JP2801141B2 - Method for producing water absorbent resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a water absorbent resin. More specifically, the present invention relates to a method for efficiently producing a highly water-absorbent resin having excellent salt resistance and low soluble content.

[0002]

2. Description of the Related Art In recent years, water-absorbing resins that absorb water tens to hundreds of times their own weight have been used as sanitary absorbents, sanitary absorbents such as disposable diapers, agricultural and horticultural water retaining agents, sludge coagulants, and optical cable stoppers. It has been put to practical use as a liquid agent, an additive for water-swelled rubber, and the like. Above all, when used as a water retention agent for agricultural and horticultural use, a coagulant for sludge, a waterstopping agent for optical cables, an additive for water-swellable rubber, etc., a high salt resistance is required as a water-absorbing resin. For example, JP-A-61-36309 discloses sulfonic acid-based resins, and JP-A-4-363383 discloses acrylamide-based salt-resistant water-absorbing resins. Also, Japanese Patent Laid-Open No. 1-1656
No. 10 and JP-A-2-253845 disclose a salt-resistant water-absorbing resin obtained by copolymerizing a nonionic monomer.

However, the object of Japanese Patent Application Laid-Open No. 1-165610 is to obtain an acrylic acid (salt) -based water-absorbing resin, in which a phase separation of a reaction mixture, which would be observed in a short time after the initiation of polymerization. Small amount (about 2-20
(% By weight) of a nonionic monomer is copolymerized with an acrylic acid (salt) -based monomer, but it has been difficult to use it in the above-mentioned application fields requiring high salt resistance.

The water-absorbing resin described in JP-A-2-253845 has been relatively well evaluated. However, when an aqueous medium is used as a polymerization solvent, workability and the obtained water-absorbing resin can be improved. There are the following problems from the viewpoint of the physical properties of the conductive resin.

That is, when a water-absorbent resin is produced using an aqueous medium, the drying efficiency and the pulverization efficiency are usually increased.
During or after the polymerization is completed, the hydrogel is crushed until it becomes a fine gel, but it has been difficult to obtain a fine gel of 2 mm or less by the method described in JP-A-2-253845. Further, in the method disclosed in the publication, the gel easily adheres to the polymerization disintegrator (kneader), and much labor is required for removal. Further disadvantageous is that the obtained water-absorbent resin has insufficient salt resistance. In addition, since water-soluble components are relatively large, it is difficult to use them for decomposition in applications requiring high safety.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of a conventional salt-resistant water-absorbent resin obtained by copolymerizing a nonionic monomer. Therefore, it is possible to efficiently produce a highly water-absorbent resin having excellent salt resistance and low soluble content.

[0007]

According to the present invention, there is provided a compound represented by the general formula (1):

[0008]

Embedded image

(Where R is hydrogen or a methyl group, X is an oxyalkylene group having 2 to 4 carbon atoms in which the mole fraction of the oxyethylene group to all oxyalkylene groups is 50% or more, and Y is 1 to 3 carbon atoms) Oxyalkylphenyl group having 1 to 5 alkoxy groups, phenoxy groups or 1 to 9 alkyl groups as substituents, and n is a positive number of 3 to 100 on average). (Meth) acrylic acid ester monomer (A) 20 to 100% by weight and (meth) acrylic acid ester monomer (A) copolymerizable with monomer (B) 80 to 0% by weight (however, When the total amount of (A) and (B) is 100% by weight) in an aqueous medium in the presence of a polymerization initiator and a crosslinking agent, the polymerization is first started at a temperature lower than the cloud point of the polymerization system. And then complete the polymerization to produce After crushing as necessary hydrogel, a method for producing a water-absorbent resin, characterized by drying.

The (meth) acrylate-based monomer (A) used in the present invention is a (meth) acrylate-based monomer having a hydrophobic hydrocarbon group at a terminal as represented by the general formula (1). Monomer, for example, methoxypolyethylene glycol mono (meth) acrylate, methoxypolyethylene glycol / polypropylene glycol mono (meth) acrylate, methoxypolyethylene glycol / polybutylene glycol mono (meth) acrylate, ethoxy polyethylene glycol mono (meth) acrylate , Ethoxy polyethylene glycol / polypropylene glycol mono (meth) acrylate, ethoxy polyethylene glycol / polybutylene glycol mono (meth) acrylate, phenoxy polyethylene glycol mono (meth) Acrylate, it can be mentioned benzyloxy polyethylene glycol mono (meth) acrylate, can be used alone or in combination of two or more thereof.

