Polystyrene biaxially oriented sheet and packaging material

Abstract

To provide a biaxially stretched polystyrene sheet that is less prone to poor appearances such as foreign gel matter and rough sheet surface, and allows low-temperature molding, and a package thereof.SOLUTION: A biaxially stretched polystyrene sheet contains a styrenic resin (A) 50.0-99.0 mass% and a terpene resin (B) 1.0-50.0 mass%, the sheet thickness being 0.05 mm or more and 0.50 mm or less, and the orientation relaxation stress being 0.1 MPa or more and 1.2 MPa or less in both the longitudinal direction and transverse direction of the sheet, and the loss tangent at 100°C being 0.15 or more and 0.80 or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polystyrene sheet containing a terpene resin, and a packaging material obtained by molding the sheet. [Background technology]

[0002] Transparent biaxially oriented polystyrene sheets made from general-purpose polystyrene resin (GPPS) and other materials have excellent properties such as rigidity, light weight, transparency, formability, and recyclability, and are used for molded products such as food packaging containers and lids. Forming into packaging containers, lids, etc. is performed by known hot plate contact heating molding, pressure molding, vacuum molding, vacuum pressure molding, and plug assist molding methods, and can be suitably used by secondary molding into the desired shape. Transparent polystyrene biaxially oriented sheets made of GPPS, etc. are particularly suitable for transparent packaging lids for foods such as lunch boxes and prepared foods. They can also be used for subdivision trays and transport containers for industrial parts, etc.

[0003] In recent years, with the growing awareness of environmental issues, there has been a demand for low-temperature molding, which aims to reduce the environmental impact of processing and improve productivity. Low-temperature molding allows processing at lower temperatures than conventional processing conditions, which reduces the energy required for heating and shortens the time required for heating and demolding, leading to reduced environmental impact and improved productivity. As polystyrene-based biaxially oriented sheets aimed at low-temperature molding, for example, Patent Documents 1 to 3 disclose sheets using styrene-acrylic acid ester copolymers. However, these techniques have problems such as the generation of gel due to unreacted copolymerized products, which tends to cause poor extrusion molding, resulting in poor sheet appearance such as lumps and gum, and rough sheet surfaces due to high melt tension caused by branched chains in the copolymer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-073133 [Patent Document 2] JP 2007-291366 A [Patent Document 3] JP 2008-248156 A Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above circumstances, an object of the present invention is to provide a polystyrene-based biaxially oriented sheet which is less susceptible to appearance defects such as gel foreign matter and rough sheet surface and which can be molded at low temperatures, and a package thereof. [Means for solving the problem]

[0006] As a result of intensive research, the inventors have found that the above problem can be solved by containing a styrene-based resin and a terpene-based resin in a predetermined ratio and applying a predetermined orientation relaxation stress by stretching, thereby setting the loss tangent at 100°C of the sheet within a predetermined range, and have thus completed the present invention.

[0007] The first invention is a polystyrene-based biaxially oriented sheet containing 50.0 to 99.0 mass% of a styrene-based resin (A) and 1.0 to 50.0 mass% of a terpene-based resin (B), characterized in that the sheet thickness is 0.05 mm or more and 0.50 mm or less, the orientation relaxation stresses in both the longitudinal and transverse directions of the sheet are 0.1 MPa or more and 1.2 MPa or less, and the loss tangent at 100°C is 0.15 or more and 0.80 or less.

[0008] In the first aspect of the present invention, the sheet preferably contains 0.1% by mass or more and 5.0% by mass or less of an impact resistant polystyrene resin (C) when the sheet is taken as 100.0% by mass.

[0009] In the first aspect of the present invention, the sheet preferably has a Vicat softening temperature of 75°C or higher and lower than 100°C.

[0010] In the first aspect of the present invention, when the sheet has a thickness of 0.18 mm, the haze is preferably 15.0% or less.

[0011] The second invention of the present invention is a package comprising the biaxially oriented polystyrene sheet of the first invention of the present invention. Effect of the Invention

[0012] The polystyrene biaxially oriented sheet of the present invention is less prone to defects in appearance, and therefore has a good production yield and is economically efficient. In addition, it can be molded at a low temperature, and therefore the energy required for molding can be reduced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described. Note that the scope of the present invention is not limited to the embodiment described below. <Polystyrene biaxially oriented sheet> The polystyrene biaxially oriented sheet of the present invention (hereinafter sometimes referred to as the sheet of the present invention) contains 50.0 to 99.0 mass % of a styrene resin (A) and 1.0 to 50.0 mass % of a terpene resin (B). Unless otherwise noted, the expression "△~△△" means "△ or more and △△ or less," and preferably means "more than △ but less than △."

[0014] (Styrene-based resin (A)) The styrene-based resin (A) used in the sheet of the present invention may be a polymer using a styrene-based monomer, or a copolymer of a styrene-based monomer and another monomer copolymerizable therewith. Examples of styrene monomers include alkyl-substituted styrenes such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, and 2,4-dimethylstyrene, α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-4-methylstyrene, and halogenated styrenes such as 2-chlorostyrene and 4-chlorostyrene. These styrene monomers may be used alone or in the form of copolymers of two or more. From the viewpoint of improving heat resistance, a copolymer of styrene and α-methylstyrene is preferred. Examples of other monomers copolymerizable with styrene-based monomers include (meth)acrylic acid, (meth)acrylic acid esters, maleic anhydride, vinyl acetate, acrylonitrile, conjugated diene-based hydrocarbons such as butadiene, isoprene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene, and α-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene. From the viewpoint of improving heat resistance, it is preferable to use (meth)acrylic acid, (meth)acrylic acid esters, maleic anhydride, and acrylonitrile, it is more preferable to use (meth)acrylic acid and (meth)acrylic acid esters, and it is particularly preferable to use (meth)acrylic acid.

