Food-packaging molded container for microwave applications

Abstract

To provide a food-packaging molded container for microwave applications, which is economically superior without requiring unnecessary steps or materials, and in which the gloss level of the inner container surface is 50% or more.SOLUTION: A low heat-resistant polystyrene-based resin foam layer (11) employs, as a base resin, (A) a polystyrene-based resin composition comprising a polystyrene-based resin having a Vicat softening point of 105°C or lower, or (B) a polystyrene-based resin composition comprising 89 to 99 mass% of a polystyrene-based resin having a Vicat softening point of 105°C or lower and 1 to 11 mass% of a polyphenylene ether resin. A high heat-resistant polystyrene-based resin foam layer (12) employs, as a base resin, (C) a polystyrene-based resin composition comprising 70 to 86 mass% of a polystyrene-based resin having a Vicat softening point of 105°C or lower and 14 to 30 mass% of a polyphenylene ether resin, or (D) a polystyrene-based resin composition containing 80 mass% or more of a styrene-(meth)acrylic acid copolymer resin.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a molded container obtained by thermoforming a polystyrene-based resin laminated foam sheet. More specifically, the molded container has at least two or more polystyrene-based resin foam layers having different base resin compositions and a polyolefin-based resin film layer located on the container inner surface, and the gloss of the polyolefin-based resin film layer, i.e., the container inner surface, is 50% or more. The molded container of the present invention is used as a food container for a microwave oven. [Background technology]

[0002] 2. Description of the Related Art Molded containers made by thermoforming, for example, polystyrene-based resin foam sheets or laminated sheets using polystyrene-based resin foam sheets as a base material, for example, are widely used as food containers for selling fish, meat, boxed lunches, and prepared dishes in supermarkets and convenience stores.

[0003] For such molded containers, different base resins for the polystyrene-based resin foam sheets are used depending on the application.

[0004] For molded containers used at refrigeration to room temperature or below, such as trays for fish or meat, a polystyrene-based resin foam sheet is used, the base resin of which is a polystyrene-based resin composition with a Vicat softening temperature of 105°C or lower and containing general-purpose polystyrene (GPPS) as the main component.

[0005] On the other hand, when used as a food container for a microwave oven, the container itself must be heat resistant, so a polystyrene-based resin foam sheet is used whose base resin is a polystyrene-based resin composition whose main component is a styrene-methacrylic acid copolymer resin and whose Vicat softening temperature is 110°C or higher, or a polystyrene-based resin foam sheet is used whose base resin is a polystyrene-based resin composition which is a resin mixture of general-purpose polystyrene resin (GPPS) and polyphenylene ether resin (PPE) and whose Vicat softening temperature is 110°C or higher (Patent Document 1, Patent Document 2).

[0006] Furthermore, as an application example of a polystyrene-based resin foam sheet using a resin mixture of general-purpose polystyrene resin (GPPS) and polyphenylene ether resin (PPE) as the base resin, there is also a case where a polystyrene-based resin multilayer foam sheet having two or more foam layers with different base resin blends is used (Patent Document 3 and Patent Document 4).

[0007] Furthermore, when used as a food container for a microwave oven, polystyrene-based resin foam sheets are at risk of melting if they come into direct contact with high-temperature oil from food heated in a microwave oven, so to prevent this, it is common to provide a polyolefin-based resin film layer on the inner surface of the container, i.e., the surface that comes into contact with food (Patent Document 5). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2006-137911 A [Patent Document 2] JP 2008-094919 A [Patent Document 3] JP 2014-168861 A [Patent Document 4] JP 2016-050314 A [Patent Document 5] JP 2019-043076 A Summary of the Invention [Problem to be solved by the invention]

[0009] The glossiness of the polyolefin resin film layer located on the inner surface of the container, i.e., the glossiness of the inner surface of the container, is preferably as high as possible. A high glossiness of the inner surface of the container can improve the appearance of the food contained therein and increase purchasing motivation for the product.

[0010] A polyolefin resin film layer has a glossiness of 90% or more before being laminated on a polystyrene resin foam sheet. However, when laminated on a polystyrene resin foam sheet, the glossiness decreases. Therefore, various methods for preventing the decrease in glossiness have been studied.

[0011] The foaming container (C) described in paragraph 0047 and Table 1 of Patent Document 5 is produced by first laminating a 15 μm thick PS film on one side of a PSP sheet to prepare a laminated sheet, and then heat-laminating a laminated film (CPP 25 μm / PS 20 μm) on the PS film side of this laminated sheet. Patent Document 5 describes that in this example, the expected glossiness and expected adhesive strength were both achieved. However, this method is not economically preferable because an extra PS film is required to be laminated on the PSP at first, and a process of laminating the film by heat fusion is required twice.

[0012] The object of the present invention is to provide a molded container for use as a food container for a microwave oven, which does not require extra steps or materials and is economically excellent, and in which the gloss of the polyolefin resin film located on the inner surface of the container, i.e., the gloss of the inner surface of the container, is 50% or more. [Means for solving the problem]

[0013] As a result of extensive investigations aimed at solving the above-mentioned problems, the present inventors have found the following configuration.

[0014] That is, the food packaging molded container for use in a microwave oven according to the present invention is made of a polystyrene-based resin laminated foam sheet having a polystyrene-based resin multi-layer foam sheet layer and a polyolefin-based resin laminated film layer, and is formed so that the polyolefin-based resin laminated film layer constitutes the inner surface of the container, the polystyrene-based resin multi-layer foamed sheet layer has at least two layers, a low heat-resistant polystyrene-based resin foamed layer located on the lamination surface with the polyolefin-based resin laminated film layer, and a high heat-resistant polystyrene-based resin foamed layer located on the outer side of the low heat-resistant polystyrene-based resin foamed layer, The low heat-resistant polystyrene-based resin foam layer has a polystyrene-based resin composition of either (A) or (B) below as a base resin, and the high heat-resistant polystyrene-based resin foam layer has a polystyrene-based resin composition of either (C) or (D) below as a base resin, (A) a polystyrene-based resin composition comprising a polystyrene-based resin having a Vicat softening temperature of 105°C or less; (B) a polystyrene-based resin composition comprising 89 to 99% by mass of a polystyrene-based resin having a Vicat softening temperature of 105° C. or less and 1 to 11% by mass of a polyphenylene ether resin; (C) a polystyrene-based resin composition comprising 70 to 86% by mass of a polystyrene-based resin having a Vicat softening temperature of 105° C. or less and 14 to 30% by mass of a polyphenylene ether resin; (D) a polystyrene-based resin composition containing 80 mass% or more of a styrene-(meth)acrylic acid copolymer resin; the polyolefin-based resin laminated film layer has a polyolefin-based resin film layer located on the inner surface of the container, and a polystyrene-based resin film layer located on the lamination surface with the polystyrene-based resin multi-layer foamed sheet, The gloss of the polyolefin resin film layer, i.e., the inner surface of the container, is 50% or more.

[0015] In addition, the "Vicat softening temperature" in the present invention is measured in accordance with the B50 method (test load 50N and heating rate 50°C / h) in JIS K7206 "Plastics-Thermoplastics-Determination of Vicat softening temperature (VST)".

[0016] In addition, in the present invention, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. Effect of the Invention

[0017] According to the present invention, it is possible to provide a molded container for use as a food container for a microwave oven, which has a polyolefin resin film layer located on the inner surface of the container, i.e., a gloss level of the inner surface of the container of 50% or more, and which is economically excellent because it does not require any extra steps or materials. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing a packaging container according to a first embodiment of the present invention. [Diagram 2] (a) and (b) are enlarged views of part P in FIG. [Diagram 3] 4(a) and (b) are cross-sectional views of essential parts showing a manufacturing process of the polystyrene-based resin laminate foam sheet used for the packaging container. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The term "main component" in the present invention is defined as follows. The main component of a polymer is a monomer that accounts for 50% by mass or more of its constituent elements. The main component of a resin composition made of multiple polymers is a polymer that accounts for 50% by mass or more of its constituent elements.

[0020] Fig. 1 is a schematic diagram for explaining one embodiment (first embodiment) of the molded container of the present invention. Fig. 1 shows the molded container. Fig. 2 shows the layer structure of the molded container, and Fig. 3 shows the layer structure of the polystyrene-based resin multi-layer foamed sheet and polyolefin-based resin laminate film, which are the constituent materials of the molded container. Hereinafter, the embodiment of the present invention will be explained with reference to this figure.

[0021] (Layer structure and manufacturing method of molded container) The molded container (1) is made by forming a laminated polystyrene resin foam sheet (1S) into a container shape by thermoforming such as vacuum forming.

