JP2010253283A - Water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-absorbing resin suitable for use in an absorber and an absorbent article which permit the thickness to be reduced without causing a problem in an actual use condition. <P>SOLUTION: The water-absorbing resin 9 shows a pressure absorption quantity of 10 g/g or below of artificial urine 30 seconds later from the start of absorption and shows a pressure absorption quantity of 20 g/g or above of the artificial urine 30 minutes later from the start of absorption. The water-absorbing resin 9 is combined with hydrophilic fibers to make the absorber. In the absorber, the water-absorbing resin 9 accounts for 30 wt.% or higher and lower than 100 wt.% of the total weight of the absorber. The absorber forms an absorbent article by being held between a liquid-permeable sheet and a liquid-impermeable sheet. The water-absorbing resin 9 is finished hydrophobic and preferably be given surface bridging in addition to the finish. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an absorbent body used for sanitary materials such as disposable diapers, incontinence pads, sanitary napkins, and a water absorbent resin suitable for incorporation into absorbent articles.

  Absorbent articles such as disposable diapers, incontinence pads and sanitary napkins are placed between a flexible liquid-permeable sheet placed on the side in contact with the body and a liquid-impermeable sheet placed on the opposite side in contact with the body. Furthermore, it has a structure in which an absorber that absorbs and retains an aqueous liquid such as urine or body fluid is retained.

  The absorbent body is composed of hydrophilic fibers made of cotton-like pulp obtained from wood and a water-absorbing resin. The aqueous liquid passes through the liquid permeable sheet made of a nonwoven fabric or the like and is absorbed by the absorber. The absorbed aqueous liquid is temporarily held by the hydrophilic fiber, and is transferred to and held by the water absorbent resin.

  The hydrophilic fiber and the water-absorbent resin in the absorbent body have different roles in absorbing and holding the aqueous liquid.

  First, the hydrophilic fiber has a feature that the water absorption amount per unit amount is small and the absorbed aqueous liquid is easily released when pressure is applied, but the water absorption speed is very fast and the liquid diffusibility is good. Therefore, the hydrophilic fiber has a role of holding the aqueous liquid until the water absorbent resin absorbs the aqueous liquid and diffusing the aqueous liquid in the absorbent body. Furthermore, the swollen water-absorbing resin is deformed to close gaps between the particles, and also has a role of preventing gel blocking that hinders the flow of liquid through the gaps between the particles.

  On the other hand, the water-absorbent resin is characterized by a large amount of water absorption per unit amount. Therefore, the water-absorbent resin has a role of absorbing and holding the aqueous liquid held and diffused by the hydrophilic fiber.

  Due to the difference in characteristics, the ratio between the hydrophilic fiber and the water-absorbing resin in the absorbent body is a factor that greatly affects the water-absorbing characteristics of the absorbent body, such as the absorption / diffusibility of aqueous liquid and the amount of reversal. That is, when the ratio of the hydrophilic fibers is large, the absorbent body has good diffusibility of the aqueous liquid, but the water absorption amount is small and the reversion amount is large. Conversely, if the proportion of the water-absorbent resin is large, the amount of water absorption is large and the amount of reversal decreases, but gel blocking due to the water-absorbent resin is likely to occur, so the diffusibility of the aqueous liquid deteriorates and the absorber is effective Can no longer be used.

  In recent years, absorbent articles such as paper diapers, incontinence pads, sanitary napkins and the like have been made thinner. That is, in the absorbent body composed of hydrophilic fibers and a water-absorbent resin, the proportion of hydrophilic fibers that are bulky and have a low ability to retain aqueous liquid is reduced, and the proportion of the water-absorbent resin that is small in volume and has a high ability to retain aqueous liquid. By increasing the thickness, it is possible to reduce the thickness of the absorbent article without reducing the water absorption amount.

  However, if the proportion of the water-absorbent resin in the absorbent body is increased to reduce the thickness of the absorbent article, gel blocking is likely to occur relatively early after the start of water absorption due to the above-described reason, and the diffusibility of the aqueous liquid deteriorates. Thus, the absorber becomes difficult to be effectively used, and the aqueous liquid is absorbed only in a small area of the absorber. For this reason, in the actual use state, since the total amount of the aqueous liquid that can be absorbed by the absorber becomes small, there is a problem that the amount of reversion increases without being absorbed and the urine leaks.

  Therefore, an object of the present invention is to provide a water-absorbent resin suitable for incorporation into an absorbent body and an absorbent article that can achieve a reduction in thickness without causing problems in actual use conditions.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors paid attention to the relationship between the pressurized water absorption amount at the beginning of water absorption and the pressurized water absorption amount at the latter stage of water absorption, and the water absorption characteristics of the absorbent article. To find out that the above problems can be solved by using a water-absorbing resin having a pressurized water absorption amount at the start of the initial phase that is equal to or less than a specific value and that has a pressurized water absorption amount at or later than the specific value. It came.

  That is, in the present invention, the pressure water absorption amount of the artificial urine 30 seconds after the start of water absorption is 10 g / g or less, and the water absorption amount of the artificial urine 30 minutes after the start of water absorption is 20 g / g or more. A functional resin is provided.

  In the water-absorbent resin of the present invention, the pressurized water absorption amount of the artificial urine 30 seconds after the start of water absorption is 5 g / g or less, and the pressurized water absorption amount of the artificial urine 30 minutes after the start of water absorption is 30 g / g or more. The saturated water absorption with respect to physiological saline is preferably 40 g / g or more.

  Moreover, it is preferable that the weight average particle diameter of the water absorbent resin of the present invention is 200 to 600 μm.

  Furthermore, the water-absorbing resin of the present invention is preferably subjected to a hydrophobic treatment, and in addition to the hydrophobic treatment, it is preferable to perform surface crosslinking.

  In constructing an absorbent body by combining the water absorbent resin of the present invention with hydrophilic fibers, the proportion of the water absorbent resin is preferably in the range of 30% by weight or more and less than 100% by weight of the total weight of the absorbent body. Moreover, in order to comprise an absorbent article using such an absorber, the absorber described above is held between the liquid permeable sheet and the liquid impermeable sheet.

