JPH0455586B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a laminated foam sheet for forming microwave cooking containers, which has excellent heat resistance and can easily and inexpensively produce molded containers that can be heated in a microwave oven. [Prior Art] In recent years, with the rapid spread of microwave ovens, the method of cooking food in a microwave oven while it is still in a container is becoming more widespread, and various containers for this purpose have been developed. Examples of these containers include containers made of paper containers laminated with polyester film, polymethylpentene film, etc., and containers made of polypropylene sheets, which are widely used. However, these containers have problems such as not being able to be made into arbitrary shapes, and the container itself being heated when food is cooked in a microwave oven, making it impossible to directly remove it from the microwave with bare hands. In order to eliminate these drawbacks, a molded container made of a sheet made of a polypropylene film laminated on a foamed styrene sheet has been developed. However, because the heat resistance of the expanded styrene sheet that forms the base of this molded container is not sufficient, the polypropylene film needs to be made thicker.As a result, the adhesive between the expanded styrene sheet and the polypropylene film may separate during molding. Problems are more likely to occur,
At present, it is extremely difficult to produce molded products without problems. Furthermore, Japanese Utility Model Application Publication No. 55-1179750 proposes a microwave cooking container made of a foam sheet made from a styrene-maleic anhydride copolymer, but the foam sheet is very thin and not sticky. There are problems such as the sheet may be torn by the sheet feeding chain when it is placed in a continuous molding machine, and it is extremely difficult to mold and the product yield is low. Furthermore, JP-A-61-137740 discloses that one side of a foamed sheet made of a styrene monomer-acrylic acid monomer copolymer is made of either polyolefin resin or polyester resin with an adhesive layer interposed therebetween. A sheet made of laminated non-foamed films has been proposed. However, even with this laminated foam sheet, there are problems such as the foam sheet made of styrene monomer-acrylic acid monomer copolymer is not soft and sticky, and the sheet may break during the winding process during foam sheet manufacturing. be. Furthermore, since the foamed sheet and the non-foamed film are laminated using an adhesive, the price increases due to the use of the adhesive and the need for an adhesive application process. In addition, there is the problem that the adhesive surface may peel off during molding, and the product yield is also reduced. Because it is completely incompatible with resin or polyester resin, it is impossible to reuse the laminated foam sheet scraps after punching out the product molding.
In addition to being economically disadvantageous, there is a problem in that a large amount of laminated foam sheet waste is generated and must be disposed of as waste. [Problems to be Solved by the Invention] The present invention solves the problem that the above-mentioned laminated foam sheet is thin and not sticky, and it is not possible to laminate a film on the foam sheet without using an adhesive. Foam sheet waste cannot be reused, there are problems with moldability, and cooking in a microwave oven makes the container so hot that it cannot be touched with bare hands.In addition, containers of any shape can be made inexpensively and economically. This was done in order to solve the problem of conventional foam sheets for forming containers for microwave heating. [Means for solving the problems] The present invention provides a copolymer resin of 96 to 84% (by weight, the same applies hereinafter) from styrene and acrylic acid monomer.
Thickness 1.2 to 2.7 mm, density 0.07 to 2.7 mm, based on a resin composition of 4 to 16% high impact styrene resin.
Regarding a laminated foam sheet for forming containers for microwave oven cooking, which is made by laminating a 0.15 g/cc foam sheet and a styrene resin film, by using the above-mentioned specific resin composition as a base material and forming a specific foam sheet. , it is possible to improve the foam moldability of heat-resistant styrene-based resins and the thin and brittle properties of product moldings, and it is also possible to reuse the foam sheet scraps after forming the product moldings, and it does not require the use of adhesives. This method was completed based on the discovery that the heat resistance of foam sheets during cooking in a microwave oven could be improved by laminating foam sheets using films that can be laminated without any heat. [Example] In the present invention, the thickness is 1.2~2.7mm, density 0.07~
A foam sheet of 0.15 g/cc is formed. The copolymer resin of styrene and acrylic acid monomer used in the present invention was found to be free from food hygiene problems, easy to extrude into foamed sheets, and easy to obtain after studying various heat-resistant styrene resins. This material was selected from the viewpoint of its beautiful, heat-resistant properties and low fragility compared to the resin's fragility. As the content of the acrylic acid monomer in the copolymer resin of styrene and acrylic acid monomer increases, the heat resistance improves, but the produced foam sheet becomes thinner and the thermal adhesion and compatibility with the styrene resin film decreases. This makes it difficult to reuse the laminated foam sheet waste. Therefore, from the point of view of heat resistance, the acrylic acid monomer content is 5%.
