Manufacturing method of water-absorbent resin

Abstract

Provided is a method for producing a nonionic water-absorbent resin, which can suppress the charging of powder in the production of the resin. [Solution] A method for producing a water-absorbent resin, the method comprising the steps of: polymerizing a monomer component containing a non-crosslinkable monomer and a crosslinkable monomer; adding a surfactant to the product obtained in the polymerization step; drying the product obtained after the surfactant addition step; and pulverizing and / or classifying the product obtained in the drying step, wherein the monomer component contains 50 mol % or more of a nonionic non-crosslinkable monomer and 0.05 mol % or more of a crosslinkable monomer, and the surfactant is an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a water-absorbing resin, and more particularly to a method for producing a water-absorbing resin useful as an additive for cement, etc. [Background technology]

[0002] Water-absorbent resins are capable of absorbing and expanding hundreds to thousands of times their own weight in water, and are therefore widely used in various fields such as hygiene products, food, agriculture and forestry, civil engineering, etc. Widely used water-absorbent resins include polyacrylic acid, polymethacrylic acid, and neutralized salts thereof.

[0003] Aqueous solution polymerization is often used as a method for producing a water-absorbent resin, and the hydrogel polymer obtained by this method is dried and pulverized to obtain a powdered water-absorbent resin. Because absorbent resins are easily charged, there was a problem in that the powder would easily adhere to the production line during crushing and classification. To address this issue, a method using a surfactant is known as a method for preventing powder from becoming electrically charged, but Patent Document 1 discloses a technology that uses a powder of an inorganic compound containing zinc or calcium as a constituent element.

[0004] As mentioned above, water-absorbent resins are widely used in various fields, and it is known that when added to a cement composition, the water-absorbent resin absorbs a portion of the mixing water, thereby improving various physical properties of the hardened concrete.

[0005] Regarding cement additives containing a water-absorbing resin, Patent Document 2 discloses a cement additive containing a water-absorbing resin, wherein the water-absorbing resin is obtained by polymerizing a monomer mixture containing 50 mol % or more of a nonionic non-crosslinkable monomer and 0.1 mol % or more of a nonionic crosslinkable monomer, and the content of anionic monomers in the monomer mixture is 20 mol % or less. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 02-178332 [Patent Document 2] International Publication No. 2020 / 209057 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, cement additives containing water-absorbent resins have been disclosed in the past, but the present inventors have found that in the production of nonionic water-absorbent resins, powdered water-absorbent resins have a greater problem of adhesion due to electrostatic charge than ionic water-absorbent resins such as polyacrylic acid, and have felt the need to improve this.

[0008] The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide a method for producing a water-absorbent resin which can suppress electrification of powder in the production of a nonionic water-absorbent resin. [Means for solving the problem]

[0009] The present inventors have conducted various studies on the method for producing a nonionic water absorbent resin, and have found that the above-mentioned problems can be solved beautifully by adding an ionic surfactant and / or a polyoxyalkylene glycol type nonionic surfactant to a product obtained by polymerizing a monomer component containing a predetermined amount of a non-crosslinkable monomer and a crosslinkable monomer, and then pulverizing and / or classifying the product after drying, thereby suppressing the charging of the powder during pulverization and / or classification, and have arrived at the present invention.

[0010] The present invention includes the following method for producing a water-absorbent resin. [1] A method for producing a water-absorbent resin, the method comprising the steps of: polymerizing a monomer component containing a non-crosslinkable monomer and a crosslinkable monomer; adding a surfactant to a product obtained in the polymerization step; drying the product obtained after the surfactant addition step; and pulverizing and / or classifying the product obtained in the drying step, wherein the monomer component contains 50 mol % or more of a nonionic non-crosslinkable monomer and 0.05 mol % or more of a crosslinkable monomer, and the surfactant is an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant. [2] The method for producing a water-absorbent resin according to the above [1], wherein the ionic surfactant is an amphoteric surfactant. [3] The method for producing a water-absorbent resin according to the above [1] or [2], wherein the polyoxyalkylene glycol-type nonionic surfactant is a polyoxyalkylene sorbitan fatty acid ester. [4] The method for producing a water-absorbent resin according to any one of the above [1] to [3], wherein the nonionic non-crosslinkable monomer is at least one selected from the group consisting of a (meth)acrylamide-based monomer, an N-vinyl lactam-based monomer, a hydroxyl group-containing (meth)acrylate, and a vinyl cyanide-based monomer. [5] The method for producing a water-absorbent resin according to any one of the above [1] to [4], wherein an amount of the surfactant added in the surfactant addition step is 0.01 to 10 mass % relative to 100 mass % of the solid content of the product obtained in the polymerization step. [6] A cement additive comprising a water-absorbing resin and a surfactant, wherein the water-absorbing resin has structural units derived from a nonionic non-crosslinkable monomer and structural units derived from a crosslinkable monomer, the proportion of the structural units derived from the nonionic non-crosslinkable monomer being 50 mol % or more and the proportion of the structural units derived from the crosslinkable monomer being 0.05 mol % or more, and the surfactant being an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant. [7] The cement additive according to [6], wherein the ionic surfactant is an amphoteric surfactant. [8] The cement additive according to [6] or [7] above, wherein the polyoxyalkylene glycol-type nonionic surfactant is a polyoxyalkylene sorbitan fatty acid ester. [9] The cement additive according to any one of [6] to [8], wherein the nonionic non-crosslinkable monomer is at least one selected from the group consisting of (meth)acrylamide-based monomers, N-vinyl lactam-based monomers, hydroxyl group-containing (meth)acrylates, and vinyl cyanide-based monomers.

[10] The cement additive according to any one of [6] to [9], wherein the content of the surfactant is 0.01 to 10 mass % relative to 100 mass % of the solid content of the water-absorbing resin.

[11] A cement composition comprising the cement additive according to any one of [6] to

[10] above and cement. [Effects of the Invention]

[0011]

[0044] The method for producing a water absorbent resin of the present invention has the above-mentioned constitution, and can suppress charging of powder during pulverization and / or classification, and therefore, a water absorbent resin can be produced efficiently and the risk of dust explosion can be reduced, and the obtained water absorbent resin can be suitably used as an additive for cement, etc. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description and can be appropriately modified and applied within the scope of the present invention. Note that combinations of two or more of the individual preferred embodiments of the present invention described below also fall within the scope of preferred embodiments of the present invention.

[0013] [Method for producing water-absorbent resin] The method for producing a water absorbent resin of the present invention comprises the steps of: polymerizing a monomer component containing a non-crosslinkable monomer and a crosslinkable monomer; adding a surfactant to a product obtained in the polymerization step; drying the product obtained after the surfactant addition step; and pulverizing and / or classifying the product obtained in the drying step, wherein the monomer component contains 50 mol % or more of a nonionic non-crosslinkable monomer and 0.05 mol % or more of a crosslinkable monomer relative to 100 mol % of the monomer component, and the surfactant is an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant. Although nonionic water-absorbent resins are more easily charged than ionic water-absorbent resins, the use of the above-mentioned specific surfactants can sufficiently suppress the charging of the resin and sufficiently prevent the resin from adhering to equipment during pulverization and / or classification. By coating the resin surface with the above-mentioned specific surfactant, the surfactant on the resin surface adsorbs moisture in the air and forms a conductive layer, thereby reducing the electrostatic charge of the resin and thereby reducing the adhesion of the resin. Furthermore, the product obtained in the polymerization step is in a viscoelastic gel state and is likely to adhere to a drying net or the like during drying, but in the production method of the present invention, by coating the resin surface with the above-mentioned predetermined surfactant, it is possible to prevent the gel-like product from adhering to a drying net or the like used in the drying step. This also makes it possible to efficiently produce a water-absorbent resin. Furthermore, the composition containing the water absorbent resin obtained by the production method of the present invention contains the above-mentioned surfactant, and when this is used in a cement composition, it can improve the physical properties of concrete in the same way as when it is produced by a conventional production method.

[0014] (Polymerization process of monomer components) The polymerization step is not particularly limited as long as it polymerizes a monomer component containing 50 mol % or more of a nonionic non-crosslinkable monomer and 0.05 mol % or more of a crosslinkable monomer relative to 100 mol % of the monomer component, thereby obtaining a nonionic water-absorbing resin. The proportion of the nonionic non-crosslinkable monomer is preferably 50 to 99.95 mol%, more preferably 60 to 99.95 mol%, even more preferably 70 to 99.95 mol%, still more preferably 80 to 99.95 mol%, and particularly preferably 90 to 99.95 mol%, relative to 100 mol% of the monomer component. In one embodiment, the proportion of the nonionic non-crosslinkable monomer may be 99 mol % or less, 98 mol % or less, 97 mol % or less, 96 mol % or less, or 95 mol % or less. In this specification, 100 mol % of the monomer component means 100 mol % in total of the non-crosslinkable monomer and the crosslinkable monomer.

[0015] The monomer component may contain an ionic non-crosslinkable monomer, the proportion of which may be 49.95 mol % or less relative to 100 mol % of the monomer component. The proportion of the ionic non-crosslinkable monomer is preferably 40 mol % or less, more preferably 30 mol % or less, even more preferably 20 mol % or less, particularly preferably 10 mol % or less, and most preferably 5 mol % or less.

