JPH08187068A - Water absorbing sheet - Google Patents

Abstract

PURPOSE: To obtain a sheet for water absorption useful for preserving freshness by dehydration and drying of perishable food and improving a taste, having a high water absorption rate, being readily produced/handled and having an excellent external appearance, by fusing and laminating a water absorbing resin sheet consisting essentially of ethylene oxide to a semipermeable PVA sheet. CONSTITUTION: A water absorbing resin sheet consisting essentially of ethylene oxide is fused and laminated to a semipermeable PVA sheet not permeating a tasty component. Water is absorbed from a food through the semipermeable PVA sheet in the water absorbing resin sheet. The semipermeable PVA sheet is obtained by a method for making a completely saponified PVA into a film and the water absorbing resin sheet insoluble in water is obtained by cross- linking a resin consisting essentially of ethylene oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet having the ability to absorb water, and more particularly to a sheet for water absorption which can be used for maintaining freshness and improving the taste of fresh foods by dehydration and drying.

[0002]

2. Description of the Related Art Conventionally, as a water absorbent sheet,
Paper, cloth, non-woven fabric, etc. have been used, but they have drawbacks such as low water absorption, weak water retention, and liberation of water due to external stimulation.

In response to these problems, dehydration sheets utilizing osmotic pressure have been developed mainly for foods (Japanese Patent Publication No. Sho 5).
8-58124, etc.). By applying or encapsulating a high-concentration solution of saccharides and an acrylic acid-based polymer absorbent on a semi-permeable membrane, they utilize the osmotic pressure of the high-concentration solution and the water absorption capacity of the polymer absorbent to achieve strong dehydration. It is to gain strength. However, since a high-concentration solution of saccharides has a high viscosity, it is difficult to handle at the time of production, and bubbles remain in the finished product without being removed, which is a problem in appearance. The present applicant has previously proposed a water absorbing sheet using a sheet-like material as the water absorbing material, but as a result of studies to obtain a water absorbing sheet having a higher water absorbing speed, the present invention has been completed.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a water-absorbent sheet which has a high water-absorption rate, is easy to manufacture and handle, and has a good appearance. The gist thereof is a semi-permeable polyvinyl alcohol. A water-absorbing sheet obtained by fusion-bonding a sheet of a water-absorbent resin mainly composed of ethylene oxide on a sheet. A water-absorbent resin sheet mainly composed of ethylene oxide is fused and laminated on one surface of a semi-permeable polyvinyl alcohol sheet, and a non-water-permeable plastic sheet is laminated on the other surface of the water-absorbent resin sheet for water absorption. It provides a seat.

The present invention will be described in detail below. In the water-absorbing sheet of the present invention, a semi-permeable polyvinyl alcohol sheet and a water-absorbent resin sheet containing ethylene oxide as a main component are fusion-laminated. This polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) sheet comes to the side that comes into contact with food etc. when used, and has a strong affinity with water but is insoluble in water, and has no water molecules or odor components. It has a semipermeable property that allows permeation, but does not allow umami components having large molecules to permeate. Such a sheet can be obtained by forming a completely saponified polyvinyl alcohol film. This PVA sheet can also contain a plasticizer such as glycerin in order to impart flexibility.

A resin mainly composed of ethylene oxide exhibits water-solubility or water-swellability depending on its composition, but when it is crosslinked, it becomes insoluble in water and exhibits water absorption. The water-absorbent resin sheet mainly composed of ethylene oxide in the present invention may be any of these, and can be selected according to the required amount of water absorption and the method of use.

[0007] At the time of use, the semipermeable membrane P that comes into contact with food etc.
Water is absorbed by the water absorbent resin sheet through the VA sheet. At that time, the PVA sheet and the water-absorbent resin sheet are fusion-bonded and laminated, no gap is formed between the both layers, and there is no layer that inhibits moisture permeation such as an adhesive. Is caused. The semipermeable membrane PVA sheet may be laminated on one side or both sides of the water absorbent resin sheet. At that time, the semipermeable membrane PVA sheet and the water absorbent resin sheet on the back surface side and / or the side in contact with the food can be partially fused and laminated. As a result, there is an advantage that the water absorption rate does not decrease so much as in the case of fusing the entire surface of the sheet and the flexibility of the entire sheet increases.

When the semipermeable membrane PVA sheet is laminated on one side, a non-water-permeable plastic sheet, for example, a sheet of polyethylene, polypropylene, ethylene-vinyl acetate copolymer resin, polyethylene terephthalate or the like can be laminated on the other side. . This non-water-permeable plastic sheet is for preventing the water absorbed by the water-absorbent resin sheet from leaking to the outside, but it is preferable that the water-absorbent resin sheet is laminated by a partially fixed portion. .