  In the absorbent article (absorber) incorporating the water-absorbent resin of the present invention, the water-absorbent resin has the above-described characteristics. Therefore, in an actual use state, the absorbent article has excellent diffusibility and suppresses the amount of reversion. Thinning of the (absorber) can be achieved.

  That is, the hydrophilic fiber has a very high water absorption rate for the aqueous liquid and is excellent in diffusibility but has a low retention capacity, while the water absorbent resin is excellent in the retention capacity of the aqueous liquid, but is inferior in diffusibility. For this reason, it is preferable that the hydrophilic fibers absorb and diffuse the aqueous liquid, particularly in the initial stage where the absorbent article absorbs the aqueous liquid, and the water absorbent resin does not impede the absorption and diffusion functions of the hydrophilic fibers as much as possible. Is desirable. Since the water-absorbing resin of the present invention has a low initial absorption rate, in the initial absorption stage, the aqueous liquid is diffused widely using hydrophilic fibers, and then the aqueous liquid is quickly absorbed from the hydrophilic fibers. For this reason, when the absorbent article absorbs the aqueous liquid, the quick absorption / diffusion function of the hydrophilic fiber and the high holding ability of the aqueous liquid of the water absorbent resin can be effectively used. As a result, the absorbent article (absorber) has excellent performance (water absorption characteristics) such as maintaining extremely high liquid diffusibility and water absorption, while suppressing the occurrence of problems in actual use conditions. In addition, it is possible to achieve a thinner absorbent article (absorber).

It is a schematic diagram which shows schematic structure of the apparatus for measuring pressurized water absorption.

  The absorbent body and absorbent article using the water absorbent resin of the present invention will be described below. Examples of absorbent articles include paper diapers, incontinence pads, sanitary napkins, and the like, but the present invention is not limited to these.

  The absorbent article incorporating the water-absorbent resin of the present invention includes a liquid-permeable sheet (top sheet) that can pass an aqueous liquid, and a liquid-impermeable sheet (back sheet) that does not pass an aqueous liquid. In between, it has the structure which hold | maintained the absorber which absorbs and hold | maintains an aqueous liquid. The liquid permeable sheet is disposed on the side that contacts the body, and the liquid impermeable sheet is disposed on the side that does not contact the body.

  Examples of the liquid permeable sheet include, but are not limited to, a nonwoven fabric made of polyethylene, polypropylene, polyester, polyamide, or the like, or a porous synthetic resin sheet.

  Examples of the liquid-impermeable sheet include, but are not limited to, synthetic resin films made of polyethylene, polypropylene, polyvinyl chloride, and the like, and films made of composite materials of these synthetic resins and nonwoven fabrics.

  The absorber is composed of a hydrophilic fiber and a water absorbent resin. The proportion of the water-absorbent resin in the absorbent body is 30% by weight or more and less than 100% by weight, preferably 40% by weight or more and less than 100% by weight, more preferably, in order to achieve thinning of the absorbent article. 50 wt% or more and less than 100 wt%, most preferably 60 wt% or more and less than 100 wt%. As the structure of the absorbent body, for example, a mixing structure in which a water-absorbing resin and a hydrophilic fiber are uniformly blended, a sandwich structure in which a water-absorbing resin is held between layered hydrophilic fibers, or a water-absorbing resin and a hydrophilic fiber are used. Examples include structures wrapped with tissue, but are not limited to these. In addition, in the absorber, the synthetic fiber may be included as a reinforcing material.

  Known hydrophilic fibers include cellulose fibers such as cotton-like pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood, and artificial cellulose fibers such as rayon and acetate. Moreover, you may contain synthetic fibers, such as polyamide, polyester, and polyolefin. The hydrophilic fiber is not limited to these.

  The water-absorbent resin of the present invention has a pressure water absorption amount of 10 g / g or less, preferably 5 g / g or less, more preferably 0.1 to 5 g / g after 30 seconds from the start of water absorption. 30 minutes after, the pressure water absorption amount of the artificial urine is 20 g / g or more, preferably 30 g / g or more, and more preferably 30 to 70 g / g. In the water absorbent resin of the present invention, the saturated water absorption amount with respect to physiological saline is 40 g / g or more, preferably 40 to 100 g / g, more preferably 40 to 90 g / g, and further preferably 40 to 80 g / g. This is because if the pressurized water absorption amount or saturated water absorption amount after a certain time has elapsed since the start of water absorption is too low, the absorption amount of the absorber becomes too low and the object of the present invention cannot be achieved.

Here, the pressurized water absorption amount for artificial urine and the saturated water absorption amount for physiological saline referred to in the present invention are those measured by the method described later. Moreover, the artificial urine in the present invention, with respect to 100 parts by weight of distilled water, 1 part by weight of NaCl, CaCl ₂ · 2H ₂ O 0.03 parts by weight, MgCl ₂ · 6H ₂ O 0.06 parts by weight The physiological saline referred to in the present invention refers to a 0.9% by weight sodium chloride aqueous solution.

  The water-absorbent resin is mainly used for absorbent articles such as disposable diapers, and needs to absorb a large amount of aqueous liquid without inhibiting diffusion of the aqueous liquid in a composite with hydrophilic fibers. Moreover, since some load is applied to the water absorbent resin when the absorbent article is used, the water absorbent resin used for the absorbent article has the above-described performance under a certain amount of pressure. Required.

  In contrast, the water-absorbing resin of the present invention has a relatively small amount of pressurized water absorption 30 seconds after the start of water absorption, so that gel blocking is unlikely to occur. Immediately after the start of water absorption, diffusion of the aqueous liquid becomes dominant, and water absorption starts. After 30 minutes, the water absorption is dominant. Therefore, the absorber is configured based on an evaluation that takes into consideration the composite state of the water-absorbent resin and the hydrophilic fiber, and is extremely practical with excellent diffusibility and suppressed reversion. In addition, as a result of having such characteristics, when the absorber is used for absorbent articles, it is possible to sufficiently diffuse and absorb the aqueous liquid even if the proportion of the water absorbent resin is increased, thus avoiding the conventional problems However, it is possible to reduce the thickness of the absorbent article.

