JP2020056025A - Absorbing resin particle and method for producing the same - Google Patents

Abstract

To provide absorbing resin particles which can prevent urine leakage before a user enters water while preventing expansion after water has entered a disposable swimming suit, and an absorbing article using the same.SOLUTION: Absorbing resin particles in which resin particles containing a crosslinked polymer (A) containing a vinyl monomer (a) and a crosslinking agent (b) as essential constitutional units are crosslinked with a post-crosslinking agent (c), in which [water absorption magnification in ion exchange water] is 10-120 (g/g), and [flow rate of liquid through gel of absorbing resin particle] is 350 (ml/min) or more.SELECTED DRAWING: None

Description

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

  In recent years, disposable swimwear (also called swimming pants) having a function of preventing excretions such as urine and stool from diffusing into water, which are premised on use in pools of infants and the like, are commercially available ( For example, see Patent Documents 1 and 2.

  Such a disposable swimsuit has, as basic elements, an absorbent body that absorbs urine, and a liquid-permeable front side layer and a back side layer that cover the front side and the back side, respectively.

  As an absorber, a pile of pulp fibers is generally used. Since disposable swimwear is used underwater, water that has entered inside is also absorbed by the absorber. Therefore, when a disposable diaper that is not intended for use in water is used in water as an absorbent body for disposable swimwear, the crotch part will hang down or slip off due to the increase in weight of itself after entering water or in water. As a result, the appearance and the feeling of wearing deteriorate.

  Therefore, unlike a disposable diaper that is not supposed to be used in water, such an absorbent body for a disposable swimsuit does not contain an absorbent resin in the absorbent body so that the absorbent body does not swell, or a small amount even if it is contained. It is considered that it is preferable to use a water-absorbent resin containing only water or having a small water absorption capacity.

  However, if the absorbent resin is not contained or contains only a small amount, the urine absorption performance is inferior, and if there is urination before entering the water or when it is not determined whether to enter the water just by playing at the waterside, Leakage could occur due to little or no absorption. Conventionally, there has been known a method of producing an absorbent resin having a small absorption capacity of water (ion-exchanged water) by using a large amount of an internal crosslinking agent (see Patent Document 3). Although the swelling of the absorbent body after absorbing water can be suppressed, the gel flow rate of the absorbent resin is low, and urine is hardly diffused into the absorbent body at the time of urination, and there is a possibility of leakage. Further, in the case of an absorbent resin using a large amount of an internal crosslinking agent, the absorbent resin may be colored during long-term storage, giving the user discomfort. On the other hand, techniques for improving the gel flow rate include: (1) a method of forming a physical space by adding an inorganic compound such as silica and talc; and (2) a hydrophobic property having a small surface free energy such as a modified silicone. A method of forming a gel gap by suppressing coalescence between swollen gels by surface treatment with a polymer and a method of adding (3) aluminum sulfate, aluminum lactate, or the like are already known (for example, Patent Documents) 4, see Patent Documents 5 and 6). However, in these methods, when transporting, spraying, supplying or mixing absorbent resin, or when transporting absorbent articles, collision or friction between particles, collision or friction between particles on a device wall or the like, or the like. As a result, the surface of the absorbent resin particles may be broken and the gel flow rate may be reduced.

JP 2009-178382 A JP, 2018-50912, A Patent No. 5190116 JP 2012-161788 A JP 2013-133399 A JP 2014-512440 A

  An object of the present invention is to provide a absorbent article such as a disposable swimwear using absorbent resin particles, while suppressing expansion of the absorber after absorbing water, and preventing urine leakage before absorbing water, Another object of the present invention is to provide an absorbent resin particle capable of exhibiting prevention of coloring under high temperature and high humidity for a long period of time, a method for producing the same, and an absorbent article containing the absorbent resin particle.

The present inventor has earnestly studied to achieve the above object, and as a result, has reached the present invention. That is, the present invention relates to absorbent resin particles obtained by crosslinking a resin particle 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). 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. The weight of the ion-exchanged water that absorbs water per unit weight [the water absorption capacity in the ion-exchanged water] is 10 to 120 (g / g), immersed in physiological saline for 30 minutes to swell, and then compressed by applying a load. Absorbent resin particles having a velocity [absorbent resin particle gel flow rate] of 350 (ml / min) or more when physiological saline passes through the absorbed absorbent resin particles; Absorption containing the absorbent resin particles ; An absorbent article containing the absorbent body.
The present invention also relates to the method for producing absorbent resin particles, comprising a crosslinked polymer (A) having a vinyl monomer (a) and a crosslinking agent (b) as essential constituent units, and having a water content of 22 to 90. A method for producing absorbent resin particles, which comprises a step of reacting the resin particles, which is a weight percentage, with a post-crosslinking agent (c).

  The absorbent resin particles of the present invention exhibit an appropriate amount of water retention and a high gel flow rate while suppressing the water absorption capacity. Therefore, when the absorbent resin particles of the present invention are used for absorbent articles such as disposable swimwear, the absorbent of the absorbent article is unlikely to swell even when water enters the interior of the absorbent article, and therefore the absorbent article is It is hard to slip down. On the other hand, also in the case where urination occurs before entering water or when it is not decided whether to enter the water just by playing on the waterside, the absorbent article of the present invention can sufficiently absorb urine and suppress leakage.

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

  The absorbent resin particles of the present invention are 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). Particles, and 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.

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 disclosed in paragraphs 0007 to 0023 of Japanese Patent No. 3648553 and an ethylenically unsaturated monomer. Vinyl monomers having a saturated group (for example, anionic vinyl monomers, nonionic vinyl monomers and cationic vinyl monomers); anionic vinyl monomers disclosed in paragraphs 0009 to 0024 of JP-A-2003-165883; Vinyl monomers and cationic vinyl monomers, and carboxy, sulfo, phosphono, hydroxyl, carbamoyl, amino and ammonium groups disclosed in paragraphs 0041 to 0051 of JP-A-2005-75982. At least one Vinyl monomers can be used to.
In addition, the water solubility of the water-soluble vinyl monomer, when expressed by using a quantity, means that, for example, at least 100 g of a solute is dissolved in 100 g of water at 25 ° C.

A vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis [hereinafter also referred to as a hydrolyzable vinyl monomer (a2). Is not particularly limited, and is a known vinyl monomer, for example, a vinyl monomer having at least one hydrolyzable substituent which becomes a water-soluble substituent by hydrolysis disclosed in paragraphs 0024 to 0025 of Japanese Patent No. 3648553. And at least one hydrolyzable substituent [1,3-oxo-2-oxapropylene (-CO-O-CO-) group, acyl group disclosed in paragraphs 0052 to 0055 of JP-A-2005-75982. Group and cyano group etc.].
The hydrolysis means that the hydrolyzable vinyl monomer (a2) is decomposed into a water-soluble vinyl monomer (a1) in the presence of water, using a catalyst (acid or base or the like) as necessary. The hydrolysis of the hydrolyzable vinyl monomer (a2) may be performed during, after, or both of the polymerization, but is preferably performed after the polymerization from the viewpoint of the absorption performance of the resulting absorbent resin particles.

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

The “carboxy (salt) group” means “carboxy group” or “carboxylate group”, and the “sulfo (salt) group” means “sulfo group” or “sulfonate group”. Also, (meth) acrylic acid (salt) means acrylic acid, acrylate, methacrylic acid or methacrylic acid, and (meth) acrylamide means acrylamide or methacrylamide.
Examples of the salt include alkali metal (such as lithium, sodium and potassium) salts, alkaline earth metal (such as magnesium and calcium) salts, and ammonium (NH ₄ ) salts. Among these salts, alkali metal salts and ammonium salts are preferred from the viewpoint of absorption performance, more preferred are alkali metal salts, and particularly preferred are sodium salts.

