JP2020125472A - Water-absorbing resin particles and method for producing the same - Google Patents

Abstract

To provide a water-absorbing resin particle which can prevent liquid leakage such as urine leakage, even if the particle has been applied to an absorbent body using a large amount of hydrophilic fibers, or to an absorbent body using a small amount of hydrophilic fibers, even if the adsorbent body has been used for a long time, or even if urine has been repeatedly discharged onto the adsorbent body; and a method for producing the same.SOLUTION: The water-absorbing resin particle includes: a cross-linked polymer (A) that contains a water-soluble vinyl monomer (a1) and/or a hydrolyzable vinyl monomer (a2), and a cross-linking agent (b), as essential constituent units; a hydrophobic substance (c); and a polyvalent metal salt (d), wherein the absorption index is 95 or larger; the water-retaining amount (g/g) for 0.9 wt% physiological saline is 37 or more and less than 47; the liquid flow rate (ml/min) of 0.9 wt% physiological saline in which the water-absorbing resin particles have been immersed for 30 minutes is 10 or less under a pressurized state to 2.1 kPa; and the water content (%) is 5 or more and less than 15. The production method includes: adding (c) whose melting point is 90°C or lower, in the gel pulverizing step; and kneading and chopping the mixture at a temperature of the melting point or higher and 120°C or lower.SELECTED DRAWING: None

Description

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

In absorbent articles such as paper diapers, sanitary napkins and incontinence pads, hydrophilic fibers such as pulp and water-absorbent resin particles containing acrylic acid (salt) as a main raw material are widely used as an absorber. In recent years, from the viewpoint of improving QOL (Quality of Life), demand for these absorbent articles is shifting to lighter weight and thinner, and accordingly, reduction in the amount of hydrophilic fibers used is desired. It was Therefore, there is an increasing need for the water-absorbent resin particles themselves to play the roles of initial absorption and liquid diffusibility in the absorbent body, which have been carried out by hydrophilic fibers.

An important function of the absorber is prevention of liquid leakage outside the absorption system. In particular, in an absorber in which the amount of hydrophilic fibers used is small, the hydrophilic fibers usually have low initial absorbency and liquid diffusibility, and the problem of liquid leakage becomes apparent. Conventionally, there have been many proposals for preventing liquid leakage of an absorbent having a small amount of hydrophilic fibers, but even if the evaluation in the table test is good, excellent absorption performance is obtained under the conditions in which the absorbent article is actually used. It was difficult to secure. For example, an absorbent article is often used in a pressurized environment such as a sitting position and a recumbent position, and under such conditions, the absorbent performance of the absorbent body is significantly deteriorated as compared to use in a non-pressurized environment, Liquid leakage tends to occur. In particular, in an absorber having a small hydrophilic fiber usage ratio, the absorption performance in the early stage of urination deteriorates, and liquid leakage from the absorber is likely to occur. Therefore, usually, the initial absorption performance can be improved by increasing the absorption rate and the liquid diffusibility of the water absorbent resin particles under pressure. On the other hand, in order to improve the initial absorption performance of the water-absorbent resin particles, when the absorption rate under pressure and the liquid diffusibility are increased, as the usage ratio of the hydrophilic fiber in the absorber increases, the inside of the absorber increases. If the liquid permeability becomes too good and there are multiple urinations, the absorption will not catch up with the flow of the liquid and the liquid will leak from the absorber, especially in the latter stage of swelling when the absorption rate of the water-absorbent resin particles slows down. There were cases. As described above, in an absorber with a small usage ratio of hydrophilic fibers, a change in the usage amount of the hydrophilic fibers greatly affects the liquid leakage of the absorbent body. It has been difficult to realize water-absorbent resin particles having absorption performance applicable to a wide range of absorbers.

Conventionally, as a technique that can be applied to an absorber with a small amount of hydrophilic fibers used, by controlling the water absorption rate pattern of the water absorbent resin particles by incorporating a hydrophobic substance inside or on the surface of the crosslinked polymer, Water-absorbent resin particles that uniformly diffuse urine have been proposed. For example, water-absorbent resin particles having a structure containing a hydrophobic substance inside a cross-linked polymer (Patent Document 1), and a hydrophobic substance attached to the surface of the cross-linked polymer can improve powder fluidity and the like. There are known improved water-absorbent resin particles (Patent Document 2), water-absorbent resin particles (Patent Document 3) containing a hydrophobic substance inside and on the surface thereof.

However, in these conventional techniques, the absorbent article containing the water-absorbent resin particles has satisfactory initial water absorption performance and absorption amount under pressure depending on the usage ratio of hydrophilic fibers, especially when the ratio is low. However, there is still a problem that the liquid does not enter the absorber and leaks, or the liquid that cannot be completely absorbed in the absorber diffuses and leaks.

JP, 2005-097569, A JP, 2004-261796, A JP, 2011-252088, A

The object of the present invention is to apply a liquid such as a urine leak even when it is used for a long time or repeatedly urinates, even if it is applied to an absorber with a large amount of hydrophilic fibers used, or even if it is applied to an absorber with a small amount of hydrophilic fibers It is an object of the present invention to provide a water absorbent resin particle capable of preventing leakage and a method for producing the same.

The present invention relates to a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis and a cross-linked polymer (A) containing a cross-linking agent (b) as an essential constituent unit. A water-absorbent resin particle containing a hydrophobic substance (c) and a polyvalent metal salt (d) and satisfying the following (1) to (4):
(1) The absorption index represented by the following formula 1 is 95 or more,
Absorption index = Water retention (X) x 2 + Pressurized DW 10 minutes value (Y) (Equation 1)
[In the formula 1, the water retention capacity (X) is the water retention capacity (g/g) with respect to 0.9 wt% physiological saline, and the pressurized DW 10-minute value (Y) is 2.1 kPa added measured by the Demand Wettability test method. Represents the absorption (g/g) of 0.9 wt% saline after 10 minutes under pressure]
(2) The water retention capacity (g/g) with respect to 0.9 wt% physiological saline is 37 or more and less than 47,
(3) The liquid-passing speed (ml/min) of 0.9 wt% saline under pressure of 2.1 kPa after immersion of the water-absorbent resin particles in 0.9 wt% physiological saline for 30 minutes is 10 or less,
(4) Water content (%) is 5 or more and less than 15.
The present invention also relates to the above-mentioned method for producing water-absorbent resin particles, which comprises a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a crosslinking agent (b). Polymerizing a monomer composition having an essential constitutional unit) to obtain a hydrogel containing a crosslinked polymer (A), a gel pulverizing step of kneading the hydrogel to obtain hydrogel particles, The method comprises a step of obtaining resin particles containing the crosslinked polymer (A) by classifying the hydrogel particles after drying and pulverizing, and a step of surface-treating the resin particles. Before and/or at the same time as kneading and shredding, a hydrophobic substance (c) having a melting point of 90° C. or lower is added, and the kneading and shredding temperature is at least the melting point of the hydrophobic substance (c) and It is a method for producing water-absorbent resin particles having a temperature of 120° C. or lower.

The water-absorbent resin particles of the present invention have the above-mentioned constitution, and in particular, have an excellent absorption amount under pressure and have good initial absorption performance. The water-absorbent resin particles of the present invention can be applied to both a large absorber and a small absorber of the amount of hydrophilic fiber used, when applied to the absorber and the absorbent article, in a pressurized environment such as sitting and lying down, Even after long-term use or repeated urination, liquid does not easily leak outside the absorption system.

The water-absorbent resin particle of the present invention comprises a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a cross-linking polymer containing the cross-linking agent (b) as essential constituent units. Water-absorbent resin particles containing a coalesced product (A), a hydrophobic substance (c), and a polyvalent metal salt (d).

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 group and ethylenic vinyl group disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 3648553 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 JP2003-165883A. 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 2005-75982 A. Vinyl monomers having at least one of

Vinyl monomer (a2) that becomes water-soluble vinyl monomer (a1) by hydrolysis {hereinafter, also referred to as hydrolyzable vinyl monomer (a2). } Is not particularly limited, and is publicly known [for example, a vinyl monomer having at least one hydrolyzable substituent to be a water-soluble substituent by hydrolysis disclosed in paragraphs 0024 to 0025 of Japanese Patent No. 3648553, JP At least one hydrolyzable substituent disclosed in paragraphs 0052 to 0055 of 2005-75982 {1,3-oxo-2-oxapropylene (-CO-O-CO-) group, acyl group and cyano group. Vinyl monomer having a group, etc.] and the like can be used. The water-soluble vinyl monomer is a concept well known to those skilled in the art, but if expressed in terms of quantity, it means, for example, a vinyl monomer that is soluble in at least 100 g in 100 g of water at 25°C. The hydrolyzability of the hydrolyzable vinyl monomer (a2) means, for example, the property of being hydrolyzed by the action of water and, if necessary, a catalyst (acid or base etc.) to become water-soluble. The hydrolysis of the hydrolyzable vinyl monomer (a2) may be carried out during the polymerization, after the polymerization, or both of them, but the polymerization is preferable from the viewpoint of the absorption performance of the water-absorbent resin particles obtained.

Among these, water-soluble vinyl monomers (a1) are preferable from the viewpoint of absorption performance, and more preferable are the above-mentioned anionic vinyl monomers, carboxy (salt) groups, sulfo (salt) groups, amino groups, carbamoyl groups, Vinyl monomers having an ammonio group or a mono-, di- or tri-alkylammonio group, even more preferably vinyl monomers having a carboxy (salt) group or a carbamoyl group, and particularly preferably (meth)acrylic acid (salt) And (meth)acrylamide, particularly preferred is (meth)acrylic acid (salt), most preferred 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 and ammonium (NH ₄ ) salts. Among these salts, alkali metal salts and ammonium salts are preferable, alkali metal salts are more preferable, and sodium salts are particularly preferable, from the viewpoint of absorption performance and the like.

