JPH1081714A - Water absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject resin, comprising a specific copolymer, capable of sufficiently absorbing an alkaline aqueous solution and excellent in tackiness of a powder when absorbing moisture and useful for paper diapers, etc. SOLUTION: This water absorbing resin comprises a copolymer prepared by copolymerizing a carboxylic acid having vinyl group (e.g. acrylic acid) or a sulfonic acid (e.g. vinylsulfonic acid) with a carboxylate or a sulfonate having the vinyl group (e.g. sodium as a salt) at (6-4):(4-6) molar ratio of the carboxylic acid or sulfonic acid to the carboxylate or sulfonate, preferably in the presence of an unpolymerizable salt, especially an alkali metallic salt (e.g. sodium chloride). Furthermore, the inorganic salt is preferably added in an amount of, e.g. about 5-5,000ppm based on the total weight of the vinyl monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbent resin which is excellent in absorbability of an alkaline, especially strongly alkaline aqueous solution, and has good adhesion when absorbing moisture. It can be used as a water absorbent or freshness preserving sheet for disposable diapers and sanitary products, and is also effective in the construction field such as cement admixture, the civil engineering field such as tunnel construction, the agricultural field in alkaline soil, etc., especially for alkaline batteries. What is used. Further, the water-absorbent resin of the present invention can be effectively used as a building material for a general visible part such as a humidity regulator and an anti-condensation agent, since the used water-absorbent resin powder does not fall off. . Therefore, the present invention relates to a technology for producing a water-absorbent resin, and more broadly to a technology for producing a chemical product, and also relates to a technology for producing the above-mentioned various products utilizing a water-absorbent resin.

[0002]

2. Description of the Related Art A water-absorbent resin that absorbs water several hundred times its own weight has been mainly used as an absorbent for sanitary materials such as disposable diapers and sanitary napkins. Furthermore, attention has been paid to selective absorption and the like, and the use thereof is expanding to cold insulation materials, artificial snow, agricultural water retention agents, industrial dehydrating agents, and the like. As raw materials for these water-absorbing resins, crosslinked products of carboxymethylcellulose, partially crosslinked products of polyoxyethylene, hydrolysates of starch acrylonitrile graft copolymer, partially crosslinked products of polyacrylate, and the like are used.

[0003]

Among the water-absorbing resins composed of various materials, the water-absorbing resin composed of a partially crosslinked polyacrylate represented by sodium polyacrylate is:
It is excellent in water absorbency and water retention, and exhibits excellent absorption capacity when the water to be absorbed is in a weakly acidic region such as a pH 5 to 9 and a weakly alkaline region.
An aqueous solution in the medium to strong alkaline region of 9 or more has its absorption ability remarkably impaired or cannot be absorbed at all, and its use range has been limited. In addition, when used in disposable diapers, water-absorbent resin is spread over pulp or the like and used as a sheet-like water retention material. Could not be demonstrated. The present inventors have solved the above problems,
The intent was to provide an excellent water-absorbing resin.

[0004]

Means for Solving the Problems The present inventors have found that a polymer obtained by polymerizing a carboxylic acid or a sulfonic acid and a salt thereof at a molar ratio of acid to salt of about 1/1 is an acid and a salt thereof. The alternating copolymer of salts has hemi-bonds, and the water-absorbing resin composed of the copolymer sufficiently absorbs an alkaline aqueous solution having a pH of 9 or more, and has excellent adhesiveness of powder during moisture absorption. Thus, the present invention was completed. That is, the present invention comprises a polymer obtained by copolymerizing a carboxylic acid or a sulfonic acid having a vinyl group and a carboxylate or a sulfonic acid salt having a vinyl group in a molar ratio of 6 to 4: 4 to 6. The present invention relates to a water-absorbent resin characterized by the following.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION As the carboxylic acid having a vinyl group used in the present invention, acrylic acid, methacrylic acid,
Maleic acid, itaconic acid, and the like.Examples of the sulfonic acid having a vinyl group include vinyl sulfonic acid, acrylic sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, and 2-sulfonic acid.
Acrylamide-2-methylpropanesulfonic acid and the like. It is preferable to use acrylic acid or an acrylic acid derivative among such vinyl monomers. These carboxylic acids and sulfonic acids having a vinyl group may be used alone or in combination of two or more. The carboxylate or sulfonic acid salt having a vinyl group is a salt of the above carboxylic acid or sulfonic acid, and as the salt, an alkaline earth metal salt such as a magnesium salt or a calcium salt is also used. Is an alkali metal salt, particularly preferably a sodium salt or a potassium salt. Regarding the combined ratio of the carboxylic acid or sulfonic acid having a vinyl group and the carboxylate or sulfonic acid salt having a vinyl group, those in which both are copolymerized at a molar ratio of 1/1 exhibit the most excellent properties. However, in order to achieve the object of the present invention, the molar ratio may be copolymerized at a ratio of 6 to 4: 4 to 6, or conversely, a nonionic vinyl monomer or the like described later. And at least 60 mol% of the copolymer is an alternating copolymer of a carboxylic acid or a sulfonic acid having a vinyl group and a carboxylate or a sulfonic acid salt having a vinyl group. More preferably, a carboxylic acid or a sulfonic acid having a vinyl group and a carboxylate or a sulfonic acid salt having a vinyl group have a molar ratio of 1: 0.9 to 1.
10, particularly preferably a molar ratio of 1: 0.95 to 1.05.