  When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the water-soluble vinyl monomer (a1), it is preferable that a part of the acid group-containing monomer is neutralized with a base from the viewpoint of water absorption performance and remaining monomers. . As the base to be neutralized, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide and alkali metal carbonates such as sodium carbonate, sodium hydrogen carbonate and potassium carbonate can be used. Neutralization may be performed in the production of the absorbent resin particles, before polymerization, during polymerization, after polymerization, or both of them.For example, a method of neutralizing an acid group-containing monomer before polymerization or after polymerization. A preferred example is a method of neutralizing an acid group-containing polymer in a state of a hydrogel.

  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 has high tackiness, and the workability during production and use may be deteriorated. Furthermore, the water retention of the obtained 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 case where safety for human skin is concerned.

  When any of the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) is used as a constituent unit, one kind may be used alone as a constituent unit, and if necessary, two or more kinds may be used as a constituent unit. good. The same applies to the case where the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are used as constituent units. When the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) are the constituent units, the content molar ratio [(a1) / (a2)] thereof is preferably from 75/25 to 99/1. More preferably, it is from 85/15 to 95/5, particularly preferably from 90/10 to 93/7, and most preferably from 91/9 to 92/8. When it is in this range, the absorption performance is further improved.

  The vinyl monomer (a) can be copolymerized with the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2) in addition to the water-soluble vinyl monomer (a1) and the hydrolyzable vinyl monomer (a2). Other vinyl monomers (a3) can be used as constituent units. As the other vinyl monomer (a3), one type may be used alone, or two or more types may be used in combination.

The other copolymerizable vinyl monomer (a3) is not particularly limited, and examples thereof include a hydrophobic vinyl monomer disclosed in paragraphs 0028 to 0029 of Japanese Patent No. 3648553 and paragraph 0025 of JP-A-2003-165883. And known hydrophobic vinyl monomers such as the vinyl monomer disclosed in paragraph 0058 of JP-A-2005-75982, and specifically, for example, the following vinyl monomers (i) to (iii) and the like. Can be used.
(I) Aromatic ethylenic monomer having 8 to 30 carbon atoms Styrene such as styrene, α-methylstyrene, vinyltoluene and hydroxystyrene, and halogen-substituted styrene such as vinylnaphthalene and dichlorostyrene.
(Ii) C2-C20 aliphatic ethylenic monomers alkenes (such as ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene and octadecene); and alkadienes (such as butadiene and isoprene).
(Iii) alicyclic ethylenic monomers having 5 to 15 carbon atoms, monoethylenically unsaturated monomers (such as pinene, limonene and indene); and polyethylene-based vinyl monomers (such as cyclopentadiene, bicyclopentadiene and ethylidene norbornene).

  The content of the other vinyl monomer (a3) unit is preferably 0 to 5 mol%, more preferably, based on the total number of moles of the water-soluble vinyl monomer (a1) unit and the hydrolyzable vinyl monomer (a2) unit. 0 to 3 mol%, particularly preferably 0 to 2 mol%, particularly preferably 0 to 1.5 mol%, and from the viewpoint of absorption performance and the like, the content of other vinyl monomer (a3) units is 0 mol%. Is most preferred.

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

  The content of the crosslinking agent (b) in the crosslinked polymer (A) depends on the total weight of the vinyl monomers (a) constituting the crosslinked polymer (A) (that is, the water-soluble vinyl monomer (a1), the hydrolyzable vinyl monomer). (Total weight of (a2) and other vinyl monomers (a3)), preferably from 0.2 to 5% by weight, more preferably from 0.3 to 3% by weight, most preferably from 0.4 to 1% by weight. It is. When the content is less than 0.2% by weight, the soluble component of the absorbent resin particles increases, and the gel flow rate may decrease. On the other hand, when the content is more than 5% by weight, the crosslinking density inside the absorbent resin particles becomes too high, so that a sufficient water retention capacity cannot be exhibited, and discoloration during long-term storage is liable to occur. The weight of the vinyl monomer (a) and the weight of the crosslinking agent (b) contained in the crosslinked polymer (A) may be the weight of the vinyl monomer (a) and the weight of the crosslinking agent used in the polymerization reaction when producing the crosslinked polymer (A). Use the weight of (b).

  As a method for producing the crosslinked polymer (A), there are known solution polymerization (such as adiabatic polymerization, thin film polymerization and spray polymerization; JP-A-55-133413, etc.), known suspension polymerization and reverse phase polymerization. A hydrogel polymer (containing at least a crosslinked polymer and water) obtained by turbid polymerization (JP-B-54-30710, JP-A-56-26909, JP-A-1-5808, etc.) is required. And can be obtained by drying. The crosslinked polymer (A) may be a single type or a mixture of two or more types.

  The crosslinked polymer (A) essentially contains a water-soluble vinyl monomer (a1) and / or a vinyl monomer (a) containing a vinyl monomer (a2) which becomes a water-soluble vinyl monomer (a1) by hydrolysis, and a crosslinker (b). It can be obtained by polymerizing the monomer composition as a structural unit, but among the polymerization methods, a solution polymerization method is preferable, and there is no need to use an organic solvent or the like, which is advantageous in terms of production cost. Therefore, an aqueous solution polymerization method is particularly preferred, and a water-soluble adiabatic polymerization method is most preferable because a crosslinked polymer having a large water retention amount and a small amount of a water-soluble component is obtained and temperature control during polymerization is unnecessary. .

  When performing aqueous solution polymerization, a mixed solvent containing water and an organic solvent can be used. Examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N, N-dimethylformamide, dimethyl sulfoxide, and two or more of these. And mixtures thereof. 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 a catalyst is used for the polymerization, a conventional catalyst for radical polymerization can be used. For example, azo compounds [azobisisobutyronitrile, azobiscyanovaleric acid and 2,2′-azobisamidinopropane dihydrochloride and the like], Inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides such as benzoyl peroxide, di-tert-butyl peroxide, cumene hydroperoxide, succinic peroxide and disulfide (2-ethoxyethyl) peroxydicarbonate and the like] and a redox catalyst (a reducing agent such as an alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite and ascorbic acid and an alkali metal persulfate, ammonium persulfate, Combination with oxidizing agents such as hydrogen peroxide and organic peroxides That Is) or the like from the combined like. These catalysts may be used alone or in combination of two or more. 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 when other vinyl monomers (a3) are used, (a1) to (a3). 0.0005 to 5% by weight, more preferably 0.001 to 2% by weight.

  When a suspension polymerization method or a reversed 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. In the case of the reverse phase suspension polymerization method, polymerization can be carried out using a conventional hydrocarbon solvent such as xylene, normal hexane and normal heptane.

  The polymerization initiation temperature can be appropriately adjusted depending on the type of the 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 (longest diameter) of the gel after shredding is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, the drying property in the drying step is further improved.

  Shredding can be performed by a known method, and can be shredded using a shredding device (for example, Vex Mill, Rubber Chopper, Pharma Mill, mincing machine, impact mill, roll mill) and the like.

  Further, as described above, a base may be mixed with the hydrogel polymer of the acid group-containing polymer obtained after the polymerization, if necessary, for neutralization.

  As a method of distilling off the solvent (including water) of the hydrogel polymer and drying it, a method of distilling (drying) with hot air at a temperature of 80 to 230 ° C, a drum dryer heated to 100 to 230 ° C Etc., a thin-film drying method by (e.g.) heating, reduced-pressure drying method (heating), freeze-drying method, drying method by infrared rays, decantation, filtration and the like can be applied.

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

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

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

  The hydrogel polymer is dried to obtain a crosslinked polymer (A), and then further pulverized to obtain resin particles containing the crosslinked polymer (A). The pulverizing method is not particularly limited, and a pulverizing apparatus (for example, a hammer-type pulverizer, an impact-type pulverizer, a roll-type pulverizer, and a shet air-flow type pulverizer) can be used. The particle size of the resin particles can be adjusted by sieving or the like, if necessary.

  If sieved as necessary, the weight average particle diameter of the resin particles is preferably 100 to 800 μm, more preferably 200 to 700 μm, then 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 is further improved.