The monomer (B) used in the present invention is not particularly limited, and a wide range of monomers can be used. For example, acrylic acid, methacrylic acid, crotonic acid or their monovalent metals, divalent metals, ammonia, unsaturated monocarboxylic acid monomers such as partially neutralized or fully neutralized products with organic amines, maleic acid, Unsaturated dicarboxylic acid monomers such as fumaric acid, itaconic acid, citraconic acid or partially or completely neutralized products thereof with monovalent metals, divalent metals, ammonia and organic amines, vinyl sulfonic acid, allyl sulfone Acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide, -Allyloxy-2-hydroxypropanesulfonic acid or monovalent thereof Sulfonic acid-based monomers such as genus, divalent metal, ammonia, and partially or completely neutralized products with organic amines, and amides such as (meth) acrylamide, isopropylacrylamide, and t-butyl (meth) acrylamide Monomers, hydrophobic monomers such as (meth) acrylate, styrene, 2-methylstyrene and vinyl acetate, 2-hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, and propylene glycol (meth) Acrylate, allyl alcohol, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, 3-methyl-3-buten-1-ol (isoprenol), polyethylene glycol monoisoprenol ether, polypropylene glycol monoisopreno Ether, 3-methyl-2-buten-1-ol (prenol), polyethylene glycol monoprenol ether, polypropylene glycol monoprenol ether, 2-methyl-3-buten-2-ol (isoprene alcohol), polyethylene glycol mono Isoprene alcohol ether, polypropylene glycol monoisoprene alcohol ether, N-methylol (meth)
Hydroxyl-containing unsaturated monomers such as acrylamide, glycerol mono (meth) acrylate, glycerol monoallyl ether, and vinyl alcohol; cationic monomers such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide; Nitrile monomers such as (meth) acrylonitrile, phosphorus-containing monomers such as (meth) acrylamide methanephosphonic acid, (meth) acrylamide methanephosphonic acid methyl ester, and 2- (meth) acrylamide-2-methylpropanephosphonic acid Among these, unsaturated monocarboxylic acid monomers and unsaturated sulfonic acid monomers which are inexpensive and have excellent copolymerizability with the (meth) acrylate monomer (A) are particularly preferable. preferable.

The copolymerization ratio of the (meth) acrylate monomer (A) and the monomer (B) copolymerizable with the (meth) acrylate monomer (A) is (A) 20 ~
100% by weight and (B) 80 to 0% by weight.

When the copolymerization ratio of (A) is less than 20% by weight, the salt resistance of the obtained water-absorbing resin is unfavorably deteriorated. Preferred copolymerization ratios are (A) 40 to 90% by weight and (B) 60 to 10% by weight. When the copolymerization ratio of (A) exceeds 90% by weight, the water absorption capacity tends to decrease, and it may be difficult to use depending on the application.

In the present invention, an aqueous medium is used as a polymerization solvent. The aqueous medium means water or a mixed solvent of water and an inorganic or organic solvent soluble in water. Alcohol having 1 to 4 carbon atoms as an example of an organic solvent soluble in water,
Examples thereof include lower ketone solvents.

Examples of the crosslinking agent in the present invention include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and polyethylene glycol di (meth) acrylate. In one molecule of acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol di (meth) acrylate, N, N-methylenebisacrylamide, triallyl isocyanurate, trimethylolpropane diallyl ether, etc. Compounds having two or more ethylenically unsaturated groups; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, Li glycerine, propylene glycol, diethanolamine, triethanolamine,
Polyhydric alcohols such as polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitan, sucrose, glucose; ethylene glycol diglycidyl ether, glycerin diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol di Glycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane triglycidyl ether,
Examples thereof include polyepoxy compounds such as glycerin triglycidyl ether, and one or more of these can be used.

A particularly preferred crosslinking agent is polyethylene glycol di (meth) acrylate. The number of moles of ethylene oxide added to the polyethylene glycol di (meth) acrylate is preferably 4 to 100 mol, and particularly preferably 5 to 50 mol in view of the crosslinking efficiency.

