Styrene-based resin composition and molded product thereof

Abstract

To provide a styrene-based resin composition which reduces the environmental load by using a biomass raw material, retains excellent mechanical strength, and excels in moldability into a biaxially stretched sheet, releasability during molding, and sheet appearance, the styrene-based resin composition having high transparency, and a molded product thereof.SOLUTION: The present disclosure discloses a styrene-based resin composition which contains a styrene-based polymer (A) and a biomass plasticizer (B) of 0.1 mass% to 5.0 mass% with a biomass carbon ratio (pMC) of 10% or more. A plate of 2 mm thick including the styrene-based resin composition has a total light transmittance of 70% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a styrene-based resin composition and a molded article made of the styrene-based resin. [Background technology]

[0002] Styrenic resins are used in a wide range of applications due to their moldability and mechanical strength, and highly transparent styrene resins in particular have a wide range of uses, including miscellaneous goods, transparent food containers, packaging materials, and office equipment. Furthermore, biomass raw materials have attracted attention from the perspective of reducing environmental impact, and the development of composite materials made from styrene resins and naturally derived raw materials is progressing. For example, Patent Document 1 discloses a styrene resin composition containing rubber-modified polystyrene, polylactic acid, and a styrene monomer unit elastomer. Patent Document 2 also discloses a styrene resin composition containing plant-derived polyethylene and a compatibilizer.

[0003] Because styrene-based resins are transparent and have excellent rigidity, they have recently been widely used in food container applications, not only as biaxially oriented sheets and molded articles obtained by secondary processing of biaxially oriented sheets, but also as injection-molded articles. Biaxially oriented sheets and injection-molded articles using styrene-based resins can suffer from problems such as reduced productivity and increased thickness unevenness if the styrene-based resin has low fluidity or mold releasability. On the other hand, if the styrene-based resin has high fluidity, drawdown is likely to occur during sheet molding, resulting in poor sheet moldability. Therefore, the balance between the fluidity and mold releasability of the entire composition is important. For example, in order to control the fluidity of a styrene-based resin, there is a method of adding liquid paraffin. Patent Document 3 discloses an example in which liquid paraffin is added to a highly branched styrene-based resin. Another technique for controlling the fluidity of a resin is to adjust the molecular weight and molecular weight distribution of the resin. For example, Patent Document 4 discloses a styrene-based resin composition that has fluidity suitable for a biaxially oriented sheet by adjusting the molecular weight and molecular weight distribution of a styrene-methacrylic acid copolymer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2016-199652 [Patent Document 2] Japanese Patent Publication No. 2020-193274 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-100430 [Patent Document 4] Patent No. 6389574 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology of Patent Document 1 above considers a polymer alloy of polylactic acid, which has a relatively high melting point and toughness among plant-derived biodegradable polymers, with a styrene-based resin. However, the compatibility of polylactic acid with styrene-based resins is very low, making it difficult to design products that meet the mechanical properties required in the market, such as impact resistance or stretchability. Furthermore, the incompatibility of polylactic acid with styrene-based resins impairs the transparency of the polymer alloy as a whole. Another problem is the difficulty of recycling waste materials containing polylactic acid and styrene-based resins.

[0006] The technology of Patent Document 2 above studies a polystyrene-based resin containing plant-derived polyethylene and a compatibilizer, but because polystyrene and polyethylene have low compatibility, it is difficult to maintain high transparency even when a compatibilizer is used.

[0007] The technology of Patent Document 3 above studies a highly branched styrene-based resin composition that has excellent biaxially oriented sheet moldability and productivity. However, because liquid paraffin is added, it is thought that the appearance of the sheet may be deteriorated due to bleed-out and generation of volatile gas during molding. The technology of Patent Document 4 above studies a styrene-based resin composition that has excellent biaxially stretched sheet formability and productivity by adjusting the molecular weight of a styrene-methacrylic acid copolymer to control fluidity. However, since the molecular weight is relatively low to increase fluidity, there is a concern that the mechanical strength may decrease. When obtaining an injection-molded article, a biaxially oriented sheet, or a molded article obtained by secondary processing of a biaxially oriented sheet, the releasability of the molded article from the mold becomes important for improving productivity depending on the shape of the molded article and molding conditions. However, Patent Documents 1 to 4 do not consider the releasability of the molded article during molding. Furthermore, the above Patent Documents 3 and 4 do not use biomass raw materials, which have been attracting attention in recent years for the purpose of reducing environmental impact. Therefore, the techniques of the above Patent Documents 1 to 4 do not consider highly transparent resins that maintain high mechanical strength and are excellent in releasability during molding, moldability into biaxially oriented sheets, and sheet appearance, nor plasticizers that use biomass raw materials. Therefore, an object of the present disclosure is to provide a highly transparent styrene-based resin composition and a molded article thereof, which use biomass raw materials to reduce the environmental load, maintain high mechanical strength, and have excellent mold releasability during molding, moldability into a biaxially oriented sheet, and sheet appearance. [Means for solving the problem]

[0008] In view of the above problems, the present inventors have conducted extensive research and experiments, and as a result have found that the above problems can be solved by using a styrene-based resin composition containing a styrene-based polymer (A) and a predetermined amount of a biomass plasticizer (B) having a high boiling point and a biomass carbon ratio (pMC%) of 10% or more, and have completed the present inventions [1] to [8] below. [1] A styrene-based resin composition comprising a styrene-based polymer (A) and 0.1% by mass to 5.0% by mass of a biomass plasticizer (B) having a biomass carbon ratio (pMC) of 10% or more, wherein the total light transmittance of a 2 mm thick plate is 70% or more. [2] The styrene-based resin composition according to [1], which has a Vicat softening temperature of 85°C or higher. [3] The styrene-based resin composition according to [1] or [2], wherein the SP value of the biomass plasticizer is 7.5 to 10.5, and the difference in SP value between the styrene-based polymer (A) and the biomass plasticizer (B) is less than 2.0. [4] The styrene-based resin composition according to any one of [1] to [3], wherein the toluene-insoluble content of the styrene-based resin composition is 3 mass % or less. [5] The styrene-based resin composition according to any one of [1] to [4], wherein the content of the styrene-based polymer (A) is 95.0 to 99.9 mass% based on the total amount of the styrene-based resin composition, and the content of the styrene-based monomer unit contained in the styrene-based polymer (A) is 50 mass% or more based on the total amount of the styrene-based polymer (A). [6] The biomass plasticizer (B) is a mixture of vegetable oil and a moldability adjusting compound that adjusts moldability, and the moldability adjusting compound is contained in an amount of 0.01 to 5% by mass based on the total amount of the styrene-based resin composition (A); The styrene-based resin composition according to any one of [1] to [5], wherein the moldability-controlling compound is one or more compounds selected from the group consisting of liquid paraffin and fatty acid-based compounds. [7] The styrene-based resin composition according to any one of [1] to [6], which contains a bluing agent in an amount of 0.001 ppm to 10 ppm relative to the styrene-based resin composition (A). [8] A molded article made of the styrene-based resin composition according to any one of [1] to [7]. [Effects of the Invention]

[0009] The present disclosure provides a transparent styrene-based resin composition that reduces the environmental load, maintains high mechanical strength, and has excellent mold releasability during molding, moldability into a biaxially oriented sheet, and sheet appearance, and a biaxially oriented sheet molded article made of the styrene-based resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail an embodiment of the present invention (hereinafter referred to as "the present embodiment"); however, the present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist.

