JPH10217398A - Water absorbing multilayer sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce curl without softening even if drip is absorbed by absorbing the drip with the passage of time. SOLUTION: In the water absorbing multilayer sheet obtained by laminating a semipermeable film at least one surface of a water absorbing film containing polyethylene oxide polymer as a main component, a rigid sheet is laminated on either one surface of outer surfaces of the sheet. The rigid sheet and the absorbing film or semipermeable film are preferably partly laminated. And, the absorbing film and the permeable film are further preferably partly laminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbing multilayer sheet for absorbing moisture. More specifically, the present invention relates to a water-absorbent multilayer sheet suitable for maintaining freshness and transporting fresh food products.

[0002]

2. Related Art and Problems to be Solved by the Invention
At the time of processing and transportation, fresh foodstuffs are liable to be damaged and need to be protected with a rigid sheet or the like. At the same time, water (drip) contained in the foodstuffs oozes out at this time, causing a decrease in workability and a decrease in freshness of the foodstuffs. Therefore, a method has been adopted in which fresh food is wound around paper, cloth, nonwoven fabric, or the like to absorb the generated drip.

[0003] However, the above-mentioned conventional method can absorb the drip from the fresh food product at the initial stage of winding, but softens as the drip is absorbed, the effect of preventing damage is reduced, and the fresh food product is damaged. It will be easier.
In addition, drip occurs over time, and more often as perishables become damaged. However, the above-mentioned conventional method does not have an absorbing ability to absorb a newly generated drip.

[0004] In other words, for protection of fresh food products, it is desired that drip can be absorbed over time without being softened even if absorbed.

[0005]

The gist of the present invention is to provide a water-absorbent multilayer sheet comprising a semi-permeable film attached to at least one of a water-absorbent film mainly composed of a polyethylene oxide polymer. A water-absorbent multilayer sheet characterized in that a rigid sheet is attached to one of the outer surfaces of the multilayer sheet. It is preferable that the rigid sheet and the water-absorbing film or the semipermeable film are partially adhered. More preferably, the water-absorbing film and the semipermeable film are partially adhered.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The water-absorbent multilayer sheet of the present invention comprises a water-absorbent film comprising a polyethylene oxide polymer as a main component, one of which is a semipermeable membrane and the other is a rigid sheet. Are both semipermeable membrane films, and one is a rigid sheet.

A water-absorbing film containing a polyethylene oxide-based polymer as a main component will be described. A resin containing polyethylene oxide as a main component shows water solubility or water swelling depending on its composition, but becomes insoluble in water and shows water absorption by crosslinking the resin. The water-absorbing resin film 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 or the method of use. And it is preferably insoluble in water.

As the semipermeable membrane used in the present invention, polyvinyl alcohol (hereinafter sometimes abbreviated as PVA), cellophane or the like is used. The semi-permeable membrane comes to the side that comes into contact with food etc. when used, has a strong affinity for water but is insoluble in water, allows water molecules and odor components to permeate, but has a large molecule umami component Has a semipermeable membrane property that does not allow transmission. Such films are
For example, it can be obtained by forming a completely saponified PVA into a film. The PVA film may also contain a plasticizer such as glycerin to impart flexibility.

The rigid sheet used in the present invention imparts rigidity, so-called stiffness, to the water-absorbing multilayer sheet of the present invention, and achieves the object and achieves the above-mentioned water-absorbing film or semipermeable membrane. The material is not particularly limited as long as it can be attached, and for example, cardboard, nonwoven fabric, plastic film, and the like are used.

Since the water-absorbing film absorbs water and expands only when it is placed in a humid environment, the water-absorbing multilayer sheet to which the rigid sheet is attached as in the present invention is liable to curl. Using a curled water-absorbent multilayer sheet,
Packaging is not efficient.

Therefore, it is preferable to partially adhere the rigid sheet and the water-absorbing film or the semipermeable film. Further, it is preferable that the water-absorbing film and the semipermeable film are partially adhered. Curling can be prevented by leaving the inflated portion to the unattached portion by partially attaching.

The term "partially pasted" as used in the present invention means that there is a part that is not pasted, rather than pasted over the entire surface. Specifically, heat bonding or adhesive bonding in a point-like, linear, or lattice-like manner may be mentioned.
The area to be pasted is appropriately about 5 to 50% of the whole,
If this area is less than 5%, the bonding strength is insufficient, and 50%
When the value exceeds, the effect of preventing curling or the like is insufficient, and the meaning of partial application is reduced. It is preferable that the attachment is provided so as to be uniformly dispersed throughout.

