JP6775622B2 - Biaxially stretched sheet and molded product - Google Patents

Description

The present invention relates to a biaxially stretched sheet and a molded product.

Conventionally, in stores such as supermarkets, convenience stores, department stores, and lunch boxes, a lid made of a synthetic resin sheet and a container body are fitted as a container used when selling groceries, processed foods, etc. A packaging container configured in the above is used.

Biaxially stretched polystyrene sheets are widely used in the field of food packaging because of their excellent transparency and high rigidity. However, if they are stored for a long time with oil attached, the sheet surface may become white. , Biaxially stretched polystyrene sheets with improved oil resistance have been required (for example, Patent Documents 1 and 2).

Further, as described in Patent Documents 1 and 2, in addition to oil resistance, biaxially stretched polystyrene sheets have mechanical strength, impact resistance, heat resistance, oil resistance, transparency, thermoforming property, etc. Various characteristics of are also required.

Japanese Unexamined Patent Publication No. 10-7817 Japanese Unexamined Patent Publication No. 2001-105489

An object of the present invention is to provide a biaxially stretched sheet and a molded product having an excellent balance in all of oil resistance, hue, appearance (for example, appearance at the time of molding, appearance of coating) and antifogging property.

The present invention provides the biaxially stretched sheet and the molded product shown below.
(1) A biaxially stretched resin layer obtained by biaxially stretching a resin composition containing acrylonitrile and styrene as a monomer unit and containing a copolymer having an acrylonitrile / styrene mass ratio of 16/84 to 32/68. , A coating layer that covers at least one surface of the biaxially stretched resin layer, and has (A) a sucrose fatty acid ester and (B) a degree of saponification of 85 to 95 mol% and a degree of polymerization of 300 to 2000. A biaxially stretched sheet comprising a coating layer containing polyvinyl alcohol and having a mass ratio of (A) sucrose fatty acid ester / (B) polyvinyl alcohol of 80/20 to 50/50.
(2) The biaxially stretched sheet according to (1), wherein the mass of the coating layer per unit area is 20 to 100 mg / m ² .
(3) The fatty acid constituting (A) sucrose fatty acid ester 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 stretched sheet.
(4) The biaxially stretched sheet according to any one of (1) to (3), wherein the total residual amount of methanol and methyl acetate in polyvinyl alcohol is 4% by mass or less.
(5) A molded product obtained by molding the biaxially stretched sheet according to any one of (1) to (4).
(6) The molded product according to (5), which is a food packaging container or a lid material for a food packaging container.
(7) The molded product according to (5) or (6), which is a food packaging container for heating in a microwave oven or a lid material for the food packaging container.
(8) The molded product according to any one of (5) to (7), which is a food packaging container for refrigeration or a lid material for the food packaging container.

According to the present invention, it is possible to provide a biaxially stretched sheet and a molded product having an excellent balance in all of oil resistance, hue, appearance (for example, appearance at the time of molding, appearance of coating) and antifogging property.

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

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

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

Examples of the acrylonitrile-based monomer unit constituting the acrylonitrile-styrene copolymer include units such as acrylonitrile and methacrylonitrile, but the acrylonitrile unit is preferable. These acrylonitrile-based monomer units may be used alone or in combination of two or more.

Examples of the styrene-based monomer unit constituting the acrylonitrile-styrene copolymer include units of styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, pt-butylstyrene and the like. Although it can be mentioned, it is preferably a styrene unit. These styrene-based monomer units may be used alone or in combination of two or more.

The mass ratio of the acrylonitrile-based monomer unit to the styrene-based monomer unit (acrylonitrile / styrene) 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, and even more preferably 22/78 to 27/73. When the mass ratio is at least the above lower limit value, it is further excellent in terms of oil resistance and heat resistance. When the mass ratio is not more than the above upper limit value, it is further excellent in terms of hue.

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

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

A known example can be adopted as the massive 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 the styrene-based monomer and the acrylonitrile-based monomer for polymerization. More preferred.

At the time of polymerization, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (T-Butyl Peroxy) -Cyclohexane, 2,2-Bis (4,4-Di-Butyl Peroxycyclohexyl) Propane, t-Butyl Peroxyisopropyl Monocarbonate, Di-t-Butyl Peroxide, Dicumyl Peroxide , Ethyl-3,3-di- (t-butylperoxy) butyrate and other known organic peroxides may be added, and 4-methyl-2,4-diphenylpentene-1, t- A known molecular weight modifier such as dodecyl mercaptan or n-dodecyl mercaptan may be added.

