Food container

Abstract

An object of the present disclosure is to provide a food container having excellent heat resistance, deep drawing formability, mechanical strength, and cold impact resistance.SOLUTION: The present disclosure is a food container having a recess capable of accommodating food, wherein the food container is composed of a styrene-based resin composition containing 65 to 97% by mass of a styrene-unsaturated carboxylic acid-based resin (A) and 3 to 20% by mass of an ethylene-carboxylic acid ester-based copolymer (B).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to food containers. [Background technology]

[0002] Styrene-unsaturated carboxylic acid resins, typified by styrene-methacrylic acid copolymer resins, have excellent heat resistance, transparency, rigidity, and appearance, and are inexpensive, and therefore are widely used as packaging materials for food containers such as boxed lunches and prepared meals, foam boards for residential insulation, diffusion plates containing diffusing agents for LCD televisions, etc. In particular, with the recent spread of high-power microwave ovens for commercial use in convenience stores and the like, styrene-unsaturated carboxylic acid resins are being used as materials for containers that can withstand the temperatures used during cooking in high-power microwave ovens, and for lids that seal or cover these containers.

[0003] However, styrene-unsaturated carboxylic acid resins are more brittle than general polystyrene resins, which has led to problems with cracking of food containers and lids. Furthermore, their melt viscosity is higher than that of general-purpose styrene resins, which results in poor moldability, which leads to problems with the mechanical strength and appearance of the molded food containers. Meanwhile, a recent trend in the food market has been that frozen foods, which contribute to reducing food waste, are attracting attention. Therefore, there is a demand for the development of food packaging materials that are both cold-shock resistant and heat-resistant, allowing them to be used from freezing to microwave cooking. For example, Patent Documents 1 and 2 are examples of technologies related to food containers that can be used in microwave cooking. Patent Document 1 discloses a styrene-based resin composition consisting of a styrene-(meth)acrylic acid copolymer and an MBS resin, while Patent Document 2 discloses a styrene-based resin composition consisting of a styrene-(meth)acrylic acid copolymer, a polyphenylene ether resin, and a metal element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-156880 [Patent Document 2] Japanese Patent Application Publication No. 2019-194287 Summary of the Invention [Problem to be solved by the invention]

[0005] Although Patent Documents 1 and 2 examine the mechanical strength and thermal deformation resistance of food containers, these prior documents make no mention of the appearance or cold shock resistance of food containers. It has been confirmed that a new problem occurs when food containers are heated from a frozen state in a short time using microwave cooking, with holes forming on the inner wall of the bottom of the food container, causing the contents to leak out. It has been confirmed that these holes are particularly likely to form at the corners of the recessed portions of the food container, where the wall thickness is thin due to uneven thickness during container molding. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a food container that is excellent in heat resistance, deep-draw formability, mechanical strength, and cold impact resistance. [Means for solving the problem]

[0006] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that a food container made from a composition containing 65 to 97 mass% of a styrene-unsaturated carboxylic acid resin (A) and 3 to 20 mass% of an ethylene-carboxylic acid ester copolymer (B) can provide a food container with excellent appearance, moldability, heat resistance, mechanical strength, and cold impact resistance, and have completed the present invention.

[0007] [1] A food container having a recess capable of accommodating food, The food container is characterized in that it is made from a styrene-based resin composition containing 65 to 97 mass% of a styrene-unsaturated carboxylic acid-based resin (A) and 3 to 20 mass% of an ethylene-carboxylic acid ester-based copolymer (B).

[0008] [2] The styrene-based resin composition contains, relative to the total amount of the styrene-based resin composition, 65 to less than 97 mass% of the styrene-unsaturated carboxylic acid-based resin (A), 3 to 20 mass% of the ethylene-carboxylic acid ester-based copolymer (B), and more than 0 to 20 mass% of core-shell type rubbery polymer particles (C). [1] The food container according to [1].

[0009] [3] The food container according to [1] or [2], wherein the styrene-based resin composition further contains one or more selected from the group consisting of impact-resistant styrene-based resins (D), styrene-based elastomers (E), and acrylic elastomers (F).

[0010] [4] The food container according to any one of [1] to [3], wherein the ratio (d / r) of the depth d of the recess to the opening diameter r of the recess is 1.5 or less.

[0011] [5] The food container according to any one of [1] to [4], which is formed from an extruded sheet obtained by molding the styrene-based resin composition.

[0012] [6] The food container according to any one of [1] to [5], wherein the styrene-based resin composition further contains inorganic particles (G) in an amount of 0.05 to 3.0 mass% relative to the total amount of the styrene-based resin composition, and is formed from a foamed extruded sheet obtained by molding the styrene-based resin composition.

[0013] [7] A first layer composed of the styrene-based resin composition; A food container formed from a laminate having a surface layer laminated on the surface of the first layer, The food container according to any one of [1] to [6], wherein the surface layer contains a styrene-based resin or a polyolefin-based resin. [Effects of the Invention]

[0014] According to the present disclosure, a food container having excellent appearance, heat resistance, deep-draw formability, mechanical strength, and cold impact resistance can be provided. According to the present disclosure, a food container can be provided that reduces the risk of holes being formed when the food is heated from a frozen state in a short time by microwave cooking. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view showing an example of a food container having a food container body 2 and a lid 3 that covers an opening 6 of the food container body 2. As shown in FIG. [Figure 2] FIG. 2 is a schematic diagram showing a cross section of a mold 9 used to manufacture the food container 1 (particularly the food container body 2) of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention.

[0017] [Food containers] The present disclosure relates to a food container having a recess capable of accommodating food. The food container is formed from a styrene-based resin composition containing 65 to 97 mass% of a styrene-unsaturated carboxylic acid resin (A) and 3 to 20 mass% of an ethylene-carboxylic acid ester copolymer (B). The food container has a recess capable of accommodating food, and it is preferable that the ratio (d / r) of the depth d of the recess to the opening diameter r of the recess is 1.5 or less. The food container of this embodiment is made of a styrene-based resin composition having a predetermined composition and has a structure that makes it easy to store food, including liquids. Therefore, it is possible to effectively prevent the formation of holes at the contact area between the inner wall of the bottom of the food container (especially the outer periphery of the bottom of the recess) and the oil contained in the food, due to heating in a microwave oven or the like. Furthermore, since the ratio (d / r) of the depth d of the recess to the opening diameter r of the recess in the food container is 1.5 or less, and the food container is formed from a styrene-based resin composition having a predetermined composition, it is possible to more effectively prevent holes from forming at the contact area between the inner wall of the bottom portion of the food container (especially the outer periphery of the bottom of the recess) and the oil contained in the food, especially when heated in a microwave oven or the like.

[0018] A preferred embodiment of the food container of the present invention will be described below with reference to FIGS. Figure 1 shows an example of a food container 1 according to the present invention, and is a perspective view showing a food container body 2 that mainly contains noodles or rice bowl-type foods, and a lid 3 that covers an opening 6 of the food container body 2. For ease of explanation, Figure 1 shows the food container body 2 and the lid 3 that can fit into the opening 6 of the food container body 2 as an example of a food container 1 according to this embodiment, but it is sufficient for the food container 1 according to this embodiment to have only the food container body 2. FIG. 2 is a schematic diagram showing a cross section of a mold 9 used to manufacture the food container 1 (particularly the food container body 2) of FIG. The shape of a food container 1 of this embodiment and a method for forming the same will be described below with reference to FIGS. The food container body 2 of this embodiment has a recess 4 capable of accommodating food. FIG. 1 shows a food container 1 having one recess 4 as an example of the recess 4, and a groove 5 is formed around the entire periphery of the inner wall of the food container body 2 so that the amount of contents can be visually confirmed from the outside. The area of ​​the bottom surface 7 of the food container body 2 is smaller than the area of ​​the opening 6. Furthermore, the opening 6 of the food container body 2 has an outwardly protruding edge, and the edge can be fitted with the lid 3 that covers the opening 6 of the food container body 2. The shape of the recess 4 is not particularly limited, and may be, for example, a (substantially) cylindrical shape or a polygonal cylindrical shape. Furthermore, food container 1 in this embodiment may have multiple recesses 4. An example of a food container having multiple recesses 4 is a shape in which multiple side dishes are separated by partition walls, such as food containers used in commercially available boxed lunches.

[0019] The food container 1 in this embodiment can be produced, for example, using a mold 9 shown in Figure 2. As an example of this embodiment, an embodiment in which the food container 1 (food container body 2) is integrally molded from an extruded sheet 10 formed by molding the composition will be described below with reference to Figure 2. For example, a styrene-based resin composition is extruded to produce an extruded sheet 10 having a thickness of 100 to 1,000 μm. The extruded sheet 10 is preferably a laminate having a first layer and a surface layer laminated on the surface of the first layer. The first layer and / or the surface layer may be composed of a styrene-based resin composition. When the extruded sheet 10 is a laminate, the surface layer of the extruded sheet 10 may be co-extruded or film-laminated with a styrene-based resin or a polyolefin-based resin (e.g., polystyrene or polypropylene) to a thickness of 1 to 100 μm. The resulting extruded sheet 10 is then preheated at 150 to 250°C for 5 to 60 seconds, and the heated extruded sheet 10 is placed in a mold 9 so as to cover the recessed portion 11, and shaped by a predetermined molding method. For example, the recessed portion 11 can be evacuated to form a food container body 2 having a desired shape. Alternatively, the extruded sheet 10 may be placed so as to cover the recess 11 of the mold 9, and then heated and shaped by a predetermined molding method (for example, thermocompression molding, vacuum molding, pressure molding, plug-assist molding). As an example of a preferred aspect of this embodiment, the food container 1 (particularly the food container body 2) can be shaped by using the mold 9 to subject a heated extruded sheet 10 to thermo-compression molding, vacuum molding, pressure molding or plug-assisted molding. Furthermore, when manufacturing food containers 1 (particularly food container bodies 2) with different depths, the ratio (d / r) of the depth d of the recess to the diameter r of the top surface of the recess (=diameter of the opening) can be changed by using spacers 12. Figure 2 shows, as an example, a state in which spacers 12 are provided in recess 11 of depth d so that the recess has a depth d2 or a depth d1.

[0020] The average thickness (wall thickness) of the food container 1 (or food container body 2) used in the present invention is preferably 0.1 to 2 mm, and more preferably 0.15 to 1.5 mm. If the wall thickness of the container body 2 is thinner than 0.05 mm, the container will lack rigidity, and if it is thicker than 3 mm, the container will be heavy, increasing material costs and becoming bulky and difficult to dispose of as garbage. The difference in thickness between the center of the bottom surface of the food container body 2 used in the present invention and the edge of the container is preferably 0.3 mm or less, more preferably 0.1 mm or less, when the food container body 2 is a non-foam food container. When the food container body 2 is a foam food container, it is preferably 1.0 mm or less, more preferably 0.5 mm or less. If the difference in thickness between the center of the bottom surface of the container and the edge of the container is greater than the above range, the corners of the container recess will be thin, which may cause the corners of the container to crack due to impact, such as being dropped, or to develop holes in the corners when heated in a microwave oven. In this embodiment, the depth / opening diameter ratio of food container 1 (or food container body 2) is preferably 1.5 or less, more preferably 1.25 or less, and even more preferably 0.25 to 1, or 0.2 to 1. If the ratio is greater than 1.5, thickness unevenness occurs and the container strength decreases. Furthermore, if the depth / diameter ratio is less than 0.2, the container will have a flat shape, making thickness unevenness less likely to occur and reducing the oil resistance effect due to oil or oil-containing liquid remaining on the bottom surface of the food container (especially the outer periphery of the bottom surface). On the other hand, if the depth / diameter ratio is 0.2 to 1.5, not only will it be relatively easy to store contents such as food, but it will also be easier to achieve the oil resistance effect regardless of the food menu that can be stored. In this specification, the opening diameter refers to the diameter when the opening shape is circular, the minor axis when the opening shape is elliptical, and the shortest length of the diagonal when the opening shape is polygonal. In addition, in order to maintain the airtightness of the container, it is preferable to design the top of the container to have an uneven shape to improve fit. The food container used in the present invention has good shape retention due to heat, and therefore has excellent fit. The molding method for the food container according to the present invention is not limited to a molding method, and may be injection molding, injection compression molding, extrusion molding, blow molding, press molding, thermocompression molding, vacuum molding, pressure molding, plug-assist molding, foam molding, etc. For the food container used in the present invention, a method in which the food container is shaped by vacuum molding after sheet (film) molding is preferred, particularly from the standpoints of productivity and cost.

