JP2017031324A - Manufacturing method of aromatic vinyl-based resin biaxially oriented sheet and molded article and food package material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aromatic vinyl-based resin biaxially oriented sheet and a molded article, excellent in oil resistance, heat resistance, transparency and mechanical strength and good in sheet productivity at high speed.SOLUTION: There are provided an aromatic vinyl-based resin biaxially oriented sheet containing a copolymer (A) of an aromatic vinyl monomer and a vinyl cyanide monomer as an essential component, where the copolymer (A) has percentage of vinyl cyanide monomer in the copolymer of 25 mass% to 40 mass%, total content of the monomer or an oligomer of 17,000 ppm or less and heat shrinkage stress of the biaxially oriented sheet is in a range of 0.45 to 1.0 MPa in a lengthwise direction and a crosswise direction respectively and a molded article thereof.SELECTED DRAWING: None

Description

  The present invention relates to an aromatic vinyl-based resin biaxially stretched sheet and a molded product thereof that give a molded product that can be suitably used as a food packaging material because of excellent oil resistance, heat resistance, mechanical strength, and transparency.

Aromatic vinyl resin biaxially stretched sheets are often used for packaging lightweight food packaging containers and other items for reasons such as environmental hygiene, waist strength, transparency, moldability, and excellent recoverability. Yes. In particular, in recent years, convenience stores and the like are increasing the number of bento and side dishes that are heated in a microwave oven together with the container. Since lunch boxes and side dishes often contain oil-based foods, a sheet with better heat resistance and oil resistance is desired.
Among aromatic vinyl resins, styrene-methacrylic acid copolymer resins have been used in microwave oven containers because they are superior in oil resistance and heat resistance compared to general-purpose polystyrene. However, although the styrene-methacrylic acid copolymer resin can control heat resistance and oil resistance by the blending ratio of the comonomer, it is easy to gel and fluidity is lowered with improvement in heat resistance and oil resistance. In terms of productivity and aptitude for use as described above, there was a limit to oil resistance. In recent years, heating in a microwave oven has changed from `` warming '' to `` cooking '', the heating time has been extended, and the contents have also diversified, so depending on the type of oil contained in some foods, The styrene-methacrylic acid copolymer resin sheet may not satisfy the required oil resistance performance, and a sheet with higher oil resistance is required.
For this reason, a biaxially stretched sheet of a copolymer of a vinyl cyanide monomer and an aromatic vinyl monomer has been proposed as a method for improving the oil resistance of an aromatic vinyl resin biaxially stretched sheet (for example, Patent Documents). 1-3).

  Patent Document 1 describes a sheet obtained by stretching a styrene-acrylonitrile copolymer 1.5 to 20 times at a stretching speed of 5 to 40% / second. Patent Document 2 describes a composition sheet of a styrene-acrylonitrile copolymer and a styrene-acrylonitrile graft rubber. Patent Document 3 describes a method for improving the stretch processability of a styrene-acrylonitrile copolymer.

Japanese Patent Laid-Open No. 2001-104589 JP-A-50-74649 JP-A-10-007817 U.S. Pat. No. 3,213,854

Patent Document 1 describes a sheet obtained by stretching a styrene-acrylonitrile copolymer 1.5 to 20 times at a stretching speed of 5 to 40% / second. However, it is described that the resin used in this method is inferior in stretching stability at a stretching rate of 50% / second. For example, a tenter stretching method, a roll stretching method, a bubble stretching method, etc. are known as the sheet stretching method. For sequential biaxial stretching, the sheet flow direction (longitudinal direction) stretching (roll stretching) depending on the speed ratio between the rolls. And a method in which the flow direction by the tenter and the stretching in the vertical direction (lateral direction) are combined are often employed. In order to improve the productivity of the sheet, it is necessary to increase the longitudinal stretching speed in these methods, and it is difficult to say that the stretching speed of 40% / second is suitable for industrial production.
One factor that reduces the sheet production rate (stretching rate) includes adhesion of foreign matter to the extruder, die, and stretching roll, and adhesion of dirt on the sheet surface. Contamination on these production equipment and sheets is thought to be caused by bleeding out of additives such as plasticizers and lubricants added to improve the appearance of the sheet, and unreacted monomers and oligomers contained in the resin. It is done. Impurities in these resins may reduce the heat resistance of the sheet.
Patent Document 2 describes a composition sheet of a styrene-acrylonitrile copolymer and a styrene-acrylonitrile graft rubber. Patent Document 2 is intended to improve the slipperiness of a styrene resin biaxially stretched sheet by adding graft rubber. The technical disclosure on the improvement of sheet strength, heat resistance, oil resistance, and productivity is as follows. Not done. Further, Patent Document 4 exemplified as a sheet manufacturing method of Patent Document 2 relates to a simultaneous biaxial tenter stretching method, which is difficult to say as a general-purpose stretched sheet manufacturing method.
Patent Document 3 describes a method for improving the stretch processability of a styrene-acrylonitrile copolymer. This is a blend of styrene-acrylonitrile copolymer with polycaprolactone, but this method adds polycaprolactone to lower the heat resistance of the resin composition to give low temperature stretchability and improve stretch processability. ing. Since this method reduces the heat resistance of the resin composition, the heat resistance of the sheet may be insufficient.

  In view of the above situation, the object of the present invention is to improve the stretch processability of a copolymer of an aromatic vinyl monomer and a vinyl cyanide monomer, to enable high-speed sheet production, oil resistance, heat resistance, mechanical An aromatic vinyl-based resin biaxially stretched sheet having excellent strength and a secondary molded product thereof are provided.

