JPH0338977B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminated material that has the function of controlling gas permeability due to changes in humidity, has heat sealability, and is resistant to volatile substances that generate highly permeable and highly soluble vapor. It is. Conventionally, packaging systems have been filled with inert gases such as carbon dioxide gas and nitrogen gas to prevent changes in the color and aroma of foods, or to suppress the progress of oxidation and spoilage. In addition, ventilation holes are provided for powders in which vaporizable liquids such as ethyl alcohol are adsorbed onto inorganic powders such as silicic anhydride, pearlite, and synthetic zeolite, and substances that generate carbon dioxide gas through chemical reactions or exchange desorption reactions. A packaging method that achieves the same effect by filling a small bag made of film, paper, etc. and placing it in a packaging system is also used. However, for example, gas-filled packaging requires special and expensive gas-filling equipment. In addition, when a vaporizable liquid that has a food preservation effect is adsorbed onto an inorganic substance and turned into powder, there are problems such as there is a limit to the amount that can be adsorbed, the liquid is very bulky, and the packaging process is complicated due to its fluidity. be. Furthermore, since the perforated pouches are used, there is a risk that powder or adsorbed liquid may come out into the packaging system, and gas generation has the disadvantage of being extremely difficult to control. In order to solve these problems, the present inventors first developed organic acids such as ethyl alcohol, acetic acid, propionic acid, malic acid, lactic acid, succinic acid, citric acid, and aspartic acid, cinnamon oil, garlic oil, onion oil, and mustard. The outer layer is completely saponified polyvinyl alcohol film or ethene-vinyl acetate copolymer saponified film, and the inner layer has a vinyl acetate content of 3. An application has been filed for a method for preserving food, which involves enclosing the food in a bag made of a laminated film made of ethylene-vinyl acetate copolymer film with a concentration ranging from mol% to 50 mol%, packaging the bag together with the food, and sealing the bag. The bag of the present invention has the function of not emitting vapors of volatile substances during storage in a low humidity condition, but only releasing vapors of volatile substances in a high humidity condition when packaged with food. Ta. However, subsequent tests revealed that, depending on the conditions of use, this bag may be used to absorb vapor generated from volatile substances or liquid condensed from volatile substances when packaged with food at a relative humidity of 65% or higher. In some cases, the adhesive remained between the inner layers, producing many bubbles or vacuoles, or the adhesive turned white instead of being transparent. This significantly impairs the appearance of the bag and lowers its commercial value. The inventors of the present invention have conducted various studies in order to solve the above-mentioned problems, and found that by bonding both layers together using a specific adhesive and then allowing the adhesive to completely cure, the problematic air bubbles or vacuoles can occur. The present invention has been completed based on the discovery that this can be prevented. Here, fully saponified polyvinyl alcohol and saponified ethylene-vinyl acetate copolymer using the laminated material of the present invention exhibit gas barrier properties under low humidity conditions, but conversely, gas barrier properties decrease under high humidity conditions. However, these are difficult to use because they do not have heat sealability. Furthermore, ethylene-vinyl acetate copolymer has relatively high gas permeability and is known to have heat-sealability. It was something that could not be controlled. By combining these materials, the present invention enables gas permeability to be controlled by humidity and high-speed sealing. Furthermore, as an adhesive for bonding both materials, it is possible to use highly permeable substances such as solvents or volatile substances. By using a specific adhesive that does not deteriorate even when rubbed, it is possible to prevent changes in the appearance of the laminated material itself even when filled with volatile contents. Hereinafter, the present invention will be explained in detail with reference to the drawings. In the laminated material of the present invention, as shown in FIG. 1, the outer layer 1 is made of a completely saponified polyvinyl alcohol film or a saponified ethylene-vinyl acetate copolymer film, and the inner layer 2 is made of an ethylene-vinyl acetate copolymer film.
The outer layer 1 is made of a vinyl acetate copolymer film.
and the inner layer 2 are laminated together with an adhesive layer 3 interposed therebetween. Here, the outer layer 1 exhibits almost no gas permeability in a low humidity state, exhibits high gas permeability in a high humidity state, and has a function of controlling gas permeability. The thickness of the outer layer 1 is preferably 12μ to 75μ. If the thickness is less than 12 μm, there is a risk of damage or pinholes due to impact or other forces applied during handling during packaging work or during distribution. If the thickness is 75 μm or more, the initial gas permeation rate under high humidity conditions tends to be too low, and the rigidity of the film is too high, resulting in poor workability during filling. The ethylene-vinyl acetate copolymer of the inner layer 2 preferably has a vinyl acetate content ranging from 3 mol% to 50 mol%, preferably from 8 mol% to 33 mol%. The gas permeability of ethylene-vinyl acetate copolymer has relatively little dependence on the humidity in the atmosphere, but there is a large difference depending on the vinyl acetate content, and the lower the vinyl acetate content, the lower the gas permeability. If the vinyl acetate content is lower than 3 mol%, the gas permeability is too low and the outer layer 1 is