  The weight average particle size was measured using a low tap test sieve shaker and a standard sieve (JIS Z8801-1: 2006), Perry's Chemical Engineers Handbook, 6th edition (Mac Glow Hill Book Company, 1984). , Page 21). That is, the JIS standard sieves are 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 the pan. About 50 g of the particles to be measured is put into the uppermost sieve and shaken with a low tap test sieve shaker for 5 minutes. The weight of the particles measured on each sieve and the pan is weighed, and the weight fraction of the particles on each sieve is determined by taking the total as 100% by weight, and the logarithmic probability paper [the horizontal axis indicates the sieve aperture (particle size) ), The vertical axis is weight fraction], and a line connecting the points is drawn to determine a particle diameter corresponding to a weight fraction of 50% by weight, which is defined as a weight average particle diameter.

  Also, the smaller the content of the fine powder contained in the resin particles, the better the absorption performance becomes. Therefore, 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 at most 1% by weight. The content of the fine powder can be determined using a graph created when the above-mentioned weight average particle diameter is determined.

  The resin particles may contain some other components such as a residual solvent and a residual cross-linking component to the extent that their performance is not impaired.

The absorbent resin particles of the present invention are water-absorbent resin particles obtained by crosslinking the resin particles containing the crosslinked polymer (A) with a post-crosslinking agent (c). A process comprising the step of reacting a mixture containing resin particles containing A) and a post-crosslinking agent (c) to post-crosslink the resin particles, wherein the water content of the mixture is 22 to 90% by weight.
Here, the post-crosslinking is different from the technique of polymerizing a water-soluble vinyl monomer or the like in a solution state in the presence of the crosslinking agent (b) to obtain a crosslinked polymer. This is a technique to increase the crosslink density. Post-crosslinking reduces [water absorption capacity in ion-exchanged water] and improves [gel flow rate of absorbent resin particles] while maintaining the water retention required for water-absorbent resin particles in actual use by post-crosslinking. Can be done.

  Examples of the post-crosslinking agent (c) include polyglycidyl compounds, polyamines, polyaziridines and polyisocyanates described in JP-A-59-189103, JP-A-58-180233 and JP-A-58-180233. Polyhydric alcohols described in JP-A-61-16903, silane coupling agents described in JP-A-61-211305 and JP-A-61-252212, and alkylene carbonates described in JP-T-5-508425. And polyvalent oxazoline compounds described in JP-A-11-240959 and surface crosslinking agents such as polyvalent metals described in JP-A-51-136588 and JP-A-61-257235. Among these surface cross-linking agents, polyhydric glycidyl compounds, polyhydric alcohols and polyamines are preferred from the viewpoint of economy and absorption properties, more preferably polyhydric glycidyl compounds and polyhydric alcohols, and particularly preferably polyhydric glycidyl compounds and polyhydric alcohols. Multivalent glycidyl compounds, most preferred are ethylene glycol diglycidyl ethers. One type of surface cross-linking agent may be used alone, or two or more types may be used in combination.

  The total amount of the post-crosslinking agent (c) used in the absorbent resin particles can be variously changed depending on the type of the post-crosslinking agent, conditions for cross-linking, target performance, and the like. It is preferably from 1 to 4% by weight, more preferably from 1 to 3% by weight, most preferably from 1 to 2.5% by weight, based on the weight of A). Within this range, the gel flow rate will be further improved. 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 flow rate may not be sufficiently high. On the other hand, when the content is more than 4% by weight, discoloration during long-term storage tends to occur. The total amount of the post-crosslinking agent (c) used is calculated based on the weight of the post-crosslinking agent (c) used in the post-crosslinking step described later.

  As a method for post-crosslinking the resin particles, for example, a method of mixing a resin particle and a mixed solution comprising a post-crosslinking agent (c), water and a solvent to prepare a mixture, and reacting the mixture to perform post-crosslinking may be mentioned. As a method of reacting, a method of performing a heat reaction is exemplified. As a method of mixing the resin particles and the mixed solution to obtain a mixture, a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauter mixer, a double arm kneader, a flow mixer, A method of performing uniform mixing using a mixing device such as a V-type mixer, a mince mixer, a ribbon-type mixer, an airflow-type mixer, a rotating disk-type mixer, a conical blender, and a roll mixer is exemplified. Further, from the viewpoint of surface cross-linking uniformity, it is preferable to use a mixed solution diluted with water and a solvent as the post-crosslinking agent (c), and a known fluid-type humidifying and mixing granulator [Flexomics (manufactured by Hosokawa Micron Co., Ltd.) ) And Sugiflexomics (manufactured by Powrex Co., Ltd.)] with a known mixing device, or a method of dipping resin particles into the mixed solution.

  The solvent used in the mixed solution may be appropriately selected and used in consideration of the degree of penetration of the post-crosslinking agent (c) into the resin particles, the reactivity of the post-crosslinking agent (c), and the like. Preferably, a hydrophilic organic solvent that can be dissolved in water, such as methanol, diethylene glycol and propylene glycol, is used. 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 the solvent, but is preferably 1 to 10% by weight based on the weight of the resin particles before the post-crosslinking.

  The post-crosslinking is performed by a step of reacting a mixture containing the resin particles and the post-crosslinking agent (c) (hereinafter, also referred to as a post-crosslinking step). In the post-crosslinking step, it is preferable that the resin particles and the post-crosslinking agent (c) are mixed and then reacted by heating. The heating temperature during the heating reaction is preferably 80 to 230C, more preferably 100 to 180C. The reaction time can be appropriately adjusted depending on the reaction temperature, but is preferably 3 to 90 minutes, and more preferably 30 to 60 minutes. When the reaction temperature is lower than 80 ° C., the post-crosslinking reaction does not sufficiently proceed, and the [absorbency in ion-exchanged water] of the resulting absorbent resin particles may not be reduced. 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 between the resin particles and the post-crosslinking agent (c) in the post-crosslinking step may be performed once, but it is preferable to perform the mixing and the reaction twice or more each. Specifically, by performing the mixing and the reaction in the post-crosslinking step twice or more, the post-crosslinking of the resin particles is divided into two or more times and performed in the depth direction near the surface of the absorbent resin particles. It is possible to form a thick crosslinked structure, improve the balance between the [water absorption capacity in ion-exchanged water] of the absorbent resin particles and the water retention amount, and achieve both high gel flow rates. More preferably, in the case where the mixing of the resin particles and the post-crosslinking agent (c) is performed twice or more, it is preferable that the mixing is performed under the condition that the water content of the resin particles is different. In addition, the post-crosslinking agent used in the case of carrying out two or more times may be the same post-crosslinking agent or a different post-crosslinking agent each time.
When the post-crosslinking step is performed 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 crosslink density near the surface can be increased.

  When the reaction between the resin particles and the post-crosslinking agent (c) is performed twice or more in the post-crosslinking step, it is preferable to react the mixture having a water content of 22 to 90% by weight at least once. The more preferable water 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 reacting mixture is lower than 22% by weight, the resulting absorbent resin particles may not have a low [water absorption capacity in ion-exchanged water] or a high gel permeation retention rate. . Further, by performing a post-crosslinking reaction with a mixture having a water content of 22% by weight or more, the [water absorption capacity in ion-exchanged water] can be reduced, and the ion exchange water absorption index described later can be effectively reduced. preferable. On the other hand, when the water content is more than 90% by weight, the treatment time for removing water after the reaction becomes longer, which is not only economical, but also sometimes deteriorates the initial yellowness of the resulting absorbent resin particles. is there. In addition, the water content of the resin particles at the time of post-crosslinking can be adjusted by calculating the required amount of water from the water content of the resin particles before the post-crosslinking and by 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 performed in a sealed state. Heating in a closed atmosphere prevents evaporation of water during the reaction, stabilizes the water content during the reaction, and maintains [Water absorption in ion-exchanged water while maintaining the water retention required for the water-absorbent resin particles. Magnification] and a high gel flow rate can be stably obtained. In addition, when the water content of the mixture is high, the pressure is increased by heating in a closed state, so that the reaction is preferably performed in a pressure-resistant container.

