JP3479944B2 - Water absorption sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material having an ability to absorb water, such as dehydration of fresh food, absorption of drip,
The present invention relates to a water-absorbing sheet that can be used for maintaining freshness by drying and improving taste.

[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. Further, there is also one in which a super absorbent polymer is sandwiched between paper and a non-woven fabric, but it is difficult to uniformly support the super absorbent polymer on a non-woven fabric since it is in a powder form.

To address these problems, dehydration sheets utilizing osmotic pressure have been developed mainly for foods. In these, a high-concentration solution of saccharides is enclosed in a bag of a semi-permeable polyvinyl alcohol film, and a strong dehydrating power is obtained by utilizing the osmotic pressure of the high-concentration solution. However, since a high-concentration solution of saccharides has a high viscosity, it is difficult to handle during the production, and bubbles are not completely removed in the finished product, which is a problem in appearance.

The applicant of the present invention has previously proposed a water-absorbent sheet in which a water-absorbent film mainly containing ethylene oxide is used as a water-absorbent material, and the film is covered with a semipermeable polyvinyl alcohol film. It has excellent water absorption, is easy to manufacture, has a good appearance, and is extremely suitable for dehydration and freshness preservation of fresh foods. The present invention further improves it and provides a water absorbing sheet having a higher water absorbing speed.

The present invention has been made based on the above background, and provides a water absorbing sheet having a high water absorbing capacity and a high water absorbing rate, and the gist thereof is ethylene oxide as a main repeating unit. A water-absorbent sheet characterized in that a water-absorbent film made of a polymer and a semipermeable membrane cellophane are partially fusion-laminated, and a non-fusion-bonded portion is left. Further, in the present invention, a water-absorbent film composed of a polymer having ethylene oxide as a main repeating unit, and two semipermeable membrane cellophane disposed on both surfaces thereof are melt-fused at the peripheral edge to be laminated, There is provided a sheet for water absorption, which is characterized in that a fused portion is left.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The water-absorbing sheet of the present invention has a semipermeable membrane cellophane and a water-absorbing film made of a polymer having ethylene oxide as a main repeating unit as essential components.

[0007] This cellophane comes to the side that comes into contact with food during use. It has a strong affinity for water but is insoluble in water, and allows water molecules and odorous components to pass through, but has a large umami component. Has a semipermeable property that does not allow permeation. Further, there is an advantage that the water permeability is higher than that of the semipermeable membrane polyvinyl alcohol film.

The water-absorbent film is composed of a polymer containing ethylene oxide as a main repeating unit. A polymer consisting only of ethylene oxide is water-soluble, but it becomes insoluble in water by irradiation crosslinking or chemical crosslinking, and exhibits water absorption. Further, it is also possible to make water-insoluble by copolymerizing ethylene oxide with a hydrophobic group such as butylene oxide or a longer-chain alkyl oxide. An ethylene oxide homopolymer can be used as the polymer, but a preferable polymer is (A) an organic compound having two active hydrogen groups, which is obtained by addition-polymerizing an alkylene oxide containing ethylene oxide as a main component. And a high molecular weight polymer obtained by reacting (B) a polyvalent carboxylic acid, a polyvalent carboxylic acid anhydride, a lower alkyl ester of the polyvalent carboxylic acid, or a diisocyanate.

Examples of the organic compound having two active hydrogen groups include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol,
Examples thereof include bisphenol A, butylamine, aniline, polytetramethylene glycol and the like.

Examples of the alkylene oxide compound containing ethylene oxide as a main component to be addition-polymerized thereto include ethylene oxide alone or a mixture thereof with propylene oxide, butylene oxide, styrene oxide, α-olefin epoxide and the like. .

As the polyvalent carboxylic acid (B),
Examples thereof include phthalic acid, isophthalic acid, terephthalic acid, malonic acid, sebacic acid, fumaric acid and adipic acid, and examples of the dicarboxylic acid anhydride include these anhydrides.
Examples of the lower alkyl ester of dicarboxylic acid include methyl ester, dimethyl ester, ethyl ester, diethyl ester and propyl ester of the above various dicarboxylic acids.