[0016] The monomer component contains 0.05 mol % or more of a crosslinkable monomer, and the resulting resin can thereby exhibit excellent water absorbency. The proportion of the crosslinkable monomer is preferably 0.05 to 3.0 mol %, more preferably 0.05 to 2.0 mol %, still more preferably 0.05 to 1.0 mol %, and particularly preferably 0.1 to 0.75 mol %, relative to 100 mol % of the monomer component.

[0017] The nonionic non-crosslinkable monomer is not particularly limited as long as it is a nonionic monomer that does not have a reactive group involved in crosslinking, but is preferably water-soluble. In this specification, a water-soluble monomer means that it dissolves in an amount of 5 g or more in 100 g of water at 25°C. The water-soluble nonionic non-crosslinkable monomer dissolves preferably in 100 g of water at 25° C. in an amount of 10 g or more, more preferably 50 g or more, and even more preferably 100 g or more.

[0018] Examples of water-soluble nonionic non-crosslinkable monomers include (meth)acrylamide monomers, N-vinyl lactam monomers, hydroxyl group-containing (meth)acrylates, unsaturated amine monomers, vinyl cyanide monomers, and unsaturated polyalkylene glycol monomers.

[0019] The (meth)acrylamide monomer is not particularly limited, but examples thereof include (meth)acrylamide, N-monomethyl(meth)acrylamide, N-monoethyl(meth)acrylamide, N,N-hydroxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc. Among these, (meth)acrylamide is preferred.

[0020] The N-vinyl lactam monomer is not particularly limited, but examples thereof include N-vinylpyrrolidone, N-vinyl-5-methylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, 1-(2-propenyl)-2-pyrrolidone, etc. Among these, N-vinylpyrrolidone is preferred. Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0021] The vinyl cyanide monomer is not particularly limited, but examples thereof include acrylonitrile and methacrylonitrile.

[0022] From the viewpoint of water absorption properties after a long period of time, the nonionic non-crosslinkable monomer may be hydrolyzed when immersed in an aqueous solution of pH 12.9 for 24 hours at 25° C. In this case, the nonionic non-crosslinkable monomer undergoes hydrolysis under strong alkaline conditions after 24 hours, and the nonionic non-crosslinkable monomer is likely to exhibit water absorption properties after a certain period of time (for example, after 2 hours). The hydrolysis of a nonionic non-crosslinkable monomer when it is immersed in an aqueous solution of pH 12.9 at 25°C for 24 hours can be confirmed by measuring the aqueous solution after 24 hours of immersion using liquid chromatography (LC). Examples of nonionic non-crosslinkable monomers that undergo such hydrolysis include hydroxy(meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and hydroxypentyl (meth)acrylate.

[0023] From the viewpoint of suppressing initial water absorption, it is preferable that the nonionic non-crosslinkable monomer does not undergo hydrolysis when immersed in an aqueous solution of pH 12.9 for 2 hours at 25° C. Here, "not undergoing hydrolysis" means that the proportion of hydrolysis (hydrolysis rate) is 5% by mass or less. The lack of hydrolysis after 2 hours of immersion means that the nonionic non-crosslinkable monomer maintains its structure, making it difficult for the monomer to initially exhibit water absorbency. Examples of such nonionic non-crosslinkable monomers that do not initially hydrolyze include (meth)acrylamide and N,N-hydroxymethyl(meth)acrylamide.

[0024] From the viewpoint of good water absorption performance over time, the nonionic non-crosslinkable monomer preferably contains at least one selected from the group consisting of (meth)acrylamide-based monomers and hydroxy(meth)acrylates. Among these, it is more preferable to contain a (meth)acrylamide-based monomer, even more preferable to contain (meth)acrylamide, and particularly preferable to contain acrylamide. Furthermore, the nonionic non-crosslinkable monomer may be only (meth)acrylamide or only acrylamide.

[0025] The above-mentioned monomer component may contain an ionic non-crosslinkable monomer, and examples of the ionic non-crosslinkable monomer include an anionic monomer and a cationic monomer. The anionic monomer may be any monomer having an anionic group. In this specification, the term "anionic group" refers to a group having an anion or a group that generates an anion, and examples thereof include a sulfonic acid (salt) group, a sulfuric acid (salt) group, a phosphoric acid (salt) group, a phosphonic acid (salt) group, and a carboxylic acid (salt) group (a carboxyl group or a salt thereof).

[0026] Examples of the anionic monomer include carboxylic acid monomers such as (meth)acrylic acid, (anhydrous) maleic acid, itaconic acid, and cinnamic acid; sulfonic acid monomers such as vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, 2-sulfoethyl methacrylate sodium, 2-hydroxy-3-allyloxypropane sulfonic acid, isoprene sulfonic acid, 2-(meth)acrylamido-2-methylpropane sulfonic acid, 2-(meth)acryloylethane sulfonic acid, and 2-(meth)acryloylpropane sulfonic acid; and phosphoric acid monomers such as 2-hydroxyethyl (meth)acryloyl phosphate, mono(2-hydroxyethyl) methacrylic acid ester, mono(2-hydroxyethyl) acrylic acid ester, and polyalkylene glycol mono(meth)acrylate acid phosphate; and salts thereof.

[0027] The cationic monomer may be any monomer having a cationic group. In this specification, the term "cationic group" refers to a group having a cation or a group that generates a cation, and examples thereof include primary to tertiary amino groups, neutralized products of primary to tertiary amino groups with acids, quaternary ammonium bases, and iminium groups.

[0028] Examples of the cationic monomer include N,N-dialkylamino group-containing (meth)acrylates such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, and N,N-diethylaminopropyl (meth)acrylate, as well as monomers obtained by adding a quaternizing agent to the above-mentioned monomers, or neutralized products thereof with an acid such as hydrochloric acid or acetic acid; N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylate, and the like. N,N-dialkylamino group-containing (meth)acrylamides such as acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, and N,N-diethylaminopropyl (meth)acrylamide, and monomers obtained by adding a quaternizing agent to the above monomers, or their neutralization products with an acid such as hydrochloric acid; monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, monoethylaminopropyl (meth)acrylate, (meth)acrylic acid 2-(ter Monoalkylamino group-containing (meth)acrylates such as (t-butylamino)ethyl and their neutralization products with acids such as hydrochloric acid; monomethylaminoethyl (meth)acrylamide, monoethylaminoethyl (meth)acrylamide, monomethylaminopropyl (meth)acrylamide, monoethylaminopropyl (meth)acrylamide and their neutralization products with acids such as hydrochloric acid; esters of (meth)acrylic acid and alkanolamines such as 2-aminoethyl (meth)acrylate and their neutralization products with an acid such as hydrochloric acid; N,N-diallylmethylamine and a monomer obtained by adding a quaternizing agent to this, or a product thereof neutralized with an acid such as hydrochloric acid; allylamine and a product thereof neutralized with an acid such as hydrochloric acid; addition reaction products of unsaturated monomers having a cyclic ether group having 2 to 8 carbon atoms, such as 1-allyloxy-3-dibutylamino-2-ol and 1-allyloxy-3-diethanolamino-2-ol, with an amine compound having 1 to 24 carbon atoms, and a monomer obtained by adding a quaternizing agent to this, or a product thereof neutralized with an acid such as hydrochloric acid.

[0029] The crosslinkable monomer may be any monomer having two or more polymerizable unsaturated groups, but is preferably nonionic. The crosslinkable monomer is also preferably water-soluble. The definition of "water-soluble" and the preferred degree of water solubility for the crosslinkable monomer are the same as those described for the nonionic non-crosslinkable monomer.

[0030] Examples of the nonionic crosslinkable monomer include (meth)acrylamide-based crosslinkable monomers such as N,N'-methylenebis(meth)acrylamide; (poly)ethylene glycol di(meth)acrylates such as diethylene glycol diacrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, and polyfunctional (meth)acrylates such as pentaerythritol hexa(meth)acrylate; and allyl esters of cyanuric acid or isocyanuric acid such as triallyl cyanurate and triallyl isocyanurate. These may be used alone or in combination of two or more.

[0031] The crosslinkable monomer is preferably a (meth)acrylamide-based crosslinkable monomer, an allyl ester of cyanuric acid or isocyanuric acid, or a polyfunctional (meth)acrylate. A suitable nonionic non-crosslinkable monomer is a (meth)acrylamide-based monomer, and since long-term strength is also improved, it is also preferable to use a (meth)acrylamide-based crosslinkable monomer as the nonionic crosslinkable monomer. More preferred is N,N'-methylenebis(meth)acrylamide, and even more preferred is N,N'-methylenebisacrylamide.

[0032] In the polymerization step, the non-crosslinkable monomer and the crosslinkable monomer may be polymerized simultaneously, or the monomer component containing the non-crosslinkable monomer may be polymerized and then reacted with the crosslinkable monomer.

[0033] The polymerization method for the above-mentioned monomer components is not particularly limited, and for example, bulk polymerization, solution polymerization, suspension polymerization, reverse phase suspension polymerization, emulsion polymerization, reverse phase emulsion polymerization, precipitation polymerization, or cast polymerization, thin film polymerization, spray polymerization, etc. can be used. As the polymerization method, solution polymerization is preferred, and aqueous solution polymerization is more preferred. By performing solution polymerization, uneven crosslinking in the crosslinked polymer can be suppressed. The stirring method for carrying out the polymerization reaction is not particularly limited, but when a gel-like crosslinked polymer is produced, it is more preferable to use a double-arm kneader as a stirring device and stir while breaking up the polymer by the shearing force of the double-arm kneader. The polymerization step can be carried out either batchwise or continuously.

