WO2017122775A1

WO2017122775A1 - Biaxially-oriented sheet and molded article thereof

Info

Publication number: WO2017122775A1
Application number: PCT/JP2017/001000
Authority: WO
Inventors: 学横塚; 大輔吉村; 大介元井
Original assignee: デンカ株式会社
Priority date: 2016-01-15
Filing date: 2017-01-13
Publication date: 2017-07-20
Also published as: JP6389574B2; TW201736415A; TWI697508B; KR102638037B1; CN108472859A; CN108472859B; KR20180102541A; JPWO2017122775A1

Abstract

Provided are: a biaxially-oriented sheet that comprises a styrene resin composition and has excellent transparency, strength, heat resistance, film forming properties, and formability during secondary molding, as well as superior resistance to cracking during trimming; 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 a high impact polystyrene (B) in a mass ratio (A)/(B) of 97.0/3.0 to 99.9/0.1, wherein the content of a methacrylic acid monomer unit in the styrene-methacrylic acid copolymer (A) is 3–14 mass%, the Vicat softening temperature of the styrene resin composition is in the range of 106–132°C, and the orientation release stress in both the longitudinal direction and the transverse direction of the biaxially-oriented sheet is 0.5–1.2 MPa. The molded article is a molded article of said biaxially-oriented sheet.

Description

Biaxially stretched sheet and molded product thereof

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

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

A technique for obtaining a molded article using a sheet having excellent heat resistance by biaxially stretching a styrene-based heat resistant resin into a sheet has been studied (Patent Documents 2 and 4).
However, styrenic heat-resistant resins have lower fluidity during melt extrusion than ordinary polystyrene, and it is difficult to increase the resin production capacity and sheet production capacity. In order to increase the fluidity of the styrenic heat-resistant resin, a method of increasing the extrusion temperature is conceivable. However, at high temperatures, the carboxylic acid groups in the styrenic heat-resistant resin react to form a gel-like foreign material, and the sheet There is a problem that the quality deteriorates.

Therefore, attempts have been made to improve the fluidity of styrene-based heat-resistant resins. As a method for increasing the fluidity of the styrene-based heat resistant resin, for example, there is a method of adding a plasticizer such as liquid paraffin. Moreover, as a method for suppressing the gelation, a method of adding an alcohol having an effect of inhibiting the reaction of carboxylic acid groups (Patent Document 5) can be mentioned. However, a sheet containing these additives is low in transparency, and tends to cause deterioration in the quality of a molded product due to bleeding out due to heat during molding.

In addition, biaxially stretched sheets of styrenic heat-resistant resin have poor crack resistance, and have the problem that the quality of the molded product deteriorates due to defective die-cutting or generation of powder when secondary forming the sheet. ing.
Furthermore, in order to make it difficult for the contents of the lid for the microwave oven container to leak during heating, the shape of the lid and the body can be fitted together without any gap, and the lid is on the inside, It is often a so-called inner fitting lid. An inner fitting lid made of a biaxially stretched sheet of styrene-based heat-resistant resin has a problem that the fitting portion is easily broken when the lid is closed.

Further, the inner fitting lid is usually provided with a ventilation valve for releasing air when the lid is closed, and this ventilation valve also has a function of releasing steam generated during heating of the microwave oven. In order to provide such a vent valve in a molded product, it is usually necessary to make a hole using a punching blade. However, biaxially stretched sheets of styrenic heat-resistant resin are liable to cause powder adhesion and cracking in this step.
For these reasons, there is a demand for a sheet having high cracking resistance while maintaining performance such as transparency, strength, heat resistance, and film-forming property as a biaxially stretched sheet of a styrene-based heat resistant resin.

US Patent No. 3035033 JP 2003-12734 A Japanese Patent Publication No.59-15133 JP-A-55-71530 JP 2010-270179 A

The present invention is a biaxially stretched sheet comprising a styrene resin composition having excellent transparency, strength, heat resistance, film forming property, moldability during secondary molding, and excellent crack resistance during trimming, and It was made for the purpose of providing a molded article.

In order to solve the above-mentioned problems, the present inventors investigated a styrene resin excellent in heat resistance and strength, investigated an additive component to the styrene resin, and further about stretching conditions for improving crack resistance. We studied earnestly. As a result, it was found that the purpose is achieved by selecting a styrene resin to be used, adding a predetermined amount of high-impact polystyrene having an appropriate composition, and adjusting the orientation relaxation stress according to the stretching conditions. It came to complete.

