JPH0230522A - water absorbent composite material - Google Patents

Abstract

PURPOSE:To reduce omission of high water absorbing resin at the time of water absorption or water retention, by a method wherein a perforated or holeless thermoplastic resin sheet is laminated to at least a single side of a water absorbing sheet obtained by polymerizing a water-soluble ethylenic unsaturated monomer to a fibrous substrate or a spongy substrate and integrated. CONSTITUTION:A water absorbing high-molecular composite 3 forming a water absorbing sheet is obtained, by a method wherein ethylene unsaturated monomer which is to form a water absorbing polymer 2 is made into an aqueous solution, which is infiltrated into or applied to a fibrous or spongy substrate 1 for polymerization. Concretely, the same is of (meth)acrylic acid or its salt, vinyl sulfonic acid or its salt and especially preferable matter is of the (meth)acrylic acid or its salt. A crosslinking agent or an additive agent is added further to these monomer to improve absorbing capacity. In the case of lamination of thermoplastic resin layers on both the surfaces of the water absorbing sheet, at least one side of them must be a perforated sheet. The perforated resin layer can be made by imparting water vapor permeability to the same by providing very fine communication holes or slits by various methods such as heat sealing and electron ray irradiation.

Description

[Detailed description of the invention] Technical field The present invention relates to a water-absorbing composite material.

More specifically, the present invention relates to a water-absorbing composite material that causes less shedding of the super-absorbent resin, does not change its shape, and is further capable of being heat-fused and vacuum- or pressure-molded.

BACKGROUND ART Superabsorbent resins have been attracting attention for their water absorption and water retention abilities and have been applied to various fields. for example,
Focusing on its water absorption ability, its application fields include the field of dehydrating and drying foods to obtain preserved foods, the field of removing moisture from organic solvents, and it is also used for freezing and preserving fresh foods. ing.

On the other hand, as an example of application when focusing on its water retention capacity,
Examples include fire protection, water-containing sheets for firefighting, seed coating, and cover uses for transporting seedlings.

Various proposals have been made for water-absorbing or water-retaining sheets in which such superabsorbent resins are applied to water-permeable sheets (JP-A-57-103838, JP-A No. 58-104607, JP-A No. 60-2).
32935, 6]-43549, etc.) However, conventional water absorbing and water retaining sheets tend to have the following problems.

That is, powdered superabsorbent resin is spread in a thin layer on a supporting substrate such as paper or nonwoven fabric, and fixed using a glue such as starch syrup, gelatin, calhoquin methyl cellulose, or polyvinyl alcohol, or a solvent. Using a resin soluble in water as a binder, a finely powdered super absorbent resin is coated with the paint, or a layer of tissue paper, etc., with the powdered water absorbent resin sprinkled on top is layered and enhanced. Water-absorbing or water-retaining sheets made of immobilized super-absorbent resins have a problem in that the super-absorbent resin tends to separate from the supporting substrate during handling before water absorption, and furthermore after water absorption.

As one means to solve this problem, attempts have been made to cover the water-absorbing or water-retaining sheet with a heat-sealable water-permeable film or sheet to seal the periphery.

However, such a sheet containing a water-absorbing sheet is produced by fixing a super-absorbent resin onto a supporting substrate such as paper or nonwoven fabric, and wrapping and heat-sealing the water-absorbing sheet with a water-permeable film or sheet. However, it is not suitable for mass production because it has to be worked as a single cut sheet.
As a result, they tend to be expensive. Furthermore, when making a bag using a sheet that contains a water-absorbing sheet without integrating it, it becomes bulky and difficult to bend or glue. must be prepared in advance, and manufacturing is extremely inefficient.

Other water-absorbing and water-retaining sheets include those made by kneading powdered super-absorbent resin with polyethylene, ethylene-vinyl acetate copolymer, polypropylene, rubber, etc., and molding the mixture into a sheet or film shape. However, in many of these superabsorbent resins, the original water absorption speed and water absorption ability are impaired, and when water is absorbed, the dimensions change significantly due to the water absorption expansion of the superabsorbent resin. Eventually, even the shape changed.

[Summary of the invention]

Summary The present invention aims to provide a solution to the above problem,
Instead of using powdered super absorbent resin for water absorption,
This purpose can be achieved by laminating a thermoplastic resin layer on at least one side of a water-absorbing sheet made of a water-absorbing polymer composite obtained by polymerizing a super absorbent resin on a fibrous substrate or a sponge-like substrate. This is what we are trying to achieve.