As a result of intensive investigations to solve the above problems, the present inventors have used a copolymer of an aromatic vinyl monomer and a cyanidated vinyl monomer having a specific composition to obtain a sheet having a specific heat shrinkage stress. The present inventors have found that a sheet that can solve the above problems and a molded product thereof can be provided, and have completed the present invention.
That is, the present invention is as follows.

[1] A biaxially stretched sheet comprising a copolymer (A) of an aromatic vinyl monomer and a vinyl cyanide monomer as an essential component, wherein the copolymer (A) is vinyl cyanide in the copolymer. The monomer ratio is from 25% by mass to 40% by mass, the total monomer or oligomer content is 17,000 ppm or less, and the heat shrinkage stress of the biaxially stretched sheet is 0.45 to 1 in the machine direction and the transverse direction, respectively. An aromatic vinyl-based resin biaxially stretched sheet characterized by being in the range of 0.0 MPa.
[2] The aromatic vinyl resin biaxially stretched sheet according to [1], wherein the total content of monomers or oligomers is 10,000 ppm or less.
[3] The resin constituting the biaxially oriented sheet is a graft of a copolymer of an aromatic vinyl monomer and a vinyl cyanide monomer (A), and a mixture of an aromatic vinyl monomer and a vinyl cyanide monomer on a rubber polymer. One or more graft copolymer compositions (B1) selected from a polymerized graft copolymer composition (B1) or a graft copolymer composition (B2) obtained by graft-polymerizing an aromatic vinyl monomer to a rubbery polymer The aromatic vinyl according to [1] or [2], wherein the gel content in 100% by mass of the resin constituting the biaxially stretched sheet is 0.1 to 0.9% by mass. -Based resin biaxially oriented sheet.
[4] The aromatic vinyl resin biaxially stretched sheet according to [3], wherein the rubbery polymer in the graft copolymer composition (B1) has a volume average particle diameter of 0.5 to 5 μm.
[5] The aromatic vinyl resin biaxially stretched sheet according to [3], wherein the rubbery polymer in the graft copolymer composition (B2) has a volume average particle diameter of 1 to 5 μm.
[6] The heat shrinkage stress in the machine direction and the transverse direction of the biaxially oriented sheet is in the range of 0.5 to 0.8 MPa, and the average of the heat shrinkage stress in the machine direction and the transverse direction is 0.55 to 0.75 MPa. The aromatic vinyl resin biaxially stretched sheet according to any one of [1] to [5].
[7] Aromatic vinyl resin biaxial stretching according to any one of [1] to [6], wherein the thermal shrinkage rate is 2% or less when the biaxially stretched sheet is left in warm air at 105 ° C. for 10 minutes. Sheet.
[8] A molded product obtained by secondary molding of the aromatic vinyl resin biaxially stretched sheet according to any one of [1] to [7].
[9] The molded article according to [8], wherein the molded article is a food packaging material containing vegetable oil or animal oil.

  The aromatic vinyl resin biaxially stretched sheet of the present invention can be produced at a high speed, and a molded product excellent in heat resistance, oil resistance and mechanical strength can be obtained from the sheet. Thereby, it can use suitably as various lightweight packaging containers, especially a packaging material of oil-based foodstuffs.

Hereinafter, the present invention will be described in detail.
The present invention is a biaxially stretched sheet comprising a copolymer (A) of an aromatic vinyl monomer and a vinyl cyanide monomer as an essential constituent component, and a copolymer of an aromatic vinyl monomer and a vinyl cyanide monomer (A ) Is characterized in that the proportion of the vinyl cyanide monomer in the copolymer is 25 to 40% by mass and the total content of monomers or oligomers is less than 17,000 ppm.
In the present invention, examples of the aromatic vinyl monomer include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, and pt-butylstyrene. Among these, styrene and α-methylstyrene are preferable from the viewpoint of practical physical properties and productivity. These may be used alone or in combination of two or more.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, and ethacrylonitrile. Among these, acrylonitrile is preferable from the viewpoint of practical properties and productivity. These may be used alone or in combination of two or more.

The total monomer or oligomer content in the biaxially stretched sheet is preferably less than 17,000 ppm, preferably less than 10,000 ppm from the viewpoints of heat resistance, sheet productivity (roll dirt), and high-speed stretchability. Is more preferable, and it is still more preferable that it is less than 6,000 ppm.
The total content of the monomer or oligomer can be measured by gas chromatography. Specifically, it can be measured by the method described in Examples described later.
As used herein, the term “oligomer” refers to a dimer or trimer component composed of an aromatic vinyl monomer, a vinyl cyanide monomer, and other copolymerizable monomers, each monomer alone or in combination.
The ratio of the vinyl cyanide monomer in the copolymer (A) used in the present invention is preferably 25% by mass to 40% by mass from the viewpoint of oil resistance at high temperature and the color tone, and 25% by mass to 35% by mass. % Is more preferable, and it is still more preferable that it is 28 mass% to 35 mass%.

  In order to improve sheet strength and prevent blocking of the sheet, the aromatic vinyl-based resin biaxially stretched sheet of the present invention has the above copolymer (A), a rubbery polymer and an aromatic vinyl monomer and cyanide. One or more graft copolymers selected from a graft copolymer composition (B1) obtained by graft polymerization of a mixture of vinyl monomers, or a graft copolymer composition (B2) obtained by graft polymerization of an aromatic vinyl monomer to a rubber polymer. The polymer composition (B) can be mixed.

