JPH0331694Y2 - - 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 heated and cooked directly in a microwave oven (including heat treatment) 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 fully satisfactory in terms of (c) and (d),
For example, when heated in a microwave oven, the wrap film may become deformed due to its inability to withstand the shrinkage force or water vapor pressure, it may become hot and difficult to handle when held in the hand after cooking, and heated food may cool easily. It had 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 food containers that can be heated and cooked directly, and which do not feel hot even when held in the hand immediately after cooking, and which retain their shape. resin foam,
Among these, a polystyrene resin foam sheet, which is said to be relatively rigid and shape-retaining, is used. Conventionally, synthetic resin foams such as polystyrene resin foam sheets have been used for various purposes such as containers, but there is no food container on the market that can be heated directly in a microwave oven. In particular, foam sheets made of polystyrene resin, which are often used for containers such as cutlet ramen noodles, have a glass transition point that is usually around 90°C, which is a little low, so they do not have sufficient heat resistance, and their rigidity and shape retention at room temperature are problematic. However, when it is heated to around 100℃, its rigidity decreases significantly and it becomes easily deformed, so it is not suitable as a container for cooking in a microwave oven, which can reach temperatures of around 100℃ or higher. Furthermore, the oil resistance and gas barrier properties are not sufficient.

Note that other foams with good heat resistance have problems in terms of cost and moldability into a container shape compared to polystyrene resins, and are not suitable for this type of food container.

In view of the above, the present invention was developed as a result of various studies and studies aimed at using polystyrene resin foam sheets as container materials in combination with other resin films. If a resin film is laminated on the foamed sheet, it will have good thermoformability and excellent heat resistance, as well as good oil resistance and gas barrier properties, making it suitable as a food container that can be heated directly in a microwave oven for cooking. This was based on this knowledge.

In other words, ordinary saturated polyester films are usually crystallized by stretching and heat setting after film extrusion in order to retain the inherent properties of the resin, such as strength and heat resistance. Due to its poor properties, it is not suitable for food containers that need to be laminated with foam sheets, etc. and formed into a container shape.Also, unstretched films have good thermoformability but are poor in strength, heat resistance, etc., so they are rarely used. Mostly unused. The inventors of the present invention focused on the fact that this unstretched saturated polyester film has good thermoformability, and investigated the use of this film in food containers. Polybutylene terephthalate resin film, which suppresses crystallization by rapid cooling after extrusion, has excellent thermoformability, and crystallization progresses much more easily than polyethylene terephthalate resin, making it difficult to process during thermoforming. They discovered that heating or a slight amount of additional heat immediately after molding sufficiently progresses crystallization, and that during actual use the material has excellent heat resistance, that is, strength and rigidity when heated.

The present invention was developed based on the above knowledge, and by laminating an unstretched polybutylene terephthalate resin film that suppresses crystallization with a polystyrene resin foam sheet, it can be heated directly in a microwave oven, etc. This provides a suitable food container.

The features of this invention are the foaming ratio of 2 to 30 times and the thickness of 1 to 30 times.
The composite sheet is made of a composite sheet in which an unstretched polybutylene terephthalate resin film that suppresses crystallization or a multilayer film of a synthetic resin containing the same film is laminated on at least one side of a 5 mm polystyrene resin foam sheet, and the polybutylene terephthalate resin film is This food container is integrally formed with a resin film as the inner surface of the container.

Next, embodiments of the present invention will be described based on the drawings.
In the illustrated embodiment, A indicates a food container according to the present invention, in which a non-stretched polybutylene terephthalate resin with suppressed crystallization is used on at least one side of a foam sheet 1 obtained by extruding and foam-molding a polystyrene resin. The material is a composite sheet made of laminated film 2 or a multilayer synthetic resin film containing film 2 as a surface layer, and this is press-molded,
The film 2 is made into the inner surface of the container by an appropriate forming means such as vacuum forming, as shown in FIG. 1 or 6.
FIG. 7: It is integrally molded into other desired container shapes.

The polystyrene resin that is the material of the foamed sheet 1 includes polystyrene resin, a copolymer mainly composed of styrene such as a copolymer resin of styrene and maleic anhydride, paramethylstyrene resin,
ABS resin, AS resin, other polystyrene resins, or resins obtained by adding and mixing inorganic fillers such as talc to these resins can be used.

