JP2005054050A - Manufacturing process of water absorptive resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for manufacturing a water absorptive resin, which can dry the water absorptive resin containing water efficiently and quickly with hardly producing aggregated or bound bodies, such as granular, lumpy or plate-like substances, at the time of drying. <P>SOLUTION: In the presence of an emulsifier, a water-soluble ethylenically unsaturated monomer is subjected to reversed phase suspension polymerization in a hydrophobic organic solvent to obtain a liquid containing the water-bearing water absorptive resin. This water absorptive resin containing water is mixed with a water absorptive resin having a low water content to serve as a water absorptive resin for moisture control and/or a powdered water absorptive resin, then dried to manufacture the water absorptive resin. To the liquid containing the water-carrying water absorptive resin, the water absorptive resin for moisture control is added and mixed so as for the water content in the whole water absorptive resin to be 25 wt% or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a water absorbent resin. Specifically, a water-absorbing water-absorbing resin obtained by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer is added with a previously dried water-adsorbing resin for moisture adjustment, mixed and dried to obtain a powdery The present invention relates to a method for producing a water absorbent resin.

  In recent years, water-absorbing resins have been used not only for sanitary materials such as disposable diapers and sanitary products, but also for industrial applications such as water-stopping materials, anti-condensation materials, freshness-keeping materials, solvent dehydrating materials, greening, agricultural and horticultural applications, etc. Various things have been proposed so far.

  As this type of water-absorbing resin, hydrolyzate of starch-acrylonitrile graft copolymer, crosslinked carboxymethyl cellulose, crosslinked polyacrylic acid (salt), acrylic acid (salt) -vinyl alcohol copolymer, crosslinked polyethylene oxide, etc. It has been known.

  Among these, water-absorbing resins mainly made of acrylic acid are produced from the viewpoint of water-absorbing performance, ease of production, availability of raw materials, product stability, and the like. In the case of producing a water-absorbing resin using acrylic acid as a raw material, polymerization is performed using an aqueous solution of partially neutralized acrylic acid in consideration of the polymerizability of acrylic acid. For this reason, a large amount of water is present in the polymerization reaction system. After the polymerization is completed, the polymerization reaction solution is filtered and the water-absorbing water-absorbing resin is dried with a known dryer to obtain a water-absorbing resin. Yes.

  However, this method has a problem that the water-absorbing water-absorbing resins are aggregated and bound during drying to form a granule, a lump, or a plate.

  Therefore, in order to avoid this problem, there is a method of drying by azeotropic dehydration using a hydrophobic organic solvent or the like, but for azeotropic dehydration, heating must be continued for a long time. There is a concern that the cost will increase and the environmental impact will be adversely affected.

On the other hand, there has also been proposed a method in which a liquid containing an acrylate polymer is mixed with a previously dried powdered acrylate polymer and heated and dried in a dryer while stirring (Japanese Patent Laid-Open No. 57-117551). . However, in this method, when the mixed solution is directly dried with a dryer, the emulsifier used for the reverse phase suspension polymerization prevents water absorption from the water-containing water-absorbent resin to the dried water-absorbent resin. There was a problem that it took time.
JP 57-117551 A

  The present invention solves the above-mentioned conventional problems, and can efficiently and quickly dry a water-absorbent water-absorbing resin without generating agglomeration, agglomerates, aggregates of plate-like materials, and binders during drying. An object of the present invention is to provide a method for producing a water absorbent resin.

  The method for producing a water-absorbing resin of the present invention comprises obtaining a liquid containing a water-absorbing water-absorbing resin by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrophobic organic solvent in the presence of an emulsifier. The water-absorbing resin is mixed with a water-absorbing resin containing water lower than the water-containing water-absorbing resin and / or a water-adjusting water-absorbing resin composed of a powdered water-absorbing resin to adjust the water content, and then dried to absorb the water. In the method for producing a water-soluble resin, the water-adjusting water-absorbing resin is added to the liquid containing the water-containing water-absorbing resin so that the water content in the total water-absorbing resin is 25% by weight or less. To do.

  That is, as a result of intensive studies to solve the above problems, the present inventors have added and mixed the water-absorbing resin for moisture adjustment to the water-containing water-absorbing resin particles obtained by polymerization, so that the water content of the total water-absorbing resin is 25%. It was found that by reducing the content to less than or equal to% by weight, granulation, agglomeration, and plate formation due to aggregation of water-absorbent resin particles can be prevented, and the present invention has been completed.

  The method for producing a water-absorbent resin according to claim 2 is the method according to claim 1, wherein the moisture adjustment is performed after adding a surfactant having a demulsifying action to the liquid containing the water-containing water-absorbent resin or together with the surfactant. It is characterized by adding a water absorbent resin.

  The method for producing a water-absorbent resin according to claim 3 is the method according to claim 2, wherein the surfactant is an HLB nonionic surfactant having an HLB of 7 or higher and higher than the HLB of the emulsifier, and / or an anionic surfactant. It is characterized by being.

