Styrene-based biaxially oriented sheet and container

Abstract

This invention provides a styrene-based biaxially oriented sheet that exhibits excellent heat resistance, oil resistance, and toughness. [Solution] A styrene-based biaxially oriented sheet comprising a copolymer (A) containing vinyl cyanide monomer units and styrene monomer units, and a copolymer (B) containing maleimide monomer units and styrene monomer units, wherein at least one of the maximum orientation relaxation stress of MD and the maximum orientation relaxation stress of TD exceeds 0.6 MPa.

Description

Technical Field

[0001] The present invention relates to a styrene-based biaxially stretched sheet and a container.

Background Art

[0002] A biaxially stretched sheet made of a resin containing a styrene-based monomer (hereinafter referred to as "styrene-based biaxially stretched sheet") is widely used as various formed containers including food packaging containers because of its excellent transparency and rigidity. Patent Documents 1 to 2 propose styrene-based biaxially stretched sheets using heat-resistant styrene resins such as styrene-(meth)acrylic acid copolymers and styrene-maleic anhydride copolymers.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional styrene biaxially oriented sheets sometimes lack sufficient heat resistance. For example, when a container made from a molded styrene biaxially oriented sheet is heated in a microwave oven, deformation may occur due to the heat. Furthermore, some foods heated in microwave ovens contain a lot of oil. When a container containing such food is heated in a microwave oven, localized shrinkage stress may occur in the container due to (1) the heat from the food being transferred to the container and raising its temperature, and (2) the oil contained in the food penetrating the resin that makes up the container and causing the resin to plasticize. This can result in holes forming in the container or the container becoming significantly deformed. This phenomenon becomes even more pronounced when heating food in a high-power microwave oven exceeding 1000W. Therefore, food packaging containers are required to have high heat resistance and oil resistance so that they do not develop holes or deform even when heated in a high-power microwave oven.

[0005] In addition, biaxially oriented sheets used to form various containers are required to have excellent toughness. Biaxially oriented sheets with high toughness tend to have excellent film formation stability and superior strength after being formed into containers. However, with conventional styrene-based biaxially oriented sheets, it has been difficult to achieve both high heat resistance and oil resistance and sheet toughness.

[0006] Therefore, the present invention aims to provide a styrene-based biaxially oriented sheet that is excellent in heat resistance, oil resistance, and toughness, and a container using the same. [Means for solving the problem]

[0007] As a result of diligent research by the inventors, we have discovered that a biaxially oriented sheet can be obtained that is excellent in heat resistance, oil resistance, and toughness if it contains two types of styrene copolymers containing specific monomer units and the maximum orientation relaxation stress of the biaxially oriented sheet is within a specific range, thus completing the present invention.

[0008] The present invention provides, for example, the following [1] to

[12] . [1] A styrene-based biaxially oriented sheet comprising a copolymer (A) containing vinyl cyanide monomer units and styrene monomer units, and a copolymer (B) containing maleimide monomer units and styrene monomer units, wherein at least one of the maximum orientation relaxation stress MD and the maximum orientation relaxation stress TD of the styrene-based biaxially oriented sheet exceeds 0.6 MPa. [2] The styrene-based biaxially oriented sheet according to [1], wherein the copolymer (A) content is 60% by mass or more and 95% by mass or less, and the copolymer (B) content is 5% by mass or more and 40% by mass or less, based on the total amount of the styrene-based biaxially oriented sheet. [3] The styrene-based biaxially oriented sheet according to [1] or [2], wherein the vinyl cyanide monomer unit is an acrylonitrile unit and the styrene-based monomer unit is a styrene unit. [4] A styrene-based biaxially oriented sheet according to any one of [1] to [3], wherein the maleimide monomer unit is an N-phenylmaleimide unit. [5] The styrene-based biaxially oriented sheet according to [4], wherein the content of N-phenylmaleimide units is 35% by mass or more and 55% by mass or less, based on the total amount of monomer units contained in copolymer (B). [6] A styrene-based biaxially oriented sheet according to any one of [1] to [5], wherein the copolymer (B) further comprises maleic anhydride units. [7] The styrene-based biaxially oriented sheet according to [1] or [2], wherein the copolymer (B) is a copolymer comprising styrene units, N-phenylmaleimide units and maleic anhydride units. [8] The styrene-based biaxially oriented sheet according to [7], wherein the copolymer (B) further comprises acrylonitrile units. [9] A styrene-based biaxially oriented sheet according to any one of [1] to [8], wherein the maximum orientation relaxation stress of the MD and the maximum orientation relaxation stress of the TD are both 0.8 MPa or less.

[10] A styrene-based biaxially oriented sheet according to any one of [1] to [9], wherein the MD thermal shrinkage initiation temperature and the TD thermal shrinkage initiation temperature are both 107°C or higher.

[11] A container made of a styrene-based biaxially oriented sheet as described in any of [1] to

[10] .

[12] The container described in

[11] , which is for food packaging. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a styrene-based biaxially oriented sheet that is excellent in heat resistance, oil resistance, and toughness, as well as a container using the same. [Modes for carrying out the invention]

[0010] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0011] In the numerical ranges described stepwise in this specification, the upper or lower limit of one step in the numerical range can be arbitrarily combined with the upper or lower limit of another step in the numerical range. In the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples.

[0012] In this specification, "(meth)acrylic acid" means acrylic acid and methacrylic acid. Also, "(meth)acrylate" means acrylate and methacrylate.

[0013] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of copolymers refer to values ​​calculated by GPC (gel permeation chromatography) on a polystyrene basis. Specifically, these refer to values ​​measured under the following conditions. Device: Manufactured by Shodex Corporation, Product name: "Shodex SYSTEM-21" Column: PLgel MIXED-B Measurement temperature: 40℃ Solvent: tetrahydrofuran Flow rate: 1.0mL / min Detection method: RI Sample concentration: 0.2% by mass Injection volume: 100 μL Calibration curve: Using standard polystyrene (manufactured by Polymer Laboratories), the relationship between elution time and elution volume is converted to molecular weight.