  The water-absorbent resin of the present invention preferably has a weight-average particle diameter in the range of 200 to 600 μm, and more preferably in the range of 300 to 600 μm, in order to suppress the occurrence of gel blocking and the degree of foreign material feeling felt by the user. Is more preferable. If the weight average particle diameter of the water-absorbent resin is smaller than 200 μm, the proportion of small particles increases, and not only the handling of the powder deteriorates due to powdering but also the gel blocking tends to occur. This is not preferable because it is difficult to achieve. On the other hand, if the weight average particle diameter of the water absorbent resin is larger than 600 μm, when the water absorbent resin is adopted in an absorbent article such as a diaper, the user feels a foreign object and can use the absorbent article comfortably. It is not preferable because it cannot be performed.

  Examples of the water-absorbing resin of the present invention include a crosslinked polyacrylic acid partial neutralized product, a neutralized product of starch-acrylic acid graft polymer, and a hydrolyzate of starch-acrylonitrile graft polymer.

  Such a water-absorbing resin is, for example, one or more kinds of monocarboxylic acids selected from unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid and itaconic acid, or neutralized products thereof. After polymerizing or copolymerizing the polymer, the polymer is obtained by adjusting the polymer to a desired weight average particle diameter by performing operations such as pulverization and classification as necessary. As the monomer, acrylic acid and a neutralized product thereof are preferable because they are inexpensive and easily available.

  The polymerization method that can be employed as the method for producing the water-absorbent resin of the present invention is not particularly limited, and various generally known polymerization methods such as reverse phase suspension polymerization method and aqueous solution polymerization method should be adopted. Can do.

  The reverse phase suspension polymerization method as an example of the production of the water absorbent resin of the present invention will be described below.

  In the reversed-phase suspension polymerization method, polymerization is performed by using, for example, a polymerization initiator in a state where an aqueous monomer solution is dispersed in an organic solvent in the presence of a dispersion stabilizer.

  A hydrocarbon solvent is used as the organic solvent. The hydrocarbon solvent used here is an aliphatic hydrocarbon solvent or an alicyclic hydrocarbon solvent. Examples of the aliphatic hydrocarbon solvent include n-hexane and n-heptane. Examples of the alicyclic hydrocarbon solvent include cyclopentane, methylcyclopentane, cyclohexane and methylcyclohexane. Among these hydrocarbon solvents, preferred are n-hexane, n-heptane, and cyclohexane, which are industrially constant in quality, easily available, and inexpensive. In addition, you may use a hydrocarbon solvent in mixture of 2 or more types.

  Examples of the monomer aqueous solution include an unsaturated carboxylic acid aqueous solution. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, β-hydroxyacrylic acid, β-acryloxypropionic acid, and salts thereof. The concentration of the monomer in the monomer aqueous solution is, for example, 10 wt% to saturated wt%, and more preferably 25 wt% to saturated wt%.

  Examples of the salt constituting the unsaturated carboxylate include alkali metal salts, alkaline earth metal salts, ammonium salts and the like, and alkali metal salts such as sodium and potassium are particularly preferably used.

  The unsaturated carboxylic acid aqueous solution may contain a copolymer component other than the unsaturated carboxylic acid monomer. Examples of the copolymer component include (meth) acrylamide, N-substituted (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) ) Nonionic hydrophilic group-containing monomers such as acrylates; N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, etc. An amino group-containing unsaturated monomer or a quaternized product thereof may be mentioned, but the copolymerization component is not particularly limited. Further, starch, cellulose and their derivatives, water-soluble polyacrylic acid (salt) and their cross-linked products, hydrophilic polymers such as polyvinyl pyrrolidone and polyvinyl alcohol may be added to these unsaturated carboxylic acid aqueous solutions. Good.

  Examples of the dispersion stabilizer include nonionic surfactants such as sorbitan fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitol fatty acid ester, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Two or more kinds of such dispersion stabilizers may be mixed and used.

  A polymer dispersion aid may be used together with the dispersion stabilizer. These may be used in combination with a dispersion stabilizer before polymerization, or may be added after polymerization. Examples of the polymer dispersing aid include ethyl cellulose, ethyl hydroxyethyl cellulose, oxidation-modified polyethylene, maleic anhydride-modified polyethylene, maleic anhydride-modified polybutadiene, and maleic anhydride-modified EPDM (ethylene / propylene / diene / terpolymer). .

  The amount of the dispersion stabilizer and / or polymer dispersion aid used is usually 0.1 to 5% by weight, preferably 0.2 to 3% by weight, based on the unsaturated carboxylic acid aqueous solution. When the amount used is less than 0.1% by weight, dispersion is insufficient. On the contrary, even if it exceeds 5% by weight, an effect commensurate with it cannot be obtained.

  As the polymerization initiator, commonly used water-soluble radical polymerization initiators such as potassium persulfate, ammonium persulfate, and sodium persulfate are suitable, and they can be used as redox polymerization initiators using these in combination with sulfites. It is. The amount of the polymerization initiator used is preferably in the range of 0.001 mol% to 2 mol%, more preferably in the range of 0.01 mol% to 0.5 mol% with respect to the monomer.

  Although superposition | polymerization temperature changes also with the kind of polymerization initiator to be used, it is 20-110 degreeC normally, Preferably it is 40-80 degreeC. When the polymerization temperature is lower than 20 ° C., the polymerization rate is lowered and the polymerization time becomes longer, which is not economical. On the other hand, when the polymerization temperature is higher than 110 ° C., it is difficult to remove the heat of polymerization and smooth. It becomes difficult to carry out the polymerization reaction.

  The water-absorbent resin of the present invention is preferably cross-linked inside by reacting or copolymerizing with a plurality of polymerizable unsaturated groups or a crosslinking agent having a plurality of reactive groups. The water-absorbing resin may be a self-crosslinking type that does not require a crosslinking agent.

