TWI709487B - Biaxially stretched sheet and its molded products - Google Patents

Abstract

The present invention provides a biaxially stretched sheet composed of a styrene resin composition that is excellent in transparency, strength, film forming properties, and moldability, and excellent in productivity, heat resistance, oil resistance, appearance, and anti-fogging properties, and the same Molded products.

A biaxially stretched sheet, which is composed of a styrene resin composition containing a styrene-methacrylic acid copolymer and an acrylic resin, and the mass ratio of the styrene-methacrylic acid copolymer to the acrylic resin is 90/10~ 97/3, the styrene-methacrylic acid copolymer contains styrene monomer units and methacrylic acid monomer units in a mass ratio of 84/16 to 94/6. The weight average molecular weight of the styrene-methacrylic acid copolymer is 120,000~250,000, the weight average molecular weight of the acrylic resin is 1 million to 7 million, the Ficat softening temperature of the styrene resin composition is 106~132℃, and on at least one side of the biaxially stretched sheet, It has a coating layer containing sucrose fatty acid ester and water-soluble polymer; and its molded product.

Description

Biaxially stretched sheet and its molded products

The present invention relates to a biaxially stretched sheet composed of a styrene-based resin composition and a molded product thereof, which can be suitably used as a packaging container for foods heated in a microwave oven.

Biaxially stretched polystyrene sheets are excellent in transparency and rigidity, so they are molded and are mainly used for molded products such as lightweight containers. However, these containers have poor heat resistance, so they are not used for applications that directly contact boiling water or applications that are heated in a microwave oven. Therefore, attempts have been made to impart heat resistance to polystyrene as a raw material. As polystyrene with improved heat resistance, for example, styrene-acrylic acid copolymer or styrene-methacrylic acid copolymer (Patent Document 1 and Patent Document 2), styrene-maleic anhydride copolymer (Patent Document 3, Patent Document 4). These are generally known as styrene-based heat-resistant resins, which do not impair transparency and rigidity and improve heat resistance.

However, the above-mentioned styrene-based heat-resistant resin has lower fluidity during melt extrusion than ordinary polystyrene, and it is difficult to improve the production capacity of the resin or the production capacity of the sheet. In order to improve the fluidity of the styrene-based heat-resistant resin, (i) a method of increasing the extrusion temperature and (ii) a method of reducing the molecular weight of the resin are considered. If the extrusion temperature is increased, the carboxylic acid groups in the above-mentioned styrene-based heat-resistant resin will react and become a colloidal foreign substance, resulting in a decrease in the quality of the sheet. In addition, if the molecular weight of the resin is lowered, drawdown is likely to occur during sheet extrusion, and film formation becomes difficult.

As a method of increasing the extrusion temperature while suppressing the generation of gel, for example, a method of adding an antigelling agent during extrusion is proposed (Patent Document 5). However, the anti-gelling agent described in Patent Document 5 also functions as a plasticizer, and therefore the heat resistance and oil resistance of the obtained styrene-based resin sheet are reduced. Therefore, it is necessary to select additives that do not easily degrade these properties.

Moreover, as a method of reducing the molecular weight of a styrene-based resin while maintaining film formability, a method of imparting strain hardening properties 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 aforementioned styrene-based heat-resistant resin and is unlikely to exhibit the expected strain hardening properties, but also has the disadvantage that the transparency of the obtained sheet is reduced. . Therefore, it is necessary to newly select a combination of a styrene-based heat-resistant resin and a high-molecular-weight polymer that are compatible with each other.

In addition, the aforementioned styrene-based heat-resistant resin has low sheet strength, particularly low folding resistance and impact resistance, and is further reduced by reducing the molecular weight of the resin. The aforementioned styrene-based heat-resistant resins have low folding resistance and impact resistance, so they have defects such as difficulty in conveying through equipment, difficulty in die-cutting, and prone to chipping during the forming step, which reduces the productivity of molded containers. .

For these reasons, there is a need for a stretched sheet made of styrene resin that has transparency, strength, good film-forming properties and moldability, good productivity, and excellent heat resistance and oil resistance.

In addition, in packaging containers such as food containers, which are the main applications of stretched sheets made of styrene resin, a transparent appearance is emphasized, and anti-fogging properties such as being less likely to be fogged by minute water droplets are required.

Prior art literature Patent literature

Patent Document 1 Specification of U.S. Patent No. 3035033

Patent Document 2 JP 2003-12734 A

Patent Document 3 Japanese Patent Publication No. 59-15133

Patent Document 4 JP 55-71530 A

Patent Document 5 JP 56-161409 A

Patent Document 6 JP 2011-225866 A

The subject of the present invention is to provide a double-stranded styrene resin composition with excellent transparency, strength, film forming properties, and moldability, excellent productivity, heat resistance, and oil resistance, and good appearance and anti-fogging properties. Shaft extension sheet and its molded products.

In order to solve the above-mentioned problems, the inventors of the present application have repeatedly studied the components and composition of the styrene-based resin sheet. As a result, it was found that by using a styrene-methacrylic acid copolymer as a base, using a resin added with a predetermined amount of a high molecular weight acrylic resin, and selecting an appropriate anti-fogging agent, the above object can be achieved, and the present invention has been completed. .

That is, the present invention is as follows.

(1) A biaxially stretched sheet, which is a biaxially stretched sheet composed of a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), characterized in that: the benzene The mass ratio (A)/(B) of the ethylene-methacrylic acid copolymer (A) to the acrylic resin (B) is 90/10 to 97/3, and the styrene-methacrylic acid copolymer (A) is The mass ratio of 84/16 to 94/6 contains styrene monomer units and methacrylic acid monomer units. The weight average molecular weight of the styrene-methacrylic acid copolymer (A) is 120,000-250,000. The acrylic The weight average molecular weight of the resin (B) is 1 million to 7 million, and the Vicat softening temperature of the styrene resin composition is 106 to 132°C, and is on at least one side of the biaxially stretched sheet The surface has a coating layer containing sucrose fatty acid ester (C) and water-soluble polymer (D).

(2) The biaxially stretched sheet as described in (1) above, wherein the acrylic resin (B) contains methyl methacrylate monomer units and butyl acrylate monomer units.

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

(4) The biaxially stretched sheet according to any one of (1) to (3) above, which is based on the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) The ratio of 3 mass% or less further contains the impact-resistant styrene resin (E) containing a rubber component.

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

(6) The biaxially stretched sheet according to any one of (1) to (3) above, wherein the styrene monomer content in the styrene resin composition is 1000 ppm or less, and the methacrylic monomer content It is 150 ppm or less.

(7) The biaxially stretched sheet as described in any one of (1) to (3) above, the thickness of which is 0.1 to 0.7 mm, the stretch magnification in the longitudinal direction and the transverse direction is 1.8 to 3.2 times, and the longitudinal direction and The orientation relaxation stress in the transverse direction is 0.3~1.2MPa respectively.

