TW201736414A - Biaxially-oriented sheet and molded article thereof - Google Patents

Abstract

Provided are: a biaxially-oriented sheet that comprises a styrene resin composition and has excellent transparency, strength, film forming properties, and moldability, as well as superior yield, heat resistance, and oil resistance; and a molded article of the biaxially-oriented sheet. The biaxially-oriented sheet comprises a styrene resin composition that includes a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), wherein 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) includes a styrene monomer unit and a methacrylic acid monomer unit in a mass ratio of 87/13 to 94/6, the weight average molecular weight of the acrylic resin (B) is 1,000,000 to 7,000,000, and the Vicat softening temperature of the styrene resin composition is in the range of 106-132 DEG C. The molded article is a molded article of said biaxially-oriented sheet.

Description

Biaxially stretched sheet and molded article thereof

The present invention relates to a biaxially stretched sheet comprising a styrene resin composition which can be suitably used for a packaging container for foods heated in a microwave oven, and a molded article thereof.

Since the biaxially stretched sheet of polystyrene is excellent in transparency and rigidity, it is molded, and it is mainly used in a molded article such as a lightweight container. However, these containers are not used for applications in direct contact with boiling water or for heating in a microwave oven because of poor heat resistance. Therefore, an attempt to impart heat resistance to polystyrene as a raw material can be performed. Examples of the polystyrene which improves the heat resistance include a styrene-acrylic acid copolymer or a styrene-methacrylic acid copolymer (Patent Document 1, Patent Document 2), and a styrene-maleic anhydride copolymer (patent) Document 3, Patent Document 4). These are generally known as styrene-based heat-resistant resins, and the heat resistance is improved without impairing transparency and rigidity.

However, the above styrene-based heat-resistant resin has lower fluidity at the time of melt extrusion than ordinary polystyrene, and it is difficult to increase the productivity of the resin or the productivity of the sheet. In order to improve the fluidity of the styrene-based heat-resistant resin, there are a method of (i) a method of increasing the extrusion temperature and (ii) a method of lowering the molecular weight of the resin. If the extrusion temperature is increased, then The carboxylic acid group in the styrene-based heat-resistant resin reacts to form a gel-like foreign matter, resulting in deterioration of the quality of the sheet. Further, when the molecular weight of the resin is lowered, the drawdown at the time of sheet extrusion tends to occur, and film formation becomes difficult.

As a method of increasing the extrusion temperature while suppressing the generation of the gel, for example, a method of adding an anti-gelling agent at the time of extrusion can be proposed (Patent Document 5). However, since the anti-gelling agent described in Patent Document 5 also functions as a plasticizer, the heat resistance and oil resistance of the obtained styrene resin sheet are lowered. Therefore, it is necessary to select an additive which is not easy to deteriorate the performance.

In addition, as a method of reducing the molecular weight of the styrene resin and maintaining the film formability, a method of imparting strain hardenability 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 a low compatibility with the styrene-based heat-resistant resin, and is less likely to exhibit expected strain hardening properties, and has a disadvantage that the transparency of the obtained sheet is lowered. . Therefore, it is necessary to select a combination of a styrene-based heat resistant resin and a high molecular weight polymer which are compatible with each other.

Further, the styrene-based heat-resistant resin has low sheet strength, particularly low folding endurance and impact resistance, and is further reduced by lowering the molecular weight of the resin. Since the styrene-based heat-resistant resin has low folding endurance and impact resistance, it is difficult to transport through a device in a molding step, and it is easy to cause die-cutting, and it is easy to cause defects such as cutting powder, and productivity of a molded container. decline.

For these reasons, there is a need for a transparency and strength An extended sheet of a styrene-based resin which is excellent in film formability and moldability, and which is excellent in productivity and excellent in heat resistance and oil resistance.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] US Patent No. 3035033

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2003-12734

[Patent Document 3] Japanese Patent Publication No. 59-15133

[Patent Document 4] Japanese Laid-Open Patent Publication No. 55-71530

[Patent Document 5] Japanese Patent Laid-Open No. 56-161409

[Patent Document 6] Japanese Laid-Open Patent Publication No. 2011-225866

An object of the present invention is to provide a biaxially stretched sheet comprising a styrene resin composition which is excellent in transparency, strength, film formability, and moldability, and which is excellent in productivity, heat resistance, and oil resistance, and a molded article thereof.

In order to solve the above problems, the inventors of the present invention have repeatedly examined the composition or composition of the styrene resin sheet, and found that by adding a predetermined amount of high molecular weight acrylic acid by using a styrene-methacrylic acid copolymer as a basis. The resin of the resin can achieve the object and further complete the present invention.

That is, the present invention is as follows.

(1) A biaxially stretched sheet comprising a styrene resin composition a biaxially stretched sheet comprising a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), the styrene-methacrylic acid copolymer (A) and the acrylic acid The mass ratio (A)/(B) of the resin (B) is 90/10 to 97/3, and the styrene-methacrylic acid copolymer (A) contains styrene alone in a mass ratio of 84/16 to 94/6. The bulk unit and the methacrylic monomer unit, the acrylic resin (B) has a weight average molecular weight of 1,000,000 to 7,000,000, and the styrene resin composition has a Penka softening temperature of 106 to 132 °C.