[0022] The polystyrene-based resin laminated foam sheet (1S) constituting the molded container (1) is a laminated integral product of a polystyrene-based resin multi-layer foam sheet (10S) and a polyolefin-based resin laminate film (20F), and is formed so that the polystyrene-based resin multi-layer foam sheet (10S) side is located on the outside of the container and the polyolefin-based resin laminate film (20F) side is located on the inside of the container. As a result, the molded container (1) has the polystyrene-based resin multi-layer foam sheet layer (10) on the outside of the container and the polyolefin-based resin laminate film layer (20) on the inside of the container.

[0023] The polystyrene-based resin multilayer foam sheet layer (10) has a low heat-resistant polystyrene-based resin foam layer (11) located on the lamination surface with the polyolefin-based resin laminated film layer (20), and a high heat-resistant polystyrene-based resin foam layer (12) located outside the container relative to the low heat-resistant polystyrene-based resin foam layer (11).

[0024] The polyolefin resin laminated film layer (20) has a polyolefin resin film layer (21) located on the inner surface of the container, a polystyrene resin film layer (22) located on the laminated surface with the polystyrene resin multi-layer foamed sheet layer (10), and a dry laminate adhesive layer (23) located between the two film layers.

[0025] The method for thermoforming the polystyrene-based resin laminated foamed sheet (1S) into the molded container (1) is not particularly limited, and may be appropriately selected from vacuum forming, pressure forming, vacuum pressure forming, etc., within the scope in which the object of the present invention can be achieved. The heating conditions during thermoforming are also not particularly limited, and may be appropriately set within the scope in which the object of the present invention can be achieved.

[0026] (Layer structure, layer composition, and manufacturing method of polystyrene-based resin multi-layer foam sheet) The polystyrene-based resin multi-layer foamed sheet (10S), which is the material of the polystyrene-based resin multi-layer foamed sheet layer (10), is a multi-layer foamed sheet having a low heat-resistant polystyrene-based resin foamed layer (11) located at least on one outermost side, and a high heat-resistant polystyrene-based resin foamed layer (12). The method for producing the polystyrene-based resin multi-layer foamed sheet (10S) is not particularly limited, but it can generally be produced by co-extruding the low heat-resistant polystyrene-based resin foamed layer (11) and the high heat-resistant polystyrene-based resin foamed layer (12).

[0027] The polystyrene-based resin multi-layer foamed sheet (10S) is formed by adding a cell regulator and a foaming agent to a polystyrene-based resin composition as a base resin, melting and extruding the mixture, and forming a foamed sheet. In the present invention, the composition of the base resin of each of the low heat-resistant polystyrene-based resin foam layer (11) and the high heat-resistant polystyrene-based resin foam layer (12) is characteristic.

[0028] The low heat-resistant polystyrene-based resin foam layer (11) is a foam layer containing, as a base resin, either the polystyrene-based resin composition (A) or (B) shown below.

[0029] (A) A polystyrene-based resin composition having a Vicat softening temperature of 105°C or lower. (B) A polystyrene-based resin composition comprising 89 to 99 mass % of a polystyrene-based resin having a Vicat softening temperature of 105° C. or lower and 1 to 11 mass % of a polyphenylene ether resin.

[0030] Hereinafter, these polystyrene-based resin compositions are referred to as polystyrene-based resin composition (A) and polystyrene-based resin composition (B).

[0031] As the polystyrene-based resin having a Vicat softening temperature of 105°C or less constituting the polystyrene-based resin composition (A), a styrene homopolymer or a copolymer consisting of styrene and a monomer other than styrene can be used. Specific examples include general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS), styrene-acrylonitrile copolymer, styrene-(meth)acrylic acid copolymer resin, styrene-maleic anhydride copolymer, and styrene-based elastomers (SBS, SEBS, SIS, SEPS). These polystyrene-based resins having a Vicat softening temperature of 105°C or less can be used alone or in combination. Among them, general-purpose polystyrene (GPPS) and a mixture of general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS) are preferably used.

[0032] As the polystyrene resin having a Vicat softening temperature of 105° C. or less constituting the polystyrene resin composition (B), the above-mentioned resins can be used alone or in combination. Among them, general-purpose polystyrene (GPPS) is preferably used.

[0033] Examples of the polyphenylene ether resin constituting the polystyrene resin composition (B) include poly(2,6-dimethylphenylene-1,4-ether), poly(2,6-diethylphenylene-1,4-ether), etc. Among them, poly(2,6-dimethylphenylene-1,4-ether) is preferably used.

[0034] When a polystyrene resin composition (B) is used as the base resin, the lower the concentration of the polyphenylene ether resin, the higher the gloss of the polyolefin resin film layer (21) in the molded container (1). On the other hand, the higher the concentration of the polyphenylene ether resin, the higher the heat resistance of the molded container (1).

[0035] The highly heat-resistant polystyrene-based resin foam layer (12) is a foam layer containing the following polystyrene-based resin composition (C) or (D) as a base resin.

[0036] (C) A polystyrene-based resin composition comprising 70 to 86 mass % of a polystyrene-based resin having a Vicat softening temperature of 105° C. or lower and 14 to 30 mass % of a polyphenylene ether resin. (D) A polystyrene-based resin composition containing 80 mass% or more of a styrene-(meth)acrylic acid copolymer resin.

[0037] Hereinafter, these resin compositions are referred to as polystyrene-based resin composition (C) and polystyrene-based resin composition (D).

[0038] As the polystyrene resin having a Vicat softening temperature of 105° C. or less constituting the polystyrene resin composition (C), the above-mentioned resins can be used alone or in combination. Among them, general-purpose polystyrene (GPPS) is preferably used.

[0039] As the polyphenylene ether resin constituting the polystyrene resin composition (C), the above-mentioned resins can be used alone or in combination. Among them, poly(2,6-dimethylphenylene-1,4-ether) is preferably used.

[0040] An example of the polystyrene-based resin composition (C) is a polystyrene-based resin composition consisting of general-purpose polystyrene (GPPS) and a polyphenylene ether resin. The Vicat softening temperature of general-purpose polystyrene (GPPS) is around 102°C. In contrast, the Vicat softening temperature of a polystyrene-based resin composition consisting of 70-86% by mass of general-purpose polystyrene and 14-30% by mass of a polyphenylene ether resin is 110-155°C.

[0041] If the concentration of the polyphenylene ether resin in the polystyrene resin composition (C) is less than 14% by mass, the heat resistance of the molded container (10) may be insufficient. On the other hand, if the concentration exceeds 30% by mass, when the polystyrene resin foam sheet (10S) is thermoformed into a container shape, it becomes difficult to make the bubble diameters of the low heat-resistant polystyrene resin foam layer (11) and the high heat-resistant polystyrene resin foam layer (12) uniform after secondary foaming, and delamination may occur at the interface between the low heat-resistant polystyrene resin foam layer (11) and the high heat-resistant polystyrene resin foam layer (12). If delamination occurs, it causes a deterioration in the mechanical properties of the molded container (10).

[0042] Examples of styrene-(meth)acrylic acid copolymer resins constituting the polystyrene-based resin composition (D) include styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, etc., which can be used alone or as a mixture. Among them, styrene-methacrylic acid copolymers consisting of 85-95% by mass of styrene monomer and 5-15% by mass of methacrylic acid monomer are preferably used. Styrene-methacrylic acid copolymers consisting of such monomer composition usually have a Vicat softening temperature of 110°C or higher.

[0043] As long as the polystyrene-based resin composition (D) satisfies the requirement that it contains 80 mass% or more of a styrene-(meth)acrylic acid-based copolymer, it may contain polystyrene-based resins other than styrene-(meth)acrylic acid, polyphenylene ether resins, and other thermoplastic resins, within the scope that does not impair the object of the present invention.

[0044] The combination of the polystyrene resin composition (A) or (B) constituting the base resin of the low heat-resistant polystyrene resin foam layer (11) and the polystyrene resin composition (C) or (D) constituting the base resin of the high heat-resistant polystyrene resin foam layer (12) can be appropriately selected. That is, all combinations of (A) / (C), (A) / (D), (B) / (C), and (B) / (D) are possible.

[0045] The polystyrene-based resin multi-layer foam sheet (10S) can be produced by adopting the same production method as that for general resin foam sheets. The polystyrene-based resin multi-layer foam sheet (10S) is produced as a multi-layer foam sheet by blending the polystyrene-based resin composition (A), (B), (C) or (D) as a base resin with a foaming agent, a filler as a bubble regulator, and other additives, melting and extruding the mixture.

[0046] Examples of the foaming agent contained in the polystyrene resin compositions (A) to (D) include decomposition type foaming agents and physical foaming agents. Examples of the decomposition type foaming agent include inorganic decomposable foaming agents such as ammonium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium nitrite, calcium azide, sodium azide, and sodium borohydride, azo compounds such as azodicarbonamide, azobissulfuramide, azobisisobutyronitrile, and diazoaminobenzene, nitroso compounds such as N,N'-dinitrosopentanemethyleneterolamine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide, and benzenesulfonyl hydrazide.

