Biaxially oriented sheet and manufacturing method thereof, multilayer sheet, and molded product

Abstract

To provide a biaxially oriented sheet having excellent impact resistance. [Solution] A biaxially oriented sheet containing a styrene-based resin, wherein the ethylbenzene content in the biaxially oriented sheet is 245 mass ppm or less based on the total mass of the biaxially oriented sheet.

Description

[Technical Field]

[0001] The present disclosure relates to a biaxially oriented sheet and a method for producing the same, a multilayer sheet, and a molded article. [Background technology]

[0002] Biaxially oriented sheets containing styrene-based resins are used for food packaging containers, etc. There have been attempts to impart desired properties to biaxially oriented sheets containing styrene-based resins by adjusting the type of styrene-based resin constituting the biaxially oriented sheet.

[0003] For example, Patent Document 1 discloses that a biaxially stretched polystyrene resin sheet made of a resin composition containing a polystyrene resin as a main component has a shear storage modulus (G') of 1.0 × 10 at 160°C calculated using a parallel plate vibration rheometer. 5 The biaxially stretched polystyrene resin sheet is characterized by having a tensile strength of 100 Pa or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-157048 Summary of the Invention [Problem to be solved by the invention]

[0005] A biaxially oriented sheet is sometimes required to have excellent impact resistance. An object of the present disclosure is to provide a biaxially oriented sheet having excellent impact resistance. [Means for solving the problem]

[0006] During the production of styrene-based resins, ethylbenzene may be used as a raw material for styrene monomer, and unreacted ethylbenzene may remain. Therefore, ethylbenzene may also be contained in biaxially oriented sheets containing styrene-based resins. The present inventors have found that the impact resistance of biaxially oriented sheets can be improved by adjusting the ethylbenzene content in the biaxially oriented sheets. In some aspects, the present disclosure provides the following [1] to [9]. [1] A biaxially oriented sheet containing a styrene-based resin, wherein the content of ethylbenzene in the biaxially oriented sheet is 245 mass ppm or less, based on the total mass of the biaxially oriented sheet. [2] The biaxially oriented sheet according to [1], wherein the content of ethylbenzene in the biaxially oriented sheet is 150 ppm by mass or more, based on the total mass of the biaxially oriented sheet. [3] The biaxially oriented sheet according to [1] or [2], wherein the total content of volatile organic compounds in the biaxially oriented sheet is 600 mass ppm or less, based on the total mass of the biaxially oriented sheet. [4] The biaxially oriented sheet according to any one of [1] to [3], which is derived from biomass. [5] A multilayer sheet comprising a first layer made of the biaxially oriented sheet according to any one of [1] to [4] and a second layer provided on the first layer, wherein the second layer is an anti-fogging layer. [6] A molded article obtained by molding the biaxially oriented sheet according to any one of [1] to [4] or the multilayer sheet according to [5]. [7] A method for producing a biaxially oriented sheet using a styrene-based resin as a raw material, wherein the ethylbenzene content in the styrene-based resin is 100 mass ppm or less based on the total mass of the styrene-based resin. [8] The method for producing a biaxially oriented sheet according to [7], wherein the total content of volatile organic compounds in the styrene-based resin is 600 mass ppm or less, based on the total mass of the styrene-based resin. [9] The method for producing a polystyrene-based resin sheet according to [7] or [8], wherein the styrene-based resin is a biomass-derived styrene-based resin. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, a biaxially oriented sheet having excellent impact resistance is provided. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0009] The biaxially oriented sheet according to one embodiment contains a styrene-based resin. A styrene-based resin is a polymer containing mainly styrene-based monomers as monomer units. Examples of the styrene-based resin include a styrene-based resin that has been modified with rubber (hereinafter also referred to as a "rubber-modified styrene-based resin") and a styrene-based resin that has not been modified with rubber (hereinafter also referred to as a "non-rubber-modified styrene-based resin").

[0010] The styrene-based resin preferably includes a non-rubber-modified styrene-based resin. The styrene-based monomer contained as a monomer unit in the non-rubber-modified styrene-based resin may be styrene (unsubstituted styrene) or a substituted styrene. Unsubstituted styrene refers to styrene having no substituents (styrene having no functional groups other than one vinyl group). Substituted styrene refers to styrene in which at least one of the hydrogen atoms on the benzene ring and the hydrogen atoms constituting the vinyl group in styrene has been substituted with a substituent such as an alkyl group or a halogen group.

[0011] Examples of substituted styrenes include alkylstyrenes, halogenated styrenes, nitrostyrene, acetylstyrene, and methoxystyrene.

[0012] The alkylstyrene may be, for example, an alkylstyrene having 1, 2, or 3 alkyl groups. Examples of alkylstyrenes having one alkyl group include α-alkylstyrenes such as α-methylstyrene, o-alkylstyrenes such as o-methylstyrene and o-ethylstyrene, m-alkylstyrenes such as m-methylstyrene and m-ethylstyrene, and p-alkylstyrenes such as p-methylstyrene, p-ethylstyrene, and p-tert-butylstyrene.

[0013] Examples of alkylstyrenes having two alkyl groups include 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, and 4,α-dimethylstyrene (1-methyl-4-isopropenylbenzene).An example of an alkylstyrene having three alkyl groups is 2,4,6-trimethylstyrene.

[0014] Examples of halogenated styrenes include fluorostyrene, chlorostyrene, dichlorostyrene, bromostyrene, dibromostyrene, and iodostyrene.

[0015] The non-rubber-modified styrene-based resin may contain, as a monomer unit, one or more of the above-mentioned styrene-based monomers. The non-rubber-modified styrene-based resin preferably contains, as a monomer unit, at least one of styrene and α-methylstyrene, and more preferably contains styrene.

[0016] The content of styrene (styrene units) in the non-rubber-modified styrene-based resin may be 80 mass% or more, 90 mass% or more, 95 mass% or more, or 98 mass% or more, based on the total mass of the monomer units contained in the non-rubber-modified styrene-based resin, and may be 100 mass% or less.

[0017] The non-rubber-modified styrene-based resin may contain only styrene-based monomers as monomer units, or may contain other monomers besides styrene-based monomers. The content of the styrene-based monomer may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more, or 100% by mass or less, based on the total mass of the monomer units contained in the non-rubber-modified styrene-based resin.

[0018] Examples of other monomers that can be contained as monomer units in the non-rubber-modified styrene-based resin include unsaturated carboxylic acids, unsaturated carboxylic acid esters, carboxylic acid anhydrides, vinyl carboxylates, and (meth)acrylonitrile.

[0019] Examples of unsaturated carboxylic acids include (meth)acrylic acid, fumaric acid, maleic acid, and itaconic acid. Examples of unsaturated carboxylic acid esters include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and n-butyl (meth)acrylate. Examples of carboxylic acid anhydrides include maleic anhydride. Examples of vinyl carboxylates include vinyl acetate. The non-rubber-modified styrene-based resin may contain one or more of these monomers as monomer units.

[0020] In the non-rubber-modified styrene-based resin, the content of other monomers than the styrene-based monomer may be 0% by mass or more, and may be 10% by mass or less, 8% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, based on the total mass of the monomer units contained in the non-rubber-modified styrene-based resin.

[0021] The non-rubber-modified styrene-based resin may be a homopolymer or a copolymer. A homopolymer contains only one type of styrene-based monomer as a monomer unit. A copolymer may contain only two or more types of styrene-based monomer as a monomer unit, or may contain one or more types of styrene-based monomer and one or more other monomers. The non-rubber-modified styrene-based resin is preferably a homopolymer or copolymer containing only a styrene-based monomer as a monomer unit, and more preferably a homopolymer containing only one type of styrene-based monomer as a monomer unit (a homopolymer of a styrene-based monomer). The homopolymer of a styrene-based monomer may be a homopolymer of styrene. A homopolymer of styrene is also called general-purpose polystyrene (GPPS).