[0034] In the polymerization step, methods for initiating polymerization of the monomer components include adding a polymerization initiator, irradiating with UV light, applying heat, and irradiating with light in the presence of a photoinitiator.

[0035] In the case where a solvent is used in the polymerization step, examples of the solvent include one or more selected from water and alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, diethylene glycol, etc. From the viewpoint of safety of the obtained water absorbent resin, it is preferable to use water as the solvent, and in this case, a solvent substitution step or the like can be omitted, and therefore productivity is improved.

[0036] In the polymerization step, it is preferable to use a polymerization initiator when carrying out polymerization. Examples of the polymerization initiator include a photodecomposition type polymerization initiator, a thermal decomposition type polymerization initiator, and a redox type polymerization initiator. Examples of the photodegradable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, etc. Specific examples include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylbenzoin, α-phenylbenzoin, anthraquinone, methylanthraquinone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetone, benzyldiacetylacetophenone, benzophenone, p-chlorobenzophenone, 2-hydroxy-2-methylpropiophenone, diphenyl disulfide, tetramethylthiuram sulfide, α-chloromethylnaphthalene ...methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, methylanthraquinone, Examples of the hydroxybenzoates include thracene, hexachlorobutadiene, pentachlorobutadiene, Michler's ketone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-hydroxy-2-methyl-1-phenylpropan-1-one, and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one. The photodegradable polymerization initiator may be a commercially available product, such as Irgacure (registered trademark) 184 (hydroxycyclohexyl-phenyl ketone) or Irgacure (registered trademark) 2959 (1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one) available from Ciba Specialty Chemicals.

[0037] Examples of the thermally decomposable polymerization initiator include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide; and azo compounds such as 2,2'-azobis(2-amidinopropane)dihydrochloride and 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride.

[0038] Examples of the redox polymerization initiator include a system in which a reducing compound such as L-ascorbic acid or sodium hydrogen sulfite is used in combination with the persulfate or peroxide. The photodecomposition type polymerization initiator may be used in combination with the thermal decomposition type polymerization initiator. Furthermore, active energy rays such as ultraviolet rays, electron beams, and γ rays may be used alone or in combination with the above polymerization initiators.

[0039] The amount of the polymerization initiator used is preferably 0.0001 to 1 mol %, more preferably 0.0005 to 0.5 mol %, relative to 100 mol % of the amount of the monomers used (total amount of non-crosslinkable monomers and crosslinkable monomers used).

[0040] In the polymerization step, the atmosphere during polymerization is not particularly limited, but it is preferable to carry out the polymerization under an inert gas (nitrogen, argon, etc.) atmosphere. By carrying out the polymerization under an inert gas atmosphere, it is expected to have effects such as improving the pulverization efficiency of the obtained water absorbent resin and reducing the ratio of unreacted monomers and the amount of water-soluble content contained in the obtained water absorbent resin.

[0041] In the polymerization step, the polymerization temperature is not particularly limited, but is preferably 15 to 130°C, more preferably 20 to 120°C. The reaction time may be appropriately set depending on the reaction temperature, the types (properties), combinations, amounts used, etc. of the monomer components, polymerization initiator, and solvent so that the polymerization reaction is completed.

[0042] The material of the reaction vessel in which the polymerization step is carried out is not particularly limited as long as it can carry out the polymerization step, but it is preferable to use a reaction vessel made of a material such as stainless steel. By carrying out the polymerization reaction using a reaction vessel made of such a material that easily transfers heat, the polymerization reaction can be sufficiently progressed, and the content of unreacted monomer in the obtained crosslinked polymer can be reduced.

[0043] In the above production method, after the addition of the monomers is completed, an aging step may be carried out for the purpose of increasing the polymerization rate of the monomers, etc. The aging time is usually 1 to 240 minutes, preferably 1 to 180 minutes, and more preferably 1 to 120 minutes.

[0044] The temperature of the polymer solution in the aging step is preferably in the same range as the polymerization temperature. Therefore, the temperature here may also be maintained at a constant temperature or may be changed over time during aging.

[0045] (Surfactant addition process) The surfactant addition step is a step of adding an ionic surfactant and / or a polyoxyalkylene glycol type nonionic surfactant to the product obtained in the polymerization step. The amounts of the ionic surfactant and polyoxyalkylene glycol nonionic surfactant used are not particularly limited, but are preferably 0.01 to 10% by mass, more preferably 0.05 to 8% by mass, even more preferably 0.1 to 5% by mass, and particularly preferably 0.1 to 2% by mass, relative to 100% by mass of the solid content of the product obtained in the polymerization step.

[0046] Specific examples of the ionic surfactant include amphoteric surfactants (zwitterionic surfactants), anionic surfactants, and cationic surfactants, with amphoteric surfactants being preferred. The amphoteric surfactant is not particularly limited, but betaine surfactants are preferred. A betaine group is a group in which a cationic group (cationic moiety) and an anionic group (anionic moiety) are not adjacent to each other, and the substituent as a whole does not have an electric charge. The betaine surfactant may be any surfactant having a betaine group and a hydrophobic group, but is preferably a surfactant represented by the following formula (1):

[0047] [ka]

[0048] (In the formula, R 1 represents a hydrocarbon group having 8 to 20 carbon atoms which may have a hydroxyl group; W represents an organic group having a quaternary nitrogen; X represents NH, NR 2 , O or S, R 2 represents an alkyl group having 1 to 4 carbon atoms. Y represents COO, SO3, OPO(OR 3 )O or P(O)(OR 3 )O, R 3 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. p and q are the same or different and are integers of 1 to 6. r and s are the same or different and are 0 or 1.

[0049] Above R 1 The hydrocarbon group is not particularly limited, and examples thereof include alkyl groups, alkenyl groups, alkynyl groups, aryl groups, and aralkyl groups.

[0050] Examples of the alkyl group include aliphatic alkyl groups such as n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-icosyl, 1,5-dimethylhexyl, t-octyl, branched nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, stearyl, and icosyl; and alicyclic alkyl groups such as cyclooctyl, cyclohexylethyl, cyclohexylpropyl, cyclododecyl, adamantyl (C10), and cyclopentylpropyl.

[0051] Examples of the alkenyl group include an octenyl group, a nonenyl group, a decenyl group, a dodecenyl group, an octadecenyl group, and an icosenyl group. Examples of the alkynyl group include an octynyl group, a nonynyl group, a decynyl group, a dodecynyl group, an octadecynyl group, and an icosynyl group. Examples of the aryl group include a 2,3- or 2,4-xylyl group, a mesityl group, a naphthyl group, an anthryl group, a phenanthryl group, and a biphenylyl group. Examples of the aralkyl group include a phenethyl group, a phenylpropyl group, and a benzhydryl group.

[0052] The hydrocarbon group is preferably an alkyl group. More preferably, it is an n-octyl group, a sec-octyl group, a tert-octyl group, a 2-ethylhexyl group, a capryl group, a nonyl group, a decyl group, an undecyl group, a lauryl group, a tridecyl group, a myristyl group, a pentadecyl group, a cetyl group, a heptadecyl group, a stearyl group, or the like. From the viewpoint of gel dispersibility, R 1 As the alkyl group, a straight chain alkyl group is more preferred.

[0053] Also, R 1 When the hydrocarbon group in has a hydroxyl group, it is preferably a hydroxyalkyl group, such as a 2-hydroxydecyl group, a 2-hydroxyundecyl group, a 2-hydroxylauryl group, a 2-hydroxytridecyl group, a 2-hydroxymyristyl group, a 2-hydroxypentadecyl group, a 2-hydroxycetyl group, a 2-hydroxyheptadecyl group, or a 2-hydroxystearyl group.

[0054] From the viewpoint of gel dispersibility, R 1 The hydrocarbon group preferably has 8 to 20 carbon atoms, more preferably 10 to 19 carbon atoms, and even more preferably 12 to 18 carbon atoms.

[0055] The W represents an organic group having a quaternary nitrogen. The above W is preferably represented by the following formula (2): -N + (R 4 )twenty two) (In the formula, R 4 are the same or different and represent a hydrocarbon group having 1 to 4 carbon atoms which may have a hydroxyl group, or a group represented by the following formula (3):

[0056] [ka]

[0057] (In the formula, R 5 are the same or different and represent a hydrocarbon group having 1 to 4 carbon atoms which may have a hydroxyl group. Above R 4 , R 5 Examples of the hydrocarbon group in include an alkyl group, an alkenyl group, and an alkynyl group, preferably an alkyl group, more preferably a methyl group, an ethyl group, a propyl group, or a butyl group, and particularly preferably a methyl group or an ethyl group. Above R 4 , R 5 The hydrocarbon group in may have a hydroxyl group. R 5 is a hydroxyalkyl group is one of the preferred embodiments of the present invention.

[0058] The above W is preferably a group represented by formula (2). The above W is -N + The form of the group represented by (CH3)2- is a preferred embodiment of the present invention.

[0059] The above Y is COO, SO3, OPO(OR 3 )O or P(O)(OR 3 )O, R 3 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The above Y is preferably COO.