When a crosslinking agent other than polyethylene glycol di (meth) acrylate is used, a small amount (0.0005 mol to 1 mol of all monomers) is added together with the crosslinking agent.
(0.02 mol) of polyethylene glycol di (meth) acrylate. Further, the total amount of the crosslinking agent is 0.0005 to 1 mol of all monomers.
It is preferred to be in the range of 0.02 mol.

When the amount of the crosslinking agent is less than 0.0005 mol, the crushability of the hydrogel during or after the polymerization tends to be poor. In addition, the amount of soluble matter in the product after drying tends to increase. If the amount of the crosslinking agent is more than 0.02 mol, the water absorption capacity tends to decrease.

In the present invention, the polymerization initiation temperature must be lower than the cloud point of the polymerization system. The cloud point changes depending on the type, composition, monomer concentration, type of aqueous medium and the like of the monomer used. As an example, methoxypolyethylene glycol (EO) is used as the (meth) acrylate monomer (A).
The number of moles of addition 9) When methacrylate is used, sodium acrylate is used as the copolymerizable monomer (B), and water alone is used as the polymerization solvent, the cloud point differs depending on the conditions as follows. That is, (A) and (B) in the polymerization system
(A) is 40% by weight ((B) is 60% by weight) when the total monomer concentration is constant at 50% by weight.
Is 31 ° C., and 53 ° C. when (A) is 80% by weight ((B) is 20% by weight). As described above, the cloud point varies depending on the composition ratio of the monomer.

The monomer compositions (A) and (B)
When both are 50% by weight, the temperature is 59 ° C. when the monomer concentration ((A) + (B)) in the polymerization system is 30% by weight, and when the monomer concentration ((A) + (B)) is 50% by weight. Is 34 ° C. and 20 ° C. when the monomer concentration is 60% by weight. As described above, the cloud point takes different values depending on the monomer concentration. Furthermore, the cloud point differs when the types (A) and (B) are changed, or when the type or composition of the aqueous medium is changed. As described above, the cloud point varies depending on various conditions, but is uniquely determined when the polymerization system is constant. As described above, in the present invention, it is important that the polymerization initiation temperature be lower than the cloud point of the polymerization system. When polymerization is started at a temperature as high as or higher than the cloud point, the obtained water-absorbent resin has low salt resistance and low water absorption capacity. Also, the soluble component tends to increase. A further disadvantage is that the hydrated gel adheres to the polymerization vessel during or after the completion of the polymerization and is difficult to remove, resulting in a significant decrease in workability. Further, the disintegration of the gel becomes extremely poor, and efficient production becomes difficult. If the polymerization is started at a temperature lower than the cloud point, a highly water-absorbent resin having excellent salt resistance and a low soluble component content, which is the object of the present invention, can be efficiently produced. In the case where the temperature is high, it is preferable to start at a temperature of 70 ° C. or lower because the soluble portion of the obtained water-absorbent resin is reduced.

After the reaction is started at a temperature lower than the cloud point, it is of course possible to cause the reaction to proceed at a temperature higher than the cloud point by heat of polymerization or heating. It is preferable that the above monomers are polymerized at a temperature lower than the cloud point.

In the present invention, (A) and (B) are produced by polymerizing together with a polymerization initiator and a crosslinking agent in an aqueous medium.
The polymerization vessel used at this time is not particularly limited, and a wide range of polymerization vessels is used. For example, Japanese Unexamined Patent Publication No. Sho 57-3
The twin-arm type kneader described in No. 4101 can be mentioned as an example of a preferable polymerization vessel. The polymerization initiator is not particularly limited, and a wide range of initiator is used. For example, persulfates such as sodium persulfate and potassium persulfate; water-soluble azo such as hydrogen peroxide, 2-2'-azobis (2-amidinopropane) hydrochloride, and 4,4'-azobis-4-cyanovalerate Compound; benzoyl peroxide,
Organic peroxides such as lauroyl peroxide and peracetic acid; oil-soluble azo compounds such as azobisisobutyronitrile and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile); Can be. Of course, it is also possible to use a reducing agent in combination for the purpose of accelerating the decomposition of these polymerization initiators. Examples of such reducing agents are (heavy)
Examples thereof include sulfurous acid (salt), L-ascorbic acid (salt), reducing metal (salt), and amines.

[0023] During the polymerization period, the agitator can be polymerized into a product regardless of whether it is stopped (that is, static polymerization) or is operating (that is, stirring polymerization). In addition, it is of course possible to perform polymerization by combining stop and operation.

