JP2000212215A - Preparation of hydrophilic polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation process which yields with a high productivity a hydrophilic polymer with little residual monomers, wherein the physical properties of the water-containing gel-like polymer obtained through polymerization is maintained. SOLUTION: A water-containing gel-like polymer is dried at a material temperature of 90 deg.C or lower at an ordinary pressure until the moisture content of the water-containing gel-like polymer reaches from 15 to 40 wt.%. Subsequently, a condition wherein the amount of change in the moisture content of the water-containing gel-like polymer is within 5 wt.% and the material temperature is from 70 to 120 deg.C, or a condition wherein the moisture content is from 15 to 40 wt.% and the material temperature is from 70 to 120 deg.C is maintained for 10 minutes or longer. Then, finishing drying is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a hydrophilic polymer, that is, a water-soluble polymer and a water-swellable polymer. More specifically, the present invention relates to a method for producing a hydrophilic polymer having a small amount of residual monomers while maintaining the physical properties of a hydrogel polymer obtained by polymerization.

[0002]

2. Description of the Related Art A hydrophilic polymer includes a water-soluble polymer and a water-swellable polymer. Examples of the water-soluble polymer include sodium polyacrylate, partially hydrolyzed polyacrylamide,
There are polyvinyl alcohol and the like, and these water-soluble polymers are used as a flocculant for water treatment, a muddy water additive for petroleum drilling, a food additive and the like. Examples of the water-swellable polymer include a crosslinked polyacrylate, a saponified acrylate-vinyl acetate copolymer, a crosslinked polyvinyl alcohol modified product, a partially neutralized polyacrylate crosslinked product, and a crosslinked isobutylene-maleic anhydride. There are copolymers, starch-acrylic acid graft polymer, etc., used for sanitary products, absorbents for sanitary materials such as disposable diapers, or water retention agents for agriculture, forestry, horticulture, revegetation, food freshness retaining films, etc. Demand is about to grow.

The unreacted residual monomers contained in these hydrophilic polymers and the water-soluble polymers contained in the water-swellable polymer flow out under external pressure or with the passage of time, and come into contact with human skin, Or it may be absorbed into the water, which may be a serious problem in some applications. In addition, there is a risk that it will be discarded and discharged into the environment and then mixed into drinking water again.Therefore, there is a recent demand for reduction of residual monomers in hydrophilic polymers and water-soluble polymers in water-swellable polymers. Increasingly.

[0004] In general, as a method of reducing the residual monomer of a polymer, addition of ammonia and amine (Japanese Patent Publication No. 33-2646, Japanese Patent Application Laid-Open No. 40-40689) and addition of sulfite and hydrogen sulfite (US Pat. No. 2,960,486) JP-A-55-135110), a method of adding these compounds to the remaining monomer to reduce the amount, and a combination of a low-temperature decomposition type and a high-temperature decomposition type polymerization initiator (Japanese Patent Publication No. 50-44280, JP-A-59-133205,
JP-A-53-141388) or a combination of a redox catalyst and an azo-based initiator (JP-A-50-96689, JP-B-47-26430)
Discloses a method of polymerizing and lowering the residual monomer. However, ammonia, amines,
Alternatively, the addition of sulfites and bisulfites is effective in reducing the residual monomer, but the addition of these compounds is ineffective at small amounts, and furthermore, the toxicity of such additives themselves becomes a problem. Also, the method using a catalyst in combination is insufficient in effect.

[0005] On the other hand, when a hydrogel is obtained by polymerizing a hydrophilic monomer in an aqueous solution to obtain a hydrogel polymer and then drying it to produce a hydrophilic polymer, a method for reducing the residual monomer is as follows. , A hydrogel polymer in the range of 80 to 250
A method of drying while contacting with a mixed gas of water vapor having a dew point of 50 to 100 ° C. at a temperature of 50 ° C.
No. 4) is known. In this method, the dryer may be too large. In addition, a method has been proposed in which a hydrogel polymer is partially dried and then the temperature of the gel is increased by microwave irradiation to reduce residual monomers (Japanese Patent Application Laid-Open No. H5-209010). However, in this method, although the effect of reducing the residual monomer or the improvement of the absorption capacity is recognized, in the case of the water-soluble polymer, the formation of an insolubilized substance and the reduction of the molecular weight are accompanied, and in the case of the water-swellable polymer, Since the physical properties are remarkably deteriorated as compared with the hydrogel polymer, for example, an increase in the water-soluble component is observed, it is not an industrially suitable method. or,
Microwave irradiation during drying involves local heating of the material,
Not only is the physical property of the hydrogel polymer changed, but also the safety of the microwave itself, materials around microwave irradiation are limited, and equipment costs are large.There are many issues that must be overcome in the future. Not practical at present.

Further, at a reduced pressure of 60 to 120 ° C., the water content is 4
Although there is a method of reducing the weight from 0 to 70% by weight to 10 to 35% by weight (Japanese Patent Laid-Open No. 5-310806), drying under reduced pressure involves an increase in the cost of a dryer and a long drying time. Takes time and is not practical. As a related technique, there is a method of improving the absorption capacity by carrying out a steam treatment at a solid content of 20 to 60% by weight and a hydrogel temperature of 50 ° C., raising the solid content by a maximum of 30% by weight, and then drying normally (Japanese Patent Laid-Open No. However, this method cannot be said to be an appropriate method because not only the absorption capacity is increased but also the water-soluble content is increased and the physical properties are significantly reduced.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a hydrophilic polymer having a small amount of residual monomers with good productivity while maintaining the physical properties of a hydrogel polymer obtained by polymerization. To provide.