  In the absorbent resin particles of the present invention, the total content of the crosslinking agent (b) and the 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%, and most preferably 2.0 to 5.0%. If the total content of the crosslinking agent (b) and the post-crosslinking agent (c) is less than 1.0%, the water absorption capacity in ion-exchanged water may not be reduced. When the total content of the cross-linking agent (b) and the post-cross-linking agent (c) is more than 10.0%, the yellowness deteriorates after standing for 28 days in an atmosphere at 70 ± 5 ° C. and a relative humidity of 80 ± 3%. May be. When calculating the total ratio of the content of the crosslinking agent (b) and the content of the post-crosslinking agent (c), the weight of the crosslinked polymer (A) is used when producing the crosslinked polymer (A). The total weight of the vinyl monomer (a) and the crosslinking agent (b) was used, and the content of the crosslinking agent (b) and the post-crosslinking agent (c) was determined as the content of 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.

  After the post-crosslinking, the absorbent resin particles of the present invention can be obtained by distilling off or drying a 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 the particle size adjustment is preferably 100 to 600 μm, more preferably 200 to 500 μm. The content of the fine particles is preferably smaller, the content of the particles having a size of 100 μm or less is preferably 3% by weight or less, and the content of the particles having a size 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 includes 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).

  Examples of the chelating agent (B1) containing a carboxy (salt) group in a molecule include a hydroxycarboxylic acid having a hydroxyl group and / or a salt thereof (B11) and a carboxylic acid having no hydroxyl group and / or a salt thereof (B12). . Examples of the hydroxycarboxylic acid having a hydroxyl group and / or a salt thereof (B11) include citric acid (salt), lactic acid (salt), gallic acid (salt), and tartaric acid (salt). Examples of the carboxylic acid having no hydroxyl group and / or its salt (B12) include ethylenediaminetetraacetic acid (salt), diethylenetriaminepentaacetic acid (salt), hydroxyethyl-iminodiacetic acid (salt), and 1,2-diaminocyclohexanetetraacetic acid ( Salt), triethylenetetramine hexaacetic acid (salt), nitrilotriacetic acid (salt), β-alanine diacetate (salt), aspartic acid diacetate (salt), methylglycine diacetic acid (salt), iminodisuccinic acid (salt), serine Acetic acid (salt), aspartic acid (salt) and glutamic acid (salt), pyromellitic acid (salt), benzopolycarboxylic acid (salt), cyclopentanetetracarboxylic acid (salt), etc., carboxymethyloxysuccinate, oxydisuccinate Nate, maleic acid derivative, oxalic acid (salt), malonic acid (salt), succinic acid (salt), Etc. Rutaru acid (salt) and adipic acid (salts).

  Examples of the chelating agent (B2) containing a phosphonic acid (salt) group or a phosphoric acid (salt) group in a molecule include methyldiphosphonic acid (salt), aminotri (methylenephosphonic acid) (salt), 1-hydroxyethylidene- 1,1-diphosphonic acid (salt), nitrilotrismethylene phosphonic acid (salt), ethylenediaminetetra (methylenephosphonic acid) (salt), hexamethylenediaminetetra (methylenephosphonic acid) (salt), propylenediaminetetra (methylenephosphonic acid) ) (Salt), diethylenetriaminepenta (methylenephosphonic acid) (salt), triethylenetetraminehexa (methylenephosphonic acid) (salt), triaminotriethylaminehexa (methylenephosphonic acid) (salt), trans-1,2-cyclohexanediamine Tetra (methylene phosphonic acid) (salt), glyco Ether diamine tetra (methylene phosphonic acid) (salt) and tetraethylenepentamine hepta (methylene phosphonic acid) (salt), metaphosphoric acid (salt), pyrophosphoric acid (salt), tripolyphosphoric acid (salt), hexametaphosphoric acid (salt), etc. Is mentioned.

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

  Other chelating agents (B3) include N, N'-bis (salicylidene) -1,2-ethanediamine, N, N'-bis (salicylidene) -1,2-propanediamine, N, N'-bis (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, preferably a chelating agent (B1) containing a carboxy (salt) group in the molecule, more preferably a hydroxycarboxylic acid having a hydroxyl group and / or a salt thereof. (B11), most preferably citric acid (salt). One chelating agent may be used alone, or two or more chelating agents may be used in combination.

Examples of the method of adding the chelating agent (B) include a method of mixing an aqueous solution of the chelating agent (B) with the resin particles. As a method of mixing the resin particles and the aqueous solution, a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauter mixer, a double arm kneader, a flow mixer, a V mixer, A uniform mixing method using a mixing device such as a mince mixer, a ribbon mixer, an airflow mixer, a rotating disk mixer, a conical blender, and a roll mixer can be used. From the viewpoint of uniformity of addition of the chelating agent (B), it is preferable to use an aqueous solution diluted with water as the chelating agent (B), and a fluid-type humidifying and mixing granulator [Flexomics (manufactured by Hosokawa Micron Corporation) and And the like, and a method of dipping resin particles into the above-mentioned mixed solution.
The content of the chelating agent (B) unit is preferably from 0.1 to 10% by weight, more preferably from 1 to 7% by weight, particularly preferably from 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 the absorption performance.

  The absorbent resin particles of the present invention may optionally contain additives (for example, preservatives, fungicides, antibacterial agents, antioxidants, and antioxidants described in JP-A-2003-225565 and JP-A-2006-131767). UV absorbers, colorants, fragrances, deodorants, liquid permeability improvers, organic fibrous substances, etc.). When these additives are contained, the content of the additives is preferably 0.001 to 10% by weight, more preferably 0.01 to 5% by weight, particularly preferably 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 [absorption capacity in ion-exchanged water] of 10 to 120 (g / g) in which the absorbent resin particles immersed in ion-exchanged water absorb water per unit weight. The speed at which the physiological saline solution passes through the absorbent resin particles compressed by applying weight after being swelled by immersion in physiological saline for 30 minutes is 350 (ml). / Min) or more.

The [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 disposable swimwear. If the absorption capacity in ion-exchanged water is larger than 120, the absorbent resin particles used in disposable swimwear will swell greatly when they enter the water, and the crotch will sag or slip off, resulting in poor appearance and feeling of wearing. May be.
In order to set the [absorbency against deionized water] of the absorbent resin particles in the above range, in the above-mentioned production method, the water content of the resin particles in at least one of the post-crosslinking steps is set to 22 to 90% by weight, It is preferable that the total content of the crosslinking agent (b) and the post-crosslinking agent (c) be 1.0 to 10.0% based on the weight of the crosslinked polymer (A).

The [water absorption capacity in ion-exchanged water] is measured under the following conditions.
0.50 g of a measurement sample is placed in a tea bag (length 20 cm, width 10 cm) made of nylon mesh having a mesh size of 63 μm (JIS Z8801-1: 2006), and 1,000 ml of ion-exchanged water (electric conductivity 5 μS / cm or less) is used. After being immersed in the solution for 1 hour without stirring, it is pulled up, suspended for 15 minutes and drained. The weight (w1 (g)) including the tea bag is measured, and the water retention amount is determined from the following equation. (W2 (g)) is the weight of the tea bag measured by the same operation as above when there is no measurement sample. The temperature of the ion-exchanged water used and the measurement atmosphere is 25 ° C. ± 2 ° C. When the weight w1 of the bag exceeds 100 (g), the amount of the measurement sample to be charged into the tea bag is appropriately adjusted so as to be 0.50 g or less.
[Water absorption capacity in ion-exchanged water] (g / g) = ((w1)-(w2)) / weight of measurement sample

The speed at which the physiological saline solution passes through the absorbent resin particles that have been swelled by immersion in physiological saline for 30 minutes and then weighted and compressed (the gel flow rate of the absorbent resin particles) is 350 (ml / Min) or more, preferably 350 to 2000 (ml / min), more preferably 350 to 1500 (ml / min), and particularly preferably 350 to 1000 (ml / min). If the gel flow rate is less than 350, leakage may occur when used in disposable swimwear.
In order for the gel flow rate of the absorbent resin particles to be in the above range, the content of the crosslinking agent (b) unit is adjusted so that the water-soluble vinyl monomer (a1) unit, the hydrolyzable vinyl monomer (a2) unit, When a vinyl monomer (a3) unit is also used, the amount is adjusted to 0.001 to 5 mol% based on the total number of moles of the (a1) to (a3) units, and a suitable amount of the resin particles containing the crosslinked polymer (A) is added. It is preferable to crosslink with a crosslinking agent (c).