[0022] The content of the non-rubber-modified styrene-based resin in the biaxially oriented sheet may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 98% by mass or more, based on the total mass of the biaxially oriented sheet. The content of the non-rubber-modified styrene-based resin in the biaxially oriented sheet may be 100% by mass or less, or 99.5% by mass or less, based on the total mass of the biaxially oriented sheet.

[0023] The non-rubber-modified styrenic resin may comprise a first non-rubber-modified polystyrene resin and a second non-rubber-modified polystyrene resin different from the first non-rubber-modified polystyrene resin. The specific embodiments (types and amounts of monomers contained as monomer units) of the first non-rubber-modified polystyrene resin and the second non-rubber-modified polystyrene resin can be those described above as specific embodiments of the non-rubber-modified polystyrene resin. In this case, the phrase "based on the total mass of the monomer units contained in the non-rubber-modified styrenic resin" should be read as "based on the total mass of the monomer units contained in the first non-rubber-modified styrenic resin" or "based on the total mass of the monomer units contained in the second non-rubber-modified styrenic resin."

[0024] From the viewpoint of excellent moldability during production of a biaxially oriented sheet, the melt mass flow rate of the first non-rubber-modified styrene-based resin may be 1 g / 10 min or more, 2 g / 10 min or more, 2.2 g / min or more, or 2.5 g / 10 min or more, and may be 7 g / 10 min or less, 6.8 g / 10 min or less, 6.5 g / 10 min or less, 6.2 g / 10 min or less, 6 g / 10 min or less, 5.8 g / 10 min or less, 5.5 g / 10 min or less, 5.2 g / 10 min or less, 5 g / 10 min or less, 4.8 g / 10 min or less, 4.5 g / 10 min or less, 4.2 g / 10 min or less, 4 g / 10 min or less, 3.8 g / 10 min or less, 3.5 g / 10 min or less, 3.2 g / 10 min or less, or 3 g / 10 min or less. In this specification, the melt mass-flow rate refers to a value measured in accordance with JIS K7210:1999 at a test temperature of 200°C and a nominal load of 5.00 kg.

[0025] The number average molecular weight (M n ) may be 50,000 or more, 70,000 or more, 90,000 or more, 95,000 or more, or 100,000 or more, and may be 200,000 or less, 170,000 or less, 150,000 or less, 130,000 or less, or 120,000 or less, from the viewpoints of excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet. n When is within the above numerical range, the biaxially oriented sheet has superior strength even when made thin. Therefore, in a molded product (e.g., a container) using the biaxially oriented sheet, it becomes possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load.

[0026] The weight average molecular weight (M w From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 150,000 or more, 200,000 or more, 220,000 or more, 230,000 or more, 250,000 or more, or 260,000 or more, and may be 400,000 or less, 350,000 or less, 320,000 or less, 300,000 or less, or 295,000 or less. wWhen is within the above numerical range, the biaxially oriented sheet has superior strength even when made thin. Therefore, in a molded product (e.g., a container) using the biaxially oriented sheet, it becomes possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load.

[0027] The Z-average molecular weight (M z From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 300,000 or more, 350,000 or more, 380,000 or more, 390,000 or more, 400,000 or more, 410,000 or more, or 420,000 or more, and may be 600,000 or less, 550,000 or less, 520,000 or less, 500,000 or less, or 480,000 or less. z When is within the above numerical range, the biaxially oriented sheet has superior strength even when made thin. Therefore, in a molded product (e.g., a container) using the biaxially oriented sheet, it becomes possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load.

[0028] The peak top molecular weight (M top From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 150,000 or more, 200,000 or more, 230,000 or more, 250,000 or more, 260,000 or more, or 280,000 or more, and may be 400,000 or less, 370,000 or less, 350,000 or less, 330,000 or less, or 320,000 or less. top M means the molecular weight at the point where the value on the vertical axis is maximum on the differential molecular weight distribution curve. top When is within the above numerical range, the biaxially oriented sheet has superior strength even when made thin. Therefore, in a molded product (e.g., a container) using the biaxially oriented sheet, it becomes possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load.

[0029] The first non-rubber-modified styrene resin M w and M n Ratio to (M w / M n) may be 1.5 or more, 2.0 or more, or 2.3 or more, and may be 3.0 or less, 2.8 or less, or 2.6 or less. z and M w Ratio to (M z / M w ) may be 1.0 or more, 1.3 or more, or 1.6 or more, and may be 2.5 or less, 2.2 or less, or 1.9 or less.

[0030] In this specification, M n , M w , M z , and M top is determined by GPC measurement under the following conditions: Apparatus: Tosoh Corporation, GPC "HLC-8320GPC" Column: Shodex KF404 x 3 Temperature: 40℃ Solvent: tetrahydrofuran Flow rate: 0.2ml / min Pressure: 10 MPa Detection: RI Sample preparation method: 120 mg of a sample was dissolved in 15 mL of tetrahydrofuran, and then filtered through a syringe filter (Millex (registered trademark) 0.45 μm, manufactured by Merck Millipore). Injection volume: 10μl Calibration curve: Using standard polystyrene (manufactured by Polymer Laboratories), the relationship between elution time and elution amount is converted into molecular weight to determine various average molecular weights.

[0031] The toluene content in the first non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or less, 50 ppm by mass or less, 30 ppm by mass or less, or 10 ppm by mass or less, based on the total mass of the first non-rubber-modified styrenic resin. The toluene content in the first non-rubber-modified styrenic resin may be less than 10 ppm by mass, based on the total mass of the first non-rubber-modified styrenic resin.

[0032] In this specification, the contents of volatile organic compounds (toluene, ethylbenzene, cumene, n-propylbenzene, and styrene (styrene monomer)) are determined by dissolving 500 mg of a sample in 10 mL of N,N-dimethylformamide (DMF) containing cyclopentanol as an internal standard substance, and measuring the contents using gas chromatography under the following conditions: Device name: GC-12A (Shimadzu Corporation) Column: Glass column φ3 [mm] x 3 [m] Injection temperature: 220℃ Column temperature: 60 to 150°C, 10°C / min Detector temperature: 220℃ Split ratio: 30 / 1

[0033] The ethylbenzene content in the first non-rubber-modified styrenic resin may be 0 ppm by mass or more, and 230 ppm by mass or less, 200 ppm by mass or less, 150 ppm by mass or less, 100 ppm by mass or less, 50 ppm by mass or less, or 30 ppm by mass or less, based on the total mass of the first non-rubber-modified styrenic resin. The ethylbenzene content in the first non-rubber-modified styrenic resin may be less than 30 ppm by mass, based on the total mass of the first non-rubber-modified styrenic resin.

[0034] The cumene content in the first non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or less, 80 ppm by mass or less, 50 ppm by mass or less, or 30 ppm by mass or less, based on the total mass of the first non-rubber-modified styrenic resin. The cumene content in the first non-rubber-modified styrenic resin may be less than 30 ppm by mass, based on the total mass of the first non-rubber-modified styrenic resin.

[0035] The content of n-propylbenzene in the first non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or less, 80 ppm by mass or less, 50 ppm by mass or less, or 30 ppm by mass or less, based on the total mass of the first non-rubber-modified styrenic resin. The content of n-propylbenzene in the first non-rubber-modified styrenic resin may be less than 30 ppm by mass, based on the total mass of the first non-rubber-modified styrenic resin.

[0036] The content of styrene (styrene monomer) in the first non-rubber-modified styrene-based resin may be 0 ppm by mass or more, 50 ppm by mass or more, 100 ppm by mass or more, 200 ppm by mass or more, 300 ppm by mass or more, or 400 ppm by mass or more, based on the total mass of the first non-rubber-modified styrene-based resin, and may be 800 ppm by mass or less, 700 ppm by mass or less, 600 ppm by mass or less, 500 ppm by mass or less, or 450 ppm by mass or less.

