WO2020137241A1

WO2020137241A1 - Water-absorbent resin particles and method for producing same

Info

Publication number: WO2020137241A1
Application number: PCT/JP2019/044901
Authority: WO
Inventors: 佑介松原; 武南里; 艶ブン王; 宮島　徹
Original assignee: Ｓｄｐグローバル株式会社
Priority date: 2018-12-26
Filing date: 2019-11-15
Publication date: 2020-07-02
Also published as: JPWO2020137241A1; JP2023099531A; CN113227218A

Abstract

Provided are water-absorbent resin particles that quickly draw liquid from a nonwoven fabric and do not pose the problem of liquid leakage even if the content of hydrophilic fibers in an absorber is small, and water-absorbent resin particles having high absorption performance for blood capable of actualizing an excellent dry feeling when used in an absorbent article, an absorber and an absorbent article containing the same, and a method for producing water-absorbent resin particles. The present invention is water-absorbent resin particles having a structure in which resin particles containing a crosslinked polymer (A) having as essential structural units a water-soluble vinyl monomer (a1) and a crosslinking agent (b) are surface crosslinked by at least one surface crosslinking agent (d), wherein the water-absorbent resin particles have a weight average particle size of 200-420 μm and a particle size distribution index (SPAN), measured by an image analysis-type particle size distribution measurement device, of 0.30-0.75.

Description

Water absorbent resin particles and method for producing the same

The present invention relates to water absorbent resin particles and a method for producing the same.

For hygiene materials such as disposable diapers, sanitary napkins and incontinence pads, a mixture of hydrophilic fibers such as pulp and water-absorbent resin particles mainly containing acrylic acid (salt) is widely used as an absorber. Consumers in recent years tend to demand more comfort, and the demand is shifting to sanitary materials having higher dryness and thinner thickness, and accordingly, those having high dryness are desired and hydrophilic It has been desired to reduce the amount of use of the functional fiber. Therefore, it has become necessary for the water-absorbent resin particles themselves to have the role of high initial absorption rate and liquid diffusibility that the hydrophilic fibers have been playing so far. Further, in order to improve the surface dryness of the absorbent body, not only the water absorption rate of the water-absorbent resin particles themselves, but also the water-absorbent resin particles with fast liquid drawing from the surface nonwoven fabric used in the absorbent article are strongly desired. ing.

As a means for improving the water absorption rate of the water absorbent resin particles, a method of physically increasing the surface area of the water absorbent resin is generally used. For example, a method of adding microballoons to the water absorbent resin (Patent Document 1), a method of improving the water absorption rate by reducing the particle size of the water absorbent resin particles in the sieving process (Patent Document 2), and the like have been proposed. .. However, in an absorbent body in which these water-absorbent resin particles are applied to absorbent articles (paper diapers, etc.), there is no problem if the content of hydrophilic fibers is higher than the content of water-absorbent resin particles. When the content of (1) is small or not contained, there is a problem that liquid is slowly drawn from the nonwoven fabric and leakage occurs.

On the other hand, it is known that the performance of the water absorbent resin is improved by controlling the particle size distribution within a certain range (Patent Documents 3, 4, and 5). There is a problem with the slow drainage and the leak is not improved. Further, a water-absorbent resin having a narrower particle size distribution has not been studied so far because of a problem in productivity.

When blood is absorbed, unlike urine, it contains less solids such as protein and blood cells, and when it is menstrual blood, it has less water than blood. There is a problem that the water absorption performance is lower than in some cases.

Conventionally, as a technique for improving the absorption performance of blood, by attaching kaolinite to the surface of the water-absorbent resin particles and improving the blood absorption inhibition due to wetting of the water-absorbent resin particles, it is excellent for blood. There is known a method for producing a blood absorbing material having absorption performance (see Patent Documents 6 and 7). Further, by attaching a water-soluble cationic polymer to the water-absorbent resin particles and agglutinating the red blood cells in the blood, it is possible to suppress the film formation due to the accumulation of red blood cells on the surface of the water-absorbent resin particles, and to obtain excellent blood absorption performance. A sanitary product has is known (see Patent Document 8). In addition, a method of increasing the blood absorption amount by adding an additive having a specific solubility parameter (see Patent Document 9), and improving the repetitive absorbability of blood by making the particle size distribution of the water-absorbent resin particles double A method (see Patent Document 10) and the like are disclosed. However, in the above-mentioned conventional technique, not only the absorption performance is not sufficiently exhibited for blood, but there is a problem in the dry feeling of the absorber, and when a specific particle size distribution is used, a special production process is required for that purpose. There was also a problem in productivity, such as the need for.

Special table 2012-522880 bulletin JP-A-11-43508 JP 2004-261797 A Japanese Patent Publication No. 2009-510177 JP, 2017-222875, A WO 00/10496 pamphlet Japanese Patent Laid-Open No. 2000-51690 JP, 2016-107100, A Japanese Patent Laid-Open No. 2018-021133 Japanese Patent Laid-Open No. 11-246625

The object of the present invention is to provide a water-absorbent resin particle that does not cause a problem of liquid leakage, even if the content of hydrophilic fibers in the absorbent is small, and that has high water-absorbing performance for blood. It is another object of the present invention to provide a water-absorbent resin particle capable of exhibiting an excellent dry feeling when used for an absorbent article, an absorber and an absorbent article containing the same, and a method for producing the water-absorbent resin particle.

In the present invention, resin particles containing a water-soluble vinyl monomer (a1) and a cross-linked polymer (A) containing a cross-linking agent (b) as an essential constituent unit are surface-crosslinked with at least one surface cross-linking agent (d). The water-absorbent resin particles having a structure, having a weight average particle diameter of 200 to 420 μm, and having a particle size distribution index (SPAN) represented by the following formula 1 measured by an image analysis type particle size distribution measuring device of 0. Water-absorbent resin particles having a particle size of 30 to 0.75.
Particle size distribution index (SPAN)=(90% particle size in volume-based integrated particle size-10% particle size in volume-based integrated particle size)/(50% particle size in volume-based integrated particle size) (Equation 1)
The present invention also provides a method for producing the above water-absorbent resin, which comprises polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and a cross-linking agent (b) as essential constituent units to form a cross-linked polymer (A). A step of obtaining a hydrogel containing water, a step of kneading and chopping the hydrogel to obtain hydrogel particles, a step of pulverizing the hydrogel particles, a step of drying and pulverizing the hydrogel particles to obtain resin particles containing (A) And a surface treatment step of surface-treating the resin particles with a surface cross-linking agent (d), wherein a hydrophobic substance (C) is added in the gel crushing step or the surface treatment step, at which time the hydrophobic substance (C) is added. The melting point of is less than or equal to the temperature of the step of adding (C).

The water-absorbent resin particles of the present invention have a particle size and a particle size distribution within a specific range and exhibit an excellent absorption rate and liquid passage rate. It also shows excellent blood absorption and blood absorption rate. Therefore, the absorbent article to which the water-absorbent resin of the present invention is applied (paper diapers and sanitary napkins, etc.), even when the content of hydrophilic fibers in the absorbent is small, from the nonwoven fabric after contact with the liquid to be absorbed Drains quickly and does not leak.

In the water-absorbent resin of the present invention, the resin particles containing the cross-linked polymer (A) containing the water-soluble vinyl monomer (a1) and the cross-linking agent (b) as essential constituent units are formed by at least one surface cross-linking agent (d). It is a water-absorbent resin particle having a surface-crosslinked structure.

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and known monomers, for example, at least one water-soluble substituent and ethylenic vinyl group disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 36485553 are used. Vinyl monomers having a saturated group (for example, anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers), anionic vinyl monomers and nonionic compounds disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883. Vinyl monomer and cationic vinyl monomer, and selected from the group consisting of carboxy group, sulfo group, phosphono group, hydroxyl group, carbamoyl group, amino group and ammonio group disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982. Vinyl monomers having at least one of

The water-soluble vinyl monomer (a1) is preferably an anionic vinyl monomer, more preferably a carboxy (salt) group, a sulfo (salt) group, an amino group, a carbamoyl group, an ammonio group or a mono-, di- or tri-alkyl group. It is a vinyl monomer having an ammonio group. Among these, more preferably a vinyl monomer having a carboxy (salt) group or a carbamoyl group, further preferably (meth)acrylic acid (salt) and (meth)acrylamide, particularly preferably (meth)acrylic acid (salt), Most preferably, it is acrylic acid (salt).

In addition, a "carboxy (salt) group" means a "carboxy group" or a "carboxylate group", and a "sulfo (salt) group" means a "sulfo group" or a "sulfonate group". Further, (meth)acrylic acid (salt) means acrylic acid, acrylic acid salt, methacrylic acid or methacrylic acid salt, and (meth)acrylamide means acrylamide or methacrylamide. Examples of the salt include alkali metal (lithium, sodium and potassium etc.) salts, alkaline earth metal (magnesium and calcium etc.) salts, ammonium (NH ₄ ) salts and the like. Among these salts, the alkali metal salts and ammonium salts are preferable, the alkali metal salts are more preferable, and the sodium salts are particularly preferable, from the viewpoint of absorption characteristics.

When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the water-soluble vinyl monomer (a1), a part of the acid group-containing monomer can be neutralized with a base. As the base to be neutralized, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide and alkali metal carbonates such as sodium carbonate, sodium hydrogen carbonate and potassium carbonate can be usually used. Neutralization may be carried out before or during the polymerization of the acid group-containing monomer in the production process of the water-absorbent resin, and the acid group-containing polymer may be added to the acid group-containing polymer in the state of a hydrogel containing the cross-linked polymer (A) described later. It can also be neutralized.

When the acid group-containing monomer is used, the degree of neutralization of the acid group is preferably 50 to 80 mol %. When the degree of neutralization is less than 50 mol %, the resulting hydrogel polymer may have high tackiness, which may deteriorate workability during production and use. Furthermore, the centrifugal retention amount of the water-absorbent resin particles obtained may decrease. On the other hand, when the degree of neutralization exceeds 80%, the pH of the obtained resin becomes high, and there is a possibility that the safety of the skin of the human body may be concerned.

As the constitutional unit of the crosslinked polymer (A), in addition to the water-soluble vinyl monomer (a1), another vinyl monomer (a2) copolymerizable with them can be used as the constitutional unit. As the other vinyl monomer (a2), one type may be used alone, or two or more types may be used in combination.

The other copolymerizable vinyl monomer (a2) is not particularly limited and is known (for example, the hydrophobic vinyl monomer disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 36485553, JP-A No. 2003-165883). The vinyl monomers disclosed in paragraph 0025 and paragraph 0058 of Japanese Unexamined Patent Application Publication No. 2005-75982) can be used. Specifically, for example, vinyl monomers (i) to (iii) below can be used. Can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and vinylnaphthalene, and halogen-substituted styrene such as dichlorostyrene.
(Ii) C2-C20 aliphatic ethylenic monomer alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkadienes (butadiene, isoprene, etc.).
(Iii) C5-C15 alicyclic ethylenic monomers, monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylene vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidene norbornene, etc.] and the like.

The content of the other vinyl monomer (a2) unit is preferably 0 to 5 mol %, more preferably 0 to 3 mol based on the number of moles of the water-soluble vinyl monomer (a1) unit from the viewpoint of absorption performance and the like. %, particularly preferably 0 to 2 mol %, particularly preferably 0 to 1.5 mol %, and the content of other vinyl monomer (a2) units is 0 mol% from the viewpoint of absorption performance and the like. Most preferred.

The cross-linking agent (b) is not particularly limited and is known (for example, a cross-linking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 36485553, which reacts with a water-soluble substituent group). Crosslinking agent having at least one functional group to be obtained and having at least one ethylenically unsaturated group, and crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP-A-2003-165883 Cross-linking agent having two or more ethylenically unsaturated groups, a cross-linking agent having an ethylenically unsaturated group and a reactive functional group, and a cross-linking agent having two or more reactive substituents. The cross-linking vinyl monomer disclosed in paragraph 0059 of JP-A-2005-75982 and the cross-linking agent of the cross-linkable vinyl monomer disclosed in paragraphs 0015 to 0016 of JP-A-2005-95759 can be used. .. Among these, a crosslinking agent having two or more ethylenically unsaturated groups is preferable from the viewpoint of absorption performance, and more preferable are poly(meth)allyl ethers of polyhydric alcohols having 2 to 40 carbon atoms and carbon numbers. (Meth)acrylate of polyhydric alcohol having 2 to 40 carbons, (meth)acrylamide of polyhydric alcohol having 2 to 40 carbons, polyallyl ether of polyhydric alcohol having 2 to 40 carbons, and most preferable Pentaerythritol triallyl ether. As the crosslinking agent (b), one type may be used alone, or two or more types may be used in combination.

