JPWO2017122774A1 - Biaxially stretched sheet and molded product thereof - Google Patents

Abstract

Provided are a biaxially stretched sheet made of a styrenic resin composition and a molded product thereof having excellent transparency, strength, film-forming property and moldability, and excellent productivity, heat resistance and oil resistance.
A biaxially stretched sheet comprising a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), the styrene-methacrylic acid copolymer (A) and the acrylic resin The mass ratio (A) / (B) to the resin (B) is 90/10 to 97/3, and the styrene-methacrylic acid copolymer (A) is composed of a styrene monomer unit and a methacrylic acid monomer. The unit is contained in a mass ratio of 87/13 to 94/6, the acrylic resin (B) has a weight average molecular weight of 1 million to 7 million, and the Vicat softening temperature of the styrene resin composition is 106 to 132. A biaxially stretched sheet having a temperature range of ° C. and a molded product thereof.

Description

  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 articles 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 with improved heat resistance include styrene-acrylic acid copolymer or styrene-methacrylic acid copolymer (Patent Document 1, Patent Document 2), styrene-maleic anhydride copolymer (Patent Document 3, Patent document 4) is mentioned. These are generally known as styrenic heat-resistant resins, and improve heat resistance without impairing transparency and rigidity.

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

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

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

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

US Patent No. 3035033 JP 2003-12734 A Japanese Patent Publication No.59-15133 JP-A-55-71530 JP 56-161409 A JP 2011-225866 A

  An object of the present invention is to provide a biaxially stretched sheet made of a styrene-based resin composition and a molded product thereof having excellent transparency, strength, film-forming property, and moldability, and excellent productivity, heat resistance, and oil resistance. It is to be.

  As a result of intensive studies on the components and composition of the styrene resin sheet in order to solve the above problems, the present inventors added a predetermined amount of a high molecular weight acrylic resin based on a styrene-methacrylic acid copolymer. The inventors have found that the purpose is achieved by using a resin, and have completed the present invention.

That is, the present invention is as follows.
(1) A biaxially stretched sheet comprising a styrene-based resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B), the styrene-methacrylic acid copolymer (A) and The mass ratio (A) / (B) to the acrylic resin (B) is 90/10 to 97/3, and the styrene-methacrylic acid copolymer (A) is composed of a styrene monomer unit and methacrylic acid. The monomer unit is contained in a mass ratio of 84/16 to 94/6, the acrylic resin (B) has a weight average molecular weight of 1,000,000 to 7,000,000, and the Vicat softening temperature of the styrene resin composition is A biaxially stretched sheet in the range of 106 to 132 ° C.

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

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

(4) The biaxial as described in (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. Stretched sheet.

(5) The impact-resistant styrene resin (C) containing the rubber component is 3% by mass or less based on the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B). Furthermore, the biaxially stretched sheet of any one of said (1)-(4) to contain.

(6) The biaxial stretching according to (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. Sheet.

(7) 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. 2. The biaxially stretched sheet according to item 1.

(8) The thickness is 0.1 to 0.7 mm, the longitudinal and lateral stretch ratios are both 1.8 to 3.2 times, and the longitudinal and lateral orientation relaxation stresses are both 0.3 to 1. The biaxially stretched sheet according to any one of (1) to (7), which is 2 MPa.

(9) A molded product 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.

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

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

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

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

  The weight average molecular weight (Mw) of the styrene-methacrylic acid copolymer (A) is 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 fluidity is excessive, and film forming properties such as sheet drawdown and neck-in are likely to be deteriorated. On the other hand, when the weight average molecular weight exceeds 250,000, the fluidity is insufficient, and the thickness of the film during film formation and the appearance of the sheet such as die lines are liable to deteriorate.

