JP7352428B2 - Absorbent resin particles and their manufacturing method - Google Patents

Description

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

In recent years, disposable swimsuits (also known as swimming pants) have become available on the market that are designed to be used by infants and young children in pools, etc., and have the function of preventing excreta such as urine and feces from dispersing into the water. For example, see Patent Documents 1 and 2).

The basic elements of such disposable swimsuits include an absorbent body that absorbs urine, and liquid-permeable front and back layers that respectively cover the front and back sides of the absorbent body.

As the absorbent body, a stack of pulp fibers is generally used. Since disposable swimsuits are used underwater, any water that gets inside is absorbed by the absorbent material. Therefore, if a disposable swimwear absorber is used underwater that is not intended for use underwater, the crotch area may sag or fall off due to the increased weight of the diaper after being submerged or submerged in the water. This results in poor appearance and poor wearing comfort.

Therefore, unlike paper diapers, which are not intended for use underwater, the absorbent material of such disposable swimwear does not contain absorbent resin, or if it does, contains a small amount of absorbent resin to prevent the absorbent material from swelling. It is considered preferable to contain only a small amount of water or to use an absorbent resin with a low water absorption capacity.

However, if absorbent resin is not included or only a small amount is included, the urine absorption performance is poor, and if you urinate before entering the water or when you are just playing near the water and have not decided whether to enter the water, There was a risk of leakage due to little or no absorption. Conventionally, a method of manufacturing an absorbent resin with a low absorption capacity for water (ion-exchanged water) by using a large amount of internal crosslinking agent is known (see Patent Document 3), but when this is used in an absorber, Although the swelling of the absorbent body after absorbing water can be suppressed, the gel passing rate of the absorbent resin is low, making it difficult for urine to diffuse into the absorbent body during urination, and there is a risk of leakage. Furthermore, absorbent resins containing a large amount of internal crosslinking agent may become colored during long-term storage, causing discomfort to the user. On the other hand, as techniques for improving the gel passing rate, there are (1) methods of forming physical spaces by adding inorganic compounds such as silica and talc, and (2) hydrophobic materials with low surface free energy such as modified silicones. A method of suppressing the coalescence of swollen gels and forming gel gaps by surface treatment with a polymer, and (3) a method of adding aluminum sulfate, aluminum lactate, etc. are already known (for example, patent literature 4, see Patent Document 5 and Patent Document 6). However, with these methods, collisions and friction between particles and particles against equipment walls, etc. occur during transportation, spraying, supplying, mixing, etc. of the absorbent resin, or during transportation of absorbent articles. There was a risk that the surface of the absorbent resin particles would be damaged and the gel passing rate would deteriorate.

JP2009-178382A JP 2018-50912 Publication Patent No. 5190116 JP2012-161788A Japanese Patent Application Publication No. 2013-133399 JP2014-512440A

An object of the present invention is to prevent urine leakage before absorbing water while suppressing expansion of the absorbent body after absorbing water when absorbent resin particles are used in absorbent articles such as disposable swimwear. Another object of the present invention is to provide absorbent resin particles that can prevent coloring over a long period of time under high temperature and high humidity conditions, a method for producing the same, and an absorbent article containing the absorbent resin particles.

The present inventor has arrived at the present invention as a result of intensive studies aimed at achieving the above-mentioned problems. That is, the present invention provides absorbent resin particles in which resin particles containing a crosslinked polymer (A) having a vinyl monomer (a) and a crosslinking agent (b) as essential constituent units are crosslinked with a post-crosslinking agent (c). The vinyl monomer (a) contains a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes the water-soluble vinyl monomer (a1) by hydrolysis, and the absorbent resin particles immersed in ion-exchanged water are The weight of ion-exchanged water absorbed per unit weight [water absorption capacity in ion-exchanged water] is 10 to 120 (g/g), and after being soaked in physiological saline for 30 minutes to swell, it is compressed by applying weight. The speed at which physiological saline passes through the absorbent resin particles [gel liquid passing rate of absorbent resin particles] is 350 (ml/min) or more, and the gel liquid passing rate obtained by the following (Formula 4) is maintained. Absorbent resin particles with a ratio of 70% or more
(Gel liquid passage maintenance rate) = 100 x ([Gel liquid passage rate of absorbent resin particles] after fragility test)
/([gel liquid passing rate of absorbent resin particles before fragility test]) ... (Formula 4)
The [gel liquid passing rate of absorbent resin particles] before the fragility test in (Equation 4) is calculated by immersing the particles in physiological saline for 30 minutes to swell without performing the fragility test described below. This is the speed at which physiological saline passes through compressed absorbent resin particles. [Gel passing rate of absorbent resin particles] after the fragility test is determined by placing 30 g of absorbent resin particles in a 3L round separable flask, and making a 6 mm hole in the center at the top of the separable flask. A nylon net with a mesh opening of 63 μm was laid, and a four-hole separable cover was further set on top of it. Next, insert a stainless steel tube (outer diameter 6 mm, inner diameter 4 mm) from the main tube of the four-necked separable cover for the 3L round separable flask, so that the stainless steel tube passes through the nylon mesh, and the tip is attached to the separable flask. Set it so that it is 45mm from the bottom. Attach a urethane tube (length 1500 mm, inner diameter 8.5 mm) to the other side of the stainless steel tube, connect it to an air line that can achieve a pressure of 0.3 MPa or more, open the air line at a pressure of 0.2 MPa, and A fragility test was performed by air blowing for 30 minutes, and then the absorbent resin particles taken out were immersed in physiological saline for 30 minutes to swell, and then compressed under load. This is the speed at which the saline solution passes. ; an absorbent body containing the absorbent resin particles; an absorbent article containing the absorbent body.
The present invention also provides a method for producing the above-mentioned absorbent resin particles, which comprises a crosslinked polymer (A) containing a vinyl monomer (a) and a crosslinking agent (b) as essential constituent units, and has a water content of 22 to 90. % by weight of the resin particles and a post-crosslinking agent (c).
) has the effect of being excellent in emulsion stability and convergence.

The absorbent resin particles of the present invention exhibit a moderate water retention amount and a high gel passing rate while suppressing the absorption capacity for water. Therefore, when the absorbent resin particles of the present invention are used in absorbent articles such as disposable swimwear, the absorbent core of the absorbent article is difficult to swell even if water infiltrates into the absorbent article. Hard to fall off. On the other hand, even if the user urinates before entering the water or when he or she is just playing near the water and has not yet decided whether or not to enter the water, the absorbent article of the present invention can sufficiently absorb urine and suppress leakage.

FIG. 2 is a cross-sectional view schematically showing a filtration cylindrical tube for measuring gel passing rate. FIG. 2 is a perspective view schematically showing a pressurizing shaft and a weight for measuring gel flow rate.

The absorbent resin particles of the present invention are absorbent resins obtained by crosslinking resin particles containing a crosslinked polymer (A) whose essential constituent units are a vinyl monomer (a) and a crosslinking agent (b) with a post-crosslinking agent (c). The vinyl monomer (a) includes a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis.

The water-soluble vinyl monomer (a1) in the present invention is not particularly limited, and may be a known monomer, for example, at least one water-soluble substituent and an ethylenically insoluble monomer disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 3648553. Vinyl monomers having a saturated group (for example, anionic vinyl monomers, nonionic vinyl monomers, and cationic vinyl monomers), anionic vinyl monomers and nonionic vinyl monomers disclosed in paragraphs 0009 to 0024 of JP 2003-165883 A cationic vinyl monomers and cationic vinyl monomers, and carboxy groups, sulfo groups, phosphono groups, hydroxyl groups, carbamoyl groups, amino groups and ammonio groups disclosed in paragraphs 0041 to 0051 of JP-A No. 2005-75982. Vinyl monomers containing at least one of the following can be used.
In addition, water solubility in a water-soluble vinyl monomer means, if expressed using a quantity, that at least 100 g of a solute is dissolved in 100 g of water at 25° C., for example.

Vinyl monomer (a2) which becomes water-soluble vinyl monomer (a1) by hydrolysis [hereinafter also referred to as hydrolyzable vinyl monomer (a2)]. ] is not particularly limited, and may be a known vinyl monomer, for example, a vinyl monomer having at least one hydrolyzable substituent that becomes a water-soluble substituent upon hydrolysis as disclosed in paragraphs 0024 to 0025 of Japanese Patent No. 3,648,553. , at least one hydrolyzable substituent [1,3-oxo-2-oxapropylene (-CO-O-CO-) group, acyl and cyano group] can be used.
Note that hydrolysis means decomposing the hydrolyzable vinyl monomer (a2) into the water-soluble vinyl monomer (a1) in the presence of water, using a catalyst (acid, base, etc.) if necessary. The hydrolyzable vinyl monomer (a2) may be hydrolyzed during the polymerization, after the polymerization, or both, but from the viewpoint of the absorption performance of the resulting absorbent resin particles, it is preferably after the polymerization.

Among the water-soluble vinyl monomer (a1) and/or the vinyl monomer (a2) which becomes the water-soluble vinyl monomer (a1) by hydrolysis, the water-soluble vinyl monomer (a1) is preferred from the viewpoint of absorption performance and the like. As the water-soluble vinyl monomer (a1), preferred are the above-mentioned anionic vinyl monomers; carboxy (salt) group, sulfo (salt) group, amino group, carbamoyl group, ammonio group, or mono-, di-, or tri-alkyl group. Vinyl monomers having an ammonio group; more preferred are vinyl monomers having a carboxy (salt) group or carbamoyl group; particularly preferred are (meth)acrylic acid (salts) and (meth)acrylamide; particularly preferred are (meth)acrylic acid (salts) and (meth)acrylamide; Acrylic acid (salt); most preferred is acrylic acid (salt).

