JP2006274269A - Biaxially oriented styrene resin sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber-containing biaxially oriented styrene resin sheet with high rigidity, moldability and impact resistance. <P>SOLUTION: The rubber-containing biaxially oriented styrene resin sheet comprises a styrene resin composition which contains at least a styrene graft copolymer prepared by graft polymerization of at least a styrene monomer onto a rubber component, and has a thickness of 0.05-0.5 mm (0.05-0.15 mm, in particular), when biaxially oriented with an oriented ratio of 1.2-5 times both in the longitudinal direction and in the horizontal direction. The rubber component contained in the styrene graft copolymer has a swelling degree (SI) of about 7.5-20, a graft ratio (g) of 1.8-5, a product (SI×g) of the swelling degree (SI) and the graft ratio (g) of 20-80 (20-60, in particular), and the average particle size of 0.5-10 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a biaxially stretched styrene resin sheet having high rigidity, moldability and excellent impact resistance, and a molded body (for example, a container or a tray) formed from the sheet.

  Biaxially stretched styrene-based resin sheets are widely used for containers and trays in the food field because they are excellent in moldability and have a high elastic modulus. In the food industry, containers and packaging such as containers and trays tend to be thinner and lighter and simplified in response to recent environmental problems and container recycling laws. Polystyrene has a high elastic modulus and excellent rigidity, but is not sufficient in impact resistance and oil resistance. Therefore, even if the styrene-based resin sheet is made thin and light to some extent, it can maintain practical strength because of its rigidity, but it is not sufficient in impact resistance, and cracks and cracks are likely to occur. In addition, it is difficult to use for food trays containing oil such as fried foods. Therefore, as a method for improving the impact resistance and oil resistance of polystyrene, a method of incorporating a rubber component into polystyrene is used.

  Japanese Patent Publication No. 56-37051 (Patent Document 1) discloses polystyrene or a styrene-based graft copolymer containing 1 to 5% by weight of a styrene-butadiene rubber having a styrene content of 50% by weight or less, or a styrene content of 20%. A biaxially stretched polystyrene sheet using a styrene-based resin containing 5 to 15% by weight of styrene-butadiene rubber of -50% by weight as a base resin, and the rubber component in the sheet is flattened and almost uniformly dispersed in layers In addition, a rubber-reinforced biaxially stretched polystyrene sheet having improved transparency and bending strength is disclosed. This document describes that a sheet having a thickness of 0.09 to 0.13 mm was obtained. FIG. 1 of this document shows an electron micrograph in which rubber particles are dispersed in layers. In this photograph, the rubber component is extremely flattened and has a long and thin layer shape. When this photograph is analyzed, the area occupancy of the rubber component including the styrenic resin included in the salami structure with respect to the sheet cross section is about 34%, and is represented by the ratio between the major axis L and the minor axis S of the cross section of the rubber component. The average rubber flatness F (F = L / S) is about 20.5, and the number of rubber components crossing the straight line drawn in the thickness direction of the sheet cross section is about 15.5 / 10 μm. However, in order to flatten the rubber, it is necessary to produce a sheet by applying a high shrinkage stress. Therefore, the sheet is easily broken during the forming process. Moreover, since the shrinkage stress of the molded sheet is high, the secondary formability to a container or the like is also lowered.

  JP-A-54-29381 (Patent Document 2) extrudes a graft type high impact polystyrene having a rubber content of 3% by weight or more and a melt flow rate (MFR) of 8 g / mm or less. A method for producing a container is disclosed in which biaxial stretching is performed so that the heat shrinkage stress is 4 kg / cm 2 or more in both the longitudinal direction and the transverse direction, and the resulting sheet is molded without substantially returning its orientation. This document describes that when the above requirements are satisfied, the oil resistance of the container is dramatically improved. Further, this document describes that a graft type high impact polystyrene can be diluted with general-purpose polystyrene to obtain a desired rubber content, and a sheet having a thickness of about 0.3 mm or more is used.

Japanese Examined Patent Publication No. 55-35246 (Patent Document 3) contains 0.5 to 3% by weight of synthetic rubber and has an orientation relaxation stress measured in accordance with ASTM D-1504 in the range of 5 to 15 kg / cm ² . A styrenic resin sheet that has been biaxially stretched is disclosed. This document describes that graft type high impact polystyrene and general-purpose polystyrene can be used in combination, and describes that the thickness of the sheet is about 0.25 to 0.3 mm. However, the impact resistance of the sheet is low, and it is difficult to improve the impact resistance by reducing the thickness and weight of the sheet.

In these sheets, the rigidity decreases when the rubber content is increased. Therefore, it is difficult to reduce the thickness. On the other hand, when the rubber content is reduced, the impact resistance and oil resistance are lowered. Therefore, rigidity, impact resistance and oil resistance cannot be achieved at a high level.
Japanese Patent Publication No.56-37051 JP 54-29381 A Japanese Patent Publication No.55-35246

  Accordingly, an object of the present invention is to provide a resin composition, a rubber-containing biaxially stretched styrene resin sheet having high rigidity, excellent impact resistance and oil resistance, and a method for producing the same, even if the sheet is reduced in thickness and weight. There is.

  Another object of the present invention is to provide a rubber-containing biaxially stretched styrene resin sheet that is excellent in moldability and volume reduction.

  Still another object of the present invention is to provide a molded body (for example, a container or a tray) that is difficult to break even if it is thin and light-weighted in a molded body that is used at low temperatures such as frozen storage.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor has found that, in a biaxially stretched styrene-based resin sheet, a styrene-based graft copolymer containing a rubber component having a specific swelling degree and graft ratio, and, if necessary, a styrene-based Discovered that combining a resin with a rubber component in a specific dispersed state can improve sheet rigidity, impact resistance, and oil resistance even when it is thin and light, and the present invention is completed. did.

