gel pulverization process)

[0804] Next, the hydrogel (3) obtained in the polymerization reaction was cut into pieces with a mass of approximately 60g each, and then pulverized using a meat grinder (HL-G22SN, plate aperture 8.0mm / manufactured by REMACOM Corporation) to obtain particulate hydrogel (3). The amount of hydrogel (3) added was approximately 360g / min, and while adding the hydrogel (3), deionized water at a temperature adjusted to 90°C was added to the meat grinder at a rate of 50g / min, and pulverization was carried out simultaneously. The D50 (mass-average particle size) of the particulate hydrogel (3) was 700μm.

[0805] (Drying process)

[0806] Next, the particulate hydrogel (3) was spread out and placed on a metal mesh with a mesh size of 300 μm, and then placed in a hot air dryer. The particulate hydrogel (3) was then dried by passing hot air at 190°C for 30 minutes to obtain a dried polymer (3). The dried polymer (3) contained no undried material.

[0807] (Grinding process, grading process)

[0808] Next, the dried polymer (3) was fed into a roller mill (WML type roller mill, manufactured by Inokuchi Giken Co., Ltd.) for pulverization, and then classified using two JIS standard sieves with mesh sizes of 850 μm and 150 μm. Through this operation, an irregularly broken, uncrosslinked, pre-crosslinking water-absorbing resin (3) was obtained, which passed through the 850 μm sieve but remained on the 150 μm sieve.

[0809] (Surface crosslinking process)

[0810] Next, using a straight tube with an inner diameter of 0.2 mm (average droplet diameter: 0.4 mm (400 μm)), relative to 100 parts by weight of the absorbent resin (3) before surface crosslinking, 0.01 parts by weight of an aqueous solution containing 0.2 parts by weight of 1,6-hexanediol, 0.4 parts by weight of triethylene glycol, 10% by weight of polyoxyethylene (20) sorbitan monostearate (flow enhancer, trade name: Rheodol TW-S120V, manufacturer: Kao Corporation) (flow enhancer addition amount: 10 ppm), and 3.0 parts by weight of deionized water in an aqueous solution of the surface crosslinking agent (containing flow enhancer. Flow enhancer concentration in the aqueous solution: 0.03% by weight, pH of the aqueous solution: 4.7) was added and mixed uniformly. It should be noted that the above-mentioned surface crosslinking agent aqueous solution was added while stirring the water-absorbing resin (3) using a three-in-one motor equipped with anchor-type stirring blades (diameter: 57 mm, height: 70 mm) made of a metal rod with a diameter of 3 mm and a rotation speed of 450 rpm (circumferential speed: 1.34 m / s). The stirring was counted for 10 seconds from the start of addition (mixing force index: 33500), and then the resulting mixture was heated at 210°C for 40 minutes to perform surface crosslinking. Next, the mixture after heat treatment was graded using two JIS standard sieves with mesh sizes of 850 μm and 150 μm. Through this operation, surface-crosslinked water-absorbing resin (3) was obtained that passed through the 850 μm sieve and remained on the 150 μm sieve.

[0811] [Manufacturing Example 4]

[0812] In the surface crosslinking process of Manufacturing Example 3, the amount of an aqueous solution containing 10% by mass of polyoxyethylene (20) sorbitan monostearate (flow enhancer, trade name: Rheodol TW-S120V, manufacturer: Kao Corporation) was changed to 0.03 parts by mass (flow enhancer addition amount: 30 ppm) to obtain a surface crosslinking agent aqueous solution (containing flow enhancer. Flow enhancer concentration in aqueous solution: 0.08% by mass, pH of aqueous solution: 4.7). In the addition of the above surface crosslinking agent aqueous solution, the stirring time was changed to count 30 seconds from the start of addition (mixing force index: 100500). Otherwise, the same operation as in Manufacturing Example 3 was performed to obtain the surface-crosslinked water-absorbing resin...

Claims

1. A method for manufacturing a water-absorbing agent composition, wherein, The water-absorbing agent composition uses water-absorbing resin as the main component, and the manufacturing method includes: a monomer aqueous solution preparation step, a polymerization step, a gel pulverization step, a drying step, a pulverization step, a classification step, and a surface crosslinking step. In the process of said surface crosslinking step or in the process after said surface crosslinking step, the method of manufacturing said water-soluble flowability enhancer having a mass-average molecular weight of more than 0 ppm and less than 200 ppm relative to said water-absorbing resin and a mass-average molecular weight of more than 200 and less than 50,000 satisfies all of the following (a) to (d): (a) The specific surface area of ​​the water-absorbing resin is 25 m². 2 / kg or more; (b) When the water-soluble flowability improver is mixed into the water-absorbing resin, the water-soluble flowability improver is in the form of an aqueous solution of 0.01% by mass or more and 20% by mass or less; (c) When the aqueous solution is added to / mixed into the absorbent resin, the average droplet diameter of the aqueous solution is 10 μm or more and 1 mm or less; (d) When the aqueous solution is added to / mixed into the absorbent resin, the mixing power index defined by the following (Formula 1) is 70000 or more. [Formula 1] 2. The manufacturing method according to claim 1, wherein, The kinetic friction coefficient of the water-absorbing resin with a particle size of 300 μm or more and less than 600 μm after adding the water-soluble flowability improver is less than 0.