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 for neutralization, 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 used. Neutralization may be performed 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 below. 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%. If 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.

When either the water-soluble vinyl monomer (a1) or the hydrolyzable vinyl monomer (a2) is used as a constitutional unit, one type may be used alone as a constitutional unit, or if necessary, two or more types may be used as constitutional units. good. The same applies when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as the constituent units. Further, when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as the constitutional units, the content molar ratio of these {(a1)/(a2)} is preferably 75/25 to 99/1. , More preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, and most preferably 91/9 to 92/8. When it is within these ranges, the absorption performance is further improved.

As the constitutional unit of the crosslinked polymer (A), in addition to the water-soluble vinyl monomer (a1) and the hydrolysable vinyl monomer (a2), other vinyl monomer (a3) copolymerizable with them is used as the constitutional unit. You can As the other vinyl monomer (a3), one type may be used alone, or two or more types may be used in combination.

The other vinyl monomer (a3) is not particularly limited, and is publicly known (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 36485553, paragraph 0025 of JP 2003-165883 A and special features). Hydrophobic vinyl monomers such as vinyl monomers disclosed in paragraph 0058 of Japanese Unexamined Patent Publication No. 2005-75982) can be used, and specifically, the following vinyl monomers (i) to (iii) can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, 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.) and the like.
(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 (mol %) of the other vinyl monomer (a3) unit is, based on the total number of moles of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit, from the viewpoint of absorption performance and the like. 0 to 5 is preferable, 0 to 3 is more preferable, 0 to 2 is particularly preferable, 0 to 1.5 is particularly preferable, and the content of other vinyl monomer (a3) units is from the viewpoint of absorption performance and the like. Most preferably, it is 0 mol %.

The cross-linking agent (b) is not particularly limited and is publicly 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). A cross-linking agent having at least one functional group to be obtained and having at least one ethylenically unsaturated group, and a cross-linking 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 disclosed in paragraphs 0028 to 0031, 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 the like, and more preferable is polyallyl of triallyl cyanurate, triallyl isocyanurate and polyol having 2 to 40 carbon atoms. (Meth)allyl ether, particularly preferred are triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane, polyethylene glycol diallyl ether and pentaerythritol triallyl ether, and most preferred is 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 (a1) when the other vinyl monomer (a3) of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit is also used. Based on the total number of moles of (a3) to (a3), 0.001 to 5 is preferable, 0.005 to 3 is more preferable, and 0.01 to 1 is particularly preferable. Within these ranges, the absorption performance will be even better.

The method for producing water-absorbent resin particles of the present invention comprises polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and/or a hydrolyzable vinyl monomer (a2) and a crosslinking agent (b) as an essential constituent unit. Then, a polymerization step of obtaining a hydrogel containing the crosslinked polymer (A), a gel pulverization step of kneading and chopping the hydrogel to obtain hydrogel particles, drying the hydrogel particles, classifying after pulverization, and crosslinking weight The method includes a step of obtaining resin particles containing the aggregate (A), and a step of surface-treating the resin particles.

In the polymerization step, as a method for polymerizing the crosslinked polymer (A), known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization method, etc.; JP-A-55-133413, etc.) and known reverse phase suspension are used. Polymerization (Japanese Patent Publication No. 54-30710, Japanese Unexamined Patent Publication No. 56-26909, Japanese Unexamined Patent Publication No. 1-5808, etc.) can be mentioned.

The solution polymerization method is preferable as the polymerization method, 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 water retention amount and a water-soluble component amount. The aqueous solution adiabatic polymerization method is most preferable because water-absorbent resin particles having a small amount of water 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, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutyl alcohol, t-butyl alcohol can be used. , Isopentyl alcohol, acetone, methyl ethyl ketone, N,N-dimethylformamide, dimethyl sulfoxide and mixtures of two or more thereof. When carrying out aqueous solution polymerization, the amount (% by weight) of the organic solvent used is preferably 40 or less, and more preferably 30 or less, based on the weight of water.

When the initiator is used for the polymerization, an initiator for radical polymerization can be used, and examples thereof include azo compounds {azobisisobutyronitrile, azobiscyanovaleric acid, and 2,2′-azobis(2-amidinopropane)hydrochloride. }, inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides {benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide And di(2-ethoxyethyl)peroxydicarbonate} and a redox catalyst (alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite and ascorbic acid and other reducing agents and alkali metal persulfate, persulfate, (Combined with an oxidizing agent such as ammonium sulfate, 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 initiator is (a1) to (a3) when the other vinyl monomer (a3) of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) is also used. Of 0.0005-5 is preferable, and 0.001-2 is more preferable.

During the polymerization, a polymerization control agent typified by a chain transfer agent may be used in combination, and specific examples thereof include sodium hypophosphite, sodium phosphite, alkyl mercaptans, and alkyl halides. , Thiocarbonyl compounds and the like. 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 the same as that of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), or (a1) to (a3) when other vinyl monomer (a3) is also used. Based on the total weight, 0.0005-5 is preferable, and 0.001-2 is more preferable.

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 dispersant or a surfactant, if necessary. Further, in the case of the reverse phase suspension polymerization method, the polymerization can be carried out by using a 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 chopping 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 chopping 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/extruding mechanism (for example, a uniaxial or biaxial kneading extruder, a mincing machine, etc.) is preferable.

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.

As a method of distilling off the solvent (including water) of the hydrogel particles and drying, a method of distilling (drying) with hot air having a temperature of 80 to 230°C, a drum dryer heated to 100 to 230°C, etc. The thin film drying method according to, the (drying) reduced pressure drying method, the freeze drying method, the infrared drying method, decantation, filtration and the like can be applied.

When the solvent contains an organic solvent, the content (% by weight) of the organic solvent after distillation is preferably 0 to 10 based on the weight of the crosslinked polymer (A), more preferably 0 to 5 and particularly preferably. Is 0 to 3, most preferably 0 to 1. Within this range, the water absorbing resin particles will have even better absorption performance.

When the solvent contains water, the water content (% by weight) after distillation is preferably 0 to 20, more preferably 2.5 to 15, and particularly preferably 3 based on the weight of the crosslinked polymer (A). .5 to 10, most preferably 4.5 to 8. Within such a range, problems such as pulverizability in the pulverizing step, which will be described later, and clogging of equipment and piping in the classifying step and the like are reduced. The water content of the water-absorbent resin particles of the present invention is not determined only by the drying step, but can be adjusted after the post-treatment step (surface cross-linking, surface treatment step, etc.).

The content and water content of the organic solvent are measured by an infrared moisture meter [eg 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.

The resin particles containing the crosslinked polymer (A) are pulverized and then classified to adjust the weight average particle diameter and particle size distribution of the resin particles. 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 (meaning described later) may be pulverized again after classification. When the sieved product is pulverized again, the pulverizers may be the same or different, 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 having 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 (sieving product) and the particles passing through the sieve with a specific opening (subsidiary product) are removed. It is preferable.

The opening (μm) of the sieve to be a sieve product is preferably 850 to 250, more preferably 710 to 300, particularly preferably 500 to 425, and the sieve (μm) of the sieve product is 500 to 90. It is more preferably 425 to 106, particularly preferably 300 to 150. The openings of these sieves are appropriately adjusted in order to obtain the desired weight average particle size and particle size distribution.

The particles removed by the sieve (particularly, the undersize product) can be reused by using a known technique. 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 of adding water to a fine powder of a water absorbent resin and granulating at a specific surface pressure or higher (European Patent No. 844270), sufficiently moistening the fine powder of a water absorbent resin to form an amorphous gel and drying. 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 pulverization and classification if necessary is preferably 200 to 600, more preferably 300 to 500, and particularly preferably 350 to 420. .. If it is larger than these ranges, the initial absorption performance will be poor, and if it is smaller than these ranges, spot absorption or gel blocking will occur, and leakage will easily occur in any case.

The weight average particle diameter was measured 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 with a low tap test sieve shaker for 5 minutes. The weight of the measured particles on each sieve and the pan is weighed, and the total of the particles 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 is the sieve opening (particle size ), and the vertical axis is the weight fraction], and a line connecting the points is drawn to determine the particle diameter corresponding to a weight fraction of 50% by weight, which is taken as the weight average particle diameter.

Further, when the content of the fine particles contained in the resin particles containing the crosslinked polymer (A) is large, spot absorption or gel blocking occurs and liquid leakage easily occurs, so less than 106 μm in the total weight of all the resin particles ( The weight ratio (% by weight) of particles having a particle diameter of preferably less than 150 μm) is preferably 3 or less, and more preferably 1 or less. The content of the fine particles can be obtained using the graph created when obtaining the above weight average particle diameter.

The water absorbent resin particles of the present invention contain a hydrophobic substance (c). As (c), a hydrophobic substance (c1) containing a hydrocarbon group having 8 to 30 carbon atoms, a hydrophobic substance (c2) containing a hydrocarbon group having a fluorine atom, and a hydrophobic substance which is an organic polysiloxane. (C3) and the like. When the hydrophobic substance (c) is contained, blocking between the resin particles at the initial stage of swelling is suppressed, the liquid diffusion property of the absorber is improved, the initial absorption performance of the resin particles is improved, and leakage from the absorber can be prevented. ..

As the hydrophobic substance (c1) containing a hydrocarbon group having 8 to 30 carbon atoms, a long-chain fatty acid ester, a long-chain fatty acid and a salt thereof, a long-chain aliphatic alcohol, a long-chain aliphatic amide, a surface activity of HLB of 10 or less. Agents, waxes and mixtures of two or more of these.

