Sheets and containers

Abstract

To provide a sheet with excellent oil resistance. [Solution] A sheet comprising a styrene-based biaxially oriented resin layer containing a copolymer (A) containing vinyl cyanide monomer units and styrene-based monomer units, and a copolymer (B) containing maleimide-based monomer units and styrene-based monomer units, and a coating layer provided on one surface of the styrene-based biaxially oriented resin layer, the coating layer containing at least one of sucrose fatty acid ester and polyglycerin fatty acid ester, and a water-soluble polymer.

Description

[Technical Field]

[0001] This disclosure relates to sheets and containers. [Background technology]

[0002] Sheets containing styrene resins are used in food packaging containers and the like. For example, Patent Document 1 discloses a styrene biaxially oriented sheet comprising a styrene copolymer (A) containing vinyl cyanide monomer units and a styrene copolymer (B) containing maleimide monomer units, wherein the thermal shrinkage initiation temperature in the longitudinal and width directions of the styrene biaxially oriented sheet is 107°C or higher. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-100682 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Food packaging containers are sometimes heated in a microwave oven or the like while the food is still inside. In this case, the food packaging container may be heated to high temperatures while in contact with the oil contained in the food, so the constituent materials of the food packaging container are required to have high oil resistance. However, according to the inventors' studies, when a container made of a sheet containing the styrene resin described above is heated in contact with oil, holes may form in the part that comes into contact with the oil, indicating that there is room for improvement in terms of oil resistance. Therefore, one aspect of this disclosure is to provide a sheet with excellent oil resistance. [Means for solving the problem]

[0005] As a result of diligent research, the present inventors have found that a sheet having a coating layer on one side of a styrene-based biaxially oriented resin layer containing a copolymer (A) containing vinyl cyanide monomer units and styrene monomer units, and a copolymer (B) containing maleimide monomer units and styrene monomer units, with at least one of sucrose fatty acid ester and polyglycerin fatty acid ester, as well as a water-soluble polymer, exhibits superior oil resistance compared to a sheet made solely of a styrene-based biaxially oriented resin layer.

[0006] This disclosure provides, in several respects, the following [1] to

[17] . [1] A sheet comprising a styrene-based biaxially oriented resin layer comprising a copolymer (A) comprising vinyl cyanide monomer units and styrene-based monomer units, and a copolymer (B) comprising maleimide-based monomer units and styrene-based monomer units, and a coating layer provided on one surface of the styrene-based biaxially oriented resin layer, comprising at least one of sucrose fatty acid ester and polyglycerin fatty acid ester, and a water-soluble polymer. [2] The sheet according to [1], wherein the water-soluble polymer is polyvinyl alcohol. [3] The sheet according to [2], wherein the degree of polymerization of the polyvinyl alcohol is 350 or more. [4] The sheet according to [2] or [3], wherein the degree of saponification of the polyvinyl alcohol is 86 mol% or more. [5] The coating layer is a sheet according to any one of [1] to [4], comprising the sucrose fatty acid ester. [6] The sheet according to any one of claims [1] to [5], wherein the mass ratio of the content of at least one of the sucrose fatty acid ester and polyglycerol fatty acid ester to the content of the water-soluble polymer is 50 / 50 or more and 80 / 20 or less. [7] The mass of the coating layer per unit area of ​​the styrene-based biaxially oriented resin layer is 10 mg / m² 2 More than 150mg / m 2 The sheet listed in any of the following [1] to [6]. [8] A sheet according to any one of [1] to [7], wherein 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, based on the total mass of the styrene-based biaxially oriented resin layer. [9] The sheet according to any one of [1] to [8], wherein the vinyl cyanide monomer unit is an acrylonitrile unit and the styrene monomer unit in the copolymer (A) is a styrene unit.

[10] The sheet according to any one of [1] to [9], wherein the maleimide monomer unit is an N-phenylmaleimide unit.

[11] The sheet according to

[10] , wherein the content of the N-phenylmaleimide units is 35% by mass or more and 55% by mass or less, based on the total mass of monomer units contained in the copolymer (B).

[12] The sheet according to any one of [1] to

[11] , wherein the copolymer (B) further comprises maleic anhydride units.

[13] The sheet according to any one of [1] to

[12] , wherein the styrene monomer unit in the copolymer (B) is a styrene unit.

[14] The sheet according to any one of [1] to

[13] , wherein the copolymer (B) further comprises acrylonitrile units.

[15] The sheet according to any one of [1] to

[14] , wherein both the thermal shrinkage start temperature of the MD and the thermal shrinkage start temperature of the TD of the sheet are 107°C or higher.

[16] A container consisting of any of the sheets described in [1] to

[15] .

[17] The container described in

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

[0007] According to one aspect of this disclosure, it is possible to provide a sheet with excellent oil resistance. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the sheet.

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments.

[0010] FIG. 1 is a schematic cross-sectional view showing an embodiment of a sheet. The sheet 1 shown in FIG. 1 includes a styrene-based biaxially stretched resin layer (hereinafter, also simply referred to as "biaxially stretched resin layer") 11 and a coating layer 12 provided on one surface of the biaxially stretched resin layer 11.

[0011] The biaxially stretched resin layer 11 contains a copolymer (A) containing a vinyl cyanide monomer unit and a styrene-based monomer unit. Note that those corresponding to the copolymer (B) described later are not considered to correspond to the copolymer (A).

[0012] Examples of the vinyl cyanide monomer unit contained in the copolymer (A) include units of acrylonitrile, methacrylonitrile, and cyano (meth)acrylate. These vinyl cyanide monomer units may be used alone or in combination of two or more. From the viewpoint of easily obtaining a sheet 1 with excellent oil resistance, the vinyl cyanide monomer unit preferably contains an acrylonitrile unit.