[0011] [Styrene-based resin composition] The styrene-based resin composition of the present embodiment contains a styrene-based polymer (A) and 0.1 to 5.0 mass % of a biomass plasticizer (B) having a biomass carbon ratio (pMC ratio) of 10% or more. In other words, the styrene resin composition of the present embodiment contains 0.1 to 5.0 mass % of the styrene polymer (A) and the biomass plasticizer (B) relative to the entire styrene resin composition (100 mass %). A 2 mm thick plate obtained from the styrene-based resin composition has a total light transmittance of 70% or more. This makes it possible to provide a transparent styrene-based resin composition that reduces environmental impact, has good flowability and high mechanical strength, and is excellent in injection moldability, moldability into biaxially oriented sheets, and sheet appearance, and a biaxially oriented sheet molded article made from the styrene-based resin composition.

[0012] <Styrene-Based Polymer (A) (Hereinafter, also referred to as Component (A))> The styrene resin composition of the present embodiment contains a styrene polymer (A). In the present embodiment, the content of the styrene polymer (A) is 95.0 to 99.9 mass%, preferably 96.0 to 99.7 mass%, more preferably 96.5 to 99.7 mass%, and more preferably 97.0 to 99.5 mass%, relative to the total mass of the styrene resin composition (100 mass%).

[0013] In this embodiment, the monomers constituting the styrene-based polymer (A) essentially include a styrene-based monomer (a), and may optionally include a vinyl-based monomer (b) copolymerizable with the styrene-based monomer (a). Of the monomers constituting the styrene polymer (A), the content of the styrene monomer (a) is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, even more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, and still more preferably 90 to 100 mass%. The content of the styrene monomer (a), i.e., the content of the styrene monomer unit (a), can be determined by proton nuclear magnetic resonance ( 1 It can be calculated from the integral ratio of the spectrum measured by a H-NMR spectrometer. 1 If quantification is difficult using H-NMR measurement, quantification is performed using infrared spectroscopy (FTIR). Examples of the styrene-based monomer (a) include, in addition to styrene, α-methylstyrene, α-methyl-p-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, as well as styrene derivatives such as bromostyrene and indene. Styrene is particularly preferred. These styrene-based monomers can be used alone or in combination.

[0014] In the present embodiment, the vinyl monomer (b) is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, etc. These unsaturated carboxylic acid ester monomers may be used alone or in combination of two or more.

[0015] In this embodiment, polystyrene refers to a homopolymer obtained by polymerizing a styrene-based monomer (a), and a commonly available one can be appropriately selected and used. Examples of the styrene-based monomer (a) constituting polystyrene include, in addition to styrene, α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, as well as styrene derivatives such as bromostyrene and indene. From an industrial perspective, styrene is particularly preferred. These styrene-based monomers (a) can be used alone or in combination. While polystyrene may contain further monomer units other than the above-described styrene-based monomer (a) units within the scope of not impairing the effects of the present invention, polystyrene typically consists of styrene-based monomer (a) units. In a preferred embodiment of the styrene polymer (A) in this embodiment, the SP value between the styrene polymer (A) and the biomass plasticizer (B) having a biomass carbon ratio (pMC ratio) of 10% or more is controlled to be within a predetermined range. Therefore, for example, the type of monomer unit constituting the styrene polymer (A), the content of the styrene monomer (a), or the content of the vinyl monomer (b) may be adjusted depending on the SP value of the biomass plasticizer (B) used. This allows the biomass plasticizer (B) to be more easily dispersed uniformly in the composition, thereby further improving the mechanical strength.

[0016] In this embodiment, the weight average molecular weight (Mw) of the styrene polymer (A) is preferably 100,000 to 400,000, more preferably 120,000 to 350,000, and even more preferably 140,000 to 300,000. When the weight average molecular weight (Mw) is 100,000 to 400,000, a resin having an excellent balance between mechanical strength and fluidity is obtained, and the amount of gel contamination is also small. The weight average molecular weight (Mw) is a value obtained by gel permeation chromatography in terms of standard polystyrene. Furthermore, the styrene polymer (A) in the present embodiment preferably contains less than 1.0 mass% of a rubber-like polymer (e.g., polybutadiene, polybutadiene containing polystyrene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer) or a structural unit having a conjugated diene structure, relative to the total amount (100 mass%) of the styrene polymer (A).

[0017] In this embodiment, it is preferable that the styrene polymer (A) or the styrene resin composition of this embodiment is substantially free of vinyl cyanide monomers such as acrylonitrile monomer units, methacrylonitrile monomer units, etc. Specifically, the vinyl cyanide monomer is contained in an amount of preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less, based on the total amount of the vinyl monomers (b).

[0018] In the present embodiment, the polymerization method for the styrene polymer (A) is not particularly limited, but for example, a bulk polymerization method or a solution polymerization method can be suitably adopted as a radical polymerization method. The polymerization method mainly comprises a polymerization step of polymerizing polymerization raw materials (monomer components) and a devolatilization step of removing volatile components such as unreacted monomers and polymerization solvent from the polymerization product.

[0019] An example of a method for polymerizing the styrene polymer (A) that can be used in the present embodiment will be described below. When the polymerization raw materials are polymerized to obtain the styrene polymer (A), a polymerization initiator and a chain transfer agent are typically contained in the polymerization raw material composition. Examples of polymerization initiators used in the polymerization of the styrene-based polymer (A) include organic peroxides, such as peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane (Perhexa C), 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane (Pertetra A), and n-butyl-4,4-bis(t-butylperoxy)valerate; dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, and dicumyl peroxide; diacyl peroxides such as acetyl peroxide and isobutyryl peroxide; peroxydicarbonates such as diisopropyl peroxydicarbonate; peroxyesters such as t-butyl peroxyacetate; ketone peroxides such as acetylacetone peroxide; and hydroperoxides such as t-butyl hydroperoxide. From the viewpoints of decomposition rate and polymerization rate, 1,1-bis(t-butylperoxy)cyclohexane is preferred. It is preferable to add the monomer in an amount of 0.005 to 0.08% by mass based on the total amount of the monomers. Examples of chain transfer agents used in the polymerization of the styrene polymer (A) include mercaptans such as α-methylstyrene linear dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, 1-phenyl-2-fluorene, dipentene, and chloroform, terpenes, halogen compounds, and turpentines such as terpinolene. There are no particular restrictions on the amount of the chain transfer agent used, but it is generally preferable to add about 0.005 to 0.3% by weight based on the monomers.

[0020] Solution polymerization using a polymerization solvent can be used as the polymerization method for the styrene polymer (A) if necessary. Examples of polymerization solvents include aromatic hydrocarbons, such as ethylbenzene, and dialkyl ketones, such as methyl ethyl ketone. These solvents can be used alone or in combination of two or more. Other polymerization solvents, such as aliphatic hydrocarbons, can be added to the aromatic hydrocarbons as long as they do not reduce the solubility of the polymerization product. These polymerization solvents are preferably used in an amount not exceeding 25 parts by mass per 100 parts by mass of the total monomers. If the amount of polymerization solvent exceeds 25 parts by mass per 100 parts by mass of the total monomers, the polymerization rate tends to decrease significantly and the mechanical strength of the resulting resin tends to decrease significantly. Adding the polymerization solvent at a ratio of 5 to 20 parts by mass per 100 parts by mass of the total monomers before polymerization facilitates uniform quality and is also preferable in terms of controlling the polymerization temperature.

[0021] In this embodiment, the apparatus used in the polymerization step to obtain the styrene-based polymer (A) is not particularly limited and may be appropriately selected according to the polymerization method of the styrene-based resin. For example, when bulk polymerization is employed, a polymerization apparatus having one or more completely mixed reactors connected together can be used. The devolatilization step is also not particularly limited. For example, when bulk polymerization is employed, polymerization is continued until the final unreacted monomer content is preferably 50% by mass or less, more preferably 40% by mass or less, and devolatilization treatment is performed by a known method to remove volatile components such as the unreacted monomer. More specifically, for example, a conventional devolatilization apparatus such as a flash drum, a twin-screw devolatilizer, a thin-film evaporator, or an extruder can be used, but a devolatilization apparatus with a small retention area is preferred. The temperature for the devolatilization treatment is typically about 190 to 280°C, more preferably 190 to 260°C. The pressure for the devolatilization treatment is typically about 0.13 to 4.0 kPa, preferably 0.13 to 3.0 kPa, and more preferably 0.13 to 2.0 kPa. Desirable methods for devolatilization include, for example, a method of removing volatile components under reduced pressure while heating, and a method of removing volatile components through an extruder or the like designed for the purpose of removing volatile components.