[0047] Examples of physical blowing agents include nitrogen, carbon dioxide, propane, normal butane, isobutane, normal pentane, isopentane, cyclopentane, normal hexane, isohexane, cyclohexane, normal heptane, isoheptane, cycloheptane, benzene, toluene, methyl ether, water, etc. Among these, butane and mixtures of butane with other aliphatic hydrocarbons (e.g., isobutane) are preferred.

[0048] As the air bubble regulator, powders of inorganic compounds such as talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, and glass beads, and powders of organic compounds such as polytetrafluoroethylene can be used.

[0049] Examples of other additives contained in the polystyrene resin compositions (A) to (D) include antioxidants, colorants, lubricants, antistatic agents, antibacterial agents, and deodorants.

[0050] The basis weight (mass per unit area) of the polystyrene resin multi-layer foamed sheet (10S) is preferably 90 to 400 g / m 2 and more preferably 100 to 350 g / m 2 The polystyrene-based resin multi-layer foamed sheet (10S) preferably has a sheet thickness of 0.5 to 4 mm, more preferably 1 to 3 mm. The polystyrene-based resin multi-layer foamed sheet (10S) preferably has an expansion ratio of 3 to 20 times.

[0051] The expansion ratio of the low heat-resistant polystyrene-based resin foam layer (11) in the polystyrene-based resin multi-layer foam sheet (10S) is preferably 3 to 15 times, and the expansion ratio of the high heat-resistant polystyrene-based resin foam layer (12) is preferably 5 to 25 times. Since the low heat-resistant polystyrene-based resin foam layer (11) is more likely to grow bubbles by secondary expansion due to heating during thermoforming than the high heat-resistant polystyrene-based resin foam layer (12), the expansion ratio of the low heat-resistant polystyrene-based resin foam layer (11) is preferably 0.4 to 0.9 relative to the expansion ratio of the high heat-resistant polystyrene-based resin foam layer (12). By doing so, the bubble diameters of the low heat-resistant polystyrene-based resin foam layer (11) and the high heat-resistant polystyrene-based resin foam layer (12) after thermoforming are uniform, so that interlayer delamination occurring at the interface between the low heat-resistant polystyrene-based resin foam layer (10) and the high heat-resistant polystyrene-based resin foam layer (12) can be prevented.

[0052] The mass ratio of the low heat-resistant polystyrene-based resin foam layer (11) to the high heat-resistant polystyrene-based resin foam layer (12) is 20:80 to 60:40. If the mass ratio of the high heat-resistant polystyrene-based resin foam layer (12) is less than 40, the container may be deformed by heating in a microwave oven. In a two-layer structure consisting of one layer each of the low heat-resistant polystyrene-based resin foam layer (11) and the high heat-resistant polystyrene-based resin foam layer (12) as in the first embodiment shown in FIG. 1, the mass ratio is preferably 40:60 to 60:40, and more preferably 50:50.

[0053] The arithmetic mean roughness Ra of the surface of the low heat-resistant polystyrene resin foam layer (11) of the polystyrene resin multi-layer foam sheet (10S), i.e., the surface on which the polyolefin resin laminate film (20F) is laminated, is preferably 3 to 8 μm, more preferably 3 to 7 μm, and even more preferably 3 to 6 μm. The arithmetic mean roughness Ra is a value measured in accordance with JIS B0601:2013 "Product Geometric Characteristics Specifications (GPS)-Surface Properties: Profile Curve Method-Terminology, Definitions and Surface Properties Parameters". A specific method for measuring the arithmetic mean roughness Ra is described in the Examples section below. The smaller the arithmetic mean roughness Ra of the surface of the low heat-resistant polystyrene resin foam layer (11), which is the surface on which the polyolefin resin laminate film (20F) is laminated, the higher the gloss of the polyolefin resin film layer (21) in the molding container (1), i.e., the gloss of the inner surface of the container.

[0054] The expansion ratio of the polystyrene-based resin multi-layer foamed sheet layer (10) in the forming container (1) is preferably 5 to 40. The layer thickness of the polystyrene-based resin multi-layer foamed sheet layer (10) in the forming container (1) is preferably 1 to 8 mm, more preferably 1.5 to 6 mm.

[0055] The expansion ratio of the low heat-resistant polystyrene-based resin foam layer (11) and the high heat-resistant polystyrene-based resin foam layer (12) in the molded container (1) is preferably 5 to 40. As described above, the expansion ratio of the low heat-resistant polystyrene-based resin foam layer (11) in the sheet state is set lower than the expansion ratio of the high heat-resistant polystyrene-based resin foam layer (12), and as a result, the difference between the expansion ratios of the low heat-resistant polystyrene-based resin foam layer (11) and the high heat-resistant polystyrene-based resin foam layer (12) after thermoforming is small. The expansion ratios of each layer are preferably within the range of 0.8 to 1.25 relative to the expansion ratio of the other layer.

[0056] In the first embodiment shown in FIG. 1, the polystyrene-based resin multilayer foam sheet layer (10) is configured to have two layers, namely, a low heat-resistant polystyrene-based resin foam layer (11) and a high heat-resistant polystyrene-based resin foam layer (12), but it may also have a layer structure of three or more layers.

[0057] In the molded container of the present invention, the polystyrene-based resin multilayer foam sheet layer must have at least two layers, a low heat-resistant polystyrene-based resin foam layer located on the lamination surface with the polyolefin-based resin laminated film layer, and a high heat-resistant polystyrene-based resin foam layer located on the outer side of the low heat-resistant polystyrene-based resin foam layer. Therefore, the container can be configured so that a low heat-resistant polystyrene-based resin foam layer (13) is further provided on the outer side of the high heat-resistant polystyrene-based resin foam layer (12) as shown by the two-dot chain line in Figures 2(a) and 3(a) (layer configuration: 20 / 11 / 12 / 13).

[0058] In the case of a three-layer structure, the low heat-resistant polystyrene-based resin foam layer (11) and the low heat-resistant polystyrene-based resin foam layer (13) may have the same composition or different compositions, so long as each layer satisfies the requirements for the low heat-resistant polystyrene-based resin foam layer described above.

[0059] The three-layer polystyrene resin multi-layer foamed sheet (10S) can be produced by co-extrusion in the same manner as the two-layer polystyrene resin multi-layer foamed sheet (10S) (layer structure: 11 / 12 / 13).

[0060] The basis weight of the three-layer polystyrene resin multi-layer foamed sheet is preferably 90 to 400 g / m 2 and more preferably 100 to 300 g / m 2In the three-layer polystyrene-based resin multi-layer foamed sheet, the expansion ratio of the low heat-resistant polystyrene-based resin foamed layer (11, 13) is preferably 3 to 15 times, and the expansion ratio of the high heat-resistant polystyrene-based resin foamed layer (12) is preferably 5 to 25 times. Since the low heat-resistant polystyrene-based resin foamed layer (11, 13) is more likely to grow bubbles by secondary expansion due to heating during thermoforming than the high heat-resistant polystyrene-based resin foamed layer (12), the expansion ratio of the low heat-resistant polystyrene-based resin foamed layer (11, 13) in the sheet state is preferably 0.4 to 0.9 relative to the expansion ratio of the high heat-resistant polystyrene-based resin foamed layer (12). The mass ratio of the low heat-resistant polystyrene-based resin foamed layer (total of 11 and 13) to the high heat-resistant polystyrene-based resin foamed layer (12) is 20:80 to 60:40. If the mass ratio of the high heat resistant polystyrene type resin foam layer (12) is less than 40, the container may be deformed by heating in a microwave oven.

[0061] In addition, in the case of a three-layer structure in which the high heat-resistant polystyrene-based resin foam layer (12) is sandwiched between the low heat-resistant polystyrene-based resin foam layers (11 and 13) in this manner, it is preferable that the low heat-resistant polystyrene-based resin foam layer (11) and the low heat-resistant polystyrene-based resin foam layer (13) have the same composition, basis weight, and expansion ratio. In this way, the polystyrene-based resin multilayer foam sheet layer in the molded container is symmetrical in the inside and outside directions of the container, making it easier to suppress warping of the container due to the difference in the degree of thermal deformation between the low heat-resistant polystyrene-based resin foam layers (11, 13) and the high heat-resistant polystyrene-based resin foam layer (12).

[0062] (Layer structure and manufacturing method of polyolefin resin laminate film) In the first embodiment shown in Fig. 1, the polyolefin resin laminated film layer (20) has a layer structure in which a polyolefin resin film layer (21), a dry laminate adhesive layer (23), and a polystyrene resin film layer (22) are laminated in this order from the inner surface of the container. The polyolefin resin film layer (21) located on the inner surface of the container, i.e., the surface that comes into contact with food, has the function of protecting the polystyrene resin multilayer foamed sheet layer (10) from high-temperature oil derived from food heated in a microwave oven.

