JPH02253845A - Water absorbing agent having superior salt resistance - Google Patents

Abstract

PURPOSE:To improve the salt resistance of a water absorbing agent by using a polymer obtd. by polymerizing a mixture of a (meth)acrylic ester monomer with a water soluble unsatd. monomer contg. a carboxyl group with a specified amt. of a cross-linking agent. CONSTITUTION:20-80wt.% (meth)acrylic ester monomer represented by formula I (where R is H or methyl, X is 2-4C oxyalkylene, n is an integer of 3-100, the mol fraction of oxyethylene groups to all the oxyalkylene groups is >=50% and Y is 1-5C alkoxy, phenoxy, etc.) is mixed with 20-80wt.% water soluble unsatd. monomer contg. a carboxyl group. A cross-linking agent is added to the mixture by 0.001-5.0mol% and they are brought into a polymn. reaction to produce a cross-linked polymer. This polymer is used as a water absorbing agent having superior salt resistance.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a water absorbing agent with excellent salt resistance.

More specifically, it relates to a water-absorbing agent that can absorb multiple layers of aqueous liquid even when it comes into contact with an aqueous liquid containing highly concentrated salts, particularly polyvalent metal ions, and has excellent salt resistance that does not reduce its water absorption capacity over time. .

(Prior art) In recent years, water-absorbing resins that absorb tens to hundreds of times their own weight in water have been developed, and are used as water-absorbing agents for sanitary products, disposable diapers, etc., as water-retaining agents for agriculture and horticulture, and as coagulants for sludge. It is being developed for use as an anti-condensation agent for building materials, a water stopper for civil engineering, a desiccant, etc.

Examples of such water-absorbing resins include hydrolysates of starch-acrylonitrile graft polymers, starch-acrylonitrile graft polymers, and starch-acrylonitrile graft polymers.
Neutralized product of acrylic acid graft polymer, saponified product of vinyl acetate-acrylic ester copolymer, hydrolyzate of acrylonitrile copolymer or acrylamide copolymer or crosslinked products thereof, reverse phase suspension polymerization Self-crosslinking sodium polyacrylate, partially neutralized crosslinked polyacrylic acid, etc. obtained by the above method are known.

(Problem to be Solved by the Invention) However, although these water-absorbing resins have excellent ability to absorb large amounts of water or aqueous liquids, they do not absorb aqueous liquids containing polyvalent metal ions such as seawater or high concentrations. When it comes into contact with an aqueous liquid with a high salt concentration, such as an aqueous sodium chloride solution, it exhibits only a low water absorption capacity, and furthermore, it has the disadvantage that the water absorption capacity decreases over time.

Therefore, as a product with improved salt resistance, a crosslinked product of starch-acrylic acid-vinylsulfonic acid-N-methylpyridinium chloride graft copolymer (Japanese Patent Application Laid-Open No. 55-1563
No. 4), sulfomethylated starch-sodium acrylate-acrylamide graft copolymer crosslinked product with formalin and sodium bisulfite (JP-A-55-16016), and 2-acrylamide-2-methylpropanesulfonic acid-sodium acrylate self. Crosslinked product (Unexamined Japanese Patent Publication No. 1983
-161412) has been proposed.

However, although these have been recognized to have improved salt resistance, their water absorption capacity still decreases over time when they come into contact with aqueous liquids containing polyvalent metal ions.

In order to eliminate this kind of decrease in water absorption capacity over time,
Copolymerized crosslinked product containing as essential components a hydrophilic (meth)acrylic acid ester monomer having a polyethylene glycol chain as a side chain and an unsaturated monomer containing a sulfonic acid group (Japanese Patent Application Laid-Open No. 62-266140) is proposed. However, although this copolymerized crosslinked product is effective when the salt concentration is low, its water absorption capacity drops significantly for aqueous liquids where the salt concentration exceeds 10%, and it may not have sufficient salt resistance depending on the purpose of use. The reality is that it is not shown. In addition, the wood-loving monomer having a polyethylene glycol chain in its side chain and the unsaturated monomer containing a sulfonic acid group have a tendency to act between the polyethylene glycol chain and the carboxyl group, which is generally widely known. There was also the problem that there was no significant interaction, and the reaction during copolymerization of these monomers proceeded unevenly, making it difficult to obtain a copolymerized crosslinked product with a high water absorption capacity.

(-Means and effects for solving the problems) The present inventors have improved the above-mentioned drawbacks, and have demonstrated sufficient water absorption capacity even for aqueous liquids with high salt concentration, and in addition, the water absorption capacity decreases over time. As a result of intensive research to develop a water-absorbing agent with excellent salt resistance, we developed a cross-linking agent that combines a (meth)acrylic acid ester monomer with a specific structure and a carboxyl group-containing water-soluble unsaturated monomer. The present inventors have discovered that a crosslinked polymer obtained by polymerization in the presence of such a compound is effective as a water absorbing agent that can solve all of the above problems, and have completed the present invention.