(8) The biaxially stretched sheet according to any one of (1) to (3) above, wherein the mass ratio of the sucrose fatty acid ester (C) and the water-soluble polymer (D) of the coating layer (C)/ (D) is 80/20~50/50.

(9) The biaxially stretched sheet according to any one of (1) to (3) above, wherein the aforementioned sucrose fatty acid ester (C) contains sucrose laurate (F) and the carbon number of the fatty acid moiety is A mixture of sucrose fatty acid esters (G) with a degree of unsaturation of the fatty acid part of 1 or less and an HLB value of 12 or more.

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

(11) The biaxially stretched sheet according to any one of (1) to (3) above, 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 (3) above, wherein the formation amount per unit area of the coating layer is 10 to 150 mg/m ² .

(13) The biaxially stretched sheet according to any one of (1) to (3) above, which further has a silicone-containing surface layer on the outermost surface of at least one side of the biaxially stretched sheet, and The formation amount per unit area of the surface layer is 3-30mg/m ² .

(14) A molded product comprising the biaxially stretched sheet as described in any one of (1) to (3) above.

(15) The molded article described in (14) above, which is a food packaging container.

(16) The molded product described in (15) above, which is a food packaging container for microwave heating.

The biaxially stretched sheet and molded product thereof of the present invention are excellent in transparency, strength, film forming properties, and moldability, and are excellent in heat resistance and oil resistance. The biaxially stretched sheet and its molded product of the present invention are excellent in both film-forming properties and moldability, and therefore also good in productivity. The biaxially stretched sheet of the present invention and its molded product can be suitably used for packaging containers for foods heated in a microwave oven. In addition, the biaxially stretched sheet and its molded product of the present invention are also excellent in appearance and anti-fogging properties.

Implementation of the invention

The embodiments of the present invention will be described below. However, the embodiment of the present invention is not limited to the following embodiment.

The biaxially stretched sheet of the present invention contains a styrene-based resin composition in which a styrene-methacrylic acid copolymer (A) and an acrylic resin (B) are mixed in a predetermined mass ratio. The biaxially stretched sheet of the present invention can be obtained by extruding the aforementioned styrene-based 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 of 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 according to the required heat resistance and mechanical strength. From the viewpoint of easily obtaining a resin having an excellent balance of heat resistance, mechanical strength, and transparency when forming a sheet, when the total amount of styrene monomer units and methacrylic monomer units is 100% by mass, it is necessary Contains styrene monomer units and methacrylic monomer units in a mass ratio of 84/16 to 94/6. If the content of the methacrylic monomer unit is less than 6 mass%, the heat resistance is insufficient, and it becomes easy to cause perforation and deformation during heating in a microwave oven. The content of the methacrylic monomer unit is preferably 8% by mass or more, and more preferably 9% by mass or more. On the other hand, if the content of the methacrylic monomer unit is more than 16% by mass, in addition to the decrease in fluidity during film formation and the decrease in formability during secondary molding, the processability becomes easier. Causes appearance degradation due to gel production. The content of the methacrylic monomer unit is preferably 14% by mass or less, and more preferably 13% by mass or less. In addition, the styrene-methacrylic acid copolymer (A) may appropriately copolymerize styrene and monomers other than methacrylic acid as long as the effect of the invention is not impaired. The content of other monomers is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass or less. If the content of other monomers is greater than 10% by mass, the ratio of styrene or methacrylic acid will decrease, 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, and more preferably 150,000 to 200,000. If the weight-average molecular weight is less than 120,000, the fluidity is excessive, the sheet may sag or the edges are bent inward, and the film-forming properties may decrease. In addition, if the weight average molecular weight is more than 250,000, fluidity is insufficient, thickness unevenness or mold lines during film formation are likely to occur, and the appearance of the sheet may decrease.

In addition, the ratio Mw/Mn of the weight average molecular weight (Mw) to 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. If Mw/Mn is greater than 3.0, the surface roughness caused by the contact of the hot plate during container forming becomes easy to occur. On the other hand, if Mw/Mn is less than 2.0, unevenness in thickness during film formation or poor shaping during container formation due to a decrease in fluidity tends to occur. In addition, the ratio of Z average molecular weight (Mz) to Mw, Mz/Mw, is preferably 1.5 to 2.0, more preferably 1.6 to 1.9. If the Mz/Mw is less than 1.5, it becomes easy to cause the sheet to sag and the edges to bend inward, and it becomes easy to produce a decrease in film formability and insufficient stretch alignment. On the other hand, if Mz/Mw is greater than 2.0, uneven thickness or mold lines during film formation due to a decrease in fluidity tend to occur, and there is a possibility that the appearance of the sheet will decrease.

Furthermore, the number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) mentioned above are measured by GPC. The following method is used to calculate the molecular weight of each dissolution time using the dissolution curve of monodisperse polystyrene , And calculated as the molecular weight in terms of polystyrene.

Model: Shodex GPC-101 manufactured by Showa Denko Co., Ltd.

Column: PLgel 10μm MIXED-B manufactured by Polymer Laboratories

Mobile phase: Tetrahydroan

Sample concentration: 0.2% by mass

Temperature: oven 40℃, injection port 35℃, detector 35℃

Detector: Differential refractometer

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

In the polymerization of the styrene-methacrylic acid copolymer (A), a polymerization initiator and a chain transfer agent may be used as necessary. As the polymerization initiator, organic peroxides can be used. Specific examples of organic peroxides include benzoyl peroxide, tertiary butyl peroxy benzoate, 1,1-bis(tertiary butyl peroxide) cyclohexane, 1,1- Bis(tertiary butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-bis(4,4-di-tertiarybutylperoxycyclohexyl)propane, tertiary butyl Isopropyl peroxide, dicumyl peroxide, tertiary butyl cumyl peroxide, tertiary butyl peroxyacetate, tertiary butyl peroxide-2-ethyl Caproic acid ester, polyether 4 (tertiary butyl peroxy carbonate), ethyl-3,3-bis (tertiary butyl peroxy) butyrate, tertiary butyl peroxy isobutyrate, etc. 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) of the present invention is an ultra-high molecular weight homopolymer or copolymer obtained by polymerizing acrylic acid and its esters, or methacrylic acid and its esters.

As said acrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, etc. are mentioned. Examples of the above methacrylate include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, and methacrylic acid ring. Hexyl ester and so on. Among these, butyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate are preferred, and butyl acrylate and methyl methacrylate are more preferred. The acrylic resin (B) may be a homopolymer of any of the aforementioned acrylic acid and its esters, or methacrylic acid and its esters, or may be a copolymer of two or more types.