[0022] <Biomass Plasticizer (B) (hereinafter also referred to as Component (B))> The styrene-based resin composition of this embodiment contains a biomass plasticizer (B). The content of the biomass plasticizer (B) is 0.1% by mass to 5.0% by mass, preferably 0.3% by mass to 4.0% by mass, more preferably 0.3% by mass to 3.5% by mass, and even more preferably 0.5% by mass to 3.0% by mass. If the amount of biomass plasticizer is 5% by mass or more, the Vicat softening temperature falls below 85°C, making the composition unsuitable for stretched sheet applications and food packaging applications. If the amount of biomass plasticizer is less than 0.1% by mass, there is a concern that the fluidity will decrease, resulting in increased thickness unevenness during molding. Furthermore, there is a concern that the decreased fluidity will reduce productivity. Furthermore, there is also a concern that the mold releasability of the molded body will be impaired.

[0023] In this specification, the biomass carbon ratio (pMC%) refers to the carbon concentration (mass ratio) of biomass-derived components. More specifically, it refers to the radiocarbon ( 14 C) Obtained by the measurement method 14 The value of the radiocarbon content ( 14 C) The measurement method is 14 It does not contain carbon, and biomass (or biological) carbon is the carbon in the atmosphere at the time of growth. 14 By utilizing the carbon absorption of biomass materials (or living organisms), 14 This is a method to estimate the biomass carbon ratio (pMC%) from the C ratio. Therefore, C contained in the total carbon atoms in the plasticizer of this embodiment 14 The proportion of biomass-derived carbon can be calculated by measuring the proportion of biomass-derived carbon. In the present invention, the biomass carbon ratio (pMC%) is calculated by the following formula (1) using the method described in the Examples section below. Formula (1): Biomass carbon ratio (pMC%) = ( 14 C Plasticizer / 12 C plasticizer) / ( 14 C standard material / 12 C standard material)×100 In addition, oxalic acid (SRM4990) was used as a standard substance, and the AMS method was used to measure 14 C Plasticizer / 12 C plasticizer) / ( 14 C standard material / 12 C standard material) was calculated.

[0024] The weight-average molecular weight (Mw) of the biomass plasticizer of this embodiment is preferably 200 to 7500, more preferably 300 to 5000, and even more preferably 400 to 3000. When the weight-average molecular weight (Mw) of the biomass plasticizer is 200 to 7500, a styrene-based resin composition having an excellent balance between mechanical strength and fluidity is obtained, and the amount of gel contamination is also reduced. Note that the weight-average molecular weight (Mw) is a value obtained by gel permeation chromatography in terms of standard polystyrene, as described in the Examples section below.

[0025] In this embodiment, the biomass plasticizer (B) refers to a plasticizer that uses a biomass material as part or all of its raw material and has a biomass carbon ratio (pMC%) of 10% or more. The biomass plasticizer of this embodiment uses a plant-derived biomass material as at least part of its raw material and has a biomass carbon ratio (pMC%) of 10% or more. It is preferably a vegetable oil, a mixture of vegetable oil and mineral oil, or a polyester-based plasticizer, and more preferably a natural vegetable oil, a modified vegetable oil, a mixture of natural vegetable oil and mineral oil, a mixture of modified vegetable oil and mineral oil, a mixture of natural vegetable oil, modified vegetable oil and mineral oil, or a polyester-based plasticizer. In this specification, vegetable oil is a general term for oils and fats derived from plants, and includes natural vegetable oils and modified vegetable oils. In this embodiment, from the viewpoint of adjusting the balance between mold releasability and fluidity to improve molding processability, it is preferable that the biomass plasticizer (B) is a mixture of vegetable oil and a moldability adjusting compound that adjusts molding processability. A preferred form of biomass plasticizer (B) in this embodiment is a mixture of 50 to 99.99 mass% of vegetable oil and 0.01 to 50 mass% of a moldability adjusting compound in the entire biomass plasticizer (B), a mixture of 75 to 99.99 mass% of vegetable oil and 0.01 to 25 mass% of a moldability adjusting compound in the entire biomass plasticizer (B), a mixture of 85 to 99.99 mass% of vegetable oil and 0.01 to 15 mass% of a moldability adjusting compound is more preferred, and a mixture of 90 to 99.99 mass% of vegetable oil and 0.01 to 5 mass% of a moldability adjusting compound is even more preferred. If the biomass plasticizer (B) has the above-mentioned preferable composition ratio, the biomass content can be maintained at 50% or more, and therefore a greater effect of reducing the environmental load can be expected. Among these, a mixture containing 85% by mass to 99.99% by mass of vegetable oil, 1% by mass to 15% by mass of liquid paraffin, and 0.1% by mass to 5% by mass of a fatty acid compound is preferred. Adding a moldability adjusting compound to a styrene-based resin composition can improve the flowability and the releasability of a molded article from a mold, thereby improving productivity. Furthermore, the amount of the moldability adjusting compound added is preferably 0.01% by mass to 5.0% by mass, more preferably 0.01% by mass to 4.0% by mass, even more preferably 0.01% by mass to 3.0% by mass, even more preferably 0.01% by mass to 2.5% by mass, even more preferably 0.01% by mass to 2.0% by mass, even more preferably 0.01% by mass to 1.5% by mass, even more preferably 0.01% by mass to 1.2% by mass, even more preferably 0.01% by mass to 1.0% by mass, even more preferably 0.01% by mass to 0.5% by mass, and even more preferably 0.01 to 0.3% by mass, relative to the total amount (100% by mass) of the styrene-based resin composition. The moldability adjusting compound is preferably one or more compounds selected from the group consisting of liquid paraffin and fatty acid compounds. The fatty acid compound may be a fatty acid compound or a fatty acid metal salt compound, etc. Specific examples include ethylene bis-stearamide, stearic acid, bis-zinc stearate, calcium stearate, magnesium stearate, etc. In this embodiment, the amount of the fatty acid compound added is preferably 0.1 ppm to 15,000 ppm, more preferably 1 ppm to 10,000 ppm, even more preferably 5 ppm to 9,000 ppm, even more preferably 10 ppm to 8,000 ppm, even more preferably 15 ppm to 7,000 ppm, even more preferably 20 ppm to 6,000 ppm, and even more preferably 25 ppm to 5,000 ppm, relative to the total amount (100% by mass) of the styrene resin composition. When molding styrene resins using injection molding or extrusion molding, fatty acid compounds may be added. This is particularly true for complex shapes or thin-walled parts, where the addition of fatty acid compounds is necessary to prevent cracking or deformation during demolding. Addition methods include melt-kneading the fatty acid compounds into the resin, or sprinkling the fatty acid compounds in powder form on resin pellets as an external lubricant. When added as an external lubricant, it also acts as a lubricant, reducing friction between the screw and the resin during molding or kneading, improving processability. Two or more fatty acid compounds may be used in combination. When emphasis is placed on reducing the environmental load, the biomass plasticizer (B) is preferably a single vegetable oil, i.e., one or more vegetable oils. On the other hand, when emphasis is placed particularly on fluidity, the biomass plasticizer (B) is preferably a mixed oil of one or more vegetable oils and liquid paraffin. Furthermore, when emphasis is placed on the mold releasability of the molded body, the biomass plasticizer (B) is preferably a mixed oil of one or more vegetable oils and a fatty acid compound. When the biomass plasticizer (B) is a mixed oil, the methods described in the Examples section below can be used to quantify the amounts of the components contained in the biomass plasticizer (B).