Examples of the long-chain fatty acid ester include esters of fatty acids having 8 to 30 carbon atoms and alcohols 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 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 Ester, beef tallow, etc.).

Examples of long-chain fatty acids and salts thereof include fatty acids having 8 to 30 carbon atoms (for example, lauric acid, palmitic acid, stearic acid, oleic acid, behenic acid, etc.), and salts thereof include zinc, calcium, magnesium or aluminum. (Hereinafter, abbreviated as Zn, Ca, Mg, and Al) (for example, Ca palmitate, Al palmitate, Ca stearate, Mg stearate, Al stearate, etc.).

Examples of the long-chain aliphatic alcohol include aliphatic alcohols having 8 to 30 carbon atoms (for example, lauryl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol, etc.). From the viewpoint of preventing liquid leakage of the absorbent article, palmityl alcohol, stearyl alcohol, and oleyl alcohol are preferable, and stearyl alcohol is more preferable.

As the long-chain aliphatic amide, an amidation product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms, ammonia or a primary amine having 1 to 7 carbon atoms And an amidation product of a long-chain fatty acid having 8 to 30 carbon atoms, an amidation product of a long-chain aliphatic secondary amine having at least one aliphatic chain having 8 to 30 carbon atoms, and a carboxylic acid having 1 to 30 carbon atoms, and An amidation product of a secondary amine having two aliphatic hydrocarbon groups having 1 to 7 carbon atoms and a long chain fatty acid having 8 to 30 carbon atoms can be mentioned.

As an amidation product of a long-chain aliphatic primary amine having 8 to 30 carbon atoms and a carboxylic acid having a hydrocarbon group having 1 to 30 carbon atoms, a product obtained by reacting a primary amine with a carboxylic acid in a ratio of 1:1 is used. : It can be divided into those reacted with 2. Examples of the 1:1 reaction product include acetic acid N-octylamide, acetic acid N-hexacosylamide, heptacosanoic acid N-octylamide, and heptacosanoic acid N-hexacosylamide. Examples of the reaction of 1:2 include diacetic acid N-octylamide, diacetic acid N-hexacosylamide, diheptacosanoic acid N-octylamide and diheptacosanoic acid N-hexacosylamide. When the primary amine and the carboxylic acid are reacted at a ratio of 1:2, the carboxylic acids used may be the same or different.

The amidation product of ammonia or a primary amine having 1 to 7 carbon atoms and a long-chain fatty acid having 8 to 30 carbon atoms is 1:2 with a reaction product of ammonia or primary amine and carboxylic acid at 1:1. It can be divided into reacted products. As the reaction product at 1:1, nonanoic acid amide, nonanoic acid methylamide, nonanoic acid N-heptylamide, heptacosanoic acid amide, heptacosanoic acid N-methylamide, heptacosanoic acid N-heptylamide and heptacosanoic acid N-hexacosylamide Etc. Those reacted at 1:2 include dinonanoic acid amide, dinonanoic acid N-methylamide, dinonanoic acid N-heptylamide, dioctadecanoic acid amide, dioctadecanoic acid N-ethylamide, dioctadecanoic acid N-heptylamide, diheptacosanoic acid amide. , Diheptacosanoic acid N-methylamide, diheptacosanoic acid N-heptylamide, diheptacosanoic acid N-hexacosylamide, and the like. The carboxylic acids used may be the same as or different from each other as the reaction product of ammonia or primary amine and carboxylic acid in a ratio of 1:2.

Examples of the amidation product of a long-chain aliphatic secondary amine having at least one aliphatic chain having 8 to 30 carbon atoms and a carboxylic acid having 1 to 30 carbon atoms include N-methyloctylamide acetate and N-methylhexaacetic acid acetate. Lamide, acetic acid N-octylhexacosylamide, acetic acid N-dihexacosylamide, heptacosanoic acid N-methyloctylamide, heptacosanoic acid N-methylhexacosylamide, heptacosanoic acid N-octylhexacosylamide and heptacosane Acid N-dihexacosylamide etc. are mentioned.

As the amidation product of a secondary amine having two aliphatic hydrocarbon groups having 1 to 7 carbon atoms and a long chain fatty acid having 8 to 30 carbon atoms, nonanoic acid N-dimethylamide, nonanoic acid N-methylheptylamide, Examples thereof include nonanoic acid N-diheptylamide, heptacosanoic acid N-dimethylamide, heptacosanoic acid N-methylheptylamide, and heptacosanoic acid N-diheptylamide.

Examples of the surfactant having an HLB of 10 or less include alkylene oxide (hereinafter abbreviated as AO) addition type nonionic surfactants and polyvalent alcohol type nonionic surfactants. The HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is determined by the Oda method (Surfactant Primer, page 212, Takehiko Fujimoto, Sanyo Chemical Industry Co., Ltd., 2007).

The AO addition type nonionic surfactant is a higher fatty acid added to polyalkylene glycol obtained by directly adding AO to higher alcohol, higher fatty acid or alkylamine, or adding AO to glycol. Or the like, or by adding AO to the esterified product obtained by reacting a polyhydric alcohol with a higher fatty acid, or by adding AO to a higher fatty acid amide.

Examples of AO include ethylene oxide (hereinafter abbreviated as EO), propylene oxide (hereinafter abbreviated as PO), and butylene oxide (hereinafter abbreviated as BO). Of these, preferred are EO single adducts and random or block adducts of EO and PO.

Specific examples of the AO addition type nonionic surfactant include oxyalkylene alkyl ethers (eg, octyl alcohol EO adduct, lauryl alcohol EO adduct, stearyl alcohol EO adduct, oleyl alcohol EO adduct, lauryl alcohol EO). PO block adduct, etc.); polyoxyalkylene higher fatty acid ester (eg, stearyl acid EO adduct, lauric acid EO adduct, etc.); polyoxyalkylene polyhydric alcohol higher fatty acid ester (eg, polyethylene glycol lauric acid Diesters, oleic acid diesters of polyethylene glycol, stearic acid diesters of polyethylene glycol, etc.); polyoxyalkylene alkylphenyl ethers (for example, nonylphenol EO adducts, nonylphenol EO/PO block adducts, octylphenol EO adducts, bisphenol A. EO adduct, dinonylphenol EO adduct, styrenated phenol EO adduct, etc.); polyoxyalkylene alkylamino ether (eg, laurylamine EO adduct, stearylamine EO adduct, etc.); polyoxyalkylene alkylalkano- Examples thereof include amide adducts of hydroxyethyllauric acid amide, EO adducts of hydroxypropyloleic acid amide, EO adducts of dihydroxyethyllauric acid amide, and the like.

Examples of polyhydric alcohol type nonionic surfactants include polyhydric alcohol fatty acid esters, polyhydric alcohol fatty acid ester AO adducts, polyhydric alcohol alkyl ethers, polyhydric alcohol alkyl ether AO adducts, and the like.

Specific examples of the polyhydric alcohol fatty acid ester include pentaerythritol monolaurate, pentaerythritol monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan monolaurate, sorbitan dilaurate, sorbitan dioleate and sucrose monostearate. Is mentioned.
Specific examples of the polyhydric alcohol fatty acid ester AO adduct include ethylene glycol monooleate EO adduct, ethylene glycol monostearate EO adduct, trimethylolpropane monostearate EO/PO random adduct, sorbitan monolaurate EO adduct. Compounds, sorbitan monostearate EO adducts, sorbitan distearate EO adducts, sorbitan dilaurate EO/PO random adducts, and the like.
Specific examples of the polyhydric alcohol alkyl ether include pentaerythritol monobutyl ether, pentaerythritol monolauryl ether, sorbitan monomethyl ether, sorbitan monostearyl ether, methyl glycoside, and lauryl glycoside.
Specific examples of the polyhydric alcohol alkyl ether AO adduct include sorbitan monostearyl ether EO adduct, methyl glycoside EO/PO random adduct, lauryl glycoside EO adduct, and stearyl glycoside EO/PO random adduct.

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.).

Examples of the hydrophobic substance (c2) containing a hydrocarbon group having a fluorine atom include perfluoroalkane, perfluoroalkene, perfluoroaryl, perfluoroalkyl ether, perfluoroalkylcarboxylic acid, perfluoroalkyl alcohol and these 2 Mixtures of more than one species are included.

Examples of perfluoroalkanes include alkanes having 4 to 42 fluorine atoms and 1 to 20 carbon atoms (for example, trifluoromethane, pentafluoroethane, pentafluoropropane, heptafluoropropane, heptafluorobutane, nonaflufluorohexane, tridecafluoro). Octane and heptadecafluorododecane).

Examples of perfluoroalkenes include alkenes having 4 to 42 fluorine atoms and 2 to 20 carbon atoms (for example, trifluoroethylene, pentafluoropropene, trifluoropropene, heptafluorobutene, nonaflufluorohexene, tridecafluorooctene and hepta). Decafluorododecene etc.).

As perfluoroaryl, aryl having 4 to 42 fluorine atoms and 6 to 20 carbon atoms (for example, trifluorobenzene, pentafluorotoluene, trifluoronaphthalene, heptafluorobenzene, nonaflufluoroxylene, tridecafluorooctylbenzene and Heptadecafluorododecylbenzene and the like).

Examples of perfluoroalkyl ethers include ethers having 2 to 82 fluorine atoms and 2 to 40 carbon atoms (for example, ditrifluoromethyl ether, dipentafluoroethyl ether, dipentafluoropropyl ether, diheptafluoropropyl ether, diheptafluoro). Butyl ether, dinonafluorofluorohexyl ether, ditridecafluorooctyl ether, diheptadecafluorododecyl ether and the like).