[0014] The styrene-based biaxially stretched sheet according to one embodiment of the present invention includes a copolymer (A) containing a vinyl cyanide monomer unit and a styrene-based monomer unit, and a copolymer (B) containing a maleimide-based monomer unit and a styrene-based monomer unit. Further, at least one of the maximum orientation relaxation stress in the MD and the maximum orientation relaxation stress in the TD of this styrene-based biaxially stretched sheet exceeds 0.6 MPa. In this specification, the "biaxially stretched sheet" means a sheet obtained by sequentially stretching or simultaneously stretching an unstretched sheet in the MD and TD.

[0015] In this specification, the "MD of the styrene-based biaxially stretched sheet" means the resin flow direction (MD: Machine Direction) when forming the sheet. Also, the "TD of the styrene-based biaxially stretched sheet" means the direction orthogonal to the MD (TD: Transverse Direction).

[0016] The styrene-based biaxially stretched sheet according to this embodiment (hereinafter, also simply referred to as "biaxially stretched sheet") has the above configuration, and thus is excellent in heat resistance and oil resistance, and further excellent in toughness. By using this biaxially stretched sheet for a container, a container having sufficient strength and high heat resistance and oil resistance can be obtained. In particular, if this biaxially stretched sheet is used as a food packaging container, in addition to having sufficient strength as a container, even when heated in a high-power microwave oven with food containing oil, for example, it can be made into a container that is less likely to deform and have holes.

[0017] The styrene-based biaxially stretched sheet according to this embodiment contains a copolymer (A) (hereinafter also simply referred to as "copolymer (A)") containing a vinyl cyanide monomer unit and a styrene-based monomer unit as monomer units. By including the copolymer (A) in the biaxially stretched sheet, the toughness of the biaxially stretched sheet can be made excellent, and the appearance of the sheet (for example, transparency, color tone, etc.) can also be made excellent.

[0018] Examples of the vinyl cyanide monomer unit contained in the copolymer (A) include units such as acrylonitrile, methacrylonitrile, cyano (meth) acrylate, etc. These vinyl cyanide monomers may be used alone or in combination of two or more. Among these, from the viewpoint of further enhancing oil resistance, the vinyl cyanide monomer unit preferably contains an acrylonitrile unit.

[0019] The content of the vinyl cyanide monomer unit in the copolymer (A) is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, particularly preferably 24% by mass or more, based on the total amount of monomer units contained in the copolymer (A), and is preferably 40% by mass or less, more preferably 35% by mass or less, still more preferably 32% by mass or less. The content of the vinyl cyanide monomer unit may be less than 30% by mass or may be 27% by mass or less based on the total amount of monomer units contained in the copolymer (A). If the content of the vinyl cyanide monomer unit is within this range, the transparency and color tone of the biaxially stretched sheet can be made more excellent.

[0020] Examples of the styrene-based monomer unit contained in the copolymer (A) include units such as styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, p-t-butylstyrene, etc. These may be used alone or in combination of two or more. Among these, the styrene-based monomer unit preferably contains a styrene unit.

[0021] The content of styrene monomer units in copolymer (A) is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 68% by mass or more, based on the total amount of monomer units contained in copolymer (A). The content of styrene monomer units may be greater than 70% by mass and may be 73% by mass or more, based on the total amount of monomer units contained in copolymer (A). Furthermore, the content of styrene monomer units is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 76% by mass or less, based on the total amount of monomer units contained in copolymer (A). If the content of styrene monomer units is within this range, the transparency and color of the biaxially oriented sheet can be made even better.

[0022] Copolymer (A) may optionally contain monomer units other than styrene monomer units and vinyl cyanide monomer units (also called other monomer units (x)). Examples of other monomer units (x) include vinyl monomer units. Examples of vinyl monomer units include (meth)acrylate units such as (meth)acrylic acid, maleic anhydride, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-methylhexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate. These may be used individually or in combination of two or more.

[0023] If the copolymer (A) contains other monomer units (x), the content of the other monomer units (x) is preferably 1% by mass or more, preferably less than 10% by mass, and more preferably 5% by mass or less, based on the total amount of monomer units contained in the copolymer (A).

[0024] In copolymer (A), from the viewpoint of further enhancing the effects of the present invention, it is preferable that the vinyl cyanide monomer units are acrylonitrile units and the styrene monomer units are styrene units. That is, in one embodiment, copolymer (A) is a copolymer containing only acrylonitrile units and styrene units (also called an acrylonitrile-styrene copolymer). In other words, the styrene-based biaxially oriented sheet according to one embodiment preferably contains an acrylonitrile-styrene copolymer. The preferred content of acrylonitrile units and styrene units in the acrylonitrile-styrene copolymer is the same as the range described above.

[0025] The content of copolymer (A) in the styrene-based biaxially oriented sheet is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and particularly preferably 75% by mass or more, based on the total amount of the styrene-based biaxially oriented sheet, and also preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the content of copolymer (A) is within this range, the toughness of the biaxially oriented sheet will be better.

[0026] Copolymer (A) is obtained by polymerizing a monomer mixture containing vinyl cyanide monomer units and styrene monomer units, preferably by polymerizing acrylonitrile and styrene. The polymerization method is not particularly limited, but continuous bulk polymerization is preferred from the viewpoint of easily reducing odor.

[0027] Known methods can be used for bulk continuous polymerization. Of these, it is preferable to carry out polymerization by adding a solvent such as ethylbenzene, toluene, or methyl ethyl ketone in an amount of 10 to 40 parts by mass per 100 parts by mass of the monomer mixture. In addition, conventionally known organic peroxides, molecular weight adjusters, etc. can be added as needed during polymerization. The polymerization temperature is preferably 80°C to 170°C, and more preferably 100°C to 160°C.