The gel content in the mixed resin of (A) and (B) can be measured by dissolving the sheet in a solvent and measuring directly from the solvent insoluble matter, or (A) and (B) the graft copolymer before mixing the resin. The composition (B) can be dissolved in a solvent, the solvent insoluble content in the resin (B) can be measured, and the calculation can be obtained from the mixed composition ratio of (A) and (B). The gel content referred to in the present invention is a mass ratio of a solvent-insoluble component in the mixed resin containing the copolymer (A) and the graft copolymer composition (B), and is also referred to as a gel fraction. It is calculated from the following.
Gel content (mass%) = solvent insoluble mass / sample mass before dissolution × 100
In this invention, the solvent insoluble content in 100 mass% of resin which comprises a biaxially stretched sheet is defined as a gel.
As the solvent, 2-butanone is used.

As for gel content, 0.1-0.9 mass% is preferable in 100 mass% of resin which comprises a biaxially stretched sheet, More preferably, it is 0.2-0.7 mass%. By making gel content into a preferable range, the transparency deterioration of the sheet | seat obtained can be suppressed and sheet strength improvement effect, an antiblocking effect, etc. can be provided.
The amount of the graft polymer in the graft copolymer composition (B) is preferably 15 to 40% by mass, more preferably 20 to 30% by mass. When the amount of the graft polymer is 15% by mass or more, the sheet can be prevented from blocking and the strength can be improved. Moreover, the transparency of a sheet | seat can be maintained as it is 40 mass% or less.

  The graft copolymer composition (B1) that can be preferably used in the present invention comprises a graft polymer obtained by grafting an aromatic vinyl monomer, a vinyl cyanide monomer, and, if necessary, other copolymerizable monomers to a rubbery polymer. , A copolymer of an aromatic vinyl monomer and a vinyl cyanide monomer that are simultaneously formed, and, if necessary, other copolymerizable monomers.

  As the rubber polymer, any of diene rubber, acrylic rubber, ethylene rubber and the like can be used. Examples of the rubber polymer include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methacrylic acid. Methyl copolymer, butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, ethylene -A methyl acrylate copolymer etc. are mentioned. Among these, polybutadiene, a styrene-butadiene copolymer, a styrene-butadiene block copolymer, and an acrylonitrile-butadiene copolymer from the viewpoint that sufficient impact resistance can be easily obtained in the biaxially stretched sheet of the present embodiment. Is preferred. These may be used alone or in combination of two or more.

  Examples of the aromatic vinyl monomer to be graft-polymerized include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, o-ethylstyrene, p-ethylstyrene, pt-butylstyrene, and the like. Among these, styrene and α-methylstyrene are preferable from the viewpoint of practical physical properties and productivity. These may be used alone or in combination of two or more.

  Examples of the vinyl cyanide monomer to be graft-polymerized include acrylonitrile, methacrylonitrile, ethacrylonitrile and the like. Among these, acrylonitrile is preferable from the viewpoint of practical properties and productivity. These may be used alone or in combination of two or more.

  Other copolymerizable monomers used in obtaining the graft copolymer, and other copolymerizable monomers used in the above-mentioned copolymer are, for example, acrylic monomers, N-phenylmaleimide, maleic anhydride Etc. These may be used alone or in combination of two or more.

  The rubbery polymer contained in the graft copolymer composition (B1) preferably has a volume average particle size of 0.5 to 5 μm. More preferably, it is 0.5-3 micrometers. When the volume average particle diameter is 0.5 μm or more, the slipperiness of the sheet is improved, which is effective for preventing blocking and improving strength. Moreover, the favorable transparency of a sheet | seat can be maintained as it is 5 micrometers or less.

  Among these, the graft copolymer composition (B1) is preferably an ABS resin made of styrene, acrylonitrile and a rubbery polymer from an industrial viewpoint.

  In the graft copolymer composition (B2) that can be preferably used in the present invention, a rubber polymer particle is dispersed in a matrix of an aromatic vinyl resin, and an aromatic vinyl monomer is dispersed in the presence of the rubber-like polymer. It can be produced by polymerization.

  Examples of the aromatic vinyl monomer constituting the aromatic vinyl resin include styrene, alkylated styrene such as α-methylstyrene, p-methylstyrene, and ethylstyrene, halogenated styrene such as bromostyrene and chlorostyrene, and styrene derivatives. Is mentioned. Among these, styrene and α-methylstyrene are preferable from the viewpoint of practical physical properties and productivity. These aromatic vinyl monomers can be used alone or in combination of two or more.

Examples of the rubbery polymer include polybutadiene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer. As the polybutadiene, either high-cis polybutadiene or low-cis polybutadiene can be used. As the styrene-butadiene copolymer, either a random structure or a block structure can be used. These rubber polymers can be used alone or in combination of two or more.
Further, the graft copolymer composition (B2) may be obtained by copolymerizing one or more acrylic monomers such as methyl (meth) acrylate and butyl (meth) acrylate as necessary.

  The rubbery polymer contained in the graft copolymer composition (B2) preferably has a volume average particle size of 1 to 5 μm. More preferably, it is 1.5-4 micrometers. When the volume average particle diameter is 1 μm or more, the slipperiness of the sheet is improved, which is effective for preventing blocking and improving strength. Moreover, the favorable transparency of a sheet | seat can be maintained as it is 5 micrometers or less.