[Gel-flow rate of absorbent resin particles] is measured by the following operation using the instrument shown in FIGS. 1 and 2.
0.32 g of the measurement sample is immersed in 150 ml of physiological saline 1 (0.9% salt concentration) for 30 minutes to prepare swollen gel particles 2. A vertical cylinder 3 mm diameter (inner diameter) 25.4 mm, length 40 cm, scale lines 4 and 5 are provided at positions 60 ml and 40 ml from the bottom, respectively. With the cock 7 closed in a filtration cylindrical tube having 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) at the bottom of｝, After transferring the prepared swollen gel particles 2 together with physiological saline, a circular wire mesh 8 (aperture 150 μm, diameter 25 mm) having a pressure axis 9 that is perpendicular to the wire mesh surface is placed on the swollen gel particles 2. Was placed so that the metal mesh and the swollen gel particles were in contact with each other, and a weight 10 (88.5 g) was further placed on the pressing shaft 9 (weight 22 g, length 47 cm) and allowed to stand for 1 minute. Subsequently, the cock 7 is opened and the time (T1; second) 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 by the following formula. Ask for.
Gel flow rate (ml / min) = 20 ml × 60 / (T1-T2)
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 described above when there was no measurement sample.

The weight of the physiological saline absorbed by the absorbent resin particles of 1.00 g of the present invention immersed in the physiological saline (the water retention amount of the absorbent resin particles with respect to the physiological saline) is preferably 10 to 20 (g / g). And more preferably 12 to 18 (g / g), and most preferably 14 to 16 (g / g). When the water retention is less than 10, urine may not be sufficiently absorbed when used in a disposable swimsuit. If the amount of water retention is greater than 20, the amount of urine absorbed is sufficient, but the amount of water absorbed also increases, so when used in disposable swimwear and enters the water, the absorbent resin particles swell greatly, and the crotch may hang down In some cases, the appearance and the feeling of wearing may be deteriorated due to slipping and falling.
In order to maintain the water retention 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) by hydrolysis are used. When the content of the crosslinking agent (b) unit to be selected is selected from (a1) to (a3) when a water-soluble vinyl monomer (a1) unit, a hydrolyzable vinyl monomer (a2) unit, and other vinyl monomer (a3) units are also used. ) It is preferred to make 0.001 to 5 mol% based on the total number of moles of the unit and to polymerize the monomer composition.

The water retention of the absorbent resin particles in physiological saline is measured under the following conditions.
1.00 g of a measurement sample is placed in a tea bag (length 20 cm, width 10 cm) made of nylon mesh having a mesh size of 63 μm (JIS Z8801-1: 2006), and the sample is placed in 1,000 ml of physiological saline (salt concentration: 0.9%). After being immersed for 1 hour in a non-agitated state, it is pulled up, suspended for 15 minutes and drained. Then, the whole tea bag is put 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 calculated from the following equation. (H2) is the weight of the tea bag measured by the same operation as above when there is no measurement sample. The temperature of the physiological saline used and the measurement atmosphere is 25 ° C. ± 2 ° C.
Water retention (g / g) = (h1)-(h2)

The absorption index of ion-exchanged water in the absorbent resin particles of the present invention is represented by the following (Equation 3) using the above-mentioned [water absorption capacity in ion-exchanged water] and the water retention of the absorbent resin particles in physiological saline. It is an index defined and is expressed by the ratio of the water absorption capacity of absorbent resin particles in ion-exchanged water to the water retention of the absorbent resin particles with respect to physiological saline. Therefore, the smaller the ion-exchanged water absorption index, the smaller the [absorption ratio in ion-exchanged water] with respect to the amount of the absorbent resin particles held in 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) (Equation 3)

  The ion exchange water absorption index is preferably from 1.0 to 6.0, more preferably from 1.5 to 5.5, and most preferably from 2.0 to 5.0. If the ion-exchange water absorption index is less than 1.0, when used in a disposable swimsuit, it may not be able to absorb urine and may leak. When the ion-exchange water absorption index is larger than 6.0, the absorbent resin particles used in disposable swimwear greatly swell when entering the water, and the crotch hangs down or slips off, resulting in poor appearance and feeling of wearing. May be.

  As the absorptive resin particles of the present invention, absorptive resin particles having a yellowness (YI value) of 20 or less measured after being left in an atmosphere of 70 ± 5 ° C. and a relative humidity of 80 ± 3% for 28 days are preferable. Absorbent resin particles having a yellowness of 18 or less, as measured under the above conditions, are more preferred, and absorbent resin particles of 15 or less are most preferred. When the yellowness measured under the above conditions is the absorbent resin particles larger than 20, when the disposable swimwear is used after long-term storage, the discolored absorbent resin particles inside the disposable swimwear may be conspicuously seen from the outside. There is.

The degree of yellowness is measured by using the absorbent resin particles according to the method described in JIS K7373 Plastic-Determination of Yellowness and Yellowing Degree.
The degree of yellowness can be evaluated for the initial coloring (coloring immediately after production) of the absorbent resin and the ease with which coloring proceeds in a long-term storage or applied product, and after leaving for 28 days in an atmosphere at a relative humidity of 80 ± 3%. The measured yellowness is measured under a color acceleration test (70 ± 5 ° C., relative humidity 80 ± 3%) using a simple spectral colorimeter (Nippon Denshoku Industries Co., Ltd., NF333, sensor part ND120 inner diameter φ8 mm). , For 28 days) to measure the yellowness. Yellowness indicates that the smaller the value is, the more the coloring is suppressed.
The procedure of the coloring promotion test (left in an atmosphere of 70 ± 5 ° C. and relative humidity of 80 ± 3% for 28 days) is as follows.
10 g of an absorbent resin is placed in a glass Petri dish with an inner diameter of 90 mm, and the surface is evenly leveled. This was taken at 70 ± 5 ° C., 80 ± 3% R.F. H. For 28 days in a thermo-hygrostat. Thereafter, the petri dish is taken out from the thermo-hygrostat and returned to room temperature, and then the yellowness after the coloring acceleration test is measured.

The liquid retention rate (%) of the absorbent resin particles of the present invention is defined by the following (Equation 4), and the gel liquid penetration rate of the absorbent resin particles is the same as the gel liquid penetration rate of the absorbent resin particles before the fragility test. Since they have the same meaning, the liquid-passing retention ratio means the ratio of the gel-flowing speed of the absorbent resin particles before and after the breakability test described later. Therefore, the higher the liquid permeation retention rate, the more absorptive resin particles are resistant to breakage with respect to the gel liquid permeation speed.
(Liquid penetration rate) = 100 × ([Gel penetration rate of absorbent resin particles after fragility test] / ([Gel penetration rate of absorbent resin particles before fragility test]) ・ ・ ・ ( Equation 4)

The liquid 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 liquid permeation retention rate is less than 70%, leakage may occur when used for disposable swimwear. In order to improve the liquid retention rate, it is necessary to increase the durability of the water-absorbent resin particles against physical impact, and it is preferable to perform the above-described post-crosslinking step. That is, by performing the post-crosslinking step of the present invention, a higher gel flow rate can be achieved as compared with a conventional gel flow rate improving technique using a surface treatment agent such as an inorganic compound such as silica or a polyvalent metal salt such as aluminum sulfate. Not only can the liquid velocity be exhibited, but also durability can be imparted to the water-absorbing resin particles, and the liquid retention rate can be improved.
In order to maintain the liquid retention rate of the absorbent resin particles in the above range, the water content of the resin particles in the post-crosslinking step needs to be 22 to 90% by weight. Since the cross-linking agent penetrates into the resin particles and has a uniform cross-linking structure throughout the resin particles, even if the particle surface is broken, a new cross-linking surface appears inside, so that the gel flow retention rate can be maintained. .