The content (mol %) of the crosslinking agent (b) unit is the number of moles of the water-soluble vinyl monomer (a1) unit, and when other vinyl monomer (a2) is used, the total number of moles of (a1) to (a2) Based on the above, 0.001 to 5 is preferable, 0.005 to 3 is more preferable, and 0.01 to 1 is particularly preferable. Within this range, the absorption performance will be further improved.

The method for producing water-absorbent resin particles of the present invention comprises a cross-linked polymer (A) obtained by polymerizing a monomer composition containing the above-mentioned water-soluble vinyl monomer (a1) and a cross-linking agent (b) as essential constituent units. Polymerization step to obtain hydrous gel, kneading and chopping the hydrous gel to obtain hydrous gel particles, and gel pulverizing step, and drying and pulverizing the hydrous gel particles to classify resin particles containing a crosslinked polymer (A). Including the step of obtaining.

As the polymerization step, known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc.; JP-A-55-133413, etc.), known suspension polymerization method, reverse phase suspension polymerization (JP-B-54- 30710, JP 56-26909 A, JP 1-5808 A, etc.) to obtain a hydrogel containing a crosslinked polymer (A) (a hydrogel in which the crosslinked polymer contains water). You can The crosslinked polymer (A) may be a single type or a mixture of two or more types.

Among the polymerization methods, the solution polymerization method is preferable, and since it is advantageous in terms of production cost that it is not necessary to use an organic solvent or the like, particularly preferable is the aqueous solution polymerization method, which has a large centrifugal retention amount, and water. The aqueous solution adiabatic polymerization method is most preferable because a water-absorbent resin having a small amount of soluble components can be obtained and temperature control during polymerization is unnecessary.

When carrying out aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used, and as the organic solvent, methanol, ethanol, acetone, methylethylketone, N,N-dimethylformamide, dimethylsulfoxide and two or more of them can be used. A mixture of
When carrying out aqueous solution polymerization, the amount of organic solvent used (% by weight) is preferably 40 or less, and more preferably 30 or less, based on the weight of water.

The polymerization concentration, that is, the charged concentration (% by weight) of the water-soluble vinyl monomer (a1) and the other vinyl monomer (a2) in the polymerization liquid is not particularly limited, but the weight of the polymerization liquid, that is, the water-soluble vinyl monomer, for example, 10 to 55 are preferable, and 20 to 45 are more preferable, based on the total weight of the monomer (a1) and other vinyl monomer (a2), the solvent, the cross-linking agent (b) and the below-mentioned polymerization catalyst and polymerization control agent. If the polymerization concentration is lower than this range, the productivity will be low, and if the polymerization concentration is higher than this range, side reactions such as self-crosslinking will occur, and the centrifugal retention amount of the water-absorbent resin particles obtained will be reduced.

When a catalyst is used for the polymerization, conventionally known radical polymerization catalysts can be used, and examples thereof include azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2′-azobis(2-amidinopropane) hydrochloride. Etc.], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate and sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, persuccinate] Oxide and di(2-ethoxyethyl)peroxydicarbonate and the like] and redox catalyst (alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite and ascorbic acid and other reducing agents and alkali metal persulfate, (Combined with an oxidizing agent such as ammonium persulfate, hydrogen peroxide and organic peroxide). These catalysts may be used alone or in combination of two or more.
The amount (% by weight) of the radical polymerization catalyst used is 0.0005 based on the total weight of the water-soluble vinyl monomer (a1) and (a1) to (a2) when the other vinyl monomer (a2) is used. It is preferably from 5 to 5, more preferably from 0.001 to 2.

During the polymerization, a polymerization control agent such as a chain transfer agent may be used in combination, if necessary, and specific examples thereof include sodium hypophosphite, sodium phosphite, alkyl mercaptans, alkyl halides and thiocarbonyl compounds. Etc. These polymerization control agents may be used alone or in combination of two or more thereof.
The amount (% by weight) of the polymerization control agent is 0.0005 based on the total weight of the water-soluble vinyl monomer (a1) and (a1) to (a2) when the other vinyl monomer (a2) is used. It is preferably from 5 to 5, more preferably from 0.001 to 2.

When the suspension polymerization method or the reverse phase suspension polymerization method is adopted as the polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersant or surfactant, if necessary. Further, in the case of the reverse phase suspension polymerization method, the polymerization can be carried out using a conventionally known hydrocarbon solvent such as xylene, normal hexane, and normal heptane.

The polymerization initiation temperature can be appropriately adjusted depending on the type of catalyst used, but is preferably 0 to 100°C, more preferably 2 to 80°C.

The gel crushing step is a step of kneading and cutting the hydrogel containing the crosslinked polymer (A) obtained in the above-mentioned polymerization step to obtain hydrogel particles. The size (longest diameter) of the hydrogel particles after the gel crushing step is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 500 μm to 1 cm. Within this range, the drying property in the drying step will be further improved.

The gel pulverization can be performed by a known method, and kneading and shredding can be performed using a pulverizing device (eg, kneader, universal mixer, uniaxial or biaxial kneading extruder, mincing machine, meat chopper, etc.). From the viewpoint of controlling the water absorption time by the Vortex method, a crushing device equipped with a kneading and extruding mechanism (for example, a uniaxial or biaxial kneading extruder, a mincing machine, etc.) is preferable.

The solid content concentration (% by weight) of the gel in the gel crushing step is preferably 10 to 55, more preferably 25 to 45. If the solid content concentration is lower than this range, the productivity will be poor, and if it is higher than this range, the energy required for pulverization will be too high and the pulverization device may be damaged.

The gel temperature in the gel crushing step is preferably 70 to 120°C, more preferably 80 to 110°C. If the gel temperature is lower than this range, a cooling step is required after the polymerization step, unnecessary energy is required, and the stickiness of the gel increases, and the size of hydrous gel particles tends to increase, and the gel temperature falls within this range. If it is higher, bumping of water occurs and stable pulverization cannot be performed.

Further, as described above, the hydrogel of the acid group-containing polymer obtained after the polymerization can be neutralized by mixing a base before or during the gel crushing step. The preferred range of the base and the degree of neutralization used when neutralizing the acid group-containing polymer is the same as when the acid group-containing monomer is used.

The resin particles containing the crosslinked polymer (A) can be obtained by drying the hydrated gel particles, pulverizing and classifying them.

The method for drying the water-containing gel particles (including distilling off the solvent) includes drying with hot air at a temperature of 80 to 230° C., thin film drying with a drum dryer heated to 100 to 230° C. (heating ) A reduced pressure drying method, a freeze drying method, an infrared drying method, decantation, filtration and the like can be applied.

When the solvent contains water, the water content (% by weight) after drying is preferably 0 to 20, more preferably 1 to 15, particularly preferably 2 to 13, based on the weight of the crosslinked polymer (A). Most preferably, it is 3-12. Within this range, the absorption performance will be further improved.

When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after drying is preferably 0 to 10, more preferably 0 to 5, and particularly preferably, based on the weight of the crosslinked polymer (A). It is 0 to 3, most preferably 0 to 1. Within this range, the absorbent performance of the water absorbent resin particles will be further improved.

In addition, the content and water content of the organic solvent are measured by an infrared moisture measuring instrument [for example, JE400 manufactured by KETT Co., Ltd.: 120±5° C., 30 minutes, atmospheric humidity before heating 50±10% RH, lamp specification 100V. , 40 W] and the weight loss of the measurement sample when heated.

After drying, other components such as residual solvent and residual crosslinking component may be included to some extent as long as the performance is not impaired.

The particle size and particle size distribution of the resin particles containing the crosslinked polymer (A) are adjusted by classifying after crushing. The method of crushing is not particularly limited, and a known crushing device (for example, a hammer crusher, an impact crusher, a roll crusher, a shett airflow crusher, etc.) can be used. Among these, a roll type crusher is preferable from the viewpoint of controlling the particle size distribution. Further, in order to control the particle size distribution, the sieve product after classification, that is, the particles remaining on the sieve having a specific opening may be pulverized again. When the sieved product is pulverized again, the respective pulverizers may be the same, different pulverizers may be used, or different types of pulverizers may be used.

Regarding the classification method, in order to control the particle size distribution of the crushed resin particles, a plurality of sieves with specific openings may be used or a single sieve may be used for classification. The classifying device is not particularly limited, but a known method such as a vibrating screen, an in-plane moving screen, a movable mesh type screen, a forced stirring screen, and a sonic screen is used, and a vibrating screen and an in-plane moving screen are preferably used. In order to control the particle size distribution of resin particles, some or all of the particles remaining on the sieve with a specific opening (oversize product) and particles that have passed through the sieve with a specific opening (undersize product) are removed. It is preferable.

The size of the sieve to be the sieve product is preferably 850 to 250 μm, more preferably 710 to 300 μm, particularly preferably 500 to 425 μm, and the size of the sieve to be the undersize product is preferably 500 to 90 μm, further preferably 425. ˜106 μm, particularly preferably 300˜150 μm. If the amount is out of these ranges, the ratio of the particles to be reused, which will be described later, increases, and not only the productivity decreases, but also the desired particle size distribution may not be obtained.

Note that known technology for reusing particles removed by sieving (particularly unsieved products) can be used. For example, a method of mixing hot water and fine powder of a water-absorbent resin and drying (US Pat. No. 6,228,930) or a method of mixing fine powder of a water-absorbent resin with a water-soluble vinyl monomer and polymerizing (US Pat. No. 5,264,495). ), a method in which water is added to fine powder of the water-absorbent resin and granulation is performed at a specific surface pressure or higher (European Patent No. 844270), the fine powder of the water-absorbent resin is sufficiently moistened to form an amorphous gel and dried. It is possible to use a method of pulverizing (US Pat. No. 4,950,692), a method of mixing fine powder of a water absorbent resin and a polymer gel (US Pat. No. 5,478,879), and the like.

The weight average particle diameter (μm) of the resin particles containing the crosslinked polymer (A) after classification is preferably 200 to 420, more preferably 250 to 410, particularly preferably 300 to 400, and most preferably 350 to 390. Is. When it is larger than this range, the absorption time by the Vortex method becomes long and the absorption amount of ion-exchanged water for 60 seconds decreases, and when it is smaller than this range, spot absorption and gel blocking are likely to occur.

The weight average particle diameter is determined by using a low tap test sieve shaker and a standard sieve (JIS Z8801-1:2006), Perry's Chemical Engineers Handbook 6th edition (MacGlow Hill Book Company, 1984). , Page 21). That is, the JIS standard sieve is combined from the top in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and a saucer. About 50 g of the measurement particles are put into the uppermost sieve, and shaken for 5 minutes by a low tap test sieve shaker. The weight of the measured particles on each sieve and the pan is weighed, and the total is taken as 100% by weight to obtain the weight fraction of the particles on each sieve, and this value is used as a logarithmic probability paper [the horizontal axis indicates the sieve opening (particle size ), the vertical axis is a weight fraction], and a line connecting the points is drawn to obtain a particle diameter corresponding to a weight fraction of 50% by weight, which is defined as a weight average particle diameter.

Since the smaller the content of the fine particles contained in the resin particles containing the crosslinked polymer (A) after classification, the better the absorption performance, fine particles having a particle size of 106 μm or less (preferably 150 μm or less) in the total weight of the resin particles. The content (% by weight) of is preferably 3 or less, more preferably 1 or less. The content of the fine particles can be determined using the graph created when determining the above weight average particle diameter.

The particle size distribution index (SPAN) of the resin particles containing the crosslinked polymer (A) after classification, measured by an image analysis type particle size distribution measuring device, is 0.30 to 0.75. If it is higher than this range, the absorption amount of the ion-exchanged water absorbed for 60 seconds is deteriorated, and the drainage from the nonwoven fabric is deteriorated. Also, setting the SPAN lower than this range is not realistic because the reuse ratio of the water-absorbent resin particles becomes too high. It is preferably 0.30 to 0.65, more preferably 0.30 to 0.60.

