Styrene resin composition, biaxially oriented sheet, extruded sheet, foamed extruded sheet, and food container

Abstract

The present disclosure provides a styrene resin composition having excellent heat resistance, mechanical strength, and low-temperature impact resistance.SOLUTION: The present disclosure is a styrene-based resin composition containing 60 to 97% by mass of a styrene-unsaturated carboxylic acid-based resin (A) and 3 to 20% by mass of a metal salt of an ethylene-unsaturated carboxylic acid-based resin (B).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a styrene-based resin composition, a biaxially oriented sheet, an extruded sheet, a foamed extruded sheet, and a food container. [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. However, styrene-unsaturated carboxylic acid resins are more brittle than general polystyrene resins, and cracking of food containers and lids has become a problem. The following documents are known as techniques for improving the mechanical strength of styrene-unsaturated carboxylic acid resins. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-196415 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned Patent Document 1 describes a technology for improving strength and moldability while maintaining practical heat resistance by using a styrene-methacrylic acid copolymer resin, a high-molecular-weight acrylic resin, and a styrene-based resin composition containing the acrylic resin. However, although Patent Document 1 describes a styrene-based resin composition having excellent heat resistance, mechanical strength, and moldability, and a stretched sheet using the same, it does not describe any study on improving cold impact resistance. Therefore, the problem to be solved by the present disclosure is to provide a styrene-based resin composition having excellent heat resistance, mechanical strength, and cold impact resistance. Another problem to be solved by the present disclosure is to provide a biaxially oriented sheet, an extruded sheet, a foamed extruded sheet, and a food container obtained by secondary molding of the extruded sheet and the foamed extruded sheet, which contain the styrene-based resin composition and exhibit excellent heat resistance, mechanical strength, cold impact resistance, and appearance during molding. [Means for solving the problem]

[0005] The present inventors have conducted extensive research in light of the above problems and have found that a styrene-based resin composition excellent in heat resistance, mechanical strength, and cold impact resistance can be obtained by incorporating a styrene-unsaturated carboxylic acid-based resin (A) and a metal salt of an ethylene-unsaturated carboxylic acid-based resin (B) in predetermined amounts, thereby completing the present invention.

[0006] [1] A styrene-based resin composition containing 60 to 97 mass % of a styrene-unsaturated carboxylic acid-based resin (A) and 3 to 20 mass % of a metal salt of an ethylene-unsaturated carboxylic acid-based resin (B).

[0007] [2] The styrene-based composition according to [1], further comprising more than 0 to 20 mass % of core-shell type rubbery polymer particles (C).

[0008] [3] The styrene-based resin composition according to [1] or [2], further comprising one or more selected from the group consisting of an impact-resistant styrene-based resin (D), a styrene-based elastomer (E), an acrylic elastomer (F), and an ethylene-carboxylic acid ester copolymer (G).

[0009] [4] The styrene-based resin composition according to any one of [1] to [3], wherein the styrene-unsaturated carboxylic acid-based resin (A) is a copolymer containing styrene monomer units (a1) and (meth)acrylic acid monomer units (a2-1), and the (meth)acrylic acid monomer units (a2-1) are contained in an amount of 2 to 15 mass% based on the total amount of the styrene-unsaturated carboxylic acid-based resin (A).

[0010] [5] The styrene-based resin composition according to any one of [1] to [4], wherein the styrene-unsaturated carboxylic acid-based resin (A) contains (meth)acrylic acid monomer units (a2-1) and (meth)acrylic acid ester monomer units (a2-2).

[0011] [6] The styrene-based resin composition according to any one of [1] to [5], wherein the metal salt of the ethylene-unsaturated carboxylic acid-based resin (B) essentially contains an ethylene monomer unit (b1) and an unsaturated carboxylic acid-based monomer unit (b2).

[0012] [7] The styrene resin composition according to any one of [1] to [6], wherein the metal ion contained in the metal salt of the ethylene-unsaturated carboxylic acid resin (B) is a zinc ion.

[0013] [8] A masterbatch for producing the styrene-based resin composition according to any one of [1] to [7], A masterbatch containing at least two resins selected from the group consisting of a styrene-unsaturated carboxylic acid resin (A), a metal salt of an ethylene-unsaturated carboxylic acid resin (B), and core-shell type rubber polymer particles (C).

[0014] [9] An extruded sheet obtained by molding the styrene-based resin composition according to any one of [1] to [7].

[0015]

[10] The styrene-based resin composition according to any one of [1] to [7], further comprising inorganic particles (H) in an amount of 0.05 to 3.0% by mass relative to the total amount of the styrene-based resin composition.

[0016]

[11] An extruded foam sheet obtained by molding the styrene resin composition according to any one of [1] to [7].

[0017]

[12] A food container formed from the foamed extruded sheet according to

[11] . [Effects of the Invention]

[0018] According to the present disclosure, there is provided a styrene-based resin composition having excellent heat resistance, mechanical strength, and cold impact resistance. According to the present disclosure, it is possible to provide a biaxially oriented sheet, an extruded sheet, a foamed extruded sheet, and a foamed container that can be frozen and can be cooked in a microwave oven, which have excellent heat resistance, mechanical strength, cold impact resistance, and appearance. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the embodiments for carrying out the present invention (hereinafter referred to as "present embodiments") will be described in detail. Note that the present invention is not limited to the following embodiments, and can be practiced with various modifications within the scope of the gist. Definitions of various compositions in this disclosure are shown below.

[0020] [Styrene-based resin composition] The styrene-based resin composition of this embodiment contains a styrene-unsaturated carboxylic acid resin (A) and a metal salt of an ethylene-unsaturated carboxylic acid resin (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 a styrene-based monomer unit (a1) and an unsaturated carboxylic acid monomer unit (a2). The ethylene-unsaturated carboxylic acid resin metal salt (B) may be at least one resin having an ethylene-based monomer unit (b1) and an unsaturated carboxylic acid monomer unit (b2). The content of the styrene-unsaturated carboxylic acid resin (A) is 60 to 97% by mass, and the content of the ethylene-unsaturated carboxylic acid resin metal salt (B) is 3 to 20% by mass, based on the total amount (100% by mass) of the styrene-based resin composition. Furthermore, the styrene-based resin composition may contain 0 to 20 mass% of the core-shell type rubber polymer particles (C) as an optional component relative to the total amount (100 mass%) of the styrene-based resin composition. By constructing a food container from the styrene-based resin composition having a composition adjusted within the above range, it is possible to provide a food container that is excellent in appearance, heat resistance, 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 core-shell rubbery polymer particles (C), impact-resistant styrene-based resins (D), styrene-based elastomers (E), acrylic elastomers (F), and ethylene-carboxylic acid ester copolymers (G). This makes it possible to provide a styrene-based resin composition with excellent heat resistance, mechanical strength, and cold impact resistance. The styrene-based resin composition of this embodiment may optionally contain inorganic particles (H). Adding inorganic particles (H) to the styrene-based resin composition serves as a foam nucleating agent during foam molding and contributes to improving the rigidity of food containers.

[0021] 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 can contribute 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) relative to the total amount (100% by mass) of the styrene-based resin composition is 65 to 97% by mass, preferably 70 to 90% by mass, more preferably 75 to 88% by mass, even 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.

[0022] <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.

[0023] 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 into a single bond (-CC-) through a polymerization reaction or crosslinking reaction of the styrene-based monomer (a1). Therefore, the styrene-based monomer (a1) can be a precursor of the styrene-based monomer unit (a1). The other monomer units in this specification have the same meaning.

[0024] <Unsaturated Carboxylic Acid Monomer Unit (a2)> In the styrene-unsaturated carboxylic acid resin (A) of this embodiment, the unsaturated carboxylic acid monomer unit (a2) can play 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). Examples of the unsaturated carboxylic acid monomer unit (a2) include not only the (meth)acrylic acid monomer unit (a2-1) and the (meth)acrylic acid ester monomer unit (a2-2) described below, but also, for example, maleic anhydride, maleic acid, maleic acid esters (e.g., dimethyl maleate), fumaric acid, fumaric acid esters (dimethyl fumarate, diethyl fumarate, ethyl fumarate), itaconic acid, itaconic acid esters, cinnamic acid, and cinnamic acid esters.

[0025] <<(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) can play 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), the content of the (meth)acrylic acid monomer units (a2-1) in the styrene-unsaturated carboxylic acid resin (A) is preferably 2 to 30 mass%, more preferably 3 to 25 mass%, even more preferably 4 to 20 mass%, even more preferably 5 to 15 mass%, and most preferably 8 to 11 mass%, based on the total amount of the styrene-unsaturated carboxylic acid resin (A). In another embodiment, the content of the (meth)acrylic acid monomer units (a2-1) is preferably 3 to 20 mass%, more preferably 4 to 17 mass%, and even more preferably 8 to 14 mass%, based on the total amount of the styrene-unsaturated carboxylic acid resin (A). If the content of the (meth)acrylic acid monomer units (a2-1) is less than 2 mass%, the effect of significantly improving heat resistance is small. Furthermore, if the content of the (meth)acrylic acid monomer unit (a2-1) exceeds 30% by mass, the resin viscosity increases, resulting in a decrease in moldability, and the water absorption rate increases, leading to the generation of bubbles during molding and a tendency for the viscosity to increase during production. By setting the content of the (meth)acrylic acid monomer unit (a2-1) to 2% by mass or more, the heat resistance can be improved, and by setting the content to 30% by mass or less, excessive viscosity increase can be prevented. In particular, by setting the content of the (meth)acrylic acid monomer unit (a2-1) to 3 to 25% by mass, a resin excellent in both heat resistance and moldability can be obtained. 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.