[0060] The above p and q are the same or different and are integers of 1 to 6. p is preferably 2 to 5, and more preferably 3. The above q is preferably 1 to 4, more preferably 1 to 2, and even more preferably 1.

[0061] The above r and s may be the same or different and each represents 0 or 1. The above embodiment in which r and s are 0 is a preferred embodiment of the present invention.

[0062] The above X is NH, NR 2 , O or S, R 2 represents an alkyl group having 1 to 4 carbon atoms. The above X is preferably NH.

[0063] In the above formula (1), R 1 is an alkyl group, W is a group represented by formula (2), and R 4 is a methyl group, r and s are 0, q is 1, and Y is COO, which is a preferred embodiment of the present invention, and the chemical formula is 1 -N + (CH3)2-CH2COO - The compound is generally known as alkyldimethylaminoacetic acid betaine. Specific examples of alkyldimethylaminoacetic acid betaine include capryldimethylaminoacetic acid betaine, lauryldimethylaminoacetic acid betaine, myristyldimethylaminoacetic acid betaine, stearyldimethylaminoacetic acid betaine, etc. From the viewpoint of gel dispersibility and the physical properties of the water-absorbent resin, capryldimethylaminoacetic acid betaine, lauryldimethylaminoacetic acid betaine, or stearyldimethylaminoacetic acid betaine is preferred, and lauryldimethylaminoacetic acid betaine is more preferred.

[0064] Capryldimethylaminoacetic acid betaine is commercially available as "Amogen (registered trademark) HB-C" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Lauryldimethylaminoacetic acid betaine is commercially available as "Amchtol (registered trademark) 20BS" and "Amchtol (registered trademark) 24B" manufactured by Kao Corporation, "Nissan Anon (registered trademark) BL" and "Nissan Anon (registered trademark) BL-SF" manufactured by NOF Corporation, "Obazolin (registered trademark) LB" and "Obazolin (registered trademark) LB-SF" manufactured by Toho Chemical Industry Co., Ltd., "Rekabion (registered trademark) A-100" manufactured by New Japan Chemical Co., Ltd., "Amogen (registered trademark) K" and "Amogen (registered trademark) SH" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Stearyldimethylaminoacetic acid betaine is commercially available as "Amchtol (registered trademark) 86B" manufactured by Kao Corporation.

[0065] In the above formula (1), R 1 is an alkyl group, W is a group represented by formula (2), and R 4 is a methyl group, X is NH, r is 1, s is 0, p is 3, q ​​is 1, and Y is COO, the chemical formula is R 1 -CO-NH(CH2)3-N + (CH3)2-CH2COO - The general name of the compound is alkylamidopropyl betaine. Specific examples of alkylamidopropyl betaine include lauric acid amidopropyl betaine, coconut oil fatty acid amidopropyl betaine, palm kernel oil fatty acid amidopropyl betaine, etc. From the viewpoint of gel dispersibility and physical properties of the water-absorbing agent, lauric acid amidopropyl betaine or coconut oil fatty acid amidopropyl betaine is preferred, and lauric acid amidopropyl betaine is more preferred.

[0066] Lauryl amidopropyl betaine is commercially available as "Anchor (registered trademark) 20AB" manufactured by Kao Corporation, "Rekabion (registered trademark) B-300" manufactured by New Japan Chemical Co., Ltd., "Amogen (registered trademark) LB-C" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., and "Nissan Anon (registered trademark) BDL-SF" manufactured by NOF Corporation. In addition, the coconut oil fatty acid amidopropyl betaine is commercially available as "Anchor (registered trademark) 55AB" manufactured by Kao Corporation, "Obazoline (registered trademark) CAB30" manufactured by Toho Chemical Industry Co., Ltd., "Rekabion (registered trademark) B-200" manufactured by New Japan Chemical Co., Ltd., and "Amogen (registered trademark) CB-H" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

[0067] In the above formula (1), R 1 is an alkyl group, W is a group represented by formula (2), and R 4 is a methyl group, r is 0, s is 1, q is 1, and Y is SO3, the chemical formula is R 1 -N + (CH3)2-CH2CH(OH)CH2SO3 - and the common name of the compound is alkylhydroxysulfobetaine. Specific examples of alkylhydroxysulfobetaines include laurylhydroxysulfobetaine. From the viewpoint of gel dispersibility and the physical properties of the water-absorbing agent, laurylhydroxysulfobetaine is preferred. The above-mentioned laurylhydroxysulfobetaine is commercially available as "Anthol (registered trademark) 20HD" manufactured by Kao Corporation.

[0068] In the above formula (1), R 1 is an alkyl group, W is a group represented by formula (3), and R 5 When is a hydroxyethyl group, r and s are 0, q is 1, and Y is COO, common names for the compounds include alkylcarboxymethylhydroxyethylimidazolinium betaine. A specific example of alkylcarboxymethyl hydroxyethyl imidazolinium betaine is 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine. From the viewpoint of gel dispersibility and the physical properties of the water-absorbing agent, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine is preferred. The 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine is commercially available as "Amphitheater (registered trademark) 20YB" manufactured by Kao Corporation, "Nissan Anon (registered trademark) GLM-R-LV" manufactured by NOF Corporation, "Obazoline (registered trademark) 552" manufactured by Toho Chemical Industry Co., Ltd., etc.

[0069] The anionic surfactant is not particularly limited as long as it has a hydrophobic group and a hydrophilic group that dissociates into anions, and examples thereof include alkyl or alkenyl sulfate ester salts; polyoxyalkylene alkyl or alkenyl ether sulfate ester salts having an oxyalkylene group; anionic surfactants having a sulfonate group; fatty acids or salts thereof, sulfosuccinate esters, etc.

[0070] More specific examples of the alkyl or alkenyl sulfate ester salts include alkyl sulfate ester salts in which the alkyl group has 10 to 18 carbon atoms, and alkenyl sulfate ester salts in which the alkenyl group has 10 to 18 carbon atoms.

[0071] More specific examples of the polyoxyalkylene alkyl or alkenyl ether sulfate salts having an oxyalkylene group include polyoxyalkylene alkyl ether sulfate salts having an alkyl group with 10 to 18 carbon atoms and an average number of added moles of alkylene oxide of 1 to 5, and polyoxyalkylene alkenyl ether sulfate salts having an alkenyl group with 10 to 18 carbon atoms and an average number of added moles of alkylene oxide of 1 to 5. Among these, polyoxyethylene alkyl ether sulfate salts having an average number of added moles of ethylene oxide of 1 to 3 are preferred, and polyoxyethylene alkyl ether sulfate salts having an alkyl group with 12 to 14 carbon atoms and an average number of added moles of ethylene oxide of 1 to 3 are more preferred, and sodium salts thereof are even more preferred.

[0072] More specific examples of the anionic surfactant having a sulfonate group include one or more anionic surfactants selected from alkylbenzenesulfonates having an alkyl group with 10 to 18 carbon atoms, alkenylbenzenesulfonates having an alkenyl group with 10 to 18 carbon atoms, alkanesulfonates having an alkyl group with 10 to 18 carbon atoms, α-olefinsulfonates having an α-olefin moiety with 10 to 18 carbon atoms, α-sulfofatty acid salts having a fatty acid moiety with 10 to 18 carbon atoms, α-sulfofatty acid lower alkyl ester salts having a fatty acid moiety with 10 to 18 carbon atoms and an ester moiety with 1 to 5 carbon atoms, and internal olefinsulfonates having 12 to 16 carbon atoms. Among these, alkylbenzenesulfonates having an alkyl group with 11 to 16 carbon atoms are preferred, and sodium alkylbenzenesulfonate having an alkyl group with 11 to 16 carbon atoms is more preferred.

[0073] The fatty acid or salt thereof may be a fatty acid or salt thereof having 10 to 20 carbon atoms. The fatty acid or salt thereof preferably has 12 to 18 carbon atoms, and more preferably has 14 to 18 carbon atoms.

[0074] The sulfosuccinate ester or salt thereof may be a sulfosuccinate ester or salt thereof having a hydrocarbon group having 5 to 18 carbon atoms.

[0075] The cationic surfactant is not particularly limited as long as it has a hydrophobic group and a hydrophilic group that dissociates into a cation, and examples thereof include quaternary ammonium salt type cationic surfactants. Examples of quaternary ammonium salt-type cationic surfactants include quaternary ammonium salts in which, of the four groups bonded to the nitrogen atom, one or two are hydrocarbon groups having 6 to 24 carbon atoms, and the remaining groups are hydrocarbon groups having 1 to 3 carbon atoms. Specific examples of the cationic surfactant include one or more compounds selected from N-ethyl-N,N-dimethyltetradecylammonium salt, trimethylhexadecyl salt, N,N-dioctyl-N,N-dimethylammonium salt, N,N-dinonyl-N,N-dimethylammonium salt, N,N-didecyl-N,N-dimethylammonium salt, N,N-dioctyl-N-ethyl-N-methylammonium salt, N,N-dinonyl-N-ethyl-N-methylammonium salt, and N,N-didecyl-N-ethyl-N-methylammonium salt. Mono-long chain ammonium salts and di-long chain ammonium salts can also be used in combination. Among these, N,N-didecyl-N-ethyl-N-methylammonium salt is preferred. Counterions for these salts include, for example, CH3SO4 - , CH3CH2SO4 - or halide ions such as chloride ions.