The particle size distribution index (SPAN) indicates the degree of spread of the particle size distribution. The smaller this value, the narrower the particle size distribution and the more uniform the particle diameter. SPAN can be calculated by measuring the weight fraction of 10%, the weight fraction of 50%, and the weight fraction of 90% using a logarithmic probability paper when measuring the weight average particle diameter. In the invention, the calculation can be performed in finer sections and a more accurate value can be obtained as compared with the method using the standard sieve, and therefore the calculation is performed by measuring with an image analysis type particle size distribution measuring device. For example, it can be measured using a Camsizer (registered trademark) image analysis system (Lecce Technology Co., Ltd.).

The particle size distribution index (SPAN) is calculated from (Equation 1). The volume-based cumulative particle size here is the minimum value obtained by measuring the maximum crossover length (maximum code diameter) of the projected image of the particle from 64 directions, and the particle size (Xcmin) is measured. Particle diameters corresponding to 50% and 90% were determined.
Particle size distribution index (SPAN)=(90% particle size in volume-based integrated particle size-10% particle size in volume-based integrated particle size)/(50% particle size in volume-based integrated particle size) (Equation 1)

The weight average particle diameter, the content of fine particles and the particle size distribution index (SPAN) of the water absorbent resin particles of the present invention can be adjusted even after the surface treatment step described later, but the surface treatment described below (including surface crosslinking) From the viewpoint of uniformity, it is preferable to adjust to the above range at the stage of resin particles before surface treatment.

The water absorbent resin particles of the present invention preferably contain a hydrophobic substance (C) from the viewpoint of liquid diffusibility. Examples of the hydrophobic substance (C) include a hydrophobic substance (C1) containing a hydrocarbon group and a hydrophobic substance (C2) which is a polysiloxane.

As the hydrophobic substance (C1) containing a hydrocarbon group, polyolefin resin, polyolefin resin derivative, polystyrene resin, polystyrene resin derivative, wax, long chain fatty acid ester, long chain fatty acid and its salt, long chain aliphatic alcohol, Quaternary ammonium salt type surfactants, mixtures of two or more of these, and the like are included.

As a polyolefin resin, a weight of an olefin having 2 to 4 carbon atoms (ethylene, propylene, isobutylene, isoprene, etc.) as an essential constituent monomer (the content of the olefin is at least 50% by weight based on the weight of the polyolefin resin). Examples thereof include polymers having an average molecular weight of 1,000 to 1,000,000 (eg, polyethylene, polypropylene, polyisobutylene, poly(ethylene-isobutylene), isoprene and the like).

As the polyolefin resin derivative, a polymer having a weight average molecular weight of 1,000 to 1,000,000 obtained by introducing a carboxy group (—COOH) or 1,3-oxo-2-oxapropylene (—COOCO—) into a polyolefin resin (for example, polyethylene heat Degradation products, polypropylene thermal degradation products, maleic acid modified polyethylene, chlorinated polyethylene, maleic acid modified polypropylene, ethylene-acrylic acid copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, maleated Polybutadiene, ethylene-vinyl acetate copolymer, and ethylene-vinyl acetate copolymer maleated product}.

As the polystyrene resin, a polymer having a weight average molecular weight of 1,000 to 1,000,000 can be used.

As the polystyrene resin derivative, a polymer having a weight average molecular weight of 1,000 to 1,000,000 (eg, styrene-containing styrene) as an essential constituent monomer (the content of styrene is at least 50% by weight based on the weight of the polystyrene derivative) is used. And maleic anhydride copolymers, styrene-butadiene copolymers and styrene-isobutylene copolymers.

Examples of the wax include waxes having a melting point of 50 to 200° C. (for example, paraffin wax, beeswax, carnauba wax, beef tallow, etc.).

The long-chain fatty acid ester is an ester of a fatty acid having 8 to 25 carbon atoms and an alcohol having 1 to 12 carbon atoms (for example, methyl laurate, ethyl laurate, methyl stearate, ethyl stearate, methyl oleate, oleic acid). Ethyl, glycerin lauric acid monoester, glycerin stearic acid monoester, glycerin stearic acid diester, glycerin oleic acid monoester, pentaerythritol lauric acid monoester, pentaerythritol stearic acid monoester, pentaerythritol oleic acid monoester, sorbit Lauric acid monoester, sorbit stearic acid monoester, sorbit oleic acid monoester, sucrose palmitic acid monoester, sucrose palmitic acid diester, sucrose palmitic acid triester, sucrose stearic acid monoester, sucrose stearic acid diester, Sucrose stearic acid triester, beef tallow, and the like}. Among these, glycerin stearic acid monoester, glycerin stearic acid diester, sucrose stearic acid monoester, sucrose stearic acid diester, and sucrose stearic acid triester are preferable from the viewpoint of the leak resistance of the absorbent article, and further. Preferred are glycerin stearic acid monoester, glycerin stearic acid diester, sucrose stearic acid monoester and sucrose stearic acid diester.

Examples of the long-chain fatty acid and its salt include fatty acids having 8 to 25 carbon atoms (for example, lauric acid, palmitic acid, stearic acid, oleic acid, behenic acid, etc.). Examples of the salt include salts with calcium, magnesium or aluminum (hereinafter, abbreviated as Ca, Mg, Al) {for example, Ca palmitate, Al palmitate, Ca stearate, Mg stearate, Al stearate, etc.}. From the viewpoint of leak resistance of the absorbent article, Ca stearate, Mg stearate, and Al stearate are preferable, and Mg stearate is more preferable.

Examples of long-chain aliphatic alcohols include aliphatic alcohols having 8 to 25 carbon atoms (eg, lauryl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol, etc.). From the viewpoint of leakage resistance of the absorbent article, palmityl alcohol, stearyl alcohol and oleyl alcohol are preferable, and stearyl alcohol is more preferable.

As the quaternary ammonium salt type surfactant, a quaternary ammonium salt containing 1 to 2 aliphatic chains having 8 to 25 carbon atoms (eg, didecyldimethylammonium chloride, benzyldimethyldecylammonium chloride, benzyldimethyl) And tetradecyl ammonium chloride, dimethyl distearyl ammonium chloride}, and preferably didecyl dimethyl ammonium chloride and dimethyl distearyl ammonium chloride.

Examples of the mixture of two or more of these include a mixture of a long-chain fatty acid ester and a long-chain aliphatic alcohol {for example, a mixture of sucrose stearate diester and stearyl alcohol}.

As the hydrophobic substance (C2) which is a polysiloxane, polydimethylsiloxane, polyether modified polysiloxane {polyoxyethylene modified polysiloxane and poly(oxyethylene/oxypropylene) modified polysiloxane etc.}, carboxy modified polysiloxane, epoxy Modified polysiloxanes, amino modified polysiloxanes, alkoxy modified polysiloxanes and the like and mixtures thereof are included.

The position of the organic group (modified group) of the modified silicone {polyether modified polysiloxane, carboxy modified polysiloxane, epoxy modified polysiloxane, amino modified polysiloxane, etc.} is not particularly limited, but the side chain of polysiloxane, polysiloxane , Both ends of the polysiloxane, one end of the polysiloxane, and both of the side chain and both ends of the polysiloxane. Of these, the side chains of polysiloxane and both the side chains of polysiloxane and both ends are preferable, and the side chains and both ends of polysiloxane are more preferable, from the viewpoint of absorption characteristics.

The organic group (modifying group) of the polyether modified polysiloxane includes a group containing a polyoxyethylene group or a poly(oxyethylene/oxypropylene) group. The content (number) of oxyethylene groups and/or oxypropylene groups contained in the polyether modified polysiloxane is preferably 2 to 40, more preferably 5 to 30, and particularly preferably, per 1 molecule of the polyether modified polysiloxane. It is 7 to 20, most preferably 10 to 15. Within this range, the absorption characteristics will be further improved. When it contains an oxyethylene group and an oxypropylene group, the content (% by weight) of the oxyethylene group is preferably 1 to 30, more preferably 3 to 25, and particularly preferably 5 based on the weight of the polysiloxane. Is up to 20. Within this range, the absorption characteristics will be further improved.

The polyether-modified polysiloxane can be easily obtained from the market and, for example, the following commercial products {modified position, type of oxyalkylene} can be preferably exemplified.
-Shin-Etsu Chemical Co., Ltd. KF-945 {side chain, oxyethylene and oxypropylene}, KF-6020 {side chain, oxyethylene and oxypropylene}, X-22-6191 {side chain, oxyethylene and oxypropylene} , X-22-4952 {side chain, oxyethylene and oxypropylene}, X-22-4272 {side chain, oxyethylene and oxypropylene}, X-22-6266 {side chain, oxyethylene and oxypropylene}

-Toray Dow Corning Co., Ltd. FZ-2110 {both ends, oxyethylene and oxypropylene}, FZ-2122 {both ends, oxyethylene and oxypropylene}, FZ-7006 {both ends, oxyethylene and oxypropylene}, FZ-2166 {both ends, oxyethylene and oxypropylene}, FZ-2164 {both ends, oxyethylene and oxypropylene}, FZ-2154 {both ends, oxyethylene and oxypropylene}, FZ-2203 {both ends, oxy Ethylene and oxypropylene} and FZ-2207 {both ends, oxyethylene and oxypropylene}

The organic group (modifying group) of the carboxy-modified polysiloxane includes a group containing a carboxy group and the like, and the organic group (modifying group) of the epoxy-modified polysiloxane includes a group containing an epoxy group etc. Examples of the organic group (modifying group) of polysiloxane include a group containing an amino group (a primary, secondary, or tertiary amino group). The content (g/mol) of the organic group (modifying group) of these modified silicones is preferably 200 to 11000, more preferably 600 to 8000, and particularly preferably 1000 to 4000 in terms of carboxy equivalent, epoxy equivalent or amino equivalent. Is. Within this range, the absorption characteristics will be further improved. The carboxy equivalent is measured according to "16. Total acid value test" of JIS C2101:1999. The epoxy equivalent is calculated according to JIS K7236:2001. The amino equivalent is measured according to JIS K2501:2003 “8. Potentiometric titration method (base number/hydrochloric acid method)”.

The carboxy-modified polysiloxane can be easily obtained from the market and, for example, the following commercial products {modified position, carboxy equivalent (g/mol)} can be preferably exemplified.
・Shin-Etsu Chemical Co., Ltd. X-22-3701E {side chain, 4000}, X-22-162C {both ends, 2300}, X-22-3710 {one end, 1450}

・By Toray Dow Corning Co., Ltd. BY 16-880 {side chain, 3500}, BY 16-750 {both ends, 750}, BY 16-840 {side chain, 3500}, SF8418 {side chain, 3500}

The epoxy-modified polysiloxane can be easily obtained from the market, and the following products {modified position, epoxy equivalent} can be preferably exemplified.
・Shin-Etsu Chemical Co., Ltd. X-22-343 {side chain, 525}, KF-101 {side chain, 350}, KF-1001 {side chain, 3500}, X-22-2000 {side chain, 620} , X-22-2046 {side chain, 600}, KF-102 {side chain, 3600}, X-22-4741 {side chain, 2500}, KF-1002 {side chain, 4300}, X-22-3000T {Side chain, 250}, X-22-163 {both ends, 200}, KF-105 {both ends, 490}, X-22-163A {both ends, 1000}, X-22-163B {both ends, 1750}, X-22-163C {both ends, 2700}, X-22-169AS {both ends, 500}, X-22-169B {both ends, 1700}, X-22-173DX {one end, 4500} , X-22-9002 {side chain/both ends, 5000}

-Toray Dow Corning Co., Ltd. FZ-3720 {side chain, 1200}, BY 16-839 {side chain, 3700}, SF 8411 {side chain, 3200}, SF 8413 {side chain, 3800}, SF 8421{ Side chain, 11000}, BY 16-876 {side chain, 2800}, FZ-3736 {side chain, 5000}, BY 16-855D {side chain, 180}, BY 16-8 {side chain, 3700}

