JPH0555523B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a salt-resistant and light-resistant water absorbing agent. More specifically, it relates to a water-absorbing agent that absorbs a large amount of aqueous liquid when it comes into contact with an aqueous liquid containing salts, and does not deteriorate even when exposed to light. (Conventional technology) 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 absorbents for sanitary products, disposable diapers, etc., water retention agents for agriculture and horticulture, and sludge. It is being developed for use as a coagulant, anti-condensation agent for building materials, water-stopping material for civil engineering, desiccant, etc. Examples of such water-absorbing resins include hydrolysates of starch-acrylonitrile graft polymers, neutralized starch-acrylic acid graft polymers, saponified products of vinyl acetate-acrylic acid ester copolymers, and acrylonitrile-based copolymers. Hydrolyzed or acrylamide copolymer hydrolysates or crosslinked products thereof, self-crosslinking sodium polyacrylate obtained by reverse phase suspension polymerization, crosslinked partially neutralized polyacrylic acid products, etc. are known. There is. (Problem to be solved by the invention) Although these water-absorbing resins have an excellent ability to absorb large amounts of water or aqueous liquids, they absorb aqueous liquids containing salt such as sweat, blood, urine, or seawater. In some cases, the water absorption capacity is significantly reduced. Moreover, these conventional water-absorbing resins all have excellent stability in a dry state, but are poor in stability in a water-absorbed state. For example, if a gel-like material that has absorbed water is exposed to sunlight, it deteriorates in just a few hours and becomes fluid, making it impossible to maintain its gel-like form. The above-mentioned drawbacks are a major obstacle when used as a water-stopping material. Therefore, as products with improved salt resistance, crosslinked products of starch-acrylic acid-vinylphosphonic acid-N-methylpyridium chloride graft copolymer (Japanese Patent Application Laid-open No. 15634-1983), starch-sodium acrylate-acrylamide graft copolymer A sulfomethylated product of formalin and sodium bisulfite (Japanese Unexamined Patent Publication No. 55-16016) and a self-crosslinked product of 2-acrylamide-2-methylpropanesulfonic acid-sodium acrylate (Japanese Unexamined Patent Publication No. 56-161412) have been proposed. However, these have poor light resistance and lack stability in a water-absorbed state. Furthermore, the ability to absorb aqueous liquids containing high concentrations of salts is also insufficient. On the other hand, a method of mixing carbon black or activated carbon with water-absorbing resin to improve light resistance (Japanese Patent Laid-Open No. 59-38271)
has been proposed, but although this method effectively improved light resistance, it was insufficient in improving salt resistance. As described above, a water-absorbing resin that has both salt resistance and light resistance has not been known until now. The present inventors have conducted intensive research to improve the above-mentioned problems of salt resistance and light resistance, and as a result have completed the present invention. (Means and effects for solving the problems) The present invention is based on the general formula (However, R ¹ is hydrogen or a methyl group, n is an integer of 2 or 3, and X is hydrogen, an alkali metal, or an ammonium group.) One type selected from sulfoalkyl (meth)acrylate monomers represented by or 20 to 100 mol% of two or more monomers (A), general formula (However, R ² is hydrogen or methyl group, Y is hydrogen,
Indicates an alkali metal or ammonium group. ) 0 to 80 mol% of one or more monomers (B) selected from the (meth)acrylic acid monomers represented by
and other anionic and/or nonionic polymerizable monomers (C) from 0 to 50 mol% (however, the total of components (A), (B), and (C) is 100 mol%). Monomer mixture () to crosslinker () in a molar ratio of 0.00001 to 0.1 to monomer mixture ()
The present invention provides a salt-resistant and light-resistant water-absorbing agent made of a water-insoluble water-absorbing resin obtained by polymerization in the presence of. The monomer (A) in the present invention is a sulfoalkyl (meth)acrylate monomer represented by the above general formula, such as 2-sulfoethyl acrylate or its alkali metal salt or ammonium salt, 2-sulfoethyl methacrylate or its One or more monomers are selected from alkali metal salts or ammonium salts, 3-sulfopropyl acrylate and its alkali metal salts or ammonium salts, and 3-sulfopropyl methacrylate and its alkali metal salts or ammonium salts. It is used as Monomer (A) has the effect of imparting salt resistance to the resulting water-insoluble water-absorbing resin due to the strong dissociability of the sulfonic acid group present in monomer (A). Monomer (A) must be used in a proportion of 20 mol% or more in the monomer mixture (). If the amount is less than 20 mol%, the resulting water-insoluble water-absorbing resin will have insufficient salt resistance, which is not preferable. The monomer (B) in the present invention is a (meth)acrylic acid monomer represented by the above general formula, and includes, for example, acrylic acid, its alkali metal salt or ammonium salt, methacrylic acid, its alkali metal salt, or Ammonium salts can be mentioned,
One or more monomers are selected from these and used. Monomer (B) is used in a proportion of 80 mol% or less in the monomer mixture (). If it is used in an amount exceeding 80 mol%, the salt resistance of the resulting water-insoluble water-absorbing resin will decrease, which is not preferable. Other anionic and/or nonionic polymerizable monomers (C) in the present invention include only water-soluble monomers such as (meth)acrylate, hydroxypropyl (meth)acrylate, maleic acid, and itaconic acid. Even if the monomer is water-insoluble, as long as it can be copolymerized with monomer (A) or (B), it may be used within the range that does not significantly reduce the water-absorbing capacity of the resulting water-insoluble water-absorbing resin. Can be used. The amount of monomer (C) used is 50% in the monomer mixture ().