The polymer preferably used in the present invention is obtained by adding (B) to the above (A) and dehydrating or dealcoholizing under heating and reduced pressure. The polymer thus obtained has a weight average molecular weight of 50,000-
It is preferably set in the range of 300,000.

The water-absorbing sheet of the present invention is prepared by molding a polymer containing ethylene oxide as a main repeating unit into a film. As a method for producing the film, a solution casting method can be used for an ethylene oxide homopolymer and a melt extrusion method can be used for a reaction polymer of the above (A) and (B).

When the polymer is water soluble, it is crosslinked to render it water insoluble. The cross-linking can be performed by irradiating with ionizing radiation or ultraviolet rays, and as the ionizing radiation, 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. When the irradiation dose of ionizing radiation is less than 0.5 Mrad, the degree of crosslinking is small and water insolubilization is insufficient, and when it exceeds 20 Mrad, the water absorption is extremely reduced.
The range of Mrad is preferred. Further, as a cross-linking method, a cross-linking agent may be blended to perform heat-cross-linking.

The water absorbing sheet of the present invention is a laminate of the water absorbing film described above and the semipermeable membrane cellophane. This can be used by placing the semipermeable membrane cellophane on the side in contact with food or the like and laying it under the food, sandwiching the food from above and below with two sheets, or wrapping the food so as to wrap it. Water is absorbed by the water-absorbent resin film through the semipermeable membrane cellophane in contact with the food, but the umami component of the food remains without permeation.

As a specific embodiment, first, a water-absorbent film and a semipermeable membrane cellophane are fused and laminated on the entire surface. Since cellophane is not thermoplastic, it is not possible to seal cellophanes into bags.
In the case of the present invention, fusion bonding can be performed by utilizing the thermoplasticity of the water-absorbent film. In this case, the semipermeable membrane cellophane in contact with food and the water-absorbent resin film are fusion-laminated so that no gap is created between the two layers, and there is no layer that inhibits moisture permeation such as an adhesive. Therefore, there is an advantage that the water absorption rate becomes high.

In this embodiment, a semipermeable membrane cellophane can be laminated on the other surface of the water absorbent film. Further, a non-water-permeable plastic film, for example, a film made of polyethylene, polypropylene, ethylene-vinyl acetate copolymer resin, polyethylene terephthalate or the like can be laminated on the other surface of the water-absorbent film. These three-layer water-absorbent sheets prevent moisture absorbed from food from seeping out to the outer surface, and further, have a odor-blocking property and have no hindrance even if water is splashed from the outside, moisture resistance, and sheets to each other. It has advantages such as blocking prevention.

In another embodiment, the water-absorbent film and the semipermeable membrane cellophane are partially fusion-bonded and laminated, and the non-fusion-bonded portion is left. That is, since cellophane is stronger than polyvinyl alcohol film, if the entire surface is fusion-bonded, the water-absorbent sheet loses flexibility and may be difficult to adhere to food or the like. Therefore, if the fusion is partially stopped, the flexibility is increased as a whole, and both films are kept substantially in contact with each other even in the non-fusion portion during use, so that the water absorption rate can be maintained at a high level.

Partial fusing can be performed in a dot shape, a linear shape, a grid shape or the like, but it is particularly preferable that the fusing is performed at the peripheral portions of both films (so to speak, like a frame) and the central portion is not. It is to be in a fused state. In this way, the flexibility is increased, and the rigidity of the peripheral portion is increased, so that the water absorbing sheet can be easily handled. In that case, cellophane can be laminated on one side of the water-absorbent film, but in practice it is preferable to overlay cellophane on both sides. Further, the non-water-permeable plastic film may be provided in place of one of the cellophanes.