In order to make a polymer obtained by copolymerizing a carboxylic acid or a sulfonic acid having a vinyl group and a carboxylate or a sulfonic acid salt having a vinyl group into an excellent water-absorbing resin, the polymer must have a crosslinked structure. It is necessary to introduce post-crosslinking after polymerization as a means for this. However, a simple and preferable method is to use a cross-linking agent in combination with the above-mentioned vinyl monomer (a vinyl group-containing polymerizable Is a compound having one or more polymerizable double bonds and is preferably copolymerizable. Specific examples of the compound include, for example, N,
N-methylenebisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, allyl glycidyl ether, trimethylolpropane diallyl ether, pentaerythritol triallyl ether, pentaerythritol diacrylate monostearate, bisphenol diacrylate, isocyanuric acid diacrylate, tetra Allyloxyethane, diallyloxy acetate and the like can be mentioned. Among these crosslinking agents, preferred are stable crosslinking agents having an ether bond in the molecule. It is preferable to avoid using a cross-linking agent having an ester bond because it is easily hydrolyzed and may impair the properties of the resulting water-absorbent resin. These cross-linking agents can be used alone, or two or more of them can be used in combination as needed.A cross-linking agent having a group that reacts with a carboxyl group or a sulfone group in the molecule can also be used in combination. It is possible. The amount of the copolymerizable crosslinking agent is preferably 0.005 to 5%, more preferably 0.01 to 5%, based on the total weight of the vinyl monomer, in order to obtain an excellent water-absorbing resin. The combined amount of 2%. The preferred amount of the cross-linking agent varies depending on the type of the cross-linking agent.
If it is less than 05%, the strength of the water-absorbent resin obtained by polymerization is insufficient after water absorption, and the gel that has absorbed the water cannot easily maintain its shape and tends to be in a sol form. Is high, but it is difficult to obtain sufficient water absorption capacity.

In the present invention, a nonionic vinyl monomer can be used in combination with the carboxylic acid and sulfonic acid having a vinyl group and a copolymerizable crosslinking agent thereof, if necessary. . Examples of the nonionic vinyl monomer include acrylamide, methacrylamide, vinylpyrrolidone, hydroxyethyl acrylate, hydroxyethyl methacrylate and the like. The amount used when these nonionic vinyl monomers are used in combination is 40 mol% or less of the total vinyl monomers,
Preferably it is 20 mol% or less. When a nonionic vinyl monomer exceeding 40 mol% is used, the hemi-bonded portion in the copolymer obtained as described above becomes 60% or less, and a sufficient alkali aqueous solution absorbing ability and a sufficient hygroscopic adhesiveness can be obtained. Disappears.

[0008] The hemi-bond means that, for example, sodium acrylate and acrylic acid are alternately copolymerized to form -C
It is a gradual electrical bond that occurs between OOH and -COONa, and the formation of hemi-bonds enhances the strength of the resin aimed at by the present invention and prevents degradation of polymer chains. It seems to be. As means for introducing the hemi-bond into the polymer to achieve the above-mentioned purpose, a carboxylic acid or a sulfonic acid having a vinyl group, which is adjusted so that the degree of neutralization becomes 0.4 to 0.6, is prepared in advance. Set aside and polymerize. Alternatively, a method is considered in which after the polymerization of the carboxylic acid or sulfonic acid having a degree of neutralization of 0.4 to 0.6 progresses to some extent, a carboxylic acid or sulfonic acid having a different degree of neutralization is added to continue the polymerization. .