  According to the methods of claims 2 and 3, by deactivating the emulsifier used for the reverse phase suspension polymerization adhering to the surface of the water-containing water-absorbent resin, the water-absorbing rate by the water-absorbing resin for moisture adjustment is increased and drying is performed. (This time is the total time of the water adjustment time by the water adjusting water-absorbing resin and the subsequent drying time) can be further shortened.

  The method for producing a water absorbent resin according to claim 4 is the method according to any one of claims 1 to 3, wherein the surface of the water absorbent water absorbent resin is washed with a hydrophobic organic solvent prior to the addition of the water absorbent resin for moisture adjustment. It is characterized by that.

  According to the method of claim 4, the surface of the water-absorbing water-absorbing resin is washed with a hydrophobic organic solvent to remove the emulsifier adhering to the surface of the water-containing water-absorbing resin, thereby increasing the water absorption rate by the water-adsorbing resin for moisture adjustment. Thus, the processing time for drying can be further shortened.

  The method for producing a water absorbent resin according to claim 5 is the method according to claim 4, wherein the water content in the total water absorbent resin is obtained by washing the surface of the water absorbent water absorbent resin with a hydrophobic organic solvent and then mixing the water absorbent resin for moisture adjustment. It is characterized by adding an additional emulsifier after adjusting to 25% by weight or less.

  According to the method for producing a water-absorbent resin of claim 5, by removing and deactivating the emulsifier on the surface of the water-containing water-absorbent resin, the water absorption rate by the water-absorbing resin for moisture adjustment is increased and the treatment for drying is performed. By further shortening the time and further adding an additional emulsifier, aggregation of the water-absorbent resin particles can be suppressed.

  The method for producing a water absorbent resin according to claim 6 is the method according to any one of claims 1 to 5, wherein the moisture adjusting water absorbent resin is added to the water-absorbent water absorbent resin to reduce the water content in the total water absorbent resin. After adjusting to 15 to 25% by weight, a surface cross-linking step of the water absorbent resin is performed.

  According to the method of the sixth aspect, the surface crosslinking can be performed without adjusting the moisture content again by adjusting the moisture content required for the surface crosslinking step to 15 to 25% by weight.

  According to the method for producing a water-absorbent resin of the present invention, a water-absorbent resin previously dried on a water-containing water-absorbent resin obtained by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer is used as a water-adsorbing resin for moisture adjustment. After adding, mixing and reducing the water content, and drying to produce a powdered water absorbent resin, adding water absorbent resin for moisture adjustment to a predetermined moisture content will cause aggregation and condensation. It is possible to perform quick and efficient drying while suppressing the generation of the adherend. According to the present invention, it is possible to produce a water-absorbing resin at a low cost by an extremely simple operation that is not conventionally performed, in which the amount of water after simply mixing the water-absorbing resin for moisture adjustment is quickly controlled. The water-absorbent resin is suitable for various uses such as paper diapers, sanitary napkins, soil water retention agents, and the like.

  Embodiments of the method for producing a water absorbent resin of the present invention will be described in detail below.

  In the present invention, the amount of water in the water-absorbent resin refers to the ratio (% by weight) of water to the sum of the weight of the water-absorbent resin and the amount of water absorbed in the water-absorbent resin.

  First, in the present invention, a method for preparing a liquid containing a water-absorbing water-absorbing resin by reverse-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrophobic organic solvent in the presence of an emulsifier will be described.

[Preparation of water-containing water-absorbing resin]
(Water-soluble ethylenically unsaturated monomer)
The water-soluble ethylenically unsaturated monomer used in the present invention can be basically any one that is soluble in water. For example, ionic monomers such as (meth) acrylic acid and / or its alkali metal salt, ammonium salt, 2- (meth) -acrylamido-2-methylsulfonic acid and / or its alkali metal salt; ) Nonionic monomers such as acrylamide, N, N-dimethylacrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide; amino groups such as diethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylate Examples thereof include unsaturated monomers and quaternized products thereof, and one or more selected from these groups can be used. Here, the term “(meth) acryl” means both “acryl” and “methacryl”.

  Among these, (meth) acrylic acid and / or its alkali metal salt, ammonium salt, and (meth) acrylamide are preferable. Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt, rubidium salt, etc., but sodium salt or potassium salt is preferable from the viewpoint of the performance of the polymer obtained, industrial availability, safety and the like. .

  The monomer concentration of the water-soluble ethylenically unsaturated monomer in the aqueous solution is generally 20% by weight or more, preferably 25% by weight to the saturated concentration. In addition, (meth) acrylic acid, 2-methyl-acrylamide-2-sulfonic acid and the like are used in a form in which a part or all of them are neutralized with an alkali metal compound or an ammonium compound. The ratio (referred to as the degree of neutralization) is 20 to 100 mol%, preferably 30 to 100 mol%.

(emulsifier)
As the emulsifier used in the present invention, any emulsifier can be used as long as it is soluble or compatible with a hydrophobic organic solvent and basically forms a W / O type emulsion system. Specifically, such an emulsifier is generally a nonionic and / or anionic surfactant having an HLB of 1 to 9, preferably 2 to 7.