  The ratio Mw / Mn of 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. Moreover, it is preferable that ratio Mz / Mw of Z average molecular weight (Mz) and Mw is 1.5-2.0, More preferably, it is 1.6-1.9. 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: Polymer Laboratories PLgel 10 μm MIXED-B
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer

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

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

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

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

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

  Moreover, 40-100 degreeC is preferable, as for the glass transition point of acrylic resin (B), More preferably, it is 50-90 degreeC, More preferably, it is 60-80 degreeC. If the glass transition point is too low, the heat resistance may be lowered during mixing with the styrene-methacrylic acid copolymer (A). Moreover, when too high, an acrylic resin will become difficult to melt | dissolve at the time of mixing with the said styrene-methacrylic acid copolymer (A), and it may become difficult to mix uniformly.

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

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

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

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

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

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

  The content of the impact-resistant styrene resin (C) is 3% by mass with respect to the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) in order to maintain the appearance and transparency of the sheet. The following is preferable. Moreover, in order to give the improvement effect of the brittleness of a sheet | seat, and the blocking property of a container fully, it is 0.5 mass% or more with respect to the total amount of a styrene-methacrylic acid copolymer (A) and acrylic resin (B). It is preferable.

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

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

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

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

  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 is likely to occur during microwave heating. The Vicat softening temperature is preferably 108 ° C or higher, more preferably 110 ° C or higher. On the other hand, if the Vicat softening temperature exceeds 132 ° C., the workability during film formation and container molding may be reduced. The Vicat softening temperature is preferably 128 ° C. or lower, more preferably 126 ° C. or lower. The Vicat softening temperature was measured in accordance with JIS K7206 under conditions of a heating rate of 50 ° C./hr and a test load of 50N.

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 step or devolatilization step and granulation step of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B), and 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 | deviate from the Vicat softening temperature and transparency range 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-4methyl-1-decanol, 2- (1,5-dimethylhexyl)-(5,9-dimethyl) -1-decanol, and the like. 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'-thiodipropionate , Dilauryl-3,3′-thiodipropionate, ditetradecyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, dioctyl-3,3′-thiodipropionate, etc. Sulfur-based antioxidant, trisnonylphenyl phosphite, 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-ditridecyl) phosphite, (tridecyl) pentaerythritol diphosphite, bis ( Octadecyl) pentaerythritol diphosphite, bis (di-t-butylphenyl) pentaerythritol diphosphite, bis (di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, dinonylphenyloctylphosphonite, Tetrakis (2,4-di-t-butylphenyl 1,4-phenylene-diphosphonite, tetrakis (2,4-di-t-butylphenyl) 4,4′-biphenylene-di-phosphonite, 10-decyloxy-9,10-dihydro-9-oxa-10 -Phosphorus antioxidants such as 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 ratios in the machine direction and the transverse direction of the biaxially stretched sheet are both 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, the shrinkage rate at the time of thermoforming is too large, and the formability is impaired.
In addition, the measuring method of the draw ratio of this invention is as follows. A straight line Y having a length of 100 mm is drawn in the machine direction (MD) and the transverse direction (TD) 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

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

  The 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.), an antistatic agent (for example, various nonionic surfactants, cationic surfactants, anionic surfactants, etc.) You may apply | coat to both surfaces.

  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.

  There is no restriction | limiting in particular as a method of obtaining a molded article from the biaxially stretched sheet of this invention, The method currently used in the secondary forming method of the conventional biaxially stretched sheet can be used. For example, the secondary molding can be performed by a thermoforming method such as a vacuum forming method or a pressure forming method. These methods are described in, for example, “Plastic Processing Technology Handbook” edited by the Society of Polymer Science, Nikkan Kogyo Shimbun (1995). As a use of the molded product of the biaxially stretched sheet of the present invention, there are various containers, which can be widely used for packaging containers for various articles. Among these, a food packaging container for heating a microwave oven is particularly preferable because the features of the present invention are sufficiently exhibited.

