JPS6140683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for making an improved salt-resistant water-absorbing material. Materials that absorb water or aqueous liquids to a high degree and retain it are indispensable materials for diapers, sanitary products, and various pads used to treat bodily fluids such as sweat, blood, and urine. It is well known that many fiber materials such as pulp, paper, cotton cloth, absorbent cotton, and chemical fibers are used. In addition, recent attempts have been made to use hydrophilic polymers or water-insoluble hydrophilic polymers as modified products of water-soluble polymers in this type of materials, for example, Japanese Patent Publication No. 49-43395, Japanese Patent Publication No. 47 -No. 17965, Japanese Patent Application Publication No. 1256853, Japanese Patent Application Publication No. 1972
-20987 and JP-A-52-25886, and representative examples thereof include saponified starch-acrylonitrile graft copolymers, cross-linked etherified cellulose, and saponified polyacrylonitrile. Although these new materials have a superior ability to absorb significantly higher amounts of water or aqueous liquids than traditional materials, they may be less effective when absorbing salt-containing aqueous liquids such as sweat, blood, urine, or seawater. The water absorption capacity of these materials usually deteriorates, and these materials are used for the above-mentioned purposes and industrial purposes such as water stop agents, sludge treatment agents, antifogging agents, sponge additives, and paper additives, as well as for agricultural and horticultural purposes. This is an obstacle when using it for cultivation soil, etc. Therefore, there is a long-awaited material that has high water absorption and liquid absorption properties even in the presence of salt. The reason for the poor salt resistance of conventional water-absorbing materials is not entirely clear, but the main reason for their water-absorbing ability is that the ionizable groups of the materials, in the example above, the -COONa groups, act as electrolytes. Based on the knowledge that it has a tendency to absorb water, it is thought that a water-absorbing material with excellent salt resistance can be obtained by introducing a group that is as unaffected by common ions as possible. Therefore, the present inventors have carried out various studies in order to introduce a group with a large degree of dissociation to increase salt resistance and at the same time increase water absorption performance, and have now provided the present invention. That is, (a) a monomer having at least one selected from starch, cellulose, guar gum, or derivatives thereof, and an addition-polymerizable double bond and a carboxyl group or a group that produces a carboxyl group upon hydrolysis; and at least one monomer selected from monomers having an addition-polymerizable double bond and having an amide group or a group that generates an amide group by hydrolysis, if necessary. It is obtained by copolymerizing using an agent and further hydrolyzing if necessary, and the weight ratio of carboxyl group to amide group present in one molecule is 9:1 to 1.
A copolymer having a ratio of 2:8 and (b) 0.3 to 1.2 equivalents of formalin and bisulfite to the amide group present in the copolymer are reacted, and in the salt-resistant water-absorbing material obtained. This is a method for producing an improved salt-resistant water-absorbing material characterized in that sulfonic acid groups are present in an amount of 3% or more. Starch, cellulose, guar gum or derivatives thereof used in the present invention include, for example, raw starch such as corn starch, wheat starch, sweet potato starch, rice starch, tapioca starch, oxidized starch, roasted starch,
Modified starches such as dialdehyde starch, etherified starch, oxyalkylated starch, and cyanoethylated starch; cellulose obtained from wood, leaves, pods, gin bark, and waste paper; ethers such as methylcellulose, ethylcellulose, hydroethylulose, and carboxymethylcellulose; Examples include processed cellulose such as oxidized cellulose and oxidized cellulose, etherified guar such as guar gum, hydroxyethylated guar, and carboxyethylated guar, and oxyalkylated guar. Examples of monomers that have an addition-polymerizable double bond and also have a carboxyl group or a group that produces a carboxyl group upon hydrolysis include (meth)
Carboxyl group-containing monomers such as acrylic acid and maleic anhydride, (meth)acrylic acid sodium salt, (meth)acrylic acid trimethylamine salt,
A monomer having a carboxyl group in the form of a salt such as sodium maleate or methylamine maleate,
Monomers with amide groups such as (meth)acrylamide, N-vinylpyrrolidone, N-methylolated acrylamide, N-methylacrylamide, N,N-dimethylacrylamide, methyl (meth)acrylate, ethyl (meth)acrylate , monomers having an ester bond such as butyl (meth)acrylate, and monomers having a nitrile group such as (meth)acrylonitrile. Examples of the monomer having an addition-polymerizable double bond and also having an amide group or a group that produces an amide group by hydrolysis include the above-mentioned monomers having an amide group and monomers having a nitrile group. It will be done. Examples of the crosslinking agent used in the present invention include di- or tri(meth)acrylic acid esters of polyols such as ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, and polyoxypropylene glycol, and the aforementioned polyols. unsaturated polyesters obtained by reacting with unsaturated acids such as maleic acid, bisacrylamides such as N/N-methylenebisacrylamide, polyepoxides and (meth)
Di- or tri(meth)acrylic acid esters obtained by reacting with acrylic acid, di- or tri(meth)acrylic acid esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethyl diisocyanate with hydroxyethyl (meth)acrylate.