  That is, the biaxially stretched styrene resin sheet of the present invention is composed of a styrene resin composition containing at least a styrene graft copolymer in which at least a styrene monomer is graft-polymerized to a rubber component, and in the longitudinal and lateral directions. In which the thickness is biaxially stretched at a stretch ratio of 1.2 to 5 times and the thickness is 0.05 to 0.5 mm (particularly 0.05 to 0.15 mm), and the following (1) The requirements of (3) are satisfied.

(1) The rubber component in the styrene-based graft copolymer has a degree of swelling (SI) of about 7.5 to 20, a graft ratio (g) of 1.8 to 5, and a degree of swelling (SI). And the graft ratio (g) (SI × g) is 20 to 80 (particularly 20 to 60), and the average particle size is 0.5 to 10 μm. (2) In the styrene-based resin composition The rubber component content is 0.7 to 12% by weight (preferably more than 3% by weight and 10% by weight or less, more preferably 3.3 to 5% by weight). (3) Sheet surface along the stretching direction (I) the major axis of the rubber component is substantially parallel to the sheet surface, and is represented by the ratio of the major axis L and minor axis S of the rubber component cross section. Rubber flatness F (F = L / S) is 5 to 21.2, and (ii) the rubber component is layered The layered rubber component is at least partially overlapped when viewed in the thickness direction from the plane of the sheet, and (iii) the number of rubber components crossing the straight line drawn in the thickness direction of the cross section is 1. It should be ˜13 / 10 μm.

In the sheet cross section cut in the direction perpendicular to the sheet surface along the stretching direction of the biaxially stretched styrene resin sheet, the ratio (area occupation ratio) of the rubber component to the sheet cross section may be about 10 to 25%. . The styrene resin composition comprises a styrene graft copolymer and a styrene resin, the former / the latter = 30/70 to 80/20 (weight ratio), preferably 50/50 to 70/30 (weight ratio). ) May be included. The tensile modulus of elasticity of the sheet measured in accordance with JIS K 7113 may be 2.8 × 10 ⁹ Pa or more. The total absorbed energy of the sheet measured in accordance with the polymer material center standard “instrumented multiaxial impact test method for hard plastics” is, for example, 3 J / mm or more at −30 ° C. and 20 ° C. preferable. The present invention also relates to a method for improving the rigidity, impact resistance and oil resistance of a thin and light biaxially stretched styrene sheet resin sheet, wherein the biaxially stretched styrene resin sheet is used, Also included are methods for improving the stiffness, impact resistance and oil resistance of the. In this improvement method, in the sheet cross section cut in the direction perpendicular to the sheet surface along the stretching direction, the ratio (area occupancy) of the cross section of the rubber component to the sheet cross section is adjusted to about 10 to 25%. The rigidity, impact resistance and oil resistance of the resin sheet may be improved. Furthermore, the present invention includes a molded body (for example, a container or a tray) formed of the sheet.

  In the present invention, since the biaxially stretched sheet is formed of a specific styrene-based resin composition, it has high rigidity and excellent impact resistance even if the sheet is reduced in thickness and weight. In addition to high rigidity and excellent impact resistance, it also has excellent moldability. Furthermore, it is excellent in volume reduction and oil resistance. Since the sheet of the present invention is difficult to break even if it is thin and light, it can be suitably used for food container packaging applications such as containers and trays.

  The biaxially stretched styrene resin sheet of the present invention is a styrene resin containing at least a styrene graft copolymer (styrene graft copolymer or graft type high impact polystyrene) in which at least a styrene monomer is graft-polymerized to a rubber component. The rubber composition can be composed of a resin composition, and in the styrene-based graft copolymer or styrene-based resin composition, a rubber component is dispersed in a styrene-based resin matrix.

  The styrene graft copolymer can be obtained by graft polymerization of at least a styrene monomer in the presence of a rubber component. Examples of the rubber component include diene rubbers (for example, polybutadiene, polyisoprene, chloroprene rubber, styrene-butadiene copolymer, styrene-isoprene copolymer, butadiene-acrylonitrile copolymer, isobutylene-isoprene copolymer, styrene). -Isoprene-butadiene copolymer, butadiene- (meth) acrylic acid ester copolymer, etc.), ethylene-vinyl acetate copolymer, acrylic rubber, butyl rubber, ethylene-α-olefin-polyene copolymer (for example, ethylene- Propylene-diene rubber (EPDM), etc.), urethane rubber, silicone rubber, hydrin rubber (eg, epichlorohydrin rubber, etc.), butyl rubber, fluoro rubber, chlorosulfonated polyethylene, ethylene ionomer, thermoplastic elastomer For example, polyurethane-based elastomer (TPU), polyester-based elastomer (TPEE), fluoropolymer-based elastomers, polyamide-based elastomer (TPAE), and olefin-based elastomer (TPO)), and the like. The copolymer constituting the rubber component may be a block or random copolymer. These rubber components may be hydrogenated as necessary. These rubber components may be used alone or in combination of two or more. Of the rubber components, diene rubber is preferable, and butadiene rubber, isoprene rubber, and styrene-butadiene copolymer (random or block copolymer) are particularly preferable. The styrene content in the styrene-butadiene block copolymer is 10 to 50% by weight, preferably 10 to 40% by weight, and more preferably 10 to 30% by weight.

