JP2019077195A - Biaxially stretched sheet and molded article - Google Patents

Abstract

To provide a biaxially stretched sheet which is excellent in all of oil resistance, color tone, appearance (for instance, appearance during molding and coating appearance), and antifogging properties in good balance.SOLUTION: A biaxially stretched sheet has a biaxially stretched resin layer formed by biaxially stretching a resin composition containing a copolymer which contains acrylonitrile and styrene as monomer units and has a mass ratio between the acrylonitrile and the styrene of 16/84 to 32/68; and a coating layer which covers at least one surface of the biaxially stretched resin layer, contains (A) sucrose fatty acid ester and (B) polyvinyl alcohol having a saponification degree of 85-95 mol% and a polymerization degree of 300-2,000, and has a mass ratio between (A) the sucrose fatty acid ester and (B) the polyvinyl alcohol of 80/20 to 50/50.SELECTED DRAWING: None

Description

  The present invention relates to a biaxially oriented sheet and a molded article.

  Conventionally, a lid made of a synthetic resin sheet and a container main body are fitted as a container used when selling foodstuffs, processed foods, etc. in stores such as supermarkets, convenience stores, departments, and valve shops. Packaging containers are used.

  Biaxially stretched polystyrene sheet is widely used in the field of food packaging containers because of its excellent transparency and high rigidity, but whitening phenomenon of the sheet surface is observed when it is stored for a long time with oil attached. There has been a need for biaxially oriented polystyrene sheets with improved oil resistance (e.g., Patent Documents 1 and 2).

  Further, as described in Patent Documents 1 and 2, the biaxially stretched polystyrene sheet has, in addition to oil resistance, mechanical strength, impact resistance, heat resistance, oil resistance, transparency, thermoforming property, etc. The various characteristics of are also sought.

JP 10-7817 A JP 2001-105489 A

  An object of the present invention is to provide a biaxially oriented sheet and a molded article which are excellent in all of oil resistance, hue, appearance (for example, appearance during molding, coating appearance) and antifogging properties in a well-balanced manner.

The present invention provides the biaxially oriented sheet and molded article shown below.
(1) A biaxially stretched resin layer obtained by biaxially stretching a resin composition containing acrylonitrile and styrene as monomer units and a copolymer having an acrylonitrile / styrene mass ratio of 16/84 to 32/68 A coating layer for covering at least one surface of the biaxially oriented resin layer, wherein (A) sucrose fatty acid ester, and (B) saponification degree is 85 to 95 mol%, polymerization degree is 300 to 2000 A biaxially stretched sheet comprising a polyvinyl alcohol-containing coating layer wherein the mass ratio of (A) sucrose fatty acid ester / (B) polyvinyl alcohol is 80/20 to 50/50.
(2) The biaxially stretched sheet as described in (1) whose mass per unit area of a coating layer is 20-100 mg / m < ² >.
(3) The fatty acid constituting the sucrose fatty acid ester (A) is at least one selected from the group consisting of lauric acid, myristic acid, palmitic acid and stearic acid according to (1) or (2) Biaxially oriented sheet.
(4) The biaxially stretched sheet in any one of (1)-(3) whose sum total of the residual amount of methanol and methyl acetate in (B) polyvinyl alcohol is 4 mass% or less.
(5) The molded article which shape | molded the biaxially stretched sheet in any one of (1)-(4).
(6) The molded article according to (5), which is a lid of a food packaging container or a food packaging container.
(7) The molded article according to (5) or (6), which is a food packaging container for microwave heating or a lid of a food packaging container.
(8) The molded article according to any one of (5) to (7), which is a food packaging container for refrigeration or a lid of a food packaging container.

  According to the present invention, it is possible to provide a biaxially stretched sheet and a molded article which are excellent in all of oil resistance, hue, appearance (for example, appearance during molding, coating appearance) and antifogging properties in a well-balanced manner.

  Hereinafter, embodiments of the present invention will be described in detail.

  The biaxially oriented sheet according to the present embodiment includes a biaxially oriented resin layer and a covering layer that covers at least one surface of the biaxially oriented resin layer.

