JP2006160774A - Manufacturing method of water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a water-absorbing resin suffering from neither discoloration nor deterioration in re-wettability. <P>SOLUTION: The manufacturing method of the water-absorbing resin comprises a step for mixing a hydrous gel (A), composed of a water-absorbing resin and water, with a low-melting auxiliary drying agent (B1) ämelting point (1013.25 hPa) of lower than 50°C} having a solubility in water (25°C) of 0-2 g/100 g water and a Hazen color number of 0-300 after a heat treatment at 150°C for 3 hr and/or a high-melting auxiliary drying agent (B2) ämelting point of 50°C or higher} having a solubility in water (25°C) of 0-2 g/100 g water and a Hunter whiteness of 40-94 after a heat treatment at 150°C for 3 hr to obtain a mixture and a step for drying the mixture in a still standing state. Preferably, the amount of (B1) and/or (B2) used is 0.001-1 wt% based on the weight of the water-absorbing resin. Preferably, (B1) and (B2) have each an HLB value of 0-10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a water absorbent resin.

In the production process of the water-absorbent resin, when drying the water-containing gel comprising the water-absorbent resin and water, a surfactant is added to the water-containing gel in order to prevent the water-containing gel from fusing together and causing a decrease in drying efficiency. A method of drying under standing is known (Patent Document 1).
JP 2000-143720 A

  However, in the conventional method, there is a problem that the obtained water-absorbing resin is colored due to the influence of the surfactant to be added, or the rewetting property when the obtained water-absorbing resin is applied to a water-absorbent article is lowered. is there. That is, an object of the present invention is to provide a production method for obtaining a water-absorbent resin that is free from coloring and rewetting.

As a result of intensive studies in order to solve the above problems, the present inventors have found that a specific production method achieves the above object and have reached the present invention.
That is, the method for producing a water-absorbent resin of the present invention includes a water-containing gel (A) comprising a water-absorbent resin and water,
Low melting point drying aid (B1) having a solubility in water (25 ° C.) of 0 to 2 g / 100 g water and a Hazen unit color number of 0 to 300 after heat treatment at 150 ° C. for 3 hours {melting point (1013. 25 hPa) is less than 50 ° C.} and / or water solubility (25 ° C.) is 0 to 2 g / 100 g water, and the hunter whiteness after heat treatment at 150 ° C. for 3 hours is 40 to 94. Mixing the agent (B2) {melting point is 50 ° C. or higher} to obtain a mixture,
In addition, the gist includes a step of drying the mixture in a stationary state.

  According to the production method of the present invention, the resulting water-absorbent resin is free from coloring and rewetting. Furthermore, since the water-containing gel can be dried very efficiently, the drying time of the water-containing gel can be shortened, and the productivity of the water-absorbent resin can be significantly improved.

The water-absorbing resin constituting the hydrogel (A) is a crosslinked polymer that swells by absorbing water, and becomes a water-absorbing resin by drying.
Examples of the water-absorbing resin include the polymers (1) to (9), but are not limited to these and widely include water-absorbing resins that can absorb water. A mixture of two or more of these polymers may be used.
-Starch-acrylic acid (salt) graft-crosslinked copolymer (1) described in JP-B-53-46199 or JP-B-53-46200.
-Crosslinked polyacrylic acid (salt) (2) obtained by aqueous solution polymerization (adiabatic polymerization, thin film polymerization, spray polymerization, etc.) described in JP-A-55-133413.
-Crosslinked polyacrylic acid (salt) (3) obtained by reverse phase suspension polymerization described in JP-B-54-30710, JP-A-56-26909 or JP-A-11-5808.
A saponified product (4) of a copolymer of a vinyl ester and an unsaturated carboxylic acid or a derivative thereof described in JP-A-52-14689 or JP-A-52-27455.
A copolymer (5) of acrylic acid (salt) and a sulfo (sulfonate) group-containing monomer described in JP-A-58-2312 or JP-A-61-36309.
A saponified product of a crosslinked isobutylene-maleic anhydride copolymer described in US Pat. No. 4,389,513 (6).
-A starch-acrylonitrile copolymer hydrolyzate described in JP-A-46-43995 and the like (7).
A crosslinked carboxymethyl cellulose derivative (8) described in US Pat. No. 4,650,716.
-JP2003-052742A, JP2003-082250A, JP2003-165883A, JP20031655883A, JP2003-176421A, JP2003-183528A, JP2003. High-performance water absorption described in JP-A No. 192732, JP-A No. 2003-225565, JP-A No. 20030386696, JP-A No. 2003-335970, JP-A No. 2004-091673 or JP-A No. 2004-123835 Resin (9).

  Among these, from the viewpoint of production cost and absorption performance, etc., starch-acrylic acid (salt) graft copolymer crosslinked product (1), crosslinked polyacrylic acid (salt) obtained by aqueous solution polymerization (2), reverse phase suspension Cross-linked polyacrylic acid (salt) (3) and high-performance water-absorbing resin (9) obtained by polymerization are preferred, (2), (3) and (9) are more preferred, and (2) and (9 are particularly preferred. ).

The polymerization method of the water-absorbent resin is not particularly limited, and examples thereof include aqueous solution polymerization and reverse layer suspension polymerization. Polymerization concentration, polymerization initiation temperature, polymerization initiator, presence / absence of heat removal during polymerization, polymerization apparatus, etc. There are no particular limitations on the polymerization conditions, and known conditions can be applied.
The water-absorbent resin preferably contains a salt structure {carboxylate (carboxylate group), sulfonate (sulfonate group), etc.} in the structure.
In order to obtain such a salt structure, some or all of the monomers may be polymerized after being converted into a salt, or may be converted into a salt after polymerization, or a combination thereof.
As a polymerization method, aqueous solution polymerization is carried out using acrylic acid as an essential constituent monomer, and then neutralized with an alkali metal compound (sodium hydroxide, sodium hydrogen carbonate, potassium hydroxide, lithium hydroxide, etc.) to obtain a hydrous gel (A). It is preferable to include the process of obtaining.

The water-absorbent resin can be subjected to surface crosslinking treatment with a surface crosslinking agent. The surface-crosslinked water-absorbing resin is suitable because the amount of absorbed liquid under load is increased.
Examples of the surface cross-linking agent include polyhydric glycidyl described in JP-A-59-189103, polyhydric alcohol, polyhydric amine described in JP-A-58-180233, JP-A-61-16903, and the like. , Polyaziridines and polyisocyanates, silane coupling agents described in JP-A-61-211305 or JP-A-61-225212 and the like, and JP-A-51-136588 or JP-A-61- And multivalent metals described in Japanese Patent No. 257235. Among these surface cross-linking agents, a comparatively low surface cross-linking reaction and a viewpoint that a water-absorbing resin excellent in the amount of liquid absorbed under load can be obtained by forming a strong covalent bond with a carboxyl (carboxylate) group. From the viewpoint of being economical because it can be carried out at a low temperature, polyvalent glycidyl, polyvalent amine and silane coupling agent are preferred, more preferred are polyvalent glycidyl and silane coupling agent, and particularly preferred are polyvalent glycidyl. Glycidyl.

