WO2020144948A1 - Water absorbent resin particles and production method therefor - Google Patents

Abstract

Provided are: water absorbent resin particles that can maintain a stable absorption rate and liquid permeability in a duration from immediately after production of the water absorbent resin particles until the use of an absorbent article, and exhibit excellent texture when used in an absorbent article; and a production method for the water absorbent resin particles. The present invention is water absorbent resin particles obtained by surface-crosslinking resin particles containing a crosslinked polymer (A) of a water-soluble vinyl monomer and a crosslinking agent as essential constituent units, wherein the particles have irregular shapes, are in a pulverized form, have an average sphericity of 0.800-0.900, and have a variation width of the average sphericity of 0-0.015 after an impact resistance test; and a method for producing the water absorbent resin particles, the method comprising, as production steps, adding a gel blocking prevention agent before a drying step for obtaining dry powder containing the crosslinked polymer (A), and performing drying using an agitation dryer in the drying step so that the proportion by weight of particles having a particle size of 2.8 mm or more with respect to the total weight of the dry powder of (A) obtained after the drying is 50 wt% or less.

Description

Water absorbent resin particles and method for producing the same

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

Sanitary materials such as paper diapers, sanitary napkins, incontinence pads, etc. are composed of hydrophilic fibers such as pulp and a water-absorbent resin (Super Absorber Polymer: hereinafter referred to as SAP) whose main raw material is acrylic acid (salt). , Absorbers are widely used. From the viewpoint of improving QOL (quality of life) in recent years, the demand for these sanitary materials is shifting to lighter and thinner, and along with this, there is a desire to reduce the amount of hydrophilic fibers used. It was Therefore, SAP is now required to play the role of hydrophilic fibers in the absorber.

　For example, an important function of diapers is the reduction of leaks by rapid absorption of urine. The conventional absorbent body has a high absorption rate of urine due to the physical space existing between the bulky hydrophilic fibers, but in the absorbent body with a high SAP ratio in which the amount of hydrophilic fibers used is reduced, the SAP particles are filled with each other. Therefore, there is a problem in that the physical space is small and the absorption rate of urine is slow. Further, the conventional absorbent body has a high urine diffusibility due to the hydrophilic fiber and can diffuse urine throughout the absorbent body, whereas the absorbent body having a high SAP ratio inhibits the diffusion of urine by the swollen gel. Therefore, the diffusivity of urine in the absorber is significantly reduced. This decrease in diffusivity, together with the decrease in absorption rate described above, causes a serious cause of so-called diaper leakage, that is, urine reversion.

For the above-mentioned problems, techniques for improving the liquid permeability of SAP or improving both liquid permeability and absorption rate are being studied. For example, a method is known in which the surface of SAP is crosslinked with an aqueous solution containing a specific organic crosslinking agent compound and an aqueous solution containing a specific cation to suppress the deformation of the surface of the swollen gel to efficiently form a gel gap (for example, , Patent Document 1). However, surface cross-linking alone was not sufficient for liquid permeability between swollen gels. Further, as other methods for improving liquid permeability, (1) a method of forming a physical space by adding an inorganic compound such as silica and talc, (2) hydrophobicity such as modified silicone having a small surface free energy A method of suppressing the coalescence of swollen gels to form a gel gap by surface treatment with a polymer and (3) a method of adding aluminum sulfate, aluminum lactate or the like are already known (for example, Patent Document 1). 2, refer to Patent Document 3 and Patent Document 4). However, in these methods, even when excellent properties are exhibited immediately after the production of SAP, even during the transportation of SAP, the production of absorbent articles such as spraying, supplying, and mixing of SAP, and further the transportation and transportation of absorbent articles, At the time of use, the liquid permeability and the absorption speed of the water-absorbent resin particles may be reduced due to collision and friction between the particles or particles of the apparatus wall surface. Particularly, with the recent increase in the SAP ratio in the absorber, the above problem is becoming apparent.

Further, due to the increase in the SAP ratio in the absorber, not only the problem of physical property deterioration due to contact between particles as described above, but also the actual contact of the absorbent article with the contact between particles of SAP particles causes jarring or lumpiness. There is a need for improvement in the deterioration of such feeling.

International Publication No. 00/053664 Pamphlet JP 2012-161788 A JP, 2013-133399, A JP, 2014-512440, A

The object of the present invention is to maintain a stable absorption rate and liquid permeability from immediately after the production of the water-absorbent resin particles to the use of the absorbent article, and to exhibit excellent texture when used for the absorbent article. To provide a resinous resin particle and a method for producing the same.

The present invention provides a water-absorbing structure in which resin particles containing a water-soluble vinyl monomer (a1) and a cross-linked polymer (A) containing a cross-linking agent (b) as an essential constituent unit are surface cross-linked by a surface cross-linking agent (d). Resin particles having an irregular crushed particle shape, an average sphericity (SPHT) of 0.800 to 0.900, and an average sphericity (SPHT) after an impact resistance test. The water absorbent resin particles have a change width of 0 to 0.015.
The present invention also includes a polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and a crosslinking agent (b) as essential constituent units to obtain a hydrogel containing the crosslinked polymer (A). A gel crushing step of kneading and chopping the hydrogel to obtain hydrogel particles containing (A); a drying step of drying the hydrogel particles to obtain a dry powder containing (A); A method for producing water-absorbent resin particles, which comprises a step of further pulverizing and/or classifying a powder to obtain resin particles containing (A), and a step of surface-crosslinking the surface of the resin particles with a surface-crosslinking agent (d). In addition, the gel blocking inhibitor (c) is added before the drying step, and in the drying step, drying is performed using a stirring dryer, and the dried powder of (A) obtained after drying is A method for producing water-absorbent resin particles, wherein the weight ratio of particles having a particle diameter of 2.8 mm or more to the total weight is 50% by weight or less.

The water-absorbent resin particles of the present invention have a specific average sphericity, maintain the particle shape even after the impact resistance test, and exhibit stable absorption rate and liquid permeability. Further, the water-absorbent resin particles obtained by the production method of the present invention can suppress the generation of coarse particles in the dry powder, and can increase the average sphericity of the water-absorbent resin particles, which is preferable for the present invention. Water absorbent resin particles can be obtained. Therefore, the absorbent article to which the water-absorbent resin particles of the present invention and the water-absorbent resin particles obtained by the production method of the present invention are applied, has stable absorption performance immediately after the production of the water-absorbent resin particles until the use of the absorbent article. In addition to exhibiting excellent properties, the absorbent article does not have a crunchy feel and is excellent in texture when actually used.

It is sectional drawing which represented typically the filtration cylindrical tube for measuring a gel passage speed. FIG. 3 is a perspective view schematically showing a pressurizing shaft and a weight for measuring a gel passage rate.