[0026] In this embodiment, the biomass plasticizer may be a modified vegetable oil. Modified vegetable oil refers to a compound made from vegetable oil, and more specifically, it is a compound in which a portion of a hydrocarbon oil of plant origin has been modified with a functional group. Preferably, the vegetable oil has been modified with an epoxy group, an amino group, or an ester bond. Examples of such vegetable oil include triesters of glycerin and fatty acids, fatty acid monoesters obtained by adding a monoalcohol to a vegetable oil and subjecting them to a transesterification reaction, fatty acid monoesters obtained by subjecting a fatty acid to an esterification reaction with a monoalcohol, and ethers derived from fatty acids. In this embodiment, the modifying group (epoxy group, amino group, or ester bond functional group) of the modified vegetable oil preferably does not substantially polymerize with other components (including the styrene resin (A)) or with the modified vegetable oil itself in the styrene resin composition. In this embodiment, the modification rate of the modified vegetable oil per gram of the modified vegetable oil is preferably 1 mmol% to 50 mmol%. The modification rate of the modified vegetable oil is as described in the Examples below. 1 Calculated by H-NMR measurement.

[0027] Specific examples of the natural vegetable oils include cottonseed oil, tung oil, shea oil, alfalfa oil, poppy seed oil, pumpkin oil, winter squash oil, millet oil, barley oil, quinoa oil, rye oil, kukui oil, passionflower oil, shea butter, aloe vera oil, sweet almond oil, peach kernel oil, soybean oil, cashew oil, peanut oil, avocado oil, baobab oil, borage oil, broccoli oil, calendula oil, camellia oil, canola oil, carrot oil, safflower oil, and niacin. Included are hemp oil, rapeseed oil, cottonseed oil, coconut oil, pumpkin seed oil, wheat germ oil, jojoba oil, lily oil, macadamia oil, corn oil, medfoam oil, monoi oil, hazelnut oil, apricot kernel oil, walnut oil, olive oil, evening primrose oil, palm oil, blackcurrant seed oil, kiwi seed oil, grapeseed oil, pistachio oil, musk rose oil, sesame oil, soybean oil, sunflower oil, castor oil, watermelon oil, or mixtures of these oils. In this embodiment, the modified vegetable oil may be an oil obtained by hydrogenating the above-exemplified natural vegetable oil (e.g., hydrogenated castor oil), an oil obtained by epoxidizing the above-exemplified natural vegetable oil (e.g., modified epoxidized oil), or an oil obtained by amminating the above-exemplified natural vegetable oil (e.g., modified aminated oil). The modified epoxidized oil includes oils in which the epoxy functional group has been ring-opened, such as hydroxylated soybean oil, oils that have been directly hydroxylated in advance, and cashew oil-based polyols.

[0028] Specific examples of the biomass plasticizer (B) of this embodiment include palm oil, epoxidized soybean oil, epoxidized linseed oil, polyoxyethylated castor oil, polyoxyethylated hydrogenated castor oil, oleic acid esters, and lauric acid esters, and examples thereof include "Polycizer W-1810-BIO" and "Epocizer" manufactured by DIC Corporation; "Newcizer 510R" and "Newcizer 512" manufactured by NOF Corporation; "Pionin D Series" manufactured by Takemoto Oil & Fat Co., Ltd.; and "Multi-Ace 20(S)" and "Refined Palm Oil (S)" manufactured by Nisshin Oillio Group, Ltd.

[0029] In this embodiment, the viscosity of the vegetable oil (including natural vegetable oil and modified vegetable oil) at 50°C is preferably 1000 mPa·s or less, more preferably 10 to 1000 mPa·s, and even more preferably 20 to 800 mPa·s.

[0030] The melting point of the biomass plasticizer (B) in this embodiment is preferably −30 to 80°C, more preferably −25 to 77°C, even more preferably −22 to 74°C, still more preferably −18 to 70°C, even more preferably −15 to 67°C, even more preferably −10 to 64°C, even more preferably −8 to 61°C, and particularly preferably −3 to 58°C. When the melting point of the biomass plasticizer (B) is in the range of −30 to 80°C, compatibility with the polymer matrix phase of the rubber-modified styrene-based resin (A) is further improved, making the biomass plasticizer (B) more easily dispersible in the styrene-based resin composition. Furthermore, when the melting point of the biomass plasticizer (B) is lower than −30°C, the amount of volatile components increases, tending to increase mold fouling. When the melting point of the biomass plasticizer (B) is higher than 80°C, it is difficult to melt, making the addition process difficult.

[0031] In this embodiment, the SP value of the styrene polymer (A) and the SP value of the biomass plasticizer (B) ((cal / cm 3 ) 1 / 2 ) is preferably less than ±2.5, more preferably less than ±2.3, even more preferably less than ±2.0, still more preferably less than ±1.8, even more preferably less than ±1.5, even more preferably less than ±1.3, and particularly preferably less than ±1.0. If the difference between the SP value of the styrene polymer (A) and the SP value of the biomass plasticizer (B) is ±2.5 or more, the two become less compatible with each other. As a result, it becomes difficult to uniformly disperse the biomass plasticizer (B) in the styrene resin composition, and the mechanical strength of the entire styrene resin composition tends to decrease. One preferred aspect of this embodiment is a composition containing a styrene-based polymer (A) and a biomass plasticizer (B), wherein the SP value of the styrene-based polymer (A) and the SP value of the biomass plasticizer (B) ((cal / cm 3 ) 1 / 2 ) is less than ±2.5, and the total light transmittance of a 2 mm thick plate is 70% or more. The SP value of the styrene polymer (A) in this embodiment is 7 to 11 (cal / cm 3 ) 1 / 2), and more preferably 7.5 to 10 ((cal / cm 3 ) 1 / 2 ), more preferably 8.0 to 9.5 ((cal / cm 3 ) 1 / 2 ), and even more preferably 8.0 to 9.0 ((cal / cm 3 ) 1 / 2 ) The SP value of the biomass plasticizer (B) in this embodiment is 7.0 to 11.0 ((cal / cm 3 ) 1 / 2 ), and more preferably 7.5 to 10.0 ((cal / cm 3 ) 1 / 2 ), and even more preferably 7.7 to 9.5 ((cal / cm 3 ) 1 / 2 ), and even more preferably 7.9 to 9.0 ((cal / cm 3 ) 1 / 2 ) The solubility parameter (SP value) defined in this embodiment is calculated using the cohesive energy density function shown in the following formula. SP value ((cal / cm 3 ) 1 / 2 )=(△E / V) 1 / 2 Formula (1) (△E is the intermolecular cohesive energy (heat of vaporization), V is the total volume of the mixture, and △E / V is the cohesive energy density.) The change in heat quantity due to mixing, ΔHm, is expressed by the following formula using the SP value: △Hm=V(δ1-δ2)·Φ1·Φ2 ····Formula (2) (δ1 represents the SP value of the solvent, δ2 represents the SP value of the solute, Φ1 represents the volume fraction of the solvent, and Φ2 represents the volume fraction of the solute.) From the above equations (1) and (2), the closer the values ​​of δ1 and δ2 are, the smaller ΔHm becomes and the smaller the Gibbs free energy becomes, so that molecules with a small difference in SP values ​​have a high affinity with each other. The SP value in this specification is calculated by comparing the solubility of the resin with various solvents whose SP values ​​are known, and then calculating the SP value of the unknown resin from the SP value of the solvent with which it is most compatible, specifically by using turbidimetric titration. In this embodiment, the value calculated from the monomer composition is mainly used.

