JP7708731B2 - Styrenic resin composition and molded article thereof - Google Patents

Description

The present invention relates to a styrene-based resin composition and a molded article made of the styrene-based resin.

Styrene-based resins are used for a wide range of purposes due to their moldability and mechanical strength, and styrene-based resins with particularly high transparency are used in a wide range of applications, including miscellaneous goods, transparent food containers, packaging materials, and office equipment. In addition, biomass raw materials have attracted attention from the perspective of reducing environmental impact, and the development of composite materials made from styrene-based resins and naturally derived raw materials is underway. For example, Patent Document 1 discloses a styrene-based resin composition containing rubber-modified polystyrene, polylactic acid, and a styrene-based monomer unit elastomer. Patent Document 2 discloses a styrene-based resin composition containing plant-derived polyethylene and a compatibilizer.

Since styrene resins are transparent and have excellent rigidity, in recent years, biaxially oriented sheets and molded articles obtained by secondary processing of biaxially oriented sheets as well as injection molded articles have been widely used for food container applications. In biaxially oriented sheets and injection molded articles using styrene resins, if the fluidity or releasability of the styrene resin is low, problems such as reduced productivity and worsening thickness unevenness may occur. On the other hand, if the fluidity of the styrene resin is high, drawdown is likely to occur during sheet molding, and sheet moldability is deteriorated. Therefore, the balance between the fluidity and 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 having fluidity suitable for a biaxially oriented sheet by adjusting the molecular weight and molecular weight distribution of a styrene-methacrylic acid copolymer.

JP 2016-199652 A JP 2020-193274 A JP 2013-100430 A Patent No. 6389574

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, and styrene-based resin. However, since the compatibility of polylactic acid with styrene-based resin is very low, there is a problem that it is difficult to design a product that satisfies the mechanical properties required in the market, such as impact resistance or elasticity. In addition, since polylactic acid is incompatible with styrene-based resin, the transparency of the polymer alloy as a whole is impaired. Furthermore, there is also the problem that it is difficult to recycle waste materials containing polylactic acid and styrene-based resin.

The technology in Patent Document 2 considers 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.

The technology of the above-mentioned Patent Document 3 studies a highly branched styrene-based resin composition having excellent biaxially oriented sheet moldability and productivity. However, since liquid paraffin is added, it is considered that the appearance of the sheet is deteriorated due to bleed-out and generation of volatile gas during molding.
In the technology of the above-mentioned Patent Document 4, a styrene-based resin composition excellent in biaxially stretched sheet moldability and productivity is studied by controlling the flowability by adjusting the molecular weight of a styrene-methacrylic acid copolymer. However, since the molecular weight is relatively low to increase the flowability, there is a concern that the mechanical strength will 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 a mold becomes important in terms of increasing productivity depending on the shape of the molded article and the 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 the environmental load. Therefore, the techniques of the above Patent Documents 1 to 4 do not consider highly transparent resins that maintain high mechanical strength and have excellent releasability during molding, moldability into a biaxially oriented sheet, and sheet appearance, and plasticizers using 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 a biomass raw material to reduce the environmental load, maintain high mechanical strength, and have excellent releasability during molding, moldability into a biaxially oriented sheet, and sheet appearance.

In view of the above problems, the present inventors have conducted intensive research and repeated 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, and having a total light transmittance of 70% or more when measured using a 2 mm-thick plate.
[2] The styrene-based resin composition according to [1], having 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 matter in 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% by mass based on the entire styrene-based resin composition, and the content of a styrene-based monomer unit contained in the styrene-based polymer (A) is 50% by 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 for adjusting 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 adjusting compound is one or more 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], containing 0.001 ppm to 10 ppm of a bluing agent 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].

The present disclosure provides a transparent styrene-based resin composition that reduces the environmental impact, maintains high mechanical strength, and has excellent releasability during molding, moldability into a biaxially oriented sheet, and sheet appearance, as well as a biaxially oriented sheet molded article made of the styrene-based resin composition.