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

When using an acid group-containing monomer such as acrylic acid or methacrylic acid as the water-soluble vinyl monomer (a1), it is preferable that part of the acid group-containing monomer is neutralized with a base from the viewpoint of water absorption performance and residual monomer. . As the base for neutralization, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as sodium carbonate, sodium bicarbonate, and potassium carbonate can be used. Neutralization may be carried out before, during, after, or both of the above in the production of absorbent resin particles. Preferred examples include methods such as neutralizing the acid group-containing polymer in the form of a hydrogel.

Further, 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 will have high stickiness, and workability during production and use may deteriorate. Furthermore, the water retention capacity of the resulting absorbent resin particles may be reduced. On the other hand, if the degree of neutralization exceeds 80%, the pH of the resulting resin may become high and there may be concerns about safety for human skin.

When using either the water-soluble vinyl monomer (a1) or the hydrolyzable vinyl monomer (a2) as a structural unit, one type of each may be used alone, or two or more types may be used as a structural unit if necessary. good. The same applies when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as the constituent units. In addition, when the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent units, the molar ratio of their content [(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. Within this range, the absorption performance will be even better.

In addition to the above-mentioned water-soluble vinyl monomer (a1) and hydrolyzable vinyl monomer (a2), the vinyl monomer (a) can be copolymerized with the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2). Other vinyl monomers (a3) can be used as structural units. The other vinyl monomers (a3) may be used alone or in combination of two or more.

The other copolymerizable vinyl monomer (a3) is not particularly limited, and examples thereof include the hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553, and paragraph 0025 of Japanese Patent Application Publication No. 2003-165883. Known hydrophobic vinyl monomers such as the vinyl monomer disclosed in paragraph 0058 of JP-A No. 2005-75982 can be used, and specifically, for example, the following vinyl monomers (i) to (iii) can be used. Can be used.
(i) Aromatic ethylenic monomers having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted products of styrene such as vinylnaphthalene and dichlorostyrene.
(ii) Aliphatic ethylenic monomers having 2 to 20 carbon atoms Alkenes (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.); and alkadienes (butadiene, isoprene, etc.).
(iii) Alicyclic ethylenic monomers having 5 to 15 carbon atoms, monoethylenically unsaturated monomers (pinene, limonene, indene, etc.); and polyethylenic vinyl monomers [cyclopentadiene, bicyclopentadiene, ethylidene norbornene, etc.].

The content of other vinyl monomer (a3) units is preferably 0 to 5 mol%, more preferably The content of other vinyl monomer (a3) units is 0 to 3 mol%, particularly preferably 0 to 2 mol%, particularly preferably 0 to 1.5 mol%, and from the viewpoint of absorption performance etc., the content of other vinyl monomer (a3) units is 0 mol%. Most preferably.

The crosslinking agent (b) is not particularly limited and may include known crosslinking agents, such as crosslinking agents having two or more ethylenically unsaturated groups disclosed in paragraphs 0031 to 0034 of Japanese Patent No. 3648553, and water-soluble substituents. A crosslinking agent having at least one functional group capable of reacting with a water-soluble substituent and at least one ethylenically unsaturated group, and a crosslinking agent having at least two functional groups capable of reacting with a water-soluble substituent, JP-A-2003- A crosslinking agent having two or more ethylenically unsaturated groups, a crosslinking agent having an ethylenically unsaturated group and a reactive functional group, and two or more reactive substituents disclosed in paragraphs 0028 to 0031 of Publication No. 165883 A crosslinking agent having a crosslinking agent, a crosslinkable vinyl monomer disclosed in paragraph 0059 of JP 2005-75982, a crosslinkable vinyl monomer disclosed in paragraphs 0015 to 0016 of JP 2005-95759, and JP 2018- Polyvalent glycidyl compounds disclosed in paragraph 0066 of No. 39929 can be used.
Among these, from the viewpoint of absorption performance, etc., crosslinking agents having two or more ethylenically unsaturated groups are preferred, and more preferred are bis(meth)acrylamides such as N,N'-methylenebisacrylamide; (poly) Poly(meth)acrylates of polyhydric alcohols such as alkylene glycol, trimethylolpropane, glycerin, pentaerythritol and sorbitol; ) Polyvalent (meth)allyl compounds such as allyl ether, tetraallyloxyethane, and triallyl isocyanurate, and the most preferred are polyvalent (meth)allyl compounds. The crosslinking agent (b) may be used alone or in combination of two or more.

The content of the crosslinking agent (b) in the crosslinked polymer (A) is the total weight of the vinyl monomers (a) constituting the crosslinked polymer (A) (i.e., the water-soluble vinyl monomer (a1), the hydrolyzable vinyl monomer (a2) and other vinyl monomers (a3)) is preferably 0.2 to 5% by weight, more preferably 0.3 to 3% by weight, most preferably 0.4 to 1% by weight. It is. When the content is less than 0.2% by weight, the soluble content of the absorbent resin particles increases, and the gel passing rate may decrease. On the other hand, if the content is more than 5% by weight, the crosslinking density inside the absorbent resin particles becomes too high, making it impossible to exhibit sufficient water retention, and also discoloring during long-term storage. The weights of the vinyl monomer (a) and crosslinking agent (b) contained in the crosslinked polymer (A) are as follows: Use the weight in (b).

Methods for producing the crosslinked polymer (A) include known solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc.; JP-A-55-133413, etc.), known suspension polymerization, and reverse phase suspension. A hydrogel polymer (containing at least a crosslinked polymer and water) obtained by turbidity polymerization (Japanese Patent Publication No. 54-30710, JP-A-56-26909, JP-A-1-5808, etc.) is required. It can be obtained by drying. The crosslinked polymer (A) may be used alone or in a mixture of two or more.

The crosslinked polymer (A) essentially contains a vinyl monomer (a) containing a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a crosslinking agent (b). It can be obtained by polymerizing a monomer composition as a structural unit, but among the polymerization methods, solution polymerization is preferred, as it does not require the use of organic solvents and is advantageous in terms of production costs. Therefore, the aqueous solution polymerization method is particularly preferable, and the aqueous solution adiabatic polymerization method is the most preferable because it yields a crosslinked polymer with a large water retention capacity and a small amount of water-soluble components, and there is no need to control the temperature during polymerization. .

When performing aqueous polymerization, a mixed solvent containing water and an organic solvent can be used, and examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N,N-dimethylformamide, dimethyl sulfoxide, and two or more of these. A mixture of When a mixed solvent containing water and an organic solvent is used in the aqueous solution polymerization, the amount of the organic solvent used is preferably 40% by weight or less, more preferably 30% by weight or less, based on the weight of water.

When using a catalyst for polymerization, conventional radical polymerization catalysts can be used, such as azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid, 2,2'-azobisamidinopropane dihydrochloride, etc.], Inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic peroxide, (2-ethoxyethyl) peroxydicarbonate, etc.] and redox catalysts (alkali metal sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, reducing agents such as ascorbic acid, alkali metal persulfates, ammonium persulfates, (composed of a combination of hydrogen peroxide and an oxidizing agent such as an organic peroxide). These catalysts may be used alone or in combination of two or more thereof. The amount of the radical polymerization catalyst used is based on the total weight of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2), and (a1) to (a3) when using the other vinyl monomer (a3). The amount is preferably 0.0005 to 5% by weight, more preferably 0.001 to 2% by weight.

When a suspension polymerization method or a reverse phase suspension polymerization method is used as the polymerization method, the polymerization may be carried out in the presence of a conventional dispersant or surfactant, if necessary. Furthermore, in the case of reversed-phase suspension polymerization, polymerization can be carried out using conventional hydrocarbon solvents 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 5 to 80°C.

The hydrogel polymer obtained by polymerization can be shredded as necessary before drying. The size of the gel after shredding (longest diameter) is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, particularly preferably 1 mm to 1 cm. Within this range, the drying properties in the drying step will be even better.

Shredding can be performed by a known method, using a shredding device (for example, a Bex mill, a rubber chopper, a Pharma mill, a mincer, an impact crusher, a roll crusher), or the like.

Furthermore, as described above, the hydrogel polymer of the acid group-containing polymer obtained after polymerization can be neutralized by mixing a base as necessary.

Methods for distilling off and drying the solvent (including water) of the hydrogel polymer include distillation (drying) using hot air at a temperature of 80 to 230°C, and a drum dryer heated to 100 to 230°C. Thin film drying methods such as (heating) vacuum drying methods, freeze drying methods, drying methods using infrared rays, decantation, filtration, etc. can be applied.

When the solvent (organic solvent, water, etc.) of the hydrogel polymer contains an organic solvent, the content of the organic solvent after drying is preferably 0 to 10% by weight based on the weight of the crosslinked polymer (A), More preferably 0 to 5% by weight, particularly preferably 0 to 3% by weight, and most preferably 0 to 1% by weight. Within this range, the absorption performance of the absorbent resin particles becomes even better.