The amount is less than 50 mol %, and if it is used in excess of 50 mol %, not only the salt resistance but also the water absorption capacity of the resulting water-insoluble water-absorbing resin will decrease, which is not preferable. Among the monomer mixtures () in the present invention consisting of 20 to 100 mol% of monomer (A), 0 to 80 mol% of monomer (B) and 0 to 50 mol% of monomer (C), So that the total amount of the sulfoalkyl methacrylate monomer in the monomer (A) and the methacrylic acid monomer in the monomer (B) is 20 mol% or more in the monomer mixture (). It is preferable to select monomers (A) and (B) to form a monomer mixture () because the light resistance of the resulting water-insoluble water-absorbing resin can be improved. If the total amount of the sulfoalkyl methacrylate monomer in monomer (A) and the methacrylic acid monomer in monomer (B) is less than 20 mol% in the monomer mixture (), Depending on the type and ratio of the monomer mixture () and crosslinking agent () used, the resulting water-insoluble water-absorbing resin may have insufficient light resistance. Sulfoalkyl (meth)acrylate as the monomer (A) and (meth)acrylic acid as the monomer (B) may reduce the water absorption capacity of the water-insoluble water-absorbing resin obtained when these acids are used extensively. However, it is useful for adjusting the pH of the water-absorbing resin to neutrality or other desired ranges, and for acting as a crosslinking point when polyhydric alcohol is used as a crosslinking agent. Therefore, monomer (A) is an alkali metal salt of sulfoalkyl (meth)acrylate,
and monomer (B) is (meth)acrylic acid 1 to 50 mol%
and alkali metal salts of (meth)acrylic acid 50~
It is preferable to use a monomer mixture (2) having a ratio of 99 mol %, since this allows the resulting water-absorbing resin to maintain a high water-absorbing capacity and also allows the pH of the water-absorbing resin to be adjusted to neutral. In the present invention, a water-insoluble water-absorbing resin is obtained by polymerizing the monomer mixture () in the presence of a crosslinking agent (). This is essential in order to freely control and obtain a water-insoluble water-absorbent resin.
Even in the polymerization in the absence of the crosslinking agent (2), the monomer mixture (2) partially self-crosslinks, but it does not become a water-insoluble water-absorbing resin to the extent that it can generally be used as a water-absorbing agent. By appropriately selecting and using the type and amount of crosslinking agent (), monomer (A)
Even when polymerizing a single monomer or a monomer mixture () with a large proportion of monomer (A) used, the crosslinking density of the resulting water-insoluble water-absorbing resin can be easily controlled, and the water-absorbing resin has excellent salt resistance. can be easily obtained. In addition, the crosslinking agent () is not only effective in obtaining a water absorbing agent with excellent salt resistance as described above, but also effective in obtaining a water absorbing agent with excellent light resistance. By adjusting the amount of the agent () to be appropriate depending on the type of the monomer mixture (), the stability of the resulting water-absorbing resin when exposed to sunlight in a water-absorbed state can be increased. 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, trimethylolpropane Compounds having two or more ethylenically unsaturated groups in one molecule such as diallyl ether; ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin,
Examples include polyhydric alcohols such as polyglycerin, propylene glycol, diethanolamine, triethanolamine, polypropylene glycol, polyvinyl alcohol, pentaerythritol, sorbitol, sorbitan, glucose, mannitol, mannitan, sucrose, and glucose, and one of these or Two or more types can be used. The amount of the crosslinking agent ( ) to be used is in the range of 0.00001 to 0.1 in molar ratio to the monomer mixture ( ). If the amount exceeds 0.1, even though the resulting water-insoluble water-absorbent resin has good light resistance, the crosslinking density tends to become too large, resulting in a decrease in viscosity and water-absorbing ability. On the other hand, if the amount is less than 0.00001, the crosslinking density is too small and the thickening property is low, resulting in stickiness after absorbing an aqueous liquid, resulting in insufficient light resistance and initial water absorption rate. The polymerization method for obtaining the salt-resistant and light-resistant water absorbing agent of the present invention may be any conventionally known method, such as a method using a radical polymerization catalyst, a method using radiation,
Examples include methods of irradiating with electron beams, ultraviolet rays, 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 withstands crosslinking polymerization becomes large. 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 water-insoluble water-absorbing resin 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; Considering ease of control, yield, and economy, 20