[0013] The content of the vinyl cyanide monomer unit may be 5% by mass or more, 10% by mass or more, 20% by mass or more, or 24% by mass or more based on the total mass of the monomer units contained in the copolymer (A), and from the viewpoint of the sheet 1 having more excellent transparency, it may be 40% by mass or less, 35% by mass or less, 32% by mass or less, less than 30% by mass, or 27% by mass or less. When the content of the vinyl cyanide monomer unit in the copolymer (A) is within the above range, the color, appearance, and film-forming property of the sheet 1 are more likely to be better.

[0014] Examples of styrene monomer units contained in copolymer (A) include styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, and pt-butylstyrene units. These styrene monomer units may be used individually or in combination of two or more. It is preferable that the styrene monomer units include styrene units.

[0015] The content of styrene monomer units in copolymer (A) may be 60% by mass or more, 65% by mass or more, 68% by mass or more, more than 70% by mass, or 73% by mass or more, based on the total mass of monomer units contained in copolymer (A), from the viewpoint of achieving better transparency of sheet 1. Alternatively, the content of styrene monomer units in copolymer (A) may be 95% by mass or less, 90% by mass or less, 80% by mass or less, or 76% by mass or less, based on the total mass of monomer units contained in copolymer (A). When the content of styrene monomer units in copolymer (A) is within the above range, the color of sheet 1 tends to be better.

[0016] Copolymer (A) may optionally further contain monomer units other than vinyl cyanide monomer units and styrene 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)acrylic acid, maleic anhydride, and (meth)acrylate units such as 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 other monomer units may be used individually or in combination of two or more.

[0017] If the copolymer (A) contains other monomer units (x), the content of the other monomer units (x) may be 1% by mass or more, less than 10% by mass, or 5% by mass or less, based on the total mass of monomer units contained in the copolymer (A).

[0018] In copolymer (A), it is preferable that the vinyl cyanide monomer units are acrylonitrile units and the styrene monomer units are styrene units. Copolymer (A) may be, for example, a copolymer consisting only of acrylonitrile units and styrene units (also called "acrylonitrile-styrene copolymer"). The content of acrylonitrile units and styrene units in the acrylonitrile-styrene copolymer may be within the numerical ranges described above as the content of vinyl cyanide monomer units and styrene monomer units in copolymer (A), respectively.

[0019] Copolymer (A) is obtained by polymerizing a monomer mixture containing a vinyl cyanide monomer (e.g., acrylonitrile) and a styrene monomer (e.g., styrene). The polymerization method is not particularly limited, but from the viewpoint of easily reducing odor, a bulk continuous polymerization method is preferred.

[0020] Known methods can be used as the bulk continuous polymerization method. An example of a bulk continuous polymerization method is a method in which 10 to 40 parts by mass of a solvent such as ethylbenzene, toluene, or methyl ethyl ketone is added to 100 parts by mass of the monomer mixture and polymerization is carried out. During polymerization, conventionally known organic peroxides, molecular weight adjusters, etc. may be added as needed. The polymerization temperature may be 80°C or higher, or 100°C or higher, and 170°C or lower, or 160°C or lower.

[0021] In one embodiment, copolymer (A) may be a mixture of multiple copolymers. In this case, multiple copolymers may be obtained individually by any polymerization method, and then the multiple copolymers may be mixed to form copolymer (A).

[0022] The weight-average molecular weight (Mw) of copolymer (A) may be 50,000 or more, or 100,000 or more, and may be 250,000 or less, or 200,000 or less. Having the Mw of copolymer (A) within the above range makes it easier for sheet 1 to have excellent strength and film-forming properties. Similarly, the number-average molecular weight (Mn) of copolymer (A) may be 25,000 or more, or 30,000 or more, and may be 125,000 or less, or 80,000 or less.

[0023] The polydispersity (Mw / Mn), which is the ratio of Mw to Mn in copolymer (A), may be 2.0 or higher, or 2.1 or higher, and may be 3.0 or lower, or 2.5 or lower. When the polydispersity of copolymer (A) is within the above range, the strength of sheet 1 is less likely to decrease, and oil resistance tends to be better.

[0024] In this specification, Mw and Mn refer to values ​​calculated by GPC (gel permeation chromatography) on a polystyrene basis. Specifically, they 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: 100μL Calibration curve: Using standard polystyrene (manufactured by Polymer Laboratories), the relationship between elution time and elution amount is converted to molecular weight to determine various average molecular weights.

[0025] The Vicat softening temperature (VST) of copolymer (A) may be 100°C or higher, 105°C or higher, or 107°C or higher, and may be 120°C or lower, 115°C or lower, or 110°C or lower. When the VST of copolymer (A) is within the above range, the film-forming properties of sheet 1 tend to be good. In this specification, VST means the temperature measured under a 50N load according to the JIS K 7206 B50 method.

[0026] The copolymer (A) content may be 60% by mass or more, 65% by mass or more, 70% by mass or more, or 75% by mass or more, based on the total mass of the biaxially oriented resin layer 11, from the viewpoint of sheet 1 having superior transparency, color and toughness, and may be 95% by mass or less, 90% by mass or less, or 85% by mass or less, based on the total mass of the biaxially oriented resin layer 11, from the viewpoint of sheet 1 having superior heat resistance and oil resistance.

[0027] The biaxially oriented resin layer 11 contains a copolymer (B) comprising maleimide monomer units and styrene monomer units. Examples of maleimide monomer units contained 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 units. These maleimide monomer units may be used individually or in combination of two or more. The maleimide monomer units preferably contain maleimide units or N-phenylmaleimide units, and more preferably contain N-phenylmaleimide units.

[0028] If the maleimide monomer unit contains N-phenylmaleimide units, the proportion of N-phenylmaleimide units may be 50% by mass or more, or 90% by mass or more, based on the total mass of the maleimide monomer unit, from the viewpoint of improving the heat resistance of sheet 1 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.