When using a surface cross-linking agent, the amount (% by weight) of the surface cross-linking agent is not particularly limited because it can be variously changed depending on the type of surface cross-linking agent, surface cross-linking conditions, target performance, etc. From the viewpoint of absorption performance, etc., 0.001 to 3 is preferable, more preferably 0.005 to 2, and particularly preferably 0.01 to 1, based on the weight of the water absorbent resin before surface crosslinking.
When the water absorbent resin is produced in the presence of water (usually produced in this manner), the surface cross-linking agent is used before the water-containing gel (A) containing the water absorbent resin and water is dried (A It may be performed at any stage such as during the drying of (A) and after the drying of (A), but from the viewpoint of adjusting the crosslinking conditions, the stage during the drying of (A) or after the drying of (A) preferable. In addition, when surface cross-linking after drying, there is a difference in whether the water-absorbent resin contained in the hydrogel (A) and the produced water-absorbent resin are surface cross-linked or not, but for convenience, the same terms are used. Yes.

As a method for performing the surface cross-linking treatment, a conventionally known method can be applied, for example, a mixed solution composed of a surface cross-linking agent, water and / or an organic solvent is mixed with a water-absorbent resin or a hydrous gel (A), and subjected to a heat reaction, etc. Is applicable.
In the case of the above method, the amount (% by weight) of water used for the surface cross-linking treatment is based on the weight of the water-absorbent resin before surface cross-linking from the viewpoint of the penetration of the surface cross-linking agent into the water-absorbent resin. 1 to 10 is preferable, more preferably 1.5 to 8, and particularly preferably 2 to 7.
In the case of the above method, as the type of organic solvent used in the surface cross-linking treatment, a conventionally known hydrophilic solvent or the like can be used, the permeability of the surface cross-linking agent into the water-absorbent resin, It can be selected as appropriate in consideration of reactivity, etc., but it can be dissolved in water at an arbitrary ratio such as alcohol having 1 to 4 carbon atoms (methanol, ethanol, ethylene glycol, propylene glycol, diethylene glycol, etc.). A solvent is preferred.
An organic solvent may be used independently and may use 2 or more types together.
Moreover, when using an organic solvent, the amount used (% by weight) can be variously changed depending on the type of the organic solvent, but is 0.2 to 20 based on the weight of the water-absorbent resin before surface crosslinking. More preferably, it is 0.5-15, Most preferably, it is 1-10.
Moreover, when using water and an organic solvent, the usage-ratio of the organic solvent with respect to water can be changed arbitrarily, but the usage-amount (weight%) of an organic solvent is 20-80 based on the weight of water. More preferably, it is 25-75, Most preferably, it is 30-70.
The surface crosslinking treatment temperature (° C.) is preferably 80 to 200, more preferably 90 to 180, and particularly preferably 100 to 160.
Further, the reaction time (minutes) of the surface crosslinking treatment can be changed depending on the reaction temperature or the like, but is preferably 3 to 60, more preferably 5 to 50, and particularly preferably 10 to 40.
The water absorbent resin obtained by surface cross-linking with a surface cross-linking agent may be subjected to additional surface cross-linking with the same type of surface cross-linking agent or a different type of surface cross-linking agent. The amount of the additional surface cross-linking agent used, the processing method, the processing temperature, the processing time, etc. are the same as in the above case.

The hydrogel (A) is a non-fluid gel-like body composed of a water-absorbing resin and water, and is usually 15 to 90 (preferably 30 to 85, more preferably 45 to 45) based on the weight of (A). 75) Contains water by weight.
The size of the hydrogel (A) is not particularly limited. However, from the viewpoint of drying efficiency and the like, the size (mm, maximum length) of the hydrogel (A) is preferably from 1 to 15, more preferably from 1 to 15 when the hydrogel (A) is obtained by an aqueous solution polymerization method. 10, then preferably 1 to 8, particularly preferably 2 to 7, most preferably 3 to 7. When the hydrogel (A) is obtained by the reverse layer suspension polymerization method, 0.1 to 4 More preferably 0.15 to 3, then preferably 0.2 to 2.5, particularly preferably 0.25 to 2.0, and most preferably 0.3 to 1.5.

The low melting point drying aid (B1) and the high melting point drying aid (B2) are used to prevent the fusion of the hydrogel (A) between the gels in the process of drying the hydrogel (A) in a stationary state. It is a compound that can improve the air permeability of hot air and improve the drying efficiency.
Further, the low melting point drying aid (B1) and the high melting point drying aid (B2) may be either liquid or solid, and in the case of a solid, the shape is not particularly limited, but is preferably granular. The shape is preferably spherical, granular, crushed, acicular, flaky, or agglomerated such that these primary particles are fused together. In the case of a solid, the size of (B) is not particularly limited, but the particle size (μm) of 90% by weight or more (preferably 93% by weight or more, more preferably 95% by weight or more) of the total weight. Is preferably 38 to 850, more preferably 63 to 710, particularly preferably 106 to 500, and most preferably 150 to 300 or less.
In addition, content (weight%) of each particle diameter is measured using the sieve prescribed | regulated to the low tap test sieve shaker and JISZ8801-1: 2000 based on JISZ8815-1994. That is, JIS standard sieves are combined in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 300 μm, 150 μm and the saucer from the top, or in the order of 425 μm, 300 μm, 250 μm, 150 μm, 106 μm, 75 μm, 38 μm and the saucer from the top. . About 50 g of measurement sample particles are put in the uppermost stage sieve and vibrated for 5 minutes with a low-tap test sieve shaker. The weight of the measurement sample on each sieve and the pan is weighed, and the weight fraction of the measurement sample on each sieve is obtained by taking the total as 100% by weight. The value of each sieve is a logarithmic probability paper {horizontal axis is sieve opening After plotting (particle diameter) and ordinate is weight fraction}, a line connecting the points is drawn to obtain a “particle diameter-weight fraction” line. And content of each particle diameter range is computed from this line.

  The solubility (g) of the low melting point drying aid (B1) and the high melting point drying aid (B2) in 100 g of water at 25 ° C. is preferably 0 to 2, more preferably 0 to 1.5, and then preferably. Is 0 to 1, particularly preferably 0 to 0.5, still more preferably 0 to 0.2, and most preferably 0 to 0.1. Within this range, the drying property of the hydrogel (A) and the rewetting property of the water-absorbent resin are further improved.

The HLB value of the low melting point drying aid (B1) and the high melting point drying aid (B2) is preferably 0 to 10, more preferably 0 to 7, then preferably 0 to 5, particularly preferably 0 to 4, More preferably, it is 1-4, and most preferably 1-3. Within this range, the drying property of the hydrogel (A) and the rewetting property of the water-absorbent resin are further improved.
The HLB value means a hydrophilic-hydrophobic balance (HLB) value, and is determined by the Griffin method (Introduction of new surfactants, pages 127-129, Takehiko Fujimoto, Sanyo Chemical Industries, Ltd., published in 1981). It is done.

The melting point (1 atm = 101.25 hPa) of the low melting point drying aid (B1) is not particularly limited as long as it is less than 50 ° C, but is preferably 25 ° C or less, more preferably 15 ° C or less, from the viewpoint of handling properties. Especially preferably, it is 0 degreeC or less.
The melting point (1 atm = 101.25 hPa) of the high melting point drying aid (B2) is not particularly limited as long as it is 50 ° C. or higher, but is preferably 50 to 100 ° C., more preferably 50 to 80 from the viewpoint of handling properties. ° C, particularly preferably 50 to 65 ° C.
The melting point is measured according to JIS K0064: 1992.

  The Hazen unit color number after heating at 150 ° C. for 3 hours of the low melting point drying aid (B1) is preferably 0 to 300, more preferably 0 to 250, still more preferably 0 to 200, and then preferably 0 to 150, Especially preferably, it is 0-100, More preferably, it is 0-80, Most preferably, it is 0-50. Within this range, coloring of the resulting water-absorbent resin can be further suppressed. The Hazen unit color number is measured according to JIS K0071-1: 1998.