It is preferably in the range of ~60% by weight. Various forms of polymerization can be adopted, including reverse-phase suspension polymerization, cast polymerization, and methods in which a hydrogel polymer is polymerized while being fragmented by the shearing force of a double-arm kneader (Japanese Patent Laid-Open No. 57-34101). is preferred. A fragrance, a deodorizing agent, or carbon black or activated carbon may be mixed with the salt-resistant and light-resistant water absorbing agent of the present invention before or after polymerization for the purpose of further improving light resistance. (Effects of the Invention) The salt-resistant and light-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 high concentrations such as seawater. It absorbs water-based liquids containing salts at a high absorption rate, and once absorbed, water can be retained for a long time even under pressure.It also has good light resistance, so it can withstand long-term exposure to sunlight. Because it maintains the above absorption capacity without deteriorating, it is suitable as a water stop material for civil engineering,
It can be effectively used for water retention agents for agriculture and horticulture, medical hygiene materials, 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 1 172.8 g of sodium salt of 2-sulfoethyl methacrylate in a 500 ml cylindrical separable flask.
(0.80 mol), acrylic acid 3.6 g (0.05 mol), sodium acrylate 14.1 g (0.15 mol), N,N-
0.154 g (0.001 mol) of methylenebisacrylamide and 260 g of water were charged and stirred to uniformly dissolve them. After purging with nitrogen, heat to 40℃ using hot water.
10% ammonium persulfate aqueous solution 1.0g and 1%L
- 0.5 g of ascorbic acid aqueous solution was added and stirring was stopped to allow polymerization. After the start of polymerization, heat was generated, and the temperature rose to 68°C after 40 minutes. After confirming that the temperature of the polymerization system had begun to drop, the water bath was raised to 90°C and heated for an additional hour. The obtained water-containing gel of the water-absorbing resin was divided into small pieces, dried in a hot air dryer at 150°C for 5 hours, and pulverized to obtain the water-absorbing agent 1 of the present invention. Example 2 220 ml of n-hexane was charged into a 500 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, and the flask was purged with nitrogen. In a dropping funnel, add 23.0 g (0.10 mol) of sodium salt of 3-sulfopropyl methacrylate and 3.6 g of acrylic acid.
(0.05 mol), sodium acrylate 9.41 g (0.10
mole), trimethylolpropane acrylate
After 0.0296 g (0.0001 mol) was dissolved in 50 g of water and 0.05 g of potassium persulfate, nitrogen gas was blown into the aqueous solution to remove oxygen present in the aqueous solution. Next, the contents of the dropping funnel were added to the four-necked flask and dispersed, and the polymerization reaction was continued for 3 hours while maintaining the temperature of the polymerization system at 60 to 65°C with a hot water bath while introducing a slight amount of nitrogen gas. Thereafter, n-hexane was distilled off under reduced pressure, and the remaining water-containing gel of the water-absorbing resin was dried under reduced pressure at 80°C to obtain water-absorbing agent 2 of the present invention. Example 3 80.9 g of sodium salt of 2-sulfoethyl acrylate in a 500 ml cylindrical separable flask
(0.40 mol), methacrylic acid 21.5 g (0.25 mol), sodium methacrylate 27.0 g (0.25 mol), acrylamide 7.1 g (0.10 mol), glycerin 0.46 g
(0.005 mol) and 190 g of water were charged, 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 water-containing gel of the water-absorbing resin was divided into small pieces, dried at 180°C for 2 hours, and crushed to form water-absorbing agent 3.
I got it. Example 4 250 ml of cyclohexane was charged into the same four-necked flask as used in Example 2, 2.0 g of sorbitan monostearate was added and dissolved, and the flask was purged with nitrogen. Into the dropping funnel were 9.7 g (0.05 mol) of 3-sulfopropyl acrylate, 21.6 g (0.10 mol) of sodium salt of 3-sulfopropyl acrylate, 9.41 g (0.10 mol) of sodium acrylate, 5.40 g (0.05 mol) of sodium methacrylate, After adding and dissolving 0.0428 g (0.0002 mol) of diethylene glycol diacrylate, 60 g of water, and 0.1 g of potassium persulfate, nitrogen gas was blown into the solution to remove oxygen present in the aqueous solution. Next, the contents of the dropping funnel were added to the four-necked flask and dispersed, and a polymerization reaction was carried out in the same manner as in Example 2. After distilling off the cyclohexane, the resulting water-containing gel of the water-absorbing resin was
Water absorbent 4 of the present invention was obtained by drying under reduced pressure at °C. Example 5 The contents of the dropping funnel in Example 2 were changed to 21.6 g of sodium salt of 2-sulfoethyl methacrylate.