That is, the water-absorbing composite material according to the present invention has a water-absorbing property obtained by impregnating or coating a fibrous substrate or a sponge-like substrate with a water-soluble ethylenically unsaturated monomer, and then polymerizing the water-soluble ethylenically unsaturated monomer. It is made by laminating and integrating a perforated or non-porous thermoplastic resin sheet on at least one side of a water absorbent sheet made of a polymer composite, and when the thermoplastic resin sheet is laminated on both sides of the water absorbent sheet, at least It is characterized by having holes on one side.

effect The water-absorbing composite material according to the present invention has the following advantages.

■ Because it is made of a water-absorbent sheet or a water-absorbent polymer composite that is produced and fixed directly on a substrate with a superabsorbent resin, the superabsorbent resin does not fall off from the substrate when absorbing or retaining water. Very few. In addition, compared to bulky water-absorbent sheets made by immobilizing super-absorbent resin on paper such as tissue paper by embossing, it can be made extremely thin (for example, about 0.2 mm), making it easy to stack layers by laminating, and Even when bag making and molding processing is performed, the processability is improved.

(2) Since it has a thermoplastic resin layer on at least one side, it can be made into bags or containers by heat fusion with the resin layer as the inner surface, and can also be air-pressure molded.

Therefore, functions for various uses suitable for the aforementioned fields of use can be realized not only as a single sheet but also as a bag, tray, or box. For example, when used for the purpose of absorbing drips from fish meat, etc., the fish meat, etc. can be placed in a bag made of the water-absorbing composite sheet of the present invention to retain tripping during storage or transportation, and to prevent leakage. Work can be streamlined.

■ If a water-impermeable thermoplastic resin layer is adhered to the back side of the water-absorbing sheet, the water absorbed by the water-absorbing sheet will not penetrate further to the back side and will be absorbed into the water-absorbing composite abrasive. The container is retained and thus absorbs condensation.
It is ideal for applications where moisture penetration is not allowed, such as food items, lei, medical supplies, and bed-wetting sheets.

■ By laminating and integrating a thermoplastic resin layer onto a water-absorbing sheet, the strength of the material is significantly improved. In other words, the base of the water-absorbent sheet is made of a porous material such as a fibrous base or a sponge-like base in order to strengthen the bond with the supported superabsorbent resin and increase the water absorption rate. In cases where the strength is insufficient when used alone, such as core wire coating tape, this point can be improved by laminating thermoplastic resin.

■ Since the surface of the water-absorbing sheet has a perforated thermoplastic resin layer, in the case of food packaging, there is no direct contact between the super-absorbent resin and the food, which is preferable from a sanitary standpoint.

■ Since the water-absorbent sort can be handled and processed as a continuous roll sheet, it is ideal for mass production, and it is possible to significantly reduce costs when manufacturing sheets for various uses.

■ Conventional water-absorbing sheets are difficult to print because they use non-woven fabric as the base material, but this water-absorbing composite abrasive material has a thermoplastic resin layer on the surface of the water-absorbing sheet, making it suitable for printing. If you choose a thermoplastic resin with good quality, you can easily express illustrations, text, etc. with bright color printing, and it can be used for disposable diapers,
The value of products aimed at children, such as bed-wetting sheets, can be improved.

[Detailed description of the invention]

1) Water-absorbing sorting A preferred example of the water-absorbing sheet constituting the water-absorbing composite material according to the present invention is one made of a water-absorbing polymer composite. Note that "a material made of a water-absorbing polymer composite" refers to a material that is not only made of a water-absorbing sheet or a polymer composite, but may also contain other materials as long as the effects of the present invention are recognized. It shows good things.

Hereinafter, the present invention will be described in detail with reference to the drawings.

(A) Water-absorbing polymer composite Figure 2 shows a cross section of a water-absorbing polymer composite used as a water-absorbing sheet.

The water-absorbing polymer composite 3 forming a water-absorbing sheet in the water-absorbing composite material according to the present invention is obtained by impregnating or coating a fibrous substrate or a sponge-like substrate with an ethylenically unsaturated monomer to form a water-absorbing polymer as an aqueous solution. , obtained by polymerization.

FIG. 1 is an enlarged conceptual diagram of this water-absorbing polymer composite 3. FIG. As shown in this figure, the water-absorbing polymer 2 is firmly adhered to and held on the fibrous substrate or the sponge-like substrate 1.