[0037] The total content of volatile organic compounds in the first non-rubber-modified styrenic resin may be 10 ppm by mass or more, 30 ppm by mass or more, 50 ppm by mass or more, 70 ppm by mass or more, 100 ppm by mass or more, 200 ppm by mass or more, 300 ppm by mass or more, 350 ppm by mass or more, or 400 ppm by mass or more, based on the total mass of the first non-rubber-modified styrenic resin. It may be 1000 ppm by mass or less, 800 ppm by mass or less, 700 ppm by mass or less, 600 ppm by mass or less, or 500 ppm by mass or less. In this specification, the total content of volatile organic compounds means the sum of the contents of toluene, ethylbenzene, cumene, n-propylbenzene, and styrene (styrene monomer) determined as above.

[0038] The content of styrene dimer in the first non-rubber-modified styrene-based resin may be 0.000% by mass or more, 0.005% by mass or more, 0.010% by mass or more, 0.030% by mass or more, 0.040% by mass or more, or 0.050% by mass or more, based on the total mass of the first non-rubber-modified styrene-based resin, and may be 1.000% by mass or less, 0.500% by mass or less, 0.100% by mass or less, or 0.080% by mass or less.

[0039] In this specification, the content of styrene oligomers (styrene dimer and styrene trimer) is determined by measurement using gas chromatography under the following conditions. Device name: GC-12A (Shimadzu Corporation) Column: Glass column φ3 [mm] x 3 [m] Quantitative method: Internal standard method (cyclopentanol)

[0040] The content of styrene trimer in the first non-rubber-modified styrenic resin may be, based on the total mass of the first non-rubber-modified styrenic resin, 0.000% by mass or more, 0.005% by mass or more, 0.010% by mass or more, 0.030% by mass or more, 0.040% by mass or more, 0.050% by mass or more, 0.100% by mass or more, 0.200% by mass or more, 0.300% by mass or more, 0.350% by mass or more, 0.400% by mass or more, 0.500% by mass or more, or 0.550% by mass or more, and may be 3.000% by mass or less, 2.000% by mass or less, 1.500% by mass or less, 1.000% by mass or less, 0.800% by mass or less, or 0.600% by mass or less.

[0041] The total content of styrene oligomers in the first non-rubber-modified styrene resin may be 0.000% by mass or more, 0.005% by mass or more, 0.010% by mass or more, 0.030% by mass or more, 0.040% by mass or more, 0.050% by mass or more, 0.100% by mass or more, 0.300% by mass or more, 0.500% by mass or more, or 0.600% by mass or more, based on the total mass of the first non-rubber-modified styrene resin. It may be 3.000% by mass or less, 2.000% by mass or less, 1.000% by mass or less, 0.800% by mass or less, or 0.700% by mass or less. In this specification, the total content of styrene oligomers means the sum of the contents of styrene dimer and styrene trimer determined as above.

[0042] The white oil content in the first non-rubber-modified styrenic resin may be 0% by mass or more, and may be 3% by mass or less, 1% by mass or less, 0.5% by mass or less, 0.3% by mass or less, 0.2% by mass or less, or 0.1% by mass or less, based on the total mass of the first non-rubber-modified styrenic resin. In this specification, the white oil content is determined by the following method. First, a sample is prepared by adding 2.5 mL of methanol to a solution of 1 g of styrenic resin dissolved in 10 mL of MEK (methyl ethyl ketone). The sample is centrifuged to separate the polymer component and the solution phase. The resulting solution phase is measured by gas chromatography under the following conditions to determine the white oil content. Judging from the boiling point, white oil is a mixture of liquid saturated hydrocarbons that belong to the lubricating oil fraction. In this specification, the white oil content refers to the total mass of the mixture. Equipment name: GC-17Apf (Shimadzu Corporation) Column: φ0.25 [mm] x 30 [m] Filler: 100% dimethylpolysiloxane Film thickness: 0.1 μm Column bath temperature: 100°C for 2 minutes → increase at 5°C / min → 260°C, hold for 5 minutes Column gas flow rate (nitrogen): 1.9 ml / min Detector: WFID

[0043] The content of the first non-rubber-modified styrene-based resin may be 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 4% by mass or more, 4.5% by mass or more, 6% by mass or more, or 8% by mass or more, based on the total mass of the biaxially oriented sheet. The content of the first non-rubber-modified styrene-based resin may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 26% by mass or less, 22% by mass or less, 20% by mass or less, 18% by mass or less, 15% by mass or less, or 12% by mass or less, based on the total mass of the biaxially oriented sheet.

[0044] From the viewpoint of excellent moldability during production of a biaxially oriented sheet, the melt mass flow rate of the second non-rubber-modified styrene-based resin may be 2 g / 10 min or more, 2.2 g / min or more, 2.4 g / min or more, 2.6 g / 10 min or more, 2.8 g / 10 min or more, 3 g / 10 min or more, 3.2 g / 10 min or more, 3.4 g / 10 min or more, 3.5 g / 10 min or more, 3.6 g / min or more, 3.8 g / 10 min or more, or 4 g / min or more. The melt mass-flow rate of the second non-rubber-modified styrenic resin may be 8 g / 10 min or less, 7 g / 10 min or less, 6.8 g / 10 min or less, 6.6 g / 10 min or less, 6.4 g / 10 min or less, 6.2 g / 10 min or less, 6 g / 10 min or less, 5.8 g / 10 min or less, 5.6 g / 10 min or less, 5.4 g / 10 min or less, 5.2 g / 10 min or less, 5 g / 10 min or less, 4.8 g / 10 min or less, 4.6 g / 10 min or less, 4.5 g / 10 min or less, or 4.4 g / 10 min or less. The melt mass-flow rate of the second non-rubber-modified styrenic resin may be greater than the melt mass-flow rate of the first non-rubber-modified styrenic resin.

[0045] Second non-rubber modified styrene resin M n From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 50,000 or more, 80,000 or more, 100,000 or more, or 120,000 or more, and may be 200,000 or less, 170,000 or less, 150,000 or less, or 130,000 or less. nWhen the M of the second non-rubber-modified styrene-based resin is within the above range, the biaxially oriented sheet has excellent strength even when made thin, so that in a molded product (e.g., a container) using the biaxially oriented sheet, it is possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load. n is the first non-rubber-modified styrene resin M n Bigger is better.

[0046] Second non-rubber modified styrene resin M w From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 150,000 or more, 200,000 or more, 230,000 or more, 260,000 or more, or 280,000 or more, and may be 400,000 or less, 350,000 or less, 320,000 or less, 300,000 or less, or 295,000 or less. w When the M of the second non-rubber-modified styrene-based resin is within the above range, the biaxially oriented sheet has excellent strength even when made thin, so that in a molded product (e.g., a container) using the biaxially oriented sheet, it is possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load. w is the first non-rubber-modified styrene resin M w Bigger is better.

[0047] Second non-rubber modified styrene resin M z From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 300,000 or more, 350,000 or more, 400,000 or more, 430,000 or more, or 460,000 or more, and may be 600,000 or less, 580,000 or less, 540,000 or less, 520,000 or less, or 500,000 or less. z When the M of the second non-rubber-modified styrene-based resin is within the above range, the biaxially oriented sheet has excellent strength even when made thin, so that in a molded product (e.g., a container) using the biaxially oriented sheet, it is possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load. z is the first non-rubber-modified styrene resin M z Bigger is better.