Among these, the graft copolymer composition (B2) is preferably an impact-resistant polystyrene resin composed of styrene and butadiene or a styrene-butadiene copolymer from an industrial viewpoint.
The graft copolymer composition (B) can be used by selecting one or more of the above-mentioned (B1) or (B2), or (B1) and (B2) may be used in combination. Good. When emphasizing the transparency of the sheet, (B1) is preferable, and when emphasizing the slipperiness and blocking prevention of the sheet, (B2) is preferable.

  The volume average particle diameter of the rubber polymer can be determined by observing the graft copolymer composition (B) or the aromatic vinyl resin biaxially stretched sheet with osmium tetroxide or the like by observation with an electron microscope. Since the rubber particles in the aromatic vinyl resin biaxially stretched sheet are deformed by stretching, the sheet is heat-treated at a temperature of 160 ° C. or more for 30 minutes or more to relax the orientation, and then the volume average particle diameter It is good to measure.

  If necessary, the resin composition constituting the biaxially stretched sheet of the present invention includes other resins and additives such as lubricants, antiblocking agents, antioxidants, ultraviolet absorbers, mold release agents, antifogging agents, and antistatic agents. Agents, plasticizers such as liquid paraffin, dyes, pigments, various fillers and the like may be added.

  In the present invention, the heat shrinkage stress of the stretched sheet measured in accordance with ASTM D1504 of the aromatic vinyl resin biaxially stretched sheet is 0. 0 in each of the sheet flow direction (longitudinal direction) and its vertical direction (lateral direction). 45-1,0 MPa. When the heat shrinkage stress is 0.45 MPa or more, a sheet with less sheet thickness unevenness can be obtained. Further, when the heat shrinkage stress is 1.0 MPa or less, the secondary formability is improved. Among them, the heat shrinkage stress is preferably 0.5 to 0.8 MPa in the vertical direction and the horizontal direction, respectively, and the average value is preferably 0.55 to 0.75 MPa. A sheet with particularly small thickness unevenness at a stretching speed and a stretching ratio described later by stretching so that the heat shrinkage stress in the longitudinal direction and the transverse direction is 0.5 MPa or more and the average value is 0.55 MPa or more, respectively. Is obtained. In addition, a sheet having a vertical and horizontal heat shrinkage stress of 0.8 MPa or less and an average value of 0.75 MPa or less is used in a mold having a complicated shape or a deep drawing ratio when the sheet is secondarily formed. In addition, it is possible to obtain a sheet in which molding whitening hardly occurs.

  In addition, when an aromatic vinyl-based resin biaxially stretched sheet is formed into a container lid, and the lid is used for a lid of an oil-based food packaging container heated by a microwave oven, the sheet is heated under 105 ° C. It is preferable that the shrinkage rate when left for 10 minutes is 2% or less. The 2% shrinkage temperature of 105 ° C. or more of the sheet is a preferable region for preventing deformation of the lid due to water vapor generated from the contents or a small amount of scattered oil by heating in the microwave oven.

The aromatic vinyl-based resin biaxially stretched sheet of the present invention can be produced by extruding the resin or composition prepared as described above from a die after melt-kneading and biaxially stretching in the longitudinal and lateral directions.
The stretching method is not particularly limited, such as simultaneous biaxial stretching by the tenter method, sequential biaxial stretching, bubble method stretching, etc., but the unstretched sheet extruded from the T-die is subjected to the speed difference between rolls and the tenter. The utilized method of sequential biaxial stretching is preferred from the viewpoint of productivity.
The draw ratio can be adjusted according to the purpose, but in the present invention, the draw ratio in the longitudinal direction and the transverse direction is preferably in the range of 1.8 to 3.5 times, respectively. A preferable range of the draw ratio is a region that can be stably stretched over a wide temperature range. As a result, it is possible to impart mechanical strength and good secondary formability to the obtained sheet and its molded product. Among them, the draw ratio is more preferably 2.0 to 3.0 times.

  In the sequential biaxial stretching, the longitudinal stretching step is generally a method in which stretching is performed depending on the speed difference of the roll, and is also a preferred method in the present invention. The stretching temperature in the longitudinal stretching step is preferably from the Vicat softening point (VSP) to VPS + 40 ° C. of the copolymer (A) from the viewpoint of film formation stability, and from the viewpoint of balancing the strength and secondary formability of the sheet, VSP + 10 ° C. -VSP + 35 degreeC is more preferable. The Vicat softening point can be measured according to JIS K7206.

  The stretching speed is preferably 50 to 800% / second, more preferably 55 to 600% / second, and further preferably 60 to 400% / second, from the viewpoints of stretched film formation stability and high-speed sheet productivity. .

  The transverse stretching step is preferably performed at a stretching speed of 1 to 50% / second by the tenter method at the same temperature range as the longitudinal stretching step, more preferably 2 to 40% / second.

An antifogging agent, an antistatic agent, and silicone oil can be appropriately applied to the surface of the aromatic vinyl resin biaxially stretched sheet. In the present invention, it is preferable to apply silicone oil from the standpoint that various effects such as the sheet blocking property, the releasability of the secondary molded product, and the scratch resistance improving effect become remarkable. In particular, in the present invention, even when silicone oil is applied to the sheet surface, the appearance of the secondary molded product is excellent.
The amount of silicone oil applied is not particularly limited, but it is preferable to apply at least one surface in the range of 5 to 100 mg / m ^{2 in} order to exhibit the above sheet performance. Further, as the silicone oil, polydimethylsiloxane is preferable because it does not easily attack the surface of the sheet during high temperature molding.