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 practiced in various modifications within the scope of the gist of the invention.

[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-based resin composition of the present embodiment contains the styrene-based polymer (A) and 0.1 to 5.0 mass% of the biomass plasticizer (B) with respect to the entire styrene-based resin composition (100 mass%).
A plate having a thickness of 2 mm obtained from the above 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 which reduces the environmental load, has good flowability and high mechanical strength, and is excellent in injection moldability, moldability into a biaxially oriented sheet, and sheet appearance, and a biaxially oriented sheet molded article made of the styrene-based resin composition.

<Styrene-Based Polymer (A) (hereinafter also referred to as Component (A))>
The styrene-based resin composition in this embodiment contains a styrene-based polymer (A). In this embodiment, the content of the styrene-based 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%, based on the entire styrene-based resin composition (100 mass%).

In this embodiment, the monomer constituting the styrene-based polymer (A) essentially contains a styrene-based monomer (a), and may contain a vinyl-based monomer (b) copolymerizable with the styrene-based monomer (a) as necessary.
Of the monomers constituting the styrene polymer (A), the content of the styrene monomer (a) is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, even more preferably 70 to 100% by mass, even more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass. The content of the styrene monomer (a), i.e., the content of the styrene monomer unit (a), can be determined from the integral ratio of the spectrum measured by a proton nuclear magnetic resonance ( ¹ H-NMR) measuring device. In addition, when it is difficult to quantitatively determine the content by ¹ H-NMR measurement, the quantitative determination is performed by infrared spectroscopy (FTIR) measurement.
Examples of the styrene 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, or styrene derivatives such as bromostyrene and indene. Styrene is particularly preferred. These styrene monomers can be used alone or in combination.

In this 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, and cyclohexyl (meth)acrylate. These unsaturated carboxylic acid ester monomers can be used alone or in combination of two or more.

In this embodiment, polystyrene is a homopolymer obtained by polymerizing a styrene-based monomer (a), and generally available ones can be appropriately selected and used. As the styrene-based monomer (a) constituting polystyrene, in addition to styrene, α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, or styrene derivatives such as bromostyrene and indene can be mentioned. Styrene is particularly preferable from an industrial viewpoint. One or more of these styrene-based monomers (a) can be used. Although polystyrene does not exclude further monomer units other than the above-mentioned styrene-based monomer (a) units within a range that does not impair the effects of the present invention, it is typically composed of styrene-based monomer (a) units.
In the present embodiment, the styrene polymer (A) is preferably formed such that 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 makes it easier for the biomass plasticizer (B) to be uniformly dispersed in the composition, thereby further improving the mechanical strength.

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 a better balance between mechanical strength and fluidity is obtained, and the amount of gel contamination is small. The weight average molecular weight (Mw) is a value obtained by using gel permeation chromatography and converting it into standard polystyrene.
In addition, the styrene-based 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-based polymer (A).

In this embodiment, it is preferable that the styrene-based polymer (A) or the styrene-based resin composition of this embodiment does not substantially contain vinyl cyanide monomers such as acrylonitrile monomer units or methacrylonitrile monomer units. Specifically, it is preferable that the vinyl cyanide monomer is contained in an amount of 10 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less, based on the total amount of vinyl monomer (b).

In this embodiment, the polymerization method for the styrene-based 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 includes a polymerization step in which the polymerization raw materials (monomer components) are polymerized, and a devolatilization step in which volatile matters such as unreacted monomers and polymerization solvents are removed from the polymerization product.

Hereinafter, an example of a polymerization method for the styrene-based polymer (A) that can be used in the present embodiment will be described.
When the polymerization raw materials are polymerized to obtain the styrene-based polymer (A), a polymerization initiator and a chain transfer agent are typically contained in the polymerization raw material composition.
Examples of the polymerization initiator used in the polymerization of the styrene-based polymer (A) include organic peroxides, for example, peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane (Perhexa C), 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane (Pertetra A), 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-butylperoxyacetate, 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 the chain transfer agent used in the polymerization of the styrene-based polymer (A) include mercaptans such as α-methylstyrene linear dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, 1-phenyl-2-fluorene, dipentene, chloroform, etc., terpenes, halogen compounds, turpentines such as terpinolene, etc. The amount of the chain transfer agent used is not particularly limited, but it is generally preferable to add about 0.005 to 0.3% by weight based on the monomer.