In the water-absorbent resin particles of the present invention, resin particles containing a water-soluble vinyl monomer (a1) and a cross-linked polymer (A) containing a cross-linking agent (b) as an essential constituent unit are surface-crosslinked by the surface cross-linking agent (d). It has a different structure.

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and known monomers such as at least one water-soluble substituent and an 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 nonionics disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883. Vinyl monomer and cationic vinyl monomer, and selected from the group consisting of carboxy group, sulfo group, phosphono group, hydroxyl group, carbamoyl group, amino group and ammonio group disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982. Vinyl monomers having at least one of

From the viewpoint of absorption performance and the like, the water-soluble vinyl monomer (a1) is preferably an anionic vinyl monomer, more preferably a carboxy (salt) group, a sulfo (salt) group, an amino group, a carbamoyl group, an ammonio group or mono-. A vinyl monomer having a di- or tri-alkylammonio group. Among these, more preferably a vinyl monomer having a carboxy (salt) group or a carbamoyl group, further preferably (meth)acrylic acid (salt) and (meth)acrylamide, particularly preferably (meth)acrylic acid (salt), Most preferably, it is acrylic acid (salt).

In addition, a "carboxy (salt) group" means a "carboxy group" or a "carboxylate group", and a "sulfo (salt) group" means a "sulfo group" or a "sulfonate group". Further, (meth)acrylic acid (salt) means acrylic acid, acrylic acid salt, methacrylic acid or methacrylic acid salt, and (meth)acrylamide means acrylamide or methacrylamide. Examples of salts 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, the alkali metal salts and ammonium salts are preferable, the alkali metal salts are more preferable, and the sodium salts are particularly preferable, from the viewpoint of absorption 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 neutralizing base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide and alkali metal carbonates such as sodium carbonate, sodium hydrogen carbonate and potassium carbonate can be usually used. Neutralization may be carried out either before or during the polymerization of the acid group-containing monomer in the production process of the water absorbent resin, or the acid group-containing polymer may be treated in the state of a hydrogel containing the cross-linked polymer (A) described later. It can also be neutralized.

When the acid group-containing monomer is used, the degree of neutralization of the acid group is preferably 50 to 80 mol %. When the degree of neutralization is less than 50 mol %, the resulting hydrogel polymer may have high tackiness, which may deteriorate workability during production and use. Further, the water retention amount of the resulting water absorbent resin particles 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 concern about the safety of the skin of human body.

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

The other copolymerizable vinyl monomer (a2) is not particularly limited and is known (for example, the hydrophobic vinyl monomer disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, JP-A-2003-165883). The vinyl monomers disclosed in paragraph 0025 and paragraph 0058 of Japanese Unexamined Patent Publication No. 2005-75982) can be used, and specifically, for example, vinyl monomers (i) to (iii) below can be used. Can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and vinylnaphthalene, and halogen-substituted styrene such as dichlorostyrene.
(Ii) C2-C20 aliphatic ethylenic monomer alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkadienes (butadiene, isoprene, etc.).
(Iii) C5-C15 alicyclic ethylenic monomers, monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylene vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidene norbornene, etc.] and the like.

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

The cross-linking agent (b) is not particularly limited and is known (for example, a cross-linking agent having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 36485553, which reacts with a water-soluble substituent group). Crosslinking agent having at least one functional group to be obtained and having at least one ethylenically unsaturated group, and crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP-A-2003-165883. Cross-linking agent having two or more ethylenically unsaturated groups 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 more preferable is a poly(meth)allyl ether of a polyhydric alcohol having 2 to 40 carbon atoms and a carbon number. (Meth)acrylate of polyhydric alcohol having 2 to 40 carbons, (meth)acrylamide of polyhydric alcohol having 2 to 40 carbons, polyallyl ether of polyhydric alcohol having 2 to 40 carbons, and most preferable Pentaerythritol triallyl ether. As the crosslinking agent (b), one type may be used alone, or two or more types may be used in combination.

The content (mol %) of the crosslinking agent (b) unit is based on the total number of moles of the water-soluble vinyl monomer (a1) unit and (a1) to (a2) when another vinyl monomer (a2) unit is used. It is preferably 0.001 to 5, more preferably 0.005 to 3, and particularly preferably 0.01 to 1. When it is in the range of 0.001 to 5, the absorption performance is further improved.

The method for producing water-absorbent resin particles of the present invention comprises a cross-linked polymer (A) obtained by polymerizing a monomer composition containing the above water-soluble vinyl monomer (a1) and a cross-linking agent (b) as essential constituent units. A step of polymerizing to obtain a hydrogel, a step of kneading and chopping the hydrogel to obtain hydrogel particles containing (A), and a step of drying the hydrogel particles to obtain a dry powder containing (A). A step of obtaining a body, a step of further pulverizing and/or classifying the dry powder to obtain resin particles containing (A), and a step of surface-crosslinking the surface of the resin particles with a surface-crosslinking agent (d). including.

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

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

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

The polymerization concentration, that is, the charging concentration of the water-soluble vinyl monomer (a1) in the polymerization liquid and the other vinyl monomer (a2) used as necessary is not particularly limited, but the weight of the polymerization liquid, that is, the water-soluble vinyl monomer 10 to 55% is preferable based on the total weight of (a1) and other vinyl monomer (a2) optionally used, solvent, internal cross-linking agent (b) and polymerization catalyst and polymerization control agent described later, and 20 to 45%. % Is more preferable. When the polymerization concentration is lower than 10%, the productivity may be lowered, and when the polymerization concentration is higher than 55%, the water retention capacity of the resulting water-absorbent resin particles is lowered due to side reactions such as self-crosslinking. There is.

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

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

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

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

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

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

The gel temperature in the gel crushing step is preferably 70 to 120°C, more preferably 80 to 110°C. When the gel temperature is lower than the range of 70 to 120° C., not only the cooling step is required after the polymerization step but unnecessary energy is required, but also the adhesiveness of the hydrous gel particles increases and the pulverization of the hydrous gel particles becomes insufficient. If the gel temperature is higher than this range, bumping of water may occur and stable pulverization may not be possible.

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.

In the method for producing water absorbent resin particles of the present invention, the gel blocking inhibitor (c) is added before the drying step described later. The gel blocking inhibitor (c) is an additive that suppresses blocking due to aggregation of the hydrogel particles obtained in the gel crushing step described above. By adding the gel blocking inhibitor (c), generation of coarse particles (particles having a particle size of 2.8 mm or more) in the dry powder obtained after drying is suppressed, and water absorbency is achieved. The average sphericity of the resin particles can be increased, and the change width of the average sphericity after the impact resistance test can be reduced.