(2) The biaxially stretched sheet according to the above (1), wherein the styrene-methacrylic acid copolymer (A) has a weight average molecular weight of from 120,000 to 250,000.

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

(4) The biaxially stretched sheet according to the above (3), 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. .

(5) The biaxially stretched sheet according to the above (1) or (2), which is 3% by mass based on the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) The following ratio further includes an impact-resistant styrene-based resin (C) containing a rubber component.

(6) The biaxially stretched sheet according to the above (5), 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 diameter is 1.2 to 12 μm.

(7) A biaxially stretched sheet as described in the above (1) or (2) above The content of the unreacted styrene monomer in the styrene resin composition is 1000 ppm or less, and the content of the unreacted methacrylic monomer is 150 ppm or less.

(8) The biaxially stretched sheet according to the above (1) or (2), wherein the thickness is 0.1 to 0.7 mm, and the stretching ratio in the longitudinal direction and the transverse direction are both 1.8 to 3.2 times, and the longitudinal direction and the transverse direction are aligned. The relaxation relaxation stress is 0.3~1.2MPa.

(9) A molded article comprising the biaxially stretched sheet according to (1) or (2) above.

(10) The molded article according to the above (9), which is a food packaging container for microwave oven heating.

The biaxially stretched sheet of the present invention and the molded article thereof are excellent in transparency, strength, film formability, and moldability, and are excellent in heat resistance and oil resistance. Since the biaxially stretched sheet of the present invention and the molded article thereof are excellent in film formability and moldability, productivity is also excellent. The biaxially stretched sheet of the present invention and a molded article thereof can be suitably used for a packaging container of a food heated in a microwave oven.

[Formation of the Invention]

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

The biaxially stretched sheet of the present invention comprises a mixture of specified mass ratios A styrene resin composition of a styrene-methacrylic acid copolymer (A) and an acrylic resin (B). The biaxially stretched sheet of the present invention can be obtained by extrusion molding 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 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 to methacrylic acid can be variously set depending on the desired heat resistance, mechanical strength, and the like. When the total amount of the styrene monomer unit and the methacrylic acid monomer unit is 100% by mass, it is necessary to obtain a resin having excellent heat resistance, mechanical strength, and transparency in the form of a sheet. The styrene monomer unit and the methacrylic monomer unit are contained in a mass ratio of 84/16 to 94/6. When the content of the methacrylic monomer unit is less than 6% by mass, heat resistance is insufficient, and perforation and deformation are likely to occur when the microwave oven is heated. 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, when the content of the methacrylic acid monomer unit is more than 16% by mass, it is easy to be deteriorated in workability such as a decrease in fluidity at the time of film formation or a decrease in formability at the time of secondary molding. A decrease in appearance caused by the generation of glue. The content of the methacrylic monomer unit is preferably 14% by mass or less, and particularly preferably 13% by mass or less. Further, the styrene-methacrylic acid copolymer (A) may be appropriately mixed with other monomers other than methacrylic acid as long as the effects of the invention are not impaired, if necessary. polymerization. The content of the other monomer is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less. When the content of the other monomer is more than 10% by mass, the ratio of styrene or methacrylic acid is lowered, and sufficient transparency, mechanical strength, and heat resistance are not obtained.

The weight average molecular weight (Mw) of the styrene-methacrylic acid copolymer (A) is preferably from 120,000 to 250,000, more preferably from 140,000 to 220,000, and still more preferably from 150,000 to 200,000. When the weight average molecular weight is less than 120,000, in addition to excessive fluidity, it is easy to cause a decrease in film formability such as the occurrence of the sheet being stretched and the edge being bent inward. In addition, when the weight average molecular weight is more than 250,000, the thickness is not uniform even when the film is formed, and the appearance of the sheet such as a mold line is likely to be lowered.

Further, 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 from 2.0 to 3.0, more preferably from 2.2 to 2.8. If Mw/Mn is more than 3.0, it becomes easy to cause surface roughness caused by contact of the hot plate at the time of container formation. On the other hand, when Mw/Mn is less than 2.0, thickness unevenness at the time of film formation, and formation failure at the time of container formation are easy to fall. Further, the ratio Mz/Mw of the Z average molecular weight (Mz) to Mw is preferably from 1.5 to 2.0, more preferably from 1.6 to 1.9. When Mz/Mw is less than 1.5, it is easy to cause a decrease in the film forming property such as the occurrence of the sag of the sheet and the inward bending of the edge, and the shortage of the extension alignment. On the other hand, when Mz/Mw is more than 2.0, thickness unevenness at the time of film formation due to a decrease in fluidity or a decrease in the appearance of a sheet such as a mold line is likely to occur.

Furthermore, the above number average molecular weight (Mn), weight flat The average molecular weight (Mw) and the Z average molecular weight (Mz) were measured by GPC, and the molecular weight of each elution time was calculated from the dissolution profile of monodisperse polystyrene by the following method, and was calculated as a molecular weight in terms of polystyrene.

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

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

Mobile phase: tetrahydrofuran

Sample concentration: 0.2% by mass

Temperature: oven 40 ° C, injection port 35 ° C, detector 35 ° C

Detector: differential refractometer

The polymerization method of the styrene-methacrylic acid copolymer (A) is a known polymerization method such as a bulk polymerization method such as polystyrene, a solution polymerization method, or a suspension polymerization method. In terms of quality or productivity, a bulk polymerization method, a solution polymerization method, and preferably a continuous polymerization is preferred. As the solvent, for example, an alkanebenzene such as benzene, toluene, ethylbenzene or xylene, a ketone such as acetone or methyl ethyl ketone, or an aliphatic hydrocarbon such as hexane or cyclohexane can be used.