There is a problem in that the gas permeability control function of completely saponified polyvinyl alcohol or saponified ethylene-vinyl acetate copolymer is not utilized. If the vinyl acetate content is higher than 50 mol%, the adhesive strength of the film will be too high and the slip property will be extremely poor, causing problems in workability during filling operations. The thickness of the inner layer 2 is preferably in the range of 20μ to 80μ. If the thickness is less than 20μ, there is a problem in impact resistance due to low heat sealing strength. Furthermore, if the thickness is 80 μm or more, the initial gas permeation rate will be low, resulting in a problem that the gas permeation function will not be fast-acting. The adhesive layer 3 is a two-component curing adhesive made of a urethane prepolymer having terminal isocyanate groups and a glycol curing agent added thereto. By using an adhesive having an isocyanate group in the base resin itself, a urethane bond is formed between the terminal isocyanate group of the base resin and the hydroxyl group of the fully saponified polyvinyl alcohol or saponified ethylene-vinyl acetate copolymer of the outer layer 1. This makes the adhesion stronger, and by completely curing the adhesive after bonding, the outer layer 1 and the inner layer 2 are firmly bonded. As a method for laminating the outer layer 1 and the inner layer 2 using the adhesive layer 3, a general dry lamination method can be applied. As shown in Fig. 2, the laminated material of the present invention is used by making a bag by heat sealing with an inner layer 2 of ethylene-vinyl acetate copolymer as the inner surface, and then forming a bag with ethyl alcohol, acetic acid, propionic acid, malic acid, etc. It can generally be used in the form of a sachet filled with volatile substances 4 such as organic acids, essential oils of spices such as cinnamon oil and mustard oil. The pouch has a vapor release control function that does not release the vapor of the volatile substance contained therein in a low humidity state during storage, but releases vapor only in a high humidity state where the bag coexists with the food. The laminated material of the present invention can be used in this sachet even in high humidity conditions where the vapor generated by volatile substances that tend to deteriorate adhesion tends to accumulate in the form of bubbles or vacuoles between the outer layer and the inner layer. When used as a material, the extremely strong adhesion between the outer and inner layers prevents the generation of bubbles and vacuoles, and furthermore prevents the color of the material from changing due to whitening of the adhesive layer. was completed. As explained in detail above, the laminated material of the present invention has a gas permeability control function that enables vapor release control that is effective for improving the shelf life of foods and maintaining quality, but also reduces the product value as a packaging material. Since it does not cause any change in appearance, it has great utility value as a food preservation material. Next, examples of the present invention will be described. Example 1 Completely saponified polyvinyl alcohol film
25μ (Vinylon-U, manufactured by Nippon Film) and 40μ of an ethylene-vinyl acetate copolymer film with a vinyl acetate content of 10% were combined with a polyester-type urethane prepolymer with terminal isocyanate groups (Adcoat).
527, manufactured by Toyo Morton) and a glycol-based curing agent (Adcoat 9L-1, manufactured by Toyo Morton) using a dry lamination method, and then under the conditions of 40°C and 20% RH. A laminated material was obtained which had been storage aged for 7 days. (Invention 1) For comparison, the same film as in Invention 1 was used, and an epoxy-modified polyester having a terminal hydroxyl group (Adcoat 503 manufactured by Toyo Morton) was mixed with a urethane curing agent having an isocyanate group at the terminal (Adcoat 503 manufactured by Toyo Morton).
CAT-10 (manufactured by Toyo Morton Co., Ltd.) was added to the two-component curing adhesive by a dry lamination method, and then aged under the same conditions as above to obtain a laminated material. (Comparative Example 1) In addition, a 15μ film of a saponified ethylene-vinyl acetate copolymer (Eval-F, manufactured by Kuraray) and a 40μ film of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 19% were added to the invention 1. After laminating using the dry lamination method using the same adhesive as 40
A laminated material was obtained which was stored and aged for 7 days under the conditions of ℃-20% RH. (Invention 2) For comparison, a film similar to the above was prepared using an epoxy-modified polyester having a terminal hydroxyl group (EPS75, manufactured by Dainippon Ink and Chemicals) and a urethane curing agent having a terminal isocyanate group (KW-40, manufactured by Dainippon Ink and Chemicals). The materials were bonded together by a dry lamination method using a two-component curing adhesive to which was added, and then aged under the same conditions as above to obtain a laminated material. (Comparative Example 2) Using the above four types of laminated materials, heat-seal the ends with the ethylene-vinyl acetate copolymer side facing inside to make a bag-shaped packaging bag with dimensions of 7 cm x 5 cm, and fill it with 6 g of ethanol. and completely sealed. When this packaging bag was placed in a humidity-controlled room at a temperature of 25° C. for 3 days, the ethanol vapor permeability and appearance of the packaging bag were observed. The results are shown in Table 1. In addition, when a packaging bag similar to the above was placed in a bag made of vinylidene chloride coated stretched polypropylene/polyethylene and the humidity of the air inside was adjusted, the concentration of ethanol vapor contained in the air inside the bag was measured using gas chromatography after 15 days. The values measured and the appearance of the packaging bag were observed, and the results are shown in Table 2. However, the volume of air in the bag is 500ml.