That is, the present invention has the following configuration.
(1) Containing styrene-methacrylic acid copolymer (A) and high impact polystyrene (B) in a mass ratio (A) / (B) = 97.0 / 3.0 to 99.9 / 0.1 A biaxially stretched sheet comprising a styrene resin composition, wherein the styrene-methacrylic acid copolymer (A) has a methacrylic acid monomer unit content of 3 to 14% by mass, and the styrene resin composition A biaxially stretched sheet in which the Vicat softening temperature of the product is in the range of 106 to 132 ° C., and the orientation relaxation stress in the longitudinal direction and the transverse direction of the biaxially stretched sheet is 0.5 to 1.2 MPa.

(2) The styrene-methacrylic acid copolymer (A) has a weight average molecular weight (Mw) of 120,000 to 250,000, and a ratio Mw / Mn between the weight average molecular weight (Mw) and the number average molecular weight (Mn). Is 2.0 to 3.0, and the ratio Mz / Mw of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is 1.5 to 2.0. Sheet.

(3) In the above (1) or (2), the content of the rubber component derived from the high impact polystyrene (B) is 0.005 to 0.36% by mass with respect to the styrenic resin composition. The biaxially stretched sheet as described.

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

(5) The biaxially stretched sheet according to any one of (1) to (4), wherein the content of the six-membered cyclic acid anhydride in the styrene-based resin composition is 1.0% by mass or less.

(6) The biaxially stretched sheet according to any one of (1) to (5), wherein the styrene-based resin composition has a melt flow index at 200 ° C. of 0.5 to 4.5 g / 10 minutes. .

(7) The biaxially stretched sheet according to any one of (1) to (6), wherein the rubber component derived from the high impact polystyrene (B) has an average rubber particle diameter of 1 to 9 μm.

(8) The biaxially stretched sheet according to any one of (1) to (7), which has a silicone oil coating film on at least one surface.

(9) A molded article comprising the biaxially stretched sheet according to any one of (1) to (8).

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

(11) The molded article according to (9) or (10) above, which is a hood pack composed of a main body portion and a lid material that can be fitted to the main body portion, and the shape of the fitting portion is an inner fitting.

The biaxially stretched sheet of the present invention and its molded product are excellent in transparency, strength, heat resistance, film-forming property, moldability during secondary molding, and excellent crack resistance during trimming. The biaxially stretched sheet and the molded product of the present invention can be suitably used for food packaging containers heated in a microwave oven.

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

The biaxially stretched sheet of the present invention comprises a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and a high impact polystyrene (B) at a specific mass ratio. The biaxially stretched sheet of the present invention can be obtained by extruding the styrene resin composition and biaxially stretching the obtained unstretched sheet. Hereinafter, each component of the styrene resin composition will be described.

(Styrene-methacrylic acid copolymer (A))
The styrene resin composition in the present invention contains a styrene-methacrylic acid copolymer (A) obtained by copolymerizing styrene and methacrylic acid. In the styrene-methacrylic acid copolymer (A) used in the present invention, the copolymerization ratio of styrene and methacrylic acid can be variously set depending on the desired heat resistance and mechanical strength. The content of the methacrylic acid monomer unit needs to be 3 to 14% by mass from the viewpoint that a resin excellent in balance of heat resistance, mechanical strength, and transparency when formed into a sheet can be easily obtained. . When the content of the methacrylic acid monomer unit is less than 3% by mass, the heat resistance is insufficient, and holes are formed during the microwave heating, and deformation is likely to occur. The content of the methacrylic acid monomer unit is preferably 6% by mass or more, more preferably 8% by mass or more. On the other hand, when the content of the methacrylic acid monomer unit exceeds 14% by mass, fluidity during film formation and appearance deterioration due to gel generation are likely to occur. The content of the methacrylic acid monomer unit is preferably 12% by mass or less, more preferably 10% by mass or less. In addition, the styrene-methacrylic acid copolymer (A) may be appropriately copolymerized with other monomers other than styrene and methacrylic acid, if necessary, as long as the effects of the invention are not impaired. The content of other monomers is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 3% by mass or less. When the content of other monomers exceeds 10% by mass, the ratio of styrene or methacrylic acid decreases, 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 preferably 120,000 to 250,000, more preferably 140,000 to 220,000, and even more preferably 150,000 to 200,000. When the weight average molecular weight is less than 120,000, the film tends to deteriorate due to film formation such as sheet drawdown and neck-in, insufficient stretch orientation, and contact with the hot plate during container molding. On the other hand, when the weight average molecular weight exceeds 250,000, unevenness in thickness at the time of film formation due to lowering of fluidity, deterioration of sheet appearance such as die lines, and poor molding at the time of container molding tend to occur.