  As the crosslinking agent, for example, as the polymerizable crosslinking agent, di- or tri (meth) acrylic esters of polyols such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin. Unsaturated polyesters obtained by reacting the above polyols with unsaturated acids such as maleic acid and fumaric acid; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; polyepoxide and (meth) acrylic Ditri (meth) acrylic acid esters obtained by reacting with an acid; poly (isocyanates) such as tolylene diisocyanate and hexamethylene diisocyanate obtained by reacting hydroxyethyl (meth) acrylate Data) acrylic acid carbamic esters; allylated starch, allylated cellulose, diallyl phthalate, N, N ', N "- triallyl diisocyanate rate, and divinylbenzene.

  Among these, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, propylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, diallyl phthalate, N, N ′, N ″ -triallyl isocyanurate, N N'-methylenebisacrylamide and the like are usually used.

  On the other hand, examples of the crosslinking agent utilizing the reaction with the unsaturated carboxylic acid or the carboxyl group in the polymer include a diglycidyl ether compound, an isocyanate compound, and a haloepoxy compound. Among these, the diglycidyl ether compound is particularly preferable. Is suitable.

  Specific examples of the diglycidyl ether compound include (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether. Among them, polyethylene glycol diglycidyl ether is the most suitable result. give. Examples of the haloepoxy compound include epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and the like. Examples of the isocyanate compound include 2,4-tolylene isocyanate and hexamethylene diisocyanate. These crosslinking agents may be used alone or in combination of two or more. Of the exemplified compounds, it is more preferable to use a compound having a plurality of polymerizable unsaturated groups as a crosslinking agent.

  The amount of the crosslinking agent used to crosslink the interior of the water absorbent resin is 0.001 to 3% by weight, preferably 0.003 to 2% by weight, based on the total amount of monomers when producing the water absorbent resin. More preferably, it is 0.005 to 1 weight%. When the amount of the crosslinking agent used is less than 0.001% by weight, the gel strength at the time of water absorption of the water-absorbent resin is lowered and cannot be achieved. On the other hand, when the amount exceeds 3% by weight, the water absorption is extremely reduced. Absent.

  The water-absorbent resin of the present invention is preferably subjected to a hydrophobic treatment or surface crosslinking in addition to the hydrophobic treatment.

  Here, when the hydrophobic treatment is performed, the water-absorbent resin is less likely to swell during initial water absorption, and gel blocking is less likely to occur, so that the diffusibility of the aqueous liquid is improved. On the other hand, the surface cross-linking means that the surface layer of the water-absorbent resin particles is cross-linked and the degree of cross-linking of the surface layer is increased as compared with the inner layer. For this reason, the surface-crosslinked particles have higher surface layer strength than those not surface-crosslinked, so that even when liquid is taken into the particles, they are not easily deformed and gel blocking is unlikely to occur. Therefore, the diffusibility at the time of water absorption can be improved, the absorber can be used effectively, and the amount of reversion can be reduced. Therefore, if hydrophobic treatment or surface cross-linking is applied, at the initial stage of water absorption, diffusion of liquid can be dominant, and the amount of pressurized water absorption and saturation water absorption after a certain time (for example, 30 minutes) has elapsed since the start of water absorption. A large amount can be secured.

  Hydrophobic treatment is performed by, for example, dissolving a hydrophobic material in various solvents, or by melting it by heating, spraying and drying the water-absorbent resin, or coating the hydrophobic material, or manufacturing the water-absorbent resin. It can carry out by superposing | polymerizing and coating in presence of. In the present invention, the method of hydrophobic treatment is not limited to these.

  The amount of the hydrophobic material added varies depending on the type, but is preferably in the range of 0.001 to 10 parts by weight with respect to 100 parts by weight of the water absorbent resin. When the amount used is less than 0.001 part by weight, the effect is insufficient. Conversely, when it exceeds 10 parts by weight, an economic effect corresponding to the amount is not seen.

  Examples of the hydrophobic material include substantially water-insoluble materials such as higher aliphatic hydrocarbons such as n-dodecane, n-hexadecane, and n-heptadecane, and higher grades such as dodecan-1-ol and hexadecan-1-ol. Higher aliphatic compounds such as fatty alcohols, higher fatty acid esters such as sorbitan fatty acid esters, polyglycerin fatty acid esters, sorbitol fatty acid esters, and sucrose fatty acid esters; higher fatty acid amides such as lauric acid amide, oleic acid amide, and erucic acid amide Polyolefins such as polyethylene, polypropylene, ethylene / vinyl acetate copolymer, oxidation modified polyethylene, maleic anhydride modified polyethylene, maleic anhydride modified polybutadiene, maleic anhydride modified EPDM (ethylene propylene diene terpolymer); Polyamides such as polyethylene terephthalate; Cellulose derivatives such as cellulose acetate, cellulose propionate, cellulose butyrate, ethyl cellulose, benzyl cellulose, ethyl hydroxyethyl cellulose; Hydrophobized inorganic powder such as hydrophobic silica, etc. Is mentioned. These may be used alone or in combination of two or more. Of these, fatty acid esters are preferable, and fatty acid esters having HLB of 5 or less, preferably HLB of 4 or less, and more preferably HLB of 3 or less are particularly preferable.

  As the surface cross-linking agent, one capable of reacting with a carboxyl group in the water-absorbent resin is used. For example, epoxy compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, (poly) propylene glycol diglycidyl ether, glycidol; epichlorohydrin, epibromhydrin, α-methyl epichlorohydride Halogenated epoxy compounds such as phosphorus; (poly) ethylene glycol, (poly) propylene glycol, 1,3-propanediol, (poly) glycerin, diols, pentanediols, hexanediols, cyclohexanediols, trimethylolpropane , Diethanolamine, triethanolamine, polyoxypropylene, pentaerythritol, sorbitol and other polyhydric alcohol compounds; ethylenediamine, diethylenetriamine, triethylenete Polyamines such as lamin, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polyamidepolyamine; polyisocyanate compounds such as 2,4-tolylene diisocyanate, hexamethylene diisocyanate; 1,2-ethylenebisoxazoline, etc. Polyvalent oxazoline compounds; silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltrimethoxysilane; hydroxides such as aluminum, magnesium, titanium, and polyvalent metal compounds such as chloride Although it is mentioned, it is not particularly limited.