[0076] The polyoxyalkylene glycol-type nonionic surfactant has a hydrophobic group and a polyoxyalkylene group as a hydrophilic group, and is not particularly limited as long as it is nonionic, but a compound having a structure derived from a polyhydric alcohol, a polyoxyalkylene group, and a hydrophobic group is preferred. Examples of the polyhydric alcohol include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol; glycerol (glycerin), 1,2,3-butanetriol, 1,2,4-butanetriol, 1,2,3-pentanetriol, 1,2,4-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 3-methylpentane-1,3,5-triol, 2,4-dimethyl-2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, and 1,3,5-cyclohexane. Trihydric alcohols such as triol, pentamethylglycerin, trimethylolethane, and trimethylolpropane; tetrahydric alcohols such as tetramethylolmethane (pentaerythritol) and diglycerin; pentahydric alcohols such as arabitol, galactose, xylitol, glucose, fructose, mannose, allose, glucose, idose, and talose. Examples include hexahydric alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, and inositol; heptahydric alcohols such as perseitol; polyhydric aliphatic alcohols such as octahydric alcohols such as sucrose, maltose, and lactose; and cyclic ether polyhydric alcohols obtained by dehydration of tetrahydric or higher alcohols such as sorbitan and sorbide. Among these, cyclic ether polyhydric alcohols are preferred, and sorbitan is more preferred.

[0077] The polyoxyalkylene group is not particularly limited as long as it is a group having the same structure as that obtained by addition polymerization of an alkylene oxide, and examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, 1-butene oxide, 2-butene oxide, and styrene oxide. The alkylene oxide preferably has 2 to 18 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 carbon atoms. The alkylene oxide is preferably ethylene oxide, propylene oxide or butylene oxide, more preferably ethylene oxide.

[0078] The average number of moles of oxyalkylene groups added in the polyoxyalkylene glycol nonionic surfactant is not particularly limited, but is preferably 1 to 100, more preferably 2 to 80, even more preferably 5 to 60, still more preferably 8 to 50, and particularly preferably 10 to 30.

[0079] The hydrophobic group may be any hydrophobic organic group, and examples thereof include hydrocarbon groups having 6 to 30 carbon atoms. Examples of the hydrocarbon group having 6 to 30 carbon atoms include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, etc. The hydrophobic group is preferably an alkyl group or an alkenyl group.

[0080] The hydrophobic group preferably has 8 to 24 carbon atoms, more preferably 10 to 22 carbon atoms, and even more preferably 12 to 20 carbon atoms.

[0081] Examples of the alkyl group include an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, an n-icosyl group, a 1,3-dimethylbutyl group, a 3,3-dimethylbutyl group, a 2-ethylbutyl group, a 2-ethyl-2-methylpropyl group, a 1-methylheptyl group, a 2-ethylhexyl group, a 1-methyl ... aliphatic alkyl groups such as 5-dimethylhexyl, t-octyl, branched nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, stearyl, and icosyl groups; and alicyclic alkyl groups such as cyclohexyl, cyclohexylmethyl, cycloheptyl, cyclooctyl, cyclohexylpropyl, cyclododecyl, norbornyl (C7), adamantyl (C10), and cyclopentylethyl groups.

[0082] Examples of the alkenyl group include a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, a dodecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, and an icosenyl group. Examples of the alkynyl group include a hexynyl group, a heptynyl group, an octynyl group, a nonynyl group, a decynyl group, a dodecynyl group, an octadecynyl group, and an icosynyl group.

[0083] Examples of the aryl group include a phenyl group, an o-, m- or p-tolyl group, a 2,3- or 2,4-xylyl group, a mesityl group, a naphthyl group, an anthryl group, a phenanthryl group, and a biphenylyl group. Examples of the aralkyl group include a benzyl group, a phenethyl group, a phenylpropyl group, and a benzhydryl group.

[0084] The polyoxyalkylene glycol nonionic surfactant is represented by the following formula (4): (H-(OA 1 )k1 ) i -Z-((A 2 O) k2 -(CO) l -R 6 ) j (4) (In the formula, OA 1 and A 2 O may be the same or different and represent an oxyalkylene group. k1 and k2 represent the number of moles of oxyalkylene groups added and are numbers from 0 to 100. However, the total number of oxyalkylene groups present in formula (4), i.e., the sum of i k1s and j k2s, is 1 to 100. i and j may be the same or different and are numbers from 1 to 6. Z is a group derived from a polyhydric alcohol. l is 0 or 1. R 6 represents a hydrophobic group.

[0085] In the above formula (4), Z is a group derived from a polyhydric alcohol, and is a group obtained by abstracting a hydrogen atom from a hydroxyl group of the polyhydric alcohol. Specific examples and preferred forms of the polyhydric alcohol are as described above.

[0086] The above k1 and k2 are numbers from 0 to 100, and the total number of oxyalkylene groups present in formula (4) (the sum of i k1s and j k2s) is from 1 to 100. The preferred range of the total number of oxyalkylene groups present in formula (4) is the same as that described for the average number of moles of oxyalkylene groups added.

[0087] The above i and j are the same or different and are numbers from 1 to 6. The above i is preferably 1 to 5, more preferably 1 to 4, and even more preferably 1 to 3. j is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1. The above l is 0 or 1. Preferably, l is 1.

[0088] Above R 6represents a hydrophobic group. Specific examples and preferred embodiments of the hydrophobic group are as described above. The above OA 1 and A 2 O may be the same or different and represents an oxyalkylene group. Specific examples and preferred embodiments of alkylene oxides forming the oxyalkylene group are as described above.

[0089] The polyoxyalkylene glycol type nonionic surfactant is preferably a compound obtained by adding an alkylene oxide to a polyhydric alcohol and then esterifying a fatty acid. The fatty acid is not particularly limited as long as it is a carboxylic acid having a hydrocarbon group having 6 to 30 carbon atoms, and examples thereof include saturated fatty acids such as enanthic acid, caprylic acid, 2-ethylhexanoic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, and arachidic acid; and monounsaturated fatty acids such as myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid (paulic acid), erucic acid, and nervonic acid. Examples of such fatty acids include diunsaturated fatty acids such as linoleic acid, eicosadienoic acid, and docosadienoic acid; triunsaturated fatty acids such as α-linolenic acid, γ-linolenic acid, pinolenic acid, eleostearic acid, midoic acid, dihomo-γ-linolenic acid, and eicosatrienoic acid; tetraunsaturated fatty acids such as stearidonic acid, arachidonic acid, eicosatetraenoic acid, and adrenic acid; pentaunsaturated fatty acids such as bosseopentaenoic acid, eicosapentaenoic acid, docosapentaenoic acid, osbondoic acid, sardine acid, and tetracosapentaenoic acid; and hexaunsaturated fatty acids such as docosahexaenoic acid and herring acid. Among these, saturated fatty acids and monounsaturated fatty acids are preferred, and monounsaturated fatty acids are more preferred.

[0090] The polyoxyalkylene glycol type nonionic surfactant is preferably a polyoxyalkylene sorbitan fatty acid ester, more preferably polyoxyethylene sorbitan monooleate.

[0091] The method for adding the surfactant in the surfactant addition step is not particularly limited, but it is preferable to add the surfactant while stirring the product obtained in the polymerization step. Specifically, it is more preferable to use a twin-arm kneader as the stirring device and stir the product obtained in the polymerization step while breaking it up by the shearing force of the twin-arm kneader.

[0092] (drying process) The drying step is a step of drying the product obtained after the surfactant addition step. The drying method for the product in the drying step is not particularly limited, and can be carried out by a commonly used method such as a ventilation band dryer, a rotary ventilation dryer, an agitator dryer, a fluidized bed dryer, or a vibration fluidized bed dryer, preferably a belt dryer.

[0093] The drying temperature in the drying step is not particularly limited, but is preferably 100 to 250°C, more preferably 120 to 230°C, and even more preferably 130 to 200°C. The drying temperature is usually determined by the temperature of the heat medium. For example, in the case of hot air drying, it is the temperature of the hot air. However, in the case of microwave drying or the like, which cannot be determined by the temperature of the heat medium, the drying temperature is determined by the temperature of the product to be dried. Furthermore, the drying temperature may be constant throughout the drying process or may be changed as appropriate during drying. The drying time in the drying step is preferably 30 to 300 minutes, more preferably 60 to 240 minutes, and even more preferably 90 to 210 minutes.

[0094] (Crushing and / or classification process) The pulverization and / or classification step is a step in which the product obtained in the drying step is pulverized and / or classified. The product is preferably pulverized using a pulverizer. Examples of pulverizers include high-speed rotary pulverizers such as roll mills, hammer mills, screw mills, and pin mills, as well as vibration mills, knuckle-type pulverizers, and cylindrical mixers. A roll mill is preferred.

[0095] The classification step is preferably carried out after the pulverization step. The particle size adjustment in the classification step is preferably carried out by sieve classification using a JIS standard sieve (JIS Z8801-1(2000)), air classification, etc. From the viewpoint of classification efficiency, sieve classification is more preferred.

