JPS63186712A - Improvement in water-absorptivity of sponge - Google Patents

Abstract

PURPOSE:To obtain a sponge excellent in water retentivity, elasticity and softness, free of a feeling of sliminess and free of releasement of hydrated gel upon squeezing, by impregnating a spongy porous elastomer with a mixture comprising a specified acrylic acid monomer, water, a crosslinking agent and a photopolymerization initiator and irradiating it with ultraviolet rays. CONSTITUTION:An open-cellular spongy porous elastomer (A) such as dried polyvinyl acetal sponge is impregnated with a mixture comprising 1-1,000wt.%, based on component A, acrylic monomer (B) based on (meth)acrylic acid and/or a monomer formed by neutralizing at least 20% of the entire COOH groups into an alkali metal or ammonium salt group, water (C), 0.01-10wt.%, based on component B, crosslinking agent (D) having at least two polymerizable vinyl groups in the molecule (e.g., N,N'-methylenebisacrylamide) and 0.01-10wt.%, photpolymerization initiator (E) (e.g., (4-benzoylbenzyl)trimethylammonium chloride] and irradiated with ultraviolet rays under conditions including an ultraviolet lamp of 40-100W/cm, an irradiation time of 0.5-10min and a distance between the lamp and the object of 5-15cm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] Industrial Application Field The present invention relates to a method for improving the water absorption of a sponge having internal continuous pores, that is, a method for producing a sponge with improved water absorption;
Regarding.

The sponge obtained by the method of the present invention absorbs and retains a large amount of water, does not easily release water even when some pressure is applied, and the super absorbent polymer inside the sponge does not separate. . In addition, because of its soft and elastic texture, it can be advantageously used in various water absorbing agents, cleaning materials, etc.

Conventional technology Sponge-like porous elastic materials have excellent hydrophilicity and good water absorption, and because of their flexibility and elastic texture, they have been used as cleaning materials, water-absorbing materials, cosmetic puffs, handkerchiefs, etc. It has been applied to

However, its water absorption is very high, at most several times its own weight to 10
In order to absorb or retain a large amount of water, a large amount of material is required, which results in an extremely bulky structure. In addition, there was a drawback that if an elastic body that had absorbed water was pressurized even slightly, the water would be easily released.

As a method for improving the water absorbency and water retention after water absorption of such porous elastic materials, a method has been proposed in which highly water-absorbent resin powder is added to the inside of the porous material (Unexamined Japanese Patent Publication No. However, in this method, the superabsorbent resin powder is simply physically applied to the inside of the porous material, so the porous material after water absorption is not pressurized or squeezed. In some cases, the superabsorbent resin gel on the inside and outside surfaces of the porous body easily separates, making it difficult to reuse.

In addition, when this type of water absorbing material absorbs water, the porous exterior becomes slimy, which is extremely problematic in use.

[Summary of the invention]

Summary The present invention improves the above-mentioned drawbacks by providing a sponge-like porous elastic body and a superabsorbent polymer that have high water absorption properties and a large water absorption and retention ability, and in which the gel of the superabsorbent polymer that absorbs water does not easily separate. The present invention aims to provide a method for producing a water-absorbing sponge comprising:

As a result of various studies to solve the above-mentioned problems, the present inventors made a sponge with a continuous network porous structure, mixed with acrylic acid monomer, water, and two polymerizable vinyl groups per molecule. The sponge is impregnated with a mixed solution consisting of a cross-linking agent and a photopolymerization initiator, and then irradiated with ultraviolet rays to convert the acrylic acid monomer into a highly water-absorbing polymer in the sponge. The present invention was completed based on the discovery that the gel of a superabsorbent polymer that absorbs and retains water is extremely difficult to separate.

That is, the method for improving the water absorbency of a sponge according to the present invention includes adding an acrylic acid monomer containing acrylic acid and/or methacrylic acid and/or an alkali metal salt or ammonium salt thereof as a main component to a continuous sponge-like porous elastic body; water,
A mixed solution consisting of a crosslinking agent and a photopolymerization initiator having two or more polymerizable vinyl groups in one molecule is impregnated, and then ultraviolet rays are irradiated to convert the acrylic acid monomer into a super absorbent polymer. It is characterized by the ability to convert

Effects According to the method of the present invention, the above-mentioned problems are solved because the superabsorbent resin derived from the acrylic acid monomer is basically chemically bonded to the sponge.