In the polymerization of the styrene-methacrylic acid copolymer (A), a polymerization initiator or a chain transfer agent may be used as needed. As the polymerization initiator, an organic peroxide can be used. Specific examples of the organic peroxide include benzamidine peroxide, tertiary butyl peroxybenzoate, 1,1-di(tri-butylperoxy)cyclohexane, and 1,1- Bis(tertiary butyl peroxy)-3,3,5-trimethylcyclohexane, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, tert-butyl Isopropyl carbonate, dicumyl peroxide Dicumyl peroxide, tertiary butyl cumyl peroxide, tertiary butyl peroxyacetate, tertiary butyl peroxy-2-ethylhexanoate, polyether oxime (three Butylated butyl peroxycarbonate), ethyl-3,3-di(tertiary butyl peroxy) butyrate, tertiary butyl peroxy isobutyrate, and the like. Specific examples of the chain transfer agent include aliphatic thiols, aromatic thiols, pentaphenylethane, α-methylstyrene dimers, and terpinolene.

(acrylic resin (B))

The acrylic resin (B) of the present invention is an ultrahigh molecular weight homopolymer or copolymer comprising acrylic acid and its ester, or methacrylic acid and an ester thereof.

Examples of the acrylate include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. Examples of the methacrylate include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate, and a methacrylic acid ring. Hexyl ester and the like. Among these, butyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate are preferable, and butyl acrylate and methyl methacrylate are especially preferable. The acrylic resin (B) may be a homopolymer of any of the above acrylic acid and its ester, or methacrylic acid and an ester thereof, or may be a copolymer of two or more kinds.

When methyl methacrylate is used as the methacrylic acid-based acrylic resin (B), the content of methyl methacrylate is preferably 65 to 85% by mass, more preferably 70 to 80% by mass, particularly preferably 72~78% by mass. When the content of methyl methacrylate is less than 65% by mass, the transparency of the sheet is lowered when mixed with the styrene-methacrylic acid copolymer (A). On the other hand, if the content of methyl methacrylate is greater than 85 When the amount is 5%, the content of butyl acrylate described later is lowered, and the insoluble matter of the acrylic resin is likely to be generated.

Further, in the case of using butyl acrylate as the acrylic resin (B) of acrylate, the content of butyl acrylate is preferably 15 to 35% by mass, more preferably 20 to 30% by mass, particularly preferably 22 to 28% by mass. %. When the content of the 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 likely to be generated. On the other hand, when the content of butyl acrylate is more than 35% by mass, the content of the above methyl methacrylate is lowered, and the transparency of the sheet is lowered.

Therefore, in the case of using the acrylic resin (B) of methyl methacrylate and butyl acrylate, it is preferred to contain a methyl methacrylate monomer unit and a butyl acrylate monomer in a mass ratio of 65/35 to 85/15. The acrylic resin (B) of the bulk unit.

Further, the glass transition point of the acrylic resin (B) is preferably 40 to 100 ° C, more preferably 50 to 90 ° C, and particularly preferably 60 to 80 ° C. When the glass transition point is too low, there is a possibility that the heat resistance is lowered when it is mixed with the styrene-methacrylic acid copolymer (A). In addition, when it is too high, when it mixes with the said styrene-methacrylic acid copolymer (A), it is difficult to melt|dissolve an acrylic resin, and it becomes difficult to mix uniformly.

The weight average molecular weight (Mw) of the acrylic resin (B) is from 1,000,000 to 7,000,000, preferably from 1.2 million to 6,000,000, more preferably from 1.5 million to 5,000,000. When the weight average molecular weight of the acrylic resin (B) is less than 1,000,000, the microwave oven heat resistance cannot be sufficiently exhibited. On the other hand, when the weight average molecular weight of the acrylic resin (B) is more than 7,000,000, the insoluble matter of the acrylic resin (B) is generated as a gel and is damaged by the biaxially stretched sheet. View. The measurement of the weight average molecular weight of the acrylic resin (B) can be carried out according to the method for measuring the weight average molecular weight of the styrene-methacrylic acid copolymer (A).

The polymerization method of the acrylic resin (B) may, for example, be a known polymerization method such as emulsion polymerization, soap-free emulsion polymerization, fine suspension polymerization, suspension polymerization, bulk polymerization, or solution polymerization. Among these superposition methods, emulsion polymerization is preferred from the viewpoint that the formation of a high polymer is easy.

A known emulsifier can be used as the emulsifier when the acrylic resin (B) is produced by emulsion polymerization. For example, an anionic emulsifier, a nonionic emulsifier, a polymer emulsifier, and a reactive emulsifier having a radically polymerizable unsaturated double bond in the molecule can be mentioned.

(styrene 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 acid copolymer (A) to the acrylic resin (B) of the styrene 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 against heating in a microwave oven cannot be sufficiently exhibited. On the other hand, when the content of the acrylic resin (B) is more than 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 (C) containing a rubber component in an amount that does not impair the appearance and transparency may be added. By adding an impact resistant styrene resin (C), It can improve the brittleness of the sheet and the adhesion of the container.