[0028] In one embodiment, copolymer (A) may be a mixture of multiple copolymers. In this case, each copolymer may be polymerized by any method, and then the multiple copolymers may be mixed to form copolymer (A).

[0029] The weight-average molecular weight (Mw) of copolymer (A) is preferably 50,000 or more, more preferably 100,000 or more, and also preferably 250,000 or less, and more preferably 200,000 or less. When the Mw of copolymer (A) is within this range, the toughness of the biaxially oriented sheet tends to be good, and the film-forming properties tend to be better. From a similar viewpoint, the number-average molecular weight (Mn) of copolymer (A) is preferably 25,000 or more, more preferably 30,000 or more, and also preferably 125,000 or less, and more preferably 80,000 or less.

[0030] The polydispersity (Mw / Mn) of copolymer (A), which is the ratio of Mw to the number-average molecular weight (Mn), is preferably 2.0 or higher, more preferably 2.1 or higher, and also preferably 3.0 or lower, more preferably 2.5 or lower. If the polydispersity of copolymer (A) is within this range, the toughness of the biaxially oriented sheet is less likely to decrease, and the oil resistance tends to be better.

[0031] The Vicat softening temperature (VST) of copolymer (A), measured under the conditions of JIS K 7206 B50, is preferably 100°C or higher, more preferably 105°C or higher, even more preferably 107°C or higher, and also preferably 120°C or lower, more preferably 115°C or lower, and even more preferably 110°C or lower. If the VST of copolymer (A) is within this range, the film-forming properties of the biaxially oriented sheet tend to be good.

[0032] The styrene-based biaxially oriented sheet according to this embodiment contains a copolymer (B) (hereinafter also simply referred to as "polymer (B)") which includes maleimide monomer units and styrene monomer units as monomer units. The inclusion of copolymer (B) in the styrene-based biaxially oriented sheet improves the heat resistance and oil resistance (including oil resistance at high temperatures) of the biaxially oriented sheet.

[0033] Examples of maleimide monomer units included in copolymer (B) include maleimide, N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-toluylmaleimide, N-xylylenemaleimide, N-naphthylmaleimide, Nt-butylmaleimide, N-orthochlorophenylmaleimide, and N-orthomethoxyphenylmaleimide. These may be used individually or in combination of two or more. Of these, the maleimide monomer units preferably include maleimide units or N-phenylmaleimide units, and more preferably include N-phenylmaleimide units.

[0034] When the maleimide monomer unit contains N-phenylmaleimide units, the content of N-phenylmaleimide units is preferably 50% by mass or more, more preferably 90% by mass or more, based on the total amount of maleimide monomer units, from the viewpoint of improving the heat resistance of the biaxially oriented sheet and suppressing yellowing. In one embodiment, the maleimide monomer unit may be N-phenylmaleimide units. That is, the maleimide monomer unit may contain only N-phenylmaleimide units.

[0035] The content of maleimide monomer units in copolymer (B) is preferably 35% by mass or more, more preferably 38% by mass or more, even more preferably 40% by mass or more, and also preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 52% by mass or less, based on the total amount of monomer units contained in copolymer (B). If the content of maleimide monomer units is within this range, the heat resistance of the biaxially oriented sheet tends to be improved and the color tends to be better. Even when the maleimide monomer units are N-phenylmaleimide units, the content of N-phenylmaleimide units may be within a similar range.

[0036] The styrene monomer units included in copolymer (B) are the same as those listed for copolymer (A), and the preferred examples are also the same. The styrene monomer units may be used alone or in combination of two or more types. Of these, it is preferable that the styrene monomer units include styrene units.

[0037] The content of styrene monomer units in copolymer (B) is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 47% by mass or more, and also preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 53% by mass or less, based on the total amount of monomer units contained in copolymer (B). If the content of styrene monomer units is within this range, the appearance of the biaxially oriented sheet can be made excellent.

[0038] Copolymer (B) may optionally contain monomer units other than styrene monomer units and maleimide monomer units. Examples of such monomer units include the other monomer units (x) described above. When copolymer (B) contains other monomer units (x), the content of other monomer units (x) is preferably 1% by mass or more, preferably less than 10% by mass, and more preferably 8% by mass or less, based on the total amount of monomer units contained in copolymer (B).

[0039] As for other monomer units (x), it is preferable to include maleic anhydride units from the viewpoint of improving heat resistance. That is, the copolymer (B) preferably further contains maleic anhydride units in addition to maleimide monomer units and styrene monomer units.

[0040] When copolymer (B) contains maleic anhydride units, the content of maleic anhydride units is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and preferably 2% by mass or less, and more preferably 1.1% by mass or less, based on the total amount of monomer units contained in copolymer (B). If the maleic anhydride content is within this range, the compatibility between copolymer (A) and copolymer (B) tends to be good.

[0041] In one embodiment, copolymer (B) may be a copolymer containing styrene units, N-phenylmaleimide units, and maleic anhydride units. The presence of styrene units, N-phenylmaleimide units, and maleic anhydride units in copolymer (B) makes it easier to improve the heat resistance and oil resistance of the biaxially oriented sheet. In one embodiment, copolymer (B) may be a copolymer containing only styrene units, N-phenylmaleimide units, and maleic anhydride units (also called a styrene-N-phenylmaleimide-maleic anhydride copolymer). The preferred content of styrene units, N-phenylmaleimide units, and maleic anhydride units in the styrene-N-phenylmaleimide-maleic anhydride copolymer is the same as the range described above.

[0042] A copolymer containing styrene units, N-phenylmaleimide units, and maleic anhydride units may further contain acrylonitrile units. That is, copolymer (B) may be a copolymer containing styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units.