[0096] [Cement additives] The present invention also provides a cement additive comprising a water-absorbing resin and a surfactant, wherein the water-absorbing resin has structural units derived from a nonionic non-crosslinkable monomer and structural units derived from a crosslinkable monomer, the proportion of the structural units derived from the nonionic non-crosslinkable monomer being 50 mol % or more relative to 100 mol % of all structural units, and the proportion of the structural units derived from the crosslinkable monomer being 0.05 mol % or more, and the surfactant being an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant. The cement additive of the present invention contains the above surfactant, but does not affect the water absorption or fluidity, and can improve various physical properties of concrete such as compressive strength.

[0097] The content of the surfactant in the cement additive is not particularly limited, but is preferably 0.01 to 10 mass %, more preferably 0.05 to 8 mass %, even more preferably 0.1 to 5 mass %, and particularly preferably 0.1 to 2 mass %, relative to 100 mass % of the solid content of the water absorbent resin. The content of the surfactants mentioned above means the total content of the ionic surfactant and the polyoxyalkylene glycol type nonionic surfactant. Specific examples and preferred embodiments of the surfactant in the cement additive are as described above.

[0098] The content of the water-absorbing resin in the cement additive is not particularly limited, but is preferably 50 to 99.99 mass%, more preferably 60 to 99.9 mass%, and even more preferably 70 to 99 mass%, relative to 100 mass% of the cement additive.

[0099] The cement additive may contain other components in addition to the water-absorbing resin and surfactant, and the content ratio thereof is not particularly limited, but is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, particularly preferably 10% by mass or less, and most preferably 0% by mass, relative to 100% by mass of the cement additive.

[0100] The water-absorbing resin has structural units derived from a nonionic non-crosslinkable monomer and structural units derived from a crosslinkable monomer, and the proportion of the structural units derived from the nonionic non-crosslinkable monomer is 50 mol % or more and the proportion of the structural units derived from the crosslinkable monomer is 0.05 mol % or more relative to 100 mol % of all structural units. This makes it possible to sufficiently suppress the initial water absorption in the cement composition and has little effect on fluidity, allowing the amount of dispersant used to be reduced.

[0101] The proportion of structural units derived from nonionic non-crosslinkable monomers in the water absorbent resin is preferably 50 to 99.95 mol%, more preferably 60 to 99.95 mol%, even more preferably 70 to 99.95 mol%, still more preferably 80 to 99.95 mol%, and particularly preferably 90 to 99.95 mol%. In one embodiment, the proportion of the structural units derived from the nonionic non-crosslinkable monomer may be 99 mol % or less, 98 mol % or less, 97 mol % or less, 96 mol % or less, or 95 mol % or less.

[0102] The water-absorbing resin may have structural units derived from ionic non-crosslinkable monomers, and the proportion thereof may be 49.95 mol % or less relative to 100 mol % of all structural units, preferably 40 mol % or less, more preferably 30 mol % or less, even more preferably 20 mol % or less, particularly preferably 10 mol % or less, and most preferably 5 mol % or less.

[0103] The proportion of structural units derived from crosslinkable monomers in the water absorbent resin is 0.05 mol % or more, preferably 0.05 to 3.0 mol %, more preferably 0.05 to 2.0 mol %, still more preferably 0.05 to 1.0 mol %, and particularly preferably 0.1 to 0.75 mol %, relative to 100 mol % of all structural units.

[0104] Specific examples and preferred embodiments of the nonionic non-crosslinkable monomer, crosslinkable monomer, and ionic non-crosslinkable monomer that constitute the water-absorbent resin are as described above.

[0105] The water-absorbent resin preferably has a water absorption capacity of less than 20 g / g when immersed in 50 mL of an aqueous solution of pH 12.9 at 25°C for 2 hours. This makes it possible to suppress the initial viscosity and further increase the fluidity when the cement additive of the present invention is added to a cement composition, resulting in superior workability. The water absorption capacity is more preferably less than 18 g / g, and even more preferably less than 17.0 g / g. The lower the water absorption capacity when immersed in an aqueous solution of pH 12.9 at 25°C for 2 hours, the better, but it is usually 5 g / g or more.

[0106] In this specification, the pH 12.9 aqueous solution is a mixture of 1.72 g of CaSO4·2H2O, 6.96 g of Na2SO4, 4.76 g of K2SO4, 7.12 g of KOH, and 979.4 g of deionized water. The pH 12.9 aqueous solution is a cement simulant that simulates the strong alkalinity that occurs when cement is added. Therefore, this aqueous solution can mimic the behavior of a water-absorbent resin when water is added to a cement composition containing a cement additive.

[0107] The water absorption capacity of the water-absorbent resin when immersed in an aqueous solution of pH 12.9 at 25° C. for 28 days is, for example, 10 g / g or more, and from the viewpoint of improving long-term strength, it is preferably 20 g / g or more. It is more preferably 30 g / g or more, even more preferably 31 g / g or more, and particularly preferably 35 g / g or more. The water absorption capacity when immersed in an aqueous solution of pH 12.9 at 25°C for 28 days is preferably as high as possible, and although there is no particular upper limit, it is usually 50 g / g or less, and preferably 45 g / g or less.

[0108] The form of the water-absorbent resin is not particularly limited, but it is preferably in the form of a powder. The shape of the powder is not particularly limited, and may be spherical or an aggregate thereof, or may be an irregular (crushed) shape obtained by a pulverization step, but is preferably an irregular (crushed) shape.

[0109] The average particle size of the water-absorbent resin (powder) is not particularly limited, but is preferably 10 to 1000 μm, more preferably 10 to 750 μm, and even more preferably 100 to 500 μm. Furthermore, the particle size distribution of the water-absorbent resin (powder) is not particularly limited, but from the viewpoint of further improving long-term strength, it is preferable that 90% by mass or more of the particles are in the range of 45 to 850 μm. More preferably, it is in the range of 100 to 850 μm, even more preferably, it is in the range of 150 to 850 μm, even more preferably, it is in the range of 150 to 700 μm, and particularly preferably, it is in the range of 150 to 600 μm. It is believed that an increase in the average particle size of the water-absorbent resin (powder) enhances the sustained release of water, further improving long-term strength. Furthermore, an average particle size of the water-absorbent resin (powder) of 850 μm or less results in more excellent freeze-thaw resistance.

[0110] The mass average particle diameter (D50) of the water-absorbent resin (powder) can be measured by the same method as "Average Particle Diameter and Distribution of Particle Diameter" disclosed in European Patent No. 0349240. That is, 10 g of the water-absorbent resin is classified using JIS standard sieves (JIS Z8801-1 (2000)) having mesh sizes of 850 μm, 710 μm, 600 μm, 500 μm, 420 μm, 300 μm, 212 μm, 150 μm, 106 μm, and 45 μm or equivalent sieves, and the masses of the water-absorbent resin remaining on each sieve and the water-absorbent resin that passed through all the sieves are measured. Classification is carried out for 5 minutes using a vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65, SER. No. 0501), and the particle size distribution is obtained by plotting the residual percentage R on logarithmic probability paper. The particle diameter corresponding to R=50% by mass is then read as the mass average particle diameter (D50), which can be used as the average particle diameter.

[0111] The other components that may be contained in the cement additive other than the water-absorbing resin and the surfactant are not particularly limited, but examples thereof include other surfactants other than ionic surfactants and polyoxyalkylene glycol-type nonionic surfactants, color inhibitors, reducing agents, etc.

[0112] [Cement composition] The present invention also relates to a cement composition containing the cement additive of the present invention and cement. The content of the cement additive in the cement composition is not particularly limited, but is preferably 0.01 to 10 mass %, more preferably 0.02 to 5 mass %, and even more preferably 0.05 to 3 mass %, relative to 100 mass % of cement, calculated as solid content. In the cement composition, the proportion of the water-absorbing resin in the cement additive is preferably 0.01 to 10 mass% in terms of solid content relative to 100 mass% of cement, more preferably 0.02 to 5 mass%, and even more preferably 0.05 to 3 mass%. The solid content of the water-absorbing resin can be measured by the following method. <Solid content measurement method> 1. Accurately weigh the aluminum dish. Accurately weigh the solid content measurement material into the aluminum dish that was accurately weighed in 2.1. 3. Place the solid content measured in step 2 in a dryer adjusted to 180°C in an air atmosphere for 1 hour. After 4.1 hours, remove from the dryer and allow to cool in a desiccator at room temperature for 15 minutes. 5. After 15 minutes, remove from the desiccator and accurately weigh the aluminum dish and the sample. 6. Subtract the mass of the aluminum dish obtained in 1 from the mass obtained in 5, and divide the result by the mass of the solids measurement sample obtained in 2 to measure the solids content.

[0113] The cement contained in the cement composition is not particularly limited, but examples include Portland cement (normal, early strength, ultra-early strength, moderate heat, sulfate-resistant, and each low-alkali form), various blended cements (blast furnace cement, silica cement, fly ash cement), white Portland cement, alumina cement, ultra-rapid-hardening cement (1-clinker rapid-hardening cement, 2-clinker rapid-hardening cement, magnesium phosphate cement), cement for grouting, oil well cement, low-heat cement (low-heat blast furnace cement, fly ash mixed low-heat blast furnace cement, high-bilite cement), ultra-high-strength cement, cement-based solidification material, and ecocement (cement produced using one or more of municipal waste incineration ash and sewage sludge incineration ash as raw materials).

[0114] The cement composition preferably contains aggregate. Examples of the above aggregate include gravel, crushed stone, granulated slag, recycled aggregate, and also refractory aggregate such as silica, clay, zircon, high alumina, silicon carbide, graphite, chromium, chromium-magnesium, and magnesia. Furthermore, fine powders such as fly ash, blast furnace slag, silica fume, limestone, and burnt clay may be added.