  In addition, the value measured under the same conditions as the above-mentioned [gel flow rate of the absorbent resin particles] is used as the [gel flow rate of the absorbent resin particles] before the breakability test. The [gel flow rate of the absorbent resin particles] after the breakability test is the same as the above [gel flow rate of the absorbent resin particles] except that the absorbent resin particles after the breakability test are used. Measure under conditions.

In addition, the [gel flow rate of the absorbent resin particles] after the breakability test is measured under the following conditions.
30 g of absorptive resin particles are charged into a 3 L round separable flask (made by ASONE), and a nylon mesh having a mesh size of 63 μm (JIS Z8801-1: 2000) having a 6 mm hole at the center is formed on the upper part of the separable flask. ), And a four-port separable cover (main tube TS29 / 42, side tubes TS24 / 40, 24/40, 15/35 made by ASONE) is set thereon. Next, a stainless steel (outer diameter 6 mm, inner diameter 4 mm) tube was inserted from the main tube TS29 / 42 of the four-port separable cover for a 3 L round separable flask, and the stainless steel tube penetrated the nylon mesh and the tip was the same as above. Set so as to be 45 mm from the bottom of the separable flask. A urethane tube (length: 1500 mm, inner diameter: 8.5 mm) is attached to the other end of the stainless steel tube, connected to an air line capable of achieving a pressure of 0.3 MPa or more, and an air line is opened at a pressure of 0.2 MPa. After performing a break test by air blowing for one minute, the absorbent resin particles are taken out, and then the absorbent resin particles after compression are subjected to a physiological saline solution under the same conditions as in the above [gel flow rate of the absorbent resin particles]. Measure the speed at which 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, and particularly preferably 0.58 to 0.60 g / ml. is there. Within this range, the antifogging property of the absorbent article is further improved. The apparent density of the absorbent resin particles is measured at 25 ° C. according to JIS K7365: 1999.

  The shape of the absorbent resin particles of the present invention is not particularly limited, and examples thereof include irregular crushed shapes, scaly shapes, pearl shapes, and rice grain shapes. Of these, the irregularly crushed shape is preferred from the viewpoint of good entanglement with the fibrous material in disposable swimwear applications 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, then preferably 250 to 600 μm, particularly preferably 300 to 500 μm, and most preferably 350 to 450 μm. . Within this range, the absorption performance is further improved.

  Also, the smaller the content of the fine powder contained in the resin particles, the better the absorption performance becomes. Therefore, 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 at most 1% by weight. The content of the fine powder can be determined using a graph created when the above-mentioned weight average particle diameter is determined.

  The absorber of the present invention contains the absorbent resin particles of the present invention. As the absorber, the absorbent resin particles may be used alone, or may be used together with other materials to form the absorber. Other materials include fibrous materials. The structure and manufacturing method of the absorber when used together with the fibrous material are the same as those in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, and the like.

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

  Examples of the cellulosic fibers include natural fibers such as fluff pulp and cellulosic chemical fibers such as viscose rayon, acetate and cupra. The raw material (coniferous tree, hardwood, etc.), production method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.) and bleaching method of the cellulosic natural fiber are not particularly limited.

  Examples of the 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 fibers having different melting points). , A fiber obtained by blending at least two of the above-mentioned fibers into a sheath-core type, an eccentric type, a side-by-side type, a fiber obtained by blending at least two types of the above-mentioned fibers, and a fiber obtained by modifying the surface layer of the above-mentioned fibers.

  Among these fibrous base materials, preferred are cellulose-based natural fibers, polypropylene-based fibers, polyethylene-based fibers, polyester-based fibers, heat-fusible conjugate fibers and mixed fibers thereof. The fluff pulp, the heat-fusible conjugate fiber, and the mixed fiber thereof in that the obtained water-absorbing agent has excellent shape retention after water absorption.

  The length and thickness of the fibrous material are not particularly limited, and may 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 denier. The shape is not particularly limited as long as it is fibrous, and examples thereof include a thin cylindrical shape, a split yarn shape, a staple shape, a filament shape, a web shape, and the like.

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

  The absorbent article of the present invention uses the above absorber. As an absorbent article, it is applicable as a sanitary article such as a disposable swimsuit, a disposable diaper, a sanitary napkin, an absorbent or a retainer for various aqueous liquids, and a gelling agent, and is preferably used. It is a disposable swimsuit. The manufacturing method of the absorbent article and the like are the same as those described in JP-A-2003-225565, JP-A-2006-131767, JP-A-2005-097569, and the like.

  Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified, “part” indicates “part by weight” and “%” indicates “% by weight”.

<Example 1>
100 parts of acrylic acid (purity 100%, manufactured by Mitsubishi Chemical Corporation), 0.4 parts of a cross-linking agent (pentaerythritol triallyl ether, manufactured by Daiso Co., Ltd.) and 220 parts of ion-exchanged water were stirred and mixed at 3 ° C. Kept. After introducing nitrogen into the 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% of 2,2′-azobis 0.1 part of an aqueous solution of amidinopropane dihydrochloride was added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ° C., polymerization was carried out at 90 ± 2 ° C. for about 5 hours to obtain a hydrogel.

  Next, this water-containing gel was shredded with a mincing machine (12VR-400K, manufactured by ROYAL), and 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the mixture. 72%). Further, the neutralized hydrogel was dried with a ventilation dryer (200 ° C., air velocity 2 m / sec) to obtain a dried product. The dried product is pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), sieved, and adjusted to a particle diameter range of 710 to 150 μm to obtain resin particles (A-1) containing a crosslinked polymer. Was. The water content of the resin particles (A-1) was 3%.

  Then, while stirring 100 parts of the obtained resin particles (A-1) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.4 parts of propylene glycol was added thereto, and ethylene glycol distillate was used as a post-crosslinking agent. A mixed solution obtained by mixing 0.18 parts of glycidyl ether and 3.6 parts of ion-exchanged water was added and uniformly mixed. The water content of the mixture after uniform mixing of the resin particles (A-1) and the post-crosslinking agent was 6%. Thereafter, the mixture was heated at 130 ° C. for 30 minutes in a ventilation dryer (open to the atmosphere) to react with the first post-crosslinking agent to obtain absorbent resin particles (B-1). The water content of the absorbent resin particles (B-1) was 3%.

  Next, 100 parts of the obtained absorbent resin particles (B-1) were stirred at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), and 2.0 parts of propylene glycol was added thereto. A mixed solution obtained by mixing 2.0 parts of glycol diglycidyl ether and 40 parts of ion-exchanged water was added and uniformly mixed to obtain a mixture. The water content of the mixture containing the water-absorbent resin particles (B-1) and the post-crosslinking agent after the uniform mixing was 28%. Thereafter, the mixture was charged into a PTFE crucible (manufactured by Freon Industry Co., Ltd.), sealed, and then heated at 130 ° C. for 60 minutes to perform a second reaction with the post-crosslinking agent. After heating, the PTFE crucible was opened, and heated at 130 ° C. for 20 minutes to remove water, thereby obtaining absorbent resin particles (C-1).

  Then, while stirring 100 parts of the obtained absorbent resin particles (C-1) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.6 parts of sodium citrate as a chelating agent and ion A mixture obtained by mixing 2.4 parts of exchanged water was added to obtain the 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 used as the absorbent resin particles (P-2) of the present invention.

