JPH09104478A - Water absorbent sheet and water absorbent bag - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide a water-absorbing sheet and bag having a small elution amount with respect to water, which can be used for maintaining freshness and improving taste by dehydration and drying of fresh food. SOLUTION: A water-absorbent film composed of a polymer having ethylene oxide as a main repeating unit is used, in which potassium permanganate consumption (ppm) is 10 or less, and water vapor permeability (g / g).
m ² · 24 hr) is 600 to 2000, swelling degree is 25 to
A water-absorbing sheet coated with a semi-permeable polyvinyl alcohol film having a crystallinity of 60% and a crystallinity of 20 to 50%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material capable of absorbing water, for example, dehydration of fresh food, drying,
The present invention relates to a water-absorbing sheet and a water-absorbing bag that can be used for maintaining freshness by improving humidity and improving taste.

[0002]

2. Description of the Related Art Conventionally, as a water absorbing 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 addition, there is a resin in which the superabsorbent resin is sandwiched between paper and nonwoven fabric. However, since the superabsorbent resin is powdery, it is difficult to uniformly support the nonwoven fabric or the like.

To solve these problems, dewatering sheets utilizing osmotic pressure have been developed mainly for foods. By encapsulating a high-concentration solution of saccharides in a semipermeable membrane, they obtain a strong dehydrating power by utilizing the osmotic pressure of the high-concentration solution. However, a high-concentration solution of a saccharide has a high viscosity, so that it is difficult to handle at the time of production, and air bubbles easily remain in the finished product without being completely removed, which is a problem in appearance.

The present applicant has previously used a water-absorbent film mainly composed of ethylene oxide as a water-absorbent material, and this is a semipermeable polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be abbreviated as "PVA"). )
A water-absorbent sheet coated with was proposed. It has excellent water absorption, is easy to produce and has good appearance, and is extremely suitable for dehydrating fresh food and maintaining freshness.

By the way, as a water absorbing sheet material used together with food, it is desirable that the amount of components eluted from the water absorbing sheet by water is as small as possible. In the above water-absorbing sheet, the material that comes into direct contact with food is semipermeable PVA.
Although it is a film, it has a semi-permeable P
It is considered that the components elute from the VA film and the elution amount from the water-absorbing material that permeates and elutes from the semipermeable membrane, and preferably both are at low levels.

[0006]

The present invention has been made under such a background, and provides a water absorbing sheet which has a high water absorbing ability, is easy to manufacture, has a good appearance, and has a very small elution amount with respect to water. The gist of the invention is that a water-absorbent film made of a polymer having ethylene oxide as a main repeating unit is used, and potassium permanganate consumption (ppm) is 10 or less, and water vapor transmission rate (g / m ² · 24 hr).
Is 600 to 2000, the degree of swelling is 25 to 60%, and the degree of crystallinity is 20 to 50%.

Still another subject matter of the present invention is a water-absorbing sheet obtained by fusion-bonding a water-absorbent film made of a polymer having ethylene oxide as a main repeating unit to a semipermeable polyvinyl alcohol film having the above-mentioned characteristics. is there.
Yet another aspect of the invention is a water-absorbent sheet as described above,
It is a water-absorbent bag formed by making a semi-permeable polyvinyl alcohol film inside.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The water-absorbent sheet or water-absorbent bag of the present invention has a semipermeable membrane-having polyvinyl alcohol film having specific performance and a water-absorbent film made of a polymer having ethylene oxide as a main repeating unit as essential components. Is. The semipermeable membrane PVA film comes on the side that comes into contact with foods, etc. when it is used. It has a strong affinity with water but is insoluble in water and allows water molecules and odor components to pass through, but has a large umami taste. It has a semi-permeable property that does not allow components to pass through. It is important that this PVA film has the characteristics described below.

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 a water-soluble material that absorbs water and dissolves, but it is water-absorbing and insoluble in water by irradiation crosslinking or chemical crosslinking. 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. The water-absorbent film in the present invention may be a water-soluble material as it is when it is used in a bag of a PVA film, but a water-insoluble material is generally preferable.