(1) Fibrous substrate or sponge-like substrate The fibrous substrate to be impregnated with or coated with the ethylenically unsaturated monomer aqueous solution may be formed by loosely forming fibers, such as a pad, curved ink, or air-laying. Web, tissue paper, woven fabric like cotton gauze,
It is a knitted fabric or a nonwoven fabric obtained by various manufacturing methods such as spunbond, dry method, and wet method. A "formed" fibrous substrate is defined as a web that is already in the form of a web, even though cutting, joining, shaping, etc. may be required to incorporate the fibrous substrate into an article. Forming operations refer to those that do not require further application.

It is generally preferred to use absorbent fibers such as wood pulp, rayon, cotton and other cellulosic fibers and/or polyester fibers as the main component in the fibrous substrate. However, other types of fibers, such as polyethylene, polypropylene, polystyrene, polyamide, etc.
Even if fibers such as polyvinyl alcohol-based, polyvinyl chloride-based, polyvinylidene chloride-based, polyacrylonitrile-based, polyurea-based, polyurethane-based, polyfluoroethylene-based, polycyanized vinylidene-based, etc. are included in a molded fibrous substrate. good.

Furthermore, the spongy substrate used in the present invention is a polymeric foam such as polyvinyl acetal sponge, rubber sponge, polyethylene foam, polypropylene foam, urethane foam, etc., and has a continuous network porous structure. Either is fine as long as it is.

(2) Water-soluble ethylenically unsaturated monomer The water-soluble ethylenically unsaturated monomer to be impregnated or applied to the fibrous substrate or sponge-like substrate should be one that can be converted into a water-absorbing polymer and has good water-absorbing performance after polymerization and drying. Anything is fine as long as it can be given.

Water-soluble monomers that provide such performance include carboxylic acids or (and) salts thereof, phosphoric acids or (and) as functional groups.
and) salts thereof, water-soluble ethylenically unsaturated monomers having groups derived from sulfonic acids or (and) salts thereof. Specific examples include (meth)acrylic acid or a salt thereof, vinylsulfonic acid or a salt thereof, vinylphosphonic acid or a salt thereof, and the like. Among these, (meth)acrylic acid (ie, acrylic acid or methacrylic acid) or a salt thereof is particularly preferred. The resulting polymer may be a homopolymer or copolymer of these monomers, or a craft polymer of starch or cellulose.

Furthermore, it is also possible to add crosslinking agents and additives to these monomers to improve absorption performance. As the crosslinking agent, water-soluble polyfunctional ethylenically unsaturated monomers such as methylene bisacrylamide, ethylene glycol di(meth)acrylate, and polyethylene fluoride di(meth)acrylate, ethylene glycol diglyndyl ether,
Polyglycidyl ethers such as polyethylene glycol diglycidyl ether, polyols such as glycerin and pentaerythritol, and polyamines such as ethylenediamine, which have two or more functional groups that can react with functional groups such as carboxylic acid, phosphoric acid, and sulfonic acid. Water-soluble compounds are preferably used.

In order to apply an aqueous solution consisting of such a monomer to a fibrous substrate or a sponge-like substrate, any suitable means or mode may be used as long as the monomer is uniformly dispersed on the fibrous long body and can be polymerized. It can be done by One typical means for this purpose is to impregnate the fibrous substrate or the like with an aqueous monomer solution or to spray the monomer aqueous solution onto the fibrous substrate or the like.

Note that the monomer aqueous solution may contain a small amount of a water-soluble organic solvent dissolved therein, if desired.

(3) Production of water-absorbing polymer composite The step of polymerizing monomers uniformly dispersed on such a fibrous substrate or sponge-like substrate may be any suitable step. A typical method for such a method is one based on the action of a water-soluble radical polymerization initiator, specifically,
Either the radical polymerization initiator is added to the monomer aqueous solution and then decomposed on the fibrous or sponge-like substrate, or the radical polymerization initiator is prepared as a solution separate from the monomer and the fibers are treated with the monomer aqueous solution. Either the radical polymerization initiator is applied uniformly by spraying or the like onto a fibrous substrate, etc. and decomposed on the fibrous substrate, etc., or the radical polymerization initiator is applied as a solution separate from the monomer to the fibrous substrate, etc., and then the hemotsuma aqueous solution is applied to the fibrous substrate, etc. It is to uniformly apply by spraying, coating, etc. It goes without saying that the "radical polymerization initiator" here includes so-called redox systems, and when the monomer and radical polymerization initiator are present separately in the above, only one of the redox systems is present in the monomer. Needless to say, there are different types. Another means of initiating polymerization is irradiation with high energy radiation.