[0048] Second non-rubber modified styrene resin M top From the viewpoints of achieving excellent formability during production of the biaxially oriented sheet and excellent strength of the biaxially oriented sheet, M may be 150,000 or more, 200,000 or more, 230,000 or more, 260,000 or more, or 280,000 or more, and may be 400,000 or less, 370,000 or less, 350,000 or less, or 330,000 or less. top When the M of the second non-rubber-modified styrene-based resin is within the above range, the biaxially oriented sheet has excellent strength even when made thin, so that in a molded product (e.g., a container) using the biaxially oriented sheet, it is possible to reduce the amount of resin used while maintaining the strength of the molded product, which contributes to further reducing the environmental load. top is the first non-rubber-modified styrene resin M top Bigger is better.

[0049] Second non-rubber modified styrene resin M w and M n Ratio to (M w / M n ) may be 1.5 or more, 1.8 or more, or 2.2 or more, and may be 3.0 or less, 2.7 or less, or 2.4 or less. z and M w Ratio to (M z / M w ) may be 1.0 or more, 1.3 or more, or 1.6 or more, and may be 2.5 or less, 2.2 or less, or 1.9 or less.

[0050] The toluene content in the second non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or less, 50 ppm by mass or less, 30 ppm by mass or less, or 10 ppm by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The toluene content in the second non-rubber-modified styrenic resin may be less than 10 ppm by mass, based on the total mass of the second non-rubber-modified styrenic resin.

[0051] The ethylbenzene content in the second non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or more, 200 ppm by mass or more, or 250 ppm by mass or more, and may be 900 ppm by mass or less, 800 ppm by mass or less, 750 ppm by mass or less, or 700 ppm by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The ethylbenzene content in the second non-rubber-modified styrenic resin (amount based on the total mass of the second non-rubber-modified styrenic resin) may be higher than the ethylbenzene content in the first non-rubber-modified styrenic resin (amount based on the total mass of the first non-rubber-modified styrenic resin).

[0052] The cumene content in the second non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or less, 80 ppm by mass or less, 50 ppm by mass or less, or 30 ppm by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The cumene content in the second non-rubber-modified styrenic resin may be less than 30 ppm by mass, based on the total mass of the second non-rubber-modified styrenic resin.

[0053] The content of n-propylbenzene in the second non-rubber-modified styrenic resin may be 0 ppm by mass or more, 100 ppm by mass or less, 80 ppm by mass or less, 50 ppm by mass or less, or 30 ppm by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The content of n-propylbenzene in the second non-rubber-modified styrenic resin may be less than 30 ppm by mass, based on the total mass of the second non-rubber-modified styrenic resin.

[0054] The content of styrene (styrene monomer) in the second non-rubber-modified styrene-based resin may be 0 ppm by mass or more, 50 ppm by mass or more, 100 ppm by mass or more, 200 ppm by mass or more, 300 ppm by mass or more, or 400 ppm by mass or more, based on the total mass of the second non-rubber-modified styrene-based resin, and may be 800 ppm by mass or less, 700 ppm by mass or less, 600 ppm by mass or less, 500 ppm by mass or less, or 450 ppm by mass or less.

[0055] The total content of volatile organic compounds in the second non-rubber-modified styrenic resin may be 10 ppm by mass or more, 30 ppm by mass or more, 50 ppm by mass or more, 70 ppm by mass or more, 100 ppm by mass or more, 200 ppm by mass or more, 300 ppm by mass or more, 350 ppm by mass or more, 400 ppm by mass or more, 500 ppm by mass or more, or 600 ppm by mass or more, and 1000 ppm by mass or less, 900 ppm by mass or less, 800 ppm by mass or less, 750 ppm by mass or less, or 700 ppm by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The total content of volatile organic compounds in the second non-rubber-modified styrenic resin (amount based on the total mass of the second non-rubber-modified styrenic resin) may be higher than the total content of volatile organic compounds in the first non-rubber-modified styrenic resin (amount based on the total mass of the first non-rubber-modified styrenic resin).

[0056] The styrene dimer content in the second non-rubber-modified styrenic resin may be 0.000% by mass or more, 0.005% by mass or more, 0.010% by mass or more, 0.020% by mass or more, or 0.030% by mass or more, and may be 1.000% by mass or less, 0.500% by mass or less, 0.100% by mass or less, 0.080% by mass or less, 0.070% by mass or less, or 0.050% by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The styrene dimer content in the second non-rubber-modified styrenic resin (amount based on the total mass of the second non-rubber-modified styrenic resin) may be less than the styrene dimer content in the first non-rubber-modified styrenic resin (amount based on the total mass of the first non-rubber-modified styrenic resin).

[0057] The content of styrene trimer in the second non-rubber-modified styrenic resin may be, based on the total mass of the second non-rubber-modified styrenic resin, 0.000% by mass or more, 0.005% by mass or more, 0.010% by mass or more, 0.030% by mass or more, 0.040% by mass or more, 0.050% by mass or more, 0.100% by mass or more, 0.200% by mass or more, 0.300% by mass or more, 0.400% by mass or more, 0.500% by mass or more, 0.600% by mass or more, 0.650% by mass or more, or 0.700% by mass or more, and may be 3.000% by mass or less, 2.000% by mass or less, 1.500% by mass or less, 1.000% by mass or less, 0.800% by mass or less, or 0.750% by mass or less. The styrene trimer content in the second non-rubber-modified styrene-based resin (amount based on the total mass of the second non-rubber-modified styrene-based resin) may be greater than the styrene trimer content in the first non-rubber-modified styrene-based resin (amount based on the total mass of the first non-rubber-modified styrene-based resin).

[0058] The total content of styrene oligomers in the second non-rubber-modified styrenic resin may be, based on the total mass of the second non-rubber-modified styrenic resin, 0.000% by mass or more, 0.005% by mass or more, 0.010% by mass or more, 0.030% by mass or more, 0.040% by mass or more, 0.050% by mass or more, 0.100% by mass or more, 0.300% by mass or more, 0.500% by mass or more, 0.600% by mass or more, or 0.700% by mass or more, and may be 3.000% by mass or less, 2.000% by mass or less, 1.500% by mass or less, 1.000% by mass or less, or 0.800% by mass or less. The total content of styrene oligomers in the second non-rubber-modified styrene-based resin (amount based on the total mass of the second non-rubber-modified styrene-based resin) may be greater than the total content of styrene oligomers in the first non-rubber-modified styrene-based resin (amount based on the total mass of the first non-rubber-modified styrene-based resin).

[0059] The white oil content in the second non-rubber-modified styrenic resin may be 0% by mass or more, more than 0%, 0.1% by mass or more, or 0.2% by mass or more, and may be 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0.7% by mass or less, based on the total mass of the second non-rubber-modified styrenic resin. The white oil content in the second non-rubber-modified styrenic resin (amount based on the total mass of the second non-rubber-modified styrenic resin) may be greater than the white oil content in the first non-rubber-modified styrenic resin (amount based on the total mass of the first non-rubber-modified styrenic resin).

[0060] The content of the second non-rubber-modified polystyrene resin may be 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 85% by mass or more, based on the total mass of the biaxially oriented sheet, and may be 100% by mass or less, 95% by mass or less, or 92% by mass or less.

[0061] The mass ratio of the content of the first non-rubber-modified polystyrene resin to the content of the second non-rubber-modified polystyrene resin (content of first non-rubber-modified polystyrene resin / content of second non-rubber-modified polystyrene resin) may be 1 / 99 or more, 2 / 98 or more, 3 / 97 or more, 4 / 96 or more, 5 / 95 or more, 6 / 94 or more, 7 / 93 or more, 8 / 92 or more, 9 / 91 or more, or 10 / 90 or more, and may be 99 / 1 or less, 95 / 5 or less, 90 / 10 or less, 80 / 20 or less, 70 / 30 or less, 60 / 40 or less, 50 / 50 or less, 45 / 55 or less, 40 / 60 or less, 35 / 65 or less, 30 / 70 or less, or 25 / 75 or less.