[0015] The weight average molecular weight of the styrene-based resin (A) is not particularly limited, but is preferably 150,000 to 2,000,000, more preferably 150,000 to 1,800,000. When it is in this range, the extrusion moldability is good due to the melt viscosity characteristics. In addition, when it is 150,000 or more, the mechanical strength of the sheet is sufficient, and when it is 2,000,000 or less, the elastic modulus of the sheet is suitable and the low-temperature moldability is improved. The MFR of the styrene-based resin (A) is preferably 1.5 g / 10 min or more and 5.0 g / 10 min or less, and more preferably 2.0 g / 10 min or more and 4.0 g / 10 min or less.

[0016] The styrene-based resin (A) preferably has a glass transition temperature of 80° C. or more and 140° C. or less, and more preferably has an upper limit of 130° C. or less. When the glass transition temperature is within this range, the sheet has an excellent balance between mechanical strength and low-temperature moldability when blended with the terpene-based resin (B). Specifically, a glass transition temperature of 80° C. or more can impart practical heat resistance to the sheet, and a glass transition temperature of 140° C. or less provides good low-temperature moldability. The glass transition temperature is determined from the value when the temperature is increased again at 10° C. / min by differential scanning calorimetry based on JIS K7121:2012.

[0017] (Terpene resin (B)) The terpene resin (B) used in the sheet of the present invention is a resin obtained by polymerizing compounds (terpene compounds) that have a terpene skeleton such as hydrocarbons containing the chemical formula isoprene (C5H8) as the main monomer component and their oxygen-containing derivatives, for example, monoterpenes (C10 compounds), sesquiterpenes (C15 compounds), and diterpenes (C20 compounds). Specifically, terpene resins, which are homopolymers of terpene compounds, aromatic modified terpene resins obtained by copolymerizing terpene compounds and aromatic compounds, terpene phenol resins, which are copolymers of terpene compounds and phenol compounds, fully hydrogenated resins thereof, or partially hydrogenated resins thereof, etc. can be used. Among these, terpene resins and aromatic modified terpene resins are preferred because of their ease of availability, low price, and low odor. These may be used alone or in combination of two or more.

[0018] The terpene compound is not particularly limited, but examples thereof include α-pinene, β-pinene, carvone, camphene, 2-carene, 3-carene, dipentene, d-limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-ionone, β-ionone, β-citronellene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, β-citronellol, α-terpineol, β-terpineol, γ-terpineol, etc. These may be used alone or in combination of two or more kinds. These terpene compounds are either of plant or animal origin, are naturally biosynthesized, and are renewable resources.

[0019] Examples of terpene resins, which are homopolymers of terpene compounds, include α-pinene resin, β-pinene resin, dipentene resin, etc. These resins have a biomass ratio close to 100%, so they can be effectively used from the perspective of the circular economy due to the recent increase in environmental awareness.

[0020] Aromatic modified terpene resins are copolymers of terpene compounds and aromatic compounds. Examples of aromatic compounds that can be copolymerized with terpene compounds include styrene, α-methylstyrene, alkylstyrene, alkoxystyrene, vinyltoluene, styrene derivatives such as unsaturated hydrocarbon group-containing styrene, coumarone, indene, etc. These may be used alone or in combination of two or more. As the aromatic modified terpene resin, copolymers with a styrene monomer, such as α-pinene-styrene copolymer, dipentene-styrene copolymer, β-pinene-styrene copolymer, α-pinene-α-styrene copolymer, and limonene-styrene copolymer, are preferred. The copolymerization mass composition ratio of the terpene compound / aromatic compound in the aromatic modified terpene resin is preferably 5 / 95 to 99 / 1, more preferably 20 / 80 to 95 / 5, and even more preferably 40 / 60 to 95 / 5. In order to increase the biomass ratio of the aromatic modified terpene resin, it is advisable to use an aromatic compound derived from biomass and / or to increase the copolymerization composition ratio of the terpene compound. The biomass ratio (unit %) is determined by the ratio of the dry weight of the component derived from the biomass raw material to the total dry weight of the resin. These copolymers can be obtained, for example, by mixing a terpene compound and an aromatic compound in an organic solvent and copolymerizing the mixture in the presence of a Friedel-Crafts catalyst.

[0021] The weight average molecular weight of the terpene resin (B) is not particularly limited, but the upper limit is preferably 6000 or less, more preferably 5000 or less, and even more preferably 4000 or less. The lower limit is preferably 300 or more, more preferably 500 or more, and even more preferably 700 or more. A molecular weight of 6000 or less improves compatibility with the styrene resin (A), and the softening point of the terpene resin (B) is lowered, improving the low-temperature moldability of the sheet. A molecular weight of 300 or more ensures sufficient mechanical strength and heat resistance of the sheet.