For use in protecting fresh foods, heat fusion is preferred for food hygiene. For example, in order to heat-bond a rigid sheet and a water-absorbing film, an SP value (Solubility Parameter) which is a parameter of the compatibility of the polyethylene oxide polymer constituting the water-absorbing film is used.
ter) and the SP value of the rigid sheet are preferably within 1.0. Examples of the rigid sheet satisfying this condition include polyvinyl chloride, polycarbonate, and polyethylene terephthalate.

Also, when bonding the water-absorbing film and the semi-permeable film, if an adhesive is used, the adhesive often does not have water permeability, so that thermal bonding is preferred. As a method of laminating a water-absorbent resin film mainly composed of polyethylene oxide on a PVA film used as a semipermeable film, a film of the water-absorbent resin formed by a method described later and the PVA film may be nip rolled. And a method of thermocompression bonding using a press plate. In this case 6
Since the water-absorbent resin film is melted and fused to the PVA film at a low temperature of about 0 to 100 ° C., the PVA film is not adversely affected by heat. Alternatively, P
There is a method in which a molten water-absorbing resin is coated on a VA film while being extruded into a film.

The adhesive used for adhesive bonding is not particularly limited, but care must be taken when the water-absorbing multilayer sheet of the present invention is used for foodstuffs as described above. Generally used adhesives are isocyanate-based, PVA-based, starch-based adhesives, and when the water-absorbing multilayer sheet of the present invention is used for foodstuffs, the adhesive used is PVA.
Systems and starch systems are preferred.

The polyethylene oxide-based polymer constituting the water-absorbent film used in the present invention is not particularly limited, but a repeating unit represented by the following general formula is preferred because of its good thermoformability.

[0017]

Embedded image Where A is

Embedded image

Embedded image Consisting of

Embedded image Where x, y and z are each an integer of 1 or more, and a weight ratio calculated from x, y and z, 44 (x + z)
/ (Molecular weight of α-olefin oxide having 3 or more carbon atoms)
y is from 80/20 to 94/6, X is a residue of an organic compound having two active hydrogen groups, Y is a hydrocarbon group having 1 or more carbon atoms, R ₂ is a residue of a dicarboxylic acid compound or a diisocyanate. Compound residue.

This high molecular compound is formed by reacting a dicarboxylic acid compound or a diisocyanate compound with polyalkylene oxide formed by addition polymerization of ethylene oxide to ethylene glycol, then addition polymerization of alkylene oxide, and addition polymerization of ethylene oxide. can do.

The dicarboxylic acid compound is preferably a cyclic dicarboxylic acid compound or a linear dicarboxylic acid compound, and examples thereof include dicarboxylic acids, dicarboxylic anhydrides, and lower alkyl esters of dicarboxylic acids. Examples of the dicarboxylic acid include phthalic acid, isophthalic acid, terephthalic acid, malonic acid, succinic acid, sebacic acid, maleic acid, fumaric acid, adipic acid, and itaconic acid. Also,
Examples of the dicarboxylic anhydride include anhydrides of the various dicarboxylic acids. Further, as the lower alkyl ester of the dicarboxylic acid, methyl ester, dimethyl ester, ethyl ester of the various dicarboxylic acids,
Examples include diethyl ester, propyl ester, dipropyl ester and the like.

Particularly preferred are straight-chain dicarboxylic acids having 12 to 36 carbon atoms and lower alkyl esters thereof. Specific examples of the linear dicarboxylic acid having 12 to 36 carbon atoms include 1,10-decamethylenedicarboxylic acid, 1,14-tetradecamethylenedicarboxylic acid,
Examples thereof include 18-octadecamethylene dicarboxylic acid and 1,32-dotriacontamethylene dicarboxylic acid. Examples of the lower alkyl esters include methyl, ethyl, propyl and dipropyl esters of these dicarboxylic acids. Can be These can be used alone or in combination of two or more. Among them, it is preferable to use the above-mentioned dicarboxylic anhydrides and lower alkyl esters of dicarboxylic acids, particularly from the viewpoint of ease of reaction.