  As the graft component for the rubber component, at least a styrene monomer may be used, and a styrene monomer alone or a copolymerizable monomer copolymerizable with the styrene monomer can be used. Examples of the styrene monomer include aromatic vinyl compounds (for example, styrene, alkylstyrene (for example, vinyltoluene (o-, m-, p-methylstyrene), vinylethylbenzene (p-ethylstyrene, etc.), p-isobutyl). Styrene, pt-butylstyrene, vinylxylene, etc.), α-alkylstyrene (eg, α-methylstyrene, etc.), mono- to pentahalostyrene (eg, chlorostyrene, bromostyrene, etc.), α-halo-substituted styrene (eg, For example, α-chlorostyrene, α-bromostyrene, etc.), β-halo-substituted styrene (eg, β-chlorostyrene, β-bromostyrene, etc.), etc. These styrenic monomers may be used alone or in combination. A combination of two or more species may be used.Styrene monomers are usually styrene, vinyl. Toluene, α-methylstyrene and the like can be used, and in particular, styrene can be used.

Examples of the copolymerizable monomer include (meth) acrylic monomers [(meth) acrylic acid, (meth) acrylic acid esters (for example, methyl (meth) acrylate, ethyl (meth) acrylate, ( (Meth) acrylic acid C _1-6 alkyl ester such as butyl acrylate)], vinyl cyanide (eg (meth) acrylonitrile etc.), vinyl ester (eg vinyl acetate, vinyl propionate etc.), Saturated polycarboxylic acid or anhydride thereof (eg, maleic acid, itaconic acid, citraconic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, etc.), maleimide monomer (eg, maleimide, N-methylmaleimide, N-alkylmaleimide such as N-butylmaleimide, N-phenylmaleimide) and the like. These copolymerizable monomers may be used alone or in combination of two or more. Of these copolymerizable monomers, (meth) acrylic acid esters such as acrylonitrile and methyl methacrylate, and maleimide monomers such as maleic anhydride and N-phenylmaleimide can be usually used. The usage-amount of a copolymerizable monomer can be selected from the range of about 0-100 mol with respect to 100 mol of styrene-type monomers, Preferably it is 0-50 mol, More preferably, it is about 0-25 mol.

  A typical styrene-based graft copolymer is high-impact polystyrene (HIPS).

  Since the sheet of the present invention is composed of a styrene-based graft copolymer containing a rubber component having a specific degree of swelling and graft ratio, the impact resistance and rigidity of the sheet can be greatly improved. The product (SI × g) of the swelling degree (SI) and the graft ratio (g) of the rubber component is 13 to 80, preferably 15 to 70, more preferably 20 to 60 (particularly 20 to 40). For example, it may be about 23 to 55. When the product (SI × g) is smaller than the above range, the flatness of the rubber component becomes small, and the impact resistance of the sheet decreases. Further, in the styrene-based graft copolymer, if the rubber component is forcibly flattened, the formability of the sheet is lowered and the secondary moldability to a container or the like is also lowered. When the product (SI × g) is larger than the above range, the impact resistance and oil resistance of the sheet are lowered.

  The swelling degree (SI) and graft ratio (g) of the rubber component are not particularly limited as long as the product (SI × g) of the swelling degree (SI) and the graft ratio (g) is within the above range. The degree of swelling (SI) is usually about 7.5 to 20, preferably about 10 to 20, and more preferably about 11 to 18. The graft ratio (g) is usually about 1 to 5, preferably about 1.2 to 5, more preferably about 1.5 to 5 (particularly about 1.8 to 4.5).

  The swelling degree (SI) of the rubber component is usually used as an index indicating the degree of crosslinking of the rubber component. The smaller this value, the harder the rubber component is flattened by stretching. The degree of swelling (SI) is determined by, for example, dissolving a styrene-based graft copolymer in a solvent (for example, toluene), the swelling gel weight (AI) of the styrene-based graft copolymer swollen with the solvent, and the swollen styrene-based polymer. The dry gel weight (BI) obtained by drying the graft copolymer can be measured and determined from the ratio (AI / BI) of both.

  The graft ratio (g) is used as an index indicating the ratio of the graft component to the rubber component. The larger this value, the easier the rubber component is flattened by stretching. The graft ratio (g) can be calculated by the following formula using the gel fraction (G) of the styrene-based graft copolymer and the rubber component content (RC).

g = (G-RC) / RC
In the above formula, the gel fraction (G) is about 10 to 72%, preferably about 11 to 72%, and more preferably about 12 to 70% (for example, 14 to 66%). The gel fraction (G) is, for example, the weight (CI) of the styrene-based graft copolymer and the styrene-based graft copolymer dissolved in a solvent (for example, a mixed solvent of methyl ethyl ketone and acetone) and swollen with the solvent. The dry gel weight (DI) obtained by drying the gel-like styrene-based graft copolymer can be measured and determined from the ratio (DI / CI) of both.

  The rubber component content (RC) in the styrene-based graft copolymer is about 3 to 15% by weight, preferably about 4 to 13% by weight, and more preferably about 5 to 12% by weight (for example, 8 to 12% by weight). is there. When the content of the rubber component is too small, the impact resistance of the sheet and the molded product is lowered, and when it is too much, the rigidity is lowered.

  The average particle size of the rubber component in the styrene-based graft copolymer is about 0.5 to 10 μm, preferably about 1 to 7 μm, and more preferably about 1 to 5 μm. When the average particle diameter is out of the above range, the impact resistance of the sheet and the molded product is lowered. The shape of the rubber component is not particularly limited, and examples thereof include a salami structure, a small particle size salami structure, a core shell structure, and a structure in which a large particle size salami structure and a small particle size salami structure are mixed. The rubber component in the salami structure may include a styrene resin.

  The styrene resin composition may be composed of a styrene graft copolymer or may be composed of a combination of a styrene graft copolymer and a styrene resin. The styrene resin may be a homopolymer or copolymer of a styrene monomer, or a copolymer of a copolymerizable monomer copolymerizable with a styrene monomer. . Examples of the styrene monomer and copolymerizable monomer include monomers exemplified in the above-mentioned styrene graft copolymer (for example, aromatics such as styrene, vinyltoluene, α-methylstyrene, etc.). Group vinyl monomers, (meth) acrylic monomers, acrylonitrile, maleimide monomers, etc.) can be used. Examples of the styrene resin include polystyrene such as general-purpose polystyrene (GPPS), styrene-methyl methacrylate copolymer, and the like. By using a combination of a styrene-based graft copolymer and a styrene-based resin, a resin having an excellent balance of physical properties such as impact resistance and rigidity can be obtained, and the moldability can be greatly improved.