[0022] The softening point of the terpene resin (B) is preferably 60°C or higher and 160°C or lower, more preferably 70°C or higher and 150°C or lower, and even more preferably 80°C or higher and 140°C or lower. A softening point of 60°C or higher can impart practical heat resistance to the sheet. A softening point of 160°C or lower can lower the Vicat softening temperature and glass transition temperature of the sheet, improving low-temperature moldability. The softening point of the terpene resin (B) is measured in accordance with JIS K5902:2006.

[0023] (Sheet composition) The sheet of the present invention can exhibit low-temperature moldability by mixing the styrene resin (A) and the terpene resin (B). This is because the glass transition temperature and softening point of the terpene resin (B) can be easily controlled by the molecular weight. In addition, the aromatic modified terpene resin, particularly the styrene modified terpene resin, can adjust the compatibility between the styrene resin (A) and the terpene resin (B) by styrene, which is a common component with the styrene resin (A), so that the glass transition temperature and Vicat softening temperature of the sheet made of the resin composition of both resins can be easily controlled.

[0024] In the sheet of the present invention, when the sheet is 100.0% by mass, the mixed mass composition ratio of the styrene-based resin (A) to the terpene-based resin (B) is 50.0-99.0:1.0-50.0. When the mixed mass composition ratio of the terpene-based resin (B) is 1.0% by mass or more, the low-temperature formability of the sheet is improved, and when it is 50.0% by mass or less, the compatibility with the styrene-based resin (A) is good, and the sheet surface is less likely to become rough, improving the sheet appearance. In particular, when the mixed mass composition ratio of the styrene-based resin (A) and the terpene-based resin (B) is 80.0-99.0:1.0-20.0, the sheet has high colorless transparency and is suitable for use in packaging applications where visibility of the contents and aesthetic appearance are required, such as in molded products such as container lids, etc. The ratio is more preferably 90.0-99.0:1.0-10.0, and even more preferably 95.0-99.0:1.0-5.0. Furthermore, when the mixed mass composition ratio of the styrene-based resin (A) and the terpene-based resin (B) is 50.0-80.0:20.0-50.0, the whiteness of the sheet increases and printed characters and patterns stand out, making the sheet suitable for packaging applications consisting of molded products such as highly designed sheets and bottom containers. A ratio of 50.0-70.0:30.0-50.0 is more preferable. From the viewpoint of reducing the amount of petroleum-derived resin used and reducing the environmental load, the higher the mixing ratio of the biomass-derived terpene resin (B) is, the more preferable. For example, the biomass ratio of the sheet is preferably 0.5% or more, and more preferably 2.5% or more. The biomass ratio (unit %) is calculated from the ratio of the dry weight of the biomass used to the dry weight of the product.

[0025] (Impact-resistant polystyrene resin (C)) The sheet of the present invention may contain an impact-resistant polystyrene resin (C). The inclusion of the impact-resistant polystyrene resin (C) improves the blocking resistance and impact resistance of the sheet. The content of the impact-resistant polystyrene resin (C) is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 4.0% by mass or less, when the sheet is taken as 100.0% by mass.

[0026] The impact-resistant polystyrene resin (C) may be any polystyrene resin containing a component such as rubber, and may be one containing a rubber component in a styrene homopolymer. Examples of the rubber component include polybutadiene, styrene-butadiene copolymer, polyisoprene, butadiene-isoprene copolymer, etc. The rubber component may be one in which the rubber component is dispersed independently in particulate form in polystyrene, which is the matrix resin, or one in which the rubber component is graft-polymerized to polystyrene and dispersed in particulate form.

[0027] From the viewpoint of achieving both impact resistance and stretch moldability, the content of the rubber component in the impact resistant polystyrene resin (C) is preferably 1.0 mass% or more and 15.0 mass% or less, more preferably 3.0 mass% or more and 15.0 mass% or less, and even more preferably 5.0 mass% or more and 15.0 mass% or less, where the impact resistant polystyrene resin (C) is taken as 100.0 mass%. The rubber content is determined by measuring the diene content by potentiometric titration using iodine monochloride, potassium iodide, and sodium thiosulfate standard solutions, and calculating the diene content as the rubber polymer content. The measurement method is described in, for example, "New Edition Polymer Analysis Handbook," edited by the Polymer Analysis Research Forum of the Japan Society for Analytical Chemistry, Kinokuniya Shoten (1995 edition), p. 659 (3) Rubber Content. The MFR of the impact resistant polystyrene resin (C) is preferably 1.5 g / 10 min or more and 5.0 g / 10 min or less, and more preferably 2.0 g / 10 min or more and 4.0 g / 10 min or less.

[0028] (Compatibilizer) The sheet of the present invention may contain a compatibilizer in order to improve the compatibility between the styrene-based resin (A) and the terpene-based resin (B) and obtain a homogeneous sheet. The compatibilizer is not particularly limited as long as it is a component that can obtain a compatibility effect between the styrene-based resin (A) and the terpene-based resin (B), and examples thereof include styrene-based thermoplastic elastomers, and specific examples thereof include styrene-butadiene-styrene block copolymers (SBS), styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-butadiene-butylene-styrene block copolymers (SBBS), styrene-isoprene-styrene block copolymers (SIS), and styrene-isobutylene-styrene block copolymers (SIBS). The content of the compatibilizer is preferably 0 to 30% by mass, more preferably 1 to 20% by mass, and even more preferably 2 to 10% by mass, when the sheet is taken as 100% by mass. When the content of the compatibilizer is 30% by mass or less, the rubber components such as ethylene, propylene, butylene, isobutylene, butadiene, and isoprene in the styrene-based thermoplastic elastomer are less susceptible to thermal deterioration during the sheet film formation process and secondary processing, and the sheet appearance, biaxial stretchability, and low-temperature moldability are improved.