  Of the above surface cross-linking agents, epoxy compounds and polyhydric alcohol compounds are more preferably used. These surface crosslinking agents may be used alone or in combination of two or more.

  The amount of the surface cross-linking agent used is 0.01 to 5% by weight, preferably 0.02 to 4% by weight, more preferably 0.03 to 3% by weight, based on the total amount of the monomers. If the amount of the crosslinking agent used is less than 0.01% by weight, the gel strength at the time of water absorption of the water-absorbent resin may be lowered and the purpose may not be achieved. On the other hand, if it exceeds 5% by weight, the amount of water absorption may be extremely reduced, which is not preferable.

  The timing for adding the surface crosslinking agent is not particularly limited as long as it is after the polymerization of the monomer, but it is preferable to add it in the presence of water. About the quantity of water, it is 1-300 weight part with respect to 100 weight part of water-absorbing-resin solid content, Preferably it is desirable that it is 5-200 weight part.

  The method for adding the surface cross-linking agent is, for example, a method in which a certain amount of water is distilled off from the water-containing polymer immediately after completion of the polymerization, or a surface cross-linking agent dispersed in a small amount of water is sprayed on a powdered water absorbent resin. However, it is not particularly limited.

  Hereinafter, while describing this invention with an Example and a comparative example, the measuring method is demonstrated about the measurement item in each Example and a comparative example.

  500 ml of n-heptane was added to a 1000 ml five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube. To this, 1.38 g of hexaglyceryl monobehenylate having an HLB of 13.1 was added and dispersed, and the mixture was heated to 50 ° C. and dissolved, and then cooled to 30 ° C.

  On the other hand, a 500 ml Erlenmeyer flask was prepared, and 92 g of an 80 wt% aqueous acrylic acid solution was added. While cooling with ice from the outside, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% to prepare a partially neutralized aqueous solution of acrylic acid. Furthermore, 0.46 g of hydroxyethyl cellulose was added and dissolved by stirring for 2 hours. Thereafter, 50.3 g of water and 0.11 g of potassium persulfate as a polymerization initiator were added to obtain an aqueous monomer solution.

  Next, the monomer aqueous solution is added to and dispersed in the five-necked cylindrical round bottom flask under stirring, and the system is sufficiently substituted with nitrogen. Went. After completion of the polymerization, water was distilled off from the hydrated gel by azeotroping with n-heptane. 92.0 mg of ethylene glycol diglycidyl ether dissolved in 4.6 g of water was added to the dehydrated hydrous gel, and the mixture was kept at 80 ° C. for 2 hours. Thereafter, 0.92 g of powdery ethylcellulose dispersed in 50 ml of n-heptane was added, and the mixture was further maintained for 1 hour. Thereafter, excess water and n-heptane were removed by distillation and dried, followed by classification with a 850 μm sieve to obtain a water absorbent resin (A).

  A water-absorbent resin (B) was obtained in the same manner as in Example 1 except that 0.92 g of powdered maleic anhydride-modified polyethylene was used instead of ethyl cellulose.

  A water absorbent resin (C) was obtained in the same manner as in Example 1 except that 0.92 g of sorbitan trioleate having an HLB of 1.8 was used instead of ethyl cellulose.

  500 ml of n-heptane was added to a 1000 ml five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube. To this, 1.38 g of hexaglyceryl monopehenylate having an HLB of 13.1 was added and dispersed, heated to 50 ° C. and dissolved, and then cooled to 30 ° C.

  On the other hand, two 500 ml Erlenmeyer flasks were prepared, and first, 92 g of an 80 wt% aqueous acrylic acid solution was added. While cooling with ice from the outside, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% to prepare a partially neutralized aqueous solution of acrylic acid. Further, 50.3 g of water and 0.11 g of polymerization initiator potassium persulfate were added to obtain a monomer aqueous solution (a) for the first stage polymerization. Next, 119.1 g of 80 wt% aqueous acrylic acid solution was added to another 500 ml Erlenmeyer flask, and 132.2 g of 30 wt% aqueous sodium hydroxide solution was added dropwise while cooling as described above. After the addition, 27.4 g of water and 0.14 g of potassium persulfate were added to obtain a monomer aqueous solution (b) for the second stage polymerization.

  Next, in the five-necked cylindrical round bottom flask, the monomer aqueous solution (a) for the first stage polymerization was added and dispersed under stirring, and the system was sufficiently replaced with nitrogen. The polymerization reaction was carried out for 1 hour. Thereafter, the polymerization slurry was cooled to 40 ° C., and a monomer aqueous solution (b) for the second stage polymerization was added. After addition of the entire amount, the system was sufficiently replaced with nitrogen again, and then the temperature was raised to 70 ° C. and the second stage polymerization reaction was carried out for 1 hour. After the completion of the second stage polymerization, water was distilled off from the hydrated gel with heating with n-heptane. 211.0 mg of ethylene glycol diglycidyl ether dissolved in 10.5 g of water was added to the dehydrated hydrogel, and the mixture was kept at 80 ° C. for 2 hours. Thereafter, 2.1 g of powdered maleic anhydride-modified polyethylene dispersed in 50 ml of n-heptane was added, and the mixture was further maintained for 1 hour. Thereafter, excess water and n-heptane were removed by distillation and dried, followed by classification with a 850 μm sieve to obtain a water absorbent resin (D).

  A water-absorbent resin (E) was obtained in the same manner as in Example 4 except that 1.0 g of powdered hydrophobic silica was used instead of maleic anhydride-modified polyethylene.

  500 ml of n-heptane was added to a 1000 ml five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube. To this, 0.92 g of sucrose fatty acid ester having an HLB of 3.0 was added and dispersed, heated to 55 ° C. and dissolved, and then cooled to 30 ° C.