The impact-resistant styrene-based resin (C) may be a styrene-based resin containing a rubber component, and may include a rubber component in a homopolymer of styrene and a rubber in a styrene-methacrylic acid copolymer. Any component or the like can be suitably used. The rubber component may be dispersed in a particulate form in a polystyrene or styrene-methacrylic acid copolymer which is a matrix resin, or may be a copolymer of polystyrene or styrene-methacrylic acid in a rubber component. The material is graft-polymerized and dispersed into particles.

The rubber component may, for example, be a polybutadiene, a styrene-butadiene copolymer, a polyisoprene or a butadiene-isoprene copolymer. Particularly preferred is a polybutadiene, styrene-butadiene copolymer.

In order to maintain the appearance and transparency of the sheet, the content of the impact-resistant styrene-based resin (C) is preferably 3% by mass based on the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B). the following. In addition, it is preferable that the total amount of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) is 0.5% by mass or more in order to sufficiently improve the brittleness of the sheet and the adhesiveness of the container.

The content of the rubber component derived from the impact-resistant styrene resin (C) is preferably 0.05 to 0.3% by mass based on the rubber component in the biaxially stretched sheet. When the content of the rubber component is less than 0.05% by mass, the effect of improving the sheet brittleness cannot be sufficiently exhibited. On the other hand, when the content of the rubber component is more than 0.3% by mass, the transparency of the sheet is lowered. Further, the average rubber particle diameter of the rubber component in the biaxially stretched sheet is preferably 1.2 to 12 μm. When the average rubber particle diameter is less than 1.2 μm, the effect of improving the brittleness of the sheet cannot be sufficiently exhibited. On the other hand, if Ping When the average rubber particle diameter is more than 12 μm, the transparency of the sheet is lowered.

The content of the rubber component in the biaxially stretched sheet is obtained by dissolving the biaxially stretched sheet in chloroform and adding iodine monochloride to react the double bond in the rubber component, and then adding potassium iodide to leave residual iodine monochloride. The measurement was carried out by changing to iodine and counter-titrating the iodine monochloride method with sodium thiosulfate.

The average rubber particle size of the rubber component in the biaxially stretched sheet is cut by the ultrathin sectioning method so that the observation surface is parallel to the plane of the sheet, and the rubber component is dyed with osmium tetroxide (OsO ₄ ). The particle diameter of 100 particles was measured by a microscope, and the numerical value calculated by the following formula was used.

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

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

The content of the unreacted styrene monomer in the styrene resin composition is preferably 1000 ppm or less, and the content of the unreacted methacrylic monomer is 150 ppm or less. When the content of the unreacted monomer is more than a predetermined amount, the mold is attached to a mold of a molding machine at the time of forming the sheet, and the appearance of the molded article is impaired, and the mold is contaminated and damaged. Concerns about the appearance of the shaped container.

Further, the amount of the unreacted styrene monomer and the unreacted methacrylic monomer was measured by an internal standard method using gas chromatography as described below.

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

Column: glass column 3[mm]×3[m]

Quantitative method: internal standard method (cyclopentanol)

The styrene resin composition must have a thicar softening temperature in the range of 106 to 132 °C. If the Fenaka softening temperature is less than 106 ° C, the heat resistance of the sheet is insufficient, and it becomes easy to cause deformation when heated in a microwave oven. The Fica softening temperature is preferably 108 ° C or higher, more preferably 110 ° C or higher. On the other hand, if the Fenaka softening temperature exceeds 132 ° C, the workability at the time of film formation and container molding may be lowered. The thicarb softening temperature is preferably 128 ° C or less, more preferably 126 ° C or less. Further, the Fika softening temperature was measured in accordance with JIS K7206 at a temperature increase rate of 50 ° C / hr and a test load of 50 N.

Further, in the styrene resin composition of the present invention, various additives may be blended in accordance with the use. Examples of the additive include an antioxidant, an anti-gelling agent, an ultraviolet absorber, a light stabilizer, a slip agent, a plasticizer, a colorant, an antistatic agent, a flame retardant, an additive such as mineral oil, and a glass fiber. Fillers such as reinforcing fibers such as carbon fibers and aromatic polyamide fibers, talc, ceria, mica, and calcium carbonate. Moreover, from the viewpoint of the appearance when the styrene resin composition is flaky, it is preferred to blend two or more types of antioxidants and antigelling agents, either singly or in combination. These additives may be added in the polymerization step, the devolatilization step, the granulation step of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B), or may be added in the production of the styrene resin composition. .

The amount of the above-mentioned additive to be added is not limited, but it is preferably added so as not to exceed the range of the thixo softening temperature and transparency of the styrene resin composition.

The anti-gelling agent has an effect of suppressing the gelation reaction caused by the dehydration reaction of methacrylic acid. As an anti-gelling agent, for example, an aliphatic alcohol Wait for it to be effective. As a general aliphatic alcohol, 7-methyl-2-(3-methylbutyl)-1-octanol and 5-methyl-2-(1-methylbutyl)-1-octyl are mentioned. Alcohol, 5-methyl-2-(3-methylbutyl)-1-octanol, 2-hexyl-1-nonanol, 5,7,7-trimethyl-2-(1,3,3 -trimethylbutyl)-1-octanol, 8-methyl-2-(4-methylhexyl)-1-nonanol, 2-heptyl-1-undecyl alcohol, 2-heptyl-4 Methyl-1-nonanol, 2-(1,5-dimethylhexyl)-(5,9-dimethyl)-1-nonanol, and the like.