[0115] In the above cement composition, 1 m 3The unit water amount, cement amount used, and water / cement ratio per unit are not particularly limited, but preferably, the unit water amount is 100 kg / m 3 ~185kg / m 3 The amount of cement used is 250 kg / m 3 ~800kg / m 3 and the water / cement ratio (mass ratio) is 0.1 to 0.7, and more preferably, the unit water content is 120 kg / m 3 ~180kg / m 3 The amount of cement used is 270 kg / m 3 ~800kg / m 3 and the water / cement ratio (mass ratio) is 0.12 to 0.65.

[0116] The cement composition may contain a conventionally known cement dispersant. The cement dispersant is not particularly limited, but examples thereof include polyalkylarylsulfonates such as naphthalenesulfonic acid formaldehyde condensates; melamine formalin resin sulfonates such as melamine sulfonic acid formaldehyde condensates; aromatic aminosulfonates such as aminoarylsulfonic acid-phenol-formaldehyde condensates; lignin sulfonates such as lignin sulfonates and modified lignin sulfonates; various sulfonic acid dispersants having a sulfonic acid group in the molecule, such as polystyrene sulfonates; copolymers obtained from polyalkylene glycol mono(meth)acrylate monomers, (meth)acrylic acid monomers, and monomers copolymerizable with these monomers, as described in Japanese Patent Publication No. 59-18338 and Japanese Patent Application Laid-Open No. 7-223852; 6858, JP 2001-220417, JP 2002-121055, JP 2002-121056, JP 2018-111622 A, various polycarboxylic acid dispersants having (poly)oxyalkylene groups and carboxyl groups in the molecule, such as copolymers obtained from unsaturated (poly)alkylene glycol ether monomers, maleic acid monomers or (meth)acrylic acid monomers; various phosphoric acid dispersants having (poly)oxyalkylene groups and phosphoric acid groups in the molecule, such as copolymers obtained from (alkoxy)polyalkylene glycol mono(meth)acrylates, phosphoric acid monoester monomers, and phosphoric acid diester monomers, as described in JP 2006-52381 A, and phosphoric acid dispersants described in JP 2008-517080 A. Among them, it is preferable to use a polycarboxylic acid-based dispersant as the cement dispersant. Only one type of cement dispersant may be used, or two or more types may be used.

[0117] The cement composition may contain any other appropriate cement additives as long as the effects of the present invention are not impaired. Examples of other cement additives include the following (1) to (12) as examples of other cement additives. (1) Water-soluble polymeric substances: non-ionic cellulose ethers such as methylcellulose, ethylcellulose, and carboxymethylcellulose; polysaccharides produced by microbial fermentation such as yeast glucan, xanthan gum, and β-1,3 glucans; polyacrylamide, etc. (2) Polymer emulsions: copolymers of various vinyl monomers such as alkyl (meth)acrylates, etc. (3) Hardening retarders: hydroxycarboxylic acids such as gluconic acid, glucoheptonic acid, arabinose, malic acid, and citric acid, or their salts; monosaccharides such as glucose, fructose, galactose, mannose, xylose, arabinose, ribose, and isomerized sugars; disaccharides such as maltose, sucrose, and lactose; trisaccharides such as raffinose; oligosaccharides such as dextrin, erythritol, xylitol, Sugars or sugar alcohols such as D-arabinitol, L-arabinitol, ribitol, volemitol, perseitol, sorbitol, mannitol, galactitol, D-threitol, L-threitol, D-iditol, D-glycidol, D-erythro-D-galacto-octitol, etc.; polyhydric alcohols such as glycerin; phosphonic acids such as aminotri(methylenephosphonic acid) and their derivatives, etc.

[0118] (4) Early strengthening agents and accelerators: soluble calcium salts such as calcium chloride, calcium nitrite, calcium nitrate, calcium bromide, calcium iodide, etc.; chlorides such as iron chloride and magnesium chloride; sulfates; potassium hydroxide; sodium hydroxide; carbonates; thiosulfates; formic acid and formates such as calcium formate; alkanolamines; alumina cement; calcium aluminate silicate, etc. (5) Oxyalkylene-based antifoaming agents: (poly)oxyalkylenes such as (poly)oxyethylene-(poly)oxypropylene adducts; polyoxyalkylene acetylene ethers; polyoxypropylene polyoxyethylene laurylamine (1 to 20 moles of propylene oxide adduct, 1 to 20 moles of ethylene oxide adduct, etc.), polyoxyalkylene alkylamines such as amines derived from fatty acids obtained from hardened beef tallow to which alkylene oxide has been added (1 to 20 moles of propylene oxide adduct, 1 to 20 moles of ethylene oxide adduct, etc.); polyoxyalkylene amides, etc. (6) Antifoaming agents other than oxyalkylene-based: mineral oil-based, oil-based, fatty acid-based, fatty acid ester-based, alcohol-based, amide-based, phosphate ester-based, metal soap-based, silicone-based, and other antifoaming agents.

[0119] (7) Air-entraining agents: resin soaps, saturated or unsaturated fatty acids, sodium hydroxystearate, lauryl sulfate, ABS (alkylbenzenesulfonic acid), alkanesulfonates, polyoxyethylene alkyl (phenyl) ethers, polyoxyethylene alkyl (phenyl) ether sulfates or salts thereof, polyoxyethylene alkyl (phenyl) ether phosphates or salts thereof, protein materials, alkenyl sulfosuccinates, α-olefin sulfonates, etc. (8) Surfactants: Nonionic surfactants other than polyoxyalkylene glycol type. (9) Waterproofing agents: fatty acids (salts), fatty acid esters, oils and fats, silicone, paraffin, asphalt, wax, etc. (10) Rust inhibitors: nitrites, phosphates, zinc oxide, etc. (11) Crack reducers: polyoxyalkyl ethers, etc. (12) Expansive materials: ettringite-based, coal-based, etc.

[0120] Other known cement additives include cement wetting agents, thickeners, separation reducing agents, flocculants, drying shrinkage reducing agents, strength enhancing agents, self-leveling agents, rust inhibitors, colorants, and mildew inhibitors. These known cement additives (materials) may be used alone or in combination with one or more other types. Furthermore, other cement additives are blended in appropriate amounts into the cement composition, taking into account the purpose of their addition.

[0121] The above cement composition has excellent workability and can be effective for ready-mixed concrete, concrete for secondary concrete products, concrete for centrifugal molding, concrete for vibration compaction, steam-cured concrete, sprayed concrete, etc. The cement composition can also be effective for mortar and concrete that require high fluidity, such as medium-fluidity concrete (concrete with a slump value of 22 to 25 cm), high-fluidity concrete (concrete with a slump value of 25 cm or more and a slump flow value of 50 to 70 cm), self-compacting concrete, and self-leveling materials. [Example]

[0122] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass."

[0123] [Example 1] A 10-liter double-arm kneader was charged with 2940 g of 50% aqueous acrylamide, 15.9 g of N,N-methylenebisacrylamide, and 1577 g of water and dissolved uniformly. The resulting monomer mixture, consisting of acrylamide and N,N-methylenebisacrylamide, contained 99.5 mol% acrylamide and 0.5 mol% N,N-methylenebisacrylamide. After purging with nitrogen, the kneader was adjusted to 20°C, and 24.8 g of a 25% aqueous sodium persulfate solution and 29.7 g of a 2% aqueous L-ascorbic acid solution were added. Polymerization was carried out with stirring. After polymerization began, heat was generated and the temperature rose to 90°C after 10 minutes. When the liquid temperature stopped rising, the bath temperature was maintained at 60°C and the mixture was aged for 30 minutes. In a double-arm kneader, 299 g of a 5% aqueous solution of lauryldimethylaminoacetic acid betaine was added to the obtained gel polymer (hydrogel), and after stirring for 10 minutes, the mixture was taken out on a drying net and dried with hot air at 130°C for 160 minutes, and then pulverized with a roll mill to obtain a powdery water absorbent resin. The particle size distribution of the water absorbent resin was such that 90 mass% or more was in the range of 45 to 850 μm.

[0124] [Examples 2 to 5, Comparative Examples 1 and 2, and Reference Example 1] Using a monomer mixture selected from acrylamide, N,N-methylenebisacrylamide, and sodium acrylate, polymerization was carried out in the same manner as in Example 1 above, and an additive selected from lauryldimethylaminoacetic acid betaine, polyoxyethylene sorbitan monooleate, and polyethylene glycol (average molecular weight: approximately 600) was added in the same manner as in Example 1 above, or no additive was added, to prepare water absorbent resins of Examples 2 to 5, Comparative Examples 1 and 2, and Reference Example 1. The amounts of raw materials and additives used in the examples, comparative examples, and reference examples are as shown in Table 1 below.