[0062] The styrene resin may include a rubber-modified styrene resin. The rubber-modified styrene resin is a styrene polymer matrix in which rubber polymer particles are dispersed. The rubber-modified styrene resin may be, for example, a diene-based rubber-modified styrene resin containing a rubbery diene polymer. The diene-based rubber-modified styrene resin is obtained, for example, by dissolving a rubbery diene polymer in a styrene monomer and polymerizing (preferably graft polymerizing) the resulting mixture.

[0063] As the styrene-based monomer, for example, the styrene-based monomers mentioned above as those that can be contained in the non-rubber-modified styrene-based resin can be used. The above-mentioned monomers can be used alone or in combination of two or more. The rubber-modified styrene-based resin can be a rubber-modified polystyrene (HIPS) containing only styrene as the styrene-based monomer.

[0064] Examples of rubbery diene polymers that can be used include polymers of one or more conjugated 1,3-dienes (e.g., butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro-1,3-butadiene, piperylene, etc.), butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, and butadiene-styrene-acrylonitrile copolymers.

[0065] The content of the diene rubber component (hereinafter also simply referred to as "rubber component") may be 0.01% by mass or more, 0.02% by mass or more, 0.05% by mass or more, or 0.08% by mass or more, based on the total mass of the biaxially oriented sheet, and may be 3.0% by mass or less, 2.0% by mass or less, 1.5% by mass or less, 1.0% by mass or less, 0.8% by mass or less, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less.

[0066] The rubber content of the biaxially oriented sheet, based on its total mass, can be measured by dissolving 0.25 g of the biaxially oriented sheet in 50 ml of chloroform, adding iodine monochloride to react with the double bonds in the rubber component, then adding potassium iodide to convert the remaining iodine monochloride to iodine, and back-titrating with sodium thiosulfate (iodine monochloride method). The analytical method is described, for example, in "(3) Rubber Content" on page 659 of "New Edition Polymer Analysis Handbook," edited by the Polymer Analysis Research Forum of the Japan Society for Analytical Chemistry, Kinokuniya Shoten (1995 edition), and can be used to measure the content.

[0067] The content of the rubber-modified styrene-based resin may be 0.1% by mass or more, 0.3% by mass or more, 0.5% by mass or more, or 0.8% by mass or more, based on the total mass of the biaxially oriented sheet, and may be 5.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less, or 1.5% by mass or less.

[0068] The mass ratio of the content of non-rubber-modified styrene-based resin in the biaxially oriented sheet to the content of rubber-modified styrene-based resin (content of non-rubber-modified styrene-based resin / content of rubber-modified styrene-based resin) may be 95 / 5 or more, 96 / 4 or more, 97 / 3 or more, 98 / 2 or more, or 98.5 / 1.5 or more, and may be 99.9 / 0.1 or less, 99.7 / 0.3 or less, or 99.5 / 0.5 or less.

[0069] At least one resin selected from the group consisting of the first non-rubber-modified styrene-based resin, the second non-rubber-modified styrene-based resin, and the rubber-modified styrene-based resin may be a biomass-derived styrene-based resin.

[0070] In this specification, "biomass-derived" means that biomass-derived characteristics have been assigned using the mass balance method. Here, the mass balance method refers to "a method of assigning a certain characteristic to a portion of a product in accordance with the amount of raw material with that characteristic when raw materials with a certain characteristic (e.g., biomass-derived raw materials) are mixed with raw materials without that characteristic (e.g., petroleum-derived raw materials) during the processing and distribution process from raw materials to products" ("Bioplastics Introduction Roadmap" (established by the Ministry of the Environment, Ministry of Economy, Trade and Industry, Ministry of Agriculture, Forestry and Fisheries, and Ministry of Education, Culture, Sports, Science and Technology in January 2021)).

[0071] According to the mass balance approach, biomass-derived characteristics can be assigned to individual products within a range corresponding to the input amount of biomass-derived raw materials, regardless of the actual content of biomass components in each product. Certification systems are utilized to ensure the reliability of the assignment of biomass-derived characteristics. A biomass-derived styrenic resin may be certified by any certification system as a styrenic resin assigned biomass-derived characteristics by the mass balance approach. Examples of certification systems include international certification systems such as ISCC PLUS, ISCC EU, RSB Global Advanced Products, and REDcert. The certification system may be one or more selected from the group consisting of ISCC PLUS, ISCC EU, RSB Global Advanced Products, and REDcert.

[0072] The content of biomass-derived styrene-based resins (total content of biomass-derived styrene-based resins) may be 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 4% by mass or more, 4.5% by mass or more, 6% by mass or more, or 8% by mass or more, based on the total mass of the biaxially oriented sheet. The content of biomass-derived styrene-based resins may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 26% by mass or less, 22% by mass or less, 20% by mass or less, 18% by mass or less, 15% by mass or less, or 12% by mass or less, based on the total mass of the biaxially oriented sheet.

[0073] At least one resin selected from the group consisting of the first non-rubber-modified styrenic resin, the second non-rubber-modified styrenic resin, and the rubber-modified styrenic resin may actually be produced from a biomass raw material, in which case at least one resin selected from the group consisting of the first non-rubber-modified styrenic resin, the second non-rubber-modified styrenic resin, and the rubber-modified styrenic resin contains a biomass component.

[0074] At least one resin selected from the group consisting of the first non-rubber-modified styrene-based resin, the second non-rubber-modified styrene-based resin, and the rubber-modified styrene-based resin contains styrene as a monomer unit, and the styrene may be styrene derived from chemical recycling. The styrene derived from chemical recycling may be styrene obtained by thermal decomposition of a styrene-containing polymer, for example.

[0075] At least one selected from the group consisting of the first non-rubber-modified styrene-based resin, the second non-rubber-modified styrene-based resin, and the rubber-modified styrene-based resin contains styrene as a monomer unit, and the styrene contains styrene derived from chemical recycling, which may be one or more selected from the group consisting of the first non-rubber-modified styrene-based resin containing styrene as a monomer unit, and the styrene contains styrene derived from chemical recycling, the second non-rubber-modified styrene-based resin containing styrene as a monomer unit, and the styrene contains styrene derived from chemical recycling, and the rubber-modified styrene-based resin containing styrene as a monomer unit, and the styrene contains styrene derived from chemical recycling.

[0076] The biaxially oriented sheet may further contain other components. Examples of other components include antioxidants, antigelling agents (e.g., polyoxyethylene alkyl ether (POE)), ultraviolet absorbers, light stabilizers, lubricants, plasticizers, colorants, antistatic agents, flame retardants, mineral oil, reinforcing fibers such as glass fiber, carbon fiber, and aramid fiber, and fillers such as talc, silica, mica, and calcium carbonate. The total content of other components may be, for example, 0% by mass or more and 1.0% by mass or less, based on the total mass of the biaxially oriented sheet.

[0077] The content of the plasticizer may be 5% by mass or less, 3% by mass or less, 1% by mass or less, 0.5% by mass or less, 0.3% by mass or less, or less than 0.1% by mass, based on the total mass of the biaxially oriented sheet, from the viewpoint of suppressing bleed-out in the biaxially oriented sheet and preventing poor appearance due to changes over time. The biaxially oriented sheet may be substantially free of plasticizer. In this specification, "substantially free of a certain component" means that the component is not contained at all, or that the component is contained only as an unavoidable impurity.

[0078] The biaxially oriented sheet may actually contain a biomass component. For example, when at least one resin selected from the group consisting of the first non-rubber-modified styrene-based resin, the second non-rubber-modified styrene-based resin, and the rubber-modified styrene-based resin contains a biomass component, the biaxially oriented sheet contains a biomass component. The proportion of the biomass component (biomass ratio) in the biaxially oriented sheet is preferably 10% by mass or more, independently of the total mass of the biaxially oriented sheet.

