JPH0417090B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a salt-resistant water absorbing agent. More specifically, the present invention relates to a salt-resistant water-absorbing agent that absorbs a large amount of aqueous liquid when it comes into contact with an aqueous liquid containing salts, particularly polyvalent metal ions, and whose water absorption capacity does not decrease 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 for sludge removal. It is being developed for use as a coagulant, anti-condensation agent for building materials, water stopper for civil engineering, desiccant, etc. Examples of such water-absorbing resins include hydrolyzed products of starch-acrylonitrile graft polymers, neutralized products of starch-acrylic acid graft polymers, saponified products of vinyl acetate-acrylic acid ester copolymers, and acrylonitrile-based copolymers. Hydrolyzates of polymers or acrylamide copolymers or crosslinked products thereof, self-crosslinking sodium polyacrylate obtained by reverse phase suspension polymerization, crosslinked products of partially neutralized polyacrylic acid, etc. are known. ing. (Problem to be Solved by the Invention) However, although these water-absorbing resins have an excellent ability to absorb large amounts of water or aqueous liquids, they cannot be used when they come into contact with aqueous liquids containing polyvalent metal ions such as seawater. It has the disadvantage that it sometimes shows only a low water absorption capacity, and the water absorption capacity decreases over time. Therefore, as products with improved salt resistance, crosslinked starch-acrylic acid-vinylphosphonic acid-N-methylpyridium chloride graft copolymers (Japanese Patent Application Laid-open No. 15634/1983), starch-sodium acrylate-acrylamide graft copolymers, etc. Sulfomethylated polymer crosslinked product with formalin and sodium bisulfite (JP-A-55-16016) and 2-acrylamide-2-methylpropanesulfonic acid-sodium acrylate self-crosslinked product (JP-A-56-161412)
is proposed. However, although these have been recognized to have improved salt resistance, when they come into contact with aqueous liquids containing polyvalent metal ions, their water absorption capacity still economically decreases, and it is difficult to say that they have sufficient salt resistance. The present inventors have conducted extensive research in order to improve the above-mentioned drawbacks and to develop a salt-resistant water absorbing agent that exhibits sufficient water absorption capacity for aqueous liquids containing polyvalent metal ions and that does not economically reduce the water absorption capacity. As a result of repeated efforts, the present invention was completed. (Means and effects for solving the problems) The present invention is based on the general formula (R is hydrogen or methyl group, X has 2 carbon atoms
~4 alkylene group, Y is hydrogen, an alkyl phenyl group having 1 to 3 substituents of an alkyl group having 1 to 5 carbon atoms, a phenyl group, or an alkyl group having 1 to 9 carbon atoms, and n is an average of It is a number from 1 to 100. ) (meth)acrylic acid ester monomer A (hereinafter referred to as monomer A) 3 to 95 mol %, sulfonic acid group-containing unsaturated monomer B (hereinafter referred to as monomer B). ) 5 to 97 mol% and other polymerizable monomer C (hereinafter referred to as monomer C) 0 to 50 mol% (however, the total of components A, B and C is 100
It is mole%. ), a monomer mixture () consisting of
The present invention provides a salt-resistant water absorbing agent made of a crosslinked polymer obtained by polymerization in the presence of a crosslinking agent. Monomer A used in the present invention is a (meth)acrylic acid ester monomer represented by the above general formula, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate,
Polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polybutylene glycol(meth)acrylate, methoxypolyethylene glycol mono(meth)acrylate, methoxypolypropylene glycol mono(meth)acrylate, methoxypolybutylene glycol mono(meth)acrylate Acrylate, Ethoxypolyethylene glycol mono(meth)acrylate, Ethoxypolypropylene glycol mono(meth)acrylate, Ethoxypolybutylene glycol mono(meth)acrylate,
Examples include methoxypolyethylene glycol/polypropylene glycol mono(meth)acrylate, phenoxypolyethylene glycol mono(meth)acrylate, benzyloxypolyethylene glycol mono(meth)acrylate, and one or more of these may be used. I can do it. Examples of monomer B used in the present invention include vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfone acid,
2-sulfoethyl (meth)acrylate, 3-sulfopropyl (meth)acrylate, 1-sulfopropan-2-yl (meth)acrylate, 2-
Sulfopropyl (meth)acrylate, 1-sulfobutan-2-yl (meth)acrylate, 2-
Examples include unsaturated sulfonic acids such as sulfobutyl (meth)acrylate and 3-sulfobutan-2-yl (meth)acrylate, and their alkali metal salts, alkaline earth metal salts, ammonium salts, and substituted ammonium salts. One type or two or more types can be used from among them. As the water-soluble monomer C used in the present invention,
For example, acrylic acid, methacrylic acid, crotonic acid,
Carboxyl group-containing unsaturated monomers or (meth) unsaturated carboxylic acids such as itaconic acid, maleic acid, fumaric acid, and citraconic acid, and their alkali metal salts, alkaline earth metal salts, ammonium salts, and substituted ammonium salts. Examples include acrylamide, and one or more of these can be used. In addition to these water-soluble monomers C, water-insoluble monomers that can be copolymerized with monomer A or B can significantly improve the absorbability of the resulting crosslinked polymer. It can be used as long as it does not cause any deterioration. Monomer A acts to impart salt resistance and water absorption to the resulting crosslinked polymer through its non-dissociable hydrophilic group. Monomer B acts to impart high water absorption to aqueous liquids containing polyvalent metal ions to the resulting crosslinked polymer due to the strong dissociative properties of the sulfonic acid groups. In the present invention, in the monomer mixture (), monomer A is 3 to 95 mol%, monomer B is 5 to 97%, and monomer C is 0 to 50 mol% (However, A, B and C