  The content of the rubber component in the styrene-based resin composition can be selected from a range that does not impair characteristics such as impact resistance and moldability, and is 0.7 to 12% by weight (for example, 2.5 to 10% by weight). It is preferably more than 3 wt% and not more than 10 wt% (for example, 3.2 to 7 wt%), more preferably about 3.3 to 5 wt% (for example, 3.3 to 4 wt%). When the content of the rubber component is too small, the impact strength of the sheet is lowered, and when it is too much, the rigidity is lowered.

  The ratio (weight ratio) between the styrene-based graft copolymer and the styrene-based resin can be selected from the range of the former / the latter = 5/95 to 100/0, and is usually 20/80 to 90/10, preferably 30 / It is 70-80 / 20, More preferably, it is about 50 / 50-70 / 30 (especially 55 / 45-65 / 35) grade. When the ratio of the styrene resin is larger than the above range, the impact resistance is lowered, and when it is smaller than the above range, the rigidity is lowered.

  The melt flow rate (M1) of the styrene-based graft copolymer is 2 to 20 g / 10 minutes, preferably 2 to 10 g / 10 minutes, more preferably about 2 to 5 g / 10 minutes at a temperature of 200 ° C. and a load of 5 kg. is there. The melt flow rate (M2) of the styrenic resin is 1 to 20 g / 10 minutes, preferably 1 to 10 g / 10 minutes, more preferably about 1 to 5 g / 10 minutes at a temperature of 200 ° C. and a load of 5 kg.

  The ratio (M1 / M2) between the melt flow rate (M1) of the styrene-based graft copolymer and the melt flow rate (M2) of the styrene-based resin is 0.1 to 20, preferably 0.2 to 10, and more preferably Is about 0.4-5. When the ratio (M1 / M2) of the melt flow rate deviates from the above range, the impact resistance of the thinned sheet decreases.

  The styrenic resin composition may include other thermoplastic resins (for example, olefin resins, vinyl resins, (meth) acrylic resins, polyvinyl ketone resins, polyamide resins, polyester resins, Ether resins, polyphenylene oxide resins, thermoplastic polyimides, etc.) may be added.

  The styrenic resin composition further includes various additives as required, for example, stabilizers (for example, UV absorbers, antioxidants, heat stabilizers, etc.), flame retardants, antifogging agents, and dispersing agents. , Plasticizers (phthalate esters, fatty acid plasticizers, phosphoric acid plasticizers, etc.), low molecular antistatic agents, antibacterial agents, colorants, fillers, reinforcing materials (fiber fillers such as glass fibers and carbon fibers) ), Fluidity improvers, thickeners and the like may be added.

  The biaxially stretched styrene resin sheet of the present invention, which is composed of the styrene resin composition and is biaxially stretched, has a rubber component dispersed in a specific form. In addition to excellent impact resistance, it has high secondary formability.

  That is, in the sheet cross section obtained by cutting the sheet in a direction perpendicular to the sheet surface, the major axis of the rubber component is generally substantially parallel to the sheet surface. In the present invention, the impact resistance can be improved even if the ratio (area occupancy) of the rubber component in the sheet cross section is small. For example, the ratio (area occupancy) is 10 to 25%, preferably It may be about 12 to 22%, more preferably about 14 to 20%. If the area occupation ratio is too small, the impact resistance is lowered, and if it is too large, the rigidity is lowered. The area occupancy rate includes a styrene resin encapsulated in the salami structure in the rubber component having the salami structure.

  In the sheet cross section, since the rubber component is usually dispersed in a layered form, impact resistance can be improved. The rubber flatness F (F = L / S) represented by the ratio of the major axis L to the minor axis S of the cross section of the rubber component is 5 to 18, preferably 8 to 15, and more preferably about 10 to 14. . If the rubber flatness is too small, impact resistance and oil resistance are lowered, and if the rubber flatness is too large, secondary moldability to a container or the like is lowered.

  Furthermore, it is preferable that the layered rubber component at least partially overlaps when seen through in the thickness direction from the plane of the sheet. When the rubber component is partially overlapped, it is easy to absorb the impact on the sheet, and not only the impact resistance is remarkably improved, but also the moldability is not impaired.

  In the cross section of the sheet, the number of rubber components passing through a straight line drawn in the thickness direction of the cross section is 1 to 13/10 μm (for example, 3 to 13/10 μm), preferably 5 to 13/10 μm, and more preferably. Is about 8 to 13 pieces / 10 μm (particularly, 8 to 10 pieces / 10 μm). When the number of rubber components is too large, the rigidity of the sheet decreases, and when it is too small, the impact resistance decreases.

  Although the thickness of the said sheet | seat is not specifically limited, Usually, it can select from the range of 0.05-0.5 mm (for example, 0.05-0.4 mm), but the biaxially-stretched styrene resin sheet of this invention is thickness. Even if it is thin, impact resistance and rigidity can be improved. Therefore, from the viewpoint of reducing the thickness and weight, the thickness of the biaxially stretched styrene resin sheet is usually 0.05 to 0.25 mm, preferably 0.05 to 0.2 mm (particularly 0.08 to 0.15 mm). Degree. Even if the sheet of the present invention has a thickness of about 0.05 to 0.13 mm or is thin and light, it has an excellent balance between rigidity and impact resistance.