In the case of the acrylic resin (B) using methyl methacrylate as the methacrylate, the content of methyl methacrylate is preferably 65 to 85% by mass, more preferably 70 to 80% by mass, and still more preferably It is 72~78% by mass. If the content of methyl methacrylate is less than 65% by mass, the transparency of the sheet may decrease when it is mixed with the aforementioned styrene-methacrylic acid copolymer (A). On the other hand, if the content of methyl methacrylate is more than 85% by mass, the content of butyl acrylate described later will decrease, and it will become easy to produce insoluble materials of acrylic resin.

Moreover, in the case of using butyl acrylate as the acrylic resin (B) of the acrylate, the content of butyl acrylate is preferably 15 to 35% by mass, more preferably 20 to 30% by mass, and still more preferably 22 to 28 quality%. If the content of butyl acrylate is less than 15% by mass, the fluidity of the acrylic resin (B) is reduced, so that insoluble matter of the acrylic resin is likely to be generated. On the other hand, if the content of butyl acrylate exceeds 35% by mass, the content of the methyl methacrylate may decrease, and the transparency of the sheet may decrease.

Therefore, when the acrylic resin (B) of methyl methacrylate and butyl acrylate is used, it is preferable to contain methyl methacrylate monomer unit and butyl acrylate monomer in a mass ratio of 65/35 to 85/15. Bulk acrylic resin (B).

In addition, the glass transition point of the acrylic resin (B) is preferably 40 to 100°C, more preferably 50 to 90°C, and still more preferably 60 to 80°C. If the glass transition point is too low, there is a possibility that the heat resistance may decrease when it is mixed with the aforementioned styrene-methacrylic acid copolymer (A). Moreover, if it is too high, it may become difficult to melt|melt the acrylic resin at the time of mixing with the said styrene-methacrylic acid copolymer (A), and it may become 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 million, the durability against microwave heating is insufficient. On the other hand, if the weight average molecular weight of the acrylic resin (B) exceeds 7 million, the insoluble matter of the acrylic resin (B) is generated as a gel, and the appearance of the biaxially stretched sheet is impaired. The measurement of the weight average molecular weight of the acrylic resin (B) can be carried out in accordance with the measurement method of the weight average molecular weight of the aforementioned styrene-methacrylic acid copolymer (A).

Examples of the polymerization method of the acrylic resin (B) include well-known polymerization methods such as emulsion polymerization, soap-free emulsion polymerization, fine suspension polymerization, suspension polymerization, bulk polymerization, and solution polymerization. Among these superposition methods, emulsion polymerization is preferred from the viewpoint of easy production of high polymers.

As an emulsifier when the acrylic resin (B) is produced by emulsion polymerization, a well-known emulsifier can be used. Examples thereof include anionic emulsifiers, nonionic emulsifiers, polymer emulsifiers, and reactive emulsifiers having radically polymerizable unsaturated double bonds in the molecule.

(Styrenic resin composition)

The styrene resin composition of the present invention contains a styrene-methacrylic acid copolymer (A) and an acrylic resin (B). The mass ratio (A)/(B) of the styrene-methacrylic copolymer (A) and the acrylic resin (B) of the styrene-based resin composition is 90/10 to 97/3. The mass ratio (A)/(B) is preferably 91/9 to 96/4, more preferably 93/7 to 95/5. When the content of the acrylic resin (B) is less than 3% by mass, the durability for microwave heating is insufficient. On the other hand, if the content of the acrylic resin (B) exceeds 10% by mass, the insoluble matter of the acrylic resin is generated as a gel, and the appearance of the biaxially stretched sheet is impaired.

In the styrene-based resin composition, an impact-resistant styrene-based resin (E) containing a rubber component in an amount that does not impair the appearance and transparency may be added. By adding impact-resistant styrene resin (E), the brittleness of the sheet and the adhesion of the container can be improved.

As the impact-resistant styrene resin (E), any styrene resin containing a rubber component may be sufficient, and a styrene homopolymer contains a rubber component, and a styrene-methacrylic acid copolymer contains rubber. The ingredients can be used appropriately. The rubber component, in the polystyrene or styrene-methacrylic acid copolymer that becomes the matrix resin, can be dispersed as particles independently, or in the rubber component, polystyrene or styrene-methacrylic acid copolymer It is dispersed into particles by graft polymerization.

Examples of the rubber component include polybutadiene, styrene-butadiene copolymer, polyisoprene, butadiene-isoprene copolymer, and the like. Especially preferred are polybutadiene and styrene-butadiene copolymer.

In order to maintain the appearance and transparency of the sheet, the content of the impact-resistant styrene resin (E) is preferably 3 mass relative to the total amount of the styrene-methacrylic acid copolymer (A) and acrylic resin (B) %the following. Furthermore, in order to sufficiently impart the effect of improving the brittleness of the sheet and the adhesiveness of the container, it is preferably 0.5% by mass or more with respect to the total amount of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B).

The content of the rubber component derived from the impact-resistant styrene-based resin (E) is preferably 0.05 to 0.3% by mass, more preferably 0.07 to 0.2% by mass in the biaxially stretched sheet. When the content of the rubber component is less than 0.05% by mass, the effect of improving the fragility of the sheet may not be fully exhibited. On the other hand, if the content of the rubber component exceeds 0.3% by mass, the transparency of the sheet may decrease. In addition, the average rubber particle size of the rubber component in the biaxially stretched sheet is preferably 1.2 to 12 μm. When the average rubber particle size is less than 1.2 μm, the effect of improving flake brittleness may not be fully exhibited. On the other hand, if the average rubber particle size is larger than 12 μm, the transparency of the sheet may decrease.

The content of the rubber component in the biaxially stretched sheet is determined by dissolving the biaxially stretched sheet in chloroform and adding iodine monochloride to react the double bonds in the rubber component. Potassium iodide is added to remove the remaining iodine monochloride. It was changed to iodine and measured by the iodine monochloride method of reverse titration with sodium thiosulfate.

The average rubber particle size of the rubber component in the biaxially stretched sheet is the ultra-thin section method, the observation surface is cut in a direction parallel to the plane of the sheet, and the rubber component is dyed with osmium tetroxide (OsO ₄ ). The transmission type is adopted The particle size of 100 particles was measured with a microscope, and the value was calculated using the following formula.

Average rubber particle size = Σni(Di) ⁴ /Σni(Di) ³

Here, ni represents the number of measured objects, and Di represents the measured particle size.

Preferably, the content of the styrene monomer in the styrene resin composition is 1000 ppm or less, and the content of the methacrylic monomer is 150 ppm or less. If the content of these monomers is higher than the prescribed amount, it may adhere to the mold of the molding machine during the sheet forming process, which may damage the appearance of the molded product, cause mold fouling, and damage the appearance of the subsequent molded container. doubt.

In addition, the quantification of styrene monomer and methacrylic monomer was measured by the internal standard method using the gas chromatography described below.