[0043] When copolymer (B) is a copolymer containing styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units, the content of acrylonitrile units is preferably less than 15% by mass, and more preferably 10% by mass or less, based on the total amount of monomer units contained in copolymer (B). The lower limit of the acrylonitrile unit content is not particularly limited and may be greater than 0% by mass, and may be 5% by mass or more, based on the total amount of monomer units contained in copolymer (B). If the acrylonitrile unit content is within this range, the compatibility between copolymer (A) and copolymer (B) is less likely to deteriorate, and the appearance of the sheet will be better.

[0044] Copolymer (B) may be a copolymer containing only styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units (also called styrene-N-phenylmaleimide-maleic anhydride-acrylonitrile copolymer). The preferred content of styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units in the styrene-N-phenylmaleimide-maleic anhydride-acrylonitrile copolymer is the same as the range described above.

[0045] The content of copolymer (B) in the styrene-based biaxially oriented sheet is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, based on the total amount of the styrene-based biaxially oriented sheet, and also preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less. When the content of copolymer (B) is within this range, the toughness of the biaxially oriented sheet is improved.

[0046] Copolymer (B) is obtained by polymerizing a monomer mixture containing a maleimide monomer and a styrene monomer. Copolymer (B) may also be obtained by polymerizing styrene, N-phenylmaleimide, maleic anhydride, and optionally acrylonitrile. For example, solution polymerization and bulk polymerization can be used as polymerization methods.

[0047] In one embodiment, copolymer (B) may be a mixture of multiple copolymers. In this case, each copolymer may be polymerized by any method, and then the multiple copolymers may be mixed to form copolymer (B).

[0048] The weight-average molecular weight (Mw) of copolymer (B) is 50,000 or more, more preferably 80,000 or more, and also preferably 150,000 or less, more preferably 140,000 or less. If the Mw of copolymer (B) is within the above range, the appearance tends to be good. Furthermore, from a similar viewpoint, the number-average molecular weight (Mn) of copolymer (B) is preferably 15,000 or more, more preferably 25,000 or more, and also preferably 80,000 or less, more preferably 60,000 or less.

[0049] The polydispersity (Mw / Mn) of copolymer (B) is preferably 2.0 or higher, more preferably 2.3 or higher, and also preferably 3.0 or lower, more preferably 2.8 or lower. If the polydispersity of copolymer (B) is within this range, it is likely to have good compatibility with copolymer (A).

[0050] The Melt Flow Rate (MFR) of copolymer (B) is preferably 1.0 g / 10 min or more, more preferably 3 g / 10 min or more, and also preferably 100 g / 10 min or less, more preferably 70 g / 10 min or less. If the MFR of copolymer (B) is within the above range, the appearance of the biaxially oriented sheet tends to be good. In this specification, MFR refers to the value measured in accordance with JIS K 7210 under load conditions of 265°C and 98 N.

[0051] The styrene-based biaxially oriented sheet according to this embodiment may contain resins other than copolymer (A) and copolymer (B). Examples of other resins include styrene-based copolymers other than copolymer (A) and (B) (polymers containing styrene-based monomer units), high-impact polystyrene, ABS resin, AES resin, rubber-reinforced resins such as styrene-butadiene block copolymer resin, etc. When the biaxially oriented sheet contains other resins, it is preferable that the amount of other resins is less than 3% by mass based on the total amount of the styrene-based biaxially oriented sheet from the viewpoint of transparency and heat resistance.

[0052] Furthermore, the styrene-based biaxially oriented sheet according to this embodiment may optionally contain other additives such as ultraviolet absorbers, light stabilizers, antioxidants, lubricants, plasticizers, colorants, antistatic agents, flame retardants, and mineral oil, as well as reinforcing fibers such as glass fibers, carbon fibers, and aramid fibers, and fillers such as talc, silica, mica, and calcium carbonate. These may be used individually or in combination of two or more.

[0053] Examples of UV absorbers include 2-(5'-methyl-2'-hydroxyphenyl)benzotriazol, 2-(5'-t-butyl-2'-hydroxyphenyl)benzotriazol, 2-[2'-hydroxy-3',5'-bis(α,α-dimethylbenzyl)phenyl]benzotriazol, 2-(3',5'-di-t-butyl-2'-hydroxyphenyl)benzotriazol, 2-(3'-t-butyl-5'-methyl-2'-hydroxyphenyl)-5-chlorobenzotriazol, and 2-(3',5'-di-t-butyl-2'-hydroxyphenyl) Benzotriazole-based UV absorbers such as hydroxyphenyl)-5-chlorobenzotriazole, 2-(3',5'-di-t-amyl-2'-hydroxyphenyl)benzotriazole, 2-[3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methyl-2'-hydroxyphenyl]benzotriazole, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazole-2-yl)phenol]; 2-ethoxy-2'-ethyloxalate bisanilide, 2-ethoxy-5-t- Oxalate anilide-based UV absorbers such as tyl-2'-ethyl bisanilide oxalate and 2-ethoxy-4'-isodecylphenyl bisanilide oxalate; and hydroxy-4-n-octoxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, and 2-hydroxy-4-methoxy-2'-carboxybenzophenone. Examples include phenophenone-based UV absorbers; salicylic acid-based UV absorbers such as phenyl salicylate, pt-butylphenyl salicylate, and p-octylphenyl salicylate; cyanoacrylate-based UV absorbers such as 2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate and ethyl-2-cyano-3,3'-diphenyl acrylate; and titanium dioxide-based UV stabilizers such as rutile-type titanium dioxide, anatase-type titanium dioxide, alumina, silica, silane coupling agents, and titanium-based coupling agents.These may be used individually or in combination of two or more types.

[0054] Examples of light stabilizers include bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, dimethyl succinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, and poly[[6,(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl] Examples include [(2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene-[(2,2,6,6-tetramethyl-4-piperidyl)imino]], 1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine, etc. These may be used individually or in combination of two or more.