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

(Experimental example 1) [Production of styrene-methacrylic acid copolymer (A-1)]
100 kg of pure water and 100 g of polyvinyl alcohol were added to an autoclave with an internal volume of 200 L and a stirrer, and the mixture was stirred at 130 rpm. Subsequently, 72.0 kg of styrene, 4.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, the temperature was raised to 110 ° C., and polymerization was performed for 5 hours (Step 1). Further, 4.0 kg of methacrylic acid was uniformly added over 2 hours from the time when the polymerization temperature reached 110 ° C. (Step 2). Further, the temperature was maintained 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 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 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 11) [Production of styrene-methacrylic acid copolymer (A-2 to 11)]
Various raw material charging amounts in Experimental Example 1 were adjusted to obtain various styrene-methacrylic acid copolymers (A-2 to 11) shown in Table 1.

(Experimental example 12) [Production of acrylic resin (B-1)]
In a separable flask (capacity 5 liters) equipped with a thermometer, a nitrogen introduction tube, a cooling tube and a stirrer, 300 parts by mass (3,000 g) of ion-exchanged water as a dispersion medium and 1.1 parts by mass of sodium dodecylbenzenesulfonate as an emulsifier In addition, 0.01 parts by mass of n-octyl mercaptan was added as a chain transfer agent, and 75 parts by mass of methyl methacrylate and 25 parts by mass of butyl acrylate were added as monomers. The atmosphere in the flask was replaced with nitrogen by passing a nitrogen stream through the separable flask. Next, the internal temperature was raised to 60 ° C., and 0.15 parts by mass of potassium persulfate and 5 parts by mass of deionized water were added. Thereafter, heating and stirring were continued for 2 hours to complete the polymerization, and an acrylic resin latex was obtained.
The obtained acrylic resin latex was cooled to 25 ° C., dropped into 500 parts by mass of 70 ° C. hot water containing 5 parts by mass of calcium acetate, and then heated to 90 ° C. for coagulation. The obtained coagulated product was separated and washed, and then dried at 60 ° C. for 12 hours to obtain an acrylic resin (B-1). It was 60 degreeC when the glass transition point of acrylic resin (B-1) was measured by the differential scanning calorimetry (DSC) according to the transition temperature measuring method of JISK7121: 2012 plastics.

(Experimental Examples 13 to 17) [Production of acrylic resin (B-2 to 6)]
The amounts of various monomers and chain transfer agents charged in Experimental Example 12 were adjusted to obtain various acrylic resins (B-2 to 6) shown in Table 2.

(Experimental example 18) [Production of impact-resistant styrenic resin (C-1)]
Using 3.4% by mass of low-cis polybutadiene rubber (trade name: Diene 55AS, manufactured by Asahi Kasei) as a rubbery polymer, dissolved in 91.6% 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 temperature was 140 ° C., and the rotation speed was 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 obtained resin liquid was heated to 230 ° C. and then sent to a devolatilization tank having a vacuum degree of 5 torr to separate and recover unreacted monomers and solvents. Then, after extracting with a gear pump from the devolatilization tank and making it a strand through a die plate, it pelletized through the water tank and collect | recovered as a product. The resin ratio of the obtained resin (C-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)}
Moreover, rubber component content in obtained resin (C-1) was 10.0 mass%, and the average rubber particle diameter was 2.0 micrometers.

(Experimental Examples 19 to 22) [Production of Impact Resistant Styrene Resin (C-2 to 5)]
Various raw material charging amounts of Experimental Example 18 were adjusted to obtain various impact-resistant styrene resins (C-2 to 5) shown in Table 3.

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

<Examples 2 to 19 and Comparative Examples 1 to 7>
The compounding amount of the resin of Example 1 and the extrusion conditions of the resin composition were adjusted, and biaxially stretched sheets described in Table 4, Table 5, and Table 7 were obtained.

<Examples 20 to 26>
The impact-resistant styrene 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 Example 1 was described. The pellets were obtained by an extruder and a styrene-based resin composition was obtained. Then, biaxially stretched sheets described in Tables 5 and 6 were obtained under the film forming conditions and stretching conditions described in Example 1.