That is, since the water-absorbent resin sheet expands when it absorbs water, if the non-water-permeable plastic sheet is stuck on the entire surface, the whole sheet tends to curl, and as a result, the water-absorbent resin sheet is prevented from expanding due to water absorption. The water absorption rate and water absorption amount may decrease. As a method of partially fixing, there is a method of heat fusion or adhesive bonding in a dot shape, a linear shape, a lattice shape, or the like. Here, the fixed area is 5 to 50% of the whole.
If the area is less than 5%, the fixing strength will be insufficient, and if it exceeds 50%, the effect of curling prevention will be insufficient and the meaning of partial fixing will be reduced. The fixed part is
It is preferable to disperse it uniformly over the entire surface, and as a fixing method, the same fusion as described above is practical.

When the water-absorbent resin sheet is not cross-linked, the degree of water absorbability can be adjusted by the composition of the resin, but generally, when water is absorbed, it gels and easily flows. It may be preferred to stack the sheets. It is suitable for applications with relatively small water absorption. When the water-absorbent resin sheet is cross-linked, the sheet-like shape is maintained even if it absorbs water and gels, so that there is no problem even with a two-layer structure of the PVA sheet and the water-absorbent resin sheet.

The resin containing ethylene oxide as the main component used in the present invention is not particularly limited, but the main component of the organic compound having two active hydrogen groups is ethylene oxide (preferably 60% or more, more preferably 80%). % Or more) and a high molecular weight compound obtained by reacting a polymer obtained by addition-polymerizing alkylene oxide with polyvalent carboxylic acid, polyvalent carboxylic anhydride, lower alkyl ester of polyvalent carboxylic acid or diisocyanate It is a suitable resin because it has good moldability.

Here, as the organic compound having two active hydrogen groups, there are ethylene glycol, propylene glycol, bisphenol A, aniline propylene glycol, polytetramethylene glycol and the like, and alkylene having ethylene oxide as a main component added thereto. Examples of the oxide include ethylene oxide alone or a mixture thereof with propylene oxide, butylene oxide, styrene oxide, α-olefin epoxide and the like.

Further, as the polycarboxylic acid, phthalic acid,
Examples thereof include isophthalic acid, terephthalic acid, sebacic acid, dimer acid, pyromellitic acid, and their anhydrides or lower alkyl esters. Examples of the lower alkyl esters include methyl ester, dimethyl ester and diethyl ester.

Examples of diisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and xylidene diisocyanate.

As a method for producing a sheet from a resin containing ethylene oxide as a main component, there are a solution casting method, a melt extrusion method, a calender method and the like. If it is a homopolymer of ethylene oxide, a sheet can be obtained by forming an aqueous solution into a sheet by a casting method or an extrusion method and drying the sheet. Further, the above resins can be easily formed into a sheet by melt extrusion molding by utilizing good thermoplasticity. In the sheet, heat stabilizer, as long as it does not affect food etc.,
Antioxidants, colorants and the like can be contained as necessary.

When the sheet is cross-linked, it can be irradiated with ionizing radiation or ultraviolet rays. As the ionizing radiation, an electron beam, γ ray, X ray or the like can be used. Irradiation is preferably carried out in a substantially oxygen-free state such as substitution with an inert gas such as nitrogen. If the irradiation dose of ionizing radiation is less than 0.5 Mrad, the degree of crosslinking is too small and water solubility remains, which is not preferable in the case of a use mode requiring crosslinking. Therefore, the absorbed dose is 0.5 to 20M
A range of rad is preferred. As a method of crosslinking, it is also possible to blend a resin mainly composed of ethylene oxide with a crosslinking agent and perform heat crosslinking.

As a method for laminating a sheet of a water-absorbent resin mainly containing ethylene oxide on a PVA sheet, an uncrosslinked or crosslinked sheet of the water-absorbent resin previously formed as described above and a PVA sheet are combined with a Nipro roll or a press. There is a method of thermocompression bonding with a plate. In this case, 60-100
Since the water-absorbent resin sheet is melted and fused to the PVA sheet at a low temperature of about 0 ° C., the PVA sheet is not adversely affected by heat. As another method, there is a method of covering the PVA sheet while extruding the molten water absorbent resin into a sheet shape.

Further, when the non-water-permeable sheet is laminated on the back surface of the water-absorbent resin sheet, it can be produced according to the above method, and the water-absorbent resin sheet and the non-water-permeable sheet are co-extruded to form a two-layer sheet. It can also be laminated to a PVA sheet. When the water-absorbent resin sheet and the PVA sheet or the non-water-permeable sheet are laminated by a partially fixed part, for example, engraving is performed on a nip roll or a press plate for lamination to give unevenness, and not the entire surface. It is possible to partially fix only appropriate portions.

The thickness of each layer can be appropriately set according to the application, but as an example, the PVA sheet is about 5 to 20 μm in consideration of moisture permeability, strength, etc., and the water absorbent resin sheet is 30 to 200 μm from the viewpoint of water absorption. It is preferable to make the non-water-permeable sheet as thin as possible.

