WO2018012373A1 - Biaxially stretched sheet and shaped article of same - Google Patents

Abstract

Provided are: a biaxially stretched sheet which is formed from a styrene resin composition and has good transparency, strength, film forming properties and formability, while having excellent productivity, heat resistance, oil resistance, appearance and antifogging properties; and a shaped article of this biaxially stretched sheet. A biaxially stretched sheet which is formed from a styrene resin composition containing a styrene-methacrylic acid copolymer and an acrylic resin, and wherein: the mass ratio of the styrene-methacrylic acid copolymer to the acrylic resin is from 90/10 to 97/3; the styrene-methacrylic acid copolymer contains a styrene monomer unit and a methacrylic acid monomer unit at a mass ratio of from 84/16 to 94/6; the styrene-methacrylic acid copolymer has a weight average molecular weight of from 120,000 to 250,000; the acrylic resin has a weight average molecular weight of from 1,000,000 to 7,000,000; and the styrene resin composition has a Vicat softening temperature of from 106°C to 132°C. This biaxially stretched sheet has a coating layer, which contains a sucrose fatty acid ester and a water-soluble polymer, on at least one surface. A shaped article of this biaxially stretched sheet.

Description

Biaxially stretched sheet and molded product thereof

The present invention relates to a biaxially stretched sheet comprising a styrenic resin composition that can be suitably used for food packaging containers heated in a microwave oven, and a molded product thereof.

Polystyrene biaxially stretched sheets are excellent in transparency and rigidity, and thus are molded and used mainly in molded products such as lightweight containers. However, since these containers are inferior in heat resistance, they are rarely used for applications that directly contact boiling water or those that are heated in a microwave oven. Thus, attempts have been made to impart heat resistance to polystyrene as a raw material. Examples of polystyrene having improved heat resistance include styrene-acrylic acid copolymer or styrene-methacrylic acid copolymer (Patent Document 1, Patent Document 2), styrene-maleic anhydride copolymer (Patent Document 3, Patent document 4) is mentioned. These are generally known as styrenic heat-resistant resins, and improve heat resistance without impairing transparency and rigidity.

However, the styrenic heat-resistant resin has lower fluidity during melt extrusion than ordinary polystyrene, and it is difficult to increase the resin production capacity and sheet production capacity. In order to increase the fluidity of the styrenic heat-resistant resin, (i) a method of increasing the extrusion temperature and (ii) a method of decreasing the molecular weight of the resin can be considered. When the extrusion temperature is increased, the carboxylic acid group in the styrene heat-resistant resin reacts to form a gel-like foreign material, resulting in a reduction in sheet quality. Further, when the molecular weight of the resin is lowered, drawdown at the time of sheet extrusion tends to occur and film formation becomes difficult.

As a method for suppressing gel generation while increasing the extrusion temperature, for example, a method of adding an antigelling agent during extrusion has been proposed (Patent Document 5). However, since the anti-gelling agent described in Patent Document 5 also works as a plasticizer, the heat resistance and oil resistance of the resulting styrene resin sheet are lowered. Therefore, it is necessary to select an additive that does not easily lower these performances.

Also, as a method for maintaining the film-forming property while lowering the molecular weight of the styrene resin, a method of imparting strain curability by adding a small amount of high molecular weight polystyrene is known (Patent Document 6). However, the high molecular weight polystyrene described in Patent Document 6 has low compatibility with the styrenic heat-resistant resin, and has the disadvantages that the expected strain-hardening property is not easily obtained and the transparency of the resulting sheet is lowered. Therefore, it is necessary to newly select a combination of a styrene heat resistant resin and a high molecular weight polymer that are compatible with each other.

The styrenic heat-resistant resin has low sheet strength, particularly folding resistance and impact resistance, and is further reduced by lowering the molecular weight of the resin. The styrenic heat-resistant resin has low folding resistance and impact resistance, so that it is difficult to pass paper especially in the molding process, it is difficult to remove the die, and chips are likely to be produced. Container productivity is reduced.
For these reasons, there is a need for a stretched sheet made of a styrene resin that has transparency and strength, has good film forming properties and moldability, is excellent in productivity, and is excellent in heat resistance and oil resistance.

In addition, in packaging containers such as food containers, which are the main uses of stretched sheets made of styrene-based resins, a transparent appearance is emphasized, and anti-fogging properties such as being less clouded by minute water droplets are also required.

US Pat. No. 30,350,33 Japanese Patent Laid-Open No. 2003-12734 Japanese Patent Publication No.59-15133 JP-A-55-71530 JP 56-161409 A JP 2011-225866 A

The subject of the present invention is a biaxially composed of a styrenic resin composition having good transparency, strength, film-forming property and moldability, excellent productivity, heat resistance and oil resistance, and excellent appearance and antifogging properties. It is to provide a stretched sheet and a molded product thereof.

The inventors of the present invention have made extensive studies on the components and composition of the styrene resin sheet in order to solve the above problems. As a result, it has been found that the above object can be achieved by using a resin based on a styrene-methacrylic acid copolymer and having a predetermined amount of a high molecular weight acrylic resin added, and selecting an appropriate antifogging agent. The present invention has been completed.

That is, the present invention is as follows.
(1) A biaxially stretched sheet comprising a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), the styrene-methacrylic acid copolymer (A) and The mass ratio (A) / (B) to the acrylic resin (B) is 90/10 to 97/3, and the styrene-methacrylic acid copolymer (A) is composed of a styrene monomer unit and methacrylic acid. The monomer unit is contained in a mass ratio of 84/16 to 94/6, the weight average molecular weight of the styrene-methacrylic acid copolymer (A) is 120,000 to 250,000, and the acrylic resin (B) The styrene resin composition has a Vicat softening temperature of 106 to 132 ° C., and sucrose fatty acid ester (C) is present on at least one surface of the biaxially stretched sheet. And water Biaxially oriented sheet characterized by having a coating layer containing a sex polymer (D).

(2) The biaxially stretched sheet according to (1), wherein the acrylic resin (B) contains a methyl methacrylate monomer unit and a butyl acrylate monomer unit.

(3) The biaxial as described in (2), wherein the acrylic resin (B) contains a methyl methacrylate monomer unit and a butyl acrylate monomer unit in a mass ratio of 65/35 to 85/15. Stretched sheet.

(4) The impact-resistant styrene resin (E) containing a rubber component is not more than 3% by mass with respect to the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B). The biaxially stretched sheet according to any one of (1) to (3), which is further contained.

(5) The rubber component described in (4), wherein the content of the biaxially stretched sheet is 0.05 to 0.3% by mass, and the average rubber particle diameter is 1.2 to 12.0 μm. Biaxially stretched sheet.

(6) The content of the styrene monomer in the styrene resin composition is 1000 ppm or less, and the content of the methacrylic acid monomer is 150 ppm or less. Biaxially stretched sheet.