Next, the PVA film in the present invention will be specifically described. The PVA film of the present invention has a potassium permanganate consumption amount (ppm) of 10 or less and a moisture vapor transmission rate (g / m 2 · 24 hr) of 600 to 200.
0, swelling degree is 25 to 60%, and crystallinity is 20 to 50%. That is,
It is desired that the PVA film has small elution to water and high water permeability, and in order to meet these requirements, it is necessary to have the characteristics within the above range.

Here, the water vapor transmission rate is 600 g / m 2 · 24 h
If it is less than r or the degree of swelling is less than 25%, the water permeability becomes poor, and the water absorbing performance as a water absorbing sheet, particularly the water absorbing speed, is impaired. Also, when the crystallinity exceeds 50%, the water permeability is lowered, which is not preferable.

On the other hand, if the crystallinity is less than 20%, the amount of elution with respect to water increases, which is not suitable for the present invention. Also,
When the water vapor permeability exceeds 2000 g / m 2 · 24 hr or the swelling degree exceeds 60%, the water permeability is good, but it becomes difficult to suppress the elution content to water to a low level.

The above-mentioned properties are set so that the PVA film has a potassium permanganate consumption (ppm) of 10 or less, which is a measure of elution with water. Here, the consumption amount of potassium permanganate is based on the Ministry of Health and Welfare Notification No. 370 standard test method, and represents a value for an eluate corresponding to 2 ml per 1 cm ² of the surface area of the film.

The consumption amount of potassium permanganate is achieved by suppressing the amount of unreacted components in PVA as a raw material of the PVA film and setting the characteristics of the film within the above range. Also, as the film thickness increases, the amount of potassium permanganate consumption increases correspondingly, so setting the film thickness is also important.

As PVA, the degree of polymerization is 500 to 300.
0, preferably about 1000 to 2600, and a saponification degree of 80 to 100 mol%, preferably about 99 to 100 mol% are used. PVA is not limited to a saponified vinyl acetate homopolymer, but is a monomer copolymerizable with vinyl acetate, such as ethylenically unsaturated carboxylic acid, its ester, its salt, or ethylenic sulfonate, A modified PVA obtained by saponifying a copolymer of vinyl acetate and a monomer such as unsaturated amide, unsaturated nitrile, or olefins may be used.

The PVA film may contain a plasticizer such as glycerin in order to impart flexibility, and the above properties may be satisfied in the plasticizer-containing state. In order to obtain a PVA film having the above properties, the raw material such as the degree of polymerization of PVA, the degree of saponification, the content of plasticizer and water, as well as the casting method, the melt molding method and the like can be used. The factors of the manufacturing conditions of the film to be formed are also large.

As a practical method, the PVA film may be heat-treated under appropriate conditions. That is, the saponified PVA film obtained by a usual method is heated by means such as contact with a hot roll or passage through a hot air circulating furnace. In order to obtain the above characteristics, the heat treatment temperature and the heat treatment time are the main conditions, and in principle, a short time treatment at a high temperature and a long time treatment at a low temperature are performed. The heat treatment temperature may be appropriately selected from 150 to 260 ° C., and the heat treatment time may be appropriately selected from 5 seconds to 100 minutes.

Next, the water-absorbent film of the present invention will be specifically described. The water-absorbent film may be a homopolymer of ethylene oxide, but preferably a polymer obtained by reacting the following components (A) and (B) can be used.

(A) A polymer obtained by addition-polymerizing an alkylene oxide containing ethylene oxide as a main component to an organic compound having two active hydrogen groups (B) Polyvalent carboxylic acid, polyvalent carboxylic anhydride, polyvalent carboxylic acid Lower alkyl ester of acid or diisocyanate Examples of the organic compound having two active hydrogen groups include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, bisphenol A, aniline and polytetramethylene glycol. Examples of the alkylene oxide containing ethylene oxide as a main component include ethylene oxide alone or a mixture thereof with propylene oxide, butylene oxide, styrene oxide, α-olefin epoxide and the like. Examples of the polycarboxylic acid include phthalic acid, isophthalic acid, terephthalic acid, sebacic acid, dimer acid, pyromellitic acid, and anhydrides or lower alkyl esters thereof. As the lower alkyl ester, methyl ester, Examples include dimethyl ester and diethyl ester.

