JPS63143906A - Dehydration sheet containing water absorbable resin - Google Patents

Abstract

PURPOSE:To obtain a dehydration sheet not causing the release of a gel from a base material at the time of water absorption and easy to handle, by coating or impregnating a cellulosic or Poval type fiber material with a water absorbable acrylic acid type polymer to form a sheet like water absorbable material and adding an aqueous sugar solution to said material to wet the same. CONSTITUTION:A sheet composed of a cellulosic or Poval type fiber such as a pulp type nonwoven fabric is coated or impregnated with an aqueous solution prepared by adding caustic soda and a radical initiator such as potassium persulfate to an aqueous acrylic acid solution containing a crosslinkable copolymerizable monomer such as methylenebisacrylamide and the impregnated one is polymerized under heating in inert gas. An aqueous sucrose solution is added to the water absorbable acrylic acid polymer-containing sheet like water absorbing sheet thus obtained to wet the same and a semipermeable film such as a vinylon film is superposed to both surfaces of the wetted material and the peripheral edge part is sealed to obtain a dehydration sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a dehydration method containing a water-absorbing acrylic acid group polymer, which is effective for selectively removing and drying water from articles to be dehydrated such as fresh foods through a semipermeable membrane. Regarding the seat.

BACKGROUND OF THE INVENTION Dehydration sheets are known that utilize the high water absorption and water retention properties of water absorbent resins to dry fresh foods.

For example, Japanese Patent Publication No. 58-58124 discloses a contact dehydration sheet using osmotic pressure, which is formed by scattering acrylic acid polymer powder on a half-six membrane film coated with an aqueous sucrose solution.

In addition, as a method for fixing the water-absorbing agent to a support such as paper or cloth in a dehydration sheet made of a combination of a water-permeable sort and a water-absorbing agent, a method has been proposed in which the water-absorbing agent powder is fixed to the support using an adhesive. (Japanese Unexamined Patent Publication No. 57-167134).

Problems to be Solved by the Invention In a dehydration sheet made of a combination of a water-absorbing acrylic polymer and a semi-permeable membrane film, in order to effectively transfer the water contained in the dehydrated article to the water-absorbing resin, a difference in osmotic pressure is required. It is desirable to make it work effectively. For this purpose, there is a method in which a mixture of a water-absorbing resin and an aqueous solution with high osmotic pressure is brought into contact with the article to be dehydrated through a semipermeable membrane film.

A water-absorbing acrylic acid polymer is a water-soluble acrylic acid polymer made insolubilized by crosslinking or grafting, and has the ability to absorb several hundred times its own weight in pure water.

The water absorption capacity is significantly reduced by the presence of metal ions, and in particular has the property of being coagulated by metal ions of divalent or higher valence.

Therefore, by combining the resin with a non-electrolyte aqueous solution such as sucrose as an aqueous solution with high osmotic pressure, the high water absorption capacity of the resin can be maintained.

Water-absorbing resins are usually supplied in the form of powder, and water-absorbing sheets are also available in which the powder is spread on paper or the like, moistened with water, and then swelled and crimped to fix the paper.

When a dehydration sheet made by sandwiching a water absorbing agent consisting of a resin powder or the above-mentioned powder-spreading sheet and a sucrose aqueous solution between two films including a semipermeable membrane film is water-recirculated according to its water absorption capacity, the following results are obtained. There are some inconveniences.

Most of the absorbed water is transferred to the water-absorbing resin, and the resin swells to several 10 to 100 times its original volume.

In the case of resin powder alone, if it is dispersed in a high viscosity aqueous solution such as starch syrup, the sheet will have a stable shape, but if it absorbs a large amount of water, the contents will become fluid and become unevenly distributed, making it difficult to handle. cause trouble.

Also, when resin powder is spread and fixed on a support, the swollen gel-like resin particles are released from the support, and separation of the gel particles is unavoidable even if they are fixed using an adhesive, resulting in similar problems. It will be done.

In particular, when a water-absorbed dehydration sheet is dried and used repeatedly, the above-mentioned difficulties are doubled.

In order to alleviate this difficulty, a quilting method has been proposed in which the contents of the dehydration sheet are divided into small sections.
It's not a fundamental solution. Practically, a high viscosity liquid such as starch syrup is used as the high osmotic pressure aqueous solution.