[0026] <<(Meth)acrylic acid ester monomer unit (a2-2)>> In this embodiment, the unsaturated carboxylic acid monomer unit (a2) constituting the styrene-unsaturated carboxylic acid resin (A) may contain a (meth)acrylic acid ester monomer unit (a2-2). 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. The "alkyl group" in this specification may be linear, branched, or cyclic, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group (n-butyl group, isobutyl group, sec-butyl group, tert-butyl group), a pentyl group (n-pentyl group, isopentyl group, tert-pentyl group, neopentyl group), a 1,2-dimethylpropyl group, an n-hexyl group, an isohexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and a cyclononyl group.

[0027] 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.

[0028] <Preferred 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).

[0029] That is, the styrene-unsaturated carboxylic acid resin (A) of this embodiment may be a binary copolymer of a styrene-based monomer unit (a1) and a (meth)acrylic acid monomer unit (a2-1), or a binary copolymer of a styrene-based monomer unit (a1) and a (meth)acrylic acid ester monomer unit (a2-2), or a terpolymer in which a styrene-based monomer (a1), a (meth)acrylic acid monomer (a2-1), and a (meth)acrylic acid ester monomer (a2-2) are copolymerized, a terpolymer containing a styrene-based monomer unit (a1) and two (meth)acrylic acid ester monomer units (a2-2), or a terpolymer containing a styrene-based monomer unit (a1) and two (meth)acrylic acid monomer units (a2-1). This further improves the compatibility with other resins or the mechanical strength. Among these, the styrene-unsaturated carboxylic acid resin (A) is preferably a binary copolymer of a styrene-based monomer unit (a1) and a (meth)acrylic acid monomer unit (a2-1), a terpolymer containing a styrene-based monomer (a1), a (meth)acrylic acid monomer (a2-1), and a (meth)acrylic acid ester monomer (a2-2), or a terpolymer containing a styrene-based monomer unit (a1) and two kinds of (meth)acrylic acid monomer units (a2-1). 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.

[0030] 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 having an excellent balance of heat resistance, mechanical strength, and cold impact resistance can be obtained.

[0031] <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) and (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 unit (a3) ​​may be copolymerized with a monomer other than the two monomers described above, without any particular limitation, as long as it is copolymerizable with the styrene-based monomer unit (a1), the (meth)acrylic acid monomer unit (a2-1) and / or the (meth)acrylic acid ester monomer unit (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 (meth)acrylonitrile, maleimide, and nucleus-substituted maleimide. In the present embodiment, when the styrene-unsaturated carboxylic acid resin (A) has the other monomer unit (a3), the content of the other monomer unit (a3) ​​in the styrene-unsaturated carboxylic acid resin (A) is preferably 0 to 12 mass%, more preferably 0 to 5 mass%, even more preferably 2 mass% or less, and even more preferably less than 2 mass%, relative to the total amount of the styrene-unsaturated carboxylic acid resin (A). In particular, in the present embodiment, when the styrene-unsaturated carboxylic acid resin (A) has a (meth)acrylonitrile monomer unit, the content of the (meth)acrylonitrile monomer unit in the styrene-unsaturated carboxylic acid resin (A) may be preferably 0 to 12 mass%, more preferably 0 to 5 mass%, even more preferably 2 mass% or less, still more preferably less than 2 mass%, and particularly preferably less than 1 mass%, relative to the total amount of the styrene-unsaturated carboxylic acid resin (A). If the content of (meth)acrylonitrile monomer units in the styrene-unsaturated carboxylic acid resin (A) is 2% by mass or more, the compatibility decreases, and strength such as impact resistance and fold resistance tends to be difficult to exhibit sufficiently.

[0032] <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.

[0033] 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 of heat resistance, mechanical strength, and cold impact resistance can be obtained, and as a result, molded articles such as food containers 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.

[0034] 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 (or the reaction product).

[0036] 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.

[0037] 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.

[0038] "Metal salts of ethylene-unsaturated carboxylic acid resins (B)" The metal salt of an ethylene-unsaturated carboxylic acid resin (B) in this embodiment is a copolymer resin (hereinafter simply referred to as resin (B)) essentially composed of ethylene monomer units (b1) and unsaturated carboxylic acid monomer units (b2) and / or neutralized monomer units (b3) in which the hydrogen ions of the unsaturated carboxylic acid monomer units (b2) are replaced with metal ions, and contributes to improving the fluidity, mechanical strength, and cold impact resistance of the entire composition. Furthermore, if necessary, the metal salt of an ethylene-unsaturated carboxylic acid resin (B) may contain (meth)acrylic acid ester monomer units (b4) and / or other monomer units (b5) in addition to the ethylene monomer units (b1), unsaturated carboxylic acid monomer units (b2), and neutralized monomer units (b3) in which the hydrogen ions of the unsaturated carboxylic acid monomer units (b2) are replaced with metal ions. The neutralized monomer unit (b3) is a monomer unit in which the hydrogen ion of the carboxylic acid in the unsaturated carboxylic acid monomer unit (b2) is substituted with a metal ion.

[0039] In other words, the metal salt of the ethylene-unsaturated carboxylic acid resin (B) in this embodiment can be a copolymer (=ethylene-unsaturated carboxylic acid copolymer) containing an ethylene monomer and an unsaturated carboxylic acid monomer unit (b2) that has been partially or completely neutralized with metal ions. Therefore, the metal salt of the ethylene-unsaturated carboxylic acid resin (B) is a resin in which some or all of the carboxyl groups of the ethylene-unsaturated carboxylic acid copolymer have been neutralized with metal ions, and therefore can also be called an ionomer resin. Therefore, the metal salt of the ethylene-unsaturated carboxylic acid resin (B) in this embodiment may contain an ethylene monomer unit (b1), an unsaturated carboxylic acid monomer unit (b2), and a neutralization product monomer unit (b3) in which the hydrogen ion of the unsaturated carboxylic acid monomer unit (b2) is replaced with a metal ion (hereinafter, also simply referred to as the neutralization product monomer unit (b3)).

[0040] The metal ion constituting the metal salt (B) (particularly the metal salt) of the ethylene-unsaturated carboxylic acid resin may be either a monovalent metal ion or a polyvalent metal ion, and examples thereof include alkali metal ions such as lithium ion, sodium ion, and potassium ion, and polyvalent metal ions selected from the group consisting of magnesium ion, calcium ion, zinc ion, cobalt ion, nickel ion, manganese ion, lead ion, copper ion, titanium ion, iron ion, aluminum ion, and zirconium ion. These metal ions may be used alone or in combination of two or more. Of the above metal ions, the metal ion constituting the metal salt (B) of the ethylene-unsaturated carboxylic acid resin of the present embodiment is preferably a sodium ion, a zinc ion, or a magnesium ion. In the styrene-based resin composition of the present embodiment, the metal salt (B) of the ethylene-unsaturated carboxylic acid-based resin may be used alone or in combination of two or more. In addition to the above metal ions, Lewis basic compounds such as amino compounds, such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, and 1,3-dimethylaminocyclohexane, may also be contained.

[0041] The metal salt of the ethylene-unsaturated carboxylic acid resin (B) of this embodiment is preferably a random copolymer. In this embodiment, the content of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin is 3 to 20% by mass, preferably 4 to 15% by mass, more preferably 5 to 12% by mass, and most preferably 5 to 10% by mass, relative to the total amount (100% by mass) of the styrene resin composition. By making the content of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin 3% by mass or more, the effect of improving the flowability, mechanical strength, and cold impact resistance of the entire composition can be sufficiently obtained, and by making it 20% by mass or less, a decrease in compatibility of the entire composition is suppressed, and production stability and moldability are improved.

[0042] <Ethylene monomer unit (b1)> The metal salt (B) of an ethylene-unsaturated carboxylic acid resin of this embodiment essentially contains an ethylene monomer unit (b1). The content of the ethylene monomer unit (b1) in the metal salt (B) of an ethylene-unsaturated carboxylic acid resin of this embodiment is preferably 40 to 98 mass%, more preferably 50 to 95 mass%, even more preferably 55 to 90 mass%, still more preferably 60 to 85 mass%, and most preferably 75 to 80 mass%, based on the total amount of the metal salt (B) of an ethylene-unsaturated carboxylic acid resin. When the content of the ethylene monomer unit (b1) is within the specified range, the flowability, mechanical strength, and cold impact resistance of the composition are improved.

