JPH02138307A - Filmlike highly water-absorbing sheet and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain easily the title sheet consisting of a cured film with excel lent strength and water-absorbing characteristics by casting an aq. soln. of a compsn. with a specified compsn. on a base material, curing it with electron beams and, if necessary, peeling the cured film from the base material. CONSTITUTION:An aq. soln. of a mixed compsn. wherein 3-80 pts.wt. mixture of acrylic acid and an acrylic acid salt at a molar ratio of 90:10-10:90, 97-20 pts.wt. water-soluble polymeric substance selected from pref. PVA, polyethylene oxide, polyacrylic acid (and its salts), polyvinylpyrrolidone and water-soluble cellulose deriv. and water are main components is cast on a base material (e.g. a PET film) and is cured with electron beams to form a film and, if neces sary, the cured film is peeled from the base material.

Description

[Detailed Description of the Invention] The present invention relates to a film-like super absorbent sheet and a method for producing the same.
More specifically, the present invention relates to a super absorbent sheet in the form of a film that has sufficient strength as a film made of substantially only a super absorbent material and has a high water absorbing ability, and a method for producing the same.

Kzhengi ■ As a super absorbent sheet, paper or non-woven fabric is used as the base material.
In addition, a highly water-absorbent material is partially added (44-bonded fibrous sheet, a synthetic resin or rubber mixed with a highly water-absorbent material and formed into a film or sheet shape, or a water-soluble polymer IT). There are membrane-like sheets made of crosslinked materials.

Among the above-mentioned conventional technologies, the latter film-like superabsorbent sheet is generally made into a sheet by mixing a superabsorbent substance with synthetic resin or rubber. It is used as a waterproof material and backing material.
It could not be said that the performance was fully satisfactory. Because the highly water-absorbing material is embedded in non-water-absorbing synthetic resin or rubber, the responsiveness of water lid ifl is low, and it takes a long time to absorb water, making it unsuitable for applications that require instant water release. There have been problems in that the water absorbing ability of the super absorbent material is hindered by the coexisting synthetic resin or rubber, making it impossible to obtain a material with a high water absorbing ability. In addition, there are products in which water-soluble polymeric substances are crosslinked by radiation or chemical methods, but these products also have low water absorption performance and are not satisfactory.

The above-mentioned problems are due to the fact that there was no film-like sheet made only of highly water-absorbing substances, or even if there was, there was only one with inferior performance. As a result of intensive research into a method for manufacturing a film-like water-absorbing sheet that has high strength and high water-absorbing performance, we have developed a mixed water droplet of a mixture of acrylic acid and acrylates and a water-soluble polymer substance. The present invention was completed by discovering that it can be obtained by irradiating with an electron beam.

That is, the present invention provides (a) a molar ratio of 90:1 on the substrate;
3 to 80 parts by weight of a mixture of acrylic acid and acrylate in a ratio of 0 to 10:90 and (1) 97 to 97 parts of a water-soluble polymeric substance.
A film-like super water-absorbent product characterized in that after casting a water III solution of a mixed composition containing 20 parts by weight and water as main components and curing with an electron beam, the substrate is peeled off from the cured film if necessary. The present invention provides a sheet manufacturing method and a film-like superabsorbent sheet produced by such a manufacturing method.

First, the film-like superabsorbent sheet of the present invention can be used with the base material attached or as a single film with the base material removed, so it can be used as a flexible base material. Porous or non-porous materials can be used as long as they are flexible and can be rolled up. However, in the case of porous materials, depending on the viscosity of the aqueous composition iα, it is not desirable to have a density that is so low that the composition will penetrate into the interior of the base material and will not form a film. What should be used is film,
Paper, woven fabrics, non-woven fabrics, etc.

Next, we will discuss the mixed composition used for film formation.The aims of the film-like superabsorbent sheet of the present invention are (1) to have sufficient strength to be used as a film alone, and (2) to be able to be used when immersed in water. The objective is to obtain a film-like sheet with a water absorption capacity sufficient to swell up to hundreds of times its original size, and for this purpose, it is essential to cure a mixed composition meeting the following conditions with an electron beam. I found that it is acceptable.