Examples of diisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and xylidene diisocyanate. The molecular weight of this polymer is preferably 50,000 or more, preferably 50,000 to 300,000. In the water-absorbent sheet of the present invention, the above-mentioned polymer is formed into a film as a water-absorbent film. To use. As a method for producing a film, a hydrous extrusion method or an aqueous solution casting method can be adopted for an ethylene oxide homopolymer (water-soluble). Further, if it is a polymer obtained by the reaction of the above-mentioned components (A) and (B), a melt extrusion method,
It can be easily formed into a film by hot melt molding such as calendering. When the alkylene oxide (A) is substantially composed of ethylene oxide, the resulting polymer is water-soluble, and becomes water-insoluble when the amount of the other alkylene oxide copolymerized is increased. When the water-soluble polymer is made insoluble in water, it can be crosslinked by irradiation with ionizing radiation or ultraviolet rays. As ionizing radiation,
Electron beams, γ rays, X rays and 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 dose of ionizing radiation is less than 0.5 Mrad, the degree of cross-linking is small and the whole may not be completely insoluble in water.
If it exceeds 20 Mrad, crosslinking will proceed excessively and the water absorption will be extremely reduced.
The range of d is preferred. Further, as a cross-linking method, chemical cross-linking in which a cross-linking agent is mixed and heated can be used.

Next, an example of the form of the water absorbing sheet of the present invention will be described. As one embodiment of the water-absorbing sheet of the present invention, a water-absorbing film stored in a bag of a semipermeable membrane PVA film can be mentioned. That is, a water-absorbent film is sandwiched between two semipermeable membrane PVA films to form a semipermeable membrane PV.
It can be obtained by heat-sealing the four sides of the A film. This water-absorbent sheet is sheet-shaped as a whole and thin, has a good appearance and is easy to manufacture. Then, it can be used under the food or wrapped around the food. Water is absorbed by the water absorbent resin film through the semipermeable membrane PVA film in contact with the food, but the umami component of the food remains without permeation. Further, since the water-absorbent resin film is a polymer, it is difficult for the semipermeable membrane PVA film to permeate even when there is a component that is soluble in water, and it is possible to achieve low elution of the water-absorbent sheet as a whole.

In another embodiment, a water absorbent film is fused and laminated on a semipermeable membrane PVA film. During use, water is absorbed by the water-absorbent resin film through the semipermeable membrane PVA film that is in contact with food, but the PVA film and the water-absorbent resin film are fused and laminated at this time, and a gap is formed between both layers. Since it does not occur and there is no layer such as an adhesive that inhibits moisture permeation, it has an advantage of increasing the water absorption rate.

In this embodiment, the semipermeable membrane PVA film may be laminated on the other surface of the water-absorbent film to more reliably block the eluate from 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
The layered water-absorbing sheet prevents moisture absorbed from food from seeping out to the outer surface, and imparts an appropriate level of rigidity to the entire water-absorbing sheet to facilitate handling, and further, it has an odor blocking property and an outer side. It has advantages such as no damage even if it is splashed with water, moisture resistance, and blocking between sheets.

In the laminated water-absorbing sheet, or the water-absorbing sheet having a semipermeable membrane PVA film or a non-permeable plastic film added thereto, the semipermeable membrane PVA film on the outer surface side and / or the side in contact with foods The non-water-permeable plastic film may be partially fixed and laminated on the water-absorbent film.

As a result, the flexibility of the entire water-absorbing sheet is increased, curling at the time of absorbing water is prevented, and the water-absorbing ability of the water-absorbing sheet can be fully exhibited. That is,
Since the water-absorbent film expands when it absorbs water, if a non-water-permeable plastic film or the like is stuck on the entire surface, the whole will easily curl, and the water-absorption and expansion of the water-absorbent resin film will be suppressed. May decrease.

As a method for partially fixing, there is a method of heat fusion or adhesive bonding in a dot shape, a line shape, a grid shape, or the like.
About 5 to 50% of the total fixed area is appropriate here.
If this area is less than 5%, the fixing strength will be insufficient, and if it exceeds 50%, the effect of preventing curling will be insufficient and the meaning of partial fixing will be reduced. It is preferable that the fixing portion is uniformly dispersed and provided, and as the fixing method, fusion bonding similar to the above is practical.