Amino-modified silicone can be easily obtained from the market and, for example, the following commercial products {modified position, amino equivalent} can be preferably exemplified.
・Shin-Etsu Chemical Co., Ltd. KF-86 {side chain, 5000}, KF-864 {side chain, 3800}, KF-859 {side chain, 6000}, KF-393 {side chain, 350}, KF-860 {Side chain, 7600}, KF-880 {Side chain, 1800}, KF-8004 {Side chain, 1500}, KF-8002 {Side chain, 1700}, KF-8005 {Side chain, 11000}, KF-867 {Side chain, 1700}, X-22-3820W {Side chain, 55000}, KF-869 {Side chain, 8800}, KF-861 {Side chain, 2000}, X-22-3939A {Side chain, 1500} , KF-877 {side chain, 5200}, PAM-E {both ends, 130}, KF-8010 {both ends, 430}, X-22-161A {both ends, 800}, X-22-161B {both End, 1500}, KF-8012 {both ends, 2200}, KF-8008 {both ends, 5700}, X-22-1660B-3 {both ends, 2200}, KF-857 {side chain, 2200}, KF -8001 {side chain, 1900}, KF-862 {side chain, 1900}, X-22-9192 {side chain, 6500}

-Toray Dow Corning Co., Ltd. FZ-3707 {side chain, 1500}, FZ-3504 {side chain, 1000}, BY 16-205 {side chain, 4000}, FZ-3760 {side chain, 1500}, FZ -3705 {side chain, 4000}, BY 16-209 {side chain, 1800}, FZ-3710 {side chain, 1800}, SF 8417 {side chain, 1800}, BY 16-849 {side chain, 600}, BY 16-850 {side chain, 3300}, BY 16-879B {side chain, 8000}, BY 16-892 {side chain, 2000}, FZ-3501 {side chain, 3000}, FZ-3785 {side chain, 6000}, BY 16-872 {side chain, 1800}, BY 16-213 {side chain, 2700}, BY 16-203 {side chain, 1900}, BY 16-898 {side chain, 2900}, BY 16- 890 {side chain, 1900}, BY 16-893 {side chain, 4000}, FZ-3789 {side chain, 1900}, BY 16-871 {both ends, 130}, BY 16-853C {both ends, 360} , BY 16-853U {both ends, 450}

Examples of the mixture include a mixture of polydimethylsiloxane and carboxyl-modified polysiloxane, and a mixture of polyether-modified polysiloxane and amino-modified polysiloxane.

The viscosity (mPa·s, 25° C.) of the hydrophobic substance that is a polysiloxane is preferably 10 to 5,000, more preferably 15 to 3,000, and particularly preferably 20 to 1,500. Within this range, the absorption characteristics, particularly the blood absorption characteristics, will be further improved. The viscosity is JIS Z8803-1991 "Liquid viscosity" 9. Measured according to the viscosity measurement method using a cone and a cone-plate type rotational viscometer (for example, E-type viscometer whose temperature is adjusted to 25.0±0.5° C. (RE80L manufactured by Toki Sangyo Co., Ltd., radius 7 mm , Cone-shaped cone with an angle of 5.24×10 ⁻² rad). }

The HLB value of the hydrophobic substance (C) is preferably 1 to 9, more preferably 2 to 8, and particularly preferably 3 to 7. Within this range, the absorbent article has further improved resistance to leakage. The HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is determined by the Oda method (Introduction to New Surfactants, page 197, Takehiko Fujimoto, Sanyo Chemical Industry Co., Ltd., 1981). ..

Of these hydrophobic substances (C), long-chain fatty acid esters, long-chain fatty acid salts, long-chain fatty acid alcohols, and quaternary ammonium salt-type interfaces from the viewpoints of liquid diffusion and blood absorbability of absorbent articles, etc. The activator is preferably a hydrophobic substance which is a polysiloxane, and more preferably glycerin stearic acid monoester, glycerin stearic acid diester, sucrose stearic acid monoester, sucrose stearic acid diester, stearyl alcohol, dimethyl distearyl ammonium chloride, amino. Modified polysiloxanes and carboxy modified polysiloxanes, particularly preferably glycerin stearic acid diester, sucrose stearic acid monoester, sucrose stearic acid diester, stearyl alcohol, dimethyl distearyl ammonium chloride, and carboxy modified polysiloxane.

The content (% by weight) of the hydrophobic substance (C) is preferably 0.001 to 5.0, more preferably 0.08 to 1.0, and particularly preferably, based on the weight of the crosslinked polymer (A). Is 0.08 to 0.16. Within this range, the absorbent article is excellent in anti-fogging property, which is preferable.

The hydrophobic substance (C) may be added in any step such as a polymerization step, a gel crushing step, a surface treatment step of surface-treating with a surface cross-linking agent (d) described later, or the like, but the gel crushing It is preferable to add in the step or surface treatment step, and in the gel pulverizing step, a method of adding before and/or simultaneously kneading and shredding the hydrous gel is more preferable.

In the gel crushing step, the temperature at which the hydrogel is kneaded and shredded is preferably 70 to 120°C, more preferably 80 to 110°C. If the temperature at which the hydrogel is kneaded and shredded is lower than this range, a cooling step is required after the polymerization step, which not only requires unnecessary energy but also increases the tackiness of the gel and tends to increase the size of the hydrogel particles. When the temperature at which the hydrogel is kneaded and shredded is higher than this range, bumping of water occurs and stable pulverization cannot be performed.

Also, the melting point of the hydrophobic substance (C) is below the temperature of the step of adding (C). When the melting point is higher than this range, the hydrophobic substance (C) is aggregated and present in the solid state, resulting in poor uniformity, and when it is in this range, the hydrophobic substance (C) is melted to cause gel surface The water absorption time by the Vortex method can be shortened because the fine structure is maintained by preventing the gels from adhering to each other, the pulverization efficiency is improved, and the recycling rate of the water absorbent resin during classification can be reduced. it can. Therefore, in the production method of the present invention, the melting point of the hydrophobic substance (C) is lower than or equal to the temperature of the step of adding (C), for example, lower than or equal to the temperature at which the hydrogel is kneaded and shredded. Is below room temperature to 90° C., particularly preferably 50 to 80° C. Examples of the hydrophobic substance (C) having a melting point not higher than the temperature at which the hydrogel is kneaded and shredded are glycerin stearic acid monoester (melting point 78 to 81°C), glycerin stearic acid diester (melting point 72 to 74°C), and Examples thereof include sugar stearates (60 to 80° C.), stearyl alcohol (59 to 60° C.), and polysiloxane hydrophobic substances (liquid at room temperature without melting point data). Further, the melting point may be lowered due to the presence of the hydrophobic substance in the mixture, or the substance may be dissolved in a solvent and added.

The water-absorbent resin particles of the present invention have a structure in which resin particles containing the crosslinked polymer (A) are surface-crosslinked with at least one surface crosslinking agent (d). Therefore, the production method of the present invention includes a step of surface-treating the resin particles containing the crosslinked polymer (A) with the surface crosslinking agent (d). By having a structure that has been surface-crosslinked with the surface-crosslinking agent (d), gel blocking can be suppressed, and when surface crosslinking is not carried out, the absorption amount under load and the liquid passage rate become low.

Known surface cross-linking agents (d) are disclosed in JP-A-59-189103, JP-A-58-180233, JP-A-61-16903, JP-A-61-212305, and JP-A-61-212305. 61-252212, JP-A-51-136588 and JP-A-61-257235} surface cross-linking agents {polyhydric glycidyl, polyhydric alcohol, polyhydric amine, polyhydric aziridine, polyhydric isocyanate, Silane coupling agents, polyvalent metals, etc. can be used. Among these surface cross-linking agents, from the viewpoint of economic efficiency and absorption characteristics, polyhydric glycidyl, polyhydric alcohol and polyhydric amine are preferred, more preferably polyhydric glycidyl and polyhydric alcohol, particularly preferably polyhydric glycidyl, most preferred. Preferred is ethylene glycol diglycidyl ether.

The amount (% by weight) of the surface cross-linking agent (d) is not particularly limited because it can be variously changed depending on the type of the surface cross-linking agent (d), the conditions for cross-linking, the target performance, etc. From the viewpoint and the like, 0.001 to 3 is preferable, 0.005 to 2 is more preferable, and 0.01 to 1 is particularly preferable, based on the weight of the resin particles containing the crosslinked polymer (A).

The method of performing the surface treatment with the surface cross-linking agent (d) is a known method (for example, Japanese Patent No. 36485553, Japanese Patent Laid-Open No. 2003-165883, Japanese Patent Laid-Open No. 2005-75982, Japanese Patent Laid-Open No. 2005-95759). Can be applied.

After the step of surface-treating with the surface cross-linking agent (d), the particle size may be adjusted by further sieving. Suitable ranges of the weight average particle diameter of the water-absorbent resin particles obtained after the particle size adjustment, the content of the fine particles, and the particle size distribution index (SPAN) will be described later.

The water-absorbent resin particles of the present invention may further contain inorganic fine particles and/or a polyvalent metal salt. Therefore, in the production method of the present invention, the resin particles containing the crosslinked polymer (A) are inorganic. A step of surface-treating with fine particles and/or a polyvalent metal salt may be included. By containing the inorganic fine particles and/or the polyvalent metal salt, the blocking resistance and the liquid passing speed of the water absorbent resin particles are improved.

Examples of the inorganic fine particles include silica, alumina, zirconia, titania, zinc oxide, talc and the like. As the polyvalent metal salt, at least one metal selected from the group consisting of magnesium, calcium, zirconium, aluminum and titanium and an inorganic acid, for example, sulfuric acid, hydrochloric acid, nitric hydrobromic acid, sulfuric acid, sulfamic acid, Phosphoric acid or the like, or organic acids such as acetic acid, propionic acid, succinic acid, glycolic acid, stearic acid, lactic acid, malic acid, tartaric acid, citric acid, ascorbic acid, pamoic acid, maleic acid, hydroxymaleic acid, phenylacetic acid, Salts with glutamic acid, benzoic acid, salicylic acid, sulfanilic acid, 2-acetoxy-benzoic acid, fumaric acid, toluenesulfonic acid, methanesulfonic acid, ethanedisulfonic acid, oxalic acid, isethionic acid, trifluoroacetic acid (TFA), etc. Are listed. Of these, silica, alumina, aluminum sulfate, sodium aluminum sulfate, and aluminum lactate are preferable. These may be used alone or in combination of two or more.

From the viewpoint of liquid permeability and blocking resistance, the amount of the inorganic fine particles or polyvalent metal salt used (% by weight) is 0.01 to 2. based on the weight of the resin particles containing the crosslinked polymer (A). 0 is preferable, and 0.05 to 1.0 is more preferable.

When the surface treatment is performed with the inorganic fine particles and/or the polyvalent metal salt, the step of mixing with the inorganic fine particles and/or the polyvalent metal salt is performed before the step of performing the surface treatment with the surface cross-linking agent, after the above step, and the above step. It can be performed at any one of the above and the same time.

In the production method of the present invention, the particle size may be further adjusted after the step of performing the surface treatment with the inorganic fine particles and/or the polyvalent metal salt.

The water-absorbent resin particles of the present invention may contain other additives (for example, known antiseptics, antifungal agents, antibacterial agents, antioxidants, ultraviolet rays, etc. (Japanese Patent Laid-Open Nos. 2003-225565 and 2006-131767). Absorbents, colorants, fragrances, deodorants, organic fibrous substances, etc.} can also be included. When these additives are contained, the content (% by weight) of the additive is preferably 0.001 to 10 based on the weight of the crosslinked polymer (A), more preferably 0.01 to 5, It is preferably 0.05 to 1, and most preferably 0.1 to 0.5.

Regarding the shape of the water-absorbent resin particles of the present invention, crushed irregular shape, flaky shape, pearl shape, rice grain shape, etc. may be mentioned. Among them, the irregular crushed shape is preferable from the viewpoint that it has good entanglement with the fibrous material for use in a disposable diaper and the like, and there is no fear of falling off from the fibrous material.

The apparent density (g/ml) of the water absorbent resin particles of the present invention is preferably 0.52 to 0.67, more preferably 0.55 to 0.65, and particularly preferably 0.57 to 0.63. .. Within this range, the absorbent article will have even better absorption characteristics. The apparent density is measured at 25°C according to JIS K7365:1999.

The weight average particle diameter (μm) of the water absorbent resin particles of the present invention is 200 to 420, preferably 250 to 410, more preferably 300 to 400, and most preferably 350 to 390. When it is larger than the range of 200 to 420, the absorption time by the Vortex method becomes long, the absorption amount of ion-exchanged water for 60 seconds decreases, and the blood absorption time becomes long. If it is less than this range, spot absorption or gel blocking tends to occur. The weight average particle diameter can be measured in the same manner as described above for the resin particles containing the crosslinked polymer (A), that is, the resin particles before surface crosslinking.