It is preferably at least 20%, and conversely, from the viewpoint of the stiffness of the foam sheet, it is preferably at most 20%. Specific examples of the acrylic acid monomer include:
Examples include acrylic acid and methacrylic acid, which may be used alone or in combination, but methacrylic acid is preferable from the viewpoint of heat resistance. Foamed sheets are manufactured from copolymer resins of styrene and acrylic acid monomers using the general extrusion foaming method, that is, the resin, nucleating agent, and other additives are placed in an extruder, mixed, heated, and melted. A method in which a low boiling point halogenated hydrocarbon such as dichlorodifluoromethane or a low boiling point hydrocarbon such as propane or butane is injected as a foaming agent, and then the molten resin composition is cooled to an appropriate foaming temperature, and then extruded through a Cirkimura die to foam. This can be easily done by However, the crispness of the foam sheet has not yet been sufficiently improved, and problems such as cracking may occur if the core diameter is small when winding the foam sheet into a roll. If you fill a container with water and heat it in a microwave to bring it to a boil, the container may deform or shrink, and the cells on the surface of the foam sheet that come into contact with the boiling water may expand, making the surface of the foam sheet feel rough. The gloss on the surface of the foam sheet may also disappear. The high-impact styrene resin used in the present invention has a phenomenon in which containers made from foamed sheets made solely from a copolymer resin of styrene and acrylic acid monomers lack heat resistance, deform, or shrink (styrene and acrylic acid monomers). This is thought to be because foamed sheets made of copolymerized resins with monomers tend to retain molding distortion. High-impact styrene resin is normally considered undesirable because it reduces the heat resistance of the resin, but this resin is 4-16% compared to 96-84% of a copolymer resin of styrene and acrylic acid monomer.
A molded container made of a foamed sheet made from a resin composition blended in a specific ratio does not deform or shrink even when subjected to a similar boiling water test, and the heat resistance of the container is improved. Moreover, as an accompanying effect, the stiffness of the foam sheet has been improved,
The effect is that even when the core diameter is small, the core can be wound without any problem. If the mixing ratio of the high impact styrene resin is less than 4%, the effect of preventing deformation and shrinkage will not be sufficiently achieved, and if it exceeds 16%, open cells will easily occur during extrusion foaming, and the resulting foam sheet will be heated. This is undesirable because moldability deteriorates. In the resin composition of the copolymer resin of styrene and acrylic acid monomer and high impact styrene resin, other styrene resins, nucleating agents, moldability improvers, colorants, etc. are appropriately blended and used. Good too. The suitable thickness of the foam sheet is 1.2 to 2.7 mm. If the thickness is less than 1.2 mm, even if the film is laminated and then molded, the strength and heat resistance of the molded product will not be sufficient, the molded product will be easily broken, and the container itself will become hot. On the other hand, if the thickness exceeds 2.7 mm, moldability deteriorates and it becomes difficult to obtain a molded article with a complicated shape. In addition, the density of the foam sheet is 0.07 to 0.15.