[0043] <Unsaturated carboxylic acid monomer unit (b2)> The metal salt (B) of the ethylene-unsaturated carboxylic acid resin of this embodiment may contain unsaturated carboxylic acid monomer units (b2). When the metal salt (B) of the ethylene-unsaturated carboxylic acid resin of this embodiment contains the unsaturated carboxylic acid monomer units (b2), the content of the unsaturated carboxylic acid monomer units (b2) is preferably 2 to 60 mass%, more preferably 5 to 50 mass%, more preferably 10 to 40 mass%, even more preferably 15 to 35 mass%, and most preferably 20 to 25 mass%, based on the total amount of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin. When the content of the unsaturated carboxylic acid 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 composition are improved.

[0044] As described above, the metal salt (B) of the ethylene-unsaturated carboxylic acid resin can be synthesized by neutralizing an ethylene-(meth)acrylic acid copolymer with a metal ion. In other words, the metal salt (B) of the ethylene-unsaturated carboxylic acid resin can be a resin obtained by reacting an ethylene-unsaturated carboxylic acid copolymer (e.g., an ethylene-(meth)acrylic acid copolymer) with a metal ion (or a metal compound) as reaction raw materials. In this case, the content of the unsaturated carboxylic acid monomer unit (b2) in the ethylene-unsaturated carboxylic acid copolymer before neutralization with the metal salt (B) of the ethylene-unsaturated carboxylic acid resin is preferably 1% by mass or more, more preferably 5% by mass or more, based on the ethylene-unsaturated carboxylic acid copolymer before neutralization. Furthermore, the content of the unsaturated carboxylic acid monomer unit (b2) is preferably 30% by mass or less, more preferably 40% by mass or less.

[0045] In this embodiment, the unsaturated carboxylic acid monomer unit (b2) may be a monomer unit having a carboxylic acid and an unsaturated double bond. Examples of the unsaturated carboxylic acid monomer (b2) include (meth)acrylic acid, maleic acid, fumaric acid, and cinnamic acid. These may be used alone or in combination. In particular, it is particularly preferable to use acrylic acid or methacrylic acid, which are easily available industrially, as the unsaturated carboxylic acid monomer (b2).

[0046] <Neutralized product monomer unit (b3)> The neutralized monomer unit (b3) in this embodiment may be a neutralized monomer unit (b3) in which a hydrogen atom of the unsaturated carboxylic acid monomer unit (b2) is substituted with a metal ion. A preferred example of the neutralized monomer unit (b3) is a monomer unit in which a hydrogen atom of a carboxylic acid in a monomer unit selected from the group consisting of a (meth)acrylic acid monomer unit, a maleic acid monomer unit, a fumaric acid monomer unit, and a cinnamic acid monomer unit is substituted with a metal ion. In this embodiment, the content of the neutralization monomer unit (b3) is preferably 1 to 59 mass%, more preferably 2 to 50 mass%, more preferably 5 to 45 mass%, even more preferably 7 to 40 mass%, and most preferably 10 to 35 mass%, based on the total amount of the metal salt of the ethylene-unsaturated carboxylic acid resin (B). When the content of the neutralization monomer unit (b3) is within the specified range, compatibility with the styrene-unsaturated carboxylic acid resin (A) is improved, and the production stability and moldability of the composition are improved.

[0047] <(Meth)acrylic acid ester monomer unit (b4)> The metal salt of the ethylene-unsaturated carboxylic acid resin (B) of this embodiment may further contain (meth)acrylic acid ester monomer units (b4) as necessary. When the metal salt of the ethylene-unsaturated carboxylic acid resin (B) of this embodiment contains (meth)acrylic acid ester monomer units (b4), the content of the (meth)acrylic acid ester monomer units (b4) is 2 to 30 mass %, preferably 5 to 20 mass %, and more preferably 10 to 15 mass %, based on the total amount of the metal salt of the ethylene-unsaturated carboxylic acid resin (B). When the content of the (meth)acrylic acid monomer units (b4) is within the specified range, compatibility with the styrene-unsaturated carboxylic acid resin (A) is improved, and the production stability and moldability of the composition are improved. The (meth)acrylic acid ester monomer (b4) is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (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 (b3), methyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate are preferred because of their industrial availability.

[0048] <Other monomers (b5)> In this embodiment, the metal salt (B) of the ethylene-unsaturated carboxylic acid resin contains not only the essential components of ethylene monomer units (b1), unsaturated carboxylic acid monomer units (b2), and / or neutralized monomer units (b3), but also the optional component of (meth)acrylic acid ester monomer units (b4), and may further contain other monomer units (b5). Examples of the other monomer units (b5) include, but are not limited to, propylene monomer units. By limiting the content of the other monomer units (b5) to 1% by mass or less, deterioration in heat resistance and mechanical strength can be minimized.

[0049] The metal salt of an ethylene-unsaturated carboxylic acid resin (B) of this embodiment can be a resin obtained by using an ethylene monomer, an unsaturated carboxylic acid monomer, and a metal ion (or metal compound) as reaction raw materials (1). The metal salt (B) of the ethylene-unsaturated carboxylic acid resin is preferably a resin prepared from 40 to 80% by mass (more preferably 50 to 70% by mass) of ethylene monomer, 5 to 35% by mass (more preferably 10 to 25% by mass) of an unsaturated carboxylic acid monomer, and 15 to 60% by mass (more preferably 25 to 50% by mass) of a metal compound as reaction raw materials (1). In other words, the metal salt (B) of the ethylene-unsaturated carboxylic acid resin is preferably a resin prepared from 35 to 80% by mass (more preferably 45 to 70% by mass) of an ethylene-unsaturated carboxylic acid copolymer and 20 to 65% by mass (more preferably 30 to 55% by mass) of a metal compound as reaction raw materials (2). Examples of the metal compounds include metal oxides, metal hydroxides, metal chlorides, metal nitrides, metal sulfates, metal nitrates, and hydrates thereof, which contain metal atoms of the metal ions.

[0050] <Preferable Example of Metal Salt of Ethylene-Unsaturated Carboxylic Acid Resin (B)> As the metal salt (B) of the ethylene-unsaturated carboxylic acid resin, from the viewpoint of easy availability, an ionomer resin of an ethylene-acrylic acid copolymer and an ionomer resin of an ethylene-methacrylic acid copolymer are more preferred, and a zinc ionomer of an ethylene-acrylic acid copolymer, a sodium ionomer of an ethylene-acrylic acid copolymer, a zinc ionomer of an ethylene-methacrylic acid copolymer, and a sodium ionomer of an ethylene-methacrylic acid copolymer are particularly preferred.

[0051] <Characteristics of metal salts of ethylene-unsaturated carboxylic acid resins (B)> The contents of the ethylene monomer unit (b1), the unsaturated carboxylic acid monomer unit (b2), the neutralization product monomer unit (b3), the (meth)acrylic acid ester monomer unit (b4) and the other monomer unit (b5) in the metal salt of the ethylene-unsaturated carboxylic acid resin (B) in this embodiment can be quantified by infrared absorption spectroscopy. In some cases, the contents of the ethylene monomer unit (b1), the unsaturated carboxylic acid monomer unit (b2), the neutralized product monomer unit (b3), the (meth)acrylic acid ester monomer unit (b4) and the other monomer unit (b5) in the metal salt (B) of the ethylene-unsaturated carboxylic acid resin of the present embodiment can be analyzed by the following procedure. First, the constituent units (each monomer unit) in the metal salt (B) of the ethylene-unsaturated carboxylic acid resin are identified by pyrolysis gas chromatography (pyrolysis GC-MS), and then the content of each can be evaluated using nuclear magnetic resonance spectroscopy (NMR) and elemental analysis. IR or Raman analysis can also be combined. Prior to these analyses, it is preferable to remove components other than the metal salt (B) of the ethylene-unsaturated carboxylic acid resin by reprecipitation or Soxhlet extraction. Details of the measurement method for the metal salt (B) of the ethylene-unsaturated carboxylic acid resin of this embodiment are as follows. The metal salts (B) of the ethylene-unsaturated carboxylic acid resins synthesized in the Examples section were dissolved in a mixed solvent of dehydrated toluene / dehydrated acetic acid (75 / 25% by mass), reacted at 100°C for 2 hours, and then reprecipitated in a mixed solvent of acetone / water (80 / 20% by mass), thereby converting the neutralized monomer units (b3) into unsaturated carboxylic acid monomer units (b2). The resulting metal salts (B) of the ethylene-unsaturated carboxylic acid resins were then thoroughly washed with water and dried, and the dried resin was subjected to the following operations (I) to (IV). (1) The components of the monomer units that make up the resin were analyzed by pyrolysis GC-MS. (2) The acid value of the resin was measured in accordance with JIS K0070-1992. (3) Using a mixed solvent of deuterated toluene and deuterated methanol, the metal salt of ethylene-unsaturated carboxylic acid resin (B)1 H-NMR measurements were carried out. (4) The metal salts (B) of the ethylene-unsaturated carboxylic acid resins obtained in the examples and comparative examples were each subjected to microwave decomposition pretreatment with nitric acid, and then the type and amount of metal ions in the neutralized monomer units (b3) were identified by ICP emission spectrometry. The types and structures of the unsaturated carboxylic acid monomer units (b2) and the (meth)acrylic acid ester monomer units (b4) were identified by the above procedure (1). The ratio of the ethylene monomer units (b1):(meth)acrylic acid ester monomer units (b4):to the total amount of the unsaturated carboxylic acid monomer units (b2) and the neutralized monomer units (b3) was calculated by the above procedure (1) to (3). The ratio of the ethylene monomer units (b1):(meth)acrylic acid ester monomer units (b4):unsaturated carboxylic acid monomer units (b2):neutralized monomer units (b3) was calculated by the above procedure (4).