The water-absorbing polymer composite thus obtained is usually dried by means such as hot air, microwaves, and infrared rays. If unreacted monomers, etc. remain in the composite, it is preferable to wash the composite with water or warm water prior to drying.

2) Perforated thermoplastic resin layer The perforated thermoplastic resin layer in the present invention is a resin that has been conventionally laminated on a base material for the purpose of providing the resulting composite sheet with good thermal adhesion performance and strength retention performance. , namely polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl acetate copolymer, polystyrene, ethylene-α-olefin copolymer,
Ethylene-α, β-unsaturated carboxylic acid copolymers, metal neutralized products thereof, ethylene-α, β-unsaturated carboxylic acid ester copolymers, and thermoplastic elastomers; monomers of mixtures of two or more of these resins; In addition to layered or multilayered films, heat-sealable nonwoven fabrics such as saturated polyester, polyamide, polyolefin, etc. can be used.

Since the composite material according to the present invention is a water-absorbing composite material, when laminating thermoplastic resin layers on both sides of the water-absorbing sheet,
At least one of them must be a perforated sheet. The porous thermoplastic resin layer can be formed by providing moisture permeability by providing fine communication holes, slits, etc. using various methods such as hot rolling or electron beam irradiation.

3) Lamination method When producing the water-absorbing composite material of the present invention, lamination can be carried out by means known per se. For example, a dry lamination method in which a thermoplastic resin is made into a film or nonwoven fabric by inflation, T-die molding, or other methods and a water-absorbing sheet I is made using an adhesive such as a urethane adhesive. , an extrusion lamination method in which a thermoplastic resin is melt-extruded using a water-absorbing sheet as a base material and an anchor coating agent such as an isocyanate-based agent, or the like.

4) Water-absorbing composite material The water-absorbing composite material according to the present invention is composed of a water-absorbing sheet made of a water-absorbing polymer composite and a thermoplastic resin sheet,
At least one side of a water-absorbing sheet is laminated with a thermoplastic resin sheet so as to be integrated, and the whole is water-absorbent.

Here, "composed of a water-absorbing sheet and a thermoplastic resin sheet" refers to a two-layer laminate in which a water-absorbing sheet and a thermoplastic resin sheet are laminated one by one; This indicates that the above-mentioned water-absorbing sheet or thermoplastic resin sort may be further laminated, or a multilayer laminate made of other purpose-built sheets, materials, etc. may be laminated. Examples of other sheets and materials include metals such as aluminum, iron, and copper in the form of foils or plates, paper, cellophane, cloth, nonwoven fabrics, asbestos, and crows in the form of plates or fibers.

Some layer configurations of the water-absorbing composite material according to the present invention, which is formed by laminating such water-absorbing sheets, thermoplastic resin sheets, (and other sheets), etc., are as follows.

■ 2-layer laminate: water-absorbing sheet/thermoplastic resin sheet, ■ 3-layer laminate: thermoplastic resin sheet/water-absorbing sheet/
Thermoplastic resin sheets, other sheets/water absorbent sheets/thermoplastic resin sheets, water absorbent sheets/thermoplastic resin sheets/
Water-absorbing sheet■ 4-layer laminate Other sheets/Plastic resin sheet/Water-absorbing resin sheet/Thermoplastic resin sheet Figure 3 consists of a water-absorbing polymer composite 3, a thermoplastic resin sheet 5, and another sheet 4. 1 shows a cross-section of a four-layer laminate water-absorbing composite material. If this water-absorbing composite material is made into a bag with the thermoplastic resin layer on the inside as shown in Figure 4, it can easily be used as packaging with various functions such as dehydration, freshness preservation, water retention, cold storage, etc. You can easily create bags.

Further, FIG. 5 shows a cross section of a sheet made of a water-absorbing composite material, which is a three-layer laminate consisting of a water-absorbing polymer composite 3, a thermoplastic resin sheet 9, and another sheet 8. FIG. 6 shows this molded into a tray shape. Trays formed in this way are ideal as packaging containers with various functions such as drip absorption, freshness preservation, cold storage, and other functions.