The gel blocking inhibitor (c) includes a hydrophobic substance (c1) containing a hydrocarbon group and a hydrophobic substance (c2) which is a polysiloxane.

Examples of the hydrophobic substance (c1) containing a hydrocarbon group include polyolefin resins, polyolefin resin derivatives, polystyrene resins, polystyrene resin derivatives, waxes, long chain fatty acid esters, long chain fatty acids and salts thereof, long chain aliphatic alcohols, Quaternary ammonium salt type surfactants, mixtures of two or more of these, and the like are included.

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

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

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

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

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

The long-chain fatty acid ester is an ester of a fatty acid having 8 to 25 carbon atoms and an alcohol having 1 to 12 carbon atoms (for example, methyl laurate, ethyl laurate, methyl stearate, ethyl stearate, methyl oleate, oleic acid). Ethyl, glycerin lauric acid monoester, glycerin stearic acid monoester, glycerin stearic acid diester, glycerin oleic acid monoester, pentaerythritol lauric acid monoester, pentaerythritol stearic acid monoester, pentaerythritol oleic acid monoester, sorbit Lauric acid monoester, sorbit stearic acid monoester, sorbit oleic acid monoester, sucrose palmitic acid monoester, sucrose palmitic acid diester, sucrose palmitic acid triester, sucrose stearic acid monoester, sucrose stearic acid diester, Sucrose stearic acid triester and beef tallow, etc.}.

Examples of long-chain fatty acids and salts thereof include fatty acids having 8 to 25 carbon atoms (eg, lauric acid, palmitic acid, stearic acid, oleic acid, behenic acid, etc.). Examples of the salt include salts with calcium, magnesium or aluminum (hereinafter abbreviated as Ca, Mg and Al) {for example, Ca palmitate, Al palmitate, Ca stearate, Mg stearate, Al stearate, etc.}.

Examples of long-chain aliphatic alcohols include aliphatic alcohols having 8 to 25 carbon atoms (for example, lauryl alcohol, palmityl alcohol, stearyl alcohol, oleyl alcohol, etc.).

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

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

As the hydrophobic substance (c2) which is a polysiloxane, polydimethylsiloxane, polyether-modified polysiloxane {polyoxyethylene-modified polysiloxane and poly(oxyethylene/oxypropylene)-modified polysiloxane, etc.}, carboxy-modified polysiloxane, epoxy Modified polysiloxanes, amino modified polysiloxanes, alkoxy modified polysiloxanes and the like and mixtures thereof are included.

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

The organic group (modifying group) of the polyether modified polysiloxane includes a group containing a polyoxyethylene group or a poly(oxyethylene/oxypropylene) group. The content (number) of oxyethylene groups and/or oxypropylene groups contained in the polyether modified polysiloxane is preferably 2 to 40, more preferably 5 to 30, and particularly preferably, per 1 molecule of the polyether modified polysiloxane. It is 7 to 20, most preferably 10 to 15. When it is in the range of 2 to 40, the absorption property is 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, particularly preferably 5 based on the weight of the polysiloxane. Is up to 20. When it is in the range of 1 to 30, coarse particles can be further reduced.

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

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

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

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

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

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

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

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

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

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

The viscosity (mPa·s, 25° C.) of the hydrophobic substance (c2), which is a polysiloxane, is preferably 10 to 5000, more preferably 15 to 3000, and particularly preferably 20 to 1500. When it is in the range of 10 to 5000, the absorption property is further improved. The viscosity is JIS Z8803-1991 “Liquid viscosity”. Measured according to the viscosity measurement method using a cone and a cone-plate type rotational viscometer {for example, an E-type viscometer whose temperature is adjusted to 25.0±0.5° C. (RE80L manufactured by Toki Sangyo Co., Ltd., radius 7 mm , Cone cone with an angle of 5.24×10 ⁻² rad). }.

Of these gel blocking inhibitors (c), from the viewpoint of reducing coarse particles, a long-chain fatty acid ester, a long-chain fatty acid salt, a long-chain fatty acid alcohol, and a hydrophobic substance such as polysiloxane are preferable, and sucrose is more preferable. Stearic acid ester, Mg stearate, stearyl alcohol, amino-modified polysiloxane, carboxy-modified polysiloxane, particularly preferably sucrose stearate monoester, sucrose stearate diester, Mg stearate, stearyl alcohol, amino-modified polysiloxane. ..

The step of adding the gel blocking inhibitor (c) is not particularly limited as long as it is before the drying step described later, but from the viewpoint of reducing coarse particles by the gel blocking inhibitor (c), it is preferably a polymerization step or gel pulverization. In the step, more preferably in the gel crushing step, particularly preferably in the gel crushing step, a method of adding the gel blocking inhibitor (c) before or during the gel crushing is preferable.

The addition amount (% by weight) of the gel blocking inhibitor (c) is preferably 0.05 to 5.0, more preferably 0.08 to 1.0, particularly preferably 0.08 to 1.0, based on the weight of the crosslinked polymer (A). It is preferably 0.1 to 0.5. If it is less than 0.05, the effect of reducing coarse particles becomes insufficient and the average sphericity tends to be low, and if it is higher than 5.0, not only the effect of reducing coarse particles does not correspond to the addition amount but it is uneconomical. Absorption characteristics may deteriorate.

The drying step is a step of drying the hydrogel particles obtained by the gel crushing step to obtain a dry powder containing the crosslinked polymer (A). At that time, the solid content concentration of the gel before the drying step is preferably 10 to 55%, more preferably 25 to 45%. If the solid content concentration is lower than the range of 10 to 55%, the productivity will be poor, and if it is higher than this range, the energy required for the pulverization will be too high and the pulverization device may be damaged.

In the method for producing water-absorbent resin particles of the present invention, drying is performed using a stirring dryer in the drying process. By using a stirring dryer, to prevent aggregation of hydrogel particles during drying, to suppress the amount of coarse particles in the dry powder obtained after drying, high average sphericity in the pulverization step described later, and The change width of the average sphericity after the impact resistance test can be reduced.

In the present invention, the agitating dryer is not limited as long as the hydrogel particles to be dried are agitated, and may have a form having an agitating means such as an agitating blade, a rotating container, and an air flow. Specific stirring dryers include, for example, groove-type stirring dryers, rotary dryers, disk dryers, Nauta-type dryers, fluidized-bed dryers, and airflow dryers. Among these, from the viewpoint of preventing aggregation of gel particles and convenience of operation, a stirring dryer having a stirring blade and a stirring means for a rotating container is preferable.

Also, the heating means of the dryer is not limited as long as it can add the amount of heat required for drying, and examples thereof include heating means by convective heat transfer, conductive heat transfer, microwaves, infrared rays, and the like.