(7) The thickness is 0.1 to 0.7 mm, the stretching ratios in the machine direction and the transverse direction are 1.8 times to 3.2 times, respectively, and the orientation relaxation stress in the machine direction and the transverse direction are each 0.2. The biaxially stretched sheet according to any one of (1) to (6), which is 3 to 1.2 MPa.

(8) The mass ratio (C) / (D) of the sucrose fatty acid ester (C) to the water-soluble polymer (D) in the coating layer is 80/20 to 50/50 (1) to (7) The biaxially stretched sheet according to any one of the above.

(9) The sucrose fatty acid ester (C) is a sucrose laurate ester (F) having a fatty acid moiety with 16 or more carbon atoms, a fatty acid moiety with an unsaturation degree of 1 or less, and an HLB value of 12 or more. 9. The biaxially stretched sheet according to any one of (1) to (8), which is a mixture containing a sugar fatty acid ester (G).

(10) The biaxial as described in (9) above, wherein the mass ratio (F) / (G) of the sucrose laurate ester (F) and the sucrose fatty acid ester (G) is 90/10 to 99/1 Stretched sheet.

(11) The biaxially stretched sheet according to any one of (1) to (10), wherein the degree of polymerization of the water-soluble polymer (D) is 300 to 2000.

(12) The biaxially stretched sheet according to any one of (1) to (11), wherein the amount of the coating layer formed per unit area is 10 to 150 mg / m ² .

(13) On the outermost surface of at least one of the biaxially stretched sheets, a surface layer containing silicone is further provided, and the formation amount per unit area of the surface layer is 3 to 30 mg / m ² (1 The biaxially stretched sheet according to any one of items 1) to (12).

(14) A molded article comprising the biaxially stretched sheet according to any one of (1) to (13).

(15) The molded product according to (14), which is a food packaging container.

(16) The molded product according to (15), which is a food packaging container for microwave heating.

The biaxially stretched sheet of the present invention and its molded product have good transparency, strength, film-forming property and moldability, and are excellent in heat resistance and oil resistance. Since the biaxially stretched sheet and the molded product thereof according to the present invention are excellent in film formability and moldability, they are also excellent in productivity. The biaxially stretched sheet and the molded product of the present invention can be suitably used for food packaging containers heated in a microwave oven. Moreover, the biaxially stretched sheet of the present invention and its molded product are excellent in appearance and antifogging properties.

Embodiments of the present invention will be described below. However, embodiments of the present invention are not limited to the following embodiments.

The biaxially stretched sheet of the present invention comprises a styrene resin composition in which a styrene-methacrylic acid copolymer (A) and an acrylic resin (B) are mixed at a predetermined mass ratio. The biaxially stretched sheet of the present invention can be obtained by extruding the styrene resin composition and biaxially stretching the obtained unstretched sheet. Hereinafter, each component of the styrene resin composition will be described.

(Styrene-methacrylic acid copolymer (A))
The styrene resin composition in the present invention contains a styrene-methacrylic acid copolymer (A) obtained by copolymerizing styrene and methacrylic acid. In the styrene-methacrylic acid copolymer (A) used in the present invention, the copolymerization ratio of styrene and methacrylic acid can be variously set depending on the desired heat resistance and mechanical strength. When the total amount of styrene monomer units and methacrylic acid monomer units is 100% by mass, a resin excellent in balance of heat resistance, mechanical strength, and transparency when formed into a sheet can be easily obtained. In addition, it is necessary to contain a styrene monomer unit and a methacrylic acid monomer unit in a mass ratio of 84/16 to 94/6. When the content of the methacrylic acid monomer unit is less than 6% by mass, the heat resistance is insufficient, and a hole is formed when the microwave oven is heated, and deformation tends to occur. The content of the methacrylic acid monomer unit is preferably 8% by mass or more, more preferably 9% by mass or more. On the other hand, if the content of the methacrylic acid monomer unit exceeds 16% by mass, in addition to a decrease in processability such as a decrease in fluidity during film formation and a decrease in moldability during secondary molding, Appearance deterioration tends to occur. The content of the methacrylic acid monomer unit is preferably 14% by mass or less, more preferably 13% by mass or less. In addition, the styrene-methacrylic acid copolymer (A) may be appropriately copolymerized with other monomers other than styrene and methacrylic acid, if necessary, as long as the effects of the invention are not impaired. The content of other monomers is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 3% by mass or less. When the content of other monomers exceeds 10% by mass, the ratio of styrene or methacrylic acid is lowered, and sufficient transparency, mechanical strength, and heat resistance may not be obtained.

The weight average molecular weight (Mw) of the styrene-methacrylic acid copolymer (A) is 120,000 to 250,000, preferably 140,000 to 220,000, more preferably 150,000 to 200,000. When the weight average molecular weight is less than 120,000, the fluidity is excessive, the sheet is likely to be drawn down or necked in, and the film forming property may be deteriorated. On the other hand, if the weight average molecular weight exceeds 250,000, the fluidity is insufficient, thickness unevenness during film formation and die lines are likely to occur, and the sheet appearance may be deteriorated.

The ratio Mw / Mn between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the styrene-methacrylic acid copolymer (A) is preferably 2.0 to 3.0, more preferably. 2.2 to 2.8. When Mw / Mn exceeds 3.0, surface roughness due to hot plate contact during container molding tends to occur. On the other hand, when Mw / Mn is less than 2.0, unevenness in thickness at the time of film formation due to a decrease in fluidity and molding failure at the time of container molding tend to occur. Further, the ratio Mz / Mw between the Z average molecular weight (Mz) and Mw is preferably 1.5 to 2.0, more preferably 1.6 to 1.9. When Mz / Mw is less than 1.5, sheet drawdown and neck-in are likely to occur, and film-forming property is deteriorated, and insufficient stretch orientation is likely to occur. On the other hand, when Mz / Mw exceeds 2.0, unevenness in thickness and die line during film formation due to a decrease in fluidity are likely to occur, and the sheet appearance may be deteriorated.

The number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z average molecular weight (Mz) described above are calculated by the GPC measurement and the molecular weight at each elution time from the elution curve of monodisperse polystyrene by the following method. And calculated as a molecular weight in terms of polystyrene.
Model: Shodex GPC-101 manufactured by Showa Denko KK
Column: PLgel 10 μm MIXED-B manufactured by Polymer Laboratories
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer

Examples of the polymerization method of the styrene-methacrylic acid copolymer (A) include known polymerization methods such as a bulk polymerization method, a solution polymerization method, and a suspension polymerization method that are industrialized with polystyrene and the like. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane can be used.