The antioxidant may, for example, be triethylene glycol-bis[3-(3-tris-butyl-5-methyl-4-hydroxyphenyl)propionate] or 2,4-bis(n-octane). Thio)-6-(4-hydroxy-3,5-di-tertiary butylanilino)-1,3,5-three , pentaerythritol ruthenium [3-(3,5-di-tri-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tertiary butyl-4- Hydroxyphenyl) propionate, 2,2-thiobis(4-methyl-6-tertiary butylphenol) and 1,3,5-trimethyl-2,4,6-para (3,5 a phenolic antioxidant such as di-tris-butyl-4-hydroxybenzyl)benzene, di-trisyl-3,3'-thiodipropionate, dilauryl-3,3'- Thiodipropionate, di-tetradecyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, dioctyl-3,3' - a sulfur-based antioxidant such as thiodipropionate, ginseng phenyl phosphite, 4,4'-butylene-bis(3-methyl-6-tributylphenyl-di-tride Phosphite, (tridecyl) pentaerythritol diphosphite, bis(octadecyl)pentaerythritol diphosphite, bis(di-tertiary butylphenyl) pentaerythritol diphosphite, bis(di- Tert-butyl-4-methylphenyl)pentaerythritol diphosphite, dinonylphenyloctylphosphonate, bismuth (2,4-di-tri-butylphenyl) 1,4-benzene -di-phosphonate, bismuth (2,4-di-tert-butylphenyl) 4,4'-extended biphenyl-di-phosphonate, 10-decyloxy-9,10-di Hydrogen-9-oxa-10-phosphaphenanthrene The phosphorus-based antioxidant.

(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 mold (particularly a T-die). Next, a biaxially stretched sheet is produced by sequentially or simultaneously extending in the biaxial direction of the longitudinal direction (MD: Machine direction) and the lateral direction (TD: Transverse Direction).

In order to secure the strength of the sheet and the container, particularly to ensure rigidity, the thickness of the biaxially stretched sheet is preferably 0.1 mm or more, more preferably 0.15 mm or more, and particularly preferably 0.2 mm or more. On the other hand, the thickness of the biaxially stretched sheet is preferably 0.7 mm or less, more preferably 0.6 mm or less, and particularly preferably 0.5 mm or less from the viewpoint of moldability and economy.

The stretching ratio in the longitudinal direction and the transverse direction of the biaxially stretched sheet is preferably in the range of 1.8 to 3.2 times. When the stretching ratio is less than 1.8 times, the folding endurance of the sheet is liable to lower. On the other hand, when the stretching ratio is more than 3.2 times, the shrinkage ratio at the time of thermoforming is excessively large to impair the formability.

Further, the method for measuring the stretching ratio of the present invention is as follows. A straight line Y of 100 mm length was drawn in the longitudinal direction (MD) and the lateral direction (TD) with respect to the test piece of the biaxially stretched sheet. The test piece was allowed to stand in an oven at a temperature higher than the Fica softening temperature of the sheet measured in accordance with JIS K7206 by 30 ° C for 60 minutes, and the length Z [mm] of the straight line after shrinking. The stretching ratio (times) in the longitudinal direction and the lateral direction are numerical values each calculated by the following formula.

Extension ratio (times) = 100/Z

The directional relaxation stress in the longitudinal direction and the transverse direction of the biaxially stretched sheet is preferably in the range of 0.3 to 1.2 MPa. Small relaxation stress At 0.3 MPa, there is a flaw in the folding endurance of the sheet. On the other hand, when the orientation relaxation stress is more than 1.2 MPa, the shrinkage ratio at the time of thermoforming is excessively large and the formability is impaired.

Further, the orientation relaxation stress of the biaxially stretched sheet of the present invention is determined according to ASTM D1504 as a peak stress value in a polyfluorinated oxygen oil having a temperature higher than a Fica softening temperature of a resin composition constituting the sheet by 30 ° C. Value.

In the biaxially stretched sheet of the present invention, a well-known release agent, a release agent (for example, a polyoxygenated oil), an antifogging agent (for example, a nonionic such as a sucrose fatty acid ester or a polyglycerol fatty acid ester) may be mixed. One of an antistatic agent (for example, various nonionic surfactants, a cationic surfactant, an anionic surfactant, etc.), such as a surfactant, a polyether modified polyoxygenated oil, or a cerium oxide. One or two or more types are applied to one side or both sides of the sheet.

The method of applying the coating agent to the biaxially stretched sheet 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 exemplified. Further, spraying, dipping, or the like can also be employed.

The method for obtaining a molded article from the biaxially stretched sheet of the present invention is not particularly limited, and a method conventionally used in a secondary molding method of a conventional biaxially stretched sheet can be used. For example, secondary molding can be carried out by a hot forming method such as a vacuum forming method or a pressure forming method. These methods are described, for example, in the "Plastic Processing Technical Manual", Journal of the Polymer Society, Nikkan Kogyo Shimbun (1995). As a molded article of the biaxially stretched sheet of the present invention, there are various containers and can be widely used in various materials. Packaging containers, etc. Among them, the food packaging container for microwave oven heating and the like can sufficiently exhibit the features of the present invention, and thus is particularly preferable.