  Specific examples of the emulsifier include sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkylphenyl ether, ethyl cellulose, ethyl hydroxyethyl cellulose, oxidized polyethylene, anhydrous maleated polyethylene, anhydrous Examples thereof include maleated polybutadiene, maleated anhydride ethylene / propylene / diene / terpolymer, a copolymer of α-olefin and maleic anhydride or a derivative thereof, and a phosphate ester surfactant. Examples of the phosphate ester surfactant include those represented by the following general formula [I]. An emulsifier may be used individually by 1 type and may use 2 or more types together.

（式中、Ｒ^１は炭素数８〜３０のアルキル基又はアルキルアリール基を表し、Ｒ^２はＯＨ基又は式−（ＣＨ_２ＣＨ_２Ｏ）_ｍ−ＯＲ^１の基を表す。ｍ及びｎは１〜３０の整数である。）

(In the formula, R ¹ represents an alkyl group having 8 to 30 carbon atoms or an alkylaryl group, R ² represents an OH group or a group of formula — (CH ₂ CH ₂ O) _m —OR ¹ , and m and n are It is an integer from 1 to 30.)

In the general formula [I], R ¹ is preferably an alkyl group having 1 to 23 carbon atoms or a monoalkylphenyl group (that is, an alkyl group having 2 to 17 carbon atoms). The former alkyl group is particularly preferred. m and n are each preferably 1-20. When this phosphate ester is a diester, R ² is preferably R ¹ O— (CH ₂ CH ₂ O) _n — which is the same as the polyoxyethylene ether containing R ¹ described above.

  The amount of the emulsifier is usually 0.05 to 10% by weight, preferably 0.1 to 1% by weight, based on the hydrophobic organic solvent.

(Hydrophobic organic solvent)
The hydrophobic organic solvent used in the present invention is basically hardly soluble in water, and any one can be used as long as it is inert to polymerization. For example, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, aromatic carbons such as benzene, toluene and xylene Hydrogen etc. are mentioned. N-hexane, n-heptane, and cyclohexane can be mentioned as preferable solvents from the viewpoint of industrial availability, quality, and the like. A hydrophobic organic solvent may be used individually by 1 type, and may use 2 or more types together.

  The amount of the hydrophobic organic solvent used is usually 0.5 to 10 times by weight, preferably 0.6 to 5 times by weight with respect to the water-soluble ethylenically unsaturated monomer aqueous solution.

(Polymerization initiator)
The polymerization initiator used in the present invention is a water-soluble radical polymerization initiator. Examples thereof include persulfates such as hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, 2,2′-azobis- (2-amidinopropane) dihydrochloride, 2,2′-azobis- ( N, N'-dimethyleneisobutylamidine) dihydrochloride, 2,2'-azobis {2methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide} and other azo-based initiators It is an agent. These water-soluble radical initiators may be used as a mixture of two or more. Hydrogen peroxide and persulfate can also be used as a redox initiator by combining reducing substances such as sulfite and L-ascorbic acid and amines.

  The amount of the polymerization initiator used is usually 0.001 to 5% by weight, preferably 0.01 to 1% by weight, based on the ethylenically unsaturated monomer.

(Crosslinking agent)
In this invention, a crosslinking agent can be used as needed. If necessary, in the present invention, for example, self-crosslinking by the monomer itself occurs even in the absence of a crosslinking agent depending on the monomer conditions (type of monomer, concentration of monomer in aqueous solution, degree of neutralization, etc.) This is because a water absorbent resin can be formed thereby. However, a cross-linking agent may be necessary depending on required performance such as water absorption capacity, water absorption speed, and the like. Examples of the crosslinking agent used in the present invention include a crosslinking agent having two or more polymerizable unsaturated groups and / or reactive functional groups.

  Examples of the crosslinking agent having two or more polymerizable unsaturated groups include di- or tri (meth) acrylic polyols such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin. Acid esters, unsaturated polyesters obtained by reacting the polyols with unsaturated acids such as maleic acid and fumaric acid, bisacrylamides such as N, N'-methylenebisacrylamide, polyepoxides and (meth) acrylic Di (meth) acrylates obtained by reacting polyisocyanates such as di- or tri (meth) acrylic acid esters, tolylene diisocyanate and hexamethylene diisocyanate obtained by reacting with acid and hydroxyethyl (meth) acrylate Polyvalents such as carbamyl esters of allylate, allylated starch, allylated cellulose, diallyl phthalate, tetraallyloxyethane, pentaerythritol triallyl ether, trimethylolpropane triallyl ether, diethylene glycol diallyl ether, triallyl trimellitate An allyl type is mentioned. Among these, in the present invention, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N′-methylenebis (meth) acrylamide, etc. Is usually used.

  Examples of the crosslinking agent having two or more reactive functional groups include diglycidyl ether compounds, haloepoxy compounds, and isocyanate compounds. Of these, diglycidyl ether compounds are particularly preferred. Specific examples of the diglycidyl ether compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, polyglycerin diglycidyl ether, and the like. Among these, ethylene glycol diglycidyl ether is preferable. Other examples of the haloepoxy compound include epichlorohydrin, epibromohydrin, β-methylepichlorohydrin, and the like, and examples of the isocyanate compound include 2,4-tolylene diisocyanate, hexamethylene diisocyanate, and the like. These crosslinking agents may be used individually by 1 type, and may use 2 or more types together.