Examples of the diisocyanate compound include 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, xylylene diisocyanate, isophorone isocyanate, and methylene biscyclohexyl diisocyanate (H12MDI). These can be used alone or in combination of two or more.

As a method for producing a film from a resin containing a polyethylene oxide polymer as a main component, there are a solution casting method, a melt extrusion method, a calendering method and the like. In the case of a homopolymer of ethylene oxide, a film can be obtained by forming an aqueous solution into a film by a casting method or an extrusion method and drying the film. Also, if the above resin,
A film can be easily formed by melt extrusion molding utilizing good thermoplasticity. In the film, a heat stabilizer, an antioxidant, a colorant, and the like can be contained as needed, as long as the film does not affect food.

In the present invention, it is not necessary to crosslink the absorbent film as described above.
Irradiation with ionizing radiation or ultraviolet light can be performed. Electron beams, γ-rays, X-rays and the like can be used as ionizing radiation. Irradiation is preferably performed in a substantially oxygen-free state, such as by substituting with an inert gas such as nitrogen. As a crosslinking method, it is also possible to blend a crosslinking agent into a resin mainly composed of ethylene oxide and carry out thermal crosslinking.

The use of the water-absorbent multilayer sheet of the present invention is not limited at all, but it is useful for removing excess moisture and odor from fresh food, absorbing drip generated when frozen food is thawed, and the like. It is suitable not only for distribution and processing of foods, but also for home cooking.

Further, the water-absorbing multilayer sheet of the present invention may be not only in sheet form but also in plate-like dish form, and is not limited to the shape used. The sheet may be bent into an arbitrary shape, and a water-absorbent film and a semipermeable membrane may be laminated on the bent rigid sheet.

[0026]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples.

Example 1 After addition polymerization of ethylene glycol with ethylene oxide, butylene oxide was addition-polymerized, and methyl octadecane-1,18-dicarboxylate was added to polyalkylene oxide obtained by addition polymerization of ethylene oxide. A transesterification reaction was performed.
The thus obtained polymer compound having a weight average molecular weight of 150,000 is melted by an extruder, extruded at a T-die temperature of 140 ° C. to a thickness of 50 μm, and a water-absorbing film containing a polyethylene oxide-based polymer as a main component is formed. Manufactured.

On both sides of the obtained water-absorbent film, PVA
A film (thickness 15 μm, glycerin 6% added, fully saponified film) was rolled at a temperature of 65 ° C., a linear pressure of 3.0 kg / cm, and a take-up speed of 1.5 m / min using a partially uneven nip roll. Crimped. The water-absorbing film and the semipermeable film were partially adhered.

Further, the adhesive Nichibon VF was placed on one side in a width direction and a longitudinal direction at intervals of 5 cm and a width of 2 mm.
(Nippon Synthetic Chemical Co., Ltd.) is applied, and as a rigid sheet, a thick white paper NK350 (Keio Paper Co., Ltd.)
Was subjected to roll pressure bonding at a linear pressure of 3.0 Kg / cm and a take-up speed of 1.5 m / min using a nip roll having partially unevenness, and the cardboard and the water-absorbent film were partially adhered. A water-absorbing multilayer sheet was obtained. In addition, cardboard in advance,
Moisture is removed through a drying process. In the obtained water-absorbent multilayer sheet, a semipermeable film is partially adhered to both surfaces of the water absorbent film, and a rigid sheet is partially adhered to one of the semipermeable films.

The obtained water-absorbent multilayer sheet was cut into a B5 size sheet, layered on a B5 size cotton nonwoven fabric (basis weight 150 g / m ² ) containing 40 cc of ion-exchanged water, and heated at 25 ° C. × 60% R. H. Table 1 shows the relationship between the standing time and the dehydration rate (%). Furthermore, the B5 size water-absorbing multilayer sheet is applied for 24 hours for 25 hours.
° C x 60% R.C. H. Table 1 shows the value obtained by measuring the floating height of the end face from the horizontal plane
It was shown to. The dehydration rate was determined as follows.