Device name: GC-12A (manufactured by Shimadzu Corporation)

Column: glass column φ3[mm]×3[m]

Quantitative method: internal standard method (cyclopentanol)

The styrene resin composition must have a Ficat softening temperature in the range of 106 to 132°C. If the Fica softening temperature is less than 106°C, the heat resistance of the sheet is insufficient, and it becomes easy to deform when heated in a microwave oven. The Ficatin softening temperature is preferably 108°C or higher, more preferably 110°C or higher. On the other hand, if the Fica softening temperature is higher than 132°C, the processability during film formation and container formation may be reduced. The Ficatin softening temperature is preferably 128°C or less, more preferably 126°C or less. In addition, the Ficat softening temperature is measured based on JIS K7206 under the conditions of a temperature increase rate of 50°C/hr and a test load of 50N.

Furthermore, in the styrene resin composition of the present invention, various additives may be blended for application. Examples of additives include antioxidants, antigelling agents, ultraviolet absorbers, light stabilizers, slip agents, plasticizers, colorants, antistatic agents, flame retardants, mineral oil and other additives, glass fibers , Carbon fiber and polyaramide fiber and other reinforcing fibers, talc, silica, mica, calcium carbonate and other fillers. In addition, from the viewpoint of the appearance when the styrene-based resin composition is formed into a sheet, it is preferable to blend two or more types of antioxidants and antigelling agents alone or in combination. These additives can be added in the polymerization step, devolatilization step, and granulation step of the styrene-methacrylic acid copolymer (A) and acrylic resin (B), and can also be added in the production of the styrene resin composition .

The addition amount of the above-mentioned additives is not limited, but it is preferable to add them so as not to impair the softening temperature and transparency of the styrenic resin composition.

The antigelling agent has the effect of inhibiting the gelation reaction caused by the dehydration reaction of methacrylic acid. As antigelling agents, for example, aliphatic alcohols and the like are effective. Examples of general aliphatic alcohols include 7-methyl-2-(3-methylbutyl)-1-octanol and 5-methyl-2-(1-methylbutyl)-1-octyl alcohol. Alcohol, 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-undecyl alcohol, 2-heptyl-4 Methyl-1-decanol, 2-(1,5-dimethylhexyl)-(5,9-dimethyl)-1-decanol, etc.

、季戊四醇基肆〔3-(3,5-二-三級丁基-4-羥苯基)丙酸酯〕、十八基-3-(3,5-二-三級丁基-4-羥苯基)丙酸酯、2,2-硫代雙(4-甲基-6-三級丁酚)及1,3,5-三甲基-2,4,6-參(3,5-二-三級丁基-4-羥苯甲基)苯等之酚系抗氧化劑、二-十三基-3,3’-硫代二丙酸酯、二月桂基-3,3’-硫代二丙酸酯、二-十四基-3,3’-硫代二丙酸酯、二硬脂基-3,3’-硫代二丙酸酯、二辛基-3,3’-硫代二丙酸酯等之硫系抗氧化劑、參壬苯基亞磷酸鹽、4,4’-亞丁基-雙(3-甲基-6-三級丁基苯基-二-十三基)亞磷酸鹽、(十三基)季戊四醇二亞磷酸鹽、雙(十八基)季戊四醇二亞磷酸鹽、雙(二-三級丁基苯基)季戊四醇二亞磷酸鹽、雙(二-三級丁基-4-甲基苯基)季戊四醇二亞磷酸鹽、二壬基苯基辛基膦酸鹽、肆(2,4-二-三級丁基笨基)1,4-伸苯基-二-膦酸酯、肆(2,4-二-三級丁基笨基)4,4’-伸聯苯基-二-膦酸酯、10-癸氧基-9,10-二氫-9-氧雜-10-磷雜菲等之磷系抗氧化劑。 As antioxidants, for example, triethylene glycol-bis[3-(3-tributyl-5-methyl-4-hydroxyphenyl)propionate], 2,4-bis(n-octyl Thio)-6-(4-hydroxy-3,5-di-tertiary butylanilino)-1,3,5-tri

, Pentaerythritol base four [3-(3,5-di-tertiary butyl-4-hydroxyphenyl) propionate], octadecyl-3-(3,5-di-tertiary butyl-4- Hydroxyphenyl) propionate, 2,2-thiobis(4-methyl-6-tertiary butyl phenol) and 1,3,5-trimethyl-2,4,6-ginseng (3,5 -Di-tertiary butyl-4-hydroxybenzyl) phenolic antioxidants such as benzene, di-tridecyl-3,3'-thiodipropionate, dilauryl-3,3'- Thiodipropionate, di-tetradecyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, dioctyl-3,3' -Sulfur-based antioxidants such as thiodipropionate, ginsenophenyl phosphite, 4,4'-butylene-bis(3-methyl-6-tertiary butylphenyl-di-tridecan Phosphate, (tridecyl) pentaerythritol diphosphite, bis(octadecyl) pentaerythritol diphosphite, bis(di-tertiary butylphenyl) pentaerythritol diphosphite, bis(di- Tertiary butyl-4-methylphenyl) pentaerythritol diphosphite, dinonylphenyl octyl phosphonate, tetrakis (2,4-di-tertiary butyl phenyl) 1,4-phenylene -Di-phosphonate, Si (2,4-di-tertiary butyl phenyl) 4,4'-biphenyl-di-phosphonate, 10-decyloxy-9,10-di Phosphorus antioxidants such as hydrogen-9-oxa-10-phosphaphenanthrene.

(Biaxially stretched sheet)

The biaxially stretched sheet of the present invention can be manufactured by the following method. First, the aforementioned styrene-based resin composition is melt-kneaded with an extruder, and extruded from a die (especially a T-die). Then, the biaxially stretched sheet is produced by successively or simultaneously extending in the biaxial directions of the longitudinal direction (the sheet moving direction, MD; Machine Direction) and the lateral direction (the direction perpendicular to the sheet moving direction, TD; Transverse Direction).

In order to ensure the strength of the sheet and the container, especially the rigidity, the thickness of the biaxially stretched sheet is preferably 0.1 mm or more, more preferably 0.15 mm or more, and still more preferably 0.2 mm or more. On the other hand, from the viewpoint of shaping properties and economic efficiency, the thickness of the biaxially stretched sheet is preferably 0.7 mm or less, more preferably 0.6 mm or less, and still more preferably 0.5 mm or less.

The stretching magnifications in the longitudinal direction and the lateral direction of the biaxially stretched sheet are preferably in the range of 1.8 to 3.2 times each. When the stretching ratio is less than 1.8 times, the folding resistance of the sheet is likely to decrease. On the other hand, if the stretching ratio is more than 3.2 times, the shrinkage during thermoforming is too large and the shaping properties are impaired.