The most preferred form of polymerization is static polymerization.
The static polymerization has an advantage that a soluble content is small and a product having a high water absorption capacity is easily obtained.

In the case of static polymerization, it is necessary to break down the hydrogel by operating a stirrer after the polymerization is completed.

According to the production method of the present invention, the hydrogel obtained by the static polymerization method can be very easily crushed into fine gels.

The monomer concentration at the time of polymerization is not particularly limited, but is preferably in the range of 30 to 95% by weight. A particularly preferred range is from 55 to 80% by weight. 30% by weight
At low monomer concentrations below, the gel disintegration tends to decrease slightly. Further, in the case of polymerization at a high monomer concentration exceeding 95% by weight, it may be difficult to remove the heat of polymerization.

The hydrogel thus obtained by polymerization is used as it is or as necessary, as a sulfite, a hydrogen sulfite, a pyrosulfite, a nitrite, a nitrite, a phosphite, a hypophosphorous acid. Adding an oxygen-containing reducing inorganic salt such as a salt,
After reducing the residual monomer, it is subjected to a dryer. The drying temperature is preferably from 100 to 160C. A particularly preferred temperature is from 120 to 140C. If the drying temperature is lower than 100 ° C., undried matter may be easily generated. When the temperature is as high as over 160 ° C., the water absorption capacity of the obtained water absorbent resin tends to decrease. In addition, since the water-absorbent resin in the present invention may undergo thermal degradation, it is particularly preferable to dry the resin under reduced pressure.

The dried product is used, if necessary, by using a pulverizer such as a hammer mill or a jet mill to pulverize the particles to an average particle diameter of several μm to several hundred μm.

[0030]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. In the examples, parts and% indicate parts by weight and% by weight, respectively.

<Example 1> A 2.5-liter capacity table-top jacketed kneader equipped with a thermometer (the inner surface was lined with ethylene trifluoride) and 517.5 parts of a 37% aqueous sodium acrylate solution (32% by weight) ), Methoxypolyethylene glycol (9 moles of EO added) methacrylate 408.5 parts (68% by weight), ion-exchanged water 26
1.5 parts and polyethylene glycol (E
O-added mole number 8 mol) diacrylate (PEGDA-
8) 0.68 parts (0.05 mol% based on monomer) were charged.

The contents were heated to 40 ° C. by flowing warm water at 40 ° C. into the jacket while stirring under N ₂ stream, and then 10% 2,2′-azobis (2-%) was used as a polymerization initiator.
After adding 11.8 parts of an aqueous solution of (amidinopropane) hydrochloride (V-50, 0.15 mol%) and stirring for 10 seconds,
Stirring was stopped. (In this case, the monomer concentration of the polymerization system was 50% and the cloud point was 42 ° C.) The polymerization started immediately, and reached a peak temperature of 69 ° C in 59 minutes. Next, the jacket temperature was raised to 80 ° C., and the mixture was aged for 1 hour. After the completion of the ripening, crushing was performed for 10 minutes at a blade rotation speed of 36 rpm. The kneader was inverted and the hydrogel was removed from the polymerization vessel. No adhesion of the hydrogel to the polymerization vessel was observed. The average particle diameter of the hydrogel was 1 mm, and the gel was very well crushed. No ball gel having a particle diameter of 5 mm or more was observed at all.

The fine hydrogel thus obtained was dried in a hot air circulating drier at 120 ° C. for 4 hours. After drying, the powder was pulverized using a simple tabletop pulverizer (manufactured by Kyoritsu Riko Co., Ltd.) to obtain a water-absorbent resin fine powder (1). The water content of the water absorbent resin (1) was 4.5%. The physical properties of the water-absorbent resin fine powder (1) thus obtained were measured according to the following methods. The results are shown in Tables 1 and 2.

<Method of Measuring Water Absorption Ratio> About 0.3 g of the water-absorbent resin fine powder (1) was placed in a tea bag, immersed in 3.5% NaCl water for a predetermined time, and the weight was calculated. .