When the styrene-methacrylic acid copolymer (A) is polymerized, a polymerization initiator and a chain transfer agent can be used as necessary. An organic peroxide can be used as the polymerization initiator. Specific examples of the organic peroxide include benzoyl peroxide, t-butylperoxybenzoate, 1,1-di (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3. , 3,5-trimethylcyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t -Butyl peroxyacetate, t-butylperoxy-2-ethylhexanoate, polyether tetrakis (t-butylperoxycarbonate), ethyl-3,3-di (t-butylperoxy) butyrate, t-butyl Examples include peroxyisobutyrate. Specific examples of the chain transfer agent include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene and the like.

(Acrylic resin (B))
The acrylic resin (B) in the present invention is an ultrahigh molecular weight homopolymer or copolymer obtained by polymerizing acrylic acid and its ester or methacrylic acid and its ester.

Examples of the acrylic ester include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and the like. Examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and the like. Of these, butyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate are preferred, and butyl acrylate and methyl methacrylate are particularly preferred. The acrylic resin (B) may be a homopolymer of any of the above acrylic acid and its ester or methacrylic acid and its ester, or may be a copolymer of two or more. .

In the case of the acrylic resin (B) using methyl methacrylate as the methacrylate ester, the content of methyl methacrylate is preferably 65 to 85% by mass, more preferably 70 to 80% by mass, and still more preferably 72 to 78%. % By mass. When the content of methyl methacrylate is less than 65% by mass, the transparency of the sheet may be lowered during mixing with the styrene-methacrylic acid copolymer (A). On the other hand, when the content of methyl methacrylate exceeds 85% by mass, the content of butyl acrylate described later is lowered, and an insolubilized product of acrylic resin is likely to be generated.
In the case of the acrylic resin (B) using butyl acrylate as the acrylate ester, the content of butyl acrylate is preferably 15 to 35% by mass, more preferably 20 to 30% by mass, and still more preferably 22 Is 28% by mass. When the content of butyl acrylate is less than 15% by mass, the fluidity of the acrylic resin (B) is lowered, so that an insoluble matter of the acrylic resin is easily generated. On the other hand, when the content of butyl acrylate exceeds 35% by mass, the content of the methyl methacrylate is lowered, and the transparency of the sheet may be lowered.
Accordingly, in the case of the acrylic resin (B) using methyl methacrylate and butyl acrylate, the methyl methacrylate monomer unit and the butyl acrylate monomer unit are contained in a mass ratio of 65/35 to 85/15. Acrylic resin (B) is preferable.

The glass transition point of the acrylic resin (B) is preferably 40 to 100 ° C., more preferably 50 to 90 ° C., and further preferably 60 to 80 ° C. If the glass transition point is too low, the heat resistance may decrease when mixed with the styrene-methacrylic acid copolymer (A). On the other hand, if it is too high, the acrylic resin is difficult to melt when mixed with the styrene-methacrylic acid copolymer (A), and it may be difficult to mix uniformly.

The weight average molecular weight (Mw) of the acrylic resin (B) is 1 million to 7 million, preferably 1.2 million to 6 million, more preferably 1.5 million to 5 million. When the weight average molecular weight of the acrylic resin (B) is less than 1,000,000, durability against microwave heating is not sufficient. On the other hand, when the weight average molecular weight of the acrylic resin (B) exceeds 7 million, an insolubilized product of the acrylic resin (B) is generated as a gel, and the appearance of the biaxially stretched sheet is impaired. The weight average molecular weight of the acrylic resin (B) can be measured according to the method for measuring the weight average molecular weight of the styrene-methacrylic acid copolymer (A).

Examples of the polymerization method of the acrylic resin (B) include known polymerization methods such as emulsion polymerization, soap-free emulsion polymerization, fine suspension polymerization, suspension polymerization, bulk polymerization, and solution polymerization. Among these polymerization methods, emulsion polymerization is preferable because it is easy to produce a high molecular weight product.

A known emulsifier can be used as an emulsifier when the acrylic resin (B) is produced by emulsion polymerization. Examples include an anionic emulsifier, a nonionic emulsifier, a polymer emulsifier, and a reactive emulsifier having an unsaturated double bond capable of radical polymerization in the molecule.

(Styrenic resin composition)
The styrene resin composition in the present invention contains a styrene-methacrylic acid copolymer (A) and an acrylic resin (B). The mass ratio (A) / (B) of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) in the styrene resin composition is 90/10 to 97/3. The mass ratio (A) / (B) is preferably 91/9 to 96/4, and more preferably 93/7 to 95/5. When the content of the acrylic resin (B) is less than 3% by mass, the durability against microwave heating is not sufficient. On the other hand, when the content of the acrylic resin (B) exceeds 10% by mass, an insolubilized product of the acrylic resin is generated as a gel, and the appearance of the biaxially stretched sheet is impaired.

The styrenic resin composition may contain an impact-resistant styrenic resin (E) containing a rubber component in an amount that does not impair the appearance and transparency. By adding the impact-resistant styrene resin (E), the brittleness of the sheet and the blocking property of the container can be improved.
The impact-resistant styrene resin (E) may be a styrene resin containing a rubber component, and a styrene homopolymer containing a rubber component, or a styrene-methacrylic acid copolymer. Any of those containing a rubber component can be suitably used. The rubber component may be dispersed in the form of particles independently in the polystyrene or styrene-methacrylic acid copolymer used as the matrix resin, or the rubber component may be grafted with polystyrene or styrene-methacrylic acid copolymer. It may be polymerized and dispersed in the form of particles.

Examples of the rubber component include polybutadiene, styrene-butadiene copolymer, polyisoprene, butadiene-isoprene copolymer, and the like. In particular, polybutadiene and styrene-butadiene copolymer are preferable.

The content of the impact-resistant styrene resin (E) is 3% with respect to the total amount of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) in order to maintain the appearance and transparency of the sheet. % Or less is preferable. Further, in order to sufficiently improve the brittleness of the sheet and the blocking property of the container, the content is 0.5% by mass or more based on the total amount of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B). It is preferable.

The content of the rubber component derived from the impact-resistant styrene resin (E) is preferably 0.05 to 0.3% by mass as the content of the rubber component in the biaxially stretched sheet, and is preferably 0.07 to More preferably, it is 0.2 mass%. If the content of the rubber component is less than 0.05% by mass, the effect of improving sheet brittleness may not be sufficiently exhibited. On the other hand, if the content of the rubber component exceeds 0.3% by mass, the transparency of the sheet may be lowered. The average rubber particle diameter of the rubber component in the biaxially stretched sheet is preferably 1.2 to 12 μm. If the average rubber particle size is less than 1.2 μm, the effect of improving sheet brittleness may not be sufficiently exhibited. On the other hand, if the average rubber particle diameter exceeds 12 μm, the transparency of the sheet may be lowered.

The content of the rubber component in the biaxially stretched sheet is obtained by dissolving the biaxially stretched sheet in chloroform, adding iodine monochloride to react the double bond in the rubber component, and then adding potassium iodide and remaining. It is measured by the iodine monochloride method in which iodine monochloride is changed to iodine and back titrated with sodium thiosulfate.