The drying temperature in the above-mentioned agitating dryer is preferably 100 to 230°C, more preferably 120 to 200°C from the viewpoint of drying efficiency and thermal deterioration of the crosslinked polymer. In the case of introducing hot air for drying, the hot air temperature can be increased from the viewpoint of improving the drying rate, though it depends on the water content of the gel particles to be dried, and is preferably 100 to 400° C., more preferably Is 200 to 400°C.

When the solvent contains water, the water content (% by weight) of the dry powder of the crosslinked polymer (A) is preferably 0 to 20 and more preferably 1 to 15 based on the weight of the crosslinked polymer (A). , Particularly preferably 2 to 13, and most preferably 3 to 12. When it is in the range of 0 to 20, the absorption performance is further improved.

When the solvent contains an organic solvent, the content (% by weight) of the organic solvent in the dry powder of the crosslinked polymer (A) is preferably 0 to 10 based on the weight of the crosslinked polymer (A), and more preferably Is 0 to 5, particularly preferably 0 to 3, and most preferably 0-1. When it is in the range of 0 to 10, the absorbent performance of the water absorbent resin particles is further improved.

In addition, 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.

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

The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dried powder of the crosslinked polymer (A) obtained after drying is 50% by weight or less, preferably 45% by weight or less, and more preferably It is 40% by weight or less, particularly preferably 35% or less, most preferably 30% by weight or less. When the weight ratio of the particles having a particle diameter of 2.8 mm or more is higher than 50% by weight, the average sphericity of the water-absorbent resin particles is low and the variation range of the average sphericity after the impact resistance test is large. There is a risk of becoming. On the other hand, the lower limit is preferably as low as possible and is not particularly limited, but from the viewpoint of productivity of the water absorbent resin particles, it is preferably 0% by weight or more, and more preferably 10% by weight or more.

The weight ratio of the particles having a particle size of 2.8 mm or more to the total weight of the dry powder is determined by using a low tap test sieve shaker and a standard sieve (JIS Z8801-1:2006). It is measured by the method described in Ars Handbook 6th edition (MacGraw-Hill Book Company, 1984, p. 21). That is, the JIS standard sieve is assembled in the order of 4.0 mm, 2.8 mm, 1.4 mm and the pan from the top. About 50 g of the measurement particles are put into the uppermost sieve, and shaken for 5 minutes with a low tap test sieve shaker. The weight of the measured particles on each sieve and the pan is weighed, and the total weight is set to 100% by weight to obtain the weight fraction of the particles on each sieve. The total weight fraction of particles of 4.0 mm or more and 2.8 mm or more is defined as the weight ratio of particles having a particle diameter of 2.8 mm or more.

The particle size and particle size distribution of the resin particles containing the crosslinked polymer (A) are adjusted by crushing and/or classification. 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 sieved product may be pulverized again after the 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 with specific openings may be used or a single sieve may be used for classification. The classifying device is not particularly limited, but a known method such as a vibrating screen, an in-plane moving screen, a movable mesh 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 particles that have passed through the sieve with a specific opening (subsidiary product) are removed. It is preferable.

The weight average particle diameter (μm) of the resin particles containing the crosslinked polymer (A) obtained by pulverization and/or classification is preferably 200 to 450, more preferably 200 to 400, and particularly preferably 200 to 370. is there. When it is larger than the range of 200 to 450, the average sphericity of the water-absorbent resin particles tends to be low, and the variation range of the average sphericity after the impact resistance test tends to be large. On the other hand, when the amount is smaller than this range, the fluidity of the particles is deteriorated, and the addition amount tends to be varied during the production of diapers.

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

The water-absorbent resin particles of the present invention have a structure in which the resin particles containing the crosslinked polymer (A) are surface-crosslinked with the surface crosslinking agent (d). By having a structure that has been surface-crosslinked with the surface-crosslinking agent, it is possible to improve the absorption characteristics (liquid passing speed, absorption amount under load, etc.).

In the production method of the present invention, as the surface cross-linking agent (d) in the step of subjecting the resin particles containing the cross-linked polymer (A) to the surface cross-linking treatment with the surface cross-linking agent, there are known {JP-A-59-189103, JP-A-58-180233, JP-A-61-16903, JP-A-61-2111305, JP-A-61-252212, JP-A-51-136588 and JP-A-61-257235. The surface cross-linking agent {polyhydric glycidyl, polyhydric alcohol, polyhydric amine, polyhydric aziridine, polyhydric isocyanate, silane coupling agent, polyhydric metal, etc.} can be used. Of these surface cross-linking agents, from the viewpoints of economic efficiency and absorption characteristics, polyhydric glycidyl, polyhydric alcohols and polyhydric amines are preferred, more preferably polyhydric glycidyls and polyhydric alcohols, particularly preferably polyhydric glycidyl, most preferred. Preferred is ethylene glycol diglycidyl ether.

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

As a method for surface-crosslinking with a surface-crosslinking agent, known methods (for example, Japanese Patent No. 36485553, Japanese Patent Laid-Open No. 2003-165883, Japanese Patent Laid-Open No. 2005-75982, Japanese Patent Laid-Open No. 2005-95759) can be applied. ..

After the step of surface cross-linking with a surface cross-linking agent, it may be further sieved to adjust the particle size.

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

Examples of the inorganic fine particles include silica, alumina, zirconia, titania, zinc oxide, talc and the like. Examples of the polyvalent metal salt include salts of at least one metal selected from the group consisting of magnesium, calcium, zirconium, aluminum and titanium with the above-mentioned inorganic acid or organic acid. Of these, silica, alumina, aluminum sulfate, sodium aluminum sulfate, and aluminum lactate are preferable. These may be used alone or in combination of two or more.

The amount (% by weight) of the inorganic fine particles or the polyvalent metal salt used is based on the weight of the resin particles containing the crosslinked polymer (A), from the viewpoint of absorption performance (particularly, liquid permeability and blocking resistance). It is preferably 0.01 to 2.0, more preferably 0.05 to 1.0.

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

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

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

The particle shape of the water-absorbent resin particles of the present invention is an irregular crushed shape. Due to the irregular crushed particle shape, not only water-absorbent resin particles with a high water absorption rate (especially short water absorption time by the Vortex method) can be obtained, but it also has good entanglement with fibrous materials such as paper diapers. It is preferable from the standpoint that there is no fear of falling off from the fibrous material. Further, the particle shape may be an aggregate (or granule) thereof or a porous structure thereof, as long as it has an irregular crushed shape. Therefore, it is preferably not a perfect spherical shape as produced by, for example, the reverse phase suspension polymerization method. The preferable average sphericity of the water-absorbent resin particles will be described later.