[0029] (Other ingredients) The sheet of the present invention may contain other components such as resins other than the above-mentioned resins and additives, within the scope of not impairing the effects of the present invention. Examples of other resins include polyolefin resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polyester resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, ethylene vinyl acetate copolymers, polymethylpentene resins, polyvinyl alcohol resins, cyclic olefin resins, polylactic acid resins, polybutylene succinate resins, polyacrylonitrile resins, polyethylene oxide resins, cellulose resins, polyimide resins, polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, polyamideimide resins, polyamide bismaleimide resins, polyarylate resins, polyetherimide resins, polyether ether ketone resins, polyether ketone resins, polyether sulfone resins, polyketone resins, polysulfone resins, aramid resins, and fluorine-based resins. The sheet may also contain recycled resins made from trimming waste from sheet edges generated during the sheet manufacturing process.

[0030] Examples of additives include processing aids, melt viscosity improvers, antioxidants, antiaging agents, heat stabilizers, light stabilizers, weather resistance stabilizers, ultraviolet absorbers, neutralizing agents, nucleating agents, crosslinking agents, lubricants, antiblocking agents, mineral oils, slip agents, antifogging agents, antibacterial agents, deodorants, flame retardants, antistatic agents, colorants, and pigments.

[0031] The anti-blocking agent may be inorganic particles or organic particles. The inorganic particles may be, for example, silica, glass beads, etc., or those that have been subjected to chemical treatment on the surface. The organic particles may be, for example, polystyrene, polymethyl methacrylate, etc., or those that have been subjected to heat treatment or chemical treatment. Among them, spherical silica mainly composed of silicon oxide is preferred, because it is chemically stable, does not denature resin by catalytic action, and has the ability to be applied to the sheet surface with silicone oil as a release agent, as described below. The content of the antiblocking agent in the sheet is preferably 50 to 500 ppm, and the average particle size is preferably 1 to 20 μm.

[0032] (Anti-fog layer, release layer) The sheet of the present invention can be provided with an anti-fogging layer and a release layer by applying a coating liquid containing an anti-fogging agent, a release agent, etc. to the surface and drying the coating liquid. By providing an anti-fogging layer on one side of the sheet and a release layer on the other side, the sheet can have good releasability when forming and using a package such as a lid or container, and can have good anti-fogging properties when containing moisture-containing contents such as food. As the anti-fogging agent, known surfactants can be used, and polyhydric alcohol fatty acid esters such as sucrose fatty acid esters and polyglycerin fatty acid esters are preferred. Furthermore, the addition of water-soluble polymers such as polyvinyl alcohol, acrylic polymers, polyoxyethylene polyoxypropylene block copolymers, and / or polysaccharide mixtures such as methyl cellulose and cyclodextrin improves the dispersibility and retention of the polyhydric alcohol fatty acid esters on the sheet surface, which is preferred in terms of improving anti-fogging properties. As the releasing agent, silicone oil is preferred, and from the standpoint of safety, releasing property, etc., alkylpolysiloxane is preferred, and polydimethylsiloxane is particularly preferred. The thicknesses of the anti-fogging layer and the release layer are not particularly limited, but in order to fully exhibit their performance, the anti-fogging layer is preferably 20 to 100 nm, and the release layer is preferably 1 to 50 nm.

[0033] (Sheet manufacturing method) The polystyrene biaxially oriented sheet of the present invention can be produced by a known method, for example, by melt-kneading raw materials in an extruder, extruding the raw materials into a sheet form from a die, and cooling and solidifying the sheet with a cooling roll, air cooling, or water cooling to produce an unstretched sheet, which is then stretched in the machine direction and the cross direction to obtain a biaxially oriented sheet.

[0034] As a detailed example of a method for producing an unstretched sheet, the raw materials constituting the sheet are mixed, and then an extruder such as a single screw extruder, a counter-rotating twin screw extruder, or a co-rotating twin screw extruder is used to promote uniform dispersion and distribution of the composition. The raw materials may be mixed in a mixer such as a tumbler mixer, a mixing roll, a Banbury mixer, a ribbon blender, or a super mixer, and then fed into the extruder, or a strand die may be connected to the tip of another kneader, and the raw materials may be pelletized once by a method such as strand cutting or die cutting, and the resulting pellets may then be fed into the extruder. Next, the resin composition melted by the extruder is molded into a sheet by connecting a die such as a T-die to the tip of the extruder, and then cooled and solidified by a cooling roll. The extrusion temperature is preferably about 180 to 260°C, more preferably 190 to 250°C.

[0035] As a detailed example of the stretching method of the unstretched sheet, it is preferable to perform biaxial stretching by roll stretching in the flow direction of the sheet (machine direction, MD) or tenter stretching in a direction perpendicular to the flow direction of the sheet (transverse direction, TD). Moreover, the sheet may be stretched in the machine direction and then in the transverse direction, or may be stretched in the transverse direction and then in the machine direction. Moreover, if the sheet has been stretched in the machine direction and the transverse direction, it may be stretched two or more times in the same direction. Moreover, the sheet may be stretched in the machine direction, then in the transverse direction, and then in the machine direction. Moreover, the sheet may be stretched in the machine direction, then in the transverse direction, and then in the machine direction. Moreover, the sheet may be stretched in the machine direction and then in the transverse direction at the same time by a simultaneous biaxial stretching machine. Furthermore, the unstretched sheet may be cut and biaxially stretched by a batch-type stretching machine.