As a polymerization method for the styrene-based polymer (A), solution polymerization using a polymerization solvent can be adopted as necessary. Examples of the polymerization solvent used include aromatic hydrocarbons, such as ethylbenzene, and dialkyl ketones, such as methyl ethyl ketone, and each of these may be used alone or in combination of two or more. Other polymerization solvents, such as aliphatic hydrocarbons, can be further mixed with the aromatic hydrocarbons as long as the solubility of the polymerization product is not reduced. 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 the polymerization solvent exceeds 25 parts by mass per 100 parts by mass of the total monomers, the polymerization rate is significantly reduced and the mechanical strength of the obtained resin tends to be significantly reduced. It is preferable to add 5 to 20 parts by mass per 100 parts by mass of the total monomers before polymerization, as this makes it easier to uniformize the quality and is also preferable in terms of polymerization temperature control.

In this embodiment, the apparatus used in the polymerization step for obtaining 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. There is also no particular limit to the devolatilization step. For example, when bulk polymerization is employed, polymerization is continued until the final amount of unreacted monomer is preferably 50% by mass or less, more preferably 40% by mass or less, and devolatilization is performed by a known method to remove volatile matters such as unreacted monomer. More specifically, for example, a normal 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 portion is preferred. The temperature of the devolatilization treatment is usually about 190 to 280°C, more preferably 190 to 260°C. The pressure of the devolatilization treatment is usually 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, removing volatiles by reducing pressure under heating, and removing volatiles through an extruder or other device designed for this purpose.

<Biomass plasticizer (B) (hereinafter also referred to as component (B))>
The styrene-based resin composition in this embodiment contains a biomass plasticizer (B). The content of the biomass plasticizer in 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, more preferably 0.5% by mass to 3.0% by mass. If the amount of the biomass plasticizer is 5% by mass or more, the Vicat softening temperature falls below 85°C, and the composition is not suitable for stretched sheet applications and food packaging applications. If the amount of the biomass plasticizer is less than 0.1 mass, there is a concern that the fluidity will decrease, resulting in a worsening of thickness unevenness during molding. In addition, there is a concern that the productivity will decrease if the fluidity decreases. There is also a concern that the releasability of the molded body will deteriorate.

In this specification, the biomass carbon ratio (pMC%) indicates the carbon concentration (mass ratio) of a biomass-derived component, and more specifically, is the value of the ¹⁴ C content obtained by a radiocarbon ( ¹⁴ C) measurement method in accordance with ASTM-D 6866. This radiocarbon ( ¹⁴ C) measurement method is a method for estimating the biomass carbon ratio (pMC%) from ^{the 14} C ratio in carbon contained in a biomass material (or organism), utilizing the fact that fossil fuels do not contain ¹⁴ C and that carbon derived from biomass (or organisms) absorbs ¹⁴ C from the atmosphere at the time of growth.
Therefore, the proportion of carbon derived from biomass can be calculated by measuring the proportion of ^C14 in the total carbon atoms in the plasticizer of this embodiment. 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
Furthermore, oxalic acid (SRM4990) was used as the standard substance, and ( ¹⁴ C plasticizer/ ¹² C plasticizer)/( ¹⁴ C standard substance/ ¹² C standard substance) was calculated by the AMS method.

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 small. The weight average molecular weight (Mw) is a value obtained by using gel permeation chromatography and converting it into standard polystyrene, as described in the Examples section below.