<Example 3>
In the first reaction with the post-crosslinking agent in Example 1, 2.0 parts of ethylene glycol diglycidyl ether added to 100 parts of the absorbent resin particles (B-1) were converted to 1.2 parts of ethylene glycol diglycidyl ether. Except for the change, the same operation as in Example 1 was performed to obtain the absorbent resin particles (P-3) of the present invention. The water content of the mixture containing the resin particles and the post-crosslinking agent before the first heat reaction with the post-crosslinking agent was 28%.

<Example 4>
In the first reaction with the post-crosslinking agent of Example 1, 2.0 parts of ethylene glycol diglycidyl ether added to 100 parts of the absorbent resin particles (B-1) were changed to 0.9 parts of ethylene glycol diglycidyl ether. Except for the change, the same operation as in Example 1 was performed to obtain the absorbent resin particles (P-4) of the present invention. The water content of the mixture before performing the heat reaction with the first post-crosslinking agent was 28%.

<Example 5>
100 parts of acrylic acid (purity 100%, manufactured by Mitsubishi Chemical Corporation), 0.4 parts of a cross-linking agent (pentaerythritol triallyl ether, manufactured by Daiso Co., Ltd.) and 220 parts of ion-exchanged water were stirred and mixed at 3 ° C. Kept. After introducing nitrogen into the 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% of 2,2′-azobis 0.1 part of an aqueous solution of amidinopropane dihydrochloride was added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ° C., polymerization was carried out at 90 ± 2 ° C. for about 5 hours to obtain a hydrogel.
Next, this water-containing gel was shredded with a mincing machine (12VR-400K, manufactured by ROYAL), and 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the mixture. 72%). Further, the neutralized hydrogel was dried with a ventilation dryer (200 ° C., air velocity 2 m / sec) to obtain a dried product. The dried product is pulverized with a juicer mixer (Osterizer Blender, manufactured by Oster), sieved and adjusted to a particle size range of 710 to 150 μm to obtain resin particles (A-5) containing a crosslinked polymer. Was. The water content of the resin particles (A-5) was 3%.

  Then, while stirring 100 parts of the obtained resin particles (A-5) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.4 parts of propylene glycol was added thereto, and ethylene glycol distillate was used as a post-crosslinking agent. A mixed solution obtained by mixing 0.18 parts of glycidyl ether and 3.6 parts of ion-exchanged water was added and uniformly mixed to obtain a mixture. The water content of the mixture containing the resin particles (A-5) and the post-crosslinking agent was 6%. Thereafter, the mixture was heated at 130 ° C. for 30 minutes in a ventilation dryer (open to the atmosphere) to perform a first reaction between the resin particles and the post-crosslinking agent, thereby obtaining absorbent resin particles (B-5). The water content of the absorbent resin particles (B-5) was 3%.

  Next, 100 parts of the obtained absorbent resin particles (B-5) were stirred at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), and 2.0 parts of propylene glycol was added thereto. A mixed solution obtained by mixing 2.0 parts of glycol diglycidyl ether and 100 parts of ion-exchanged water was added and uniformly mixed to obtain a mixture. The water content of the mixture containing the water-absorbent resin particles (B-5) and the post-crosslinking agent was 49%. Thereafter, the mixture was put into a PTFE crucible (manufactured by Freon Industry Co., Ltd.), sealed, and then heated at 130 ° C. for 60 minutes to perform a second reaction with the post-crosslinking agent. After heating, the PTFE crucible was opened and heated at 130 ° C. for 20 minutes to remove water, thereby obtaining absorbent resin particles (C-5).

  Then, while stirring 100 parts of the obtained absorbent resin particles (C-5) at a high speed (a high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.6 parts of sodium citrate as a chelating agent and A liquid mixture obtained by mixing 2.4 parts of ion-exchanged water was added to obtain the absorbent resin particles (P-5) of the present invention.

<Example 6>
100 parts of acrylic acid (manufactured by Mitsubishi Chemical Corporation, 100% purity), 5.0 parts of a crosslinking agent (pentaerythritol triallyl ether, manufactured by Daiso Co., Ltd.) and 220 parts of ion-exchanged water were stirred and mixed at 3 ° C. Kept. After introducing nitrogen into the 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% of 2,2′-azobis 0.1 part of an aqueous solution of amidinopropane dihydrochloride was added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ° C., polymerization was carried out at 90 ± 2 ° C. for about 5 hours to obtain a hydrogel.

  Next, this water-containing gel was shredded with a mincing machine (12VR-400K, manufactured by ROYAL), and 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the mixture. 72%). Further, the neutralized hydrogel was dried with a ventilation dryer (200 ° C., air velocity 2 m / sec) to obtain a dried product. The dried product is pulverized with a juicer mixer (Osterizer Blender, manufactured by Oster), sieved and adjusted to a particle size range of 710 to 150 μm to obtain resin particles (A-6) containing a crosslinked polymer. Was. The water content of the resin particles (A-6) was 3%.

  Next, 100 parts of the obtained resin particles (A-6) were stirred at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), and 4.0 parts of propylene glycol was added thereto. A mixed liquid obtained by mixing 2.0 parts of glycidyl ether and 18.8 parts of ion-exchanged water was added and uniformly mixed to obtain a mixture. The water content of the mixture containing the resin particles (A-6) and the post-crosslinking agent was 17%. Thereafter, the mixture was heated at 130 ° C. for 30 minutes in a ventilation dryer (open to the atmosphere) to perform a first reaction with the post-crosslinking agent to obtain absorbent resin particles (B-6). The water content of the absorbent resin particles (B-6) was 3%.

  Then, 100 parts of the obtained absorbent resin particles (B-6) were stirred at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), and fumed silica (Aerosil 200 manufactured by Aerosil Co.) was added thereto. A mixed solution obtained by mixing 5 parts, 1.6 parts of sodium citrate as a chelating agent and 2.4 parts of ion-exchanged water was added to obtain absorbent resin particles (P-6) of the present invention.

<Example 7>
Same as Example 5 except that 2.0 parts of ethylene glycol diglycidyl ether used in the reaction with the second post-crosslinking agent in Example 5 was changed to 3.6 parts of ethylene glycol diglycidyl ether. By performing the operation, absorbent resin particles (P-7) were obtained. The water content of the mixture containing the water-absorbent 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 with the absorbent resin particles (C-5) was changed to 5.0 parts of sodium citrate, and 2.4 parts of ion-exchanged water was 7.5 parts of ion-exchanged water. Except for changing to, the same operation as in Example 5 was performed to obtain absorbent resin particles (P-8).

<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 part to 0.2 part, the absorption was performed. 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 (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm). And a mixed solution obtained by mixing 2.4 parts of ion-exchanged water with each other 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 Co., Ltd.) and 220 parts of ion-exchanged water were heated to 3 ° C. while stirring and mixing. Kept. After introducing nitrogen into the 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% of 2,2′-azobis 0.1 part of an aqueous solution of amidinopropane dihydrochloride was added and mixed to initiate polymerization. After the temperature of the mixture reached 90 ° C., polymerization was carried out at 90 ± 2 ° C. for about 5 hours to obtain a hydrogel.

  Next, this water-containing gel was shredded with a mincing machine (12VR-400K, manufactured by ROYAL), and 82 parts of a 48.5% aqueous sodium hydroxide solution was added to mix and neutralize the mixture. 72%). Further, the neutralized hydrogel was dried with a ventilation dryer (200 ° C., air velocity 2 m / sec) to obtain a dried product. The dried product was pulverized with a juicer mixer (OSTERIZER BLENDER manufactured by Oster), sieved, and adjusted to a particle diameter range of 710 to 150 μm to obtain absorbent resin particles (RA-2). The water content of the absorbent resin particles (RA-2) was 3%.

  Then, while stirring 100 parts of the obtained absorbent resin particles (HA-2) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.6 parts of sodium citrate as a chelating agent and A mixed solution obtained by mixing 2.4 parts of ion-exchanged water was added to obtain comparative absorbent resin particles (R-2).