[0029] The content of maleimide monomer units may be 35% by mass or more, 38% by mass or more, or 40% by mass or more, and may be 60% by mass or less, 55% by mass or less, or 52% by mass or less, based on the total mass of monomer units contained in copolymer (B). When the content of maleimide monomer units is within the above range, the heat resistance of sheet 1 tends to be improved and the color tends to be better. If the maleimide monomer units are N-phenylmaleimide units, the content of N-phenylmaleimide units may be within the above numerical range as the content of maleimide monomer units.

[0030] Examples of styrene monomer units contained in copolymer (B) include those mentioned above as examples of styrene monomer units contained in copolymer (A). Styrene monomer units may be used individually or in combination of two or more types. It is preferable that the styrene monomer units contain styrene units.

[0031] The content of styrene monomer units in copolymer (B) may be 40% by mass or more, 45% by mass or more, or 47% by mass or more, and may be 60% by mass or less, 55% by mass or less, or 53% by mass or less, based on the total mass of monomer units contained in polymer (B). Having a styrene monomer unit content within the above range tends to result in a superior appearance for sheet 1.

[0032] Copolymer (B) may optionally further contain monomer units other than maleimide monomer units and styrene monomer units. Examples of such monomer units include the other monomer units (x) described above.

[0033] If the copolymer (B) contains other monomer units (x), the content of the other monomer units (x) may be 1% by mass or more, less than 10% by mass, or 8% by mass or less, based on the total mass of monomer units contained in the copolymer (B).

[0034] From the viewpoint of improving heat resistance, copolymer (B) preferably contains maleic anhydride units. That is, copolymer (B) preferably further contains maleic anhydride units in addition to maleimide monomer units and styrene monomer units.

[0035] If copolymer (B) contains maleic anhydride units, the content of maleic anhydride units may be 0.1% by mass or more, or 0.3% by mass or more, and 2% by mass or less, or 1.1% by mass or less, based on the total mass of monomer units contained in copolymer (B). Having a maleic anhydride content within the above range tends to result in good compatibility between copolymer (A) and copolymer (B).

[0036] In one embodiment, copolymer (B) may be a copolymer containing styrene units, N-phenylmaleimide units, and maleic anhydride units. By copolymer (B) being a copolymer containing styrene units, N-phenylmaleimide units, and maleic anhydride units, the heat resistance and oil resistance of sheet 1 are more easily improved. In one embodiment, copolymer (B) may be a copolymer consisting only of styrene units, N-phenylmaleimide units, and maleic anhydride units (also referred to as "styrene-N-phenylmaleimide-maleic anhydride copolymer"). The content of styrene units, N-phenylmaleimide units, and maleic anhydride units in the styrene-N-phenylmaleimide-maleic anhydride copolymer may be within the numerical ranges described above as the content of styrene units, N-phenylmaleimide units, and maleic anhydride units in copolymer (B), respectively.

[0037] Copolymer (B) may further contain acrylonitrile units. In this case, the toughness of sheet 1 tends to be better. The acrylonitrile unit content in copolymer (B) may be greater than 0% by mass, or 5% by mass or more, and less than 15% by mass, or 10% by mass or less, based on the total mass of monomer units contained in copolymer (B). Having the acrylonitrile unit content within the above range makes it easier to suppress deterioration of compatibility between copolymer (A) and copolymer (B), and also tends to result in a better appearance of sheet 1.

[0038] For example, the copolymer containing styrene units, N-phenylmaleimide units, and maleic anhydride units described above 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. In one embodiment, copolymer (B) may be a copolymer consisting only of styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units (also referred to as "styrene-N-phenylmaleimide-maleic anhydride-acrylonitrile copolymer"). The content of styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units in the styrene-N-phenylmaleimide-maleic anhydride-acrylonitrile copolymer may be within the numerical range described above as the content of styrene units, N-phenylmaleimide units, maleic anhydride units, and acrylonitrile units in copolymer (B), respectively.

[0039] Copolymer (B) is obtained by polymerizing a monomer mixture containing a maleimide monomer (e.g., N-phenylmaleimide) and a styrene monomer (e.g., styrene). The monomer mixture may optionally contain maleic anhydride and acrylonitrile. Examples of polymerization methods include solution polymerization and bulk polymerization.

[0040] In one embodiment, copolymer (B) may be a mixture of multiple copolymers. In this case, multiple copolymers may be obtained individually by any polymerization method, and then the multiple copolymers may be mixed to form copolymer (B).

[0041] The Melt Flow Rate (MFR) of copolymer (B) may be 1 g / 10 min or more, or 3 g / 10 min or more, and may be 100 g / 10 min or less, or 70 g / 10 min or less. Having the MFR of copolymer (B) within the above range tends to result in a good appearance for sheet 1. In this specification, MFR refers to the value measured in accordance with JIS K 7210 under load conditions of 265°C and 98 N.

[0042] The Mw of copolymer (B) may be 50,000 or more, or 80,000 or more, and may be 150,000 or less, or 140,000 or less. Having the Mw of copolymer (B) within the above range tends to result in a good appearance for sheet 1. From a similar viewpoint, the Mn of copolymer (B) may be 15,000 or more, or 25,000 or more, and may be 80,000 or less, or 60,000 or less.

[0043] The polydispersity (Mw / Mn) of copolymer (B) may be 2.0 or higher, or 2.3 or higher, and may be 3.0 or lower, or 2.8 or lower. Having the polydispersity of copolymer (B) within the above range tends to result in good compatibility between copolymer (A) and copolymer (B).

[0044] The content of copolymer (B) may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total mass of the biaxially oriented resin layer 11, from the viewpoint of sheet 1 having superior heat resistance and oil resistance, and may be 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less, from the viewpoint of sheet 1 having superior transparency, color and toughness.