The apparent density (g/ml) of the water absorbent resin particles is preferably 0.54 to 0.70, more preferably 0.56 to 0.68, and particularly preferably 0.58 to 0.66. When it is in the range of 0.54 to 0.70, the absorption performance is further improved. The apparent density is measured at 25°C according to JIS K7365:1999.

The average sphericity (SPHT) of the water absorbent resin particles is 0.800 to 0.900, preferably 0.800 to 0.870, more preferably 0.800 to 0.850, most preferably 0.800. It is about 0.840. If it is less than 0.800, not only the variation range of the average sphericity (SPHT) after the impact resistance test described below becomes large, but also the feeling of jaggedness or lumpiness due to the contact between SAP particles increases, and Feels worse. On the other hand, when it is larger than 0.900, the absorbent body comes off from the fibrous material. The average sphericity of the water-absorbent resin particles can be controlled by reducing the coarse particles of the dry powder obtained after drying, as described above.

Note that the average sphericity can be measured by a method of deriving the average sphericity of the measurement sample by image analysis, for example, using a Camsizer (registered trademark) image analysis system (manufactured by Retsch Technology GmbH). That is, 30.0 g of the measurement sample is allowed to fall in small amounts, and the falling measurement sample is continuously photographed with a CCD camera. The average sphericity of the measurement sample is derived by analyzing the captured image. The arithmetic mean value of the average sphericity of the particles derived by the analysis point N=3 is defined as the average sphericity of the present invention.

The change range of the average sphericity (SPHT) after the impact resistance test is 0 to 0.015, preferably 0 to 0.0130, and more preferably 0 to 0.010. If it is out of the range of 0 to 0.015, the physical properties of the water-absorbent resin particles after the impact resistance test are deteriorated, and the liquid permeability and the absorption rate are easily changed. The change width of the average sphericity of the water absorbent resin particles after the impact resistance test can be controlled by reducing the coarse particles of the dry powder obtained after drying, as described above.

<Measurement method of average sphericity (SPHT) after impact resistance test>
The average sphericity (SPHT) after the impact test of the present invention was measured as follows. 30 g of water-absorbent resin particles was placed in a 3 L round separable flask (manufactured by ASONE), and a nylon net (JIS Z8801-1:2000) with an opening of 63 mm and a 6 mm hole in the center was placed in the upper part of the separable flask. ) Is placed, and a 4-port separable cover (main tube TS29/42 made by ASONE, side tubes TS24/40, 24/40, 15/35) is set on it. Next, a stainless steel pipe (outer diameter 6 mm, inner diameter 4 mm) was set in a TS29/42 main pipe having a 4-neck separable cover so that the nylon net penetrated through the nylon net and the tip was at a position 45 mm from the bottom surface of the separable flask. The other side of the stainless steel pipe is equipped with a urethane tube (length 1500 mm, inner diameter 8.5 mm) and connected to an air line capable of achieving a pressure of 0.3 MPa or more. Next, the air line is opened at a pressure of 0.2 MPa, and after air blowing for 3 minutes, the water absorbent resin particles are taken out. Using the water absorbent resin particles, the average sphericity (SPHT) after the impact resistance test is measured using the Camsizer (registered trademark) image analysis system (manufactured by Retsch Technology GmbH) as described above. The change width of the average sphericity (SPHT) after the impact resistance test is obtained by the following equation.
(Width of change in average sphericity after impact resistance test)=(Average sphericity after impact resistance test)-(Average sphericity before impact resistance test)

The weight average particle diameter (μm) of the water absorbent resin particles of the present invention is preferably 200 to 450, more preferably 200 to 400, and particularly preferably 200 to 370. If it is larger than the range of 200 to 450, the average sphericity of the water-absorbent resin particles tends to be low, and the variation range of the average sphericity after the impact resistance test may be large. On the other hand, when the amount is smaller than this range, the fluidity of the particles is deteriorated, and the addition amount tends to be varied during the production of diapers.

In the water-absorbent resin particles of the present invention, the weight ratio of particles having a particle diameter of 500 μm or more is preferably 5% by weight or less, more preferably 3% by weight or less, based on all the water-absorbent resin particles. When the content is more than 5% by weight, the average sphericity of the water-absorbent resin particles tends to be low, and the change width of the average sphericity after the impact resistance test becomes large, or the jaggies or lumps due to the contact between the SAP particles are lumpy or lumpy. The touching feeling may increase, and the texture of the absorber may deteriorate.

In the water-absorbent resin particles of the present invention, the weight ratio of particles having a particle diameter of less than 150 μm is preferably 3% by weight or less, more preferably 1% by weight or less, based on all the water-absorbent resin particles. If it is more than 3% by weight, the gel flow rate may decrease.

The water-absorbent resin particles of the present invention preferably have a water retention capacity of physiological saline (0.9% by weight saline; the same below) of 25 to 45 g/g, more preferably 30 to 40 g/g. When it is in the range of 25 to 45 g/g, the absorbent article can exhibit a sufficient amount of absorption and can be compatible with the liquid passage rate.

The gel permeation rate of the water-absorbent resin particles of the present invention with physiological saline is preferably 10 ml/min or more, more preferably 40 ml/min or more, and particularly preferably 70 ml/min or more. If it is less than 10 ml/min, the permeation rate into the absorbent is slow, and leakage may occur. The higher the upper limit, the more preferable it is not particularly limited, but from the viewpoint of compatibility with the water retention amount, it is preferably 1000 ml/min or less, more preferably 500 ml or less, and particularly preferably 100 ml or less.

The absorption rate of the water-absorbent resin particles of the present invention by the Vortex method is preferably 45 seconds or less, more preferably 40 seconds or less, and particularly preferably 35 seconds or less. If it is longer than 45 seconds, the absorbent body tends to leak. The lower limit is preferably as low as possible and is not particularly limited, but from the viewpoint of compatibility with the average sphericity, it is preferably 10 seconds or more, more preferably 15 seconds or more.

The water content (% by weight) of the water-absorbent resin particles of the present invention is preferably 0 to 20, more preferably 1 to 15, particularly preferably 2 to 13, and most preferably 3 to 12. When it is in the range of 0 to 20, the absorption performance may be further improved, and the change width of the average sphericity after the impact resistance test may be small.

The water-absorbent resin particles of the present invention form an absorbent body included in an absorbent article. As the absorber, water-absorbent resin particles may be used alone, or may be used together with other materials to form the absorber. Examples of other materials include fibrous materials. The structure and manufacturing method of the absorber when used together with the fibrous material are the same as known ones (JP 2003-225565 A, JP 2006-131767 A, JP 2005-097569 A, etc.). is there.