The Hunter whiteness of the high melting point drying aid (B2) after heating at 150 ° C. for 3 hours is preferably 40 to 94, more preferably 50 to 94, still more preferably 60 to 94, and then preferably 70 to 90, particularly Preferably it is 75-90, More preferably, it is 75-85, Most preferably, it is 77-83. Within this range, coloring of the water absorbent resin obtained after drying can be further suppressed.
The Hunter whiteness is calculated from the following equation using the stimulus value (Z) measured by the condition d in accordance with 5.3 of JIS Z8722: 2000 {for example, the colorimetric color difference meter ZE-2000 (Measured using Nippon Denshoku Industries Co., Ltd.)}.
Hunter whiteness is measured using a cooled plate-shaped measurement sample after a 150 ° C. melt is put into a measurement cell when the melting point of the high melting point drying aid (B2) is 50 to 150 ° C. When the melting point of the high melting point drying aid (B2) exceeds 150 ° C., the measurement sample (B) is pulverized and measured using a measurement sample passed through a 1000 μm sieve.

  As the low melting point drying aid (B1), monohydric alcohol (B11) having 10 to 16 carbon atoms, polyhydric (2 to 5 valent) alcohol (B12) having 6 to 16 carbon atoms, silicone oil (B13), modified Silicone oil (B14), oxyethylene-containing compound (B15), oxypropylene-containing compound (B16), ester (B17) and the like are included.

  As monohydric alcohol (B1) having 10 to 16 carbon atoms, n-decyl alcohol, n-dodecyl alcohol, n-tetradecyl alcohol, n-pentadecyl alcohol, n-hexadecyl alcohol, isodecyl alcohol, isododecyl alcohol , Isotetradecyl alcohol, isopentadecyl alcohol, and isohexadecyl alcohol.

  Examples of the polyhydric (2-5 valent) alcohol (B12) having 6 to 16 carbon atoms include 1,6-hexanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, , 16-hexadecanediol, diglycerin, triglycerin and the like.

  Examples of the silicone oil (B13) include dimethyl silicone oil having a viscosity at 25 ° C. of 5 to 30000 (preferably 10 to 10000, more preferably 15 to 5000, particularly preferably 20 to 1000) mPa · s.

As the modified silicone oil (B14), alkyl-modified silicone oil (KF-412: manufactured by Shin-Etsu Chemical Co., Ltd. and SH230: manufactured by Toray Dow Corning Co., Ltd.), phenyl-modified silicone oil (SH510: manufactured by Toray Dow Corning Co., Ltd.) , Fluorine-modified silicone oil (FS1265: manufactured by Toray Dow Corning Co., Ltd.), amino-modified silicone oil (KF-880: manufactured by Shin-Etsu Chemical Co., Ltd. and SF8417: manufactured by Toray Dow Corning Co., Ltd.), epoxy-modified silicone oil (KF105: Shin-Etsu Chemical Co., Ltd. and SF8411: manufactured by Toray Dow Corning Co., Ltd.), phenol-modified silicone oil (X-22-1821: manufactured by Shin-Etsu Chemical Co., Ltd. and BY16-752: manufactured by Toray Dow Corning Co., Ltd.), carboxyl-modified silicone Oil (X-22- 701E: manufactured by Shin-Etsu Chemical Co., Ltd. and SF8418: manufactured by Toray Dow Corning Co., Ltd.), mercapto-modified silicone oil (KF-2001: manufactured by Shin-Etsu Chemical Co., Ltd.) and methacryl-modified silicone oil (X-22-2426: Shin-Etsu Chemical Co., Ltd.) Etc.).
The viscosity (mPa · s) of the modified silicone oil (B14) is preferably 5 to 30000, more preferably 10 to 10000, and particularly preferably 20 to 3000 from the viewpoints of drying efficiency and handling properties. There is no restriction | limiting about the modification | denaturation position (both terminal modification | denaturation, one terminal modification | denaturation, side chain modification, etc.) of the modified silicone oil (B4) and the degree of modification.

As the oxyethylene-containing compound (B15), an ethylene oxide 1-8 mol adduct (B151) of alcohol and an ethylene oxide 1-8 mol adduct (B152) of carboxylic acid can be used.
The number of additions (moles) of ethylene oxide is preferably 1 to 8, more preferably 1 to 6, particularly preferably 1 to 4, then preferably 1 to 3, and most preferably 1 or 2 in one molecule. .
Examples of the alcohol include monohydric alcohol (B11) having 10 to 16 carbon atoms, polyhydric (2 to 5 valent) alcohol (B12) having 6 to 16 carbon atoms, monohydric alcohol having 17 to 30 carbon atoms, and 2 to 2 carbon atoms. 5 polyhydric (2 to 6 valent) alcohols, polyhydric (hexavalent) alcohols having 6 to 30 carbon atoms, and the like are included.
Examples of the monohydric alcohol having 17 to 30 carbon atoms include isooctadecyl alcohol, isoicosyl alcohol, and isotriacontyl alcohol.
Examples of the polyhydric (2-6 valent) alcohol having 2 to 5 carbon atoms include ethylene glycol, diethylene glycol, propylene glycol, glycerin, pentaerythritol, 1,4-butanediol and the like.
Examples of the polyhydric (hexavalent) alcohol having 6 to 30 carbon atoms include dipentaerythritol, tetraglycerin and sorbitol.

Examples of the carboxylic acid include monovalent carboxylic acid and polyvalent (2-6 valent) carboxylic acid.
Examples of monovalent carboxylic acids include carboxylic acids having 1 to 30 carbon atoms such as formic acid, acetic acid, propionic acid, myristic acid, stearic acid, linoleic acid, linolenic acid, oleic acid, glycolic acid, lactic acid, and gluconic acid. Is mentioned.
Examples of polyvalent (2-6 valent) carboxylic acids include carboxylic acids having 4 to 10 carbon atoms such as succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, itaconic acid and tartaric acid. Can be mentioned.

As the oxypropylene-containing compound (B16), propylene oxide 1-70 mol adduct (B161) of alcohol, propylene oxide 1-70 mol adduct (B162) of carboxylic acid, and propylene oxide 1 of the above oxyethylene-containing compound -70 mol addition compound (B163) etc. can be used.
The addition number (mol) of propylene oxide is preferably 1 to 70, more preferably 2 to 50, particularly preferably 4 to 35, next preferably 6 to 30, and most preferably 8 to 25 in one molecule. is there.
Examples of the alcohol include monohydric alcohols having 1 to 9 carbon atoms in addition to the above alcohols.
Examples of the monohydric alcohol having 1 to 9 carbon atoms include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-hexanol, and n-pentanol. , 2-ethylhexanol, n-octanol and the like.

Examples of the ester (B17) include organic acids {monovalent carboxylic acids, polyvalent (2-6 valent) carboxylic acids and the like described above and below] or inorganic acids {sulfuric acid and phosphoric acid and the like}, monovalent alcohols, poly An ester compound with a divalent (2-6 valent) alcohol, an alcohol or carboxylic acid ethylene oxide adduct, or an alcohol or carboxylic acid propylene oxide adduct can be used.
Examples of the ester (B17) include butyl acetate and ethylene glycol acetic acid diester.
These ester compounds are not limited as long as they have at least one ester bond, and the ester (B17) has a carboxylate group {alkali metal (sodium, potassium, etc.) ions etc. as counter ions}. May be included.