  The biaxially stretched resin layer biaxially stretches a resin composition containing an acrylonitrile-styrene copolymer containing acrylonitrile and styrene as monomer units and having an acrylonitrile / styrene mass ratio of 16/84 to 32/68. It has become.

  As an acrylonitrile type monomer unit which comprises an acrylonitrile styrene copolymer, although units, such as an acrylonitrile and methacrylonitrile, can be mentioned, Preferably it is an acrylonitrile unit. These acrylonitrile monomer units may be used alone or in combination of two or more.

  As a styrene-type monomer unit which comprises an acrylonitrile styrene copolymer, units, such as styrene, alpha-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, p-t-butylstyrene, etc. And preferably styrene units. These styrenic monomer units may be used alone or in combination of two or more.

  The mass ratio (acrylonitrile / styrene) of the acrylonitrile-based monomer unit to the styrene-based monomer unit is 16/84 to 32/68 from the viewpoint of excellent oil resistance and hue. The mass ratio is preferably 18/82 to 30/70, more preferably 20/80 to 28/72, still more preferably 22/78 to 27/73. When the mass ratio is equal to or more than the above lower limit value, the oil resistance is further improved, and the heat resistance is also excellent. It is further excellent in the point of a hue that the said mass ratio is below the said upper limit.

  The acrylonitrile-styrene copolymer may contain other copolymerizable vinyl monomer units, if necessary. Other vinyl monomer units include, for example, methacrylic acid esters such as acrylic acid, methacrylic acid, maleic anhydride, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dicyclopentanyl methacrylate, isobornyl methacrylate, etc. Examples include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate. The content of the other vinyl monomer unit may be, for example, less than 10 parts by mass with respect to a total of 100 parts by mass of the styrene monomer unit and the acrylonitrile monomer unit.

  An acrylonitrile-styrene copolymer is obtained by polymerizing an acrylonitrile-based monomer and a styrene-based monomer. The polymerization method is not particularly limited, but bulk continuous polymerization is preferable to reduce odor.

  A known example can be adopted as the bulk continuous polymerization method, but when a solvent such as ethylbenzene, toluene or methyl ethyl ketone is added in an amount of 10 to 40 parts by mass with respect to a total of 100 parts by mass of styrenic monomer and acrylonitrile monomer, More preferable.

  During polymerization, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (T-butylperoxy) -cyclohexane, 2,2-bis (4,4-di-butylperoxycyclohexyl) propane, t-butylperoxyisopropyl monocarbonate, di-t-butyl peroxide, dicumyl peroxide It is also acceptable to add known organic peroxides such as ethyl-3,3-di- (t-butylperoxy) butyrate, and 4-methyl-2,4-diphenylpentene-1, t- Known molecular weight modifiers such as dodecyl mercaptan and n-dodecyl mercaptan may be added.

  The polymerization temperature is preferably 80 to 170 ° C, more preferably 100 to 160 ° C.

  Although the weight average molecular weight of polystyrene conversion measured by SEC method of an acrylonitrile styrene copolymer is not specifically limited, It is preferable that it is 100,000 to 250,000, and it is more preferable that it is 1 to 200,000. If the weight average molecular weight is less than 100,000, the strength of the resin is reduced, and the sheet strength and folding resistance are reduced. When the viscosity is 250,000 or more, the sheet film formability and the container formability decrease because of the increase in viscosity.

The SEC measurement is conducted under the following conditions.
Device: Showa Denko Shodex "SYSTEM-21"
Column: PLgel MIXED-B
Temperature: 40 ° C
Solvent: tetrahydrofuran Flow rate: 1.0 ml / min Detection: RI
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 amount is converted to molecular weight to obtain various average molecular weights.

  The content of the acrylonitrile-styrene copolymer in the resin composition containing an acrylonitrile-styrene copolymer is preferably 98.5 to 99.9 mass%, more preferably 99.0 to 9% by mass, based on the total amount of the resin composition. It may be 99.9% by mass, more preferably 99.3 to 99.7% by mass.

  The resin composition containing an acrylonitrile-styrene copolymer may further contain a rubber modified high impact polystyrene resin (HIPS). The content of the rubber modified high impact polystyrene resin is preferably 0.1 to 3.0% by mass based on the total amount of the resin composition.