In addition, the foam sheet 1 has a foaming ratio of 2 to 30 times,
It is necessary to set the thickness to 1 to 5 mm. In other words, if the expansion ratio exceeds 30 times, even if the thickness is 5 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 it is less than twice that, 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 inappropriate. Furthermore, if the thickness exceeds 5 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 rigidity. Such expansion ratio and thickness can be arbitrarily set by changing the conditions of extrusion foam molding.

As the polybutylene terephthalate resin film 2 laminated on the foamed sheet 1, in addition to polybutylene terephthalate resin, a copolymer mainly composed of the same resin component or a modified product mainly composed of the same resin component is used. However, all of these are unstretched films that suppress crystallization (crystallization) by rapid curing (quenching) immediately after extrusion during film production, that is, they contain a crystallization nucleating agent in the resin. It is necessary that the film be non-stretched and formed in an amorphous manner.

This polybutylene terephthalate resin film 2 is laminated in a single layer on one or both sides of the foamed sheet 1 as shown in FIG.
As shown in FIGS. 3 to 5, it is possible to use a composite sheet which is a constituent material of It is desirable that the multilayer film 4 is laminated on the foamed sheet 1 with the film 2 as a surface layer. That is, even if the polybutylene terephthalate resin film 2 is laminated alone on the foamed sheet 1, it can sufficiently exhibit properties such as oil resistance, gas barrier properties, and heat resistance. By forming a composite sheet with sheet 1, even higher quality can be obtained. For example, if a printed polystyrene resin film is used as the other resin film layer 3 and the film layer is used as an intermediate layer on the foam sheet 1, the printed surface will not be exposed on the surface, resulting in a sanitary appearance. better, and also has higher rigidity. The resin film layer 3 serving as the intermediate layer also has another function. In other words, when a styrene polymer is used alone as the foamed sheet 1, the thermal adhesion with the polybutylene terephthalate resin usually deteriorates, but there is a resin film layer between the foamed sheet 1 and the polybutylene terephthalate resin film 2. 3
By interposing the adhesive layer, the resin film layer 3 can serve as an adhesive layer between the two, and examples of the resin film layer 3 in this case include acrylic modified polystyrene and modified polyurethane adhesives.

In any case, the polybutylene terephthalate resin film 2 laminated on the foam sheet 1
The multilayer film 4 including the same film 2 must be provided with the same film 2 as a surface layer at least on the inner surface of the container, and does not necessarily need to be provided on the outer surface of the container, but of course, as shown in FIG. If it is also provided on the outer surface of the container, higher quality products can be obtained. Furthermore, as another embodiment of the present invention, a polybutylene terephthalate resin film 2 or a multilayer film 4 containing the same film 2 as a surface layer is provided on the inner surface of the container, and the film is further laminated on the outer surface of the container. The film layer on the outer surface of the container does not necessarily have to be the above-mentioned polybutylene terephthalate resin film or a multilayer film containing this film, but may have the characteristics desired for use as a container, such as hardness, oil resistance, and printability. Other resin films, such as polystyrene, polyolefin, etc., which are usually laminated depending on the
Polyvinylidene chloride and other resin films can be used in single or multiple layers, but among them, polystyrene resin films such as high impact polystyrene and biaxially oriented polystyrene have excellent fusibility,
It is particularly preferred from the viewpoints of moldability, rigidity, printability, improved appearance, and low cost.

Note that the polybutylene terephthalate resin film 2 or the multilayer film 4 may be laminated onto the foamed sheet 1 by heat fusion or by using an adhesive between the two. In this lamination process, it is necessary to cool as quickly as possible to minimize the progress of crystallization.

Further, the thickness of the polybutylene terephthalate resin film 2 is preferably 30 to 500 microns; if this thickness is too thin, the effect of laminating the films, that is, the heat resistance, especially the effect of maintaining rigidity when heated, decreases. If the container is too thick, the container itself becomes heavy and costs increase, which is not preferable. Further, when used as a multilayer film 4, 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 set to about 35 to 550 microns. It is desirable that the film be too thick, but it is also undesirable because it becomes heavy and expensive.