[0008]

The above object is achieved by the following method. (1) A method for producing a hydrophilic polymer by drying a hydrogel polymer by aqueous solution polymerization of a hydrophilic monomer to obtain a hydrogel polymer, wherein the drying step comprises: Until the water content of the polymer becomes 15 to 40% by weight,
A partial drying step of drying at a material temperature of 90 ° C. or lower at normal pressure, and after the partial drying step, a change in the water content of the hydrogel polymer is within 5% by weight, and the material temperature is 70 to 120.
And a finishing drying step of drying the hydrated gel-like polymer to a desired moisture content after the heating aging step. Manufacturing method of coalescence. (2) In a method for producing a hydrophilic polymer by drying a hydrogel polymer after obtaining a hydrogel polymer by aqueous solution polymerization of a hydrophilic monomer, the drying step includes the hydrogel process. Until the water content of the polymer becomes 15 to 40% by weight,
A partial drying step in which the material is dried at normal temperature at a temperature of 90 ° C. or less, and after the partial drying step, a state in which the water-containing gel polymer has a water content of 15 to 40% by weight and a material temperature of 70 to 120 ° C. for 10 minutes. A method for producing a hydrophilic polymer, comprising: a heating aging step for maintaining the above; and a finishing drying step after the heating aging step, in which the hydrogel polymer is dried until a desired water content is obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogel polymer subjected to drying in the present invention is a water-soluble or water-swellable hydrogel obtained by polymerizing a hydrophilic monomer in an aqueous solution. Contains monomer. If necessary, a particulate hydrogel polymer may be finely divided in order to secure a surface area necessary for drying.

As such a hydrogel polymer, there is, for example, a hydrogel polymer obtained by polymerizing an aqueous monomer solution in a mold as described in JP-B-48-42466. A product obtained by pulverizing the coalesced as necessary using a meat chopper, extruder, kneader, or the like. JP-A-57-34101, JP-A-10-67805, as described in JP-A-10-67805, a hydrogel polymerized in a kneader or the like having a stirring blade capable of subdividing the hydrogel polymer inside Of fine polymer. A hydrated gel polymer polymerized on a belt conveyor as described in JP-A-58-49714, which is pulverized and divided by a meat chopper, an extruder, a kneader or the like as necessary. Etc.

The hydrophilic monomer used for obtaining the hydrogel polymer of the present invention includes, for example, (meth) acrylic acid or an alkali metal salt or ammonium salt thereof; (meth) acrylamide; (meth) acrylonitrile; Maleic acid, unsaturated dibasic acids such as fumaric acid or semi-esterified products of these unsaturated dibasic acids or
Alkali metal salts or ammonium salts of these unsaturated dibasic acids or half-esterified products; 2-acrylamide-2
-Unsaturated sulfonic acids such as methylpropanesulfonic acid and 2- (meth) acryloylethanesulfonic acid, or alkali metal salts or ammonium salts thereof; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, etc. And one of these
Species or a mixture of two or more can be used. Further, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, vinyl acetate,
It may be used in an amount that does not extremely inhibit the hydrophilicity of the hydrogel polymer from which monomers other than the hydrophilic monomer such as vinyl propionate can be obtained. Further, in obtaining a water-containing gel-like polymer of a water-swellable polymer, for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene Glycol diacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, N, N −
A cross-linking agent such as methylene bisacrylamide, triallyl isocyanurate, pentaerythritol diacrylate, pentaerythritol dimethacrylate and the like may be used in combination with the hydrophilic monomer.

The polymerization for forming a hydrogel polymer is an aqueous solution polymerization of a hydrophilic monomer, and is generally formed by dissolving a hydrophilic monomer component, a polymerization initiator and an optional crosslinking agent in water. After degassing the aqueous hydrophilic monomer solution with an inert gas such as nitrogen gas, for example, JP-B-48-42466
JP-A-57-34101, a cast polymerization in which polymerization is carried out in a mold as described in JP-A-57-34101, a polymerization on a belt conveyor as described in JP-A-58-49714 This can be achieved by a method of polymerizing in a kneader or the like having a stirring blade capable of subdividing a hydrogel polymer inside as described in the gazette. The polymerization initiator can be used without any particular limitation. Examples thereof include ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride) and the like. A redox initiator or the like is used in combination with a reducing agent such as sodium hydrogen sulfite, L-ascorbic acid, and ferrous salt. Persulfate is preferably used in combination with a reducing agent if necessary. This is because the persulfate has a high thermal decomposition temperature and thus easily remains in the hydrogel polymer after polymerization, and the remaining monomer can be reduced by reacting the persulfate with the remaining monomer.

The water content of the hydrogel polymer is preferably 80 to 60% by weight. The water content of the hydrogel polymer can be adjusted by the concentration of the aqueous hydrophilic monomer solution. The amount of the polymerization initiator to be used is usually 0.0001 to 3% by weight, preferably 0.0
002 to 2% by weight, for water-swellable polymers, usually 0.01 to 2% by weight, preferably 0.05 to 1% by weight, based on the monomer.
% By weight.

In practicing the present invention, the hydrogel polymer obtained by polymerization may be already pulverized, but in many cases, it is necessary to divide the polymer into a form that can be easily dried. . As a method of subdividing, for example, pulverization using a meat chopper, an extruder, a kneader, or the like is effective. Usually, the residual monomer of the hydrogel polymer obtained by polymerization is at least 1000 ppm, but upon drying in the present invention, it is usually at least 10,000 ppm, preferably at least 20,000 ppm, more preferably at least 30,000 ppm.
A hydrogel polymer having a content of at least ppm, most preferably at least 40,000 ppm is used. If an attempt is made to reduce the residual monomer only by the polymerization, the polymerization time is prolonged, and the productivity is reduced. In addition, if the amount of the polymerization initiator is used in a large amount to reduce the residual monomer, the absorption capacity of the resulting water-absorbent resin under no pressure is reduced, or the physical properties such as an increase in the soluble component are caused. . Therefore, it is preferable to stop the polymerization in a state in which the amount of the residual monomer is large and to dry the polymer in terms of productivity and physical properties.

In the present invention, when the hydrogel polymer is dried, drying is performed at a material temperature of 90 ° C. or less at normal pressure until the water content reaches 15 to 40% by weight (partial drying step). Change within 5% by weight, material temperature 70 ~
120 ° C. or water content of 15 to 40% by weight,
This is achieved by providing a finish drying step in which a heating and aging step of maintaining the state of the material temperature of 70 to 120 ° C. for 10 minutes or more and then drying until a desired moisture content is achieved are provided.