  Of these low melting point drying aids (B1), silicone oil (B13), modified silicone oil (B14), oxyethylene-containing compound (B15) and oxypropylene-containing compound (B16) are preferable, and more preferably modified silicone oil. (B14), oxyethylene-containing compound (B15) and oxypropylene-containing compound (B16), particularly preferably oxyethylene-containing compound (B15) and oxypropylene-containing compound (B16), most preferably oxyethylene-containing compound (B15). preferable.

As the high melting point drying aid (B2), a monohydric alcohol (B21) having 17 to 30 carbon atoms, a polyhydric (hexavalent) alcohol (B22) having 6 to 30 carbon atoms, an oxyethylene-containing compound (B23) and an ester (B24) and the like are included.
Examples of the monohydric alcohol (B21) having 17 to 30 carbon atoms include n-octadecyl alcohol, n-icosyl alcohol, n-triacontyl alcohol, isooctadecyl alcohol, isoicosyl alcohol and isotriacontyl alcohol. It is done.
Examples of the polyvalent (hexavalent) alcohol (B22) having 6 to 30 carbon atoms include dipentaerythritol, tetraglycerin and sorbitol.

As the oxyethylene-containing compound (B23), an ethylene oxide 1 to 8 mol adduct (B231) of alcohol and an ethylene oxide 1 to 8 mol adduct (B232) of carboxylic acid can be used.
The number of additions (moles) of ethylene oxide is preferably 1 to 8, more preferably 1 to 6, particularly preferably 1 to 4, then preferably 1 to 3, and most preferably 1 or 2 in one molecule. .
Examples of the alcohol include a monohydric alcohol (B21) having 17 to 30 carbon atoms and a polyvalent (hexavalent) alcohol (B22) having 6 to 30 carbon atoms.
Examples of the carboxylic acid include polyvalent (2-6 valent) carboxylic acids.
Examples of monovalent carboxylic acids include carboxylic acids having 1 to 30 carbon atoms, such as formic acid, acetic acid, propionic acid, myristic acid, stearic acid, linoleic acid, linolenic acid, oleic acid, glycolic acid, lactic acid, and gluconic acid. Is mentioned.
The polyvalent (2 to 6 valent) carboxylic acids include carboxylic acids having 4 to 10 carbon atoms, and include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid, and pyromellitic acid. An acid etc. are mentioned.

As the ester (B24), an organic acid {the above-mentioned monovalent carboxylic acid, polyvalent (2 to 6-valent) carboxylic acid, etc.} or an inorganic acid {sulfuric acid, phosphoric acid, etc.} and the above-mentioned monohydric alcohol, polyvalent ( Divalent to hexavalent) alcohols, alcohol or carboxylic acid ethylene oxide adducts, or ester compounds of alcohol or carboxylic acid propylene oxide adducts can be used.
Examples of the ester (B17) include ethylene glycol stearic acid monoester and ethylene glycol stearic acid diester.
These ester compounds are not limited as long as they have at least one ester bond, and the ester (B4) has a carboxylate group {alkali metal (sodium, potassium, etc.) ions etc. as counter ions}. May be included.

  Of these high melting point drying aids (B2), oxyethylene-containing compounds (B23) and esters (B24) are preferred, and oxyethylene-containing compounds (B23) are more preferred.

Preferred examples of the low melting point drying aid (B1) include the following compounds.

Preferred examples of the high melting point drying aid (B2) include the following compounds.

The used amount (% by weight) of the low melting point drying aid (B1) and / or the high melting point drying aid (B2) is 0.001-1 based on the weight of the water-absorbent resin contained in the hydrogel (A). More preferably 0.002 to 0.7, next preferably 0.005 to 0.4, particularly preferably 0.01 to 0.2, still more preferably 0.02 to 0.15, most preferably Preferably it is 0.03-0.1. Within this range, the drying property of the hydrogel (A) is further improved, and coloring of the water absorbent resin can be further suppressed.
When both the low melting point drying aid (B1) and the high melting point drying aid (B2) are used, their use ratio (B1 / B2; weight ratio) is preferably 90 to 10/10 to 90, and more preferably. Is 75-25 / 25-75, particularly preferably 60-40 / 40-60.

  There is no particular limitation on the method of mixing the hydrogel (A) with the low melting point drying aid (B1) and / or the high melting point drying aid (B2), and (B1) and (B2) are the surfaces of (A). And / or may be mixed so that they exist inside, and may be mixed so that (B1) and (B2) exist uniformly or non-uniformly. The low melting point drying aid (B1) and the high melting point drying aid (B2) are preferably present on at least the surface of (A).

  As a method of mixing the hydrous gel (A) with the low melting point drying aid (B1) and / or the high melting point drying aid (B2), (1) (A) is stirred while (B1) and / or ( B2) is added (including spray, etc., the same applies hereinafter) and mixed. (2) In advance, (B1) and / or (B2) is mixed with (A) at a high concentration to prepare a master batch. In addition, a method of adding the master batch to (A) and mixing so that a predetermined addition amount as (B1) and / or (B2) can be applied.

The low-melting-point drying aid (B1) and / or the high-melting-point drying aid (B2) can be added directly (in neat form such as a lump, powder, liquid, etc.) or in any form of a solution or a dispersion, It is preferable to add in the form of a solution or a dispersion.
When adding with the form of a solution or a dispersion liquid, a well-known thing can be used as a solvent or a dispersion medium used in order to set it as these forms.
When added as a solution or dispersion, the ratio of the low melting point drying aid (B1) and the high melting point drying aid (B2) to the solvent or dispersion medium {(B1) and (B2) / solvent or dispersion medium} is particularly Although there is no restriction | limiting, 0.01-10 / 100 is preferable, More preferably, it is 0.01-5 / 100, Most preferably, it is 0.05-5 / 100.
Moreover, when adding with a dispersion liquid, a dispersing agent can be used as needed and a well-known thing can be used as a dispersing agent. When the dispersant is used, the ratio of the low melting point drying aid (B1) and the high melting point drying aid (B2) to the dispersant {(B1) and (B2) / dispersant} is not particularly limited. 100 / 0.01-20 are preferable, More preferably, it is 100 / 0.1-15, Most preferably, it is 100 / 1-10, Most preferably, it is 100 / 3-7.

The addition timing of the low melting point drying aid (B1) and / or the high melting point drying aid (B2) is not particularly limited as long as it is before the step of drying the mixture in a stationary state, but in the case of aqueous solution polymerization, Immediately before the polymerization step, during the polymerization step, immediately after the polymerization step, during the chopping step of the hydrogel, immediately after the chopping step of the hydrogel and immediately before the drying step of the mixture, more preferably immediately before the polymerization step, during the polymerization step, Immediately after the polymerization step, during the chopping step of the hydrogel and immediately after the chopping step of the hydrogel, particularly preferably immediately before the polymerization step, during the polymerization step, immediately after the polymerization step and during the chopping step of the hydrogel, most preferably of the polymerization step Immediately before, immediately after the polymerization step and during the shredding step of the hydrogel.
In the case of reverse phase suspension polymerization, immediately before the polymerization step, during the polymerization step, immediately after the polymerization step, during the step of separating the water-swellable crosslinked polymer obtained by the polymerization and the organic solvent used for the polymerization, and in the polymerization Preferably after the step of separating the obtained water-swellable crosslinked polymer and the organic solvent used for the polymerization, more preferably immediately before the polymerization step, immediately after the polymerization step, and the water-swellable crosslinked polymer obtained by polymerization and polymerization After the step of separating the organic solvent used for the polymerization, particularly preferably immediately after the polymerization step and after the step of separating the water-swellable crosslinked polymer obtained by the polymerization and the organic solvent used for the polymerization, most preferably immediately after the polymerization step It is.