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

The polystyrene-equivalent weight average molecular weight of the acrylonitrile-styrene copolymer measured by the SEC method is not particularly limited, but is preferably 100,000 to 250,000, and more preferably 15 to 200,000. If the weight average molecular weight is less than 100,000, the strength of the resin is lowered, so that the sheet strength and the folding resistance are lowered. Further, when the viscosity is 250,000 or more, the film forming property and the container forming property are lowered due to the increase in viscosity.

The SEC measurement is carried out under the following conditions.
Equipment: Showax Shodex "SYSTEM-21"
Column: PLgelMIXED-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 the elution time and the elution amount is converted into the molecular weight to obtain various average molecular weights.

The content of the acrylonitrile-styrene copolymer in the resin composition containing the acrylonitrile-styrene copolymer is preferably 98.5-99.9% by mass, more preferably 99.0 to 99.9% 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 the acrylonitrile-styrene copolymer may further contain a rubber-modified impact-resistant polystyrene-based resin (HIPS). The content of the rubber-modified impact-resistant polystyrene-based resin is preferably 0.1 to 3.0% by mass based on the total amount of the resin composition.

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

Examples of the ultraviolet absorber include 2- (5'-methyl-2'-hydroxyphenyl) benzotriazole, 2- (5'-t-butyl-2'-hydroxyphenyl) benzotriazole, and 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-t-butyl-2'-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3', 5'-di-t-amyl-2'-hydroxyphenyl) benzotriazole, 2- [3'-(3 ", 4", 5 ", 6" -tetrahydro-phthalimidemethyl) -5 '-Methyl-2'-Hydroxyphenyl] benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazole-2-yl) phenol] Etc., benzotriazole-based ultraviolet absorbers, 2-ethoxy-2'-ethyl bisanilide, 2-ethoxy-5-t-butyl-2'-ethyl bisanilide, 2-ethoxy-4'-isodecylphenyl bisanilide, etc. Hyalate anilide UV absorber, 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, 2-hydroxy-4-methoxy-2'-carboxybenzophenone and other benzophenone UV absorbers, phenylsalicylate, Salicylic acid-based UV absorbers such as pt-butylphenyl salicylate and p-octylphenyl salicylate, 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate, ethyl-2-cyano-3,3'-diphenylacrylate Cyanacrylate-based ultraviolet absorbers such as, rutyl-type titanium oxide, anatase-type titanium oxide, and titanium oxide-based such as titanium oxide treated with surface treatment agents such as alumina, silica, silane coupling agents and titanium-based coupling agents. Examples include UV stabilizers.

Examples of the light stabilizer include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and 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) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like.

Antioxidants include triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] and 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], octadecyl-3-3 (3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2-thiobis (4-methyl-6-t-butylphenol) and 1,3,5-trimethyl-2,4,6-tris (3,5-Di-t-Butyl-4-hydroxybenzyl) Phenolic antioxidants such as benzene, ditridecyl-3,3'-thiodipropionate, dilauryl-3,3'-thiodipropionate, ditetradecyl Sulfur-based antioxidants such as -3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, dioctyl-3,3'-thiodipropionate, 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 octylphosphonite, tetrakis (2,4-di-t-butylphenyl) 1 , 4-Phenylene diphosphonite, tetrakis (2,4-di-t-butylphenyl) 4,4'-biphenylene-di-phosphonite, 10-decyloxy-9,10-dihydro-9-oxa-10- Examples thereof include phosphorus-based antioxidants such as phosphaphenanthrene.

The resin composition containing an acrylonitrile-styrene copolymer reinforces talc, plasticizer, colorant, antistatic agent, flame retardant, mineral oil and other additives, glass fiber, carbon fiber and aramid fiber depending on the application. A filler such as fiber, talc, silica, mica, and calcium carbonate may be further contained within a range that does not impair the performance of the biaxially stretched resin layer.

The content of the above-mentioned optional components such as additives and fillers is, for example, 1% by mass or less based on the total amount of the resin composition.

As a method for producing the biaxially stretched resin layer, a resin composition containing an acrylonitrile-styrene copolymer is melt-kneaded by an extruder and extruded from a die (particularly a T die), and then sequentially or simultaneously in the biaxial direction. Examples thereof include a manufacturing method for stretching. The thickness of the biaxially stretched 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 stretched resin layer, when the resin composition is melt-kneaded, an antioxidant, a lubricant, a mold release agent, a plasticizer, a pigment, a dye, and foaming are required as long as the object of the present invention is not impaired. Known additives such as agents, foam nucleating agents, inorganic fillers, and antistatic agents may be further added to the resin composition.