[0021] [Extruded sheet] The extruded sheet 10 in this embodiment may be either non-foamed or foamed, and may be a non-foamed extruded sheet or a foamed extruded sheet. A commonly known method can be used to manufacture the extruded sheet 10. The non-foamed extruded sheet can be manufactured using a single-screw or twin-screw extruder equipped with a T-die, followed by a sheet take-up device with a single-screw or twin-screw stretching machine. The foamed extruded sheet can be manufactured using an extrusion foaming machine equipped with a T-die or circular die. In this embodiment, the thickness of the non-foamed extruded sheet is preferably, for example, about 0.1 to 1.0 mm from the viewpoints of rigidity and thermoforming cycle. Furthermore, a uniaxial sheet may be formed by simply stretching at a normal low roll ratio, while a biaxially oriented sheet is preferably formed by stretching about 1.3 to 7 times in the machine direction (MD) with a roll and then stretching about 1.3 to 7 times in the transverse direction (TD) with a tenter in terms of strength. Furthermore, the non-foamed sheet may be multilayered with a styrene-based resin other than the composition, such as a polystyrene resin. Furthermore, the non-foamed sheet may be multilayered with a resin other than a styrene-based resin. Examples of the resin other than a styrene-based resin include PET resin and nylon resin.

[0022] The biaxially oriented sheet of the present embodiment can be produced by a commonly known method. The biaxially oriented sheet can be produced by stretching the sheet in the machine direction (MD) with rolls and then stretching it in the transverse direction (TD) with a tenter. Alternatively, the sheet can be produced by sequentially or simultaneously biaxially stretching a plate-shaped composition in a tenter while heating the composition to a temperature about 10 to 40°C above its Vicat softening temperature. The biaxially oriented sheet of this embodiment is preferably stretched at a stretch ratio of about 1.3 to 7.0 times in the MD direction and about 1.3 to 7.0 times in the TD direction in terms of strength. The average thickness of the biaxially oriented sheet of this embodiment is preferably 0.1 mm or more, more preferably 0.15 mm or more, and even more preferably 0.2 mm or more to ensure the strength, particularly rigidity, of the sheet and container, while from the viewpoint of economy, it is preferably 0.7 mm or less, more preferably 0.6 mm or less, and even more preferably 0.5 mm or less. The orientation relaxation stress in the machine direction and the cross direction of the biaxially stretched sheet of this embodiment is preferably in the range of 0.4 to 1.3 MPa. By adjusting the orientation relaxation stress within this range, the strength of the molded product of the biaxially stretched sheet can be maintained. When the biaxially oriented sheet of this embodiment is used as a food packaging container, a known anti-fogging agent may be applied to at least one surface of the biaxially oriented sheet to prevent fogging due to moisture volatilizing from the food. Examples of such anti-fogging agents include nonionic surfactants such as sucrose fatty acid esters and polyglycerin fatty acid esters, and polyether-modified silicone oils. The method for applying the antifogging agent to the biaxially oriented sheet of this embodiment is not particularly limited, and examples of convenient methods include application using a roll coater, knife coater, gravure roll coater, etc. Spraying, immersion, etc. may also be employed. Furthermore, the biaxially oriented sheet may be surface-treated by corona treatment, ozone treatment, primer treatment, etc. prior to application to improve the wettability of the surface before application. The foamed extruded sheet of this embodiment can be obtained by a conventionally known method, so-called extrusion foaming, in which the base resin and various additives, such as a foam nucleating agent (cell regulator) described below, which are added as needed, are heated, melted, and kneaded using an extruder, a physical foaming agent is injected and further kneaded, and the foamable molten resin, adjusted to an appropriate resin temperature, is extruded through a die under atmospheric pressure to foam.

[0023] In this embodiment, when forming a foamed extruded sheet, a substance commonly used as a foaming agent during extrusion foaming can be used. Examples of foaming agents that can be used include normal butane, isobutane, pentane, chlorofluorocarbons, carbon dioxide, water, and diethyl ether. Butane, isobutane, and diethyl ether are preferred, and two or more of the above foaming agents can also be used in combination. The amount of foaming agent added during foam molding is preferably 0.5 to 8.0 mass%, more preferably 1.0 to 6.0 mass%, even more preferably 2.0 to 5.0 mass%, and even more preferably 2.5 to 4.5 mass%, based on 100 mass% of the composition to be foamed. A foaming agent in the range of 2.0 to 5.0 mass% provides excellent resin plasticization and foamability. In this embodiment, when forming a foamed extruded sheet, a substance commonly used as a foam nucleating agent during extrusion foaming can be used. For example, talc, silica, mica, etc., which are listed above as inorganic particles (D), can be used. The content of the foam nucleating agent is preferably 0.1 to 7.0 mass%, more preferably 0.2 to 6.0 mass%, and even more preferably 0.3 to 4.0 mass%, when the total amount of the composition is taken as 100 mass%. By setting the content within the range of 0.1 to 7.0 mass%, a sheet with an expansion ratio suitable for a foamed extruded sheet for food packaging can be obtained. The foam nucleating agent can be added directly, or a masterbatch can be used, in which resin pellets in which a high concentration of foam nucleating agent has been dispersed by extrusion kneading are added.

[0024] In this embodiment, the thickness of the foamed extruded sheet is preferably 0.3 mm to 5.0 mm, more preferably 0.5 to 3.0 mm. By setting the thickness in the range of 0.5 to 3.0 mm, it is possible to provide a foamed extruded sheet with an excellent balance between strength and productivity. In this embodiment, the apparent density of the foamed extruded sheet is 0.05 to 0.30 g / cm 3 It is preferable that the density is 0.06 to 0.20 g / cm. 3 , more preferably 0.07 to 0.10 g / cm 3 In particular, 0.07 to 0.10 g / cm 3By setting the range, it is possible to provide a foamed extruded sheet having an excellent balance between strength and productivity. In this embodiment, the basis weight of the foamed extruded sheet is 70 to 300 g / m 2 is preferably 75 to 250 g / m 2 , and more preferably 80 to 200 g / m 2 , and even more preferably 90 to 150 g / m 2 Especially 80 to 200 g / m 2 By setting the range, it is possible to provide a foamed extruded sheet having an excellent balance between strength and productivity. In this embodiment, the expansion ratio of the foamed extruded sheet is preferably 3 to 18 times, more preferably 4 to 17 times, even more preferably 5 to 16 times, and even more preferably 6 to 15 times. In this embodiment, the closed cell ratio of the foamed extruded sheet determined in accordance with the method of JIS K7138: 2006 is preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, even more preferably 83% or more, and even more preferably 86% or more. In particular, by setting the closed cell ratio to 80% or more, there will be fewer fragile open cells, and therefore a foamed extruded sheet with excellent strength can be obtained. In this embodiment, the average cell diameter of the foamed extruded sheet is preferably 200 to 500 μm, more preferably 250 to 450 μm. By setting the range to 200 to 500 μm, it is possible to provide a foamed extruded sheet with an excellent balance between strength and productivity.

[0025] The foam-extruded sheet of this embodiment may be multilayered by further laminating a film. The type of film used may be any film commonly used for polystyrene. For example, a PP (polypropylene) / PS (polystyrene) dry laminate film may be used. The thickness of the laminated film is preferably in the range of 5 to 200 μm, more preferably 10 to 150 μm, and even more preferably 20 to 100 μm. A thickness in the range of 20 to 100 μm provides an excellent balance of weight reduction, strength, and oil resistance reinforcement. A preferred foam extruded sheet of this embodiment is a laminate having a foam layer of the composition, a polystyrene layer provided on at least one side of the foam layer, and a polyolefin layer provided on the surface of the polystyrene layer. This structure provides a polyolefin layer as the outermost layer that may come into contact with food, etc., thereby providing a container with excellent oil resistance. The polyolefin layer may be made of polyethylene, polypropylene, polyvinyl acetate, polyvinyl alcohol, or the like, and may also be a copolymer. Polypropylene is particularly preferred from the standpoint of oil resistance. Methods for laminating the surface layer to the first layer include co-extrusion using an extruder and film lamination. The styrene-based resin sheet used in the present invention has excellent adhesion to polyolefins and is characterized by its low peeling due to heating, etc.

[0026] [Styrene-based resin composition] The styrene-based resin composition of the present embodiment can be used as a raw material for the extruded sheet 10 (for example, a foamed extruded sheet and / or a non-foamed extruded sheet). The styrene-based resin composition of this embodiment contains a styrene-unsaturated carboxylic acid resin (A) and an ethylene-carboxylic acid ester copolymer (B). If necessary, the styrene-based resin composition may contain core-shell rubbery polymer particles (C). The styrene-unsaturated carboxylic acid resin (A) may be at least one resin having styrene-based monomer units (a1) and unsaturated carboxylic acid monomer units (a2). The ethylene-carboxylic acid ester copolymer (B) may be at least one resin having ethylene monomer units (b1) and carboxylic acid ester monomer units (b2). The content of the styrene-unsaturated carboxylic acid resin (A) is 65 to 97% by mass, and the content of the ethylene-carboxylic acid ester copolymer (B) is 3 to 20% by mass, based on the total amount (100% by mass) of the styrene-based resin composition. Furthermore, the core-shell rubbery polymer particles (C), as an optional component, may be contained in an amount of 0 to 20% by mass, based on the total amount (100% by mass) of the styrene-based resin composition. By constructing a food container from the styrene-based resin composition whose composition is adjusted within the above range, it is possible to provide a food container that has excellent appearance, heat resistance, deep-draw formability, mechanical strength, and cold impact resistance. Furthermore, the styrene-based resin composition of this embodiment may optionally contain one or more selected from the group consisting of impact-resistant styrene-based resins (D), styrene-based elastomers (E), and acrylic elastomers (F). This makes it possible to provide a styrene-based resin composition having excellent heat resistance, mechanical strength, and cold impact resistance. The styrene-based resin composition of this embodiment may optionally contain inorganic particles (G). Addition of the inorganic particles (G) to the styrene-based resin composition serves as a foam nucleating agent during foam molding and contributes to improving the rigidity of the food container.

[0027] Hereinafter, each component contained in the styrene-based resin composition of the present disclosure and its physical properties will be described in detail. "Styrene-unsaturated carboxylic acid resin (A)" The styrene-unsaturated carboxylic acid resin (A) in this embodiment is a copolymer resin (hereinafter also simply referred to as resin (A)) containing a styrene monomer unit (a1) and an unsaturated carboxylic acid monomer unit (a2) as essential components, and contributes to improving the heat resistance of the entire styrene resin composition. As described below, the unsaturated carboxylic acid monomer unit (a2) of this embodiment preferably contains one or more monomer units selected from the group consisting of unsaturated carboxylic acid monomer units (e.g., (meth)acrylic acid monomer units (a2-1)) and unsaturated carboxylic acid alkyl ester monomer units (e.g., (meth)acrylic acid ester monomer (a2-2)). Furthermore, the styrene-unsaturated carboxylic acid resin (A) may further contain other monomer units (a3) ​​in addition to the essential components of the styrene monomer units (a1) and the unsaturated carboxylic acid monomer units (a2), if necessary. The styrene-unsaturated carboxylic acid resin (A) of this embodiment is preferably a random copolymer or an alternating copolymer. In this embodiment, the content of the styrene-unsaturated carboxylic acid resin (A) is 65 to 97 mass%, preferably 70 to 90 mass%, more preferably 75 to 88 mass%, even more preferably 76 to 87 mass%, and most preferably 78 to 85 mass%, relative to the total amount (100 mass%) of the styrene-based resin composition. By making the content of the styrene-unsaturated carboxylic acid resin (A) 65 mass% or more, the effect of imparting heat resistance can be sufficiently obtained. On the other hand, by making the content of the styrene-unsaturated carboxylic acid resin (A) 97 mass% or less, a significant decrease in the flowability of the styrene-based resin composition can be prevented, and thickness deviation during deep drawing can be suppressed.

[0028] <Styrene-based monomer unit (a1)> The styrene-unsaturated carboxylic acid resin (A) of this embodiment essentially contains a styrene-based monomer (a1). The content of the styrene-based monomer units (a1) in the styrene-unsaturated carboxylic acid resin (A) of this embodiment is preferably 70 to 98 mass%, more preferably 80 to 97 mass%, even more preferably 82 to 96 mass%, and even more preferably 84 to 95 mass%, based on the total amount of the styrene-unsaturated carboxylic acid resin (A). If the content of the styrene-based monomer units (a1) is less than 70 mass%, the remarkable effect of improving fluidity is reduced. On the other hand, if the content of the styrene-based monomer units (a1) is more than 98 mass%, it becomes difficult to incorporate the desired amount of the unsaturated carboxylic acid monomer (a2), and in particular, the remarkable effect of improving heat resistance due to the unsaturated carboxylic acid monomer (a2), typified by the (meth)acrylic acid monomer unit (a2-1), is reduced. In this embodiment, the styrene-based monomer (a1) is not particularly limited, but examples thereof include styrene, α-methylstyrene, β-methylstyrene, paramethylstyrene, orthomethylstyrene, metamethylstyrene, chlorostyrene, bromostyrene, etc. From an industrial viewpoint, styrene and α-methylstyrene are particularly preferred, and styrene is more preferred. As the styrene-based monomer (a1), these may be used alone or in combination of two or more. In this specification, the term "styrene-based monomer unit (a1)" refers to a repeating unit constituting a polymer obtained by polymerizing a styrene-based monomer (a1), and is a repeating unit (or structural unit) in which a carbon-carbon double bond in the styrene-based monomer (a1) is converted to a single bond (-CC-) through a polymerization reaction or crosslinking reaction of the styrene-based monomer (a1). Other monomer units in this specification have the same meaning.