  The resin composition containing an acrylonitrile-styrene copolymer may further contain one or more additives selected from an ultraviolet light absorber, a light stabilizer, and an antioxidant.

  As a UV absorber, 2- (5'-methyl-2'-hydroxyphenyl) benzotriazole, 2- (5'-t-butyl-2'-hydroxyphenyl) benzotriazole, 2- [2'-hydroxy- 3 ', 5'-bis (α, α-dimethylbenzyl) phenyl] benzotriazole, 2- (3', 5'-di-t-butyl-2'-hydroxyphenyl) benzotriazole, 2- (3'-) t-Butyl-5′-methyl-2′-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3 ′, 5′-di-tert-butyl-2′-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3 ', 5'-di-t-amyl-2'-hydroxyphenyl) benzotriazole, 2- [3'-(3 ", 4", 5 ", 6" -tetrahydro phthalimide Methyl) -5'-methyl-2'-hydroxyphenyl] benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-2-) Ultraviolet light absorbers such as 2-phenol-2'-ethyl succinate, 2-ethoxy-5-t-butyl-2'-ethyl succinate bis-anilide and 2-ethoxy-4'-isodecyl UV absorbers of oxalic acid anilide such as phenylsuccinic acid bisanilide, 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 Benzophenone UV absorbers such as dihydroxy-4,4'-dimethoxybenzophenone and 2-hydroxy-4-methoxy-2'-carboxybenzophenone, phenyl salicylate, p-tert-butylphenyl salicylate, p-octylphenyl salicylate, etc. Salicylic acid based UV absorbers, 2-ethylhexyl 2-cyano-3,3'-diphenyl acrylate, cyanoacrylate based UV light absorbers such as ethyl 2-cyano-3,3'-diphenyl acrylate, rutile type titanium oxide, anatase Type titanium oxide, and titanium oxide based ultraviolet light stabilizers such as titanium oxide treated with surface treatment agents such as alumina, silica, silane coupling agent and titanium based coupling agent.

  As a light stabilizer, 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, poly [[6, (1,1,3,3-tetramethylbutyl) amino-1,3 5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl) imino] hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino ] And 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl] -4- [3- (3,5-di-t-butyl-4) -Hydroxyphenyl) propionilo Shi] -2,2,6,6 there tetramethyl piperidine.

  As an antioxidant, triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,4-bis (n-octylthio) -6- (4-hydroxy) 3,5-Di-tert-butylanilino) -1,3,5-triazine, pentaerythrityl tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2-thiobis (4-methyl-6-tert-butylphenol) and 1,3,5-trimethyl-2,4,6-tris Phenolic antioxidants such as (3,5-di-t-butyl-4-hydroxybenzyl) benzene, ditridecyl-3,3'-thiodipropionate, dilau 3,3'-thiodipropionate, ditetradecyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, dioctyl-3,3'-thiodipropionate, etc. Sulfur-based antioxidant, trisnonylphenyl phosphite, 4,4'-butylidene-bis (3-methyl-6-t-butylphenyl-ditridecyl) phosphite, (tridecyl) pentaerythritol diphosphite, bis (octadecyl) ) Pentaerythritol diphosphite, bis (di-t-butylphenyl) pentaerythritol diphosphite, bis (di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, dinonylphenyl octyl phosphonite, tetrakis (2,4-di-t-butylphenyl) 1,4- Enylene diphosphonite, tetrakis (2,4-di-t-butylphenyl) 4,4′-biphenylene-di-phosphonite, 10-decyloxy-9,10-dihydro-9-oxa-10-phospha And phosphorus-based antioxidants such as phenanthrene.

  A resin composition containing an acrylonitrile-styrene copolymer is a lubricant, a plasticizer, a colorant, an antistatic agent, a flame retardant, additives such as mineral oil, reinforcement of glass fiber, carbon fiber, aramid fiber, etc. depending on the application. A filler such as fiber, talc, silica, mica, calcium carbonate and the like may be further contained in the range not to impair the performance of the biaxially oriented resin layer.

  The content of the optional components such as the additive and the filler described above is, for example, 1% by mass or less based on the total amount of the resin composition.