The average rubber particle diameter of the rubber component in the biaxially stretched sheet is cut by an ultrathin section method so that the observation surface is parallel to the sheet plane, and the rubber component is dyed with osmium tetroxide (OsO ₄ ). The particle diameter of 100 particles is measured with a transmission microscope, and is a value calculated by the following equation.
Average rubber particle size = Σni (Di) ⁴ / Σni (Di) ³
Here, ni represents the number of measured particles, and Di represents the measured particle size.

The styrene monomer content in the styrene-based resin composition is preferably 1000 ppm or less, and the methacrylic acid monomer content is preferably 150 ppm or less. If the content of these monomers is greater than the specified amount, the sheet will adhere to the mold of the molding machine when molding the sheet, impairing the appearance of the molded product, or causing the mold to become dirty. There is a concern of deteriorating the appearance of the molded container.
The styrene monomer and the methacrylic acid monomer were quantified by the internal standard method using the gas chromatography described below.
Device name: GC-12A (manufactured by Shimadzu Corporation)
Column: Glass column φ3 [mm] x 3 [m]
Quantitative method: Internal standard method (cyclopentanol)

The styrenic resin composition needs to have a Vicat softening temperature in the range of 106 to 132 ° C. When the Vicat softening temperature is less than 106 ° C., the heat resistance of the sheet is insufficient, and deformation is likely to occur during microwave heating. The Vicat softening temperature is preferably 108 ° C or higher, more preferably 110 ° C or higher. On the other hand, if the Vicat softening temperature exceeds 132 ° C., the workability during film formation and container molding may be reduced. The Vicat softening temperature is preferably 128 ° C. or lower, more preferably 126 ° C. or lower. The Vicat softening temperature was measured in accordance with JIS K 7206 under the conditions of a heating rate of 50 ° C./hr and a test load of 50 N.

Furthermore, you may mix | blend various additives with the styrene resin composition in this invention according to a use. Examples of additives include antioxidants, anti-gelling agents, ultraviolet absorbers, light stabilizers, lubricants, plasticizers, colorants, antistatic agents, flame retardants, mineral oils, glass fibers, and carbon fibers. And reinforcing fibers such as aramid fibers, and fillers such as talc, silica, mica and calcium carbonate. Moreover, it is preferable to mix | blend antioxidant and an antigelling agent individually or in combination of 2 or more types from a viewpoint of the external appearance when the said styrene-type resin composition is sheeted. These additives may be added in the polymerization process or devolatilization process or granulation process of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B), or a styrene resin composition is produced. You may add when you do.
Although there is no restriction | limiting in the addition amount of the said additive, It is preferable to add in the range which does not impair the Vicat softening temperature and transparency of a styrene-type resin composition.

The gelation inhibitor has an effect of suppressing the gelation reaction due to the dehydration reaction of methacrylic acid. As an anti-gelling agent, for example, an aliphatic alcohol is effective. Common aliphatic alcohols include 7-methyl-2- (3-methylbutyl) -1-octanol, 5-methyl-2- (1-methylbutyl) -1-octanol, 5-methyl-2- (3-methylbutyl ) -1-octanol, 2-hexyl-1-decanol, 5,7,7-trimethyl-2- (1,3,3-trimethylbutyl) -1-octanol, 8-methyl-2- (4-methylhexyl) ) -1-decanol, 2-heptyl-1-undecanol, 2-heptyl-4-methyl-1-decanol, 2- (1,5-dimethylhexyl)-(5,9-dimethyl) -1-decanol, etc. It is done.

Examples of the antioxidant include triethylene glycol-bis [3- (3-tert-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], 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 -Phenolic antioxidants such as tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, ditridecyl-3,3'-thiodipropione Dilauryl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, dioctyl-3,3′-thiodipropionate Sulfur-based antioxidants such as trisnonylphenyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-ditridecyl) phosphite, (tridecyl) pentaerythritol diphosphite, bis (Octadecyl) pentaerythritol diphosphite, bis (di-tert-butylphenyl) pentaerythritol diphosphite, bis (di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite, dinonylphenyloctylphosphonite Tetrakis (2,4-di-t-butylpheny ) 1,4-phenylene diphosphonite, tetrakis (2,4-di-t-butylphenyl) 4,4′-biphenylene di-phosphonite, 10-decyloxy-9,10-dihydro-9-oxa Examples thereof include phosphorus-based antioxidants such as 10-phosphaphenanthrene.

(Biaxially stretched sheet)
The biaxially stretched sheet of the present invention can be produced by the following method. First, the styrene resin composition is melt-kneaded by an extruder and extruded from a die (particularly a T die). Next, the biaxially stretched sheet is stretched sequentially or simultaneously in the biaxial directions of the machine direction (sheet flow direction, MD; Machine Direction) and the transverse direction (direction perpendicular to the sheet flow direction, TD; Transverse Direction). Is manufactured.

The thickness of the biaxially stretched sheet is preferably 0.1 mm or more, more preferably 0.15 mm or more, and further preferably 0.2 mm or more in order to ensure the strength and particularly rigidity of the sheet and the container. On the other hand, from the viewpoints of formability and economy, the thickness of the biaxially stretched sheet is preferably 0.7 mm or less, more preferably 0.6 mm or less, and even more preferably 0.5 mm or less.

The stretching ratio in the machine direction and the transverse direction of the biaxially stretched sheet is preferably in the range of 1.8 to 3.2 times, respectively. When the draw ratio is less than 1.8 times, the folding resistance of the sheet tends to decrease. On the other hand, when the draw ratio exceeds 3.2 times, the shrinkage rate at the time of thermoforming is too large, and the formability is impaired.
In addition, the measuring method of the draw ratio of this invention is as follows. A straight line Y having a length of 100 mm is drawn in the machine direction (MD) and the transverse direction (TD) on the test piece of the biaxially stretched sheet. The length Z [mm] of the straight line after the test piece is left to shrink for 60 minutes in an oven having a temperature 30 ° C. higher than the Vicat softening temperature of the sheet measured in accordance with JIS K7206 is measured. The draw ratio (times) in the machine direction and the transverse direction are numerical values calculated by the following equations, respectively.
Stretch ratio (times) = 100 / Z

The orientation relaxation stress in the machine direction and the transverse direction of the biaxially stretched sheet is preferably in the range of 0.3 to 1.2 MPa, respectively. If the orientation relaxation stress is less than 0.3 MPa, the folding resistance of the sheet may be lowered. On the other hand, if the orientation relaxation stress exceeds 1.2 MPa, the shrinkage stress during thermoforming is too large, and the formability may be impaired.
The orientation relaxation stress of the biaxially stretched sheet of the present invention is a value measured as a peak stress value in silicone oil at a temperature 30 ° C. higher than the Vicat softening temperature of the resin composition constituting the sheet according to ASTM D1504. It is.