[0029] <Unsaturated Carboxylic Acid Monomer Unit (a2)> In the styrene-unsaturated carboxylic acid resin (A) of this embodiment, the unsaturated carboxylic acid monomer unit (a2) plays a role in improving heat resistance. The content of the unsaturated carboxylic acid monomer unit (a2) in the styrene-unsaturated carboxylic acid resin (A) of this embodiment is preferably 2 to 30 mass%, more preferably 3 to 25 mass%, even more preferably 5 to 20 mass%, and most preferably 8 to 16 mass%, based on the total amount of the styrene-unsaturated carboxylic acid resin (A). If the content of the unsaturated carboxylic acid monomer unit (a2) is less than 2 mass%, the effect of significantly improving heat resistance is small. Furthermore, if the content of the unsaturated carboxylic acid monomer unit (a2) exceeds 30 mass%, there is a tendency for problems to arise, such as a decrease in moldability due to an increase in resin viscosity and the generation of bubbles during molding due to an increase in water absorption. In particular, by setting the content of the unsaturated carboxylic acid monomer unit (a2) to 10 to 20 mass%, a resin with excellent both heat resistance and fluidity can be obtained. The unsaturated carboxylic acid monomer unit (a2) in this specification includes unsaturated carboxylic acids and their esters, and specific examples thereof include (meth)acrylic acid monomer units (a2-1) and (meth)acrylic acid ester monomer units (a2-2).

[0030] <<(Meth)acrylic acid monomer unit (a2-1)>> In this embodiment, the styrene-unsaturated carboxylic acid resin (A) may contain a (meth)acrylic acid monomer unit (a2-1) as the unsaturated carboxylic acid monomer unit (a2). In the styrene-unsaturated carboxylic acid resin (A) of this embodiment, the (meth)acrylic acid monomer unit (a2-1) plays a role in improving heat resistance. When the styrene-unsaturated carboxylic acid resin (A) of this embodiment contains (meth)acrylic acid monomer units (a2-1) as the unsaturated carboxylic acid monomer units (a2) constituting the resin, the content of the (meth)acrylic acid monomer units (a2-1) in the resin (A) is preferably 2 to 30% by mass, more preferably 3 to 25% by mass, even more preferably 4 to 20% by mass, even more preferably 5 to 15% by mass, and most preferably 8 to 11% by mass, based on the total mass of the resin (A). If the content of the (meth)acrylic acid monomer units (a2-1) is less than 2% by mass, the effect of significantly improving heat resistance is small. On the other hand, if the content of the (meth)acrylic acid monomer units (a2-1) exceeds 30% by mass, the resin viscosity increases, resulting in poor moldability, and the water absorption rate increases, leading to the generation of bubbles during molding, and the viscosity tends to increase during production. Furthermore, by setting the content of the (meth)acrylic acid monomer unit (a2-1) to 2% by mass or more, it is possible to obtain an effect of improving heat resistance, and by setting the content to 30% by mass or less, it is possible to prevent the viscosity from increasing too much. In particular, by setting the content of the (meth)acrylic acid monomer unit (a2-1) to 3 to 25% by mass, it is possible to obtain a resin that is excellent in both heat resistance and moldability. Examples of the (meth)acrylic acid monomer (a2-1) include acrylic acid and methacrylic acid. From an industrial viewpoint, these may be used alone or in combination as the (meth)acrylic acid monomer unit (a2-1). As the (meth)acrylic acid monomer unit (a2-1), methacrylic acid is particularly preferred because of its significant effect of improving heat resistance.

[0031] <<(Meth)acrylic acid ester monomer unit (a2-2)>> In this embodiment, the styrene-unsaturated carboxylic acid resin (A) may contain a (meth)acrylic acid ester monomer unit (a2-2) as the unsaturated carboxylic acid monomer unit (a2). The (meth)acrylic acid ester monomer unit (a2-2) serves to improve mechanical strength. The (meth)acrylic acid ester monomer unit (a2-2) may be a unit represented by the following general formula (1-1): [ka] (In the above general formula (1-1), R 1 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R 2 represents an ester substituent, specifically an alkyl group having 1 to 12 carbon atoms. In this embodiment, the ester substituent (R 2 The number of carbon atoms in the ester substituent is preferably 10 or less, more preferably 8 or less, and even more preferably 4 or less. By making the number of carbon atoms in the ester substituent 10 or less, the styrene-unsaturated carboxylic acid resin (A) can have a significant effect of improving heat resistance. Specific examples of the (meth)acrylic acid ester monomer (a2-2) in this embodiment include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and decyl (meth)acrylate. These can be used alone or in combination. As the (meth)acrylic acid ester monomer (a2-2), methyl (meth)acrylate or butyl (meth)acrylate is preferred from the viewpoint of industrial availability, and methyl methacrylate is particularly preferred from the viewpoint of suppressing a decrease in heat resistance. When the styrene-unsaturated carboxylic acid resin (A) of this embodiment contains (meth)acrylic acid ester monomer units (a2-2) as the unsaturated carboxylic acid monomer units (a2), the content of the (meth)acrylic acid ester monomer units (a2-2) in the styrene-unsaturated carboxylic acid resin (A) of this embodiment is, for example, preferably 2 to 30 mass%, more preferably 3 to 26 mass%, more preferably 3 to 20 mass%, even more preferably 3 to 17 mass%, still more preferably 3 to 12 mass%, and even more preferably 4 to 10 mass%, based on the total amount of the styrene-unsaturated carboxylic acid resin (A). By setting the content of the (meth)acrylic acid ester monomer units (a2-2) to 2 mass% or more, mechanical strength is improved, and by setting it to 30 mass% or less, deterioration of moldability can be suppressed.

[0032] <Preferable Form of Styrene-Unsaturated Carboxylic Acid Resin (A)> The styrene-unsaturated carboxylic acid resin (A) of this embodiment may be a multicomponent polymer containing (meth)acrylic acid monomer units (a2-1) and (meth)acrylic acid ester monomer units (a2-2). That is, the styrene-unsaturated carboxylic acid resin (A) of this embodiment may be a binary copolymer of the styrene-based monomer units (a1) and the (meth)acrylic acid monomer units (a2-1), or a terpolymer in which the styrene-based monomer (a1), the (meth)acrylic acid monomer (a2-1), and the (meth)acrylic acid ester monomer (a2-2) are copolymerized, or a terpolymer containing the styrene-based monomer units (a1) and two types of (meth)acrylic acid monomer units (a2-1). This further improves the mechanical strength. In particular, when emphasis is placed on improving heat resistance, the styrene-unsaturated carboxylic acid resin (A) preferably contains (meth)acrylic acid monomer units (a2-1). In particular, when emphasis is placed on improving appearance and mechanical strength, the styrene-unsaturated carboxylic acid resin (A) preferably contains (meth)acrylic acid ester monomer units (a2-2). Furthermore, when an unsaturated carboxylic acid ester monomer unit such as a (meth)acrylic acid ester monomer unit (a2-2) is arranged adjacent to an unsaturated carboxylic acid monomer unit such as a (meth)acrylic acid unit (a2-1) in the polymer chain, an effect such as suppressing a crosslinking reaction between unsaturated carboxylic acids can be obtained. When the styrene-unsaturated carboxylic acid resin (A) in the present embodiment has styrene-based monomer units (a1), (meth)acrylic acid monomer units (a2-1) and (meth)acrylic acid ester monomer units (a2-2), it is preferable that the content of the styrene-based monomer units (a1) is 50 to 98 mass%, the content of the (meth)acrylic acid monomer units (a2-1) is 2 to 30 mass%, and the content of the (meth)acrylic acid ester monomer units (a2-2) is 0 to 20 mass%, more preferably the content of the styrene-based monomer units (a1) is 50 to 97 mass%, the content of the (meth)acrylic acid monomer units (a2-1) is 2 to 30 mass%, and the content of the (meth)acrylic acid ester monomer units (a2-2) is 0 to 20 mass%, based on the total amount of the styrene-unsaturated carboxylic acid resin (A). The content of the units (a2-1) is 2 to 30 mass%, and the content of the (meth)acrylic acid ester monomer units (a2-2) is 1 to 20 mass%, more preferably the content of the styrene-based monomer units (a1) is 60 to 96.5 mass%, the content of the (meth)acrylic acid monomer units (a2-1) is 2 to 25 mass%, and the content of the (meth)acrylic acid ester monomer units (a2-2) is 1.5 to 15 mass%, and even more preferably the content of the styrene-based monomer units (a1) is 67 to 96 mass%, the content of the (meth)acrylic acid monomer units (a2-1) is 2 to 20 mass%, and the content of the (meth)acrylic acid ester monomer units (a2-2) is 2 to 13 mass%. By setting the content of each monomer unit within the specified range, a styrene-based resin composition excellent in both heat resistance and moldability can be obtained.

[0033] <Other monomers (a3)> The styrene-unsaturated carboxylic acid resin (A) in this embodiment may further have other monomer units (a3) ​​other than the above-mentioned styrene monomer units (a1), (meth)acrylic acid monomer units (a2-1) and / or (meth)acrylic acid ester monomer units (a2-2). That is, in the present embodiment, the other monomer (a3) ​​may be copolymerized with a monomer other than the two monomers shown above, without any particular limitation, as long as it is copolymerizable with the styrene-based monomer (a1), the (meth)acrylic acid monomer (a2-1) and / or the (meth)acrylic acid ester monomer (a2-2), within a range that does not impair the effects of the invention. For example, examples of the other monomer (a3) ​​other than the three monomers shown above include maleic anhydride, maleic acid, fumaric acid, itaconic acid, (meth)acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, maleimide, and nucleus-substituted maleimide. In the present embodiment, when the styrene-unsaturated carboxylic acid resin (A) contains the other monomer (a3), the content of the other monomer (a3) ​​in the styrene-unsaturated carboxylic acid resin (A) is preferably 0 to 12 mass%, more preferably 0 to 5 mass%, and even more preferably 2 mass% or less, based on the total amount of the styrene-unsaturated carboxylic acid resin (A).

[0034] <Characteristics of styrene-unsaturated carboxylic acid resin (A)> The contents of the styrene-based monomer units (a1), the (meth)acrylic acid monomer units (a2-1), the (meth)acrylic acid ester monomer units (a2-2) and the optionally blended other monomer units (a3) ​​in the styrene-unsaturated carboxylic acid resin (A) in this embodiment can be quantified using pyrolysis GC / MS with a calibration curve prepared from resins in which the respective monomer units are known. The melt flow rate of the styrene-unsaturated carboxylic acid resin (A) at 200°C in this embodiment is preferably 0.3 to 3.0, more preferably 0.4 to 2.5, and even more preferably 0.4 to 2.0. A melt flow rate of 0.3 or more is preferred from the viewpoint of moldability, and a melt flow rate of 3.0 or less is preferred from the viewpoint of the mechanical strength of the resin. In the present disclosure, the melt flow rate is a value measured in accordance with ISO 1133 at 200°C under a load of 49 N. The weight-average molecular weight (Mw) of the styrene-unsaturated carboxylic acid resin (A) in this embodiment is preferably 100,000 to 400,000, and more preferably 120,000 to 320,000. When the weight-average molecular weight is 100,000 to 350,000, a styrene resin composition having an excellent balance between mechanical strength and moldability can be obtained, and as a result, a food container with good appearance can be obtained. On the other hand, the number average molecular weight (Mn) of the styrene-unsaturated carboxylic acid resin (A) is preferably in the range of 40,000 to 150,000, more preferably 50,000 to 120,000, and even more preferably 60,000 to 110,000. The weight average molecular weight and number average molecular weight can be measured by gel permeation chromatography (GPC) in terms of polystyrene standard. The Vicat softening temperature of the styrene-unsaturated carboxylic acid resin (A) in this embodiment is preferably 105 to 140°C, more preferably 107 to 135°C, even more preferably 108 to 130°C, and even more preferably 115 to 125°C. By making the Vicat softening temperature of the styrene-unsaturated carboxylic acid resin (A) 105°C or higher, it is possible to obtain an effect of improving the heat resistance of the styrene resin composition. The Vicat softening temperature in this specification is measured in accordance with ISO 306.