  The amount of the crosslinking agent used is usually 0 to 10% by weight, preferably 0.001 to 5% by weight, based on the ethylenically unsaturated monomer.

(Polymerization reaction operation and conditions)
In the present invention, a water-soluble ethylenically unsaturated monomer aqueous solution is first subjected to reverse phase suspension polymerization using a polymerization initiator in the presence of a W / O emulsifier, in a hydrophobic organic solvent, and optionally in the presence of a crosslinking agent. I do.

  The polymerization reaction solution obtained by reverse phase suspension polymerization varies depending on the type and amount of the emulsifier used and other polymerization conditions, but usually contains an average of about 10-300 μm hydrogel, excess emulsifier and hydrophobic organic solvent. The resulting slurry mixture. As the polymerization method at this time, any of a batch polymerization method in which a monomer aqueous solution is charged all at once from the beginning into a reactor or a dropping method in which a monomer aqueous solution is dropped into a hydrophobic organic solvent can be used.

  Next, a method for drying the water-containing water-absorbent resin in the polymerization reaction solution obtained in this manner after adjusting the water content with the water-adjusting water-absorbing resin will be described.

[Moisture adjustment and drying treatment of water-containing water-absorbent resin]
(Water-absorbing resin for moisture adjustment)
The water-absorbing resin for adjusting moisture used in the present invention may not have the same polymerization composition as the water-containing water-absorbing resin, but also has the same polymerization composition in order to recycle and use the water-absorbing resin particles after drying. It is desirable that In addition, when the water content of the water-adsorbing resin for moisture adjustment is large, it is necessary to add a large amount of water-absorbing resin for moisture adjustment for drying the water-containing water-absorbing resin. Is desirably 10% by weight or less.

  In the present invention, it is essential that the moisture adjusting water-absorbing resin is added so that the total moisture content of the water-absorbing resin and the moisture adjusting water-absorbing resin is 25% by weight or less. . When this moisture content exceeds 25% by weight, the water-absorbing resins are aggregated to generate a large amount of granulated bodies, lumps and plates, and it is difficult to obtain a powdery water-absorbing resin. However, excessively reducing the water content impairs industrial productivity because a large amount of water-adsorbing resin for water adjustment is required.

  In the present invention, the moisture content of the water-absorbing resin having a moisture content of 10 wt% or less, for example, about 5 to 10 wt%, is 15 to It is preferable to adjust the water content to 25% by weight.

  The time required for moisture adjustment by water absorption after adding the water-absorbing resin for moisture adjustment to the water-containing water-absorbent resin is the moisture adjustment condition (the amount of water-adjusting water-absorbing resin added, the amount of moisture after adding the water-adsorbing resin for moisture adjustment) In general, it is preferable to select a condition such that water absorption is completed in 10 to 120 minutes, depending on whether a surfactant described later is added or whether or not the substrate is washed with a hydrophobic organic solvent.

(Surfactant)
In the present invention, after the reverse phase suspension polymerization is substantially completed, for example, after the polymerization rate is 90% or more, preferably 95% or more, the water-absorbing water-adjusting agent is contained in the polymerization reaction liquid containing the hydrous polymer gel particles. The water is adjusted by adding a resin. Prior to the addition of the water-absorbing resin for moisture adjustment, or together with the addition of the water-absorbing resin for moisture adjustment, a surfactant having a demulsifying action is added to deactivate the emulsifier. By doing so, water absorption by the water-adjusting resin for moisture adjustment can be performed more rapidly.

  The surfactant having the demulsifying action is not particularly limited as long as it is a combination that demulsifies the emulsifier used at the time of polymerization, but a surfactant having a different HLB range from the emulsifier used at the time of polymerization is used. Usually, an HLB nonionic surfactant or anionic surfactant having a HLB of 7 or more and higher than the HLB of the emulsifier used in the reverse phase suspension polymerization, or a mixture thereof can be used. In addition, the HLB of the surfactant is usually preferably one or more higher than that of the emulsifier used for the reverse phase suspension polymerization.

  Specific examples thereof include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene polyoxypropylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan as nonionic surfactants. Examples include fatty acid esters, polyoxyethylene alkylamine ethers, fatty acid diethanolamides, sucrose fatty acid esters, polyglycerin fatty acid esters, and the like.

  Anionic surfactants include fatty acid salts such as sodium oleate, castor oil potash, semi-cured beef tallow soda, sodium lauryl sulfate, higher alcohol sulfate soda salt, lauryl alcohol sulfate / triethanolamine salt, lauryl alcohol sulfate. Alkyl benzene sulfonates and alkyl naphthalene sulfonates, naphthalene sulfonate formalin condensates such as higher alcohol sulfates such as ester ammonium salts, dodecylbenzene sulfonate triethanolamine salts, sodium dodecylbenzene sulfonate, sodium alkylnaphthalene sulfonate, etc. Dialkyl sulfosuccinates such as sodium dialkyl sulfosuccinate, (di) alkyl phosphate salts, polyoxyethylene alkyl sulfate soda, Polyoxyethylene alkylphenyl sulfate soda salt polyoxyethylene sulfate salts, etc., polyoxyethylene polyoxypropylene glycol ether sulfate ammonium salt, polyoxyethylene distyrenated phenyl ether sulfate ammonium salt, and other polymeric special anions.