[0032] In this embodiment, examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil (including liquid paraffin), intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; mineral oils obtained by subjecting the distillates to one or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and mineral oils obtained by isomerizing wax (GTL wax) produced by the Fischer-Tropsch process or the like. These mineral oils may be used alone or in combination of two or more. In this embodiment, when a mixture of vegetable oil and mineral oil is used as the biomass plasticizer (B), there are no particular restrictions as long as the biomass carbon ratio (pMC ratio) of the entire biomass plasticizer (B) is 10% or more. For example, it is preferable to mix 10 to 100 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of vegetable oil. The amount of mineral oil added is preferably 0.01% by mass to 5.0% by mass, more preferably 0.01% by mass to 4.0% by mass, even more preferably 0.01% by mass to 3.0% by mass, even more preferably 0.01% by mass to 2.0% by mass, even more preferably 0.01% by mass to 1.5% by mass, even more preferably 0.01% by mass to 1.2% by mass, even more preferably 0.01% by mass to 1.0% by mass, even more preferably 0.01% by mass to 0.5% by mass, and even more preferably 0.01% by mass to 0.3% by mass, relative to the total amount (100% by mass) of the styrene-based resin composition. The quantification and identification of liquid paraffin in this embodiment can be confirmed by methods commonly known to those skilled in the art. For example, a solution is prepared by dissolving fragments of a styrene-based resin composition or a molded article of the composition in a solvent that dissolves matrix resins, such as tetrahydrofuran. Then, while stirring this solution with a stirrer, n-hexane is added dropwise in small amounts to precipitate the polymer matrix and rubber-like polymer. The filtrate is then filtered through a glass filter, evaporated to dryness, and then made to a constant volume with n-hexane. The solution is passed through a polytetrafluoroethylene membrane filter and separated by liquid chromatography to calculate the content of liquid paraffin in the composition or molded article. Liquid paraffin can also be analyzed by pyrolysis GC-MS, 1 H-NMR or 13 Identification, quantification, and molecular weight measurement can be performed using various analytical devices such as C-NMR.

[0033] The toluene-insoluble content of the styrene-based resin composition is preferably 3% by mass or less, more preferably less than 1% by mass, as measured by the method described in the Examples section below.

[0034] <Optional addition ingredients> In addition to the components (A) and (B), the styrene-based resin composition of this embodiment may contain optional components such as known additives and processing aids, as needed, provided that the effects of the present invention are not impaired. These optional components may include moldability-adjusting compounds made from the liquid paraffin and fatty acid compounds, mold release agents, flame retardants, dispersants, antioxidants, weathering agents, antistatic agents, fillers, antiblocking agents, colorants, bluing agents, surface treatment agents, antibacterial agents, and eye discharge inhibitors (such as silicone oils described in JP 2009-120717 A, monoamide compounds of higher aliphatic carboxylic acids, and monoester compounds obtained by reacting higher aliphatic carboxylic acids with monohydric to trihydric alcohol compounds). In this embodiment, the styrene-based resin composition may contain known flame retardants (phosphorus-based flame retardants, halogen-based flame retardants such as bromine-based flame retardants). However, from the viewpoint of the risk of generating gases such as hydrogen bromide by reaction with the biomass plasticizer (B) contained in the styrene-based resin composition, the content of the halogen-based flame retardant is preferably less than 3 mass %, more preferably less than 1 mass %, relative to the total amount (100 mass %) of the styrene-based resin composition. In the present embodiment, by adding a moldability adjusting compound comprising liquid paraffin and a fatty acid-based compound to a styrene-based resin composition, the effects of increasing fluidity and improving the releasability of a molded article from a mold can be imparted, thereby improving productivity.

[0035] In this embodiment, it is preferable to add an anthraquinone-based compound as a bluing agent to adjust the color tone depending on the application. When the bluing agent has an anthraquinone skeleton, a hydrogen abstraction reaction by an excited carbonyl or electron transfer from anions occurs, making it easier to adjust the color tone (i.e., it is easier to suppress yellowness). Therefore, an anthraquinone-based compound having an electron-withdrawing group relative to the anthraquinone skeleton is particularly preferable. In this embodiment, by adding a bluing agent that is an anthraquinone-based compound, it is possible to obtain a molded product with the color tone and appearance required for some applications. For example, when the styrene-based resin composition of this embodiment is molded into a biaxially oriented sheet and used as a lid for a food packaging container, it is necessary to suppress the yellowness of the resin so that the food in the packaging container does not appear yellowish. The amount of the bluing agent added is preferably 0.001 ppm to 10 ppm, more preferably 0.01 ppm to 5.0 ppm, more preferably 0.03 ppm to 3.0 ppm, even more preferably 0.05 ppm to 2.5 ppm, even more preferably 0.08 ppm to 2.2 ppm, even more preferably 0.1 ppm to 2.0 ppm, and even more preferably 0.12 ppm to 1.8 ppm, relative to the total amount (100% by mass) of the styrene resin composition. Within the above-mentioned range of addition, it is possible to suppress the yellowing of the resin and obtain a molded product with excellent appearance. Two or more types of bluing agents may be used in combination. Since most biomass plasticizers (B) with a biomass carbon ratio (pMC%) of 10% or more tend to be yellowish, the styrene-based resin composition of this embodiment containing up to 5% by mass of the biomass plasticizer (B) with a biomass carbon ratio (pMC%) of 10% or more tends to be yellowish. This makes it difficult to use the composition as a transparent material for food products, such as lunch box lids, or as an optical material (e.g., a light guide plate). However, the color tone can be adjusted by adding a bluing agent.

[0036] The styrene-based resin composition in the present embodiment preferably does not contain any metal except for unavoidable impurities, and more specifically, the metal content is preferably less than 3 mass % and more preferably less than 1 mass % relative to the total amount (100 mass %) of the styrene-based resin composition. In this embodiment, the dispersant may be a fatty acid ester compound, a polyethylene glycol compound, a terpene compound, a rosin compound, a fatty acid amide, a fatty acid compound, or a fatty acid metal salt compound. Examples of the antioxidant include phenolic compounds, phosphorus compounds, and thioether compounds. The total content of the above-mentioned optional additive components may be 0.01 to 5% by mass based on the entire styrene-based resin composition.

[0037] As described above, the moldability adjusting compound may be liquid paraffin, a fatty acid compound, a fatty acid metal salt compound, or the like.

[0038] The styrene-based resin composition of the present embodiment may consist essentially of only the component (A), the component (B), and optional additional components, or may consist of only the component (A) and the component (B), or only the component (A), the component (B), and optional additional components. The phrase "consisting essentially of only the component (A), the component (B), and any additional components" means that 95 to 100 mass% (preferably 98 to 100 mass%) of the total amount of the styrene resin composition is the component (A) and the component (B), or the component (A), the component (B), and any additional components. The styrene-based resin composition of the present embodiment may contain unavoidable impurities in addition to the component (A), the component (B), and any optional additional components, as long as the effects of the present invention are not impaired.

[0039] When a modified vegetable oil is used as the biomass plasticizer (B) contained in the styrene-based resin composition of this embodiment, the content of the hydroxyl group-containing compound is preferably less than 3 mass%, more preferably less than 1 mass%, relative to the total amount (100 mass%) of the styrene-based resin composition. The hydroxyl group-containing compound of this embodiment refers to a compound having a hydroxyl group in the polymer, such as (meth)acrylic acid, maleic acid, or phthalic acid. If the hydroxyl group-containing compound is present in an amount of 3 mass% or more, it will react with the modified vegetable oil, causing gelation, which will result in reduced moldability or adverse effects such as a deterioration in the appearance of injection-molded articles. When a natural vegetable oil is used as the biomass plasticizer contained in the styrene-based resin composition, the amount of the hydroxyl group-containing compound is not specified.