The smaller the content of the fine particles of the water-absorbent resin particles of the present invention, the better the absorption performance, and the content of the fine particles of 106 μm or less in all particles is preferably 3% by weight or less, more preferably 150 μm or less in all particles. The content of fine particles is 3% by weight or less. The content of fine particles can be measured in the same manner as described above.

The particle size distribution index (SPAN) of the water absorbent resin particles of the present invention measured by an image analysis type particle size distribution measuring device is 0.30 to 0.75, preferably 0.30 to 0.65, and more preferably It is 0.30 to 0.60. If it is higher than this range, the absorption amount of the ion-exchanged water absorbed for 60 seconds is deteriorated, and the drainage from the nonwoven fabric is deteriorated. Further, the blood absorption rate is deteriorated and the dryness is deteriorated. On the other hand, setting the SPAN lower than this range is not realistic because the reuse ratio of the water-absorbent resin particles becomes too high. The particle size distribution index (SPAN) can be measured in the same manner as described above.

The water-absorbent resin particles of the present invention preferably have a liquid flow rate of physiological saline (saline concentration of 0.9% by weight; hereinafter the same) of 80 ml/min or more under a load of 0.71 kPa. More preferably, it is 100 ml/min or more. When it is 80 ml/min or more, the permeation rate into the absorber is high, and leakage can be reduced. The higher the upper limit is, the more preferable it is not particularly limited, but it is preferably 1000 ml/min or less from the viewpoint of being compatible with the centrifugal retention amount. The liquid passing rate is measured by the following method.

<A measuring method of the permeation rate of physiological saline under a load of 0.71 kPa>
0.32 g of the measurement sample is immersed in 150 ml of physiological saline for 30 minutes to prepare hydrous gel particles. Then, a vertical cylinder [diameter (inner diameter) 25.4 mm, length 40 cm, graduation lines (m1) and (m2) are provided at positions of 40 ml and 60 ml from the bottom, respectively. ] The water content prepared with the cock closed in a filtration cylindrical tube having a wire mesh (opening 106 μm, JIS Z8801-1:2006) and an openable/closable cock (inner diameter 5 mm, length 10 cm) After transferring the gel particles together with physiological saline, a circular wire mesh (opening 150 μm, diameter 25 mm: a pressure axis (weight 22 g, length 47 cm) that is connected perpendicularly to the wire mesh surface is placed on the water-containing gel particles. ) Is placed so that the metal net and the hydrogel particles come into contact with each other, and a weight (14.8 g) is further placed on the pressure shaft and left still for 1 minute. Then, open the cock and measure the time (T1; seconds) required for the liquid level in the filtration cylindrical tube to change from the 60 ml scale line (m2) to the 40 ml scale line (m1). Minutes). The temperature of the physiological saline used and the measurement atmosphere is 25°C ± 2°C.
Flow rate (ml/min) = 20 ml x 60/(T1-T2)
Note that T2 is the time measured by the same operation as above in the case where there is no measurement sample.

The water-absorbent resin particles of the present invention preferably have an absorption time of 15-40 seconds by the Vortex method. More preferably, it is 20 to 35 seconds. If it is slower than 15 to 40 seconds, oblique leakage of the absorbent body is likely to occur, and if it is faster than this range, spot absorption is excessive and the permeation speed becomes slow. The absorption time by the Vortex method is measured by the following method.

<Method of measuring absorption time by Vortex method>
Put 50 g of physiological saline in a 100 ml beaker and adjust the temperature to 25±2°C. Next, a stirrer piece (length 30 mm, center diameter 8 mm, end diameter 7 mm) is placed in the center of the beaker, and physiological saline is stirred at 600 rpm. 2.000 g of the measurement sample is put in the vicinity of the beaker wall surface. In addition, the measurement sample to be used is adjusted by using a sample splitter or the like so as to be sampled in a state of its typical particle size. The time (seconds) until the measurement is started from the time when the measurement sample is added and the level of the liquid mixture of the measurement sample and physiological saline becomes flat (the point at which diffused light from the level disappears) Is the absorption time. The test is conducted at 25±3° C. and 60±5 RH%.

The water-absorbent resin particles of the present invention preferably have a physiological saline retention of 25 to 45 g/g. Within this range, the absorber can sufficiently retain the liquid, and can be compatible with the liquid passage rate. The amount of physiological saline retained by centrifugation is measured by the following method.

<Method of measuring the amount of saline retained by centrifugation>
1.00 g of the measurement sample was placed in a tea bag (length 20 cm, width 10 cm) made of nylon mesh with an opening of 63 μm (JIS Z8801-1:2006), and immersed in 1,000 ml of physiological saline solution for 1 hour without stirring. After that, hang it for 15 minutes to drain water. Then, each tea bag is placed in a centrifuge, centrifugally dehydrated at 150 G for 90 seconds to remove excess physiological saline, and the weight (h1) including tea bag is measured to determine the centrifugal retention amount from the following formula.
Centrifuge retention amount (g/g) = (h1)-(h2)
The temperature of the physiological saline used and the measurement atmosphere is 25°C ± 2°C. The weight of the tea bag after centrifugal dehydration is measured in the same manner as above except that the measurement sample is not used, and is designated as (h2).

The water-absorbent resin particles of the present invention preferably have an absorbed amount of physiological saline under a load of 15 to 30 g/g. Within this range, the liquid can be sufficiently absorbed even when the absorber is placed under a load. The amount of physiological saline absorbed under load is measured by the following method.

<Measurement method of physiological saline absorption under load>
In a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) with a nylon mesh of 63 μm (JIS Z8801-1:2006) attached to the bottom, a 30-mesh sieve and a 60-mesh sieve were used to measure 250-500 μm. After weighing 0.16 g of the measurement sample sieved in the range and arranging the cylindrical plastic tube vertically so that the measurement sample has a substantially uniform thickness on the nylon net, a weight (weight: 210.6 g, outer diameter: 24.5 mm,). After measuring the total weight (M1) of the cylindrical plastic tube, the cylindrical plastic tube containing the measurement sample and the weight was vertically set in a petri dish (diameter: 12 cm) containing 60 ml of physiological saline, and a nylon mesh was used. The side is placed as the lower surface and the plate is immersed in physiological saline and left standing for 60 minutes. After 60 minutes, the cylindrical plastic tube was pulled up from the petri dish, the physiological saline adhering to the bottom was collected at one position by tilting it to remove excess physiological saline by dropping it as a water drop, and then a measurement sample and The total weight (M2) of the cylindrical plastic tube containing the weight is measured, and the absorption amount under load is calculated from the following formula. The temperature of the physiological saline used and the measuring atmosphere is 25°C ± 2°C.
Absorption under load (g/g)={(M2)-(M1)}/0.16

The water-absorbent resin particle of the present invention preferably absorbs ion-exchanged water for 60 seconds and has an absorption amount of 50 to 100 g/g. Within this range, the liquid is quickly drawn from the nonwoven fabric at a high swelling ratio and the dryness is enhanced. The absorbed amount of ion-exchanged water absorbed for 60 seconds is measured by the following method.

<Measurement method for absorption of ion-exchanged water for 60 seconds>
0.16 g of the measurement sample was weighed into a cylindrical plastic tube (inner diameter: 25 mm, height: 34 mm) having a nylon net with an opening of 63 μm (JIS Z8801-1:2006) attached to the bottom surface, and the cylindrical plastic tube was attached. After vertically arranging the measurement sample on a nylon net so as to have a substantially uniform thickness, the total weight (M1) of the cylindrical plastic tube is measured. Next, a cylindrical plastic tube containing the measurement sample was placed vertically in a Petri dish (diameter: 12 cm) containing 60 ml of ion-exchanged water, soaked in ion-exchanged water with the nylon net side facing down and left for 60 seconds. To do. After 60 seconds, the cylindrical plastic tube is pulled up from the petri dish, the weight (M2) of the measurement sample and the entire cylindrical plastic tube is weighed, and the absorbed amount of ion-exchanged water is absorbed for 60 seconds from the following formula. The temperature of the ion-exchanged water used and the measurement atmosphere is 25°C ± 2°C.
Absorption amount of ion-exchanged water for 60 seconds (g/g)={(M2)-(M1)}/0.16

The water absorbent resin particles of the present invention preferably have a blood absorption amount of 10 to 30 g/g, more preferably 12 to 30 g/g. If it is lower than this range, the amount of blood absorbed is low and the dryness may deteriorate. If it is higher than this range, the dryness is improved, but problems such as swelling of the absorbent body may occur. The blood absorption amount is measured by the following method.

<Measurement method of blood absorption>
0.100 g of the measurement sample is added to a tea bag (3.5 cm in length, 3.5 cm in width) made of a nylon net having an opening of 63 μm (JIS Z8801-1:2006), and heat sealed on all sides. In advance, 15.0 g of horse blood (horse EDTA whole blood, manufactured by Japan Lamb Co., Ltd.) is prepared in a 100-ml beaker with a flat bottom defined in JIS R 3503, and a nylon mesh bag containing a measurement sample is immersed for 15 minutes. After 15 minutes, the nylon mesh is taken out and suspended for 1 minute to remove excess blood, and the weight (h3) is measured to obtain the blood absorption amount from the following formula. The temperature of the horse blood and the measurement atmosphere used is 25°C ± 2°C. The weight (h4) is the weight of the tea bag measured by the same operation as above when there is no measurement sample.
Blood absorption (g/g)=((h3)-(h4))/0.100

The water-absorbent resin particles of the present invention preferably have a blood absorption time of 120 seconds or less, more preferably 30 to 100 seconds. If it is higher than this range, the dryness becomes poor, and if it is lower than this range, spot absorption is excessive and the absorption speed to the absorber becomes slower, which may result in poor dryness. The blood absorption time is measured by the following method.

<Measurement method of blood absorption time>
0.2 g of the measurement sample was evenly spread over the entire bottom surface in a 9 ml screw vial, and 1.0 g of horse blood (horse EDTA whole blood, manufactured by Japan Lamb Co., Ltd.) was added all at once, and then the horse blood lost its fluidity. The time until (second) is measured with the naked eye and used as the blood absorption rate (second). In addition, in this measurement, the term “no fluidity” means that there is no blood that flows independently of the water-absorbent resin particles when the bottom surface of the screw vial is tilted at 45 degrees with respect to the horizontal. The temperature of the horse blood and the measurement atmosphere used is 25°C ± 2°C.

The water-absorbent resin particles of the present invention constitute, for example, an absorbent body used for sanitary materials such as paper diapers, sanitary napkins, incontinence pads, and medical pads, and are suitably used for absorbent articles provided with the absorbent body. It is suitably used particularly for for absorbing menses or blood. As the absorbent article for absorbing blood or menstrual blood, for example, a sanitary napkin, a tampon, a medical sheet, a drip absorbent, a wound protective material, a wound healing material, a surgical liquid waste treatment agent and the like have blood absorption characteristics. Included items required.

An absorbent body using the water-absorbent resin particles of the present invention has an excellent absorption amount of body fluid such as menstrual blood or blood, an excellent liquid uptake rate, and a dry touch property under pressure after absorption.

The absorber of the present invention contains the water absorbent resin particles of the present invention and a nonwoven fabric.

The nonwoven fabric used in the present invention is not particularly limited as long as it is a known nonwoven fabric, but from the viewpoint of liquid permeability, flexibility and strength when used as an absorber, polyolefin such as polyethylene (PE) and polypropylene (PP). Fibers, polyester fibers such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polyamide fibers such as nylon, rayon fibers, non-woven fabrics made of other synthetic fibers, cotton, silk, Non-woven fabrics produced by mixing hemp, pulp (cellulose) fibers, and the like are included. Among these non-woven fabrics, non-woven fabrics made of synthetic fibers are preferable, and more preferably non-woven fabrics made of rayon fibers, polyolefin fibers, and polyester fibers, from the viewpoint of increasing the strength of the absorber. These non-woven fabrics may be a single non-woven fabric of the above fibers or a non-woven fabric in which two or more kinds of fibers are combined.

The non-woven fabric used in the present invention is a non-woven fabric that is appropriately bulky and has a large basis weight from the viewpoint of imparting good liquid permeability, flexibility, strength and cushioning properties to the absorber and accelerating the liquid permeation rate of the absorber. Is preferred. The basis weight is preferably 5 to 300 g/m ² , more preferably 8 to 200 g/m ² , even more preferably 10 to 100 g/m ² , and even more preferably 11 to 50 g/m ^2. Is. The thickness of the nonwoven fabric is preferably 20 to 800 μm, more preferably 50 to 600 μm, and further preferably 80 to 450 μm.

