JPS63295251A - Dehydrating or water retentive sheet - Google Patents

Abstract

PURPOSE:To fix a water absorbing polymer to a dehydrating or water retentive sheet securely by providing a high water absorbing high-molecular composite material constituted of a high water absorbing polymer adhered to a fiber base or a sponge-like base between two sheets, at least one of which is water- permeable, which can be heat sealed. CONSTITUTION:As a water-permeable sheet, for instance, a sufficiently fine mesh non-woven cloth constituted of thermoplastic materials or any other water absorbing materials which can be heat sealed and are constituted of thermoplastic sheet prepared as non-water-permeable in one stage and provided with fine through holes prepared by means of electronic beam irradiation or the like. As for a fiber base which a water absorbing polymer is adhered to and retained on, timber pulp, rayon, cotton and other cellulose group fibers and/or absorption fibers such as polyester group fibers are generally used as preference as main components. A water absorbing high-molecular composite material is prepared by impregnating the fiber base or a sponge-like base with ethylenic unsaturated monomer as water solution forming the water absorbing polymer and polymerizing the same.

Description

[Detailed description of the invention] Technical field The present invention relates to a sheet for dehydration or water retention.

More specifically, in the present invention, when the water-absorbing material provided inside removes moisture from the object, it acts as a dehydration sheet,
The present invention also relates to a sheet that functions as a water-retaining sheet when moisture is applied to an object from the water-absorbing material.

TECHNICAL FIELD Superabsorbent polymers have long attracted attention for their dehydration and water retention abilities, and have been used in a number of fields. For example, if we focus on its dehydration ability, its application fields include dehydrating and drying foods to obtain preserved foods;
It is used in the field of removing water from several types of solvents, and is also used for freezing and preserving fresh foods.

On the other hand, as an example of application when focusing on its water retention capacity,
For example, there are water-containing sheets for fire protection, coated cloth for seed coating, and seedling survival.

Various proposals have been made for dewatering and water-retaining sheets in which such superabsorbent polymers are applied to water-permeable sheets (Japanese Patent Application Laid-open Nos. 56-75054 and 57-167).
No. 73, No. 57-103838, No. 58-58124
No. 58-104607, No. 60-130334, No. 60-232935, No. 61-43549, etc.).

However, conventional dehydration and water retention sheets all use powdered super absorbent polymers as water absorbing agents (or water retaining agents), and therefore tend to have the following problems.

In other words, according to such conventional technology, dehydration and water retention sheets are
First, a highly water-absorbing polymer is dispersed in a thin layer on a supporting substrate such as paper or non-woven fabric to form a water-absorbing portion, and this is then covered with a heat-sealable water-permeable film. However, with such a sheet, during transportation of the sheet,
Or, during handling, the superabsorbent polymer easily separates from the supporting substrate and moves, and in some cases, the superabsorbent polymer becomes unevenly distributed in the corners of the sheet, resulting in a significant drop in efficiency of water absorption and water retention, and stability. cause a decline.

In order to solve this problem, measures have been taken to fix polymeric substances to paper or nonwoven fabrics, etc. Specifically, methods include using starch syrup, gelatin, propylene glycol, alginic acid, polyvinyl alcohol, and other glues. , it is common to immobilize a super absorbent polymer substance.

However, this measure has various problems as described below, and is not necessarily satisfactory for practical use.

(1) Since a glue is used, the water absorption or water retention performance of the super absorbent polymer may be reduced.

(2) A sheet that has been used once and re-dried may not be able to be reused due to the immobilization of the superabsorbent polymer.

(3) The sheet manufacturing process is complicated, resulting in lower manufacturing costs and
Variations in quality are likely to occur at m points.

[Summary of the invention]

Abstract: Instead of using a powdered superabsorbent polymer as a water-absorbing material, the present inventors have developed a superabsorbent polymer composite in which a superabsorbent polymer is attached to a fibrous substrate or a sponge-like substrate. The inventors have found that the above-mentioned problems can be solved to a large extent, and have completed the present invention.