(1) As one component, the molar ratio is 90:10 to 10:
A mixture of acrylic acid and acrylate salts having a concentration of 90% is used. Here, acrylates are in the form of salts of metals such as sodium, lithium, potassium, calcium, and magnesium, especially sodium,
Salts of alkali metals such as lithium and potassium are preferable.

(2) It! ! A water-soluble polymer substance is used as a component. Here, water-soluble polymer substances may be water-soluble polymer substances, either natural or synthetic, but in particular polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyacrylates, polyvinylpyrrolidone,
Water-soluble cellulose derivatives alone or in combination are desirable.

(3) The mixing ratio of the mixture of acrylic acid and acrylic acid salts and the water-soluble polymer substance is 3 to 80:97 to 20 by weight.

(4) The mixed composition shall be used in the form of an aqueous solution. The concentration of the aqueous solution is not particularly limited, but it is necessary that the solution is uniform, and the concentration is preferably 10% or more.

The above are the essential conditions for the mixed composition of the present invention,
Even if one of them is missing, the desired film-like super absorbent sheet cannot be obtained.

First, regarding the mixing ratio of acrylic acid and acrylate, these components are used to increase the water absorption capacity of the sheet, but when acrylic acid is less than 10 mol%, the reactivity decreases and Under the electron beam reaction conditions, only water-soluble polymers were obtained; on the other hand, acrylic acid was 90 mol%
If it becomes E, only a product with poor water absorption performance can be obtained.

Water-soluble polymeric substances are essential for maintaining sufficient strength in the film. However, it is also possible to crosslink only water-soluble polymeric substances to make water-absorbing substances, but in this case, the water-absorbing capacity can only be increased by several tens of times at most. To obtain a sheet, it is necessary to use acrylic acid in combination with an acrylate mixture in the above ratio. If the mixing ratio of acrylic acid, acrylate mixture and water-soluble polymer substance is less than 3:97, a film with low water absorption capacity will be obtained, and if it is greater than 80:20, a film with sufficient strength will be obtained. I won't be able to do it.

Although these mixed compositions are used in the form of water mtα, using them as a uniform aqueous solution is one of the important requirements for obtaining a film-like sheet, which is the object of the present invention. Here, homogeneous means that it is transparent or nearly transparent as an aqueous solution, and a homogeneous solution is necessary to obtain a film with sufficient strength. The water in aiα has the effect of promoting the reaction caused by electron beam irradiation, and if there is no water in the mixed composition, the normal electron y
Under pre-irradiation conditions A, the curing reaction does not occur sufficiently. Although the concentration of the mixed composition aqueous solution is not particularly limited, it is preferably 10% or more in terms of reactivity and film-forming properties.

Composition mixed water? Regarding the method for preparing liquid a, any method that falls within the above range may be used, for example, acrylic acid,
The acrylate mixture may be prepared by simply mixing the two, or by adding an alkaline aqueous solution (for example, an aqueous solution of sodium hydroxide) to acrylic acid to partially neutralize it. In addition, the water-soluble polymer substance can be mixed by preparing a water-soluble polymer substance in advance and mixing this, or by directly mixing the water-soluble polymer substance with an aqueous solution of acrylic acid or acrylate. You can leave out the one that dissolves.

It is also possible to add small amounts of monomers to the mixed composition in order to control the reaction. Any monomer can be used as long as it mixes with the mixed composition, but
Particularly preferred are water-soluble bifunctional monomers such as polyethylene glycol diacrylate, N,N-methylenebisacrylamide, and the like. The amount added is based on the mixed composition.
It is generally used in an amount of about 0.01% to 5%. Of course, such monomers do not necessarily need to be added, and the desired sheet can be obtained even without addition as long as other conditions are appropriately set.

It is also possible to add colorants and organic or inorganic fillers to the mixed composition, and thickeners, surfactants, etc. can also be added for the purpose of improving the coating properties of the composition. I can do it.