[0079] The thickness of the biaxially oriented sheet may be 0.1 mm or more, 0.15 mm or more, or 0.2 mm or more, and may be 0.7 mm or less, 0.5 mm or less, 0.4 mm or less, or 0.3 mm or less. The thickness of the biaxially oriented sheet may be, for example, 0.1 to 0.7 mm, or 0.1 to 0.3 mm.

[0080] The melt mass-flow rate of the biaxially oriented sheet may be 1 g / 10 min or more, 2 g / 10 min or more, 2.2 g / min or more, 2.4 g / min or more, 2.6 g / 10 min or more, 2.8 g / 10 min or more, 3 g / 10 min or more, 3.2 g / 10 min or more, 3.4 g / 10 min or more, 3.5 g / 10 min or more, 3.6 g / min or more, 3.8 g / 10 min or more, or 4 g / min or more, and may be 8 g / 10 min or less, 7 g / 10 min or less, 6.8 g / 10 min or less, or 8 g / 10 min or less. minutes or less, 6.6 g / 10 minutes or less, 6.4 g / 10 minutes or less, 6.2 g / 10 minutes or less, 6 g / 10 minutes or less, 5.8 g / 10 minutes or less, 5.6 g / 10 minutes or less, 5.5 g / 10 minutes or less, 5.4 g / 10 minutes or less, 5 .2g / 10min or less, 5g / 10min or less, 4.8g / 10min or less, 4.6g / 10min or less, 4.4g / 10min or less, 4.2g / 10min or less, 4g / 10min or less, or 3.8g / 10min or less.

[0081] The Mw of the biaxially oriented sheet may be 130,000 or more, 150,000 or more, 180,000 or more, 200,000 or more, 230,000 or more, or 250,000 or more, and may be 400,000 or less, 350,000 or less, 320,000 or less, 300,000 or less, 295,000 or less, 270,000 or less, or 260,000 or less. The Mw of the biaxially oriented sheet may be, for example, 200,000 to 300,000.

[0082] The stretching ratios of the biaxially oriented sheet in the MD (Machine Direction; sheet flow direction) and TD (Transverse Direction; direction perpendicular to the sheet flow direction) may be 1.9 times or more, 2.0 times or more, 2.3 times or more, or 2.4 times or more, and may be 4.0 times or less, 3.5 times or less, or 3.0 times or less. When the stretching ratio is equal to or greater than the above lower limit, the strength of the molded article is superior. When the stretching ratio is equal to or less than the above upper limit, the formability of the biaxially oriented sheet is superior. The MD stretching ratio and the TD stretching ratio may be the same or different.

[0083] When the MD stretching ratio of the biaxially oriented sheet is m and the TD stretching ratio is n, the areal stretching ratio represented by m×n may be 4 times or more, 5 times or more, or 6 times or more, and may be 16 times or less, 13 times or less, or 10 times or less.

[0084] The stretching ratio in this specification is calculated as the rate of change in a test piece of a biaxially stretched sheet before and after heating. Specifically, the stretching ratio is calculated by the following formula: Stretching ratio = Y / Z (unit [times]) In this formula, Y represents the length [mm] of a straight line drawn in MD or TD on a test piece of a biaxially oriented sheet before heating, and Z represents the length [mm] of the straight line after the test piece is allowed to stand for 60 minutes in an oven at a temperature 30°C higher than the Vicat softening point temperature of the biaxially oriented sheet measured in accordance with JIS K7206 and allowed to shrink. The MD stretch ratio can be calculated by drawing a straight line in MD, and the TD stretch ratio can be calculated by drawing a straight line in TD.

[0085] The heat shrinkage stress in the MD and TD of the biaxially oriented sheet may be independently 0.2 MPa or more, 0.3 MPa or more, 0.4 MPa or more, 0.5 MPa or more, or 0.6 MPa or more, and may be 1.0 MPa or less, 0.9 MPa or less, or 0.8 MPa or less.

[0086] The heat shrinkage stress of a biaxially oriented sheet is determined using the following method. First, a rectangular biaxially oriented sheet sample measuring 20 mm wide and 150 mm long is prepared. Next, both ends of the sample are gripped with chucks and heated to 130°C. The molecular orientation is relaxed by thermal motion, and the load applied to the chucks is measured as the sample thermally shrinks. The heat shrinkage stress is determined by dividing the maximum load by the cross-sectional area of ​​the sample. If the longitudinal direction of the sample is defined as the MD of the biaxially oriented sheet, the MD heat shrinkage stress can be determined. If the longitudinal direction of the sample is defined as the TD of the biaxially oriented sheet, the TD heat shrinkage stress can be determined. The heat shrinkage stress is an indicator of the degree of molecular orientation of the biaxially oriented sheet.

[0087] The MD heat shrinkage of the biaxially oriented sheet may be 40% or more, 50% or more, 55% or more, or 58% or more, and 80% or less, 70% or less, 65% or less, or 63% or less.The TD heat shrinkage of the biaxially oriented sheet may be 40% or more, 50% or more, 53% or more, or 55% or more, and 80% or less, 70% or less, 65% or less, or 63% or less.

[0088] The heat shrinkage of a biaxially oriented sheet in the MD and TD is determined by the following method. First, a 100 mm long straight line is drawn in the MD and TD on a test piece of the biaxially oriented sheet. The test piece is allowed to stand for 30 minutes in an oven at a temperature 30°C higher than the Vicat softening temperature of the sheet measured according to JIS K7206:2016, and then the length L of the straight line drawn in the MD is measured. MD [mm] and the length of the straight line drawn on TD L TD The heat shrinkage (%) in the MD and TD directions was calculated using the following formula. MD heat shrinkage (%) = {(100 - L MD ) / 100}×100 Heat shrinkage rate of TD (%) = {(100 - L TD ) / 100}×100

[0089] The toluene content in the biaxially oriented sheet may be 0 ppm by mass or more, 100 ppm by mass or less, 50 ppm by mass or less, 30 ppm by mass or less, or 10 ppm by mass or less, based on the total mass of the biaxially oriented sheet. The toluene content in the biaxially oriented sheet may be less than 10 ppm by mass, based on the total mass of the biaxially oriented sheet.

[0090] The ethylbenzene content of the biaxially oriented sheet is 245 ppm by mass or less, based on the total mass of the biaxially oriented sheet. From the viewpoint of the biaxially oriented sheet having superior impact resistance and tensile elongation, the ethylbenzene content of the biaxially oriented sheet may be 240 ppm by mass or less, 235 ppm by mass or less, or 225 ppm by mass or less, based on the total mass of the biaxially oriented sheet. From the viewpoint of the biaxially oriented sheet having superior tensile elongation, the ethylbenzene content of the biaxially oriented sheet may be 10 ppm by mass or more, 50 ppm by mass or more, 100 ppm by mass or more, 150 ppm by mass or more, or 180 ppm by mass or more, based on the total mass of the biaxially oriented sheet.

[0091] The cumene content of the biaxially oriented sheet may be 0 ppm by weight or more, 100 ppm by weight or less, 80 ppm by weight or less, 50 ppm by weight or less, or 30 ppm by weight or less, based on the total weight of the biaxially oriented sheet. The cumene content of the biaxially oriented sheet may be less than 30 ppm by weight, based on the total weight of the biaxially oriented sheet.

[0092] The biaxially oriented sheet may have an n-propylbenzene content of 0 ppm by weight or more, 100 ppm by weight or less, 80 ppm by weight or less, 50 ppm by weight or less, or 30 ppm by weight or less, based on the total weight of the biaxially oriented sheet. The biaxially oriented sheet may have an n-propylbenzene content of less than 30 ppm by weight, based on the total weight of the biaxially oriented sheet.

[0093] The content of styrene (styrene monomer) in the biaxially oriented sheet may be 0 ppm by mass or more, 50 ppm by mass or more, 100 ppm by mass or more, 200 ppm by mass or more, 300 ppm by mass or more, or 330 ppm by mass or more, based on the total mass of the biaxially oriented sheet, and may be 800 ppm by mass or less, 600 ppm by mass or less, 500 ppm by mass or less, 450 ppm by mass or less, or 400 ppm by mass or less.