The biaxially stretched styrene resin sheet of the present invention exhibits a high elastic modulus. The tensile elastic modulus is, for example, 2.8 × 10 ⁹ Pa or more (for example, 2.8 × 10 ^{9 to} 7 × 10 ⁹ Pa), preferably 3.3 × 10 ^{9 to} 6 × 10 ⁹ Pa, and further preferably from ^{3.8 × 10 9 ~6 × 10 9} Pa approximately. The tensile elastic modulus can be measured by a measuring method based on JIS K7113. If the tensile elastic modulus is smaller than the above range, the sheet having a thickness reduced to about 0.05 to 0.25 mm is insufficient in rigidity, and practical strength cannot be obtained. The sheet of the present invention also has high impact resistance at low temperatures. For example, in the biaxially stretched sheet of the present invention, the total absorbed energy at −30 ° C. and 20 ° C. is 3 J / mm or more (for example, 3 to 50 J / mm), preferably 3.5 J / mm or more (for example, 3.5 ˜20 J / mm), more preferably about 5 J / mm or more (for example, 5 to 15 J / mm). The total absorbed energy can be measured according to the polymer material center standard “Instrumentation multiaxial impact test method for hard plastics”. When the total absorbed energy is smaller than the above range, the impact resistance (particularly, cold impact resistance) of the sheet is lowered. In particular, when the thickness of the sheet is reduced to about 0.05 to 0.2 mm, the sheet is cracked or cracked at a low temperature.

  The sheet of the present invention is excellent in volume reduction in addition to high rigidity and excellent impact resistance. Since the sheet has a specific return angle, it is easy to be crushed or rolled, and is excellent in volume reduction. The return angle is an average thickness of 0.2 mm and a sheet of 1.5 (MD) cm × 11 (TD) cm folded at 180 ° at an intermediate position in the longitudinal direction. The folded sheet has a diameter of 150 mm and a weight of 1 kg. It means the angle of the sheet after applying a load with a weight for 1 minute, then removing the load and leaving it for 30 minutes. The return angle of the sheet of the present invention is about 100 ° or less (for example, 10 to 100 °), preferably about 70 ° or less (for example, 10 to 70 °), more preferably about 60 ° or less (for example, 10 to 60 °). It is. If the return angle exceeds 100 °, it is difficult to reduce the volume during recovery or disposal. The condition is that the sheet is a sheet that does not break even if the folding is performed three times or more.

  The biaxially stretched styrene resin sheet of the present invention is obtained by biaxially stretching an unstretched sheet of a styrene resin composition.

  A styrene resin sheet can be produced using an extruder (for example, a single screw extruder or a twin screw extruder) or a calendar molding machine using the styrene resin composition. The styrenic resin composition is melt-kneaded in an extruder and molded by extrusion from a die (die) at the tip of the extruder. The die (die) may be a ring die used for inflation molding, but usually a T die such as a multi-manifold die or a flat die can be used.

Extrusion molding conditions can be selected according to the type of the extruder or the styrene resin composition, and the molding temperature is usually 100 to 200 ° C, preferably 110 to 180 ° C, more preferably about 120 to 140 ° C. The molding pressure may be 1 to 10 kg / cm ² , preferably ² to 8 kg / cm ² , more preferably about 3 to 6 kg / cm ² .

  A biaxially stretched styrene resin sheet can be formed by biaxially stretching (sequentially or simultaneously) the sheet extruded from a die. Examples of the sequential stretching include a method of stretching an unstretched sheet prepared using a T die or a calendar in a uniaxial direction and then stretching in a direction perpendicular to the stretching direction. Examples of simultaneous biaxial stretching include a method in which longitudinal and lateral stretching are simultaneously performed in tenter stretching, and an inflation method.

  The draw ratio can be usually selected from the range of 1.2 to 5 times in the longitudinal and transverse directions, preferably 1.5 to 4 times, more preferably about 2 to 3 times. When the draw ratio is lower than the above range, the impact resistance becomes insufficient. When the draw ratio is higher than the above range, the uniformity of the sheet thickness cannot be obtained, and the moldability to a container or the like also deteriorates. In addition, the heating temperature of the sheet | seat at the time of extending | stretching is 100-130 degreeC, Preferably it is 110-130 degreeC, More preferably, it is 120-130 degreeC. If the heating temperature deviates from the above range, stretching becomes difficult, and the uniformity of the sheet thickness decreases.

  Since the sheet of the present invention is excellent in formability and secondary formability, various forming methods such as pressure forming (extrusion pressure forming, hot plate pressure forming, vacuum pressure forming, etc.), vacuum forming, free blow forming, etc. The molded product can be easily obtained by conventional thermoforming such as bending, matched mold molding, hot plate molding and the like. From the viewpoint of easily forming a three-dimensional shaped body having a concave shape such as a container or a tray, pressure forming that presses the heated sheet against the mold with compressed air, or between the mold and the heated sheet Vacuum forming is preferably performed by drawing the heating sheet into the mold side by forming a vacuum.

  Sheets and molded articles such as containers and trays of the present invention have high rigidity and excellent impact resistance (especially cold shock resistance), and are difficult to break even if they are thin, so foods such as confectionery trays and delicacy trays Suitable for packaging applications. Moreover, since the said molded article is excellent also in oil resistance, it is suitable also for the food packaging use containing oil components, such as a tray for grilled meat. Furthermore, since the molded article is also excellent in impact resistance (particularly cold impact resistance), it is particularly suitable for food packaging applications such as frozen food trays. Examples of packaged products include various foods such as meat, vegetables, seafood, fries (croquettes, fish fries, etc.), non-fries (roasted meat, hamburgers, rice balls, etc.), confectionery (snack, cheese rice cakes, seaweeds) Delicacy), ice confectionery (ice cream, ice sherbet, etc.), frozen foods and the like.