The partial drying step is performed at normal pressure, and the material temperature is 90 ° C. or lower, preferably 80 ° C. or lower. If the material temperature exceeds 90 ° C., the amount of residual monomers increases and the hydrogel deteriorates, which is not preferable. In addition, drying under reduced pressure involves an increase in the cost of a dryer device, requires a long drying time, and is not practical. The partial drying process has a water content of 15 to 4
0% by weight, and preferably 20 to 35% by weight. When the water content at the end of the partial drying step is higher than 40% by weight, the effect of reducing the residual monomer in the next heat aging step is insufficient, and the deterioration of the hydrogel polymer becomes large, and The dissolved content increases. On the other hand, if the water content at the end of the partial drying step is lower than 15% by weight, the effect of reducing residual monomers is poor.

In the heat aging step, the amount of change in the water content is within 5% by weight, the material temperature is 70 to 120 ° C., or
In order to maintain the state of the water content of 15 to 40% by weight and the material temperature of 70 to 120 ° C. for 10 minutes or more, for example, heating in a closed container to suppress drying, or reducing the air volume in hot air drying, or It can be realized by filling the inside of the dryer with steam. The material temperature at this time is 70 to 120
° C, preferably 80 to 100 ° C. When the material temperature exceeds 120 ° C., the deterioration of the polymer increases,
In addition, the content of the water-soluble polymer increases, and if the temperature is lower than 70 ° C., it takes too much time to reduce the residual monomer, which is not practical. The aging time is at least 10 minutes, preferably at least 20 minutes. When the aging time is less than 10 minutes, the effect of reducing the residual monomer is insufficient. The water content at this time is in the range of 15 to 40% by weight, preferably 20 to 35% by weight, or the change is within 5% by weight, preferably within 4% by weight. If the water content exceeds 40% by weight or less than 15% by weight, or if the variation exceeds 5% by weight, the amount of residual monomers increases or the hydrogel polymer deteriorates greatly.

The material after the heat aging step is subjected to finish drying until the desired moisture content is reached. The drying temperature at this time is preferably from 80 to 250 ° C, and more preferably from 80 to 170 ° C to prevent the degradation of the hydrogel polymer. Increasing the drying temperature with decreasing water content is also sometimes effective. The drying temperature here refers to the temperature of the gas used or the temperature of the material to be dried.
The desired moisture content can be appropriately set according to the purpose, but is usually 0%.
10 to 10% by weight, preferably 3 to 7% by weight.

The form of the dryer used in the present invention is not limited, and examples thereof include a conductive heat transfer dryer, a radiation heat transfer dryer, and a hot air transfer dryer. In a step after the partial drying step and the finish drying step, particularly for the purpose of drying, a hot air heat transfer dryer (hereinafter, referred to as a hot air dryer) is particularly preferable from the viewpoint of drying efficiency. As a hot air dryer,
Examples include a ventilation band type, a ventilation rotation type, a vertical ventilation type, a parallel flow band type, a ventilation tunnel type, a ventilation groove type stirring type, a fluidized bed type, an air flow type, and a spray type. Examples of the radiation heat transfer type device include infrared and far-infrared dryers, and examples of the conduction heat transfer type device include a paddle dryer and a drum dryer. The gas used at this time is not particularly limited, and examples thereof include air, nitrogen, carbon dioxide, helium, and water vapor.

According to the present invention, the hydrogel polymer is dried to obtain the desired hydrophilic polymer. After drying, pulverization and, if necessary, classification, a known method for a water-swellable polymer is used. It is preferable to perform a surface cross-linking treatment. In the surface cross-linking treatment, for example, after mixing the water-swellable polymer particles with a surface cross-linking agent capable of reacting with a functional group (for example, an acidic group) on the surface of the water-swellable polymer particles, To further crosslink the vicinity of the surface. The amount of the surface crosslinking agent is preferably from 0.01 to 10 parts by weight, more preferably from 0.5 to 5 parts by weight, based on 100 parts by weight of the water-swellable polymer.

Examples of such a surface crosslinking agent include, for example,
Ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-
Trimethyl-1,3-pentadiol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4
-Butanediol, 1,5-pentanediol, 1,6
-Hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine,
Polyhydric alcohol compounds such as polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol and sorbitol; ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol poly Polyhydric epoxy compounds such as glycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether and glycidol; polyamine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine; Their inorganic or organic salts (e.g., aztinium salts); 2,4- Li diisocyanate, polyvalent isocyanate compound such as hexamethylene diisocyanate; 1,2-ethylene polyvalent oxazoline compound of bisoxazoline, and the like; 1,3-dioxolan-2-one, 4-
Methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1, 3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxane-
2-one, 4,6-dimethyl-1,3-dioxane-2
Alkylene carbonate compounds such as -one and 1,3-dioxopan-2-one; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin, and polyamine adducts thereof (for example, Hercules Sponge: registered trademark); silane coupling agents such as γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane; hydroxides and chlorides such as zinc, calcium, magnesium, aluminum, iron, zirconium and the like Metal compounds such as organic compounds. Among these, polyhydric alcohol compounds, polyvalent epoxy compounds, alkylene carbonate compounds, and polyvalent metal compounds are preferred. These surface cross-linking agents may be used alone or in combination of two or more.

According to the present invention, a hydrophilic polymer having a small amount of residual monomers can be produced while maintaining the physical properties of a hydrogel polymer obtained by polymerization. In particular, when the hydrophilic polymer is a water-absorbing resin, the rate of change in absorption capacity under no pressure before and after the drying step can be 10% or less, the rate of change in solubles can be 100% or less, and the residual monomer can be reduced. It can be reduced to 300 ppm or less.

The hydrophilic polymer produced according to the present invention comprises:
Less adverse effect on human body and environment, water treatment flocculant,
It is suitably used for applications such as muddy oil additives for oil drilling, food additives, absorbents for sanitary materials, water retention agents, food freshness retaining films, and the like.

[0024]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the scope of the present invention is not limited only to these Examples. In the present invention, water content, solid content, absorption capacity under no pressure, soluble matter, residual monomer, absorption capacity under pressure, and swelling gel pressure were measured by the following methods. (A) Moisture content Particulate hydrogel polymer finely divided to 1 mm or less or 3
Approximately 2.0 g of a powder of 00 μm to 500 μm was weighed into a wheel container, and the water content was determined from the dry weight after drying at 180 ° C. for 5 hours.