[0036] The stretching ratio of the biaxially stretched sheet is preferably 1.1 to 4.0 times in both the longitudinal and transverse directions of the sheet, more preferably 1.5 to 3.0 times, and even more preferably 2.0 to 2.5 times. A stretching ratio of 1.1 times or more provides a molded product obtained by molding the sheet with sufficient impact strength, while a stretching ratio of 4.0 times or less provides good shaping properties and shape reproducibility when the sheet is thermoformed. The stretch ratio in the present invention is obtained by drawing a straight line on a test piece of a biaxially stretched sheet, heat shrinking the test piece, and determining the change rate of the straight line length before and after shrinkage.Specifically, it is a value calculated by the formula [stretch ratio=Y / Z], in which Y is the length (mm) of a straight line drawn on the test piece of a biaxially stretched sheet in the longitudinal and transverse directions of the sheet using a ruler and a writing instrument, and Z is the length (mm) of the straight line after the test piece is immersed in a silicon oil bath at a temperature 40° C. higher than the Vicat softening temperature of the sheet measured according to JIS K7206 for 10 minutes and shrinks.

[0037] (Sheet thickness) The thickness of the sheet of the present invention is 0.05 mm or more and 0.50 mm or less. In this range, ease of handling in the secondary processing step for producing molded products such as packaging bodies and strength of the molded products are good, and 0.10 mm or more and 0.40 mm or less are preferable, and 0.15 mm or more and 0.3 mm or less are more preferable. When it is 0.05 mm or more, the molded products have sufficient mechanical strength, and when it is 0.50 mm or less, it is easy to perform secondary processing.

[0038] (Sheet properties) ·Transparency When the sheet of the present invention is used for packaging, such as a molded product such as a container lid, where visibility of the contents and good appearance are required, the higher the transparency of the sheet, the better. For example, when the sheet has a thickness of 0.18 mm, the sheet has a haze of preferably 15.0% or less, more preferably 10.0% or less, even more preferably 5.0% or less, and particularly preferably 2.0% or less. The total light transmittance is preferably 80% or more, more preferably 84% or more, and even more preferably 90% or more. On the other hand, when the mixed composition ratio of the terpene resin (B) is increased to increase the biomass content of the sheet, when the mixed composition ratio of the impact-resistant polystyrene resin (C) is increased to increase the strength of the thin-walled molded product, or when a compatibilizer is included to improve the compatibility of the resins constituting the sheet, the whiteness of the sheet is likely to be high. In these cases, the sheet can be suitably used for packaging such as highly designed sheets and bottom containers in which printed characters and patterns stand out. For example, when the sheet thickness is 0.18 mm, the haze is likely to be more than 10.0% and 70.0% or less, and is likely to be 15.0% or more and 50.0% or less, and is preferably 15.0% or more and 30.0% or less in terms of compatibility with the mechanical strength and heat resistance of the sheet. Haze can be measured in accordance with JIS K7136:2000 and is the ratio of diffuse transmittance to total light transmittance. Total light transmittance can be measured in accordance with JIS K7361-1:1997.

[0039] Vicat softening temperature, glass transition temperature The sheet of the present invention has a lower Vicat softening temperature and glass transition temperature due to the inclusion of the terpene resin (B), and is superior in low-temperature formability to biaxially oriented sheets made of homopolystyrene that are available on the market. The upper limit of the Vicat softening temperature is preferably less than 100° C., more preferably 99° C. or less, and even more preferably 98° C. or less, from the viewpoint of low-temperature formability of the sheet. The lower limit is preferably 75° C. or more, more preferably 80° C. or more, and even more preferably 85° C. or more, from the viewpoint of practical heat resistance. The upper limit of the glass transition temperature is preferably less than 100° C., more preferably 99° C. or lower, from the viewpoint of low-temperature formability of the sheet. The lower limit is preferably 80° C. or higher, more preferably 85° C. or higher, from the viewpoint of practical heat resistance. The Vicat softening temperature can be measured in accordance with JIS K7206:2016. The glass transition temperature is determined based on JIS K7121:2012 using a differential scanning calorimeter and is the glass transition temperature when the temperature is increased again at 10° C. / min. The object for measuring the Vicat softening temperature and the glass transition temperature may be any of the resin composition constituting the sheet, the unstretched sheet, and the heat-shrunk product of the biaxially stretched sheet.