<Examples 27 to 33>
After obtaining a resin composition comprising the styrene-methacrylic acid copolymer (A-1), acrylic resin (B-1), and impact-resistant styrene resin (C) of Example 21, Example 1 was described. Using a sheet extruder and a biaxial stretching machine, adjusting the lip opening during film formation, the stretching ratio, and the preheating temperature, the biaxially stretched sheet having the thickness, stretching ratio, and orientation relaxation stress described in Table 6 Obtained.

  About the obtained sheet | seat, various performance was measured by the method described below, and evaluation was performed. 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 4-7.

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

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

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

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

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

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

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

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

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

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

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

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

  From the results of Tables 4 to 7, Examples 1 to 33 all satisfy the provisions of the present invention, and film forming properties (film forming properties, fluidity, sheet appearance, stretchability), transparency, The sheet strength (rigidity, folding resistance), formability (moldability, mold stain resistance), heat resistance, oil resistance, and microwave heating resistance were all excellent.

  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-10), and is inferior in heat resistance and microwave heating resistance. Met. Since the comparative example 2 had much content of the methacrylic acid monomer unit in a styrene-methacrylic acid copolymer (A-11), it was inferior to fluidity | liquidity and a moldability. Since the weight average molecular weight of acrylic resin (B-6) was small, the comparative example 3 was inferior to microwave oven heat resistance. Since the comparative example 4 had little content of acrylic resin (B-1), it was inferior to microwave oven heat resistance. Comparative Example 5 did not contain the acrylic resin (B), and was inferior in microwave oven heat resistance and oil resistance. Since the comparative example 6 had much content of acrylic resin (B-1), the insolubilization material of acrylic resin generate | occur | produced as a gel, and it was inferior to fluidity | liquidity and a sheet | seat external appearance. In Comparative Example 7, the content of the methacrylic acid monomer unit in the styrene-methacrylic acid copolymer (A-2) is relatively small, and the butyl acrylate monomer unit in the acrylic resin (B-4). Since the content of is relatively large and the blending ratio of the acrylic resin (B-4) is slightly large, the Vicat softening temperature is low, and the heat resistance and the microwave oven heat resistance are poor.

Claims (10)

A biaxially stretched sheet comprising a styrene resin composition containing a styrene-methacrylic acid copolymer (A) and an acrylic resin (B),
The mass ratio (A) / (B) of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B) is 90/10 to 97/3,
The styrene-methacrylic acid copolymer (A) contains a styrene monomer unit and a methacrylic acid monomer unit in a mass ratio of 84/16 to 94/6,
The acrylic resin (B) has a weight average molecular weight of 1 million to 7 million,
A biaxially stretched sheet in which the Vicat softening temperature of the styrene-based resin composition is in the range of 106 to 132 ° C.   The biaxially stretched sheet according to claim 1, wherein the styrene-methacrylic acid copolymer (A) has a weight average molecular weight of 120,000 to 250,000.   The 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 according to 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.   Further containing an impact-resistant styrene resin (C) containing a rubber component at a ratio of 3% by mass or less with respect to the total of the styrene-methacrylic acid copolymer (A) and the acrylic resin (B). The biaxially stretched sheet according to any one of claims 1 to 4.   The biaxially stretched sheet according to claim 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.   The content of unreacted styrene monomer in the styrenic resin composition is 1000 ppm or less, and the content of unreacted methacrylic acid monomer is 150 ppm or less. Axial stretched sheet.   The thickness is 0.1 to 0.7 mm, the longitudinal and lateral stretching ratios are both 1.8 to 3.2 times, and the longitudinal and lateral orientation relaxation stresses are both 0.3 to 1.2 MPa. The biaxially stretched sheet according to any one of claims 1 to 7.   The molded article which consists of a biaxially stretched sheet of any one of Claims 1-8.   The molded article according to claim 9, which is a food packaging container for heating in a microwave oven.