The biomass plasticizer (B) in this embodiment refers to a plasticizer that uses a biomass material as a part or all of the raw material, and refers to a plasticizer with a biomass carbon ratio (pMC%) of 10% or more. The biomass plasticizer in this embodiment uses a plant-derived biomass material as at least a part of the raw material, and has a biomass carbon ratio (pMC%) of 10% or more, and 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 releasability and fluidity to improve molding processability, it is preferable that the biomass plasticizer (B) is a mixture of a vegetable oil and a moldability adjusting compound that adjusts the molding processability.
A preferred form of the biomass plasticizer (B) in this embodiment is a mixture of 50 to 99.99% by mass of vegetable oil and 0.01 to 50% by mass of a moldability adjusting compound in the entire biomass plasticizer (B), a mixture of 75 to 99.99% by mass of vegetable oil and 0.01 to 25% by mass of a moldability adjusting compound in the entire biomass plasticizer (B), a mixture of 85 to 99.99% by mass of vegetable oil and 0.01 to 15% by mass of a moldability adjusting compound is more preferable, and a mixture of 90 to 99.99% by mass of vegetable oil and 0.01 to 5% by mass of a moldability adjusting compound is even more preferable.
If the biomass plasticizer (B) has a preferable composition ratio, the biomass degree can be maintained at 50% or more, and therefore a higher environmental load reduction effect 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 to 5% by mass of a fatty acid-based compound is preferred. By adding a moldability adjusting compound to a styrene-based resin composition, it is possible to impart the effects of increasing fluidity and improving the releasability of a molded body from a mold, thereby improving productivity.
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-based 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 mass%) of the styrene-based resin composition.
When a molded product is obtained by injection molding or extrusion molding, a fatty acid compound may be added to the styrene resin. In particular, when a molded product having a complex shape or a molded product having a thin wall is obtained, it may be necessary to add a fatty acid compound to prevent cracks or deformation of the molded product when it is released from the mold. The method of addition includes a method of melt-kneading the fatty acid compound into the resin, and a method of sprinkling the fatty acid compound in powder form on the resin pellets as an external lubricant. When added as an external lubricant, it also has the effect of acting as a lubricant to reduce friction between the screw and the resin during molding or kneading processing and improve processability. Two or more fatty acid compounds may be used in combination.
When the viewpoint of reducing the environmental load is important, the biomass plasticizer (B) is preferably a single vegetable oil, i.e., one or more kinds of vegetable oils. On the other hand, when the viewpoint of fluidity is particularly important, the biomass plasticizer (B) is preferably a mixed oil of one or more kinds of vegetable oils and liquid paraffin. Furthermore, when the viewpoint of releasability of a molded body is important, the biomass plasticizer (B) is preferably a mixed oil of one or more kinds of vegetable oils and a fatty acid compound.
When the biomass plasticizer (B) is a mixed oil, the amount of each component contained in the biomass plasticizer (B) can be determined by the method described in the Examples section below.

In this embodiment, the biomass plasticizer may be modified vegetable oil. The modified vegetable oil refers to a compound made from vegetable oil, and more specifically, a part of a hydrocarbon oil of plant origin is modified with a functional group, and the vegetable oil is preferably modified with an epoxy group, an amino group, or an ester bond. The vegetable oil includes a triester of glycerin and a fatty acid, a fatty acid monoester obtained by adding a monoalcohol to a vegetable oil and subjecting it to an ester exchange reaction, a fatty acid monoester obtained by subjecting a fatty acid to an esterification reaction with a monoalcohol, and an ether derived from a fatty acid.
In the present embodiment, it is preferable that the modified group (epoxy group, amino group, or ester bond functional group) of the modified vegetable oil does not substantially polymerize with other components (including the styrene-based resin (A)) or with the modified vegetable oil itself in the styrene-based resin composition. In addition, in the present embodiment, it is preferable that the modification rate of the modified vegetable oil per 1 g of the modified vegetable oil is 1 mmol% to 50 mmol%.
The modification rate of the modified vegetable oil is calculated by ¹ H-NMR measurement as described in the Examples below.