[0040] Viscoelasticity The sheet of the present invention has a loss tangent (tan δ) of 0.15 or more, preferably 0.20 or more, at 100° C., measured using a dynamic viscoelasticity measuring device at a vibration frequency of 10 Hz. The upper limit of the loss tangent (tan δ) is 0.80 or less, preferably 0.70 or less, and more preferably 0.60 or less. Loss tangent (tan δ) is the ratio of loss modulus (E") to storage modulus (E'), i.e., loss tangent (tan δ = E" / E'). A high loss tangent (tan δ) means that the loss modulus (E") of the material, i.e., the contribution of viscosity, is large in that temperature range. The sheet of the present invention has excellent low-temperature moldability. Since the general molding temperature of polystyrene biaxially oriented sheets is around 100°C to 140°C, the thermoformability of the sheet can be considered from the magnitude of the loss tangent (tan δ) by setting the temperature index of viscoelasticity at 100°C. When the loss tangent (tan δ) is 0.15 or more, the sheet deforms appropriately when heated and molded into a package, improving moldability. When the loss tangent (tan δ) is 0.80 or less, the sheet does not deform too much when heated and molded into a package, making it difficult to cause molding defects such as tearing and uneven thickness. The loss tangent (tan δ) is generally controlled by the glass transition temperature, molecular structure, molecular orientation, etc. of the material. In the present invention, the loss tangent (tan δ) of the sheet can be adjusted to a desired range by optimizing the mixing composition ratio of the terpene resin (B) having a low glass transition temperature. Specifically, by increasing the mixing amount of the terpene resin (B), the glass transition temperature can be shifted to the low temperature side, and the loss tangent can be increased. In this case, the mixing amount of the terpene resin (B) is preferably in the above-mentioned range of 1.0 to 50.0%.

[0041] ·Orientation relaxation stress The sheet of the present invention has an orientation relaxation stress in both the machine direction and the transverse direction of 0.1 MPa to 1.2 MPa, preferably 0.2 MPa to 1.0 MPa, and more preferably 0.3 MPa to 0.8 MPa. At 0.1 MPa or more, the impact resistance of the sheet, molded product, and package is improved, making them less likely to crack or tear, and when the sheet is thermoformed by hot plate heating type compressed air molding, etc., molding defects such as tearing at the frame part around the outer periphery of the mold are less likely to occur. At 1.2 MPa or less, the shapeability and shape reproducibility during thermoforming are good. In order to reduce defects during thermoforming due to anisotropy of physical properties in the longitudinal and transverse directions of the sheet, the absolute difference in orientation relaxation stress between the longitudinal and transverse directions is preferably 0.6 MPa or less, more preferably 0.4 MPa or less, and even more preferably 0.1 MPa or less. The orientation relaxation stress of the sheet is a physical property that is obtained by orienting the resin molecules by biaxial stretching, and when the longitudinal stretching temperature and the transverse stretching temperature are lowered and stretched, the orientation relaxation stress in the longitudinal and transverse directions increases, whereas when the longitudinal stretching temperature and the transverse stretching temperature are raised and stretched, the orientation relaxation stress in the longitudinal and transverse directions decreases. In order to set both the orientation relaxation stress in the longitudinal and transverse directions to 0.1 MPa or more and 1.2 MPa or less, it is recommended to set the longitudinal stretching temperature to 100 to 130°C, the longitudinal stretching ratio to 1.1 to 4.0 times, the transverse stretching temperature to 100 to 140°C, and the transverse stretching ratio to 1.1 to 4.0 times. The orientation relaxation stress of the sheet is determined in accordance with ASTM D 1504 by measuring the maximum shrinkage stress generated when a 15 mm wide test piece is immersed in a silicone oil bath at a temperature 30°C higher than the Vicat softening temperature of the sheet.

[0042] Shock resistance In order to prevent the sheet of the present invention from cracking during secondary processing or from cracking or tearing during handling of the package, the sheet preferably has impact resistance of 0.5 J or more, more preferably 0.7 J or more, as measured in accordance with JIS K7124-2:1999.

[0043] Tensile modulus The sheet of the present invention preferably has a tensile modulus of 2.0 GPa or more, more preferably 2.2 GPa or more, and even more preferably 2.5 GPa or more, measured at an atmospheric temperature of 23° C. in accordance with JIS K7161-1:2014. The upper limit is not particularly limited, but is generally 6.0 GPa or less. If the tensile modulus is 2.0 GPa or more, the rigidity of the sheet or package is sufficiently high, and deformation due to an external force is suppressed, which is preferable, especially when the sheet thickness is reduced.

[0044] <Package> The sheet of the present invention can be used for packaging products after being molded. The packaging body is formed into a shape according to various applications, for example, packaging body for storing food such as fresh produce, prepared foods, dried foods, confectionery, and industrial parts, and examples of the shape include box-shaped bottom containers, cups, plates, trays, containers with lids, lids, and the like. The sheet of the present invention can be formed by a known method. For example, hot plate contact molding, pressure molding, vacuum molding, vacuum pressure molding, plug assist molding, etc. Among them, hot plate contact molding is preferred from the viewpoint of uniformity of thickness of the molded product and molding production efficiency. The sheet may be molded continuously using a sheet roll, or may be molded shot by shot using a cut plate sheet.

[0045] In the case of the hot plate contact thermoforming method, the hot plate temperature condition is preferably the Vicat softening temperature of the sheet +10°C to +30°C from the viewpoint of low-temperature formability, with the upper limit being more preferably +20°C or less, and even more preferably +15°C or less. When the mold shape is complex or deep, it is recommended to set the Vicat softening temperature +16°C to +20°C. From the viewpoint of low-temperature formability of the sheet, the hot plate temperature condition is preferably as low as possible within a range in which sufficient shaping is obtained. By setting the hot plate temperature condition to the Vicat softening temperature +30°C or less, it is easy to achieve both a short molding cycle time and suppression of raindrop generation in the molded product. The heating time condition for the above-mentioned various molding methods is preferably 0.5 to 10.0 seconds, more preferably 0.5 to 5.0 seconds. The heating time refers to the sum of the time during which the sheet is in contact with the hot plate under vacuum and / or compressed air, and the delay time until the desired vacuum and / or compressed air state is reached for spreading the sheet into the mold. EXAMPLES

[0046] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples as long as it does not depart from the gist of the present invention. <Ingredients> The components, physical properties and abbreviations of the raw materials used in the examples and comparative examples are as follows. The melt flow rates (MFR) of the styrene resin (A) and the impact-resistant polystyrene resin (C) are values ​​measured at a temperature of 200°C and a load of 5 kgf in accordance with JIS K7210-1:2014. The MFR of the compatibilizer is a value measured at a temperature of 230°C and a load of 2.16 kgf in accordance with JIS K7210-1:2014. The softening point of the terpene resin (B) is a value measured in accordance with JIS K5902:2006.