The coating layer covers at least one surface of the biaxially stretched resin layer. The coating layer may cover the entire surface of the biaxially stretched 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 2000.

(A) The sucrose fatty acid ester is an ester of sucrose and a fatty acid. Examples of fatty acids constituting the sucrose fatty acid ester include saturated fatty acids having 6 to 30 carbon atoms such as caproic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and montanic acid, and lindenic acid. Examples thereof include unsaturated fatty acids having 10 to 24 carbon atoms such as palmitooleic acid, oleic acid, elaidic acid, isooleic acid, erucic acid, linoleic acid, and linolenic acid. These fatty acids may be one kind alone or a mixture of two or more kinds. 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 further excellent antifogging property, storage stability, and economic efficiency.

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, and the content of vinyl alcohol units is, for example, 50% by mass or more.

The degree of saponification of PVA is 85 to 95 mol% from the viewpoint of excellent appearance (for example, coating appearance) and antifogging property. The degree of saponification of PVA is preferably 86 to 93 mol%, more preferably 87 to 92 mol%, and even more preferably 88 to 90 mol%. When the degree of saponification is at least the above lower limit value, it is further excellent in terms of antifogging property (for example, antifogging property when heated in a microwave oven) and also excellent in terms of stain resistance during molding. When the degree of saponification is not more than the above upper limit value, it is further excellent in terms of anti-fog property (for example, anti-fog property during refrigeration) and further excellent in appearance (for example, coating appearance).

The degree of polymerization of PVA is 300 to 2000 from the viewpoint of excellent appearance (for example, appearance at the time of molding, appearance at the time of coating). The degree of polymerization of PVA is preferably 400 to 1700, more preferably 400 to 1500, and even more preferably 400 to 1000. When the degree of polymerization is at least the above lower limit value, it is further excellent in terms of appearance (for example, appearance at the time of molding). When the degree of polymerization is not more than the above upper limit value, it is further excellent in terms of appearance (for example, coating appearance).

The viscosity of the aqueous solution at 20 ° C. when PVA is made into 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 residual amount of methanol and methyl acetate in PVA is preferably 4% by mass or less, more preferably 3.7% by mass or less, still more preferably 3.2% by mass or less. When the total of the residual amounts is not more than the above upper limit value, it is further excellent in terms of appearance (for example, appearance at the time of molding).

The mass ratio of (A) sucrose fatty acid ester / (B) polyvinyl alcohol is 80/20 to 50/50 from the viewpoint of excellent antifogging property (for example, antifogging property when heated or refrigerated in a microwave oven). The mass ratio is preferably 75/25 to 50/50, more preferably 73/27 to 53/47, and even more preferably 70/30 to 55/45. When the mass ratio is at least the above lower limit value, it is further excellent in terms of anti-fog property (for example, anti-fog property at the time of refrigeration), and further excellent in terms of appearance at the time of molding and contamination. When the mass ratio is not more than the above upper limit value, it is further excellent in antifogging property (for example, antifogging property when heated in a microwave oven) and also excellent in moldability.

The content of the sucrose fatty acid ester (A) may be, for example, 30 to 80% by mass based on the total amount of the coating layer. The content of (B) 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.} When the mass is at least the above lower limit value, it is further excellent in antifogging property (for example, antifogging property when heating or refrigerating in a microwave oven). When the mass is not more than the above upper limit value, it is further excellent in terms of appearance and stainability at the time of molding.

The coating layer is formed, for example, by applying a solution of (A) sucrose fatty acid ester and (B) polyvinyl alcohol in a solvent to at least one surface of the biaxially stretched resin layer. Water, alcohol and the like are used as the solvent, but the solvent is not particularly limited thereto. As the solvent, water is preferable in terms of 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 based on the total amount of the solution. The method of applying the solution is not particularly limited, and examples thereof include a method of applying using a roll coater, a knife coater, a gravure roll coater, or the like. Further, the coating layer may be formed by spraying, dipping or the like.