That is, the sponge obtained by the method of the present invention is
As is clear from Example 3 below, the water absorption and retention power is large,
In addition, the porous exterior does not feel slimy when water is absorbed, and the water-absorbing gel does not separate from the sponge even when squeezed. Also, because of its soft and elastic texture, it can be advantageously used in various water absorbing agents, cleaning materials, etc.

[Detailed description of the invention]

Sponge-like poroelastic body The "sponge-like poroelastic body" referred to in the present invention is not limited to any particular material.

The sponge-like porous elastic body targeted by the present invention usually has a continuous network-like porous structure.

That is, the sponge-like porous elastic material used in the present invention is a polymer foam such as polyvinyl acetal sponge, rubber sponge, polyethylene foam, polypropylene foam, urethane foam, etc., and has a continuous network porous structure. It is. Among these, polyvinyl acecool sponge is particularly preferred in the present invention. Polyvinyl acetal sponge has free OH groups in its molecules and forms a complete three-dimensional dendritic network continuous structure, and can be prepared by any convenient method, such as dissolving polyvinyl alcohol in water. A suitable pore forming agent is added to the aqueous solution, and an aldehyde such as formaldehyde, formaldehyde, etc. is added to the solution in the presence of a mineral acid catalyst.
It can be easily obtained by reacting. Specific examples of this are already under construction with product names such as Surapex and Plus Chamois (all manufactured by Kanebo Co., Ltd.).

The monomers used in the present invention, such as acrylic acid monomers, are acrylic acid and/or methacrylic acid, and 20% or more, preferably 50% or more of the total carboxyl groups thereof are neutralized with an alkali metal salt or an ammonium salt. The main component is If the degree of neutralization becomes too low, the amount of water absorbed will drop significantly and the strength of the resulting water-absorbing gel will also be extremely low.

Alkali metal hydroxides, bicarbonates, etc. can be used to neutralize acid monomers to alkali metal salts, but alkali metal hydroxides are preferred, and specific examples include water. Examples include sodium oxide, potassium hydroxide, and lithium hydroxide. Sodium hydroxide is most preferred in terms of industrial availability, price, and safety.

In the present invention, as monomers other than the above, (a) itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acryloylpropanesulfonic acid and salts thereof. , (b) alkyl or alkoxy esters of dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid, (c) acrylato, (d) vinylsulfonic acid, (v) acrylic acid methyl ester, acrylic acid ethyl ester, etc. (f) (meth)acrylic acid hydroxyethyl ester, (meth)acrylic acid hydroxypropyl ester, (g) polyethylene glycol mono (meth)
It is also possible to use copolymerizable monomers such as acrylate, N-methylol (meth)acrylamide, glycidyl (meth)acrylate, and the like. Here, "(meth)acrylic acid" or "F(meth)acrylate" means acrylic acid and methacrylic acid or acrylate and methacrylate.

Further, the crosslinking agent used in the present invention may be any crosslinking agent as long as it has two or more polymerizable vinyl groups in one molecule. Water-soluble ones are generally preferred. Specific examples include N,N'-methylenebisacrylamide,
Examples include polyethylene glycol di(meth)acrylate, glycerin tri(meth)acrylate, diallyl phthalate, and diallyl maleate.

The amount of these crosslinking agents used is 0.01 to 10% by weight, preferably 0.1 to 1.0% by weight, based on the acrylic acid monomer.

The photopolymerization initiators used in the present invention include (a) benzoin alkyl ethers such as benzyl, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; (b) diacetyl, benzophenone, acetophenone, benzoin silyl ether, (4-
carbonyl compounds such as benzoylbenzyl) trimethylammonium chloride, (c) peroxides such as di-t-butyl peroxide, (d) azoisobutyronitrile,
Azo compounds such as azodibenzoyl and azo-2,4-dimethyl-4-methoxyvaleronitrile; (e) sulfur compounds such as dibenzothiazolyl sulfide and decylphenyl sulfide; and (f) other halogens such as carbon tetrabromide. Examples include chemical substances.

Among these, compounds having carbonyl are particularly preferred in the present invention, and among these, (4-benzoylbenzyl)trimethylammonium chloride is particularly effective.