Examples include (meth)acrylic acid carbamyl esters, allylated starch, allylated cellulose, etc., and further crosslinking under certain reaction conditions such as methylolated (meth)acrylamide, glyoxal, phthalic acid, adipic acid, and ethylene glycol. difunctional compounds or polyvalent metal salts such as calcium oxide and zinc diacetate. Next, as formalin and bisulfite,
Examples include 30% formalin aqueous solution, paraformaldehyde, sodium bisulfite, ammonium bisulfite, and the like. In the present invention, the reason why the product obtained by reacting 0.3 to 1.2 equivalents of formalin and bisulfite with respect to the amide groups present in the copolymer is extremely salt resistant is that the amide group easily forms a sulfate group. It is thought that the large ionic dissociation of this group confers salt tolerance. A sulfate base is extremely effective when present in a small amount, but it is ineffective when the amount is less than the equivalent amount as defined in the present invention, and insolubilization becomes difficult when the amount exceeds the equivalent amount. The weight of the carboxyl group here refers to the weight in the form of a completely neutralized salt, and the same applies to the sulfonic acid group. The polymerization method suitable for the production method of the present invention may be any conventionally known method, such as a method of irradiating with radiation, electron beam, ultraviolet light, etc. or ultraviolet visible light in the presence of a sensitizer, ceric salt, Hydrogen peroxide, benzoyl peroxide, azobisisobutyronitrile, azobisisovaleric acid,
Examples include a method of polymerization using a radical polymerization catalyst such as ammonium persulfate. It goes without saying that these polymerization methods include, for example, graft polymerization as a polymerization type. Furthermore, water, methanol, ethanol, acetone, N·N-dimethylformamide, dimethyl sulfoxide, and mixtures thereof can also be used as a polymerization solvent if necessary in the polymerization. Further, in the present invention, the temperature when polymerizing using a catalyst varies depending on the type of catalyst, but is usually 0°C to 180°C, preferably 10°C.
~120℃. In addition, the hydrolysis carried out if necessary in the present invention may be carried out by any conventionally known method, but usually in an aqueous solvent or a mixed solvent of water and alcohol such as sodium hydroxide, potassium hydroxide, etc. The process is carried out at a temperature of 30 to 210°C and optionally under pressure. If free carboxyl groups are present in the resulting copolymer, they can be neutralized to form a salt by a conventionally known method. In addition, in the present invention, when reacting the amide group of the copolymer with formalin and bisulfite, respectively, the copolymer is suspended or dispersed in water, and predetermined amounts of formalin and bisulfite are successively added, Under stirring or standing at room temperature or 100℃
The reaction is carried out under heating up to ℃. The salt-resistant water-absorbing material obtained by the production method of the present invention is
Due to its excellent salt resistance, it absorbs not only sweat, blood, urine, etc., but also water containing seawater, and once absorbed, it retains water for a long time even under pressure. Because of its properties, it exhibits excellent effects when used as an additive in paper diapers, sanitary products, various disposable cloths, paper, etc. It can also be effectively used as a flocculant for sludge near river mouths, a water stopper for civil engineering, etc. Hereinafter, the present invention will be specifically explained with reference to examples, but it is not limited to these examples. Example 1 100 parts of corn starch and 600 parts of water were charged into a reaction vessel, stirred at 60°C for 1 hour, cooled to 20°C, and further added with 140 parts of sodium anuryl acid, 60 parts of acrylamide, and 1 part of methylene bis. Acrylamide and 0.2 parts of 30% hydrogen peroxide solution and 0.1 parts of L-ascorbic acid were added as a polymerization catalyst.
Copolymerization was carried out by stirring at 25° C. for 2 hours in a nitrogen atmosphere. After the reaction was completed, it was dried under reduced pressure at 90°C for 12 hours to obtain a copolymer. Next, 150 parts of the copolymer is finely ground and dispersed in 1500 parts of water. 15 parts of a 30% formalin aqueous solution and 52 parts of a 30% sodium bisulfite aqueous solution are charged one after another and left overnight at room temperature. After standing overnight, centrifugation was performed, and the separated product was dried under reduced pressure at 80°C for 12 hours to obtain a water-absorbing material. This was designated as sample A. Example 2 100 parts of the copolymer obtained in Example-1 was finely ground, dispersed in 1000 parts of water, and successively added with 20 parts of 30% formalin aqueous solution and 67 parts of 30% sodium bisulfite aqueous solution. A salt-resistant water-absorbing material was obtained by preparing and performing the same operations as in Reference Example-1. This was designated as sample B. Example 3 Charge 40 parts of CMC with a DS of 0.7 and add 250 parts of methanol-nitric acid solution (100 parts in 1 l of methanol).