Moreover, when using a secondary molded product as a food packaging material, it is preferable to apply a silicone oil on one side and an antifogging agent on the other side. In the present invention, when silicone oil is applied to one surface and an antifogging agent is applied to the other surface, various effects such as sheet blocking property, improvement of releasability of secondary molded products, and improvement of scratch resistance are obtained. This maintains the antifogging property of the secondary molded product. Although the application amount of the antifogging agent is not particularly limited, in order to exhibit the above sheet performance, it is preferable to apply at least one side in the range of 10 to 100 mg / m ² . As the antifogging agent, known surfactants can be used, and polyhydric alcohol fatty acid esters (sucrose fatty acid ester, polyglycerin fatty acid ester, etc.) are particularly preferable. An oxyethylene polyoxypropylene block copolymer and the like) and a mixture of two or more of polysaccharides (such as methylcellulose and cyclodextrin) are particularly preferred. When applying these, it is preferable to perform a corona treatment so that the contact angle of the sheet surface with water is 20 ° to 80 °. Moreover, the oil resistance of a sheet | seat may improve further by apply | coating an anti-fogging agent composition.

  The aromatic vinyl resin biaxially stretched sheet of the present invention preferably has a stretched sheet thickness of 0.1 to 0.5 mm from the viewpoint of easy secondary molding, particularly 0.15 to 0. Preferably it is in the range of 4 mm. In addition, the said sheet | seat may laminate | stack the same kind or a different kind of thermoplastic resin by coextrusion, dry lamination, etc. as needed. When the aromatic vinyl resin biaxially stretched sheet of the present invention is laminated on the same or different thermoplastic resin sheet surface, a thickness of 0.01 to 0.1 mm may be preferable.

  The use of the aromatic vinyl resin biaxially oriented sheet of the present invention is not particularly limited, but from the viewpoint of excellent oil resistance, heat resistance and image clarity of the molded product, the aromatic vinyl resin 2 of the present invention The axially stretched sheet is secondarily formed into a desired container shape by hot plate pressure air vacuum forming method (direct heating method), pressure air forming method, vacuum pressure air forming method (indirect heating method), and suitably used as a food packaging material. Can do. Because of its particularly good oil resistance, food containers such as lunchboxes and prepared dishes containing vegetable oils and animal oils and ingredients for cooking, and food containers for cooking these foods in a microwave oven Suitable for lids and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention should not be limited to the scope of these examples. Hereinafter, “part” and “%” are based on mass unless otherwise specified.

[Melt flow rate]
Based on ISO 1133, the measurement was performed under conditions of a temperature of 220 ° C. and a load of 10 kg.

[Total content of monomer or oligomer]
The total content of residual monomers or oligomers contained in the resins produced in Examples and Comparative Examples described below were measured under the following conditions and equipment.
Sample: The prepared sheet was cut to obtain a sample for measuring the total content of monomers or oligomers.
Measuring device: GC-1700 manufactured by Shimadzu Corporation
Column used: TC-1 φ0.32mm × 30m × 0.25μm
Carrier gas: Nitrogen (1.3mL / min)
Split ratio: (1: 5)
Linear velocity: 23 cm / sec
Column pressure 42 kPa
Total flow rate 11mL / min
Injection volume 0.8μL
Set temperature INJ / DET = 230 ℃ / 300 ℃
Temperature increase program 45 ° C. (held for 5 minutes) → Temperature increased to 90 ° C. at 10 ° C./min. → The temperature was raised to 190 ° C at 30 ° C / min. → The temperature was raised to 220 ° C at 10 ° C / min. → The temperature was raised to 300 ° C at 50 ° C / min.
The total monomer or oligomer content was calculated using a calibration curve prepared in advance for the monomer species or oligomer species to be measured.

[Volume average particle diameter]
The volume average particle diameter of the rubbery polymer was determined as follows.
The volume average particle size is obtained by embedding the copolymer composition (B) in an epoxy resin and dyeing it with a staining agent such as osmium tetroxide or ruthenium tetroxide to produce an ultrathin section, and a transmission electron microscope. (TEM) Observation, photographing an arbitrary range of 10 μm × 10 μm of the ultrathin slice, the stained part is observed as the rubber polymer part, the volume average particle diameter of the dyed part is measured, and the rubber polymer The volume average particle diameter was used.

[Gel content]
The composition consisting of (A) and (B) is dissolved in 2-butanone and separated into 2-butanone soluble and insoluble by a centrifuge. The 2-butanone-insoluble component at this time is a rubber polymer and a component (graft component) graft-reacted with the rubber polymer, and is defined as gel.

[Sheet thickness uniformity]
The sheet thickness was continuously measured with a β-ray continuous thickness meter manufactured by Yokogawa Electric Co., Ltd. installed in the sheet stretching line, and the sheet thickness uniformity was evaluated based on the thickness variation according to the following criteria.
○: Sheet thickness variation range is less than 24% with respect to sheet average thickness. Δ: Sheet thickness variation range is from 24% to less than 29% with respect to sheet average thickness. X: Sheet thickness variation range is with respect to sheet average thickness. 29% or more

[Stability of sheet longitudinal stretching]
The width of the uniaxially stretched sheet coming out of the sheet longitudinal stretching machine, the occurrence of notches, and the like, and the presence or absence of sheet cracking due to slippage of the clip at the tenter inlet were evaluated.
A: Stable longitudinal uniaxial stretching is obtained, and stable tenter stretching is possible.
○: Width variation may occur in a uniaxially stretched sheet, and sheet cracking occurred in rare cases.
Δ: Many width fluctuations and notches occurred in the uniaxially stretched sheet, and many sheet cracks occurred in the tenter.
X: Tenter stretching is impossible with a uniaxially stretched sheet, with severe width fluctuations and notches.