  As a method for producing a biaxially oriented resin layer, a resin composition containing an acrylonitrile-styrene copolymer is melt-kneaded by an extruder and extruded from a die (especially a T-die), and then, biaxially sequentially or simultaneously The manufacturing method to draw is mentioned. The thickness of the biaxially oriented resin layer is not particularly limited, but is usually 0.05 mm or more and less than 0.6 mm, preferably 0.1 mm or more and less than 0.5 mm.

  In the production of the biaxially oriented resin layer, an antioxidant, a lubricant, a mold release agent, a plasticizer, a pigment, a dye, a foam, as needed within a range not to impair the purpose of the present invention at the time of melt kneading of the resin composition. Well-known additives, such as an agent, a foaming nucleating agent, an inorganic filler, and an antistatic agent, may be further added to the resin composition.

  The coating layer covers at least one surface of the biaxially oriented resin layer. The coating layer may coat the entire surface of the biaxially oriented resin layer or may partially cover the surface. The coating layer contains (A) sucrose fatty acid ester, and (B) polyvinyl alcohol having a degree of saponification of 85 to 95 mol% and a degree of polymerization of 300 to 2,000.

  (A) Sucrose fatty acid ester is an ester of sucrose and fatty acid. Examples of the fatty acid constituting the sucrose fatty acid ester include caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, saturated fatty acid having 6 to 30 carbon atoms such as montanic acid, and lindenic acid C10-24 unsaturated fatty acids, such as palmitoleic acid, oleic acid, elaidic acid, isooleic acid, erucic acid, linoleic acid, linolenic acid, etc. are mentioned. These fatty acids may be used alone or in combination of two or more. Among these fatty acids, one or more fatty acids selected from lauric acid, myristic acid, palmitic acid, and stearic acid are preferable from the viewpoint of being more excellent in antifogging property, storage property and economy.

  Polyvinyl alcohol (hereinafter also referred to as “PVA”) is a homopolymer comprising a vinyl alcohol unit or a copolymer comprising a vinyl alcohol unit and a vinyl acetate unit, and the content of the vinyl alcohol unit is, for example, 50% by mass or more.

  The saponification degree of PVA is 85 to 95 mol% from the viewpoint of excellent appearance (for example, coating appearance) and antifogging properties. The degree of saponification of PVA is preferably 86 to 93 mol%, more preferably 87 to 92 mol%, still more preferably 88 to 90 mol%. When the degree of saponification is at least the above lower limit value, the resin composition is further excellent in the antifogging property (for example, the antifogging property at the time of microwave heating) and excellent in the contamination property at the time of molding. When the degree of saponification is equal to or less than the above upper limit, the resin is further excellent in antifogging property (for example, antifogging property at the time of refrigeration) and further excellent in terms of appearance (for example, coating appearance).

  The polymerization degree of PVA is 300-2000 from a viewpoint which is excellent in an external appearance (for example, the external appearance at the time of shaping | molding, a coating external appearance). The polymerization degree of PVA is preferably 400 to 1700, more preferably 400 to 1500, and still more preferably 400 to 1000. It is further excellent in the point of an external appearance (for example, the external appearance at the time of shaping | molding) that polymerization degree is more than said lower limit. It is further excellent in the point of an external appearance (for example, coating external appearance) as a polymerization degree is below the said upper limit.

  The viscosity of the aqueous solution at 20 ° C. when PVA is a 4% aqueous solution is not particularly limited, but is preferably 4 cps or more, more preferably 4 cps or more and 60 cps or less.

  The total of the remaining amounts of methanol and methyl acetate in PVA is preferably 4% by mass or less, more preferably 3.7% by mass or less, and still more preferably 3.2% by mass or less. It is further excellent in the point of an external appearance (for example, the external appearance at the time of shaping | molding) that the sum total of the said residual amount is below said upper limit.

