JP2000302178A - Food packaging body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unseal an opening/closing port of a packaging material automatically or with a small force by adhering the opening/closing port of the packaging material storing a food inside by an adhesive layer containing thermal expandable small balls, and expanding the thermal expandable small balls by the heat generated by a microwave oven or an oven. SOLUTION: A food packaging body is manufactured by adhering an opening/ closing port of the packaging material storing a food inside by an adhesive layer 3 containing thermal expandable small balls. The contained thermal expandable small balls are deformed unevenly by the heat using such an adhesive layer 3, the adhesive force is reduced or lost to enable the opening of the opening/closing port of the packaging material at an arbitrary time. The adhesive layer 3 containing the thermal expandable small balls is provided together with a base material 1, a rubber-like organic elastic layer 2 and a separator 4 as necessary. The thermal expandable small balls include a micro capsule internally housed inside a shell formed of an appropriate substance to be easily gasified and show the thermal expandability, for example, a thermal melting substance or a substance to be destroyed through thermal expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a food package that can be easily opened by heat treatment and that is suitable for packaging frozen foods.

[0002]

2. Description of the Related Art Conventionally, a food package having a sealed opening / closing opening in a packaging material such as a bag or a tray with a lid for containing frozen foods, etc., is obtained by fusing the packaging material in the opening / closing portion, an adhesive layer, and the like. What was adhered by the adhesive layer was known. However, when thawing or cooking by heating frozen foods in a microwave oven or oven, etc., when the packaging material ruptures due to an increase in internal pressure due to water vapor etc. and the contents scatter or the opening / closing opening is opened. There has been a problem that high-temperature steam or the like is ejected and burns occur, or a tray or the like is deformed by the force when the opening and closing opening is opened, and the contents are discharged.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to develop a food package capable of preventing the rupture of the packaging material due to the increase in internal pressure caused by the heat treatment, the ejection of high-temperature gas when opening the opening and closing, and the deformation of the container. And

[0004]

According to the present invention, there is provided a food package characterized in that an opening and closing opening of a packaging material containing food therein is adhered with an adhesive layer containing heat-expandable microspheres.

[0005]

According to the present invention, the heat-expandable microsphere-containing pressure-sensitive adhesive layer exhibits a strong adhesive force before heating, thereby achieving the sealing treatment of the opening and closing of the packaging material, and at the same time as the microwave oven and oven. The heat-expandable microspheres contained in the pressure-sensitive adhesive layer expand by heating through a heating cooker, and the pressure-sensitive adhesive layer is deformed unevenly, and the adhesive force is reduced or lost.

As a result of the above, the opening and closing of the packaging material can be easily opened by heating the frozen food or the like for the purpose of thawing or cooking. When the internal pressure of the packaging material rises with steam or the like, the opening and closing opening is opened. As a result, degassing is achieved, and an increase in the internal pressure leading to the rupture of the packaging material is prevented, so that the scatter of the stored material due to the rupture is prevented.

[0007] Further, when the opening and closing port is opened by degassing, the ejection of high-temperature gas can be prevented, and burns can be prevented. Further, the opening / closing opening of the packaging material can be opened automatically or with a small force, so that the container such as a tray can be prevented from being deformed by the opening force, and the contents can be prevented from flowing out or spilling. be able to.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A food package according to the present invention is one in which an opening and closing port of a packaging material containing food is adhered to an adhesive layer containing thermally expandable microspheres. As described above, the pressure-sensitive adhesive layer is subjected to uneven deformation by heating based on the contained heat-expandable microspheres to reduce or lose the adhesive force.

Therefore, the food package can be heated at any time to open the opening of the packaging material. FIG. 1 shows an example of the above-mentioned adhesive layer. 3 is an adhesive layer containing heat-expandable microspheres. In addition, 1, 2, and 4 are a base material, a rubber-like organic elastic layer, and a separator, respectively, provided as needed.

The pressure-sensitive adhesive layer can be formed, for example, as a mixed layer of one or more pressure-sensitive adhesives and one or more heat-expandable microspheres. The pressure-sensitive adhesive is not particularly limited, and an appropriate one can be used. By the way, examples include rubber-based and acrylic-based, styrene-conjugated diene block copolymer-based and fluorine-based, vinyl alkyl ether-based and silicone-based, polyester-based and polyamide-based,
Those using polymers such as urethanes are exemplified.

[0011] Examples of the pressure-sensitive adhesive include those in which a heat-melting resin having a melting point of about 200 ° C or less is blended to improve the creep characteristics. The pressure-sensitive adhesive to be used is, if necessary, one of appropriate additives such as a crosslinking agent and a tackifier, a plasticizer and a softener, a filler and a pigment, a colorant and an antioxidant.
It may be a mixture of seeds or two or more kinds.