The gel content in the biaxially stretched sheet is preferably small from the viewpoint of workability and appearance during secondary molding. Specifically, the content is preferably 1% by mass or less, and more preferably 0.5% by mass or less in the biaxially stretched sheet. Further, the total content of monomers and oligomers in the biaxially stretched sheet is preferably 20000 ppm or less, more preferably 10,000 ppm, and even more preferably 5000 ppm or less from the viewpoints of processability, appearance, and heat resistance.

(Coating layer)
The biaxially stretched sheet of the present invention has a coating layer containing sucrose fatty acid ester (C) and water-soluble polymer (D) on at least one surface thereof. Sucrose fatty acid ester (C) is an excellent antifogging agent. By having the coating layer, the biaxially stretched sheet can exhibit excellent antifogging properties.

Sucrose fatty acid ester (C) is an ester of sucrose and a fatty acid. Examples of fatty acids constituting the sucrose fatty acid ester include caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and montanic acid, saturated fatty acids having about 6 to 30 carbon atoms, and lindenic acid. And unsaturated fatty acids having about 10 to 24 carbon atoms such as palmitooleic acid, oleic acid, elaidic acid, isooleic acid, erucic acid, linoleic acid, linolenic acid, etc., and these fatty acids may be used alone or in combination. Of these fatty acids, lauric acid is preferred.

Furthermore, the HLB (Hydrophile-Lipophile Balance) of the sucrose fatty acid ester (C) is preferably 13 or more, more preferably 14 or more, and still more preferably 15 or more. Here, the HLB value of the sucrose fatty acid ester is determined by the Griffin method.

More preferably, the sucrose fatty acid ester (C) is a mixture of the sucrose laurate ester (F) and another type of sucrose fatty acid ester. Another type of sucrose fatty acid ester is preferably a sucrose fatty acid ester (G) having a fatty acid moiety having 16 or more carbon atoms, an unsaturation degree of the fatty acid moiety of 1 or less, and an HLB value of 12 or more.

Since the sucrose fatty acid ester (G) is excellent in storage stability, the fatty acid portion preferably has 16 or more carbon atoms, and more preferably 18 or more. Moreover, since sucrose fatty acid ester (G) is excellent in storage stability (for example, appearance after storage, antifogging property), the degree of unsaturation of the fatty acid portion is preferably 1 or less. 0 is more preferable. Moreover, it is preferable that the HLB value of sucrose fatty acid ester (G) is 12 or more from a viewpoint that it is excellent in an external appearance (for example, external appearance when a coating layer is formed by coating). The HLB value of the sucrose fatty acid ester (G) is more preferably 13 or more, still more preferably 14 or more, and most preferably 15 or more. Preferable specific examples of the fatty acid of the sucrose fatty acid ester (G) include stearic acid, oleic acid, palmitic acid and the like.

The mass ratio (F) / (G) of sucrose laurate (F) and sucrose fatty acid ester (G) is preferably 90/10 to 99/1. When it is in the above range, it has more excellent effects in terms of appearance (for example, coating appearance) and storage stability (for example, appearance after storage, antifogging property).

Water-soluble polymer (D) is used to form a coating film containing sucrose fatty acid ester (C) on a biaxially stretched sheet. As will be described later, since it is a water-soluble polymer, it can be applied as an aqueous solution.

Examples of the water-soluble polymer (D) include polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylic acid, carboxymethyl cellulose, methyl cellulose, sodium alginate, carrageenan, corn starch and the like. Among these, synthetic alcohols such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyacrylic acid are preferable because of no variation in performance.

The degree of polymerization of the water-soluble polymer (D) is preferably 300 to 2000. When the degree of polymerization is within the above range, the coating has an appropriate viscosity and is excellent in handleability and appearance of the coating film. Here, the degree of polymerization is the number of monomers constituting the polymer.

The mass ratio (C) / (D) of the sucrose fatty acid ester (C) to the water-soluble polymer (D) in the coating layer is preferably 80/20 to 50/50. When it exists in said range, it is excellent in coating property and can provide anti-fogging property effectively to a biaxially stretched sheet.

The formation amount of the coating layer per unit area is preferably 10 to 150 mg / m ² . The amount of the coating layer formed per unit area is more preferably 20 to 80 mg / m ² , still more preferably 30 to 70 mg / m ² . When in the above range, it is excellent in terms of antifogging properties and appearance (for example, coating appearance, appearance after storage).

The coating layer is formed, for example, by coating a coating liquid obtained by dissolving sucrose fatty acid ester (C) and water-soluble polymer (D) in a solvent on at least one surface of the biaxially stretched sheet. . As the solvent, water, alcohol or the like is used, but is not particularly limited thereto. As the solvent, water is preferable from the viewpoint of handleability. The coating method is not particularly limited, and examples thereof include a coating method using a roll coater, a knife coater, a gravure roll coater and the like. Further, the coating layer may be formed by spraying, dipping, or the like.

(Surface layer)
A surface layer containing silicone may further be provided on at least one outermost surface of the biaxially stretched sheet. The surface layer may be provided directly on the surface of the biaxially stretched sheet, or may be provided on the biaxially stretched sheet via a coating layer or the like. By having a surface layer containing silicone on the outermost surface, the biaxially stretched sheet can exhibit excellent lubricity. Here, silicone is also called a silicon resin and is a general term for polymers having a siloxane bond (—Si—O—Si—) as a skeleton (main chain). As required, various functional groups are bonded to the side chain.

Viscosity at 23 ° C. of the silicone is preferably 1000 ~ 30000mm ² / s, more preferably 5000 ~ 25000mm ² / s. By setting the viscosity of the silicone within this range, it is possible to obtain better lubricity while suppressing a decrease in antifogging property due to silicone transfer after storage.

The formation amount of the surface layer per unit area is preferably 3 to 30 mg / m ² , more preferably 4 to 25 mg / m ² , and further preferably 5 to 20 mg / m ² . When it is in the above range, it is excellent in terms of lubricity and appearance (for example, coating appearance, appearance after storage).

The surface layer is formed, for example, by applying a coating solution in which silicone is dissolved in a solvent to at least one surface of the biaxially stretched sheet. As the solvent, water, alcohol or the like is used, but is not particularly limited thereto. The solvent is preferably water for handling. The method for coating the solution is not particularly limited, and examples thereof include a coating method using a roll coater, a knife coater, a gravure roll coater, and the like. Further, the surface layer may be formed by spraying, dipping, or the like.

(Molding)
There is no restriction | limiting in particular as a method of obtaining a molded article from the biaxially stretched sheet of this invention, The method currently used in the secondary forming method of the conventional biaxially stretched sheet can be used. For example, the secondary molding can be performed by a thermoforming method such as a vacuum forming method or a pressure forming method. These methods are described in, for example, “Plastic Processing Technology Handbook” edited by the Society of Polymer Science, Nikkan Kogyo Shimbun (1995).