That is, the present invention provides the following formula:
is an oxyalkylphenyl group having 1 to 3 substituents of an alkoxy group having 1 to 5 carbon atoms, a phenoxy group, or an alkyl group having 1 to 9 carbon atoms, and n is 3 to 10 on average.
It is the number of 0. ) A (meth)acrylic acid ester monocatalyst (A
) (hereinafter referred to as 111 body (A)) 20 to 80% Shigeyama and carboxyl group-containing water-soluble unsaturated monomer (B) (hereinafter referred to as
A monomer mixture (I) consisting of 20 to 80% by weight of monomer (8)) is added at a concentration of 0.00% by weight to the monomer mixture (I).
1-5. The present invention relates to a water-absorbing agent having excellent salt resistance and comprising a crosslinked polymer obtained by polymerization in the presence of Omot% of a crosslinking agent (n).

The present invention also provides hydrophilic properties in which the vicinity of the surface of the crosslinked polymer obtained by polymerizing the monomer mixture (I) in the presence of a crosslinking agent (n) is reacted with a carboxyl group and/or a carboxylate group. This invention relates to a water-absorbing agent with excellent salt resistance, which is cross-linked with a cross-linking agent (Ill).

The monomer (A) used in the present invention has a hydrophobic hydrocarbon group at the terminal as represented by the above-mentioned (meta)
Acrylic acid ester monomers, such as methoxypolyethylene glycol mono(meth)acrylate, methoxypolyethylene glycol/polypropylene glycol mono(meth)acrylate, methoxypolyethylene glycol/polybutylene glycol mono(meth)acrylate, and ethoxypolyethylene glycol mono(meth)acrylate. Meta)
Examples include acrylate, ethoxypolyethylene glycol/polypropylene glycol mono(meth)acrylate, ethoxypolyethylene glycol/polybutylene glycol mono(meth)acrylate, phenoxypolyethylene glycol mono(meth)acrylate, benzyloxypolyethylene glycol mono(meth)acrylate, etc. One or more of these can be used.

For example, in polyethylene glycol mono(meth)acrylate having a terminal hydroxyl group, which does not have a hydrophobic hydrocarbon group at the terminal, the monomer (8
) may cause an esterification reaction with the carboxyl group of the polymer, resulting in a decrease in the water absorption capacity of the resulting crosslinked polymer, making it impossible to obtain an excellent water absorption agent with a high water absorption capacity as intended by the present invention.

In addition, the mole fraction of oxyedyl group to all oxyalkylene groups in the single m substance (^) must be 50% or more, and those with this mole fraction of less than 50%, such as alkoxypolypropylene glycol mono(meth)acrylate, etc. When phenoxypolyethylene glycol mono(meth)acrylate etc. is used instead of monomer (A),
A crosslinked polymer with high water absorption capacity cannot be obtained.

The monomer (B) used in the present invention is not particularly limited as long as it has a carboxyl group and is water-soluble, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, citraconic acid, maleic acid, Examples include fumaric acid and salts thereof, and one or more of these may be used.

In the present invention, in the monomer mixture (I), monomer (
A) C: 20 to 80% by weight, 1FF (B) C: 20 to 80% by weight. Monomer (^) is 2
If the amount is less than 0% by weight, the salt resistance of the water absorbing agent obtained will decrease, and the effect of using the monomer (A) will not be apparent. Moreover, when a multilayer monomer (A) is used in an amount exceeding 80% by weight, the water absorption capacity of the obtained water absorbing agent decreases. In addition, some monomers other than the monomer (^) and the monomer (B) may be mixed with the monomer composite (I) to the extent that the performance of the water absorbing agent of the present invention is not impaired. Good too.

In the present invention, the monomer mixture (I) is replaced with the monomer mixture (I).
0.001 to 5. QIIO 1% crosslinker (
A crosslinked polymer is obtained by polymerization in the presence of II), and the crosslinking agent (IF) controls the crosslink density when polymerizing the monomer mixture (I) to obtain a highly water-absorbent crosslinked polymer. It is essential for Even in the polymerization in the absence of the crosslinking agent (I), the monomer mixture (I) partially self-crosslinks, but does not become a highly water-absorbing crosslinked product that can generally be used as a water-absorbing agent.

By appropriately selecting and using the type and amount of crosslinking agent (I), a water absorbing agent with better salt resistance can be obtained.

Examples of the crosslinking agent (II) in the present invention include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, and propylene glycol di(meth)acrylate.
meth)acrylate, polyprolene glycol di(meth)acrylate, trimethylolbuO pantri(meth)
Acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, N,N-methylenebis(meth)acrylamide, triallyl isocyanurate, trimethylolpropane diallyl ether, etc. have two ethylenically unsaturated groups in one molecule. Compounds having two or more functional groups that react with the carboxyl group in monomer (B), such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, jetanol Amine, triethanolamine, polypropylene glycol, pentaerythritol, sorbitol, sorbitan,
Polyhydric alcohols such as glucose, mannitol, mannitan, sucrose, and glucose, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and neopentyl. Examples include polyepoxy compounds such as glycol diglycidyl ether, 1,6-hexanesiol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane triglycidyl ether, and glycerin triglycidyl ether, and one or two of these The above can be used. When a polyhydric alcohol is used as a crosslinking agent (IF), it is preferable to heat-treat at 150 to 250°C, and when a polyepoxy compound is used, heat treatment is preferably carried out at 50 to 250°C during or after polymerization.

