JPH0423634Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a food container for heating in a microwave oven. More specifically, the present invention relates to a microwave cooking food container made of a laminated foam sheet with excellent heat resistance and capable of being cooked in a high frequency range such as a microwave oven. [Prior Art] In recent years, with the rapid spread of microwave ovens, a method of cooking food in a microwave oven while it is still in a container is being adopted. Containers made of paper containers coated with a film such as polyester film or polymethylpentene (hereinafter referred to as paper coated containers) and containers made of polypropylene sheets are often used. However, with paper-coated containers, it is difficult to obtain a container with the desired shape, and the container itself is also heated when food is heated in the microwave, so it is difficult to remove the container directly from the microwave by hand. There are problems such as not being able to do it. In addition, molded polypropylene sheet containers are not only difficult to mold, but also expensive because they require the use of thick sheets of 1 mm or more in order to maintain the rigidity of the container at high temperatures. Similarly, there are problems such as the container itself being heated when the food is heated. In order to solve these problems, especially the problem that the container itself gets heated when heating food, a molded container made of a laminated film made by laminating a polypropylene film on a foamed styrene sheet has been developed. If the thickness of the laminated film that makes up the container is as thin as 25 to 70 μm, boiling water may cause wrinkles on the surface of the molded container or the molded container itself may become deformed. Therefore, it cannot be applied to containers for cooking in a microwave oven. In order to obtain a molded container that can be used for cooking in a microwave oven and is not deformed by boiling water, the thickness of the polypropylene film must be 200 μm.
It is necessary to make it more than a certain degree. However, in this case, since the difference in heat softening temperature and heat shrinkage rate between the foamed styrene sheet and the polypropylene film is large, molding is extremely difficult, and there are problems such as peeling on the laminated surface. In addition, in sheets made by laminating a polypropylene film on a foamed styrene sheet, polystyrene and polypropylene are not compatible with each other, so it is not possible to melt and recycle the remaining laminated sheet after punching the molded product, which is economically disadvantageous. However, there is a problem in that a large amount of waste is generated and it is difficult to dispose of it. [Problems that the invention attempts to solve] Therefore, the inventors of the present invention have conducted extensive research to solve the above-mentioned problems, and have found that no deformation occurs even when boiling water is poured into the product. We have discovered a food container for cooking in a microwave oven that can be used as a container for cooking in a microwave oven and has a desired shape that does not cause the outside to become hot even when food is cooked. I've come to the point where I can complete it. [Means for solving the problem] In other words, the present invention has a softening point of 115°C.
A food container made of a laminated foam sheet made by thermally bonding a biaxially stretched film made of the copolymer of styrene and a carboxyl group-containing monomer as described above to a foam sheet made of a styrene resin with a Vikatsu softening point of 95°C or higher. and the softening point of the copolymer of styrene and a carboxyl group-containing monomer is lower than or equal to a temperature 35° C. higher than the Vikato softening point of the styrenic resin constituting the foamed sheet,
The present invention also relates to a food container for heating in a microwave oven, characterized in that the biaxially stretched film is provided on the inner surface of the container. [Example] The food container for cooking in a microwave oven of the present invention will be described in detail below. The food container for cooking in a microwave oven of the present invention is made of a copolymer of styrene and a carboxyl group-containing monomer, which has a Vikatsu softening point of 115°C or higher.
It consists of a laminated foam sheet in which an axially stretched film is thermally bonded to a foam sheet made of a styrene resin having a Vikato softening point of 95°C or higher, and the softening point of the copolymer of styrene and a carboxyl group-containing monomer is The temperature is 35° C. higher than the Vikato softening point of the styrene resin constituting the sheet, and the biaxially stretched film is provided on the inner surface of the container. Examples of the copolymer of styrene and a carboxyl group-containing monomer having a Vikatsu softening point of 115°C or higher include styrene-maleic anhydride copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, and styrene. Examples include copolymers of styrene and carboxyl group-containing monomers such as - itaconic acid copolymers, and blends of these copolymers with polymers such as polystyrene, polycarbonate, and polyphenylene oxide. By the way, since the copolymer of styrene and a carboxyl group-containing monomer has hydrophilicity, a copolymer with a Vikatto softening point lower than 115°C may shrink in boiling water.
It is necessary to use a copolymer that has a temperature of at least ℃. Note that in this specification, the Vikato softening point is a value measured based on ASTM D-1525. When a film made of a copolymer of styrene and a carboxyl group-containing monomer having a Vikatsu softening point of 115°C or higher is an unstretched or uniaxially stretched film, the film lacks toughness in the unstretched direction, and the film becomes weak during molding. may break, so
It must be biaxially stretched. Further, in order to prevent the film from tearing during molding, it is preferable that the folding strength measured based on ASTM D2176 is about 5 times or more. The orientation ratio of the biaxial direction of the biaxially stretched film, that is, the extrusion direction/width direction, is 0.7/1.0 to 1.4/1.0,
It is particularly preferable that the ratio is 1/1. The orientation ratio is
If it is smaller than 0.7/1.0 or larger than 1.4/1.0, the resulting molded product may be deformed in the direction of stronger orientation. Note that the orientation referred to in this specification is based on the shrinkage when the film is immersed for 5 seconds in an oil bath at a temperature 50°C higher than the Vikato softening point of the raw material resin. ]/[Dimensions of the film after being immersed in an oil bath and shrunk], and both the orientation in the extrusion direction and the orientation in the width direction are preferably 1.3 or more.
If the orientation is less than 1.3, it becomes difficult to secure toughness of about 5 times bending strength. Furthermore, as a result of investigating the influence of the biaxially stretched film on the heat resistance and moldability of a molded container, it was found that it is closely related to the hot stretching behavior of the film at high temperatures. Tensile load is particularly important in hot stretching behavior, and the tensile load at 10% elongation is 1.0Kg/1cm width or more in a 100℃ atmosphere and 0.7Kg/1cm width or less in a 130℃ atmosphere. Preferably.
The above-mentioned tensile load varies depending on the thickness of the film and the type of film material, but the directionality of the tensile load is governed by the strength in the direction of strength, and the tensile load at 10% elongation in an atmosphere of 100°C is 1.0 kg/ 1cm
When water is poured into a molded body made from a laminated foam sheet made by laminating a biaxially stretched film smaller than the width of the foam sheet, and the water is boiled in a microwave oven, the surface of the foam sheet resists the force of expansion due to heating. Unevenness occurs on the surface of the film, and the molded product is deformed due to shrinkage of the film. In addition, for biaxially stretched films whose tensile load at 10% elongation in an atmosphere of 130°C is greater than 0.7 kg/1 cm width, the flesh around the molded body is difficult to be drawn into the molded body during molding, and the side walls of the molded body As a result, the foamed sheet may be torn, its heat resistance may be significantly reduced, and it may be difficult to obtain a molded product having a desired shape. As mentioned above, the physical properties of the biaxially stretched film laminated to the foam sheet are extremely closely related to the formability and heat resistance of the laminated foam sheet.