Further, when the solvent of the hydrogel polymer contains water, the water content after drying is preferably 0 to 20% by weight, more preferably 1 to 10% by weight, based on the weight of the crosslinked polymer (A). Particularly preferably from 2 to 9% by weight, most preferably from 3 to 8% by weight. Within this range, the crushability will be good in the subsequent crushing step, and the absorption performance will be even better.

The content and moisture content of the organic solvent were measured using an infrared moisture meter [JE400 manufactured by KETT Co., Ltd.: 120±5°C, 30 minutes, atmospheric humidity before heating 50±10%RH, lamp specification 100V, 40W] from the weight loss of the measurement sample when heated.

After drying the hydrogel polymer to obtain the crosslinked polymer (A), it is further pulverized to obtain resin particles containing the crosslinked polymer (A). There are no particular limitations on the pulverization method, and pulverizers (for example, hammer-type pulverizers, impact-type pulverizers, roll-type pulverizers, Schette air-flow pulverizers), etc. can be used. The particle size of the resin particles can be adjusted by sieving or the like, if necessary.

The weight average particle diameter of the resin particles, when sieved if necessary, is preferably 100 to 800 μm, more preferably 200 to 700 μm, next preferably 250 to 600 μm, particularly preferably 300 to 500 μm, and most preferably 350 to 450 μm. It is. Within this range, the absorption performance will be even better.

The weight average particle diameter was determined using a low-tap test sieve shaker and a standard sieve (JIS Z8801-1:2006), according to Perry's Chemical Engineers Handbook, 6th edition (McGraw-Hill Books Company, 1984). , p. 21). That is, JIS standard sieves are assembled in the following order from the top: 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. Approximately 50 g of the particles to be measured are placed in the top sieve and shaken for 5 minutes using a low-tap test sieve shaker. Weigh the particles to be measured on each sieve and saucer, take the total as 100% by weight, determine the weight fraction of particles on each sieve, and compare this value with logarithmic probability paper [the horizontal axis is the sieve opening (particle diameter ), the vertical axis is the weight fraction], a line is drawn connecting each point, the particle diameter corresponding to a weight fraction of 50% by weight is determined, and this is defined as the weight average particle diameter.

In addition, the smaller the content of fine powder contained in the resin particles, the better the absorption performance, so the content of particles of 106 μm or less (preferably 150 μm or less) in the total weight of the resin particles is preferably 3% by weight or less, More preferably, it is 1% by weight or less. The content of fine powder can be determined using the graph created when determining the weight average particle diameter.

Note that the resin particles may contain some other components such as a residual solvent and a residual crosslinking component within a range that does not impair its performance.

The absorbent resin particles of the present invention are water-absorbent resin particles obtained by crosslinking resin particles containing the crosslinked polymer (A) with a post-crosslinking agent (c), and the manufacturing method of the present invention includes the crosslinked polymer (A). This production method includes a step of reacting a mixture containing resin particles containing A) and a post-crosslinking agent (c) to post-crosslink the resin particles, and the water content of the mixture is 22 to 90% by weight.
Here, post-crosslinking is different from the technique of obtaining a crosslinked polymer by polymerizing a water-soluble vinyl monomer or the like in a solution state in the presence of the crosslinking agent (b) described above. This is a technology that increases crosslink density. By post-crosslinking, while maintaining the required water retention capacity of the water-absorbing resin particles in actual use, the [water absorption capacity in ion-exchanged water] is reduced, and the [gel liquid passing rate of the absorbent resin particles] is improved. can be done.

Examples of the post-crosslinking agent (c) include polyvalent glycidyl compounds, polyvalent amines, polyvalent aziridine compounds, and polyvalent isocyanate compounds described in JP-A-59-189103; Polyhydric alcohols described in JP-A No. 61-16903, silane coupling agents described in JP-A No. 61-211305 and JP-A-61-252212, alkylene carbonates described in Japanese Patent Application Publication No. 5-508425 , the polyvalent oxazoline compounds described in JP-A No. 11-240959, and surface crosslinking agents such as polyvalent metals described in JP-A-51-136588 and JP-A-61-257235, etc. can be used. Among these surface crosslinking agents, polyglycidyl compounds, polyhydric alcohols, and polyhydric amines are preferred, polyglycidyl compounds and polyhydric alcohols are more preferred, and polyhydric alcohols are particularly preferred. most preferred is ethylene glycol diglycidyl ether. One type of surface crosslinking agent may be used alone, or two or more types may be used in combination.

The total amount of post-crosslinking agent (c) used in the absorbent resin particles is not particularly limited, as it can be varied depending on the type of post-crosslinking agent, crosslinking conditions, target performance, etc. Based on the weight of A), 1 to 4% by weight is preferred, more preferably 1 to 3% by weight, most preferably 1 to 2.5% by weight. Within this range, the gel passing rate becomes even better. If the content is less than 1% by weight, the [water absorption capacity in ion-exchanged water] may not be sufficiently low, and the gel passing rate may not be sufficiently high. On the other hand, if the content is more than 4% by weight, discoloration tends to occur during long-term storage. The total usage amount of the post-crosslinking agent (c) is calculated based on the weight of the post-crosslinking agent (c) used in the post-crosslinking step described below.

Examples of methods for post-crosslinking resin particles include a method in which a mixture is prepared by mixing resin particles, a post-crosslinking agent (c), water and a solvent, and the mixture is reacted to post-crosslink. Examples of the reaction method include a heating reaction method. Methods for obtaining a mixture by mixing resin particles and a mixed solution include a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a double-arm kneader, a fluid mixer, Examples include a method of uniformly mixing using a mixing device such as a V-type mixer, a mincing mixer, a ribbon-type mixer, an airflow-type mixer, a rotating disk-type mixer, a conical blender, and a roll mixer. In addition, from the viewpoint of uniformity of surface crosslinking, it is preferable to use a mixed solution diluted with water and a solvent as the post-crosslinking agent (c), using a known fluidized humidification mixing granulation device [Flexomix (manufactured by Hosokawa Micron Co., Ltd.)]. ) and Shugi Flexomics (manufactured by Powrec Co., Ltd.), etc., using a mixing device equipped with a known spraying device, and a method of dipping resin particles in the above mixed solution.

Further, the solvent used in the mixed solution may be selected and used as appropriate, taking into consideration the degree of penetration of the post-crosslinking agent (c) into the resin particles, the reactivity of the post-crosslinking agent (c), etc. Preferably, it is a water-soluble hydrophilic organic solvent such as methanol, diethylene glycol, propylene glycol, etc. The solvents may be used alone or in combination of two or more. The amount of the solvent used can be appropriately adjusted depending on the type of solvent, but is preferably 1 to 10% by weight, based on the weight of the resin particles before post-crosslinking.

Post-crosslinking is performed by a step of reacting a mixture containing resin particles and a post-crosslinking agent (c) (hereinafter also referred to as post-crosslinking step). In the post-crosslinking step, it is preferable to mix the resin particles and the post-crosslinking agent (c) and then heat them to react. The heating temperature during the heating reaction is preferably 80 to 230°C, more preferably 100 to 180°C. Further, the reaction time can be appropriately adjusted depending on the reaction temperature, but is preferably 3 to 90 minutes, more preferably 30 to 60 minutes. If the reaction temperature is less than 80° C., the post-crosslinking reaction may not proceed sufficiently, and the [water absorption capacity in ion-exchanged water] of the resulting absorbent resin particles may not become small. On the other hand, if the reaction temperature is 230° C. or higher, the yellowness of the absorbent resin particles after the post-crosslinking reaction may deteriorate.

In the present invention, the mixing and reaction of the resin particles and the post-crosslinking agent (c) in the post-crosslinking step may be carried out once, but it is preferable to carry out the mixing and the reaction two or more times each. Specifically, by carrying out the mixing and reaction in the post-crosslinking step two or more times, the post-crosslinking of the resin particles is carried out in two or more parts, and in the depth direction near the surface of the absorbent resin particles. It becomes possible to form a thick crosslinked structure, improve the balance between the [water absorption capacity in ion-exchanged water] and water retention capacity of the absorbent resin particles, and achieve a high gel passing rate. More preferably, when the resin particles and the post-crosslinking agent (c) are mixed in two or more times, it is preferable to carry out the mixing in two or more times under conditions in which the water content of the resin particles is different each time. In addition, the post-crosslinking agent used when carrying out two or more times may be the same post-crosslinking agent each time, or may be a different post-crosslinking agent.
When the post-crosslinking step is carried out two or more times, the water content of the mixture obtained in the first post-crosslinking step is preferably 10% by weight or less. Within this range, the crosslinking density near the surface can be increased.

When the reaction between the resin particles and the post-crosslinking agent (c) in the post-crosslinking step is carried out two or more times, it is preferable to react a mixture having a water content of 22 to 90% by weight at least once. A more preferable moisture content of the mixture containing the resin particles and the post-crosslinking agent (c) is 25 to 60% by weight, most preferably 30 to 50% by weight. If the water content of the reaction mixture is lower than 22% by weight, the [water absorption capacity in ion-exchanged water] of the resulting absorbent resin particles may not be reduced or the gel permeation retention rate may not be high. . In addition, by performing a post-crosslinking reaction with a mixture with a water content of 22% by weight or more, the [water absorption capacity in ion-exchanged water] can be reduced, and the ion-exchanged water absorption index, which will be described later, can be effectively reduced. preferable. On the other hand, if the water content is greater than 90% by weight, the treatment time for removing water after the reaction will be long, which is not only uneconomical but also may worsen the initial yellowness of the resulting absorbent resin particles. be. The water content of the resin particles during post-crosslinking can be adjusted by calculating the required amount of water from the water content of the resin particles before post-crosslinking, and adjusting the amount of water in the mixed solution.