[0045] The biaxially oriented resin layer 11 may contain resins other than copolymer (A) and copolymer (B). Examples of other resins include styrene copolymers other than copolymer (A) and copolymer (B) (polymers containing styrene monomer units), and specifically, rubber-reinforced resins such as high-impact polystyrene, ABS resin, AES resin, and styrene-butadiene block copolymer resin. When the biaxially oriented resin layer 11 contains other resins, the content of the other resins may be less than 3% by mass of the total mass of the biaxially oriented resin layer 11, from the viewpoint of providing sheet 1 with superior transparency and heat resistance.

[0046] Furthermore, the biaxially oriented resin layer 11 may contain, as needed, other additives such as ultraviolet absorbers, light stabilizers, antioxidants, lubricants, plasticizers, colorants, antistatic agents, flame retardants, and mineral oil; 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.

[0047] 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 phenyl)-5-chlorobenzotriazol, 2-(3',5'-di-t-amyl-2'-hydroxyphenyl)benzotriazol, 2-[3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methyl-2'-hydroxyphenyl]benzotriazol, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol]; 2-ethoxy-2'-ethyl oxalate bisanilide, 2-ethoxy-5-t-butyl Oxalate anilide-based UV absorbers such as bisanilide 2'-ethyl oxalate and bisanilide 2-ethoxy-4'-isodecylphenyl oxalate; and benzylbenzophenone such as 2-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 zophenone-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 titanium dioxide treated with surface treatment agents 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.

[0048] 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.

[0049] 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-4 Phenolic antioxidants such as -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'-thio Sulfur-based antioxidants such as dipropionate 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- Examples of phosphorus-based antioxidants include t-butyl-4-methylphenyl)pentaerythritol diphosphite, dinonylphenyloctylphosphonite, tetrakis(2,4-di-t-butylphenyl)1,4-phenylene-diphosphonite, tetrakis(2,4-di-t-butylphenyl)4,4'-biphenylene-diphosphonite, and 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene. These may be used individually or in combination of two or more.

[0050] The biaxially oriented resin layer 11 may contain known reinforcing rubber. Examples of reinforcing rubber include butadiene rubber, styrene-butadiene rubber, methyl (meth)acrylate-butadiene-styrene rubber, ethylene-propylene rubber, etc. These may be used individually or in combination of two or more. When the biaxially oriented resin layer 11 contains reinforcing rubber, the reinforcing rubber content may be less than 10% by mass of the total mass of the biaxially oriented resin layer 11, from the viewpoint of superior transparency.

[0051] The thickness of the biaxially oriented resin layer 11 may be, for example, 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.

[0052] The biaxially oriented resin layer 11 can be manufactured by a method that includes, for example, 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, and then stretching the obtained unoriented sheet sequentially or simultaneously in the biaxial direction. The temperature during melt-mixing may be, for example, 220°C or higher, or 240°C or higher, and 300°C or lower, or 280°C or lower. The thickness of the unoriented sheet may be 1.0 mm or higher, or 1.4 mm or higher, 5.0 mm or lower, or 2.5 mm or lower, from the viewpoint of easily obtaining a sheet of a thickness suitable for use as a packaging container.

[0053] As for the stretching method, conventionally known methods can be employed, such as stretching an unstretched sheet using a biaxial stretcher. The stretching ratio of the MD may be 2 times or more, or 2.5 times or more, and may be 4 times or less, or 3 times or less. The stretching ratio of the TD may be 2 times or more, or 2.5 times or more, and may be 4 times or less, or 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").

[0054] The temperature during stretching may be 140°C or higher, or 145°C or higher, and 160°C or lower, or 155°C or lower. Furthermore, the stretching speed may be 20 mm / second or higher, or 25 mm / second or lower, and 40 mm / second or lower, or 35 mm / second or lower, from the viewpoint of orientation relaxation stress.

[0055] The coating layer 12 is provided on one surface of the biaxially oriented resin layer 11. As shown in Figure 1, the coating layer 12 may cover the entire surface of one side of the biaxially oriented resin layer 11, or it may cover only a portion of it. The coating layer 12 contributes to improving the oil resistance of the sheet 1 (especially oil resistance at high temperatures). The coating layer 12 contains at least one of sucrose fatty acid ester and polyglycerin fatty acid ester.

[0056] The fatty acids constituting sucrose fatty acid esters may be saturated fatty acids or unsaturated fatty acids. The number of carbon atoms in saturated fatty acids may be 6 or more, 8 or more, or 10 or more, or 30 or less, 26 or less, or 22 or less. Examples of saturated fatty acids include caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and montanic acid.

[0057] The number of carbon atoms in unsaturated fatty acids may be, for example, 10 or more, or 24 or less. Examples of unsaturated fatty acids include lindeic acid, palmitoleic acid, oleic acid, elaidic acid, isoleic acid, erucic acid, linoleic acid, and linolenic acid.

[0058] The fatty acids constituting the sucrose fatty acid ester may be one of the above-mentioned fatty acids used alone, or two or more may be used in combination. From the viewpoint of further superior oil resistance, shelf life, and economic efficiency, the fatty acids constituting the sucrose fatty acid ester are preferably one or more fatty acids selected from lauric acid, myristic acid, palmitic acid, and stearic acid.

[0059] The degree of polymerization of the polyglycerin constituting the polyglycerin fatty acid ester may be 2 or more, 4 or more, 6 or more, or 8 or more, and may be 16 or less, 14 or less, or 12 or less. The fatty acids constituting the polyglycerin fatty acid ester may be saturated fatty acids or unsaturated fatty acids. The number of carbon atoms in the fatty acids may be 10 or more, and may be 18 or less, 16 or less, or 14 or less. Examples of fatty acids include capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, and linoleic acid.