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

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

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

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

(High impact polystyrene (B))
The high impact polystyrene (B) in the present invention may be a styrene resin containing a particulate rubber component, and a styrene homopolymer containing a rubber component, a styrene-methacrylic acid copolymer Any of those containing a rubber component can be suitably used. The rubber component may be dispersed in the form of particles independently in the polystyrene or styrene-methacrylic acid copolymer used as the matrix resin, or the rubber component may be grafted with polystyrene or styrene-methacrylic acid copolymer. It may be polymerized and dispersed in the form of particles.

Examples of the rubber component include polybutadiene, styrene-butadiene copolymer, polyisoprene, butadiene-isoprene copolymer, and the like. In particular, it is preferably contained as a polybutadiene or styrene-butadiene copolymer.

For example, high impact polystyrene (B) is obtained by copolymerizing styrene and butadiene to obtain a styrene-butadiene copolymer, and then dissolving the copolymer in styrene alone or in a mixture of styrene and methacrylic acid. By performing polymerization, the copolymer can be obtained as a styrene resin that becomes particles dispersed in a matrix resin (polystyrene or styrene-methacrylic acid) that becomes a continuous layer.

The content of the rubber component of the high impact polystyrene (B) is preferably, for example, 5.0 to 12.0% by mass in consideration of the amount of the rubber component in the styrene resin composition.

(Styrenic resin composition)
In the styrene resin composition of the present invention, the styrene-methacrylic acid copolymer (A) and the high impact polystyrene (B) have a mass ratio (A) / (B) = 97.0 / 3.0 to 99.9. It is necessary to contain at /0.1. The mass ratio (A) / (B) is more preferably 99.0 / 1.0 to 99.5 / 0.5. By mixing at this mass ratio, it is possible to maintain the transparency of the obtained sheet and molded product, as well as breakage and generation of chips during sheet trimming, occurrence of defective mold release and generation of extracted powder. Can be difficult.

The content of unreacted styrene monomer in the styrene-based resin composition is preferably 1000 ppm or less, and the content of unreacted methacrylic acid monomer is preferably 150 ppm or less. If the content of these unreacted monomers is larger than the specified amount, the sheet surface tends to bleed out, or when it comes into contact with the roll of an extruder or stretching machine, surface roughness and dirt are likely to occur. Further, when the sheet is formed, there is a concern that it adheres to the mold or the like of the molding machine and damages the appearance of the molded product or causes the mold to become dirty, thereby damaging the appearance of the subsequent molded product.
The unreacted styrene monomer and unreacted methacrylic acid monomer were quantified by an internal standard method using gas chromatography described below.
Device name: GC-12A (manufactured by Shimadzu Corporation)
Column: Glass column φ3 [mm] x 3 [m]
Quantitative method: Internal standard method (cyclopentanol)

In addition, two adjacent methacrylic acid monomer units contained in the styrene-methacrylic acid copolymer (A) may form a six-membered cyclic acid anhydride in an extrusion process at high temperature and high vacuum. The styrene-based resin composition containing a large amount of the six-membered cyclic acid anhydride is manifested as a transparent gel-like foreign material when formed into a sheet, which may impair the appearance of the sheet. Therefore, the content of the six-membered cyclic acid anhydride in the styrene resin composition is preferably 1.0% by mass or less.
The content of the six-membered cyclic acid anhydride was determined from the integral ratio of the spectrum measured with a carbon nuclear magnetic resonance ( ¹³ C-NMR) measuring device.

The styrenic resin composition must have a Vicat softening temperature in the range of 106 to 132 ° C. When the Vicat softening temperature is less than 106 ° C., the heat resistance of the sheet is insufficient, and deformation easily occurs during heating in the microwave oven. The Vicat softening temperature is preferably 112 ° C or higher, more preferably 116 ° C or higher. On the other hand, if the Vicat softening temperature exceeds 132 ° C., the workability during film formation and container molding may be reduced. The Vicat softening temperature is preferably 128 ° C. or lower, more preferably 126 ° C. or lower. The Vicat softening temperature was measured in accordance with JIS K-7206 under conditions of a heating rate of 50 ° C./hr and a test load of 50 N.

The melt flow index (MFI) of the styrenic resin composition is preferably in the range of 0.5 to 4.5 g / 10 minutes, more preferably 0 from the viewpoint of drawdown during film formation and thickness uniformity. 9.9 to 3.6 g / 10 min, more preferably 1.3 to 2.7 g / 10 min. The melt flow index (MFI) was measured according to JIS K7210 H condition (200 ° C., 5 kg).