The reaction of the mixture containing the resin particles and the post-crosslinking agent (c) in the post-crosslinking step is preferably carried out under closed conditions. By heating under airtight conditions, water evaporation during the reaction can be prevented and the water content during the reaction can be stabilized. magnification] and can stably obtain a high gel passing rate. Furthermore, when the water content of the mixture is high, heating in a closed container increases the pressure, so it is preferable to conduct the reaction in a pressure-resistant container.

In the absorbent resin particles of the present invention, the total content of the crosslinking agent (b) and post-crosslinking agent (c) is preferably 1.0 to 10.0% based on the weight of the crosslinked polymer (A). , more preferably 1.8 to 7.0%, most preferably 2.0 to 5.0%. If the total content of the crosslinking agent (b) and post-crosslinking agent (c) is less than 1.0%, the water absorption capacity in ion-exchanged water may not become small. If the total content of the crosslinking agent (b) and post-crosslinking agent (c) is more than 10.0%, the degree of yellowness deteriorates after being left in an atmosphere of 70 ± 5 ° C. and relative humidity of 80 ± 3% for 28 days. There are cases where In addition, when calculating the total content ratio of the crosslinking agent (b) and the post-crosslinking agent (c), the weight of the crosslinked polymer (A) is based on the weight used when producing the crosslinked polymer (A). The total weight of the vinyl monomer (a) and crosslinking agent (b) used in the polymerization was used, and the content of the crosslinking agent (b) and post-crosslinking agent (c) was calculated based on the crosslinking agent (b) used in the polymerization of the crosslinked polymer (A). ) and the total weight of the post-crosslinking agent (c) used in the post-crosslinking step, respectively.

After post-crosslinking, the absorbent resin particles of the present invention can be obtained by distilling off or drying the solvent such as water in the resin particles and, if necessary, sieving to adjust the particle size. The weight average particle size of the particles obtained after particle size adjustment is preferably 100 to 600 μm, more preferably 200 to 500 μm. 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.

The absorbent resin particles of the present invention preferably further contain a chelating agent (B) from the viewpoint of discoloration during long-term storage.

The chelating agent (B) is not particularly limited, and may include a chelating agent (B1) containing a carboxy (salt) group in the molecule, a chelating agent containing a phosphonic acid (salt) group or a phosphoric acid (salt) group in the molecule. (B2) and other chelating agents (B3).

Chelating agents (B1) containing a carboxy (salt) group in the molecule include hydroxycarboxylic acids and/or salts thereof having hydroxyl groups (B11) and carboxylic acids and/or salts thereof having no hydroxyl groups (B12). . Examples of the hydroxycarboxylic acid having a hydroxyl group and/or its salt (B11) include citric acid (salt), lactic acid (salt), gallic acid (salt), and tartaric acid (salt). Examples of carboxylic acids and/or salts thereof (B12) that do not have hydroxyl groups include ethylenediaminetetraacetic acid (salt), diethylenetriaminepentaacetic acid (salt), hydroxyethyl-iminodiacetic acid (salt), and 1,2-diaminocyclohexanetetraacetic acid (salt). salt), triethylenetetraminehexaacetic acid (salt), nitrilotriacetic acid (salt), β-alanine diacetic acid (salt), aspartic acid diacetic acid (salt), methylglycine diacetic acid (salt), iminodisuccinic acid (salt), seringic acid Acetic acid (salt), aspartic acid (salt), glutamic acid (salt), pyromellitic acid (salt), benzopolycarboxylic acid (salt), cyclopentanetetracarboxylic acid (salt), etc., carboxymethyloxysuccinate, oxydisuccinate nate, maleic acid derivatives, oxalic acid (salt), malonic acid (salt), succinic acid (salt), glutaric acid (salt), and adipic acid (salt).

Examples of the chelating agent (B2) containing a phosphonic acid (salt) group or a phosphoric acid (salt) group in the molecule include methyldiphosphonic acid (salt), aminotri(methylenephosphonic acid) (salt), 1-hydroxyethylidene- 1,1-diphosphonic acid (salt), nitrilotrismethylenephosphonic acid (salt), ethylenediaminetetra (methylenephosphonic acid) (salt), hexamethylenediaminetetra (methylenephosphonic acid) (salt), propylenediaminetetra (methylenephosphonic acid) ) (salt), diethylenetriaminepenta(methylenephosphonic acid) (salt), triethylenetetramine hexa(methylenephosphonic acid) (salt), triaminotriethylamine hexa(methylenephosphonic acid) (salt), trans-1,2-cyclohexanediamine Tetra (methylene phosphonic acid) (salt), glycol ether diamine tetra (methylene phosphonic acid) (salt) and tetraethylenepentamine hepta (methylene phosphonic acid) (salt), metaphosphoric acid (salt), pyrophosphoric acid (salt), tripolyline Examples include acid (salt) and hexametaphosphoric acid (salt).

Among these salts, from the viewpoint of discoloration during long-term storage, alkali metal salts and ammonium salts are preferred, alkali metal salts are more preferred, and sodium salts are particularly preferred.

Other chelating agents (B3) include N,N'-bis(salicylidene)-1,2-ethanediamine, N,N'-bis(salicylidene)-1,2-propanediamine, and N,N'-bis(salicylidene)-1,2-propanediamine. Examples include (salicylidene)-1,3-propanediamine and N,N'-bis(salicylidene)-1,4-butanediamine.

Among the chelating agents (B), from the viewpoint of discoloration during long-term storage, the chelating agent (B1) preferably contains a carboxy (salt) group in the molecule, and more preferably the hydroxycarboxylic acid having a hydroxyl group and/or its salt. (B11), most preferably citric acid (salt). One type of chelating agent may be used alone, or two or more types may be used in combination.

Examples of the method for adding the chelating agent (B) include a method of mixing an aqueous solution of the chelating agent (B) with resin particles. Methods for mixing resin particles and aqueous solution include a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a double-arm kneader, a fluid mixer, a V-type mixer, Examples include a method of uniformly mixing using a mixing device such as a mincing mixer, a ribbon mixer, an airflow mixer, a rotating disk mixer, a conical blender, and a roll mixer. In addition, from the viewpoint of uniformity of addition of the chelating agent (B), it is preferable to use an aqueous solution diluted with water. Examples include a method of spraying using a mixing device equipped with a spraying device such as Shugi Flexomics (manufactured by Powrex Co., Ltd.), and a method of dipping resin particles in the above mixed solution.
The content of the chelating agent (B) units is preferably 0.1 to 10% by weight, more preferably 1 to 7% by weight, particularly preferably 1.5 to 5% by weight, based on the weight of the crosslinked polymer (A). %. Within this range, discoloration during long-term storage is suppressed without deteriorating absorption performance.

The absorbent resin particles of the present invention may optionally contain additives (for example, preservatives, fungicides, antibacterial agents, antioxidants, etc. described in JP-A-2003-225565 and JP-A-2006-131767, etc.). (ultraviolet absorbers, colorants, fragrances, deodorants, liquid permeability improvers, organic fibrous materials, etc.). When these additives are included, the content of the additives is preferably 0.001 to 10% by weight, more preferably 0.01 to 5% by weight, particularly 0.01 to 5% by weight, based on the weight of the crosslinked polymer (A). Preferably it is 0.05-1% by weight, most preferably 0.1-0.5% by weight.

The absorbent resin particles of the present invention have a weight of ion-exchanged water absorbed per unit weight of the absorbent resin particles immersed in ion-exchanged water [water absorption capacity in ion-exchanged water] of 10 to 120 (g/g). Yes, the speed at which physiological saline passes through absorbent resin particles that have been immersed in physiological saline for 30 minutes to swell and then compressed under weight [absorbent resin particle gel passing rate] is 350 (ml). /min) or more.

The above-mentioned [water absorption capacity in ion-exchanged water] is 10 to 120 (g/g), preferably 40 to 110 (g/g), and more preferably 45 to 70 (g/g). If the [water absorption capacity in ion-exchanged water] is less than 10, leakage may occur when used in a disposable swimsuit. If the absorption capacity in ion-exchanged water is greater than 120, the absorbent resin particles will swell significantly when used in disposable swimsuits and enter the water, causing the crotch area to sag or slip off, resulting in poor appearance and poor wearing comfort. It may happen.
In order to make the [water absorption capacity in ion-exchanged water] of the absorbent resin particles within the above range, in the above manufacturing method, the water content of the resin particles in at least one post-crosslinking step is set to 22 to 90% by weight, The total content of the crosslinking agent (b) and post-crosslinking agent (c) is preferably 1.0 to 10.0% based on the weight of the crosslinked polymer (A).