Specific examples of the natural vegetable oil 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 linseed oil. 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-listed natural vegetable oils (e.g., hydrogenated castor oil); an oil obtained by epoxidizing the above-listed natural vegetable oils (e.g., modified epoxidized oil); or an oil obtained by amminating the above-listed natural vegetable oils (e.g., modified aminated oil). The modified epoxidized oil includes oils in which the epoxy functional group has been ring-opened, such as hydroxylated modified soybean oil, oils that have been directly hydroxylated in advance, and cashew oil-based polyols.

Specific examples of the biomass plasticizer (B) of this embodiment include palm oil, epoxidized soybean oil, epoxidized linseed oil, polyoxyethylated castor oil, polyoxyethylated hardened castor oil, oleic acid esters, and lauric acid esters, and 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 Co., Ltd.; and "Multi-Ace 20 (S)" and "Refined Palm Oil (S)" manufactured by Nisshin Oillio Group, Ltd.

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.

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

In this embodiment, the difference between the SP value of the styrene-based polymer (A) and the SP value of the biomass plasticizer (B) ((cal/ ^cm3 ) ^1/2 ) is preferably less than ±2.5, more preferably less than ±2.3, even more preferably ±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-based polymer (A) and the SP value of the biomass plasticizer (B) is ±2.5 or more, the two become difficult to be compatible with each other. As a result, it becomes difficult to uniformly disperse the biomass plasticizer (B) in the styrene-based resin composition, and the mechanical strength of the entire styrene-based resin composition tends to decrease.
One preferred aspect of this embodiment contains a styrene-based polymer (A) and a biomass plasticizer (B), in which the difference between the SP value of the styrene-based polymer (A) and the SP value of the biomass plasticizer (B) ((cal/ ^cm3 ) ^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-based polymer (A) in this embodiment is preferably 7 to 11 ((cal/cm ³ ) ^1/2 ), more preferably 7.5 to 10 ((cal/cm ³ ) ^1/2 ), even more preferably 8.0 to 9.5 ((cal/cm ³ ) ^1/2 ), and still more preferably 8.0 to 9.0 ((cal/cm ³ ) ^1/2 ).
In addition, the SP value of the biomass plasticizer (B) in this embodiment is preferably 7.0 to 11.0 ((cal/cm ³ ) ^1/2 ), more preferably 7.5 to 10.0 ((cal/cm ³ ) ^1/2 ), 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) specified in this embodiment is calculated using a function of cohesive energy density shown in the following formula.
SP value ((cal/cm ³ ) ^1/2 )=(ΔE/V) ^1/2 Equation (1)
(ΔE represents the intermolecular cohesive energy (heat of vaporization), V represents the total volume of the mixed liquid, and ΔE/V represents 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(δ ₁ - _{δ 2} )・Φ1・Φ2 ...Formula (2)
(δ ₁ indicates the SP value of the solvent, δ ₂ indicates the SP value of the solute, Φ ₁ indicates the volume fraction of the solvent, and Φ ₂ indicates the volume fraction of the solute.)
According to the above formulas (1) and (2), the closer the values of _δ1 and _δ2 are, the smaller ΔHm becomes and the smaller the Gibbs free energy becomes. Therefore, the affinity between molecules with a small difference in SP value becomes high.
In the present specification, the SP value is calculated by comparing the solubility of the resin with various solvents whose SP values are known, and calculating the SP value of the unknown resin from the SP value of the most compatible solvent, specifically, by using a turbidimetric titration method. In this embodiment, the value calculated by calculation from the monomer composition is mainly used.