The amount of the crosslinking agent (I[) used is 0.001 to 5.0 mol% theal based on the monomer mixture (I).

If the amount exceeds 5.0 mo1%, the crosslink density of the resulting crosslinked polymer tends to become too high, resulting in a decrease in water absorption capacity. On the other hand, if the suspension is less than 0.001, the crosslinking density is too small and the crosslinked M1 polymer becomes sticky after absorbing the aqueous liquid, resulting in a significant decrease in the initial absorption rate.

The polymerization method for obtaining the crosslinked polymer effective as the water-absorbing agent of the present invention can be any conventionally known method, such as a method using a radical polymerization catalyst, irradiation with radiation, electron beams, ultraviolet rays, etc. Examples include methods. Examples of radical polymerization catalysts include peroxides such as hydrogen peroxide, benzoyl peroxide, and cumene hydroperoxide; azo compounds such as azobisisobutyronitrile and 2,2'-azobis-2-amidinopropane hydrochloride; Examples include persulfur 11m such as ammonium persulfate, potassium persulfate, and potassium persulfate. These polymerization initiators are 2
It is also possible to use a mixture of two or more species, and furthermore, it may be used as a redox initiator in combination with a reducing agent such as sulfite, ascorbic acid, or ferric salt.

Although the polymerization temperature varies depending on the type of catalyst used, it is preferably in the range of 20 to 100°C in order to obtain a sufficiently large molecular weight of the resulting crosslinked polymer and to ensure completion of the polymerization.

It is also possible to subject the monomer mixture (I) to polymerization after dissolving and diluting it in a solvent. Examples of such polymerization solvents include water, methanol, ethanol, acetone, dimethylformamide, etc., and mixtures thereof. can be used.

When using a solvent solution of monomer mixture (I), there is no particular restriction on the concentration of the solution, but considering ease of control of the polymerization reaction, yield, and economy, it is 20% by weight to saturated concentration or less. It is preferable.

Examples of the polymerization form include sorbitan fatty acid ester,
Cellulose esters such as sucrose fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, ethyl cellulose, cellulose acetate, cellulose ether, carboxyl group-containing polymers such as α-olefin-maleic anhydride copolymer, etc. are used as dispersants. Reverse-phase suspension polymerization by dispersing an aqueous monomer solution in a hydrophobic organic solvent, casting polymerization, a method of polymerizing while fragmenting a hydrous glue-like polymer using the shear force of a double-arm kneader, and thin films. Various methods such as polymerization method and spray polymerization method can be employed.

Furthermore, the present invention provides the monomer mixture (I) with a crosslinking agent (II).
A water absorbing agent made of a crosslinked polymer obtained by further crosslinking the surface vicinity of the crosslinked polymer obtained by polymerization in the presence of a hydrophilic crosslinking agent (DI) to introduce a crosslink density gradient between the surface vicinity and the interior. We also provide A water absorbing agent obtained by further crosslinking near the surface of a crosslinked polymer has the effect of having a faster initial water absorption rate than a water absorbing agent that is not crosslinked near the surface.

The hydrophilic crosslinking agent (III) used for crosslinking near the surface of the crosslinked polymer is a hydrophilic compound containing two or more functional groups in the molecule that can react with carboxyl groups and/or carboxylate groups. For example, polyhydric alcohols such as glycerin, ethylene glycol, and pentaerythritol; polyepoxy compounds such as ethylene glycol diglycidyl ether; ethylenediamine, diethylenetriamine, triethylenetetraamine,
Polyvalent amines such as tetraethylenepentamine, pentaethylene hexazine, polyethyleneimine; polyvalent aldehydes such as glutaraldehyde and glyoxal; aluminum chloride, magnesium chloride, calcium chloride, aluminum sulfate, magnesium sulfate,! 111M! Examples include polyvalent metal salts such as calcium.

The amount of these hydrophilic crosslinking agents (1) to be used is preferably in the range of 0.005 to 5% by weight based on the crosslinked polymer to be crosslinked near the surface.

Furthermore, there is no particular restriction on the method of crosslinking near the surface of the crosslinked polymer; Hydrophilic crosslinking agent (
Hydrophilic crosslinking agent (1) was added to a dispersion obtained by dispersing crosslinked polymer powder in a hydrophobic organic solvent. A method of heating may be adopted later if necessary.

In addition, the water absorbing agent of the present invention may absorb deodorants, fragrances, drugs, plant growth agents, bactericides, fungicides, foaming agents, pigments, dyes, carbon black, activated carbon, silica fine particles, hydrophilic single fibers, etc. They can also be dispersed and mixed to provide new functions.