In addition, [water absorption capacity in ion-exchanged water] is measured under the following conditions.
Put 0.50 g of the measurement sample into a tea bag (20 cm long, 10 cm wide) made of nylon mesh with an opening of 63 μm (JIS Z8801-1:2006), and add 1,000 ml of ion-exchanged water (electrical conductivity 5 μS/cm or less). After being immersed in the water for 1 hour without stirring, the tea bag was taken out and hung for 15 minutes to drain, the weight (w1 (g)) including the tea bag was measured, and the amount of water retained was determined from the following formula. (w2(g)) is the weight of the tea bag measured by the same operation as above in the case where there is no measurement sample. The temperature of the ion-exchanged water used and the measurement atmosphere was 25°C±2°C. In addition, when the weight w1 of the bag exceeds 100 (g), the amount of the measurement sample to be put into the tea bag is adjusted as appropriate so that it is 0.50 g or less.
[Water absorption capacity in ion-exchanged water] (g/g) = ((w1)-(w2))/weight of measurement sample

The speed at which physiological saline passes through absorbent resin particles that have been immersed in physiological saline for 30 minutes to swell and then compressed under weight [absorbent resin particle gel passing rate] is 350 (ml/ml). min) or more, preferably 350 to 2000 (ml/min), more preferably 350 to 1500 (ml/min), particularly preferably 350 to 1000 (ml/min). If the gel flow rate is less than 350, there is a risk of leakage when used in a disposable swimsuit.
In order to keep the gel passing rate of the absorbent resin particles within the above range, the content of the crosslinking agent (b) units must be adjusted to include water-soluble vinyl monomer (a1) units, hydrolyzable vinyl monomer (a2) units, and other units. When vinyl monomer (a3) units are also used, the amount should be 0.001 to 5 mol% based on the total number of moles of units (a1) to (a3), and an appropriate amount of resin particles containing the crosslinked polymer (A) should be added. It is preferable to crosslink with a crosslinking agent (c).

[Gel passing rate of absorbent resin particles] is measured by the following operation using the instrument shown in FIGS. 1 and 2.
Swelling gel particles 2 are prepared by immersing 0.32 g of the measurement sample in 150 ml of physiological saline 1 (salt concentration 0.9%) for 30 minutes. A vertical cylinder 3 (diameter (inner diameter) 25.4 mm, length 40 cm) has scale lines 4 and 5 at 60 ml and 40 ml positions from the bottom, respectively. } is placed in a filtration cylindrical tube that has a wire mesh 6 (opening 106 μm, JIS Z8801-1:2006) and a cock 7 that can be opened and closed (inner diameter of the liquid passage part 5 mm), with the cock 7 closed. After transferring the prepared swollen gel particles 2 together with physiological saline, a circular wire mesh 8 (opening 150 μm, diameter 25 mm) having a pressurizing shaft 9 bonded perpendicularly to the surface of the wire mesh is placed on top of the swollen gel particles 2. was placed so that the wire mesh and the swollen gel particles were in contact with each other, and a weight 10 (88.5 g) was placed on the pressure shaft 9 (weight 22 g, length 47 cm), and the mixture was allowed to stand for 1 minute. Next, open the cock 7, measure the time (T1; seconds) required for the liquid level in the filtration cylindrical tube to go from the 60ml scale line 4 to the 40ml scale line 5, and calculate the gel flow rate (ml/min) using the following formula. seek.
Gel flow rate (ml/min) = 20ml x 60/(T1-T2)
Note that the temperature of the physiological saline used and the measurement atmosphere was 25° C.±2° C., and T2 is the time measured by the same operation as above for the case where there is no measurement sample.

The weight of physiological saline absorbed by 1.00 g of the absorbent resin particles of the present invention immersed in physiological saline [water retention amount of absorbent resin particles relative to physiological saline] is preferably 10 to 20 (g/g). It is more preferably 12 to 18 (g/g), and most preferably 14 to 16 (g/g). If the water retention amount is less than 10, urine may not be absorbed sufficiently when used in a disposable swimsuit. If the water retention capacity is greater than 20, the amount of urine absorbed will be sufficient, but the amount of water absorbed will also increase, so when used in disposable swimsuits and submerged in water, the absorbent resin particles will swell significantly, causing the groin area to sag. , the product may slip down, resulting in poor appearance and poor wearing comfort.
In order to keep the water retention amount of the absorbent resin particles in physiological saline within the above range, an appropriate water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) upon hydrolysis must be used. The content of crosslinking agent (b) units to be selected is water-soluble vinyl monomer (a1) units and hydrolyzable vinyl monomer (a2) units, and when other vinyl monomer (a3) units are also used, the content is (a1) to (a3). ) is preferably 0.001 to 5 mol % based on the total number of moles of units and polymerization of the monomer composition.

The water retention amount of the absorbent resin particles in physiological saline is measured under the following conditions.
Put 1.00 g of the measurement sample into a tea bag (length 20 cm, width 10 cm) made of nylon mesh with an opening of 63 μm (JIS Z8801-1:2006), and add it to 1,000 ml of physiological saline (salt concentration 0.9%). After soaking for 1 hour without stirring, remove and hang for 15 minutes to drain. Thereafter, each tea bag is placed in a centrifuge, centrifuged at 150 G for 90 seconds to remove excess physiological saline, the weight (h1) including the tea bag is measured, and the water retention amount is determined from the following formula. (h2) is the weight of the tea bag measured in the same manner as above in the case where there is no measurement sample. The temperature of the physiological saline used and the measurement atmosphere was 25°C±2°C.
Water retention amount (g/g) = (h1) - (h2)

The ion-exchanged water absorption index of the absorbent resin particles of the present invention is determined by the following (Formula 3) using the above-mentioned [water absorption capacity in ion-exchanged water] and the water retention amount of the above-mentioned absorbent resin particles in physiological saline. It is a defined index, and is expressed as the ratio of the [water absorption capacity in ion-exchanged water] of the absorbent resin particles to the water retention amount of the absorbent resin particles with respect to physiological saline. Therefore, the smaller the ion-exchanged water absorption index, the smaller the [water absorption capacity in ion-exchanged water] of the absorbent resin particles relative to the water retention amount of physiological saline.
(Ion-exchanged water absorption index) = ([Water absorption capacity of absorbent resin particles in ion-exchanged water]) / (Water retention amount of absorbent resin particles in physiological saline) ... (Formula 3)

The ion exchange water absorption index is preferably 1.0 to 6.0, more preferably 1.5 to 5.5, and most preferably 2.0 to 5.0. If the ion-exchanged water absorption index is less than 1.0, when used in a disposable swimsuit, urine may not be absorbed completely and leakage may occur. If the ion-exchange water absorption index is greater than 6.0, the absorbent resin particles will swell significantly when used in disposable swimsuits and enter the water, causing the crotch area to sag or slip off, resulting in poor appearance and poor wearing comfort. It may happen.

The absorbent resin particles of the present invention are preferably absorbent resin particles whose yellowness (YI value) measured after being left in an atmosphere of 70±5°C and 80±3% relative humidity for 28 days is 20 or less. , absorbent resin particles having a yellowness of 18 or less as measured under the above conditions are more preferred, and absorbent resin particles having a yellowness of 15 or less are most preferred. If the absorbent resin particles have a yellowness value greater than 20 when measured under the above conditions, the discolored absorbent resin particles inside the disposable swimsuit will be noticeable from the outside when the disposable swimsuit is used after long-term storage. There is.

The yellowness is measured using absorbent resin particles according to the method described in JIS K7373 Plastics - How to determine yellowness and yellowing.
Yellowness can be used to evaluate the initial coloration of absorbent resin (coloration immediately after production) and the ease with which coloration progresses during long-term storage or applied products. The yellowness to be measured is measured using a color acceleration test (70±5℃, relative humidity 80±3% atmosphere) using a simple spectrophotometer (main body NF333, manufactured by Nippon Denshoku Industries Co., Ltd., sensor part ND120, inner diameter φ8 mm). Evaluation is made by measuring the degree of yellowness after leaving the sample for 28 days. The smaller the yellowness value, the more suppressed the coloring is.
The procedure for the coloring acceleration test (left in an atmosphere of 70±5° C. and relative humidity 80±3% for 28 days) is as follows.
10 g of absorbent resin is placed in a glass petri dish with an inner diameter of 90 mm, and the surface is evenly leveled. This was heated at 70±5°C and 80±3% R. H. Store in a constant temperature and humidity chamber for 28 days. Thereafter, the petri dish is taken out from the constant temperature and humidity chamber and returned to room temperature, and then the degree of yellowness after the color acceleration test is measured.

The liquid passage retention rate (%) of the absorbent resin particles of the present invention is defined by the following (Equation 4), and the gel liquid passage rate of the absorbent resin particles is the gel liquid passage rate of the absorbent resin particles before the fragility test. Since they are synonymous, the fluid flow retention rate means the ratio of gel fluid flow rates of absorbent resin particles before and after the fragility test described below. Therefore, the higher the liquid passage retention rate, the more resistant the absorbent resin particles are to breakage in terms of gel liquid passage rate.
(Liquid passing maintenance rate) = 100 × ([Gel passing rate of absorbent resin particles after fragility test]) / ([Gel passing rate of absorbent resin particles before fragility test]) ... ( Equation 4)

The liquid passage retention rate of the absorbent resin particles of the present invention is preferably 70% or more, more preferably 80% or more, and most preferably 90% or more. If the fluid flow retention rate is less than 70%, leakage may occur when used in disposable swimwear. In order to improve the liquid flow retention rate, it is necessary to increase the durability of the water-absorbing resin particles against physical impact, and it is preferable to carry out the above-mentioned post-crosslinking step. In other words, by performing the post-crosslinking step of the present invention, a higher gel passage rate can be achieved compared to conventional gel passage speed improvement techniques using surface treatment agents such as inorganic compounds such as silica or polyvalent metal salts such as aluminum sulfate. In addition to being able to exhibit high liquid speed, it is also possible to impart durability to the water-absorbing resin particles and improve the liquid flow retention rate.
In order to keep the liquid permeation retention rate of the absorbent resin particles within the above range, the water content of the resin particles in the post-crosslinking step needs to be 22 to 90% by weight. By penetrating the crosslinking agent into the interior of the resin particles, the entire resin particle has a uniform crosslinked structure, so even if the particle surface is broken, a new crosslinked surface appears inside, maintaining the gel permeation rate. .