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

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

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

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

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

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

The biaxially stretched sheet of the present invention can be obtained by biaxially stretching the styrene resin composition. Furthermore, in order to ensure the strength of the sheet and the molded product, particularly crack resistance, it is necessary that the orientation relaxation stress in the longitudinal and lateral directions of the sheet satisfy the range of 0.5 to 1.2 MPa. If the orientation relaxation stress is less than 0.5 MPa, the crack resistance of the sheet cannot be ensured, tearing or chipping in the trimming process, cracking or chipping in the container punching process occur frequently, and sheet and molding The productivity of the product is significantly impaired. On the other hand, when the orientation relaxation stress exceeds 1.2 MPa, it becomes difficult to achieve both stable stretchability and mass productivity in the sheet stretching step, and shapeability at the time of container molding is impaired. In addition, if the orientation relaxation stress in either the longitudinal direction or the lateral direction is out of the above numerical range, it becomes easier to tear in the direction in which the orientation relaxation stress is higher, and the sheet breaks in the sheet trimming process or the container removal process. It tends to occur.
The orientation relaxation stress of the biaxially stretched sheet of the present invention is a value measured as a peak stress value in silicone oil at a temperature 30 ° C. higher than the Vicat softening temperature of the resin composition constituting the sheet according to ASTM D1504. It is.

The content of the rubber component derived from the high impact polystyrene (B) in the styrene resin composition in the present invention is preferably 0.005 to 0.36% by mass with respect to the styrene resin composition. In order to prevent blocking of the biaxially stretched sheet, the rubber component content is preferably 0.005% by weight or more. 0.010% by weight or more is more preferable, and 0.040% by weight or more is more preferable. On the other hand, the content of the rubber component is preferably 0.36% by weight or less in order to maintain the transparency of the biaxially stretched sheet. 0.24% by weight or less is more preferable, and 0.12% by weight or less is more preferable. The content of the rubber component in the styrene resin composition is obtained by dissolving the styrene resin composition in chloroform, adding iodine monochloride to react the double bond in the rubber component, adding potassium iodide, The remaining iodine monochloride is converted to iodine and measured by the iodine monochloride method in which back titration is performed with sodium thiosulfate.

The average rubber particle diameter of the rubber component derived from the high impact polystyrene (B) in the biaxially stretched sheet of the present invention is preferably 1 to 9 μm. The average rubber particle size of the rubber component is preferably 1 μm or more in order to prevent blocking of the sheet. On the other hand, the average rubber particle diameter of the rubber component is preferably 9 μm or less in order to maintain the transparency of the biaxially stretched sheet.
The average rubber particle size of the rubber component in the biaxially stretched sheet is cut by an ultrathin section method so that the observation surface is parallel to the sheet plane, and the rubber component is dyed with osmium tetroxide (OsO ₄ ). The particle diameter of 100 particles is measured with a transmission microscope, and is a value calculated by the following equation.
Average rubber particle size = Σni (Di) ⁴ / Σni (Di) ³
Here, ni represents the number of measured particles, and Di represents the measured particle size.

The biaxially stretched sheet of the present invention includes known release agents / release agents (for example, silicone oil), antifogging agents (for example, nonionic surfactants such as sucrose fatty acid ester and polyglycerin fatty acid ester, polyether-modified silicone) Oil, silicon dioxide, etc.) and an antistatic agent (for example, various nonionic surfactants, cationic surfactants, anionic surfactants, etc.) and at least one of the sheets is mixed. You may apply to the surface of. In particular, the biaxially stretched sheet of the present invention preferably has a silicone oil coating on at least one surface in terms of the peelability of the sheet and the molded product.

Examples of the silicone oil used as the release agent / release agent of the present invention include, for example, methyl hydrogen polysiloxane, dimethyl polysiloxane, methylphenyl polysiloxane, diphenyl polysiloxane and the like known as this type of release agent. . Further, a modified product in which a functional group is partially introduced into the silicone oil, for example, a polyether-modified silicone oil, an amino-modified silicone oil, an epoxy-modified silicone oil, a carboxyl-modified silicone oil, a fluorine-modified silicone oil, or the like may be used. Among these, dimethylpolysiloxane is particularly preferable from the viewpoints of releasability, odor and economy.

The method for coating these coating agents on 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 simply mentioned. Moreover, spraying, immersion, etc. can also be employ | adopted.

The method for obtaining a molded product from the biaxially stretched sheet of the present invention is not particularly limited, and a method commonly used in the conventional secondary molding method of a biaxially stretched sheet can be used. For example, the secondary molding can be performed by a thermoforming method such as a vacuum forming method or a pressure forming method. These methods are described in, for example, “Plastic Processing Technology Handbook” edited by the Society of Polymer Science, Nikkan Kogyo Shimbun (1995).

The use of the molded product of the biaxially stretched sheet of the present invention includes various containers and can be widely used for packaging containers for various articles. Among these, a food packaging container for heating a microwave oven is preferable because the features of the present invention are sufficiently exhibited. In addition, a molded product having a main body portion and a lid material that can be fitted to the main body portion, the shape of the fitting portion being an internal fitting, is further enhanced by the excellent crack resistance of the present invention. Therefore, it is particularly preferable.