[Sheet roll dirt]
When the test resin composition was supplied to an extruder and extruded from a T-die to form a stretched film, the stain on the casting roll and the transfer of the stain to the sheet were evaluated according to the following criteria.
○: No stain on the casting roll even after continuous film formation for 3 hours or more, and no transfer of the stain to the sheet.
Δ: The casting roll is soiled at the time of continuous film formation for 3 hours, but the soil is not transferred to the sheet.
X: The casting roll was soiled within 3 hours and transferred to the sheet.

[Sheet ORS]
The heat shrinkage stress (ORS) of the sheet was measured as a peak stress value according to ASTM D-1504.

[Heat resistance of sheet]
The sheet cut out to 10 cm × 10 cm was left in a hot air dryer for 10 minutes, and the heat resistance was evaluated from the temperature at which the thermal shrinkage rate in either the vertical direction or the horizontal direction was 2%. When this temperature is 105 ° C. or higher, it indicates that the thermal contraction rate when left in a warm air of 105 ° C. for 10 minutes is 2% or less.

[Folding strength of sheet]
The folding strength of the sheet was measured according to JIS P8115, and the average value in the vertical and horizontal directions was determined.

[Shock resistance of sheet]
For the impact resistance of the sheet, the DART impact strength was measured in accordance with JIS K7124.

[Transparency of sheet]
The transparency of the sheet was evaluated by HAZE measured according to JIS K7136.

[White sheet forming]
The sheet was opened 100 × 100 mm, depth 30 mm, 27 mm, 24 mm with a single hot plate pressure vacuum forming machine in which the hot plate temperature was adjusted to the Vicat softening point of the copolymer (A) constituting the sheet +20 to 40 ° C. The container was thermoformed. The obtained molded products of three types of depth were visually observed, and the molded products molded at the maximum temperature at which no raindrop occurred were checked for the presence or absence of whitening and evaluated according to the following criteria.
A: Whitening does not occur in containers of all depths.
○: The container with a depth of 30 mm is whitened, but the container with a depth of 27 mm or less is not whitened.
Δ: Containers with a depth of 27 mm or more are whitened, but containers with a depth of 24 mm or less are not whitened.
X: All containers are whitened.

[Oil resistance at high temperatures]
Using a single hot plate pressure air vacuum forming machine, produce a molded product with a drawing of 0.3, put 5 g of MCT oil (trade name White F-1, manufactured by Fuji Seiki) into the molded product, and dry at 60-100 ° C The sample was left in the machine for 5 minutes, and the state was observed (observed in increments of 5 ° C.) to determine the maximum temperature at which no whitening occurred.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples.
Raw materials used in Examples and Comparative Examples

<Copolymer resin (A)>
(A-1) AS resin comprising 30% by mass of acrylonitrile and 70% by mass of styrene, a melt flow rate of 27 g / 10 min, and a total monomer or oligomer content of 4,600 ppm (A-2) 34% by mass of acrylonitrile AS resin consisting of 66% by mass of styrene, a melt flow rate of 10 g / 10 min, and a total monomer or oligomer content of 2,700 ppm. (A-3) 29% by mass of acrylonitrile, 71% by mass of styrene, AS resin having a flow rate of 9 g / 10 min and a total monomer or oligomer content of 15,500 ppm (A-4) Consisting of 21% by mass of acrylonitrile and 79% by mass of styrene, melt flow rate of 12 g / 10 min, monomer Or an AS tree with a total oligomer content of 14,500 ppm (A-5) Ceviane N-080SF (trade name: AS manufactured by Daicel) comprising 31% by mass of acrylonitrile and 69% by mass of styrene, having a melt flow rate of 18 g / 10 min and a total monomer or oligomer content of 20,900 ppm Resin).

<Graft copolymer>
(B-1) The volume average particle diameter of the rubber polymer is 0.73 μm, the soluble content is 79% by mass, the insoluble content is 21% by mass, the soluble content is 26% by mass of acrylonitrile, 74% by mass of styrene, ABS resin having a reduced viscosity of 0.54 m 3 / kg and an insoluble content of 10% by mass of acrylonitrile, 35% by mass of styrene, and 55% by mass of butadiene.
(B-2) The volume average particle diameter of the rubber polymer is 1.8 μm, the soluble content is 75 mass%, the insoluble content is 25 mass%, the soluble content is polystyrene, and the insoluble content is 68 mass% of styrene. , 32 mass% HIPS resin of butadiene.