[0035] <Method for producing styrene-unsaturated carboxylic acid resin (A)> The method for producing the styrene-unsaturated carboxylic acid resin (A) of this embodiment will be described below. The method for producing the styrene-unsaturated carboxylic acid resin (A) of the present embodiment preferably includes the steps of: mixing a styrene monomer (a1), an unsaturated carboxylic acid monomer (a2) (e.g., a (meth)acrylic acid monomer (a2-1) and / or a (meth)acrylic acid ester monomer (a2-2)), and a solvent to prepare a mixed solution; polymerizing the mixed solution to produce a reaction product; and recovering the reaction product. The polymerization method for the styrene-unsaturated carboxylic acid resin (A) is not particularly limited, but for example, a radical polymerization method, among which a bulk polymerization method or a solution polymerization method can be preferably used. Specifically, the polymerization method mainly comprises a polymerization step of polymerizing polymerization raw materials (monomer components) and a devolatilization step of removing volatile components such as unreacted monomers and polymerization solvents from the polymerization product. In this embodiment, when the polymerization raw materials are polymerized to obtain the styrene-unsaturated carboxylic acid resin (A), a polymerization initiator is typically contained in the polymerization raw material styrene resin composition. Examples of the polymerization initiator include organic peroxides, such as peroxyketals such as 2,2-bis(t-butylperoxy)butane, 1,1-bis(t-butylperoxy)cyclohexane, and n-butyl-4,4-bis(t-butylperoxy)valerate, dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, and dicumyl peroxide, diacyl peroxides such as acetyl peroxide and isobutyryl peroxide, peroxydicarbonates such as diisopropyl peroxydicarbonate, peroxyesters such as t-butyl peroxyacetate, ketone peroxides such as acetylacetone peroxide, and hydroperoxides such as t-butyl hydroperoxide. Among these, 1,1-bis(t-butylperoxy)cyclohexane is preferred from the viewpoint of decomposition rate and polymerization rate. In this embodiment, a chain transfer agent may be used as needed during polymerization of the styrene-unsaturated carboxylic acid resin (A). Examples of the chain transfer agent include α-methylstyrene linear dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-octyl mercaptan. The polymerization method for the styrene-unsaturated carboxylic acid resin (A) can be solution polymerization using a polymerization solvent. The polymerization solvent is preferably an aromatic solvent such as toluene, ethylbenzene, propylbenzene, or butylbenzene, and if necessary, a solvent system in which the solubility of the styrene-unsaturated carboxylic acid resin (A) is adjusted by combining a polar solvent such as an alcohol or a ketone may be used. In this embodiment, the polymerization solvent is preferably used in the range of 3 to 35% by mass, more preferably 5 to 30% by mass, relative to 100% by mass of all monomers constituting the styrene-unsaturated carboxylic acid resin (A). If the polymerization solvent exceeds 35% by mass relative to 100% by mass of all monomers, the polymerization rate decreases and the molecular weight of the resulting resin also decreases, tending to reduce the mechanical strength of the resin. Furthermore, if the polymerization solvent is less than 3% by mass, it may become difficult to control heat removal during polymerization. Adding the polymerization solvent in a ratio of 3 to 35% by mass relative to 100% by mass of all monomers is preferred in terms of facilitating uniform quality and controlling the polymerization temperature. Furthermore, when a monohydric alcohol having 10 or more carbon atoms, which is an optional component of the styrene-based resin composition of the present embodiment, is added from the polymerization system, it is preferable to add the monohydric alcohol having 10 or more carbon atoms in an amount of 1 to 10 mass % relative to 100 mass % of the total polymerization solvent. The apparatus used in the polymerization step to obtain the styrene-unsaturated carboxylic acid resin (A) in this embodiment is not particularly limited and may be appropriately selected according to a typical styrene resin polymerization method. For example, in the case of bulk polymerization, a polymerization apparatus having one or more complete mixing reactors connected together can be used. The devolatilization step is also not particularly limited. In the case of bulk polymerization, polymerization is continued until the final unreacted monomer content is preferably 50% by mass or less, more preferably 40% by mass or less, and devolatilization treatment is performed by a known method to remove volatile components such as the unreacted monomer. For example, conventional devolatilization apparatuses such as flash drums, twin-screw devolatilizers, thin-film evaporators, and extruders can be used, but devolatilization apparatuses with small retention areas are preferred. The devolatilization temperature is typically about 190 to 280°C, and more preferably 190 to 260°C from the viewpoint of suppressing decomposition. The devolatilization pressure is typically about 0.13 to 4.0 kPa, preferably 0.13 to 3.0 kPa, and more preferably 0.13 to 2.0 kPa. Desirable methods for devolatilization include, for example, a method of removing volatile components under reduced pressure while heating, and a method of removing volatile components through an extruder or the like designed for the purpose of removing volatile components.

[0036] "Ethylene-carboxylic acid ester copolymer (B)" The ethylene-carboxylic acid ester copolymer (B) in this embodiment is a copolymer resin (hereinafter simply referred to as resin (B)) containing ethylene monomer units (b1) and carboxylic acid ester monomer units (b2) as essential components, and contributes to improving the flowability, mechanical strength, and cold impact resistance of the entire styrene-based resin composition. If necessary, the ethylene-carboxylic acid ester copolymer (B) may contain other monomer units (b3) in addition to the ethylene monomer units (b1) and carboxylic acid ester monomer units (b2). The ethylene-carboxylic acid ester copolymer (B) of this embodiment is desirably a random copolymer. In this embodiment, the content of the ethylene-carboxylic acid ester copolymer (B) is 3 to 20% by mass, preferably 5 to 17% by mass, more preferably 7 to 15% by mass, and most preferably 8 to 12% by mass, relative to the total amount (100% by mass) of the styrene-based resin composition. By making the content of the ethylene-carboxylic acid ester copolymer (B) 3% by mass or more, the effect of improving the flowability, mechanical strength, and cold impact resistance of the entire styrene-based resin composition can be sufficiently obtained, contributing to the suppression of thickness deviation during deep drawing. By making the content of the ethylene-carboxylic acid ester copolymer (B) 20% by mass or less, the decrease in compatibility of the entire styrene-based resin composition is suppressed, and production stability, moldability, and the appearance of food containers are improved.

[0037] <Ethylene monomer unit (b1)> The ethylene-carboxylic acid ester copolymer (B) of this embodiment essentially contains ethylene monomer units (b1). The content of the ethylene monomer units (b1) in the ethylene-carboxylic acid ester copolymer (B) of this embodiment is 40 to 98 mass% relative to the total amount of the ethylene-carboxylic acid ester copolymer (B), preferably 50 to 95 mass%, more preferably 55 to 90 mass%, even more preferably 60 to 85 mass%, and most preferably 65 to 80 mass%. By setting the content of the ethylene monomer units (b1) to 95 mass% or less, a decrease in the compatibility of the entire styrene-based resin composition is suppressed, and production stability, moldability, and the appearance of the food container are improved. By setting the content of the ethylene monomer units (b1) to 50 mass% or more, the mechanical strength and cold impact resistance of the food container are improved.

[0038] <Carboxylic acid ester monomer unit (b2)> The ethylene-carboxylic acid ester copolymer (B) of this embodiment essentially contains carboxylic acid ester monomer units (b2). The content of the carboxylic acid ester monomer units (b2) in the ethylene-carboxylic acid ester copolymer (B) of this embodiment is 2 to 60 mass%, preferably 5 to 50 mass%, more preferably 10 to 45 mass%, even more preferably 15 to 40 mass%, and most preferably 20 to 35 mass%, based on the total amount of the ethylene-carboxylic acid ester copolymer (B). When the content of the carboxylic acid ester monomer units (b2) is within the specified range, compatibility with the styrene-unsaturated carboxylic acid resin (A) is improved, and the production stability and moldability of the styrene resin composition are improved. The carboxylic acid ester monomer unit (b2) in this embodiment means a repeating unit constituting a polymer obtained by polymerizing a monomer having a carboxy group (-C(=O)-O-) and an unsaturated double bond (carbon-carbon double bond) in at least one of two groups directly bonded to the carboxy group. Therefore, examples of the carboxylic acid ester monomer unit (b2) in this embodiment include (meth)acrylic acid ester monomer units, acetic acid ester monomer units having a functional group containing an unsaturated double bond, maleic acid ester monomer units, and fumaric acid ester monomer units. These can be used alone or in combination. In particular, it is preferable to use methyl methacrylate, vinyl acetate, or ethyl acrylate, which are easily available industrially, as the carboxylic acid ester monomer (b2).

[0039] The carboxylic acid ester monomer unit (b2) of this embodiment is preferably represented by the following general formula (1-2). [ka] (In the above general formula (1-2), R 3 represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, or a phenyl group; R 4 represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, provided that -CH2- in the alkyl group may be replaced by -O- or -C(=O)-; L 1 and L 2 are each independently a linking group and represent a single bond, -C(=O)-O-, or -OC(=O)-; R 5 and R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. In the above general formula (1-2), R 5 and R 6 At least one of L preferably represents an alkyl group having 1 to 5 carbon atoms. 2 represents a single bond, and R 6 is preferably a hydrogen atom.

[0040] <Other monomers (b3)> The ethylene-carboxylic acid ester copolymer (B) in this embodiment may further contain other monomer units (b3) as necessary in addition to the essential components of the ethylene monomer units (b1) and the carboxylic acid ester monomer units (b2). The other monomer units (b3) are not particularly limited, but examples thereof include propylene monomer units. By controlling the content of the other monomer units (b3) to 1% by mass or less, it is possible to minimize the deterioration of heat resistance and mechanical strength.

[0041] <Characteristics of ethylene-carboxylic acid ester copolymer (B)> The contents of the ethylene monomer units (b1), the carboxylic acid ester monomer units (b2), and the other monomer units (b3) blended as necessary in the ethylene-carboxylic acid ester copolymer (B) in this embodiment can be quantified by infrared absorption spectroscopy. The melt flow rate of the ethylene-carboxylic acid ester copolymer (B) at 190°C in this embodiment is 0.2 to 30.0, preferably 0.5 to 25.0, and even more preferably 1.0 to 20.0. A melt flow rate of 0.2 or more is preferred from the viewpoint of moldability of the styrene-based resin composition, and a melt flow rate of 30.0 or less is preferred from the viewpoints of compatibility with the styrene-unsaturated carboxylic acid resin (A) and the mechanical strength and cold impact resistance of the food container. The melt flow rate in this embodiment is a value measured in accordance with ISO 1133 at 190°C under a load of 21.6 N. The melting point of the ethylene-carboxylic acid ester copolymer (B) in this embodiment is 110°C or lower, preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 85°C or lower. By setting the melting point to 110°C or lower, crystallization of the styrene resin composition during molding can be suppressed, contributing to improved moldability. The melting point in this disclosure is a value measured by differential scanning calorimetry (DSC) in accordance with ISO 3146.

[0042] <Method for producing ethylene-carboxylic acid ester copolymer (B)> The method for producing the ethylene-carboxylic acid ester copolymer (B) of the present embodiment is not particularly limited, but preferably includes a polymerization step of polymerizing an ethylene monomer (b1), a carboxylic acid ester monomer (b2), and other monomers (b3) that are blended as necessary to produce a reaction product, and a recovery step of recovering the reaction product. The polymerization method for the ethylene-carboxylic acid ester copolymer (B) is preferably a radical polymerization reaction using a polymerization initiator. The polymerization initiator is not particularly limited, but examples thereof include peroxides such as t-butyl-peroxy-2-ethylhexanoate and t-butylperoxypiperate. In this embodiment, a chain transfer agent may be used as needed during polymerization of the ethylene-carboxylic acid ester copolymer (B). Examples of the chain transfer agent include alcohols such as methanol and ethanol, alkanes such as ethane and propane, and ketones such as acetone and methyl ethyl ketone. The apparatus used in the polymerization step for obtaining the ethylene-carboxylic acid ester copolymer (B) in this embodiment is not particularly limited, and examples thereof include a vessel-type reactor and a tubular-type reactor. In the recovery step, volatile components such as unreacted monomers are removed by a known devolatilization method, such as a method of removing volatile components under reduced pressure while heating, or a method of removing volatile components through an extruder or the like designed for the purpose of devolatilization.