That is, the dehydration or water retention sheet according to the present invention has a water-absorbing polymer composite provided between two heat-sealable sheets, at least one of which is water-permeable, and the water-absorbing polymer composite is capable of absorbing water. The method is characterized in that it is obtained by impregnating or coating a fibrous substrate or sponge-like substrate with an ethylenically unsaturated monomer to form a polyester polymer as an aqueous solution and polymerizing it.

Effects In the water-absorbing or water-retaining sheet according to the present invention, since the water-absorbing polymer is reliably fixed, the water-absorbing polymer will not become unevenly distributed during sheet transportation or handling. Further, unlike fixing methods using glue or the like, there is no deterioration in water absorption or water retention performance during fixation, and the product can withstand repeated use.

Fibrous Substrate or Sponge-like Substrate The fibrous substrate to which the water-absorbing polymer is attached and held is specifically formed by loosely molding fibers, such as batt, carded or air-laid web, tissue paper, cotton. It can be a woven fabric like gauze, a knitted fabric, or a non-woven fabric.

Here, a "formed" fibrous substrate means that cutting, joining, shaping, etc. may be necessary to incorporate the fibrous substrate into an article, but no further web forming operations are required. mean something

It is generally preferred to use a fibrous substrate based on absorbent fibers such as wood pulp, rayon, cotton or other cellulosic fibers and/or polyester fibers. However, other types of fibers, such as polyethylene, polypropylene, polystyrene, polyamide, polyvinyl alcohol, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyurea, polyurethane, polyfluoroethylene The molded fibrous substrate may include fibers such as polycyanide, vinylidene polycyanide, and the like.

The spongy substrate used in the present invention is a polymer foam such as polyvinyl acetal sponge, rubber sponge, polyethylene foam, polypropylene foam, or urethane foam, and has a continuous network porous structure. Any item is fine.

The main role of these fibrous substrates or sponge-like substrates is to retain the adhesion of water-absorbing polymers, but when this substrate is made of water-absorbing fibers as described above, they also function as water-retaining materials in the same way as water-absorbing polymers. also fulfill.

Water-absorbing polymer composite The water-absorbing polymer composite of the present invention is obtained by impregnating a fibrous substrate or a sponge-like substrate with an ethylenically unsaturated monomer to form a water-absorbing polymer as an aqueous solution and polymerizing it. It is something.

The water-soluble ethylenically unsaturated monomer that can be impregnated or applied onto a fibrous substrate or sponge-like substrate may be any monomer that can be converted into a water-absorbing polymer and provides good water-absorbing performance after polymerization and drying.

Water-soluble polymers that provide such performance include carboxylic acid or (and) a salt thereof, phosphoric acid or (and) as a functional group.
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, nyl sulfonic acid or a salt thereof, vinylphosphonic acid or a salt thereof, and the like. Among these, (meth)acrylic acid or a salt thereof is particularly preferred. The resulting polymer may be a homopolymer or copolymer of these seven polymers, a graft polymer to starch or cellulose, or the like.

Furthermore, it is also possible to add crosslinking agents and additives to these monomers to improve absorption performance. As a crosslinking agent, methylene bisacrylamide, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)
Water-soluble polyfunctional ethylenically unsaturated monomers such as acrylates, polyglycidyl ethers such as ethylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether, polyols such as glycerin and pentaerythritol, and polyamines such as ethylene diamine, etc. Water-soluble compounds having two or more functional groups that can react with functional groups such as acid, phosphoric acid, and sulfonic acid can be preferably used.

An aqueous solution of such monomers may be applied to a fibrous or sponge-like substrate by any convenient means or manner as long as the monomers are maintained uniformly dispersed on the fibrous substrate and can be polymerized. be able to. 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.