[0063] The polyolefin resin laminate film layer (20) is a layer formed by laminating a polyolefin resin laminate film (20F) on a polystyrene resin multi-layer foam sheet (10S). In the embodiment shown in FIG. 1, the polyolefin resin laminate film (20F) has a polyolefin resin film layer (21), a polystyrene resin film layer (22), and a dry laminate adhesive layer (23). The polystyrene resin film layer (22) is a layer for thermally fusing the polyolefin resin laminate film (20F) to the polystyrene resin multi-layer foam sheet (10S). The dry laminate adhesive layer (23) is a layer for bonding the polyolefin resin film layer (21) and the polystyrene resin film layer (22) together to form the polyolefin resin laminate film (20F).

[0064] The polyolefin resin constituting the polyolefin resin film layer (21) may be a homopolymer or copolymer with propylene, ethylene or α-olefin as a monomer, and these may be used alone or in a mixture. Among them, from the viewpoints of heat resistance and oil resistance, propylene polymers containing propylene as the main component (propylene homopolymer, propylene-ethylene random copolymer, propylene-ethylene block copolymer, etc.) are preferably used. The thickness of the polyolefin resin film layer (21) is preferably 10 to 80 μm, more preferably 40 μm or more from the viewpoint of oil resistance, and more preferably 10 to 25 μm from the viewpoint of economy. For the polyolefin resin film layer (21), a polyolefin resin film can be used as the material, and suitable examples include an unstretched polypropylene film (CPP film) and a polypropylene resin film slightly stretched in a uniaxial direction (a CPP film made of homopolypropylene having a melting peak temperature of 160°C or higher, which is heat-treated at 135 to 140°C and stretched in a uniaxial direction by 1.2 to 1.5 times).

[0065] The polystyrene resin constituting the polystyrene resin film layer (22) is a styrene homopolymer, a copolymer of styrene and a monomer other than styrene, or a mixture thereof, and examples thereof include general-purpose polystyrene (GPPS), high impact polystyrene (HIPS), and styrene elastomers (SBS, SEBS, SIS, SEPS). Among these, those containing general-purpose polystyrene (GPPS) as a main component are preferred. The thickness of the polystyrene resin film layer (22) is preferably 10 to 100 μm.

[0066] The thicker the polystyrene-based resin film layer (22), the higher the glossiness of the polyolefin-based resin film layer (21) in the molded container (1), i.e., the glossiness of the inner surface of the container. Therefore, simply from the viewpoint of glossiness, the thickness of the polystyrene-based resin film layer (22) is more preferably 25 μm or more.

[0067] On the other hand, as described below, by using a method of improving the surface smoothness of the low heat-resistant polystyrene resin foam layer (11), which is the surface to which the polyolefin resin laminate film (20F) is laminated, or by using a biaxially oriented polystyrene film (OPS film) as the material for the polystyrene resin film layer (22), the gloss of the polyolefin resin film layer (21) in the molded container (1), i.e., the gloss of the inner surface of the container, can be increased without increasing the thickness of the polystyrene resin film layer (22). Therefore, from the viewpoint of achieving both glossiness and economic efficiency, 10 to 20 μm is more preferable.

[0068] A polystyrene resin film can be used as the material for the polystyrene resin film layer (22). As the polystyrene resin film, a non-stretched PS film, a biaxially stretched PS film (OPS film), etc. can be used. In particular, when an OPS film is used, the gloss of the polyolefin resin film layer (21) in the molded container (1), i.e., the gloss of the inner surface of the container, can be efficiently increased without increasing the thickness of the OPS film. The reason why the gloss can be efficiently increased when an OPS film is used will be described in detail in the section on examples.

[0069] The dry laminate adhesive layer (23) is an adhesive layer for laminating the polyolefin resin film layer (21) and the polystyrene resin film layer (22). As described above, when a polyolefin resin film is used as the material for the polyolefin resin film layer (21) and a polystyrene resin film is used as the material for the polystyrene resin film layer (22), the two films are bonded together with a dry laminate adhesive to produce a polyolefin resin laminate film (20F). Examples of dry laminate adhesives constituting the dry laminate adhesive layer (23) include urethane-based, acrylic-based, epoxy-based, ester-based, ether-based, and vinyl acetate-based dry laminate adhesives. Among these, urethane-based adhesives are preferred because of their excellent adhesive strength. The thickness or application amount of the dry laminate adhesive layer is not particularly limited, but is preferably 0.5 to 5 g / m. 2 and more preferably 1 to 3 g / m 2 It is.

[0070] A printed layer may be provided between the polyolefin resin film layer (21) and the polystyrene resin film layer (22). In that case, the layer structure may be either polyolefin resin film layer (21) / printed layer / dry laminate adhesive layer (23) / polystyrene resin film layer (22) or polyolefin resin film layer (21) / dry laminate adhesive layer (23) / printed layer / polystyrene resin film layer (22).

[0071] The polyolefin-based resin laminate film (20F) produced as described above is laminated and integrated with the low heat-resistant polystyrene-based resin foam layer (11) side of the polystyrene-based resin multi-layer foamed sheet (10S) by a thermal lamination method, with the polystyrene-based resin film layer (22) serving as a heat-sealing layer, to form a polystyrene-based resin laminated foamed sheet (1S).

[0072] In the molded container (1) of the present invention, a polystyrene-based resin film layer (30) may be further provided on the container outer side of the polystyrene-based resin multi-layer foamed sheet layer (10) as shown by the two-dot chain line in Fig. 2(b) (layer structure: 20 / 10 / 30). In this case, a printed layer may be provided between the polystyrene-based resin multi-layer foamed sheet layer (10) and the polystyrene-based resin film layer (30) (layer structure: 20 / 10 / printed layer / 30).

[0073] The polystyrene resin constituting the polystyrene resin film layer (30) may be the same as that of the polystyrene resin film layer (22), and the preferred thickness range is also the same. The material of the polystyrene resin film layer (30) may be a polystyrene resin film (30F). As shown by the two-dot chain line in Fig. 3(b), the polystyrene resin film (30F) may be laminated on the outside of the container of the polystyrene resin multi-layer foamed sheet (10S) by a thermal lamination method, in the same manner as laminating the polyolefin resin laminate film (20F) on the polystyrene resin multi-layer foamed sheet (10S).

[0074] (Second and third embodiments) The microwave food container of the present invention may have the following layer configurations in addition to the first embodiment shown in Fig. 1. Second and third embodiments will be described below.

[0075] In the second and third embodiments, the polyolefin resin laminate film layer has a gas barrier layer. The gas barrier layer may be made of any suitable gas barrier resin that provides gas barrier properties, such as ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), nylon (NY), polyethylene terephthalate (PET), etc.

[0076] The second embodiment has the following layer configuration: (Polyolefin resin film layer / dry laminate adhesive layer / gas barrier resin film layer / dry laminate adhesive layer / polystyrene resin film layer) / polystyrene resin multi-layer foam sheet layer.

[0077] The polyolefin resin film layer, the polystyrene resin film layer, and the gas barrier resin film layer can be a polyolefin resin film, a polystyrene resin film, and a gas barrier resin film, respectively. These three types of films can be bonded together with a dry lamination adhesive to form a polyolefin resin laminate film. The polyolefin resin laminate film thus produced can be laminated to the low heat-resistant polystyrene resin foam layer of the polystyrene resin multi-layer foam sheet by a thermal lamination method, with the polystyrene resin film layer as a heat-sealing layer, to form the layer structure of the second embodiment.

[0078] In addition, a printed layer can be provided between the polyolefin resin film layer and the dry laminate adhesive layer, between the dry laminate adhesive layer and the gas barrier resin layer, and between the dry laminate adhesive layer and the polystyrene resin film layer.

[0079] The third embodiment has the following layer configuration: ((Polyolefin resin layer / adhesive resin layer / gas barrier resin layer / adhesive resin layer / polyolefin resin layer) / dry laminate adhesive layer / polystyrene resin film layer) / polystyrene resin multi-layer foam sheet layer.

[0080] In the third embodiment, a co-extruded film of (polyolefin resin layer / adhesive resin layer / gas barrier resin layer / adhesive resin layer / polyolefin resin film layer) can be used as the polyolefin resin film layer. Such a co-extruded film and a polystyrene resin film can be bonded together with a dry lamination adhesive to form a polyolefin resin laminated film. The polyolefin resin laminated film thus produced can be laminated on the low heat-resistant polystyrene resin foamed layer side of a polystyrene resin multi-layer foamed sheet by a thermal lamination method, with the polystyrene resin film layer as a heat-sealing layer, to form the layer structure of the third embodiment.

[0081] In addition, a printed layer can be provided between the polyolefin resin film layer and the dry laminate adhesive layer, or between the dry laminate adhesive layer and the polystyrene resin film layer.