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

(Experimental example 1) [Production of styrene-methacrylic acid copolymer (A-1)]
100 kg of pure water and 100 g of polyvinyl alcohol were added to an autoclave with an internal volume of 200 L and a stirrer, and stirred at 130 rpm. Subsequently, 72.0 kg of styrene, 8.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, the temperature was raised to 110 ° C., and polymerization was carried out for 5 hours (Step 1). Further, the temperature was maintained at 140 ° C. for 3 hours to complete the polymerization (Step 2). The obtained beads were washed, dehydrated, dried and then extruded to obtain pellet-shaped styrene-methacrylic acid copolymer (A-1) shown in Table 1. As a result of analysis using pyrolysis gas chromatography, the mass ratio of styrene monomer unit / methacrylic acid monomer unit was 90/10. 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 to 20) [Production of styrene-methacrylic acid copolymer (A-2 to 20)]
Various raw material charges in Experimental Example 1 were adjusted to obtain various styrene-methacrylic acid copolymers (A-2 to 20) shown in Tables 1 and 2.

(Experimental example 21) [Production of styrene-methacrylic acid copolymer (A-21)]
100 kg of pure water and 100 g of polyvinyl alcohol were added to an autoclave with an internal volume of 200 L and a stirrer, and stirred at 130 rpm. Subsequently, 64.0 kg of styrene, 4.0 kg of butadiene, 8.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, the temperature was raised to 110 ° C., and polymerization was carried out for 5 hours (Step 1). . Further, the temperature was maintained at 140 ° C. for 3 hours to complete the polymerization (Step 2). The obtained beads were pelletized by the same method as in Experimental Example 1 to obtain a styrene-methacrylic acid copolymer (A-21). As a result of analysis using pyrolysis gas chromatography, the mass ratio of styrene monomer unit / butadiene monomer unit / methacrylic acid monomer unit was 85/5/10. 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 example 22) [Production of styrene-methacrylic acid copolymer (A-22)]
100 kg of pure water and 100 g of polyvinyl alcohol were added to an autoclave with an internal volume of 200 L and a stirrer, and stirred at 130 rpm. Subsequently, 64.0 kg of styrene, 4.0 kg of maleic anhydride, 8.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, the temperature was raised to 110 ° C., and polymerization was carried out for 5 hours (step 1). Further, the temperature was maintained at 140 ° C. for 3 hours to complete the polymerization (Step 2). The obtained beads were pelletized by the same method as in Experimental Example 1 to obtain a styrene-methacrylic acid copolymer (A-22). As a result of analysis using pyrolysis gas chromatography, the mass ratio of styrene monomer unit / maleic anhydride monomer unit / methacrylic acid monomer unit was 85/5/10. 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 example 23) [Production of styrene-methacrylic acid copolymer (A-23)]
100 kg of pure water and 100 g of polyvinyl alcohol were added to an autoclave with an internal volume of 200 L and a stirrer, and stirred at 130 rpm. Subsequently, 64.0 kg of styrene, 4.0 kg of methyl methacrylate, 8.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, the temperature was raised to 110 ° C., and polymerization was performed for 5 hours (Step). 1). Further, the temperature was maintained at 140 ° C. for 3 hours to complete the polymerization (Step 2). The obtained beads were pelletized by the same method as in Experimental Example 1 to obtain a styrene-methacrylic acid copolymer (A-23). As a result of analysis using pyrolysis gas chromatography, the mass ratio of styrene monomer unit / methyl methacrylate monomer unit / methacrylic acid monomer unit was 85/5/10. 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 example 24) [Production of styrene-methacrylic acid copolymer (A-24)]
Polymerization was carried out by the same formulation and polymerization method as in Example 1. After washing, dehydrating and drying the obtained beads, 1 part by mass of liquid paraffin (“White Rex 335” manufactured by Mobil Petroleum) was added to 100 parts by mass of the resulting styrene-methacrylic acid copolymer and extruded. The pellet-shaped styrene-methacrylic acid copolymer (A-24) shown in Table 2 was obtained. 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 example 25) [Production of styrene-methacrylic acid copolymer (A-25)]
Polymerization was carried out by the same blending and polymerization method as in Experimental Example 21 except that 75.2 kg of styrene, 2.4 kg of butadiene and 2.4 kg of methacrylic acid were used, and a styrene-methacrylic acid copolymer (A-25) was obtained. Obtained.