[0043] "Core-shell type rubber polymer particles (C)" The styrene-based resin composition of this embodiment may contain core-shell rubbery polymer particles (C) as an optional component. The inclusion of the core-shell rubbery polymer particles (C) contributes to improving the mechanical strength and cold impact resistance of food containers. The core-shell rubbery polymer particles (C) preferably have a structure (core-shell structure) comprising a core layer (also referred to as a polymer core layer) made of rubber particles and a shell layer made of a polymer grafted onto the rubber particles. It is more preferable that the core-shell structure be such that the graft copolymer constituting the shell layer contains a monomer unit having a higher polarity than the styrene monomer unit. A specific core-shell rubbery polymer particle (C) is more preferably a core-shell structure comprising a polymer core layer containing conjugated diene-based monomer units (c1) or acrylic acid ester monomer units (c2) and a shell layer containing (meth)acrylic acid ester monomer units (c3) and / or styrene-based monomer units (c4) that coats at least a portion of the polymer core layer. Therefore, it is preferable that the preferred styrene-based resin composition of this embodiment further contains core-shell type rubbery polymer particles (C) formed by grafting a copolymer mainly composed of (meth)acrylic acid ester monomer units (c3) onto the polymer core layer containing the conjugated diene-based monomer units (c1) or the acrylic acid ester monomer units (c2). The core-shell type rubbery polymer particles (C) of this embodiment preferably have a structure in which a particle containing a conjugated diene-based monomer unit (c1) or an acrylic acid ester monomer unit (c2) serves as a core, and the core is at least partially coated with a copolymer containing a (meth)acrylic acid ester monomer unit (c3) and / or a styrene-based monomer unit (c4). In this embodiment, the content of the core-shell type rubbery polymer particles (C) relative to the total amount (100% by mass) of the styrene-based resin composition is 0 to 20% by mass, preferably more than 0 to 20% by mass, more preferably 1 to 18% by mass, even more preferably 3 to 15% by mass, and most preferably 5 to 13% by mass. By setting the content of the core-shell type rubbery polymer particles (C) to 20% by mass or less, it is possible to improve the mechanical strength and cold impact resistance while suppressing a decrease in the heat resistance of the food container.

[0044] The conjugated diene monomer (c1) forming the rubber particles of the core-shell type rubbery polymer particles (C) in this embodiment is a diolefin having a pair of conjugated double bonds, such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Examples of the acrylic acid ester monomer (c2) that forms the rubber particles of the core-shell type rubbery polymer particles (C) in this embodiment include methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methoxyethyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, and benzyl acrylate, and from an industrial viewpoint, ethyl acrylate and n-butyl acrylate are preferred. In this embodiment, the (meth)acrylic acid ester monomer units (c3) constituting the graft copolymer of the core-shell type rubbery polymer particles (C) include methacrylic acid ester monomer units and acrylic acid ester monomer units. In this case, examples of the (meth)acrylic acid ester monomer include methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, benzyl acrylate, methyl methacrylate, butyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, and benzyl methacrylate. Among these, methyl acrylate, n-butyl acrylate, and methyl methacrylate are preferred because of their industrial availability and low cost. The styrene-based monomer (c4) forming the graft copolymer of the core-shell type rubbery polymer particles (C) in this embodiment is not particularly limited, and examples thereof include styrene, α-methylstyrene, β-methylstyrene, paramethylstyrene, orthomethylstyrene, metamethylstyrene, chlorostyrene, bromostyrene, etc. From an industrial viewpoint, styrene and α-methylstyrene are particularly preferred, and styrene is more preferred.

[0045] The average particle size of the core-shell type rubbery polymer particles (C) in this embodiment is preferably 0.05 to 0.90 μm, more preferably 0.10 to 0.75 μm, even more preferably 0.15 to 0.60 μm, and still more preferably 0.20 to 0.50 μm. In particular, by setting the particle size in the range of 0.20 to 0.30 μm, the effect of imparting strength to food containers is excellent. In the present disclosure, the average particle size is a value measured from a cross-sectional observation image taken with a transmission electron microscope.

[0046] "Impact-resistant styrene resin (D)" The impact-resistant styrene-based resin (D) of this embodiment may be a so-called high-impact polystyrene resin (HIPS resin) obtained by dispersing particles of a rubbery polymer (D-2) (hereinafter also referred to as rubbery polymer particles (D-2)) in a polymer matrix (D-1) of a resin composed of a styrene-based monomer (d1) and, optionally, a (meth)acrylic acid ester monomer (d2) and / or other monomers (d4), and polymerizing monomer units such as the styrene-based monomer (d1) in the presence of the rubbery polymer (D-2). In other words, the impact-resistant styrene-based resin (D) of this embodiment contains the polymer matrix (D-1) and the rubbery polymer particles (D-2). The polymer matrix (D-1) contains a polymer obtained by polymerizing the styrene-based monomer (d1) and, optionally, the (meth)acrylic acid ester monomer (d2) and other monomers (d4). The rubber-like polymer particles (D-2) are particles of a rubber-like polymer (D-2) mainly composed of conjugated diene-based monomer units (d3), and if necessary, the surfaces of the particles may be grafted with a polymer containing styrene-based monomer units (d1) or a polymer containing the styrene-based monomer units (d1), (meth)acrylic acid ester monomer units (d2) and other monomers (d4).

[0047] <Polymer matrix (D-1)> In this embodiment, the polymer matrix (D-1) of the impact-resistant styrene-based resin (D) may contain styrene-based monomer units (d1) and, if necessary, (meth)acrylic acid ester monomer units (d2) and other monomer units (d4). When the polymer matrix (D-1) contains both the styrene-based monomer unit (d1) and the (meth)acrylic acid ester monomer unit (d2), the content of the (meth)acrylic acid ester monomer unit (d2) relative to 100 mass% of the impact-resistant styrene-based resin (D) is preferably 10 to 50 mass%, more preferably 20 to 40 mass%. By setting the content of the (meth)acrylic acid ester monomer unit (d2) within a predetermined range, the compatibility between the styrene-unsaturated carboxylic acid-based resin (A) and the polymer matrix (D-1) is improved, which contributes to improving the mechanical strength. When the styrene-based resin composition of this embodiment contains an impact-resistant styrene-based resin (D), the content of the polymer matrix (D-1) is preferably 0 to 10 mass% relative to the total amount (100 mass%) of the styrene-based resin composition. The content of the polymer matrix (D-1) is converted into the content of the impact-resistant styrene-based resin (D). Therefore, the content of the impact-resistant styrene-based resin (D) refers to the total amount of the polymer matrix (D-1) and the rubber-like polymer particles (D-2).

[0048] <Rubber-like polymer particles (D-2)> In this embodiment, the rubbery polymer (D-2) constituting the rubbery polymer particles (D-2) in the impact-resistant styrene-based resin (D) is preferably formed from a conjugated diene-based monomer (d3), and more preferably a polymer having conjugated diene-based monomer units (d3). Specific examples of the rubbery polymer (D-2) include polybutadiene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer. However, from an industrial viewpoint, polybutadiene and styrene-butadiene copolymer are preferred. The polybutadiene may be a high-cis polybutadiene having a high cis content, a low-cis polybutadiene having a low cis content, or both. The structure of the styrene-butadiene copolymer may be a random structure, a block structure, or a combination thereof. These rubbery polymers may be used alone or in combination of two or more. Saturated rubbers obtained by hydrogenating butadiene rubbers may also be used. The conjugated diene monomer (d3) is a diolefin having a pair of conjugated double bonds among the monomer units constituting the rubber-like polymer particles (D-2), and examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. The rubbery polymer particles (D-2) in this embodiment preferably contain a polymer containing a styrene-based monomer unit (d1) or a polymer containing the styrene-based monomer unit (d1), a (meth)acrylic acid ester monomer (d2) and other monomers (d4) in dispersed particles of the rubbery polymer (D-2). The form of the containment is preferably a so-called salami structure type dispersed particle in which a plurality of domain phases of a polymer having a styrene-based monomer unit (d1) are contained in the rubbery polymer (D-2). In this embodiment, the content of the impact-resistant styrene-based resin (D) relative to the total amount (100% by mass) of the styrene-based resin composition is 0 to 20% by mass, preferably 0.5 to 15% by mass, more preferably 1 to 10% by mass, even more preferably 2 to 8% by mass, and most preferably 3 to 5% by mass. By keeping the content of the impact-resistant styrene-based resin (D) at 20% by mass or less, it is possible to improve the mechanical strength of the food container while preventing a decrease in heat resistance.

[0049] <Other monomers (d4)> Examples of the other monomer unit (d4), which is an optional component of the impact-resistant styrene-based resin (D) of this embodiment, include (meth)acrylic acid ester-based monomers such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isopropyl acrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, and isopropyl methacrylate. Of these, methyl acrylate and n-butyl acrylate are preferred in terms of industrial availability. The styrene-based monomer (d1) is the same as the above-mentioned styrene-based monomer (a1), and the contents of the styrene-based monomer (a1) are incorporated herein by reference. The (meth)acrylic acid ester monomer (d2) is the same as the (meth)acrylic acid ester monomer (a2-2), and refers to a monomer other than the above-mentioned other monomer (d4), and the contents of the (meth)acrylic acid ester monomer (a2-2) are incorporated herein by reference.

[0050] <Content of conjugated diene monomer units (d3)> In the present embodiment, the content of the conjugated diene monomer unit (d3) in the impact resistant styrene resin (D) is preferably 0.5 to 15.0 mass%, more preferably 1.0 to 13.0 mass%, based on the total amount of the impact resistant styrene resin (D). The content of the conjugated diene monomer unit (d-3) in the impact resistant styrene resin (D) and the styrene resin composition can be measured by the procedure described in the Examples section below, or a method equivalent thereto.

[0051] <Average particle size of rubber-like polymer particles (D-2)> In this embodiment, the rubbery polymer (D-2), which is the rubber component in the impact-resistant styrene-based resin (D), is present in the styrene-based resin composition as particles of the rubbery polymer (D-2). In this case, the average particle size of the rubbery polymer particles (D-2) is preferably 0.3 to 5.0 μm, more preferably 0.5 to 4.0 μm, and even more preferably 0.7 to 3.0 μm. The impact-resistant styrene-based resin (D) is obtained by polymerizing a styrene-based monomer (d1) and, optionally, a (meth)acrylic acid ester monomer (d2) and other monomers (d4) in the presence of the rubbery polymer particles (D-2) in a reactor equipped with a stirrer. The average particle size of the rubbery polymer particles (D-2) can be adjusted by the stirrer rotation speed, the molecular weight of the rubbery polymer (D-2), and other factors. The average particle size of the rubbery polymer particles (D-2) in this disclosure is a value measured from a cross-sectional image observed using a transmission electron microscope.

[0052] "Styrene-based elastomer (E)" In a preferred aspect of this embodiment, the styrene-based resin composition of this embodiment may further contain a styrene-based elastomer (E) (also simply referred to as elastomer (E)). The styrene-based elastomer (E) used in the styrene-based resin composition of this embodiment is a block copolymer of a styrene-based monomer unit (e1) and a conjugated diene-based monomer unit (e2) and a hydrogenated product thereof (i.e., a hydrogenated product). Examples of the styrene-based monomer (e1) include the same monomers as the above-mentioned styrene-based monomer (a1). Examples of the conjugated diene-based monomer (e2) include the same monomers as the above-mentioned conjugated diene-based monomer (d2). The chain structure of the block copolymer of the styrene-based elastomer (E) is preferably a styrene-butadiene-styrene type, a styrene-ethylene-butadiene-butylene-styrene type, or a styrene-ethylene-butylene-styrene type. The content of the styrene-based monomer units (e1) constituting the styrene-based elastomer (E) is preferably 30 to 80 mass%, more preferably 35 to 75 mass%, and even more preferably 50 to 70 mass%, relative to the total amount of the styrene-based elastomer (E). If the content of the styrene-based monomer units (e1) is 35 to 65%, dispersibility in the styrene-unsaturated carboxylic acid resin (A) is improved, and a product excellent in mechanical strength and appearance can be obtained. The styrene-based elastomer (E) such as styrene-butadiene elastomer can be produced by radical polymerization, anionic polymerization, or polymer reaction, with anionic polymerization being preferred from an industrial viewpoint. The content of the styrene elastomer (E) in the styrene resin composition of this embodiment is preferably 0.5 to 15 mass %, more preferably 1 to 10 mass %, even more preferably 2 to 7 mass %, and most preferably 3 to 5 mass %, based on the total amount of the styrene resin composition. By setting the content within the above range, it is possible to prevent a decrease in heat resistance of the food container and improve the mechanical strength.

[0053] "Acrylic elastomer (F)" In a preferred embodiment of this embodiment, the styrene-based resin composition of this embodiment may further contain an acrylic elastomer (F) (also simply referred to as elastomer (F)). The acrylic elastomer (F) used in the styrene-based resin composition of this embodiment is a block copolymer having hard blocks of methyl methacrylate monomer units (f1) and soft blocks of acrylic ester monomer units (f2). The acrylic elastomer (F) is more preferably a block copolymer having hard blocks of methyl methacrylate monomer (units) and soft blocks of acrylic ester monomer units (f2). Examples of the acrylic acid ester monomer (f2) include methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, benzyl acrylate, methyl methacrylate, butyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, and benzyl methacrylate, among which methyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate are preferred from the viewpoints of industrial availability and low cost. Examples of the chain structure of the block copolymer of the acrylic elastomer (F) include a methyl methacrylate-acrylic acid ester (f2) block type, a methyl methacrylate-acrylic acid ester (f2)-methyl methacrylate triblock type, and an acrylic acid ester (f2)-methyl methacrylate-acrylic acid ester (f2) triblock type. From the viewpoint of improving mechanical strength, the methyl methacrylate-acrylic acid ester (f2)-methyl methacrylate triblock type is preferred. Regarding the content of the methyl methacrylate monomer (f1) and the acrylic ester monomer (f2) constituting the acrylic elastomer (F), the content of the methyl methacrylate monomer (f1) is preferably 5 to 65 mass%, more preferably 10 to 50 mass%, and most preferably 15 to 40 mass%. On the other hand, the total content of the acrylic ester monomer (f2) is the remainder of 100 mass%. When the content of the methyl methacrylate monomer (f1) is 20 to 65%, dispersibility in the styrene-unsaturated carboxylic acid resin (A) is suitably improved, and food containers excellent in mechanical strength and appearance can be obtained. The content of the acrylic elastomer (F) in the styrene-based resin composition of this embodiment is preferably 0.5 to 15 mass %, more preferably 1 to 10 mass %, even more preferably 2 to 7 mass %, and most preferably 3 to 5 mass %, based on the total amount of the styrene-based resin composition. By setting the content within the above range, it is possible to prevent a decrease in heat resistance of the food container and improve the mechanical strength.