[Examples]

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

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

100 kg of pure water and 100 g of polyvinyl alcohol were placed in an autoclave with a sheath and a stirrer having a content of 200 L, 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, and the autoclave was sealed, and the temperature was raised to 110 ° C, and polymerization was carried out for 5 hours (step 1). Further, it took 2 hours from the time when the polymerization temperature reached 110 ° C, and 4.0 kg of methacrylic acid was additionally added thereto (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 a pellet-shaped styrene-methacrylic acid copolymer (A-1) shown in Table 1. As a result of analysis by thermal decomposition gas chromatography, the mass ratio of the styrene monomer unit/methacrylic acid monomer unit was 90/10. Further, the number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z average molecular weight (Mz) determined by GPC measurement were respectively 80,000, 200,000, and 360,000.

(Experimental Examples 2 to 11) [Manufacture of styrene-methacrylic acid copolymer (A-2 to 11)]

The amount of each raw material added in Experimental Example 1 was adjusted to obtain various styrene-methacrylic acid copolymers (A-2 to 11) described in Table 1.

(Experimental Example 12) [Manufacture of Acrylic Resin (B-1)]

In a separate flask (capacity: 5 liters) equipped with a thermometer, a nitrogen introduction tube, a cooling tube, and a stirring device, 300 parts by mass (3000 g) of ion-exchanged water as a dispersion medium, and dodecylbenzenesulfonic acid as an emulsifier were charged. 1.1 parts by mass of sodium, 0.01 parts by mass of n-octylmercaptan as a chain transfer agent, 75 parts by mass of methyl methacrylate as a monomer, and 25 parts by mass of butyl acrylate. Nitrogen substitution in the gas atmosphere in the flask was carried out by flowing a nitrogen stream through the separation 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, the mixture was continuously heated and stirred for 2 hours to complete the polymerization, thereby obtaining an acrylic resin emulsion.

After the obtained acrylic resin emulsion was cooled to 25° C., it was added dropwise to 500 parts by mass of warm water of 70° C. containing 5 parts by mass of calcium acetate, and then the temperature was raised to 90° C. and coagulation was carried out. The obtained condensate was separated and washed, and then dried at 60 ° C for 12 hours to obtain an acrylic resin (B-1). The glass transition point of the acrylic resin (B-1) was 60 ° C when measured by differential scanning calorimetry (DSC) according to JIS K 7121:2012 plastic conversion temperature measurement method.

(Experimental Examples 13 to 17) [Manufacture of Acrylic Resin (B-2 to 6)]

The amount of each monomer and chain transfer agent added in Experimental Example 12 was adjusted to obtain various acrylic resins (B-2 to 6) described in Table 2.

(Experimental Example 18) [Manufacture of impact-resistant styrene-based resin (C-1)]

3.4% by mass of a low-cis polybutadiene rubber (manufactured by Asahi Kasei Co., Ltd., trade name: Diene 55AS) was used as a rubbery polymer, and dissolved in 91.6% by mass of styrene and 5.0% by mass of ethylbenzene as a solvent. Polymerization of raw materials. Further, a rubber-containing antioxidant (manufactured by Ciba-Geigy, trade name: IRGANOX 1076) was added in an amount of 0.1 part by mass. The polymerization raw material was supplied at 12.5 kg/hr to a 14-liter sheathed reactor (R-01) having an anchor type stirring blade having a blade diameter of 0.285 m. The reaction was carried out at a reaction temperature of 140 ° C and a number of revolutions of 2.17 sec ^-1 . The obtained resin liquid was introduced into a plug-in plug flow reactor equipped with two internal volumes of 21 liters arranged in series. In the first plug flow reactor (R-02), the sheath temperature is adjusted so that the reaction temperature has a gradient of 120 to 140 ° C in the flow direction of the resin liquid, and the second plug flow reactor (R- In 03), the sheath temperature is adjusted so that the reaction temperature has a gradient of 130 to 160 ° C in the flow direction of the resin liquid. The obtained resin liquid was heated to 230 ° C, and then sent to a devolatilization tank having a vacuum of 5 torr, and the unreacted monomer and solvent were separated and recovered. Thereafter, the self-desorption groove is pumped out by a gear pump, and is formed into a strand through a die plate, and then pelletized by a water tank to be recovered as a product. The resin ratio of the obtained resin (C-1) was 70%. Here, the resin ratio is calculated by the following formula.

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

Further, the content of the rubber component in the obtained resin (C-1) was 10.0% by mass, and the average rubber particle diameter was 2.0 μm.

(Experimental Examples 19 to 22) [Manufacture of impact-resistant styrene resin (C-2 to 5)]

The amount of each raw material added in Experimental Example 18 was adjusted to obtain various impact-resistant styrene-based resins (C-2 to 5) described in Table 3.