[0060] Examples of polyglycerol fatty acid esters include diglycerol laurate, diglycerol stearate, diglycerol oleate, tetraglycerol laurate, tetraglycerol stearate, tetraglycerol oleate, hexaglycerol stearate, hexaglycerol oleate, decaglycerol laurate, decaglycerol stearate, and decaglycerol oleate.

[0061] The HLB (Hydrophilic-Lipophilic Balance) of polyglycerin fatty acid esters may be 12 or higher, 13 or higher, 14 or higher, or 15 or higher, and may be 20 or lower, 19 or lower, 18 or lower, 17 or lower, 16 or lower, or 15 or lower. In this specification, HLB refers to the HLB calculated by the Atlas method.

[0062] The hemoglobin level (HLB) of polyglycerol fatty acid esters can be adjusted by controlling the relative amounts of hydrophilic and hydrophobic groups in the polyglycerol fatty acid ester. Specifically, for example, increasing the number of carbon atoms in the fatty acids constituting the polyglycerol fatty acid ester increases the relative amount of hydrophobic groups in the polyglycerol fatty acid ester, thus decreasing the HLB of the polyglycerol fatty acid ester. Conversely, decreasing the number of carbon atoms in the fatty acids constituting the polyglycerol fatty acid ester decreases the relative amount of hydrophobic groups in the polyglycerol fatty acid ester, thus increasing the HLB of the polyglycerol fatty acid ester.

[0063] The content of at least one of sucrose fatty acid ester and polyglycerin fatty acid ester may be 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more, based on the total mass of the coating layer 12, and may be 80% by mass or less, 75% by mass or less, 70% by mass or less, or 65% by mass or less.

[0064] The coating layer 12 may contain, for example, only one of sucrose fatty acid esters and polyglycerin fatty acid esters, or it may contain both sucrose fatty acid esters and polyglycerin fatty acid esters. The mass ratio of the sucrose fatty acid ester content to the polyglycerin fatty acid ester content (sucrose fatty acid ester content / polyglycerin fatty acid ester content) may be 1 / 99 or more, or 5 / 95 or more, or 30 / 70 or less, or 20 / 80 or less.

[0065] The coating layer 12 contains a water-soluble polymer. When the coating layer 12 contains a polyglycerin fatty acid ester, the lubricity of the sheet 1 tends to deteriorate. However, by using a water-soluble polymer together with the polyglycerin fatty acid ester, it becomes easier to obtain a sheet 1 with excellent lubricity. Examples of water-soluble polymers include polyvinyl alcohol, polysaccharides, acrylic acid polymers or their salts, vinylpyrrolidone homopolymers or copolymers, and polyoxyethylene-polyoxypropylene copolymers. The water-soluble polymer is preferably polyvinyl alcohol.

[0066] Polyvinyl alcohol (hereinafter also referred to as "PVA") is a homopolymer composed of vinyl alcohol units or a copolymer composed of vinyl alcohol units and vinyl acetate units. The degree of polymerization of polyvinyl alcohol may be 200 or more, 300 or more, 350 or more, or 400 or more, from the viewpoint of providing superior oil resistance for sheet 1 and superior appearance of sheet 1 after long-term storage (e.g., 6 months). The degree of polymerization of polyvinyl alcohol may be 2500 or less, and from the viewpoint of providing superior appearance of sheet 1, it may be 2000 or less, 1500 or less, 1200 or less, 1000 or less, 900 or less, 800 or less, 700 or less, or 600 or less. The degree of polymerization of polyvinyl alcohol refers to the degree measured according to JIS K 6726:1994.

[0067] The degree of saponification of polyvinyl alcohol may be 78 mol% or more, 80 mol% or more, 83 mol% or more, 85 mol% or more, or 86 mol% or more from the viewpoint of providing superior oil resistance for sheet 1, and may be 99 mol% or less, 97 mol% or less, 96 mol% or less, or 95 mol% or less from the viewpoint of providing superior appearance for sheet 1. The degree of saponification of polyvinyl alcohol refers to the degree measured in accordance with JIS K 6726:1994.

[0068] The content of the water-soluble polymer in the coating layer 12 may be 25% by mass or more, 30% by mass or more, or 35% by mass or more, and may be 55% by mass or less, 50% by mass or less, or 45% by mass or less, based on the total mass of the coating layer 12.

[0069] The mass ratio of the content of at least one of sucrose fatty acid ester and polyglycerin fatty acid ester to the content of water-soluble polymer in the coating layer 12 (at least one of sucrose fatty acid ester and polyglycerin fatty acid ester / water-soluble polymer) may be 40 / 60 or more, 45 / 55 or more, 50 / 50 or more, or 55 / 45 or more from the viewpoint of providing better oil resistance of sheet 1 and suppressing appearance and contamination during sheet 1 molding, and may be 80 / 20 or less, 75 / 25 or less, 70 / 30 or less, or 65 / 35 or less from the viewpoint of providing better oil resistance and moldability of sheet 1.

[0070] The amount of the coating layer 12 provided on at least one surface of the biaxially stretched resin layer 11 can be set as appropriate. The mass of the coating layer 12 per unit area of the biaxially stretched resin layer 11 is 1 mg / m 2 or more, 5 mg / m 2 or more, 10 mg / m 2 or more, or 20 mg / m 2 or more, from the viewpoint that the sheet 1 is excellent in oil resistance. The mass of the coating layer 12 per unit area of the biaxially stretched resin layer 11 is 250 mg / m 2 or less, 200 mg / m 2 or less, 180 mg / m 2 or less, 150 mg / m 2 or less, or 130 mg / m 2 or less, from the viewpoint that the sheet 1 is excellent in transparency.