  On the other hand, a 500 ml Erlenmeyer flask was prepared, and 92 g of an 80 wt% aqueous acrylic acid solution was added. While cooling with ice from the outside, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% to prepare a partially neutralized aqueous solution of acrylic acid. To this, 0.46 g of hydroxyethylcellulose was added and dissolved by stirring for 2 hours. Thereafter, 50.3 g of water and 0.11 g of potassium persulfate as a polymerization initiator were added to obtain an aqueous monomer solution.

  Next, the monomer aqueous solution is added to and dispersed in a five-necked cylindrical round bottom flask under stirring, and the inside of the system is sufficiently substituted with nitrogen. Then, the temperature is raised to 70 ° C. and a polymerization reaction is performed for 1 hour. went. After completion of the polymerization, water was distilled off from the hydrated gel with heating with n-heptane. 92.0 mg of ethylene glycol diglycidyl ether dissolved in 4.6 g of water was added to the dehydrated hydrous gel, and the mixture was kept at 80 ° C. for 2 hours. Thereafter, excess water and n-heptane were removed by distillation and dried, followed by classification with a 850 μm sieve to obtain a water absorbent resin (F).

  500 ml of n-heptane was added to a 1000 ml five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube. To this, 0.92 g of sucrose fatty acid ester having an HLB of 3.0 was added and dispersed, heated to 55 ° C. and dissolved, and then cooled to 30 ° C.

  On the other hand, two 500 ml Erlenmeyer flasks were prepared, and first, 92 g of an 80 wt% aqueous acrylic acid solution was added. While cooling with ice from the outside, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% to prepare a partially neutralized aqueous solution of acrylic acid. Further, 50.3 g of water and 0.11 g of polymerization initiator potassium persulfate were added to obtain a monomer aqueous solution (a) for the first stage polymerization. Next, 119.1 g of 80 wt% aqueous acrylic acid solution was added to another 500 ml Erlenmeyer flask, and 132.2 g of 30 wt% aqueous sodium hydroxide solution was added dropwise while cooling as described above. After the addition, 27.4 g of water and 0.14 g of potassium persulfate were added to obtain a monomer aqueous solution (b) for the second stage polymerization.

  Next, in the five-necked cylindrical round bottom flask, the whole amount of the monomer aqueous solution (a) for the first stage polymerization is added and dispersed under stirring, and the inside of the system is sufficiently replaced with nitrogen. The temperature was raised and the polymerization reaction was carried out for 1 hour. Thereafter, the polymerization slurry was cooled to 40 ° C., and a monomer aqueous solution (b) for the second stage polymerization was added. After addition of the entire amount, the system was sufficiently replaced with nitrogen again, and then the temperature was raised to 70 ° C., and the second stage polymerization reaction was carried out for 1 hour. After the completion of the second stage polymerization, water was distilled off from the hydrated gel with heating with n-heptane. 211.0 mg of ethylene glycol diglycidyl ether dissolved in 10.5 g of water was added to the dehydrated hydrogel, and the mixture was kept at 80 ° C. for 2 hours. Thereafter, excess water and n-heptane were removed by distillation and dried, followed by classification with a 850 μm sieve to obtain a water absorbent resin (G).

  As the operation after the completion of the second stage polymerization, 211.0 mg of ethylene glycol diglycidyl ether dissolved in 10.5 g of water was added to the dehydrated hydrogel and kept at 80 ° C. for 2 hours. The same operation as in Example 7 was performed except that 0.92 g of powdered ethylcellulose in which n-heptane was dispersed was added and held for 1 hour, and then excess water and n-heptane were removed by distillation and dried. The water absorbent resin (H) was obtained.

Comparative Example 1

  500 ml of n-heptane was added to a 1000 ml five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube. To this, 1.38 g of hexaglyceryl monopehenylate having an HLB of 13.1 was added and dispersed, heated to 50 ° C. and dissolved, and then cooled to 30 ° C.

  On the other hand, two 500 ml Erlenmeyer flasks were prepared, and first, 92 g of an 80 wt% aqueous acrylic acid solution was added. While cooling with ice from the outside, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% to prepare a partially neutralized aqueous solution of acrylic acid. Further, 50.3 g of water and 0.11 g of polymerization initiator potassium persulfate were added to obtain a monomer aqueous solution (a) for the first stage polymerization. Next, 119.1 g of 80 wt% aqueous acrylic acid solution was added to another 500 ml Erlenmeyer flask, and 132.2 g of 30 wt% aqueous sodium hydroxide solution was added dropwise while cooling as described above to neutralize 75 mol%. Then, 27.4 g of water and 0.14 g of potassium persulfate were added to obtain a monomer aqueous solution (b) for the second stage polymerization.

  Next, in the five-necked cylindrical round bottom flask, the whole amount of the monomer aqueous solution (a) for the first stage polymerization is added and dispersed under stirring, and the inside of the system is sufficiently replaced with nitrogen. The temperature was raised and the polymerization reaction was carried out for 1 hour. Thereafter, the polymerization slurry liquid was cooled, and the monomer aqueous solution (b) for second-stage polymerization that had been cooled in advance was added. After addition of the entire amount, the system was sufficiently replaced with nitrogen again, and the second stage polymerization reaction was carried out for 1 hour while maintaining the bath temperature at 70 ° C. After the completion of the second stage polymerization, water was distilled off from the hydrated gel with heating with n-heptane. 211.0 mg of ethylene glycol diglycidyl ether dissolved in 10.5 g of water was added to the dehydrated hydrogel, and the mixture was kept at 80 ° C. for 2 hours. Thereafter, excess water and n-heptane were removed by distillation and dried, followed by classification with a 850 μm sieve to obtain a water absorbent resin (I).

Comparative Example 2

  500 ml of n-heptane was added to a 1000 ml five-necked cylindrical round bottom flask equipped with a stirrer, reflux condenser, dropping funnel, thermometer and nitrogen gas introduction tube. To this, 1.84 g of sorbitan monolaurate having an HLB of 8.7 was added and dispersed, heated to 50 ° C. and dissolved, and then cooled to 30 ° C.

  On the other hand, a 500 ml Erlenmeyer flask was prepared, and 92 g of an 80 wt% aqueous acrylic acid solution was added. While cooling with ice from the outside, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% to prepare a partially neutralized aqueous solution of acrylic acid. Further, 50.3 g of water and 0.11 g of polymerization initiator potassium persulfate were added to obtain an aqueous monomer solution.