[0047] (Styrene-based resin (A)) A-1: Styrene homopolymer, MFR 3.5g / 10min (Terpene resin (B)) B-1: Aromatic modified terpene resin, YS Resin TO125 manufactured by Yasuhara Chemical Co., Ltd., softening point 125°C, biomass ratio 70%, weight average molecular weight 1500 B-2: β-pinene resin, softening point 115℃, biomass ratio 90%, weight average molecular weight 3400

[0048] (Impact-resistant polystyrene resin (C)) C-1: Styrene-polybutadiene rubber graft copolymer, polybutadiene rubber content 9.0 mass%, MFR 3.0g / 10min (compatibilizer); D-1: Styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene content 67% by mass, MFR 2.0g / 10min

[0049] <Examples 1 to 8, Comparative Example 1> The raw materials for the sheet composition shown in Table 1 were fed into a single screw extruder, melt-kneaded at a set temperature of 200°C, extruded into a sheet through a T-die connected to the tip of the single screw extruder, taken up on a casting roll set at a temperature of 100°C, and cooled and solidified to obtain an unstretched sheet. The unstretched sheet obtained was then stretched 2.5 times in the longitudinal direction and 2.5 times in the transverse direction using a simultaneous biaxial stretching machine at the stretching temperature shown in Table 1 to obtain a biaxially stretched sheet. The biomass degree of the sheet was calculated by multiplying the mixed mass composition ratio of the terpene resin (B) by the biomass ratio of the terpene resin (B) when the mass of the sheet was taken as 100%, and is shown in Table 1.

[0050] <Evaluation> The sheets obtained in the examples and comparative examples were evaluated as follows and the results are summarized in Table 1. (1) Sheet thickness The biaxially oriented sheet was measured for thickness using a stand-type constant pressure thickness measuring device in accordance with JIS K7130:1999. (2) Seat appearance Five test pieces measuring 250 mm in the longitudinal direction and 250 mm in the transverse direction were cut from the biaxially oriented sheet, and the number of defects in appearance such as gel foreign bodies, unmelted particles, and gum were counted. The total number of the five test pieces was evaluated according to the following criteria. Good: Fewer than 3 defects Acceptable: 3 to less than 8 defects Unacceptable: 8 or more defects (3) Transparency (haze, total light transmittance) For the biaxially stretched sheet, the haze was measured according to JIS K7136:2000 using a haze meter NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd., and the total light transmittance was measured according to JIS K7361:1997.

[0051] (4) Vicat softening temperature The measurement was performed in accordance with JIS K7206:2016 using an unstretched sheet prior to biaxial stretching. (5) Glass transition temperature In accordance with JIS K7121:2012, using a PerkinElmer DSC8500, approximately 10 mg of a biaxially oriented sheet was heated from 0°C to 200°C at a heating rate of 10°C / min, held at 200°C for 1 minute, then cooled to 0°C at a heating rate of 10°C / min, and heated again to 200°C at a heating rate of 10°C / min, and the glass transition temperature upon re-heating was analyzed.

[0052] (5) Viscoelasticity The viscoelastic curve of the biaxially oriented sheet in the width direction was measured using a dynamic viscoelasticity measuring device based on JIS K7244:1999, under conditions of a vibration frequency of 10 Hz and a strain of 0.1%, when the temperature was raised from -100°C to 200°C, and the storage modulus (E') and loss tangent (tan δ) were determined at 100°C and 115°C. The temperature at which the loss tangent (tan δ) peaked was defined as the peak temperature of the loss tangent (tan δ). (6) Orientation relaxation stress Using a biaxially stretched sheet, test pieces 15 mm wide and approximately 120 mm long were cut parallel to the machine direction, and test pieces 15 mm wide and approximately 120 mm long were cut parallel to the cross direction. The shrinkage stress of each test piece was measured in a silicone oil bath at a temperature 30°C higher than the Vicat softening temperature of the sheet in accordance with ASTM D-1504, and the maximum value was recorded as the orientation relaxation stress.

[0053] (7) Tensile modulus For the biaxially stretched sheet, three test pieces measuring 10 mm wide and 100 mm long were cut in the machine direction and measured using a tensile tester in accordance with JIS K7161-1:2014 at an atmospheric temperature of 23°C and a tensile speed of 5 mm / min, and the average of the measured values ​​for the three pieces was calculated. (8) Tensile elongation at break For the biaxially oriented sheet, in accordance with JIS K7127:1999, a total of 10 dumbbell-shaped test pieces (test piece type 5, width of narrow parallel part 6 mm) were punched out with a cutting blade, five in each of the longitudinal and transverse directions of the sheet, and a benchmark was marked on the narrow parallel part with a gauge distance of 25 mm. A tensile test was performed under conditions of an initial distance between chucks of 80 mm, a measurement atmospheric temperature of 23°C, and a test speed of 200 mm / min, and the average tensile elongation at break of the 10 pieces was calculated. (9) Impact resistance (surface impact strength) For the biaxially oriented sheet, five test pieces of 100 mm x 100 mm were punched out with a cutting blade in accordance with JIS K7124-2:1999. An impact test was performed under conditions of an ambient temperature of 23°C and an impact speed of 3.0 m / sec, and the average surface impact strength (maximum impact point energy) of the five pieces was calculated.