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

  Then, while stirring 100 parts of the obtained absorbent resin particles (RA-3) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.4 parts of propylene glycol was added thereto, and ethylene glycol was used as a crosslinking agent. A mixed solution obtained by mixing 0.18 parts of diglycidyl ether and 3.6 parts of ion-exchanged water was added and uniformly mixed to obtain a mixture. The water content of the mixture was 6%. Thereafter, the mixture was heated at 130 ° C. for 30 minutes using a ventilation dryer (open to the atmosphere) to obtain absorbent resin particles (RB-3).

  Then, while stirring 100 parts of the obtained absorbent resin particles (RB-3) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.6 parts of sodium citrate as a chelating agent and A liquid mixture obtained by mixing 2.4 parts of ion-exchanged water was added to obtain comparative absorbent resin particles (R-3).

<Comparative Example 4>
Using the absorbent resin particles (B-1) obtained in Example 1 as they were, comparative absorbent resin particles (R-4) were obtained.

<Comparative Example 5>
While 100 parts of the absorbent resin particles (B-1) obtained in Example 1 were stirred at high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 2.0 parts of propylene glycol was added thereto, and ethylene was used as a crosslinking agent. A mixed solution obtained by mixing 2.0 parts of glycol diglycidyl ether and 40 parts of ion-exchanged water was added and uniformly mixed to obtain a mixture. The water content of the mixture after uniform mixing was 28%. Thereafter, the mixture was heated at 130 ° C. for 30 minutes in a ventilation dryer (open to the atmosphere) to obtain absorbent resin particles (RC-5).

  Then, while stirring 100 parts of the obtained absorbent resin particles (RC-5) at a high speed (high-speed stirring turbulizer manufactured by Hosokawa Micron: 2,000 rpm), 1.6 parts of sodium citrate and 2 parts of ion-exchanged water were added thereto. A mixed solution obtained by mixing .4 parts was added to obtain comparative absorbent resin particles (R-5).

<Comparative Example 6>
Comparative Example 5 was repeated 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. Absorbent resin particles (R-6) for use. The water content of the mixture containing the water-absorbent resin particles (B-1) and the crosslinking agent was 6%.

<Comparative Example 7>
Comparative Example 5 was repeated 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) were obtained. The water 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 performed except that 40 parts of ion-exchanged water used in post-crosslinking the absorbent resin particles (B-1) in Example 1 was changed to 25 parts of ion-exchanged water, and a comparative sample was used. 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 of the obtained absorbent resin particles (P-1) to (P-9) and comparative absorbent resin particles (R-1) to (R-8) in ion-exchanged water, absorption of ion-exchanged water Evaluation results of index, water retention, yellowness after leaving for 28 days in an atmosphere of 70 ± 5 ° C. and relative humidity of 80 ± 3%, gel permeation speed, gel permeation speed after breakability test, and permeation retention rate Are shown in Table 1.

  From the results shown in Table 1, it can be seen that the absorbent resin particles of the present invention are excellent in gel flow rate and small in the absorption capacity of ion-exchanged water and the absorption index of ion-exchanged water. On the other hand, in the comparative example, even if the gel flow rate is good, the ion exchange water absorption index is large, or the gel flow rate is inferior even if the ion exchange water absorption index is small. That is, it was found that the example had a significant difference from the comparative example from the viewpoint of compatibility between the gel flow rate and the absorption capacity of the small 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 for a water-absorbent article into which a large amount of water may enter. Therefore, it is favorably used for sanitary articles such as napkins (such as sanitary napkins), 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 articles, but also for various uses such as a waterproofing agent and artificial snow.

DESCRIPTION OF SYMBOLS 1 Physiological saline 2 Hydrous gel particle 3 Cylinder 4 Scale line 60 ml from the bottom 5 Scale line 40 ml from the bottom 6 Wire mesh 7 Cock 8 Round wire mesh 9 Pressure shaft 10 Weight

Claims (13)

  Absorbent resin particles obtained by crosslinking a resin particle 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 the absorbent resin particles immersed in ion-exchanged water absorb water per unit weight. The weight of the ion-exchanged water [the water absorption capacity in the ion-exchanged water] is 10 to 120 (g / g), and the absorbent resin particles compressed by applying a weight after being immersed in a physiological saline for 30 minutes to swell. Absorbent resin particles having a velocity [absorbent resin particle gel flow rate] of 350 (ml / min) or more when physiological saline passes.   The absorbent resin particles according to claim 1, wherein the shape of the absorbent resin particles is irregularly crushed. [Water absorption capacity in ion-exchanged water] and weight of physiological saline absorbed by 1.00 g of absorbent resin particles immersed in physiological saline [water retention amount of absorbent resin particles with respect to physiological saline] The absorbent resin particle according to claim 1, wherein the ion-exchanged water absorption index defined by the following (formula 3) is 1.0 to 6.0.
(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) (Equation 3)   After standing for 28 days in an atmosphere of 70 ± 5 ° C. and 80 ± 3% relative humidity, the yellow color is measured using a simplified spectral colorimeter according to the method described in JIS K7373 Plastics—Method for Determining Yellowness and Yellowing Degree. The absorbent resin particles according to any one of claims 1 to 3, wherein the degree is 20 or less.   The absorbent resin particles according to any one of claims 1 to 4, wherein a water retention amount of the absorbent resin particles in physiological saline is 10 to 20 (g / g).   The absorbent resin particles according to any one of claims 1 to 5, further comprising a chelating agent (B). The absorbent resin particles according to any one of claims 1 to 6, wherein a gel permeation retention rate obtained by the following (Formula 4) is 70% or more.
(Gel permeation retention rate) = 100 × ([Gel permeation rate of absorbent resin particles after breakability test]) / ([Gel permeation rate of absorbent resin particles before breakability test]) (Equation 4)
In the (Equation 4), the [gel flow rate of the absorbent resin particles] before the breakability test is determined by immersing the gel in physiological saline for 30 minutes to swell without performing the breakability test described below, and then applying a load. This is the speed at which physiological saline passes through the compressed absorbent resin particles. [Geling rate of absorbent resin particles] after the fragility test is as follows: 30 g of the absorbent resin particles are charged into a 3 L round separable flask, and a 6 mm hole is formed at the center of the upper part of the separable flask. A nylon net having a mesh size of 63 μm is laid, and a four-port separable cover is set thereon. Next, a stainless steel (outer diameter 6 mm, inner diameter 4 mm) tube was inserted from the main tube of the four-port separable cover for a 3 L round separable flask, and the stainless steel tube penetrated the nylon net, and the tip was the separable flask. Set so that the position is 45 mm from the bottom. A urethane tube (length 1500 mm, inner diameter 8.5 mm) is attached to the other end of the stainless steel tube, connected to an air line that can achieve a pressure of 0.3 MPa or more, and an air line is opened at a pressure of 0.2 MPa. A breakability test is performed by air blowing for a minute, and then the absorbent resin particles taken out are immersed in physiological saline for 30 minutes to be swollen, and then compressed by applying a load. The speed at which the saline solution passes.   The absorption according to any one of claims 1 to 7, wherein the content of the crosslinking agent (b) is 0.2 to 5% by weight based on the total weight of the vinyl monomer (a) constituting the crosslinked polymer (A). Resin particles.   The absorbent resin particles according to any one of claims 1 to 8, 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 absorber containing the absorbent resin particles according to claim 1.   An absorbent article containing the absorbent body according to claim 10.   A mixture containing the vinyl monomer (a) and the resin particles containing the cross-linked polymer (A) having the cross-linking agent (b) as an essential constituent unit and the post-crosslinking agent (c) is reacted to form the resin particles. The method for producing absorbent resin particles according to any one of claims 1 to 9, further comprising a step of post-crosslinking, wherein the water content of the mixture is 22 to 90% by weight. The method for producing absorbent resin particles according to claim 12, wherein the resin particles containing the crosslinked polymer (A) are reacted with a post-crosslinking agent (c) in a sealed state.

Images