[0082] The polyolefin resin film layer and the polystyrene resin film layer in the second and third embodiments correspond to the polyolefin resin film layer (21) and the polystyrene resin film layer (22) in the first embodiment, respectively, and the resins constituting each layer and the preferred thickness ranges are the same as those described in the first embodiment. The same applies to the dry lamination adhesive.

[0083] (Properties of Molded Container) <Glossiness of polyolefin resin film layer> In the molded container of the present invention, the gloss of the polyolefin resin film located on the inner surface of the container, i.e., the gloss of the inner surface of the container, is preferably 50% or more, more preferably 60% or more. The gloss in the present invention is measured according to the 60-degree mirror method of JIS Z8741:1997 "Specular gloss - measuring method". The specific method for measuring the gloss is described in the section of the examples.

[0084] <Adhesive strength of polyolefin resin laminated film layer> In the molded container of the present invention, the adhesive strength between the polystyrene resin multi-layer foamed sheet layer and the polyolefin resin laminated film layer is preferably 5.0 N / 15 mm or more.

[0085] The adhesive strength between the polystyrene-based resin multi-layer foamed sheet layer and the polyolefin-based resin laminated film layer is related to the occurrence of "bubbles" that may occur when the molded container is heated in a microwave oven. Bubbles are a phenomenon in which the residual gas in the polystyrene-based resin foamed sheet layer expands due to microwave heating, causing the adhesive interface between the polystyrene-based resin foamed sheet and the polyolefin-based resin laminated film to peel off and rise, causing the polyolefin-based resin laminated film to swell like a blister. This phenomenon is not preferable from the viewpoint of appearance. In the molded container of the present invention, the polystyrene-based resin multi-layer foamed sheet layer and the polyolefin-based resin laminated film layer have the above-mentioned adhesive strength, so that the occurrence of bubbles can be effectively suppressed. A specific method for measuring the adhesive strength is described in the section of the examples. EXAMPLES

[0086] Hereinafter, the sheet extrusion direction is referred to as the "machine direction", and the direction perpendicular to the sheet extrusion direction is referred to as the "width direction".

[0087] The present invention will be specifically described below with reference to examples. The present invention is not limited to these examples. The evaluation results of the examples and comparative examples are shown in Tables 1 to 9.

[0088] [Table 1]

[0089] [Table 2]

[0090] [Table 3]

[0091] [Table 4]

[0092] [Table 5]

[0093] [Table 6]

[0094] [Table 7]

[0095] [Table 8]

[0096] [Table 9]

[0097] (Evaluation method) <Expansion ratio of polystyrene resin foam sheet (underwater replacement method)> The expansion ratio of the polystyrene-based resin foamed sheets used in the examples and comparative examples was measured as follows.

[0098] A 10cm x 10cm piece was cut out from three locations in the width direction of the sheet, 5cm inside from the center and both ends, to be used as a measurement sample. The apparent overall density (definition: mass per unit volume of the sample including all skins formed during molding) of the obtained measurement sample was measured in accordance with JISK7222:2005 "Foamed plastics and rubber - Determination of apparent density". Next, the measurement sample was pressed with a hot press machine to make a non-foamed sample, and the density was measured in accordance with JISK7112-1:2023 "Plastics - Determination of density of non-foamed plastics - Part 1: Underwater displacement method, liquid pycnometer method and float-sink method" A method: Underwater displacement method. The expansion ratio was then calculated using the following formula. The three obtained expansion ratios were used as the expansion ratios to be measured. Expansion ratio = apparent total density (kg / m 3 )÷density(kg / m 3 )

[0099] <Expansion ratio of each foam layer of polystyrene resin multi-layer foam sheet (method of calculation from measured thickness and true density)> First, the thickness of the foam layer for which the expansion ratio is to be calculated is measured by cross-sectional observation using a microscope with a length measuring function. Next, the thickness of the foam layer when it is not foamed is calculated based on the density of the base resin constituting the foam layer, i.e., the true density. Finally, the expansion ratio is calculated by dividing the actually measured thickness of the foam layer by the calculated thickness when the foam layer is not foamed.

[0100] (Specific examples) ·Layer basis weight: 55g / m 2 -Actual thickness of foam layer: 0.00075m Density when the foam layer is non-foamed: 1.05×10 6 g / m 3 Basis weight 55g / m 2 In the case where the foam layer is not foamed, the layer thickness is 55(g / m 2 )÷1.05×10 6 (g / m 3 ) ≒ 0.00005 (m) Therefore, the expansion ratio is 0.00075(m) ÷ 0.00005(m) = 15 times.

[0101] <Arithmetic mean roughness Ra of polystyrene resin foam sheet> The arithmetic mean roughness Ra of the surface of the polystyrene resin foam sheet used in each of the Examples and Comparative Examples, on which the polyolefin resin laminate film was laminated, was measured in accordance with JIS B0601:2013 "Geometric characteristic specifications for products (GPS)-Surface quality: Contour curve method-Terminology, definitions and surface quality parameters" using a Mitutoyo arithmetic mean roughness measuring instrument "SURFTEST SV-2100" under the conditions of λc (parameter for removing waviness from the measured cross-sectional curve): 2.5 mm, λs (parameter for removing noise from the measured cross-sectional curve): 8 μm, and evaluation length: 12.5 mm.

[0102] The samples were taken as follows: 2cm x 2cm samples were taken from three locations across the width of the sheet, 5cm in from the center and both ends, and the arithmetic mean roughness Ra was measured in the sheet flow direction and width direction for each sample. The average of the six measured values ​​was taken as the measured value for the sheet being measured.

[0103] <Glossiness of polyolefin resin film layer in molded container, i.e., inner surface of container> The gloss of the inner surface of the container was measured in accordance with the 60-degree mirror method of JIS Z 8741: 1997 "Specular gloss - measurement method". From the flat part of three molded containers produced under the same conditions in each Example and Comparative Example, a 2 cm x 2 cm area was arbitrarily cut out at one place per container to be used as a measurement sample. If there was no flat part, a flat surface with a large curvature was selected and cut out. The gloss of the obtained sample was measured using a gloss meter "GlossMeter VG7000" manufactured by Nippon Denshoku Industries Co., Ltd., and the average value of the three measured values ​​was used as the gloss of the measurement target.

[0104] <Peel strength of polyolefin resin laminate film layer> Test pieces measuring 15 mm wide x 70 mm long were cut out from the flat bottom of the molded containers produced in the examples and comparative examples in the extrusion direction and width direction of the polystyrene resin foam sheet that constitutes the molded container. The samples were measured using Shimadzu Corporation's "Autograph AG-Xps" in accordance with JIS K6854-1:1999 "Adhesives - Test method for peel adhesion strength - Part 1: 90 degree peel".

[0105] A specific method will be described. The polyolefin resin laminate film layer is peeled off 20 mm from the short side of one end of the test piece in the long side direction. The test piece is held by a roller-type peeling device, and the peeled film is fixed by an autograph gripper. While maintaining a peel angle of 90 degrees, peeling is performed over 50 mm at a test speed of 500 mm / min, and the average load is taken as the peel strength. When this measurement is performed, if the adhesion between the polystyrene resin foam sheet layer and the polyolefin resin laminate film layer is strong, the polyolefin resin laminate film does not peel off at the interface of the polystyrene resin multi-layer foam sheet, and the polyolefin resin laminate film peels off while destroying the polystyrene resin multi-layer foam sheet. In this case, the peel strength is considered to be 5N / 15mm or more, which is the adhesive strength between the polyolefin resin film layer and the polystyrene resin film layer laminated by the dry laminate adhesive, and the measured value is recorded as 5N / 15mm or more.

[0106] <Whether or not there is delamination at the interface between the low heat-resistant polystyrene-based resin foam layer (first layer, film lamination side foam layer) and the high heat-resistant polystyrene-based resin foam layer (second layer, container outer side foam layer) in the molded container> The cross-section of the polystyrene-based resin multi-layer foam sheet layer in the molded container was observed under a microscope to confirm the presence or absence of delamination at the interface between the low heat-resistant polystyrene-based resin foam layer and the high heat-resistant polystyrene-based resin foam layer. Observations were made on three molded containers. The observation sites were three locations on the bottom of each molded container, two locations on the connection between the bottom and the side wall, and two locations on the side wall, each of which was observed in a 10 mm wide cross-section. A case in which there was no delamination was rated as ○, and a case in which there was even one delamination was rated as ×. The target standard was set as ○.