[0055] Examples of antioxidants include triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, pentaerythrityltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and octadecyl-3-(3,5-di-t-butyl Phenolic antioxidants such as -4-hydroxyphenyl)propionate, 2,2-thiobis(4-methyl-6-t-butylphenol) and 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene; ditridecyl-3,3'-thiodipropionate, dilauryl-3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate Sulfur-based antioxidants such as odipropionate and dioctyl-3,3'-thiodipropionate; trisnonylphenyl phosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecyl) phosphite, (tridecyl)pentaerythritol diphosphite, bis(octadecyl)pentaerythritol diphosphite, bis(di-t-butylphenyl)pentaerythritol diphosphite, bis(di Phosphorus-based antioxidants such as (t-butyl-4-methylphenyl)pentaerythritol diphosphite, dinonylphenyloctylphosphonite, tetrakis(2,4-di-t-butylphenyl)1,4-phenylene-diphosphite, tetrakis(2,4-di-t-butylphenyl)4,4'-biphenylene-diphosphite, and 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene are examples. These may be used individually or in combination of two or more.

[0056] The styrene-based biaxially oriented sheet according to this embodiment may optionally contain known reinforcing rubber. Examples of reinforcing rubber include butadiene rubber, styrene-butadiene rubber, methyl (meth)acrylate-butadiene-styrene rubber, and ethylene-propylene rubber. These may be used individually or in combination of two or more. When the biaxially oriented sheet contains reinforcing rubber, from the viewpoint of transparency, it is preferable that the amount is less than 10% by mass based on the total amount of the styrene-based biaxially oriented sheet.

[0057] In the styrene-based biaxially oriented sheet according to this embodiment, at least one of the maximum orientation relaxation stress of MD and the maximum orientation relaxation stress of TD exceeds 0.6 MPa. That is, in the styrene-based biaxially oriented sheet, the maximum orientation relaxation stress of MD may exceed 0.6 MPa, and the maximum orientation relaxation stress of TD may exceed 0.6 MPa. Having the maximum orientation relaxation stress within this range makes the toughness of the biaxially oriented sheet excellent. The maximum orientation relaxation stresses of MD and TD may be the same or different. From the viewpoint of further improving the toughness of the biaxially oriented sheet, both the maximum orientation relaxation stress of MD and the maximum orientation relaxation stress of TD may exceed 0.6 MPa.

[0058] From the viewpoint of improving the toughness of the biaxially oriented sheet, the maximum orientation relaxation stresses of MD and TD are preferably 0.62 MPa or higher, more preferably 0.65 MPa or higher, and even more preferably 0.7 MPa or higher, respectively. Furthermore, the maximum orientation relaxation stresses of MD and TD are preferably 1.2 MPa or lower, more preferably 1.0 MPa or lower, and even more preferably 0.8 MPa or lower, respectively. If the lower limit of the maximum orientation relaxation stresses of MD and TD is within this range, the heat resistance and oil resistance of the biaxially oriented sheet will be improved, and the effects of the present invention can be further enhanced. The maximum orientation relaxation stresses of MD and TD of the biaxially oriented sheet can be measured according to the conditions of ASTM D1540, and more specifically, according to the method described in the examples below.

[0059] The ratio of the maximum orientation relaxation stress of MD to the maximum orientation relaxation stress of TD (MD / TD) is preferably 0.5 or more, more preferably 0.7 or more, even more preferably 0.8 or more, and also preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less.

[0060] The thermal shrinkage initiation temperature of the styrene-based biaxially oriented sheet according to this embodiment may be 107°C or higher, or 110°C or higher, respectively. The upper limit of the thermal shrinkage initiation temperature is not particularly limited, but may be, for example, 130°C or lower, 123°C or lower, or 120°C or lower. The thermal shrinkage initiation temperature in this specification can be measured according to the method described in the examples below.

[0061] The thickness of the styrene-based biaxially oriented sheet according to this embodiment is not particularly limited, but may be 0.15 mm or more, or 0.20 mm or more, and may be 0.35 mm or less, or 0.30 mm or less.

[0062] The film impact strength of the styrene-based biaxially oriented sheet according to this embodiment, as measured in accordance with ASTM-D3420, is preferably 1.8 mm / J or more and 2.5 mm / J or less.

[0063] In this embodiment, a styrene-based biaxially oriented sheet is manufactured by introducing copolymer (A), copolymer (B), and other components as needed into an extruder, melt-mixing them, and then extruding them from a die (preferably a T-die) to produce an unoriented sheet. The thickness of the unoriented sheet is preferably 1.0 mm or more, more preferably 1.4 mm or more, and preferably 5.0 mm or less, more preferably 2.5 mm or less, from the viewpoint of providing a thickness suitable for packaging containers. Subsequently, a biaxially oriented sheet can be manufactured by stretching the unoriented sheet sequentially or simultaneously in the biaxial direction.

[0064] As for the stretching method, conventionally known methods can be employed, such as stretching an unstretched sheet using a biaxial stretcher.

[0065] The stretching ratio to the MD is preferably 2 times or more, more preferably 2.5 times or more, and also preferably 4 times or less, more preferably 3 times or less. The stretching ratio to the TD is preferably 2 times or more, more preferably 2.5 times or more, and also preferably 4 times or less, more preferably 3.5 times or less. The stretching ratio is a ratio based on the length of the MD and TD of the unstretched sheet (i.e., a ratio when the lengths of the MD and TD of the unstretched sheet are set to "1").

[0066] The temperature during melt mixing is preferably 220°C or higher, more preferably 240°C or higher, and also preferably 300°C or lower, more preferably 280°C or lower. The temperature during stretching is preferably 140°C or higher, more preferably 145°C or higher, and also preferably 160°C or lower, more preferably 155°C or lower. Furthermore, the stretching speed is preferably 20 mm / second or higher, more preferably 35 mm / second or lower, and preferably 40 mm / second or lower, more preferably 35 mm / second or lower, from the viewpoint of orientation relaxation stress.