Experimental Example 26 [Production of styrene-methacrylic acid copolymer (A-26)]
Polymerization was carried out by the same composition and polymerization method as in Experimental Example 22 except that 66.4 kg of styrene, 2.4 kg of maleic anhydride and 11.2 kg of methacrylic acid were used, and a styrene-methacrylic acid copolymer (A-26) was obtained. )

(Experimental example 27) [Production of high impact polystyrene (B-1)]
Using 5.5% by mass low-cis polybutadiene rubber (product name: Diene 55AS, manufactured by Asahi Kasei) as a rubbery polymer, dissolved in 89.5% by mass of styrene and 5.0% by mass of ethylbenzene as a solvent. A polymerization raw material was used. Moreover, 0.1 mass part of antioxidant (made by Ciba Geigy, trade name Irganox 1076) of rubber was added. This polymerization raw material was supplied at 12.5 kg / hr to a 14-liter jacketed reactor (R-01) equipped with a vertical stirring blade having a blade diameter of 0.285 m. The reaction was carried out at a reaction temperature of 140 ° C. and a rotation speed of 2.17 sec ⁻¹ . The obtained resin solution was introduced into two jacketed plug flow reactors having an internal volume of 21 liters arranged in series. In the first plug flow reactor (R-02), the reaction temperature is 120 to 140 ° C. in the flow direction of the resin liquid. In the second plug flow reactor (R-03), the reaction temperature is resin. The jacket temperature was adjusted to have a gradient of 130 to 160 ° C. in the liquid flow direction. The resin ratio at the R-01 outlet was 25%, and the resin ratio at the R-02 outlet was 50%. The obtained resin liquid was heated to 230 ° C. and then sent to a devolatilization tank having a vacuum degree of 5 torr to separate and recover unreacted monomers and solvents. After that, it was extracted from the devolatilization tank with a gear pump, turned into a strand through a die plate, cooled in a water tank, pelletized through a pelletizer, and recovered as a product to obtain high impact polystyrene (B-1) shown in Table 3 It was. The resin ratio of the obtained resin (B-1) was 70%. Here, the resin rate is calculated by the following formula.
Resin ratio (%) = 100 × (Amount of polymer produced) / {(Amount of monomer charged) + (Amount of solvent)}
Further, the rubber component content in the obtained resin (B-1) was 8.0% by mass, and the average rubber particle size of the rubber component was 2.0 μm.

(Experimental examples 28 to 36) [Production of high impact polystyrene (B-2 to 10)]
Various raw material charges in Experimental Example 27 were adjusted to obtain various high impact polystyrenes (B-2 to 10) shown in Table 3.

<Example 1>
99.0% by mass of the styrene-methacrylic acid copolymer (A-1) of Experimental Example 1 and 1.0% by mass of the high impact polystyrene (B-1) of Experimental Example 25 were hand blended, and a pellet extruder (vacuum vent) Using a twin-screw co-directional extruder TEM35B (manufactured by Toshiba Machine) with a extrusion temperature of 230 ° C., a rotational speed of 250 rpm, and a vacuum vent gauge pressure of −760 mmHg, the strand is passed through a die plate, and then cooled in a water bath. Pelletized through a pelletizer to obtain a resin composition. The gauge pressure of the vacuum vent is shown as a differential pressure value with respect to normal pressure. The content of the unreacted styrene monomer in the obtained resin composition was 500 ppm, the content of the unreacted methacrylic acid monomer was 50 ppm, and the six-membered cyclic acid anhydride derived from the styrene-methacrylic acid copolymer (A-1) The content was 0.5% by mass. Further, the Vicat softening temperature at a heating rate of 50 ° C./hr, a test load of 50 N was 120 ° C., and the melt flow index (MFI) under JIS K7210 H condition (200 ° C., 5 kg) was 1.8 g / 10 min. The above resin composition was unstretched using a sheet extruder (T-die width 500 mm, lip opening 1.5 mm, φ40 mm extruder (manufactured by Tanabe Plastic Machinery Co., Ltd.)) at an extrusion temperature of 230 ° C. and a discharge rate of 20 kg / h. A sheet was obtained. This sheet is preheated to (Vicat softening temperature +30) ° C. with a batch type biaxial stretching machine (Toyo Seiki), and the strain rate is 0.1 / sec. The MD direction is 2.4 times and the TD direction is 2.4 times (surface magnification 5). .8 times) to obtain a biaxially stretched sheet shown in Table 1. The thickness of the obtained sheet was 0.25 mm, and the orientation relaxation stress (longitudinal / lateral) of the obtained sheet was 0.7 / 0.7 MPa. The rubber component content in the sheet was 0.080% by mass, and the average rubber particle size of the rubber component was 5.0 μm. A silicone emulsion (TSM6343 (manufactured by Momentive Performance Materials. Inc.)) was applied to both sides of the obtained sheet with a bar coater, dried in an oven at 105 ° C. for 1 minute, and the biaxially stretched sheet described in Table 4 Got.