[0054] (10) Low temperature formability A square test piece measuring 250 mm in the longitudinal direction and 250 mm in the transverse direction was cut out from the biaxially stretched sheet, and the evaluation mold was attached to a hot plate heating type compressed air molding machine PK-450 manufactured by Kansai Automatic Forming Machine Co., Ltd., and the heating time was 2.0 seconds and the heating pressure was 1.0 kg / cm. 2 , molding time 1.0 seconds, molding pressure 3.0kg / cm 2 A molding test was performed on the test pieces with the mold temperature at 60°C and the hot plate temperature conditions changed, and the molded sheets were observed to evaluate the faithful reproduction of the mold (mold reproducibility). The hot plate temperature conditions were 88°C to 108°C in 4°C increments, 116°C, and 124°C. The evaluation mold used in the molding test was a rectangle with a long side of 200 mm and a short side of 150 mm, with the long side aligned parallel to the vertical direction of the sheet and the short side aligned parallel to the horizontal direction of the sheet. Within the rectangle, there were 10 grooves with an opening width of 10 mm and a length of 50 to 70 mm in the vertical and horizontal directions, and the 10 grooves had drawing ratios, which are expressed as the maximum depth relative to the opening width of the groove, ranging from 0.3 to 1.2 in increments of 0.1. The larger the drawing ratio, the higher the difficulty of mold reproducibility, and a good maximum drawing ratio for mold reproducibility in each of the vertical and horizontal directions is required for each test piece. Regarding mold reproducibility, if the grooves of the molded sheet are expressed as concave, the sheet is inverted so that the grooves (concave) face upwards (convex) and illuminated to observe, and the height of the convex, which corresponds to the depth of the groove, is examined to see whether it is uniform over the entire length of the groove, and the maximum drawing ratio of the grooves that were evaluated as good was taken as the maximum drawing ratio. For the evaluation, first, two test pieces are molded for each hot plate temperature condition, and the maximum drawing ratios in the vertical and horizontal directions of the two pieces are calculated, totaling four points, and the average value is calculated. Next, the average maximum drawing ratios for each hot plate temperature condition are plotted on a graph with the hot plate temperature on the horizontal axis and the maximum drawing ratio on the vertical axis, and the hot plate temperature at which the maximum drawing ratio is 0.6 is read using a quadratic function approximation curve. The lower this temperature, the better the low-temperature formability can be evaluated to be. Note that if the maximum drawing ratios in the vertical and horizontal directions, totaling four points, are all less than 0.3, or if the molded sheet has severe raindrop, they are not plotted on the graph.

[0055] [Table 1]

[0056] As seen from Table 1, the sheets of Examples 1 to 8, containing the terpene resin (B), had lower Vicat softening temperatures and glass transition temperatures than those of Comparative Example 1, and were excellent in low-temperature moldability. This is because the sheets contained a terpene resin and were stretched so that the orientation relaxation stress was 1.2 MPa or less, resulting in a high loss tangent (tan δ) of 0.15 or more at 100°C, and the sheets easily deformed during thermoforming. In addition, there was little gel-like matter or gum, and the sheet appearance was good in all cases. Examples 1, 2, 3, 5 and 7 had a haze of 10.0% or less, and showed transparency suitable for use as a food packaging material. [Industrial Applicability]

[0057] The polystyrene biaxially oriented sheet of the present invention is less prone to defects in appearance, and therefore has a good production yield and is economically efficient. In addition, it can be molded at a low temperature, and therefore the energy required for molding can be reduced. Furthermore, the use of resin made from terpene raw materials derived from biomass also contributes greatly to reducing the environmental impact.

Claims

1. A sheet containing 50.0 to 99.0% by mass of a styrene-based resin (A) and 1.0 to 50.0% by mass of a terpene-based resin (B), The sheet contains 0.1% by mass or more and 5.0% by mass or less of an impact-resistant polystyrene-based resin (C) which is a styrene-butadiene graft copolymer, when the sheet is taken as 100.0% by mass, The sheet thickness is 0.05 mm or more and 0.50 mm or less, and A polystyrene-based biaxially oriented sheet characterized in that the orientation relaxation stresses in both the longitudinal and transverse directions of the sheet are 0.1 MPa or more and 1.2 MPa or less, and the loss tangent at 100°C when the temperature is raised from -100°C to 200°C under conditions of a vibration frequency of 10 Hz and a strain of 0.1% based on JIS K7244:1999 using a dynamic viscoelasticity measuring device is 0.15 or more and 0.80 or less.

2. 2. The polystyrene biaxially oriented sheet according to claim 1, wherein the sheet has a Vicat softening temperature of 75°C or higher but lower than 100°C.

3. 3. The polystyrene-based biaxially oriented sheet according to claim 1, wherein the haze is 15.0% or less when the sheet thickness is 0.18 mm.

4. A packaging material comprising the biaxially oriented polystyrene sheet according to any one of claims 1 to 3.

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