[0054] "Inorganic particles (G)" In a preferred aspect of this embodiment, the styrene-based resin composition of this embodiment may further contain inorganic particles (G). By adding the inorganic particles (G) to the styrene-based resin composition, they serve as a foam nucleating agent during foam molding and contribute to improving the rigidity of a molded article including the styrene-based resin composition and the foam extruded sheet. Examples of inorganic particles (G) that can be used include kaolin, mica, silica, calcium carbonate, sodium carbonate, barium carbonate, barium sulfate, calcium sulfate, titanium oxide, aluminum oxide, clay, bentonite, talc, diatomaceous earth, etc. Among these, talc is preferred because it has a long history of use in food packaging and its safety is guaranteed. The content of the inorganic particles (G) is preferably 0.1 to 7.0 parts by mass, more preferably 0.2 to 6.0 parts by mass, and even more preferably 0.3 to 4.0 parts by mass, when the total amount of the styrene-based resin composition is taken as 100% by mass. By setting the content in the range of 0.1 to 7.0 parts by mass, a sheet with an expansion ratio suitable for an extruded foam sheet for food packaging can be obtained. There is no particular limitation on the method for adding the inorganic particles (G) to the styrene-based resin composition. The inorganic particles (G) may be directly blended with the styrene-based resin composition when extrusion kneading the composition, or, for ease of industrial production, a resin masterbatch containing the inorganic fine particles (G) at a known high concentration may be prepared in advance and then added.

[0055] "Monohydric alcohols with 10 or more carbon atoms" The styrene-based resin composition in the present embodiment may contain one or more selected from the group consisting of monohydric alcohols having 10 or more carbon atoms and additive components, as necessary. The monohydric alcohols having 10 or more carbon atoms and additive components will be described below. In this embodiment, the monohydric alcohol having 10 or more carbon atoms (hereinafter simply referred to as alcohol) is an optional component that inhibits gelation of the styrene-unsaturated carboxylic acid resin (A) during molding, thereby contributing to improved appearance. The content of the monohydric alcohol having 10 or more carbon atoms is 0.01 to 1.0 mass%, preferably 0.03 to 0.8 mass%, more preferably 0.05 to 0.6 mass%, and even more preferably 0.07 to 0.5 mass%, relative to the total amount (100 mass%) of the styrene-based resin composition. By ensuring that the content of the monohydric alcohol having 10 or more carbon atoms is 0.01 mass% or more, gelation of the styrene-unsaturated carboxylic acid resin (A) during molding and processing can be inhibited, while by ensuring that the content is 1.0 mass% or less, deterioration in heat resistance and generation of odor can be suppressed. By ensuring that the content of the monohydric alcohol having 10 or more carbon atoms is 0.07 to 0.5 mass%, a sufficient gel-inhibiting effect can be obtained without particularly decreasing heat resistance. The monohydric alcohol having 10 or more carbon atoms in this embodiment is an alcohol having 10 or more carbon atoms and one hydroxyl group. The carbon chain constituting the alcohol may contain heteroatoms such as oxygen or nitrogen, and the carbon chain may contain bonds other than single bonds, such as double bonds, triple bonds, ester bonds, and amide bonds. The number of carbon atoms is preferably 16 or more, more preferably 17 or more, and even more preferably 18 to 50. The monohydric alcohol having 10 or more carbon atoms may be contained in a styrene-based resin composition or a molded article made of a styrene-based resin composition. Therefore, by having a monohydric alcohol having 10 or more carbon atoms present in (or added to) the polymerization solution used in polymerizing the styrene-unsaturated carboxylic acid resin (A), the monohydric alcohol may remain in the final product, the styrene-based resin composition. Alternatively, the monohydric alcohol may be added during kneading of the styrene-unsaturated carboxylic acid resin (A) and the ethylene-carboxylic acid ester copolymer (B) and then mixed in an extruder to contain the monohydric alcohol. In this embodiment, the boiling point of the monohydric alcohol having 10 or more carbon atoms is preferably 260° C. or higher, more preferably 270° C. or higher, and even more preferably 290° C. or higher. If the boiling point of the alcohol is lower than 260° C., it becomes highly volatile and tends to generate an unpleasant odor during molding, etc. The monohydric alcohol having 10 or more carbon atoms is not particularly limited, but examples thereof include 1-hexadecanol, isohexadecanol, 1-octadecanol, 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)-1-octanol, isooctadecanol, 1-isoisoeicosanol, 8-methyl-2-(4-methylhexyl)-1-decanol, 2-heptyl-1-undecanol, 2-heptyl-4-methyl-1-decanol, 2-(1,5-dimethylhexyl)-(5,9-dimethyl)-1-decanol, and polyoxyethylene alkyl ethers. The polyoxyethylene alkyl ethers are preferably compounds represented by the following general formula (2): [ka] (In the above general formula (2), R is an alkyl group having 12 to 20 carbon atoms, and X represents the average number of ethylene oxides added and is an integer of 1 to 15.) Specific examples of preferred alcohols include "Fine Oxocol 180" manufactured by Nissan Chemical Industries, Ltd. and "Emulgen 109P" manufactured by Kao Corporation.

[0056] "Additional ingredients" In addition to the resin (A), resin (B), core-shell rubbery polymer particles (C), impact-resistant styrene-based resin (D), styrene-based elastomer (E), acrylic elastomer (F), inorganic particles (G), and monohydric alcohol having 10 or more carbon atoms, the styrene-based resin composition of this embodiment may also contain various optional additives commonly used in styrene-based resins to achieve known effects. Examples of optional additives in this embodiment include stabilizers, higher fatty acid surfactants, antioxidants, UV absorbers, lubricants, mold release agents, plasticizers, antiblocking agents, antistatic agents, antifogging agents, and mineral oils. The method of addition is not particularly limited, but examples include adding the additives during polymerization, or premixing the additives in a blender after polymerization and before melt-kneading, followed by melt-kneading in an extruder or Banbury mixer. The content of the additive component is not particularly limited as long as it does not impede the object of the present invention, and may be, for example, preferably in the range of 0 to 15% by mass, and more preferably in the range of 0.001 to 13% by mass, relative to the total amount of the styrene-based resin composition. Examples of the antioxidant include hindered phenol-based antioxidants such as octadecyl-3-(3,5-tert-butyl-4-hydroxyphenyl)propionate and 4,6-bis(octylthiomethyl)-o-cresol (product Irganox 1076), and phosphorus-based antioxidants such as tris(2,4-di-tert-butylphenyl)phosphite (product Irgafos 176). These stabilizers may be used alone or in combination of two or more. There are no particular limitations on the timing of addition, and they may be added during either the polymerization process or the devolatilization process. Alternatively, the stabilizer may be mixed into the product using a mechanical device such as an extruder or Banbury mixer. In a preferred aspect of this embodiment, the styrene-based resin composition preferably contains a higher fatty acid surfactant. The addition of a higher fatty acid surfactant not only prevents blocking of the foamed extruded sheet, but also contributes to reducing torque between pellets and metering stability during kneading of the styrene-based resin composition by adding an appropriate amount. Therefore, the content of the higher fatty acid surfactant is preferably in the range of 0.002 to 0.1% by mass relative to the total amount of the styrene-based resin composition. While the above effects can be achieved, a content of 0.1% by mass or less can prevent the surfactant from acting as a gelling agent for the styrene-unsaturated carboxylic acid resin (A). The higher fatty acid surfactant may be added during polymerization of each resin, or may be additionally kneaded in when the styrene-unsaturated carboxylic acid resin (A) and the ethylene-carboxylic acid ester copolymer (B) are kneaded together. The higher fatty acid surfactant is not particularly limited, but examples thereof include stearic acid, calcium stearate, calcium stearate, and ethylene bisstearamide, with ethylene bisstearamide being preferred.

[0057] [Preferred composition of styrene-based resin composition] In this embodiment, the content of the styrene-unsaturated carboxylic acid resin (A) relative to the total amount (100% by mass) of the styrene-based resin composition is 65 to 97% by mass, preferably 65 to less than 97% by mass, more preferably 70 to 90% by mass, even more preferably 75 to 88% by mass, still more preferably 76 to 87% by mass, and most preferably 78 to 85% by mass. By making the content of the styrene-unsaturated carboxylic acid resin (A) 65% by mass or more, the effect of imparting heat resistance can be sufficiently obtained. On the other hand, by making the content of the styrene-unsaturated carboxylic acid resin (A) 97% by mass or less, a significant decrease in the fluidity of the styrene-based resin composition can be prevented, and thickness deviation during deep drawing can be suppressed. In this embodiment, the content of the ethylene-carboxylic acid ester copolymer (B) is 3 to 20 mass%, preferably 5 to 17 mass%, more preferably 7 to 15 mass%, and most preferably 8 to 12 mass%, relative to the total amount (100 mass%) of the styrene-based resin composition. By making the content of the ethylene-carboxylic acid ester copolymer (B) 3 mass% or more, the effect of improving the flowability, mechanical strength, and cold impact resistance of the entire styrene-based resin composition can be sufficiently obtained, and by making it 20 mass% or less, the decrease in compatibility of the entire styrene-based resin composition is suppressed, and production stability, moldability, and the appearance of food containers are improved.

[0058] In this embodiment, the content of the core-shell type rubbery polymer particles (C) relative to the total amount (100% by mass) of the styrene-based resin composition is 0 to 20% by mass, preferably more than 0% by mass to 20% by mass, more preferably 1 to 18% by mass, even more preferably 3 to 15% by mass, and most preferably 5 to 13% by mass. By setting the content of the core-shell type rubbery polymer particles (C) to 20% by mass or less, it is possible to improve the mechanical strength and cold impact resistance while suppressing a decrease in the heat resistance of the food container. In the present embodiment, the total content of the styrene-unsaturated carboxylic acid resin (A) and the ethylene-carboxylic acid ester copolymer (B) relative to the total amount (100% by mass) of the styrene resin composition is 80 to 100% by mass, preferably 85 to 97% by mass, and more preferably 90 to 95% by mass. In the present embodiment, the total content of the styrene-unsaturated carboxylic acid resin (A), the ethylene-carboxylic acid ester copolymer (B), and the optional additional components is 80 to 100% by mass, preferably 85 to 97% by mass, and more preferably 90 to 95% by mass, relative to the total amount (100% by mass) of the styrene resin composition. In this embodiment, the total content of the styrene-unsaturated carboxylic acid resin (A), the ethylene-carboxylic acid ester copolymer (B), and the core-shell rubber polymer particles (C) relative to the total amount (100% by mass) of the styrene resin composition is 85 to 100% by mass, preferably 88 to 97% by mass, and more preferably 90 to 95% by mass. In this embodiment, the total content of the styrene-unsaturated carboxylic acid resin (A), the ethylene-carboxylic acid ester copolymer (B), the core-shell rubbery polymer particles (C) and the optional additional components is 85 to 100% by mass, preferably 88 to 97% by mass, and more preferably 90 to 95% by mass, relative to the total amount (100% by mass) of the styrene resin composition.

[0059] [Characteristics of food containers] <Heat mold retention> The heat retention of the food container of this embodiment was measured by adding a predetermined amount of water to the food container, heating it in a microwave oven, and checking the rate of change in the bottom surface. The rate of change was calculated using the following formula (1). Rate of change (%) = |{Bottom diameter length before heating L1 (mm) - Bottom diameter length after heating L2 (mm)}| / [Bottom diameter length before heating L1 (mm)] × 100 The rate of change is preferably 10% or less, and more preferably 5% or less. If the rate of change is within this range, the food container can be used in a microwave oven. <Oil resistance> The oil resistance of the food container of this embodiment is preferably such that the container does not deform when a predetermined amount of oil such as salad oil is added to the container and heated in a microwave oven.