In order to provide these moldability and heat resistance, it is necessary to use a copolymer of styrene and a methacrylic acid monomer, especially a methacrylic acid monomer in a copolymer of 5 to 30% by weight, among the copolymers of styrene and a carboxyl group-containing monomer. Preferably 5-15% by weight
A copolymer containing the same is preferred. Note that the thickness of the biaxially stretched film can be arbitrarily selected, and the present invention is not limited to the thickness of the biaxially stretched film. The biaxially stretched film is integrated with a foamed sheet made of styrene resin by thermal adhesion. Thermal bonding methods include, for example, a method in which the biaxially stretched film alone or both the film and the foamed sheet are heated and compressed, and polystyrene or high-impact polystyrene is bonded between the biaxially stretched film and the foamed sheet. Examples include a method of melting and extruding a styrene resin such as styrene resin, etc., and any method may be used for thermal bonding in the present invention. When thermally adhering them, it is necessary that the resin constituting the biaxially stretched film and the resin constituting the foamed sheet melt each other, and it is preferable that the softening temperatures of both resins are close to each other. If the softening temperatures of the two resins are different from each other, it is not only difficult to bond the biaxially stretched film and the foamed sheet, but also wrinkles, spots, and striped patterns may appear on the bonded surface, and even worse. When molding a laminated foam sheet, it becomes difficult to suppress the cell breakage of the foam sheet and mold it in a regular manner. Therefore, the Vikatto softening point of the raw material resin for the film made of a copolymer of styrene and a carboxyl group-containing monomer to be bonded must be 35°C higher than the Vikatto softening point of the raw material resin for the foamed sheet made of styrene resin to be bonded. be. In this case, since no foreign matter such as adhesive is mixed in during thermal bonding, it becomes possible to recycle the remaining laminated sheet after punching out the molded product. It is preferable that the raw material resin for the foamed sheet made of styrene resin has the ability to withstand the heat passed through the biaxially stretched film, that is, has a Vikato softening point of 95° C. or higher. Such styrenic resins having a softening point of 95°C or higher include polystyrene; copolymers of styrene with monomers such as acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, α-methylstyrene and methyl methacrylate, and mixtures thereof. can be given. The higher the Vikato softening point of the copolymer, the better, and in the present invention, there is no particular restriction on the upper limit. In addition, in order to improve the insulation effect of the foam sheet to the extent that it does not heat up to the outside of the container and eliminates handling problems, the thickness of the foam sheet must be 1 to 3 mm.
It is preferable to The laminated foam sheet thus obtained is molded into a container using a general molding machine for molding styrene foam, with the film side facing the inner surface of the container. A food container for cooking in a microwave oven that can be easily molded by simply adjusting the heating temperature of the film surface and foam sheet surface, and can be easily shaped with a molding cycle similar to that of ordinary foamed polyethylene, with almost no shrinkage or deformation after molding. It can be grown. Even if you fill the food container of the present invention with water, place a paper lid on it, and heat it in the microwave for longer than the boiling time of the water, the container will not deform or the film on the inside of the container will wrinkle. There are no outbreaks. Furthermore, when the water is heated to boiling point, the outside of the container is not hot to the touch, and the container is rigid and does not deform when handled by hand, making it extremely easy to handle. In addition, in the present invention, a polystyrene film or a high-impact polystyrene film may be interposed between the biaxially stretched film and the foam sheet in order to improve thermal adhesion and reduce the thickness of the biaxially stretched film. . Next, the microwave cooking food container of the present invention will be explained based on the drawings. FIG. 1 is a perspective view showing an embodiment of the microwave cooking food container of the present invention, and FIG. 2 is an enlarged sectional view taken along line A--A in FIG. 1. food container 1
is molded from a laminated foam sheet for molding so that the biaxially stretched film 2 is the inner surface and the foam sheet 3 is the outer surface, and the shape and size of this food container 1 are arbitrary in the present invention. , is determined as appropriate depending on the type and amount of food contained in the container. Note that the outer surface of the food container 1 may be decorated with printing, a decorative film, or the like. FIG. 3 is a sectional view of the bowl-shaped food container for heating in a microwave oven of the present invention. FIG. 4 is a sectional view of the bowl-shaped food container for heating in a microwave oven of the present invention. The food container 1 is formed from a laminated foam sheet for molding so that the biaxially stretched film 2 is the inner surface and the foam sheet 3 is the outer surface.A polystyrene film 4 is further provided on the outer surface of the food container 1. This has the advantage that the surface is smooth, making it easier to apply decorations such as printing. Next, the present invention will be explained in more detail based on examples, but the present invention is not limited to these examples. Examples 1-5 90% by weight styrene and 10% by weight methacrylic acid
A copolymer (Vikatto softening point: 126°C) is extruded using a T-die, and then passed through a tenter and biaxially stretched to an orientation ratio of approximately 1/1 in the extrusion direction/width direction. A laminated foam sheet for molding was prepared by thermally bonding a foamed styrene sheet (thickness: 2.0 mm, basis weight: 260 g/m ² ) using a 185° C. hot roll. In addition, the tensile load of the obtained biaxially stretched film was measured according to the following method. The obtained laminated foam sheet was molded using a single-shot molding machine for molding foamed styrene sheets, and the inner diameter was 135 mm as shown in Figure 3.
A bowl-shaped container with a depth of 50 mm was created. water in the container
Add 150c.c. (water temperature: 20℃) and 3c.c. of salad oil,
It was heated in a 600W microwave oven with a paper lid placed on it.
Note that at this time, the water began to boil 2 minutes after heating in the microwave. The condition of the container after heating was examined according to the following method. The results are shown in Table 1. (Tensile load of biaxially stretched film) Measurement was carried out using a JIS No. 1 test piece with a Strograph manufactured by Toyo Seiki Co., Ltd., at a gage spacing of 40 mm and a tensile speed of 10 mm/min. (Molded state of bowl-shaped container) Visually observe the shape of the bowl-shaped container obtained,
Evaluation was made based on the following criteria. (Judgment Criteria) ○: A molded article conforming to the shape of the mold was obtained. Δ: The uneven portions and corners of the mold were not shaped exactly as the mold. ×: There was a difference in the shape of the mold, and dimensions such as depth could not be determined. (Deformation status after heating in microwave oven) Deformation status after heating the resulting bowl-shaped container in a microwave oven was evaluated based on the following criteria. (Judgment criteria) ◎: No noticeable change. ○: There was no noticeable change when heated to boiling, but small wrinkles appeared on the film surface when heating was continued. Δ: Small wrinkles were generated on the film surface when heated to boiling. ×: Deformed before boiling.