In the absorbent body of the present invention, the absorbent layer contains water-absorbent resin particles, a non-woven fabric and optionally an adhesive, and further contains a hydrophilic fiber such as fluff pulp, if desired. The water-absorbent resin particles are evenly dispersed on the coated non-woven fabric, and if necessary, the non-woven fabric coated with the adhesive is further overlaid, and if necessary, heated under pressure. It is also formed by uniformly dispersing the mixed powder of the water-absorbent resin particles and the adhesive on the non-woven fabric, stacking the non-woven fabrics, and heating the mixture near the melting temperature of the adhesive, if necessary, by heating under pressure. To be done. Fluff pulp can be evenly distributed between the non-woven fabric and the water-absorbent resin particles.
In the absorbent body of the present invention, the absorbent layers may be stacked to form two or more layers.

Examples of the adhesive used in the present invention include rubber-based adhesives such as natural rubber-based, butyl rubber-based, and polyisoprene; styrene-isoprene block copolymer (SIS), styrene-butadiene block copolymer (SBS), Styrene-based elastomer adhesives such as styrene-isobutylene block copolymer (SIBS) and styrene-ethylene-butylene-styrene block copolymer (SEBS); ethylene-vinyl acetate copolymer (EVA) adhesives; ethylene-acrylic acid Ethylene-acrylic acid derivative copolymer adhesives such as ethyl copolymer (EEA) and ethylene-butyl acrylate copolymer (EBA); ethylene-acrylic acid copolymer (EAA) adhesives; copolymerized nylon and dimer Polyamide adhesives such as acid-based polyamides; Polyolefin adhesives such as polyethylene, polypropylene, atactic polypropylene, copolymerized polyolefins; Polyester adhesives such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), copolymerized polyesters Etc., and acrylic adhesives. In the present invention, an ethylene-vinyl acetate copolymer adhesive, a styrene-based elastomer adhesive, from the viewpoint that the adhesive strength is strong and peeling of the nonwoven fabric in the water-absorbent sheet structure and the dissipation of the water-absorbent resin particles can be prevented Polyolefin adhesives and polyester adhesives are preferred. These adhesives may be used alone or in combination of two or more.

When a heat-melting type adhesive is used, the melting temperature (softening temperature) of the adhesive is 60 to 180 from the viewpoint of sufficiently fixing the water-absorbent resin particles to the nonwoven fabric and preventing thermal deterioration and deformation of the nonwoven fabric. C. is preferable, 70 to 150.degree. C. is more preferable, and 75 to 125.degree. C. is further preferable.

The content ratio of the adhesive in the absorbent body is preferably 0.05 to 2.0 times, more preferably 0.08 to 1.5 times the content (mass basis) of the water absorbent resin particles, and more preferably 0. The range of 1 to 1.0 times is more preferable. From the viewpoint of preventing peeling of the non-woven fabric and dissipation of the water-absorbent resin particles by sufficient adhesion and improving the shape retention of the absorber, the content ratio of the adhesive is preferably 0.05 times or more, and the adhesion becomes strong. The content ratio of the adhesive is preferably 2.0 times or less from the viewpoint of avoiding the swelling inhibition of the water-absorbent resin particles due to excess and improving the permeation rate of the absorber and the liquid leakage.

The weight% of the water-absorbent resin particles of the present invention and the above-mentioned non-woven fabric is 40% by weight or more based on the weight of the water-absorbent resin particles {weight of water-absorbent resin particles/(weight of water-absorbent resin particles+weight of non-woven fabric)}. Is more preferable, 60% by weight or more is more preferable, and 80% by weight is particularly preferable.

Moreover, it is preferable that the above-mentioned absorber constitutes an absorbent article {paper diaper, sanitary napkin, etc.}. A method of manufacturing an absorbent article, etc., is the same as the known one (except JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, etc.), except that the above-mentioned absorber is used. Is the same.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, parts are parts by weight and% is% by weight.

<Production Example 1>
Water-soluble vinyl monomer (a1-1) {acrylic acid, manufactured by Mitsubishi Chemical Corporation, purity 100%} 155 parts, crosslinking agent (b-1) {pentaerythritol triallyl ether, manufactured by Daiso Corporation} 0.50 parts And 340.39 parts of deionized water were maintained at 3° C. with stirring and mixing. After nitrogen was introduced into this mixture to adjust the dissolved oxygen amount to 1 ppm or less, 0.62 parts of a 1% aqueous hydrogen peroxide solution, 1.16 parts of a 2% aqueous ascorbic acid solution and 2% of 2,2'-azobis[ 2.33 parts of an aqueous solution of 2-methyl-N-(2-hydroxyethyl)-propionamide] was added and mixed to initiate polymerization. After the temperature of the mixture reached 90° C., the mixture was polymerized at 90±2° C. for about 5 hours to obtain a hydrogel (1).

Next, 128 parts of a 48.5% aqueous sodium hydroxide solution was added while chopping 500 parts of this hydrogel (1) at a gel temperature of 90° C. with a mincing machine (ROYAL 12VR-400K, plate diameter 8 mm). After mixing and kneading once and then shredding, 0.124 parts of glycerin distearate ester (manufactured by Fuji Film Wako Pure Chemical Industries, melting point 73° C.) as a hydrophobic substance (C) is added and mixed, and kneaded three times. Shredded. The temperature of the gel was measured immediately after chopping and it was 82°C. The gel was spread on a SUS bat (width 59 cm square, depth 5 cm) and dried at 150° C. for 45 minutes in a safety oven manufactured by ESPEC to obtain a dried body. The dried material was crushed for the first time by a roll mill (clearance 0.4 mm), and then classified by a sieve composed of openings of 500 μm and openings of 150 μm in order from the top, and then the particles of 500 μm or more were roll-milled ( The second pulverization was performed with a clearance of 0.2 mm), and the second classification was performed using a sieve composed of openings 850 μm and openings 150 μm in order from the top. Particles between 500 μm and 150 μm in the first classification and particles between 850 μm and 150 μm in the second classification were mixed to obtain a resin particle (A-1) containing a crosslinked polymer.

<Example 1>
While stirring 100 parts of the resin particles (A-1) at high speed (high-speed stirring turbulator manufactured by Hosokawa Micron: rotation speed 2000 rpm), 0.06 part of ethylene glycol diglycidyl ether as a surface cross-linking agent and 1 part of propylene glycol 0.0 parts, 2.4 parts of water, 0.9 parts of Clevozol 30CAL25 (manufactured by Merck) as inorganic fine particles were added and mixed uniformly, and then dried by standing at 130° C. for 30 minutes, Water-absorbent resin particles (P-1) were obtained by passing through a sieve having an opening of 850 μm. The weight average particle diameter of (P-1) was 384 μm, and SPAN was 0.60.

<Production Example 2>
In Production Example 1, 0.124 parts of glycerin distearate was changed to 0.248 parts, the roll mill clearance of the first grinding was 0.2 mm, and the sieve openings in the first classification were 300 μm and 150 μm, and 300 μm. The above particles were subjected to the second pulverization, the roll mill clearance of the second pulverization was 0.2 mm, and the sieve openings in the second classification were 300 μm and 150 μm, and the particle size was between 300 μm and 150 μm in the first classification. Resin particles (A-2) containing a crosslinked polymer were obtained in the same manner except that the particles were mixed with particles having a particle size of 300 μm and 150 μm in the second classification. Immediately after shredding, the temperature of the gel was measured and found to be 79°C.

<Example 2>
Water-absorbent resin particles (P-2) were obtained in the same manner as in Example 1 except that the resin particles (A-1) were changed to (A-2). The weight average particle diameter of (P-2) was 211 μm, and SPAN was 0.61.

<Production Example 3>
In Production Example 2, the roll mill clearance of the first crushing was 0.3 mm, the sieve openings in the first classification were 425 μm and 300 μm, and particles of 425 μm or more were subjected to the second crushing, and the second crushing roll mill. A cross-linked polymer was prepared in the same manner except that the clearance was 0.3 mm, the sieve openings in the second classification were 425 μm and 300 μm, and particles between 425 μm and 300 μm in the first and second classification were mixed. Resin particles (A-3) were obtained. The temperature of the gel was measured immediately after chopping and it was 82°C.

<Example 3>
Water-absorbent resin particles (P-3) were obtained in the same manner as in Example 1, except that the resin particles (A-1) were changed to (A-3). The weight average particle diameter of (P-3) was 387 μm, and SPAN was 0.32.

<Production Example 4>
Resin particles (A-4) containing a crosslinked polymer were obtained in the same manner as in Production Example 1 except that 0.124 parts of glycerin distearate ester was not used. The temperature of the gel was measured immediately after chopping and it was 83°C.

<Example 4>
While stirring 100 parts of the resin particles (A-4) at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), 0.06 part of ethylene glycol diglycidyl ether as a surface cross-linking agent and 1 part of propylene glycol 0.2 parts of water, 0.01 parts of a carboxy-modified polysiloxane (X-22-3701E (manufactured by Shin-Etsu Chemical Co., Ltd.)) as a hydrophobic substance (C) was added, and mixed uniformly. After that, it is dried by allowing it to stand at 130° C. for 30 minutes, 0.2 parts of Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd.) is mixed as inorganic fine particles, and the mixture is passed through a sieve with an opening of 850 μm to give water-absorbent resin particles ( P-4) was obtained. The weight average particle diameter of (P-4) was 384 μm, and SPAN was 0.71.

<Production Example 5>
Resin particles containing a crosslinked polymer in the same manner as in Production Example 1 except that 0.124 parts of glycerin distearate ester was changed to 0.124 parts of magnesium stearate (manufactured by Fuji Film Wako Pure Chemical Industries, melting point 120° C.) ( A-5) was obtained. The temperature of the gel was measured immediately after chopping and it was 81°C.

<Example 5>
Water-absorbent resin particles (P-5) were obtained in the same manner as in Example 1, except that the resin particles (A-1) were changed to (A-5). The weight average particle diameter of (P-5) was 390 μm, and SPAN was 0.64.

<Example 6>
While stirring 100 parts of the resin particles (A-1) at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotational speed 2000 rpm), 0.18 parts of ethylene glycol diglycidyl ether as a surface cross-linking agent and 1 part of propylene glycol 0.8 parts, water 4.8 parts, and a mixed solution of 0.3 parts of Clevozol 30CAL25 (manufactured by Merck) as inorganic fine particles, 0.8 parts of propylene glycol, 1.6 parts of water, and sodium aluminum sulfate as a polyvalent metal salt. A mixed solution of 0.30 parts of hexahydrate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added at the same time, and after uniformly mixing, the mixture was dried by standing at 130° C. for 30 minutes, and then sieved with a sieve having an opening of 850 μm. By passing through, water-absorbent resin particles (P-6) were obtained. The weight average particle diameter of (P-6) was 387 μm, and SPAN was 0.61.

<Production Example 6>
Water-soluble vinyl monomer (a1-1) {acrylic acid, manufactured by Mitsubishi Chemical Corporation, purity 100%} 135 parts, crosslinking agent (b-1) {pentaerythritol triallyl ether, manufactured by Daiso Corporation} 0.37 parts and 356.38 parts of deionized water was kept at 3° C. with stirring and mixing. After nitrogen was introduced into this mixture to adjust the dissolved oxygen content to 1 ppm or less, 0.50 parts of 1% hydrogen peroxide solution, 1.0 parts of 2% ascorbic acid solution and 2% of 2,2'-azobis( Polymerization was initiated by adding and mixing 6.75 parts of a 2-methylpropionamidine)dihydrochloride aqueous solution. After the temperature of the mixture reached 82°C, the mixture was polymerized at 82±2°C for about 8 hours to obtain a hydrogel (2).