Note that the [gel liquid passing rate of absorbent resin particles] before the fragility test uses a value measured under the same conditions as the above-mentioned [gel liquid passing rate of absorbent resin particles]. [Gel liquid passing rate of absorbent resin particles] after the fragility test is the same as the above [Gel liquid passing rate of absorbent resin particles] except that the absorbent resin particles that have been subjected to the fragility test are used. Measure under the conditions.

Note that the [gel liquid passing rate of absorbent resin particles] after the fragility test is measured under the following conditions.
30 g of absorbent resin particles were placed in a 3L round separable flask (manufactured by ASONE), and a 63 μm nylon mesh (JIS Z8801-1:2000) with a 6 mm hole in the center was placed on the top of the separable flask. ), and then set a four-way separable cover (made by ASONE, main pipe TS29/42, side pipe TS24/40, 24/40, 15/35) on top of it. Next, insert a stainless steel tube (outer diameter 6 mm, inner diameter 4 mm) from the main pipe TS29/42 of the four-necked separable cover for the 3L round separable flask, and make sure that the stainless steel tube passes through the nylon mesh and that the tip is Set it at a position 45 mm from the bottom of the separable flask. Attach a urethane tube (length 1500 mm, inner diameter 8.5 mm) to the other side of the stainless steel tube, connect it to an air line that can achieve a pressure of 0.3 MPa or more, open the air line at a pressure of 0.2 MPa, and Perform a fragility test by air blowing for 1 minute, then take out the absorbent resin particles, and place the compressed absorbent resin particles in physiological saline under the same conditions as [Gel passing rate of absorbent resin particles]. Measure the speed as it passes.

The apparent density of the absorbent resin particles of the present invention is preferably 0.54 to 0.70 g/ml, more preferably 0.56 to 0.65 g/ml, particularly preferably 0.58 to 0.60 g/ml. be. Within this range, the rash resistance of the absorbent article will be even better. Note that the apparent density of the absorbent resin particles is measured at 25° C. in accordance with JIS K7365:1999.

The shape of the absorbent resin particles of the present invention is not particularly limited, and examples thereof include amorphous crushed shapes, scale shapes, pearl shapes, and rice grain shapes. Among these, the amorphous crushed form is preferable from the viewpoint that it entangles well with the fibrous material in disposable swimwear and the like and there is no fear of falling off from the fibrous material.

The weight average particle diameter of the absorbent resin particles of the present invention is preferably 100 to 800 μm, more preferably 200 to 700 μm, next preferably 250 to 600 μm, particularly preferably 300 to 500 μm, and most preferably 350 to 450 μm. . Within this range, the absorption performance will be even better.

In addition, the smaller the content of fine powder contained in the resin particles, the better the absorption performance, so the content of particles of 106 μm or less (preferably 150 μm or less) in the total weight of the resin particles is preferably 3% by weight or less, More preferably, it is 1% by weight or less. The content of fine powder can be determined using the graph created when determining the weight average particle diameter.

The absorbent body of the present invention contains the absorbent resin particles of the present invention. As the absorber, absorbent resin particles may be used alone or together with other materials to form an absorber. Other materials include fibrous materials and the like. The structure, manufacturing method, etc. of the absorber when used with a fibrous material are the same as those in JP-A No. 2003-225565, JP-A No. 2006-131767, and JP-A No. 2005-097569.

Preferred as the fibrous material are cellulose fibers, organic synthetic fibers, and mixtures of cellulose fibers and organic synthetic fibers.

Examples of cellulose fibers include natural fibers such as fluff pulp, and cellulose chemical fibers such as viscose rayon, acetate, and cupro. The raw materials (softwood, hardwood, etc.), manufacturing method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), bleaching method, etc. of this cellulosic natural fiber are not particularly limited.

Examples of organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and heat-fusible composite fibers (the above-mentioned fibers with different melting points). Examples include fibers in which at least two of the above fibers are combined into a sheath-core type, eccentric type, parallel type, etc., fibers in which at least two of the above fibers are blended, and fibers in which the surface layer of the above fibers is modified.

Among these fibrous base materials, preferred are cellulose-based natural fibers, polypropylene-based fibers, polyethylene-based fibers, polyester-based fibers, heat-fusible composite fibers, and mixed fibers thereof, and more preferred are fluff pulp, heat-fusible conjugate fibers, and mixed fibers thereof, because they have excellent shape retention properties after water absorption.

There are no particular limitations on the length and thickness of the fibrous material, and it can be suitably used as long as the length is in the range of 1 to 200 mm and the thickness is in the range of 0.1 to 100 deniers. The shape is not particularly limited as long as it is fibrous, and examples thereof include a thin cylinder, a split yarn, a staple, a filament, and a web.

When absorbent resin particles are used as an absorber together with fibrous materials, the weight ratio of absorbent resin particles to fibers (weight of absorbent resin particles/weight of fibers) is preferably 40/60 to 90/10, more preferably is 70/30 to 80/20.

The absorbent article of the present invention uses the above absorbent body. The absorbent article can be used for various purposes such as disposable swimwear, disposable swimwear, disposable diapers, sanitary napkins, etc., absorption and retention agent for various aqueous liquids, and gelling agent. It's a disposable swimsuit. The manufacturing method of the absorbent article is the same as that described in JP-A No. 2003-225565, JP-A No. 2006-131767, JP-A No. 2005-097569, and the like.

The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, parts refer to parts by weight, and % refers to % by weight, unless otherwise specified.

<Example 1>
100 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation, purity 100%), 0.4 parts of a crosslinking agent (pentaerythritol triallyl ether, manufactured by Daiso Corporation), and 220 parts of ion-exchanged water were heated to 3°C while stirring and mixing. I kept it. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.4 part of a 1% aqueous hydrogen peroxide solution, 0.8 part of a 2% aqueous ascorbic acid solution, and 2% 2,2'-azobis 0.1 part of amidinopropane dihydrochloride aqueous solution was added and mixed to initiate polymerization. After the temperature of the mixture reached 90°C, a hydrogel was obtained by polymerizing at 90±2°C for about 5 hours.

Next, while chopping this water-containing gel into pieces using a mincing machine (ROYAL 12VR-400K), 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the gel (neutralization degree: 72%). Furthermore, the neutralized hydrogel was dried in a ventilation dryer {200° C., wind speed 2 m/sec} to obtain a dried product. After pulverizing the dried body with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), it was sieved and adjusted to a particle size range of 710 to 150 μm to obtain resin particles (A-1) containing a crosslinked polymer. Ta. The water content of the resin particles (A-1) was 3%.

Next, 100 parts of the obtained resin particles (A-1) were mixed with 1.4 parts of propylene glycol and ethylene glycol dichloromethane as a post-crosslinking agent while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixture of 0.18 parts of glycidyl ether and 3.6 parts of ion-exchanged water was added and mixed uniformly. The water content of the mixture after uniformly mixing the resin particles (A-1) and the post-crosslinking agent was 6%. Thereafter, it was heated at 130° C. for 30 minutes in a ventilation dryer (air-open system) to perform a first post-crosslinking reaction, thereby obtaining absorbent resin particles (B-1). The moisture content of the absorbent resin particles (B-1) was 3%.

Next, 100 parts of the obtained absorbent resin particles (B-1) were stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 2.0 parts of propylene glycol and ethylene were added as a post-crosslinking agent. A mixture of 2.0 parts of glycol diglycidyl ether and 40 parts of ion-exchanged water was added and mixed uniformly to obtain a mixture. After homogeneous mixing, the water content of the mixture containing the water absorbent resin particles (B-1) and the post-crosslinking agent was 28%. Thereafter, it was placed in a PTFE crucible (manufactured by Freon Kogyo Co., Ltd.) and sealed, and then heated at 130° C. for 60 minutes to perform a second post-crosslinking reaction. After further heating, the PTFE crucible was opened and heated at 130° C. for 20 minutes to remove moisture, yielding absorbent resin particles (C-1).

Next, 1.6 parts of sodium citrate and ions were added as a chelating agent to 100 parts of the obtained absorbent resin particles (C-1) while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixed solution containing 2.4 parts of exchanged water was added to obtain absorbent resin particles (P-1) of the present invention.

<Example 2>
In the same manner as in Example 1, the absorbent resin particles (C-1) in Example 1 were made into absorbent resin particles (P-2) of the present invention.