[0067] In this embodiment, the styrene-based biaxially oriented sheet may, if necessary, be coated with an anti-fogging agent on the sheet surface that comes into contact with the contents of food or the like.

[0068] When applying an antifogging agent, for example, conventionally known antifogging agents for styrene-based biaxially oriented sheets can be used. Examples of antifogging agents include nonionic surfactants, polyvinyl alcohol and its copolymers, polyvinylpyrrolidone and its copolymers, and water-soluble polymers, and these antifogging agents may be applied to the surface of the stretched sheet. The amount of application is not particularly limited, for example, 10 mg / m². 2 More than 150mg / m 2 The following adjustments can be made as needed. Conventional known coating methods can be employed.

[0069] The styrene-based biaxially oriented sheet according to this embodiment can be molded into a container by known methods. For example, it can be made into a container by methods such as vacuum forming or pressure forming. More specifically, a molded product with good mold reproducibility can be obtained by hot plate heating pressure forming. The "container" in this invention includes not only a main container for storing contents, but also a lid material that can be fitted to the main container.

[0070] A container formed from the styrene-based biaxially oriented sheet according to this embodiment can be used, for example, as a food packaging container. The food packaging container can be used for microwave heating or refrigeration. Because the container made from the styrene-based biaxially oriented sheet according to this embodiment has excellent toughness, heat resistance, and oil resistance (including oil resistance at high temperatures), it is particularly suitable for use as a food packaging container for microwave heating. However, the use of a container obtained from the biaxially oriented sheet according to this embodiment is not limited to food packaging. [Examples]

[0071] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0072] The monomer unit composition ratios in copolymers (A) and (B) were measured by the method described below. Mw, Mn, VST, and MFR were measured according to the measurement methods described above. <Composition ratio of monomer units: Pyrolysis gas chromatography> Pyrolysis device: Manufactured by Japan Analysis Industry Co., Ltd. Product name: "JPS-220" Thermal decomposition temperature: 590℃ Gas chromatograph: Hewlett-Packard Corporation, Product name: "5890 SERIES I" Column: Micro-polarity column, manufactured by Agilent Technologies, Inc., product name: "DB-5" Carrier gas: Helium, pressure 2 psi Temperature conditions: Hold at 50°C for 5 minutes, then increase the temperature to 250°C at a rate of 18°C / min, and hold at 250°C for 7 minutes. Detection: FID Samples of copolymers (A) and (B) were weighed at 0.3 mg and measured under the above conditions. The monomer composition ratio was determined from the peak area ratio of the detected components.

[0073] [Production of copolymer (A-1)] Copolymers containing vinyl cyanide monomer units and styrene monomer units were produced by continuous bulk polymerization. One fully mixed stirring tank was used as the reactor, and polymerization was carried out with a capacity of 30 L. A raw material solution of 60% by mass of styrene, 22% by mass of acrylonitrile, and 18% by mass of ethylbenzene was prepared and continuously supplied to the reactor at a flow rate of 9.5 L / h. In addition, 160 ppm of t-butyl peroxyisopropyl monocarbonate was added to the raw material solution as a polymerization initiator, and 400 ppm of n-dodecyl mercaptan was added as a chain transfer agent, continuously added to the raw material solution supply line. The reaction temperature of the reactor was adjusted to 145°C. The copolymer solution continuously withdrawn from the reactor was supplied to a vacuum defloration tank with a preheater to separate unreacted styrene, acrylonitrile, and ethylbenzene. The temperature of the preheater was adjusted so that the temperature of the copolymer in the defloration tank was 235°C. Furthermore, the pressure inside the defoliation tank was set to 0.4 kPa. The copolymer was extracted from the vacuum defoliation tank using a gear pump, extruded into strands, cooled with cooling water, and then cut to obtain pelletized copolymer (A-1). The constituent units of copolymer (A-1) were 73.5% by mass of styrene units and 26.5% by mass of acrylonitrile units. The weight-average molecular weight was 146,000. The VST was 107°C. Details of copolymer (A-1) are shown in Table 1.

[0074] [Production of copolymers (A-2) to (A-3)] Copolymers (A-2) to (A-3) were prepared in the same manner as copolymer (A-1), except that the ratio of acrylonitrile and styrene in the monomer mixture was changed. Details of copolymers (A-2) to (A-3) are shown in Table 1.

[0075] [Table 1]

[0076] [Production of copolymer (B-1)] A copolymer (B-1) containing maleimide monomer units and styrene monomer units was prepared. In an autoclave with a volume of approximately 120 L equipped with a stirrer, 42 parts by mass of styrene, 10 parts by mass of acrylonitrile, 4 parts by mass of maleic anhydride, 0.6 parts by mass of 2,4-diphenyl-4-methyl-1-pentene, and 27 parts by mass of methyl ethyl ketone were charged. After replacing the gas phase with nitrogen gas, the mixture was heated to 92°C over 40 minutes while stirring. While maintaining the temperature at 92°C, a solution of 21 parts by mass of maleic anhydride and 0.15 parts by mass of t-butyl peroxy-2-ethylhexanoate dissolved in 85 parts by mass of methyl ethyl ketone, and 20 parts by mass of styrene were continuously added to the autoclave over 4.5 hours. Furthermore, after the addition of the solution containing maleic anhydride was completed, a solution of 0.02 parts by mass of t-butyl peroxy-2-ethylhexanoate dissolved in 9 parts by mass of methyl ethyl ketone and 3 parts by mass of styrene were continuously added over 30 minutes. After the addition, the temperature was raised to 120°C and the reaction was allowed to proceed for 30 minutes to complete the polymerization. Subsequently, 23 parts by mass of aniline and 0.4 parts by mass of triethylamine were added to the polymerization solution and the reaction was carried out at 140°C for 7 hours. The imidization reaction solution after the reaction was put into a vented screw extruder, and volatile components were removed to obtain a pellet-shaped maleimide copolymer (B-1). Copolymer (B-1) consisted of 52% by mass of styrene units, 8% by mass of acrylonitrile units, 39% by mass of N-phenylmaleimide units, and 1% by mass of maleic anhydride units, with a weight-average molecular weight Mw of 80,000 and a polydispersity (Mw / Mn) of 2.4. Furthermore, the MFR (265°C, 98N) was 70g / 10min. Details of copolymer (B-1) are shown in Table 2.