  Next, the monomer aqueous solution is added to and dispersed in a five-necked cylindrical round bottom flask under stirring, and the inside of the system is sufficiently substituted with nitrogen. Then, the temperature is raised to 70 ° C. and a polymerization reaction is performed for 1 hour. went. After completion of the polymerization, water was distilled off from the hydrated gel with heating with n-heptane. 92.0 mg of ethylene glycol diglycidyl ether dissolved in 4.6 g of water was added to the dehydrated hydrous gel, and the mixture was kept at 80 ° C. for 2 hours. Thereafter, excess water and n-heptane were removed by distillation and dried, followed by classification with a 850 μm sieve to obtain a water absorbent resin (J).

Pressurized water absorption :
The pressurized water absorption after 30 seconds and 30 minutes from the start of water absorption was performed using the measuring device X whose schematic configuration is shown in FIG.

  The measuring device X shown in FIG. 1 is placed on a balance 1, a bottle 2 placed on the balance 1, an air suction pipe 3, a conduit 4, a glass filter 5, and the glass filter 5. It consists of a measurement unit 6. The balance 1 is connected to a computer 7 so that the weight change can be recorded in seconds or minutes. The bottle 2 holds the artificial urine 8 therein, and the air suction pipe 3 is inserted into the opening at the top thereof, while the conduit 4 is attached to the trunk portion. The lower end of the air suction tube 3 is immersed in the artificial urine 8. The diameter of the glass filter 5 is 25 mm. As the glass filter 5, glass filter No. 1 (pore diameter 100-160 μm) was used. The bottle 2 and the glass filter 5 are communicated with each other by a conduit 4. The glass filter 5 is fixed at a slightly higher position with respect to the lower end of the air suction pipe 3. The measurement unit 6 includes a cylinder 60, a nylon mesh 61 attached to the bottom of the cylinder 60, and a weight 62. The inner diameter of the cylinder 60 is 2 cm. The nylon mesh 61 is formed to 200 mesh (eye size: 75 μm). A predetermined amount of water-absorbing resin 9 is uniformly distributed on the nylon mesh 61. The weight 62 is placed on the water absorbent resin 9 so that a load of 5 g can be uniformly applied to the water absorbent resin 9.

In the measuring apparatus X having such a configuration, first, a predetermined amount of artificial urine 8 and an air suction pipe 3 are placed in the bottle 2 to prepare for measurement. Artificial urine 8 was composed of 5934.6 g of distilled water, 60 g of NaCl, 1.8 g of CaCl ₂ .2H ₂ O, 3.6 g of MgCl ₂ .6H ₂ O, and colored with edible blue No. 1. Next, 0.10 g of the water absorbent resin 9 was uniformly spread on the nylon mesh 61 of the cylinder 60, and the weight 62 was placed on the water absorbent resin 9. The measuring unit 6 was placed on the glass filter 5 so that the center thereof coincided with the center of the glass filter 5.

  On the other hand, the weight of the artificial urine 8 in the bottle 2 (the weight of the artificial urine 8 absorbed by the water-absorbent resin 9) continuously from the time when the computer 7 connected to the electronic balance 1 is started and begins to absorb water. Wa (g) was recorded on the computer 7 in minutes, preferably in seconds, based on the value obtained from the balance 1. The pressure water absorption amount of the water absorbent resin 9 30 seconds and 30 minutes after the start of water absorption was obtained by dividing the weight Wa (g) at each time point by the weight of the water absorbent resin 9 (0.10 g).

Saturated water absorption :
2.0 g of the water-absorbent resin was dispersed in 500 g of physiological saline (0.9 wt% NaCl aqueous solution) in a 500 ml beaker and sufficiently swollen by gently stirring for 1 hour. On the other hand, the weight Wb (g) of a 75 μm standard sieve (corresponding to JIS-Z8801-1982) was measured, and the aqueous solution containing the swollen gel was filtered with a 75 μm standard sieve. The 75 μm standard sieve was allowed to stand for 30 minutes with the angle formed with respect to the horizontal being about 30 degrees, and excess physiological saline was removed from the water absorbent resin. The sieve weight Wc (g) including the swollen gel was measured, and the weight Wc (g) minus the weight Wb (g) of the 75 μm standard sieve was divided by the weight of the water absorbent resin (2.0 g). The saturated water absorption was calculated.

Weight average particle size :
100 g of the water-absorbent resin was weighed and its weight was defined as the charged amount Wd (g). Put the water-absorbing resin on the top sieve of 8 standard sieves corresponding to JIS-Z8801-1982 (mesh opening 850μm, 500μm, 355μm, 300μm, 250μm, 180μm, 106μm, stacked in order of bottom container) The weight We (g) of the sieve containing the water-absorbent resin was measured after vibrating for 10 minutes using a type sieve vibrator. The weight ratio of the water-absorbing resin remaining on each sieve is the weight Wg (g) of the water-absorbing resin remaining on the sieve by subtracting the weight Wf (g) of the sieve from the weight We (g) of the sieve containing the water-absorbing resin. ) Was measured, and the weight Wg (g) was divided by the charged amount Wd (g) and multiplied by 100. Then, the weight of the water-absorbent resin remaining on each sieve was measured, and based on the result, the weight average particle diameter at which the integrated weight was 50% by weight of the total weight was calculated by the following formula.

  In the formula, A is the cumulative value (g) when the weight is sequentially accumulated from the coarser particle size distribution, and the cumulative value at the point closest to 50% by weight is less than 50% by weight. And B is the knot opening (μm) when the integrated value is obtained. Further, D is the integrated value (g) when the integrated values are obtained in order from the coarser particle size distribution, and the integrated value of the point closest to 50% by weight is 50% by weight or more. Yes, and C is the knot opening (μm) when the integrated value is obtained.