g/cc is suitable. If the density exceeds 0.15 g/cc, the foamed sheet will be hard, causing problems such as cracking of the foamed sheet when it is wound up, or tearing of the foamed sheet during molding. On the other hand, the density is 0.07g/
If it is less than cc, heat resistance and strength will decrease, which is not preferable. In the present invention, a styrene resin film is laminated with the foam sheet to produce the laminated foam sheet for molding a microwave cooking container of the present invention. The styrene resin film is a styrene homopolymer resin, styrene and acrylonitrile, acrylic acid, methacrylic acid, acrylic ester,
A film made from a copolymer resin of a monomer copolymerizable with styrene, such as an acrylic monomer such as methacrylic acid ester, or a styrene monomer such as α-methylstyrene or p-methylstyrene;
a film from a mixed resin composition containing the resin;
Examples include films made from resins made from the above-mentioned resins and resin compositions with high impact properties using rubber components such as polybutadiene. There is no particular limit to the thickness of the styrene resin film, but thin films are difficult and expensive due to technical problems in film production, and thick films have a large basis weight and are expensive. For these reasons, a film with a thickness of about 25 to 150 μm is preferable. In the present invention, the reason why the styrene resin film is laminated with the foam sheet is as follows. In other words, the phenomenon in which the foam sheet and the cells on the surface of a molded container made of a foamed sheet made from a resin composition mainly composed of a copolymer resin of styrene and an acrylic acid monomer expands in boiling water is caused by the styrene acrylic acid monomer. This may seem strange considering the heat resistance of the copolymer resin with styrene and acrylic acid monomer, but because the copolymer resin with styrene and acrylic acid monomer has an affinity for water, the cell membrane softens and expands in boiling water. Conceivable. Therefore, an attempt was made to solve this problem by pasting a film on the surface of the foam sheet. The film to be applied to the foam sheet for heat-resistant containers for microwave cooking is generally made of a resin film having a heat resistance with a softening point of about 120° C. or higher, such as polypropylene, polyethylene terephthalate, or polymethylpentene. This is because the heat resistance of the film plays an important role in maintaining the heat resistance of the container. However, in the present invention, it is sufficient that the foam sheet has a function of preventing boiling water from coming into contact with the surface.
It can also be used as a film made of resin with a heat resistance of 100°C or less, and can be thermally bonded without adhesive to a foam sheet made of a resin composition mainly composed of a copolymer resin of styrene and acrylic acid monomers, and It uses a styrene resin film that allows the reuse of laminated foam sheet waste. In the present invention, a foamed sheet is formed by laminating a styrene resin film on a foamed sheet made of a resin composition based on a resin composition of a copolymer resin of styrene and acrylic acid monomer and a high impact styrene resin. Therefore, even if you pour water into the molded body and heat it in a microwave to bring the water to a boil,
A laminated foam sheet refill for forming microwave cooking containers that has the remarkable effect of not causing deformation or shrinkage of the molded product, and that the surface cells of the foam sheet laminated with film do not expand, and has sufficient heat resistance for practical use. It will be done. There are various methods for laminating the foam sheet and the styrene resin film, and there are no particular limitations, but the most preferred method is to heat the film with a hot roll and press it onto the foam sheet. A method may also be adopted in which a molten styrene resin is poured between the foam sheet and the film to press them together. It goes without saying that the styrene resin films to be laminated may be printed or colored in advance. A foamed sheet made of a resin composition based on a resin composition of 96 to 84% copolymer resin of styrene and acrylic acid monomer obtained in this way and 4 to 16% of high impact styrene resin. A laminated foam sheet for molding with a resin film laminated thereon can be used as it is or after a similar film is adhered to the non-laminated surface of the film, and then the film surface according to the present invention becomes the inner surface of the container, and then the laminated foam sheet for molding is made of general styrene foam. It can be easily formed by simply adjusting the heating conditions in a sheet forming machine. The resulting molded product is very beautiful, has sufficient strength as a container, does not break even under freezing conditions of -20℃, and has heat resistance and insulation properties that can withstand cooking in a microwave oven. There is. The laminated foam sheet of the present invention will be explained in more detail by giving specific examples below. Reference Examples 1 to 3 and Comparative Reference Examples 1 to 3 Copolymer resin consisting of 85% styrene and 15% methacrylic acid (hereinafter referred to as SMA resin) and YH-489
(high-impact styrene resin manufactured by Mitsubishi Monsanto Kasei Co., Ltd.) in the proportions shown in Table 1, and further 1.0 part of talc (part by weight, same below) as a nucleating agent.