The sum of the components is 100 mol%. ) ratio. If the amount of monomer A is small, such as less than 3 mol %, the water absorbing ability of the resulting water absorbing agent will decrease. 50 monomer C
If used in excess of mol%, salt tolerance may decrease,
This is not preferable because the water absorption capacity may decrease. When using an unsaturated monomer containing a carboxylic acid group as monomer B or monomer C, unsaturated sulfonic acids and unsaturated carboxylic acids may reduce the water absorption capacity of the resulting water absorbing agent if used in large quantities. However, it is useful in adjusting the pH of the water-absorbing agent to neutrality or other desired range, and in acting as a crosslinking point when a polyhydric alcohol is used as a crosslinking agent. Therefore, in the monomer mixture ( ), monomer B is an alkali metal salt of an unsaturated sulfonic acid, and monomer C is an alkali metal salt of an unsaturated carboxylic acid and an alkali of an unsaturated carboxylic acid. Metal salt 25~
It is preferable to use the water absorbent at a ratio of 99 mol %, since the water absorbing ability of the obtained water absorbing agent can be kept high and the pH of the water absorbing agent can be adjusted to neutral. In the present invention, the monomer mixture () is polymerized in the presence of a crosslinking agent () to obtain a crosslinked polymer;
The crosslinking agent () is essential for freely controlling the crosslinking density during polymerization of the monomer mixture () to obtain a highly water-absorbent crosslinked polymer. Even in the polymerization in the absence of the crosslinking agent (2), the monomer mixture (2) partially self-crosslinks, but it does not result in a highly water-absorbent crosslinked polymer that can generally be used as a water-absorbing agent. By appropriately selecting and using the type and amount of the crosslinking agent (), a water absorbing agent with excellent salt resistance can be obtained. 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,
Polyethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di(meth)acrylate, N,N-methylenebisacrylamide, triallyl isocyanurate, trimerolpropane diallyl ether Compounds having two or more ethylenically unsaturated groups in one molecule such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol,
Polyhydric alcohols such as diethanolamine, triethanolamine, 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 diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane triglycidyl ether, glycerin triglycidyl ether, etc. These polyepoxy compounds can be used alone or in combination of two or more. When a polyhydric alcohol is used as the crosslinking agent (), it is preferable to carry out the post-polymerization heat treatment at 150°C to 250°C, and when a polyepoxy compound is used, it is preferably carried out at 50°C to 250°C. The amount of the crosslinking agent () to be used is preferably 0.00001 in molar ratio to the monomer mixture ().
~0.1 range. If the amount exceeds 0.1, the crosslinking density of the resulting crosslinked polymer tends to become too high, resulting in a decrease in viscosity and water absorption ability. Conversely, 0.00001
If the amount is less than 50%, the crosslinking density is too low and the viscosity is low, resulting in stickiness after absorbing the aqueous liquid.
The initial water absorption rate becomes insufficient. The polymerization method for obtaining the salt-resistant water absorbing agent of the present invention may be any conventionally known method, and examples thereof include a method using a radical polymerization catalyst, a method of irradiating with radiation, electron beam, ultraviolet ray, etc.
Radical polymerization catalysts include hydrogen peroxide, peroxides such as benzoyl peroxide and kyumene hydroperoxide, azo compounds such as azobisisobutyronitrile, and radicals such as persulfates such as ammonium persulfate and potassium persulfate. A redox initiator is used, which is a generator or a combination of these and a reducing agent such as sodium bisulfite, L-ascorbic acid, or ferrous salt. As the polymerization solvent, for example, water, methanol, ethanol, acetone, dimethylformamide, dimethyl sulfoxide, and mixtures thereof can be used. The temperature during polymerization varies depending on the type of catalyst used, but a relatively low temperature is preferable because the molecular weight of the crosslinked polymer increases. However, in order to complete the polymerization, the temperature is preferably within the range of 20°C or higher and 100°C or lower. As mentioned above, since the crosslinking density of the crosslinked polymer obtained by using the crosslinking agent () can be freely controlled, there is no particular restriction on the concentration of the monomer mixture () in the polymerization system, but it is possible to control the polymerization reaction. Considering ease, yield, and economy, it is preferably in the range of 20 to 80% by weight. Various forms of polymerization can be adopted, including reverse-phase suspension polymerization, cast polymerization, and a method in which a hydrogel polymer is polymerized while being fragmented by the shearing force of a double-arm kneader (Japanese Unexamined Patent Application Publication No. 1983-1999).