[0060] <Deep drawability> Regarding the deep drawing formability of the food container of this embodiment, when the food container of this embodiment is a non-foamed food container, the absolute value of the difference between the thickness of the center of the bottom surface of the non-foamed food container and the thickness of the end of the bottom surface of the non-foamed food container is preferably less than 0.3 mm, and more preferably less than 0.1 mm. Regarding the deep drawing formability of the food container of this embodiment, when the food container of this embodiment is a foamed food container, the absolute value of the difference between the thickness of the center of the bottom surface of the foamed food container and the thickness of the end of the bottom surface of the foamed food container is preferably less than 1.0 mm, and more preferably less than 0.5 mm. The center of the bottom of a food container is defined as the intersection of 10 randomly drawn diameters (diagonals) of the bottom. The ends of the bottom of a food container are defined as the ends with the longest length of the 10 randomly drawn diameters (diagonals).

[0061] [Food container manufacturing method] The food container of this embodiment is manufactured by preparing a styrene-based resin composition and then fitting it into the desired shape using a known molding method (e.g., injection molding, injection compression molding, extrusion molding, blow molding, press molding, vacuum molding, or foam molding). The styrene-based resin composition can be manufactured by melt-kneading the components using any method. For example, a high-speed mixer such as a Henschel mixer, a batch-type kneader such as a Banbury mixer, a single- or double-screw continuous kneader, a roll mixer, or the like can be used alone or in combination. The heating temperature during kneading is usually selected from the range of 180 to 250°C.

[0062] The food container of this embodiment is suitable for use as a container for prepared foods, lunch boxes, microwave oven containers, bowls, cups, trays, etc. [Example]

[0063] Hereinafter, the embodiments of the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to these examples in any way. "Evaluation methods for each resin, styrene-based resin composition, sheet body, and food container used in Examples and Comparative Examples" 1. Composition evaluation of each resin and styrene-based resin composition (1-1) Measurement of the content of each monomer unit The content of each monomer unit contained in the styrene-based resin compositions prepared in the Examples and Comparative Examples was measured by pyrolysis GC / MS under the following conditions. Sample preparation: Each resin and the resin compositions prepared in the Examples and Comparative Examples were dissolved in chloroform at 5% by mass, and 20 μL of the solution was dropped into a sample cup and dried in vacuum at 80° C. for 24 hours. Measurement conditions Pyrolysis Unit Equipment: Frontier Labs PY-3030D Furnace temperature: 600℃ GC Equipment: Shimadzu GCMS-GP2020NX Column: Ultra Alloy-CW (Length 30m, film thickness 0.25μm, diameter 0.25mmφ) Column temperature: held at 40°C for 3 minutes, heated at 10°C / min, and held at 250°C for 10 minutes. Inlet temperature: 250℃ Detector temperature: 230℃ Split ratio: 1 / 300 Carrier gas: Helium Detection method: Mass spectrometer (MSD) In detecting each monomer peak, in order to avoid peak overlap and saturation of peak intensity, pretreatment such as dilution rate of the sample, the column to be used, and detection conditions may be adjusted as appropriate.

[0064] (1-2) Measurement of the content of monohydric alcohols having 10 or more carbon atoms in each styrene-based resin composition The content of monohydric alcohols having 10 or more carbon atoms relative to the total amount of the styrene-based resin compositions prepared in the examples and comparative examples was measured using gas chromatography under the following conditions. Sample preparation: 1.0 g of resin was dissolved in 5 mL of methyl ethyl ketone, and then 5 mL of hexane containing p-diethylbenzene as a standard substance adjusted to 200 μg / g was added to reprecipitate the polymer component, and the supernatant was collected and used as the measurement solution. Measurement equipment: Agilent 6850 series GC system Detector: FID Column: DB-WAX Length: 60m Film thickness: 0.50 μm Diameter: 0.320mmφ Injection volume: 1μL Split ratio: 50:1 Column temperature: Hold at 100°C for 5 minutes → Heat to 130°C at 10°C / min → Heat to 180°C at 10°C / min → Hold at 180°C for 10 minutes → Heat to 220°C at 20°C / min → Hold at 220°C for 10 minutes Inlet temperature: 230℃ Detector temperature: 300℃ Carrier gas: Helium When detecting the peak of a monohydric alcohol having 10 or more carbon atoms, in order to avoid overlapping with other peaks or saturation of peak intensity, pretreatment such as the dilution rate of the sample, the column to be used, and the detection conditions may be appropriately adjusted.

[0065] 2. Evaluation of the properties of each resin and styrene-based resin composition (2-1) Measurement of molecular weight The average molecular weights (Mn, Mw, Mz) of each resin prepared in the examples and comparative examples were measured as molecular weights converted into standard polystyrene by gel permeation chromatography (GPC) using a calibration curve method using standard polystyrene under the following conditions. Measuring equipment: Tosoh HLC-8220 Separation column: Two TSK gel Super HZM-H (inner diameter 4.6 mm) manufactured by Tosoh Corporation connected in series Guard column: Tosoh TSK guard column Super HZ-H Measurement solvent: tetrahydrofuran (THF) Sample concentration: 5 mg of the measurement sample was dissolved in 10 mL of solvent and filtered through a 0.45 μm filter. Injection volume: 10μL Measurement temperature: 40℃ Flow rate: 0.35mL / min Detector: differential refractometer The calibration curve was created using 11 types of TSK standard polystyrene (F-850, F-450, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000) manufactured by Tosoh Corporation. The calibration curve was created using a linear approximation equation. If any THF-insoluble matter was present in the composition, it was removed using a 0.2-0.4 μm membrane filter before measurement.

[0066] (2-2) Melt mass flow rate (MFR) measurement The melt mass flow rate (g / 10 min) of each resin and styrene-based resin composition used in the examples and comparative examples was measured in accordance with ISO1133 under conditions of 200°C, 49N or 190°C, 21.6N.

[0067] (2-3) Measurement of Vicat softening temperature The Vicat softening temperature of each resin and styrene-based resin composition used in the examples and comparative examples was measured in accordance with ISO 306. The load was 50 N and the heating rate was 50° C. / h.

[0068] (2-4) DSC melting point measurement The melting points of the resins used in the examples and comparative examples were measured using a differential scanning calorimeter (Shimadzu Corporation, DSC-60) at a heating rate of 10°C / min under a nitrogen atmosphere using 10 mg of each resin placed in a 40 μL aluminum pan.

[0069] (2-5) Average particle size of rubber-like polymer particles The average particle size (μm) of the core-shell type rubbery polymer particles (C) or the rubbery polymer particles contained in the impact-resistant styrene-based resin (D) is determined by measuring the average particle size (μm) of 200 rubbery polymer particles observed by cross-sectional observation using a transmission electron microscope using the following formula (1): Average particle diameter=Σ(n i ×D i 4 ) / Σ(n i ×D i 3 ) {In the above formula (1), n i is the particle diameter D i is the number of rubbery polymer particles having i is the average value of the major and minor diameters of the rubber-like polymer particles.} The particle diameter was calculated by averaging the particle diameters obtained from images of five fields of view.

[0070] 3. Food container evaluation method The food containers obtained in each of the Examples and Comparative Examples were evaluated according to the following methods. (3-1) Appearance evaluation of food containers The appearance of the food containers produced by the method described below was visually inspected. Containers without holes were rated as "good."

[0071] (3-2) Heat mold retention 30 ml of water was placed in a food container made using the method described below, and heated in a 500 W microwave for 3 minutes to determine the rate of change in the bottom surface. There is a thin-walled area around the bottom, and this thin-walled area is particularly susceptible to deformation.

[0072] (3-3) Impact strength (impact resistance at room temperature (23°C)) A 200g weight was placed in a food container prepared by the method described below, and the container was dropped from a height of 30cm in a thermostatic chamber at a room temperature of 23°C to check for cracks. The number of food containers that did not crack out of 100 food containers was used as an index for evaluation, and evaluation was performed according to the following criteria. -Evaluation criteria- A: The number of food containers that did not crack was 90 or more. B: The number of food containers that did not crack was 80 to 89. C: The number of food containers that did not crack was 79 or less.

[0073] (3-4) Impact strength (impact resistance at low temperatures (-30°C)) A 200g weight was placed in a food container prepared using the method described below, and the container was cooled in a thermostatic chamber at -30°C for 3 hours. Immediately after removing the container from the thermostatic chamber, the food container with the weight was dropped from a height of 30cm to check for cracks. The number of food containers that did not crack out of 100 food containers was used as an evaluation index, and evaluation was performed according to the following criteria. -Evaluation criteria- A: The number of food containers that did not crack was 85 or more. B: The number of food containers that did not crack was 75 to 84. C: The number of food containers that did not crack was 74 or less. (3-5) Deep drawing formability For food containers manufactured using the method described below, the thickness of the center of the container bottom and the thickness of the edge of the container bottom were measured, and the difference between the two thicknesses was calculated. The smaller the thickness difference, the smaller the thickness deviation of the resin during container molding, and the better the deep drawability was evaluated. The thickness of 10 of the food containers was measured in the same way, the difference in thickness between the two points was calculated, and the average value of the 10 thickness differences was used as an index for evaluating deep drawability. -Evaluation criteria- (For non-foam food containers) A: Thickness difference is less than 0.1 mm B: Thickness difference is 0.1 mm or more and less than 0.3 mm C: Thickness difference is 0.3 mm or more (For foam food containers) A: Thickness difference is less than 0.5 mm B: Thickness difference is between 0.5 mm and 1.0 mm C: Thickness difference is 1.0 mm or more

[0074] 4. Examples and Comparative Examples "Preparation of Resins Used in Examples and Comparative Examples and Production Examples of Resin Compositions" The preparation of each resin and a specific method for producing the styrene-based resin composition will be described below. <Production Example of Styrene-Unsaturated Carboxylic Acid Resin (A)> -Preparation of styrene-unsaturated carboxylic acid resin (A-1)- A polymerization raw material liquid consisting of 65.5% by mass of styrene, 5.8% by mass of methacrylic acid, 3.3% by mass of methyl methacrylate, 22.9% by mass of ethylbenzene, 2.5% by mass of 2-ethyl-1-hexanol, and 0.027% by mass of 1,1-bis(t-butylperoxy)cyclohexane was fed at a rate of 0.8 L / h into a 3.6 L complete mixing reactor and then continuously fed to a devolatilizer connected to a single-screw extruder to remove volatile components such as unreacted monomer and polymerization solvent. The polymerization temperature in the complete mixing reactor was 130°C. The temperature of the single-screw extruder was set to 210-230°C and the pressure to 10 torr to devolatilize volatile components such as unreacted monomer and polymerization solvent. The devolatilized volatile components were condensed in a condenser using a -5°C refrigerant and recovered as unreacted liquid, and the resin was recovered as pellets. The physical properties of the styrene-unsaturated carboxylic acid resin (A-1) (hereinafter referred to as resin (A-1)) obtained by the above-mentioned analytical methods are shown in Table 1 below.

[0075] -Preparation of styrene-unsaturated carboxylic acid resins (A-2) to (A-5)- Resins (A-2) to (A-5) were prepared in the same manner as for Resin (A-1) by adjusting the feed amount of each monomer and the polymerization conditions. The compositions of Resins (A-1) to (A-5) obtained are shown in Table 1.

[0076] [Table 1]

[0077] <Production Example of Ethylene-Carboxylic Acid Ester Copolymer (B)> -Preparation of ethylene-carboxylic acid ester copolymer (B-1) Ethylene, methyl methacrylate, and t-butyl peroxy-2-ethylhexanoate as a polymerization initiator were fed into a tubular reactor, which was then continuously fed to a devolatilizer connected to a single-screw extruder to remove volatile components such as unreacted monomers and polymerization solvents. The gas concentration of methyl methacrylate in the feed gas was 5.5% by mass. The polymerization temperature in the tubular reactor was 220°C. The temperature of the single-screw extruder was set to 150-170°C and the pressure to 10 torr to devolatilize volatile components such as unreacted monomers and polymerization solvents. The resin was recovered as pellets. The physical properties of the ethylene-carboxylic acid ester copolymer (B-1) (hereinafter referred to as resin (B-1)) obtained by the above-mentioned analytical methods are shown in Table 2 below.

[0078] -Preparation of ethylene-carboxylic acid ester copolymers (B-2) to (B-9)- Resins (B-2) to (B-9) were prepared in the same manner as for Resin (B-1) by adjusting the type of each monomer, the feed amount of each monomer, and the polymerization conditions. The compositions of Resins (B-1) to (B-9) obtained are shown in Table 2.

