JPS6331957Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a food container whose main material is a synthetic resin foam sheet, and particularly to a food container suitable for heating and cooking in a microwave oven.

BACKGROUND ART Recently, food storage containers that can be directly cooked (including heating treatment) in a microwave oven have been put on the market as packaging containers for various foods. The performances normally desired for such food containers are: (a) heat resistance that does not substantially cause dimensional changes or deformation even when heated while storing food;

(b) It must have enough rigidity to be held by holding one end while storing food.

(c) It must have enough insulation to be able to be held directly in the hand after cooking.

(d) Stored food retains heat well once heated.

(e) Must be water and oil resistant.

(f) There should be no food hygiene problems.

(g) Give a favorable impression in terms of appearance.

etc.

Conventionally, containers made of a composite material of paper and polyester resin have been used as food storage containers that can be heated and cooked.
It is not completely satisfactory in points B, C, and D. For example, when heated in a microwave oven, the wrap film may become deformed due to its shrinkage force or water vapor pressure, or it may become hot when held in the hand immediately after cooking. It had drawbacks such as being difficult to handle and allowing heated food to cool easily. Furthermore, since the base material of the container is paper, it is necessary to overlap the corner portions in order to make it into a container shape during manufacturing. There was a problem in that the container was difficult to manufacture.

Therefore, the inventors of the present invention attempted to develop a food container that can be heated and cooked directly, and which does not feel hot even when held in the hand immediately after cooking, and which retains its shape. A study was conducted assuming that synthetic resin foam was not used. Traditionally,
Synthetic resin foams such as polystyrene resin foam sheets are used for various purposes such as containers, but there is no food product on the market that can be directly heated in a microwave oven. this is,
In particular, polystyrene resin foams, etc., which are often used in containers such as cutlet ramen, do not have sufficient heat resistance, and although there are no problems with rigidity and shape retention at room temperature, the rigidity decreases significantly when heated. It becomes easily deformed, does not necessarily have sufficient oil resistance at high temperatures, and is not suitable as a container for cooking in a microwave oven, which can reach temperatures around 100℃ or higher, and other foams with good heat resistance are not suitable. This is because, in the case of containers, there are problems such as high cost and difficulty in molding them into container shapes.

In view of the above, the inventors of the present invention have conducted further research and consideration, and have found that a foamed sheet made of a mixed resin of polyphenylene ether resin and polystyrene resin has high rigidity and heat resistance, and has high rigidity when heated. In particular, if a thermoplastic resin film with a high glass transition temperature is laminated on this foam sheet,
It was discovered that the rigidity and shape retention during heating can be further enhanced, and the moldability and other attributes can also be improved, making it extremely suitable for use as a food container that can be heated and cooked directly in a microwave oven.The present invention is based on this knowledge. This is what was done.

That is, the present invention uses 10 to 50% by weight of polyphenylene ether resin and 90 to 50% by weight of polystyrene resin.
Foaming ratio 3 to 80 made from resin mixed with weight%
A food product that is integrally formed from a composite sheet made by laminating a thermoplastic resin film with a glass transition point of 100°C or higher, or a multilayer synthetic resin film containing the same film, on at least one side of a foamed sheet with a thickness of 1 to 6 mm. The gist is the container.

Next, embodiments of the present invention will be described based on the drawings.
In the figure, A indicates a food container according to the present invention,
At least one side of a foamed sheet 1 obtained by extruding and foam-molding a mixed resin of a polyphenylene ether resin and a polystyrene resin contains a thermoplastic resin film 2 having a glass transition point of 100° C. or higher, or the same film 2. The material is a composite sheet made by laminating multiple layers of synthetic resin films, and this is press-molded.
It is integrally molded into a desired container shape as shown in FIG. 1, FIG. 3, FIG.

The mixed resin that is the material of the foamed sheet 1 is composed of polyphenylene ether resin and polystyrene resin, and one of the polyphenylene ether resins is poly(2,6-
Phenylene ether resins known in the art such as dimethylphenylene-1,4-ether) and poly(2,6-diethylphenylene-1,4-ether) can be used, and styrene compounds can be copolymerized. You can also use On the other hand, as the polystyrene resin, in addition to polystyrene resin, a copolymer resin of styrene and maleic anhydride, other styrene-based copolymers, AS resin, ABS resin, etc. can be used. Further, a resin obtained by adding and mixing an inorganic filler such as talc to the above-mentioned mixed resin can also be used. It is preferable to reduce the foaming ratio of the skin layer of this foamed sheet, or to form a skin layer that is hardly foamed.