The biaxially stretched sheet according to the present embodiment can be used for molded products such as packaging containers by molding. As the molded product, a food packaging container (that is, a packaging container containing food as a content) and a lid material for the food packaging container are suitable, and particularly when the food is a food containing fats and oils. Further, the food packaging container and the lid material of the food packaging container can be used for heating or refrigerating in a microwave oven. When a biaxially stretched sheet is used as a lid material for a food packaging container or a food packaging container, the raw materials used for the biaxially stretched sheet are registered in the food additive official standard and the positive list of the Polyolefin Hygiene Council. It is preferable to use a material whose hygiene and stability are publicly recognized.

Examples of a method for obtaining a molded product from a biaxially stretched sheet include a method using a commercially available general hot plate compressed air molding machine. It is desirable that the molding machine to be used is of a type that can set the time during which the sheet is pressed against the hot plate, the time during which the sheet is formed by compressed air, the time lag during switching from sheet pressure contact to compressed air forming, the forming cycle, and the like. These methods are described, for example, in the "Handbook of Plastic Processing Technology" edited by the Society of Polymer Science, Japan, Nikkan Kogyo Shimbun (1995).

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples.

<Example 1>
A devolatilization tank in which the first reactor, which is a complete mixing type stirrer with a volume of about 20 L, and the second reactor, which is a tower-type plug-flow type reactor with a stirrer with a volume of about 40 L, are connected in series and further equipped with a preheater. Was connected in series to each other. 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. The raw material solution was used. This raw material solution was introduced into a first reactor controlled at 125 ° C. at 6.0 kg / h. The reaction solution was continuously withdrawn from the first reactor and introduced into the second reactor adjusted to have a gradient of 125 ° C. to 160 ° C. in the direction of flow. Next, it was introduced into the first devolatilization tank which was heated to 160 ° C. with a preheater and then reduced to 67 kPa, and further introduced into the second volatilization tank which was heated to 230 ° C. with a preheater and then decompressed to 1.3 kPa. Residual monomers and solvent were removed. This was extruded into a strand and cut to obtain a pellet-shaped acrylonitrile-styrene copolymer. As shown in Table 1, the composition of this copolymer (mass ratio of monomer unit) was 12% by mass of acrylonitrile unit and 88% by mass of styrene unit.

This copolymer was extruded with a sheet extruder (T-die width 500 mm, φ40 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 stretched resin layer, 0.60% of sucrose lauric acid ester (L-1570 (manufactured by Mitsubishi Chemical Foods Co., Ltd.)) and polyvinyl alcohol (degree of polymerization 500, degree of saponification 88 mol%) were added by a bar coater. , The total residual ratio of methyl acetate and methanol was 0.1% or less), 5 g / m ^{2 of an} aqueous solution containing 0.40% was applied, and the coating layer was dried in an oven at 105 ° C. for 1 minute. The mass per unit area was 50 mg / m ^{2 as shown} in Table 1.

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

[Oil resistance]
A gauze 10 x 10 mm impregnated with a test solution of salad oil (manufactured by Nisshin Oil Co., Ltd.), mayonnaise (manufactured by Ajinomoto Co., Inc.), and Coconard ML (manufactured by Kao Corporation) is pasted in the center of the bento lid formed of the biaxially stretched sheet. , The surface of the adhered portion was observed by allowing it to stand in an oven at 60 ° C. for 24 hours. If the evaluation is ◯ or Δ, it can be said that the oil resistance is excellent.
○: No change △: Slightly whitened ×: Significant whitening and cracking

[Appearance of coating]
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% Δ: Haze 1.5% or more and less than 3.0% ×: Haze 3.0% or more

[Appearance at the time of molding]
A bento lid (dimensions 241 x 193 x 28 mm) under the conditions of a hot plate temperature of 135 ° C. and a heating time of 2.0 seconds using a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering) for a biaxially stretched sheet. Was 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% Δ: Haze 1.5% or more and less than 3.0% ×: Haze 3.0% or more

[Anti-fog (refrigerated)]
A bento lid (dimensions 241 x 193 x 28 mm) under the conditions of a hot plate temperature of 135 ° C. and a heating time of 2.0 seconds using a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering) for a biaxially stretched sheet. Was molded. 50 g of water at 25 ° C. was put into the main body of the obtained container, the lid was closed, and the container was allowed to stand at 5 ° C. The visibility of the contents after 30 minutes was confirmed. If the evaluation is ◯ or Δ, it can be said that the antifogging property after storage is excellent.
◯: The contents can be clearly confirmed.
Δ: The contents are difficult to see due to dew on the lid.
X: There is a lot of dew on the lid, and the contents cannot be identified.