Examples of perfluoroalkylcarboxylic acids include carboxylic acids having 3 to 41 fluorine atoms and 1 to 21 carbon atoms (for example, pentafluoroethanoic acid, pentafluoropropanoic acid, heptafluoropropanoic acid, heptafluorobutanoic acid, nonaflufluorohexane). Acid, tridecafluorooctanoic acid, heptadecafluorododecanoic acid and salts of these metals (alkali metal and alkaline earth metal etc.).

Examples of the perfluoroalkyl alcohol include alcohols having 3 to 41 fluorine atoms and 1 to 20 carbon atoms (for example, pentafluoroethanol, pentafluoropropanol, heptafluoropropanol, heptafluorobutanol, nonaflufluorohexanol, tridecafluorooctanol and Heptadecafluorododecanol, etc.) and ethylene oxide (1 to 20 mol per 1 mol of alcohol) adducts of this alcohol, and the like.

Examples of the mixture of two or more of these include a mixture of a perfluoroalkylcarboxylic acid and a perfluoroalkyl alcohol (for example, a mixture of pentafluoroethanoic acid and pentafluoroethanol).

Examples of the hydrophobic substance (c3) which is an organic polysiloxane include polydimethylsiloxane, polyether modified polysiloxane {polyoxyethylene modified polysiloxane and poly(oxyethylene/oxypropylene) modified polysiloxane, etc.}, carboxy modified polysiloxane, Epoxy-modified polysiloxane, amino-modified polysiloxane, alkoxy-modified polysiloxane, etc. 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 the polysiloxane, the 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, from the viewpoint of absorption characteristics, etc., the side chains of polysiloxane and both the side chains of polysiloxane and both ends are preferable, and the side chains of polysiloxane and both ends are more preferable.

Examples of the organic group (modifying group) of the polyether modified polysiloxane include 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. ~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 products (modification 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, etc., 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 the amino-modified 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 as a carboxy equivalent, an epoxy equivalent or an 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. Further, the epoxy equivalent is determined 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).

-Toray Dow Corning Co., Ltd. BY16-880 (side chain, 3500), BY16-750 (both ends, 750), BY16-840 (side chain, 3500), SF8418 (side chain, 3500).

The epoxy-modified polysiloxane can be easily obtained from the market and, for example, the following products (modification 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 FZ-3720 (side chain 1200), BY16-839 (side chain, 3700), SF8411 (side chain, 3200), SF8413 (side chain, 3800), SF8421 (side chain, 11000). ), BY16-876 (side chain, 2800), FZ-3736 (side chain, 5000), BY16-855D (side chain, 180), BY16-8 (side chain, 3700).

Amino-modified silicone can be easily obtained from the market and, for example, the following 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-8880 (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), BY16-205 (side chain, 4000), FZ-3760 (side chain, 1500), FZ-. 3705 (side chain, 4000), BY16-209 (side chain, 1800), FZ-3710 (side chain, 1800), SF8417 (side chain, 1800), BY16-849 (side chain, 600), BY16-850 ( Side chain, 3300), BY16-879B (side chain, 8000), BY16-892 (side chain, 2000), FZ-3501 (side chain, 3000), FZ-3785 (side chain, 6000), BY16-872 ( Side chain, 1800), BY16-213 (side chain, 2700), BY16-203 (side chain, 1900), BY16-898 (side chain, 2900), BY16-890 (side chain, 1900), BY16-893 ( Side chain, 4000), FZ-3789 (side chain, 1900), BY16-853C (both ends, 360), BY16-853U (both ends, 450).

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

The viscosity (mPa·s, 25° C.) of the hydrophobic substance that is an organic 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 will be further improved. The viscosity is JIS Z8803-1991 "Liquid viscosity". Cones and cones-measured in accordance with a viscosity measurement method using a flat plate type rotational viscometer {for example, E-type viscometer (Toki Sangyo Co., Ltd. RE80L, radius adjusted to 25.0±0.5° C.) 7 mm, conical cone with an angle of 5.24×10 ⁻² rad). }.

Of the hydrophobic substances (c), the hydrophobic substance (c1) containing a hydrocarbon group having 8 to 30 carbon atoms is preferable from the viewpoint of preventing leakage of the absorbent article, and more preferably long-chain fatty acid ester and long-chain. Fatty acids and salts thereof, long-chain aliphatic alcohols and long-chain aliphatic amides, more preferably sorbit stearic acid ester, sucrose stearic acid ester, stearic acid, Mg stearate, stearic acid Ca, stearic acid Zn and stearic acid. Al, particularly preferably sucrose stearate and Mg stearate, most preferably sucrose stearate monoester.

The content (% by weight) of the hydrophobic substance (c) is preferably 0.001 to 5.0, more preferably from the viewpoint of preventing liquid leakage of the absorbent article, based on the weight of the crosslinked polymer (A). Is 0.08 to 1.0, and particularly preferably 0.08 to 0.16.

The hydrophobic substance (c) may be added in any step such as a polymerization step, a gel crushing step, a surface treatment step, etc., but it is necessary to prevent leakage of the absorbent article and dryness of the hydrous gel. From the viewpoint of goodness, in the gel pulverizing step, a method of adding the hydrophobic substance (c) before and/or at the same time as kneading and shredding the hydrogel is preferable. In a preferred embodiment of the present invention, by incorporating the hydrophobic substance (c) in the gel pulverizing step, the surface uniformity of the surface treating agent in the surface treating step described later is improved, and particularly, in the water absorbing resin particles, The balance between the water retention capacity and the absorption performance under pressure is improved, and liquid leakage can be prevented.

When the hydrophobic substance (c) is added in the gel crushing step, the melting point of the hydrophobic substance (c) is preferably 90° C. or lower, more preferably 80° C. or lower, particularly preferably 70° C. or lower. When the melting point is higher than these ranges, it is difficult to maintain the water-containing gel temperature in the gel crushing step above this range, and liquid leakage of the absorbent article may occur. The lower limit is not particularly limited, but from the viewpoint of handling at the time of addition, a melting point of 40° C. or higher is more preferable because it can be stably added in a solid state. Examples of the hydrophobic substance (c) having a melting point of 90° C. or lower include glycerin stearic acid monoester (melting point 78 to 81° C.), glycerin stearic acid diester (melting point 72 to 74° C.), sucrose stearic acid ester (48 ˜80° C.), stearyl alcohol (59 to 60° C.), hydrophobic substances (organic polysiloxane, liquid at room temperature although melting point data are not available), and the like. Further, the melting point may be lowered due to the presence of the hydrophobic substance together with the mixture, or the substance may be dissolved in a solvent and added.

In the method of adding the hydrophobic substance (c) in the gel crushing step, the temperature at which the hydrogel is kneaded and shredded is preferably not less than the melting point of the hydrophobic substance (c) and not more than 120° C., more preferably the melting point of the hydrophobic substance. It is not less than +10°C and not more than 110°C. When the kneading and shredding temperature is lower than these ranges, the hydrophobic substance (c) is aggregated and present in a solid state, resulting in poor uniformity and poor initial absorption performance, as well as surface treatment described later. The surface treatment in the process may become non-uniform, and the absorption performance under pressure may deteriorate. On the other hand, if the kneading and shredding temperature is higher than these ranges, bumping of water may occur and stable gel pulverization may not be possible.

In the present invention, the surface treatment step is a step of coating the surface of the resin particles containing the crosslinked polymer (A) with a surface treatment agent. As long as the surface of the resin particles is treated, the surface treatment agent includes various inorganic or organic substances in addition to the above-mentioned hydrophobic substance and the surface crosslinking agent described later.

The water absorbent resin particles of the present invention preferably have a structure in which the surface of the resin particles containing the crosslinked polymer (A) is crosslinked with the surface crosslinking agent (e). By cross-linking the surface of the resin particles containing the crosslinked polymer (A), the gel strength of the water-absorbent resin particles can be improved, and the desired water-retaining capacity of the water-absorbent resin particles and the desired absorption under pressure can be satisfied. be able to. Therefore, the surface treatment step in the production method of the present invention preferably includes a step of surface-crosslinking the resin particles containing the crosslinked polymer (A) with the surface crosslinking agent (e).

As the surface cross-linking agent (e), there are known (polyvalent glycidyl compound, polyvalent amine, polyvalent aziridine compound, polyvalent isocyanate compound, etc. described in JP-A-59-189103, JP-A-58-180233). And polyhydric alcohols described in JP-A-61-16903, silane coupling agents described in JP-A-61-211305 and 61-252212, and JP-A-5-508425. Alkylene carbonate, polyvalent oxazoline compounds described in JP-A No. 11-240959, and surface cross-linking agents for polyvalent metals described in JP-A Nos. 51-136588 and 61-257235) are used. it can. Among these surface cross-linking agents, from the viewpoints of economy and absorption characteristics, polyvalent glycidyl compounds, polyhydric alcohols and polyvalent amines are preferable, more preferable are polyvalent glycidyl compounds and polyhydric alcohols, and particularly preferable are polyhydric glycidyl compounds. A valent glycidyl compound, most preferably ethylene glycol diglycidyl ether. The surface cross-linking agents may be used alone or in combination of two or more.

The amount (parts by weight) of the surface cross-linking agent (e) is not particularly limited because it can be variously changed depending on the type of the surface cross-linking agent, the conditions for cross-linking, the target performance, etc., but from the viewpoint of absorption characteristics, etc. Based on the weight of the resin particles containing the crosslinked polymer (A), 0.001 to 3 is preferable, 0.005 to 2 is more preferable, and 0.01 to 1.5 is particularly preferable.