[0094] The total content of volatile organic compounds in the biaxially oriented sheet may be 100 ppm by mass or more, 200 ppm by mass or more, 300 ppm by mass or more, 400 ppm by mass or more, 450 ppm by mass or more, or 500 ppm by mass or more, and may be 1000 ppm by mass or less, 800 ppm by mass or less, 700 ppm by mass or less, 650 ppm by mass or less, 625 ppm by mass or less, or 600 ppm by mass or less, based on the total mass of the biaxially oriented sheet.

[0095] The styrene dimer content in the biaxially oriented sheet may be 0.000% by mass or more, 0.010% by mass or more, 0.030% by mass or more, 0.035% by mass or more, or 0.040% by mass or more, and may be 1.000% by mass or less, 0.500% by mass or less, 0.100% by mass or less, 0.080% by mass or less, or 0.060% by mass or less, based on the total mass of the biaxially oriented sheet.

[0096] The styrene trimer content in the biaxially oriented sheet may be 0.000% by mass or more, 0.100% by mass or more, 0.300% by mass or more, 0.500% by mass or more, or 0.700% by mass or more, and may be 3.000% by mass or less, 2.000% by mass or less, 1.500% by mass or less, 1.000% by mass or less, or 0.800% by mass or less, based on the total mass of the biaxially oriented sheet.

[0097] The total content of styrene oligomers in the biaxially oriented sheet may be 0.000% by mass or more, 0.100% by mass or more, 0.300% by mass or more, 0.500% by mass or more, or 0.700% by mass or more, and may be 3.000% by mass or less, 2.000% by mass or less, 1.500% by mass or less, 1.000% by mass or less, or 0.800% by mass or less, based on the total mass of the biaxially oriented sheet.

[0098] The biaxially oriented sheet can be produced by the following method. First, the raw material styrene resin and optional components (e.g., the other components described above) used as needed are mixed (e.g., melt-kneaded) and then molded (e.g., extrusion molding or press molding) to obtain an unstretched sheet. Next, the unstretched sheet is stretched in two axial directions sequentially or simultaneously to obtain a biaxially oriented sheet. The unstretched sheet may be stretched while heated. The stretching temperature may be 90°C or higher, 100°C or higher, 110°C or higher, or 120°C or higher, and may be 150°C or lower, 140°C or lower, or 135°C or lower.

[0099] When producing a biaxially oriented sheet, the ethylbenzene content in the biaxially oriented sheet can be adjusted by using raw materials with a low or high ethylbenzene content. For example, by using a styrene-based resin as the raw material, in which the ethylbenzene content in the styrene-based resin is 100 mass ppm or less based on the total mass of the styrene-based resin, the ethylbenzene content in the biaxially oriented sheet can be reduced.

[0100] Another embodiment of the present disclosure is a method for producing a biaxially oriented sheet using a styrene-based resin as a raw material, wherein the ethylbenzene content in the styrene-based resin is 100 ppm by mass or less, based on the total mass of the styrene-based resin. One embodiment of the production method may be a method for producing a biaxially oriented sheet using a first styrene-based resin and a second styrene-based resin as raw materials, wherein the ethylbenzene content in the first styrene-based resin is 100 ppm by mass or less, based on the total mass of the first styrene-based resin, and the ethylbenzene content in the second styrene-based resin (based on the total mass of the second non-rubber-modified styrene-based resin) is greater than the ethylbenzene content in the first styrene-based resin (based on the total mass of the first non-rubber-modified styrene-based resin).

[0101] As a specific embodiment of the first styrene-based resin, the specific embodiment of the first non-rubber-modified styrene-based resin described above can be applied. However, the content of ethylbenzene in the first styrene-based resin is 100 ppm by mass or less based on the total mass of the first styrene-based resin. As a specific embodiment of the second styrene-based resin, the specific embodiment of the second non-rubber-modified styrene-based resin described above can be applied. However, the content of ethylbenzene in the second styrene-based resin is higher than the content of ethylbenzene in the first styrene-based resin.

[0102] Suppliers of styrenic resins that have obtained ISCC PLUS certification can issue and attach a Sustainability Declaration (SD), a document detailing the raw materials, to their products and pass it on to downstream users. When using biomass-derived styrenic resins in the production of biaxially oriented sheets, it is recommended to receive a Sustainability Declaration (SD) for the biomass-derived styrenic resin and confirm that the supplier of the biomass-derived styrenic resin holds a valid certification at the time the SD is issued.

[0103] Another embodiment of the present disclosure is a multilayer sheet including a layer made of the biaxially oriented sheet. The multilayer sheet includes a first layer made of the biaxially oriented sheet and a second layer disposed on the first layer. The multilayer sheet may further include a third layer disposed on the side of the first layer opposite the second layer, a fourth layer disposed on the second layer, etc. Examples of the second, third, and fourth layers include an anti-fogging layer containing an anti-fogging agent, a release layer containing a release agent (peeling agent), an anti-static layer containing an anti-static agent, a design layer (a layer for applying a pattern to the multilayer sheet) containing a colorant, an antibacterial layer containing an antibacterial agent, and a gas barrier layer containing a gas barrier material (e.g., an ethylene-vinyl alcohol copolymer) that suppresses the permeation of gases (such as oxygen).

[0104] The multilayer sheet can be produced, for example, by applying a coating liquid containing components appropriate for the purpose (anti-fogging agent, release agent (peeling agent), antistatic agent, colorant, antibacterial agent, gas barrier substance, etc.) to at least one surface of a biaxially stretched sheet to form a second layer, etc. The method for applying the coating liquid is not particularly limited, and may be a method using a roll coater, knife coater, gravure roll coater, etc., or may be spraying, dipping, etc.

[0105] The biaxially oriented sheet and multilayer sheet described above can be used, for example, to produce a molded article. The molded article may be, for example, a container, or a food packaging container (food pack) for storing food. The molded article may be, for example, a lid material for a food packaging container. The biaxially oriented sheet and the multilayer sheet may each independently be used to mold a food packaging container.

[0106] There are no particular limitations on the method for obtaining a molded article from a biaxially oriented sheet, and any method commonly used in the secondary molding of conventional biaxially oriented sheets can be used. For example, secondary molding can be performed by thermoforming methods such as vacuum molding and pressure molding. These methods are described, for example, in "Plastic Processing Technology Handbook" edited by the Society of Polymer Science, Nikkan Kogyo Shimbun (1995).

[0107] The biaxially oriented sheets, multilayer sheets, and molded articles described above may each independently be biomass-derived. That is, the biaxially oriented sheets, multilayer sheets, and molded articles may each independently be biaxially oriented sheets, multilayer sheets, or molded articles that have been assigned biomass-derived characteristics using a mass balance approach. The biaxially oriented sheets, multilayer sheets, and molded articles may each independently be certified under a certification system as biaxially oriented sheets, multilayer sheets, or molded articles that have been assigned biomass-derived characteristics. Examples of certification systems include the international certification systems described above. The certification system may be one or more selected from the group consisting of ISCC PLUS, ISCC EU, RSB Global Advanced Products, and REDcert.

[0108] If a biaxially oriented sheet, multi-layer sheet, or molded article has been certified with an international standard such as ISCC PLUS, the biaxially oriented sheet, multi-layer sheet, or molded article may be provided with a Sustainability Statement (SD). [Example]

[0109] The present disclosure will be described in more detail below based on examples, although the present disclosure is not limited to these examples.