The water absorbing sheet of the present invention can be used by wrapping it around a food or the like with the PVA sheet inside, or sandwiching the food or the like between two sheets. The use of the water-absorbent sheet of the present invention is not limited in any way, it is useful for removing excess water and odor from fresh food, and is useful for absorbing drip that occurs during thawing of frozen foods, and distribution / processing of foods and the like. It is suitable not only for the process but also for domestic cooking.

[0021]

【Example】

Example 1 Ethylene glycol to ethylene oxide 8
Polyalkylene oxide compound added with 5% and 15% butylene oxide (weight average molecular weight 12,000)
2.2 parts by weight of dimethyl terephthalate was added to 100 parts by weight and subjected to polyesterification reaction to obtain a weight average molecular weight of 13
50,000 compounds were obtained. This is T by a single screw extruder
Extrusion was carried out under the condition that the die temperature was 100 ° C., and a sheet having a thickness of 50 μm was collected.

Further, it was sandwiched between two polyvinyl alcohol sheets (thickness 15 μm, glycerin 6% added, completely saponified film) with a laminator, temperature 65 ° C., linear pressure 3.0 kg / cm, take-up speed 1.5 m. Thermocompression bonding was carried out at a speed of 1 / min to obtain a laminated sheet having a thickness of 80 μm.

The laminated sheet was cut into B5 size and 4
Overlay on a B5 size cotton non-woven fabric (weight per unit weight 150 g / m ² ) containing 0 ml of deionized water,
The sample was left to stand in an atmosphere of 60 ° C and 60% RH, and the relationship between the standing time and the amount of water absorption was determined. This assumes water absorption from fresh fish.

(Comparative Example 1) The same water absorbent sheet (thickness 50 μm) as in Example 1 was cut into B5 size, and the same PVA sheet as in Example 1 was cut into a bag slightly larger than B5 size. After putting it in and heat-sealing the four sides, a water absorbent sheet was sealed in a PVA sheet bag to prepare a product. Then, a water absorption test was conducted in the same manner as in Example 1.

Comparative Example 2 A similar water absorption test was carried out on a commercially available dehydrated sheet (PVA bag in which edible sugars, sizing agents and alcohols were enclosed). Table 1 shows the amount of water absorption (unit: g, total weight minus dry weight of the sheet) obtained as a result of the above.

Table 1 Left time (hr) 0.5 1 2 3 Example 1 6.2 7.6 8.5 9.2 Comparative example 1 3.1 5.4 7.2 8.7 Comparative example 2 1 .3 3.6 6.3 8.5

From the above results, the water absorbing sheet of the present invention is
It is clear that the amount of water absorption at the initial stage is large, that is, the water absorption speed is high, and there is an advantage that water absorption / dehydration can be achieved in a short time.

(Practical test) The meat of snow crab, which is frozen and sold after boiling, is loosened, sandwiched between the water-absorbing sheets (B4 size), and stored in a refrigerator (temperature 5).
C.) and then taken out to measure the weight (g) of snow crab meat. The results are shown in Table 2.

Table 2 Weight Before water absorption A After water absorption B Dehydration amount (dehydration rate) Example 1 130 103 27 (21%) Comparative Example 1 110 89 20 (18%) Comparative Example 2 143 120 23 (16%)

It has been found that the sheet of the present invention has a large amount of dehydration in a relatively short time and is useful even when urgently needed for cooking.

[0031]

According to the present invention, a water-absorbing sheet having a high water-absorbing rate can be obtained by fusing and laminating a sheet of a water-absorbent resin mainly containing ethylene oxide on a semi-permeable polyvinyl alcohol sheet. A high water absorption / dehydration effect can be achieved in a short time. Further, by laminating a semi-permeable polyvinyl alcohol sheet or a non-water-permeable plastic sheet on the opposite surface of the water absorbent resin sheet, the water absorbed in the water absorbent resin sheet does not leak to the outside,
Easy to handle. Further, since the sheet of the present invention is in the form of a laminated sheet as a whole, it can be made relatively thin and easy to manufacture, use and handle, and has a good appearance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B32B 27/38 // A23B 4/03

Claims (4)

[Claims] 1. A water-absorbing sheet obtained by fusion-bonding a sheet of a water-absorbent resin mainly containing ethylene oxide on a semi-permeable polyvinyl alcohol sheet. 2. The water-absorbing sheet according to claim 1, wherein the semipermeable membrane-permeable polyvinyl alcohol sheet and the water-absorbent resin sheet are fusion-laminated by partial fusion-bonding portions. 3. A sheet of a water-absorbent resin mainly containing ethylene oxide is fusion-bonded and laminated on one surface of a semi-permeable polyvinyl alcohol sheet, and a non-water-permeable plastic sheet is laminated on the other surface of the water-absorbent resin sheet. Sheet for water absorption. 4. The water-absorbing sheet according to claim 3, wherein the water-absorbent resin sheet and the non-water-permeable plastic sheet are laminated by a partially fixed portion.