[0071] The coating layer 12 is formed, for example, by applying an aqueous solution (aqueous solution for the coating layer) containing the above components onto at least one surface (the surface that is corona-treated if necessary) of the biaxially stretched resin layer 11 and drying it. The content of at least one of sucrose fatty acid ester and polyglycerol fatty acid ester, and the water-soluble polymer (for example, polyvinyl alcohol) in the aqueous solution for the coating layer may be, for example, 0.01% by mass or more, and may be 10% by mass, based on the total amount of the solution. From the viewpoint of suppressing unevenness during coating and improving coating properties, the viscosity (viscosity measured by a tuning fork type vibrating viscometer) of the aqueous solution for the coating layer at 25°C may be 0.5 mPa·s or more, 0.7 mPa·s or more, or 0.9 mPa·s or more, and may be 2.0 mPa·s or less, 1.8 mPa·s or less, or 1.5 mPa·s or less.

[0072] The method of applying the aqueous solution for the coating layer is not particularly limited, and examples include a method of applying using a roll coater, a knife coater, a gravure roll coater, etc. Also, the coating layer 12 may be formed by spraying, dipping, etc.

[0073] The sheet 1 shown in Figure 1 consists of two layers: a biaxially oriented resin layer 11 and a coating layer 12 provided on one surface of the biaxially oriented resin layer 11. However, the sheet's composition is not limited to this. The sheet may consist of three or more layers. For example, the sheet may have a biaxially oriented resin layer, a first coating layer provided on one surface of the biaxially oriented resin layer, and a second coating layer provided on the other surface of the biaxially oriented resin layer. The details of the first and second coating layers may be the same as those described above for the coating layer 12, independently of each other.

[0074] The sheet may have layers other than the biaxially oriented resin layer and the coating layer. Examples of other layers include a curable resin layer containing photocurable resin, UV curable resin, thermosetting resin, etc., and a layer formed by antioxidants and antistatic agents bleed out from the biaxially oriented resin layer (e.g., an antioxidant layer containing antioxidants, an antistatic layer containing antistatic agents). Possible but not limited layer configurations include "coating layer / biaxially oriented resin layer / curable resin layer" (where the coating layer, biaxially oriented resin layer, and curable resin layer are laminated in this order) and "coating layer / biaxially oriented resin layer / antistatic layer" (where the coating layer, biaxially oriented resin layer, and antistatic layer are laminated in this order).

[0075] The maximum orientation relaxation stress (MD) of the sheet in each of the above embodiments may be 0.1 MPa or higher, 0.6 MPa or lower, or 0.5 MPa or lower. The maximum orientation relaxation stress (TD) of the biaxially oriented resin layer 11 may be 0.2 MPa or higher, 0.7 MPa or lower, or 0.6 MPa or lower. The ratio of the maximum orientation relaxation stress (MD) to the maximum orientation relaxation stress (TD) (maximum orientation relaxation stress of MD / maximum orientation relaxation stress of TD) may be 0.5 or higher, 0.6 or higher, 1.5 or lower, or 1.0 or lower. In this specification, the maximum orientation relaxation stresses of MD and TD refer to values ​​measured according to the conditions of ASTM D1540. Furthermore, MD and TD of the sheet refer to the MD and TD of the biaxially oriented resin layer, respectively.

[0076] The thermal shrinkage initiation temperatures of the MD and TD of the sheets in each of the embodiments described above may be 107°C or higher, 110°C or higher, 130°C or lower, 123°C or lower, or 120°C or lower, respectively. In this specification, the thermal shrinkage initiation temperature refers to the temperature determined by the method described in the examples below.

[0077] The film impact strength of the sheets in each of the above embodiments may be 1.8 mm / J or more, and may be 2.5 mm / J or less. In this specification, film impact strength means that which is determined according to ASTM-D3420.

[0078] The sheet described above can be used, for example, to form containers. One embodiment of this disclosure is a container made of the above sheet. In a container made of a sheet, it is preferable that the surface of the sheet on the coating layer side is the surface that comes into contact with the contents of the container (for example, food containing oil). Methods for forming the sheet into a container include, for example, vacuum forming and pressure forming. Specifically, a molded product with good mold reproducibility can be obtained by hot plate heating pressure forming. Note that the term "container" includes not only a main container for storing contents, but also a lid material that can be fitted to the main container.

[0079] The container made of the sheet described above is suitable for food packaging because of its excellent oil resistance, and is particularly suitable for food packaging that will be heated in a microwave oven. The container made of the sheet may be for food packaging or for microwave heating. However, the use of the container made of the sheet described above is not limited to food packaging. [Examples]

[0080] The present disclosure will be described in more detail below based on the examples. However, the present disclosure is not limited to these examples.

[0081] The monomer unit content in copolymers (A) and (B) was measured by the method described below. Mw, Mn, VST, and MFR were measured by the method described above.

[0082] <Method for measuring monomer content (thermolysis 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 at a pressure of 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.

[0083] [Preparation of copolymer (A-1)] The copolymer was prepared 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 in 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 remove unreacted styrene, acrylonitrile, and ethylbenzene. The temperature of the preheater was adjusted so that the copolymer temperature in the vacuum defloration tank was 235°C. The pressure in the vacuum defloration tank was set to 0.4 kPa. The obtained copolymer was extracted from the vacuum defloration tank using a gear pump, extruded into strands, cooled with cooling water, and then cut to obtain pelletized copolymer (A-1). Copolymer (A-1) contained 73.5% by mass of styrene units and 26.5% by mass of acrylonitrile units, based on the total mass of monomer units contained in copolymer (A-1). The weight-average molecular weight was 146,000, and the VST was 107°C. Details of copolymer (A-1) are shown in Table 1.

[0084] [Preparation of copolymers (A-2) to (A-3)] Copolymers (A-2) to (A-3) were obtained in the same manner as copolymer (A-1), except that the ratio of acrylonitrile and styrene in the raw material solution was changed. Details of copolymers (A-2) to (A-3) are shown in Table 1.