[0040] [Physical properties of styrene-based resin composition] <Total light transmittance (%)> The styrene-based resin composition of this embodiment has a total light transmittance (%) of 70% or more, preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. When the styrene-based resin composition has a total light transmittance (%) of 80% or more, for example, the content of particles (e.g., rubber-like polymer particles having an average particle size of 1.0 to 5.0 μm) contained in the styrene-based resin composition can be set to 3 mass% or less based on the total styrene-based resin composition, or the styrene-based resin composition can be used for transparent food containers, packaging materials, or office automation equipment applications that require transparency. Furthermore, by using a specific vegetable oil such as palm oil, epoxidized soybean oil, epoxidized linseed oil, polyoxyethylated castor oil, oleic acid ester, or lauric acid ester as the biomass plasticizer (B) of this embodiment, or by setting the SP value of the biomass plasticizer (B) of this embodiment to less than 10, the blending state within the composition changes, and the total light transmittance (%) of the styrene-based resin composition can be adjusted to a desired value (for example, 70% or more). The specific preparation method for test specimens used to measure the total light transmittance (%) of styrene-based resin compositions conforms to K7361-1, and the test specimens are confirmed to be free of defects such as scratches, bubbles, and bumps, as well as adhesion of dust and grease, and adhesion of adhesives from protective materials. Furthermore, the surface of the test specimens is free of voids and particles visible to the naked eye. When preparing the test specimens by injection molding, mirror polishing may be performed using abrasive paper, abrasive sticks, loose abrasive grains, etc., if necessary depending on the condition of the mold surface. The method for measuring the total light transmittance (%) in the present disclosure and the method for preparing the test piece used in the method for measuring the total light transmittance (%) are as described in the Examples section below.

[0041] <Melt Mass Flow Rate (MFR)> The melt mass flow rate (MFR) of the styrene resin composition of the present embodiment is 1.0 to 9.0, preferably 1.5 to 8.0, more preferably 1.8 to 7.0, more preferably 2.0 to 6.5, and still more preferably 2.2 to 6.0. If the MFR is below 1.0, sheet productivity will decrease. Also, uneven thickness of the sheet will be more likely to occur. If the MFR is higher than 9.0, it will be necessary to reduce the molecular weight of the resin or increase the amount of plasticizer. If the molecular weight of the resin is reduced, there is a risk of a decrease in mechanical strength. Furthermore, if the amount of plasticizer is increased, there is a risk of the Vicat softening temperature decreasing, making it difficult to achieve the required heat resistance. There is also a risk of drawdown occurring during sheet molding if the MFR is high. <Vicat softening temperature> The Vicat softening temperature of the styrene-based resin composition of this embodiment is 85°C or higher, preferably 85°C to 105°C, more preferably 87°C to 103°C, and even more preferably 90°C to 101°C. If the Vicat softening temperature is below 85°C, it becomes difficult to provide the biaxially oriented sheet with the heat resistance required for food packaging applications. If the Vicat softening temperature exceeds 105°C, the fluidity of the resin decreases, resulting in a decrease in sheet productivity. Furthermore, thickness unevenness in the sheet is likely to occur.

[0042] [Injection molded product] The injection-molded article can be produced by a conventional method using the styrene-based resin composition of the present embodiment as a raw material. The temperature of the molding machine is preferably 150°C to 300°C, more preferably 160°C to 260°C, and even more preferably 180°C to 240°C. If the temperature of the molding machine is higher than 300°C, the styrene resin composition will undergo thermal decomposition, which is not preferred. On the other hand, if the temperature is lower than 150°C, the composition will not be molded due to its high viscosity, which is also not preferred. [Biaxially oriented sheet] As a method for producing a biaxially oriented sheet using the styrene resin composition of the present embodiment as a raw material, a commonly known method can be used. The molding temperature of the molding machine is preferably 180°C to 280°C, more preferably 200°C to 260°C, and even more preferably 210°C to 250°C. The biaxially oriented sheet can be subjected to secondary forming by a thermoforming method such as vacuum forming or pressure forming. Applications of the biaxially oriented sheet of the present invention include various containers, and are mainly used for food packaging containers. [Example]

[0043] Hereinafter, the embodiments of the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited to these examples in any way.

[0044] <Measurement and evaluation methods> Measurement and evaluation of physical properties of the resin compositions and biaxially stretched sheets obtained in each of the Examples and Comparative Examples were carried out according to the following methods.

[0045] (1) Measurement of weight average molecular weight of styrene polymer (A) and biomass plasticizer (B) used in examples and comparative examples The weight average molecular weights of the styrene polymer (A) and the biomass plasticizer (B) were measured under the following conditions and procedures. Sample preparation: 5 mg of the sample to be measured was dissolved in 10 mL of tetrahydrofuran and filtered through a 0.45 μm filter. Measurement conditions Equipment: TOSOH HLC-8220GPC (Gel Permeation Chromatography) Column: Two SHODEX GPC KF-606M columns connected in series Guard column: SHODEX GPC KF―G 4A Temperature: 40℃ Carrier: THF 0.50mL / min Detector: RI, UV: 254 nm Calibration curve: Eleven types of TSK standard polystyrene (F-850, F-450, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000) manufactured by Tosoh Corporation were used to create the calibration curve. The calibration curve was created using a third-order linear approximation equation.

[0046] (2) Melt mass flow rate (MFR) The melt mass flow rate (g / 10 min) of the styrene resin composition used in the examples and comparative examples was measured in accordance with ISO 1133 (200° C., load 49 N).

[0047] (3) Measurement of Vicat softening temperature (℃) The Vicat softening temperature (°C) of the styrene resin compositions used in the present examples and comparative examples was measured in accordance with ISO 306 under a load of 49N.

[0048] (4) Measurement of toluene insoluble content (%) of styrene resin composition The toluene-insoluble content of the styrene-based resin composition was measured as follows. 1.00 g of the styrene-based resin composition was weighed out into a settling tube (this mass was designated W1), 20 mL of toluene was added, and the mixture was shaken at 23°C for 1 hour. It was then centrifuged for 60 minutes in a centrifuge (Sakuma Seisakusho Co., Ltd., SS-2050A, rotor: 6B-N6L) at 4°C, 20,000 rpm, and a centrifugal acceleration of 45,100 × G. The settling tube was slowly tilted at approximately 45 degrees, and the supernatant was decanted. The mass of the insoluble content, including toluene, was weighed out, followed by vacuum drying at 160°C and 3 kPa or less for 1 hour. After cooling to room temperature in a desiccator, the mass of the toluene-insoluble content was weighed out (this mass was designated W2). The content (%) of the toluene insoluble matter in the styrene-based resin composition was calculated using the following formula. Toluene insoluble content of styrene resin composition (%) = W2 / W1 × 100

[0049] (5) Measurement method for biomass carbon ratio (pMC%) The biomass carbon percentage (pMC%) of the biomass plasticizer (B) was determined by radiocarbon ( 14 C) Measurement method: AMS method using the following equation (1) 14 C Plasticizer / 12 C plasticizer) / ( 14 C standard material / 12 C standard material) was calculated. Formula (1): Biomass carbon ratio (pMC%) = ( 14 C Plasticizer / 12 C plasticizer) / ( 14 C standard material / 12 C standard material)×100 Oxalic acid (SRM4990) was used as the standard substance.