  Among the above surfactants, one or a mixture of two or more selected from polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene block polymer, and alkylbenzene sulfonate is preferable. Further, the HLB is preferably 9 or more.

  The amount of these surfactants used varies depending on the type of emulsifier used during reverse phase suspension polymerization, stirring conditions, temperature, other operating conditions, etc., but is generally 1/100 of the amount of emulsifier during reverse phase suspension polymerization. The weight is 10 times, preferably 1/10 to 5 times, and more preferably 1 to 5 times.

  The surfactant can be added by any method such as adding it to the polymerization reaction solution before adding the water-adjusting water-absorbing resin, or adding it at the same time as adding the water-adsorbing resin for adjusting the water content. The surfactant can be added as it is or dissolved or mixed in a hydrophobic organic solvent. The surface of the water-absorbing water-absorbent resin is uniformly demulsified with the surfactant, and then the water-absorbing resin for moisture adjustment is used. In the present invention, the surfactant is added by dissolving or mixing in a hydrophobic organic solvent before adding the water-absorbing resin for moisture adjustment. preferable. The temperature at which the surfactant is added can be any temperature, but is preferably room temperature or higher and lower than the azeotropic temperature of the hydrophobic organic solvent and water.

  After the water-absorbing resin for moisture adjustment is added, water absorption from the water-containing water-absorbing resin to the water-adsorbing resin for moisture adjustment occurs at a very high rate in the presence of the specific surfactant as described above, and the entire system is viscous by the absorbent gel. At this time, it is important to make the water absorption of the water-adsorbing resin for moisture adjustment as uniform as possible. That is, if the water absorption is uneven or uneven, the water-absorbing gel will partially agglomerate and adhere and stay as a large lump locally, resulting in granulation, lump, and plate shape. , Greatly affecting the stability of continuous production. There are various influencing factors on the water absorption uniformity, and not only the type and concentration of the surfactant used, but also the temperature, the number of rotations of stirring, and the feed rate of the water-absorbing resin for moisture adjustment are important. The higher the stirring speed, the lower the feed speed and the more uniform water absorption. As a preferred example for performing uniform water absorption, there is a method in which, at the initial stage of addition and mixing of the water adjusting resin for moisture adjustment, the stirring rotational speed is set to be higher than the rotational speed limit at which water can be absorbed and then gradually decreased.

(Hydrophobic organic solvent for addition or washing)
When the water-absorbing resin for moisture adjustment is added, when the water-absorbing resin for moisture adjustment absorbs water from the water-containing water-absorbent resin, the inside of the system becomes a slightly viscous slurry state, so that the stirring and mixing properties are improved. It is desirable to add a hydrophobic organic solvent before adding the water-absorbing resin for moisture adjustment. In this case, the water absorption state changes depending on whether or not a surfactant is added, the type of surfactant to be added, the addition amount, the temperature and the stirring state, so that a hydrophobic state is obtained so that a uniform mixed state can be obtained while checking the water absorption state. It is also possible to add a basic organic solvent.

  In order to further reduce the water absorption inhibition by the emulsifier, it is also a preferred method to remove the emulsifier on the surface of the water-absorbent resin by washing the water-absorbent resin with a hydrophobic organic solvent. In this case, after removing the liquid component of the polymerization reaction liquid containing the water-absorbing water-absorbing resin particles, the addition of a hydrophobic organic solvent is repeated one or more times to make the surface of the water-absorbing water-absorbing resin particles with the hydrophobic organic solvent. What is necessary is just to wash and remove an emulsifier.

  The hydrophobic organic solvent for addition or washing is preferably the same as that used for reverse phase suspension polymerization. When different types of hydrophobic organic solvents are used, it takes time and effort to recover, and the cost increases.

(Additional emulsifier)
In the present invention, the additional emulsifier is coated with the emulsifier uniformly over the entire water-absorbent resin after the water transfer from the water-containing gel after the polymerization reaction to the water-adsorbing resin for moisture adjustment is completed. It is also a preferred embodiment that it is used for the purpose of suppressing aggregation.

  As the additional emulsifier, the emulsifier used in the above-described reverse phase suspension polymerization and the addition amount can be applied.

(Surface cross-linking)
In the present invention, after water adjustment is performed by adding a water-absorbing resin for moisture adjustment so that the moisture content of the total absorbent resin is 15 to 25% by weight in the liquid containing the water-containing absorbent resin, surface crosslinking is performed. Also good. As the crosslinking agent in this case, the glycidyl ether compound, the haloepoxy compound, the isocyanate compound, etc. having two or more functional groups capable of reacting with the carboxylate described above as the crosslinking agent that can be used in the reverse phase suspension polymerization process, etc. Is mentioned. Among them, for example, diglycidyl ether compounds such as (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether are suitable. Among these, diethylene glycol diglycidyl ether is suitable. Most suitable from the reactivity with the carboxylate group in the water-absorbent resin.