  The mass ratio of (A) sucrose fatty acid ester / (B) polyvinyl alcohol is 80/20 to 50/50 from the viewpoint of excellent antifogging properties (for example, antifogging properties at the time of microwave heating and refrigeration). The mass ratio is preferably 75/25 to 50/50, more preferably 73/27 to 53/47, still more preferably 70/30 to 55/45. When the mass ratio is equal to or more than the above lower limit value, the antifogging property (for example, the antifogging property at the time of refrigeration) is further improved, and the appearance at the time of molding and the contamination property are further improved. When the mass ratio is less than or equal to the above upper limit value, the antifogging property (for example, the antifogging property at the time of microwave heating) is further excellent, and the moldability is also excellent.

  The content of (A) sucrose fatty acid ester may be, for example, 30 to 80% by mass based on the total amount of the covering layer. (B) The content of polyvinyl alcohol may be, for example, 5 to 50% by mass based on the total amount of the coating layer.

Mass per unit area of the coating layer present on the biaxially oriented sheets preferably 20 to 100 mg / ^{m 2,} more preferably 30~90mg / ^{m 2,} more preferably from 35~85mg / ^{m 2.} It is further excellent in the point of anti-fogging property (for example, the anti-fogging property at the time of microwave oven heating or refrigeration) as the said mass is more than said lower limit. When the mass is equal to or less than the above upper limit value, the appearance at the time of molding and the contamination property are further excellent.

  The covering layer is formed, for example, by applying a solution in which (A) sucrose fatty acid ester and (B) polyvinyl alcohol are dissolved in a solvent on at least one surface of the biaxially oriented resin layer. As the solvent, water, alcohol and the like are used, but it is not particularly limited thereto. As a solvent, water is preferable in handling. In this case, the content of (A) sucrose fatty acid ester and (B) polyvinyl alcohol may be, for example, 0.01 to 10% by mass on the basis of the total amount of the solution. The method of coating the solution is not particularly limited, and examples thereof include a method of coating using a roll coater, a knife coater, a gravure roll coater or the like. In addition, the coating layer may be formed by spraying, dipping or the like.

  The biaxially oriented sheet according to the present embodiment can be used for molded articles such as packaging containers by molding. As molded articles, food packaging containers (i.e., packaging containers containing food as contents) and lids for food packaging containers are suitable, and in particular, when the food is a food containing oil and fat. In addition, the food packaging container and the lid of the food packaging container can be used for microwave heating and refrigeration. When a biaxially oriented sheet is used for a food packaging container or a lid of a food packaging container, the raw materials used for the biaxially oriented sheet are registered in the Food Additives Declaration and the Positive List of the Polyolefin Hygiene Council It is preferable to use a material that is publicly recognized to be hygienic and stable.

  As a method of obtaining a molded article from a biaxially stretched sheet, a method using a commercially available general hot plate pressure forming machine can be mentioned. The molding machine to be used is preferably of the type capable of setting the time for which the sheet is in pressure contact with the heat plate, the time for forming by pressure air, the time lag for switching from sheet pressure to pressure forming, and the forming cycle. These methods are described, for example, in “Plastic Processing Technology Handbook” edited by The High Polymer Society of Japan, Nikkan Kogyo Shimbun, Ltd. (1995).

  Hereinafter, the present invention will be more specifically described based on examples, but the present invention is not limited to the following examples.

Example 1
A degassing tank connected in series with a first reactor, which is a fully-mixed stirring tank with a volume of about 20 L, and a second reactor, a tower plug flow reactor with a capacity of about 40 L, and a preheater Are connected in series. 15 parts by mass of ethylbenzene, 0.01 parts by mass of t-butylperoxyisopropyl monocarbonate, and 0.25 parts by mass of t-dodecyl mercaptan are mixed with 85 parts by mass of a monomer solution containing 12% by mass of acrylonitrile and 88% by mass of styrene It was used as a raw material solution. The raw material solution was introduced into a first reactor controlled at 125 ° C. at 6.0 kg per hour. The reaction liquid was continuously withdrawn from the first reactor, and the reaction liquid was introduced into a second reactor adjusted to have a gradient of 125 ° C. to 160 ° C. in the flow direction. Next, it is introduced into the first devolatilization tank depressurized to 67 kPa after heating to 160 ° C. with a preheater, and further introduced into a second devolatilization tank depressurized to 1.3 kPa after heating to 230 ° C. by the preheater Residual monomer and solvent were removed. By extruding and cutting this into strands, an acrylonitrile-styrene copolymer in the form of pellets was obtained. The composition (mass ratio of monomer units) of this copolymer was 12% by mass of acrylonitrile unit and 88% by mass of styrene unit as described in Table 1.