Water content (% by weight) = (weight before drying−weight after drying) / weight before drying × 100 (a) Solid content Solid content (% by weight) = 100−water content (% by weight) (C) ) Absorption capacity under no pressure Absorption of solids A (% by weight) of a particulate hydrogel polymer finely divided into 1 mm or less or powder W1 (g) pulverized and classified to 300 μm to 500 μm (about 100% solid content) 0.2
g) into a non-woven bag (60 mm x 60 mm),
It was immersed in a 0.9% by weight aqueous solution of sodium chloride. After 16 hours, pull up the bag and centrifuge at 250 G for 3 hours.
After draining for a minute, the weight W2 (g) of the bag was measured. The weight W0 (g) of the bag when the same operation was performed using only the bag without using a sample (a hydrogel or a powder) was measured. From the weights W1, W2, and W0, the absorption capacity under no pressure was calculated according to the following equation.

Absorption capacity under no pressure (g / g) = (W2-W
0) / W1 × (100 / A) -1 (d) Soluble content (water-soluble polymer content) Particulate hydrogel polymer finely divided into 1 mm or less of solid content A (% by weight) or 300 μm or less Powder W3 (g) pulverized and classified to 500 μm (about 0.5 g as 100% solid content)
Was dispersed in 1000 g of deionized water, stirred for 16 hours, and then filtered through filter paper. Then, 50 g of the obtained filtrate was added to 1
The mixture was placed in a 00 ml beaker, and 1 ml of a 0.1 N sodium hydroxide aqueous solution, 10 ml of an N / 200-methyl glycol chitosan aqueous solution, and 5 drops of a 0.1 wt% toluidine blue aqueous solution were added. Next, the solution in the above beaker was subjected to colloidal titration using an aqueous solution of N / 400 polyvinyl potassium sulfate, and a titration end point B (ml) was determined when the color of the solution changed from blue to reddish purple. or,
The same operation was performed using 50 g of deionized water instead of 50 g of the filtrate, and the titer C (ml) was obtained as a blank.
Then, based on these titration amounts B and C and the molecular weight D of the monomer constituting the polymer, the soluble content (% by weight) is calculated according to the following equation.
Was calculated.

Soluble (% by weight) = (CB) × 0.00
5 × D / W3 × (100 / A) (e) Rate of change in absorption capacity under no pressure Absorption capacity under no pressure of the hydrogel polymer is defined as GV0, and absorption of the dried hydrogel or powder under no pressure GV1 magnification
The absolute value was used as the rate of change in absorption capacity under no pressure, and was calculated according to the following equation.

Absorption magnification change rate under no pressure (%) = | GV0
−GV1 | / GV0 × 100 (f) Change rate of soluble component When the soluble component of the hydrogel polymer is Ext 0 and the soluble component of the dried hydrogel or powder is Ext 1, The absolute value was used as the change rate of the dissolved component, and was calculated according to the following equation.

Soluble change rate (%) = | Ext 0−Ext 1 |
/ Ext 0 × 100 (g) Residual monomer Approximately 3 g of a particulate hydrogel polymer having a solid content A (% by weight) finely divided into 1 mm or less (approximately 0.1% as 100% solid content).
5 g) or about 0.5 g of a powder pulverized and classified to 300 μm to 500 μm is dispersed in 1000 g of deionized water.
After stirring for 6 hours, the mixture was filtered with filter paper. The amount of the monomer contained in the filtrate was measured by high performance chromatography, and the amount of the monomer remaining in the hydrogel polymer or the pulverized powder was quantified. (H) Absorption under pressure The water-absorbent resin after the surface treatment was allowed to absorb artificial urine under a load of 0.7 psi for 1 hour, and the amount of absorption was divided by the weight of the water-absorbent resin to determine the absorption under pressure. Artificial urine contains sodium sulfate 0.
2% by weight, potassium chloride 0.2% by weight, magnesium chloride hexahydrate 0.05% by weight, calcium chloride dihydrate 0.025% by weight, ammonium dihydrogen phosphate 0.03%
5% by weight, 0.015% by weight of diammonium hydrogen phosphate
An aqueous solution containing (G) Swelling gel pressure A measuring device having a structure as shown in FIG. 1 (The Crow)
Accuforce Cadet Force Ga manufactured by Tool & Supply Company
ge (Digital Force Gauge)) and the following method. 0.358 g of the water-absorbent resin a classified to 300 to 600 μm was applied to FISHER ELECTRO-P
10 g of artificial urine c adjusted to 25 ° C. was placed in the cell b for HOTOMETER, and the dropping d made of polyethylene was floated on the cell b, and a disk e was placed on the dropping d. An additional 10 g of artificial urine c was added, the value was read 30 minutes after the water-absorbent resin (swelling gel) a that absorbed the artificial urine c dropped and reached the lid d, and the swelling pressure (Kdy) was calculated according to the following equation.
nes / cm ² ) was calculated. The artificial urine is the same as that used for measuring the absorption capacity under pressure.