In this embodiment, examples of mineral oils include atmospheric residual oils obtained by atmospheric distillation of crude oils such as paraffinic crude oil (including liquid paraffin), intermediate base crude oil, and naphthenic crude oil; distillate oils obtained by vacuum distillation of these atmospheric residual oils; mineral oils obtained by subjecting the distillate oils to one or more refining treatments 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 kinds.
In this embodiment, when a mixture of vegetable oil and mineral oil is used as the biomass plasticizer (B), there is no particular limitation 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 the liquid paraffin in this embodiment can be confirmed by a method common to those skilled in the art. For example, a solution is prepared by dissolving a fragment of a styrene-based resin composition or a molded article of the composition in a solvent that dissolves a matrix resin, such as tetrahydrofuran. Then, while stirring this solution with a stirrer, n-hexane is dropped in small amounts to precipitate the polymer matrix and the rubber-like polymer. Thereafter, the filtrate filtered through a glass filter is evaporated to dryness, and then the volume is adjusted with n-hexane, passed through a polytetrafluoroethylene membrane filter, and separated by liquid chromatography to calculate the content of liquid paraffin in the composition or molded article. In addition, the liquid paraffin can be analyzed by various analytical devices such as pyrolysis GC-MS, ¹ H-NMR, or ¹³ C-NMR to perform identification, quantification, and molecular weight measurement.

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

<Optional addition ingredients>
In addition to the above components (A) and (B), the styrene-based resin composition of the present embodiment may contain optional components such as known additives and processing aids, as necessary, within the scope of not impairing the effects of the present invention. As these optional components, moldability adjusting compounds consisting of the above liquid paraffin and fatty acid-based compounds, release agents, flame retardants, dispersants, antioxidants, weather resistance agents, antistatic agents, fillers, antiblocking agents, colorants, bluing agents, surface treatment agents, antibacterial agents, eye discharge inhibitors (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), etc. may be added.
In this embodiment, the styrene-based resin composition may contain a known flame retardant (a phosphorus-based flame retardant, a halogen-based flame retardant such as a bromine-based flame retardant). However, from the viewpoint of the possibility of generating gas 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 this embodiment, the moldability adjusting compound composed of liquid paraffin and a fatty acid-based compound is added to the styrene-based resin composition to impart the effect of increasing fluidity and the effect of improving the releasability of the molded body from a mold, thereby improving productivity.

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 (=yellowness is easier to suppress). Therefore, an anthraquinone-based compound having an electron-withdrawing group for the anthraquinone skeleton is particularly preferable. In this embodiment, by adding a bluing agent that is an anthraquinone-based compound, a molded product having a color tone and appearance required for some applications can be obtained. For example, when the styrene-based resin composition of this embodiment is molded into a biaxially stretched 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 look 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 mass%) of the styrene-based resin composition. If the amount is within the above range, it is possible to obtain a molded product with excellent appearance by suppressing the yellowness of the resin. Note that two or more types of bluing agents may be used in combination.
Since most biomass plasticizers (B) having a biomass carbon ratio (pMC%) of 10% or more have a yellowish color, the styrene-based resin composition of the present embodiment containing up to 5 masses of the biomass plasticizer (B) having a biomass carbon ratio (pMC%) of 10% or more tends to have a yellowish color. This makes it difficult to use the composition as a transparent material for food such as a lunch box lid or as an optical material (e.g., a light guide plate). However, the color tone can be adjusted by including a bluing agent.

The styrene-based resin composition in the present embodiment preferably does not contain any metal, except for unavoidable impurities. 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 phenol-based compounds, phosphorus-based compounds, and thioether-based compounds.
The total content of the above-mentioned optional components may be 0.01 to 5% by mass based on the entire styrene-based resin composition.

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

The styrene-based resin composition of the present embodiment may essentially consist of only the component (A), the component (B), and any optional additional components, or may consist of only the components (A) and (B), or only the components (A), (B), and any optional additional components.
The phrase "consisting substantially of only the component (A), the component (B), and any optional additional components" means that 95 to 100 mass% (preferably 98 to 100 mass%) of the total amount of the styrene-based resin composition is the component (A) and the component (B), or the component (A), the component (B), and any optional additional components.
The styrene-based resin composition of the present embodiment may contain inevitable 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.