  There are no particular restrictions on the device that can mix the hydrogel (A) with the low melting point drying aid (B1) and / or the high melting point drying aid (B2), but a conical blender, internal mixer (Banbury mixer), self Cleaning type mixer, gear compounder, screw type extruder, screw type kneader, mincing machine, nauter mixer, double arm type kneader, V type mixer, fluidized bed type mixer, turbulizer, screw type line blending device Mechanical mixing devices such as a ribbon mixer and a mortar mixer are preferably used. These can also be used in combination.

Drying in a stationary state means that the mixture of the hydrogel (A) and the low melting point drying aid (B1) and / or the high melting point drying aid (B2) enters the dryer and then the machine from the outside. It means to dry without adding mechanical stirring.
In addition, there is no restriction | limiting in particular in drying, even if it is batch drying or continuous drying.
Although there is no restriction | limiting in particular as an apparatus which can dry the mixture of a hydrogel (A), a low melting-point drying auxiliary agent (B1), and / or a high melting point drying auxiliary agent (B2), A parallel flow band dryer (tunnel dryer) ), An aeration band dryer, a jet flow (nozzle jet) dryer, a ventilated solid dryer, a box-type hot air dryer, and the like are preferably used. A plurality of these can also be used in combination. Moreover, it does not specifically limit about the heat sources (steam, a heat medium, etc.) of these dryers.

The production method of the present invention includes a pulverization step, a particle size adjustment step, and the like after the mixture of the hydrogel (A) and the low melting point drying aid (B1) and / or the high melting point drying aid (B2) is dried. But you can.
For the water-absorbent resin produced by the production method of the present invention, additives {preservatives, fungicides, antibacterial agents, antioxidants, ultraviolet absorbers, colorants, fragrances, deodorants, as necessary. , Inorganic powder, fibrous material, etc.} can be added.
The timing of adding these additives is not particularly limited as long as it is after the polymerization step, but in the case of aqueous solution polymerization, the hydrated gel shredding step, immediately after the hydrated gel shredding step, the mixture drying step Immediately before the surface crosslinking step and immediately after the surface crosslinking step are preferred. In the case of reverse phase suspension polymerization, immediately after the polymerization step, preferably after the step of separating the water-absorbent resin obtained by polymerization and the solvent used in the polymerization, immediately after the drying step, and immediately after the surface cross-linking step. .
When using an additive, the content of the additive is not particularly limited, but the additive is an antiseptic, fungicide, antibacterial agent, antioxidant, ultraviolet absorber, fragrance and / or deodorant. The content (% by weight) is preferably 0.00001 to 10, more preferably 0.00005 to 5, based on the weight of the water absorbent resin. When the additive is a colorant, inorganic powder and / or fibrous material, the content (% by weight) is preferably 0.1 to 25, more preferably 0 based on the weight of the water absorbent resin. 2-15.

The shape of the water-absorbing resin is not particularly limited, but is preferably granular, and more preferably spherical, granular, crushed, needle-like, flake-like, and agglomerated such that these primary particles are fused together.
The size of the water absorbent resin is not particularly limited, but the particle diameter (μm) of 90% by weight or more (preferably 93% by weight or more, more preferably 95% by weight or more) of the total weight of the water absorbent resin is 38 to 1180. More preferably, it is 63-1000, Most preferably, it is 106-850, Most preferably, it is 150-710.
The size (particle diameter) of the water-absorbent resin is measured in accordance with JIS Z8815-1994 using a low tap test sieve shaker and a sieve specified in JIS Z8801-1: 2000 (hereinafter referred to as particle diameter). Is measured by this method). That is, JIS standard sieves are combined in the order of 1180 μm, 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 300 μm and the saucer from the top, or in the order of 425 μm, 300 μm, 250 μm, 150 μm, 106 μm, 63 μm, 38 μm and the saucer from the top. . About 50 g of measurement sample particles are put in the uppermost stage sieve and vibrated for 5 minutes with a low-tap test sieve shaker. The weight of the measurement sample on each sieve and the pan is weighed, and the weight fraction of the measurement sample on each sieve is obtained with the total as 100%. The value of each sieve is logarithmic probability paper {the horizontal axis is the sieve opening ( (Particle diameter) and the vertical axis is plotted as weight fraction}, then a line connecting each point is drawn to obtain a “particle diameter-weight fraction” line. And content of each particle diameter range is computed from this line.

  The surface tension (dyne / cm) of the water-absorbent resin that can be produced by the production method of the present invention is preferably 60 to 73, more preferably 62 to 73, particularly preferably 64 to 73, still more preferably 66 to 73, Most preferably, it is 68-73. Within this range, rewetting is further improved when the water absorbent resin that can be produced by the production method of the present invention is applied to a water absorbent article such as a disposable diaper or a sanitary napkin.

The surface tension of the water absorbent resin is measured by the following method.
<Method for measuring surface tension of water-absorbent resin>
In a 250 ml glass beaker, 200 ml of a 0.9% sodium chloride aqueous solution (saline) and a stirrer piece (total length 37 mm) are stirred at 600 ± 5 rpm, and 1.000 ± 0.005 g of sample is placed. Stirring is continued for 15 minutes, and after standing for 15 minutes, 25 g of the supernatant liquid is immediately weighed in a petri dish having a diameter of 58 mm and a height of 17 mm, and is subjected to a denier surface tension meter (for example, Denyu surface tension meter manufactured by Shimadzu Corporation). Immediately measure the surface tension of the supernatant. This operation is repeated three times, and these arithmetic average values are defined as the surface tension of the water absorbent resin.

  The Hunter whiteness of the water-absorbent resin that can be produced by the production method of the present invention is preferably 60 to 94, more preferably 63 to 94, particularly preferably 66 to 94, still more preferably 69 to 94, most preferably. 72-94. Within this range, when the water-absorbing resin is applied to a water-absorbing article such as a paper diaper or sanitary napkin, the water-absorbing resin is further less noticeable and a water-absorbing article that is visually uncomfortable is obtained. .

The water absorbent resin that can be produced by the production method of the present invention is suitable as a material constituting the water absorbent article.
Sanitary goods are typical of water-absorbent articles, such as disposable diapers (children's disposable diapers and adult disposable diapers, etc.), napkins (sanitary napkins, etc.), vomit-absorbing etiquette bags, paper towels, pads (patents for incontinence) And surgical underpads) and pet sheets (pet urine absorption sheets and heat insulation sheets). In addition to these sanitary products, various household and industrial absorbent sheets (freshness-maintaining sheets, drip absorbent sheets, paddy rice seedling sheets, concrete curing sheets, water running prevention sheets such as cables, etc.) and the like can be mentioned. .
Of these, the water-absorbent resin that can be produced by the production method of the present invention is particularly suitable for disposable diapers, pads, and sanitary napkins.

The water absorbent resin obtained by the production method of the present invention and the water absorbent resin of the present invention can be applied to absorbent articles. The water-absorbent article is formed by disposing an absorber having a water-absorbent resin as an essential constituent.
The absorbent body and the water absorbent article are the same as those described in JP-A No. 2003-183528, except that the water absorbent resin obtained by the production method of the present invention or the water absorbent resin of the present invention is used as the water absorbent resin. It is.