Return amount and the diffusion length:
The amount of reversion and the diffusion length were measured in the state of the absorbent article. The absorbent article was produced by sandwiching the absorbent body with a nonwoven fabric having a size of 40 cm × 12 cm and a weight of 1 g and a polyethylene sheet having the same size and the same weight. The absorbent body is a tissue of the same size and weight after spraying water-absorbing resin and pulverized pulp (hydrophilic fiber) using a mixer and spraying the mixture onto a tissue having a size of 40 cm × 12 cm and a weight of 1 g. Were made into a sheet, and the whole was pressed by applying a load of 196 kPa.

  150 ml of artificial urine was poured in the vicinity of the center of the absorbent article over 1 minute and left for 5 minutes. Then, 20 sheets of filter paper (Toyo Filter Paper No. 2) cut to 10 cm x 10 cm are stacked and placed near the center of the absorbent article, and a 3.5 kg weight (bottom = 10 cm x 10 cm) is placed thereon for 3 minutes. Weighted. The amount of artificial urine absorbed by the filter paper was measured, and this was used as the reversal amount. Moreover, about the artificial urine absorbed by the absorbent article, the longitudinal extension of the absorbent article was measured, and this was defined as the diffusion length.

  With respect to the water absorbent resin (A) obtained in Example 1, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the method described above. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbing resin obtained in Example 1 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was prepared in the same manner as in Example 9, except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was prepared using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  With respect to the water absorbent resin (B) obtained in Example 2, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the method described above. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30% by weight using the above-described method using 8 g of the water-absorbing resin obtained in Example 2 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 11 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  For the water absorbent resin (C) obtained in Example 3, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the methods described above. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbing resin obtained in Example 3 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 13 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  For the water absorbent resin (D) obtained in Example 4, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the methods described above. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30% by weight using the above-described method using 8 g of the water-absorbent resin obtained in Example 4 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 15 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  With respect to the water absorbent resin (E) obtained in Example 5, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the methods described above. On the other hand, after producing an absorbent body having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbent resin obtained in Example 5 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 17 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  For the water absorbent resin (F) obtained in Example 6, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle size were measured by the methods described above. On the other hand, after preparing an absorbent body having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbing resin obtained in Example 6 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 19 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  For the water absorbent resin (G) obtained in Example 7, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the methods described above. On the other hand, after producing an absorbent body having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbent resin obtained in Example 7 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 21 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  For the water absorbent resin (H) obtained in Example 8, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the methods described above. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbing resin obtained in Example 8 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

  An absorbent article was produced in the same manner as in Example 23 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was produced using 15 g of the water absorbent resin and 10 g of the pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

Comparative Example 3

  With respect to the water absorbent resin (I) obtained in Comparative Example 1, the pressurized water absorption amount after 30 seconds, the pressurized water absorption amount after 30 minutes, the saturated water absorption amount, and the weight average particle diameter were measured by the method described above. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30 wt% by the above-described method using 8 g of the water-absorbing resin obtained in Comparative Example 1 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

Comparative Example 4

  In Comparative Example 3, an absorbent article was prepared in the same manner as in Comparative Example 3 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was prepared using 15 g of the water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

Comparative Example 5

  With respect to the water absorbent resin (J) obtained in Comparative Example 2, the pressurized water absorption after 30 seconds, the pressurized water absorption after 30 minutes, the saturated water absorption, and the weight average particle diameter were measured by the above-described methods. On the other hand, after producing an absorber having a weight of 26 g and a water-absorbing resin ratio of 30% by weight using the above-described method using 8 g of the water-absorbing resin obtained in Comparative Example 2 and 18 g of pulverized pulp, Absorbent articles were prepared from the absorbent and the amount of reversion and diffusion length were measured. These measurement results are shown in Table 1.

Comparative Example 6

  An absorbent article was prepared in the same manner as in Comparative Example 5 except that an absorbent body having a weight of 25 g and a water absorbent resin ratio of 60% by weight was prepared using 15 g of water absorbent resin and 10 g of pulverized pulp. The amount of reversion and the diffusion length were measured. The results are shown in Table 2.

  As is clear from Table 1 and Table 2, the absorbent article using the water absorbent resin having a small pressurized water absorption amount 30 seconds after the start of water absorption and a large pressurized water absorption amount 30 minutes after the start of water absorption is reversed. The amount is small and the diffusion length is large. Such a tendency appears in both cases where the concentration of the water-absorbent resin in the absorber is 30% by weight and 60% by weight. As described above, the absorbent article using the water absorbent resins (A) to (H) having a small initial water absorption amount and a large final water absorption amount exhibits excellent diffusibility even when the ratio of the resin in the absorber is large. In addition, it was confirmed that the amount of reversion was also reduced.

Evaluation

  As described above, the absorbent article using the water-absorbent resin of the present invention not only exhibits excellent diffusibility even when the proportion of the water-absorbent resin in the absorbent body is large, but also has a small amount of reversion. Therefore, the absorbent article can exhibit excellent performance (water absorption characteristics) capable of preventing leakage and giving a dry feeling in an actual use state.

X measuring device 1 balance 2 bottle 3 air suction pipe 4 conduit 5 glass filter 6 measuring part 60 cylinder (of measuring part)
61 Nylon mesh (for measuring part)
62 Weight (of measuring part)
7 Computer 8 Artificial urine 9 Water absorbent resin

Claims (6)

  A water-absorbing resin having a pressure water absorption amount of 10 g / g or less after 30 seconds from the start of water absorption and a pressure water absorption amount of 20 g / g or more after 30 minutes from the start of water absorption.   The pressurized water absorption amount of the artificial urine 30 seconds after the start of water absorption is 5 g / g or less, and the pressurized water absorption amount of the artificial urine 30 minutes after the start of water absorption is 30 g / g or more. Water absorbent resin.   The water absorbent resin according to claim 1 or 2, wherein a saturated water absorption amount with respect to physiological saline is 40 g / g or more.   The water-absorbent resin according to any one of claims 1 to 3, wherein the weight average particle diameter is 200 to 600 µm.   The water-absorbent resin according to any one of claims 1 to 4, which has been subjected to a hydrophobic treatment.   The water-absorbent resin according to claim 5, which is surface-crosslinked.