In order to promote alternate copolymerization efficiently,
Adding a small amount of salt to the polymerization system is a useful means.
As the salt added to the polymerization system, an inorganic alkali metal salt is preferable. Specific compounds include, for example, sodium chloride, potassium chloride, sodium nitrate, potassium nitrate,
Examples include sodium sulfate, potassium sulfate, and sodium phosphate. The addition amount of these inorganic salts is preferably from 5 to 5,000 ppm, more preferably from 10 to 1,000 ppm, based on the total weight of the vinyl monomer. 5ppm
If it is less than 5,000 ppm, it is not enough to give an electrical condition in an aqueous solution for developing alternating copolymerizability causing hemi-bonding, and if it exceeds 5,000 ppm, the water-absorbing resin obtained by polymerization Not only adversely affects the water absorption capacity of the polymer but also delays the polymerization and significantly increases unpolymerized products.

[0010] The polymerization means used in the present invention may be any polymerization method as a conventional method for producing a water-absorbent resin, such as an aqueous solution polymerization method, a gel polymerization method, and a reverse phase suspension polymerization method. As the polymerization initiating means, various methods such as redox-initiated polymerization, electron-beam-initiated polymerization, photo-initiated polymerization of ultraviolet light or the like, and thermal-initiated polymerization can be considered.

[0011]

The present invention will be described in more detail with reference to the following examples. Example 1 101 parts by weight of acrylic acid, sodium acrylate 199
Parts by weight, 0.15 parts by weight of tetraallyloxyethane, 0.03 parts by weight of sodium chloride and 700 parts by weight of water.
After degassing with nitrogen at 0.1 ° C., 0.15 part by weight of ammonium persulfate and 0.015 part by weight of sodium L-ascorbate were added, and left to stand for 1 hour to carry out copolymerization to obtain a gel-like copolymer.
This gel was cut into pieces, dried in a dryer at 130 ° C., and then pulverized to obtain a water-absorbent resin. Example 2 120 parts by weight of acrylic acid, 154 of sodium acrylate
Parts by weight, 26 parts by weight of acrylamide, 0.15 parts by weight of tetraallyloxyethane, 0.15 parts by weight of sodium nitrate and 700 parts by weight of water were degassed with nitrogen at 20 ° C., and then 0.3 parts by weight of sodium persulfate, L -0.015 parts by weight of sodium ascorbate was added, and the following procedure was carried out in the same manner as in Example 1 to obtain a water-absorbing resin. Example 3 2-acrylamido-2-methylpropanesulfonic acid 143
Parts by weight, 157 parts by weight of sodium 2-acrylamido-2-methylpropanesulfonate, 0.23 parts by weight of pentaerythritol diacrylate monostearate, 0.06 parts by weight of potassium chloride and 700 parts by weight of nitrogen at 15 ° C. After that, 0.15 parts by weight of ammonium persulfate and 0.015 parts by weight of sodium L-ascorbate were added, and a water-absorbent resin was obtained in the same manner as in Example 1 below. Example 4 54 parts by weight of acrylic acid, 116 parts by weight of sodium acrylate, 100 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 0.11 part by weight of pentaerythritol triallyl ether, 0.014 part by weight of sodium chloride and water After degassing 730 parts by weight of nitrogen at 20 ° C., 0.14 parts by weight of ammonium persulfate and 0.014 parts by weight of sodium L-ascorbate were added, and a water-absorbent resin was obtained in the same manner as in Example 1 below. . Example 5 124 parts by weight of acrylic acid, 156 of sodium acrylate
Parts by weight, 0.28 parts by weight of sodium diallyloxyacetate and 720 parts by weight of water were degassed with nitrogen at 15 ° C., and 0.14 part by weight of ammonium persulfate and 0.014 part by weight of sodium L-ascorbate were added. Was obtained in the same manner as in Example 1. Example 6 31 parts by weight of acrylic acid, 39 parts by weight of sodium acrylate, 0.07 parts by weight of sodium diallyloxyacetate, 0.007 parts by weight of sodium chloride and 130 parts by weight of water were degassed with nitrogen at 15 ° C. 0.002 parts by weight of 2-dimethoxy-1,2-diphenylethan-1-one and 0.014 parts by weight of ammonium persulfate were added, and the mixture was copolymerized by irradiation with ultraviolet rays to obtain a gel-like copolymer. This gel was cut into pieces, dried in a dryer at 130 ° C., and then pulverized to obtain a water-absorbent resin. Example 7 124 parts by weight of acrylic acid, 156 of sodium acrylate
Parts by weight, 0.021 parts by weight of sodium diallyloxyacetate, 0.028 parts by weight of sodium chloride and 720 parts by weight of water were degassed with nitrogen at 15 ° C., and then 0.14 part by weight of ammonium persulfate and 0.1 part by weight of sodium L-ascorbate. 014
A water-absorbing resin was obtained in the same manner as in Example 1 except that the weight part was added. Comparative Example 1 280 parts by weight of sodium acrylate, 0.28 part by weight of sodium diallyloxyacetate and 720 parts by weight of water
After degassing with nitrogen at 5 ° C., 0.14 part by weight of ammonium persulfate and 0.014 part by weight of sodium L-ascorbate were added, and a water-absorbent resin was obtained in the same manner as in Example 1 below. Comparative Example 2 200 parts by weight of acrylic acid, 0.2 parts by weight of N, N-methylenebisacrylamide and 800 parts by weight of water were degassed with nitrogen at 15 ° C., and then 0.1 part by weight of ammonium persulfate and sodium L-ascorbate After adding 0.01 parts by weight, a water-absorbent resin was obtained in the same manner as in Example 1 below. Comparative Example 3 56 parts by weight of acrylic acid, 224 parts by weight of sodium acrylate, 0.28 parts by weight of sodium diallyloxyacetate,
After 0.028 parts by weight of sodium chloride and 720 parts by weight of water were degassed with nitrogen at 15 ° C., ammonium persulfate 0.1 was added.
4 parts by weight and 0.014 parts by weight of sodium L-ascorbate were added to obtain a water-absorbent resin in the same manner as in Example 1 below.