Hereinafter, the usefulness of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified, parts means parts by weight, and% means% by weight.
The time required for drying the hydrous gel (A) and the rewet of the water-absorbent article were measured by the following methods. These measurement results are shown in Table 1.

<Measurement method of drying time>
The time required for the water content to reach 4% or less after the water-containing gel (A) was placed in a constant dryer at 150 ° C. was determined as the time required for drying. The moisture content was calculated from the difference in weight before and after 5 g of a measurement sample was heated and dried at 150 ° C. for 15 minutes using an infrared moisture meter (for example, FD-230, manufactured by Kett Science Laboratory Co., Ltd.). .

<Method for measuring rewetting of water-absorbent article>
A water-absorbing article for measurement is spread on a horizontal plane, and an acrylic resin cylindrical cylinder having an outer diameter of 7.0 cm, an inner diameter of 6.0 cm, and a height of 3.8 cm is placed at the center, and 0.9% is placed in the cylindrical cylinder. Inject 80 ml of an aqueous sodium chloride solution (saline). After 15 minutes from the start of injection, 80 ml of 0.9% aqueous sodium chloride solution is again injected. Five minutes after the start of re-injection, 40 sheets of 10 cm × 10 cm filter paper (A) whose weight was measured in advance were layered on the central portion, and an acrylic plate having a thickness of 10 cm × 10 cm × 5 mm was further formed thereon. Apply a load of 5 kg. After 5 minutes, the load and the acrylic plate were removed, the weight (B) of the filter paper that absorbed physiological saline was measured, and the value obtained from the following formula was defined as rewet. It shows that it is excellent in rewetting property, so that a value is small.

<Production Example 1>
A reaction vessel was charged with 81.8 parts of acrylic acid, 0.3 part of N, N′-methylenebisacrylamide and 241 parts of deionized water, and the temperature of the contents was maintained at 1 to 2 ° C. while stirring and mixing.
Next, after flowing nitrogen into the liquid layer of the contents for 30 minutes at 1 liter / min, 1 part of 1% hydrogen peroxide aqueous solution, 1.2 parts of 0.2% ascorbic acid aqueous solution and 2% of 2, 2.8 parts of 2′-azobisamidinopropane dihydrochloride aqueous solution was added and mixed to initiate polymerization (about 5 ° C.).
With the polymerization, the temperature increased to reach about 70 ° C., and subsequently polymerized while maintaining the temperature at 70 to 80 ° C. for about 8 hours in a sealed state to obtain a water-containing gel (a1) containing a water-absorbing resin.

<Production Example 2>
A hydrogel (a2) containing a water-absorbent resin was obtained in the same manner as in Production Example 1, except that 0.3 part of N, N′-methylenebisacrylamide was changed to 0.1 part.

<Production Example 3>
A hydrogel (a3) containing a water-absorbing resin was obtained in the same manner as in Production Example 1 except that 81.8 parts of acrylic acid was changed to a mixture of 22.9 parts of acrylic acid and 76.8 parts of sodium acrylate. .

<Production Example 4>
346.0 parts of 25% aqueous sodium hydroxide solution was added to a mixed liquid of 208 parts of acrylic acid and 13.5 parts of water while cooling. To this solution, 0.1 part of potassium persulfate, 0.02 part of sodium hypophosphite and 0.1 part of ethylene glycol diglycidyl ether (Nagase Chemical Industries, Ltd., trade name: Denacol EX810) were added, A monomer aqueous solution was prepared by adjusting the temperature to 10 ° C.
Next, 624 parts of cyclohexane was placed in a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas introduction tube, and polyoxyethylene octylphenyl ether phosphate ester (Daiichi Kogyo Seiyaku Co., Ltd., trade name: Ply) Surf A210G) 1.6 parts were added and dissolved, and then nitrogen gas was introduced while stirring.
Next, the reaction vessel was heated to bring the mixture of cyclohexane and polyoxyethylene octylphenyl ether phosphate to 75 ° C., and with stirring, the monomer aqueous solution maintained at 5 to 10 ° C. was kept at a substantially constant rate over 60 minutes. The solution was added dropwise together with nitrogen gas. At this time, the oxygen concentration in the flask was kept at 10 to 30 ppm. After the introduction of the aqueous monomer solution, the mixture was further stirred at 75 ° C. for 30 minutes, and then water was distilled off by azeotropy with cyclohexane. The water content of the produced water-absorbent resin was about 20% (the water content was more than the amount of water removed) When the stirring was stopped when the calculated value reached, the water-absorbing resin settled, so that the water-absorbing resin and cyclohexane were separated by decantation to obtain a hydrous gel (a4) containing the water-absorbing resin.

<Example 1>
The water-containing gel (a1) containing the water-absorbent resin obtained in Production Example 1 was shredded to a size of 3 to 7 mm with an internal mixer to obtain a shredded gel. 67.5 parts of 48% sodium hydroxide aqueous solution was added to neutralize 72 equivalent% of carboxyl groups to obtain a neutralized chopped gel. In addition, the neutralization degree of the neutralized chopped gel calculated from the acid value measured according to JIS K0113-1997 (using 0.1 N potassium hydroxide aqueous solution as a titrant, potentiometric titration method, inflection point method) Was 70.1 equivalent%.
Next, polyether modified silicone used as a dispersant for 202.5 parts of low melting point drying aid (b11) {n-tetradecyl alcohol ethylene oxide 2 mol adduct) and drying aid (b1) on 392.5 parts of neutralized chopped gel (SH3746, manufactured by Toray Dow Corning Co., Ltd.) 19.6 parts of a 1% aqueous dispersion of a mixture consisting of 0.5 parts was added and further kneaded with an internal mixer to obtain a kneaded gel. Next, this kneaded gel was laminated to a thickness of about 5 cm on a stainless steel tray having a height of 20 cm, a width of 20 cm, and a height of 10 cm, having no top plate, and having a 4 mm mesh wire mesh on the bottom plate. It dried with the ventilation type | mold band dryer (made by Inoue Metal) on the conditions of (degreeC) and the wind speed of 2.0 m / s, and obtained the dried body. The dried product was pulverized and sieved using a sieve having an aperture of 150 μm and a sieve having the same size of 710 μm to obtain a water absorbent resin (1) having a particle size of 150 to 710 μm.

<Example 2>
19.6 parts of drying aid (b1) is used as a dispersant for the low melting point drying aid (b12) {dimethylsilicone (SH200 20 mPa · s, manufactured by Toray Dow Corning)) and the drying aid (b2). A water-absorbent resin (2) was obtained in the same manner as in Example 1, except that 1% aqueous dispersion of a mixture composed of 1 part of polyether-modified silicone (SH3746, manufactured by Toray Dow Corning) was 19.6 parts. .

<Example 3>
Except for changing 19.6 parts of the drying aid (b1) to 19.0 parts of the low melting point drying aid (b13) {1% propyl alcohol solution of 15 mol glycerin propylene oxide adduct}, the same as in Example 1. Thus, a water absorbent resin (3) was obtained.

<Example 4>
Except for changing 19.6 parts of drying aid (b1) to 18.0 parts of low melting point drying aid (b14) {0.4% methanol solution of amino-modified silicone (KF880, manufactured by Shin-Etsu Chemical Co., Ltd.)}, In the same manner as in Example 1, a water absorbent resin (4) was obtained.

<Example 5>
Example 1 except that 19.6 parts of the drying aid (b1) was changed to 14.6 parts of the high melting point drying aid (b21) {1% ethyl alcohol dispersion of ethylene glycol stearic acid diester}. A water absorbent resin (5) was obtained.