  Surface cross-linking is carried out by adding such a cross-linking agent to the water-absorbing resin after the water-adjusting resin for water adjustment is added to adjust the water content, and stirring at 60 to 120 ° C. so that the surface cross-linking agent adheres uniformly. Under the heating. The treatment time depends on the temperature, but is usually 10 to 240 minutes. A nucleophilic reagent such as tin laurate may be added to accelerate the reaction. The addition amount of the crosslinking agent is usually 10 to 100000 ppm, preferably 50 to 5000 ppm with respect to the water absorbent resin. When performing surface cross-linking, the water content of the water-absorbing resin can be adjusted to 15 to 25% by weight by adding a water-adjusting water-adjusting resin, so that the surface can be directly cross-linked without adjusting the water content again. it can. That is, when the surface is crosslinked, it is necessary to adjust the water content of the water absorbent resin to 15 to 25% by weight. When this moisture content is small, the reactivity is lowered and a sufficient crosslinked structure cannot be formed. On the other hand, when the water content exceeds 25% by weight, the cross-linking agent penetrates into the water-containing water-absorbent resin, thereby increasing the internal cross-linking and reducing the water absorption performance.

  The absorbent resin after such moisture adjustment is subjected to surface treatment as required according to a known technique, dried to a moisture content of 10% by weight or less with a dryer, and then subjected to finishing treatment such as sieving. It becomes.

  The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

In the following, the granulation rate and water absorption capacity of the water absorbent resin were measured by the following methods.
(1) Granulation rate The ASTM standard sieve 12 mesh and the tray were combined in this order, and about 100 g of the water-absorbent resin was added to the uppermost sieve, and the mixture was shaken for 1 minute with a low tap type automatic sieve shaker. The weight of the water-absorbent resin remaining on the sieve was weighed, and the ratio of the total amount to 100% was calculated based on the mass.
(2) Water-absorbing capacity About 1.0 g of water-absorbing resin was precisely weighed and placed in a 250-mesh nylon bag (20 cm × 10 cm in size) and immersed in 500 cc of 0.9 wt% saline for 1 hour. Thereafter, the nylon bag was pulled up and drained for 15 minutes, and then the excess water was separated with a centrifuge (90G, 90 seconds). The weight of the swollen gel after measuring the weight, correcting the blank and separating the water was determined, and the water absorption capacity was calculated according to the following formula.

  Moreover, the water-absorbing resin for moisture adjustment used below was produced as follows.

[Production of water-absorbing resin for moisture adjustment]
After diluting 207.7 g of acrylic acid with 13.5 g of water and neutralizing with 256.2% sodium hydroxide aqueous solution by 346.2 g while cooling, 0.863 g of potassium persulfate was added and dissolved to obtain a homogeneous solution A monomer / initiator solution was prepared.

  Separately, 624 g of cyclohexane was placed in a 5-liter four-necked round bottom flask equipped with a stirrer, reflux condenser, thermometer and nitrogen gas inlet tube, and polyoxyethylene tridecyl ether phosphate (No. 1.56 g of “Plysurf A212C” (manufactured by Ichiko Pharmaceutical Co., Ltd.) was added and dispersed by stirring (300 rpm). After the atmosphere in the flask was replaced with nitrogen, the temperature was raised to 75 ° C. to reflux cyclohexane.

  The above-mentioned monomer / initiator solution was added to this over 46 minutes. After completion of the dropwise addition, the mixture was held at 75 ° C. for 30 minutes and further heated to 7 wt% based on the polymer formed by azeotropy with cyclohexane. It dried until it became the moisture content of.

Example 1
After diluting 207.7 g of acrylic acid with 13.5 g of water and cooling and neutralizing with 346.2 g of 25 wt% aqueous sodium hydroxide, 0.863 g of potassium persulfate was added and dissolved to obtain a homogeneous solution, A monomer / initiator solution was prepared.

  Separately, 624 g of cyclohexane was placed in a five-liter four-necked round bottom flask equipped with a stirrer, reflux condenser, thermometer and nitrogen gas inlet tube, and polyoxyethylene tridecyl ether phosphate (first as an emulsifier). 1.56 g of “Plysurf A212C” manufactured by Kogyo Seiyaku Co., Ltd.) was added and dispersed by stirring (250 rpm). After replacing the flask with nitrogen, the temperature was raised to 75 ° C. to reflux cyclohexane. The monomer / initiator solution described above was added to this over 46 minutes, and after completion of the dropwise addition, maintained at 75 ° C. for 30 minutes, cooled to 60 ° C., and dodecylbenzenesulfonic acid triethanolamine salt as a surfactant. 56 g (an anionic surfactant “Neogen T” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was dispersed in 1250 g of cyclohexane and added to the polymerization reaction solution at a rotational speed of 250 rpm.

