JPH0245129Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] The present invention relates to a food container made of a synthetic resin laminated sheet having heat resistance, oil resistance, and durability. [Prior Art] Food containers made of foamed polyethylene sheets or films, or food containers laminated with non-foamed synthetic resin films, have been widely used because they are inexpensive. [Problems to be solved by the invention] The conventional polystyrene resin foams mentioned above do not have sufficient heat resistance and oil resistance. If you pour boiling water over it, it will become deformed due to the high temperature of nearly 100 degrees Celsius.
In particular, the oil resistance at room temperature is not so bad, but the oil resistance at high temperatures is poor, so if the food is oily, there is a risk that it may become dented, tear, and form holes. Therefore, it has been considered undesirable to heat polystyrene resin foams in microwave ovens or the like, or to use them for handling high-temperature oily foods. Therefore, food containers made of heat-resistant and oil-resistant polystyrene resin foam have been produced by laminating a foam sheet of styrene-maleic anhydride copolymer resin and a foam sheet of high-impact polystyrene or polystyrene.
Food containers with the above-mentioned high-impact polystyrene or polystyrene facing outward, food containers with unfoamed polystyrene films laminated on both sides of a foamed polystyrene sheet, and polyethylene terephthalate films further laminated on the inside of the container have been proposed. However, the styrene constituting the container of
Foamed sheets made of maleic anhydride copolymer resin have poor moldability, and when deep-drawn containers are made from such sheets, the molded products often suffer from cracks (poor elongation), cracks, etc. The shape was quite limited. Furthermore, when the container is heated in a microwave oven or the like, the heat causes the container to shrink significantly in the height direction. Therefore, it was unsuitable as a heat-resistant container. Furthermore, both of the above containers will shrink and deform significantly if left in steam at 100°C for a long time. Therefore, the containers of and could not be used when steaming food together. In addition, conventional containers lacked sufficient strength and durability, and the container body was prone to deformation or damage due to repeated use. [Purpose] The purpose of the present invention is to eliminate the above-mentioned drawbacks found in conventional food containers. [Means for solving the problem] As shown in FIG. 1, the food container provided by the present invention is made of a non-foamed polyolefin resin layer or a polyester resin layer that is heat resistant and oil resistant. Consisting of a laminate consisting of one of the resin layers 1, an unfoamed thermoplastic resin layer 2, a styrene-acrylic acid copolymer resin foam sheet layer 3, and a thermoplastic resin unfoamed sheet layer 4. More specifically, it is a styrene-based acrylic acid copolymer resin mainly composed of styrene monomers, and the content of acrylic acid components is 2 to 15% by weight.
Either an unfoamed polyolefin resin layer or a polyester resin layer is applied to the inner surface of the styrene-acrylic acid copolymer resin foam sheet layer 3 obtained by foam-molding the foamed material, with the thermoplastic resin layer 2 interposed therebetween. It is composed of a laminate S in which a resin layer 1 is laminated and a reinforcing thermoplastic resin layer 4 is provided on the other side of a foamed sheet layer 3 (see FIG. 2). In the styrene-acrylic acid copolymer resin foam sheet layer 3, the styrene monomers constituting the copolymer resin include styrene, α-
From the viewpoint of heat resistance, it is desirable to use methylstyrene, P-methylstyrene, etc., and as the acrylic acid monomer, acrylic acid, methacrylic acid, etc. Further, the expansion ratio of the styrene-acrylic acid copolymer resin foam sheet layer 3 varies depending on the application, but is preferably 8 to 23 times based on the molded container. If the above-mentioned value is smaller than 8 times, the insulation properties will be poor, and if it is larger than 23 times, the molded container will have poor strength. In addition, regarding the thickness of the foamed sheet layer 3, it is based on the sheet thickness before molding.