(Effects of the Invention) The water-absorbing agent of the present invention obtained as described above has extremely excellent salt resistance, so it can be used to absorb body fluids such as sweat, blood, urine, seawater, domestic and industrial wastewater, etc. Not only can it absorb large amounts of aqueous liquids with low concentrations of polyvalent metal ions, but also aqueous liquids with very high concentrations of polyvalent metal ions, such as the moisture absorbed by household moisture absorbers made of battery fluid and hygroscopic salts. I can do it.

In addition, the water-absorbing agent of the present invention does not change its water-absorbing capacity for a long period of time even after absorbing these aqueous liquids, and can retain the aqueous liquid once absorbed even under pressure. It can be effectively used as a water retention agent, desiccant, etc.

Furthermore, by compounding the water absorbing agent of the present invention with TLL+M, rubber, Plus Deck, nonwoven fabric, etc. and making it into a sheet or fiber form, it can be used as a water stop material for civil engineering, a sealing material, a bagging material, etc.
A water-absorbing composite that is effective as an absorber for medical and sanitary materials, has good workability, has high absorption and retention performance, and has excellent salt resistance can be obtained.

(Examples) The present invention will be described in detail below with reference to Examples, but the scope of the present invention is not limited to these Examples.

Example 1 1.01 g of cyclohexane was placed in a 21-meter four-piece variable flask equipped with a stirrer, a flow condenser, a thermometer, a nitrogen gas inlet tube, and a dropping funnel, and 5.0 g of sorbitan monostearate was added. After dissolution, nitrogen gas was blown in to drive out the dissolved oxygen.

In a separate flask, methoxypolyethylene glycol acrylate (containing on average 10 ethylene oxide units per molecule (7)) as monomer (A) 110.
460, 1iffi body (B) toshite7'y+) le F
Li sodium 34.55 a and acrylic I! 18.8
2(l) and 0.01 g of methylenebisacrylamide as a crosslinking agent were dissolved in 153.83 g of ion-exchanged water to prepare a monomer aqueous solution with a 7-mer concentration of 50%. To this monomer aqueous solution, 0.151 J of potassium persulfate was added. After dissolving the aqueous solution, nitrogen gas was blown in to drive out the oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the separable flask and dispersed by stirring at 20 Orpm. Thereafter, the bath temperature was raised to 60° C. to initiate the polymerization reaction, and then maintained at this temperature for 2 hours to complete the polymerization. Thereafter, the water in the hydrogel of the obtained crosslinked polymer was distilled off by azeotropic dehydration with cyclohexane, and the crosslinked polymer was separated from cyclohexane by filtration.
It was dried under reduced pressure at 0°C to obtain a water absorbing agent (1).

Example 2 Cyclohexane 1 and Ol were placed in the same reaction apparatus as in Example 1, and 3.0 g of ethyl cellulose was added and dissolved therein. Nitrogen gas was then blown in to drive out dissolved oxygen.

In a separate flask, 61.68 G of methoxypolyethylene glycol acrylate (containing on average 23 ethylene oxide units per molecule).

Sodium acrylate47. OOa, acrylic acid 36,
OOa and methylenebisacrylamide 0.013
(1) was dissolved in 144.68 fl. of ion-exchanged water to prepare a monomer aqueous solution with a 7-mer concentration of 50%.

After adding and dissolving 0.131 J of N,N'-azobisamidinopropane m-acid to this aqueous solution, nitrogen gas was blown in to drive out oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the separable flask and dispersed by stirring at 20 Orpm. Thereafter, the bath temperature was raised to 60° C. to initiate the polymerization reaction, and then maintained at this temperature for 2 hours to complete the polymerization. Thereafter, in the same manner as in Example 1, the obtained crosslinked polymer was dehydrated, filtered, and dried under reduced pressure.
) was obtained.

Example 3 Internal volume 27. Opening 160! A lid was attached to a jacketed stainless steel double-armed kneader with two sigma-type blades measuring 1501 m x 1501 m, depth 135 am, and a rotating diameter of 70 m, and methoxypolyethylene glycol acrylate (on average per molecule (containing 5 ethylene oxide units) 35 (]], sodium acrylate 94.0 acrylic! 36.0 g and trimethylolpropane triacrylate 0.890 g were dissolved in 480 g of ion-exchanged water to give a heptamine concentration of 50 % monomer aqueous solution was prepared. Nitrogen gas was blown into this monomer aqueous solution to drive out oxygen dissolved in the aqueous solution.

Then, two sigma type vanes were placed at 67 and 56 respectively.
While rotating at a speed of rl)l and heating by passing hot water at 80° C. through the jacket, 0.5 g of ammonium persulfate and 0.025 o of monoascorbic acid were added as a polymerization initiator. Polymerization started 20 minutes after the addition of the polymerization initiator. 60 minutes after the addition of the polymerization initiator, the temperature in the reaction system reached 91°C, and the produced hydrogel polymer was approximately 3 m
It was subdivided into fine grains with a diameter of . After further stirring, the lid was removed 90 minutes after polymerization was started, and the hydrogel polymer was taken out.