  Since the sheet of the present invention can be reduced in thickness and weight, it is advantageous in terms of cost and is excellent in volume reduction. Therefore, the sheet can be easily collected and discarded in accordance with the container recycling method. Therefore, the biaxially stretched styrene resin sheet of the present invention is extremely useful industrially.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the resin component used in the Examples, the degree of swelling, the rubber content, the method for measuring the graft ratio, and the method for evaluating the sheet are as follows.

[Resin component]
[Styrene Graft Copolymer (HIPS)]
(HIPS1-HIPS6)
Reactor with internal capacity of 25 liters equipped with double helical stirring blades, twin-screw extruder equipped with a devolatilizer (manufactured by Nippon Steel Works, TEX44α), and gear pump (manufactured by Shimadzu Corporation, SKJV50) Is used in a nitrogen atmosphere, the reaction product is extruded from the die of an extruder, and the extruded molten strand is cooled and cut to obtain pellet-shaped HIPS. It was. Various HIPS (HIPS1 to HIPS6) shown below were prepared by changing the type and ratio of each component (for example, rubber component, solvent, polymerization initiator, etc.), reaction conditions, and extrusion conditions. Tables 1 and 2 show the rubber component content, swelling degree, and graft ratio of each HIPS.

(HIPS1)
1.5 kg of polybutadiene (manufactured by Ube Industries, BR22H), 17.5 kg of styrene monomer, 1 kg of toluene, 4 g of t-dodecyl mercaptan were charged into the reactor, and the temperature was raised to 130 ° C. to initiate the polymerization reaction. did. The reaction was carried out stepwise in the order of 130 ° C. and stirring speed 50 rpm for 2 hours, 140 ° C. and stirring speed 20 rpm for 2 hours, 150 ° C. and stirring speed 10 rpm for 1 hour. The obtained reaction product was extruded under the conditions of 230 ° C. and a gear pump output of 20%, and unreacted monomers and solvents were removed to obtain pellet-shaped HIPS.

(HIPS2)
Charge 2 kg of polybutadiene (Asapur Kasei Co., Ltd., Asaprene 760A), 16 kg of styrene monomer, 4.8 g of polymerization initiator (Nippon Yushi Co., Ltd., Perbutyl Z) into the reactor, and heat to 117 ° C. The polymerization reaction was started. The reaction was carried out stepwise in the order of 117 ° C. and a stirring speed of 40 rpm for 2 hours, 135 ° C. and a stirring speed of 20 rpm for 2 hours, and 150 ° C. and a stirring speed of 10 rpm for 1 hour. The obtained reaction product was extruded under conditions of 230 ° C. and a gear pump output of 10%, and unreacted monomers and solvents were removed to obtain pellet-shaped HIPS.

(HIPS3)
Charge 2 kg of polybutadiene (Asahi Kasei Co., Ltd., Diene 55), 16 kg of styrene monomer, 4.8 g of polymerization initiator (Nippon Yushi Co., Ltd., Perbutyl Z) into the reactor, and raise the temperature to 117 ° C. The polymerization reaction was started. The reaction was carried out stepwise in the order of 117 ° C. and stirring speed 20 rpm for 2 hours, 135 ° C. and stirring speed 20 rpm for 2 hours, 150 ° C. and stirring speed 10 rpm for 1 hour. The obtained reaction product was extruded under conditions of 230 ° C. and a gear pump output of 10%, and unreacted monomers and solvents were removed to obtain pellet-shaped HIPS.

(HIPS4)
2 kg of polybutadiene (manufactured by Nippon Zeon Co., Ltd., BR1220SL), 16 kg of styrene monomer, 4.8 g of polymerization initiator (manufactured by Nippon Oil & Fats Co., Ltd., perbutyl Z) were charged into the reactor, and the temperature was raised to 117 ° C. The polymerization reaction was started. The reaction was carried out stepwise in the order of 117 ° C. and a stirring speed of 40 rpm for 2 hours, 135 ° C. and a stirring speed of 20 rpm for 2 hours, and 150 ° C. and a stirring speed of 10 rpm for 1 hour. The obtained reaction product was extruded under the conditions of 240 ° C. and a gear pump output of 10%, and unreacted monomers and solvents were removed to obtain pellet-shaped HIPS.

(HIPS5)
Charge 2.5 kg of polybutadiene (manufactured by Nippon Zeon Co., Ltd., BR1220SG), 16 kg of styrene monomer, 7.2 g of polymerization initiator (manufactured by Nippon Oil & Fats Co., Ltd., perbutyl Z) into the reactor, and raise the temperature to 120 ° C. Then, the polymerization reaction was started. The reaction was carried out stepwise in the order of 120 ° C. and a stirring speed of 20 rpm for 2 hours, and 125 ° C. and a stirring speed of 20 rpm for 2 hours. The obtained reaction product was extruded under the conditions of 240 ° C. and a gear pump output of 10%, and unreacted monomers and solvents were removed to obtain pellet-shaped HIPS.

(HIPS6)
1.5 kg of polybutadiene (manufactured by Ube Industries, BR22H), 17.5 kg of styrene monomer, 1 kg of toluene and 4 g of t-dodecyl mercaptan are charged into the reactor, and the temperature is raised to 130 ° C. to initiate the polymerization reaction. did. The reaction was carried out stepwise in the order of 130 ° C. and stirring speed 50 rpm for 2 hours, 140 ° C. and stirring speed 20 rpm for 2 hours, 150 ° C. and stirring speed 10 rpm for 1 hour. The obtained reaction product was extruded under the conditions of 240 ° C. and a gear pump output of 10%, and unreacted monomers and solvents were removed to obtain pellet-shaped HIPS.

[Styrene resin (GPPS)]
Polystyrene (Toyo Styrene Co., Ltd., Toyo Styrol GP, HRM63C) was used.