When the water-absorbent resin particles of the present invention are used as an absorbent body together with a fibrous material, the weight ratio of the water-absorbent resin particles to the fibers (weight of water-absorbent resin particles/weight of fibers) is preferably 60/40 to 90/10. , And more preferably 75/25 to 85/15.

The absorbent article can be applied not only to hygiene products such as disposable diapers and sanitary napkins, but also to various applications such as absorption of various aqueous liquids described below, use as a retention agent, and use as a gelling agent. The manufacturing method of the absorbent article and the like are the same as known methods (the methods described in JP-A-2003-225565, JP-A-2006-131767 and JP-A-2005-097569).

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. Unless otherwise specified, parts are parts by weight and% is% by weight. The water retention capacity of the water-absorbent resin particles in the physiological saline solution, the gel passing rate by the physiological saline solution, and the absorption rate by the Vortex method were measured by the following methods.

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

<Measurement method of gel permeation rate with physiological saline>
It measured by the following operations using the instrument shown in FIG. 1 and FIG.
A swollen gel particle 2 was prepared by immersing 0.32 g of the measurement sample in 150 ml of physiological saline 1 for 30 minutes. Then, a vertically standing cylinder 3 {diameter (inner diameter) 25.4 mm, length 40 cm, graduation line 4 and graduation line 5 are provided at a position of 60 ml and 40 ml from the bottom, respectively. }, in the state where the cock 7 is closed in a filtration cylindrical tube having a wire mesh 6 (opening 106 μm, JIS Z8801-1:2006) and an openable/closable cock 7 (inner diameter of the liquid passage portion is 5 mm), After transferring the prepared swollen gel particles 2 together with a physiological saline solution, a circular wire netting 8 (opening 150 μm, diameter 25 mm) is attached onto the swollen gel particles 2 perpendicularly to the wire netting surface with a pressing shaft 9 (weight). 22 g and a length of 47 cm) were placed so that the wire net and the swollen gel particles were in contact with each other, and a weight 10 (88.5 g) was further placed on the pressure shaft 9 and left still for 1 minute. Subsequently, the cock 7 is opened, and the time (T1; seconds) required for the liquid level in the filtration cylindrical tube to change from the 60 ml scale line 4 to the 40 ml scale line 5 is measured, and the gel flow rate (ml/min) is calculated from the following formula. I asked.
Gel flow rate with physiological saline (ml/min)=20 ml×60/(T1-T2)
The temperature of the physiological saline used and the measurement atmosphere is 25° C.±2° C., and T2 is the time measured by the same operation as above in the case of no measurement sample.

<Absorption rate by Vortex method>
50 g of physiological saline was put into a 100 ml beaker, and the temperature was adjusted to 25±2°C. Next, a stirrer piece (length 30 mm, central diameter 8 mm, end diameter 7 mm) was put in the central portion of the beaker, and physiological saline was stirred at 600 rpm. 2.000 g of the measurement sample was put in the vicinity of the beaker wall surface. The measurement sample to be used was adjusted by using a sample splitter or the like so as to be sampled in the state of its typical particle size. The measurement starts from the time when the measurement sample has been added, and the time (seconds) until the liquid surface of the mixed solution consisting of the measurement sample and physiological saline becomes flat (the point at which diffused light from the liquid surface disappears) Was taken as the absorption rate. The test was conducted under the conditions of 25±3° C. and 60±5 RH%.

<Measurement of average sphericity (SPHT) after impact resistance test>
It measured by the above-mentioned measuring method.

<Gel flow rate change rate>
The rate of change of the gel flow rate was determined by the following formula. In the following formula, the gel flow rate after the impact resistance test was carried out by using the same sample as that used in the measurement of the average sphericity (SPHT) after the impact resistance test described above, and the gel with physiological saline was used. The liquid passing rate was measured.
(Gel flow rate [%])={(gel flow rate of water-absorbent resin particles [ml/min])-(gel flow rate after impact test [ml/min])}/( Gel flow rate of water-absorbent resin particles [ml/min])×100

<Change rate of absorption rate by Vortex method>
The rate of change in absorption rate by the Vortex method is calculated by the following formula. In the following formula, the absorption rate by the Vortex method after the impact resistance test is the absorption rate by the Vortex method using the same sample as the one that was used to measure the average sphericity (SPHT) after the impact resistance test described above. The speed was measured.
(Change rate of absorption rate by Vortex method [%])={(Absorption rate of water absorbent resin particles by Vortex method [sec])-(Absorption rate by Vortex method after impact test [sec])}/(Water absorption Speed of absorbing resin particles by Vortex method [sec])×100

<Evaluation method of foreign body feeling>
The feeling of foreign matter by touch was evaluated by 10 monitors. Specifically, place 100 g of water-absorbent resin particles in a polyethylene bag with a zipper (140 x 100 x 0.04 mm), and use the index finger and/or the middle finger to sample the sample in one direction within a pre-marked area. Gently knead (for example, clockwise), and the feeling of foreign matter was evaluated according to the following evaluation criteria.
◎ Less than 2 people who feels cramped ○ 2 or more but less than 4 who feels cramped △ 4 or more but less than 6 who feels cramped × 6 or more who feels cramped

<Example 1>
Water-soluble vinyl monomer (a1-1) {acrylic acid, manufactured by Mitsubishi Chemical Corporation, purity 100%} 155 parts (2.15 mole parts), cross-linking agent (b1) {pentaerythritol triallyl ether, manufactured by Daiso Co., Ltd. } 0.6225 parts (0.0024 parts by mole) and 340.27 parts of deionized water were maintained at 3°C with stirring and mixing. Nitrogen was introduced into this mixture to adjust the amount of dissolved oxygen to 1 ppm or less, and then 0.62 parts of a 1% aqueous hydrogen peroxide solution, 1.1625 parts of a 2% aqueous ascorbic acid solution and 2% of 2,2′-azobis[ 2-Methyl-N-(2-hydroxyethyl)-propionamide] aqueous solution (2.325 parts) was added and mixed to initiate polymerization. After the temperature of the mixture reached 90° C., the mixture was polymerized at 90±2° C. for about 5 hours to obtain a hydrogel (1) containing a crosslinked polymer.