The obtained hydrogel polymer was spread on a 50-mesh wire mesh and dried with hot air at a temperature of 150° C. for 2 hours. By pulverizing this dried material using a vibration mill, a water absorbing agent (3) is obtained.
I got it.

Example 4 Methoxypolyethylene glycol acrylate (
Containing on average 60 ethylene oxide units per molecule>27.26a, sodium acrylate 22.5
00 and methylenebisacrylamide 0.15% were dissolved in 49.760% ion-exchanged water, and the concentration of 7mer was 50%.
An aqueous solution of 7-summer was prepared. Nitrogen gas was blown into this aqueous monomer solution to drive out oxygen dissolved in the aqueous solution.

Then, ammonium persulfate was added as a polymerization initiator.
g was added and heated at 75° C. for 2 hours to complete the polymerization.

After that, the obtained water-containing glue-like polymer was taken out from the glass container and placed in a 5 m x 5 m x ! ! Pour the stain into a 3-sized plate in a bright place, spread it on a 50-mesh wire mesh, and heat it at 150°C.
It was dried with hot air at a temperature of 2 hours. A water absorbing agent (4) was obtained by pulverizing this dried product using a vibration mill.

Example 5 1.0 l of cyclohexane was placed in the same reaction apparatus as in Example 1, and 5.0 g of simi sugar fatty acid ester was added and dissolved therein, and then nitrogen gas was blown in to drive out dissolved oxygen.

In a separate flask, butoxypolyethylene glycol acrylate (containing on average 10 ethylene oxide units per molecule) 113.49, sodium acrylate 34.550, acrylic! ! 8.82g and methylenebisacrylamide 0.01! I+ was dissolved in 156.77Q of ion-exchanged water to prepare 11 volumes of an aqueous monomer solution with a monomer concentration of 50%. After adding and dissolving 0.15 a of potassium persulfate into this monomer aqueous solution, nitrogen gas was blown into the monomer aqueous solution to drive out oxygen dissolved in the aqueous solution.

Next, the monomer aqueous solution in this flask was added to the above-mentioned bulk flask and dispersed by stirring at 200 rpa+. After that, the bath temperature was raised to 60° C. to initiate the polymerization reaction, and then maintained at this temperature for 2 hours to complete the polymerization. Thereafter, in the same manner as in Example 1, the obtained crosslinked polymer was dehydrated, filtered, and dried under reduced pressure.
) was obtained.

Example 6 1.0 l of cyclohexane was placed in the same reaction apparatus as in Example 1, 5.0 g of sorbitan monostearate was added and dissolved, and then dissolved oxygen was expelled by blowing in nitrogen gas.

In a separate flask, ethoxypolyethylene glycolbolib O pyrene glycol acrylate (containing on average 7 ethylene oxide units and 3 propylene oxide units per molecule) 122.21), sodium acrylate 34.55 o, Acrylic Fa8.820
and 0.0io of methylene bisacrylamide were dissolved in 165.57i11 of ion-exchanged water, and the monomer concentration was 50.
% monomer aqueous solution was prepared. After adding and dissolving 0.15 g of potassium persulfate into this monomer aqueous solution, nitrogen gas was blown into the monomer aqueous solution to drive out oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the separable flask and dispersed by stirring at 200 rpm. Thereafter, the bath temperature was raised to 60° C. to initiate the polymerization reaction, and then maintained at this temperature for 2 hours to complete the polymerization. Thereafter, in the same manner as in Example 1, the obtained crosslinked polymer was dehydrated, filtered, and dried under reduced pressure.
) was obtained.

Example 7 In a kneader similar to Example 3, phenoxypolyethylene glycol acrylate (containing on average 5 ethylene oxide units per molecule) 315.6811! ,
Sodium acrylate 94.0CI, acrylic 136.
0! 7 and trimethylolpropane triacrylate 0.89 CI were dissolved in 446.57° of ion-exchanged water to prepare an aqueous monomer solution with a monomer concentration of 50%.

Nitrogen gas was blown into this aqueous solution of 7mer to drive out oxygen dissolved in the aqueous solution.

Then the two sigma type vanes are sized 67 and 55 respectively.
While rotating at a speed of rpm and heating by passing 80°C hot water through the jacket, add 0.5 g of ammonium persulfate and 0.025 CI of ascorbyl II as a polymerization initiator.
was added. Polymerization started 20 minutes after adding the polymerization initiator. 60 minutes after adding the polymerization initiator, the temperature in the reaction system reached 89°C, and the produced hydrogel polymer had a concentration of about 3I.
It was subdivided into fine particles with a diameter of 1. After further stirring, the lid was removed 90 minutes after polymerization was started, and the hydrogel polymer was taken out.

The obtained hydrogel polymer was dried and pulverized in the same manner as in Example 3 to obtain a water absorbing agent (7).