[0052] In this embodiment, the metal salt of the ethylene-unsaturated carboxylic acid resin (B) has a melt flow rate at 190°C of 0.2 to 10.0, preferably 0.5 to 5.0, and more preferably 0.8 to 3.0. A melt flow rate of 0.2 or more is preferred from the viewpoint of moldability, and a melt flow rate of 10.0 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 resin. In the present disclosure, the melt flow rate is a value measured in accordance with ISO 1133 at 190°C under a load of 21.6 N. The melting point of the metal salt of the ethylene-unsaturated carboxylic acid resin (B) in this embodiment is 120°C or lower, preferably 110°C or lower, and more preferably 100°C or lower. By setting the melting point to 120°C or lower, crystallization during molding of the composition 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.

[0053] In this embodiment, the acidic groups of the metal salt of the ethylene-unsaturated carboxylic acid resin (B) are neutralized with one or more metal ions. The type of metal ion is not particularly limited, but from an industrial viewpoint, zinc ions or sodium ions are preferred, with zinc ions being more preferred, as they further improve the mechanical strength and cold impact resistance of the composition. The styrene-unsaturated carboxylic acid resin (A) and the metal salt of the ethylene-unsaturated carboxylic acid resin (B) are crosslinked by ionic bonds via the metal ions, thereby improving the mechanical strength and cold impact resistance of the composition.

[0054] In this embodiment, the degree of neutralization of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. By setting the degree of neutralization to 90% or less, excessive ion aggregation can be suppressed, and deterioration of fluidity and moldability can be suppressed. In this disclosure, the degree of neutralization refers to the blending ratio (mol %) of metal ions relative to the number of moles of acidic groups in the metal salt (B) of the ethylene-unsaturated carboxylic acid resin. The degree of neutralization can be measured, for example, by neutralization titration.

[0055] "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 core-shell rubbery polymer particles (C) contribute 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) having 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 more preferred specific core-shell rubbery polymer particle (C) is a core-shell rubbery polymer particle (C) comprising a polymer core layer having conjugated diene-based monomer units (c1) or acrylic acid ester monomer units (c2) and a shell layer having (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).

[0056] 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).

[0057] 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 1 to 18% by mass, 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. The conjugated diene monomer (c1) constituting 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 units (c2) constituting 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. The (meth)acrylic acid ester monomer units (c3) constituting the graft copolymer of the core-shell type rubbery polymer particles (C) in this embodiment include methacrylic acid ester monomer units and acrylic acid ester monomer units. Examples of the (meth)acrylic acid ester monomer units 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. Methyl acrylate, n-butyl acrylate, and methyl methacrylate are preferred because of their industrial availability and low cost. The styrene-based monomer unit (c4) constituting 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.

[0058] 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.

[0059] "Impact-resistant styrene resin (D)" The rubber-modified 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) (particles containing the rubbery polymer (D-2) are 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, if necessary, a (meth)acrylic acid ester monomer (d2) and 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 high-impact styrene-based resin (D) of this embodiment contains a polymer matrix (D-1) and rubbery polymer particles (D-2). The polymer matrix (D-1) contains a polymer obtained by polymerizing the styrene-based monomer (d1) and, if necessary, the (meth)acrylic acid ester monomer units (d2) and other monomers (d4). The rubber-like polymer particles (D-2) are particles of a rubber-like polymer (D-2) mainly composed of a conjugated diene monomer (d3), and the surface of the particles may be grafted with a polymer containing a styrene-based monomer (d1) as necessary.

[0060] <Polymer matrix (D-1)> In this embodiment, the polymer matrix (D-1) of the impact-resistant styrene-based resin (D) contains a styrene-based monomer (d1) and, if necessary, a (meth)acrylic acid ester monomer (d2) and other monomers (d4). When the polymer matrix (D-1) contains both the styrene-based monomer (d1) and the (meth)acrylic acid ester monomer (d2), the content of the (meth)acrylic acid ester monomer (d2) relative to 100% by mass of the impact-resistant styrene-based resin (D) is preferably 10 to 50% by mass, more preferably 20 to 40% by mass. By keeping the content of the (meth)acrylic acid ester monomer (d2) within a predetermined range, compatibility with the styrene-unsaturated carboxylic acid-based resin (A) is improved, contributing to improved mechanical strength.

[0061] 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).

[0062] <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, 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.

[0063] 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) and another monomer (d4) in dispersed particles of the rubbery polymer (D-2). The form of the containment is preferably a so-called salami-structured 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.

[0064] <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.

[0065] <Content of conjugated diene monomer units (d3)> In the present embodiment, the content of the conjugated diene monomer units (d3) in the impact resistant styrene resin (D) is preferably 0.5 to 15.0 mass%, more preferably 1.0 to 13.0 mass%, and even more preferably 4.0 to 13 mass%, based on the total amount of the impact resistant styrene resin (D). The content of the conjugated diene monomer units (d3) in the impact resistant styrene resin (D) and the styrene resin composition can be measured by the procedure described in the Examples section below (for example, measurement of the content of each monomer unit) or a method equivalent thereto.

[0066] <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, even more preferably 0.7 to 3.0 μm, even more preferably 1.0 to 2.9 μm, and particularly preferably greater than 1.0 μm and up to 2.8 μm. The impact-resistant styrene-based resin (D) is obtained by polymerizing a styrene-based monomer (d1) 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), etc. In this disclosure, the average particle size of the rubbery polymer particles (D-2) is a value measured from a cross-sectional image observed using a transmission electron microscope.

[0067] <Total Content of Rubber-Like Particles (Rubber-Like Polymer Particles (D-2) and Core-Shell Type Rubber-Like Polymer Particles (C)> The styrene-based resin composition according to the present embodiment may contain rubber particles as a rubber component. The rubber particles herein may be a general term for the rubber polymer particles (D-2) and the core-shell type rubber polymer particles (C). When the styrene-based resin composition according to the present embodiment contains rubber particles (rubber-like polymer particles (D-2) and / or core-shell type rubber-like polymer particles (C)), the total content of the rubber-like particles is preferably 0 to 18% by mass, more preferably 1 to 15% by mass, and even more preferably 3 to 15% by mass, based on the total amount of the styrene-based resin composition, from the viewpoints of heat resistance, mechanical strength, cold impact resistance, and appearance.

[0068] <<Rubber particle content>> The content of the rubber-like particles may be calculated from the charged amount or by the following method: In the styrene-based resin composition in the examples described later, the content is calculated from the content of the rubber-like particles contained in the charged resin. 1 g of a styrene-based resin composition containing rubber particles was weighed into a settling tube. The weight of the weighed resin containing the rubber particles was designated W1. Then, 20 mL of various organic (mixed) solvents, such as toluene, lower alcohols (methanol, ethanol), MEK, or chloroform, were added to the tube, which acted as a good solvent for the matrix phase and a poor solvent for the rubber particles. The mixture was then shaken at 23°C for 2 hours and then centrifuged at 4°C or below and 20,000 rpm (centrifugal acceleration: 45,100 G) for 60 minutes in a centrifuge (SS-2050A, manufactured by Sakuma Seisakusho Co., Ltd., rotor: 6B-N6L). The settling tube was slowly tilted at approximately 45 degrees, and the supernatant was decanted. The insoluble matter, including the organic solvent, was then vacuum-dried at 160°C and 3 kPa or less for 1 hour. After cooling to room temperature in a desiccator, the weight of the rubber particles was weighed, and the weight of the rubber particles after cooling to room temperature was designated W2. Then, the content of the rubber particles is calculated using the following formula (1). Toluene insolubles (%) = (W2 / W1) × 100 Formula (1) In this specification, the content of the insoluble matter in the organic solvent calculated as above is defined as the content of the rubber-like particles in the styrene-based resin composition.

[0069] "Styrene-based elastomer (E)" In a preferred aspect of this embodiment, the styrene-based resin composition preferably further contains 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 the present invention 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.

[0070] 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%. When the content of the styrene-based monomer units (e1) is 35 to 65%, the 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.

[0071] "Acrylic elastomer (F)" In a preferred aspect of this embodiment, the styrene-based resin composition preferably contains an acrylic elastomer (F) (also simply referred to as elastomer (F)). The acrylic elastomer (F) used in the styrene-based resin composition of the present invention 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.

[0072] 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.