Further, the step of polymerizing the monomers uniformly dispersed on the fibrous substrate or the spongy substrate may be any suitable step. Typical of such methods is the action of a water-soluble radical polymerization initiator, specifically, adding the radical polymerization initiator to an aqueous monomer solution and decomposing it on the fibrous substrate. Alternatively, the radical polymerization initiator can be applied as a solution separate from the monomer evenly by spraying onto the fibrous substrate after the monomer aqueous solution has been applied, and the radical polymerization initiator can be decomposed on the fibrous substrate. A separate solution is applied to the fibrous substrate, and an aqueous solution of Hemotsuma is sprayed thereon.
It is applied uniformly by coating or the like. 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.

Water-permeable sheet The water-permeable sheet used in the present invention may be, for example, a sufficiently fine-grained nonwoven fabric made of a thermoplastic material, or a thermoplastic sheet that has been made water-impermeable, with fine communication holes formed therein by electron beam irradiation or the like. There are various types of seals, and any type may be used as long as it is water permeable and can be heat sealed. In the dehydration and water retention sheet of the present invention, the water-permeable portion does not need to be the entire surface of the sheet, and may be only the portion that comes into contact with the object. There is no problem even if the part not in contact with the object to be dehydrated or water-retained is made of an impermeable film such as ordinary polyolefin.

In addition, in the present invention, a superabsorbent polymer composite is sandwiched between these two heat-sealable sheets, and then these two sheets are heat-sealed to produce the desired sheet for dehydration and water retention. However, these heat-sealable sheets may be composed of only a single sheet or may be composed of a plurality of laminated sheets.

[Experiment example]

Example 1 A 70 mol% neutralized potassium acrylate aqueous solution with a solid content of 63% by weight was prepared. This solution contained 1% by weight and 500 ppm of N-N based on potassium acrylate monomer.
' Methylenebisacrylamide was dissolved, and then this aqueous solution was uniformly sprayed onto a polyester fiber web having a basis weight of 351/rrr so that the polymer coating Q was 100 g/rrr. The web coated with this monomer was left in a nitrogen-inflated oven for 10 minutes to polymerize, and then the aggregate was dried under reduced pressure at 100°C.
A super absorbent polymer composite was obtained. A polyester nonwoven fabric was used as a water-permeable and heat-sealable sheet, and the above-mentioned super absorbent polymer composite was sandwiched between the fabrics and heat-sealed to produce a desired dewatering sheet size 50 c+n x 70.

Fold this dehydration sheet into two sheets and place commercially available konjac (1 piece) between them.
6.5 x 7.5 cm, 220 to 250 g) were separated and a light plate-shaped weight of about 100 g was placed on top to measure the weight change of the konnyaku. This measurement was repeated twice, and these values were calculated as the average value. Polyvinyl acetal sponge thickness 2I11 25
cmX 35Cml (34g) was impregnated into a flat plate at a rate of 100g/rf as a solid content. This sodium vinylsulfonate was prepared and obtained as follows.

N-N' methylenebisacrylamide 1% by weight and (
0.5% by weight of 4-benzoylbenzyl)trimethylammonium chloride is dissolved.

Next, this was fixed with a clip to a glass plate, and 80W/am
The front and back sides of the sponge were irradiated with ultraviolet light for 20 seconds each at a sponge spacing of 81 using an ultraviolet lamp. This was sandwiched between sheets of polyester nonwoven fabric and heat-sealed to produce two desired dehydration sheets.

Place 1 kg of commercially available cod roe on one sheet of this dehydration sheet, place another dehydration sheet on top of the cod roe, sandwich the cod roe, place a light plate-shaped weight of about 100 g, and weigh the cod roe. Changes were measured. The results are as follows.

Claims (1)

[Claims] A water-absorbing polymer composite is provided between two heat-sealable sheets, at least one of which is water permeable, and the water-absorbing polymer composite contains an ethylenically unsaturated monomer to form the water-absorbing polymer. A sheet for dehydration or water retention, characterized in that it is obtained by impregnating or coating a fibrous substrate or sponge-like substrate as an aqueous solution and polymerizing it.