Next, 500 parts of this water-containing gel (2) was chopped at a gel temperature of 82° C. with a mincing machine (ROYAL 12VR-400K, plate diameter 8 mm) and 111.50 parts of a 48.5% aqueous sodium hydroxide solution was added. After mixing and kneading and shredding once, 0.216 parts of cation DSV (manufactured by Sanyo Kasei Co., Ltd., main component distearyldimethylammonium chloride, melting point 63° C.) is added as a hydrophobic substance (C) and mixed. The mixture was kneaded and chopped 3 times. Immediately after shredding, the temperature of the gel was measured and found to be 71°C. The gel was spread on a SUS bat (width 59 cm square, depth 5 cm) and dried at 150° C. for 45 minutes in a safety oven manufactured by ESPEC to obtain a dried body. The dried product was crushed for the first time by a roll mill (clearance: 0.3 mm), and then classified by a sieve composed of openings 600 μm and openings 300 μm in order from the top, and then particles of 600 μm or more were roll-milled ( The second pulverization was performed with a clearance of 0.2 mm), and the second classification was performed using a sieve composed of openings 850 μm and openings 150 μm in order from the top. Particles between 600 μm and 300 μm in the first classification and particles between 850 μm and 150 μm in the second classification were mixed to obtain a resin particle (A-6) containing a crosslinked polymer.

<Example 7>
While stirring 100 parts of the resin particles (A-6) at high speed (high-speed stirring turbulator manufactured by Hosokawa Micron: rotation speed 2000 rpm), 0.01 part of ethylene glycol diglycidyl ether as a surface cross-linking agent and 1 part of propylene glycol A mixed solution of 0.0 parts and 2.1 parts of water was added and uniformly mixed, and then dried by standing at 130° C. for 30 minutes to obtain 0.2 parts of Aerosil 200 (manufactured by Nippon Aerosil) as inorganic fine particles. Was mixed and passed through a sieve having an opening of 850 μm to obtain water absorbent resin particles (P-7). The weight average particle diameter of (P-7) was 412 μm, and SPAN was 0.71.

<Production Example 7>
500 parts of hydrous gel (1) prepared in the same manner as in Production Example 1 was shredded at a gel temperature of 90° C. with a mincing machine (ROYAL 12VR-400K, plate diameter 8 mm) to obtain a 48.5% sodium hydroxide aqueous solution 128. .42 parts was added and mixed, and once kneaded and shredded, 0.124 parts of glycerin distearate ester (manufactured by Fuji Film Wako Pure Chemical Industries, melting point 73° C.) was added and mixed as a hydrophobic substance (C). Then, the mixture was kneaded and shredded three times. The temperature of the gel was measured immediately after chopping and it was 82°C. The gel was spread on a SUS bat (width 59 cm square, depth 5 cm) and dried at 150° C. for 45 minutes in a safety oven manufactured by ESPEC to obtain a dried body. The dried product is crushed with a roll mill (clearance 0.3 mm), and is classified with a sieve composed of openings 710 μm and openings 150 μm in order from the top, particles between 710 μm and 150 μm are collected, and a crosslinked polymer is contained. Resin particles (A-7) were obtained.

<Comparative Example 1>
The same operation as in Example 1 was carried out except that the resin particles (A-1) were changed to (A-7) to obtain comparative water absorbent resin particles (R-1). The weight average particle diameter of (R-1) was 398 μm, and SPAN was 0.99.

<Production Example 8>
500 parts of hydrous gel (1) prepared in the same manner as in Production Example 1 was shredded at a gel temperature of 90° C. with a mincing machine (ROYAL 12VR-400K, plate diameter 8 mm) to obtain a 48.5% sodium hydroxide aqueous solution 128. .42 parts was added and mixed, and once kneaded and shredded, 0.124 parts of glycerin distearate ester (manufactured by Fuji Film Wako Pure Chemical Industries, melting point 73° C.) was added and mixed as a hydrophobic substance (C). Then, the mixture was kneaded and shredded three times. The temperature of the gel was measured immediately after chopping and it was 82°C. The gel was spread on a SUS bat (width 59 cm square, depth 5 cm) and dried at 150° C. for 45 minutes in a safety oven manufactured by ESPEC to obtain a dried body. The dried product is crushed with a roll mill (clearance 0.4 mm), and is classified with a sieve composed of openings 710 μm and openings 300 μm in order from the top, particles between 710 μm and 300 μm are collected, and a crosslinked polymer is contained. Resin particles (A-8) were obtained.

<Comparative example 2>
The same operation as in Example 1 was carried out except that the resin particles (A-1) were changed to (A-8) to obtain comparative water absorbent resin particles (R-2). The weight average particle diameter of (R-2) was 461 μm, and SPAN was 0.72.

<Comparative example 3>
The same operation as in Example 1 was carried out except that Clevozol 30CAL25 was not used, to obtain comparative water-absorbent resin particles (R-3). The weight average particle diameter of (R-3) was 388 μm, and SPAN was 0.61.

<Production Example 9>
500 parts of hydrous gel (1) prepared in the same manner as in Production Example 1 was shredded at a gel temperature of 90° C. with a mincing machine (ROYAL 12VR-400K, plate diameter 8 mm) to obtain a 48.5% sodium hydroxide aqueous solution 128. .42 parts was added and mixed, and once kneaded and shredded, 0.124 parts of glycerin distearate ester (manufactured by Fuji Film Wako Pure Chemical Industries, melting point 73° C.) was added and mixed as a hydrophobic substance (C). Then, the mixture was kneaded and shredded three times. The temperature of the gel was measured immediately after chopping and it was 82°C. The gel was spread on a SUS bat (width 59 cm square, depth 5 cm) and dried at 150° C. for 45 minutes in a safety oven manufactured by ESPEC to obtain a dried body. The dried product was pulverized with a roll mill (clearance 0.2 mm), and classified with a sieve having an opening of 300 μm to collect particles of 300 μm or less to obtain resin particles (A-9) containing a crosslinked polymer.

<Comparative example 4>
The same operation as in Example 1 was carried out except that the resin particles (A-1) were changed to (A-9) to obtain comparative water absorbent resin particles (R-4). The weight average particle diameter of (R-4) was 170 μm, and SPAN was 0.75.

<Production Example 10>
500 parts of the hydrogel (1) prepared in the same manner as in Production Example 1 was subdivided into about 1 mm square pieces with scissors, and 128.42 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed. The gel was spread on a SUS bat (width 59 cm square, depth 5 cm) and dried at 150° C. for 55 minutes in a safety oven manufactured by ESPEC to obtain a dried body. The dried material was crushed for the first time by a roll mill (clearance 0.4 mm), and then classified by a sieve composed of openings of 500 μm and openings of 150 μm in order from the top, and then the particles of 500 μm or more were roll-milled ( The second pulverization was performed with a clearance of 0.2 mm), and the second classification was performed using a sieve composed of openings 850 μm and openings 150 μm in order from the top. Particles between 500 μm and 150 μm in the first classification and particles between 850 μm and 150 μm in the second classification were mixed to obtain a resin particle (A-10) containing a crosslinked polymer.

<Comparative Example 5>
The same operation as in Example 4 was carried out except that the resin particles (A-4) were changed to (A-10) to obtain comparative water absorbent resin particles (R-5). The weight average particle diameter of (R-5) was 385 μm, and SPAN was 0.69.

<Comparative Example 6> Water-absorbent resin particles for comparison were obtained with reference to the method disclosed in Example 1 (paragraphs 0082 to 0085) of JP2004-261797A. That is, 158.3 parts of acrylic acid, 301.5 parts of water, and 48.5% sodium hydroxide aqueous solution 129 were placed in a reactor formed by attaching a lid to a stainless steel double-arm kneader with a jacket having two sigma type blades. .3 parts were mixed to prepare an aqueous solution of sodium acrylate having a neutralization ratio of 71.3 mol% (monomer concentration 39%), and 0.85 parts of polyethylene glycol diacrylate (Mw=523) was dissolved. A reaction solution was prepared, and nitrogen was flowed into this reaction solution for 30 minutes to degas. Then, 2.67 parts of a 10% sodium persulfate aqueous solution and 2.22 parts of a 0.1% ascorbic acid aqueous solution were added to the reaction solution while stirring. Polymerization started after about 1 minute, the polymerization was continued while stirring at 25 to 95° C. for 30 minutes, and after 30 minutes, the hydrogel (3) was taken out.

The hydrogel (3) was cut into pieces of about 5 mm, spread on a wire mesh with an opening of 300 μm, and dried with hot air at 180° C. for 50 minutes to obtain a dried body. The dried product was pulverized with a roll mill (clearance 0.3 mm) and classified with a sieve having openings 600 μm and openings 180 μm in order from the top. 20 parts of particles having passed through a mesh of 180 μm were agitated with 30 parts of 90° C. water in a jacketed container capable of high-speed stirring for 3 minutes to granulate, put on a 300 μm wire net, and dried at 150° C. for 2 hours. .. After drying, it was pulverized with a roll mill (clearance 0.3 mm) and classified with a sieve composed of openings 850 μm and openings 150 μm in order from the top. 90 parts of particles of 600 μm to 180 μm and 10 parts of particles of 850 μm to 150 μm were mixed to obtain resin particles (A-11) containing a crosslinked polymer.

While stirring 100 parts of the resin particles (A-11) at high speed (high speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), 1.0 part of 1,4-butanediol as a surface cross-linking agent and 4 parts of water were added thereto. After adding a mixed solution containing 0.0 part of the mixture and uniformly mixing the mixture, the mixture was dried by allowing it to stand at 195° C. for 20 minutes, and passed through a sieve having an opening of 600 μm to obtain Aerosil 200 (manufactured by Nippon Aerosil) as inorganic fine particles. By mixing 3 parts by weight, comparative water absorbent resin particles (R-6) were obtained. The weight average particle diameter of (R-6) was 317 μm, and SPAN was 0.97.

Comparative Example 7 A dried hydrogel was obtained with reference to the method disclosed in Example 1 (paragraphs 1988 to 0091) of JP-T-2017-222875. That is, 100 g of acrylic acid, 0.5 g of polyethylene glycol diacrylate (Mw=523) as a cross-linking agent, 0.033 g of diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide as a UV initiator, 50% caustic soda solution (NaOH). ) 83.3 g and 89.8 g of water were mixed to prepare a monomer aqueous solution composition having a monomer concentration of 45% by weight. Next, after the monomer aqueous solution composition was introduced through a supply section of a polymerization vessel consisting of a conveyor belt that continuously moves, it was irradiated with ultraviolet rays by a UV irradiation device (irradiation amount: ² mW/cm ² ) and UV polymerization was performed for 2 minutes. Was carried out to prepare a hydrogel (4).

After transferring the hydrogel (4) to a cutting machine, it was cut into 0.2 cm and dried at 160°C for 30 minutes with a hot air dryer to obtain a dried body. The dried product was pulverized with a roll mill (clearance 0.4 mm), and was classified with a sieve composed of openings 850 μm, 600 μm, 300 μm, 150 μm, 90 μm, and 45 μm in order from the top, and 0.57% of particles of 850 μm or more, 600-850 μm particles are mixed so as to contain 15%, 300-600 μm particles are 68.62%, 150-300 μm particles are 15%, 90-150 μm particles are 0.81%, and a cross-linked polymer is contained. Resin particles (A-12) were obtained.

While stirring 100 parts of resin particles (A-12) at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), 0.05 part of ethylene glycol diglycidyl ether as a surface cross-linking agent and 0 parts of propylene glycol were used as a surface cross-linking agent. A mixed solution of 10 parts and 4.85 parts of water was added, and after uniform mixing, the mixture was dried by standing at 130° C. for 40 minutes, passed through a sieve with an opening of 850 μm, and sieve with an opening of 150 μm. By collecting the fine product, comparative water absorbent resin particles (R-7) were obtained. The weight average particle diameter of (R-7) was 424 μm, and SPAN was 1.11.

Absorbent articles-1 and absorbent articles-2 (paper diapers) were prepared in the following manner using the water-absorbent resin particles obtained in Examples 1 to 7 and Comparative Examples 1 to 7, respectively, and surface nonwoven fabrics were prepared. The dryness (whitening time), the oblique leak test (leakage amount), the amount of reversion, and the absorption time test (absorption time) were evaluated.