[0073] "Ethylene-carboxylic acid ester copolymer (G)" The ethylene-carboxylic acid ester copolymer (G) in this embodiment is a copolymer resin (hereinafter simply referred to as resin (G)) containing ethylene monomer units (g1) and carboxylic acid ester monomer units (g2) as essential components, and contributes to improving the flowability, mechanical strength, and cold impact resistance of the entire styrene-based resin composition. Furthermore, if necessary, the ethylene-carboxylic acid ester copolymer (G) may contain other monomer units (g3) in addition to the ethylene monomer units (g1) and the carboxylic acid ester monomer units (g2).

[0074] The ethylene-carboxylic acid ester copolymer (G) of this embodiment is desirably a random copolymer. In this embodiment, the content of the ethylene-carboxylic acid ester copolymer (G) 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 (G) 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, and by making the content 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.

[0075] <Ethylene monomer unit (g1)> The ethylene-carboxylic acid ester copolymer (G) of this embodiment essentially contains ethylene monomer units (g1). The content of the ethylene monomer units (g1) in the ethylene-carboxylic acid ester copolymer (G) of this embodiment is 40 to 98 mass% relative to the total amount of the ethylene-carboxylic acid ester copolymer (G), 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 (g1) 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 (g1) to 50 mass% or more, the mechanical strength and cold impact resistance of the food container are improved.

[0076] <Carboxylic acid ester monomer unit (g2)> The ethylene-carboxylic acid ester copolymer (G) of this embodiment essentially contains carboxylic acid ester monomer units (g2). The content of the carboxylic acid ester monomer units (g2) in the ethylene-carboxylic acid ester copolymer (G) 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 (G). When the content of the carboxylic acid ester monomer units (g2) 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 (g2) 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 (g2) 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 unit (g2).

[0077] The carboxylic acid ester monomer unit (g2) 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 substituted with -O- or -C(=O)-, L1 is a linking group and represents -C(=O)-O- or -OC(=O)-, R 5 represents an alkyl group having 1 to 5 carbon atoms.

[0078] <Other Monomers (g3)> The ethylene-carboxylic acid ester copolymer (G) in this embodiment may further contain other monomer units (g3) as necessary in addition to the essential components of the ethylene-based monomer units (g1) and the carboxylic acid ester-based monomer units (g2). The other monomer units (g3) are not particularly limited, but examples thereof include propylene-based monomer units. By controlling the content of the other monomer units (g3) to 1% by mass or less, it is possible to minimize the deterioration of heat resistance and mechanical strength.

[0079] <Characteristics of ethylene-carboxylic acid ester copolymer (G)> The contents of the ethylene monomer units (g1), the carboxylic acid ester monomer units (g2), and the other monomer units (g3) that are blended as needed in the ethylene-carboxylic acid ester copolymer (G) in this embodiment can be quantified by infrared absorption spectroscopy. The melt flow rate of the ethylene-carboxylic acid ester copolymer (G) 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 higher is preferred from the viewpoint of moldability of the styrene-based resin composition, and a melt flow rate of 30.0 or lower is preferred from the viewpoints of compatibility with the styrene-unsaturated carboxylic acid-based resin (A) and the mechanical strength and cold impact resistance of the food container. In the present disclosure, the melt flow rate is a value measured at 190°C under a load of 21.6 N in accordance with ISO 1133. The melting point of the ethylene-carboxylic acid ester copolymer (G) 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-based 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.

[0080] <Method for producing ethylene-carboxylic acid ester copolymer (G)> The method for producing the ethylene-carboxylic acid ester copolymer (G) of the present embodiment is not particularly limited, but preferably includes a polymerization step of polymerizing an ethylene monomer (g1), a carboxylic acid ester monomer (g2), and other monomers (g3) that are blended as needed to produce a reaction product, and a recovery step of recovering the reaction product. The polymerization method for the ethylene-carboxylic acid ester copolymer (G) 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 (G). 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 (G) 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 removing volatile components.

[0081] "Inorganic particles (H)" In a preferred aspect of this embodiment, the styrene-based resin composition may contain inorganic particles (H) as needed. Addition of the inorganic particles (H) to the styrene-based resin composition serves as a foam nucleating agent during foam molding and contributes to improving the rigidity of molded articles including the styrene-based resin composition and the foam extruded sheet. Examples of inorganic particles (H) 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 (H) 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 (H) to the styrene-based resin composition. The inorganic particles (H) 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 (H) at a known high concentration may be prepared in advance and then added to the composition.

[0082] "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. "Monohydric alcohols with 10 or more carbon atoms" 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 setting the content of the monohydric alcohol having 10 or more carbon atoms to 0.01 mass% or more, gelation of the styrene-unsaturated carboxylic acid resin (A) during molding and processing can be inhibited, while by setting the content to 1.0 mass% or less, deterioration in heat resistance and generation of odor can be suppressed. By setting the content of the monohydric alcohol having 10 or more carbon atoms to 0.07 to 0.5 mass%, a sufficient gel-inhibiting effect can be obtained without particularly decreasing heat resistance.

[0083] 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 a heteroatom such as oxygen or nitrogen, and the carbon chain may contain a bond other than a single bond, such as a double bond, a triple bond, an ester bond, or an amide bond. 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 when the styrene-unsaturated carboxylic acid resin (A) and the metal salt of the ethylene-unsaturated carboxylic acid resin (B) are kneaded together and mixed in an extruder. 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.

[0084] 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.

[0085] "Additional ingredients" In addition to the resins (A) to (H) and the 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. While there are no particular restrictions on the method of addition, examples include a method in which the additives are added during polymerization, or a method in which the additives are mixed in a blender after polymerization and before melt-kneading, followed by melt-kneading in an extruder or Banbury mixer.

[0086] 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).

[0087] The higher fatty acid surfactant may be added during the polymerization of each resin, or may be added when the styrene-unsaturated carboxylic acid resin (A) and the metal salt of the ethylene-unsaturated carboxylic acid resin (B) are mixed. 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.

[0088] [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 70 to 90% by mass, more preferably 75 to 88% by mass, even 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. In this embodiment, the content of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin 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 metal salt (B) of the ethylene-unsaturated carboxylic acid resin 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, and by making it 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.

[0089] 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 1 to 18% by mass, 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 metal salt of the ethylene-unsaturated carboxylic acid resin (B) relative to the total amount (100% by mass) of the styrene-based 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 metal salt of the ethylene-unsaturated carboxylic acid resin (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.

[0090] In this embodiment, the total content of the styrene-unsaturated carboxylic acid resin (A), the metal salt of the ethylene-unsaturated carboxylic acid resin (B), and the core-shell rubbery polymer particles (C) relative to the total amount (100% by mass) of the styrene-based 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 metal salt of the ethylene-unsaturated carboxylic acid resin (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-based resin composition.

[0091] [Properties of styrene-based resin composition] The properties of the styrene-based composition in this embodiment are described below. <Method of producing styrene-based resin composition> The styrene-based resin composition in this embodiment may be produced by melt-kneading the raw materials in a predetermined composition ratio, or may be produced using a masterbatch. For example, the styrene resin composition can be produced by melt-kneading using a general twin-screw extruder. The resin temperature during melt-kneading is preferably 220°C to 280°C, more preferably 225°C to 275°C, and even more preferably 230°C to 270°C. By setting the resin temperature at 220°C or higher, the resin can be kneaded in a sufficiently molten state, which ultimately contributes to improving the mechanical strength of the composition.

[0092] The styrene-based resin composition of the present embodiment can also be produced by diluting and kneading a masterbatch containing at least two resins selected from the group consisting of the styrene-unsaturated carboxylic acid-based resin (A), the metal salt of the ethylene-unsaturated carboxylic acid-based resin (B), and the core-shell type rubbery polymer particles (C) with the styrene-unsaturated carboxylic acid-based resin (A). The present disclosure relates to a masterbatch for producing the styrene-based resin composition, and the masterbatch contains at least two or more resins selected from the group consisting of a styrene-unsaturated carboxylic acid-based resin (A), a metal salt of an ethylene-unsaturated carboxylic acid-based resin (B), and core-shell rubbery polymer particles (C). With respect to the total amount (100% by mass) of the masterbatch, the content of the styrene-unsaturated carboxylic acid resin (A) is 0 to 70% by mass, preferably 2 to 68% by mass, more preferably 3 to 65% by mass, and most preferably 4 to 63% by mass. With respect to the total amount (100% by mass) of the masterbatch, the content of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin is 0 to 65% by mass, preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and most preferably 17 to 50% by mass. The content of the core-shell type rubber polymer particles (C) relative to the total amount (100% by mass) of the masterbatch is 0 to 68% by mass, preferably 10 to 65% by mass, more preferably 15 to 50% by mass, and most preferably 20 to 55% by mass.

[0093] <Heat resistance of styrene-based resin composition> In this embodiment, the Vicat softening temperature of the styrene-based resin composition is preferably 105°C or higher, more preferably 110°C or higher, and even more preferably 115°C or higher. By setting the Vicat softening temperature to 105°C or higher, it is possible to obtain sheets and containers that are suitable for cooking in a general microwave oven of around 500W, and by setting the Vicat softening temperature to 115°C or higher, they can withstand cooking in a high-power commercial microwave oven of 1000W or higher found in convenience stores, etc. The Vicat softening temperature can be measured in accordance with ISO306 under conditions of a load of 50N and a heating rate of 50°C / h.