In addition, the measuring method of the stretching ratio of the present invention is as follows. With respect to the test piece of the biaxially stretched sheet, a straight line Y with a length of 100 mm is drawn in the longitudinal direction (MD) and the transverse direction (TD). The test piece was allowed to stand for 60 minutes in an oven at a temperature 30°C higher than the Ficatin softening temperature of the sheet measured in accordance with JIS K7206, and the length Z [mm] of the straight line was measured after shrinking. The stretching magnification (multiplying) in the vertical direction and the horizontal direction is the value calculated by the following formula.

Stretching ratio (times)=100/Z

The longitudinal and transverse orientation relaxation stresses of the biaxially stretched sheet are preferably in the range of 0.3 to 1.2 MPa, respectively. When the orientation relaxation stress is less than 0.3 MPa, the folding resistance of the sheet may decrease. On the other hand, if the orientation relaxation stress is greater than 1.2 MPa, the shrinkage rate during thermoforming may be too large and the shapeability may be impaired.

Furthermore, the alignment relaxation stress of the biaxially stretched sheet of the present invention is a value measured in accordance with ASTM D1504 as the peak stress value in silicone oil at a temperature 30°C higher than the Ficatin softening temperature of the resin composition constituting the sheet .

From the viewpoint of processability and appearance during secondary molding, the gel content in the biaxially stretched sheet is preferably less. Specifically, it is preferably 1% by mass or less in the biaxially stretched sheet, and more preferably 0.5% by mass or less. In addition, from the viewpoint of processability, appearance, and heat resistance, the total content of monomers and oligomers in the biaxially stretched sheet is preferably 20,000 ppm or less, more preferably 10,000 ppm, and still more preferably 5,000 ppm or less.

(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. Sucrose fatty acid ester (C) is an excellent anti-fogging agent. The biaxially stretched sheet has excellent anti-fogging properties by having the coating layer.

Sucrose fatty acid ester (C) is an ester of sucrose and fatty acid. Examples of fatty acids constituting sucrose fatty acid esters include, for example, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, dioleic acid, montanic acid, and other saturated fatty acids with about 6 to 30 carbon atoms. Linderic acid, palmitoleic acid, oleic acid, elaidic acid, isoleic acid, erucic acid, linoleic acid, hypolinoleic acid and other unsaturated fatty acids with carbon numbers around 10-24. These fatty acids can be It can be used alone or in combination. Among 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 sucrose fatty acid ester is obtained by the Griffin method.

The sucrose fatty acid ester (C) is more preferably a mixture of sucrose laurate (F) and other types of sucrose fatty acid esters. As other types of sucrose fatty acid esters, sucrose fatty acid esters (G) in which the carbon number of the fatty acid portion is 16 or more, the degree of unsaturation of the fatty acid portion is 1 or less, and the HLB value is 12 or more are preferable.

The sucrose fatty acid ester (G) has an excellent storage stability, and the carbon number of the fatty acid part is preferably 16 or more, more preferably 18 or more. In addition, the sucrose fatty acid ester (G) has excellent storage stability (for example, appearance after storage, anti-fogging properties), and the degree of unsaturation of the fatty acid portion is preferably 1 or less, more preferably unsaturated Degree 0. In addition, from the viewpoint of excellent appearance (for example, the appearance when the coating layer is formed by coating), the HLB value of the sucrose fatty acid ester (G) is preferably 12 or more. The HLB value of the sucrose fatty acid ester (G) is preferably 13 or more, more preferably 14 or more, and still more preferably 15 or more. Preferred specific examples of the fatty acid of the aforementioned sucrose fatty acid ester (G) include stearic acid, oleic acid, palmitic acid, and the like.

The mass ratio (F)/(G) of sucrose laurate (F) to sucrose fatty acid ester (G) is preferably 90/10 to 99/1. From the viewpoint of appearance (for example, coating appearance) and storage stability (for example, appearance after storage, anti-fogging properties), the above-mentioned range has a more excellent effect.

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

Examples of water-soluble polymers (D) include polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, carboxymethyl cellulose, methyl cellulose, sodium alginate, carrageenan, corn starch, etc. . From the viewpoint of non-uniformity in performance, among these, synthetic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid are preferred.

The degree of polymerization of the water-soluble polymer (D) is preferably 300 to 2000. When it is in the above-mentioned polymerization degree range, it has an appropriate viscosity when coating, and the handling property and the appearance of the coating film are excellent. 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) and the water-soluble polymer (D) of the coating layer is preferably 80/20-50/50. When it is in the above-mentioned range, coating properties are excellent, and anti-fogging properties can be effectively imparted to the biaxially stretched sheet.

The formation amount per unit area of the coating layer is preferably 10 to 150 mg/m ² . The formation amount per unit area of the coating layer is more preferably 20 to 80 mg/m ² , and still more preferably 30 to 70 mg/m ² . From the viewpoints of anti-fogging properties and appearance (for example, coating appearance, appearance after storage), it is preferable to be in the above-mentioned range.

The coating layer is formed, for example, by applying a coating solution in which sucrose fatty acid ester (C) and water-soluble polymer (D) are dissolved in a solvent on at least one surface of the biaxially stretched sheet. As a solvent, water, alcohol, etc. are used, but it is not specifically limited to these. As the solvent, water is preferred from the viewpoint of handling properties. The method of coating is not particularly limited, and a method of coating using a roll coater, a knife coater, a gravure roll coater, or the like can be mentioned. In addition, the coating layer may be formed by spraying, dipping, or the like.

(Surface layer)

It is also possible to have a surface layer containing silicone on the outermost surface of at least one side of the biaxially extending sheet. The surface layer may be directly provided on the surface of the biaxially stretched sheet, or may be provided on the biaxially stretched sheet via a coating layer or the like. The biaxially stretched sheet has a silicone-containing surface layer on the outermost surface to exhibit excellent slipperiness. Here, silicone is also referred to as silicone resin, and is a general term for a polymer having a siloxane bond (-Si-O-Si-) as a skeleton (main chain). Various functional groups are bonded to the side chain as necessary.

The viscosity of the silicone at 23°C is preferably 1000-30000 mm ² /s, more preferably 5000-25000 mm ² /s. By keeping the viscosity of the silicone within this range, the decrease in anti-fogging properties caused by the transfer of silicone after storage can be suppressed, and at the same time, better slip properties can be obtained.

Forming amount per unit area of the surface layers, preferably 3 ~ 30mg / m ^2, more preferably 4 ~ 25mg / m ^2, further more preferably 5 ~ 20mg / m ^2. From the standpoint of slipperiness and appearance (for example, coating appearance, appearance after storage), the above range is preferable.

The surface layer is formed, for example, by applying a coating solution in which silicone is dissolved in a solvent on at least one surface of the biaxially stretched sheet. As a solvent, water, alcohol, etc. are used, but it is not specifically limited to these. As the solvent, water is preferred from the viewpoint of handling. The method of applying the solution is not particularly limited, and a method of applying the solution using a roll coater, a knife coater, a gravure roll coater, or the like can be mentioned. In addition, the surface layer may be formed by spraying, dipping, or the like.