Water absorption ratio = (BC) / A A: Weight (g) of collected water-absorbent resin fine powder (1) B: Total weight including tea bag after water absorption (g) C: In blank test Weight including teabag (g) <Water-soluble matter measurement method> Water-absorbent resin fine powder (1) About 1 g (W1
To 1000 g), add 1000 g of distilled water and stir for 1 hour. After the stirring, the gel is allowed to stand for 16 hours to settle the gel. Then, the supernatant was filtered using a 0.22μ filter paper,
50 g of filtrate are obtained. 100 cc of the obtained filtrate (50 g)
And concentrated to about 2 g with an evaporator. After concentration, the concentrated solution is transferred to a vial while washing the inner wall of the flask with a small amount of distilled water, and dried at 120 ° C. for 3 hours to obtain a residue weight (W2 g). The water-soluble component was calculated according to the following equation.

Water-soluble component (%) = 2,000 × (W2 / W1) <Examples 2 to 5> Charged composition of (meth) acrylate-based monomer (A) and monomer (B) Example 1 except that the ratio, the amount of the polymerization initiator and the polymerization initiation temperature were set to the values shown in Table 1.
Polymerization and drying were carried out in the same manner as in the above to obtain water-absorbing resins (2) to (5). The gel adhesion, crushability, and physical properties were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Example 6 A water-absorbent resin (6) was obtained in the same manner as in Example 1 except that the amount of polyethylene glycol diacrylate used was 1.0 mol% based on all monomers.
The results at that time are shown in Tables 1 and 2.

Example 7 The polymerization initiation temperature was 30 ° C.
A water-absorbing resin (7) was obtained in the same manner as in Example 1 except that the amount of the polymerization initiator was changed to 0.30 mol%. The results at that time are shown in Tables 1 and 2.

Example 8 The monomer concentration at the time of polymerization was 30
%, A polymerization initiator amount of 0.40 mol%, and a polymerization initiation temperature of 6%.
A water absorbent resin (8) was obtained in the same manner as in Example 1 except that the temperature was changed to 0 ° C. The results at that time are shown in Tables 1 and 2.

<Example 9> The monomer concentration at the time of polymerization was 60
%, And a water-absorbing resin (9) was obtained in the same manner as in Example 1 except that the polymerization initiation temperature was changed to 20 ° C. The results at that time are shown in Tables 3 and 4.

Example 10 A water-absorbent resin (8) was obtained in the same manner as in Example 9 except that sodium methacrylate was used as the monomer (B). Table 3 and Table 4 show the results at that time.
It was shown to. Example 11 A water-absorbent resin (11) was prepared in the same manner as in Example 1 except that polyethylene glycol (5 moles of EO added) diacrylate was used instead of polyethylene glycol (8 moles of EO added) diacrylate. I got The results at that time are shown in Tables 3 and 4.

Example 12 A water-absorbent resin (12) was obtained in the same manner as in Example 1 except that polyethylene glycol (50 moles of EO added) diacrylate was used as a crosslinking agent. The results at that time are shown in Tables 3 and 4.

Example 13 A water-absorbent resin (13) was obtained in the same manner as in Example 1 except that methylene bisacrylamide was used as a crosslinking agent. The results at that time are shown in Tables 3 and 4.

Example 14 Example 1 was repeated except that a monomer mixture of 50 mol% of sodium acrylate and 50 mol% of acrylic acid was used as the monomer (B), and trimethylolpropane triacrylate was used as a crosslinking agent. In the same manner as in the above, a water absorbent resin (14) was obtained. The results at that time are shown in Tables 3 and 4.

Example 15 Example 1 was repeated except that 0.025 mol% of polyethylene glycol (8 moles of EO added) diacrylate and methylene bisacrylamide were used as crosslinking agents, based on all monomers. Similarly, a water absorbent resin (15) was obtained. The results at that time are shown in Tables 3 and 4.

Example 16 A water-absorbent resin (16) was obtained in the same manner as in Example 1, except that polyethylene glycol (8 moles of EO added) dimethacrylate was used as a crosslinking agent. The results at that time are shown in Tables 3 and 4.

<Examples 17 to 23> The monomers shown in Tables 3 and 5 were used as the (meth) acrylate-based monomer (A), and the monomer concentration, the amount of the polymerization initiator, and the initiation of the polymerization were measured. Water-absorbing resins (17) to (23) were obtained in the same manner as in Example 1 except that the temperatures were changed to those shown in Tables 3 and 5. The results at that time are shown in Tables 3, 4, 5, and 6.