Next, an aqueous solution of the composition is applied to the substrate, and a method generally called coating is used. Any method such as knife coating, roll coating, or gravure coating is possible.

Next, the curing reaction of the composition will be described. Conventional chemical reactions using catalysts do not work in order to polymerize monomers on a substrate, cause cross-linking of polymeric substances, and harden them into a uniform, water-wettable film. However, the desired reaction cannot be obtained even by reaction with ultraviolet rays, and it can only be achieved by reaction with electron beam irradiation as in the present invention. According to electron beam irradiation, the reaction is easy to control because it does not generate heat during the reaction, and the so-called polymerization reaction and crosslinking reaction (crosslinking reaction of both monoton polymers and polymer substances) are well balanced. This is thought to be due to the fact that the irradiation conditions are not particularly limited, but
Generally, the irradiation voltage is 100 to 2000+ (V, absorption line f1
1-20 M r a d, preferably irradiation voltage 15
Irradiation may be performed at an absorbed dose of 2 to 10 Mrad. The irradiation atmosphere may be in the air or in an inert gas such as nitrogen gas.

Using the method and conditions described in detail above, a film-like water-absorbent sheet can be obtained that is several tens to hundreds of times more absorbent.However, in order to obtain a sheet with arbitrary water-absorbing ability, it is especially important to (1) use water-soluble polymers. (2) Ratio of acrylic acid and acrylate, (3) Ratio of acrylic acid, acrylate and water-soluble polymeric substance, (4) Addition amount of reaction accelerating monomer, ( 5)
By specifically setting the concentration of the aqueous solution of the n-containing composition, (6) the electron beam irradiation conditions, etc., it is possible to make different types of products.

155 Presentation The film-like superabsorbent sheet of the present invention has sufficient strength for use as a film and has a water absorption capacity tens to hundreds of times higher, which has never been seen before. It is a super absorbent sheet. Roughly speaking, the method of the present invention is a manufacturing method with excellent controllability that enables stable production of products with desired performance in such a high water absorption capacity.

X treatment The present invention will be explained in more detail with reference to Examples below.

Example 1゜(1) Adjustment of aqueous mixed composition if 142 g of a sodium hydroxide aqueous solution containing 32 g of sodium hydroxide was added dropwise to 72 g of acrylic acid while cooling and stirring. (In this product, the mixing ratio of acrylic acid and sodium acrylate was 20:80 in molar ratio, and the concentration was 42%.
It is water i8 liquid. ) To 10 g of this solution α, 189 g of a 20% aqueous solution of polyethylene oxide (PE0-1 manufactured by Tetsuko Kagaku) was added, and 0% of polyethylene glycol diacrylate with a molecular weight of 600 was added as a monomer for reaction acceleration.
．． 084 g was added to make the mixed composition water-soluble 1α. (In this product, the ratio of acrylic acid, acrylate mixture, and polyethylene oxide is 1O:90 by weight, and the amount of polyethylene glycol diacrylate added is 0.2 parts by weight per 100 parts by weight of both. can be,
The concentration of the mixed composition aqueous solution is 21.1%. ) (2) Application of the mixed composition aqueous solution onto the base material As the base material, a PET film with a thickness of 0.1 mm (Lumirror T-
100), and the aqueous solution of the mixed composition prepared above was applied thereon to a thickness of 0.15 ntm using a knife coater.

(3) Curing by electron beam irradiation After applying the mixed composition aqueous solution to the substrate, it was immediately cured by irradiating with an electron beam under the following conditions.

8.:4Q4 Voltage: 250 KV Absorption line m: 10 Mrad Atmosphere: In dinitrogen gas (4) Post-treatment After drying at 80°C for 30 minutes, the PET film was peeled off to obtain a film-like superabsorbent sheet.

This material had sufficient strength as a film and also had about 200 times the water absorption capacity when immersed in water.