[0079] [Table 2]

[0080] <Production Example of Core-Shell Type Rubber Polymer Particles (C)> -Preparation of rubber-like polymer particles (C-1)- A pressure vessel equipped with a stirrer was charged with 200% pure water, 0.002% by mass of ethylenediaminetetraacetic acid disodium salt, 0.0012% by mass of ferrous sulfate, 0.008% by mass of ethylenediaminetetraacetic acid disodium salt, and 0.03% by mass of polyoxyethylene alkyl ether sodium phosphate. After deacidification, 100% by mass of butadiene, 0.05% by mass of sodium formaldehyde sulfoxylate, and 0.2% by mass of paramenthane hydroperoxide were added, and then 1.4% by mass of polyoxyethylene alkyl ether sodium phosphate was added dropwise over 6 hours. The reaction solution was kept at pH 6.5 to 7.5 at 50°C for 124 hours, and a diene rubber latex with a conversion rate of 98% by mass and an average particle size of 0.18 μm was obtained. Next, while maintaining the temperature of the resulting rubber latex (approximately 71 parts solids) at 60°C, 40% by weight of styrene and 20% by weight of methyl methacrylate were added over 1 hour. Simultaneously with the addition of the monomers, 0.09% by weight of t-butyl hydroperoxide and 0.1% by weight of sodium formaldehyde sulfoxylate were added. The entire amount was then added over 2 hours while maintaining the pH of the reaction solution at 6.5-7.5 and the temperature at approximately 60°C. The reaction solution was then maintained at approximately 60°C for 1 hour to prepare a graft copolymer latex with an average particle size of 0.2 μm. After adding 1% by weight of Irganox 1076 as an antioxidant, the latex was coagulated with an aqueous calcium chloride solution, washed with water, and dehydrated to obtain rubbery polymer particles (C-1) as a powder. The composition and physical properties of the rubbery polymer particles (C-1) are shown in Table 3.

[0081] -Preparation of rubber-like polymer particles (C-2) and (C-3)- The feed amount of each monomer and the polymerization conditions were adjusted, and (C-2) and (C-3) were prepared in the same manner as for the rubber-like polymer particles (C-1). The compositions and physical properties of the obtained rubber-like polymer particles (C-2) and (C-3) are shown in Table 3.

[0082] -Preparation of rubber-like polymer particles (C-4)- A pressure vessel equipped with a stirrer was charged with 195 mass% pure water, 0.0003 mass% ethylenediaminetetraacetic acid disodium salt, 0.0001 mass% ferrous sulfate, 4.7 mass% n-butyl acrylate, 0.3 mass% methyl methacrylate, 1 mass% sodium dialkyl sulfosuccinate, 0.08 mass% allyl methacrylate, and 0.02 mass% cumene hydroperoxide, and the temperature was raised to 60°C. Then, 5 mass% pure water and 0.2 mass% sodium formaldehyde sulfoxylate were added to initiate polymerization. The reaction was continued for 20 minutes, and then polymerization was completed. Then, 47% by mass of n-butyl acrylate, 3% by mass of methyl methacrylate, 0.8% by mass of allyl methacrylate, and 0.05% by mass of cumene hydroperoxide were added dropwise to the reaction vessel over 120 minutes. The reaction was then continued for one hour, yielding an acrylic rubber latex with a conversion rate of 95% and an average particle size of 0.25 μm. Next, while maintaining the temperature of the resulting rubber latex (approximately 70 parts solids) at 60°C, 40% by weight of methyl methacrylate and 5% by weight of n-butyl acrylate were added over 1 hour. Simultaneously with the addition of the monomers, 0.06% by weight of t-butyl hydroperoxide and 0.3% by weight of n-octyl mercaptan were added. The entire amount was then added over 2 hours while maintaining the pH of the reaction solution at 6.5-7.5 and the temperature at approximately 60°C. The reaction solution was then maintained at approximately 60°C for 1 hour to prepare a graft copolymer latex with an average particle size of 0.3 μm. After adding 1% by weight of Irganox 1076 as an antioxidant, the mixture was coagulated with an aqueous calcium acetate solution, washed with water, and dehydrated to obtain rubbery polymer particles (C-4) as a powder. The composition and physical properties of the rubbery polymer particles (C-4) are shown in Table 3.

[0083] -Preparation of rubber-like polymer particles (C-5)- The feed amount of each monomer and the polymerization conditions were adjusted, and rubber-like polymer particles (C-5) were prepared in the same manner as the rubber-like polymer particles (C-4). The composition and physical properties of the obtained rubber-like polymer particles (C-5) are shown in Table 3 below.

[0084] [Table 3]

[0085] <Production example of impact-resistant styrene resin (D)> -Adjustment of impact-resistant styrene resin (D1)- A polymerization apparatus consisting of three 1.5-liter laminar-flow reactors equipped with agitators connected in series and followed by a two-stage vented extruder was used to produce high-impact styrene resin (D1) (hereafter referred to as "resin (D1)"). A raw material tank equipped with agitators was charged with 82.4% by mass of styrene, 9.0% by mass of ethylbenzene, 8.6% by mass of Ube Industries' high-cis butadiene rubber 13HB (as a rubber-like polymer), and 0.02% by mass of 1,1-bis(t-butylperoxy)cyclohexane. After dissolving the rubber components with the agitator, the raw material solution was fed to the reactors at a rate of 0.75 liters / hour. Polymerization was carried out at temperatures of 110-120°C in the first reactor, 120-130°C in the second reactor, and 140-150°C in the third reactor. The extruder temperature was 210-240°C, the degree of vacuum was 3 kPa, and the total solids content of the polymerization liquid discharged from the final reactor was 70.5% by mass. The average particle size of the rubber-like polymer particles was controlled by adjusting the rotation speed of the agitator in the first-stage laminar flow reactor to 110 rpm. The composition and properties of the obtained resin (D1) are shown in Table 4.

[0086] -Preparation of Impact-Resistant Styrenic Resins (D2) and (D3)- Using styrene and methyl methacrylate as monomers, high-impact styrene resins (D2) and (D3) were produced in the same manner as for resin (D1). The compositions and properties of the resulting resins (D1) to (D3) are shown in Table 4.

[0087] [Table 4]

[0088] <Styrene-based elastomer (E) used in the examples> In the examples of this specification, the following three types of styrene-based elastomer (E) were used. (E1) Asahi Kasei styrene-ethylene-butylene-butadiene block copolymer Tuftec P2000 (E2) Styrene-ethylene-butylene block copolymer Tuftec H1043 manufactured by Asahi Kasei Corporation (E3) Asahi Kasei styrene-butadiene block copolymer Tufprene 125

[0089] <Acrylic elastomer (F) used in the examples> In the examples of this specification, the following two types of acrylic elastomer (F) were used. (F1) Kuraray Clarity LA2270 (F2) Kuraray Clarity LK9243

[0090] <Production Example of Styrene-Based Resin Composition> Detailed methods for producing the styrene resin composition, the foamed extruded sheet, and the food container are described below. [Example 1] -Production of styrene-based resin composition- A dry blend of 90.0% by mass of the styrene-(meth)acrylic acid resin (A) (resin (A-1) shown in Table 1), 10.0% by mass of the ethylene-carboxylic acid ester copolymer (B) (resin (B-1) shown in Table 2), and 0.12% by mass of Fine Oxocol 180 was prepared. The mixture was kneaded, extruded, and pelletized using a twin-screw extruder TEM26SS manufactured by Shibaura Machine Co., Ltd. to obtain a styrene resin composition [1] as a pelletized resin. The screw rotation speed was 150 rpm, the cylinder temperature was 180-230°C, and the feed rate was 10 kg / h. The resin temperature was 240-260°C. The properties and physical properties of the styrene resin composition [1] are shown in the table below.

[0091] - Non-foaming extruded sheet and manufacturing of food containers using said non-foaming extruded sheet - The styrene-based resin composition [1] obtained above was fed into an extruder equipped with a nitrogen purge and a vacuum vent. The maximum cylinder temperature of the extruder was set to 250°C. The resin composition extruded from a T-die was wound on a mirror-finished metal roll, and a 0.25 mm-thick non-foamed extruded sheet [1] was produced by adjusting the winding speed and resin output. The non-foamed extruded sheet [1] was used to produce a non-foamed food container [1] shown in Figure 1. The food container was heated for 20 seconds using a Soken Co., Ltd. sheet container molding machine at a heating zone of 220°C. The container was then placed in a food container mold with a ratio (d / r) of the recess depth d to the opening diameter r of the recess of 0.75, and vacuum formed to produce a non-foamed food container [1]. The evaluation results are shown in the table below. In addition, to investigate the relationship between the deep drawing ratio of non-foamed food containers (the ratio (d / r) of the depth d of the recess of the non-foamed food container to the diameter r of the opening of the recess) and the occurrence of holes due to uneven thickness during container molding, food container molds were prepared with ratios (d / r) of the depth d of the recess to the diameter r of the opening of the recess varying from 0.2 to 1.7, and non-foamed extruded sheets [1] were placed in each of these molds. Non-foamed food containers [1] with various (d / r) were fabricated by vacuum molding, and the appearance of the bottom surface of the recess of the food container was visually inspected to evaluate the presence or absence of holes. The evaluation results are shown in the table.

[0092] - Manufacturing of foamed extruded sheets and food containers using said foamed extruded sheets - 100 parts by mass of the styrene-based resin composition [1] obtained above and 1.0 part by mass of talc (Hifiller #12, manufactured by Matsumura Sangyo Co., Ltd.) as inorganic particles (G) were dry-blended and fed into an extruder. The maximum cylinder temperature of the extruder was set to 250°C. A mixed butane (isobutane / normal butane mass ratio 65 / 35) was added as a blowing agent to the melt-kneaded resin composition at 4.0 parts by mass per 100 parts by mass of the styrene-based resin composition [1]. The extruded cylindrical foam was extruded into a cylindrical shape and foamed. The resulting cylindrical foam was cooled by blowing air onto it, then cooled using a cooling mandrel. The cylindrical foam was then cut open in the extrusion direction to obtain a foamed extruded sheet [1] with a thickness of 1.5 mm and a basis weight of 130 g. The foamed extruded sheet [1] was used to produce the foamed food container [1] shown in Figure 1. The foamed food container was prepared by using a sheet container molding machine manufactured by Soken Co., Ltd., heating the container at a heating zone of 220°C for 20 seconds, and then placing the container in a mold for a food container with a ratio (d / r) of the depth d of the recess to the opening diameter r of the recess of 0.75, followed by vacuum forming to produce a foamed food container [1]. The evaluation results are shown in Table 5-1.

[0093] [Examples 2 to 28] Styrenic resin compositions [2] to

[28] , non-foamed extruded sheets [2] to

[28] , and foamed extruded sheets [2] to

[28] were obtained in the same manner as in Example 1, except that the formulations were changed as shown in Tables 5-1 to 5-4 below. The evaluation results of food containers obtained by secondary molding of the obtained non-foamed extruded sheets [2] to

[28] and foamed extruded sheets [2] to

[28] are shown in Tables 5-1 to 5-4. Note that no holes were observed in the bottom surface of the food containers produced in Examples 1 to 28.

[0094] [Comparative Examples 1 to 5] A styrene-based resin composition, a non-foamed extruded sheet, and a foamed extruded sheet were obtained in the same manner as in Example 1, except that the mixing formulation was changed as shown in the following Table 6. The evaluation results of food containers obtained by secondary molding the obtained non-foamed extruded sheet and foamed extruded sheet are shown in Table 6.

[0095] [Table 5-1]

[0096] [Table 5-2]

[0097] [Table 5-3]

[0098] [Table 5-4]

[0099] [Table 6] [Explanation of symbols]

[0100] 1 food container 2 Food container body 3 Lid 4 recess 5 grooves 6 Opening 7 Bottom part 9. Mold 10 Extruded Sheet 11. Mold recess 12 spacers

Claims

1. A food container having a recess capable of accommodating food, The food container is characterized in that it is composed of a styrene-based resin composition containing 65 to 97 mass% of a styrene-unsaturated carboxylic acid-based resin (A) and 3 to 20 mass% of an ethylene-carboxylic acid ester-based copolymer (B).

2. The styrene-based resin composition contains, relative to the total amount of the styrene-based resin composition, 65 to less than 97 mass% of the styrene-unsaturated carboxylic acid-based resin (A), 3 to 20 mass% of the ethylene-carboxylic acid ester-based copolymer (B), and more than 0 to 20 mass% of core-shell rubber-like polymer particles (C). The food container according to claim 1.

3. 3. The food container according to claim 1, wherein the styrene-based resin composition further contains one or more selected from the group consisting of an impact-resistant styrene-based resin (D), a styrene-based elastomer (E), and an acrylic elastomer (F).

4. 3. The food container according to claim 1, wherein the ratio (d / r) of the depth d of the recess to the opening diameter r of the recess is 1.5 or less.

5. 3. The food container according to claim 1, which is formed from an extruded sheet obtained by molding the styrene-based resin composition.

6. 3. The food container according to claim 1, wherein the styrene-based resin composition further contains inorganic particles (G) in an amount of 0.05 to 3.0% by mass relative to the total amount of the styrene-based resin composition, and is formed from a foamed extruded sheet obtained by molding the styrene-based resin composition.

7. a first layer composed of the styrene-based resin composition; A food container formed from a laminate having a surface layer laminated on the surface of the first layer, The food container according to claim 4 , wherein the surface layer comprises a styrene-based resin or a polyolefin-based resin.

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