[0125] [Table 1]

[0126] [Test Example 1: Evaluation of adhesion to drying net] The water-absorbent resins 1 to 8 produced in Examples 1 to 5, Comparative Examples 1 and 2, and Reference Example 1 were evaluated for their adhesiveness to a drying net by the following method. First, 1000 g of gel-like water-absorbent resin was placed on a drying net (a SUS net with a frame measuring 30 cm x 20 cm and a height of approximately 10 cm) and dried with hot air at 160 ° C for 130 minutes. After removing from the dryer and allowing the polymer and drying net to cool to room temperature, the drying net was turned upside down, lifted, and allowed to fall freely from a height of approximately 5 cm. This operation was repeated five times, and the weight of the fallen gel (W1 (g)) and the weight of the gel remaining on the drying net (W2 (g)) were measured. Using the measured gel weight, the value calculated according to the following formula (Equation 1) was taken as the adhesion rate to the drying net.

[0127]

number

[0128] [Test Example 2: Evaluation of electrostatic charge (measurement of electrostatic charge amount)] The chargeability (amount of electrostatic charge) of water absorbent resins 1 to 8 produced in Examples 1 to 5, Comparative Examples 1 and 2, and Reference Example 1 was evaluated by the following method. The gel dried in the above Test Example 1 was pulverized with a roll mill to prepare particles having an average particle size (D50) of approximately 400 μm. 20 g of the collected powdered water absorbent resin was placed in a SUS container and shaken 100 times in an insulated state, after which the amount of electrostatic charge was measured with a coulometer (Faraday cage method). The adhesion rates to the drying net and the amounts of electrostatic charge of the water-absorbent resins 1 to 8 determined in the above Test Examples 1 and 2 are shown in Table 2 below.

[0129] [Table 2]

[0130] The results in Table 2 above show that the water absorbent resins of Examples 1 to 5 according to the present invention have electrostatic charge amounts smaller than those of the water absorbent resins of Comparative Examples 1 and 2, are close to the electrostatic charge amount of the anionic crosslinked body of Reference Example 1, and also have improved adhesion rates to the drying net. From these results, it can be understood that the water absorbent resin to which the specific surfactant of the present invention has been added in a specific weight range has significantly improved gel adhesion to the drying net and electrostatic chargeability of the pulverized product.

[0131] [Test Example 3: Water Absorption Test (CRC)] The water absorption capacity of each water-absorbent resin (powder) was measured by the following method. First, a solution for the water absorption test was prepared by mixing 1.72 g of CaSO4·2H2O, 6.96 g of Na2SO4, 4.76 g of K2SO4, 7.12 g of KOH, and 979.4 g of deionized water (pH 12.9). Next, approximately 0.2 g of each water-absorbent resin was accurately weighed (W1 (g)), placed in a 4 cm × 5 cm nonwoven fabric tea bag, and sealed with a heat seal. This tea bag was placed in a glass screw tube with a specified capacity of 50 mL and immersed in 50 mL of the water absorption test solution at room temperature (25°C) and atmospheric pressure for either 120 or 1440 minutes. Next, the tea bag was lifted up by grasping the end of the tea bag with tweezers, placed one side down on a Kimtowel (manufactured by Nippon Paper Crecia Co., Ltd.), and left to stand for 5 seconds. Next, the tea bag was placed on the other side down on the Kimtowel and left to stand for 5 seconds to drain the liquid, and the mass of the tea bag (W2 (g)) was measured. Separately, the same procedure was performed without the water-absorbent resin, and the mass of the tea bag (W3 (g)) at that time was determined as a blank. The value calculated according to the following formula was used as the water absorption ratio.

[0132]

number

[0133] [Table 3]

[0134] The water absorption capacity of the water absorbent resin determined above is as shown in Table 3 (unit of value is g / g). The results in Table 3 show that the water absorption capacity of the water absorbent resins of Examples 1, 2 and 5 according to the present invention after 120 minutes and 1,440 minutes has been shown to be equivalent to that of the water absorbent resin of Comparative Example 2 containing no surfactant. From this result, it can be understood that the water absorbency of the water absorbent resin of the present invention is not significantly affected even if it contains a surfactant.

[0135] [Test Example 4: Concrete Compression Strength Test] The cement used was ordinary Portland cement (manufactured by Taiheiyo Cement Corporation), the fine aggregate was land sand from the Oi River basin, the coarse aggregate was crushed stone from Omi, and the mixing water was tap water. The cement was 573 kg / m 3 , water 172 kg / m 3 {Water / cement ratio (mass ratio): 0.3}, fine aggregate 768 kg / m 3 and coarse aggregate at 866 kg / m 3 A cement composition was prepared containing a water-absorbent resin and a cement dispersant (the cement dispersant is a polycarboxylic acid copolymer aqueous solution (solid content approximately 46.0 mass%) produced as described in paragraph

[0112] of JP 2020-200214 A) at a density of {fine aggregate ratio (fine aggregate / fine aggregate + coarse aggregate) (mass ratio): 47%} at a mixing ratio shown in Table 4 below (in Table 4, the amount of cement dispersant added is the amount added in aqueous solution). Note that the entire amount of the powdered water-absorbent resin was mixed with cement in a mixer before adding water, fine aggregate, and coarse aggregate. The materials used for the measurements, the forced mixing mixer, and measuring instruments were all adjusted to a temperature of 20°C during the measurements, and mixing and measurements were performed under the same temperature. To prevent air bubbles in the cement composition from affecting its fluidity, an oxyalkylene antifoaming agent was used as needed to adjust the air content to 2.0±0.5%. Under the above conditions, concrete was produced using a forced mixing mixer for a mixing time of 90 seconds, and the flow value and air content were measured. The flow value and air content were measured in accordance with the Japanese Industrial Standards (JIS-A-1101:2014, 1128:2014). The amount of cement dispersant added was determined to achieve a flow value of 300mm to 400mm. After measuring the flow value and air content, samples for compressive strength tests were prepared and the compressive strength was measured after 28 days under the following conditions. Test specimen creation: 100mm x 200mm Test specimen curing (28 days): After 24 hours of constant temperature and humidity air curing at a temperature of approximately 20°C and humidity of 60%, the test specimen was wrapped in plastic film to prevent water from passing between the concrete surface and the outside, then placed in a sealed plastic bag and allowed to cure in a sealed state for 27 days. Specimen polishing: Specimen surface polishing (using a specimen polishing finishing machine) Compression strength measurement: Automatic compression strength measuring instrument (Maekawa Manufacturing) The results are shown in Table 4 below.

[0136] [Table 4]

[0137] From the results of Table 4 above, the cement composition using the water-absorbent resin of the Example required the same amount of cement dispersant to obtain the same flow value (fluidity) as the cement composition using the water-absorbent resin of the Comparative Example. Furthermore, the cement composition using the water-absorbent resin of the Example had the same compressive strength after 28 days of sealed curing as the cement composition using the water-absorbent resin of the Comparative Example, and it was confirmed that the compressive strength was improved compared to the cement composition to which no water-absorbent resin was added. Therefore, it is clear that the water-absorbent resin of the example contains a surfactant, but does not affect the fluidity of concrete and can improve the compressive strength.

Claims

1. A method for producing a water-absorbent resin, comprising: The production method includes a step of polymerizing a monomer component including a non-crosslinkable monomer and a crosslinkable monomer; adding a surfactant to the product obtained in the polymerization step; drying the product after the surfactant addition step; and grinding and / or classifying the product obtained in the drying step, the monomer component contains 50 mol % or more of a nonionic non-crosslinkable monomer and 0.05 mol % or more of a crosslinkable monomer, The method for producing a water-absorbent resin, wherein the surfactant is an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant.

2. The method for producing a water-absorbent resin according to claim 1, wherein the ionic surfactant is an amphoteric surfactant.

3. 2. The method for producing a water-absorbent resin according to claim 1, wherein the polyoxyalkylene glycol-type nonionic surfactant is a polyoxyalkylene sorbitan fatty acid ester.

4. The nonionic non-crosslinkable monomer is at least one selected from the group consisting of (meth)acrylamide-based monomers, N-vinyl lactam-based monomers, hydroxyl group-containing (meth)acrylates, and vinyl cyanide-based monomers. The method for producing a water-absorbing resin according to claim 1.

5. 2. The method for producing a water-absorbing resin according to claim 1, wherein the amount of surfactant added in the surfactant addition step is 0.01 to 10 mass% with respect to 100 mass% of the solid content of the product obtained in the polymerization step.

6. A cement additive comprising a water-absorbing resin and a surfactant, The water-absorbent resin has a structural unit derived from a nonionic non-crosslinkable monomer and a structural unit derived from a crosslinkable monomer, the proportion of structural units derived from the nonionic non-crosslinkable monomer is 50 mol % or more, and the proportion of structural units derived from the crosslinkable monomer is 0.05 mol % or more; The cement additive, wherein the surfactant is an ionic surfactant and / or a polyoxyalkylene glycol-type nonionic surfactant.

7. 7. The cement additive according to claim 6, wherein the ionic surfactant is an amphoteric surfactant.

8. 7. The cement additive according to claim 6, wherein the polyoxyalkylene glycol type nonionic surfactant is a polyoxyalkylene sorbitan fatty acid ester.

9. The cement additive according to claim 6, wherein the nonionic non-crosslinkable monomer is at least one selected from the group consisting of (meth)acrylamide-based monomers, N-vinyl lactam-based monomers, hydroxyl group-containing (meth)acrylates, and vinyl cyanide-based monomers.

10. 7. The cement additive according to claim 6, wherein the content of the surfactant is 0.01 to 10 mass% relative to 100 mass% of the solid content of the water-absorbing resin.

11. A cement composition comprising the cement additive according to any one of claims 6 to 10 and cement.

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