[0050] (6) Determination of biomass plasticizer content The amount of biomass plasticizer in the styrene-based resin composition used in the examples and comparative examples was determined by the following method. (6-1) Creating a calibration curve Vegetable oil (glycerin fatty acid ester) was dissolved in deuterated chloroform (containing 1% TMS) containing 2-dimethoxyethane as an internal standard. 1 H-NMR measurements were performed. Taking the TMS peak as the reference point at 0 ppm, a peak derived from the proton bonded to the carbon adjacent to the ester group of the vegetable oil was detected at δ4.0-4.4 ppm, and a peak derived from 1,2-dimethoxymethane was detected at 3.4-3.6 ppm. The peak area derived from the vegetable oil was calculated by setting the peak area derived from 1,2-dimethoxymethane to 1. A calibration curve for vegetable oil concentration was created by repeating this procedure while varying the concentration of vegetable oil. (6-2) Quantification The pellet-shaped styrene resin composition obtained in the Examples or Comparative Examples was dissolved in deuterated chloroform (containing 1% TMS), 1 H-NMR measurement was carried out, and the vegetable oil content in the styrene-based resin composition was quantified using the above calibration curve. In the above method, if other peaks overlap with the peak of the internal standard and quantification is difficult, an appropriate substance may be used as the internal standard. Furthermore, vegetable oils can also be quantified using the peak derived from triglycerides detected at 5.0 to 5.5 ppm. When the biomass plasticizer (B) is a mixed oil of vegetable oil and a moldability adjusting compound, the vegetable oil content is determined by the above method, and the moldability adjusting compound content is determined separately. The moldability adjusting compound is quantified by liquid chromatography, GC-MS, 1 H-NMR or13 Identification, quantification, and molecular weight measurement can be performed using various analytical devices such as C-NMR.

[0051] (7) Calculation of denaturation rate For styrene-based resins containing modified vegetable oils, the following procedure is used: 1 It is possible to calculate the degree of modification of modified vegetable oils using H-NMR. 1 g of the pellet-like styrene resin composition obtained in the Examples or Comparative Examples was placed in a 20 mL screw bottle, and 10 mL of methyl ethyl ketone was added. The pellets were then completely dissolved using a shaker, and 5 mL of methanol was added, causing the styrene resin composition to precipitate as an insoluble component in the solution. The insoluble component was then removed, and the solution portion was placed in a recovery flask. The flask was then evacuated to a vacuum for 2 hours using an evaporator to volatilize the methyl ethyl ketone and methanol. The liquid (vegetable oil) remaining in the recovery flask was then added to deuterated chloroform (containing 1% TMS), and the resulting mixture was thawed. 1 H-NMR measurements were performed. Using TMS as the reference point at 0 ppm, peaks at δ 2.8-3.2 ppm were identified due to epoxy groups, and peaks at δ 4.0-4.4 ppm were identified due to protons bonded to carbon atoms adjacent to the ester groups of the vegetable oil. The epoxy modification rate was calculated from the ratio of the area of ​​these two peaks.

[0052] (8) Thickness measurement of biaxially oriented sheets Sheets with thicknesses of 0.95 to 1.05 mm were produced from the styrene-based resin compositions produced in the Examples and Comparative Examples using a 25 mmφ single-screw sheet extruder manufactured by Soken Co., Ltd. Sheets measuring 8 cm x 8 cm were cut out from the produced sheets. The cut sheets were subjected to simultaneous biaxial stretching under the following conditions using a biaxial stretching device (EX6-S1) manufactured by Toyo Seiki Seisakusho Co., Ltd. to produce biaxially stretched sheets. The thickness of the sheets after stretching was measured using a microgauge. Stretching temperature: Vicat softening temperature +20℃ Stretching speed: 170% Stretching ratio: 2.0 times

[0053] (9) Measurement of impact strength (kgf cm) of biaxially oriented sheet The impact strength of the sheet prepared by the method described in (8) above was measured using a film impact tester (A121807502) manufactured by Toyo Seiki Seisakusho.

[0054] (10) Seat appearance evaluation A 0.3 mm thick sheet was produced using a 25 mm diameter single-screw sheet extruder manufactured by Soken Co., Ltd., and the number of foreign matter, bubbles, and transparent or opaque deposits with an average diameter of 1 mm or more (longer diameter + shorter diameter) / 2 within 5 m of the sheet was counted.

[0055] (11) Releasability of biaxially oriented sheets The biaxially oriented sheet was cut into 3 cm x 3 cm pieces, sandwiched between two 5 mm prehardened steel sheets, and secured with clips to produce 20 pieces. The pieces were heated in an oven at 130°C for 5 minutes and then peeled from the sheets. The number of sheet samples that did not separate from the sheets was used as an index of releasability. As a result of this evaluation, the fewer samples that did not separate from the sheets, the better the releasability.

[0056] (12) Thickness uniformity of biaxially oriented sheets As an index of formability into a biaxially oriented sheet, the thickness uniformity of the biaxially oriented sheet was evaluated by the following method. On the sheet prepared by the method described in (8) above, three straight lines were drawn in a grid pattern at 5 cm intervals in the vertical and horizontal directions, and the thickness was measured at nine intersections using a microgauge. Similar thickness measurements were performed on three sheets, and the sheet thickness uniformity was evaluated by the number of thicknesses outside the range of 0.23 to 0.27 mm out of a total of 27 points.

[0057] (13) Demoldability of Injection-Molded Articles Demoldability was evaluated based on the degree of damage caused by the resistance to demolding inside the molded article when it was removed during injection molding. Specifically, a box-shaped molded article with external dimensions of 50 mm length, 90 mm width, 40 mm depth, and 2 mm thickness was used, and the mold had two 1 mm-thick ribs spaced 30 mm apart on the horizontal side. Injection molding was performed using a J100E-P molding machine (manufactured by Nippon Steel Corporation) at a temperature of 220°C and a mold temperature of 45°C. Demoldability was evaluated based on the degree of damage caused inside the molded article during demolding, according to the following criteria: ◎: No scratches at all. Good: Small, small scratches can be seen in the corners inside the molded product. △: Slight linear scratches of 2 mm or less can be seen in the corners inside the molded product. ×: Linear scratches larger than 2 mm can be seen in the corners inside the molded product.

[0058] (14) Calculation of SP value The SP value of each material used in the examples and comparative examples was calculated by turbidimetric titration with reference to literature values ​​or "J. Appl. Polym. Sci., 12, 2359 (1968)".

[0059] (15) Measurement of total light transmittance and YI (I) Test specimen preparation conditions The obtained styrene resin composition was injection molded under the following conditions using a mold for a flat plate to prepare a flat plate having a thickness of 2 mm, and then a sheet was prepared. Molding machine: Toshiba Machine Co., Ltd. EC60N Cylinder temperature: 220℃ Injection pressure: 45 MPa, Injection time: 10 seconds Cooling time: 15 seconds, mold temperature: 45℃ (II) Measurement conditions for total light transmittance The total light transmittance (%) of the test piece sheet prepared above was measured in accordance with JIS K7361-1. (III) Measurement conditions for YI (Yellow Index) The YI (yellow index) was measured in accordance with JIS K7105 using the test piece sheet prepared above.