Example 24 Example 1 was repeated except that sodium acrylate (50 mol%) and sodium methacrylate (50 mol%) were used in place of sodium acrylate.
The water absorbent resin (24) was obtained in the same manner as in the above. The results at that time are shown in Tables 5 and 6.

<Examples 25 to 28> Water-absorbing resins (25) to (28) were prepared in the same manner as in Example 1 except that the monomers shown in Table 4 were used as the monomers (B). Obtained. The results at that time are shown in Tables 5 and 6.

<Example 29> A water-absorbent resin (29) was obtained in the same manner as in Example 1 except that the stirring was not stopped during the polymerization and the rotation was kept at 36 rpm. Table 7 and Table 8 show the results at that time.
It was shown to.

Examples 30 and 31 As polymerization initiators,
Water absorbent resins (30) and (31) were obtained in the same manner as in Example 1 except that the initiators shown in Table 6 were used. The results at that time are shown in Tables 7 and 8.

Example 32 In the same polymerization vessel as used in Example 1, 350 parts (73% by weight) of methoxypolyethylene glycol (5 moles of EO added) acrylate, 94 parts of sodium acrylate, 36 parts of acrylic acid Parts (the total amount of sodium acrylate and acrylic acid is 27% by weight), trimethylolpropane triacrylate 0.1 part.
89 parts (0.114 mol% based on the monomer) and 480 parts of ion-exchanged water were charged. The contents were heated to 20 ° C. by flowing warm water at 20 ° C. into the jacket while stirring the mixture under a stream of N ₂ , and then ammonium persulfate was used as a polymerization initiator.
81 parts (0.3 mol%) and L-ascorbic acid 0.3
After adding 6 parts and stirring for 30 seconds, the stirring was stopped.
(In this case, the monomer concentration of the polymerization system was 50%, and the cloud point was 23 ° C.) The polymerization started immediately and reached a peak temperature of 47 ° C in 50 minutes. Next, the jacket concentration was raised to 80 ° C. and aging was performed for 1 hour. After the completion of ripening, crushing was performed at a blade rotation speed of 56 rpm for 10 minutes. The kneader was inverted and the hydrogel was removed from the polymerization vessel. No adhesion of the hydrogel to the polymerization vessel was observed. The average particle diameter of the hydrogel was 1 mm, and the gel was very well crushed. No ball gel having a particle diameter of 5 mm or more was observed at all. The obtained hydrogel was treated in the same manner as in Example 1 to obtain a water absorbent resin (32). The physical properties of the water-absorbent resin (32) were measured in the same manner as in Example 1, and the results are shown in Tables 7 and 8.

<Example 33> A polymerization gel was obtained in the same manner as in Example 32 except that the stirring was not stopped and the stirring was continued at 56 rpm. No adhesion of the hydrogel to the polymerization vessel was observed. The average particle size of the gel is 1
mm and was very well crushed. The particle diameter is 5m
No ball gel of m or more was observed at all. The obtained hydrogel was dried under reduced pressure at 150 ° C. for 2 hours, and pulverized in the same manner as in Example 1 to obtain a water absorbent resin (33). The physical properties of the water absorbent resin (33) were measured in the same manner as in Example 1, and the results are shown in Tables 7 and 8.

Comparative Example 1 A comparative water-absorbent resin (1) was obtained in the same manner as in Example 1 except that the polymerization initiation temperature was set to 45 ° C., which was higher than the cloud point (42 ° C.) of the polymerization point. Water absorbent resin for comparison
The water content of (1) was as high as 8.4%, and the water-soluble content was as high as 9.6%. Others are shown in Tables 9 and 10.

Comparative Example 2 The hydrogel obtained in Comparative Example 1 was dried at 160 ° C. for 4 hours, and then pulverized in the same manner as in Example 1 to obtain a comparative water absorbent resin (2). Water absorbent resin for comparison
The water-soluble content of (2) is 10.8%, and the comparative water-absorbent resin
(1) It increased further. Others are shown in Tables 9 and 10.

Comparative Example 3 Ammonium Persulfate 1.81
Using 0.5 part (0.083 mol%) instead of
A comparative water-absorbent resin (3) was obtained in the same manner as in Example 32 except that 0.025 part was used instead of ascorbic acid 0.36 part, and the polymerization initiation temperature was changed to 80 ° C. The results at that time are shown in Tables 9 and 10.