<Example 6>
Absorbency of water in the same manner as in Example 1 except that 19.6 parts of drying aid (b1) was changed to 20.8 parts of high melting point drying aid (b22) {1% isopropyl alcohol solution of n-octadecyl alcohol}. Resin (6) was obtained.

<Example 7>
Except for changing the water-containing gel (a1) containing the water-absorbent resin obtained in Production Example 1 to the water-containing gel (a2) containing the water-absorbent resin obtained in Production Example 2, water absorption was performed in the same manner as in Example 1. Resin (7) was obtained.

<Example 8>
The water-absorbent resin (8) was obtained in the same manner as in Example 1 except that the hydrogel (a1) was changed to the hydrogel (a2) and the low melting point drying aid (b11) was changed to the low melting point drying aid (b12). Got.
The neutralization degree of the neutralized chopped gel obtained using the hydrous gel (a2) was 70.7 equivalent% (the same applies hereinafter).

<Example 9>
Except for changing the hydrous gel (a1) to the hydrous gel (a2) and changing 19.6 parts of the low melting point drying aid (b11) to 15.2 parts of the low melting point drying aid (b13), the same as in Example 1. Thus, a water absorbent resin (9) was obtained.

<Example 10>
Except for changing the hydrous gel (a1) to the hydrous gel (a2) and changing 19.6 parts of the low melting point drying aid (b11) to 18.0 parts of the low melting point drying aid (b14), the same as in Example 1. Thus, a water absorbent resin (10) was obtained.

<Example 11>
Except for changing the hydrous gel (a1) to the hydrous gel (a2) and changing 19.6 parts of the low melting point drying aid (b11) to 14.6 parts of the high melting point drying aid (b21), the same as in Example 1. Thus, a water absorbent resin (11) was obtained.

<Example 12>
Same as Example 1, except that the hydrogel (a1) was changed to the hydrogel (a2) and 19.6 parts of the low melting point drying aid (b11) was changed to 20.8 parts of the high melting point drying aid (b22). Thus, a water absorbent resin (12) was obtained.

<Example 13>
The water-containing gel (a3) containing the water-absorbent resin obtained in Production Example 3 was shredded to a size of 3 to 7 mm with an internal mixer to obtain a shredded gel, and then 330.0 parts of this shredded gel 20.8 parts of low melting point drying aid (b11) was added to the mixture, and further kneaded with an internal mixer to obtain a kneaded gel. Next, this kneaded gel was laminated to a thickness of about 5 cm on a stainless steel tray having a height of 20 cm, a width of 20 cm, and a height of 10 cm, having no top plate, and having a 4 mm mesh wire mesh on the bottom plate. It dried with the ventilation type | mold band dryer (made by Inoue Metal) on the conditions of (degreeC) and the wind speed of 2.0 m / s, and obtained the dried body. The dried product was pulverized and sieved using a sieve having an opening of 150 μm and a sieve having the same size of 710 μm to obtain a water absorbent resin (13) having a particle size of 150 to 710 μm.

<Example 14>
A water absorbent resin (14) was obtained in the same manner as in Example 13 except that the low melting point drying aid (b11) was changed to the low melting point drying aid (b12).

<Example 15>
A water absorbent resin (15) was obtained in the same manner as in Example 13, except that the low melting point drying aid (b11) was changed to the low melting point drying aid (b13).

<Example 16>
A water absorbent resin (16) was obtained in the same manner as in Example 13, except that 20.8 parts of the low melting point drying aid (b11) was changed to 17.0 parts of the low melting point drying aid (b14).

<Example 17>
A water absorbent resin (17) was obtained in the same manner as in Example 13 except that 20.8 parts of the low melting point drying aid (b11) was changed to 21.6 parts of the high melting point drying aid (b21).

<Example 18>
A water absorbent resin (18) was obtained in the same manner as in Example 13 except that 20.8 parts of the low melting point drying aid (b11) was changed to 16.4 parts of the high melting point drying aid (b22).

<Example 19>
Add 22.4 parts of a low melting point drying aid (b11) to 360.0 parts of the water-containing gel (a4) containing the water-absorbent resin obtained in Production Example 4 and further knead with a Nauter mixer to knead the gel. Got. Next, this kneaded gel was laminated to a thickness of about 5 cm on a stainless steel tray having a height of 20 cm, a width of 20 cm and a height of 10 cm, having no top plate, and having a 1 mm mesh wire mesh on the bottom plate. It dried with the ventilation type | mold band dryer (made by Inoue Metal) on the conditions of (degreeC) and the wind speed of 2.0 m / s, and obtained the dried body. The dried product was sieved using a sieve having an aperture of 150 μm and a sieve having the same size of 710 μm to obtain a water absorbent resin (19) having a particle size of 150 to 710 μm.

<Example 20>
A water absorbent resin (20) was obtained in the same manner as in Example 19 except that the low melting point drying aid (b11) was changed to the low melting point drying aid (b12).

<Example 21>
A water absorbent resin (21) was obtained in the same manner as in Example 19 except that the low melting point drying aid (b11) was changed to the low melting point drying aid (b13).

<Example 22>
A water absorbent resin (22) was obtained in the same manner as in Example 19 except that 22.4 parts of the low melting point drying aid (b11) was changed to 18.6 parts of the low melting point drying aid (b14).

<Example 23>
A water absorbent resin (23) was obtained in the same manner as in Example 19 except that 22.4 parts of the low melting point drying aid (b11) was changed to 23.8 parts of the high melting point drying aid (b21).

<Example 24>
A water absorbent resin (24) was obtained in the same manner as in Example 19 except that 22.4 parts of the low melting point drying aid (b11) was changed to 18.2 parts of the high melting point drying aid (b22).

<Comparative Example 1>
The neutralized chopped gel obtained in the same manner as in Example 1 was placed on a stainless steel tray having a height of 20 cm, a width of 20 cm, and a height of 10 cm, having no top plate, and having a 4 mm mesh wire mesh on the bottom plate. The film was laminated to a thickness of 5 cm, and dried with a ventilation type band dryer (manufactured by Inoue Metal) under conditions of 150 ° C. and a wind speed of 2.0 m / s to obtain a dried product. The dried product was pulverized and sieved using a sieve having an aperture of 150 μm and a sieve having the same size of 710 μm to obtain a comparative water absorbent resin (25) having a particle size of 150 to 710 μm.

<Comparative example 2>
The neutralized chopped gel obtained in the same manner as in Example 1 {using water-containing gel (a1)} was changed to a neutralized chopped gel in the same manner as in Example 8 {using water-containing gel (a2)}. In the same manner as in Comparative Example 1, a comparative water absorbent resin (26) was obtained.

<Comparative Example 3>
The hydrogel (a3) containing the water-absorbent resin obtained in Production Example 3 was chopped to a size of 3 to 7 mm with an internal mixer to obtain a chopped gel. Next, this shredded gel is laminated to a thickness of about 5 cm on a stainless steel tray that is 20 cm long × 20 cm wide × 10 cm high, has no top plate, and has a 4 mm mesh wire mesh on the bottom plate. It dried with the ventilation type | mold band dryer (made by Inoue Metal) on the conditions of 150 degreeC and the wind speed of 2.0 m / s, and obtained the dried body. The dried product was pulverized and sieved using a sieve having an opening of 150 μm and a sieve having the same size of 710 μm to obtain a comparative water absorbent resin (27) having a particle size of 150 to 710 μm.