Next, while mixing 200 parts of the hydrogel (1) with a mincing machine (12VR-400K manufactured by ROYAL Co., Ltd.) and chopping, 51.13 parts of a 48.5% sodium hydroxide aqueous solution was added and mixed, and the mincing machine (ROYAL Co.) 12VR-400K) manufactured three times to obtain a shredded gel. Subsequently, 0.076 parts of gel blocking inhibitor (c-1) {sucrose stearate} was added and mixed, and further shredded once with a mincing machine (12VR-400K manufactured by ROYAL) to give water-containing gel particles. Got Next, all the water-containing gel particles were put into a kneader (tabletop kneader PNV-1, Irie Shokai Co., Ltd.) equipped with a sigma type rotary blade and a heat insulation jacket, and dried for 60 minutes at a rotation speed of 40 rpm and a jacket temperature of 180° C., A dry powder (1) containing a crosslinked polymer was obtained. The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (1) was 41% by weight. Subsequently, the dry powder (1) was pulverized with a roll mill (RM-10 type roll pulverizer, Asano Iron Works Co., Ltd.) with a clearance of 0.35 mm, and then sieved to obtain particles having an opening of 710 to 150 μm. The resin particles (A-1) containing the crosslinked polymer were obtained by adjusting the particle size within the range. The weight average particle diameter of the resin particles (A-1) containing the crosslinked polymer after pulverization and classification was 420 μm.

Next, to 30 parts of the above resin particles (A-1), 0.081 part of 15% ethylene glycol diglycidyl ether as a surface cross-linking agent, 0.90 part of 50% propylene glycol aqueous solution as a solvent, and clevozole (registered as inorganic fine particles) A mixed solution prepared by mixing 0.20 parts of Trademark) 30CAL25 (Colloidal silica manufactured by Merck) was added and uniformly mixed, and then heated at 130° C. for 30 minutes to obtain surface-crosslinked resin particles. Then, water-absorbent resin particles (P-1) were obtained by passing through a sieve having an opening of 850 μm.

<Example 2>
Water absorbent resin particles (P-2) were obtained in the same manner as in Example 1 except that the rotation number of the kneader was changed from 40 rpm to 30 rpm. The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (2) in Example 2 was 49% by weight, and the resin particles containing the crosslinked polymer (A-2 after pulverization and classification) were used. The weight average particle diameter of () was 436 μm.

<Example 3>
Water absorbent resin particles (P-3) were obtained in the same manner as in Example 1 except that the kneader rotation speed was changed from 40 rpm to 50 rpm. The weight ratio of the particles having a particle size of 2.8 mm or more to the total weight of the dry powder (3) in Example 3 was 35% by weight, and the resin particles (A-3 containing the crosslinked polymer after pulverization and classification were used. The weight average particle diameter of () was 400 μm.

<Example 4>
In the same manner as in Example 1, except that the gel blocking inhibitor (c-1) {sucrose stearate} 0.076 part was changed to 0.152 part, the same operation as in Example 1 was carried out to obtain the water-absorbent resin particles. (P-4) was obtained. The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (4) in Example 4 was 33% by weight, and the resin particles (A-4 containing the crosslinked polymer after pulverization and classification were used. The weight average particle diameter of () was 393 μm.

<Example 5>
In Example 1, the gel blocking inhibitor (c-1) {sucrose stearate} 0.076 parts was changed to 0.152 parts, and at the same time, the gel blocking inhibitor (c-2) {NAROACTY (registered trademark) The same operation as in Example 1 was carried out except that CL-20 and 0.113 part of an anionic surfactant (nonylphenol EOA (EO2 mol addition)) manufactured by Sanyo Kasei Co., Ltd. were used in combination, and the water-absorbent resin particles (P-5 ) Got. The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (5) in Example 5 was 27% by weight, and the resin particles containing the cross-linked polymer (A-5 after pulverization classification) were used. The weight average particle diameter of () was 385 μm.

<Example 6>
In the same manner as in Example 5, except that the opening 710-150 μm for sieving after crushing the dry powder was changed to a particle size range of 500-150 μm in Example 5, the water-absorbent resin particles (P -6) was obtained. The weight average particle diameter of the resin particles (A-6) containing the crosslinked polymer after pulverization and classification was 365 μm.

<Example 7>
In the same manner as in Example 5, except that the opening 710-150 μm for sieving after pulverizing the dry powder was changed to a particle size range of 300-150 μm in Example 5, the water-absorbent resin particles (P -7) was obtained. The weight average particle diameter of the resin particles (A-7) containing the crosslinked polymer after pulverization and classification was 202 μm.

<Example 8>
In Example 5, the same operation as in Example 5 was carried out except that the kneader rotation speed was 40 rpm and 50 rpm, and the sieve opening 710 to 150 μm after crushing the dry powder was changed to a particle diameter range of 500 to 150 μm. The water-absorbent resin particles (P-8) were obtained. The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (8) in Example 8 was 22% by weight, and the resin particles containing the crosslinked polymer (A- The weight average particle diameter of 8) was 340 μm.

<Example 9>
In Example 6, except that 0.081 part of 15% ethylene glycol diglycidyl ether as a surface crosslinking agent for the resin particles (A-6) containing the crosslinked polymer after pulverization and classification was changed to 0.200 part, The same operation as in Example 6 was performed to obtain surface-crosslinked resin particles. Subsequently, 0.045 parts of silica (Aerosil (registered trademark, hereinafter the same) 200) as inorganic fine particles was subjected to high-speed stirring (high-speed stirring turbulizer (registered trademark, hereinafter the same) manufactured by Hosokawa Micron Co., Ltd., rotation speed 2000 rpm). After the addition, the mixture was heated at 80° C. for 30 minutes, and then passed through a sieve having an opening of 850 μm to obtain water absorbent resin particles (P-9).

<Example 10>
In Example 6, 0.081 parts of 15% ethylene glycol diglycidyl ether as a surface cross-linking agent for the resin particles (A-6) containing the cross-linked polymer after pulverization and classification was changed to 0.200 parts, and as a separate solvent. Except that 0.51 parts of 50% aqueous propylene glycol solution and 0.225 parts of sodium aluminum sulfate hexahydrate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) as a polyvalent metal salt were added to carry out surface crosslinking. In the same manner as in Example 6, surface-crosslinked resin particles were obtained. While high-speed stirring (high-speed stirring turbulizer manufactured by Hosokawa Micron Co., Ltd., rotation speed 2000 rpm), 0.045 parts of silica (Aerosil 200) as inorganic fine particles was added and heated at 80° C. for 30 minutes, and then opened at 850 μm. Water-absorbent resin particles (P-10) were obtained by passing through a sieve.

<Comparative Example 1>
The same operation as in Example 1 was carried out except that the kneader rotation speed was changed from 40 rpm to 20 rpm to obtain water absorbent resin particles (R-1) for comparison. The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (ratio 1) in Comparative Example 1 was 73% by weight, and the resin particles containing the crosslinked polymer (B- The weight average particle diameter of 1) was 430 μm.