As a method for laminating the water-absorbent film on the PVA film, there is a method of thermocompression-bonding the water-absorbent film and the PVA film, which have been previously formed into a film as described above, by a nickel roll or a press plate. In this case, 60 to 10
Since the water-absorbent film is melted and fused to the PVA film at a low temperature of about 0 ° C., the PVA film is not adversely affected by heat. As another method, there is a method of coating the PVA film while extruding the molten water-absorbent resin into a film shape.

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-mentioned method, and the water-absorbent film and the non-water-permeable film are co-extruded and the two-layer film is made into a PVA film. It can also be laminated. When the water-absorbent film and the PVA film or the 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 the entire surface Therefore, it is possible to fix only appropriate portions.

As still another aspect of the present invention, there is a water-absorbing bag obtained by making the above-mentioned water-absorbing sheet having various laminated structures with the semipermeable membrane PVA film as the inner surface. The bag is used with food etc. inside, and since the whole bag is in a bag shape, the food is kept hygienic, and even if it is used in a refrigerator or the like, there is no odor transfer. In order to make the laminated water-absorbing sheet into a bag shape, it is convenient to use a general heat-sealing method, and the semipermeable membrane P on the inner surface of the bag is used.
It may be a so-called gas-sealing type seal in which VA films are joined to each other, or a so-called envelope sticking seal in which a semipermeable membrane PVA film on the inner surface and a water-absorbent resin film on the outer surface are joined. Even when a non-water-permeable film such as polyethylene is laminated, it can be easily heat-sealed with the PVA film or the water-absorbing film.

This water-absorbent bag is used with the PVA film inside and the food inside. However, since the PVA film is inside, the PVA film will spontaneously contact with water or drip present on the surface of the food. Adheres closely to food. After the food is put, the mouth of the bag can be closed with an adhesive tape or a ligature wire, or a removable adhesive can be applied to the mouth of the bag for sealing. It may also be a bag with a check.

In the various embodiments illustrated above, the thickness of each layer can be appropriately set according to the application, but as an example, P
If the VA film is thin, it lacks strength and stiffness, and wrinkles tend to occur, resulting in poor workability. If it is too thick, water permeability deteriorates and the amount eluted with water increases. The range of 25 μm is preferable. Further, the thicker the water-absorbent film is, the more excellent the water-absorbing performance is, but the usability is deteriorated. Therefore, the range of 20 to 200 μm is preferable. Furthermore, when a non-water-permeable film is used, it is preferable to make it as thin as possible.
The range can be about 50 μm.

The water absorbing sheet and the water absorbing bag of the present invention are
It is useful for removing excess water and odor from fresh foods and absorbing drip that occurs when thawing frozen foods.
It is suitable not only for distribution and processing of foods, but also for commercial use in cafeterias and for cooking at home.

By imparting specific characteristics to the semipermeable membrane PVA film that comes into direct contact with food or the like, elution with water is small and water permeation is not hindered. In addition, since most of the components eluted from the water-absorbent film have a relatively high molecular weight, they are blocked by the semipermeable membrane PVA film, and the elution of the entire water-absorbent sheet is small.

[0035]

EXAMPLES Specific examples will be described below with reference to examples. The performance evaluation method is as follows. 1) Elution amount in water (according to Ministry of Health and Welfare Notification 370) a) Consumption amount of potassium permanganate of PVA film 75 cm ² area (surface area is 150 cm ^{2 on} both sides) PV
The A film was immersed in a beaker containing 300 ml of distilled water at 60 ° C. for 30 minutes while maintaining the temperature, and then quickly filtered to collect a filtrate, and the potassium permanganate consumption of the filtrate was measured. .

B) Evaporation residue The filtrate of the above a) was concentrated and dried, and the weight of the residue was determined. 2) Water absorption rate The PVA film bag of 200 cm x 200 cm contains and seals a water absorbent film (50 μm thick), which is one size smaller, and the three grated eels are sandwiched from the top and bottom and placed in a polyethylene bag and placed in a refrigerator (4 ° C). × 65% RH) and the weight loss rate (%) was measured at predetermined time intervals.