(Molded product)

The method of obtaining a molded product from the biaxially stretched sheet of the present invention is not particularly limited, and a method commonly used in the secondary molding method of a conventional biaxially stretched sheet can be used. For example, 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, the "Plastic Processing Technology Handbook" compiled by the Society of Polymer Science, Nikkan Kogyo Shimbun (1995).

As the application of the molded product of the biaxially stretched sheet of the present invention, there are various containers, and it can be widely used in packaging containers for various articles. Among the packaging containers, the food packaging container or the lid material of the food packaging container is appropriate, especially when the food is a food containing fats and oils. Furthermore, among the packaging containers, a food packaging container for microwave heating can fully utilize the characteristics of the present invention and is therefore preferable.

Example

The following examples and comparative examples are used to further specifically explain the embodiments of the present invention, but the present invention is not limited to these examples.

(Experimental example 1) [Manufacture of styrene-methacrylic acid copolymer (A-1)]

A 200-liter autoclave with a jacket and a stirrer was charged with 100 kg of pure water and 100 g of polyvinyl alcohol, and stirred at 130 rpm. Next, 72.0 kg of styrene, 4.0 kg of methacrylic acid, and 20 g of tertiary butyl peroxide were added, the autoclave was sealed, the temperature was raised to 110°C, and polymerization was performed for 5 hours (step 1). In addition, it took 2 hours from the point of time when the polymerization temperature reached 110°C, and 4.0 kg of methacrylic acid was added uniformly (step 2). Furthermore, it was kept at 140°C for 3 hours to complete the polymerization (step 3). The obtained beads were washed, dehydrated, and dried, and then extruded to obtain the pelletized styrene-methacrylic acid copolymer (A-1) described in Table 1. As a result of analyzing this by thermal decomposition gas chromatography, the mass composition ratio of styrene monomer unit/methacrylic acid monomer was 90/10. In addition, the number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) determined by GPC measurement were 80,000, 200,000, and 360,000, respectively.

(Experimental examples 2~13) [Manufacture of styrene-methacrylic acid copolymer (A-2~13)]

The amount of various raw materials added and the polymerization time of Experimental Example 1 were adjusted to obtain various styrene-methacrylic acid copolymers (A-2 to 13) described in Table 1.

(Experimental example 14) [Production of acrylic resin (B-1)]

In a separate flask (capacity 5 liters) equipped with a thermometer, nitrogen inlet pipe, cooling pipe and stirring device, 300 parts by mass (3000 g) of ion exchange water as a dispersion medium and dodecylbenzene sulfonic acid as an emulsifier 1.1 parts by mass of sodium, 0.01 parts by mass of n-octyl mercaptan as a chain transfer agent, 75 parts by mass of methyl methacrylate as a monomer, and 25 parts by mass of butyl acrylate. By circulating a nitrogen stream in the separable flask, the atmosphere in the flask is replaced with nitrogen. Next, the internal temperature was increased to 60°C, and 0.15 parts by mass of potassium persulfate and 5 parts by mass of deionized water were added. After that, heating and stirring were continued for 2 hours to terminate the polymerization and obtain an acrylic resin latex.

After cooling the obtained acrylic resin latex to 25°C, it was added dropwise to 500 parts by mass of 70°C warm water containing 5 parts by mass of calcium acetate, and then the temperature was raised to 90°C and coagulated. After the obtained condensate was separated and washed, it was 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) based on JIS K 7121: 2012 plastic transition temperature measurement method. In addition, the weight average molecular weight (Mw) determined by GPC measurement was 3 million.

(Experimental examples 15-22) [Manufacture of acrylic resin (B-2~9)]

The addition amounts of various monomers and chain transfer agents of Experimental Example 14 were adjusted to obtain various acrylic resins (B-2 to 9) described in Table 2.

(Experimental example 23) [Production of impact-resistant styrene resin (E-1)]

Use 3.4% by mass of low-cis polybutadiene rubber (manufactured by Asahi Kasei Corporation, trade name Diene 55AS) as a rubbery polymer, and dissolved in 91.6% by mass of styrene and 5.0% by mass of ethylbenzene as a solvent. As a polymerization raw material. In addition, 0.1 parts by mass of rubber antioxidant (manufactured by Ciba-Geigy, trade name IRGANOX 1076) was added. This polymerization raw material was supplied to a 14-liter jacketed reactor (R-01) equipped with an anchor-type stirring blade with a blade diameter of 0.285 m at 12.5 kg/hr. The reaction was carried out at a reaction temperature of 140°C and a rotation speed of 2.17 sec ^-1 . The resin ratio of the obtained resin liquid was 25%. The obtained resin liquid was introduced into two plug flow reactors arranged in series, each of which contained 21 liters of jackets. In the first plug flow reactor (R-02), the jacket temperature is adjusted so that the reaction temperature has a gradient of 120~140℃ in the flow direction of the resin solution. In the second plug flow reactor ( In R-03), adjust the jacket temperature in such a way that the reaction temperature has a gradient of 130~160℃ in the flow direction of the resin liquid. The resin rate at the outlet of R-02 is 50%, and the resin rate at the outlet of R-03 is 70%. Here, the resin ratio is calculated by the following formula.

Resin rate (%)=100×(the amount of polymer produced)/{(the amount of monomer added)+(the amount of solvent)}

After the obtained resin solution was heated at 230°C, it was sent to a devolatilization tank with a vacuum of 5 torr, and the unreacted monomer and solvent were separated and recovered. After that, it is extracted from the devolatilization tank by a gear pump, and is made into strands through a template, then pelletized by a water tank, and recovered as a product. The rubber component content of the obtained resin (E-1) was 10.0% by mass, and the average rubber particle size was 2.0 μm.

(Experimental examples 24~31) [Production of impact-resistant styrene resin (E-2~9)]

The amount of various raw materials added in Experimental Example 21 was adjusted to obtain various impact-resistant styrene resins (E-2 to 9) described in Table 3.