Example 8 In a kneader similar to Example 3, penzyloxypolyethylene glycol acrylate (containing on average 5 ethylene oxide units per molecule>295.56a,
Sodium acrylate 117.591 Acrylic acid 18.
00 and trimethylolpropane triacrylate 0
89111 was dissolved in 431.95 tons of ion-exchanged water to prepare an aqueous monomer solution with a monomer concentration of 50%. Nitrogen gas was blown into this aqueous monomer solution to drive out oxygen dissolved in the aqueous solution.

Then, two sigma type vanes were placed at 67 and 56 respectively.
0.59 ammonium persulfate and 0.02 Fl of L-ascorbic acid were added as a polymerization initiator while rotating at a speed of 80°C and heating the jacket by passing hot water at 80°C. 20 minutes after adding the polymerization initiator. Afterwards, polymerization started. 60 minutes after adding the polymerization initiator, the temperature inside the reaction system reached 8.
The temperature reached 5° C., and the produced hydrogel polymer was finely divided into fine particles with a diameter of about 3 am. After further stirring, the lid was removed 90 minutes after polymerization was started, and the hydrogel polymer was taken out.

The obtained hydrogel polymer was dried and crushed in the same manner as in Example 3 to obtain a water absorbing agent (8).

Example 9 In the same manner as in Example 3, benzyloxypolyethylene glycol acrylate (containing on average 5 ethylene oxide units per molecule) 295.5611 was added to the kneader.
1, Sodium acrylate 94.49, Acrylic acid 1B
, 01), Marein? 1111.3 g and trimethylolpropane triacrylate 0.890 were dissolved in 420.15+I+ of ion-exchanged water to prepare an aqueous monomer solution with a monomer concentration of 50%.

Nitrogen gas was blown into this aqueous monomer solution to drive out oxygen dissolved in the aqueous solution.

Then, two sigma type vanes were placed at 67 and 56 respectively.
While rotating at a speed of rl)l and heating 80°C hot water through the jacket, 0.5 a of ammonium persulfate and l of L-ascorbine were added as polymerization initiators. 0.025
o was added. Polymerization started 20 minutes after adding the polymerization initiator. 60 minutes after adding the polymerization initiator, the temperature in the reaction system reaches 85°C, and the produced hydrogel polymer has a temperature of about 3
It was subdivided into fine grains with a diameter of m. After further stirring, the lid was removed 90 minutes after polymerization was started, and the hydrogel polymer was taken out.

The obtained hydrogel polymer was dried and pulverized in the same manner as in Example 3 to obtain a water absorbing agent (9).

Example 10 100g of water absorbing agent (1) obtained in Example 1 (50C)
d into 11 separable flasks containing cyclohexane. In another flask, 0.5 g of sorbitan monostearate was dissolved in 50 m of cyclohexane, and a cross-linking agent aqueous solution was prepared by mixing 0.1 g of ethylene glycol diglycidyl ether as a hydrophilic cross-linking agent (1) with 5 g of ion-exchanged water. By adding and stirring, a cyclohexane dispersion of the aqueous crosslinking agent solution was prepared. After adding this dispersion to the above separable flask while stirring, the temperature was 70°C.
It was kept for 2 hours. After that, cyclohexane was completely removed by filtration, and the water absorbing agent (
10) was obtained.

Example 11 A cross-linking agent solution prepared by mixing 100 g of the water-absorbing agent (3) obtained in Example 3 with 0.5+7 glycerin as a hydrophilic cross-linking agent (II) in 3 g of ion-exchanged water and 10 g of 2-propatool. was added, and heated at 160° C. for 10 minutes while stirring to obtain a water absorbing agent (11).

Comparative Example 1 Cyclohexane 1 and Ol were placed in the same reaction apparatus as in Example 1, and 5.0 g of sorbitan monostearate was added thereto to dissolve it, and then nitrogen gas was blown in to drive out dissolved oxygen.

Sodium acrylate 112.891 in a separate flask
28.82 g of acrylic acid and 0.022 g of methylene bisacrylamide were dissolved in 263.00 (J) of ion-exchanged water to prepare an aqueous monomer solution with a 7-mer concentration of 35%. To this aqueous monomer solution, 0.15 (J) of potassium persulfate was added. After addition and dissolution, nitrogen gas was blown into the aqueous solution to drive out oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the separable flask and dispersed by stirring at 200 rpm. The polymerization was carried out in the same manner as in Example 1, and the resulting crosslinked polymer was dehydrated, filtered, and dried under reduced pressure to obtain a comparative water absorbing agent (1).

Comparative Example 2 1.01 g of cyclohexane was placed in the same reaction apparatus as in Example 1, and 5.0 g of sorbitan monostearate was added and dissolved therein. Nitrogen gas was blown in to drive out dissolved oxygen.

In a separate flask, 7,890 methoxypolyethylene glycol acrylate (containing on average 10 ethylene oxide units per molecule), 124.83 CI sodium acrylate, 31.86 g acrylic acid and 0.024 g methylene bisacrylamide was dissolved in 164.58!J of ion-exchanged water to prepare an aqueous monomer solution with a monomer concentration of 50%.