A = weight of water-absorbent cotton nonwoven fabric B = weight of cotton nonwoven fabric dehydrated by contact with water-absorbent multilayer sheet Dehydration rate (%) = (AB) ÷ A × 100 (Example 2) Example 1 Cellophane PL (manufactured by Nimura Chemical Co., Ltd.) was applied as a semipermeable membrane to one surface of the water-absorbing film used in the above at a temperature of 70 ° C. and a linear pressure of 3.0 kg / c.
m, and thermocompression bonded to the entire surface at a take-up speed of 1.5 m / min. Further, a cardboard as a rigid film was stuck on the other surface in the same manner as in Example 1 to obtain a water-absorbing multilayer sheet in which the cardboard and the water-absorbing film were partially stuck.

In the obtained water-absorbing multilayer sheet, a semipermeable film is stuck on one surface of the water-absorbing film on the entire surface, and a rigid sheet is partially stuck on the other surface. In the same manner as in Example 1, the relationship between the standing time and the dehydration rate (%) and the curl value were determined. The results are shown in Table 1.

(Example 3) Cellophane PL-DG (manufactured by Nimura Chemical Co., Ltd.) as a semipermeable membrane, and a special white paper NK350 (Keio Paper Co., Ltd.) which is a cardboard as a rigid sheet
Between the water-absorbing film used in Example 1 and the entire surface of both surfaces of the water-absorbing film at a temperature of 70 ° C., a linear pressure of 3.0 Kg / cm, and a take-up speed of 1.5 m / min. This was pressed to obtain a water-absorbent multilayer sheet.

In the obtained water-absorbent multilayer sheet, a semipermeable film is adhered on one surface of the water-absorbent film on the whole surface, and a rigid sheet is adhered on the other surface on the entire surface. Example 1
Similarly, the relationship between the standing time and the dehydration rate (%) and the curl value were determined, and the results are shown in Table 1.

(Comparative Example 1) Cellophane PL-DG (manufactured by Nimura Chemical Co., Ltd.) and special white paper NK350 (manufactured by Keio Paper Co., Ltd.), which is a cardboard, are bonded together using molten food sugar. It was made into a sheet. The relationship between the standing time and the dehydration rate (%) and the curl value of the obtained sheet were determined in the same manner as in Example 1, and the results are shown in Table 1.

(Comparative Example 2) Nonwoven fabric made of cotton (weight per unit area: 150 g) was applied to NK350 (manufactured by Keio Paper Co., Ltd.)
/ M ² ) was adhered to the entire surface using an adhesive OSCNo1 (mansheng Suzuki Co., Ltd.). The relationship between the standing time and the dehydration rate (%) and the curl value were determined, and the results are shown in Table 1.

[0037]

[Table 1] As shown in Table 1, the water-absorbent multilayer sheet to which each film is partially adhered as in Example 1 can continuously absorb moisture even after absorbing a large amount of moisture at the initial stage, and can curl. There was almost no. As in Example 2, a semi-permeable film is attached to one surface of the water-absorbing film over the entire surface,
The water-absorbent multilayer sheet in which the rigid sheet is partially adhered to the other surface can continue to absorb water even after absorbing a large amount of water at the initial stage, but curling occurred slightly.

As in Example 3, a water-absorbent multilayer sheet in which a semipermeable film is stuck on one surface of a water-absorbent film on the entire surface and a rigid sheet is stuck on the entire surface of the other surface is
Even after absorbing a large amount of water in the early stage, the water can be continuously absorbed. However, curling easily occurs, and it is hard to say that it is suitable for work such as packaging when compared with Examples 1 and 2.

In Comparative Example 1, although water was absorbed over time, the absolute amount was small, and curling was caused by an external environment because the entire surface was uniformly adhered. In Comparative Example 2, the amount of water that oozes out is too small over time or absolutely.

[0040]

As described above, the water-absorbing multilayer sheet of the present invention can continuously absorb water even after absorbing water quickly at the initial stage. Further, by partially attaching the film, curling can be prevented.

Claims (3)

[Claims] 1. A water-absorbing multilayer sheet comprising a semi-permeable film adhered to at least one of a water-absorbing film containing a polyethylene oxide-based polymer as a main component, wherein one of the outer surfaces of the water-absorbing multilayer sheet has rigidity. A water-absorbing multi-layer sheet, wherein the sheet is attached. 2. The water-absorbent multilayer sheet according to claim 1, wherein the rigid sheet and the water-absorbent film or the semipermeable film are partially adhered. 3. The water-absorbent multilayer sheet according to claim 2, wherein the water-absorbent film and the semipermeable membrane are partially adhered.