80.

3. The manufacturing method according to claim 1, wherein, The water-soluble flowability improver is selected from one or more of nonionic substances, zwitterionic substances, anionic substances, and cationic substances.

4. The manufacturing method according to claim 3, wherein, The nonionic material is selected from polyols, modified polyol hydroxyl groups, side-chain and / or terminal polyether modified polysiloxanes, and epoxy alkyl adducts of higher aliphatic amines. The zwitterionic substance is selected from alkyl betaine and alkyl amine oxide; The anionic substance is selected from alkyl sulfate salts, sulfate salts, sulfonates, dicarboxylate salts, alkylamine diacetates, phosphate salts of higher alcohol epoxide adducts, and carboxylate salts of higher alcohol epoxide adducts; The cationic substance is selected from ammonium salts.

5. The manufacturing method according to claim 1, wherein, The water-soluble flowability enhancer contains at least one selected from nonionic substances.

6. The manufacturing method according to claim 1, wherein, The water-soluble flowability enhancer comprises at least one selected from nonionic substances having a polyalkylene glycol chain in the molecule.

7. The manufacturing method according to claim 1, wherein, The water-soluble flowability improver contains at least one selected from polyols and polyol hydroxyl modifiers.

8. The manufacturing method according to claim 1, wherein, The pH of the aqueous solution is above 4.

5.

9. The manufacturing method according to claim 1, wherein, The water-absorbing resin and the water-absorbing agent composition each contain 50% by mass or more particles with a particle size of 300 μm or more and less than 600 μm, and the reduction rate of the kinetic friction coefficient calculated by the following (Formula 2) is 10% or more. [Formula 2] In equation 2, A: The coefficient of kinetic friction of water-absorbing resin particles with a particle size of 300μm or larger and less than 600μm before the addition of water-soluble flow improvers; B: The coefficient of kinetic friction of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition after the addition of a water-soluble flow improver.

10. The manufacturing method according to claim 1, wherein, The step of further adding polyalkylene glycol is included between at least one step selected from the preparation step of the monomer aqueous solution, the polymerization step, and the gel pulverization step, and / or between each of the steps.

11. The manufacturing method according to claim 10, wherein, The polyalkylene glycol is polyethylene glycol with a mass-average molecular weight of less than 3000.

12. The manufacturing method according to claim 10, wherein, The amount of the polyalkylene glycol added is 0.01% by mass or more and 0.25% by mass or less, relative to the total mass of the monomer contained in the aqueous monomer solution.

13. A water-absorbing composition comprising a water-absorbing resin as the main component, the water-absorbing composition comprising a water-soluble flowability enhancer, and satisfying all of the following (1) to (5): (1) The specific surface area of ​​the absorbent composition is 25 m². 2 / kg or more; (2) The surface tension of the absorbent composition is 56 mN / m or higher; (3) The flow rate of the absorbent composition is 10.0 g / s or higher; (4) The mass proportion of particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition is 50% by mass or more; (5) The kinetic friction coefficient of the particles with a particle size of 300 μm or more and less than 600 μm in the absorbent composition is less than 0.

80.

14. The absorbent composition according to claim 13, wherein, The absorbent composition has a Vortex absorption rate of less than 50 seconds.

15. The absorbent composition according to claim 13, wherein, The absorbent composition has an SFC (salt water) flow induction rate of 1×10⁻⁶. -7 cm 3 • above sec / g.

16. The absorbent composition according to claim 13, wherein, The absorbent composition has a D50 (weight-average particle size) of 250 μm or more and less than 550 μm, and the mass percentage of particles with a particle size of less than 150 μm in the absorbent composition is less than 3% by mass.

17. The absorbent composition according to claim 13, wherein, The absorbent composition has an AAP (absorption rate under pressure) of 20 g / g or more.

18. An absorbent comprising a water-absorbing composition according to any one of claims 13 to 17.

19. The absorber according to claim 18, wherein, The weight per unit area of ​​pulp is 300 g / m³ 2 the following.

20. The absorber according to claim 18, wherein, The absorbent composition has a unit area weight of 450 g / m². 2 the following.

21. An absorbent article comprising an absorbent according to any one of claims 18 to 20.

22. The absorbent article according to claim 21, wherein, The absorbent material does not contain pulp.

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