The amount of these photopolymerization initiators added is generally 0.01 to 10% by weight, preferably 0.1 to 2% by weight, and C1% by weight based on the acrylic acid monomer.

In-situ (!n 5 intu) formation of water-absorbing resin The above-described acrylic acid monomer, crosslinking agent, and photopolymerization initiator are applied to the sponge-like porous elastic body as an aqueous solution. As for the application method at this time, the sponge-like porous elastic body can be impregnated using conventionally known methods such as spraying and dipping.

The amount of acrylic acid monomer impregnated at this time is generally 1 to 1000% by weight based on the sponge-like porous elastic body.
, preferably 10 to 100% by weight. If the amount of impregnation is too large, the water absorbency will be excellent, but the texture, such as flexibility and elasticity, will be lacking, and if the amount is too small, the effect of improving water absorption will be reduced.

The acrylic acid monomer, crosslinking agent, water, and photopolymerization initiator applied to the sponge-like porous elastic body are then irradiated with ultraviolet rays or radiation after ultraviolet irradiation (in the present invention, both are referred to as ultraviolet irradiation). , an acrylic acid monomer is polymerized in a sponge-like porous elastic body to convert it into a superabsorbent polymer.

For ultraviolet irradiation, a normal ultraviolet lamp may be used, and the irradiation intensity, irradiation time, etc. will depend on the type of sponge-like porous elastic material,
It varies depending on its thickness, amount of acrylic acid monomer impregnated, etc., but generally the UV lamp is 40 to 100 W/Cm.
, irradiation time 0.5~10 minutes, lamp-irradiated object interval 5~
15cI11.

Experimental Examples Example 1 13.5 g of caustic soda (95% by weight) was placed in a 1500 cc flask, and 324 g of water was added thereto to dissolve it. To this, 30 g of acrylic acid was added dropwise while cooling with water to neutralize it. Next, 0.15 g of N,N'-methylenebisacrylamide and 0.2 g of (4-benzoylbenzyl)trimethylammonium chloride were each taken and dissolved.

Place 10 g of a separately dried polyvinyl acetal sponge (trade name "Vericlen", average pore size 60μ, thickness approximately 1 inch, manufactured by Kanebo Co., Ltd.) in a Petri dish, and pour the contents of the flask onto the sponge to saturate it thoroughly. Ta. Next, the amount of impregnated sponge was adjusted using a centrifuge, and the amount of monomer impregnated was 3 g as a solid content based on the dry sponge.

Next, this was fixed to a glass plate with a clip, and 80W was applied.
/cII+ ultraviolet rays were irradiated for 15 seconds on each of the front and back surfaces of the sponge with a distance between the ultraviolet lamp and the sponge of 8 cm.

Example 2 In Example 1, another polyvinyl acetal sponge (trade name "Vericlen", average pore size 200μ,
Example 1 except that the thickness was about 11 mm and the material was manufactured by Kanebo Co., Ltd.)
It was processed in the same manner.

Example 3 The sponges obtained in Examples 1 and 2 were allowed to sufficiently absorb water in pure water, and the water absorption capacity at that time and the change in water content after water absorption over time were examined by leaving the sponges at room temperature.

Table 1 shows the results together with the blank (sponge only).

In addition, the sponges obtained in Examples 1 and 2 were soaked in pure water to fully absorb water and then squeezed, but the absorbed gel did not come out of the sponge.
The surface of the sponge was also smooth with no "slimy" feel.

Claims (1)

[Claims] 1. An acrylic acid monomer containing acrylic acid and/or methacrylic acid and/or an alkali metal salt or ammonium salt thereof as a main component, water, in one molecule of a continuous sponge-like porous elastic body. impregnated with a mixed solution consisting of a crosslinking agent having two or more polymerizable vinyl groups and a photopolymerization initiator, and then irradiated with ultraviolet rays to convert the acrylic acid monomer into a super absorbent polymer within the sponge. A method for improving the water absorbency of sponges. 2. The method according to claim 1, wherein the sponge-like porous elastic body is a polyvinyl acetal porous elastic body. 3. The acrylic acid monomer according to any one of claims 1 to 2, wherein 20% or more of its total carboxyl groups are neutralized with an alkali metal salt or an ammonium salt. Method. 4. The method according to any one of claims 1 to 3, wherein the photopolymerization initiator is (4-benzoylbenzyl)trimethylammonium chloride.