<Examples 2 to 58, Comparative Examples 1 to 10>
The blending amounts of the styrene-methacrylic acid copolymer (A) and high impact polystyrene (B) of Example 1, the resin composition extrusion conditions, sheet film forming conditions and stretching conditions, and coating conditions were adjusted. Biaxially stretched sheets described in Table 8 (Examples 2 to 58, Comparative Examples 1 to 10) were obtained.

The obtained sheet was measured and evaluated by the following method. In relative evaluation of (circle), (triangle | delta), and x, the time of (circle) or (triangle | delta) was determined as the pass. The results are shown in Tables 4 to 8.

(1) Film formability <Drawdown>
The minimum take-off speed at which film formation is possible when film formation is performed under the above sheet extrusion conditions (T-die width 500 mm, lip opening 1.5 mm, φ40 mm extruder (manufactured by Tanabe Plastic Machinery Co., Ltd., extrusion temperature 230 ° C.)) The value was evaluated according to the following criteria.
○: Less than 0.5 m / min Δ: 0.5 m / min or more, less than 10.0 m / min ×: 10.0 m / min or more

<Thickness uniformity>
The film-forming sheet is biaxially stretched, the thickness is measured using a microgauge at 25 intersection points when five straight lines are drawn in a grid pattern at intervals of 50 mm in the vertical and horizontal directions, and the average thickness and the maximum value are measured. The minimum value was calculated and evaluated according to the following criteria from the thickness range.
○: Average thickness 0.24 to 0.26 mm, thickness range: 0.23 to 0.27 mm
Δ: Average thickness 0.24 to 0.26 mm, thickness range: 0.21 to 0.29 mm
X: Thickness range other than the above

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

<Elongation uniformity>
9 sheets of 100 mm × 100 mm pieces were cut out from the biaxially stretched sheet, and the test piece was left to shrink for 60 minutes in an oven having a temperature 30 ° C. higher than the Vicat softening temperature of the resin composition. The lengths [X] and [Y] (unit: mm) of the sheet pieces in the direction were measured. The number of sheet pieces satisfying the condition calculated for the value calculated from the following equation was measured and evaluated according to the following criteria.
2.2 ≦ 100 / [X] ≦ 2.6 and 2.2 ≦ 100 / [Y] ≦ 2.6 Formula (A)
○: The number of sheet pieces satisfying the formula (A) is 15 or more. Δ: The number of sheet pieces satisfying the formula (A) is 9 to 14. ×: The number of sheet pieces satisfying the formula (A) is less than 8.

(2) Transparency According to JIS K-7361-1, the haze of the biaxially stretched sheet was measured using a haze meter NDH5000 (Nippon Denshoku).
○: Haze less than 1.5% Δ: Haze 1.5% or more, less than 3.0% ×: Haze 3.0% or more

(3) Sheet strength <Tear strength>
In accordance with JIS K-7128-2, Part 3 In accordance with the right-angled tearing method, the tear strength in the longitudinal direction and the transverse direction was measured, and the minimum value was determined and evaluated as follows.
○: 10 MPa or more Δ: 5 MPa or more, less than 10 MPa ×: less than 5 MPa

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

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

<Appearance>
The appearance of the food pack was evaluated according to the following criteria, with 1) whitening due to surface roughness, 2) transfer of dirt such as molds, and 3) raindrops as defects.
○: No defect △: There is one defect other than the top of the lid ×: Other than the above (There are defects on the top of the lid, or there are two or more defects other than the top)

<Crack resistance during trimming (removability)>
50 food packs were stacked and evaluated according to the following criteria from the number of cracks in the hinge and flange when punched with a press punching machine.
○: Occurrence of cracks 0: △: Occurrence of cracks 1 to 5 ×: Occurrence of cracks 6 or more

(5) Heat resistance <thermal deformation rate>
The lunch box lid obtained under the above molding conditions was placed in a hot air dryer set at 110 ° C. for 60 minutes, and then the deformation of the container was visually observed.
○: No deformation △: Minor deformation, outside dimension change less than 5% ×: Large deformation, outside dimension change 5% or more

<Microwave heating resistance>
Nine points of mayonnaise are attached to the center of the lid of the above food pack in a range of 5 mm × 5 mm, put 300 g of water into the container body, cover the lid container and heat for 90 seconds in a 1500 W microwave oven, The state was visually evaluated.
○: No change △: Whitening occurred, container slightly deformed ×: Perforated, container deformed significantly

(6) Lubricity In a state where the food contact surface and the food non-contact surface of the sheet cut out from the top surface of the container are overlapped, the friction angle (by the method according to JIS P8147 paper and paper-static and dynamic friction coefficient measurement method) The angle at which sliding begins) was measured and evaluated according to the following criteria.
○: Less than 15 ° △: 15 ° or more, less than 30 ° ×: 30 ° or more

From the results of Tables 4 to 8, Examples 1 to 58 all satisfy the provisions of the present invention, and film forming properties (drawdown, thickness uniformity, appearance, stretch uniformity), transparency ( Haze), sheet strength (tear strength, folding resistance), moldability (formability, appearance, crack resistance during trimming (pullability)), heat resistance (thermal deformation rate, resistance to microwave heating), lubricity In any performance of (friction angle), it had excellent performance.