[Table] From the results in Table 1, in an atmosphere of 100℃
It can be seen that the bowl-shaped container obtained in Example 1, in which films with a 10% tensile load of 1.0 kg/1 cm width or less were laminated, had low durability against boiling water when heated in a microwave oven. It can be seen that the bowl-shaped containers obtained in Examples 2 to 4 have good moldability and can withstand boiling water even when heated in a microwave oven. The bowl-shaped container obtained in Example 5, in which films with a 10% tensile load of 0.7 kg/1 cm width or more at 130° C. were laminated, had poor shape. Examples 6 to 10 Biaxially stretched films with an orientation ratio of approximately 1/1 in the extrusion direction/width direction shown in Table 2 and a Vikato softening point
A foamed styrene sheet (thickness: 1.7 mm, basis weight: 200 g/m ² ) made of foamed styrene resin at 100℃
A laminated foam sheet for molding was produced by thermally adhering them using a heated roll at ℃. The obtained laminated foam sheet was molded in the same manner as in Examples 1 to 5, 150 c.c. of water (water temperature: 20°C) and 15 c.c. of soybean oil (liquid temperature: 20°C) was added, and a paper lid was placed. and heated in a microwave oven with an output of 600W for 3 minutes.
At this time, the contents of the container started boiling after 2 minutes and 10 seconds of heating in the microwave. Next, the situation after heating in a microwave oven was investigated in the same manner as in Examples 1 to 5. The results are shown in Table 2.