The use of the molded product of the biaxially stretched sheet of the present invention includes various containers and can be widely used for packaging containers for various articles. Among the packaging containers, food packaging containers and food packaging container lid materials are suitable, particularly when the food is a food containing fats and oils. Furthermore, among the packaging containers, a food packaging container for heating in a microwave oven is particularly preferable because the features of the present invention are sufficiently exhibited.

Hereinafter, the embodiment of the present invention will be described more specifically using examples and comparative examples, but the present invention is not limited to these examples.

(Experimental example 1) [Production of styrene-methacrylic acid copolymer (A-1)]
100 kg of pure water and 100 g of polyvinyl alcohol were added to an autoclave with an internal volume of 200 L and a stirrer, and the mixture was stirred at 130 rpm. Subsequently, 72.0 kg of styrene, 4.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, the temperature was raised to 110 ° C., and polymerization was carried out for 5 hours (Step 1). Further, 4.0 kg of methacrylic acid was uniformly added over 2 hours from the time when the polymerization temperature reached 110 ° C. (Step 2). Furthermore, it hold | maintained at 140 degreeC for 3 hours, and superposition | polymerization was completed (step 3). The obtained beads were washed, dehydrated, dried and then extruded to obtain pellet-shaped styrene-methacrylic acid copolymer (A-1) shown in Table 1. As a result of analyzing this using pyrolysis gas chromatography, the mass composition ratio of styrene monomer unit / methacrylic acid monomer was 90/10. Moreover, the number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z average molecular weight (Mz) which were calculated | required by GPC measurement were 80000, 200,000, and 360,000, respectively.

(Experimental Examples 2 to 13) [Production of styrene-methacrylic acid copolymer (A-2 to 13)]
Various raw material charges and polymerization time in Experimental Example 1 were adjusted to obtain various styrene-methacrylic acid copolymers (A-2 to 13) shown in Table 1.

(Experimental example 14) [Production of acrylic resin (B-1)]
In a separable flask (capacity 5 liters) equipped with a thermometer, a nitrogen introduction tube, a cooling tube and a stirrer, 300 parts by mass (3,000 g) of ion-exchanged water as a dispersion medium and 1.1 parts by mass of sodium dodecylbenzenesulfonate as an emulsifier In addition, 0.01 parts by mass of n-octyl mercaptan was added as a chain transfer agent, and 75 parts by mass of methyl methacrylate and 25 parts by mass of butyl acrylate were added as monomers. The atmosphere in the flask was replaced with nitrogen by passing a nitrogen stream through the separable flask. Next, the internal temperature was raised to 60 ° C., and 0.15 parts by mass of potassium persulfate and 5 parts by mass of deionized water were added. Thereafter, heating and stirring were continued for 2 hours to complete the polymerization, and an acrylic resin latex was obtained.
The obtained acrylic resin latex was cooled to 25 ° C., dropped into 500 parts by mass of 70 ° C. hot water containing 5 parts by mass of calcium acetate, and then heated to 90 ° C. for coagulation. The obtained coagulated product was separated and washed, and then dried at 60 ° C. for 12 hours to obtain an acrylic resin (B-1). The glass transition temperature of the acrylic resin (B-1) was 60 ° C. when measured by differential scanning calorimetry (DSC) according to the transition temperature measurement method of JIS K 7121: 2012 plastic. Moreover, the weight average molecular weight (Mw) calculated | required by GPC measurement was 3 million.

(Experimental Examples 15 to 22) [Production of acrylic resin (B-2 to 9)]
The amounts of various monomers and chain transfer agents used in Experimental Example 14 were adjusted to obtain various acrylic resins (B-2 to 9) shown in Table 2.

(Experimental example 23) [Production of impact-resistant styrenic resin (E-1)]
Using 3.4% by mass of low-cis polybutadiene rubber (trade name: Diene 55AS, manufactured by Asahi Kasei Co., Ltd.) as a rubbery polymer, dissolved in 91.6% by mass of styrene and 5.0% by mass of ethylbenzene as a solvent. The polymerization raw material was used. Further, 0.1 part by mass of a rubber antioxidant (trade name: Irganox 1076, manufactured by Ciba Geigy Inc.) was added. This polymerization raw material was supplied at 12.5 kg / hr to a 14-liter jacketed reactor (R-01) equipped with a vertical stirring blade having a blade diameter of 0.285 m. The reaction was performed at a reaction temperature of 140 ° C. and a rotation speed of 2.17 sec ⁻¹ . The obtained resin liquid had a resin ratio of 25%. The obtained resin solution was introduced into two jacketed plug flow reactors having an internal volume of 21 liters arranged in series. In the first plug flow reactor (R-02), the reaction temperature is 120 to 140 ° C. in the flow direction of the resin liquid. In the second plug flow reactor (R-03), the reaction temperature is resin. The jacket temperature was adjusted to have a gradient of 130 to 160 ° C. in the liquid flow direction. The resin ratio at the R-02 outlet was 50%, and the resin ratio at the R-03 outlet was 70%. Here, the resin rate is calculated by the following formula.
Resin ratio (%) = 100 × (Amount of polymer produced) / {(Amount of monomer charged) + (Amount of solvent)}

The obtained resin liquid was heated to 230 ° C. and then sent to a devolatilization tank having a vacuum degree of 5 torr to separate and recover unreacted monomers and solvents. Then, after extracting with a gear pump from the devolatilization tank and making it a strand through a die plate, it pelletized through the water tank and collect | recovered as a product. The obtained resin (E-1) had a rubber component content of 10.0% by mass and an average rubber particle size of 2.0 μm.

(Experimental Examples 24 to 31) [Production of Impact Resistant Styrene Resin (E-2 to 9)]
Various raw material charges in Experimental Example 21 were adjusted to obtain various impact-resistant styrene resins (E-2 to 9) shown in Table 3.

<Example 1>
A styrene-methacrylic acid copolymer (A-1) 95.0% by mass is blended with 5.0% by mass of an acrylic resin (B-1). 1.0% by mass of Resin (E-1) was added. Using a pellet extruder (two-axis co-directional extruder with vacuum vent TEM35B (manufactured by Toshiba Machine Co., Ltd.)), a strand is made through a die plate at an extrusion temperature of 230 ° C., a rotation speed of 250 rpm, and a vent devolatilization pressure of −760 mmHg. After cooling, the mixture was pelletized through a pelletizer to obtain a resin composition. In addition, the vent devolatilization pressure was shown as a differential pressure value with respect to normal pressure. The content of the styrene monomer in the obtained resin composition was 500 ppm, and the content of the methacrylic acid monomer was 50 ppm. Further, the Vicat softening temperature was 116 ° C., and the melt flow index (MFI) under JIS K7210 H condition (200 ° C., 5 kg) was 1.0 g / 10 min. The above resin composition was unstretched using a sheet extruder (T-die width 500 mm, lip opening 1.5 mm, φ40 mm extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.)) at an extrusion temperature of 230 ° C. and a discharge rate of 20 kg / h. A sheet was obtained. This sheet is preheated to (Vicat softening temperature +30) ° C. using a batch type biaxial stretching machine (manufactured by Toyo Seiki Co., Ltd.), MD 2.4 times, TD 2.4 times (surface) at a strain rate of 0.1 / sec. The biaxially stretched sheet shown in Table 4 was obtained. The thickness of the obtained sheet was 0.3 mm, the draw ratio (MD / TD) was 2.4 / 2.4 times, and the orientation relaxation stress (MD / TD) was 0.6 / 0.6 MPa.