On the other hand, Comparative Example 1 has a low Vicat softening temperature due to a low content of methacrylic acid monomer units in the styrene-methacrylic acid copolymer (A-2), and is inferior in thermal deformation rate and resistance to microwave heating. It was a thing. In Comparative Example 2, the content of methacrylic acid monomer units in the styrene-methacrylic acid copolymer (A-8) is large, resulting in poor thickness uniformity, appearance, and moldability during film formation. It was. In Comparative Example 3, the content of high impact polystyrene (B) was large, the content of the rubber component in the styrene resin composition was large, and the appearance and transparency during film formation were poor. Comparative Example 4 does not contain high impact polystyrene (B), does not contain a rubber component in the styrene resin composition, has sheet strength (tear strength, folding resistance), cracking resistance during trimming, sliding It was inferior in nature.

In Comparative Example 5, the content of the methacrylic acid monomer unit in the styrene-methacrylic acid copolymer (A-25) is relatively small, and further, since butadiene is included as the copolymerization monomer, the Vicat softening temperature is low, It was inferior in heat distortion rate and microwave oven heat resistance. Comparative Example 6 has a relatively high content of methacrylic acid monomer units in the styrene-methacrylic acid copolymer (A-26), and further contains maleic anhydride as a copolymerization monomer. It was high and inferior in formability. Comparative Example 7 had a high orientation relaxation stress in the lateral direction, and was inferior in tear strength, moldability, and crack resistance during trimming. In Comparative Example 8, both the longitudinal and lateral orientation relaxation stresses were low, and the folding resistance and the crack resistance during trimming were inferior. In Comparative Example 9, both the longitudinal and lateral orientation relaxation stresses were high, and the moldability was inferior. Comparative Example 10 had a low orientational relaxation stress in the lateral direction, and was inferior in tear strength and crack resistance during trimming.

Claims

Styrene resin containing styrene-methacrylic acid copolymer (A) and high impact polystyrene (B) in a mass ratio (A) / (B) = 97.0 / 3.0 to 99.9 / 0.1 A biaxially stretched sheet comprising the composition,
The content of methacrylic acid monomer units in the styrene-methacrylic acid copolymer (A) is 3 to 14% by mass,
Vicat softening temperature of the styrenic resin composition is in the range of 106-132 ° C,
A biaxially stretched sheet, wherein both the longitudinal and lateral orientation relaxation stresses of the biaxially stretched sheet are in the range of 0.5 to 1.2 MPa.
The styrene-methacrylic acid copolymer (A) has a weight average molecular weight (Mw) of 120,000 to 250,000, and a ratio Mw / Mn between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of 2. The biaxially stretched sheet according to claim 1, wherein the biaxially stretched sheet is 0 to 3.0, and the ratio Mz / Mw of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is 1.5 to 2.0.
The biaxial stretching according to claim 1 or 2, wherein the content of the rubber component derived from the high-impact polystyrene (B) is 0.005 to 0.36 mass% with respect to the styrenic resin composition. Sheet.
The biaxially stretched sheet according to any one of claims 1 to 3, wherein the content of unreacted styrene monomer in the styrene-based resin composition is 1000 ppm or less and the content of unreacted methacrylic acid monomer is 150 ppm or less.
The biaxially stretched sheet according to any one of claims 1 to 4, wherein the content of the six-membered cyclic acid anhydride in the styrene-based resin composition is 1.0 mass% or less.
The biaxially stretched sheet according to any one of claims 1 to 5, wherein the styrenic resin composition has a melt flow index at 200 ° C of 0.5 to 4.5 g / 10 min.
The biaxially stretched sheet according to any one of claims 1 to 6, wherein the rubber component derived from the high impact polystyrene (B) has an average rubber particle diameter of 1 to 9 µm.
The biaxially stretched sheet according to any one of claims 1 to 7, which has a silicone oil coating film on at least one surface.
A molded article comprising the biaxially stretched sheet according to any one of claims 1 to 8.
The molded article according to claim 9, which is a food packaging container for heating in a microwave oven.
The molded article according to claim 9 or 10, wherein the molded article is a hood pack comprising a main body portion and a lid material that can be fitted to the main body portion, and the shape of the fitting portion is an inner fitting.