Evaluation method The water-absorbing resins obtained in Examples 1 to 7 and Comparative Examples 1 to 3 were evaluated as follows. 50 pieces of water absorption measuring bag made of Teflon cloth with 200mesh water absorption of alkaline aqueous solution
After being immersed in 0 ml of 40% potassium hydroxide for 30 minutes, it was taken out of the potassium hydroxide solution, suspended on a stand for 15 minutes to remove excess aqueous solution, and then weighed (W ₀ ).
1 g of the water-absorbent resin is put into the water-absorption-measurement bag, and similarly immersed in a potassium hydroxide solution.
(W ₁ ) was measured. Water absorption of alkaline aqueous solution = W ₁ −W ₀ (g / g) Spread 2.00 g of the tacky water-absorbent resin at the time of moisture absorption uniformly on a 20 cm × 20 cm tissue, and place another tissue on the tissue at 30 ° C. R
The sample was allowed to stand in a thermo-hygrostat of 80% H for 30 minutes. The sheet taken out from the thermo-hygrostat was pressurized twice with a 15 kg roller, and then dried with a dryer at 100 ° C. for 1 minute. The adhesiveness of the water-absorbing resin when the two tissues of this sheet were peeled vertically was evaluated as follows. ◎ tissue is torn, but strongly adhered ○ no peeling, peeling △ not have readily peeled × bonded by bonding a weak force, the gel strength absorbent resin 1.00g that floated tissue, 0.9 % Sodium chloride solution 3
0 cc was added, and the state of the gel after standing for 1 hour was observed. The gel strength was evaluated as follows. ◎ The gel is hard and crunchy ○ The gel is a little soft, but it keeps an independent state one by one △ The gel surface is slimy and some strings are drawn × The half sol state The results are shown in Table 1.

[0013]

[Table 1]

[0014]

The water-absorbing resin of the present invention does not dissolve or shrink even in an alkaline solution and exhibits high water-absorbing performance.
For this reason, it is possible to use a water-absorbing resin for the purpose of removing water in an alkaline substance, solidifying an alkaline aqueous solution, and the like in the field of civil engineering and agriculture, particularly in an alkaline battery or the like. In addition, since the adhesiveness is improved by slightly absorbing moisture, the water-absorbent resin powder does not move or fall off when it is made into a sheet or composite, and its application as a building material such as a dew condensation inhibitor and a moisture absorbent is expanded. It is possible.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08F 228/02 C08F 228/02 // (C08F 220/06 228: 02 216: 12) (C08F 220 / 06 220: 56 216: 02)

Claims (3)

[Claims] 1. A polymer obtained by copolymerizing a carboxylic acid or sulfonic acid having a vinyl group and a carboxylate or sulfonic acid salt having a vinyl group in a molar ratio of 6 to 4: 4 to 6 A water absorbent resin characterized by the following. 2. The water-absorbent resin according to claim 1, wherein the copolymerization is carried out in the presence of a non-polymerizable salt. 3. The water-absorbent resin according to claim 2, wherein the non-polymerizable salt is an inorganic alkali metal salt.