  The copolymer was extruded by a sheet extruder (T-die width 500 mm, φ 40 mm extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.)) to obtain a sheet. This sheet was stretched by a batch-type biaxial stretching machine (Toyo Seiki) to obtain a biaxially stretched resin layer.

On the surface of this biaxially oriented resin layer, sucrose laurate (L-1570 (manufactured by Mitsubishi Chemical Foods Co., Ltd.)) 0.60%, polyvinyl alcohol (degree of polymerization 500, degree of saponification 88% by mol) with a bar coater 5 g / m ^{2 of an} aqueous solution containing 0.40% of a total of 0.1% or less of methyl acetate and methanol) and dried in an oven at 105 ° C. for 1 minute. The mass per unit area was 50 mg / m ^{2 as} described in Table 1.

[Hue]
Ten 0.21 mm thick biaxially stretched sheets were stacked, and the b value obtained from SCI measurement (including specular reflection light) of a spectrocolorimeter CM-2500 d (Konica Minolta) was evaluated. If the b value is less than 10, it can be said that the hue is excellent.
○: less than 5 :: 5 or more and less than 10 ×: 10 or more

[Oil resistance]
Paste a gauze 10 x 10 mm impregnated with a test solution of salad oil (Nisshin Oil Co., Ltd.), mayonnaise (Ajinomoto Co.), Coconad ML (Kao) into the center of the lunchbox lid formed of biaxially oriented sheet The sample was allowed to stand in an oven at 60 ° C. for 24 hours to observe the surface of the adhered portion. In addition, if evaluation is (circle) or (triangle | delta), it can be said that it is excellent in oil resistance.
:: no change △: slight whitening x: significant whitening, cracking

[Coating appearance]
The biaxially stretched sheet was measured with a haze meter NDH5000 (Nippon Denshoku Co., Ltd.) according to JIS K-7361-1. The sheet obtained in the example was used for the measurement.
○: Haze less than 1.5% :: Haze 1.5% or more and less than 3.0% ×: Haze 3.0% or more

Appearance during molding
A lunch box lid (dimension length 241 × width 193 × height 28 mm) under the conditions of a heat plate temperature of 135 ° C and a heating time of 2.0 seconds using a biaxially oriented sheet with a heat plate molding machine HPT-400A (manufactured by Wakisaka Engineering) Molded. The molded product was measured with a haze meter NDH5000 (Nippon Denshoku Co., Ltd.) according to JIS K-7361-1. The sheet obtained in the example was used for the measurement.
○: Haze less than 1.5% :: Haze 1.5% or more and less than 3.0% ×: Haze 3.0% or more

[Anti-fogging (refrigerated)]
A lunch box lid (dimension length 241 × width 193 × height 28 mm) under the conditions of a heat plate temperature of 135 ° C and a heating time of 2.0 seconds using a biaxially oriented sheet with a heat plate molding machine HPT-400A (manufactured by Wakisaka Engineering) Molded. 50 g of water at 25 ° C. was put in the main body of the obtained container, the container was covered, and allowed to stand at 5 ° C. The content visibility after 30 minutes was confirmed. In addition, if evaluation is (circle) or (triangle | delta), it can be said that it is excellent in the antifogging property after storage.
○: The contents can be clearly confirmed.
Δ: The contents become difficult to see due to dewing on the lid.
X: There is much dew on the lid, and the contents can not be identified.

[Anti-fogging (heating)]
A lunch box lid (dimension length 241 × width 193 × height 28 mm) under the conditions of a heat plate temperature of 135 ° C and a heating time of 2.0 seconds using a biaxially oriented sheet with a heat plate molding machine HPT-400A (manufactured by Wakisaka Engineering) Molded. 50 g of water at 95 ° C. was put in the main body of the obtained container, the container was covered, and allowed to stand at 25 ° C. The content visibility after 10 minutes was confirmed. In addition, if evaluation is (circle) or (triangle | delta), it can be said that it is excellent in the antifogging property after storage.
○: The contents can be clearly confirmed.
Δ: The contents become difficult to see due to dewing on the lid.
X: There is much dew on the lid, and the contents can not be identified.