The surface cross-linking can be performed by mixing the resin particles containing the cross-linked polymer (A) and the surface cross-linking agent (e) and heating the mixture as necessary. Examples of the mixing method include a cylindrical mixer, a screw mixer, a screw extruder, a turbulator, a Nauta mixer, a double-arm kneader, a fluid mixer, a V mixer, a mince mixer, a ribbon mixer. Method for uniformly mixing resin particles containing the crosslinked polymer (A) and the surface crosslinking agent (e) using a mixing device such as a mixer, an airflow type mixer, a rotary disk type mixer, a conical blender and a roll mixer Is mentioned. At this time, the surface crosslinking agent (e) may be diluted with water and/or any solvent before use.

The temperature at the time of mixing the resin particles containing the crosslinked polymer (A) and the surface crosslinking agent (e) is not particularly limited, but is preferably 10 to 150°C, more preferably 20 to 100°C, particularly preferably 25. ~80°C.

After mixing the resin particles containing the crosslinked polymer (A) and the surface crosslinking agent (e), heat treatment is performed. The heating temperature is preferably 100 to 180° C., more preferably 110 to 175° C., and particularly preferably 120 to 170° C. from the viewpoint of the absorption characteristics of the water absorbent resin particles. If heating at 180° C. or lower, indirect heating using steam is possible, which is advantageous in terms of equipment, and if the heating temperature is lower than 100° C., absorption performance may deteriorate. The heating time can be appropriately set depending on the heating temperature, but from the viewpoint of absorption performance, it is preferably 5 to 60 minutes, more preferably 10 to 40 minutes. The water-absorbent resin obtained by surface cross-linking can be further surface cross-linked by using the same or different surface cross-linking agent as the surface cross-linking agent initially used.

The water absorbent resin particles of the present invention contain a polyvalent metal salt (d). By coating the surface of the water absorbent resin particles with the polyvalent metal salt (d), the absorption performance under pressure can be improved.

Examples of the polyvalent metal salt (d) include inorganic acid salts of zirconium, aluminum or titanium, and examples of the inorganic acid forming the polyvalent metal salt (d) include sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid and iodine. Examples thereof include hydrofluoric acid and phosphoric acid. Examples of the inorganic acid salt of zirconium include zirconium sulfate and zirconium chloride, and examples of the inorganic acid salt of aluminum include aluminum sulfate, aluminum chloride, aluminum nitrate, ammonium aluminum sulfate, potassium aluminum sulfate and sodium aluminum sulfate. Examples of the inorganic acid salt of titanium include titanium sulfate, titanium chloride and titanium nitrate.

Among these, from the viewpoint of improving the absorption performance under pressure, inorganic acid salts of aluminum are preferable, and more preferable are aluminum sulfate, aluminum chloride, potassium aluminum sulfate and sodium aluminum sulfate.

The amount (% by weight) of the polyvalent metal salt (d) is preferably 0.05 to 5, and more preferably 0. 5, based on the weight of the crosslinked polymer (A) from the viewpoint of absorption performance under pressure. 2 to 2.0, particularly preferably 0.35 to 1.5. Here, when the polyvalent metal salt (d) is a hydrate, it is based on the mass excluding the water of hydration.

The polyvalent metal salt (d) may be added in any step such as a polymerization step, a gel crushing step and a surface treatment step, but the resin particles may be added from the viewpoint of improving the absorption performance under pressure. It is preferably present on the surface and is preferably added in the surface treatment step. Further, when the surface treatment is carried out with the above-mentioned surface cross-linking agent, it can be added before the step of performing the surface treatment by the surface cross-linking, after the above-mentioned step, or simultaneously with the above-mentioned step. The equipment and temperature for mixing the polyvalent metal salt (d) can be the same as in the surface cross-linking step described above.

Further, in the surface treatment step of the invention, it is possible to perform treatment with a surface treatment agent such as a cationic organic polymer or water-insoluble inorganic fine particles, if necessary. By including the water-insoluble inorganic particles, the surface of the particles contained in the water-absorbent resin particles is surface-treated with the water-insoluble inorganic particles, whereby the blocking resistance of the water-absorbent resin particles is improved.

Examples of the water-insoluble inorganic fine particles include fumed silica, colloidal silica, kaolin, talc, mica and clay, and fumed silica is preferable from the viewpoint of easy availability and absorption performance.

The amount (% by weight) of the water-insoluble inorganic particles is preferably 0.01 to 0.4, more preferably 0.05 to 0.4, based on the weight of the crosslinked polymer (A) from the viewpoint of absorption performance. And particularly preferably 0.1 to 0.3. If it exceeds 0.4, the liquid passing speed of the water-absorbent resin particles becomes faster and the absorption speed of the water-absorbent resin particles becomes slower. The absorption cannot catch up with the liquid flow in the latter stage of swelling, and liquid leakage to the outside of the absorption system occurs. Easier to do.

After the surface treatment step, the particle size is adjusted by sieving if necessary.

The water-absorbent resin particles of the present invention may contain additives (for example, known antiseptics, antifungal agents, antibacterial agents, and oxidation agents (described in JP-A-2003-225565 and JP-A-2006-131767), if necessary. Inhibitors, UV absorbers, colorants, fragrances and deodorants may 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, and especially It is preferably 0.05 to 1, and most preferably 0.1 to 0.5.

Examples of the antibacterial agent include silver zeolite, copper zeolite, zinc zeolite, imidazole compounds and quaternary ammonium salt compounds.
Examples of the imidazole compound include methyl 2-benzimidazole carbamate, methyl 1-butylcarbamoyl-2-benzimidazole carbamate, methyl 6-benzoyl-2-benzimidazole carbamate, and 6-(2-thiophenecarbonyl)-2- Methyl benzimidazole carbamate, etc., 2-(4-thiazolyl)-benzimidazole, 2-(2-chlorophenyl)-benzimidazole, 2-(1-(3,5-dimethylpyrazolyl))benzimidazole, 2-(2 -Furyl)-benzimidazole, 2-thiocyanomethylthiobenzimidazole, 1-dimethylaminosulfonyl-2-cyano-4-bromo-6-trifluoromethylbenzimidazole and the like.
Examples of the quaternary ammonium salt compound include didecyldimethylammonium chloride, benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetrimonium bromide, domiphen bromide, dophanium chloride, laurylpyridinium chloride and cetylpyridinium chloride. To be
Of these, quaternary ammonium salt compounds are preferable, and didecyldimethylammonium chloride and benzalkonium chloride are more preferable, from the viewpoints of antibacterial properties and blocking properties.

The particle shape of the water-absorbent resin particles of the present invention is preferably an irregular crushed shape. If it is in the crushed irregular shape, it has good entanglement with the fibrous material for use in paper diapers and the like, and there is no fear of falling off from the fibrous material.

The weight average particle diameter (μm) of the water absorbent resin particles of the present invention is preferably 200 to 600 μm, more preferably 300 to 500 μm, and particularly preferably 350 to 420. If it is larger than these ranges, the initial absorption performance is deteriorated, and if it is smaller than these ranges, spot absorption and gel blocking occur, and liquid leakage tends to occur in both cases. The content of fine particles is preferably small, the content of particles of 100 μm or less is preferably 3% by weight or less, and the content of particles of 150 μm or less is more preferably 3% by weight or less. When the content of the fine particles contained in the resin particles is large, spot absorption or gel blocking occurs, and leakage easily occurs.

The apparent density (g/mL) of the water absorbent resin particles of the present invention is preferably 0.50 or more and less than 0.70, more preferably 0.51 or more and less than 0.68, and particularly preferably 0.52 or more and 0.66. Is less than. Within this range, the absorption characteristics will be further improved. The apparent density of the water-absorbent resin particles is measured at 25°C according to JIS K7365:1999.

Water-absorbent resin particles of the present invention,
(1) The absorption index represented by the following formula 1 is 95 or more,
Absorption index = Water retention (X) x 2 + Pressurized DW 10 minutes value (Y) (Equation 1)
[In Formula 1, (X) is a water retention amount (g/g) with respect to 0.9 wt% physiological saline, and (Y) is after 10 minutes under 2.1 kPa pressurization measured by the Demand Wetability test method. Of 0.9% by weight saline solution (g/g)]
(2) The water retention capacity (g/g) with respect to 0.9 wt% physiological saline is 37 or more and less than 47,
(3) The liquid-passing speed (ml/min) of 0.9 wt% saline under pressure of 2.1 kPa after immersion of the water-absorbent resin particles in 0.9 wt% physiological saline for 30 minutes is 10 or less, And (4) Water-absorbent resin particles having a water content (%) of 5 or more and less than 15.

The water retention capacity (g/g) of 0.9% by weight physiological saline of the water-absorbent resin particles of the present invention (hereinafter referred to as the water retention capacity) can be measured by the method described below, and the viewpoint of preventing liquid leakage to the outside of the absorption system. Therefore, it is 37 or more and less than 47, preferably 38 or more and less than 46, and more preferably 40 or more and less than 45. When it is less than 37, the amount of absorption as an absorber is low, and therefore leakage tends to occur during repeated use. Further, when it is 47 or more, the permeation rate into the absorber becomes slow, and blocking is likely to occur at the liquid injection part, so that liquid leakage easily occurs. The water retention amount can be appropriately adjusted by the types and amounts of the crosslinking agent (b) and the surface crosslinking agent (e).

Absorption of 0.9 wt% physiological saline solution (g/g) after 10 minutes under pressure of 2.1 kPa measured by the Demand Wettability test method for the water-absorbent resin particles of the present invention (hereinafter, pressure DW 10 minutes The value and description) can be measured by the method described below, and indicates the amount of water absorption of the absorbent body under pressure. Generally, the performance is contradictory to the water retention capacity of the water absorbent resin particles, but the performance balance can be improved by coating the surface of the water absorbent resin particles with the polyvalent metal salt (d). The pressure DW 10-minute value (g/g) is adjusted within a range that satisfies the absorption index described later.