Comparative example 1゜Example 1. 2-Hydroxy-2-methyl-1-phenylpropan-1-one (manufactured by Merck & Co., Ltd., Darocure 1173) 3 as a photoinitiator was added to 100 parts by weight of an aqueous mixed composition solution of
The same base material as in Example 1 was used to add the added part,
Example 1. The coating was applied in the same manner as above, and UV-? The film was cured by three irradiations. The film thus obtained was mostly soluble in water and was unsuitable as a film-like highly water-resistant sheet.

Example 2゜(1) Preparation of mixed composition aqueous solution Example 1. Add polyvinyl alcohol (Clari I PV) to 10 g of the same acrylic acid and sodium acrylate aqueous solution.
399 g of a 20% aqueous solution of A217) and 1600 molecules
1.68 g of polyethylene glycol diacrylate) was added to prepare a mixed composition aqueous solution. (In this product, the ratio of polyvinyl alcohol to the acrylic acid and acrylate mixture is 5=95 by weight, and the amount of polyethylene glycol diacrylate added is 2 parts by weight per 100 parts by weight of both, and the mixed composition The concentration of the aqueous solution is 2
It is 0.5%. ) (2) Application of the mixed composition aqueous solution to the base material A nylon nonwoven fabric with a basis weight of 50 g/m2 (previously rolled to smooth the surface) was used as the base material, and the mixed composition prepared above was applied to the base material. Coat the aqueous solution with a knife coater to 0.1 m
It was applied to a thickness of m.

(3) Curing by electron beam irradiation After applying the aqueous solution of the mixed composition to the group, it was immediately cured by irradiation with an electron beam under the following conditions.

Irradiation voltage: 200 + (V) Absorption line e: 10 Mrad Atmosphere: (4) Post-treatment After drying at tio'c +2, a film-like superabsorbent sheet with a base material attached was obtained.

This material had sufficient strength as a film and also had about 50 times the water absorption capacity when immersed in water.

Example 3゜(1) Preparation of mixed composition aqueous solution To 100 g of the same acrylic acid and sodium acrylate water tWtn as in Example 1, 90 g of a 20% aqueous solution of polyethylene oxide (PE0-1 manufactured by Tetsusei Kagaku) was added to prepare a mixed composition. 18 liquids of water were used. (This product has a ratio of polyethylene oxide to acrylic acid and acrylate.
@The quantity ratio is 70:30. ) (2) Application of the mixed composition water-soluble iα to the substrate As a substrate,
Thickness O,! mm PET film (Lumirror T made by Toshi)
-100), and the above-prepared mixed composition water-soluble Tα was applied thereon to a thickness of 0.2 mm using a knife coater.

(3) Electron beam p,? Curing by radiation After coating the mixed composition aqueous solution on the substrate, it was immediately cured by irradiation with an electron beam under the following conditions.

Irradiation voltage: 250 KV Absorption line flu: 10 Mrad Atmosphere: Nitrogen gas (4) Post-treatment After drying at 806C for 30 minutes, l) ET film was peeled off to obtain a film-like super absorbent sheet.

This material had sufficient strength as a film and had a water absorption capacity of about 2501 g when immersed in water.

Claims (3)

[Claims] (1) (a) 3 to 80 parts by weight of a mixture of acrylic acid and acrylate in a molar ratio of 90:10 to 10:90;
b) A film-like superabsorbent sheet comprising a film cured by electron beam of an aqueous solution of a mixed composition whose main components are 97 to 20 parts by weight of a water-soluble polymeric substance and water. (2) Claims characterized in that the water-soluble polymeric substance is selected from polyvinyl alcohol, polyethylene oxide, polyacrylic acid, polyacrylates, polyvinylpyrrolidone, and water-soluble cellulose derivatives (
1) Film-like super absorbent sheet. (3) On the base material (a) molar ratio of 90:10 to 10:90
An aqueous mixed composition solution containing 3 to 80 parts by weight of a mixture of acrylic acid and acrylate, 97 to 20 parts by weight of (b) a water-soluble polymeric substance, and water as main components was cast and cured with an electron beam. After that, if necessary, the cured film is peeled off from the base material.