As a coating solution for the coating layer, 0.57% by mass of sucrose laurate (L-1570 (manufactured by Mitsubishi Chemical Foods)), 0 of sucrose stearate (S-1570, manufactured by Mitsubishi Chemical Foods) 0.03% by mass, an aqueous solution containing 0.40% by mass of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., product number 210, polymerization degree 1000, saponification degree 88 mol%, total of methyl acetate and methanol remaining ratio is 0.1% or less) Was prepared.

5 g / m ^{2 of the} coating liquid for the coating layer was applied to the surface of the obtained biaxially stretched sheet using a bar coater and dried in an oven at 105 ° C. for 1 minute. Mass per unit area of the resulting coating layer was 50 mg / ^{m 2.}

As a coating solution for the surface layer, an aqueous solution containing 0.2% by mass of silicone (manufactured by Shin-Etsu Silicone Co., Ltd., product number KM-9745A) was prepared. On the coating layer of the biaxially stretched sheet on which the coating layer was formed, 5 g / m ^{2 of} the above surface layer coating solution was applied using a bar coater and dried in an oven at 105 ° C. for 1 minute. The amount of the surface layer formed per unit area was 10 mg / m ² .

<Examples 2 to 84, Comparative Examples 1 to 8>
Table 6 to Table 13 are used in the same manner as in Example 1 by appropriately changing the type and blending amount of the resin in Example 1, the extrusion conditions of the resin composition, the type of coating layer and surface layer, and the coating amount. A biaxially stretched sheet was obtained. Regarding the sucrose fatty acid ester (C) used in the production of these examples and comparative examples, Table 4 shows samples C-1 to C-16 of each composition. As for the water-soluble polymer (D), Table 5 shows samples D-1 to D-9 of each material.

For the obtained biaxially stretched sheet, various performances were measured and evaluated by the methods described below. In relative evaluation of (circle), (triangle | delta), and x, the time of (circle) or (triangle | delta) was determined as the pass. The results are shown in Tables 6 to 13.

(1) Film-forming property The thickness is measured using a micro gauge at 25 points of intersection when 5 straight lines are drawn in a grid pattern at intervals of 20 mm in the MD direction and TD direction on an unstretched sheet, and the standard deviation σ is calculated. Evaluation was made according to the following criteria.
○: σ is less than 0.03 mm Δ: σ is 0.03 mm or more and less than 0.07 mm ×: σ is 0.07 mm or more

(2) Fluidity (melt flow rate)
It was measured according to JIS K7210 H condition (200 ° C., 5 kg).
○: 1.0 g / 10 min or more and less than 3.0 g / 10 min Δ: 0.5 g / 10 min or more and less than 1.0 g / 10 min, or
3.0 g / 10 min or more and less than 5.0 g / 10 min x: less than 0.5 g / 10 min or 5.0 g / 10 min or more

(3) Sheet appearance About the range of the biaxially stretched sheet 350 mm × 350 mm, 1) area of roll 100 mm ² or more, 2) area of 10 mm ² or more bubbles, 3) transparent and opaque foreign matter, 4) adhesion defect, 5) A die line having a width of 3 mm or more (a defect running in the sheet flow direction generated at the T-die outlet during film formation) was regarded as a defect, and the number of defects was evaluated according to the following criteria.
○: 0 △: 1 to 2 ×: 3 or more

(4) Stretchability The thickness is measured using a microgauge at 25 points of intersection when five straight lines are drawn in a grid pattern at intervals of 50 mm in the MD direction and TD direction on a biaxially stretched sheet, and the standard deviation σ is calculated. Evaluation was made according to the following criteria.
○: σ is less than 0.05 mm △: σ is 0.05 mm or more and less than 0.10 mm ×: σ is 0.10 mm or more

(5) Transparency (haze)
The haze of the biaxially stretched sheet was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku) in accordance with JIS K-7361-1.
○: Haze less than 1.5% Δ: Haze 1.5 or more, less than 3.0% ×: Haze 3.0% or more

(6) Rigidity A weight of 500 g was put into the main body of the food pack described later, and the lunch box containers with lids were stacked in five stages, and the deformation state of the lid material after standing for 24 hours was confirmed.
○: No change in shape.
Δ: Deformed.
X: There is a crack.

(7) Folding resistance According to ASTM D2176, the bending strength in the sheet extrusion direction (longitudinal direction) and the direction perpendicular thereto (lateral direction) was measured, the minimum value was obtained, and evaluated as follows.
○: 5 times or more △: 2 times or more and less than 5 times ×: Less than 2 times

(8) Formability With a hot plate molding machine HPT? 400A (Wakisaka Engineering Co., Ltd.), under the conditions of a hot plate temperature of 150 ° C and a heating time of 2.0 seconds (dimension lid: length 150 x width 130 x 30 mm in height, main body: length 150 × width 130 × height 20 mm) was molded, and moldability was evaluated according to the following criteria.
○: Good △: Slightly poor shape at the corner ×: Remarkably different shape from the dimensions or corner

(9) Mold stain resistance When molding the food pack, the transfer of dirt on the mold and the like was evaluated according to the following criteria.
○: No transfer (clear, no cloudiness)
Δ: Transfer in part (opaque, cloudy surface)
×: Transferred throughout (opaque, surface cloudy)

(10) Heat resistance The food pack 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, outside dimension change less than 5% ×: Large deformation, outside dimension change 5% or more

(11) Oil resistance 10 × 10 mm of gauze impregnated with a test solution of salad oil (manufactured by Nissin Oil Co., Ltd.), mayonnaise (manufactured by Ajinomoto Co., Inc.), and Coconut ML (registered trademark, manufactured by Kao Co., Ltd.) Affixed and allowed to stand in a 60 ° C. oven for 24 hours to observe the surface of the adhered part.
○: No change △: Slight whitening ×: Significant whitening and cracking