[0094] [Biaxially oriented sheet] Another aspect of the present disclosure is a biaxially oriented sheet formed using the styrene-based resin composition of the present disclosure described above. A commonly known method can be used to produce a biaxially oriented sheet. 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 styrene-based resin composition formed into a plate shape can be heated to a temperature about 10 to 40°C above the Vicat softening temperature of the composition and then sequentially or simultaneously biaxially stretched in a tenter.

[0095] The biaxially oriented sheet of the present embodiment is preferably stretched at a ratio of about 1.3 to 7.0 in the MD direction and about 1.3 to 7.0 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.

[0096] 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.

[0097] [Extruded sheet] Another aspect of the present disclosure provides an extruded sheet formed using the styrene-based resin composition of the present invention described above. The extruded sheet may be either non-foamed or foamed. A commonly known method can be used to produce the extruded sheet. A method for producing a non-foamed extruded sheet can be a method using a single-screw or twin-screw extruder equipped with a T-die and a sheet take-up device with a uniaxial or biaxial stretching machine. A method for producing a foamed extruded sheet can be a method using an extrusion foaming machine equipped with a T-die or circular die.

[0098] <Foam extruded sheet> The foamed extruded sheet of the present invention 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 in 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. 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 a combination of two or more of the above foaming agents can also be used. 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 styrene-based resin composition to be foamed. A foaming agent in the range of 2.0 to 5.0 mass% provides excellent resin plasticization and foamability.

[0099] 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., as exemplified 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%, based on 100 mass% of the total amount of the styrene-based resin composition. By adjusting 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 the foam nucleating agent has been dispersed by extrusion kneading are added.

[0100] 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 3 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 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 75% or more, 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, fragile open cells are reduced, and therefore a foamed extruded sheet with excellent strength can be obtained.

[0101] 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. The foamed extruded sheet of the present invention 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 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.

[0102] A preferred foam extruded sheet of this embodiment is a laminate having a foam layer of a styrene-based resin composition, a polystyrene layer provided on at least one side of the foam layer, and a polypropylene layer provided on the lining of the polystyrene layer. This structure provides a container with excellent oil resistance because the polypropylene layer is provided as the outermost layer that may come into contact with food, etc. Furthermore, because the foam layer of the styrene-based resin composition contains styrene-based monomer units, a container with excellent compatibility and adhesion with the polystyrene layer can be provided.

[0103] [Secondary molded product] In this embodiment, the molded article obtained by thermoforming the foamed extruded sheet is suitable for use as a container for microwave-heated food. Thermoforming methods include vacuum forming and pressure forming. Such thermoforming methods are preferred because they allow containers to be obtained continuously in a short period of time. When thermoforming a laminated sheet obtained by thermocompression bonding the above-mentioned laminate film, it is preferable to mold the resulting molded article so that the polyolefin resin film with excellent oil resistance is located inside the resulting molded article. [Example]

[0104] The present disclosure will now be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The resins, extruded sheets, and the like used in the examples and comparative examples were analyzed and evaluated as follows.

[0105] "Evaluation methods for each resin, resin composition, and sheet body used in Examples and Comparative Examples" 1. Composition evaluation of each resin and resin composition (1-1) Measurement of the content of each monomer unit The content of each monomer unit contained in the 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.

[0106] (1-2) Measurement of the content of monohydric alcohols having 10 or more carbon atoms in each resin composition The content of monohydric alcohols having 10 or more carbon atoms in the entire 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.

[0107] 2. Characterization of each resin and 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.

[0108] (2-2) Melt mass flow rate (MFR) measurement The melt mass flow rate (g / 10 min) of each resin used in the examples and comparative examples was measured in accordance with ISO1133 under conditions of 200°C and a load of 49 N or 190°C and a load of 21.6 N.

[0109] (2-3) Measurement of Vicat softening temperature The Vicat softening temperature of each resin and 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. The heat resistance of the resin compositions produced in the examples and comparative examples was evaluated according to the following evaluation criteria. -Evaluation criteria- A: Vicat softening temperature is 114°C or higher B: Vicat softening temperature is lower than 114°C and 110°C or higher C: Vicat softening temperature is lower than 110℃ and 105℃ or higher

[0110] (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.

[0111] (2-5) Measurement of average particle size and content The average particle size (μm) of the core-shell type rubber polymer particles (C) or the rubber-like polymer particles (D-2) contained in the impact-resistant styrene-based resin (D) is determined by the following formula (1) for 200 rubber-like polymer particles observed by cross-sectional observation using a transmission electron microscope: Formula (1): Average particle size = 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. The content of the core-shell type rubber polymer particles (C) or the impact resistant styrene resin (D) in each resin-styrene resin composition was calculated by the measurement method for the <content of rubber particles> described in the specification.

[0112] (3) Method for measuring the degree of neutralization The degree of neutralization of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin obtained in the Examples section was measured by infrared absorption spectroscopy. -1 Peak height A and 2915 cm-1 The peak height B of the metal salt (B) of the ethylene-unsaturated carboxylic acid resin is measured after contacting the sample with hydrochloric acid containing alcohol to remove the metal ions in the resin (B), and the infrared absorption spectrum is measured. -1 Peak heights of C and 2915 cm -1 The peak height D was determined, and the value calculated using the following formula (2) was taken as the degree of neutralization (%). Formula (2): 100-100×(A / B) / (C / D)

[0113] 3. Properties and physical characteristics of biaxially oriented sheets (3-1) Heat resistance of biaxially oriented sheets The biaxially stretched sheets prepared in the examples and comparative examples were cut into strips of 10 cm x 1.5 cm and placed in an oven set at 110°C for 60 minutes. The deformation of the sheets was then visually observed, and the heat resistance was evaluated based on the thermal deformation as follows. Specifically, the dimensional change was evaluated according to the following formula (3) by measuring the change in length of 10 cm before and after thermal deformation, and the evaluation criteria were as follows: Equation (3): Dimensional change (%) = (MD length of sheet after 60 minutes in oven - MD length of sheet before oven) / MD length of sheet before oven -Evaluation criteria- A: Dimensional change is 0.5% or less B: Dimensional change is greater than 0.5% and less than 3.0% C: Dimensional deformation is greater than 3.0%

[0114] (3-2) Bending resistance of biaxially oriented sheets The biaxially stretched sheets prepared in the Examples and Comparative Examples were cut into 10 cm x 1.5 cm pieces with the MD direction as the long side direction, and the MIT folding endurance of the produced sheets was measured in accordance with JIS P8115. The folding endurance of the extruded sheets was evaluated according to the following evaluation criteria. -Evaluation criteria- A...MIT folding endurance over 400 times B: MIT folding endurance: 100 times or more but less than 400 times C...MIT folding endurance less than 100 times

[0115] (3-3) Impact resistance of biaxially oriented sheets (impact resistance properties at room temperature (23°C)) The biaxially stretched sheets prepared in the Examples and Comparative Examples were cut into 8 cm x 8 cm pieces, and the film impact was measured using a Toyo Seiki Film Impact Tester (No. 195), with the n8 average value recorded. The dart impact strength of the extruded sheets was evaluated according to the following criteria. -Evaluation criteria- A...6.0 kg cm or more B: 4.0 kg·cm or more and less than 6.0 kg·cm C···Less than 4.0 kg·cm

[0116] (3-4) Impact resistance of biaxially oriented sheets (impact resistance properties under low temperature conditions) The biaxially oriented sheets prepared in the Examples and Comparative Examples were cut into 6 cm x 6 cm pieces and cooled in a thermostatic chamber set to -30°C for at least 2 hours, after which the drop weight impact strength was immediately measured using a DuPont impact tester (No. 451) manufactured by Toyo Seiki Co., Ltd. The drop weight had a mass of 0.15 kg, a radius of the tip of the impact center of 6.3 mm, and a radius of the impact center support base of 9.4 mm. The drop weight impact strength was calculated as the value at 50% fracture, calculated as (mass of the drop weight 0.15 kg) x (height in cm), and evaluated according to the following criteria. -Evaluation criteria- A...More than 4.0 kg cm B...More than 2.0kg·cm but not more than 4.0kg·cm C...1.0 kg cm or less

[0117] 4. Properties and physical characteristics of extruded sheets (4-1) Heat resistance of extruded sheets The extruded sheets prepared in the examples and comparative examples were cut into strips of 10 cm x 1.5 cm and placed in an oven set at 110°C for 60 minutes. The deformation of the sheets was then visually observed, and the heat resistance was evaluated based on the thermal deformation as follows. Specifically, the dimensional change was evaluated by measuring the amount of change in length of 10 cm before and after thermal deformation using the following formula (4) and by the following evaluation criteria. Equation (4): Dimensional change (%) = (MD length of sheet after 60 minutes in oven - MD length of sheet before oven) / MD length of sheet before oven -Evaluation criteria- A: Dimensional change is 0.5% or less B: Dimensional change is greater than 0.5% and less than 3.0% C: Dimensional deformation is greater than 3.0%