Example 1
A composition obtained by mixing 98 parts of the copolymer resin (A-1) and 2 parts of the graft copolymer composition (B-1) with a turn blender was melt-mixed with an extruder. This was extruded from a T die to produce a sheet having a thickness of about 1.55 mm. Next, the sheet extruded from the T-die is continuously stretched 2.5 times at a stretching speed of 200% / second and a roll temperature (set value) of 129 ° C. using a biaxial stretching apparatus, and then the atmospheric temperature ( Setting value) A sheet having a thickness of 0.25 mm was obtained by stretching 2.5 times with a tenter at 138 ° C. at a stretching speed of 12.5% / second. Next, corona treatment was applied to both surfaces of the sheet, 20 to 30 mg / m ² of silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KM-9373A”) on one surface of the sheet, and 30 to 40 mg / m on the other surface. ² sucrose lauric acid ester (made by Riken Vitamin, trade name “Riquemar A”) was applied. The corona treatment strength was adjusted by adjusting the output of the high frequency power supply so that the silicone oil coated surface had a contact angle with water contact of 60 to 70 ° and the opposite surface was 35 to 45 °. The evaluation results of the sheet are shown in Table 1. MD represents the longitudinal (roll) stretching direction, and TD represents the lateral (tenter) stretching direction.

Examples 2-9
Copolymer resins (A) of the type shown in Table 1 and graft copolymer composition (B) are melt-mixed at the ratios shown in Table 1, melt-extruded in the same manner as in Example 1, and stretching temperature settings and stretching shown in Table 1 Stretching was performed at a magnification to obtain a sheet having a thickness of 0.25 mm. The sheet thickness before stretching and the stretching speed were adjusted in proportion to the stretching ratio. The evaluation results of the sheet are shown in Table 1. About Examples 1-9, the excellent result was obtained in each evaluation test.

Comparative Examples 1-4
A copolymer resin (A) of the type shown in Table 2 and a graft copolymer composition (B) were melt-mixed at the ratio shown in Table 2, melt-extruded in the same manner as in Example 1, and the stretching temperature setting shown in Table 2; It extended | stretched by the draw ratio. In Comparative Example 3, the sheet thickness before stretching was about 0.65 mm, and in Comparative Example 4, the sheet thickness before stretching was about 3.6 mm. The stretching speed was adjusted in proportion to the stretching ratio. The evaluation results of the sheet are shown in Table 2.

Comparative Examples 5 and 6
A commercially available polystyrene biaxially stretched sheet (thickness: 0.25 mm) was used to evaluate the heat resistance, folding strength, impact strength, transparency, whitening of the sheet, and oil resistance at high temperatures. The results are shown in Table 2.
As for the commercially available sheet used, Comparative Example 5 is Sandic Sheet 905 (trade name: manufactured by Sandic), and Comparative Example 6 is Sandic Sheet 210 (trade name: manufactured by Sandic).

Comparative Example 1 is an example in which the vinyl cyanide monomer in the copolymer (A) is less than 25% by mass, and the high temperature oil resistance is inferior to the examples. Comparative Example 2 is an example in which the total content of the monomer or oligomer of the copolymer (A) exceeds 17,000 ppm, and the roll soiling at the time of longitudinal stretching was severe, and the heat resistance of the sheet was inferior. Further, the composition of Comparative Example 2 lacked the stretching stability in the longitudinal stretching, and the phenomenon that the sheet on the stretching roll was partially broken also occurred. Thus, Comparative Example 2 was inferior in stretchability at high speed as compared with Examples, and stable sheet production at high speed was difficult. Comparative Example 3 is an example when the draw ratio is too low, and Comparative Example 4 is an example when the draw ratio is too high.
Comparative Examples 5 and 6 are examples of commercially available styrenic resin biaxially stretched sheets, Comparative Example 5 is a heat-resistant polystyrene biaxially stretched sheet, and Comparative Example 6 is a general-purpose polystyrene biaxially stretched sheet. It can be seen that the oil resistance of the aromatic vinyl resin biaxially stretched sheet of the present invention is greatly improved as compared with a commercially available styrene resin biaxially stretched sheet. It can also be seen that the folding strength and impact strength are equivalent or better.

Example 10
The same resin composition as in Example 1 was extruded from a T-die with a sheet thickness of about 0.95 mm, a longitudinal stretching speed of 333% / second, a lateral stretching speed of 21% / second, and a longitudinal and transverse stretching setting temperature of 1 A sheet of 0.15 mm was obtained in the same manner as in Example 1 except that the temperature was raised by 2 ° C. The ORS of the sheet was 0.68 MPa in length and 0.69 MPa in width. The obtained sheet was formed into a food pack by a single hot plate pressure forming machine. 20 g of MCT oil (trade name: White F-1, manufactured by Fuji Seiki Co., Ltd.) was placed in the food pack and left in a dryer at 100 ° C. for 5 minutes, but no deformation or whitening was observed in the molded product. The shape of the food pack is an opening of 175 mm × 105 mm with a body part depth of 27 mm and a lid part depth of 12 mm.

  The aromatic vinyl resin biaxially stretched sheet and molded product of the present invention are excellent in oil resistance, heat resistance, transparency and mechanical strength, and also have high sheet productivity at high speed. For this reason, it can carry out secondary shaping | molding to the target container shape, and can use it suitably as a food packaging material. In particular, it can be suitably used as a packaging material for foods containing vegetable oil or animal oil. Moreover, since it is excellent also in heat resistance, it can be suitably used as a lid for food containers that are cooked in a microwave oven, and plays an important role in the industry.