[0110] <Material> In the examples and comparative examples, the following materials were used. A: Non-rubber-modified styrene resin (GPPS, ISCC PLUS certified as a styrene resin with a 100% biomass-derived characteristic allocation rate, "Styrolution PS 158K" manufactured by INEOS Styrolution) B: Non-rubber-modified styrene resin (GPPS, not assigned biomass-derived characteristics, "HRM61S" manufactured by Toyo Styrene Co., Ltd.) C: Rubber-modified styrene resin (HIPS, not assigned biomass-derived characteristics, "H850N" manufactured by Toyo Styrene Co., Ltd.)

[0111] The melt mass flow rate, molecular weight, and contents of volatile organic compounds, styrene oligomers, and white oil were measured for A and B. The results are shown in Table 1.

[0112] [Table 1]

[0113] <Production of biaxially oriented sheets> The materials of the types and amounts shown in Table 2 were melt-kneaded and extruded using a single-screw extruder (manufactured by Tanabe Plastics Machinery) with a screw diameter of 40 mm to obtain pellets. The extrusion temperature was 230°C, and the screw rotation speed was 90 RPM. The obtained pellets were melt-kneaded using an extruder (manufactured by Tanabe Plastics Machinery) with a screw diameter of 40 mm at an extrusion temperature of 230°C and a screw rotation speed of 90 RPM, and extruded through a T-die (width: 500 mm) to obtain an unstretched sheet with a thickness of 1.5 mm. The unstretched sheet was sequentially biaxially stretched 2.8 x 2.8 times at a stretching temperature of 125°C using a batch stretching machine (manufactured by Ever Sokki, SDR-507D) to obtain biaxially stretched sheets of each Example and Comparative Example. The thickness of each biaxially stretched sheet was as shown in Table 2. The rubber component content based on the total mass of the biaxially stretched sheet was 0.09% by mass.

[0114] <Characteristics of biaxially oriented sheets> The contents of volatile organic compounds and styrene oligomers were measured for each of the biaxially oriented sheets produced in the Examples and Comparative Examples, and the physical properties were examined as follows. The results are shown in Table 2. The melt mass-flow rate, thickness, and M w are also shown in Table 2.

[0115] [Thermal shrinkage stress] A biaxially oriented sheet was cut into a strip measuring 20 mm wide and 150 mm long to prepare a sample, with the longitudinal direction being the MD of the biaxially oriented sheet. Both ends of the sample were held with a chuck and submerged in a 130°C oil bath for heating. The load applied to the chuck was measured when the molecular orientation relaxed due to thermal motion and the sheet thermally shrunk. The MD heat shrinkage stress was calculated by dividing the maximum load by the cross-sectional area of ​​the sample. The TD heat shrinkage stress was calculated in the same manner as above, except that the longitudinal direction of the sample was defined as the TD of the biaxially oriented sheet. The heat shrinkage stress is an indicator of the degree of molecular orientation of the biaxially oriented sheet.

[0116] [Heat shrinkage rate] A 100 mm straight line is drawn in the MD and TD on a biaxially stretched sheet specimen. The specimen is left to stand for 30 minutes in an oven at a temperature 30°C higher than the Vicat softening temperature of the sheet measured according to JIS K7206:2016, and then the length L of the straight line drawn in the MD is measured. MD [mm] and the length of the straight line drawn on TD L TD The heat shrinkage (%) in the MD and TD directions was calculated using the following formula. MD heat shrinkage (%) = {(100 - L MD ) / 100}×100 Heat shrinkage rate of TD (%) = {(100 - L TD ) / 100}×100

[0117] [Impact resistance] The biaxially stretched sheets of each example and comparative example were cut into 70 mm x 70 mm pieces to prepare measurement samples. The impact strength (pendulum impact hole opening strength) of each measurement sample was measured in accordance with ASTM D3420 under an environment of 23°C and 50% RH using a film impact tester (Yasuda Seiki Seisakusho Co., Ltd., No. 181-L). If the film impact strength of the biaxially stretched sheet is 3.3 or higher, the biaxially stretched sheet can be said to have excellent impact resistance, and the higher the film impact strength value, the more preferable it is.

[0118] [Tensile elongation, tensile modulus, and maximum tensile stress] Measurement samples were prepared by cutting a biaxially stretched sheet into the shape of a No. 1 dumbbell so that the longitudinal direction was the MD of the biaxially stretched sheet. The MD tensile elongation, tensile modulus, and maximum tensile stress were measured using an autograph (AGSX, manufactured by Shimadzu Corporation) according to ASTM D638. The TD tensile elongation, tensile modulus, and maximum tensile stress were also determined in the same manner as above, except that the longitudinal direction of the sample was the TD of the biaxially stretched sheet. The test environment was 23°C and 50% RH.

[0119] [Folding durability (MIT test)] A biaxially oriented sheet was cut into a 15 mm wide x 100 mm long strip so that the longitudinal direction of the biaxially oriented sheet was the MD of the biaxially oriented sheet, to prepare a sample. In accordance with JIS P8115:2001, the test piece was placed in an MIT folding fatigue tester (manufactured by Toyo Seiki Seisakusho, Ltd.). A bending test was performed at a test speed of 175 rpm, a bending angle of 90°, and a load of 1 kg, and the number of MD bendings until breakage was measured. Ten samples were tested, and the average value (average number of bendings) of the 10 samples was calculated. The average number of TD bendings until breakage was also calculated in the same manner as above, except that the longitudinal direction of the sample was the TD of the biaxially oriented sheet. [Haze] The haze of the biaxially stretched sheet was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000.

[0120] [Total light transmittance] The total light transmittance of the biaxially stretched sheet was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7361-1:1997.

[0121] [Hue] The color of the biaxially stretched sheet was examined using a color difference meter (product name: "Spectrophotometer CM-2500d" manufactured by Konica Minolta, Inc.) Specifically, 16 biaxially stretched sheets (thickness: approximately 0.25 mm) were stacked to prepare a sheet sample with a thickness of approximately 4 mm, and the color of the sample was evaluated under the conditions of the SCI method.

[0122] [Moldability] Using a hot plate molding machine (HPTA, manufactured by Wakisaka Engineering Co., Ltd.), lunch box lids (dimensions: length 241 mm × width 193 mm × height 28 mm) were molded under the following conditions: hot plate temperature: 123°C, mold temperature: 90°C, heating time: 2 seconds. The appearance of the molded lunch box lids was evaluated according to the following criteria. Good: No whitening due to surface roughness, good shape Defective: Whitening, raindrops, or defective shape due to rough surface (unable to be commercialized)

[0123] Table 2

Claims

1. A biaxially oriented sheet containing a styrene-based resin, The biaxially oriented sheet has an ethylbenzene content of 245 ppm by mass or less, based on the total mass of the biaxially oriented sheet.

2. 2. The biaxially oriented sheet of claim 1, wherein the biaxially oriented sheet has an ethylbenzene content of 150 ppm by mass or more, based on the total mass of the biaxially oriented sheet.

3. 3. The biaxially oriented sheet of claim 1, wherein the total content of volatile organic compounds in the biaxially oriented sheet is 600 ppm by mass or less, based on the total mass of the biaxially oriented sheet.

4. 3. The biaxially oriented sheet of claim 1 or 2, which is derived from biomass.

5. a first layer comprising the biaxially oriented sheet of claim 1; a second layer disposed on the first layer; and wherein the second layer is an anti-fogging layer.

6. A molded article obtained by molding the biaxially oriented sheet according to claim 1 or 2, or the multilayer sheet according to claim 5.

7. A method for producing a biaxially oriented sheet using a styrene-based resin as a raw material, a content of ethylbenzene in the styrene-based resin being 100 ppm by mass or less, based on the total mass of the styrene-based resin;

8. The method for producing a biaxially oriented sheet according to claim 7 , wherein the total content of volatile organic compounds in the styrene-based resin is 600 ppm by mass or less, based on the total mass of the styrene-based resin.

9. The method according to claim 7 or 8, wherein the styrene-based resin is a biomass-derived styrene-based resin.

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