(0.10 mol), acrylic acid 3.6 g (0.05 mol), sodium acrylate 9.41 g (0.10 mol), trimethylolpropane triacrylate 0.0592 g (0.0002
Water absorbing agent 5 of the present invention was prepared in the same manner as in Example 2, except that the amounts were 65 g of water and 0.05 g of potassium persulfate.
I got it. Comparative Example 1 Acrylic acid in a 500ml cylindrical separable flask
18.0g (0.25mol), sodium acrylate 70.5g
(0.75 mol), N,N-methylenebisacrylamide 0.154 g (0.001 mol) and water 121 g,
10% ammonium persulfate aqueous solution 1.0g and 1%L
- Example 1 using 0.5 g of ascorbic acid aqueous solution
Comparative water absorbing agent 1 was obtained by polymerizing, drying and pulverizing in the same manner as above. Comparative Example 2 The contents of the dropping funnel in Example 2 were changed to 4.6% of the sodium salt of 3-sulfopropyl methacrylate.
g (0.02 mol), acrylic acid 7.2 g (0.10 mol), sodium acrylate 18.8 g (0.20 mol), water 42.5 g
Comparative water absorbing agent 2 was obtained in the same manner as in Example 2, except that 0.05 g of potassium persulfate was used. Comparative Example 3 Comparative water absorbing agent 3 was obtained by repeating the same operation as in Example 1 except that N,N-methylenebisacrylamide in Example 1 was not used. Note that the heat generated after the start of polymerization rose to 65°C after 45 minutes. Example 6 Water absorbing agent 1 obtained in Examples 1 to 5 and Comparative Examples 1 to 3
- 5 and Comparative Water Absorbing Agents 1 to 3, the water absorption capacity of aqueous liquids containing salts was measured by the following method. Synthetic seawater with the composition shown in Table 1 per 1g of each water absorbing agent
After immersing in 1000ml for 24 hours, it was filtered through a 200-mesh wire mesh and drained 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】

[Table] As is clear from Table 2, the water absorbing agent of the present invention has excellent salt resistance. In addition, in Comparative Water Absorbing Agent 3, although some water-insoluble gel-like material was produced, most of it was water-soluble resin, so the water absorption capacity could not be measured. Example 7 Water absorbing agent 1 obtained in Examples 1 to 5 and Comparative Examples 1 to 3
~5 and Comparative Water Absorbing Agents 1 to 3, the light resistance was evaluated by the following method. Add 2g of each water-absorbing agent to 98g of deionized water and absorb the water to obtain a water-absorbing gel of each water-absorbing agent.
It was placed in a transparent polyethylene bag of 1.0 mm and exposed to sunlight. The state of the water-absorbing gel during exposure was observed over time, and the results were evaluated using the following five-level criteria. The evaluation results are shown in Table 3.

【table】

[Table] As is clear from Table 3, the water absorbing agent of the present invention has excellent light resistance. Furthermore, since a water-absorbing gel could not be obtained for Comparative Water-Absorbing Agent 3, the light resistance was not evaluated.

Claims (1)

[Claims] 1. General formula (However, R ¹ is hydrogen or a methyl group, n is an integer of 2 or 3, and X is hydrogen, an alkali metal, or an ammonium group.) One type selected from sulfoalkyl (meth)acrylate monomers represented by or 20 to 100 mol% of two or more monomers (A), general formula (However, R ² is hydrogen or methyl group, Y is hydrogen,
Indicates an alkali metal or ammonium group. ) 0 to 80 mol% of one or more monomers selected from the (meth)acrylic acid monomers represented by (B), and other anionic and/or nonionic polymerizable monomers (C) 0 to 50 mol% (however, (A),
The total of components (B) and (C) is 100 mol%. ), a monomer mixture () consisting of a monomer mixture ()
A water-insoluble water-absorbing resin obtained by polymerization in the presence of a crosslinking agent () in a molar ratio of 0.00001 to 0.1 to a salt-resistant and light-resistant water absorbing agent. 2 The total amount of the sulfoalkyl methacrylate monomer in monomer (A) and the methacrylic acid monomer in monomer (B) is 20 mol% or more in the monomer mixture (). Salt resistance according to claim 1, which is
Light-resistant water absorbing agent.