The above mixed resin needs to have a mixing ratio of 10 to 50% by weight of polyphenylene ether resin and 90 to 50% by weight of polystyrene resin. In other words, polyphenylene ether resin is 50% of the mixed resin.
If it exceeds 10% by weight, the heat resistance and rigidity of the obtained foamed sheet will improve, but the sheet formability will be poor and it will be difficult to form it into the desired container shape, and if it is less than 10% by weight, the sheet formability will be good. However, the resulting container has insufficient heat resistance and rigidity, making it difficult to handle after cooking in a microwave oven, which is undesirable. In addition, this mixed resin contains various known additives as necessary.

Further, the foamed sheet 1 needs to have a foaming ratio of 3 to 80 times and a thickness of 1 to 6 mm. In other words, if the expansion ratio exceeds 80 times, even if the thickness is 6 mm and the thickness of the laminated film layer is relatively thick, the rigidity will be insufficient, and when holding food by holding one end while storing it or heating it. deformation is likely to occur, and if the container is less than 3 times as large, the heat insulation properties will be insufficient and the handling after cooking will be almost the same as that of conventional paper-polyester containers, which is unsuitable. Further, if the thickness exceeds 6 mm, thermoformability deteriorates and it becomes difficult to mold into a container shape, and if the thickness is less than 1 mm, it is still unsuitable in terms of heat insulation and shape retention. Such expansion ratio and thickness can be set by changing the extrusion foam molding conditions.

Glass transition point laminated to the above foam sheet 1
As the thermoplastic resin film 2 at 100℃ or higher,
In addition to polycarbonate, polyphenylene oxide, polysulfone, high-density polystyrene, polymethyl methacrylate, polyacrylonitrile, polymethacrylonitrile, polyvinyl formal, cellulose acetate, cellulose butyrate, poly-p-vinylbenzyl alcohol, polyvinylpyrrolidone, poly- Examples include thermoplastic resins such as α-methylstyrene and poly-tert-butylstyrene, among which those with a glass transition point of 105° C. or higher are preferably used. In particular, there are various types of polycarbonates, among which many aromatic polycarbonates or aromatic-containing polycarbonates have a glass transition point of 100° C. or higher, and the polycarbonate can be appropriately selected from among them. 4,4'-dioxydiphenyl-2,2'propane polycarbonate is one of them and is highly preferred.

The glass transition point is the temperature at which glass transition occurs, and below the glass transition point of materials such as thermoplastic resins, the motion of molecules and molecular segments is frozen, and therefore they remain in an extremely rigid state. Furthermore, this glass transition point is not uniquely determined by the type of resin, but varies depending on the degree of polymerization, molecular structure, molecular form, copolymerization components, etc.

There are various methods for measuring the glass transition point, but here we will use differential thermal analysis (DTA), and if clear data cannot be obtained, thermomechanical analysis (TMA) will also be used as a supplement. In both cases, the temperature increase rate is 5°C/min. In addition, if the resins are mixed and completely alloyed, the glass transition point of the mixed product is taken as the glass transition point, and if there are multiple transition points due to insufficient kneading, the glass transition point of the component resin is weighted by the component weight ratio. Take the average.

As shown in FIG. 1 or 2, this thermoplastic resin film 2 is laminated as a single layer on one or both sides of the foamed sheet 1 to form a composite sheet that is a constituent material of the food container A. others,
As shown in FIG. 5 or 6, a multilayer film 4 is formed by the thermoplastic resin film 2 and another resin film layer 3, and the multilayer film 4 is formed into a foamed sheet 1.
It can also be carried out by laminating them. In order to further improve oil resistance, gas barrier properties, etc. as a food container, as the resin film layer 3,
We use synthetic resin films with relatively good oil resistance and gas barrier properties (including moisture and vapor barrier properties) such as polyolefin resins such as polyethylene and polypropylene, polyester resins, polyvinylidene chloride resins, and polyamide resins. use,
It is preferable that the resin film layer 3 is laminated on one side (FIG. 5) or both sides (FIG. 6) of the foam sheet so as to serve as a surface layer. In particular, when the lamination is on one side of the foam sheet, the resin film layer 3 shown in FIG. It is preferable to mold the resin film layer 3 toward the inner surface of the container. Even when the thermoplastic resin film 2 is laminated in a single layer on a foamed sheet, it is desirable to laminate or coat at least the inner surface of the container with a synthetic resin similar to the resin film layer 3 as a surface layer. In this way, if a resin film layer with good oil resistance and gas barrier properties is provided at least as the inner surface layer of the container, it is possible to prevent the harmful effects of cooking oil, etc. that occur during heating, and further enhance the preservation of the stored food. I can do it.