  After leaving for about 10 minutes, a water-adsorbing resin for moisture adjustment (1100 g) was added over about 5 minutes at 60 ° C. The system is in a slightly viscous slurry state, and 30 minutes after the end of the addition, water absorption from the water-containing water-absorbent resin particles to the water-adsorbing resin for moisture adjustment is almost completely performed (that is, the moisture adjustment time is 30 minutes). The water content (referred to as “adjusted water content”) of the total water-absorbing resin after addition of the water-adjusting resin for water adjustment was 23% by weight.

  The contents were separated into a water-absorbent resin and a polymerization solution with a centrifuge (150 G, 10 seconds). The water-absorbing resin amount (250 g) is dried for 45 minutes with a Σ-type double-arm kneader (internal volume 1 liter, temperature 110 ° C., 30 rpm) until the water content reaches 10% by weight to obtain a powdery water-absorbing resin It was.

  The obtained water-absorbent resin was examined for the granulation rate, and the results are shown in Table 1.

Example 2
In the same manner as in Example 1, except that the surfactant is 1.56 g of polyoxyethylene polyoxypropylene block polymer (HLB = 10.1, manufactured by Toho Chemical Co., Ltd., Pepol B184). A water-absorbent resin was obtained, the granulation rate was measured for this water-absorbent resin, and the results are shown in Table 1.

Example 3
A powdery water-absorbing resin was obtained by the same operation and method except that the surfactant was not added in Example 1. The granulated body ratio of this water-absorbing resin was measured, and the results are shown in Table 1.

Example 4
A powdery water absorbent resin was obtained by the same operation and method except that the water adjustment time by water absorption was changed to 60 minutes after addition of the water adjustment resin for moisture adjustment in Example 3, and this water absorbent resin was granulated. The rate was measured and the results are shown in Table 1.

Example 5
In Example 1, a water-absorbing resin having a controlled moisture content of 23% by weight was put into a Σ-type double-arm kneader (internal volume: 1 liter, temperature: 70 ° C., 30 rpm) dryer, and then 0.19 g of diethylene glycol diglycidyl ether was added. A powdery water absorbent resin was obtained in the same manner except that the reaction was carried out for 60 minutes and then the temperature was raised to 110 ° C. and dried for 45 minutes until the water content became 10% by weight. The granule fraction and water absorption capacity of the product were measured and the results are shown in Table 1.

Example 6
In Example 3, after completion of the polymerization, after cooling to 60 ° C., the polymerization reaction solution was taken out into a 3 liter beaker, allowed to stand, 500 g of supernatant cyclohexane was separated, and 500 g of purified cyclohexane was charged again to make a slurry, and the above volume was obtained. A powdery water-absorbing resin was obtained by the same operation and method except that the reactor was returned to the 5-liter reactor, and the granule fraction of this water-absorbing resin was measured. The results are shown in Table 1.

Example 7
In Example 3, after completion of the polymerization, after cooling to 60 ° C., the polymerization reaction solution was taken out into a 3 liter beaker, allowed to stand, 500 g of the supernatant cyclohexane was separated, 500 g of purified cyclohexane was charged again, and the mixture was allowed to stand after stirring. The powdered water-absorbing resin was obtained in the same manner and using the same procedure as above except that 500 g of the supernatant cyclohexane was separated and 500 g of purified cyclohexane was charged again, and the slurry was returned to the reactor having the capacity of 5 liters. The granulation rate of this water absorbent resin was measured, and the results are shown in Table 1.

Example 8
After completion of the polymerization in Example 1, after cooling to 60 ° C., the polymerization reaction solution was taken out into a 3 liter beaker, allowed to stand, 500 g of the supernatant cyclohexane was separated, and 500 g of purified cyclohexane was charged again to make a slurry and the volume A powdery water-absorbing resin was obtained by the same operation and method except that the reactor was returned to the 5-liter reactor, and the granule fraction of this water-absorbing resin was measured. The results are shown in Table 1.

Example 9
A polymerization reaction liquid was prepared by the same operation and method as in Example 1, and transferred to a 15-liter four-necked separable flask equipped with a stirrer, a reflux condenser, a thermometer, and a nitrogen gas introduction tube. As an activator, 1.56 g of dodecylbenzenesulfonic acid triethanolamine salt (Daiichi Kogyo Seiyaku Co., Ltd. anionic surfactant “Neogen T”) is dispersed in 3200 g of cyclohexane, stirring speed is 100 rpm, temperature is 60 ° C. Set. About 10 minutes later, a water-absorbing resin for moisture adjustment (2842 g) was added over about 10 minutes. 30 minutes after the completion of the addition, water absorption from the water-containing water-absorbent resin particles to the water-adjusting water-absorbing resin was almost completely performed (that is, the water adjustment time was 30 minutes). The adjusted water content was 15% by weight. Further, the content of the powdered water-absorbing resin was obtained by the same centrifugal separation, drying operation and technique as in Example 1, and the granulated body ratio of this water-absorbing resin was measured. The results are shown in Table 1.