[0107] <Heat resistance of molded containers when heated in a microwave oven> The molded containers of the examples and comparative examples (opening φ184 mm, bottom φ140 mm (area 154 cm 2 ) and a 34mm deep circular container) were filled with 300g of Neapolitan spaghetti, and 3 samples were tested under the heating conditions of 1500W x 4 minutes and 1500W x 5 minutes, for a total of 6 samples. Considering that 300g of Neapolitan spaghetti becomes just hot enough to eat after 4 minutes of heating at 1500W, the samples were evaluated according to the following criteria. The test results of the sample that deformed in the shortest time among the 3 samples under each condition were used as the evaluation results for the example and comparative example. Here, "deformed" is defined as a state where the container shape is almost lost and it is close to a sheet-like flat plate. Those that only have slight warping or twisting, but do not lose their function as a food container, are classified as "undeformed." -Even one of the samples heated for 4 minutes had a "deformation": Unacceptable All three samples heated for 4 minutes were "undeformed", but at least one sample heated for 5 minutes was "deformed". All three samples heated for 4 minutes were "undeformed" and all three samples heated for 5 minutes were "undeformed": Suitable

[0108] (Method for measuring polyphenylene ether resin concentration in polystyrene resin foam sheet) If it is necessary to know the concentration of polystyrene resins (GPPS, HIPS, etc.), polyphenylene ether resins, and styrene-(meth)acrylic acid copolymer resins with Vicat softening temperatures of 105°C or less at each location in the thickness direction of the foam sheet, it can be found by the following method.

[0109] A thin section sample is taken from a polystyrene resin foam sheet by slicing the foam layer along the direction perpendicular to the thickness direction of the sheet (planar direction). The obtained thin section sample is subjected to necessary adjustments and the presence or absence of polystyrene resins (GPPS, HIPS, etc.) with a Vicat softening temperature of 105°C or less, polyphenylene ether resins, and styrene-(meth)acrylic acid copolymer resins can be qualitatively analyzed using an FT-IR (Fourier transform infrared spectrophotometer), and then quantitative analysis can be performed using HPLC (high performance liquid chromatography) to measure the concentration of each resin component.

[0110] (Base resin for polystyrene-based resin multi-layer foam sheet) First, the resins used as the base resin of the polystyrene-based resin multi-layer foamed sheet in each of the Examples and Comparative Examples are shown below.

[0111] SABIC Noril EFN4230 A mixture of polyphenylene ether resin (PPE) and general-purpose polystyrene resin (GPPS), PPE / PS = mass ratio 70 / 30

[0112] ·DIC “XC-515” General-purpose polystyrene resin (GPPS, Vicat softening temperature 103°C)

[0113] - Toyo Styrene "T080" Styrene-methacrylic acid copolymer resin (styrene / methacrylic acid = mass ratio 92 / 8, Vicat softening temperature 117℃)

[0114] Asahi Kasei Chemicals "Tufprene 125" Styrene-butadiene block copolymer (SBS)

[0115] Toyo Styrene "E641N" High impact polystyrene resin (HIPS, Vicat softening temperature 105℃ or less)

[0116] -Toyo Styrene "HRM12" General-purpose polystyrene resin (GPPS, Vicat softening temperature 105°C or less)

[0117] [Example 1] (Preparation of polystyrene-based resin multi-layer foam sheet) A method for producing a polystyrene-based resin multi-layer foamed sheet comprising a first foamed layer made of a first mixture (base resin + cell control agent + foaming agent) and a second foamed layer made of a second mixture (base resin + cell control agent + foaming agent) will be described.

[0118] Two tandem extruders were prepared, each with a single screw extruder with a screw diameter of 90 mm on the upstream side and a single screw extruder with a screw diameter of 150 mm on the downstream side, and these were connected to a circular die via a merging die. Hereinafter, these two tandem extruders are referred to as the first extruder and the second extruder.

[0119] The first mixture was melt-kneaded in a first extruder, the second mixture was melt-kneaded in a second extruder, and the molten mixtures discharged from these extruders were co-extruded through a circular die to prepare for producing a polystyrene-based resin multi-layer foamed sheet consisting of a first foamed layer and a second foamed layer.

[0120] A resin mixture of "XC-515" / "E641N" (mass ratio 85 / 15) was prepared as the base resin of the first foamed layer. That is, the base resin of the first foamed layer is a polystyrene-based resin composition consisting of 100 mass% polystyrene-based resin having a Vicat softening temperature of 105°C or less.

[0121] 100 parts by mass of this base resin was blended with 0.8 parts by mass of Toyo Styrene's talc master batch "DSM1401M" as a cell regulator and fed to the upstream extruder of the first extruder, and 4.0 parts by mass (based on 100 parts by mass of base resin) of mixed butane consisting of 65% by mass of isobutane and 35% by mass of normal butane was added as a foaming agent during the blending, and the resulting mixture was melt-kneaded and fed to the downstream extruder. In the downstream extruder, the molten mixture was cooled to a temperature suitable for foaming and fed to a joining die at a rate of 120 kg / h.

[0122] A resin mixture of "XC-515" / "Noryl EFN4230" (mass ratio 70 / 30) was prepared as the base resin of the second foamed layer. That is, the base resin of the second foamed layer is a polystyrene-based resin composition consisting of 100 mass% of a resin mixture of 79 mass% of a polystyrene-based resin having a Vicat softening temperature of 105°C or less and 21 mass% of a polyphenylene ether resin.

[0123] 100 parts by mass of this base resin was blended with 1.0 part by mass of Toyo Styrene's talc master batch "DSM1401M" as a cell regulator and fed to the upstream extruder of the second extruder, and 5.0 parts by mass of mixed butane consisting of 65% by mass of isobutane and 35% by mass of normal butane (based on 100 parts by mass of base resin) was added as a foaming agent during the blending, melt-kneaded, and then fed to the downstream extruder. In the downstream extruder, the molten mixture was cooled to a temperature suitable for foaming and fed to a joining die at a rate of 120 kg / h.

[0124] The two types of molten mixtures fed into the joining die were joined and laminated in the joining die, and then passed through a circular die with a diameter of 125 mm to be co-extruded and foamed into a cylindrical shape with the first foamed layer (no PPE) on the inside and the second foamed layer (21% by mass of PPE) on the outside. Immediately after that, 30°C air was blown on the inside and outside of the sheet to cool it, and the sheet was taken up along the outer surface of the cooling device (mandrel), and further cut into two pieces along the extrusion direction to obtain a polystyrene resin multi-layer foamed sheet with a width of 1050 mm. The amount of 30°C air blown on the outside (first foamed layer, no PPE) was 0.09 m. 3 / m 2 The inner layer (second foam layer, PPE 21% by mass) is 0.07 mm 3 / m 2 In order to replace the foaming gas, the obtained polystyrene-based resin multi-layer foamed sheet was cured for 14 days after production.

[0125] The resulting polystyrene-based resin multi-layer foamed sheet had a basis weight of 110 g / m 2 The sheet had a thickness of 1.6 mm, and the expansion ratio measured by the underwater displacement method was 15 times.

[0126] The basis weights of the first foam layer (no PPE) and the second foam layer (PPE 21% by mass) were calculated by dividing the measured basis weight of the entire sheet by the output of the first extruder and the output of the second extruder. The basis weights of the first foam layer and the second foam layer were each 55 g / m 2 It was.

[0127] The thickness of the first foam layer (no PPE) was 0.5 to 0.6 mm, and the expansion ratio was calculated to be 9 to 11 times from that thickness. The thickness of the second foam layer (21% by mass of PPE) was 1.0 to 1.1 mm, and the expansion ratio was calculated to be 17 to 19 times.

[0128] In Example 1, the first foamed layer (without PPE) side is the lamination surface of the polyolefin-based resin laminate film. The arithmetic mean roughness Ra of the first foamed layer (without PPE) was measured and shown in the table.

[0129] (Preparation of polyolefin resin laminate film) A method for producing a polyolefin-based resin laminate film will be described. In the following examples and comparative examples, a non-oriented polypropylene film will be referred to as a CPP film, and a non-oriented polystyrene film will be referred to as a PS film.

[0130] First, a CPP film (Sun-Tox "KL12", thickness 25 μm) and a PS film (FPCO Allight, GPPS / HIPS (mass ratio 85 / 15), thickness 15 μm) were prepared. A print layer was formed by printing gravure ink on one side of the CPP film, and then a urethane-based dry lamination adhesive (Tomoflex, Toyo Morton) was applied at a rate of 2 g / m on the print layer. 2 The mixture was applied with a gravure roll, and a PS film was laminated thereon to obtain a polyolefin resin laminate film.

[0131] (Preparation of polystyrene-based resin laminated foam sheet) The first foam layer side (without PPE) of the polystyrene-based resin multi-layer foamed sheet and the CPS film side of the polyolefin-based resin laminate film were overlapped so as to face each other, and passed between the heat lamination rolls (upper roll: heated roll, lower roll: unheated pressing roll) facing each other from above and below, and the first foam layer of the polystyrene-based resin multi-layer foamed sheet and the CPS film layer of the polyolefin-based resin laminate film were heat-sealed to obtain a polystyrene-based resin laminated foamed sheet. The heat lamination conditions were an upper heat roll set temperature of 200°C and a roll feed speed of 14 m / min.