As described above, the food container of the present invention has an unstretched polybutylene terephthalate resin film 2 with suppressed crystallization or a multilayer film of a synthetic resin containing the same film 2 laminated on at least one side of the polystyrene resin foam sheet 1. The composite sheet has excellent thermoformability and can be formed into a container shape without any inconvenience, and the formed container can be used as a food container for direct cooking in a microwave oven. It has excellent oil resistance, gas barrier property, water resistance, and heat resistance, which are important factors, and particularly has good strength, rigidity, and shape retention (that is, heat resistance) when heated.

That is, the unstretched polybutylene terephthalate resin film 2 that suppresses crystallization and is laminated on the polystyrene resin foam sheet 1, which is the main material, has thermoformability unlike a general saturated polyester film that has been stretched and heat set. Combined with the good thermoformability of the polystyrene resin foam sheet 1, the composite sheet can be easily molded into various container shapes without any problems, and even complex tray-shaped containers can be molded. It can be mass-produced and provided at a relatively low cost.

Moreover, if the polybutylene terephthalate resin film 2 is not stretched and crystallization is suppressed, it will not be able to obtain sufficient properties necessary for a heated food container such as heat resistance, rigidity, and strength. For example, polyethylene terephthalate resin requires a high temperature of 110°C for crystallization and 140°C or higher for high-speed crystallization. In the case of polybutylene terephthalate resins, crystallization hardly progresses even when heated during thermoforming from composite sheets, which is usually carried out at about 110°C, but polybutylene terephthalate resins have a higher
The temperature for crystallization is as low as ~50°C, and the crystallization rate is several times faster. Therefore, in the case of the present invention, polybutylene terephthalate can be formed by heating during thermoforming from a composite sheet or by a small amount of additional heat. Resin film 2
The crystallization progresses rapidly and sufficiently, and even if the crystallization during molding is slightly insufficient, the progress of crystallization is compensated for during the use stage such as heating in a microwave oven. Crystallization improves heat resistance, rigidity, strength, etc. during actual use.
It can fully exhibit the characteristics necessary for use.
Therefore, the decrease in rigidity of the foam sheet when heated in a microwave oven can be compensated for by the laminated film layer.
It has excellent rigidity and shape retention even when heated as a food container.

Furthermore, the polybutylene terephthalate resin film has excellent oil resistance, water resistance, and gas barrier properties, and since the resin film is provided at least as a surface layer on the inside of the container,
Compared to a foam sheet alone, other attributes necessary for food containers such as oil resistance, water resistance, and gas barrier properties are also improved, and even if the food is oily, its preservation and the protective effect of the foam sheet are improved. It also has good heat insulation and heat retention properties due to the foam sheet.

Therefore, the present invention satisfies all of the above-mentioned performances (a), (b), (c), (d), (e), (f), and (g) desired for this type of food container for heating and cooking. It can be suitably used as a food container that can be heated in a microwave oven.

[Brief explanation of drawings]

The figures show an embodiment of the present invention; FIG. 1 is a perspective view, FIG. 2 is an enlarged cross-sectional view taken along the front line, and FIG. 3 is a partially cutaway perspective view showing another embodiment. Fig. 4 is an enlarged cross-sectional view along the line from the previous figure, Fig. 5 is a cross-sectional view of a portion corresponding to Fig. 2 showing another embodiment, and Figs. 6 and 7 are each with a different container shape. FIG. 1...Polystyrene resin foam sheet, 2...
Polybutylene terephthalate resin film, 4
...Multilayer film, A...Food container.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. A polystyrene resin foam sheet with an expansion ratio of 2 to 30 times and a thickness of 1 to 5 mm, at least on one side of which a non-stretched polybutylene terephthalate resin film that suppresses crystallization or the same film is applied as a surface layer. A food container made of a composite sheet made of laminated multilayer films containing a polybutylene terephthalate resin film and integrally formed with the polybutylene terephthalate resin film as an inner surface layer of the container. 2. The food container according to claim 1, wherein the polybutylene terephthalate resin film contains a crystallization nucleating agent in the resin and is a non-stretched film formed in an amorphous manner.