The resin composition was blended and put into a 40 mmφ extruder, and after the resin composition was melted, 3.0 parts of butane gas was injected as a blowing agent. Thereafter, the mixture was transferred to a 50 mmφ extruder, cooled, and then extruded through a circular die to form a foam sheet with a thickness of 1.6 mm and a density of 0.125 g/cc, and the sheet manufacturability was examined. The results are shown in Table 1. After forming the selected foam sheet into a bowl-shaped container with an inner diameter of 135 mm and a depth of 50 mm using a single-shot molding machine for forming styrene foam sheets, add 150 c.c. of water (water temperature 20°C) and 3 c of salad oil to the selected container. c., placed a paper lid on it, and heated it in a 600W microwave oven for 5 minutes to examine its heat resistance when heated in a microwave oven (hereinafter referred to as microwave heat resistance). The results are shown in Table 1. Note that water was brought to a boil by heating in a microwave oven for 2 minutes. The closed cell ratio in Table 1 is from Beckman Toshiba Corporation.
It was measured with Air Comparison Pycnometer Model 930 manufactured by Manufacturer.

[Table] From the results in Table 1, SMA resin 95-85% and
YH-489 Foamed sheets using 5 to 15% resin composition have fewer open cells (high closed cell ratio), reduce (improved) the stiffness of the foamed sheets, and are easier to wind up. It can be seen that a container can be obtained that does not cause problems such as the foam sheet cracking during handling, and the molded product does not deform in a heat resistance test when heated in a microwave oven. Examples 1 to 3 The foam sheets obtained in Reference Examples 1 to 3 have a thickness of 50μ.
After the biaxially oriented polystyrene films were adhered and laminated using a hot roll method, a molded product was molded in the same manner as in Reference Examples 1 to 3, and a heat resistance test was conducted when heating it in a microwave oven. The foam cells on the inner surface of the container made from the laminated foam sheet did not expand, and the inner surface of the container had a smooth, glossy and beautiful surface, and had sufficient heat resistance required for cooking in a microwave oven. Examples 4 to 7 and Comparative Examples 1 to 3 A mixture of 90 parts of a copolymer resin consisting of 90% styrene and 10% methacrylic acid and 10 parts of YH-489 was charged into an extruder in the same manner as in Reference Example 1. A foamed sheet having the properties shown in Table 2 was manufactured by adjusting the amount of butane gas injected and the amount of resin composition discharged. A biaxially oriented styrene resin film with a thickness of 80μ was adhered and laminated on the resulting foamed sheet using a hot roll method, and then a molded product similar to that of Reference Example 1 was formed and a boiling water test was conducted using a microwave oven. . The results are shown in Table 2.

[Table] From the results in Table 2, thickness 1.3 to 2.5 mm, density 0.07
It can be seen that a foamed sheet of ~0.15 g/cc is good, and a sheet made by laminating a styrene resin film on this foamed sheet can be used as a container for cooking by heating in a microwave oven. [Effects of the Invention] The laminated foam sheet of the present invention is made by laminating a film on a foam sheet with improved shape without using an adhesive, and it is possible to reuse scraps after punching out a product molded product. It is easy to mold, the container does not become so hot that it cannot be touched by hand when heated in a microwave oven, and a container of any shape can be obtained inexpensively and economically.

Claims (1)

[Scope of Claims] 1. Thickness 1.2-2.7 mm based on a resin composition of 96-84% by weight of copolymer resin of styrene and acrylic acid monomer and 4-16% by weight of high-impact styrene resin. , a laminated foam sheet for forming a microwave cooking container, which is formed by laminating a foam sheet with a density of 0.07 to 0.15 g/cc and a styrene resin film. 2. The sheet according to claim 1, wherein the copolymerized resin of sletin and an acrylic acid monomer is a resin obtained by copolymerizing 95 to 80% by weight of styrene and 5 to 20% by weight of an acrylic acid monomer. .