After adding 0.15 g of potassium persulfate to this aqueous solution and dissolving it, nitrogen gas was blown in to drive out oxygen dissolved in the aqueous solution.

Next, the aqueous 7mer solution in this flask was added to the separable flask and dispersed by stirring at 200 rpm+. Thereafter, polymerization was carried out in the same manner as in Example 1, and the resulting crosslinked polymer was dehydrated, filtered, and dried under reduced pressure to obtain a comparative water absorbing agent (2).

Comparative Example 3 1.01 g of cyclohexane was placed in the same reactor as in Example 1, and 1.0 g of sorbitan monostearate was added thereto to dissolve it, and then nitrogen gas was blown in to drive out dissolved oxygen.

In a separate flask, 164.7+It of methoxypolyethylene glycol acrylate (containing on average 10 ethylene oxide units per molecule) and methylenebisacrylamide O,OO4 (] were mixed with 16 mL of ion-exchanged water.
4.70 to prepare an aqueous solution of 7mer with a monomer concentration of 50%. This monomer aqueous solution contains 0 potassium persulfate.
．． 1511! After adding and dissolving the aqueous solution, nitrogen gas was blown in to drive out the oxygen dissolved in the aqueous solution.

Next, the aqueous monomer solution in this flask was added to the separable flask and dispersed by stirring at 20 Orpm. Thereafter, polymerization was carried out in the same manner as in Example 1, and the resulting crosslinked polymer was dehydrated, filtered, and dried under reduced pressure to obtain a comparative water absorbing agent (3).

Comparative Example 4 In a kneader similar to Example 3, methoxypolyethylene glycol acrylate (containing on average 5 ethylene oxide units per molecule) 350111, 1 cum of sodium acrylate 94.0 (], and acrylic acid 36. 0!
If and trimethylolpropane triacrylate 4
4.45 (J dissolved in ion exchange water 524.450,
A seven-mer aqueous solution with a monomer concentration of 50% was prepared. Nitrogen gas was blown into this aqueous monomer solution to drive out oxygen dissolved in the aqueous solution.

Then, two sigma type vanes were placed at 67 and 56 respectively.
While rotating at ram speed and heating the jacket by passing hot water at 80° C., 0.5 a of ammonium persulfate and 0.025 a of 1-ascorbic acid were added as polymerization initiators. Polymerization started 20 minutes after adding the polymerization initiator. 60 minutes after adding the polymerization initiator, the temperature in the reaction system reached 91°C, and the produced hydrogel polymer was approximately 3jl.
It was subdivided into fine particles with a diameter of 1. After stirring for an additional 60 minutes, the lid was removed and the hydrogel polymer was taken out.

The obtained water-containing glue-like polymer was spread on a 50-mesh wire mesh and dried with hot air at a temperature of 150° C. for 2 hours. A comparative water absorbing agent (4) was obtained by pulverizing this dried material using a vibration mill.

Comparative Example 5 1°Oi! of cyclohexane was added to the same reactor as in Example 1.
1 and sorbitan monostearate i~'5. O
After adding a and dissolving it, nitrogen gas was blown in to drive out the dissolved oxygen.

In a separate flask 155.2517 a. of 2-acrylamido-2-methylpropanesulfonic acid, 23.5 a. of sodium acrylate and 0.5 a.
077 (II dissolved in 178.75 g of ion-exchanged water,
An aqueous monomer solution having a monomer concentration of 50% was prepared. After adding and dissolving 0.25 (J) of N,N'-azobisamidinopropane hydrochloride to this monomer aqueous solution, nitrogen gas was blown in to drive out oxygen dissolved in the aqueous solution.

Next, the monomer aqueous solution in this flask was added to the separable flask and dispersed by stirring at 20 Orp-. Thereafter, polymerization was carried out in the same manner as in Example 1, and the resulting crosslinked polymer was dehydrated, filtered, and dried under reduced pressure to obtain a comparative water absorbing agent (5).

Comparative Example 6 In a kneader similar to Example 3, 350 g of hydroxypolyethylene glycol acrylate (containing on average 5 ethylene oxide units per molecule) and 94.0 g of sodium acrylate! I+, acrylic M 36.00 and trimethylolpropane triacrylate 0.89
111 was dissolved in 480 g of ion-exchanged water to prepare an aqueous monomer solution with a 7-mer concentration of 50%. Nitrogen gas was blown into this aqueous monomer solution to drive out oxygen dissolved in the aqueous solution.

Then, two sigma type vanes were placed at 67 and 56 respectively.
Ammonium persulfate 0.5a and L-ascorbyl l110.025 were added as polymerization initiators while rotating at a speed of rpi and heating by passing hot water at 80°C through the jacket.
CI was added. Polymerization started 20 minutes after adding the polymerization initiator. Sixty minutes after the addition of the polymerization initiator, the temperature in the reaction system reached 91° C., and the produced hydrogel polymer had been subdivided into fine particles with a diameter of about 3jIl11. After further stirring, the lid was removed 90 minutes after polymerization was started, and the hydrogel polymer was taken out.