<Example 3>
In the first reaction with a post-crosslinking agent in Example 1, 2.0 parts of ethylene glycol diglycidyl ether added to 100 parts of absorbent resin particles (B-1) was changed to 1.2 parts of ethylene glycol diglycidyl ether. Absorbent resin particles (P-3) of the present invention were obtained by carrying out the same operation as in Example 1 except for the following changes. The water content of the mixture containing the resin particles and the post-crosslinking agent before the first heating reaction with the post-crosslinking agent was 28%.

<Example 4>
In the first reaction with a post-crosslinking agent in Example 1, 2.0 parts of ethylene glycol diglycidyl ether added to 100 parts of absorbent resin particles (B-1) was changed to 0.9 parts of ethylene glycol diglycidyl ether. Absorbent resin particles (P-4) of the present invention were obtained by carrying out the same operation as in Example 1 except for the following changes. The moisture content of the mixture before the first heating reaction with the post-crosslinking agent was 28%.

<Example 5>
100 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation, purity 100%), 0.4 parts of a crosslinking agent (pentaerythritol triallyl ether, manufactured by Daiso Corporation), and 220 parts of ion-exchanged water were heated to 3°C while stirring and mixing. I kept it. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.4 part of a 1% aqueous hydrogen peroxide solution, 0.8 part of a 2% aqueous ascorbic acid solution, and 2% 2,2'-azobis 0.1 part of amidinopropane dihydrochloride aqueous solution was added and mixed to initiate polymerization. After the temperature of the mixture reached 90°C, a hydrogel was obtained by polymerizing at 90±2°C for about 5 hours.
Next, while chopping this water-containing gel into pieces using a mincing machine (ROYAL 12VR-400K), 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the gel (neutralization degree: 72%). Furthermore, the neutralized hydrogel was dried in a ventilation dryer {200° C., wind speed 2 m/sec} to obtain a dried product. After pulverizing the dried body with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), it was sieved and adjusted to a particle size range of 710 to 150 μm to obtain resin particles (A-5) containing a crosslinked polymer. Ta. The moisture content of the resin particles (A-5) was 3%.

Next, 100 parts of the obtained resin particles (A-5) were mixed with 1.4 parts of propylene glycol and ethylene glycol dichloromethane as a post-crosslinking agent while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixture of 0.18 parts of glycidyl ether and 3.6 parts of ion-exchanged water was added and mixed uniformly to obtain a mixture. The moisture content of the mixture containing the resin particles (A-5) and the post-crosslinking agent was 6%. Thereafter, the resin particles were heated for 30 minutes at 130° C. in a ventilated dryer (air-open system) to cause a first reaction between the resin particles and the post-crosslinking agent, thereby obtaining absorbent resin particles (B-5). The moisture content of the absorbent resin particles (B-5) was 3%.

Next, 100 parts of the obtained absorbent resin particles (B-5) were stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 2.0 parts of propylene glycol and ethylene were added as a post-crosslinking agent. A mixture of 2.0 parts of glycol diglycidyl ether and 100 parts of ion-exchanged water was added and mixed uniformly to obtain a mixture. The water content of the mixture containing the water-absorbing resin particles (B-5) and the post-crosslinking agent was 49%. Thereafter, it was placed in a PTFE crucible (manufactured by Freon Kogyo Co., Ltd.) and sealed, and then heated at 130° C. for 60 minutes to perform a second post-crosslinking reaction. After heating, the PTFE crucible was opened and heated at 130° C. for 20 minutes to remove moisture, yielding absorbent resin particles (C-5).

Next, 1.6 parts of sodium citrate, which is a chelating agent, and 1.6 parts of sodium citrate, which is a chelating agent, were added to 100 parts of the obtained absorbent resin particles (C-5) while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixed solution containing 2.4 parts of ion-exchanged water was added to obtain absorbent resin particles (P-5) of the present invention.

< Reference example 6>
100 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation, purity 100%), 5.0 parts of a crosslinking agent (pentaerythritol triallyl ether, manufactured by Daiso Corporation), and 220 parts of ion-exchanged water were heated to 3°C while stirring and mixing. I kept it. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.4 part of a 1% aqueous hydrogen peroxide solution, 0.8 part of a 2% aqueous ascorbic acid solution, and 2% 2,2'-azobis 0.1 part of amidinopropane dihydrochloride aqueous solution was added and mixed to initiate polymerization. After the temperature of the mixture reached 90°C, a hydrogel was obtained by polymerizing at 90±2°C for about 5 hours.

Next, while chopping this water-containing gel into pieces using a mincing machine (ROYAL 12VR-400K), 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the gel (neutralization degree: 72%). Furthermore, the neutralized hydrogel was dried in a ventilation dryer {200° C., wind speed 2 m/sec} to obtain a dried product. After pulverizing the dried body with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), it was sieved and adjusted to a particle size range of 710 to 150 μm to obtain resin particles (A-6) containing a crosslinked polymer. Ta. The moisture content of the resin particles (A-6) was 3%.

Next, 100 parts of the obtained resin particles (A-6) were stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 4.0 parts of propylene glycol and ethylene glycol dichloromethane were added as a post-crosslinking agent. A mixture of 2.0 parts of glycidyl ether and 18.8 parts of ion-exchanged water was added and mixed uniformly to obtain a mixture. The moisture content of the mixture containing the resin particles (A-6) and the post-crosslinking agent was 17%. Thereafter, it was heated for 30 minutes at 130° C. in a ventilation dryer (air-open system) to perform a first post-reaction with the crosslinking agent to obtain absorbent resin particles (B-6). The moisture content of the absorbent resin particles (B-6) was 3%.

Next, 100 parts of the obtained absorbent resin particles (B-6) were stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and 0.0 parts of fumed silica (Aerosil 200 manufactured by Aerosil Co., Ltd.) was added thereto. 5 parts of sodium citrate as a chelating agent, and 2.4 parts of ion-exchanged water were added to obtain absorbent resin particles (P-6).

<Example 7>
Same procedure as in Example 5 except that 2.0 parts of ethylene glycol diglycidyl ether used in the second post-crosslinking reaction in Example 5 was changed to 3.6 parts of ethylene glycol diglycidyl ether. The operation was performed to obtain absorbent resin particles (P-7). The water content of the mixture containing the water-absorbing resin particles (B-1) and the post-crosslinking agent when performing the second post-crosslinking reaction was 49%.

<Example 8>
In Example 5, 1.6 parts of sodium citrate mixed in the absorbent resin particles (C-5) was changed to 5.0 parts of sodium citrate, and 2.4 parts of ion-exchanged water was replaced with 7.5 parts of ion-exchanged water. Absorbent resin particles (P-8) were obtained by carrying out the same operation as in Example 5, except for changing to .

<Example 9>
The same operation as in Example 5 was carried out, except that the weight of the crosslinking agent (pentaerythritol triallyl ether, manufactured by Daiso Corporation) used in Example 5 was changed from 0.4 parts to 0.2 parts. Resin particles (P-9) were obtained.

<Comparative example 1>
1.6 parts of sodium citrate as a chelating agent was added to 100 parts of the absorbent resin particles (B-2) obtained in Example 1 while stirring at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm). A mixed solution containing 2.4 parts of ion-exchanged water was added to obtain absorbent resin particles (R-1) for comparison.

<Comparative example 2>
100 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation, purity 100%), 7.0 parts of a crosslinking agent (pentaerythritol triallyl ether, manufactured by Daiso Corporation), and 220 parts of ion-exchanged water were heated to 3°C while stirring and mixing. I kept it. After nitrogen was introduced into this mixture to reduce the amount of dissolved oxygen to 1 ppm or less, 0.4 part of a 1% aqueous hydrogen peroxide solution, 0.8 part of a 2% aqueous ascorbic acid solution, and 2% 2,2'-azobis 0.1 part of amidinopropane dihydrochloride aqueous solution was added and mixed to initiate polymerization. After the temperature of the mixture reached 90°C, a hydrogel was obtained by polymerizing at 90±2°C for about 5 hours.

Next, while chopping this water-containing gel into pieces using a mincing machine (ROYAL 12VR-400K), 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the gel (neutralization degree: 72%). Furthermore, the neutralized hydrogel was dried in a ventilation dryer {200° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized using a juicer mixer (OSTERIZER BLENDER manufactured by Oster), then sieved and adjusted to a particle size range of 710 to 150 μm to obtain absorbent resin particles (RA-2). The moisture content of the absorbent resin particles (RA-2) was 3%.

Next, 1.6 parts of sodium citrate as a chelating agent and 1.6 parts of sodium citrate as a chelating agent were added to 100 parts of the obtained absorbent resin particles (HA-2) while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixed solution containing 2.4 parts of ion-exchanged water was added to obtain absorbent resin particles (R-2) for comparison.

<Comparative example 3>
While cutting the hydrogel obtained in the same manner as in Example 1 into pieces using a mincing machine (12VR-400K manufactured by ROYAL), 82 parts of a 48.5% aqueous sodium hydroxide solution and 1.0 parts of ethylene glycol diglycidyl ether as a crosslinking agent were added. 26 parts were added and mixed and neutralized to obtain a neutralized gel (degree of neutralization: 72%). Furthermore, the neutralized hydrogel was dried in a ventilation dryer {200° C., wind speed 2 m/sec} to obtain a dried product. The dried product was pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), then sieved and adjusted to a particle size range of 710 to 150 μm to obtain absorbent resin particles (RA-3). The moisture content of the absorbent resin particles (RA-3) was 3%.