34101) is preferred. A fragrance, a deodorizing agent, or carbon black or activated carbon may be mixed with the salt-resistant water-absorbing agent of the present invention before or after polymerization for the purpose of improving light resistance. (Effects of the Invention) The salt-resistant water absorbing agent of the present invention obtained as described above has extremely excellent salt resistance, so it can be used not only in sweat, blood, urine, etc., but also in highly concentrated salts such as seawater. It absorbs aqueous liquids containing polyvalent metal ions at a high absorption rate, and its water absorption capacity does not decrease economically even when it comes into contact with aqueous liquids containing polyvalent metal ions. It is meant to be held for a long time. Therefore, the salt-resistant water-absorbing agent of the present invention can be effectively used as a water-retaining agent, desiccant, etc. for agriculture and horticulture, and the product kneaded with rubber and/or thermoplastic resin has a high expansion rate with water. Since the expansion rate does not decrease over time even when it comes into contact with an aqueous liquid containing polyvalent metal ions, it is useful as a water stop agent for civil engineering, a sealing material, a caulking material, a packing material, a medical hygiene material, etc. (Examples) Hereinafter, the present invention will be explained in detail with reference to Examples, but the scope of the present invention is not limited only to these Examples. Example 1 141 g of sodium salt of 2-sulfoethyl methacrylate in a 1000 ml cylindrical separable flask
(0.65 mol), methacrylic acid 4.35 g (0.05 mol), sodium methacrylate 16.2 g (0.15 mol), methoxypolyethylene glycol monomethacrylate (containing an average of 10 ethylene oxide units per molecule) 81 g (0.15 mol), 0.154 g (0.001 mol) of N,N-methylenebisacrylamide and 250 g of water were charged and stirred to uniformly dissolve.
After purging with nitrogen, the mixture was heated to 40° C. in a bath, 1.0 g of a 10% aqueous ammonium persulfate solution and 0.5 g of a 1% aqueous L-ascorbic acid solution were added, and stirring was stopped to allow polymerization. After the start of polymerization, heat was generated, and the temperature rose to 53°C after 55 minutes. After confirming that the temperature of the polymerization system had begun to drop, the bath was raised to 90°C and heated for an additional hour. After dividing the obtained hydrogel of the crosslinked polymer into small pieces, it was dried in a hot air dryer at 150°C for 5 hours.
The water absorbing agent 1 of the present invention was obtained by pulverization. Example 2 220 ml of n-hexane was charged into a 1000 ml four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel, and a nitrogen gas inlet tube, and 1.8 g of sorbitan monostearate was added and dissolved therein, followed by purging with nitrogen. . Into the dropping funnel were 218 g (0.95 mol) of sodium 2-acrylamido-2-methylpropanesulfonate, 115 g (0.05 mol) of ethoxypolyethylene glycol monoacrylate (containing an average of 50 ethylene oxide units per molecule), and ethylene glycol diglycidyl. After adding and dissolving 0.348 g (0.002 mol) of ether, 368 g of water, and 0.05 g of potassium persulfate, nitrogen gas was blown in to remove oxygen present in the aqueous solution. Next, the contents of the dropping funnel were added to the four-necked flask and decomposed,
While introducing a slight amount of nitrogen gas, the temperature of the polymerization system was maintained at 60 to 65°C using a hot water bath, and the polymerization reaction was continued for 3 hours. Thereafter, n-hexane was distilled off under reduced pressure, and the remaining hydrogel of the crosslinked polymer was dried under reduced pressure at 90°C to obtain water absorbing agent 2 of the present invention. Example 3 In a 1000 ml cylindrical separable flask, 26.0 g (0.8 mol) of a 25% aqueous solution of sodium vinyl sulfonate, 7.20 g (0.10 mol) of acrylic acid, 4.70 g (0.05 mol) of sodium acrylate, and methoxypolyethylene glycol monoacrylate (Contains 5 ethylene oxide units per molecule on average) 236g (0.77 mol), glycerin 0.46g (0.005
Polymerization was carried out in the same manner as in Example 1 using 1.0 g of a 10% aqueous ammonium persulfate solution and 0.5 g of a 1% aqueous L-asconbic acid solution. The obtained hydrogel of the crosslinked polymer was divided into pieces, dried at 180°C for 2 hours, and pulverized to obtain water absorbing agent 3 of the present invention. Example 4 139 g of potassium salt of 3-sulfopropyl acrylate in a 1000 ml cylindrical separable flask