The obtained hydrogel polymer was spread on a 50-mesh wire mesh and dried with hot air at a temperature of 150° C. for 2 hours. A comparative water absorbing agent (6) was obtained by pulverizing this dried material using a vibration mill.

Comparative Example 7 In a kneader similar to Example 3, 350 g of methoxypolyethylene glycol acrylate (containing on average 5 ethylene oxide units per molecule) and 2-acrylamido-2-methylpropanesulfone I! 155.25
a and trimethylolpropane triacrylate 0.
89 g was dissolved in 505.25 g of ion-exchanged water to prepare an aqueous monomer solution with a monomer concentration of 5.0%. Nitrogen gas was blown into this aqueous monomer solution to drive out oxygen dissolved in the aqueous solution.

, then two sigma type vanes with 67 and 5 sigma blades, respectively.
While rotating at a speed of 6 p- and heating by passing hot water at 80°C through the jacket, 0.5 a of ammonium persulfate and 0.025 g of ascorbic acid were added as a polymerization initiator. 60 minutes after adding the polymerization initiator, the temperature inside the reaction system reached 91°C, and the produced hydrogel polymer was about 3#1
It was subdivided into fine grains with a diameter of llI. Further stirring was continued, and 90 minutes after starting polymerization, the lid was removed and the water-containing glue-like polymer was taken out.

The obtained hydrogel polymer was spread on a 50-mesh wire mesh and dried with hot air at a temperature of 150° C. for 2 hours. A comparative water absorbing agent (7) was obtained by pulverizing this dried product using a vibration mill.

Example 12 Water absorbing agent (1) obtained in Examples 1 to 11 and Comparative Examples 1 to 7
~ (11) and comparative water absorbing agents (1) ~ (7), deionized water, synthetic seawater and
The water absorption capacity of the % calcium chloride aqueous solution was measured.

<Method for measuring the water absorption capacity of water absorbing agents> 1 g of each water absorbing agent is immersed in deionized water, synthetic seawater with the composition shown in Table 1, or 40% calcium chloride aqueous solution at 100 OId, and 200 OId 1 hour and 24 hours after immersion. - After filtering through a mesh wire mesh and draining for 10 minutes, the weight of the hydrous gel present on the 200 mesh wire mesh was measured, and the number of grams was taken as the water absorption capacity. The results are shown in Table 2.

Table Example 13 Water absorbing agent (1) obtained in Examples 1 to 11 and Comparative Examples 1 to 7
~ (11) and comparative water absorbing agents (1) ~ (7), water absorption capacity of 40% calcium chloride aqueous solution and decrease in water absorption capacity over time (water absorption capacity reduction rate) by the following method
was measured.

<Method for measuring water absorption capacity reduction rate of calcium chloride aqueous solution of water absorbing agent> 1 g of each water absorbing agent is mixed with 1000 d of 40% calcium chloride aqueous solution
After 20 days of immersion in the water, it was covered with a 200-mesh wire mesh and drained for 10 minutes.The amount of water-containing gel placed on the 200-mesh wire mesh was measured, and the number of grams was taken as the water absorption capacity after 20 days.

In addition, as an evaluation method for salt tolerance, 1
From the water absorption capacity of the 40% calcium chloride aqueous solution after hours and the water absorption capacity after 20 days, how much does the water absorption capacity after immersion for 20 days decrease compared to the water absorption capacity after immersion for 1 hour? It was calculated using the formula.

Water absorption capacity reduction rate (X) - No. table The results are shown in Table 2.

As is clear from Table 2, the water-absorbing agent of the present invention, which is composed of a specific bridge II combination, exhibits a high water-absorbing capacity for highly concentrated salt solutions, and the water-absorbing agent exhibits extremely little decrease in water absorption capacity over time. It is. Furthermore, it can be seen that the water-absorbing agent of the present invention, in which the vicinity of the surface of a cross-linked polymer is cross-linked with a hydrophilic cross-linking agent, has a very high initial water absorption rate in addition to the high salt resistance of the water-absorbing agent.

Claims (1)

[Claims] 1. General formula ▲ Numerical formulas, chemical formulas, tables, etc. Y is an oxyalkylene group having 2 to 4 carbon atoms, Y is an oxyalkylphenyl group having 1 to 3 substituents of an alkoxy group having 1 to 5 carbon atoms, a phenoxy group, or an alkyl group having 1 to 9 carbon atoms, and n is a number from 3 to 100 on average.) The (meth)acrylic acid ester monomer (A
) and a carboxyl group-containing water-soluble unsaturated monomer (B) in an amount of 0.001 to 80% by weight based on the monomer mixture (I). 5
．． A water absorbing agent with excellent salt resistance made of a crosslinked polymer obtained by polymerization in the presence of 0 mol% of crosslinking agent (II). 2. A water-absorbing agent with excellent salt resistance, characterized in that the vicinity of the surface of the crosslinked polymer according to claim 1 is crosslinked with a hydrophilic crosslinking agent (III) capable of reacting with carboxyl groups and/or carboxylate groups.