The absorption index of the present invention is a value represented by the above-mentioned formula 1. The absorption index is an index showing the optimum balance between the water retention capacity and the amount absorbed under pressure, and is useful as an index showing the liquid retention of the absorbent body. The absorption index of the water-absorbent resin particles of the present invention is 95 or more, preferably 96 to 105, and particularly preferably 97 to 10 from the viewpoint of the liquid retention of the absorber, that is, the prevention of liquid leakage to the outside of the absorption system. It is 103. However, if the water retention capacity (g/g) of the water-absorbent resin particles is not in the range of 36 or more and less than 47, even if the absorption index is 95 or more, as described above, liquid leakage to the outside of the absorption system occurs. It will be easier.

The immersion rate of the water-absorbent resin particles of the present invention in 0.9% by weight physiological saline for 30 minutes was 0.9% by weight of 0.9% by weight physiological saline under a pressure of 2.1 kPa. Is 10 or less, and preferably 6 or less from the viewpoint of preventing leakage. When it is larger than 10, the absorption rate of the water-absorbent resin particles becomes slow and the absorption cannot catch up with the flow of the liquid in the latter stage of swelling, so that the liquid easily leaks out of the absorption system.

The water content (%) of the water-absorbent resin particles of the present invention is 5 or more and less than 15, preferably 6 or more and less than 15 and more preferably 8 or more and less than 15 from the viewpoint of absorption rate, particularly the initial wettability. is there. If it is less than 5, the initial wettability is poor and the absorption rate becomes slow. Therefore, when applied to an absorber having a low pulp ratio, the absorption does not catch up with the flow of the liquid and liquid leakage easily occurs. If it is 15 or more, blocking is likely to occur in the diaper manufacturing process, which may cause clogging. The water content is appropriately adjusted in the drying step and the surface treatment step.

The water-absorbent resin particles of the present invention have a moisture absorption blocking rate (%) of preferably 0 or more and less than 10 and more preferably 0 or more and less than 3 from the viewpoint of preventing blocking between the water-absorbing resin particles. When it is 10% or more, blocking of the water-absorbent resin particles is likely to occur during storage and production of the absorber. The moisture absorption blocking rate is appropriately adjusted by the types and amounts of the hydrophobic substance (c), the polyvalent metal salt (d), the surface cross-linking agent (e), the surface treatment agent and the additive.

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 including the absorbent body. To be The absorber using the water-absorbent resin particles of the present invention has an excellent water absorption amount and an excellent liquid retention property under pressure, and therefore liquid leakage to the outside of the absorption system is unlikely to occur.

The absorber using the water-absorbent resin particles of the present invention may be configured by using the water-absorbent resin particles alone, or may be configured by the water-absorbent resin particles and hydrophilic fibers.

Specific examples of hydrophilic fibers include wood pulp fibers such as mechanical pulp, chemical pulp, semi-chemical pulp, and dissolving pulp from wood, and artificial cellulose fibers such as rayon and acetate. The preferred hydrophilic fiber is wood pulp fiber. These hydrophilic fibers may partially contain synthetic fibers such as nylon and polyester.

As the structure of the absorber, a mixed dispersion obtained by mixing the water-absorbent resin particles and the hydrophilic fibers so as to have a uniform composition, the water-absorbent resin particles are sandwiched between the layered hydrophilic fibers. And a sandwich structure, a structure in which water-absorbent resin particles and hydrophilic fibers are wrapped in a tissue, and the like. In addition, the absorbent body may be blended with other components, for example, an adhesive binder such as a heat-fusible synthetic fiber for enhancing the shape retention of the absorbent body, a hot melt adhesive, or an adhesive emulsion. ..

Further, an absorbent body using water-absorbent resin particles is held between a liquid-permeable sheet (top sheet) through which liquid can pass and a liquid-impermeable sheet (back sheet) through which liquid cannot pass. According to this, it can also be made into an absorbent article. The liquid permeable sheet is disposed on the side that contacts the body, and the liquid impermeable sheet is disposed on the opposite side that contacts the body.

Examples of the liquid permeable sheet include air-through type, spun bond type, chemical bond type, needle punch type non-woven fabrics made of fibers such as polyethylene, polypropylene and polyester, and porous synthetic resin sheets. Examples of the liquid impermeable sheet include synthetic resin films made of resins such as polyethylene, polypropylene, polyvinyl chloride and the like.

Hereinafter, the present invention will be 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% are% by weight. The water retention capacity of the water-absorbent resin particles, the pressure DW10 minute value, the liquid flow rate, the water content, the moisture absorption blocking rate, and the oblique leak test under pressure of the absorber 1 (the liquid leak test of the absorber having a high ratio of hydrophilic fibers). ) And Test 2 (liquid leakage test of absorber having a low ratio of hydrophilic fibers) were measured under the conditions of 25±2° C. and 60±5 RH% by the following method.

<Measurement method of water retention>
1.00 g of the measurement sample was placed in a tea bag (length 20 cm, width 10 cm) made of a nylon net having an opening of 63 μm (JIS Z8801-1:2006), and the mixture was stirred in 1,000 ml of 0.9 wt% physiological saline. Underneath, it was soaked for 1 hour, then pulled up, hung for 15 minutes and drained. Then, put each tea bag in a centrifuge, spin-dry for 90 seconds at 150 G to remove the excess 0.9 wt% physiological saline solution, measure the weight including the tea bag (h1), and store it from the following formula. The amount of water was calculated. The temperature of the 0.9 wt% physiological saline used and the measurement atmosphere was 25° C.±2° C. (H2) is the weight of the tea bag measured by the same operation as above in the case where there is no measurement sample.
Water retention capacity (g/g)=(h1)-(h2)

<Method of measuring pressure DW 10 minutes value>
Using water-absorbent resin particles and 0.9 wt% physiological saline, the measurement was performed according to the DW method described in paragraphs 0117 to 0121 of JP-A-2014-005472. In the DW method of the present invention, the absorption capacity (g) is used to judge the wicking capacity per 1 g of the water-absorbent resin particles under the condition of 2.1 kpa under pressure on a measuring table connected to a buret and an air introduction pipe. is there. That is, instead of placing the plain-woven nylon mesh on the measuring table and uniformly spraying 0.50 g of the water-absorbent resin particles onto the measuring table, which is the procedure of the above specification, in the present invention, the nylon mesh (opening 63 μm) is provided at the bottom. 0.16 g of water-absorbent resin was evenly dispersed in a cylinder made of acrylic resin (inner diameter 25 mm, height 34 mm) to which was adhered, and a weight (diameter 24.5 mm, mass 105.5 g) was placed on it. I placed it in the center of the measuring table. The water absorption resin particles start to absorb water, and the time when the first bubble introduced from the air introduction tube reaches the water surface of 0.9 wt% physiological saline in the buret is the measurement start time, and the buret is continuously measured. The amount of 0.9 wt% physiological saline absorbed by the water-absorbent resin particles is read from the decrease amount of 0.9 wt% physiological saline in the table, and the absorption amount per 1 g of water-absorbent resin particles 10 minutes after the start of measurement ( g/g) was determined.

<Measuring method of liquid passing speed>
0.32 g of the water-absorbent resin particles were immersed in 150 mL of 0.9 wt% physiological saline for 30 minutes in a 200 ml beaker to prepare hydrogel particles. Vertically standing 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. } In the 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} at the bottom of the water content prepared with the cock closed. After transferring the gel particles together with 0.9 wt% physiological saline, a circular wire netting (opening 150 μm, diameter 25 mm: a pressure shaft (weight: 22 g, 22 g; Length 47 cm). } Was placed so that the metal net and the hydrogel particles were in contact with each other, and a weight (88.5 g) was further placed on the pressure shaft and allowed to stand 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). min) was calculated. The temperature of the 0.9 wt% physiological saline used and the measurement atmosphere was 25° C.±2° C.
Flow rate (ml/min) = 20 ml x 60/(T1-T2)
In addition, T2 is the time measured by the same operation as above in the case where there is no measurement sample.

<Measurement method of water content>
Infrared moisture analyzer [JE400 manufactured by KETT Co., Ltd.: 120±5° C., 30 minutes, atmospheric humidity before heating 50±10% RH, lamp specification 100 V, 40 W] heated and reduced 2.00 g of sample The water content (%) was defined as the ratio of the weight to the sample weight before drying.