The mechanism of selective dehydration using a semipermeable membrane is as follows.

The water transferred to the high osmotic aqueous solution through the semipermeable membrane is absorbed by the water-absorbing resin, preventing the concentration of the aqueous solution from decreasing, so that the osmotic pressure is maintained and the dehydration ability is maintained.

The osmotic pressure of an aqueous solution is basically expressed by the following formula.

P - RTO P is osmotic pressure, R is gas constant, T is absolute temperature, and C is molar concentration of solute.

For efficient dehydration, it is best to use a highly concentrated aqueous solution with a high osmotic pressure, and therefore it is necessary to increase the molar concentration of the aqueous solution.

In order to obtain a high molar concentration with the same weight, the smaller the molecular weight, the more advantageous it is. High viscosity sugars such as starch syrup contain polymeric high-molecular polysaccharides and are therefore disadvantageous in terms of osmotic pressure of aqueous solutions.

Sucrose (012H22011
) is preferable, but glucose (06H120s
) and invert sugar hydrolyzed to fructose (06HI306) are more advantageous in terms of osmotic pressure.

Therefore, basically, even if the viscosity is low, sucrose with high concentration,
Relatively low molecular weight sugars such as glucose and fructose are preferred.

Means for Solving the Problems The present invention provides a method in which a water-absorbing acrylic acid-based polymer is coated or impregnated on a water-absorbing fiber material selected from cellulose-based and Bobal-based fiber materials, and then tightly bonded to single fibers. To provide a dehydration sheet made by adding a water-soluble saccharide aqueous solution to a sheet-like water-absorbing material to swell it, and superimposing a semipermeable membrane film on one or both sides. Ho here.

Var type fiber means Bobard derivative fiber known as vinylon fiber.

The above-mentioned sheet-like water-absorbing material is produced, for example, by the following method.

An aqueous solution of acrylic acid containing a crosslinkable copolymer is neutralized with caustic soda, and the aqueous solution containing a radical initiator is applied or impregnated onto a sheet of paper or nonwoven fabric made of cellulose or popal fibers. Polymerize the substance by heating in an inert gas (Japanese Patent Application Laid-Open No. 51-552)
02).

Or, patent application No. 61-26, which is an earlier invention of the present inventor.
As shown in No. 625, an aqueous solution prepared by adding a water-soluble peroxide radical initiator to a polyacrylic acid aqueous solution is applied or impregnated onto a sheet of paper or non-woven fabric made of the above-mentioned water-absorbing fibers, and the polymer is heated and dried in the process of heating and drying. A water-absorbing acrylic acid polymer is formed by introducing crosslinks between molecules.

A sheet-like water-absorbing material containing a water-absorbing acrylic acid polymer produced by such a method is impregnated with a water-soluble saccharide aqueous solution. Aqueous solutions of sucrose, glucose, fructose, and invert sugar are preferably used as the high osmotic pressure aqueous solution. The amount of the aqueous solution added is determined so that the sheet-like water-absorbing material swollen by the aqueous solution is in an appropriate wet state and maintains good contact with the semipermeable membrane film.
It is stipulated.

As the semipermeable membrane film, a film of cellulose, cellophane as a cellulose derivative, cellulose acetate or a saponified product thereof, or a vinylon film of a hydrophilic synthetic polymer is used, and a vinylon film is particularly preferred from the viewpoint of strength and flexibility.

The dehydration sheet of the present invention is produced by enclosing a sheet-like water-absorbing material containing a water-absorbing acrylic acid polymer moistened with an aqueous sugar solution between two films containing a semipermeable membrane film. The two films are joined at their peripheries by heat sealing or adhesive.

The content, shape, and size of the water-absorbing resin are designed depending on the object to be dehydrated.

Function The sheet-like water-absorbing material containing the water-absorbing acrylic acid polymer of the present invention is uniformly integrated with the base material in a state where the resin is closely bonded to the single fibers constituting the sheet, and when water is absorbed, the gel is formed into a base material. The wood particles do not come loose, and even after repeated water absorption and drying, there are no difficulties seen in the case of resin powder dispersion.