<Example 1>

95.0% by mass of styrene-methacrylic acid copolymer (A-1) and 5.0% by mass of acrylic resin (B-1) are blended, and impact-resistant styrene is added to the total of 100% by mass System resin (E-1) 1.0% by mass. Use a pellet extruder (biaxial co-direction extruder TEM35B (manufactured by Toshiba Machine Co., Ltd.) with a vacuum exhaust port) at an extrusion temperature of 230°C, a rotation number of 250 rpm, and an exhaust port devolatilization pressure of -760mmHg. After the template is formed into strands, it is cooled in a water tank and then pelletized by a pelletizer to obtain a resin composition. In addition, the exhaust port devolatilization pressure represents the differential pressure value with respect to normal pressure. The content of styrene monomer in the obtained resin composition was 500 ppm, and the content of methacrylic monomer was 50 ppm. In addition, the Fica softening temperature is 116°C, and the melt flow index (MFI) under the H condition (200°C, 5 kg) of JIS K7210 is 1.0 g/10 min. The above resin composition was extruded using a sheet extruder (T-die width 500mm, die lip opening 1.5mm, φ40mm extruder (manufactured by Tanabe Plastic Machinery Co.)) at an extrusion temperature of 230°C and a discharge volume of 20kg/ h An unstretched sheet is obtained. Using a batch-type biaxial stretching machine (manufactured by Toyo Seiki Co., Ltd.), the sheet was preheated to (Ficar softening temperature + 30)°C, and stretched 2.4 times in MD and 2.4 times in TD at a strain rate of 0.1/sec (surface magnification 5.8 times), and the biaxially stretched sheet described in Table 4 was obtained. The thickness of the obtained sheet is 0.3 mm, the extension ratio (MD/TD) is 2.4/2.4 times, and the orientation relaxation stress (MD/TD) is 0.6/0.6 MPa.

As the coating solution for the coating layer, sucrose laurate (L-1570 (manufactured by MITSUBISHI-CHEMICAL FOODS) 0.57% by mass and sucrose stearate (S-1570, manufactured by MITSUBISHI-CHEMICAL FOODS) 0.03% by mass were prepared. , Polyvinyl alcohol (manufactured by Kuraray, Part No. 210, polymerization degree 1000, saponification degree 88 mol%, total residual ratio of methyl acetate and methanol 0.1% or less) 0.40 mass% aqueous solution.

On the surface of the obtained biaxially stretched sheet, using a bar coater, the coating liquid for the coating layer was applied at 5 g/m ² and dried in an oven at 105° C. for 1 minute. The mass per unit area of the obtained coating layer was 50 mg/m ² .

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

<Examples 2 to 84, Comparative Examples 1 to 8>

The type of resin, the amount of blending, the extrusion conditions of the resin composition, the type of coating layer and the surface layer, and the amount of coating in Example 1 were appropriately changed, and the same procedures as in Example 1 were carried out to obtain the results described in Table 6 to Table 13. Biaxially stretched sheet. In addition, for 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. Also, for the water-soluble polymer (D), Table 5 shows samples D-1 to D-9 of each material.

With respect to the obtained biaxially stretched sheet, various properties were measured and evaluated by the methods described below. In the relative evaluation of ○, △, and ×, the case of ○ or △ was judged as pass. The results are shown in Table 6 to Table 13.

(1) Film production

For the 25 points of intersection when the unstretched sheet is drawn in the MD and TD directions with 5 straight lines at 20 mm intervals to form a grid, the thickness is measured with a micro gauge, and the standard deviation σ is measured on the following basis Evaluation.

○: σ is less than 0.03mm

△: σ is above 0.03mm and less than 0.07mm

×: σ is 0.07mm or more

(2) Fluidity (melt flow rate)

Measured in accordance with JIS K7210 H conditions (200°C, 5kg).

○: 1.0g/10 minutes or more and less than 3.0g/10 minutes

△: 0.5g/10 minutes or more and less than 1.0g/10 minutes, or, 3.0g/10 minutes or more and less than 5.0g/10 minutes

×: less than 0.5g/10 minutes or more than 5.0g/10 minutes

(3) Sheet appearance

For a biaxially stretched sheet of 350mm×350mm, 1) roller adhesion marks with an area of 100mm ² or more, 2) bubbles with an area of 10 mm ² or more, 3) transparent and opaque foreign matter, 4) adhesion defects, and 5) with a width of 3mm or more The mold line (defects that occur at the exit of the T-die in the direction of movement of the sheet during film formation) was regarded as a defect, and the number of defects was evaluated based on the following criteria.

○: 0

△: 1~2

×: 3 or more

(4) Extensibility

For the 25 points of intersection when the double-stretched sheet is drawn in the MD and TD directions with 5 straight lines at 50mm intervals to form a grid, the thickness is measured using a micro gauge, and the standard deviation σ is measured on the following basis Evaluation.

○: σ is less than 0.05m

△: σ is above 0.05mm but less than 0.10mm

×: σ is 0.10mm or more

(5) Transparency (haze)

According to JIS K-7361-1, the haze of the biaxially stretched sheet was measured using a haze meter NDH5000 (manufactured by Nippon Denshoku Corporation).

○: less than 1.5% of haze

△: Haze is above 1.5% and less than 3.0%

×: Haze above 3.0%

(6) Rigidity

Put a 500g hammer into the body of the food packaging box described later, stack 5 layers of the bento container with the lid closed, and check the deformed state of the lid material after standing for 24 hours.

○: No shape change.

△: Deformation.

×: Cracked.

(7) Folding resistance

According to ASTM D2176, the folding resistance of the sheet extrusion direction (longitudinal direction) and the direction perpendicular to it (lateral direction) was measured, the minimum value was found, and the evaluation was performed as follows.

○: 5 times or more

△: 2 times or more, less than 5 times

×: less than 2 times

(8) Formation

A hot plate forming machine HPT-400A (manufactured by WAKISAKA ENGINEERING) was used to form a food packaging box under the conditions of a hot plate temperature of 150°C and a heating time of 2.0 seconds (size lid: vertical 150 × horizontal 130 × height 30 mm, body: vertical 150×130×20 mm in height), and the shaping properties were evaluated based on the following criteria.

○: Good

△: The corners are slightly poorly shaped

×: The shape is different from the size or the corner is obviously bad

(9) Mold fouling

The transfer of stains such as molds when forming the food packaging box was evaluated based on the following criteria.

○: No transfer (transparent, no turbidity)

△: Transferred partly (opaque, turbid surface)

×: The whole has transfer (opaque, turbid surface)

(10) Heat resistance

The food packaging box obtained under the above-mentioned forming conditions was placed in a hot air dryer set at 110°C for 60 minutes, and the deformation of the container was visually observed.

○: No deformation

△: Slight deformation, less than 5% change in external dimensions

×: large deformation, 5% change in external dimensions

(11) Oil resistance

On the hinges of the above food packaging boxes are attached gauze filled with test solution of salad oil (manufactured by Nissin Oil Co., Ltd.), Mayonnaise (manufactured by Ajinomoto Co., Ltd.), and COCONAD ML (registered trademark, manufactured by Kao Corporation) 10× 10mm, stand for 24 hours in an oven at 60°C, observe the surface of the attached part.

○: No change

△: Slightly whitened

×: Significantly whitened and cracked

(12) Microwave heating resistance

9 points of mayonnaise are attached to the center of the food packaging box cover in a range of 5mm×5mm, 300g of water is added to the container body, cover the lid of the container, heated in a 1500W microwave oven for 90 seconds, visually evaluate the attachment of the mayonnaise part .