Swelling pressure (Kdynes / cm ² ) = reading scale (g) × 981 / 3.8 / 1000 (Production Example 1) 204 g of acrylic acid and 496 of sodium acrylate in a 220 mm × 300 mm stainless steel vat.
g, 1.6 g of polyethylene glycol diacrylate and 1286 g of water, and the reaction system was purged with nitrogen while maintaining the solution temperature at 20 ° C. Next, while stirring the monomer aqueous solution with a magnetic stirrer, 5% by weight V-50 (2,2′-azobis (2-amidinopropane) manufactured by Wako Pure Chemical Industries, Ltd.) was used as a polymerization initiator.
3 g of an aqueous solution of dihydrochloride), 3 g of an aqueous solution of 5% by weight of sodium persulfate, 3 g of an aqueous solution of 0.5% by weight of sodium L-ascorbate, and 3.5 g of an aqueous solution of 0.35% by weight of hydrogen peroxide were added. The polymerization started about 1 minute after the addition of the polymerization initiator. Place the stainless steel vat in a water bath at 20 ° C., cool for 20 minutes, and then
Aged with 0 ° C warm water. The polymer gel was pulverized with a meat chopper (Hiraga Seisakusho) to obtain a particulate hydrogel having an average particle size of about 3 mm and a water content of 65% by weight. (Production Example 2) 204 g of acrylic acid and 496 of sodium acrylate were placed in a 220 mm × 300 mm stainless steel bat.
g, 1.6 g of polyethylene glycol diacrylate and 1286 g of water, and the reaction system was purged with nitrogen while maintaining the solution temperature at 20 ° C. Next, while stirring the monomer aqueous solution with a magnetic stirrer, 3 g of a 5 wt% aqueous solution of V-50 was used as a polymerization initiator, 3 g of a 5 wt% aqueous solution of sodium persulfate, 0.5 g of a 0.5 wt% aqueous solution of sodium persulfate were added.
3 g of a weight% sodium L-ascorbate aqueous solution and 3.5 g of a 0.35 weight% aqueous hydrogen peroxide solution were added.
The polymerization started about 1 minute after the addition of the polymerization initiator. The stainless steel vat was placed in a water bath at 20 ° C., cooled for 20 minutes, and then aged for 40 minutes with warm water at 60 ° C. The polymer gel was pulverized with a meat chopper (Hiraga Seisakusho) to obtain a particulate hydrogel having an average particle size of about 3 mm and a water content of 65% by weight. (Production Example 3) 204 g of acrylic acid and 496 of sodium acrylate were placed in a 220 mm × 300 mm stainless steel bat.
g, 1.6 g of polyethylene glycol diacrylate and 1286 g of water, and the reaction system was purged with nitrogen while maintaining the solution temperature at 20 ° C. Then, while stirring the aqueous monomer solution with a magnetic stirrer, 3 g of a 5 wt% aqueous V-50 solution as a polymerization initiator, 6 g of a 5 wt% aqueous sodium persulfate solution,
3 g of a weight% sodium L-ascorbate aqueous solution and 3.5 g of a 0.35 weight% aqueous hydrogen peroxide solution were added.
The polymerization started about 1 minute after the addition of the polymerization initiator. The stainless steel vat was placed in a water bath at 20 ° C., cooled for 20 minutes, and then aged for 30 minutes with warm water at 60 ° C. The polymer gel was pulverized with a meat chopper (Hiraga Seisakusho) to obtain a particulate hydrogel having an average particle size of about 3 mm and a water content of 65% by weight. (Production Example 4) 204 g of acrylic acid and 496 of sodium acrylate were placed in a 220 mm × 300 mm stainless steel bat.
g, 1.6 g of polyethylene glycol diacrylate and 1286 g of water, and the reaction system was purged with nitrogen while maintaining the solution temperature at 20 ° C. Next, while stirring the aqueous monomer solution with a magnetic stirrer, 3 g of a 5 wt% aqueous solution of V-50 as a polymerization initiator, 9 g of a 5 wt% aqueous sodium persulfate solution,
3 g of a weight% sodium L-ascorbate aqueous solution and 3.5 g of a 0.35 weight% aqueous hydrogen peroxide solution were added.
The polymerization started about 1 minute after the addition of the polymerization initiator. The stainless steel vat was placed in a water bath at 20 ° C., cooled for 20 minutes, and then aged for 30 minutes with warm water at 60 ° C. The polymer gel was pulverized with a meat chopper (Hiraga Seisakusho) to obtain a particulate hydrogel having an average particle size of about 3 mm and a water content of 65% by weight. (Production Example 5) Content 10 liters, opening 220 mm x 260 m
A lid is attached to a jacketed stainless steel double-armed crane (kneader) having two sigma-type blades having a m, a depth of 240 mm, and a rotating diameter of the blades of 120 mm. In the kneader, 408 g of acrylic acid and 992 g of sodium acrylate are placed. 3.2 g of polyethylene glycol diacrylate and 2572 of water
g of the monomer aqueous solution, and put 25 g on the jacket.
The reaction system was purged with nitrogen while maintaining the liquid temperature of the aqueous monomer solution at 25 ° C. by circulating hot water at a temperature of 25 ° C. Next, while stirring the aqueous monomer solution at 40 rpm with two sigma-type stirring blades, 6 g of a 5 wt% aqueous V-50 solution as a polymerization initiator, 6 g of a 5 wt% aqueous sodium persulfate solution and 0.1 g of a 0.1 wt% aqueous sodium persulfate solution were added.
6 g of a 5% by weight sodium L-ascorbate aqueous solution and 7 g of a 0.35% by weight aqueous hydrogen peroxide solution were added. About 1 minute after the addition of the polymerization initiator, the polymerization starts. After 15 minutes, the temperature in the reaction system reaches a peak, and the temperature at this time is 63 ° C.
Met. Next, the temperature of the hot water in the jacket is set to 60 ° C.
Aged for another 10 minutes. Thereafter, the polymer gel was pulverized with a meat chopper (Hiraga Seisakusho) to obtain a particulate hydrogel having an average particle size of about 3 mm and a water content of 65% by weight. (Production Example 6) A particulate hydrogel was obtained in the same manner as in Production Example 1 except that the amount of polyethylene glycol diacrylate used was changed to 0.8 g. (Production Example 7) A 220 mm x 300 mm stainless steel vat was charged with a monomer aqueous solution composed of 184 g of acrylic acid, 1611 g of a 37% by weight aqueous sodium acrylate solution, 4.3 g of polyethylene glycol diacrylate, and 194 g of water, and the liquid temperature was maintained at 18 ° C. The reaction system was replaced with nitrogen. Next, while stirring the aqueous monomer solution with a magnetic stirrer, 20% by weight as a polymerization initiator was used.
5.3 g of an aqueous solution of sodium persulfate and 1.6 g of an aqueous solution of 5% by weight of sodium L-ascorbate were added. The polymerization started about 1 minute after the addition of the polymerization initiator. The stainless steel vat was placed in a 10 ° C. water bath, cooled for 12 minutes, and then aged for 10 minutes with 80 ° C. warm water. The polymer gel was pulverized with a meat chopper (Hiraga Seisakusho) to obtain a particulate hydrogel having an average particle size of about 2 mm and a water content of 60% by weight. (Example 1) 1 kg of the particulate hydrogel obtained in Production Example 1
Is a ventilation batch type dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
Using 6), wind speed is 1m / sec, temperature is 80 ° C, and 20
It was left to dry for a minute (partial drying step). The temperature of the material was measured at 70 ° C. by measuring the material temperature by inserting a thermometer into the center of the aggregated, squid-like aggregate at this time. The water content was 25% by weight. Next, the obtained coagulated semi-dried product was placed in a stainless steel beaker, the whole container was wrapped with an aluminum wheel and sealed, and then heated at 100 ° C. for 1 hour (heating aging step). The material temperature of the semi-dried product after heating was 95 ° C., and the water content was 23% by weight. After that, again, the flocculent aggregate was spread on a wire net and passed through a batch-type dryer for 150 minutes.
℃, finish drying for 30 minutes (finish drying step),
A dried product having a water content of 7% by weight was obtained. After pulverizing and classifying this product, the absorption capacity under no pressure, the soluble component, and the residual monomer of the powder of 500 μm to 300 μm were measured. (Example 2) The same operation as in Example 1 was carried out except that the particulate hydrogel obtained in Production Example 2 was used, and physical properties of the polymer were measured.