1.4 to 4.0 mm is preferred. If the sheet layer is thinner than 1.4 mm, the strength will be poor, and if it is thicker than 4.0 mm, it will not only be economically disadvantageous but also have poor moldability. When a polyolefin resin layer is used in the resin layer 1 of the present invention, its constituent resins include homopolypropylene without stretching, ethylene-propylene random copolymer resin, and a blend of homopolypropylene and ethylene-polypropylene random copolymer resin. Preferred materials include polypropylene, a blend of homopolypropylene and uniaxially oriented polypropylene, and high-density polyethylene. Further, when a polyester resin layer is used, the constituent resin thereof is preferably polyethylene terephthalate, polybutylene terephthalate, or the like.
The thickness of the resin layer 1 is preferably 20 to 70 μm,
If it is thinner than 20 μm, the strength will be poor, and there is a risk that micropores will open due to impact, etc., which will eventually affect the oil resistance of the container. Moreover, if the thickness of the resin layer 1 is thicker than 70 μm, it is economically disadvantageous. In addition, the thermoplastic resin layer 2 used in the present invention
is a resin layer 1 of either the polyolefin resin layer or the polyester resin layer and a styrene-acrylic acid copolymer resin foam sheet layer 3.
It is located between the two and connects the two. Therefore, the resin constituting the thermoplastic resin layer 2 may be a resin that melts at a relatively low temperature, such as an ethylene-vinyl acetate copolymer resin, a partially saponified ethylene-vinyl acetate copolymer resin, or a polystyrene resin. , a hot melt type adhesive whose main component is a polyester resin, a polyamide resin, or the like is preferable. The thickness of this thermoplastic resin layer is 15~
The thickness is preferably 40 μm. If the above-mentioned value is smaller than 15 μm, the adhesion will be poor, and if it is larger than 40 μm, it will be economically disadvantageous. An anchor coating agent may also be used to improve the adhesiveness between the resin layer 1 and the foamed sheet layer 3. Furthermore, in the present invention, as shown in FIGS. 2 and 3, a non-foamed sheet layer 4 made of thermoplastic resin is laminated on the outer surface of the foamed sheet layer 3 in order to impart strength and durability to the container. do. The resin constituting the non-foamed sheet layer 4 includes high-impact polystyrene, a blend of high-impact polystyrene and polystyrene, a high-impact styrene-acrylic acid copolymer resin, and a high-impact styrene-acrylic acid copolymer resin. A blend of styrene and acrylic acid resin is preferred because it has excellent impact resistance. The thickness of the non-foamed sheet layer 4 is preferably 50 to 200 μm, and 50 μm
A thinner container results in a container with poor impact resistance. Furthermore, if the thickness of the sheet layer 4 is more than 200 μm, the container will be expensive. The laminated sheet constituting the food container of the present invention was found to have an elongation in the MD direction (flow direction of the extruder) of 100% in the Tensilon tensile test.
%) is preferably 150 to 450%. When the elongation of the sheet in the tensile test is less than 150%, the moldability is poor, and when molded, poor elongation occurs, making it impossible to obtain a good molded container. In addition, when the above value is greater than 450%, molding can be performed well, but the molded container is extremely sensitive to heat, so food should not be placed in this container and cooked in a microwave oven, etc. case,
The container will undergo thermal deformation. The tensilon tensile test above uses a test piece of 115
The test is performed by leaving the test piece in a constant temperature bath at ℃ for 90 seconds, and then pulling it at a test speed of 20 mm/min in the constant temperature bath. In addition, the size and method of the test piece are JIS
It is similar to K6871. [Examples and Comparative Examples] Examples 1 to 4, Comparative Examples 1 to 2 A foamed styrene-acrylic acid copolymer resin (94 wt% styrene component and 6 wt% acrylic acid component) was extruded from an extruder into a sheet. sheet 3
A resin sheet 1 such as a homo-unstretched polypropylene film is bonded to one side of the laminated sheet by melting an ethylene-vinyl acetate type hot melt adhesive 2, and a reinforcing material such as high impact polystyrene is bonded to the other side of the laminated sheet. A laminated sheet in which the thermoplastic resin sheet 4 was laminated was manufactured. Next, the elongation of these laminated sheets was examined using the Tensilon tensile test. Furthermore, by molding the food container of the present invention from the laminated sheet, the moldability of the sheet was investigated, and the container was subjected to a microwave oven test and an external resistance test. For comparison, laminated sheets using polystyrene foam sheets as foam sheets (Comparative Examples 1 and 2) were also tested in the same manner as above. Table 1 shows these results.
Shown below.