<Comparative example 4>
The water-containing gel (a4) containing the water-absorbent resin obtained in Production Example 4 has a length of 20 cm, a width of 20 cm, and a height of 10 cm, and does not have a top plate. It laminated | stacked on the tray about 5 cm in thickness, and it dried with the ventilation type | mold band dryer (made by Inoue Metal) on the conditions of 150 degreeC and the wind speed of 2.0 m / s, and obtained the dried body. The dried product was sieved using a sieve having an aperture of 150 μm and a sieve having the same size of 710 μm to obtain a comparative water absorbent resin (28) having a particle size of 150 to 710 μm.

<Comparative Example 5>
Low melting point drying aid (b11) 19.6 parts of n-dodecyl alcohol ethylene oxide 14 mol adduct (solubility: 100 g / 100 g water, HLB value: 15.7, melting point: 38 ° C., Hazen unit color after heat treatment A comparative water-absorbent resin (29) was obtained in the same manner as in Example 1, except that the number was changed to 18.4 parts of a 2% aqueous solution of 100).

<Comparative Example 6>
Low melting point drying aid (b11) 19.6 parts sorbitan-n-dodecanoic acid monoester (solubility: 0.0 g / 100 g water, HLB value: 2.8, melting point 46 ° C., Hazen unit color number after heat treatment) A comparative water-absorbent resin (30) was obtained in the same manner as in Example 1, except that the amount was changed to 20.0 parts of a 2% aqueous dispersion of 500).

<Comparative Example 7>
Low melting point drying aid (b11) 19.6 parts sorbitan polyoxyethylene 20 mol adduct n-octadecanoic acid monoester (solubility 100 g / 100 g water, HLB value: 14.9, melting point 25 ° C., after heat treatment A comparative water-absorbing resin (31) was obtained in the same manner as in Example 1 except that the 2% aqueous solution (hazen unit color number: 500) was changed to 18.6 parts.

<Comparative Example 8>
Low melting point drying aid (b11) 19.6 parts polyoxyethylene 40 mol adduct n-octadecanoic acid diester (solubility: 5.0 g / 100 g water, HLB value: 16.3, melting point 46 ° C., after heat treatment A comparative water-absorbent resin (32) was obtained in the same manner as in Example 1, except that the 2% aqueous solution (hazen unit color number: 500) was changed to 20.0 parts.

<Comparative Example 9>
A comparative water-absorbing resin (33) was prepared in the same manner as in Example 13, except that 20.8 parts of the low melting point drying aid (b11) was changed to 17.6 parts of a 2% aqueous solution of a 14-mol adduct of n-dodecyl alcohol ethylene oxide. )

<Comparative Example 10>
Comparative Example 2 was used in the same manner as in Example 13 except that 20.8 parts of the low melting point drying aid (b11) was changed to 21.2 parts of a 2% aqueous solution of 20-mole adduct n-octadecanoic acid monoester of sorbitan polyoxyethylene. A water absorbent resin (34) was obtained.

<Comparative Example 11>
Water absorption for comparison in the same manner as in Example 13, except that 22.4 parts of low melting point drying aid (b11) was changed to 19.4 parts of 2% aqueous solution of polyoxyethylene 40 mol adduct n-octadecanoic acid diester. Resin (35) was obtained.

<Comparative Example 12>
Water absorption for comparison in the same manner as in Example 19, except that 22.4 parts of low melting point drying aid (b11) was changed to 23.0 parts of 2% aqueous solution of polyoxyethylene 40 mol adduct n-octadecanoic acid diester. Resin (36) was obtained.

Using the water absorbent resins (1) to (36) of Examples 1 to 24 and Comparative Examples 1 to 12, water absorbent articles (1) to (36) were prepared as follows.
<Manufacture of water-absorbing articles>
9 parts of the water-absorbent resin (1) and 11 parts of Japanese Pharmacopoeia absorbent cotton (manufactured by Kawamoto Sangyo Co., Ltd.) were defibrated by hand about 500 times with mixing until uniform in appearance.
Thereafter, the defibrated mixture is spread to a size of 15 cm × 45 cm, and then pressed at 8 kg / cm ² at 50 ° C. for 30 seconds using a heater plate press machine (model number N4008-00) manufactured by NPA System Co., Ltd. As a result, a mixture (1) of the water-absorbent resin and absorbent cotton was obtained.
Next, the mixture (1) is placed on a liquid-impermeable back sheet {polypropylene film (15 cm × 45 cm)} having a thickness of 40 μm, and a liquid-permeable top sheet {polyethylene terephthalate nonwoven fabric having a thickness of 100 μm) thereon. (15 cm × 45 cm)} was placed, and then the water absorbent article (1) was obtained by hot pressing the four sides with a width of 1 cm each.
Water-absorbing articles (2) to (36) were obtained in the same manner as described above except that the water-absorbing resin (1) was changed to the water-absorbing resins (2) to (36).
These water-absorbing articles (1) to (36) were evaluated for rewet and the results are shown in Table 1.

The water-absorbing resins (1) to (24) obtained by the production method of the present invention have a very short drying time from the water-containing gel (13 to 19 minutes), a Hunter whiteness of 66 to 73 and little coloration, The surface tension was 63 to 72 (dynes / cm), and the rewetting when applied to a water absorbent article was very good. Of these, the water-absorbing articles (1), (3) and (15) showed particularly excellent rewetting.
On the other hand, the water-absorbent resin obtained by the production method of the comparative example not only has a very long drying time from the hydrous gel (31 to 46 minutes), but also increases coloration (comparative examples 5 to 12). ), The surface tension was low (Comparative Examples 5 to 12), and when applied to a water-absorbent article, the rewetting deteriorated (Comparative Examples 5 and 7 to 12).

Claims (8)

A water-containing gel (A) comprising a water-absorbent resin and water;
Low melting point drying aid (B1) having a solubility in water (25 ° C.) of 0 to 2 g / 100 g water and a Hazen unit color number of 0 to 300 after heat treatment at 150 ° C. for 3 hours {melting point (1013. 25 hPa) is less than 50 ° C.} and / or water solubility (25 ° C.) is 0 to 2 g / 100 g water, and the hunter whiteness after heat treatment at 150 ° C. for 3 hours is 40 to 94. Mixing the agent (B2) {melting point is 50 ° C. or higher} to obtain a mixture,
And a method for producing a water-absorbent resin, comprising a step of drying the mixture in a stationary state. The production method according to claim 1, wherein the amount of the low melting point drying aid (B1) and / or the high melting point drying aid (B2) used is 0.001 to 1% by weight based on the weight of the water absorbent resin. The process according to claim 1 or 2, wherein the low melting point drying aid (B1) and the high melting point drying aid (B2) have an HLB value of 0 to 10. The process according to any one of claims 1 to 3, wherein the low melting point drying aid (B1) and / or the high melting point drying aid (B2) is an oxyethylene-containing compound having 1 to 8 oxyethylene groups. . The production method according to any one of claims 1 to 4, further comprising a step of obtaining aqueous gel (A) by performing aqueous solution polymerization using acrylic acid as an essential constituent monomer and then neutralizing with an alkali metal compound. The equipment used in the process of drying the mixture in a stationary state is a parallel flow band dryer (tunnel dryer), an aeration band dryer, a jet flow (nozzle jet) dryer, a ventilated solid dryer and a box-type hot air. The production method according to claim 1, which is at least one selected from the group consisting of dryers. A water absorbent resin that can be produced by the production method according to claim 1, wherein the surface tension is 60 to 73 dynes / cm. The water-absorbent resin according to claim 7, wherein the Hunter whiteness is 60 to 94.