[Swelling degree]
125 g of toluene was added to 3 g of accurately weighed HIPS and dissolved to obtain a solution. This solution was allowed to stand in the dark for 24 hours, and then centrifuged for 23 minutes at a temperature of −4 ° C. and a rotational speed of 1500 rpm in a cooling stretch separator (Beckman Instruments Inc., Avanti HP-30I). The supernatant was removed and the precipitate was taken out and its weight (AI) was measured (swelling gel weight). Next, the precipitate was dried at 160 ° C., normal pressure, under a nitrogen atmosphere for 45 minutes, and further at 160 ° C. in vacuum for 1 hour, and the weight after drying (BI) was measured (dry gel weight). The degree of swelling (SI) of the rubber component was determined from the ratio (AI / BI) between the swollen gel weight (AI) and the dry gel weight (BI).

[Rubber content]
The rubber content of HIPS was measured by the following procedures (1) to (4).

(1) Preparation of reagents Solutions A to C shown below were prepared.
Solution A: 5% iodine monochloride acetic acid solution (25 g of iodine monochloride was transferred to a brown bottle and dissolved in 500 g of acetic acid)
B solution: 10% potassium iodide aqueous solution (100 g of potassium iodide was dissolved in 900 g of distilled water)
Solution C: Sodium thiosulfate aqueous solution (45 g of sodium thiosulfate was precisely weighed and dissolved in distilled water to make a 1000 ml solution. 0.3 g of sodium bicarbonate was added to the solution and left overnight).

(2) Standardization of aqueous sodium thiosulfate solution To a 300 ml Erlenmeyer flask, 0.1 g of precisely weighed potassium bromate, 100 ml of distilled water, and 100 ml of B solution were added to obtain a mixed solution. To this solution was added 10 ml of concentrated hydrochloric acid and left for 3 minutes. This solution was titrated with an aqueous sodium thiosulfate solution (solution C), and the titration was terminated when the aqueous solution became colorless. The normality (N) of the C solution was calculated by the following formula.
Normality (N) of sodium thiosulfate aqueous solution (C solution) = [Weighed weight of potassium bromate (g)] / [(Titration amount of sodium thiosulfate aqueous solution (ml)) × 0.0278]

(3) Dissolution of HIPS 1 g of accurately weighed HIPS and 75 ml of tetrahydrofuran (THF) were added to a 300 ml Erlenmeyer flask and left overnight to dissolve HIPS.

(4) Measurement of rubber content Add 10 ml of A solution to THF solution of HIPS (above (3)), leave it in the dark for 15 minutes, add 100 ml of B solution, and add mixed solution (HIPS solution ). This solution was titrated with an aqueous sodium thiosulfate solution (solution C), and the titration was terminated when the aqueous solution became colorless. The same operation was performed with a solution containing no HIPS (blank solution) as a blank. The rubber content (RC) was calculated from the following formula.

RC (%) = [0.02705 × (Normality of sodium thiosulfate (N)) × {(Titration of solution C in blank solution (ml)) − (Titration of solution C in HIPS solution (ml)) } / HIPS charge weight (g)] × 100
[Graft ratio]
1 g of the HIPS sample was precisely weighed, 35 ml of a mixed solvent of methyl ethyl ketone and acetone (volume%) = 1/1 was added thereto, and the mixture was dissolved for 1.5 hours using a shaker to obtain a solution. This solution was centrifuged for 30 minutes using a refrigerated centrifuge (Beckman Instruments, Inc., Avanti HP-30I) at a temperature of −4 ° C. and a rotational speed of 10,000 rpm. The supernatant was removed, the precipitate was taken out, the precipitate was dried at 80 ° C. in vacuum for 3 hours, and the weight after drying (dry gel weight) was measured. From the dry gel weight, the gel fraction (G) was calculated using the following formula.

G (%) = [(dry gel weight) / (sample weight)] × 100
The graft ratio (g) was calculated by the following formula using the gel fraction G (%) and the rubber content RC (%).

g = (G-RC) / RC
The graft ratio (g) is calculated as a value that also takes into account the styrene resin encapsulated in the rubber component of the salami structure.

[rigidity]
The sheet was punched with a No. 2 dumbbell according to JIS K 7113 (the styrene-based graft copolymer of Comparative Example 6 and the polypropylene of Comparative Example 7 were in the resin orientation direction) to obtain a sample sheet. The tensile elasticity modulus of the obtained sample sheet was measured using Tensilon (RTA520, manufactured by Toyo Seiki Seisakusho Co., Ltd.) under a test speed of 50 mm / min. From the results, rigidity was evaluated according to the following criteria.

○: 3.3 × 10 ⁹ Pa or more Δ: 2.8 × 10 ⁹ Pa or more, less than 3.3 × 10 ⁹ Pa ×: less than 2.8 × 10 ⁹ Pa

[Impact resistance (cold shock resistance)]
The sheet was mounted on a falling weight impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the temperature of the sheet was kept constant at −40 ° C. to 20 ° C. using a thermostatic bath. A striker (diameter: 12.7 mm, total weight: 6.5 kg) is allowed to fall freely from a height of 40 cm against the sheet and collide with the sheet. Was calculated. The calculated total absorption energy at −30 ° C. and 20 ° C. was evaluated according to the following criteria.

A: 5 J / mm or more B: 3.5 J / mm or more, less than 5 J / mm Δ: 3 J / mm or more, less than 3.5 J / mm ×: less than 3 J / mm

[Volume reduction]
A sheet with an average thickness of 0.2 mm and 1.5 (MD) cm × 11 (TD) cm is folded 180 ° at an intermediate position in the longitudinal direction, and the folded sheet is loaded with a weight of 150 mm in diameter and 1 kg in weight for 1 minute. Then, after removing the load and leaving it to stand for 30 minutes, the angle of the sheet was measured, and volume reduction was evaluated according to the following criteria. However, if the sheet is bent at 180 ° and there is no break on the bend line, the sheet is further bent 360 ° in the opposite direction around the bend line, and the sheet does not break even if this is repeated three or more times. Is a condition.