Comparative Example 4 Ammonium Persulfate 1.81
Using 0.5 part (0.083 mol%) instead of
A comparative water-absorbent resin (4) was obtained in the same manner as in Example 33 except that 0.025 part was used instead of ascorbic acid 0.36 part, and the polymerization initiation temperature was 80 ° C. The results at that time are shown in Tables 9 and 10.

Comparative Example 5 A comparative water-absorbent resin was prepared in the same manner as in Example 1 except that the composition of the monomers was set to the ratios shown in Tables 9 and 10, the monomer concentration was 40%, and the polymerization initiation temperature was 20 ° C. (5) was obtained. Table 9 and Table 1 show the results at that time.
0.

Comparative Example 6 A comparative water-absorbent resin (6) was prepared in the same manner as in Example 1 except that only sodium acrylate was used as the monomer, the monomer concentration was 30%, and the polymerization initiation temperature was 30 ° C. I got The results at that time are shown in Tables 9 and 10.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

[0063]

[Table 4]

[0064]

[Table 5]

[0065]

[Table 6]

[0066]

[Table 7]

[0067]

[Table 8]

[0068]

[Table 9]

[0069]

[Table 10]

Table 11 shows the (meth) acrylate monomer (A) in Tables 1 to 10.

[0071]

[Table 11]

The monomers (B), crosslinking agents and polymerization initiators in Tables 1 to 10 are shown below.

<Monomer (B)> SA: Sodium acrylate AA: Acrylic SMA: Sodium methacrylate PA: Potassium acrylate AMPS: Sodium 2-acrylamide-2-methylpropanesulfonate SEMS: Sulfoethyl methacrylate (sodium) Salt) SVS: Sodium vinyl sulfonate <Crosslinking agent> PEGDA-8: Polyethylene glycol (EO added 8 mol) diacrylate PEGDA-5: Polyethylene glycol (EO added 5 mol) diacrylate PEGDA-50: Polyethylene glycol (EO 50 mol) Addition) diacrylate PEGDMA-8: polyethylene glycol (EO added 8 mol) dimethacrylate MBAA: methylenebisacrylamide TMPTA: trimethylolpropane triacrylate <polymerization initiator V-50: 2,2'-azobis (2-Amijipuropan) hydrochloride NaPS: sodium persulfate APS: ammonium persulfate

[0074]

The water-absorbing resin of the present invention obtained as described above has remarkably excellent salt resistance and has a high water absorption capacity over a long period of time against water or seawater containing a large amount of polyvalent metal ions. As a result, it can be used in applications requiring high salt resistance. Further, since the water-absorbent resin of the present invention has a very low soluble component content, it can be used in applications where safety is strongly required.

Further, according to the production method of the present invention, the hydrogel does not adhere to a polymerization vessel such as a kneader. Also,
Since the gel crushing property is remarkably improved (therefore, the gel particle size is reduced), the subsequent drying property and crushing property are greatly improved. In addition, since drying can be performed at a relatively low temperature, there is an effect that a dried product with little thermal deterioration is obtained. As described above, the present invention has made it possible to produce a water-absorbent resin having excellent properties at low cost and efficiently, and has extremely high industrial utility value.

Claims (3)

(57) [Claims] 1. A compound of the general formula (1) (Where R is hydrogen or a methyl group, X is an oxyalkylene group having 2 to 4 carbon atoms in which the mole fraction of the oxyethylene group to all oxyalkylene groups is 50% or more;
Is an alkoxy group having 1 to 5 carbon atoms, a phenoxy group or an oxyalkylphenyl group having 1 to 9 alkyl groups as 1 to 3 substituents, and n is an average of 3 to 10
It is a positive number of 0. 20) to 100% by weight of the (meth) acrylate monomer (A) represented and (meth)
A single monomer composed of 80 to 0% by weight of a monomer (B) copolymerizable with the acrylate monomer (A) (however, the total amount of (A) and (B) is 100% by weight). A process for producing a water-absorbent resin, which comprises, when polymerizing a monomer component in an aqueous medium in the presence of a polymerization initiator and a crosslinking agent, first starting polymerization at a temperature lower than the cloud point of the polymerization system. 2. The method according to claim 1, wherein polyethylene glycol di (meth) acrylate is used as the crosslinking agent. 3. The production method according to claim 1, wherein the polymerization reaction is completed by standing still and the produced gel is crushed.