(0.60 mol), polyethylene glycol monoacrylate (containing an average of 10 ethylene oxide units per molecule) 76.8 g (0.15 mol), acrylamide 17.8 g (0.25 mol), trimethylol propane triacrylate 0.296 g (0.001 mol) and 300 g of water, and polymerization was carried out in the same manner as in Example 1 using 1.0 g of a 10% aqueous ammonium persulfate solution and 0.5 g of a 1% aqueous L-ascorbic acid solution. The obtained hydrogel of the crosslinked polymer was divided into pieces, dried at 150°C for 3 hours, and pulverized to obtain the water absorbing agent 4 of the present invention. Comparative Example 1 In Example 1, the contents of the 1000 ml cylindrical separable flask were as follows: 216 g (1.0 mol) of sodium salt of 2-sulfoethyl methacrylate, 0.154 g of N,N-methylenebisacrylamide
Comparative water-absorbing agent 1 was obtained in the same manner as in Example 1 except that the amount of water was 324 g (0.001 mol) and 324 g of water. Comparative Example 2 In Example 1, the contents of the 1000 ml cylindrical separable flask were changed to methoxypolyethylene glycol monomethacrylate (average 1
Comparative water absorbing agent 2 was prepared in the same manner as in Example 1, except that 540 g (1.0 mol) of N,N-methylenebisacrylamide (containing 10 ethylene oxide units per molecule), 0.154 g (0.001 mol) of N,N-methylenebisacrylamide, and 200 g of water were used. Obtained. Example 5 For water absorbing agents 1 to 4 and comparative water absorbing agents 1 to 2 obtained in Examples 1 to 4 and Comparative Examples 1 to 2, the water absorption capacity of deionized water and synthetic seawater was measured by the following method. . After immersing 1 g of each water absorbing agent in 1000 ml of deionized water or synthetic seawater with the composition shown in Table 1 for 24 hours,
After filtering through a 200-mesh wire mesh and draining for 10 minutes, the weight of the water-absorbing 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 6 Regarding water absorbing agents 1 to 4 and comparative water absorbing agents 1 to 2 obtained in Examples 1 to 4 and Comparative Examples 1 to 2, the water absorption capacity and water absorption of 0.05% calcium chloride aqueous solution were determined by the following method. The decrease in magnification over time (water absorption rate decrease rate) was measured. 1g of each water absorbing agent in 0.05% calcium chloride aqueous solution
After immersing in 1000 ml for 1 hour, filtering through a 200-mesh wire mesh and draining for 10 minutes, the weight of the water-absorbing gel present on the 200-mesh wire mesh was measured, and the number of grams was taken as the water absorption capacity of the 0.05% calcium chloride aqueous solution. . Also, due to the influence of calcium ions, the water absorption capacity decreases over time depending on the soaking time.
As an evaluation method for salt resistance, the water absorption capacity is measured when immersed in a 0.05% calcium chloride aqueous solution for 10 days, and the water absorption capacity after immersion for 10 days is determined by how much it decreases compared to the water absorption capacity after immersion for 1 hour. The magnification reduction rate) was determined by the following formula. Water absorption capacity reduction rate = 100 - Water absorption capacity after immersion for 10 days/Water absorption capacity after immersion for 1 hour x 100 The results are shown in Table 2. In this case, the 0.05% calcium chloride aqueous solution was replaced with a new one every day.

[Table] As is clear from Table 2, the absorbent of the present invention shows a high water absorption capacity even in aqueous liquids with high salt concentration such as synthetic seawater, and even when it comes into contact with calcium ions, the water absorption capacity does not change over time. It has the characteristic that there is little deterioration.

Claims (1)

[Claims] 1. General formula (R is hydrogen or methyl group, X has 2 carbon atoms
~4 alkylene group, Y is hydrogen, an alkyl phenyl group having 1 to 3 substituents of an alkyl group having 1 to 5 carbon atoms, a phenyl group, or an alkyl group having 1 to 9 carbon atoms, and n is an average of It is a number from 1 to 100. ) (meth)acrylic acid ester monomer A3 to 95 mol%, sulfonic acid group-containing unsaturated monomer B 5 to 97 mol%, and other water-soluble monomers C0 to 50 mol% (however, A salt-resistant water absorbent comprising a crosslinked polymer obtained by polymerizing a monomer mixture (2) consisting of A, B and C components (the total of components A, B and C is 100 mol%) in the presence of a crosslinking agent (2).