<Measurement method of moisture absorption blocking rate>
5.0 g of the measurement sample was uniformly put in an aluminum dish having a diameter of 5 cm, and left for 3 hours in a thermo-hygrostat at 30° C. and 80% relative humidity. Weigh the water-absorbent resin after standing, lightly sieve it with a 12-mesh wire net, measure the mass of the water-absorbent resin that does not pass 12 mesh by blocking by moisture absorption, and determine the moisture absorption blocking rate (%) by the following formula. I asked.
Moisture absorption blocking rate (%)=(mass of water-absorbent resin particles remaining on the 12-mesh net after standing/mass of water-absorbent resin particles after standing)×100

<Diagonal leak test 1 of the absorber under pressure>
200 parts of fluff pulp and 250 parts of the evaluation sample {water-absorbent resin particles of Examples and Comparative Examples} were mixed by an airflow type mixing device {pad former manufactured by Autech Co., Ltd.} to obtain a mixture, and then this mixture Was evenly laminated on an acrylic plate (thickness: 4 mm) to have a basis weight of about 450 g/m ^2, and pressed at a pressure of 5 kg/cm ² for 30 seconds to obtain an absorber. This absorbent body was cut into a rectangle of 10 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 absorbent body was placed above and below each, and further. An absorbent body was prepared by disposing 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.
The obtained absorber was placed on an acrylic plate placed at an angle of 15° with respect to the placement surface so that the 10 cm side was at the top. Next, a cylinder-mounted acrylic plate (25 cm×25 cm) having a diameter of 3 cm and a height of 14 cm, which was adjusted by a weight so that the total weight was 2.5 kg, was placed on the absorber. At this time, the center of the cylinder was placed so that the center of the absorber was 15 cm from the lowest point of the absorber, and the absorber was sandwiched as a whole. Artificial urine (0.03% by weight potassium chloride, 0.08% by weight magnesium sulfate, 0.8% by weight sodium chloride and 99.09% by weight deionized water, and so on) 80 ml from a cylinder at a rate of 5 ml/sec. It was poured and left still for 10 minutes. The artificial urine was charged using a funnel whose pouring mouth was adjusted in advance so that the liquid could flow at a rate of 5 ml/sec. After standing for 10 minutes, 30 ml of artificial urine was further poured from the cylinder at a rate of 5 ml/sec, and the operation was continued for 10 minutes until the artificial urine leaked from the absorber, and the total liquid was added when the leak occurred. The amount (g) was recorded. Further, the liquid leaking from the lower end of the absorber was absorbed by a filter paper (No. 2 manufactured by ADVANTEC), and the weight increase of the filter paper was recorded as the leak liquid amount (g).

<Diagonal leak test 2 of the absorber under pressure>
50 parts of fluff pulp and 400 parts of the evaluation sample {water-absorbent resin particles of Examples and Comparative Examples} were mixed with an air flow type mixing device {pad former made by Autech Co., Ltd.} to obtain a mixture, and then this mixture Was carried out in the same manner as the oblique leakage test under pressure 1 of the absorbent body, except that the above was uniformly laminated on an acrylic plate (thickness: 4 mm) so that the basis weight was about 310 g/m ² .

<Example 1>
Acrylic acid (a1) {manufactured by Mitsubishi Chemical Corporation, purity 100%} 270 parts, cross-linking agent (b) {manufactured by Daiso Corporation, pentaerythritol triallyl ether} 0.95 parts and ion-exchanged water 712 parts were stirred. Keep at 3°C with mixing. After nitrogen was introduced into this mixture to adjust the dissolved oxygen amount to 1 ppm or less, 1.1 parts of a 1% aqueous hydrogen peroxide solution, 2.0 parts of a 2% aqueous ascorbic acid solution and 2% of 2,2'-azobis Polymerization was initiated by adding and mixing 13.5 parts of an aqueous solution of amidinopropane dihydrochloride. After the temperature of the mixture reached 80° C., a hydrogel was obtained by aging at 80±2° C. for about 5 hours.

Next, 220 parts of a 49% sodium hydroxide aqueous solution was added to and mixed with this hydrogel, and the mixture was shredded at a gel temperature of 80° C. with a mincing machine (12VR-400K manufactured by ROYAL) as a hydrophobic substance (c). 0.31 part of sucrose stearate (manufactured by Mitsubishi Kagaku Foods Co., Ltd. Ryoto Sugar Ester S-370, HLB: 3, melting point: 58° C.) was added and mixed to obtain a neutralized gel. The neutralized hydrogel is dried by aeration using a ventilation dryer (manufactured by Inoue Metal Industry Co., Ltd.) under the conditions of a supply temperature of 150° C. and a wind speed of 1.5 m/sec until the water content becomes 5%. Got the body The dried product was crushed with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), sieved, and adjusted to a particle size range of openings 710 to 150 μm to obtain resin particles (A-1) containing a crosslinked polymer. Obtained.

While stirring 100 parts of the resin particles (A-1) at high speed (high-speed stirring turbulator made by Hosokawa Micron: rotation speed 2000 rpm), sodium sulfate aluminum alum dodecahydrate as the polyvalent metal salt (d) was added thereto. After adding 0.5 parts, 0.06 parts of ethylene glycol diglycidyl ether as a surface cross-linking agent (e) and 1.2 parts of a 50% propylene glycol aqueous solution as a solvent, and uniformly mixing, By heating at 140° C. for 45 minutes, surface-crosslinked resin particles (A-2) were obtained.

Further, while 100 parts of the surface-crosslinked resin particles (A-2) were stirred at high speed (high-speed stirring turbulator manufactured by Hosokawa Micron Co., Ltd., rotation speed 2000 rpm), sodium aluminum aluminum alum 12 as polyvalent metal salt (d) 12 0.3 part of the hydrate and 4.0 parts of ion-exchanged water were uniformly mixed. Then, it heated at 80 degreeC for 30 minute(s), and obtained the water absorbent resin particle (P-1) of this invention. The water content of (P-1) was 8%, and the shape was irregular crushed.

<Example 2>
In Example 1, the same operation as in Example 1 was performed except that 4.0 parts of the ion-exchanged water used in (A-2) was changed to 10.0 parts, and the water-absorbent resin particles (P-2 ) Got. The water content of (P-2) was 14%, and the shape was irregular crushed.

<Example 3>
In Example 1, except that 0.06 parts of ethylene glycol diglycidyl ether used in (A-1) was changed to 0.09 parts and 1.2 parts of 50% propylene glycol aqueous solution was changed to 1.4 parts. The same operation as in Example 1 was performed to obtain water-absorbent resin particles (P-3). The water content of (P-3) was 9%, and the shape was irregular crushed.

<Example 4>
In Example 1, except that 0.06 part of ethylene glycol diglycidyl ether used in (A-1) was changed to 0.03 part, and 1.2 parts of 50% propylene glycol aqueous solution was changed to 1.0 part, The same operation as in Example 1 was performed to obtain water-absorbent resin particles (P-4). The water content of (P-4) was 6%, and the shape was irregular crushed.

<Example 5>
In Example 1, 0.3 part of 0.5 part of sodium sulfate aluminum alum dodecahydrate used in (A-1), 0.3 part of sodium sulfate aluminum alum dodecahydrate used in (A-2) 0.3 Water-absorbent resin particles (P-5) were obtained in the same manner as in Example 1, except that the parts were changed to 0.1 parts. The water content of (P-5) was 8%, and the shape was irregular crushed.

<Example 6>
Water-absorbent resin particles (P-6) were obtained in the same manner as in Example 1, except that the gel temperature was 60° C. when the hydrogel was shredded with a mincing machine. The water content of (P-6) was 8%, and the shape was irregular crushed.

<Example 7>
In Example 1, the same operation as in Example 1 was carried out except that 0.05 part of fumed silica (Aerosil 200 manufactured by Aerosil Co., Ltd.) as water-insoluble inorganic particles was further added to (A-2) to obtain a water-absorbing property. Resin particles (P-7) were obtained. The water content of (P-7) was 8%, and the shape was irregular crushed.

<Example 8>
In Example 1, the same operation as in Example 1 was performed except that 0.2 part of fumed silica (Aerosil 200 manufactured by Aerosil Co., Ltd.) as water-insoluble inorganic particles was further added to (A-2). Resin particles (P-8) were obtained. The water content of (P-8) was 8%, and the shape was irregular crushed.

<Example 9>
In Example 1, the same operation as in Example 1 was carried out except that 0.35 part of fumed silica (Aerosil 200 manufactured by Aerosil Co., Ltd.) as water-insoluble inorganic particles was further added to (A-2) to obtain a water-absorbing property. Resin particles (P-9) were obtained. The water content of (P-9) was 8%, and the shape was irregular crushed.

<Example 10>
Example 1 except that 0.1 part of a quaternary ammonium salt compound (Sanyo Kasei Co., Ltd., cation G-50, benzalkonium chloride) as an antibacterial agent was further added to (A-2). The same operation as in 1 was performed to obtain water-absorbent resin particles (P-10). The water content of (P-10) was 8%, and the shape was irregular crushed.

<Comparative Example 1>
In Example 1, except that 4.0 parts of ion-exchanged water was not used in (A-2), the same operation as in Example 1 was performed to obtain the water absorbent resin particles (R-1) for comparison. Obtained. The water content of (R-1) was 3%, and the shape was irregular crushed.

<Comparative example 2>
In Example 1, 0.3 part of sodium aluminum alum alum dodecahydrate used in (A-2) was changed to 1.5 parts of Klebosol 30cal25 (Colloidal silica manufactured by Merck & Co., solid content 30%, particle size 25 nm). Other than the above, the same operation as in Example 1 was performed to obtain comparative water-absorbent resin particles (R-2). (R-2) had a water content of 8% and had an irregular crushed shape.

<Comparative example 3>
In Example 1, except that 0.06 parts of ethylene glycol diglycidyl ether used in (A-1) was changed to 0.01 parts and 1.2 parts of 50% propylene glycol aqueous solution was changed to 0.2 parts, The same operation as in Example 1 was performed to obtain comparative water-absorbent resin particles (R-3). The water content of (R-3) was 7%, and the shape was irregular crushed.

<Comparative example 4>
In Example 1, except that 0.16 parts of ethylene glycol diglycidyl ether used in (A-1) was changed to 0.11 parts and 1.2 parts of 50% propylene glycol aqueous solution was changed to 1.5 parts. The same operation as in Example 1 was performed to obtain comparative water-absorbent resin particles (R-4). The water content of (R-4) was 9%, and the shape was irregular crushed.