Examples 2 to 25 and Comparative Examples 1 to 8
The prepared amount of various raw materials was adjusted to obtain an acrylonitrile-styrene copolymer having the composition described in Tables 1 to 5. Moreover, each copolymer was made into the biaxially stretched resin layer, the coating layer which has a composition of Table 1 was formed, and the biaxially stretched sheet was obtained. Each biaxially oriented sheet was evaluated in the same manner as in Example 1. The results are shown in Tables 1-5.

  Furthermore, the following evaluation was performed about the biaxially stretched sheet of each Example and a comparative example. The results are shown in Tables 6-9.

Container strength
A weight of 500 g was put in the container body, and five layers of lunch containers having a lid formed of biaxially oriented sheets were stacked, and the deformation state of the lid material after standing for 24 hours was confirmed.
○: No change in shape.
Δ: There is deformation.
X: There is a crack.

[Heat-resistant]
After placing the lunchbox lid obtained under the above molding conditions in a hot air dryer set at 110 ° C. for 60 minutes, deformation of the container was visually observed.
:: no deformation △: slight deformation, less than 5% change in outer size x: large deformation, 5% or more change in outer size

[Formability]
A lunch box lid (dimension length 241 × width 193 × height) formed from a biaxially oriented sheet under the conditions of a heat plate temperature of 135 ° C and a heating time of 2.0 seconds with a heat plate molding machine HPT-400A (manufactured by Wakisaka Engineering) 28 mm) was evaluated.
:: good △: slight whitening due to surface roughening, raindrop, poor shape ×: significant whitening due to surface roughening, raindrop, poor shape (cannot be commercialized)

[Staining (Staining on hot plate during molding)]
The biaxially oriented sheet was continuously molded using a vacuum pressure air molding machine PK400 manufactured by Kansai Automatic Molding Machine Co., Ltd. Before the molding, the heat plate was previously cleaned with a rag to remove the dirt on the heat plate. A lid container (200 mm long × 120 mm wide × 50 mm high) having a flat top surface at a molding temperature of 135 ° C. as continuous molding conditions was continuously molded for 500 shots. After molding, the heat plate was cleaned with a rag and the degree of contamination was visually evaluated.
○: The waste is hardly soiled.
Fair: More than 20% of the waste was dirty.
X: Almost the entire surface of the waste was dirty.

Claims (8)

A biaxially stretched resin layer obtained by biaxially stretching a resin composition containing acrylonitrile and styrene as monomer units, and the acrylonitrile / the styrene mass ratio being 16/84 to 32/68,
A coating layer for covering at least one surface of the biaxially oriented resin layer, wherein (A) sucrose fatty acid ester, and (B) saponification degree is 85 to 95 mol%, polymerization degree is 300 to 2000 A coating layer containing polyvinyl alcohol, wherein a mass ratio of the (A) sucrose fatty acid ester to the (B) polyvinyl alcohol is 80/20 to 50/50;
A biaxially oriented sheet comprising: The biaxially stretched sheet according to claim 1, wherein a mass per unit area of the covering layer is 20 to 100 mg / m ² .   The biaxially stretched sheet according to claim 1 or 2, wherein the fatty acid constituting the (A) sucrose fatty acid ester is at least one selected from the group consisting of lauric acid, myristic acid, palmitic acid, and stearic acid. .   The biaxially stretched sheet according to any one of claims 1 to 3, wherein a total of residual amounts of methanol and methyl acetate in the (B) polyvinyl alcohol is 4% by mass or less.   The molded article which shape | molded the biaxially stretched sheet as described in any one of Claims 1-4.   The molded article according to claim 5, which is a food packaging container or a lid of a food packaging container.   The molded article according to claim 5 or 6, which is a food packaging container for microwave heating or a lid of a food packaging container. The molded article according to any one of claims 5 to 7, which is a food packaging container for refrigeration or a lid of a food packaging container.