○: 70 ° or less Δ: Over 70 ° and 100 ° or less ×: Over 100 °

[Oil resistance]
The sheet was punched with a JIS K 7127 No. 2 dumbbell (the styrene-based graft copolymer of Comparative Example 6 and the polypropylene of Comparative Example 7 were in the orientation direction of the resin) to obtain a dumbbell-shaped sheet. Both ends of the sheet were gripped with a chuck, salad oil was applied to the center of the sheet, a load of 200 kg / cm ² was applied to the lower chuck, the breaking time was measured, and the oil resistance was evaluated according to the following criteria.

○: 10 minutes or more Δ: 5 minutes or more and less than 10 minutes ×: Less than 5 minutes.

[Container formability]
A cup-shaped container having an opening diameter of 90 mm, a bottom diameter of 80 mm, and a height of 50 mm is formed by a single vacuum forming machine (manufactured by Asano Laboratory Co., Ltd.), and the corner of the container and the bottom surface (the portion where the bottom surface and the side surface are in contact) The appearance of was visually observed and evaluated according to the following criteria.

○: Uniformly stretched and formed to have a uniform thickness Δ: Unevenness in the thickness of the bottom surface or corner ×: There is a tear in a part of the bottom surface or corner.

Examples 1-9 and Comparative Examples 1-5
Using a styrene-based graft copolymer (HIPS) shown in Tables 1-2 and general-purpose polystyrene (GPPS) in proportions shown in Tables 1-2, a twin-screw kneading extruder ( A pellet-shaped resin composition was obtained by melt-kneading with Ikegai Co., Ltd. and extrusion. The resin composition was heated at 230 ° C. for 2 minutes using a compression molding machine (manufactured by Matsuda Kogyo Co., Ltd.), and a sheet having a thickness of 1 mm (0.5 mm in Example 11, 1.5 mm in Example 12). Was molded. The obtained sheet was cut into a square having a length of 130 mm and a width of 130 mm, and using a biaxial stretching machine (manufactured by TM Long), the thickness was 0.2 mm (in Example 11, 0.1 mm, in Example 12). 0.3 mm), 295 mm in length, and 295 mm in width. The biaxial stretching conditions are a heating time of 2 minutes, a stretching speed of 900 mm / min, a stretching ratio of 2.5 times in the vertical direction × 2.5 times in the horizontal direction, and a stretching temperature of 110 ° C. to 130 ° C. The characteristic of the obtained biaxially stretched sheet is shown to Tables 1-2.

Comparative Examples 6 and 7
Instead of the resin compositions of the examples, the ratios shown in the table are general-purpose polystyrene (GPPS) and styrene-butadiene block copolymer (SB) (K resin KK38, manufactured by Philips Oil Co., Ltd., rubber content 30% by weight). A biaxially stretched sheet was obtained in the same manner as in the Example except that it was used in the above.

Comparative Example 8
A biaxially stretched sheet was obtained in the same manner as in the example except that 100% by weight of general-purpose polystyrene (GPPS) was used instead of the resin composition of the example.

Comparative Example 9
Styrene-based graft copolymer (Toyo Styrol HI E640, manufactured by Toyo Styrene Co., Ltd.) (HIPS7) was extruded from a T-die using a 65 mm diameter extruder (cylinder temperature 200 ° C.), and a sheet having a thickness of 0.2 mm Got. Using this sheet, the same evaluation as in the example was performed.

Comparative Example 10
A super cold resistant polypropylene (PP) sheet (F-32L, manufactured by Kyoei Resin Co., Ltd.) and a sheet having a thickness of 0.33 mm were used, and the same evaluation as in Examples was performed.

  In addition, the relationship between the temperature and the (cold) impact resistance (total absorbed energy) in the sheets of Comparative Example 1, Example 2, and Comparative Examples 8 to 10 is shown in FIG.

  As is apparent from the table, the sheets shown in the examples are excellent in various performances. On the other hand, in the sheet shown in the comparative example, various physical properties such as rigidity, impact resistance, and moldability or the balance thereof are not sufficient.

FIG. 1 is a graph showing the relationship between temperature and resistance to (cold) impact (total absorbed energy) in Comparative Example 1, Example 2, and Comparative Examples 8-10.

Claims (2)

The rubber component is composed of a styrene-based resin composition containing at least a styrene-based graft copolymer in which at least a styrene-based monomer is graft-polymerized. A biaxially stretched styrene resin sheet which is a styrene resin sheet having an axially stretched thickness of 0.05 to 0.5 mm, which satisfies the following requirements (1) to (3).
(1) The rubber component in the styrene-based graft copolymer has a degree of swelling (SI) of 7.5 to 20, a graft ratio (g) of 1.8 to 5, and the degree of swelling (SI) and graft. The product (SI × g) with the rate (g) is 20 to 80 and the average particle size is 0.5 to 10 μm. (2) The rubber component content in the styrene-based resin composition is 0.00. 7-3% by weight (3) In the sheet cross section cut in the direction perpendicular to the sheet surface along the stretching direction, (i) the major axis of the rubber component is substantially parallel to the sheet surface The rubber flatness F (F = L / S) represented by the ratio of the major axis L to the minor axis S of the cross section of the rubber component is 5 to 21.2, and (ii) the rubber component is in a layered form. When dispersed and seen in the thickness direction from the plane of the sheet, the layered rubber component at least partially overlaps And and (iii) the number of the rubber component across the straight line drawn in the thickness direction of the cross section is 1 to 13/10 [mu] m   A method for improving rigidity, impact resistance and oil resistance of a thin biaxially stretched styrene sheet-based resin sheet, wherein the biaxially stretched styrene resin sheet according to claim 1 is used, A method to improve impact resistance and oil resistance.

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