Next, 100 parts of the obtained absorbent resin particles (RA-3) were stirred at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm), and 1.4 parts of propylene glycol and ethylene glycol as a crosslinking agent were added thereto. A mixture of 0.18 parts of diglycidyl ether and 3.6 parts of ion-exchanged water was added and mixed uniformly to obtain a mixture. The moisture content of the mixture was 6%. Thereafter, it was heated at 130° C. for 30 minutes in a ventilation dryer (air-open system) to obtain absorbent resin particles (RB-3).

Next, 1.6 parts of sodium citrate, which is a chelating agent, and 1.6 parts of sodium citrate, which is a chelating agent, were added to 100 parts of the obtained absorbent resin particles (RB-3) while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixed solution containing 2.4 parts of ion-exchanged water was added to obtain absorbent resin particles (R-3) for comparison.

<Comparative example 4>
The absorbent resin particles (B-1) obtained in Example 1 were used as they were to prepare absorbent resin particles (R-4) for comparison.

<Comparative example 5>
100 parts of the absorbent resin particles (B-1) obtained in Example 1 were mixed with 2.0 parts of propylene glycol and ethylene as a crosslinking agent while stirring at high speed (Hosokawa Micron high speed stirring turbulizer: rotation speed 2000 rpm). A mixture of 2.0 parts of glycol diglycidyl ether and 40 parts of ion-exchanged water was added and mixed uniformly to obtain a mixture. The moisture content of the mixture after uniform mixing was 28%. Thereafter, it was heated at 130° C. for 30 minutes in a ventilation dryer (air-open system) to obtain absorbent resin particles (RC-5).

Next, 1.6 parts of sodium citrate and 2 parts of ion-exchanged water were added to 100 parts of the obtained absorbent resin particles (RC-5) while stirring at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: rotation speed 2000 rpm). A mixed solution of .4 parts was added to obtain absorbent resin particles (R-5) for comparison.

<Comparative example 6>
The same operation as in Comparative Example 5 was performed, except that the weight of ethylene glycol diglycidyl ether mixed with the absorbent resin particles (B-1) was changed from 2.0 parts to 4.0 parts, and the comparison was carried out in the same manner as in Comparative Example 5. Absorbent resin particles (R-6) were obtained. The water content of the mixture containing the water absorbent resin particles (B-1) and the crosslinking agent was 6%.

<Comparative example 7>
The same operation as in Comparative Example 5 was performed except that the weight of ethylene glycol diglycidyl ether mixed with the absorbent resin particles (B-1) was changed from 2.0 parts to 6.0 parts. Absorbent resin particles (R-7) for use were obtained. The moisture content of the mixture containing the absorbent resin particles (B-1) and the crosslinking agent was 6%.

<Comparative example 8>
The same operation as in Example 1 was carried out, except that 40 parts of ion-exchanged water used when post-crosslinking the absorbent resin particles (B-1) in Example 1 was changed to 25 parts of ion-exchanged water, and a comparison sample was prepared. Absorbent resin particles (R-8) were obtained. The water content of the mixture containing the absorbent resin particles (B-1) and the post-crosslinking agent was 20%.

Water absorption capacity in ion-exchanged water and ion-exchanged water absorption of the obtained absorbent resin particles (P-1) to (P-9) and comparative absorbent resin particles (R-1) to (R-8) Evaluation results of index, water retention amount, yellowness after being left in an atmosphere of 70 ± 5 ° C and relative humidity of 80 ± 3% for 28 days, gel passage rate, gel passage rate after fragility test, and liquid passage maintenance rate are shown in Table 1.

From the results in Table 1, it can be seen that the absorbent resin particles of the present invention have an excellent gel passing rate and a low absorption capacity for ion-exchanged water and a low absorption index for ion-exchanged water. On the other hand, in Comparative Examples, even if the gel passing rate is good, the ion-exchanged water absorption index is large, or even if the ion-exchanged water absorption index is small, the gel passing rate is poor. In other words, it was found that the Examples had a significant difference from the Comparative Examples in terms of achieving both a gel passing rate and a small absorption capacity for ion-exchanged water.

The absorbent resin particles of the present invention have a low absorption capacity in ion-exchanged water, and can suppress swelling even when used in water-absorbent articles into which a large amount of water may penetrate. Therefore, it is preferably used in sanitary products such as napkins (sanitary napkins, etc.), paper towels, and disposable swimwear, and is particularly suitable for disposable swimwear. The absorbent resin particles of the present invention are useful not only for sanitary products, but also for various uses such as water sealants and artificial snow.

1 Physiological saline 2 Water-containing gel particles 3 Cylinder 4 Graduation line 5 at a position of 60 ml from the bottom Graduation line 6 at a position of 40 ml from the bottom Wire mesh 7 Cock 8 Circular wire mesh 9 Pressure shaft 10 Weight

Claims (12)

Absorbent resin particles obtained by crosslinking resin particles containing a crosslinked polymer (A) having a vinyl monomer (a) and a crosslinking agent (b) as essential constituent units with a post-crosslinking agent (c), wherein the vinyl monomer ( a) contains a water-soluble vinyl monomer (a1) and/or a vinyl monomer (a2) that becomes a water-soluble vinyl monomer (a1) by hydrolysis, and absorbent resin particles immersed in ion-exchanged water absorb water per unit weight. The weight of ion-exchanged water [water absorption capacity in ion-exchanged water] is 10 to 120 (g/g), and absorbent resin particles are immersed in physiological saline for 30 minutes to swell and then compressed under weight. The speed at which the saline passes through [the gel passing rate of absorbent resin particles] is 350 (ml/min) or more, and the gel passing maintenance rate obtained by the following (formula 4) is 70% or more. Some absorbent resin particles.
(Gel liquid passage maintenance rate) = 100 x ([Gel liquid passage rate of absorbent resin particles] after fragility test)
/([gel liquid passing rate of absorbent resin particles before fragility test]) ... (Formula 4)
The [gel liquid passing rate of absorbent resin particles] before the fragility test in (Equation 4) is calculated by immersing the particles in physiological saline for 30 minutes to swell without performing the fragility test described below. This is the speed at which physiological saline passes through compressed absorbent resin particles. [Gel passing rate of absorbent resin particles] after the fragility test is determined by placing 30 g of absorbent resin particles in a 3L round separable flask, and making a 6 mm hole in the center at the top of the separable flask. A nylon net with a mesh opening of 63 μm was laid, and a four-hole separable cover was further set on top of it. Next, insert a stainless steel tube (outer diameter 6 mm, inner diameter 4 mm) from the main tube of the four-necked separable cover for the 3L round separable flask, so that the stainless steel tube passes through the nylon mesh, and the tip is attached to the separable flask. Set it so that it is 45mm from the bottom. Attach a urethane tube (length 1500 mm, inner diameter 8.5 mm) to the other side of the stainless steel tube, connect it to an air line that can achieve a pressure of 0.3 MPa or more, open the air line at a pressure of 0.2 MPa, and A fragility test was performed by air blowing for 30 minutes, and then the absorbent resin particles taken out were immersed in physiological saline for 30 minutes to swell, and then compressed under load. This is the speed at which the saline solution passes. The absorbent resin particles according to claim 1, wherein the absorbent resin particles have an irregularly crushed shape. Using [water absorption capacity in ion-exchanged water] and the weight of physiological saline absorbed by 1.00 g of absorbent resin particles immersed in physiological saline [water retention amount of absorbent resin particles relative to physiological saline] The absorbent resin particles according to claim 1 or 2, having an ion exchange water absorption index defined by the following (Formula 3) from 1.0 to 6.0.
(Ion exchange water absorption index) = ([Water absorption capacity of absorbent resin particles in ion exchange water]) /
(Water retention amount of absorbent resin particles with respect to physiological saline) ... (Formula 3) Yellowness measured using a simple spectrophotometer according to the method described in JIS K7373 Plastics - How to determine yellowness and yellowing after being left in an atmosphere of 70±5℃ and 80±3% relative humidity. The absorbent resin particles according to any one of claims 1 to 3, wherein the particle size is 20 or less. The absorbent resin particles according to any one of claims 1 to 4, wherein the absorbent resin particles have a water retention amount of 10 to 20 (g/g) in physiological saline. The absorbent resin particles according to any one of claims 1 to 5, further comprising a chelating agent (B). The absorbent according to any one of claims 1 to 6 , wherein the content of the crosslinking agent (b) is 0.2 to 5% by weight based on the total weight of the vinyl monomers (a) constituting the crosslinked polymer (A). resin particles. Absorbent resin particles according to any one of claims 1 to 7, wherein the total amount of the post-crosslinking agent (c) used is 1 to 4% by weight based on the weight of the crosslinked polymer (A). An absorbent body containing the absorbent resin particles according to claims 1 to 8 . An absorbent article containing the absorbent body according to claim 9 . Resin particles are produced by reacting a mixture containing the vinyl monomer (a) and the crosslinked polymer (A) having the crosslinking agent (b) as essential constituent units with a post-crosslinking agent (c). The method for producing absorbent resin particles according to any one of claims 1 to 8 , which comprises a step of post-crosslinking, and the water content of the mixture is 22 to 90% by weight. The method for producing absorbent resin particles according to claim 11 , wherein the resin particles containing the crosslinked polymer (A) are reacted with the post-crosslinking agent (c) under closed conditions.

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