<Comparative Example 5>
Acrylic acid (a1) {manufactured by Mitsubishi Chemical Corporation, purity 100%} 270 parts, cross-linking agent (b) {manufactured by Daiso Corporation, pentaerythritol triallyl ether} 0.95 parts and ion-exchanged water 712 parts were stirred. Keep at 3°C with mixing. After nitrogen was introduced into this mixture to adjust the dissolved oxygen amount to 1 ppm or less, 1.1 parts of a 1% aqueous hydrogen peroxide solution, 2.0 parts of a 2% aqueous ascorbic acid solution and 2% of 2,2'-azobis Polymerization was initiated by adding and mixing 13.5 parts of an aqueous solution of amidinopropane dihydrochloride. After the temperature of the mixture reached 80° C., a hydrogel was obtained by aging at 80±2° C. for about 5 hours.

Next, 220 parts of a 49% aqueous sodium hydroxide solution was added to and mixed with the hydrous gel, and the mixture was allowed to stand until the gel temperature reached 25°C. While slicing with a mincing machine (ROYAL 12VR-400K), sucrose stearate ester as a hydrophobic substance (c) (Mitsubishi Chemical Foods Corporation Ryoto Sugar Ester S-370, HLB: 3, melting point: (58° C.) 0.31 part was added and mixed to obtain a neutralized gel. The neutralized water-containing gel is dried by aeration using a ventilation type dryer (manufactured by Inoue Metal Industry Co., Ltd.) under the conditions of a supply temperature of 150° C. and a wind speed of 1.5 m/sec until the water content becomes 5%. Got the body The dried product was pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), sieved, and adjusted to a particle size range of openings 710 to 150 μm to obtain resin particles (A-3) containing a crosslinked polymer. Obtained.

While stirring 100 parts of the resin particles (A-3) 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 (e) and a solvent were used. The mixed solution prepared by mixing 1.2 parts of 50% propylene glycol aqueous solution was added and uniformly mixed, and then heated at 140° C. for 45 minutes to obtain surface-crosslinked resin particles (A-4).

Further, 4.0 parts of ion-exchanged water was uniformly mixed while stirring 100 parts of the surface-crosslinked resin particles (A-4) at high speed (high speed stirring turbulator manufactured by Hosokawa Micron Co., Ltd., rotation speed 2000 rpm). Then, the mixture was heated at 80° C. for 30 minutes to obtain comparative water absorbent resin particles (R-5). (R-5) had a water content of 8% and had an irregular crushed shape.

<Comparative example 6>
Acrylic acid (a1) {manufactured by Mitsubishi Chemical Corporation, purity 100%} 270 parts, cross-linking agent (b) {manufactured by Daiso Co., pentaerythritol triallyl ether} 4.75 parts and ion-exchanged water 712 parts Keep at 3°C with mixing. After nitrogen was introduced into this mixture to adjust the dissolved oxygen amount to 1 ppm or less, 1.1 parts of a 1% aqueous hydrogen peroxide solution, 2.0 parts of a 2% aqueous ascorbic acid solution and 2% of 2,2'-azobis Polymerization was initiated by adding and mixing 13.5 parts of an aqueous solution of amidinopropane dihydrochloride. After the temperature of the mixture reached 80° C., a hydrogel was obtained by aging at 80±2° C. for about 5 hours.

Next, 220 parts of 49% sodium hydroxide aqueous solution was added to and mixed with this hydrogel, and the mixture was shredded at a gel temperature of 80° C. with a mincing machine (12VR-400K manufactured by ROYAL) to obtain a hydrophobic substance (c). Sucrose stearate ester (manufactured by Mitsubishi Kagaku Foods Co., Ltd. Ryoto Sugar Ester S-370, HLB: 3, melting point: 58° C.) was added and mixed to obtain a neutralized gel. The neutralized hydrogel is dried by aeration using a ventilation dryer (manufactured by Inoue Metal Industry Co., Ltd.) under the conditions of a supply temperature of 150° C. and a wind speed of 1.5 m/sec until the water content becomes 5%. Got the body The dried product was pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), sieved, and adjusted to a particle size range of openings 710 to 150 μm to obtain a resin particle (A-5) containing a crosslinked polymer. Obtained.

While stirring 100 parts of the resin particles (A-5) at high speed (high-speed stirring turbulator manufactured by Hosokawa Micron: rotation speed 2000 rpm), 0.005 part of ethylene glycol diglycidyl ether as a surface cross-linking agent (e) and a solvent were used. 0.1% of 50% propylene glycol aqueous solution was added and mixed uniformly, and then heated at 140° C. for 45 minutes to obtain surface-crosslinked resin particles (A-6).

Further, 4.0 parts of ion-exchanged water was uniformly mixed while stirring 100 parts of the surface-crosslinked resin particles (A-6) at high speed (high speed stirring turbulator manufactured by Hosokawa Micron Co., Ltd., rotation speed 2000 rpm). Then, the mixture was heated at 80° C. for 30 minutes to obtain comparative water absorbent resin particles (R-6). The water content of (R-6) was 8%, and the shape was irregular crushed.

Water retention amount of the water absorbent resin particles (P-1) to (P-10) of Examples 1 to 10 and the comparative water absorbent resin particles (R-1) to (R-6) of Comparative Examples 1 to 6, Table 10 shows the results of evaluation of pressurized DW 10 minutes value, absorption index, liquid flow rate, water content and moisture absorption blocking rate, and oblique leakage test under pressure (abbreviated as "diagonal leakage test") of an absorbent body prepared using this. Shown in 1.

As can be seen from Table 1, the water-absorbent resin particles of the present invention (Examples 1 to 10) have a water retention capacity of 37 or more and less than 47, an absorption index of 95 or more, and a liquid passage rate of 10 or less, The water content is in the range of 5 or more and less than 15. Within this range, it is understood that the absorbent body to which the water-absorbent resin particles of the present invention are applied can suppress leakage in the oblique leakage test regardless of the pulp ratio. On the other hand, in the comparative example, all of the above characteristics did not satisfy the predetermined range, and therefore, it was not possible to suppress the leakage in the oblique leakage test regardless of the pulp ratio. That is, when the Comparative Example is confirmed in detail, in Comparative Example 1, there is no problem in the diagonal leak test 1, but in the diagonal leak test 2 in which the pulp ratio is reduced, the water content of the water absorbent resin particles is low and the initial wettability is low. By the bad thing, absorption did not catch up with the flow of the liquid and the leakability deteriorated. In Comparative Example 2, in the oblique leak test 2, the influence of the high liquid flow rate was small because the pulp ratio was small, but in the oblique leak test 1, the liquid flow rate was too high before the water-absorbent resin particles absorbed the liquid. The liquid flowed in and the leakability deteriorated. In Comparative Example 3, the absorption index was within the range, but the water retention amount was too high, so that blocking occurred at the liquid charging part, and the leakability deteriorated in both diagonal leak tests 1 and 2. In Comparative Example 4, since the water retention capacity was low and the liquid passing was too high, the diagonal leak tests 1 and 2 deteriorated in leak property. In Comparative Example 5, the water retention capacity was not a problem, but the absorption capacity under pressure was low, the absorption index deteriorated, and the leakage properties in both the diagonal leak tests 1 and 2 deteriorated. In Comparative Example 6, the absorption index deteriorated due to the low water retention amount, and the leakage properties deteriorated in both the diagonal leak tests 1 and 2.

The water-absorbent resin particles of the present invention can be applied not only to an absorber having a low pulp ratio but also to an absorber having a high pulp ratio, and an absorbent article comprising this absorber (paper diaper, sanitary napkin and medical blood retaining agent). It is useful for agents. 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.

Claims (7)

A water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a cross-linked polymer (A) containing a cross-linking agent (b) as an essential constituent unit, and a hydrophobic substance. Water-absorbent resin particles containing (c) and a polyvalent metal salt (d) and satisfying the following (1) to (4):
(1) The absorption index represented by the following formula 1 is 95 or more,
Absorption index = Water retention (X) x 2 + Pressurized DW 10 minutes value (Y) (Equation 1)
[In the formula 1, the water retention capacity (X) is the water retention capacity (g/g) with respect to 0.9 wt% physiological saline, and the pressurized DW 10-minute value (Y) is 2.1 kPa added measured by the Demand Wettability test method. The absorbed amount (g/g) of 0.9% by weight physiological saline after 10 minutes under pressure is shown. ]
(2) The water retention capacity (g/g) with respect to 0.9 wt% physiological saline is 37 or more and less than 47,
(3) The liquid-passing speed (ml/min) of 0.9 wt% saline under pressure of 2.1 kPa after immersion of the water-absorbent resin particles in 0.9 wt% physiological saline for 30 minutes is 10 or less,
(4) Water content (%) is 5 or more and less than 15. The water-absorbent resin particle according to claim 1, wherein the particle shape is an irregular crushed shape. The water absorbent resin particles according to claim 1 or 2, wherein the hydrophobic substance (c) is a hydrophobic substance containing a hydrocarbon group having 8 to 30 carbon atoms. The water-absorbent resin particles according to claim 1, wherein the polyvalent metal salt (d) is an inorganic acid salt of aluminum. An absorber comprising the water absorbent resin particles according to claim 1. An absorbent article comprising the absorbent body according to claim 5. The method for producing water-absorbent resin particles according to any one of claims 1 to 4, wherein the water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, And a polymerization step of polymerizing a monomer composition containing a cross-linking agent (b) as an essential constituent unit to obtain a hydrogel containing the cross-linked polymer (A), kneading the hydrogel and chopping the hydrogel particles. In the gel crushing step, a gel crushing step of obtaining, a step of drying the water-containing gel particles, classifying after crushing to obtain resin particles containing a crosslinked polymer (A), and a step of surface-treating the resin particles, Before and/or at the same time when the hydrogel is shredded, the hydrophobic substance (c) having a melting point of 90° C. or lower is added, and the temperature at which the kneaded shreds is the above-mentioned hydrophobic substance (c). ) Above the melting point and below 120°C.