[0085] [Table 1]

[0086] [Preparation of copolymer (B-1)] 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 temperature was raised 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. After the addition of the above 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 to the autoclave over 30 minutes. After addition, the temperature was raised to 120°C and the reaction was carried out for 30 minutes to complete the polymerization. To the obtained polymerization solution, 23 parts by mass of aniline and 0.4 parts by mass of triethylamine were added 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 pelletized copolymer (B-1). Copolymer (B-1) contained 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, based on the total mass of monomer units contained in copolymer (B-1). The weight-average molecular weight Mw was 80,000, the polydispersity (Mw / Mn) was 2.4, and the MFR (265°C, 98N) was 70 g / 10 min. Details of copolymer (B-1) are shown in Table 2.

[0087] [Preparation of copolymers (B-2) to (B-4)] Copolymer (B-2) was prepared in the same manner as copolymer (B-1), except that the conversion rate of maleic anhydride to maleimide was adjusted by adjusting the amount of aniline added, and Mw was adjusted by adding α-methylstyrene dimer. Copolymers (B-3) to (B-4) were prepared in the same manner as copolymer (B-1), except that the conversion rate of maleic anhydride to maleimide and Mw were adjusted in the same manner as above, and acrylonitrile was not added. Details of copolymers (B-2) to (B-4) are shown in Table 2.

[0088] [Table 2]

[0089] [Other materials] Details of the other materials are as follows: • Sucrose laurate ester: Manufactured by Mitsubishi Chemical Corporation, "L-1695" • Sucrose stearate: Manufactured by Mitsubishi Chemical Corporation, "S-1570" • Sucrose myristic acid ester: Manufactured by Mitsubishi Chemical Corporation, "M-1695" • Polyglycerin fatty acid ester: Polyglyceryl-10 laurate (decaglycerin laurate) (manufactured by Riken Vitamin Co., Ltd., "Poem J-0021", HLB: 15) • PVA1: Polyvinyl alcohol (degree of polymerization: 500, degree of saponification: 88 mol%) • PVA2: Polyvinyl alcohol (degree of polymerization: 300, degree of saponification: 88 mol%) • PVA3: Polyvinyl alcohol (degree of polymerization: 1000, degree of saponification: 88 mol%) • PVA4: Polyvinyl alcohol (degree of polymerization: 500, degree of saponification: 85 mol%) • PVA5: Polyvinyl alcohol (degree of polymerization: 500, degree of saponification: 95 mol%)

[0090] The method for preparing PVA1 is as follows: 3000 g of vinyl acetate, 2080 g of methanol, and 2.5 g of azobisisobutyronitrile were placed in a polymerization reactor, and after purging with nitrogen, the mixture was heated to its boiling point. Polymerization was stopped when the polymerization rate reached 92%. Next, unreacted vinyl acetate was removed, and the resulting polymer was saponified with sodium hydroxide. Then, it was hot-air dried at 90°C for 90 minutes to obtain polyvinyl alcohol. The degree of polymerization of the obtained polyvinyl alcohol (PVA1) was 500, and the average degree of saponification was 88%. By adjusting the ratio of vinyl acetate to methanol in the above method for preparing PVA1, polyvinyl alcohols with different degrees of polymerization (PVA2 and PVA3) were prepared. Furthermore, by adjusting the temperature in the saponification reaction in the above method for preparing PVA1, polyvinyl alcohols with different degrees of saponification (PVA4 and PVA5) were prepared.

[0091] [Sheet manufacturing] (Example 1) Copolymers of the types and quantities shown in Table 3 were melt-mixed and pelletized using a co-direction twin-screw extruder (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 a stretching temperature of 147°C, a stretching speed of 30 mm / sec, a stretching ratio of 2.8 times for the medium-density (MD) and a stretching ratio of 3.0 times for the tangential (TD) to obtain a biaxially oriented resin layer (thickness: 0.25 mm).

[0092] Furthermore, an aqueous coating solution was prepared by dissolving 60 parts by mass of sucrose laurate ester and 40 parts by mass of polyvinyl alcohol (PVA1) in 9900 parts by mass of water. This aqueous coating solution was applied to one surface of the biaxially oriented resin layer prepared by the above method at a rate of 5 g / m² using a bar coater. 2After application, the coating layer was formed on one side of the biaxially oriented resin layer by drying in an oven at 105°C for 1 minute, thereby obtaining the sheet of Example 1. The mass of the obtained coating layer per unit area of ​​the biaxially oriented resin layer (hereinafter also simply referred to as "mass per unit area") was 50 mg / m². 2 That was the case.

[0093] (Comparative Example 1) A sheet (a sheet consisting of a biaxially oriented resin layer) was manufactured in the same manner as in Example 1, except that a coating layer was not formed.

[0094] (Examples 2-3, 6-11) Sheets were manufactured in the same manner as in Example 1, except that the type of sucrose fatty acid ester, the type of polyvinyl alcohol, or the mass per unit area of ​​the coating layer was changed as shown in Tables 3 and 4.

[0095] (Examples 4 and 5) An aqueous coating solution was prepared by dissolving 60 parts by mass of at least one of sucrose stearate ester and polyglycerin fatty acid ester in the amounts shown in Table 3, and 40 parts by mass of polyvinyl alcohol (PVA1) in 10,000 parts by mass of water. One surface of a biaxially oriented resin layer prepared in the same manner as in Example 1 was corona-treated to adjust it to 52 dyne, and the above aqueous coating solution was applied to the corona-treated surface at a rate of 5 g / m² using a bar coater. 2 After application, the coating layer was formed on one side of the biaxially oriented resin layer by drying in a 70°C oven for 5 minutes, thereby obtaining the sheet of Example 4 or 5. The mass per unit area of ​​the obtained coating layer was 50 mg / m². 2 That was the case.