○: No change

△: There is whitening, and the container is slightly deformed

×: Perforated, the container is significantly deformed

(13) Appearance after storage

The biaxially stretched sheet was taken up and left standing at 23°C for 6 months in the state of a roll, and then measured with a haze meter NDH5000 (Nippon Denshoku Corporation) in accordance with JIS K-7361-1.

○: Haze is less than 1.5%

△: Haze is above 1.5% and less than 3.0%

×: Haze above 3.0%

(14) Appearance during forming

The biaxially stretched sheet was formed with a hot plate forming machine HPT-400A (manufactured by WAKISAKA ENGINEERING) under the conditions of a hot plate temperature of 135°C and a heating time of 2.0 seconds to form a bento cover (dimensions 241 x 193 x 28 mm in height). The molded product was measured with a haze meter NDH5000 (Nippon Denshoku Corporation) in accordance with JIS K-7361-1.

○: Haze is less than 1.5%

△: Haze is above 1.5% and less than 3.0%

×: Haze above 3.0%

(15) Anti-fog (initial)

The biaxially stretched sheet was formed with a hot plate forming machine HPT-400A (manufactured by WAKISAKA ENGINEERING) under the conditions of a hot plate temperature of 135°C and a heating time of 2.0 seconds to form a bento cover (dimensions 241 x 193 x 28 mm in height). Add 50 g of 95°C water to the body of the obtained container, cover it, and let it stand at 23°C. Confirm the content identification after 10 points.

○: The contents can be clearly confirmed.

△: It is difficult to see the contents due to condensation on the lid.

×: There is a lot of condensation on the lid, and the contents cannot be distinguished.

(16) Anti-fogging after storage

Take up the biaxially stretched sheet and leave it to stand at 23°C for 6 months in the form of a roll, then use a hot plate forming machine HPT-400A (manufactured by WAKISAKA ENGINEERING) to set a hot plate temperature of 135°C and a heating time of 2.0 seconds. Conditions, forming a lunch cover (size 241 x 193 x 28 mm in height). Add 50 g of 95°C water to the body of the obtained container, cover it, and let it stand at 23°C. Confirm the content identification after 10 points.

○: The contents can be clearly confirmed.

△: It is difficult to see the contents due to condensation on the lid.

×: There is a lot of condensation on the lid, and the contents cannot be distinguished.

(17) Slippery

In a state where the food contact surface and the food non-contact surface of the thin slices cut from the upper surface of the container are overlapped, the friction angle (the angle at which sliding starts) is measured by using the method of measuring the static and dynamic coefficient of friction of paper and cardboard according to JIS P8147 ).

○: less than 15°

△: more than 15°, less than 30°

×: more than 30°

According to the results of Table 6 to Table 13, Examples 1 to 84 all meet the requirements of the present invention, and are in terms of film-forming properties (film-forming properties, fluidity, sheet appearance, extensibility), transparency, and sheet strength (rigidity, folding resistance). Performance), formability (formability, mold fouling), heat resistance, oil resistance, microwave heating resistance, appearance after storage, appearance during molding, anti-fogging (initial), anti-fogging (after storage), slippery In any of the properties, it has excellent performance.

On the other hand, in Comparative Examples 1 to 8, in any one of the styrene-methacrylic acid copolymer (A), acrylic resin (B), and Ficatin softening temperature, the requirements of the present invention were not met, and they were being manufactured Film properties, fluidity, sheet appearance, shaping properties, heat resistance, oil resistance, and microwave heating resistance are all poor.

Claims (16)

A biaxially stretched sheet, which is a biaxially stretched sheet composed of a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), characterized in that: the styrene-methyl The mass ratio (A)/(B) of the base acrylic copolymer (A) to the acrylic resin (B) is 90/10~97/3, and the styrene-methacrylic acid copolymer (A) is 84/16 The mass ratio of ~94/6 contains styrene monomer units and methacrylic acid monomer units. The weight average molecular weight of the styrene-methacrylic acid copolymer (A) is 120,000-250,000. The acrylic resin (B ) Has a weight average molecular weight of 1 million to 7 million, the Ficatin softening temperature of the styrene resin composition is 106 to 132°C, and at least one surface of the biaxially stretched sheet has a fatty acid ester containing sucrose (C) Coating layer with water-soluble polymer (D). The biaxially stretched sheet of claim 1, wherein the acrylic resin (B) contains methyl methacrylate monomer units and butyl acrylate monomer units. Such as the biaxially stretched sheet of claim 2, wherein the acrylic resin (B) contains methyl methacrylate monomer units and butyl acrylate monomer units in a mass ratio of 65/35 to 85/15. The biaxially stretched sheet according to any one of claims 1 to 3, which is further in a ratio of 3% by mass or less with respect to the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) Contains impact-resistant styrene resin (E) containing a rubber component. Such as the biaxially stretched sheet of claim 4, wherein the content of the rubber component in the biaxially stretched sheet is 0.05 to 0.3% by mass, and the average rubber particle size is 1.2 to 12.0 μm. The biaxially stretched sheet according to any one of claims 1 to 3, wherein the styrene monomer content in the styrene resin composition is 1000 ppm or less, and the methacrylic monomer content is 150 ppm or less. For example, the biaxially stretched sheet of any one of Claims 1 to 3 has a thickness of 0.1~0.7mm, the stretching magnification in the longitudinal direction and the transverse direction is 1.8 to 3.2 times, respectively, and the orientation of the longitudinal and transverse directions is relaxed (orientation) The relaxation) stress is 0.3 to 1.2 MPa, respectively. The biaxially stretched sheet according to any one of claims 1 to 3, wherein the mass ratio (C)/(D) of the sucrose fatty acid ester (C) and the water-soluble polymer (D) of the coating layer is 80/20 ~50/50. The biaxially stretched sheet according to any one of claims 1 to 3, wherein the sucrose fatty acid ester (C) contains sucrose laurate (F), and the carbon number of the fatty acid part is 16 or more, and the fatty acid part is unsaturated A mixture of sucrose fatty acid esters (G) with a degree of 1 or less and an HLB value of 12 or more. Such as the biaxially stretched sheet of claim 9, wherein the mass ratio (F)/(G) of the sucrose laurate (F) to the sucrose fatty acid ester (G) is 90/10 to 99/1. The biaxially stretched sheet according to any one of claims 1 to 3, wherein the polymerization degree of the water-soluble polymer (D) is 300-2000. Such as the biaxially stretched sheet of any one of claims 1 to 3, wherein the formation amount per unit area of the coating layer is 10 to 150 mg/m ² . For the biaxially stretched sheet of any one of claims 1 to 3, the outermost surface of at least one side of the biaxially stretched sheet further has a surface layer containing silicone, and each unit area of the surface layer The formation amount of 3~30mg/m ² . A molded product composed of a biaxially stretched sheet as in any one of claims 1 to 3. Such as the molded product of claim 14, which is a food packaging container. For example, the molded product of claim 15, which is a food packaging container for microwave heating.