The material temperature after the partial drying step is 70 ° C., the water content is 25% by weight, and the material temperature after the heat aging step is 9%.
At 5 ° C., the water content was 23% by weight, and the water content after the finish drying step was 7% by weight. Example 3 The same operation as in Example 1 was carried out except that the particulate hydrogel obtained in Production Example 3 was used, and the physical properties of the polymer were measured.

The material temperature after the partial drying step is 73 ° C., the water content is 24% by weight, and the material temperature after the heat aging step is 9%.
At 6 ° C., the water content was 22% by weight, and the water content after the finish drying step was 6% by weight. (Example 4) The same operation as in Example 1 was carried out except that the particulate hydrogel obtained in Production Example 4 was used, and the physical properties of the polymer were measured.

The material temperature after the partial drying step is 72 ° C., the water content is 25% by weight, and the material temperature after the heat aging step is 9%.
At 6 ° C., the water content was 24% by weight, and the water content after the finish drying step was 7% by weight. Example 5 The same operation as in Example 1 was carried out except that the particulate hydrogel obtained in Production Example 5 was used, and the physical properties of the polymer were measured.

The material temperature after the partial drying step is 72 ° C., the water content is 25% by weight, and the material temperature after the heat aging step is 9%.
At 5 ° C., the water content was 25% by weight, and the water content after the finish drying step was 6% by weight. (Example 6) The same operation as in Example 1 was carried out except that the particulate hydrogel obtained in Production Example 6 was used, and the physical properties of the polymer were measured.

The material temperature after the partial drying step is 71 ° C., the water content is 24% by weight, and the material temperature after the heat aging step is 9%.
At 6 ° C., the water content was 23% by weight, and the water content after the finish drying step was 7% by weight. (Example 7) The same operation as in Example 1 was carried out except that the particulate hydrogel obtained in Production Example 7 was used, and physical properties of the polymer were measured.