[0012] The pressure-sensitive adhesive generally used in the above,
For example, a rubber-based pressure-sensitive adhesive using a rubber-based polymer such as natural rubber, polyisoprene rubber, recycled rubber or butyl rubber, polyisobutylene or NBR as a base polymer;
Styrene such as butadiene rubber, styrene / isoprene / styrene block copolymer rubber, styrene / butadiene / styrene block copolymer rubber, and hydrogenated products thereof
A styrene / conjugated diene block copolymer-based pressure-sensitive adhesive using a conjugated diene block copolymer as a base polymer.

For example, methyl, ethyl, propyl, butyl, 2-ethylhexyl, isooctyl, isononyl, isodecyl, dodecyl, lauryl, tridecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl Adhesives using an acrylic polymer containing an acrylic alkyl ester such as acrylic acid or methacrylic acid having an alkyl group having 20 or less carbon atoms, such as a nonadecyl group or an eicosyl group as a base polymer. Agents and the like are also generally used.

The above-mentioned acrylic polymers include, for example, acrylic acid and methacrylic acid, itaconic acid and hydroxyethyl acrylate, hydroxyethyl methacrylate and hydroxypropyl acrylate, hydroxypropyl methacrylate and N-methylolacrylamide, acrylonitrile and methacrylic acid. A copolymer containing one or more modified monomers such as lonitrile, glycidyl acrylate or glycidyl methacrylate, vinyl acetate or styrene, isoprene or butadiene, isobutylene or vinyl ether may be used.

The pressure-sensitive adhesive which can be preferably used from the viewpoint of forming a pressure-sensitive adhesive layer in which a strong adhesive force before heating and a decrease in adhesive force after heating are balanced has a dynamic elastic modulus in a temperature range of room temperature to 150 ° C. 50,000 to 10 million dyn / cm
^The polymer in the range of ² is used as a base polymer.

On the other hand, as the heat-expandable microspheres to be incorporated into the adhesive layer, for example, an appropriate substance which is easily gasified and has a heat-expandability, such as isobutane, propane or pentane, is subjected to coacervation method, interfacial polymerization method, Shell-forming substances in an appropriate manner, for example, vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, a heat-fusible substance such as polysulfone, and a substance which is destroyed by thermal expansion. And microcapsules contained inside a shell made of.

By using the heat-expandable microspheres, the operation of reducing the adhesive force by heating can be stably performed. In the case of a foaming agent that has not been made into a heat-expandable microsphere, the adhesive strength may not be sufficiently reduced by heating. From the viewpoint of the operability of reducing the adhesive force by heating, and particularly the stable achievement of the reduction of the adhesive force, the thermal expansion of the volume expansion before rupture is 5 times or more, especially 7 times or more, especially 10 times or more. Sexual microspheres are preferably used.

The average particle size of the heat-expandable microspheres to be used can be appropriately determined, and is generally 100 μm or less, particularly 80 μm or less, and particularly 1 to 50 μm, but is not limited thereto. From the viewpoint of preventing the adhesive strength from being reduced due to the unevenness of the surface of the adhesive layer, those having a maximum particle size smaller than the intended thickness of the adhesive layer are preferably used. Note that the heat-expandable microspheres include commercially available products such as microspheres (trade name, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.).

The amount of the heat-expandable microspheres may be appropriately determined according to the expansion ratio of the pressure-sensitive adhesive layer and the ability to reduce the adhesive strength.
Generally, per 100 parts by weight of the base polymer of the adhesive,
1 to 150 parts by weight, preferably 10 to 130 parts by weight, especially 25
１００100 parts by weight of thermally expandable microspheres are used.

The formation of the pressure-sensitive adhesive layer is performed, for example, by mixing the components such as the pressure-sensitive adhesive and the heat-expandable microspheres with a solvent, if necessary,
The mixture can be spread on a base material or a separator by an appropriate spreading method such as a casting method or a coating method to form a sheet-like layer. In forming the pressure-sensitive adhesive layer, if necessary, for example, a polymer or a wax that permits the heat expansion of the heat-expandable microspheres may be added for an appropriate purpose such as adjustment of the adhesive force.

The thickness of the pressure-sensitive adhesive layer to be formed can be appropriately determined depending on the adhesive strength and the reducing property. Generally, from the viewpoint of good adhesive strength before heating and reduction or loss of adhesive strength after heating, it is 5 to 300 μm or less, especially 10 to 200 μm.
m, particularly 20 to 150 μm.

The pressure-sensitive adhesive layer containing the heat-expandable microspheres can be formed in an appropriate form such as a form composed of a single layer having no base material or a form supported by the base material 1 as shown in the figure. . Also in the case of supporting with a substrate, for example, a form having a heat-expandable microsphere-containing adhesive layer on one or both surfaces of the substrate, or having a heat-expandable microsphere-containing adhesive layer on one surface of the substrate,
An appropriate form such as a form having an adhesive layer containing no heat-expandable microspheres on the other surface, or a form in which a substrate is embedded in the adhesive layer can be used.