[0132] (Preparation of molded container) The polystyrene-based resin laminated foam sheet prepared above was molded using a vacuum and compressed air molding machine with the polyolefin-based resin laminated film side facing the inside of a container to form a container with an opening of φ184 mm and a bottom of φ140 mm (area 154 cm). 2 A total of 12 circular containers, each 34 mm in diameter and 34 mm deep, were prepared: 3 for checking the gloss level and the presence or absence of delamination at the interface between the low heat-resistant foam layer and the high heat-resistant foam layer (for both purposes), 6 for microwave heating tests, and 3 for measuring the film adhesive strength.

[0133] (Evaluation of molded containers) For the molded containers produced above, various measurements of the glossiness of the inner surface of the container and the film adhesive strength were performed using the methods described above in the evaluation method, as well as a microwave oven heating test, and the evaluation results are shown in the table.

[0134] [Examples 2 to 4] Except for the PPE concentration of the first foamed layer being 3 mass%, 5 mass%, and 7 mass%, and the heat lamination conditions of the polyolefin resin laminate film being the conditions shown in the table, polystyrene resin laminate sheets were produced in the same manner as in Example 1, and molded containers for evaluation were obtained. The arithmetic mean roughness Ra of the first foamed layer (film lamination surface) of the polystyrene resin multi-layer foamed sheet and the evaluation results of the molded container are shown in the table. The base resin formulations of Examples 2 to 4 are shown below.

[0135] Example 2: "XC-515" / "Noryl EFN4230" (mass ratio 95.7 / 4.3) Example 3: "XC-515" / "Noryl EFN4230" (mass ratio 92.8 / 7.2) Example 4: "XC-515" / "Noryl EFN4230" (mass ratio 90.0 / 10.0)

[0136] [Examples 5 and 6] A polystyrene-based resin laminated foamed sheet was produced in the same manner as in Example 4, except that the amounts of the cell regulator and the foaming agent added and the cooling conditions of the sheet were adjusted so that the arithmetic mean roughness Ra of the first foamed layer was the value shown in the table, and a molded container for evaluation was obtained. The arithmetic mean roughness Ra of the first foamed layer (film lamination surface) of the polystyrene-based resin multi-layer foamed sheet and the evaluation results of the molded container are shown in the table.

[0137] [Examples 7 and 8] Except for changing the thickness of the PS film constituting the polyolefin resin laminate film to 25 μm and 40 μm, polystyrene resin multi-layer foamed sheets were produced in the same manner as in Example 4, and molded containers for evaluation were obtained. The evaluation results are shown in the table.

[0138] [Example 9] A polystyrene-based resin multi-layer foamed sheet was produced in the same manner as in Example 4, except that a biaxially oriented polystyrene film (OPS film) having a thickness of 14 μm was used as the PS film constituting the polyolefin-based resin laminate film, and a molded container for evaluation was obtained. The evaluation results are shown in the table.

[0139] [Example 10] A polystyrene-based resin laminated foam sheet was produced in the same manner as in Example 1, except that the base resin of the second foam layer was "T080" / "Tufprene 125S" (mass ratio 92 / 8), and a molded container for evaluation was obtained. The arithmetic mean roughness Ra of the first foam layer (film lamination surface) of the polystyrene-based resin multi-layer foam sheet and the evaluation results of the molded container are shown in the table.

[0140] [Example 11] A polystyrene-based resin laminated foam sheet was produced in the same manner as in Example 4, except that the base resin of the second foam layer was "T080" / "Tufprene 125S" (mass ratio 92 / 8), and a molded container for evaluation was obtained. The arithmetic mean roughness Ra of the first foam layer (film lamination surface) of the polystyrene-based resin multi-layer foam sheet and the evaluation results of the molded container are shown in the table.

[0141] [Examples 12 to 13, Comparative Example 1] A polystyrene-based resin foamed sheet and a molded container were produced in the same manner as in Example 1, except that the base resin formulation of the second foamed layer was as shown in the table, and various evaluations were performed. The evaluation results are shown in the table.

[0142] [Examples 14 to 17, Comparative Examples 4 to 11] A polystyrene-based resin foamed sheet and a molded container were produced in the same manner as in Example 2, except that the base resin formulations of the first and second foamed layers were as shown in the table, and various evaluations were performed. The evaluation results are shown in the table.

[0143] [Examples 18 to 19, Comparative Example 12] A polystyrene-based resin foamed sheet and a molded container were produced in the same manner as in Example 10, except that the base resin composition of the second foamed layer was as shown in the table, and various evaluations were performed. The evaluation results are shown in the table.

[0144] [Examples 20 to 23, Comparative Examples 15 to 16] A polystyrene-based resin foamed sheet and a molded container were produced in the same manner as in Example 11, except that the base resin formulations of the first and second foamed layers were as shown in the table, and various evaluations were performed. The evaluation results are shown in the table.

[0145] [Comparative Example 1] The base material is a single-layer polystyrene resin foam sheet (Sekisui Chemical Co., Ltd. "OT220A-640-300", basis weight 110g / m2) with a polystyrene resin (GPPS) having a Vicat softening temperature of 105°C or less as the base resin. 2A polystyrene-based resin laminated foamed sheet was produced in the same manner as in Example 1, except that a polystyrene-based resin laminated surface (1.8 mm thick, expansion ratio 17 times, sheet thickness 1.8 mm) was used, and a molded container for evaluation was obtained. The arithmetic mean roughness Ra of the film lamination surface of the polystyrene-based resin foamed sheet and the evaluation results of the molded container are shown in the table.

[0146] [Comparative Example 2] A polystyrene-based resin laminated foam sheet was produced in the same manner as in Example 1, except that the base resins for both the first and second foam layers were "XC-515" / "Noryl EFN4230" (mass ratio 80 / 20), and a molded container for evaluation was obtained. The arithmetic mean roughness Ra of the film laminated surface of the polystyrene-based resin foam sheet and the evaluation results of the molded container are shown in the table.

[0147] [Comparative Example 3] A polystyrene-based resin laminated foam sheet was produced in the same manner as in Example 1, except that a polyolefin-based resin laminate film was laminated on the second foam layer (PPE concentration 21 mass%) of the polystyrene-based resin multi-layer foam sheet used in Example 1, and a molded container for evaluation was obtained. The arithmetic mean roughness Ra of the second foam layer (film lamination surface) of the polystyrene-based resin foam sheet and the evaluation results of the molded container are shown in the table.

[0148] (Evaluation Results) The evaluation results of the examples and comparative examples are described with reference to the table. The terms used in the following description are defined as follows. The polystyrene-based resin foam sheet, which is the substrate, may be simply referred to as a "foam sheet". The polyolefin-based resin laminate film laminated on the polystyrene-based resin foam sheet, which is the substrate, may be simply referred to as a "laminated film". The lamination surface of the polystyrene-based resin foam sheet, which is the substrate, on which the polyolefin-based resin laminate film is laminated, may be referred to as a "film lamination surface". In the polystyrene-based resin foam sheet, which is the substrate, the foam layer on the side on which the polyolefin-based resin laminate film is laminated may be referred to as a "film lamination side foam layer". The glossiness of the polyolefin-based resin film layer in the molded container may be referred to as the "glossiness of the container inner surface" or simply as "glossiness".

[0149] Example 1, Example 4, Comparative Example 2, and Comparative Example 3 are compared. These differ in the PPE concentration in the foamed layer on the film lamination side, with the PPE concentrations being 0 mass% (none), 7 mass%, 14 mass%, and 21 mass% in the order of Example 1, Example 4, Comparative Example 2, and Comparative Example 3.

[0150] The glossiness of the container inner surface was 72%, 52%, 35%, and 20% in Example 1, Example 4, Comparative Example 2, and Comparative Example 3, respectively. The heat resistance of the molded container was evaluated as "fair" for Example 1, and as "satisfactory" for Example 4, Comparative Example 2, and Comparative Example 3. That is, in Examples 1 and 4, the glossiness of the container inner surface was 50% or more, and the container had the required heat resistance.

[0151] The factors why the gloss of the container inner surface in Examples 1 and 4 was 50% or more, and especially, the gloss of the container inner surface in Example 1 was 70% or more, will be considered. As explained in the above paragraph "Problems to be Solved by the Invention", the polyolefin resin film layer of the laminate film before being laminated on the foam sheet originally has a gloss of 90% or more, but the gloss decreases when laminated on the foam sheet.

[0152] It has been known from past knowledge that the decrease in gloss of the polyolefin-based resin film layer is due to the laminated film picking up the unevenness caused by the foam cells on the film laminated surface of the foamed sheet. In other words, the smoother the film laminated surface of the foamed sheet is, the higher the gloss of the inner surface of the container.