The material temperature after the partial drying step is 70 ° C., the water content is 25% by weight, and the material temperature after the heat aging step is 9%.
At 7 ° C., the water content was 24% by weight, and the water content after the finish drying step was 7% by weight. Example 8 In Example 1, the coagulated semi-dried product after the partial drying step was placed in a stainless steel pressure vessel, sealed, and heated at 120 ° C. for 12 minutes. The material temperature of the semi-dried product after heating was 118 ° C., and the water content was 23% by weight. After that, the agglomerate in the form of squid is spread again on a wire mesh and subjected to finish drying at 150 ° C. for 30 minutes using a batch-type air dryer.
A dried product having a water content of 7% by weight was obtained. After pulverizing and classifying the powder, the absorption capacity under non-pressurization, the soluble content, and the residual monomer of the powder of 500 to 300 μm were measured. (Comparative Example 1) 1 kg of the particulate hydrogel obtained in Production Example 1
Is a ventilation batch type dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
6), at a wind speed of 1 m / sec and a temperature of 80 ° C.,
It was left to dry for minutes. At this time, a thermometer was inserted into the center of the agglomerate-like aggregate, and the temperature of the material was measured. The water content was 50% by weight. Next, the obtained coagulated semi-dried product was put into a stainless beaker, the whole container was wrapped with an aluminum wheel, and then sealed, and then heated at 100 ° C. for 1 hour. The material temperature of the semi-dried product after heating was 90 ° C., and the water content was 45% by weight.
After that, again, the flocculent aggregates are spread on a wire mesh, and subjected to finish drying at 150 ° C. for 30 minutes in a ventilation batch type dryer.
A dried product having a water content of 7% by weight was obtained. After pulverizing and classifying this product, the absorption capacity under no pressure, the soluble component, and the residual monomer of the powder of 500 μm to 300 μm were measured. (Comparative Example 2) 1 kg of the particulate hydrogel obtained in Production Example 1
Is a ventilation batch type dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
6), the wind speed is 1 m / sec, the temperature is 80 ° C, and the temperature is 30
It was left to dry for minutes. The temperature of the material was measured at 80 ° C. by measuring the material temperature by inserting a thermometer into the center of the flocculated aggregate. The water content was 10% by weight. Next, the obtained coagulated semi-dried product was put into a stainless beaker, the whole container was wrapped with an aluminum wheel, and then sealed, and then heated at 100 ° C. for 1 hour. The material temperature of the semi-dried product after heating was 98 ° C., and the water content was 9% by weight.
After that, again, the flocculent aggregates are spread on a wire mesh, and subjected to finish drying at 150 ° C. for 30 minutes in a ventilation batch type dryer.
A dried product having a water content of 6% by weight was obtained. After pulverizing and classifying this product, the absorption capacity under no pressure, the soluble component, and the residual monomer of the powder of 500 μm to 300 μm were measured. (Comparative Example 3) 1 kg of the particulate hydrogel obtained in Production Example 1
Is a ventilation batch type dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
6), 1 m / sec wind speed, 180 ° C temperature, 1
It was left to dry for 0 minutes. The temperature of the material was measured at 95 ° C. by measuring the material temperature by inserting a thermometer into the center of the agglomerated agglomerate at this time. The water content was 25% by weight. Next, the obtained coagulated semi-dried product was put into a stainless beaker, the whole container was wrapped with an aluminum wheel, and then sealed, and then heated at 100 ° C. for 1 hour. The material temperature of the semi-dried product after heating was 98 ° C., and the water content was 23% by weight.
After that, again, the flocculent aggregates are spread on a wire mesh, and subjected to finish drying at 150 ° C. for 30 minutes in a ventilation batch type dryer.
A dried product having a water content of 7% by weight was obtained. After pulverizing and classifying this product, the absorption capacity under no pressure, the soluble component, and the residual monomer of the powder of 500 μm to 300 μm were measured. (Comparative Example 4) 1 kg of the particulate hydrogel obtained in Production Example 1
Is a ventilation batch type dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
Using 6), wind speed is 1m / sec, temperature is 80 ° C, and 20
It was left to dry for minutes. The temperature of the material was measured at 70 ° C. by measuring the material temperature by inserting a thermometer into the center of the aggregated, squid-like aggregate at this time. The water content was 25% by weight. Next, the obtained semi-dried aggregated product was placed in a stainless steel pressure vessel and heated at 140 ° C. for 8 minutes. The material temperature of the semi-dried product after heating was 125 ° C., and the water content was 22% by weight. Thereafter, the agglomerate-like aggregate was spread again on a wire net and subjected to finish drying at 150 ° C. for 30 minutes using a ventilation batch dryer to obtain a dried product having a water content of 6% by weight. After pulverizing and classifying this product, the absorption capacity under no pressure, the soluble component, and the residual monomer of the powder of 500 μm to 300 μm were measured. (Comparative Example 5) 1 kg of the particulate hydrogel obtained in Production Example 1
Is a ventilation batch type dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
6) using 4 m at a wind speed of 1 m / sec and a temperature of 170 ° C.
It was left to dry for 0 minutes to obtain a dried product having a water content of 6% by weight.
This was pulverized and classified, and the absorption capacity under no pressure, the soluble matter, and the residual monomer of a powder of 500 μm to 300 μm were measured. (Comparative Example 6) A dried product having a water content of 6% by weight was obtained in the same manner as in Comparative Example 5, except that the particulate hydrogel obtained in Production Example 2 was used. This is crushed and classified, and 500μ
Physical properties of powders of m to 300 μm were measured. (Comparative Example 7) A dried product having a water content of 6% by weight was obtained in the same manner as in Comparative Example 5, except that the particulate hydrogel obtained in Production Example 3 was used. This is crushed and classified, and 500μ
Physical properties of powders of m to 300 μm were measured. (Comparative Example 8) A dried product having a water content of 7% by weight was obtained in the same manner as in Comparative Example 5, except that the particulate hydrogel obtained in Production Example 4 was used. This is crushed and classified, and 500μ
Physical properties of powders of m to 300 μm were measured. (Comparative Example 9) A dried product having a water content of 6% by weight was obtained in the same manner as in Comparative Example 5, except that the particulate hydrogel obtained in Production Example 5 was used. This is crushed and classified, and 500μ
Physical properties of powders of m to 300 μm were measured. (Comparative Example 10) A dried product having a water content of 6% by weight was obtained in the same manner as in Comparative Example 5, except that the particulate hydrogel obtained in Production Example 6 was used. This is crushed and classified, and 500
Physical properties of powders of μm to 300 μm were measured. (Comparative Example 11) A dried product having a water content of 6% by weight was obtained in the same manner as in Comparative Example 5, except that the particulate hydrogel obtained in Production Example 7 was used. This is crushed and classified, and 500
Physical properties of powders of μm to 300 μm were measured. (Comparative Example 12) 1 k of the particulate hydrogel obtained in Production Example 1
g into a batch batch dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
6), at a wind speed of 1 m / sec and a temperature of 80 ° C.,
It was left to dry for minutes. At this time, a thermometer was inserted into the center of the agglomerate-like aggregate, and the temperature of the material was measured. The water content was 50% by weight. Next, the obtained coagulated semi-dried product is microwaved for 5 minutes.
It took 3 minutes at 00w. The material temperature of the semi-dried product after heating was 95 ° C., and the water content was 27% by weight. Thereafter, the aggregates in the form of squid are spread again on a wire mesh and finish-dried at 150 ° C. for 30 minutes using a ventilation batch type dryer.
% By weight of the dried product was obtained. After crushing and classifying this,
500 μm to 300 μm powder with no pressure absorption capacity,
The soluble components and residual monomers were measured. (Comparative Example 13) 1 k of the particulate hydrogel obtained in Production Example 1
g into a batch batch dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
Using 6), wind speed is 1m / sec, temperature is 80 ° C, and 20
It was left to dry for minutes. The temperature of the material was measured at 70 ° C. by measuring the material temperature by inserting a thermometer into the center of the aggregated, squid-like aggregate at this time. The water content was 25% by weight. Next, the obtained coagulated semi-dried product is microwaved for 5 minutes.
It took 3 minutes at 00w. The material temperature of the semi-dried product after heating was 98 ° C., and the water content was 15% by weight. Thereafter, the aggregates in the form of squid are spread again on a wire mesh and finish-dried at 150 ° C. for 30 minutes using a ventilation batch type dryer.
% By weight of the dried product was obtained. After crushing and classifying this,
500 μm to 300 μm powder with no pressure absorption capacity,
The soluble components and residual monomers were measured. (Comparative Example 14) Drying was carried out in the same manner as in Comparative Example 13 except that the coagulated semi-dried product was subjected to a microwave oven at 1500 w for 9 minutes, pulverized and classified.
The absorption capacity under no pressure, the soluble component, and the residual monomer of the powder of 00 μm to 300 μm were measured.