[Anti-fog (heating)]
A bento lid (dimensions 241 x 193 x 28 mm) under the conditions of a hot plate temperature of 135 ° C. and a heating time of 2.0 seconds using a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering) for a biaxially stretched sheet. Was molded. 50 g of water at 95 ° C. was put into the main body of the obtained container, the lid was closed, and the container was allowed to stand at 25 ° C. The visibility of the contents after 10 minutes was confirmed. If the evaluation is ◯ or Δ, it can be said that the antifogging property after storage is excellent.
◯: The contents can be clearly confirmed.
Δ: The contents are difficult to see due to dew on the lid.
X: There is a lot of dew on the lid, and the contents cannot be identified.

<Examples 2 to 25, Comparative Examples 1 to 8>
The amount of various raw materials charged was adjusted to obtain an acrylonitrile-styrene copolymer having the compositions shown in Tables 1 to 5. Further, each copolymer was used as a biaxially stretched resin layer, and a coating layer having the composition shown in Table 1 was formed to obtain a biaxially stretched sheet. Each biaxially stretched sheet was evaluated in the same manner as in Example 1. The results are shown in Tables 1-5.

Further, the biaxially stretched sheets of each Example and Comparative Example were evaluated as follows. The results are shown in Tables 6-9.

[Container strength]
A weight of 500 g was put in the container body, and a bento container with a lid formed of a biaxially stretched sheet was stacked in five stages, and the deformed state of the lid material after standing for 24 hours was confirmed.
◯: No shape change.
Δ: There is deformation.
×: There is a crack.

[Heat-resistant]
The bento lid obtained under the above molding conditions was placed in a hot air dryer set at 110 ° C. for 60 minutes, and then the deformation of the container was visually observed.
◯: No deformation △: Minor deformation, outer size change less than 5% ×: Large deformation, outer size change 5% or more

[Moldability]
A bento lid (dimensions 241 x 193 x height) formed from a biaxially stretched sheet under the conditions of a hot plate temperature of 135 ° C. and a heating time of 2.0 seconds on a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering). The appearance of (28 mm) was evaluated.
◯: Good △: Slight whitening due to surface roughness, raindrop, poor shape ×: Significant whitening due to surface roughness, raindrop, poor shape (cannot be commercialized)

[Stainability (dirt on hot plate during molding)]
The biaxially stretched sheet was continuously molded using a vacuum compressed air molding machine PK400 manufactured by Kansai Automatic Molding Machine Co., Ltd. Before the molding, the hot plate was cleaned with a waste cloth to remove dirt from the hot plate. As a continuous molding condition, a lid container (200 mm length × 120 mm width × 50 mm height) having a flat top surface was continuously molded for 500 shots at a molding temperature of 135 ° C. After molding, the hot plate was cleaned with a waste cloth and the degree of dirt was visually evaluated.
◯: The waste cloth is almost clean.
Δ: 20% or more of the waste cloth was dirty.
X: Almost the entire surface of the waste cloth was dirty.

Claims (8)

Include acrylonitrile and styrene as a monomer unit, the acrylonitrile / the mass ratio of the styrene Ri 16 / 84-32 / 68 Der, resin composition containing a resin having a weight-average molecular weight is 150,000 to 200,000 A biaxially stretched resin layer formed by biaxial stretching and
It is a coating layer that covers at least one surface of the biaxially stretched resin layer, and has (A) a sucrose fatty acid ester and (B) a degree of saponification of 85 to 95 mol% and a degree of polymerization of 300 to 2000. A biaxially stretched sheet containing polyvinyl alcohol and comprising a coating layer having a mass ratio of (A) sucrose fatty acid ester / said (B) polyvinyl alcohol of 80/20 to 50/50. The biaxially stretched sheet according to claim 1, wherein the mass of the coating layer per unit area is 20 to 100 mg / m ² . The biaxially stretched sheet according to claim 1 or 2, wherein 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. .. The biaxially stretched sheet according to any one of claims 1 to 3, wherein the total residual amount of methanol and methyl acetate in the (B) polyvinyl alcohol is 4% by mass or less. A molded product obtained by molding the biaxially stretched sheet according to any one of claims 1 to 4. The molded product according to claim 5, which is a food packaging container or a lid material for a food packaging container. The molded product according to claim 5 or 6, which is a food packaging container for heating in a microwave oven or a lid material for the food packaging container. The molded product according to any one of claims 5 to 7, which is a food packaging container for refrigeration or a lid material for the food packaging container.