[0118] (4-2) Bending resistance of extruded sheets The extruded sheets prepared in the examples and comparative examples were cut into 100 mm x 15 mm pieces with the MD direction as the long side direction, and the MIT folding endurance of the produced sheets was measured in accordance with JIS P8115. The folding endurance of the extruded sheets was evaluated according to the following evaluation criteria. -Evaluation criteria- A...MIT folding endurance over 200 times B: MIT folding endurance: 100 times or more but less than 200 times C...MIT folding endurance less than 100 times

[0119] (4-3) Impact resistance of extruded sheet (impact resistance at room temperature (23°C)) The extruded sheets prepared in the examples and comparative examples were cut into 8 cm x 8 cm pieces, and the film impact was measured using a Toyo Seiki Film Impact Tester (No. 195), with the n8 average value recorded. The dart impact strength of the extruded sheets was evaluated according to the following criteria. -Evaluation criteria- A...8.0 kg cm or more B: 5.0 kg·cm or more and less than 8.0 kg·cm C···Less than 5.0 kg·cm

[0120] (4-4) Impact resistance of extruded sheets (impact resistance properties under low temperature conditions) The extruded sheets prepared in the Examples and Comparative Examples were cut into 6 cm x 6 cm pieces and cooled in a thermostatic chamber set to -30°C for at least 2 hours, after which the drop weight impact strength was immediately measured using a DuPont impact tester (No. 451) manufactured by Toyo Seiki Co., Ltd. The drop weight had a mass of 0.15 kg, a radius of the tip of the impact center of 6.3 mm, and a radius of the impact center support base of 9.4 mm. The drop weight impact strength was calculated as the value at 50% fracture, calculated as (mass of the drop weight 0.15 kg) x (height in cm), and evaluated according to the following criteria. -Evaluation criteria- A...More than 6.0 kg cm B...More than 2.0kg·cm and less than 6.0kg·cm C...2.0 kg cm or less

[0121] 5. Properties and physical characteristics of foam extruded sheets (5-1) Basis weight of foam extrusion sheet (g / m 2 ) 20 mm from each end of the foamed extruded sheet produced in the Examples and Comparative Examples was removed to prepare 0.10 x 0.10 m sheet pieces. The mass of each piece was measured and the resulting sheet was cut into 1.0 m pieces. 2 The mass converted to basis weight (g / m 2 ) was calculated as

[0122] (5-2) Closed cell ratio of foamed extruded sheet The closed cell content of the foamed extruded sheet was measured in accordance with JIS K7138.

[0123] (5-3) Formability of foam extrusion sheets Test pieces measuring 250 mm x 250 mm were cut from the foamed extruded sheets produced in the Examples and Comparative Examples and left at 23±3°C and 50±5% relative humidity for 20 days. Then, using a Soken sheet container molding machine, the foamed extruded sheets were sandwiched between the fixed frame of the sheet molding machine and heated for 15 seconds at an average heater temperature of 230°C and an ambient temperature of 160°C. The fixed frame was then slid into a cup-shaped mold (temperature: 40°C) with a diameter of 10 cm and a depth of 3 cm or 6 cm, and vacuum molding was performed to produce 100 molded pieces. The sides of these molded pieces were visually inspected for tears, and the number of molded pieces that could be molded without tearing was counted. The moldability of the foamed extruded sheets was evaluated according to the following criteria. -Evaluation criteria- A: The number of molded bodies that could be molded was 90 or more. B: The number of moldable molded bodies is 70 or more but less than 90 C: The number of moldable compacts was less than 70

[0124] (5-4) Heat resistance of foam extrusion sheets The foamed extruded sheets produced in the examples and comparative examples were cut into strips of 10 cm x 1.5 cm with the MD direction as the long side, and placed in an oven set at 110°C for 60 minutes, after which the deformation of the foamed extruded sheets was measured and the heat resistance was evaluated based on the thermal deformation as follows. Specifically, the above-mentioned dimensional change was measured by measuring the amount of change in length of 10 cm before and after thermal deformation using the following formula (5), and the n5 average was used as the value. Equation (5): Dimensional change (%) = (MD length of foamed extruded sheet after being placed in the oven for 60 minutes - MD length of foamed extruded sheet before being placed in the oven) / MD length of foamed extruded sheet before being placed in the oven -Evaluation criteria- A: Dimensional change is 0.5% or less B: Dimensional change is greater than 0.5% and less than 3.0% C: Dimensional deformation is greater than 3.0%

[0125] (5-5) Bending strength of foam extruded sheet The foamed extruded sheets produced in the examples and comparative examples were cut into pieces of 8 cm x 2.5 cm and subjected to bending tests under the following conditions using a Shimadzu tabletop precision universal testing machine (Autograph AGS-5kNX) manufactured by Shimadzu Corporation. The area enclosed by the stress-strain curve obtained from the bending test (= the amount of energy absorbed until the test piece broke) was determined, and the bending strength of the foamed extruded sheets was evaluated according to the following evaluation criteria. -Measurement conditions- Distance between fulcrums: 25mm Indenter: R=2 Test speed: 200 mm / min -Evaluation criteria- A: The area of ​​the stress-strain curve is 1.5 MPa mm or more B: The area of ​​the stress-strain curve is 1.0 MPa·mm or more and less than 1.5 MPa·mm C: The area under the stress-strain curve is less than 1.0 MPa mm

[0126] (5-6) Surface impact of foam extrusion sheet (surface impact properties at room temperature (23°C)) The foamed extruded sheets produced in the examples and comparative examples were cut into 8 cm x 8 cm pieces, and the film impact was measured using a film impact tester (No. 195) manufactured by Toyo Seiki Seisaku-sha, with the n8 average value being used. The dart impact strength of the foamed extruded sheets was evaluated according to the following evaluation criteria. -Evaluation criteria- A...4.0 kg cm or more B: 2.0 kg·cm or more and less than 4.0 kg·cm C···Less than 2.0 kg·cm

[0127] (5-7) Surface Impact of Extruded Foam Sheet (Surface Impact Properties under Low Temperature Conditions) The foamed extruded sheets produced in the Examples and Comparative Examples were cut into 6 cm x 6 cm pieces and cooled in a thermostatic chamber set to -30°C for at least 2 hours, after which the drop weight impact strength was immediately measured using a DuPont impact tester (No. 451) manufactured by Toyo Seiki Co., Ltd. The mass of the falling weight was 0.5 kg, the radius of the tip of the impact center was 6.3 mm, and the radius of the impact center support base was 9.4 mm. The drop weight impact strength was calculated as the value at 50% fracture, calculated as (mass of the falling weight 0.15 kg) x (height in cm), and evaluated according to the following criteria. -Evaluation criteria- A...More than 1.0 kg cm B...More than 0.5kg·cm but not more than 1.0kg·cm C...0.5kg cm or less

[0128] 6. Food container evaluation method The food containers obtained in each of the Examples and Comparative Examples were evaluated according to the following methods. (6-1) 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."

[0129] (6-2) Heat mold retention 30 ml of water was placed in a food container prepared using the method described below, and heated in a 500 W microwave oven for 3 minutes, and the rate of change in the bottom surface was measured. -Evaluation criteria- A: Rate of change is less than 3% B: Change rate is 3% or more but less than 5% C: Change rate is 5% or more

[0130] (6-3) 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. (6-4) 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.

[0131] "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): Resin A in the table> -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.

[0132] -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.

[0133] [Table 1]

[0134] <Production example of metal salt of ethylene-unsaturated carboxylic acid resin (B): Resin B in the table> -Preparation of metal salt of ethylene-unsaturated carboxylic acid resin (B-1)- Ethylene, methacrylic acid, and t-butyl peroxy-2-ethylhexanoate as a polymerization initiator were fed into a tubular reactor. After polymerization proceeded, the mixture was reacted with zinc oxide and then continuously fed into a devolatilizer connected to a single-screw extruder, which removed volatile components such as unreacted monomers and polymerization solvents. 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, and volatile components such as unreacted monomers and polymerization solvents were devolatilized. The resin was recovered as pellets. The physical properties of the ethylene-(meth)acrylic acid-based resin metal salt (B-1) (hereinafter referred to as resin (B-1)) obtained by the above-mentioned analytical methods are shown in Table 2 below.

[0135] -Preparation of Metal Salts of Ethylene-Unsaturated Carboxylic Acid Resins (B-2) to (B-7)- Resins (B-2) to (B-7) were prepared by adjusting the feed amount of each monomer and the polymerization conditions in the same manner as for the resin (B-1). The compositions of the obtained resins (B-2) to (B-7) are shown in Table 2.

[0136] [Table 2]

[0137] <Production example of core-shell type rubber polymer particles (C): Resin C in the table> -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.

[0138] -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.

[0139] -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.

[0140] -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.

[0141] [Table 3]

[0142] <Manufacturing example of impact-resistant styrene resin (D): Resin D in the table> -Preparation 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.

[0143] -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 (D2) and (D3) are shown in Table 4.