[0096] (Examples 12-17) A sheet was manufactured in the same manner as in Example 1, except that the composition of the biaxially oriented resin layer was changed as shown in Table 5.

[0097] [Measurement and evaluation of the physical properties of the sheet] The physical properties of each of the manufactured example and comparative example sheets were measured and evaluated as follows.

[0098] <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") in accordance with ASTM D1540 conditions. Specifically, a sheet was cut to 150 mm (MD (MD of the biaxially oriented resin layer; the same applies hereinafter)) × 15 mm (TD (TD of the biaxially oriented resin layer; the same applies hereinafter)) to prepare a measurement sample. The measurement sample was held in the chuck portion of the measuring instrument with a chuck distance of 100 mm and immersed in a 150°C water bath. At this time, 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. In both the example and comparative example sheets, the maximum orientation relaxation stress of the MD was 0.45 MPa, and the maximum orientation relaxation stress of the TD was 0.50 MPa.

[0099] <Oil resistance (mayonnaise test)> The 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 the lid material for the container. Separately, the central part of the sheet was cut to a size of 50 mm x 50 mm, and 1 g of mayonnaise was attached to 9 locations on the cut sheet to create evaluation sheets. Three of these evaluation sheets were made and attached to the inside of the lid material for the container. In addition, a main container molded from a 2.4 mm thick expanded polystyrene (PSP) sheet was prepared, and 300 g of water was placed in the main container. The lid material with the three evaluation sheets attached was fitted onto the main container, and it was heated in a 1500 W microwave oven for 90 seconds. After that, the evaluation sheets were observed, and the number of locations where holes occurred (number of holes) was checked out of the 27 locations where mayonnaise was attached. The results are shown in Tables 3 to 5. If the number of holes is 18 or less, the sheet can be said to have excellent oil resistance, and the fewer the number of holes, the better.

[0100] <Heat resistance (temperature at which thermal shrinkage begins)> The thermal shrinkage onset 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 measurement 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 raised 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 onset temperature of the MD or TD. The results are shown in Tables 3 to 5. A higher thermal shrinkage onset temperature indicates better heat resistance of the sheet.

[0101] <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 mid-length (MD) of the biaxially oriented resin layer. Following JIS P8115:2001, the samples 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 of the MD until fracture was measured. Ten samples were tested individually, and the average value (average number of bending cycles) was calculated. Furthermore, the average number of bending cycles of the TD until fracture was determined in the same manner as above, except that the longitudinal direction of the sample was the TD of the biaxially oriented resin layer. The results are shown in Tables 3-5. A higher average number of bending cycles indicates superior sheet toughness.

[0102] [Table 3]

[0103] [Table 4]

[0104] [Table 5]

[0105] Furthermore, the transparency and color of the biaxially oriented sheets according to the examples were evaluated using the following methods. The results are shown in Tables 6 to 8.

[0106] <Transparency (haze)> The haze (%) of the sheet was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000. A smaller haze indicates better sheet transparency.

[0107] <Color tone (b * Value)> The color of the 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 sheet sample with a thickness of 1.5 mm, and the color was evaluated using the SCI method. * The value was measured. b * A smaller value indicates less yellowness and a better hue for the sheet.

[0108] [Table 6]

[0109] [Table 7]

[0110] [Table 8] [Explanation of Symbols]

[0111] 1...Sheet, 11...Biaxially oriented resin layer, 12...Coating layer.

Claims

1. A styrene-based biaxially oriented resin layer 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, A sheet comprising a coating layer provided on one surface of the styrene-based biaxially oriented resin layer, the coating layer containing at least one of a sucrose fatty acid ester and a polyglycerin fatty acid ester, and a water-soluble polymer.

2. The sheet according to claim 1, wherein the water-soluble polymer is polyvinyl alcohol.

3. The sheet according to claim 2, wherein the degree of polymerization of the polyvinyl alcohol is 350 or more.

4. The sheet according to claim 2, wherein the degree of saponification of the polyvinyl alcohol is 86 mol% or more.

5. The sheet according to any one of claims 1 to 4, wherein the coating layer comprises the sucrose fatty acid ester.

6. The sheet according to any one of claims 1 to 4, wherein the mass ratio of the content of at least one of the sucrose fatty acid ester and polyglycerol fatty acid ester to the content of the water-soluble polymer is 50 / 50 or more and 80 / 20 or less.

7. The mass of the coating layer per unit area of ​​the styrene-based biaxially oriented resin layer is 10 mg / m². ２ 150mg / m or more ２ The sheet according to any one of claims 1 to 4, which is as follows:

8. The sheet according to claim 1, wherein, based on the total mass of the styrene-based biaxially oriented resin layer, 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.

9. The sheet according to any one of claims 1 to 4, wherein the vinyl cyanide monomer unit is an acrylonitrile unit, and the styrene monomer unit in the copolymer (A) is a styrene unit.

10. The sheet according to any one of claims 1 to 4, wherein the maleimide monomer unit is an N-phenylmaleimide unit.

11. The sheet according to claim 10, wherein the content of the N-phenylmaleimide units is 35% by mass or more and 55% by mass or less, based on the total mass of monomer units contained in the copolymer (B).

12. The sheet according to claim 11, wherein the copolymer (B) further comprises maleic anhydride units.

13. The sheet according to claim 12, wherein the styrene monomer unit in the copolymer (B) is a styrene unit.

14. The sheet according to claim 13, wherein the copolymer (B) further comprises acrylonitrile units.

15. The sheet according to any one of claims 1 to 4, wherein the thermal shrinkage initiation temperature of the MD and the thermal shrinkage initiation temperature of the TD are both 107°C or higher.

16. A container made of a sheet according to any one of claims 1 to 4.

17. The container according to claim 16, for use in food packaging.

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