[0060] The materials used in the examples and comparative examples are as follows. (modified vegetable oil) [Biomass plasticizer (B)] Epoxidized soybean oil (product name "Newcizer 510R" (NOF Corporation), weight average molecular weight (Mw = 1500), biomass carbon ratio (pMC%) 100%, melting point: 5°C, SP value: 9.0 ((cal / cm 3 ) 1 / 2 ), epoxy modification rate: 5 mmol per 1 g (natural vegetable oil) Palm oil (product name "Multi-Ace 20(S)" (Nisshin Oillio Group Co., Ltd.), weight-average molecular weight (Mw = 1000), biomass carbon ratio (pMC%) 100%, melting point: 22°C, SP value (calculated by the Hansen method, distance from the origin in the three-component coordinate system of dispersion force term (δD), polar term (δP), and hydrogen bond term (δH)): 8.2 ((cal / cm 3 ) 1 / 2 )) Castor hydrogenated oil (product name "Castor Hydrogenated Oil" (Ito Oil Mills, Ltd.), weight-average molecular weight (Mw=1000), biomass carbon ratio (pMC%) 100%, melting point 85°C, SP value (calculated by the Hansen method, representing the distance from the origin in the three-component coordinate system of the dispersion force term (δD), polar term (δP), and hydrogen bond term (δH)): 10.1 ((cal / cm 3 ) 1 / 2 ))

[0061] [others] (liquid paraffin) Liquid paraffin, product name "PS350S" (manufactured by Sanko Chemical Industry Co., Ltd.), weight average molecular weight (Mw=250), biomass carbon ratio (pMC%) 0%, pour point: -12.5℃ (Polylactic acid) Polylactic acid, product name "LX175" (Total Corbinion PLA), biomass carbon ratio (pMC%) 100%, melting point: 155°C, SP value: 10.3 (cal / cm 3 ) 1 / 2 (Anthraquinone-based bluing agent) Bluing agent, product name "Plast Violet 8840" (manufactured by Arimoto Chemical Co., Ltd.) Bluing agent, product name "Plast Blue 8580" (manufactured by Arimoto Chemical Co., Ltd.) (Fatty acid compounds, fatty acid metal salt compounds) Ethylene bis(stearic acid amide), product name "Kao-Wax EB-FF" (Kao Corporation) Zinc stearate, product name "Daiwax ZP" (manufactured by Dainichi Chemical Industry Co., Ltd.)

[0062] [Method of producing styrene-based resin composition] [Example 1] (Method for producing styrene-based resin composition (PS-1)) A polymerization liquid prepared by mixing and dissolving 93.05% by mass of styrene, 6.5% by mass of ethylbenzene, 0.4% by mass of Multi-Ace 20(S) (manufactured by The Nisshin Oillio Group, Ltd.), and 0.05% by mass of liquid paraffin was continuously charged at 0.78 L / hr into a 1.5-liter laminar flow reactor-1 equipped with a stirrer and capable of temperature control in three zones, and the temperature was adjusted to 123°C / 128°C / 132°C. The stirrer rotation speed was 80 rpm. The reaction rate at the reactor outlet was 30%. The reaction mixture was then sent to a 1.5-liter laminar flow reactor-2 equipped with a stirrer connected in series with the laminar flow reactor-1 and capable of three-zone temperature control. The agitator's stirring speed was set to 40 rpm, and the temperatures were set to 133°C, 135°C, and 137°C. The reaction mixture was then sent to a 1.5-liter laminar flow reactor-3 equipped with a stirrer and capable of three-zone temperature control. The agitator's stirring speed was set to 10 rpm, and the temperatures were set to 147°C, 150°C, and 152°C. The polymer solution continuously discharged from the polymerization reactor (laminar flow reactor-3) was pelletized after devolatilization under a reduced pressure of 0.8 kPa in an extruder equipped with a vacuum vent. The temperature of the extruder was set to 220°C. Then, 0.2 ppm of Plast Violet 8840 (manufactured by Arimoto Chemical Co., Ltd.) was added to the obtained pellets in a styrene-based resin composition, which was melt-kneaded in the extruder and then pelletized. Furthermore, 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.) was added to the obtained pellets to produce a styrene-based resin composition (PS-1). The polymer matrix phase of the styrene-based resin composition (PS-1) contained polystyrene, and the SP value of the polystyrene was 8.6 (cal / cm 3 ) 1 / 2 The above-mentioned various evaluations were then carried out on the obtained styrene-based resin composition of Example 1. The evaluation results are shown in Table 2-1.

[0063] Examples 2 to 29 <Styrene-based resin compositions (PS-2) to (PS-15), (PS-24) to (PS-35), and (PS-21) to (PS-22) Styrenic resin compositions (PS-2) to (PS-15) and (PS-24) to (PS-35) were produced in the same manner as for the styrenic resin composition (PS-1), except that the polymerization conditions were changed as shown in Tables 1-1 to 1-3 below. Styrenic resin composition (PS-21) was produced by adding palm oil to the styrenic resin composition (PS-16) (plasticizer-free GPPS) so that it contained 1% by mass, and then adding 0.05% by mass of liquid paraffin and 0.2 ppm of Plast Violet 8840. The mixture was kneaded and pelletized in a twin-screw extruder, and then adding 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.) to the resulting pellets. Similarly, a styrene-based resin composition (PS-22) was prepared by adding 1% by mass of palm oil to KIBISAN (registered trademark) PN-117C (a CHI-MEI product), further adding 0.05% by mass of liquid paraffin and 0.2 ppm of Plast Violet 8840, kneading the mixture in a twin-screw extruder, and then adding 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.). The obtained styrene-based resin compositions of Examples 2 to 17 were subjected to the various evaluations described above. The evaluation results are shown in Tables 2-1 to 2-3.

[0064] Comparative Examples 1 to 6 <Styrene-based resin compositions (PS-16) to (PS-20) and (PS-23)> Styrenic resin compositions (PS-16) to (PS-20) were produced in the same manner as for the styrene resin composition (PS-1), except that the polymerization conditions were changed as shown in Table 1-2 below. The styrene-based resin composition (PS-23) was prepared by adding 2% by mass of PLA to the styrene-based resin composition (PS-16), further adding 0.05% of liquid paraffin and 0.2 ppm of Plast Violet 8840, and kneading the mixture in a twin-screw extruder. Then, 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.) was added. The resulting styrene-based resin compositions of Comparative Examples 1 to 6 were subjected to the various evaluations described above. The evaluation results are shown in Table 2-4.

[0065] [Table 1-1]

[0066] [Table 1-2]

[0067] [Table 1-3]

[0068] [Table 2-1]

[0069] [Table 2-2]

[0070] [Table 2-3]

[0071] [Table 2-4] [Industrial Applicability]

[0072] The present invention provides a highly transparent styrene-based resin composition that uses biomass raw materials, reduces environmental impact, maintains high mechanical strength, and is excellent in formability into a biaxially oriented sheet and sheet appearance, and a biaxially oriented sheet made from the styrene-based resin composition. The biaxially oriented sheet obtained from the styrene-based resin composition can be suitably used for food packaging containers and the like by secondary processing.

Claims

1. The present invention comprises a styrene-based polymer (A) and 0.1% by mass to 5.0% by mass of a biomass plasticizer (B) having a biomass carbon ratio (pMC) of 10% or more, The biomass plasticizer (B) is a mixture of 50 to 99.99 mass% of vegetable oil and 0.01 to 50 mass% of a moldability adjusting compound for adjusting moldability, based on the total mass of the biomass plasticizer (B), The moldability adjusting compound is one or more compounds selected from the group consisting of liquid paraffin and fatty acid compounds, A styrene-based resin composition characterized in that a 2 mm thick plate has a total light transmittance of 70% or more.

2. The styrene-based resin composition according to claim 1, which has a Vicat softening temperature of 85°C or higher.

3. 3. The styrene-based resin composition according to claim 1, wherein the SP value of the biomass plasticizer is 7.5 to 10.5, and the difference in SP value between the styrene-based polymer (A) and the biomass plasticizer (B) is less than 2.

0.

4. The styrene-based resin composition according to claim 1 or 2, wherein the toluene-insoluble content of the styrene-based resin composition is 3 mass % or less.

5. 3. The styrene-based resin composition according to claim 1, wherein the content of the styrene-based polymer (A) is 95.0 to 99.9 mass% based on the entire styrene-based resin composition, and the content of the styrene-based monomer unit contained in the styrene-based polymer (A) is 50 mass% or more based on the total amount of the styrene-based polymer (A).

6. 3. The styrene-based resin composition according to claim 1, wherein the styrene-based resin composition (A) contains 0.001 ppm to 10 ppm of a bluing agent.

7. A molded article made of the styrene-based resin composition according to claim 1 or 2.

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