(12) Microwave oven heat resistance After attaching 9 points of mayonnaise in the range of 5 mm x 5 mm to the center of the lid of the food pack, putting 300 g of water into the container body, covering the lid container, and heating in a 1500 W microwave oven for 90 seconds The appearance of the mayonnaise adhering portion was visually evaluated.
○: No change △: Whitening occurred, container slightly deformed ×: Perforated, container deformed significantly

(13) Appearance after storage The biaxially stretched sheet was wound up, left in a roll state at 23 ° C. for 6 months, and measured with a haze meter NDH5000 (Nippon Denshoku) according to JIS K-7361-1. .
○: Haze less than 1.5% Δ: Haze 1.5 or more, less than 3.0% ×: Haze 3.0% or more

(14) Appearance at the time of molding With a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering), a biaxially stretched sheet is heated at a temperature of 135 ° C and heated for 2.0 seconds (dimension length 241 × Horizontal 193 × height 28 mm) was molded. The molded product was measured with a haze meter NDH5000 (Nippon Denshoku) according to JIS K-7361-1.
○: Haze less than 1.5% Δ: Haze 1.5 or more, less than 3.0% ×: Haze 3.0% or more

(15) Anti-fogging property (initial)
A biaxially stretched sheet with a hot plate molding machine HPT-400A (Wakisaka Engineering Co., Ltd.) under the conditions of a hot plate temperature of 135 ° C and a heating time of 2.0 seconds (dimension 241 × width 193 × height 28 mm) Was molded. 50 g of water at 95 ° C. was put into the main body of the obtained container, covered, and left at 23 ° C. The contents visibility after 10 minutes was confirmed.
○: The contents can be clearly confirmed.
(Triangle | delta): The content becomes difficult to see by dew condensation to a cover part.
X: Much exposure to the lid, content is not discernable.

(16) Anti-fogging after storage The biaxially stretched sheet is wound up, left in a roll state at 23 ° C. for 6 months, and then heated by a hot plate molding machine HPT-400A (manufactured by Wakisaka Engineering). A lunch box lid (dimensions 241 × width 193 × height 28 mm) was molded under the conditions of a temperature of 2.0 ° C. and a heating time of 2.0 seconds. 50 g of water at 95 ° C. was put into the main body of the obtained container, covered, and left at 23 ° C. The contents visibility after 10 minutes was confirmed.
○: The contents can be clearly confirmed.
(Triangle | delta): The content becomes difficult to see by dew condensation to a cover part.
X: Much exposure to the lid, content is not discernable.

(17) Lubricity In a state where the food contact surface and the food non-contact surface of the sheet cut out from the top surface of the container are overlapped, friction is performed by a method according to JIS P 8147 method for measuring static and dynamic friction coefficients. The angle (the angle at which sliding begins) was measured.
○: Less than 15 ° △: 15 ° or more, less than 30 ° ×: 30 ° or more

From the results of Tables 6 to 13, Examples 1 to 84 all satisfy the provisions of the present invention, and film forming properties (film forming properties, fluidity, sheet appearance, stretchability), transparency, Sheet strength (rigidity, folding resistance), moldability (moldability, mold stain resistance), heat resistance, oil resistance, microwave oven heat resistance, appearance after storage, appearance during molding, antifogging (initial), The antifogging property (after storage) and the slipperiness were excellent.

On the other hand, Comparative Examples 1 to 8 do not satisfy the provisions of the present invention in any of the styrene-methacrylic acid copolymer (A), the acrylic resin (B), and the Vicat softening temperature. Performance, fluidity, sheet appearance, moldability, heat resistance, oil resistance, and microwave oven heat resistance were poor.

Claims (16)

A biaxially stretched sheet comprising a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B),
The mass ratio (A) / (B) of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) is 90/10 to 97/3,
The styrene-methacrylic acid copolymer (A) contains a styrene monomer unit and a methacrylic acid monomer unit in a mass ratio of 84/16 to 94/6,
The styrene-methacrylic acid copolymer (A) has a weight average molecular weight of 120,000 to 250,000,
The acrylic resin (B) has a weight average molecular weight of 1 million to 7 million,
The Vicat softening temperature of the styrenic resin composition is 106 to 132 ° C.,
A biaxially stretched sheet comprising a coating layer containing a sucrose fatty acid ester (C) and a water-soluble polymer (D) on at least one surface of the biaxially stretched sheet. The biaxially stretched sheet according to claim 1, wherein the acrylic resin (B) contains a methyl methacrylate monomer unit and a butyl acrylate monomer unit. The biaxially stretched sheet according to claim 2, wherein the acrylic resin (B) contains a methyl methacrylate monomer unit and a butyl acrylate monomer unit in a mass ratio of 65/35 to 85/15. Further containing an impact-resistant styrene resin (E) containing a rubber component in a proportion of 3% by mass or less based on the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B). The biaxially stretched sheet according to any one of claims 1 to 3. The biaxially stretched film according to claim 4, wherein the rubber component has a content in the biaxially stretched sheet of 0.05 to 0.3% by mass and an average rubber particle diameter of 1.2 to 12.0 µm. Sheet. The biaxially stretched sheet according to any one of claims 1 to 5, wherein the styrene-based resin composition has a styrene monomer content of 1000 ppm or less and a methacrylic acid monomer content of 150 ppm or less. The thickness is 0.1 to 0.7 mm, the longitudinal and lateral stretching ratios are 1.8 to 3.2 times, respectively, and the longitudinal and lateral orientation relaxation stresses are 0.3 to 1 respectively. The biaxially stretched sheet according to any one of claims 1 to 6, which is 2 MPa. The mass ratio (C) / (D) of the sucrose fatty acid ester (C) and the water-soluble polymer (D) in the coating layer is 80/20 to 50/50. The biaxially stretched sheet as described. The sucrose fatty acid ester (C) is a sucrose fatty acid ester having sucrose laurate ester (F), the fatty acid part having 16 or more carbon atoms, the fatty acid part having an unsaturation degree of 1 or less, and an HLB value of 12 or more. The biaxially stretched sheet according to any one of claims 1 to 8, which is a mixture containing (G). The biaxially stretched sheet according to claim 9, wherein a mass ratio (F) / (G) of the sucrose laurate ester (F) and the sucrose fatty acid ester (G) is from 90/10 to 99/1. The biaxially stretched sheet according to any one of claims 1 to 10, wherein the degree of polymerization of the water-soluble polymer (D) is 300 to 2000. The biaxially stretched sheet according to any one of claims 1 to 11, wherein the coating layer is formed in an amount of 10 to 150 mg / m ² per unit area. The surface layer containing silicone is further provided on at least one outermost surface of the biaxially stretched sheet, and the formation amount per unit area of the surface layer is 3 to 30 mg / m ² . The biaxially stretched sheet according to any one of the above. A molded article comprising the biaxially stretched sheet according to any one of claims 1 to 13. The molded article according to claim 14, which is a food packaging container. The molded product according to claim 15, which is a food packaging container for heating in a microwave oven.