【table】

[Table] From the above results, the container formed from the laminated foam sheet obtained in Example 6 (using a biaxially stretched film with a Vikat softening point of 110°C) showed shrinkage of the film when heated in a microwave oven. deformation occurred. In addition, as shown in Example 10, a biaxially stretched film (Vikat softening point: 140°C) having a Vikatsu softening point 35°C or more higher than the Vikatsu softening point (100°C) of the styrene resin that is the raw material for the foam sheet.
It can be seen that when used, a good molded product cannot be obtained as long as cell foaming (burning phenomenon) of the foam sheet does not occur. Examples 11-16 A copolymer of styrene (90% by weight) and methacrylic acid (10% by weight) (Vikatto softening point: 126°C) was
After extrusion using a die, films were prepared with orientation ratios changed as shown in Table 3 when biaxially stretched through a tenter. The orientation ratio is 5 in oil at 175℃.
This is the heat shrinkage ratio of the film in the extrusion direction/width direction when immersed for seconds. The obtained film was laminated on the same expanded styrene sheet as used in Examples 1 to 5, and
A container was molded in the same manner as in No. 5, the longest diameter and the shortest diameter of the mouth of the container were measured, and the difference therebetween (the amount of change in the molded body) was determined. The results are also listed in Table 3.

[Effect of idea]

As described above, the food container for cooking in a microwave oven of the present invention can withstand boiling water, does not deform the container or wrinkle the film on the inner surface of the container, and even when food is cooked in a microwave oven, the outside of the container remains intact. It has the effect of not getting hot and being easy to handle.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the microwave cooking food container of the present invention, and FIG. 2 is A-A of the microwave cooking food container shown in FIG. 1.
3 is a cross-sectional view of the bowl-shaped food container for cooking in a microwave oven of the present invention, and FIG. 4 is a sectional view of the bowl-shaped food container for cooking in a microwave oven of the present invention. Main symbols in the drawings: 1... food container, 2... biaxially stretched film, 3... foam sheet.

Claims (1)

[Claims for Utility Model Registration] 1. A biaxially stretched film made of a copolymer of styrene and a monomer containing a carboxyl group, which has a Vikat softening point of 115°C or higher, and a Vikat softening point of 95°C.
A food container made of a laminated foam sheet thermally bonded to a foam sheet made of a styrene-based resin at a temperature of 1. A food container for heating in a microwave oven, characterized in that the temperature is 35° C. higher than the Vikato softening point of a styrene-based resin, and the biaxially stretched film is provided on the inner surface of the container. 2 The tensile load at 10% stretching of the biaxially stretched film is
The food container for cooking in a microwave oven according to claim 1, which has a width of 1.0 kg/1 cm or more in an atmosphere of 100°C. 3 The tensile load at 10% stretching of the biaxially stretched film is
The food container for heating in a microwave oven according to claim 1, which has a width of 0.7 kg/1 cm or less in an atmosphere of 130°C. 4. The food container for cooking in a microwave oven according to claim 1, wherein the biaxially stretched film has an orientation ratio of 0.7/1.0 to 1.4/1.0 in the extrusion direction/width direction. 5. The microwave cooking food container according to claim 1, wherein the copolymer of styrene and a carboxyl group-containing monomer is a copolymer of styrene and methacrylic acid. 6. A microwave cooking food container according to claim 1, which is provided with a styrene resin film on the outer surface of the container.