ml of nitric acid) for 18 hours at 25°C. Wash the obtained acidic substance thoroughly with distilled water,
It is then charged into a reactor along with 1000 parts of water. Purge with nitrogen for 30 minutes before removing oxygen from the system. Then charge 10 parts of ammonium cerium nitrate solution [0.1 mole Ce() in 1N nitric acid] and 30 parts of acrylonitrile. The reaction is allowed to proceed for 2 hours at 25°C under nitrogen atmosphere. The resulting grafted cellulose ether was dissolved in an aqueous solution of 16 parts sodium hydroxide in methanol.
It is converted to the alkali metal salt form by treatment at 120°C for 20 hours. Then, the pH was adjusted to 7.5 with sulfuric acid, and the product was washed with methanol and dried at 105°C to obtain 70 parts of copolymer. As a result of this saponification, COONa:
The weight ratio of CONH ₂ (including COONa from CMC) was 8:2. After dispersing this in 500 parts of water, 3.4 parts of 30% formalin aqueous solution and 11.6 parts of 30% sodium bisulfite aqueous solution were successively charged, and the same operation as in Example-1 was performed to obtain a water-absorbing material. . This was designated as sample C. Example 4 50 parts of ginger starch and 500 parts of water were placed in a reactor and stirred for 1 hour at 55°C in a nitrogen atmosphere.
Cool to 15 parts acrylamide, 1.2 parts ammonium persulfate, 0.1 part sodium bisulfite and
When 0.2 part of NN methylenebisacrylamide was added and further stirred at 30°C for 5 hours to copolymerize, a white gel was obtained. PH this with dilute sulfuric acid aqueous solution.
The residue was washed with a large excess of methanol three times, and then dried under reduced pressure at 60°C for 3 hours to obtain a copolymer. After dispersing 100 parts of this copolymer in 800 parts of water, 60 parts of a 30% formalin aqueous solution,
208 parts of a 30% aqueous sodium bisulfite solution was successively charged, reacted at 50°C for 4 hours, filtered, and the residue was dried under reduced pressure at 60°C for 3 hours to obtain a water-absorbing material. This was designated as sample D. Example 5 20 parts of guar gum, 40 parts of water and 300 parts of ethanol were charged into a reactor and heated at 70°C in a nitrogen atmosphere for 1 hour.
After stirring for an hour, cool to 25°C, add 0.5 parts of azobisisobutyronitrile, 20 parts of methyl acrylate and
80 parts of acrylonitrile was charged and copolymerized by stirring at 35°C for 8 hours, resulting in a white gel. Add 40 parts of caustic soda aqueous solution to this and heat to 90℃.
Saponification is carried out by carrying out the reaction for 3 hours,
The pH was adjusted to 8.0 with dilute sulfuric acid. COONa：CONH ₂
The weight ratio was 5:5. 80 parts of 30% formalin aqueous solution in this gel,
260 parts of a 30% aqueous sodium bisulfite solution was charged one after another and heated at 60°C for 3 hours. After that, it was filtered, and the filtered material was washed with methanol and dried under reduced pressure at 60°C to obtain a water-absorbing material. This was designated as sample E. Comparative Example 1 In Example-3, 2.5 parts of 30% formalin aqueous solution was used instead of 3.4 parts of 30% formalin aqueous solution,
8.6 in place of 11.6 parts of 30% aqueous sodium bisulfite solution
A water-absorbing material was obtained in the same manner as in Example 3 except that a 30% aqueous sodium bisulfite solution was used. This was designated as sample F. Comparative Example 2 In Example-4, 15 parts of sodium acrylate was replaced with 9 parts of sodium acrylate, and the rest were the same as Reference Example-
A water-absorbing material was obtained in the same manner as in 4. This was designated as sample G. Effect Examples Examples 1 to 5, Comparative Examples 1 to 2, and various commercially available samples were subjected to water absorption tests and water solubility tests to examine their suitability as salt-resistant water-absorbing materials. The results are shown in Table 1. 【table】

Claims (1)

[Claims] 1 (a) A monomer that uses at least one selected from starch, cellulose, guar gum, or derivatives thereof and a carboxyl group or a group that produces a carboxyl group upon hydrolysis and has an addition-polymerizable double bond. At least one selected from A copolymer having a ratio of 9:1 to 2:8 is reacted with (b) 0.3 to 1.2 equivalents of formalin and bisulfite to the amide group present in the copolymer, and the resulting salt tolerance A method for producing an improved salt-resistant water-absorbing material, characterized in that sulfonic acid groups are present in the water-absorbing material in an amount of 3% or more.