Example 10
In Example 3, after completion of the polymerization, after cooling to 60 ° C., the polymerization reaction solution was taken out into a 3 liter beaker, allowed to stand, 500 g of the supernatant cyclohexane was separated, 500 g of purified cyclohexane was charged again, and the mixture was allowed to stand after stirring. Then, 500 g of the supernatant cyclohexane was separated and 500 g of purified cyclohexane was charged again, and the slurry was returned to the reactor having a capacity of 5 liters. The reactor internal temperature was set to 60 ° C., 1.56 g of polyoxyethylene tridecyl ether phosphate (“Plysurf A212C” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added, and the mixture was stirred for about 10 minutes (250 rpm). . Further, the content of the powdered water-absorbing resin was obtained by the same centrifugal separation, drying operation and technique as in Example 1, and the granulated body ratio of this water-absorbing resin was measured. The results are shown in Table 1.

Comparative Example 1
In Example 3, the water-absorbent resin granulate was obtained by the same operation and method except that the amount of the water-absorbent resin added was changed to 600 g and the adjusted water content was changed to 30% by weight. The particle ratio was measured and the results are shown in Table 1.

Comparative Example 2
In Example 1, a surfactant, additional cyclohexane and a water-adsorbing resin for moisture adjustment were not added, and the polymer was further heated and azeotroped with cyclohexane at the azeotropic dehydration time shown in Table 1. The water-absorbent resin powder was obtained in the same manner except that it was dehydrated to a moisture content of 22% by weight, and then dried with a dryer. Is shown in Table 1.

Comparative Example 3
In Example 1, the surfactant, the additional cyclohexane and the water-adsorbing resin for moisture adjustment were not added, and further heated, with respect to the polymer produced by azeotropy with cyclohexane in the azeotropic dehydration time shown in Table 1. The water-absorbent resin powder was obtained in the same manner except that it was dehydrated to a water content of 10% by weight and then dried with a dryer. It is shown in Table 1.

Comparative Example 4
In Comparative Example 2, the water-absorbent resin dehydrated to a moisture content of 22% was charged into a Σ-type double-arm kneader (internal volume 1 liter, temperature 70 ° C., 30 rpm) dryer, and then 0.19 g of diethylene glycol diglycidyl ether was charged. A powdery water-absorbing resin was obtained in the same manner except that the reaction was performed for 60 minutes, and then the temperature was raised to 110 ° C. and dried for 30 minutes until the water content became 10% by weight. The granulation rate and water absorption capacity of the resin were measured, and the results are shown in Table 1.

  As shown in Table 1, in the present invention, by adding a water-adjusting resin for moisture adjustment so as to have a predetermined moisture content, more preferably by adding a surfactant, It can be seen that rapid moisture adjustment and drying can be performed while suppressing generation. Further, it can be seen from the measurement results of the water absorption ability that the performance of the absorbent resin is not affected even if such treatment is performed.

  According to the method for producing a water absorbent resin of the present invention, particles are aggregated during drying of the water-absorbent water absorbent resin, and a granulated body, a lump or a plate-like product is hardly generated, and it is quick and efficient. Since moisture adjustment and drying can be performed to obtain a powdery water absorbent resin having an average particle diameter of 200 to 3000 μm, the water absorbent resin produced according to the present invention is not only a sanitary material such as a paper diaper or a sanitary napkin, It can be used as an agricultural field as a soil water-retaining agent, and as a civil engineering or building material as a water-stopping material, lubricant, anti-condensation material, etc.

Claims (6)

In the presence of an emulsifier, a water-soluble ethylenically unsaturated monomer is subjected to reverse-phase suspension polymerization in a hydrophobic organic solvent to obtain a liquid containing the water-absorbing water-absorbing resin. In a method for producing a water absorbent resin by mixing with a water absorbent resin containing moisture lower than moisture and / or a water absorbent resin for moisture adjustment consisting of a powdered water absorbent resin and adjusting the moisture, followed by drying,
A method for producing a water-absorbent resin, comprising adding the water-absorbing resin for moisture adjustment to a liquid containing the water-containing water-absorbent resin so that the water content in the total water-absorbent resin is 25% by weight or less.   The water-absorbing resin for moisture adjustment is added to the liquid containing the water-containing water-absorbing resin according to claim 1, after adding a surfactant having a demulsifying action, or together with the surfactant. A method for producing a water-absorbent resin.   3. The production of a water-absorbent resin according to claim 2, wherein the surfactant is an HLB nonionic surfactant and / or an anionic surfactant having an HLB of 7 or more and higher than the HLB of the emulsifier. Method.   The method for producing a water-absorbent resin according to any one of claims 1 to 3, wherein the surface of the water-containing water-absorbent resin is washed with a hydrophobic organic solvent prior to the addition of the water-adsorbing resin for moisture adjustment.   5. The emulsifier according to claim 4, wherein the surface of the water-absorbing water-absorbent resin is washed with a hydrophobic organic solvent, and the water content in the total water-absorbing resin is adjusted to 25% by weight or less by mixing the water-absorbing resin for water adjustment. A method for producing a water-absorbent resin, comprising adding   The water absorbing resin according to any one of claims 1 to 5, wherein the water absorbing resin for water adjustment is added to the water-containing water absorbing resin to adjust the water content in the total water absorbing resin to 15 to 25% by weight. A method for producing a water-absorbent resin, comprising performing a surface cross-linking step of a functional resin.