The above-mentioned single type adhesive layer and the type having an adhesive layer on both sides of a substrate are generally used in a method of arranging the inside of the packaging material and adhering the packaging material to both sides thereof. The type having a pressure-sensitive adhesive layer on one side of the material 1 is generally used in a method of bonding from the outside of the packaging material.

When the pressure-sensitive adhesive layer is supported by a substrate, the pressure-sensitive adhesive layer may be provided on the substrate via an intermediate layer.
Furthermore, it can also be formed as a separation type in which the substrate and the adhesive layer or the intermediate layer can be easily peeled off, or a fixed type in which the substrate and the adhesive layer or the intermediate layer are strongly bonded.

The above-mentioned separation type can be used, for example, when used as a single-type adhesive layer, and can be formed, for example, by using a separator as a base material. The separator is, for example, one obtained by subjecting the base material to a surface treatment with an appropriate release agent such as a silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide, or polytetrafluoroethylene, polychlorotrifluoroethylene, or polyvinyl fluoride. Low-adhesion base material composed of a fluorine-based polymer such as polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer or chlorotrifluoroethylene-vinylidene fluoride copolymer, and low adhesion material composed of a nonpolar polymer such as polyethylene or polypropylene. It can be obtained as an adhesive substrate or the like.

On the other hand, the fixed type can be formed using, for example, a substrate having excellent adhesion to the adhesive layer. The base material is, for example, a method using a strongly adhesive film made of a polymer having high polarity such as polyester, a chemical or physical method such as a chromic acid treatment, an ozone exposure, a flame exposure, a high piezoelectric shock exposure, and an ionizing radiation treatment. A suitable treatment such as a surface oxidation treatment is performed on the base material. For improving the adhesion between the substrate and the adhesive layer, a method of providing an undercoat layer on the substrate is also effective.

Examples of the base material include plastic films and papers, cloths and nonwoven fabrics, rubber sheets and foam sheets,
An appropriate thin leaf such as a metal foil, a laminate thereof, or a net can be used. Among the substrates other than the separator, those having excellent heat resistance that does not melt at the heat treatment temperature of the adhesive layer are preferable from the viewpoint of handling properties after heating. The thickness of the substrate can be appropriately determined according to strength, flexibility, and the like.
0 μm or less, especially 1 to 300 μm, especially 5 to 250 μm.

The intermediate layer optionally provided between the base material and the adhesive layer may be, for example, a coating layer of a release agent for imparting the above-mentioned releasability, or an undercoat for improving the adhesion. It may have an appropriate purpose like a layer. One or more intermediate layers can be provided between the substrate and the adhesive layer.

Incidentally, examples of the intermediate layer other than the above-mentioned release coat layer and undercoat layer include a layer for the purpose of imparting good deformability, a layer for the purpose of increasing the adhesion area with the packaging material,
A layer intended to improve the adhesive strength, a layer intended to favorably follow the surface shape of the packaging material, a layer intended to improve the processability of reducing the adhesive strength by heating, and an improved peeling property after heating. Layers for the purpose of

In the above description, it is more effective to provide the rubbery organic elastic layer 2 as an intermediate layer as shown in the figure from the viewpoints of imparting deformability and improving peelability after heating. Such a rubber-like organic elastic layer has a function of providing a large bonding area by following the surface shape of the pressure-sensitive adhesive layer when bonding the pressure-sensitive adhesive layer to the packaging material, a function of increasing the controllability of expansion of the pressure-sensitive adhesive layer during heating, and a function of heating. Thereby, the pressure-sensitive adhesive layer expands more in the thickness direction than in the plane direction, thereby promoting unevenness deformation such as a undulation structure, thereby improving the stability of reducing the adhesive force.

The rubbery organic elastic layer, which is more preferable in view of the above-mentioned workability and the like, is preferably a natural rubber or a synthetic rubber having a hardness of 50 or less, particularly 45 or less, particularly 40 or less, based on the D-type hardness measured by a D-type Shore of ASTM D-2240. It is formed of rubber, a synthetic resin having rubber elasticity, various adhesives, or the like. The thickness is usually 5 to 500 μm from the point of the above work
Hereinafter, it is particularly 10 to 300 μm, particularly 20 to 150 μm, but is not limited thereto.

Examples of the synthetic rubber or synthetic resin include synthetic rubber such as nitrile, diene and acrylic, thermoplastic elastomer such as polyolefin and polyester, ethylene-vinyl acetate copolymer, polyurethane, polybutadiene and the like. Synthetic resins having rubber elasticity, such as soft polyvinyl chloride, may be used. In the present invention, an essentially rigid polymer, such as polyvinyl chloride, having rubber elasticity in combination with a compounding agent such as a plasticizer or a softening agent may be used.