【table】

【table】

[Table] Note: The display in each column and the units and symbols in the upper, middle, and lower rows are the same as in Table 1.As described above, packaging bags using the laminated material of the present invention cannot be filled when the relative humidity is 65% or less. It almost completely blocks ethanol vapor, releases ethanol vapor well at relative humidity of 75% or higher, and does not cause white discoloration of the packaging bag or the formation of air bubbles or vacuoles as seen in the comparative example under any humidity conditions. No deterioration in appearance was observed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the laminated material of the present invention, and FIG. 2 is a cross-sectional view of a packaging bag made using the laminated material of the present invention. 1... Outer layer, 2... Inner layer, 3... Adhesive layer.

Claims (1)

[Scope of Claims] 1. An outer layer consisting of either a fully saponified polyvinyl alcohol film or a saponified ethylene-vinyl acetate copolymer film and an inner layer consisting of an ethylene-vinyl acetate copolymer film having terminal isocyanate groups. A laminated material for packaging volatile substances with an adhesive layer made of a completely cured mounting agent made by adding a glycol-based curing agent to a urethane prepolymer. 2. The laminate material according to claim 1, wherein the inner layer is an ethylene-vinyl acetate copolymer film having a vinyl acetate content ranging from 3 mol% to 50 mol%. 3. The laminated material according to claim 1, wherein the outer layer comprises a completely saponified polyvinyl alcohol film or a saponified ethylene-vinyl acetate copolymer film having a thickness of 12 to 75 μm. 4 Claim 1 in which the inner layer comprises an ethylene-vinyl acetate copolymer film having a thickness of 20 to 80μ
Laminated material according to items 3 to 3.