<Comparative example 2>
In Example 1, shredded once with a mincing machine without adding a gel blocking agent, changed the kneader rotation speed of 40 rpm to 50 rpm, and changed the kneader drying time of 1 hour to 2 hours. Other than that, the same operation as in Example 1 was performed to obtain comparative water-absorbent resin particles (R-2). The weight ratio of the particles having a particle size of 2.8 mm or more to the total weight of the dry powder (ratio 2) in Comparative Example 2 was 95% by weight, and the resin particles containing the crosslinked polymer (B- The weight average particle diameter of 2) was 385 μm.

<Comparative example 3>
In Example 1, the gel-blocking agent was not added, and the product was further shredded once with a mincing machine, and dried in a kneader using an aeration dryer (Tabay Espec Co., Ltd., drying conditions: hot air temperature 150° C., air speed 2 m). /S for 60 minutes), except that the drying was changed to the same operation as in Example 1 to obtain comparative water absorbent resin particles (R-3). In addition, the drying was performed by uniformly laying the entire amount of the hydrogel particles in a SUS vat (20 cm square, 5 cm depth). The weight ratio of the particles having a particle size of 2.8 mm or more to the total weight of the dry powder (ratio 3) in Comparative Example 3 was 98% by weight, and the resin particles containing the crosslinked polymer (B- The weight average particle diameter of 3) was 411 μm.

<Comparative example 4>
In Example 1, except that the drying in the kneader was changed to the ventilation type dryer (manufactured by Tabai Espec Co., Ltd., drying conditions: hot air temperature 150° C., wind speed 2 m/s, 60 minutes). The same operation was performed to obtain comparative water absorbent resin particles (R-4). In addition, the drying was performed by uniformly laying the entire amount of the hydrogel particles in a SUS vat (20 cm square, 5 cm depth). The weight ratio of the particles having a particle diameter of 2.8 mm or more to the total weight of the dry powder (Comparative 4) in Comparative Example 4 was 97% by weight, and the resin particles containing the crosslinked polymer (B- The weight average particle diameter of 4) was 415 μm.

Water-absorbent resin particles (P-1) to (P-10) obtained in Examples 1 to 10 and comparative water-absorbent resin particles (R-1) to (R-4) obtained in Comparative Examples 1 to 4. ), water retention, weight average particle size, average sphericity, average sphericity after impact test, gel flow rate, gel flow rate change rate, absorption rate by Vortex method, absorption rate by Vortex method Table 1 shows the rate of change and the evaluation results of the foreign substance feeling.

As shown in Table 1, the water-absorbent resin particles of the present invention (Examples 1 to 10) have an average sphericity within a specific high range as compared with the comparative water-absorbent resin particles (Comparative Examples 1 to 4). Therefore, it can be seen that the variation range of the average sphericity after the impact resistance test is small, and the result of the foreign material feeling evaluation is excellent. Further, it can be seen that the rate of change of the gel flow rate and the rate of change of the absorption rate by the Vortex method are reduced as the variation range of the average sphericity is reduced within a specific range. That is, it can be said that the water-absorbent resin particles of the present invention can exhibit stable absorption performance even if there is a physical load from the outside. Further, Examples 6 to 10 are examples in which the average sphericity and the increase range of the average sphericity are set within a specific range, and the weight average particle diameter is reduced. It can be seen from the results of the evaluation of the foreign matter feeling and the absorption rate) that these are highly compatible.
On the other hand, from the results in Table 1, in order to control the variation range of the average sphericity and the average sphericity after the impact resistance test within a specific range, it is obtained after drying in the manufacturing process of the water absorbent resin particles. It can be seen that it is effective to control the weight ratio of particles having a particle diameter of 2.8 mm or more in the dry powder within a specific range.

The water-absorbent resin particles of the present invention can be applied to an absorbent body containing the water-absorbent resin particles and a fibrous material, and an absorbent article including the absorbent body {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 warmer, gelling agent for batteries, water retention agent for plants and soil, dew condensation It can also be used for various applications such as preventive agents, waterstop agents, packing agents and artificial snow.

1 physiological saline 2 hydrogel particles 3 cylinder 4 scale line 60 ml from the bottom 5 scale line 40 ml from the bottom 6 wire net 7 cock 8 circular wire net 9 pressure shaft 10 weight

Claims (11)

1. Resin particles containing a water-soluble vinyl monomer (a1) and a cross-linked polymer (A) containing a cross-linking agent (b) as essential constituent units are water-absorbent resin particles having a structure in which the surface cross-linking agent (d) cross-links the surface. The particle shape is irregular crushed, the average sphericity (SPHT) is 0.800 to 0.900, and the change range of the average sphericity (SPHT) after the impact resistance test is 0 to 0.015 water-absorbent resin particles.
2. The water-absorbent resin particles according to claim 1, having a weight average particle diameter of 200 to 450 μm.
3. The water absorbent resin particles according to claim 2, having a weight average particle diameter of 200 to 370 μm.
4. The water absorbent resin particles according to any one of claims 1 to 3, which contain inorganic fine particles and/or a polyvalent metal salt.
5. The water-absorbent resin particles according to any one of claims 1 to 4, wherein a gel permeation rate of 0.9 wt% physiological saline is 10 ml/min or more.
6. The water-absorbent resin particles according to any one of claims 1 to 5, which have an absorption rate of 45 seconds or less according to the Vortex method.
7. The water absorbent resin particles according to any one of claims 1 to 6, wherein the water retention capacity of 0.9 wt% physiological saline is 25 to 45 g/g.
8. A polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a1) and a crosslinking agent (b) as essential constituent units to obtain a hydrogel containing the crosslinked polymer (A), and kneading the hydrogel. A step of crushing the gel to obtain hydrous gel particles containing (A); a step of drying the hydrous gel particles to obtain a dry powder containing (A); and further pulverizing the dry powder. And/or a method for producing water-absorbent resin particles, which comprises a step of classifying to obtain resin particles containing (A), and a step of surface-crosslinking the surface of the resin particles with a surface-crosslinking agent (d), wherein 1. The gel blocking inhibitor (c) is added before the drying step, and in the drying step, drying is performed using a stirring dryer, and the total weight of the dry powder (A) obtained after drying is 2. A method for producing water-absorbent resin particles, wherein the weight ratio of particles having a particle diameter of 8 mm or more is 50% by weight or less.
9. The method for producing water-absorbent resin particles according to claim 8, wherein the gel blocking inhibitor (c) is a hydrocarbon group-containing hydrophobic substance (c1) and/or a polysiloxane hydrophobic substance (c2).
10. The method for producing water-absorbent resin particles according to claim 8 or 9, wherein the addition amount of the gel blocking inhibitor (c) is 0.05 to 5.0% by weight based on the weight of the crosslinked polymer (A).
11. 11. The method for producing water-absorbent resin particles according to claim 8, wherein the solid content concentration of the hydrogel particles before the drying step is 10 to 55% by weight.

Images