[0077] [Production of copolymers (B-2) to (B-4)] Copolymer (B-2) was prepared in the same manner as copolymer (B-1), except that the amount of aniline added was adjusted to control the conversion rate of maleic anhydride to maleimide, and α-methylstyrene dimer was added to adjust the Mw. Copolymers (B-3) to (B-4) were prepared in the same manner as copolymer (B-1), except that the conversion rate to maleimide, Mw was adjusted, and acrylonitrile was not added. Details of copolymers (B-2) to (B-4) are shown in Table 2.

[0078] [Table 2]

[0079] [Example 1] Copolymer (A-1) (80% by mass of the total mass of the resin composition) and copolymer (B-1) (20% by mass of the total mass of the resin composition) were melt-mixed and pelletized using a co-directional twin-screw extruder (manufactured by Toshiba Machine Co., Ltd., product name: "TEM-35B", effective length (L / D): 32) under the conditions of cylinder temperature 260°C, feed rate 20 kg / hr, and screw rotation speed 200 rpm. The obtained pellets were melt-mixed using a single-screw extruder with a screw diameter of 40 mm at 240°C and 70 rpm, and passed through a T-die to obtain an unstretched sheet with a thickness of 1.9 mm. The obtained unstretched sheet was sequentially stretched using a twin-screw stretcher at MD stretching temperature of 145°C, TD stretching temperature of 145°C, stretching speed of 30 mm / sec, MD stretching ratio of 2.8 times, and TD stretching ratio of 3.0 times to obtain a styrene-based bi-screw stretched sheet. The maximum orientation relaxation stress of the obtained biaxially oriented sheets was measured by the following method. The maximum orientation relaxation stress of the MD (medium-weighted) and TD (tall-weighted) sections of the obtained biaxially oriented sheets was 0.71 MPa, and the maximum orientation relaxation stress was 0.73 MPa.

[0080] <Method for measuring maximum orientation relaxation stress> The thermal shrinkage stress was measured using a thermal shrinkage stress measuring instrument (manufactured by Tester Industries Co., Ltd., product name: "TP-501") according to the conditions of ASTM D1540. Specifically, the obtained sheet was cut into 150 mm (MD) x 15 mm (TD) sections to prepare measurement samples. The sheet samples were held in the chucks of the measuring instrument with a chuck distance of 100 mm and immersed in a 150°C water bath. During this process, thermal shrinkage occurred in the MD or TD of the sheet, and the load at which the thermal shrinkage stress reached its maximum was defined as the maximum orientation relaxation stress of the MD or TD.

[0081] [Examples 2-10, Comparative Examples 1-2] A stretched sheet was prepared in the same manner as in Example 1, except that the ratio of copolymers (A) and (B) and the stretching temperature were as shown in Table 3. The maximum orientation relaxation stresses of MD and TD of the obtained biaxially stretched sheet were as shown in Table 3.

[0082] [evaluation] The heat resistance (temperature at which thermal shrinkage began) and toughness (MIT strength) of the obtained sheets were evaluated using the following methods. In addition, a mayonnaise test was conducted to evaluate oil resistance under high-temperature conditions using the following method.

[0083] <Heat resistance (temperature at which thermal shrinkage begins)> The thermal shrinkage initiation temperature was measured using a thermal shrinkage stress measuring instrument (manufactured by Tester Industries Co., Ltd., product name: "TP-501"). Specifically, a sheet was cut to 150 mm (MD) x 15 mm (TD) to prepare a measurement sample. The sheet sample was held in the chuck portion of the measuring instrument with a chuck distance of 100 mm and immersed in an oil bath at 90°C or lower. Then, the temperature of the oil bath was increased from 90°C to 140°C at a heating rate of 0.5°C / min. At this time, thermal shrinkage occurred in the MD or TD of the sheet, and the temperature at which the thermal shrinkage stress reached 0.05 MPa or higher was defined as the thermal shrinkage initiation temperature of the MD or TD. A higher thermal shrinkage initiation temperature indicates higher heat resistance of the sheet, and the heat resistance of the sheet was determined according to the evaluation criteria below. An evaluation of B or higher indicates excellent heat resistance. A: The thermal shrinkage initiation temperature for both MD and TD is 109°C or higher. B: The thermal shrinkage initiation temperature for both MD and TD is 105°C or higher but less than 109°C, or one of MD and TD has a thermal shrinkage initiation temperature of 105°C or higher but less than 109°C, and the other has a thermal shrinkage initiation temperature of 109°C or higher. C: The thermal shrinkage initiation temperature of either MD or TD is less than 105°C.