As a method of laminating the water-absorbent film on the cellophane, there is a method of thermocompression-bonding the water-absorbent film and cellophane, which have been previously formed into a film as described above, by a nickel roll or a press plate. In this case, the water-absorbent film is melted at a low temperature of about 60 to 100 ° C. and fused to cellophane. Another method is to coat cellophane while extruding a molten ethylene oxide polymer into a film. Further, when the non-water-permeable film is laminated on the back surface of the water-absorbent film, it can be produced according to the above method, and the water-absorbent film and the non-water-permeable film are co-extruded and the two-layer film is laminated on cellophane. You can also When the water-absorbent film and the cellophane or non-water-permeable film are laminated by a partially fixed portion, for example, a process such as engraving on a nip roll or a press plate for lamination to give unevenness, and not a whole surface In addition, it is possible to fix only appropriate portions.

In the various embodiments illustrated above, the thickness of each layer can be appropriately set according to the use, but as an example, if cellophane is thin, it may be broken during use, and if it is too thick, water permeability deteriorates. 5 in consideration of
The range of 25 μm is preferable. Further, the thicker the water-absorbent film, the more excellent the water-absorbing performance is, but on the other hand, the usability is deteriorated. Furthermore, when a non-water-permeable film is used, it is preferable to make it as thin as possible, and in view of workability, the thickness can be set to about 10 to 50 μm.

The water-absorbing sheet of the present invention is useful for removing excess water and odor from fresh foods, absorbing drip produced when frozen foods are thawed, and not only in the process of distributing and processing foods, but also in cafeterias and the like. It is also suitable for commercial use and for domestic cooking.

[0023]

EXAMPLES Specific examples will be described below with reference to examples. (Example 1) Dimethyl terephthalate was added to a polyalkylene oxide compound obtained by addition-polymerizing ethylene oxide to ethylene glycol, and a transesterification reaction was performed to obtain a water-soluble polymer having a weight average molecular weight of 130,000.
Then, the polymer is heated at a T-die temperature of 100 ° C. by an extruder.
Was extruded to obtain a film having a thickness of 50 μm, which was irradiated with γ-rays at an absorbed dose of 10 Mrad and crosslinked to obtain a water-absorbent film.

This was sandwiched between two sheets of cellophane (thickness: 20 μm, PT300 manufactured by Tocello Co.) with a laminator, and thermocompression bonded at a temperature of 65 ° C., a linear pressure of 3.0 kg / cm, and a take-up speed of 1.5 m / min. A laminated sheet having 90 μm-thick layers fused to each other was obtained. This laminated sheet was cut into B5 size, laminated on a B5 size Kotton nonwoven fabric (weight per unit weight 150 g / m ² ) containing 40 cc of ion-exchanged water, and left in an atmosphere of 25 ° C. and 60% RH. Then, the relationship between the standing time and the water absorption (g) was determined. This assumes dehydration from fresh fish.

Comparative Example A polyvinyl alcohol film (thickness: 15 μm) was used instead of the cellophane used in the examples.
The same evaluation was carried out using. The results are shown in Table 1.

[0026]

[Table 1]

As is clear from these results, it was confirmed that the water-absorbent sheet of the present invention has a higher water-absorption rate than that using the polyvinyl alcohol film.

[0028]

EFFECTS OF THE INVENTION According to the present invention, a water-absorbing sheet having a sufficiently high water-absorbing property and a high water-absorbing speed and having an increased flexibility as a whole is obtained, which is particularly excellent as a water-absorbing sheet for foods. In particular, the water-absorbent film, and two semipermeable membrane cellophane arranged on both sides thereof are fused and laminated at the peripheral edge portion, and a non-fused portion is left, The flexibility of the whole is increased, and the rigidity of the peripheral portion is increased, so that the water absorbing sheet can be easily handled. Furthermore, since the product of the present invention is in the form of a flat laminated sheet as a whole, it is convenient for distribution and storage and has a good appearance.

Claims (2)

(57) [Claims] 1. A water-absorbent film comprising an ethylene oxide of a polymer as the main repeating unit, and a semipermeable membrane of Serofuan partially fused laminate, that left unfused portion
A sheet for water absorption characterized by 2. A water-absorbent film made of a polymer having ethylene oxide as a main repeating unit, and two semipermeable membrane cellophanes disposed on both sides of the water-absorbent film are fusion-bonded to each other at their peripheral portions to form a non- fusion film. A water-absorbing sheet characterized by leaving a landing portion .