The material temperature after heating in a microwave oven was 98 ° C., the water content was 5% by weight, and the water content of the dried product after finish drying was 4% by weight. In addition, the semi-dried product taken out of the microwave oven had a part of the surface burnt and generated an offensive odor. (Comparative Example 15) 1 k of the particulate hydrogel obtained in Production Example 1
g into a batch batch dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
Using 6), wind speed 1.0 m / sec, temperature 120 ° C.,
Hot air composed of steam and air mixed gas having a dew point of 80 ° C. was blown, and dried to a water content of 20% by weight. Then temperature 18
0 ° C, dew point 5 ° C, wind speed 1.0m / sec.
The powder was classified, and the absorption capacity under no pressure, the soluble matter, and the residual monomer of a powder of 500 μm to 300 μm were measured. (Comparative Example 16) 1 k of the particulate hydrogel obtained in Production Example 1
g into a batch batch dryer (71-S manufactured by Satake Chemical Machinery Co., Ltd.)
6), using a wind speed of 1.0 m / sec, a temperature of 130 ° C.,
Hot air consisting of steam and air mixed gas with a dew point of 80 ° C
Then, non-humidified hot air having a temperature of 160 ° C., a dew point of 5 ° C. and an air velocity of 1.0 m / sec was sprayed for 50 minutes, and dried to a water content of 6% by weight. Then crush,
The powder was classified, and the absorption capacity under no pressure, the soluble matter, and the residual monomer of a powder of 500 μm to 300 μm were measured.

[0038]

[Table 1]

Example 9 The dried product obtained in Example 6 was pulverized and classified with a roll mill, passed through an 850 μm sieve, and dried.
Particles remaining on the 0 μm sieve were obtained. The particle size distribution was 850 μm on: 0% by weight, 600 to 850 μm: 32
% By weight, 300 to 600 μm: 53% by weight, 150 to 3
00 μm: 15% by weight.

To 100 parts by weight of the particles, ethylene glycol diglycidyl ether / propylene glycol / water / isopropyl alcohol = 0.03 / 0.5 / 3/1
The surface treating solution consisting of parts by weight was mixed and stirred in an oil bath at 212 ° C. for about 40 minutes to obtain a surface-treated water-absorbing resin. The absorption capacity under no pressure was 40 (g / g).
g), the absorption capacity under pressure was 38 (g / g). (Comparative Example 17) A surface-treated water-absorbent resin was obtained in the same manner as in Example 9 except that the dried product obtained in Comparative Example 10 was used. Its absorption capacity under no pressure is 50 (g / g),
The absorbency against pressure was 30 (g / g).

As is apparent from the results of Example 9 and Comparative Example 17, according to the present invention, the water-absorbent resin is dried without undergoing deterioration, and thus exhibits excellent absorption performance under pressure. (Example 10) 500 to 300 μm obtained in Example 6
The swelling pressure of the classified particles was measured to be 23 k
dyne / cm ² . On the other hand, the swelling pressure of the particles classified into 500 to 300 μm obtained in Comparative Example 10 is 7
kdyne / cm ² .

As is evident from the results, according to the present invention, the water-absorbent resin is dried without undergoing deterioration, and therefore has a high swelling pressure. (Example 11) 500 to 300 μm obtained in Example 7
The swelling pressure of the classified particles was measured to be 53 k
dyne / cm ² . On the other hand, the swelling pressure of the particles classified into 500 to 300 μm obtained in Comparative Example 11 was 4
It was 1 kdyne / cm ² .

As is evident from the results, according to the present invention, the water-absorbent resin is dried without undergoing deterioration, and therefore has a high swelling pressure.

[0044]

According to the method of the present invention, while maintaining the physical properties of the hydrogel polymer obtained by polymerization, that is, while suppressing deterioration of the polymer due to drying, a hydrophilic polymer having a small amount of residual monomers can be produced. , With good productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus used for measuring a swelling gel pressure in Examples.

[Explanation of symbols]

 a Water absorbent resin b Cell c Artificial urine d Drop lid e Disk

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Fujita 992, Nishioki, Okihama-ku, Abashiri-ku, Himeji-shi, Hyogo 1 Inside Nippon Shokubai Co., Ltd. Nippon Shokubai

Claims (6)

[Claims] 1. A method for producing a hydrophilic polymer by polymerizing a hydrophilic monomer with an aqueous solution to obtain a hydrogel polymer, and then drying the hydrogel polymer to produce a hydrophilic polymer, wherein the drying step comprises: A partial drying step of drying at a material temperature of 90 ° C. or less at normal pressure until the water content of the gel polymer becomes 15 to 40% by weight; and after the partial drying step, a water content of the water-containing gel polymer A heat aging step in which the amount of change is within 5% by weight and a material temperature of 70 to 120 ° C. for 10 minutes or more; and drying after the heat aging step until the hydrogel polymer has a desired water content. And a finish drying step. 2. A method for producing a hydrophilic polymer by subjecting a hydrophilic monomer to aqueous solution polymerization to obtain a hydrogel polymer, and then drying the hydrogel polymer to produce a hydrophilic polymer, wherein the drying step comprises: A partial drying step of drying at a material temperature of 90 ° C. or less at normal pressure until the water content of the gel polymer becomes 15 to 40% by weight; and after the partial drying step, a water content of the water-containing gel polymer 15-40% by weight, material temperature 70-120 ° C
A method for producing a hydrophilic polymer, comprising: a heat aging step of maintaining for 0 minute or more; and a finish drying step of drying the water-containing gel polymer until a desired water content is obtained after the heat aging step. . 3. The method for producing a hydrophilic polymer according to claim 1, wherein the water content of the hydrogel polymer obtained by the polymerization is in the range of 80 to 60% by weight. 4. The method for producing a hydrophilic polymer according to claim 1, wherein the aqueous polymerization of the hydrophilic monomer is performed using a persulfate. 5. The hydrogel polymer obtained by polymerization has a residual monomer content of 10,000 ppm or more.
Or a method for producing a hydrophilic polymer according to item 2. 6. A method for producing a water-absorbent resin by producing a water-containing gel polymer by polymerizing a hydrophilic monomer in an aqueous solution and then drying the water-containing gel polymer, comprising: Magnification change rate is 10%
Hereinafter, a method for producing a water-absorbent resin, wherein a change rate of a soluble component is 100% or less and a residual monomer of the obtained water-absorbent resin is 300 ppm or less.