[0144] [Table 4]

[0145] <Styrene-based elastomer (E) used in the examples: Resin E in the table> In the examples of this specification, the following two types of styrene-based elastomer (E) were used. (E-1) Asahi Kasei styrene-ethylene-butylene-butadiene block copolymer Tuftec P2000 (E-2) Styrene-ethylene-butylene block copolymer Tuftec H1043 manufactured by Asahi Kasei Corporation

[0146] <Acrylic elastomer (F) used in the examples: Resin F in the table> In the examples of this specification, the following two types of acrylic elastomer (F) were used. (F-1) Kuraray Clarity LA2270 (F-2) Kuraray Clarity LK9243

[0147] <Production example of ethylene-carboxylic acid ester copolymer (G): Resin G in the table> Preparation of ethylene-carboxylic acid ester copolymer (G-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 (G-1) (hereinafter referred to as resin (G-1)) obtained by the above-mentioned analytical methods are shown in Table 5 below.

[0148] -Preparation of ethylene-carboxylic acid ester copolymers (G-2) and (G-3)- Resins (G-2) and (G-3) were prepared in the same manner as for Resin (G-1) by adjusting the type of each monomer, the feed amount of each monomer, and the polymerization conditions. The compositions of the resulting resins (G-2) and (G-3) are shown in Table 5.

[0149] [Table 5]

[0150] <Production Example of Styrene-Based Resin Composition> The detailed production methods of the styrene resin composition and the foamed extruded sheet 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) listed in Table 1, 10.0% by mass of the metal salt of the ethylene-unsaturated carboxylic acid resin (B) (resin B-1) listed in Table 2, and 0.12% by mass of Fine Oxocol 180 (external additive) was used. The mixture was kneaded, extruded, and pelletized using a twin-screw extruder TEM26SS manufactured by Shibaura Machine Co., Ltd. to obtain a styrene-based 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. Table 6 shows the evaluation results of the properties of the styrene-based resin composition [1].

[0151] - Manufacturing of biaxially oriented sheets - (For evaluating heat resistance and bending resistance) The styrene-based resin composition [1] obtained above was processed by press molding into a 10 cm x 10 cm x 0.7 mm plate. The plate was preheated at 155°C for 10 minutes in a batch biaxial stretching machine EX6-S1 manufactured by Toyo Seiki Seisakusho, with the chuck distance set to 85 mm, and then biaxially stretched simultaneously at an X-axis magnification of 3 and a Y-axis magnification of 1.4 to obtain a heat-shrinkable film with a thickness of approximately 0.15 mm. The stretching speed was 195.5 mm / min in the X-axis direction and 39 mm / min in the Y-axis direction. The evaluation results of the obtained biaxially stretched sheet [1] are shown in Table 6.

[0152] (For impact resistance evaluation) The styrene-based resin composition [1] obtained above was processed by press molding into a plate measuring 10 cm x 10 cm x 1.2 mm. The plate was preheated at 155°C for 10 minutes in a batch biaxial stretching machine EX6-S1 manufactured by Toyo Seiki Seisaku-sho, with the chuck distance set to 85 mm, and then biaxially stretched simultaneously at an X-axis magnification of 2.5 and a Y-axis magnification of 2.5 to obtain a heat-shrinkable film with a thickness of approximately 0.15 mm. The stretching speed was 212.5 mm / min in both the X-axis and Y-axis directions. The evaluation results of the obtained biaxially stretched sheet [1] are shown in Table 6.

[0153] -Extruded sheet manufacturing- The styrene-based resin composition [1] obtained above was fed into an extruder equipped with a vacuum vent and capable of nitrogen purge. The maximum cylinder temperature of the extruder was set to 250°C. The resin composition extruded from the T-die was wound on a mirror-finished metal roll, and a 0.25 mm thick extruded sheet [1] was produced by adjusting the winding speed and the resin extrusion rate. The evaluation results of the obtained extruded sheet [1] are shown in Table 6.

[0154] -Manufacturing foam extrusion sheets and food containers- 100 parts by mass of the styrene-based resin composition [1] obtained above and 1.0 part by mass of talc (Hi-Filler #12 manufactured by Matsumura Sangyo Co., Ltd.) as inorganic particles (H) were dry-blended and fed into an extruder. The maximum cylinder temperature of the extruder was set to 250°C. A mixed butane (65 / 35 mass ratio of isobutane / normal butane) was injected into the melt-kneaded resin composition at 4.0 parts by mass per 100 parts of the styrene-based resin composition [1] as a blowing agent, and the mixture was extruded into a cylindrical shape through an annular die for foaming. 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]. A 910 ml bowl-shaped food container (opening diameter 19.5 cm) [1] was produced using the foamed extruded sheet [1]. The food containers were heated for 20 seconds at a heating zone of 220°C using a Soken sheet container molding machine, and then placed in a food container mold with a ratio (d / r) of the depth d of the recess to the opening diameter r of the recess of 0.75, and vacuum formed into food containers [1]. The evaluation results are shown in Table 6-1.

[0155] [Examples 2 to 21] Styrenic resin compositions [2] to

[21] , biaxially oriented sheets [2] to

[21] , extruded sheets [2] to

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

[21] were obtained in the same manner as in Example 1, except that the formulations were changed as shown in Tables 6-1 to 6-3 below. The evaluation results of the obtained styrenic resin compositions [2] to

[21] , biaxially oriented sheets [2] to

[21] , extruded sheets [2] to

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

[21] , as well as the evaluation results of foamed containers obtained by secondary molding of the foamed extruded sheets, are shown in Tables 6-1 to 6-3.

[0156] [Examples 22 to 25] Styrenic resin compositions

[22] to

[25] , biaxially oriented sheets

[22] to

[25] , and extruded sheets

[22] to

[25] were obtained in the same manner as in Example 1, except that the formulation was changed as shown in the following Table 7. The evaluation results of the obtained styrenic resin compositions

[22] to

[25] , biaxially oriented sheets

[22] to

[25] , and extruded sheets

[22] to

[25] are shown in Table 7.

[0157] [Comparative Examples 1 to 3] Resin compositions, biaxially oriented sheets, extruded sheets, and foamed extruded sheets were obtained in the same manner as in Example 1, except that the mixing formulation was changed as shown in Table 8 below. The evaluation results of the obtained resin compositions and foamed sheets, and the evaluation results of foamed containers obtained by secondary molding of the foamed sheets are shown in Table 8. In Comparative Examples 3 and 4, the compatibility of the entire composition was poor, and it was not possible to mold a biaxially oriented sheet, extruded sheet, foamed extruded sheet, or foamed container.

[0158] [Table 6-1]

[0159] [Table 6-2]

[0160] [Table 6-3]

[0161] [Table 7]

[0162] [Table 8]

Claims

1. A styrene-based resin composition comprising 60 to 97 mass % of a styrene-unsaturated carboxylic acid-based resin (A) and 3 to 20 mass % of a metal salt of an ethylene-unsaturated carboxylic acid-based resin (B).

2. The styrenic composition according to claim 1, further comprising more than 0 to 20 mass% of core-shell type rubbery polymer particles (C).

3. The styrenic resin composition according to claim 1, further comprising one or more selected from the group consisting of an impact-resistant styrenic resin (D), a styrenic elastomer (E), an acrylic elastomer (F), and an ethylene-carboxylic acid ester copolymer (G).

4. 3. The styrene-unsaturated carboxylic acid resin composition according to claim 1, wherein the styrene-unsaturated carboxylic acid resin (A) is a copolymer containing a styrene monomer unit (a1) and a (meth)acrylic acid monomer unit (a2-1), and the (meth)acrylic acid monomer unit (a2-1) is contained in an amount of 2 to 15 mass% based on the total amount of the styrene-unsaturated carboxylic acid resin (A).

5. 3. The styrene-based resin composition according to claim 1, wherein the styrene-unsaturated carboxylic acid-based resin (A) comprises a (meth)acrylic acid monomer unit (a2-1) and a (meth)acrylic acid ester monomer unit (a2-2).

6. 3. The styrene-based resin composition according to claim 1, wherein the metal salt of the ethylene-unsaturated carboxylic acid-based resin (B) essentially contains an ethylene monomer unit (b1) and an unsaturated carboxylic acid-based monomer unit (b2).

7. 3. The styrene-based resin composition according to claim 1, wherein the metal ion contained in the metal salt of the ethylene-unsaturated carboxylic acid-based resin (B) is a zinc ion.

8. A masterbatch for producing the styrene-based resin composition according to claim 1 or 2, A masterbatch containing at least two or more resins selected from the group consisting of a styrene-unsaturated carboxylic acid resin (A), a metal salt of an ethylene-unsaturated carboxylic acid resin (B), and core-shell type rubber polymer particles (C).

9. An extruded sheet obtained by molding the styrene-based resin composition according to claim 1 or 2.

10. 3. The styrene-based resin composition according to claim 1, further comprising inorganic particles (H) in an amount of 0.05 to 3.0% by mass relative to the total amount of the styrene-based resin composition.

11. A foamed extruded sheet obtained by molding the styrene-based resin composition according to claim 1 or 2.

12. A food container formed by molding the foamed extruded sheet according to claim 11.

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