<Preparation of absorber>
A styrene-butadiene-styrene copolymer (SBS; softening point 85° C.) was used as an adhesive on a non-woven fabric A (unit weight 40 g/m ² , thickness 0.5 mm, made of polypropylene) chopped into a rectangle of 10 cm×40 cm. A hot-melt coating machine (AD41, manufactured by Nordson) was applied uniformly so that the basis weight was 2.85 g/m ² . The evaluation sample {respective water-absorbent resin particles} 11.6 g (weight per unit area 290 g/m ² ) was evenly spread on the surface coated with the adhesive, and then the non-woven fabric B was cut into a rectangle of 10 cm×40 cm (weight per unit area). 45 g/m ² , thickness 7.0 mm, made of polypropylene). A sheet of non-woven fabric A-water-absorbent resin-non-woven fabric B was sandwiched between acrylic plates (thickness: 4 mm) and pressed at a pressure of 5 kg/cm ² for 30 seconds. After pressing, the acrylic plate on the non-woven fabric A side is removed, the adhesive, the water-absorbent resin and the non-woven fabric B are laminated in the same manner as described above, sandwiched between the acrylic plates again, and pressed at a pressure of 5 kg/cm ² for 30 seconds, Each absorber using each water-absorbent resin particle was prepared.

<Preparation of absorbent article-1>
A polyethylene sheet (polyethylene film UB-1 manufactured by Tama Poly Co., Ltd.) is arranged on one surface of each of the above-mentioned absorbers, and a non-woven fabric (basis weight 20 g/m ² , Ertus Guard manufactured by Asahi Kasei Corporation) is arranged on the opposite surface of each absorbent body. A sex article-1 was prepared.

<Drying property test by drawing liquid from surface non-woven fabric>
Each of the absorbent articles-1 prepared above was placed in a box (made of stainless steel) having a width of 11 cm, a length of 41 cm, a height of 4 cm, and an upper portion (11 cm×41 cm surface) vacant. 500 ml of ion-exchanged water adjusted to 25±5° C. was prepared and poured into the box containing the absorber at once. The time measurement was started at the same time when the ion-exchanged water came into contact with the absorber. The time until the deionized water retained on the surface non-woven fabric was absorbed by the water absorbent resin and the area where the surface non-woven fabric appeared white was half of the non-woven fabric was defined as the whitening time (second). The measurement was stopped in 180 seconds.

<Diagonal leak test>
Each absorbent article-1 was placed on a table having an inclination of 40 degrees so that the long side was along the inclined surface, and 2 cm of the upper side was fixed to the table with gum tape. 80 ml of physiological saline was dropped from a position of 1 cm in height from the upper end to the center position on the left and right, 10 cm from the upper end, and the weight of the physiological saline leaked from the lower end of the absorber was measured to obtain the leak amount (g). ..

<Absorption time test>
Each absorbent article-1 was placed on a flat plate, a SUS ring having a diameter of 6 cm and a height of 3 cm was placed at the center of the absorbent article, and 80 ml of physiological saline was added to the center of the absorbent body at a height of 1 cm with a dropping funnel. It was dripped from there. After standing for 5 minutes, 80 ml of physiological saline was again dropped from a height of 1 cm with a dropping funnel, and the measurement of time was started at the same time when the absorbent was contacted. The absorption time (second) was defined as the time until the physiological saline in the SUS ring was absorbed by the absorber and could not be visually confirmed.

<Preparation of absorbent article-2>
400 parts of fluff pulp and 100 parts of the evaluation sample {each absorbent resin particle obtained in the examples and comparative examples} were mixed with an air flow type mixing device {pad former made by Autech Co., Ltd.} to obtain a mixture. Then, this mixture was uniformly laminated on an acrylic plate (thickness: 4 mm) so that the basis weight was about 500 g/m ^2, and pressed at a pressure of 5 Kg/cm ² for 30 seconds to use each water-absorbent resin particle. Each absorber was obtained. Each of the absorbers was cut into a rectangle of 5 cm×20 cm, and water absorbent paper (basis weight: 15.5 g/m ² , Advantech, filter paper No. 2) of the same size as the absorber was arranged above and below the absorber. Each absorbent article-2 was prepared by arranging a polyethylene sheet (polyethylene film UB-1 manufactured by Tama Poly Co., Ltd.) on the back surface and a non-woven fabric (basis weight 20 g/m ² , Eltas Guard manufactured by Asahi Kasei Corporation) on the front surface.

<Evaluation of blood dryness of absorbent articles>
Each absorbent article-2 prepared above was placed on a flat plate, and 5 g of horse blood (horse EDTA whole blood, manufactured by Japan Lamb Co., Ltd.) was poured all at once in the center of the absorbent article, and at the same time when it contacted the absorbent body. Time measurement has started. The time until the surface horse blood was absorbed by the absorber and could not be visually confirmed was defined as the blood absorption time (second). In addition, after 5 minutes, the weight (W0) was previously measured, and 20 pieces of filter paper shredded into a size of 5 cm×5 cm were placed on the central part of the absorbent article, a weight of 175 g was placed on the absorbent article, and the weight was held for 20 seconds. (W1) was measured. The blood reversion amount (g) was calculated from the following formula. It should be noted that if the absorption time is slow, it takes a long time to feel a dry feeling, and thus the dryness is poor.
Blood reversion amount (g)=W1(g)-W0(g)

Water-absorbent resin particles (P-1) to (P-7) of Examples 1 to 7 and water-absorbent resin particles (R-1) to (R-7) of Comparative Examples 1 to 7 and were prepared using these. For each absorber, weight average particle size, particle size distribution index (SPAN) measured by an image analysis type particle size distribution measuring device, blood absorption amount, blood absorption time, physiological saline flow rate under a load of 0.71 kPa , Absorption time by Vortex method, Apparent density, Centrifuge retention of physiological saline, Absorption of physiological saline under load, Absorption of ion-exchanged water for 60 seconds, Dryability test (whitening time) by draining, oblique leakage Tables 1 and 2 show the test (leakage amount), absorption time, blood dryness evaluation (blood reversion amount), and blood absorption time evaluation results.

As can be seen from Tables 1 and 2, the absorbent resin particles of the present invention have a weight average particle diameter and a particle size distribution index (SPAN) in a specific range, and the absorbent resin particles are Both the amount of reversion and the evaluation result of the absorption time related to the dryness are excellent. It is also found that the absorbent resin particles of the present invention are superior to the comparative examples in terms of blood absorption amount and blood absorption time of the absorbent resin particles themselves. The water-absorbent resin particles of the present invention have a specific weight average particle size range, a narrow particle size distribution (low particle size distribution index SPAN), and a physiological saline flow rate of 80 ml/min under a load of 0.71 kPa. As described above, the absorption time by the Vortex method is within a specific range. When the particle size distribution is narrow and the absorption time by the Vortex method is within a specific range, the absorption amount of ion-exchanged water for 60 seconds is high and the whitening time is short, so the liquid from the nonwoven fabric under high swelling ratio It can be said that it is excellent in dryness because it is found to have good pullability. Further, when the absorption time by the Vortex method is short, the amount of leakage is small, and when the flow rate of physiological saline is 80 ml/min or more under a load of 0.71 kPa, the absorption time of the absorber is short, and It can be said that leakage is reduced when used. When the detailed comparative examples are confirmed, the comparative example 1 has a high particle size distribution index SPAN, a low blood absorption amount, a large reversion amount, a 60-second absorption amount of ion-exchanged water, and a low whitening time. ing. In Comparative Example 2, since the weight average particle size is too large, the blood absorption amount is low and the blood absorption time is long, the reversion amount is further deteriorated, and the absorption amount by the Vortex method is long, the amount of leakage is large, Exchanged water is absorbed for 60 seconds and the absorbed amount is low, and the whitening time is long. In Comparative Example 3, since the weight average particle size is too small, spot absorption and gel blocking are likely to occur. Although the absorption time by the Vortex method is short, the liquid passing speed is slow, the whitening time is long, and the absorption time of the absorber is long. Is getting longer. In Comparative Example 4, the physiological saline solution passing rate under a load of 0.71 kPa is low, and therefore the absorption time of the absorber is long. In Comparative Example 5, the extrusion kneading mechanism was not used in the gel crushing step, and the absorption time by the Vortex method was long, and the whitening time and the amount of leakage were large. In Comparative Examples 6 and 7, tracing of a known document was performed which is characterized by a narrow particle size distribution, but the particle size distribution is wider and the whitening time is longer than in the present invention.

Further, comparing Example 1 with Examples 4 and 5, Example 1 in which a hydrophobic substance (C) having a melting point equal to or lower than the gel temperature for kneading and shredding in the gel crushing step is added has a low particle size distribution index SPAN, It can be seen that the process has the effect of lowering the particle size distribution index. In other words, when the same particle size distribution index is obtained by the sieving operation, the recycling rate in Example 1 can be reduced as compared with Examples 4 and 5, and the productivity is high.

The water-absorbent resin particles of the present invention can be applied not only to an absorbent body containing water-absorbent resin particles and a nonwoven fabric, but also to an absorbent body containing water-absorbent resin particles and a fibrous material. It is useful for absorbent articles provided (paper diapers, sanitary napkins, medical blood-holding agents, etc.). In addition, pet urine absorbent, urine gelling agent for mobile toilets, freshness-maintaining agent for fruits and vegetables, drip absorbent for meat and seafood, ice pack, disposable body warmer, gelling agent for batteries, water retention agent for plants and soil, dew condensation It can also be used in various applications such as preventive agents, waterstop agents, packing agents and artificial snow. In particular, since it has high blood absorption performance, absorbent articles for menstrual blood or blood absorption such as sanitary napkins, tampons, medical sheets, drip absorbents, wound protection materials, wound healing materials, surgical waste liquid treatment agents, etc. Useful for.

Claims

Water absorption having a structure in which resin particles containing a water-soluble vinyl monomer (a1) and a cross-linked polymer (A) containing a cross-linking agent (b) as an essential constituent unit are surface-cross-linked with at least one surface cross-linking agent (d). Resin particles having a weight average particle diameter of 200 to 420 μm and a particle size distribution index (SPAN) represented by the following formula 1 measured by an image analysis type particle size distribution measuring device of 0.30 to 0. 75 water-absorbent resin particles.
Particle size distribution index (SPAN)=(90% particle size in volume-based integrated particle size-10% particle size in volume-based integrated particle size)/(50% particle size in volume-based integrated particle size) (Equation 1)
The water absorbent resin particles according to claim 1, further containing a hydrophobic substance (C).
The water-absorbent resin according to claim 1 or 2, wherein the rate of passage of 0.9 wt% physiological saline under a load of 0.71 kPa is 80 ml/min or more, and the absorption time by the Vortex method is 15 to 40 seconds. particle.
The water absorption amount according to any one of claims 1 to 3, which has a blood absorption amount of 10 to 30 g/g and a blood absorption time of 120 seconds or less, which is a time from when the blood is added to when the fluidity of the blood disappears. Resin particles.
The water-absorbent resin particle according to any one of claims 1 to 4, wherein the particle shape is an irregular crushed shape.
The water-absorbent resin particles according to any one of claims 1 to 5, containing inorganic fine particles and/or a polyvalent metal salt.
7. The centrifugal retention amount of 0.9 wt% physiological saline is 25 to 45 g/g, and the absorption amount of 0.9 wt% physiological saline under load is 15 to 30 g/g. The water-absorbent resin particles according to.
The water-absorbent resin particles according to any one of claims 1 to 7, wherein the ion-exchanged water is absorbed for 60 seconds and has an absorption amount of 50 to 100 g/g.
An absorber containing the water-absorbent resin particles according to any one of claims 1 to 8 and a nonwoven fabric.
An absorbent article comprising the absorbent body according to claim 9.
The absorbent article according to claim 10, which is for absorbing menstrual blood or blood.
The method for producing water-absorbent resin particles according to any one of claims 1 to 5, wherein a monomer composition containing the water-soluble vinyl monomer (a1) and the crosslinking agent (b) as essential constituent units is polymerized, Polymerization step for obtaining a hydrogel containing the crosslinked polymer (A), gel crushing step for kneading and chopping the hydrogel to obtain hydrogel particles, drying and classifying the hydrogel particles, and containing (A) And a surface treatment step of surface-treating the resin particles with a surface cross-linking agent (d), wherein a hydrophobic substance (C) is added in the gel crushing step or the surface treatment step, in which case A method for producing water-absorbent resin particles, wherein the melting point of the hydrophobic substance (C) is not higher than the temperature of the step of adding (C).
The method for producing water-absorbent resin particles according to claim 12, wherein the hydrophobic substance (C) is added before and/or at the same time as the gel grinding in the gel grinding step.
The method for producing water-absorbent resin particles according to claim 12 or 13, wherein the kneading and shredding temperature is a temperature of 70 to 120°C.