[0153] Generally, in resin compositions consisting of GPPS and PPE, the higher the PPE concentration, the more difficult it becomes to control the bubbles, and the surface of the foamed sheet tends to become rough. Since PPE has extremely low fluidity when melted, the more PPE is mixed in, the more the extruder temperature needs to be raised. However, if the extruder temperature is raised to ensure the fluidity of the PPE, the melt viscosity of the main component, GPPS, drops more than necessary, and the melt viscosity of the entire resin composition also drops accordingly. As a result, when the molten resin leaves the die and is released to atmospheric pressure, the growth of the bubbles cannot be stopped to the expected size, and larger bubbles tend to be mixed in, which tends to cause the surface of the foamed sheet to become rough.

[0154] The arithmetic mean roughness Ra of the film laminated surface of the foamed sheet was 4.0 μm, 6.0 μm, 9.5 μm, and 11.5 μm in the order of Example 1, Example 4, Comparative Example 2, and Comparative Example 3. As the PPE concentration increased, the arithmetic mean roughness Ra increased, and accordingly, the gloss of the molded container also showed a lower value.

[0155] Examples 2, 3, and 4 are compared. These differ in the PPE concentration of the foamed layer on the film lamination side, which is 3 mass%, 5 mass%, and 7 mass% for Examples 2, 3, and 4, respectively. The glossiness of the inner surface of the container was 66%, 59%, and 52%, respectively for Examples 2, 3, and 4, and the lower the PPE concentration of the foamed layer on the film lamination side, the higher the glossiness. Regarding the container heat resistance, Example 2 was rated "passable," while Examples 3 and 4 were rated "satisfactory."

[0156] Initially, it was expected that the arithmetic mean roughness Ra of the film laminated surface would be smaller as the PPE concentration decreased, provided that the cooling conditions of the extruded sheet were the same. However, the arithmetic mean roughness Ra of the film laminated surface of the foamed sheets of Examples 2, 3, and 4 did not differ significantly within the range of 5.9 to 6.0 μm. This was thought to be because the melt viscosity of the base resin during extrusion did not change significantly when the PPE concentration fell below a certain level.

[0157] Therefore, from the comparison with Example 2, Example 3, and Example 4, it was found that the lower the PPE concentration of the foam layer on the film lamination side, the higher the gloss of the inner surface of the container, regardless of the arithmetic mean roughness Ra of the film lamination side. Since GPPS and PPE are completely compatible alloys, the lower the PPE concentration, the lower the Vicat softening temperature. The inventors considered that the lower the PPE concentration of the foam layer on the film lamination side, i.e., the lower the Vicat softening temperature of the foam layer on the film lamination side, the easier it is for the film lamination side of the foam sheet to soften during thermal lamination, and the unevenness of the film lamination side is smoothed out, resulting in a high gloss value on the inner surface of the container.

[0158] Examples 4, 5, and 6 are compared. The PPE concentration in the foam layer on the film lamination side in Examples 4, 5, and 6 is all 7% by mass, but in Examples 5 and 6, the amount of bubble regulator added is adjusted (the amount of bubble regulator, i.e., foam nucleating agent added is increased to increase the number of bubbles and refine the foam cells) and the cooling conditions for the foam sheet emerging from the die are adjusted (the foam sheet emerging from the die is cooled somewhat rapidly to thicken the skin layer of the foam layer), thereby improving the smoothness of the film lamination surface compared to Example 4.

[0159] As a result, the glossiness of the container inner surface of Example 4 (arithmetic mean roughness Ra 6.0 μm) was 52%, while the glossiness of the container inner surface of Example 5 (arithmetic mean roughness Ra 5.1 μm) improved to 55%, and the surface glossiness of Example 6 (arithmetic mean roughness Ra 3.0 μm) improved to 63%. The container heat resistance evaluation was "suitable" for all of Examples 4, 5, and 6, indicating that the container had sufficient heat resistance.

[0160] In other words, it was found that even if the PPE concentration of the base resin of the low heat-resistant polystyrene resin foam layer is 7% or more, by improving the smoothness of the film laminate surface, it is possible to achieve both a gloss level of 60% or more on the inner surface of the container and sufficient heat resistance of the container.

[0161] Examples 4, 7, and 8 are compared. Examples 4, 7, and 8 are obtained by changing the thickness of the polystyrene resin film layer of the laminated film. In the order of Examples 4, 7, and 8, the thickness of the polystyrene resin film layer is 13 μm, 25 μm, and 40 μm, and the glossiness of the inner surface of the container is 52%, 60%, and 66%, and the glossiness is improved as the thickness of the polystyrene resin film layer increases. This is presumed to be because the thicker the polystyrene resin film layer, the more the unevenness of the film laminated surface of the foamed sheet is absorbed, and as a result, the glossiness of the inner surface of the container is improved. In addition, the container heat resistance was all "suitable".

[0162] Thus, in the case where the PPE concentration in the foam layer on the film lamination side is 7% by mass, it was found that the glossiness of the container inner surface can be increased to 60% or more by using a method of making the thickness of the polystyrene resin film layer 25 μm or more in addition to improving the smoothness of the film lamination surface as in the above-mentioned Examples 5 and 6. In other words, it was found that it is possible to achieve both a glossiness of the container inner surface of 50% or more and necessary and sufficient heat resistance of the container.

[0163] Example 9 is an example in which a biaxially oriented polystyrene film (OPS film) having a thickness of 14 μm was used as the polystyrene resin film constituting the polyolefin resin laminate film. The OPS film has a higher tensile modulus than the unstretched PS film (13 μm) used in the examples and comparative examples other than Example 9. Since the OPS film has a higher tensile modulus than the unstretched PS film, it is considered that the OPS film can smooth out the irregularities on the film laminate surface of the foamed sheet more efficiently than the unstretched PS film, and as a result, it can exhibit a gloss level of 60% or more.

[0164] In Examples 10 and 11, a styrene-methacrylic acid copolymer resin was used as the base resin of the foam layer located on the outside of the container, and the PPE concentration in the foam layer on the film lamination surface was zero (0 mass%) or 7 mass%. As a result, the evaluation results of Example 9 were equivalent to those of Example 1, and the evaluation results of Example 10 were equivalent to those of Example 4.

[0165] Comparative Example 1 is an example using a single-layer polystyrene-based resin foamed sheet made of a polystyrene-based resin composition having a Vicat softening temperature of 105° C. or less. The foamed layer on the film laminated surface was substantially the same as that in Example 1, and the glossiness was 60% or more, but the heat resistance evaluation was “unacceptable.” [Explanation of symbols]

[0166] 1 Molded container 10 Polystyrene resin multi-layer foam sheet layer 11 Low heat resistant polystyrene resin foam layer 12 High heat resistant polystyrene resin foam layer 13 Low heat resistant polystyrene resin foam layer 20 Polyolefin resin laminated film layer 21 Polyolefin resin film layer 22 Polystyrene resin film layer 23 Dry laminate adhesive layer 30 Polystyrene resin film layer 1S Polystyrene resin laminated foam sheet 10S Polystyrene resin multi-layer foam sheet 20F Polyolefin resin laminated film 30F Polystyrene resin film

Claims

[Claim 1] A molded container comprising a polystyrene-based resin laminated foam sheet having a polystyrene-based resin multi-layer foam sheet layer and a polyolefin-based resin laminated film layer, the polyolefin-based resin laminated film layer constituting an inner surface of the container, the polystyrene-based resin multi-layer foamed sheet layer has at least two layers, a low heat-resistant polystyrene-based resin foamed layer located on the lamination surface with the polyolefin-based resin laminated film layer, and a high heat-resistant polystyrene-based resin foamed layer located on the outer side of the low heat-resistant polystyrene-based resin foamed layer, The low heat-resistant polystyrene-based resin foam layer has a polystyrene-based resin composition of either (A) or (B) below as a base resin, and the high heat-resistant polystyrene-based resin foam layer has a polystyrene-based resin composition of either (C) or (D) below as a base resin, (A) a polystyrene-based resin composition comprising a polystyrene-based resin having a Vicat softening temperature of 105° C. or less; (B) a polystyrene-based resin composition comprising 89 to 99% by mass of a polystyrene-based resin having a Vicat softening temperature of 105° C. or less and 1 to 11% by mass of a polyphenylene ether resin; (C) a polystyrene-based resin composition comprising 70 to 86% by mass of a polystyrene-based resin having a Vicat softening temperature of 105° C. or less and 14 to 30% by mass of a polyphenylene ether resin; (D) a polystyrene-based resin composition containing 80% by mass or more of a styrene / (meth)acrylic acid copolymer resin; the polyolefin-based resin laminated film layer has a polyolefin-based resin film layer located on the inner surface of the container, and a polystyrene-based resin film layer located on the lamination surface with the polystyrene-based resin multi-layer foamed sheet, The polyolefin resin film layer, i.e., the inner surface of the container, has a glossiness of 50% or more.

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