3) Water vapor transmission rate of PVA film According to JIS-Z0208 (cutting method). 4) Swelling degree of PVA film According to JIS-K7209 (water absorption rate).

5) Crystallinity of PVA film The latent heat of fusion ΔHm (juule / g) was measured by the DSC method at an initial temperature of 30 ° C. (holding for 3 minutes), an ending temperature of 300 ° C., and a temperature rising rate of 10 ° C./min. It was calculated by the following formula. (ΔHm / 156.063) × 100 (%) (Example 1) Dimethyl terephthalate was added to a polyalkylene oxide compound obtained by addition-polymerizing ethylene oxide to ethylene glycol, and transesterification reaction was performed to obtain a water solution having a weight average molecular weight of 130,000. A polymeric compound was obtained. Then, a film having a thickness of 50 μm is made from the water-soluble polymer compound by the melt extrusion method, and the absorbed dose of γ rays is 1
It was irradiated with 0 Mrad and crosslinked to obtain a water-absorbent film.

On the other hand, a completely saponified P film formed by the casting method
The VA film was heat-treated by passing it through a hot air circulation furnace to obtain various PVA films (thickness 15 μm). The heat treatment temperature and heat treatment time of each PVA film are shown in Table 1. In addition, Table 1 also shows the characteristics of each PVA film, and the measured values of potassium permanganate consumption and evaporation residue.

[0040]

[Table 1]

Further, the water absorption rate of the water absorbing sheet was measured using each PVA film. Table 2 shows the results.

[0042]

[Table 2]

As is clear from these results, the water absorbing sheet (No. 3) using the PVA film having the characteristics within the range specified in the present invention has a sufficient water absorbing property and a high water absorbing speed. The amount eluted in water was also extremely small. On the other hand, No. Nos. 1 and 2 have a large consumption amount of potassium permanganate, and Nos. In No. 4, although the consumption amount of potassium permanganate was extremely small, the water absorption rate was low. In addition, No. Using the PVA film of No. 3, a bag having a surface area (total of both sides) of 150 cm ² was prepared, the water-absorbent film was housed and sealed in the bag, and the amount of potassium permanganate consumption was measured in the same manner as in a) above. As a result, the consumption amount of potassium permanganate was 10 ppm (this is because the amount of PVA film was doubled by making it into a bag), and the amount eluted from the water-absorbent film in the bag was P.
It was found to be blocked by the VA film.

[0044]

According to the present invention, a water absorbing sheet having a sufficiently high water absorbing property and a small elution amount with respect to water is obtained, which is particularly excellent as a water absorbing sheet for food.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Edazawa 2-80, Kamiya, Ogaki-shi, Gifu Higo Film Co., Ltd. (72) Osamu Kakishita 5-8 Mitsuya-cho, Nagahama-shi, Shiga Mitsubishi Jushi Corporation Nagahama factory inside

Claims (4)

[Claims] 1. A water-absorbent film made of a polymer having ethylene oxide as a main repeating unit, wherein the consumption amount of potassium permanganate (ppm) is 10 or less, and the water vapor permeability (g / g / g).
m ² · 24 hr) is 600 to 2000, swelling degree is 25 to
A water-absorbing sheet coated with a semi-permeable polyvinyl alcohol film having a crystallinity of 60% and a crystallinity of 20 to 50%. 2. A water-absorbent film made of a polymer containing ethylene oxide as a main repeating unit, wherein the consumption amount of potassium permanganate (ppm) is 10 or less, and the water vapor transmission rate (g / g / g).
m ² · 24 hr) is 600 to 2000, swelling degree is 25 to
A water-absorbing sheet obtained by fusion-bonding and laminating a semi-permeable polyvinyl alcohol film having 60% and a crystallinity of 20 to 50%. 3. The water absorbing sheet according to claim 2, wherein a non-water-permeable plastic film is laminated on the other surface of the water absorbing film. 4. A water absorbing bag obtained by making the water absorbing sheet according to claim 2 or 3 with a semipermeable membrane polyvinyl alcohol film as an inner surface.