[Type of resin]

PS: Polystyrene PS ^* : Anchor-coated polystyrene SA: Styrene-acrylic acid copolymer resin CPP: Homo-unstretched polypropylene HDPE: High-density polyethylene PET: Polyethylene terephthalate EVA: Ethylene-vinyl acetate type hot melt adhesive HIPS: High Impact polystyrene HISA: High impact polystyrene-acrylic acid copolymer resin [Moldability] ○: Can be molded according to the shape of the mold, and the molded product has no cracks (poor elongation) or cracks. ×: The mold cannot be molded according to the mold, and there are defects and cracks in the molded product. [Microwave test] Put tempura (3 pieces) + hot water (300ml) into a container.
Cook the whole container in a microwave oven (high frequency output 500W). Then, look at the change in the appearance of the container before and after cooking. ○: No dimensional change was observed (to the naked eye) before and after cooking, and no wrinkles were generated in the film. ×: A dimensional change was observed (with the naked eye) before and after cooking, or wrinkles were generated in the film. [Durability test] Pour 350 ml of water into a container with a lip diameter of 143 mm and a height of 79 mm that has been left undisturbed, and use a 2 cm wide clip to insert the lip of the container 4 cm below the top and lift it up for 3 minutes. Repeat this operation three times, and after the third time, lift it up and observe the change in the appearance of the container. ○: No damage to the container was observed and no deformation was observed. ×: Part of the container was damaged and deformed. As can be seen from the test results in Table 1 above, Tensilon's elongation in the tensile test falls within the range of 150 to 450% (thickness of the styrene-acrylic acid copolymer resin foam sheet is in the range of 1.4 to 4.0 mm). thing)
If so, the laminated sheet will have excellent moldability, and the molded container will be resistant to heat (Examples 1 to 4). Further, if Tensilon has an elongation of more than 450% in a tensile test, the sheet will have excellent moldability, but the molded container will be sensitive to heat (Comparative Examples 1 and 2). Example 5, Comparative Examples 3 to 4 Next, containers as shown in Table 2 were prepared, with the innermost surface of the container as the first layer, and the outer surface as the second, third, and fourth layers.

【table】

[Table] Example 5 is a food container of the present invention, Comparative Example 3 is a food container of the present invention in which the foam layer is replaced with a polystyrene foam layer, and Comparative Example 4 is a food container of the present invention with a conventional heat-resistant and oil-resistant food container. be. In addition, the sizes of the various containers were all 143 mm in lip diameter and 79 mm in height. Next, these containers were subjected to a gear oven test, a microwave oven test, and a heat resistance test using silicone oil. The results are shown below. (1) Gear oven test Place the above three types of containers in a gear oven,
It was heated at 100°C for 1 hour and its dimensions before and after heating were observed.

[Table] I was.
(2) Microwave oven test Tempura, hot water, and udon noodles were placed in three types of containers and cooked in a microwave oven for a predetermined period of time, and the appearance and dimensional changes of the containers were observed. The results are shown in Table-3.

[Table] (3) Silicone oil test 400ml of silicone oil heated to a predetermined temperature was placed in the three types of containers mentioned above, and the appearance of the containers was observed after being left for 5 minutes. The results are shown in Table-4.

[Table]
[Effects] As explained above, the food container of the present invention is a container made of a styrene-acrylic acid copolymer resin foam sheet, and has a polyolefin resin layer or a polyester resin layer on the inner surface of the container foam layer 3. One of the resin layers 1 is a thermoplastic resin layer 2
Since the non-foamed sheet layer 4 of thermoplastic resin is provided on the outer surface of the foamed layer 3, it maintains the characteristics of conventional foamed food containers and also eliminates its weaknesses. Heat resistance, oil resistance and durability can be effectively improved. Therefore, it can be used not only in fields where conventional foam food containers have been used, but also in fields where conventional foam food containers have had problems in terms of heat resistance, oil resistance, and durability, such as in microwave ovens. heating cooking container,
Even when used in the field of storage containers for freshly fried tempura, etc., or steaming containers for shiyu-mai, etc., the food containers of the present invention can sufficiently withstand these heat and hot oils. Furthermore, since a foamed sheet of styrene-acrylic acid copolymer resin is used for the foam layer 3, the sheet has excellent moldability. Therefore, the container of the present invention has a beautiful appearance without any cracks or scratches. Furthermore, since a non-foamed sheet layer 4 of thermoplastic resin is provided on the outer surface of the foam layer 3, strength and durability are improved, and it is said that the container will not lose its shape or break even after repeated use. It has the following advantages.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal section showing an example of the present invention, FIG. 2 is a cross-sectional explanatory view of a laminate used in the present invention, and FIG. 3 is a partially cutaway perspective view showing another embodiment of the present invention. 1... Either one of the polyolefin resin layer or the polyester resin layer, 2... Thermoplastic resin layer, 3... Styrene-acrylic acid copolymer resin foam sheet layer, 4... Non-foamed sheet of thermoplastic resin layer.

Claims (1)

[Scope of utility model registration request] The container is entirely formed of a synthetic resin laminate sheet, and the laminate sheet includes, from the inside of the container, either a polyolefin resin layer or a polyester resin layer, a thermoplastic resin layer,
A food container made of a synthetic resin laminated sheet, characterized in that a styrene-acrylic acid copolymer resin foam sheet layer and a non-foamed thermoplastic resin sheet layer are laminated outward in this order.