The above remarkable fact is recognized because the cellulose or bovar fibers selected as the material for the base sheet are highly hydrophilic and have good compatibility with the monomer or polymer stock solution and the produced water-absorbing resin.

On the other hand, when a non-woven fabric made of non-hydrophilic fibers such as polyolefin or polyester is used as a base material, the water-absorbing resin and the base material are not sufficiently compatible and separation of the two is observed, which is not suitable.

Aqueous solutions of relatively low molecular weight sugars such as sucrose, glucose, fructose, and invert sugar used as high osmotic solutions have a remarkable effect of increasing osmotic pressure, and even at high concentrations they have a lower viscosity than starch syrup, etc., but they absorb water in the form of sheets. When impregnated into a material, it forms a uniformly stable swollen body and exhibits good shape stability even when water is absorbed. Thus, another feature of the present invention is that it is possible to use a relatively low molecular weight saccharide aqueous solution. There is one.

Example 1゜Acrylic acid 72g1 Caustic soda (93% purity) 32g1
Methylenebisacrylamide 0.14 g water 240 g,
A monomer stock solution with a concentration of 25% prepared from 4 g of persulfuric acid IJO was uniformly impregnated into a bulb-type nonwoven fabric, and polymerized by heating at a temperature of 80° C. for 1 hour in a nitrogen atmosphere. The dry weight of the product is 100. , containing 2.1 g of polymer per j. The water absorption capacity of this sheet when immersed in pure water was 360 g/g, calculated per 1 g of polymer.

The sheet was cut into a size of 10 cyn x 20 tyn, and 25 rat of 36% sucrose aqueous solution was added to it.
was added to moisten it. This sheet is coated with a 20 micron thick vinylon film (Kuraray vinylon film φ200).
0) were stacked one on top of the other, and the periphery was sealed using vinylon adhesive to produce a dehydration sheet.

A flat piece of raw squid meat weighing 80 g was sandwiched between the two dehydration sheets, and a 700 g iron plate was placed on top of it and left to dehydrate at room temperature. After 6 hours the weight of the sample decreased to 46 g.

Example 2 72g of acrylic acid was dissolved in 290g of water, and 48%
163 g of an aqueous solution of caustic soda was added and cooled, and to this was added 0.21 g of ammonium persulfate and 0.07 g of acidic sodium sulfite.
The gt-added aqueous solution was polymerized while stirring in a nitrogen atmosphere. Polymerization was initiated by heating the aqueous solution to about 500°C, which rose to 70°C after 1 hour due to the heat of polymerization. The mixture was further stirred at 8,000°C for 2 hours to complete the polymerization. The product is a highly viscous aqueous solution with a polymer concentration of 20%.

The aqueous solution was diluted with water to a polymer concentration of 8%, and ammonium persulfate was added at a ratio of 3% by weight based on the polymer to prepare a stock solution. Polymer has 75% carboxyl groups
is polyacrylic acid neutralized to sodium salt.

Next, the stock solution was applied to a valve-type nonwoven fabric and dried by heating in a microwave oven to prepare a nonwoven fabric impregnated with a radically crosslinked polymer. This water-absorbing resin-containing nonwoven fabric has 1
00c4 per 2. Contains Og resin. This product has a water absorption capacity of 410 g/g of pure water in terms of 1 g of resin.

This non-woven fabric was cut into a size of 10(7) x 20(7), moistened with a 40% glucose aqueous solution, and a 20 micron thick vinylon film was layered on both sides.
A dehydration sheet was created by gluing the peripheral parts.

The thickness between the two dehydration sheets is approximately 6 mm, and the weight is 50 g.
A piece of beef was placed between the plates, a 700 g iron plate was placed on the plate, and the plate was left at room temperature to dehydrate. After 6 hours the weight of the sample decreased to 19g.

As seen in the effect examples, using the dehydration sheet of the present invention,
Water can be selectively removed from articles such as fresh foods to dry them to a desired degree.

Claims (1)

[Claims] A water-absorbing acrylic acid polymer is coated or impregnated on a water-absorbing fibrous material selected from cellulose-based and Bobal-based fiber materials, and water-soluble saccharides are added to the sheet-like water-absorbing material formed by closely bonding with single fibers. Add an aqueous solution to moisten the
A dehydrating sheet made of a semi-permeable film layered on one or both sides.