<Example 1>

The styrene-methacrylic acid copolymer (A-1) was 95.0% by mass, and the acrylic resin (B-1) was mixed by 5.0% by mass, and a pellet extruder (double with a vacuum exhaust port) was used. The same direction extrusion machine TEM35B (manufactured by Toshiba Machine Co., Ltd.) was extruded at a temperature of 230 ° C, a rotation number of 250 rpm, and a venting pressure of -760 mmHg, which was passed through a die plate and then cooled by a water tank. The pelletizer was pelletized to obtain a resin composition. Further, the venting pressure of the exhaust port is expressed as a differential pressure value with respect to the normal pressure. The content of the unreacted styrene monomer in the obtained resin composition was 500 ppm, and the content of the unreacted methacrylic monomer was 50 ppm. Further, the Fika softening temperature was 116 ° C, and the melt flow index (MFI) of the H condition (200 ° C, 5 kg) of JIS K7210 was 1.0 g/10 min. The above resin composition was used as a sheet extrusion machine (T-die width 500 mm, lip opening 1.5 mm, A 40 mm extruder (manufactured by Tanabe Plastics Co., Ltd.) was used to obtain an unstretched sheet at an extrusion temperature of 230 ° C and a discharge amount of 20 kg / h. The sheet was preheated to (Fika softening temperature + 30) ° C using a batch type double-axis stretching machine (made by Toyo Seiki Co., Ltd.), and extended to 2.4 times in MD and 2.4 times in TD at a strain rate of 0.1/sec. 5.8 times), the biaxially stretched sheets described in Table 4 were obtained. The obtained sheet had a thickness of 0.3 mm, a stretching ratio (MD/TD) of 2.4/2.4 times, and an orientation relaxation stress (MD/TD) of 0.6/0.6 MPa.

<Examples 2 to 19, Comparative Examples 1 to 7>

The blending amount of the resin of Example 1 and the extrusion conditions of the resin composition were adjusted to obtain biaxially oriented sheets described in Tables 4, 5 and 7.

<Examples 20 to 26>

The impact-resistant styrene-based resin (C) shown in Table 1 was added to 100% by mass of the total of the styrene-methacrylic acid copolymer (A-1) and the acrylic resin (B-1), and the examples were as follows. After the granulation was carried out to obtain a styrene resin composition, the biaxially oriented sheets described in Tables 5 and 6 were obtained under the film formation conditions and elongation conditions described in Example 1.

<Examples 27 to 33>

The resin composition containing the styrene-methacrylic acid copolymer (A-1), the acrylic resin (B-1), and the impact-resistant styrene resin (C) of Example 21 was obtained, and then described in Example 1 The sheet extrusion machine and the biaxial stretching machine adjust the opening degree of the lip when the film is formed, the magnification at the time of stretching, and the preheating temperature to obtain a biaxially stretched sheet having the thickness, the stretching ratio, and the orientation relaxation stress described in Table 6. .

With respect to the obtained sheet, various properties were measured and evaluated by the methods described below. In the relative evaluation of ○, △, and ×, the case of ○ or Δ was judged as pass. The results are shown in Tables 4 to 7.

(1) Film forming property

The thickness was measured using a micrometer at 25 points of the intersection when the unstretched sheets were pulled out at intervals of 20 mm in the MD direction and the TD direction at a distance of 20 mm, and the standard deviation σ was evaluated by the following criteria.

○: σ is less than 0.03 mm

△: 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)

The measurement was carried out in accordance with the H condition (200 ° C, 5 kg) of JIS K7210.

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

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

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

(3) Sheet appearance

For the range of 350 mm × 350 mm of the biaxially stretched sheet, 1) roll adhesion marks of 100 mm ² or more, 2) bubbles of 10 mm ² or more, 3) transparent and opaque foreign matter, 4) adhesion defects, 5) width of 3 mm or more The mold line (a defect occurring in the direction in which the sheet was moved at the T-die exit at the time of film formation) was a disadvantage, and the number of defects was evaluated on the basis of the following criteria.

○: 0

△: 1~2

×: 3 or more

(4) Extensibility

In the case where the double-stretched sheet was pulled out at five points in the MD direction and the TD direction at intervals of 50 mm to form a grid shape, the thickness was measured using a micrometer, and the standard deviation σ was evaluated by the following criteria.

○: σ is less than 0.05m

△: σ is 0.05 mm or more and less than 0.10 mm

×: σ is 0.10 mm or more

(5) Transparency

The haze of the biaxially stretched sheet was measured in accordance with JIS K-7361-1 using a haze meter NDH5000 (Nippon Denshoku Co., Ltd.).

○: less than haze 1.5%

△: haze of 1.5% or more and less than 3.0%

×: Haze of 3.0% or more

(6) Rigidity

A 500 g hammer was placed in the main body of the food packaging box to be described later, and the five-layer lunch container with the lid closed was placed, and the deformation state of the lid material after standing for 24 hours was confirmed.

○: No shape change.

△: There is deformation.

×: There is a crack.

(7) folding resistance

The folding strength of the sheet extrusion direction (longitudinal direction) and the direction perpendicular thereto (lateral direction) was measured in accordance with ASTM D2176, and the minimum value was determined and evaluated as follows.

○: 5 or more times

△: 2 or more times and less than 5 times

×: less than 2 times

(8) Formability

Using hot plate forming machine HPT-400A (WAKISAKA ENGINEERING Company system), the food packaging box (size cover: vertical 150 × horizontal 130 × height 30 mm, body: vertical 150 × horizontal 130 × height 20 mm) is formed under the conditions of a hot plate temperature of 150 ° C and a heating time of 2.0 seconds. The formability was evaluated on the basis of the following criteria.