[1] A copolymer (A) of an aromatic vinyl monomer and a vinyl cyanide monomer ,
A graft copolymer composition (B1) obtained by graft polymerizing a mixture of an aromatic vinyl monomer and a vinyl cyanide monomer to a rubber polymer; or
Biaxially composed of a mixed resin with one or more graft copolymer compositions (B) selected from graft copolymer compositions (B2) obtained by graft-polymerizing an aromatic vinyl monomer to a rubber polymer. An aromatic vinyl resin biaxially stretched sheet characterized by the following (1) to (4).
(1) copolymer (A), the ratio of the vinyl cyanide monomer in the copolymer is Ru 40% by mass from 25% by mass.
(2) the total content of the monomer or oligomer Ru der less 17,000Ppm.
(3) The gel content in 100% by mass of the resin constituting the biaxially stretched sheet is 0.1 to 0.9% by mass.
(4) The heat shrinkage stress of the biaxially stretched sheet is in the range of 0.45 to 1.0 MPa in the longitudinal direction and the lateral direction, respectively .
[2] The aromatic vinyl resin biaxially stretched sheet according to [1], wherein the total content of monomers or oligomers is 10,000 ppm or less.
[ 3 ] The aromatic vinyl resin biaxially stretched sheet according to [1] or [2] , wherein the volume average particle diameter of the rubber polymer in the graft copolymer composition (B1) is 0.5 to 5 μm. .
[ 4 ] The aromatic vinyl resin biaxially stretched sheet according to [1] or [2] , wherein the rubbery polymer in the graft copolymer composition (B2) has a volume average particle diameter of 1 to 5 μm.
[ 5 ] The heat shrinkage stress in the machine direction and the transverse direction of the biaxially stretched sheet is in the range of 0.5 to 0.8 MPa, and the average of the heat shrinkage stress in the machine direction and the transverse direction is 0.55 to 0.75 MPa. The aromatic vinyl resin biaxially stretched sheet according to any one of [1] to [ 4 ].
[ 6 ] The aromatic vinyl resin biaxial stretching according to any one of [1] to [ 5 ], wherein the heat shrinkage rate when the biaxially stretched sheet is allowed to stand in warm air at 105 ° C. for 10 minutes is 2% or less. Sheet.
[7] [1] - [6] or a manufacturing method of a molded article, which comprises forming the secondary aromatic vinyl resin biaxially oriented sheets described in the.
[ 8 ] The method for producing a molded product according to [ 7 ] , wherein the molded product is a food packaging material containing vegetable oil or animal oil.
[9] A food packaging material comprising the aromatic vinyl resin biaxially stretched sheet according to any one of [1] to [6].

Examples 2 to 9 [Example 7 (Reference Example 1)]
Copolymer resins (A) of the type shown in Table 1 and graft copolymer composition (B) are melt-mixed at the ratios shown in Table 1, melt-extruded in the same manner as in Example 1, and stretching temperature settings and stretching shown in Table 1 Stretching was performed at a magnification to obtain a sheet having a thickness of 0.25 mm. The sheet thickness before stretching and the stretching speed were adjusted in proportion to the stretching ratio. The evaluation results of the sheet are shown in Table 1. About Examples 1-9, the excellent result was obtained in each evaluation test.

Claims (9)

A biaxially oriented sheet comprising a copolymer (A) of an aromatic vinyl monomer and a vinyl cyanide monomer as an essential component,
The copolymer (A) has a vinyl cyanide monomer ratio in the copolymer of 25% by mass to 40% by mass,
The total monomer or oligomer content is 17,000 ppm or less,
A biaxially stretched sheet of aromatic vinyl resin, wherein the heat shrinkage stress of the biaxially stretched sheet is in the range of 0.45 to 1.0 MPa in the longitudinal direction and the lateral direction, respectively.   The aromatic vinyl resin biaxially stretched sheet according to claim 1, wherein the total content of monomers or oligomers is 10,000 ppm or less. The resin constituting the biaxially stretched sheet is
A copolymer (A) of an aromatic vinyl monomer and a vinyl cyanide monomer;
Graft copolymer composition (B1) obtained by graft polymerization of a mixture of an aromatic vinyl monomer and a vinyl cyanide monomer to a rubber polymer, or a graft copolymer composition obtained by graft polymerization of an aromatic vinyl monomer to a rubber polymer It is a mixed resin with one or more graft copolymer compositions (B) selected from (B2),
The aromatic vinyl-based resin biaxially stretched sheet according to claim 1 or 2, wherein a gel content in 100 mass% of the resin constituting the biaxially stretched sheet is 0.1 to 0.9 mass%.   The aromatic vinyl-based resin biaxially stretched sheet according to claim 3, wherein the volume average particle diameter of the rubber polymer in the graft copolymer composition (B1) is 0.5 to 5 µm.   The aromatic vinyl resin biaxially stretched sheet according to claim 3, wherein the rubbery polymer in the graft copolymer composition (B2) has a volume average particle diameter of 1 to 5 µm.   The biaxially stretched sheet has a longitudinal and transverse heat shrinkage stress in the range of 0.5 to 0.8 MPa, and an average of the longitudinal and transverse heat shrinkage stress is 0.55 to 0.75 MPa. Item 6. The aromatic vinyl resin biaxially stretched sheet according to any one of Items 1 to 5.   The aromatic vinyl resin biaxially stretched sheet according to any one of claims 1 to 6, which has a thermal shrinkage rate of 2% or less when the biaxially stretched sheet is left in a warm air of 105 ° C for 10 minutes.   A molded article obtained by secondary molding of the aromatic vinyl resin biaxially stretched sheet according to any one of claims 1 to 7.   The molded article according to claim 8, wherein the molded article is a food packaging material containing vegetable oil or animal oil.