[0084] <Oil resistance (mayonnaise test)> The obtained biaxially oriented sheet was molded using a hot plate molding machine (manufactured by Wakisaka Engineering Co., Ltd., product name: "HPT-400A") under the conditions of a hot plate temperature of 145°C and a mold temperature of 90°C to obtain a container lid. In addition, a main container was prepared by molding a 2.4 mm thick expanded polystyrene (PSP) sheet. Meanwhile, the central part of the obtained biaxially oriented sheet was cut to a size of 50 mm x 50 mm, and 1 g of mayonnaise was attached to each of the nine locations to create evaluation sheets. Three of these evaluation sheets were prepared and attached to the inside of the container lid made using the method described above. Next, 300 g of water was placed in the container body made using the method described above, the container lid with the three evaluation sheets attached was fitted on top, and it was heated in a 1500 W microwave oven for 90 seconds. After that, the number of holes in the evaluation sheets was counted and evaluated according to the following evaluation criteria. If the evaluation is B or higher, it can be said that the heat resistance and oil resistance when oil is attached is excellent. A: Out of 27 areas where mayonnaise was applied, fewer than 10 areas on the evaluation sheet had holes. B: Of the 27 areas where mayonnaise was applied, 10 to 20 areas on the evaluation sheet had holes. C: Out of 27 areas where mayonnaise was present, more than 20 areas on the evaluation sheet had holes.

[0085] <Toughness (MIT Strength)> Samples were prepared by cutting the sheet into strips measuring 15 mm wide x 100 mm long, with the longitudinal direction being the midpoint (MD) of the sheet. Following JIS P8115:2001, the test specimens were placed in an MIT folding fatigue testing machine (manufactured by Toyo Seiki Seisakusho Co., 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 bending cycles along the MD until fracture was measured. Ten samples were tested individually, and the average value (average number of bending cycles) was calculated. Additionally, the average number of bending cycles along the TD (tension-to-distance) until fracture was determined in the same manner as above, except that the longitudinal direction of the sample was set to the TD (tension-to-distance) of the biaxially oriented sheet. A higher average number of bending cycles indicates greater sheet toughness, and the sheet's toughness (strength) was evaluated according to the following evaluation criteria. A rating of B or higher indicates excellent toughness. A: Both MD and TD have an average of 14 or more flexion counts. B: The average number of flexions for both MD and TD is 11 or more but less than 14, or one of the average number of flexions for MD or TD is 11 or more but less than 14, and the other is 14 or more. C: Either the average number of flexions for MD or TD is less than 11.

[0086] As shown in Table 3, a styrene-based biaxially oriented sheet containing a styrene copolymer (A) containing vinyl cyanide monomer units and styrene monomer units, and a styrene copolymer (B) containing maleimide monomer units and styrene monomer units, and in which at least one of the maximum orientation relaxation stress of MD and the maximum orientation relaxation stress of TD exceeds 0.6 MPa, exhibits superior heat resistance, oil resistance, and toughness. On the other hand, among the biaxially oriented sheets of the comparative examples that did not meet these conditions, even if one of them exhibited superior heat resistance, oil resistance, or toughness, none of them exhibited superiority in all of these areas.

[0087] [Table 3]

[0088] Furthermore, the transparency and color of the styrene-based biaxially oriented sheets according to Examples 1 to 8 were evaluated using the following method. The results are shown in Table 4.

[0089] <Sheet Transparency> The haze (%) of a styrene-based biaxially oriented sheet was measured using an NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000. Haze represents the degree of cloudiness, including both the surface and interior of the sheet. A lower haze value indicates higher transparency; a haze of 1.5% or less indicates excellent sheet transparency.

[0090] <Sheet color> The color of styrene-based biaxially oriented sheets was evaluated using a colorimeter (Konica Minolta, Inc., product name: "Spectrophotometer CM-2500d"). Specifically, six sheets with a thickness of 0.25 mm were stacked to create a 1.5 mm thick sheet sample, and the color of the sample was evaluated under SCI (Science Color Isolation) conditions. A smaller b* value indicates less yellowness and better hue, and a b* value of 15 or less indicates excellent sheet color.

[0091] [Table 4]

Claims

1. A copolymer (A) containing vinyl cyanide monomer units and styrene monomer units, A styrene-based biaxially oriented sheet comprising a copolymer (B) containing maleimide monomer units and styrene monomer units, A styrene-based biaxially oriented sheet wherein at least one of the maximum orientation relaxation stress of the MD and the maximum orientation relaxation stress of the TD exceeds 0.6 MPa.

2. The styrene-based biaxially oriented sheet according to claim 1, wherein, based on the total amount of the styrene-based biaxially oriented sheet, the content of copolymer (A) is 60% by mass or more and 95% by mass or less, and the content of copolymer (B) is 5% by mass or more and 40% by mass or less.

3. The styrene-based biaxially oriented sheet according to claim 1 or 2, wherein the vinyl cyanide monomer unit is an acrylonitrile unit and the styrene-based monomer unit is a styrene unit.

4. The styrene-based biaxially oriented sheet according to claim 1 or 2, wherein the maleimide monomer unit is an N-phenylmaleimide unit.

5. The styrene-based biaxially oriented sheet according to claim 4, wherein the content of the N-phenylmaleimide units is 35% by mass or more and 55% by mass or less, based on the total amount of monomer units contained in the copolymer (B).

6. The styrene-based biaxially oriented sheet according to claim 1 or 2, wherein the copolymer (B) further comprises maleic anhydride units.

7. The styrene-based biaxially oriented sheet according to claim 1 or 2, wherein the copolymer (B) is a copolymer comprising styrene units, N-phenylmaleimide units, and maleic anhydride units.

8. The styrene-based biaxially oriented sheet according to claim 7, wherein the copolymer (B) further comprises acrylonitrile units.

9. The styrene-based biaxially oriented sheet according to claim 1 or 2, wherein the maximum orientation relaxation stress of the MD and the maximum orientation relaxation stress of the TD are both 0.8 MPa or less.

10. The styrene-based biaxially oriented sheet according to claim 1 or 2, wherein the thermal shrinkage initiation temperature of the MD and the thermal shrinkage initiation temperature of the TD are both 107°C or higher.

11. A container made of a styrene-based biaxially oriented sheet according to claim 1 or 2.

12. The container according to claim 11, which is for food packaging.

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