○: Good

△: The corner is slightly in poor shape

×: The shape or the corner is different from the size and the shape is not good.

(9) mold fouling

The transfer of the above-mentioned food packaging box and the transfer of dirt such as a mold were evaluated on the basis of the following criteria.

○: no transfer (transparent, no turbidity)

△: Part of the transfer (opaque, turbid surface)

×: All transfer (opaque, turbid surface)

(10) Heat resistance

The food packaging box obtained under the above molding 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, external dimensional change is less than 5%

×: large deformation, external size change of 5% or more

(11) Oil resistance

The gauze of the test liquid filled with salad oil (manufactured by Nisshin Oil Co., Ltd.), Mina Zi (made by Ajinomoto Co., Ltd.), COCONAD ML (registered trademark, Kaosha Co., Ltd.) is attached to the hinge portion of the food packaging box. 10 mm, and allowed to stand in an oven at 60 ° C for 24 hours, and the surface of the attached portion was observed.

○: no change

△: slightly whitened

×: Significantly whitened, cracked

(12) Microwave heating tolerance

In the center of the lid of the above-mentioned food packaging box, the nails were attached to the center of the container in a range of 5 mm × 5 mm, and 300 g of water was placed in the container body, and the lid container was covered, and heated in a microwave oven of 1500 W for 90 seconds, and the adhesion portion of the mayon was visually evaluated. Happening.

○: no change

△: There is whitening, the container is slightly deformed

×: There is a perforation, and the container is significantly deformed

According to the results of Tables 4 to 7, all of Examples 1 to 33 satisfy the requirements of the present invention, and film formability (film formation property, fluidity, sheet appearance, elongation), transparency, sheet strength (rigidity, folding resistance). Excellent performance in any of the properties of moldability, moldability, mold fouling, heat resistance, oil resistance, and microwave oven heat resistance.

On the other hand, in Comparative Example 1, since the content of the methacrylic monomer unit in the styrene-methacrylic acid copolymer (A-10) was small, the thicar softening temperature was low, and the heat resistance was inferior to the heat resistance of the microwave oven. In Comparative Example 2, since the content of the methacrylic acid monomer unit in the styrene-methacrylic acid copolymer (A-11) was large, the fluidity and the formability were inferior. In Comparative Example 3, since the weight average molecular weight of the acrylic resin (B-6) was small, the microwave oven was inferior in heat resistance. In Comparative Example 4, since the content of the acrylic resin (B-1) was small, the heat resistance of the microwave oven was inferior. Comparative Example 5 did not contain the acrylic resin (B), and the microwave oven was inferior in heat resistance and oil resistance. In Comparative Example 6, since the content of the acrylic resin (B-1) was large, the insoluble matter of the acrylic resin was generated as a gel, and the fluidity or the sheet appearance was inferior. In Comparative Example 7, the content of the methacrylic monomer unit in the styrene-methacrylic acid copolymer (A-2) was relatively small, and the content of the butyl acrylate monomer unit in the acrylic resin (B-4) was relatively large. Further, since the blending ratio of the acrylic resin (B-4) is slightly larger, the Pena softening temperature is low, and heat resistance and heat resistance of the microwave oven are inferior.

Claims (10)

A biaxially stretched sheet comprising a biaxially stretched sheet comprising a styrene resin composition of a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), the styrene-methacrylic acid copolymer The mass ratio (A)/(B) of (A) to the acrylic resin (B) is 90/10 to 97/3, and the styrene-methacrylic acid copolymer (A) is 84/16 to 94/6. The mass ratio includes a styrene monomer unit and a methacrylic monomer unit, and the acrylic resin (B) has a weight average molecular weight of 1,000,000 to 7,000,000, and the thixo softening temperature of the styrene resin composition (Vicat softening) Temperature) is in the range of 106 to 132 °C. The biaxially stretched sheet of claim 1, wherein the styrene-methacrylic acid copolymer (A) has a weight average molecular weight of from 120,000 to 250,000. A biaxially stretched sheet according to claim 1 or 2, wherein the acrylic resin (B) contains a methyl methacrylate monomer unit and a butyl acrylate monomer unit. The biaxially stretched sheet of claim 3, 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. The biaxially stretched sheet according to claim 1 or 2, further comprising a rubber component in an amount of 3% by mass or less based on the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) Impact resistant styrenic resin (C). A biaxially stretched sheet of claim 5, wherein the biaxially stretched sheet The content of the rubber component is 0.05 to 0.3% by mass, and the average rubber particle diameter is 1.2 to 12 μm. The biaxially stretched sheet according to claim 1 or 2, wherein the content of the unreacted styrene monomer in the styrene resin composition is 1000 ppm or less, and the content of the unreacted methacrylic monomer is 150 ppm or less. The biaxially extending sheet of claim 1 or 2 has a thickness of 0.1 to 0.7 mm, and the stretching ratios of the longitudinal direction and the transverse direction are both 1.8 to 3.2 times, and the orientation relaxation stresses of the longitudinal direction and the transverse direction are both 0.3~1.2MPa. A molded article comprising the biaxially oriented sheet of claim 1 or 2. The molded article of claim 9, which is a food packaging container for microwave oven heating.