The foamed sheet 1 and the thermoplastic resin film 2 and the thermoplastic resin film 2 and the resin film layer 3
In any case of lamination, there are two methods: heat-sealing without an intermediate layer and methods using an intermediate layer for adhesion. The intermediate layer may be a single layer or multiple layers of different types, and may be a heat-sealable thermoplastic resin film or a material commonly called an adhesive. Each of these may be used alone or both may be used in combination. However, in the case of adhesives containing volatile components, it is preferable to use adhesives that can be dry laminated (heat fused) after application and drying. A curable type containing no volatile components is also preferred. As a specific example, an acrylic resin type adhesive, a urethane resin type adhesive, or the like is used as the adhesive. Further, as the heat-fusion film, ethylene vinyl acetate copolymer resin, polystyrene resin, etc. are suitable. Note that in order to make the adhesion stronger, it may be preferable to use what is called an anchor coating agent.

In addition, the thickness of the thermoplastic resin film 2 is 30~
The preferred thickness is 500 microns; if this thickness is too thin, the effect of laminating the films, that is, the rigidity retention effect, especially when heated, will be reduced, and if it is too thick, the container itself will become heavy. This also increases costs, which is undesirable. Furthermore, the thickness of the other resin film layer 3 used together with the film 2 is preferably about 5 to 200 microns, and the thickness of the multilayer film 4 as a whole is preferably set to about 35 to 550 microns, so that it is not too thick. If it is too large, it becomes heavy and costly, which is not preferable.

As mentioned above, in the food container of the present invention, the foam sheet 1, which is the main component thereof, is made of a mixed resin of polyphenylene ether resin and polystyrene resin, and this itself has good rigidity and heat resistance, and can be heated easily. In addition to being able to maintain considerable rigidity, especially when one side of this foam sheet 1 has a glass transition temperature of 100
Since it is laminated with a thermoplastic resin film 2 or a multilayer film of synthetic resin containing thermoplastic resin film 2 with a temperature of ℃ or above, rigidity and shape retention are important factors when used as a food container for direct cooking in a microwave oven. is further improved, and can maintain sufficient rigidity and shape retention even when heated. In other words, since the thermoplastic resin film 2 has a glass transition point of 100°C or higher, even when heated to around 100°C, it can maintain almost the same rigidity as at room temperature. The rigidity of the foam sheet when heated in a microwave oven is compensated for by the laminated film layer, and it has extremely excellent rigidity and shape retention even when heated as a food container.

In particular, when the thermoplastic resin film 2 is laminated on both sides of the foamed sheet 1, a so-called skin-core-skin sandwich structure is formed, which is more effective in exhibiting heat-resistant rigidity from a mechanical standpoint. Moreover, other attributes such as water resistance and oil resistance are improved by the laminated film layer compared to the foam sheet alone, and of course, the foam sheet 1 also has good insulation properties and heat retention of heated foods. .
Therefore, the container of the present invention has the above-mentioned performances desired as a food container for heating and cooking.
It satisfies all of E, F and G,
It can be suitably used as a food container that can be heated in a microwave oven. Further, the moldability of the composite sheet is good, and food containers having complicated tray shapes as shown in FIGS. 3 and 4 can be easily molded, mass-produced, and provided at a relatively low cost.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, in which Fig. 1 is a perspective view, Fig. 2 is an enlarged sectional view taken along the line - front figure, and Figs. 3 and 4 are partially cutaway views of containers with different shapes. The cutaway perspective view, FIG. 5, and FIG. 6 are respectively sectional views corresponding to FIG. 2 showing other embodiments. A... Food container, 1... Foamed sheet of mixed resin, 2... Thermoplastic resin film, 3... Other resin film layer.

Claims (1)

[Scope of claims for utility model registration] 1. Polyphenylene ether resin 10-50% by weight
Foaming ratio 3 to 80 times, thickness 1 to 6, made from a mixed resin of 90 to 50% by weight of polystyrene resin
A food container that is integrally formed from a composite sheet in which a thermoplastic resin film with a glass transition point of 100°C or higher or a multilayer film of a synthetic resin containing the same film is laminated on at least one side of a foam sheet of 1.0 mm in diameter. 2. The food container according to claim 1, wherein the thermoplastic resin film having a glass transition point of 100° C. or higher is made of polycarbonate resin. 3. The multilayer sheet is provided with a resin film layer of any one of polyolefin resin, polyester resin, polyvinylidene chloride resin, and polyamide resin as the inner surface layer of the container. The food container according to item 1 or 2.