The formation of the rubber-like organic elastic layer is carried out by an appropriate method such as a method of applying a solution of the forming material on a base material or a method of bonding a film or the like made of the forming material to the base material. be able to. Therefore, the target adhesive layer can be formed by a method in which a rubbery organic elastic layer and an adhesive layer separately formed are sequentially laminated. The rubbery organic elastic layer may be formed of an adhesive substance containing the above-mentioned forming material as a main component, or may be formed of a foamed film or the like mainly containing such a component.

The adhesive layer according to the present invention forms the food package by bonding the opening and closing opening of the packaging material containing the food therein as described above. It is preferable to temporarily attach the separator 4 or the like to the pressure-sensitive adhesive layer as shown in the figure to prevent a decrease in adhesive strength due to contamination.

There is no particular limitation on the packaging material to be bonded, and for example, any suitable packaging paper or sheet or container such as a bag or a tray with a lid can be used as the bonding target. There is no limitation. The material of the packaging material is not particularly limited because it can be bonded by a pressure bonding method via an adhesive layer. Therefore, it can be applied to any of the known packaging materials.

Further, there is no particular limitation on the opening / closing opening of the packaging material to which the adhesive layer is adhered, and it is also possible to carry out an adhesive treatment at two or more places which can serve as the opening / closing opening. The form of the opening and closing port for bonding the adhesive layer is also arbitrary. In addition, the adhesive treatment is usually a sealing treatment method for the purpose of preserving packaged food, etc.,
It is not limited to this.

In the food package according to the present invention, the adhesive force of the pressure-sensitive adhesive layer can be reduced or lost by a heat treatment through a heating cooker such as a microwave oven or an oven, so that the opening and closing opening of the packaging material can be opened. By the way, it depends on the temperature of 90-250 ° C.
In the usual case of a heat treatment for 2 seconds to 20 minutes, especially 10 seconds to 5 minutes, a treatment for reducing the adhesive strength of the adhesive layer can be achieved.

The food package according to the present invention can be preferably applied to frozen foods to be thawed or cooked while stored in a packaging material, but is not limited to this, and can be applied to the packaging of various foods.

[0039]

EXAMPLE 1 Thermally expandable microspheres (75 parts by weight of butyl acrylate, 100 parts of an acrylic copolymer composed of 25 parts of ethyl acrylate and 5 parts of acrylic acid) were added to a toluene solution containing 75 parts of butyl acrylate (the same applies hereinafter). An acrylic pressure-sensitive adhesive containing 50 parts of Microsphere F-50D) and 5 parts of a polyurethane-based cross-linking agent was applied to a thickness of 5 parts.
0μm polyester film separator coated on the silicone release coating surface, dried to a thickness of 40μ
After forming a pressure-sensitive adhesive layer of m, a small amount of water was put between the polymer tray and the paper lid through the pressure-sensitive adhesive layer peeled off from the separator to obtain a food package.

Example 2 Acrylic adhesive obtained by mixing 10 parts of a terpene-based tackifying resin and 3 parts of a polyurethane-based crosslinking agent in a toluene solution containing 100 parts of an acrylic copolymer composed of 100 parts of butyl acrylate and 5 parts of acrylic acid. The agent was applied on a polyester film having a thickness of 50 μm and dried to form a rubber-like organic elastic layer having a thickness of 35 μm, on which an adhesive layer containing the heat-expandable microspheres obtained according to Example 1 was separated. More transfer to obtain an adhesive sheet, glue it from the outside of a paper lid attached to a polymer tray filled with a small amount of water and seal it,
A food package was obtained.

Evaluation Test The food package obtained in the above example was placed in a household microwave oven and heated at 120 ° C. for 2 minutes. As a result, the adhesive force of the adhesive layer was substantially lost, and the lid could be spontaneously peeled off. At that time, neither the ejection of steam nor the leakage of water due to the deformation of the tray occurred.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of an adhesive layer.

[Explanation of symbols]

 1: base material 2: rubbery organic elastic layer 3: adhesive layer containing heat-expandable microspheres 4: separator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Muraki Akiri 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Kazuyuki Kiuchi 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation F term (reference) 3E064 HN02 3E067 AA11 AB01 BA07A BA10A BA12A BB14A BC07A CA17 CA24 EA06 EA12 GB02 4B022 LB02 LJ06

Claims (2)

[Claims] 1. A food package wherein an opening and closing opening of a packaging material containing food therein is adhered with an adhesive layer containing heat-expandable microspheres. 2. The food package according to claim 1, wherein the stored food is frozen food, the packaging material is a bag or a tray with a lid, and the adhesive layer is supported by a single layer or a base material.