〔Example〕

Example 1 A 70 mol % neutralized aqueous potassium acrylate solution with a solid content of 63% by weight was prepared. In this solution, 0.4% by weight of N-N' methylene bisacrylamide and 0.3% by weight of potassium persulfate were dissolved in potassium acrylate monomer, and then the polyester with a basis weight of 40 g/r& Fiber nonwoven fabric (Maric's 904 manufactured by Unitika Co., Ltd.)
03WSO) This aqueous solution was uniformly impregnated to a thickness of 0.23 mm so that the polymer basis weight was about 50 g/d.

The nonwoven fabric impregnated with this monomer is placed in an oven purged with nitrogen for 1 hour to polymerize and crosslink the monomer, and then dried under reduced pressure at 100°C to form a water absorbent sheet made of a water absorbent polymer composite. Obtained.

This water-absorbing sheet and 0.2mmφ pitch], 4+++
+n perforated polyethylene (PE) 30 μ thick film is bonded with a urethane adhesive layer, and a biaxially stretched polyethylene terephthalate (PET) 12 μ thick film is bonded to the water absorbent sheet surface of this laminate using the same urethane adhesive layer. The materials were laminated together using an adhesive layer to obtain a composite sheet of PET/water-absorbent and perforated PE.

The water-absorbing composite sheet thus obtained is 1.5 cm thick.
Two sheets with a size of 20cm x 20cm were prepared, and the water absorption capacity was measured, and the following results were obtained.

Example 2 A monomer-impregnated sheet was obtained using the same base material and method as in Example 1. This is irradiated with an electron beam at a dose of 10 megarads from an electromagnetic beam device equipped with a dynamidron accelerator to polymerize and crosslink the monomer, and then dried under reduced pressure at 100°C to absorb water made of a water-absorbing polymer composite. I got a sex sheet. This water absorbent sheet was used in the same manner as in Example 1 to obtain a composite sheet of PET/water absorbent/perforated PE. Two water-absorbing composite sheets obtained in this way were prepared in a size of 15 x 20 cm, and their water-absorbing capacity was measured, and the following results were obtained.

]9 In the sheets obtained in Examples 1 and 2, the polymer does not fall off even when folded, the water-absorbing gel does not fall off from the base material even after water absorption, and the sheets can be easily torn and have high strength. I kept it. Further, even when water was absorbed, there was no change in dimensions due to expansion of the water-absorbent sheet layer.

Example 3 The sheet of the water-absorbing composite material obtained in Example 1 was coated with perforated PE.
When a bag was made using a hot bar type heat sealer with the film inside, it was possible to easily obtain a bag with high seal strength. This bag (20X), 55 cm in size, was filled with 50 cc of water colored with ink, sealed, and left to stand.There was no leakage to the outside, and when the bag was cut open after 30 minutes, the colored water was absorbed. It was fixed to the adhesive sheet layer and did not remain on the surface (perforated PE film surface).

[Brief explanation of the drawing]

FIG. 1 is an enlarged conceptual diagram of a water-absorbing sheet made of a water-absorbing polymer composite, and FIG. 2 is a cross-sectional view thereof. FIG. 3 is a sectional view of the water absorbent composite material according to the present invention, and FIG. 4 is a specific example of the material processed into a bag shape. Fifth
The figure is a sectional view of a specific example of the water absorbent composite material according to the present invention, and FIG. 6 shows a specific example of the material processed into a tray shape. DESCRIPTION OF SYMBOLS 1... Fibrous or spongy base, 2... Super water-absorbing resin, 3... Water-absorbing polymer composite, 4, 8... Other sheets, 59... Thermoplastic resin layer, 6... ...Adhesion part by heat seal, 7...Bending part. Applicant's agent - Yu Sato (a) Kozu Ko 2 Fig. 4 Fig. (b) Ko 5 Fig.

Claims (1)

[Claims] At least a water-absorbing sheet made of a water-absorbing polymer composite obtained by impregnating or coating a fibrous substrate or a sponge-like substrate with a water-soluble ethylenically unsaturated monomer and then polymerizing the water-soluble ethylenically unsaturated monomer. It is made by laminating and integrating a perforated or non-porous thermoplastic resin sheet on one side, and when the thermoplastic resin sheet is laminated on both sides of the water absorbent sheet, at least one of the sheets is perforated. , water absorbent composite material.