When 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. In this embodiment, the hydroxyl group-containing compound 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 3 mass% or more, it will react with the modified vegetable oil and gel, causing a decrease in moldability or a negative effect of deteriorating the appearance of the injection molded product. When 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.

[Physical properties of styrene-based resin composition]
<Total light transmittance (%)>
The total light transmittance (%) of the styrene resin composition of this embodiment is 70% or more, preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. When the total light transmittance (%) of the styrene resin composition is 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 resin composition is 3 mass% or less based on the entire styrene resin composition, or the styrene resin composition is usable 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 making the SP value of the biomass plasticizer (B) of this embodiment less than 10, the blend 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 of the test specimen used to measure the total light transmittance (%) of the styrene resin composition is in accordance with K7361-1, and it is confirmed that the test specimen has no defects such as scratches, bubbles, bumps, adhesion of dirt and grease, and adhesion of adhesives from protective materials. In addition, the surface of the test specimen is free of voids and particles visible to the naked eye. When preparing the test specimen by injection molding, if necessary depending on the condition of the surface of the mold used, it may be appropriately polished to a mirror finish using abrasive paper, a stick grindstone, loose abrasive grains, etc.
The method for measuring the total light transmittance (%) in the present disclosure and the method for preparing a test piece used in the method for measuring the total light transmittance (%) are as described in the Examples section below.

<Melt Mass Flow Rate (MFR)>
The melt mass flow rate (MFR) of the styrene-based 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, the productivity of the sheet decreases. Also, the thickness of the sheet is likely to be uneven. If the MFR is higher than 9.0, it is necessary to lower the molecular weight of the resin or increase the amount of plasticizer. If the molecular weight of the resin is lowered, there is a concern that the mechanical strength will decrease. Also, if the amount of plasticizer is increased, there is a concern that the Vicat softening temperature will decrease, making it difficult to provide the required heat resistance. Also, there is a concern that a drawdown will occur 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 lower than 85°C, it becomes difficult to provide the heat resistance required for biaxially oriented sheets and food packaging applications. If the Vicat softening temperature exceeds 105°C, the fluidity of the resin decreases, and the productivity of the sheet decreases. In addition, the sheet is more likely to have uneven thickness.

[Injection molded product]
As a method for producing an injection molded article using the styrene-based resin composition of the present embodiment as a raw material, a commonly known method can be used. 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-based resin composition will undergo thermal decomposition, which is not preferred. On the other hand, if the temperature is lower than 150° C., molding will not be possible due to 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 a vacuum forming method or a pressure forming method. The biaxially oriented sheet of the present invention can be used for forming various containers, mainly food packaging containers.

The following provides a more detailed explanation of the present invention based on examples and comparative examples, but the present invention is not limited to these examples.

<Measurement and evaluation methods>
The physical properties of the resin compositions and biaxially stretched sheets obtained in the respective Examples and Comparative Examples were measured and evaluated according to the following methods.

(1) Measurement of weight average molecular weight of styrene-based polymer (A) and biomass plasticizer (B) used in examples and comparative examples The weight average molecular weight of the styrene-based polymer (A) and the biomass plasticizer (B) was measured under the following conditions and procedures.
Sample preparation: 5 mg of a measurement sample 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: 2 SHODEX GPC KF-606M connected in series Guard column: SHODEX GPC KF-G 4A
Temperature: 40℃
Carrier: THF 0.50 mL/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.

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

(3) Measurement of Vicat Softening Temperature (° C.) The Vicat softening temperature (° C.) of each of the styrene-based resin compositions used in the present examples and comparative examples was measured under a load of 49 N in accordance with ISO 306.

(4) Measurement of the content (%) of toluene insolubles in styrene resin composition The toluene insolubles in the styrene resin composition were measured as follows. 1.00 g of the styrene resin composition was weighed out in a precipitation tube (this mass was designated as W1), 20 milliliters of toluene was added, and the mixture was shaken at 23°C for 1 hour, and then centrifuged for 60 minutes at 4°C, 20,000 rpm, and 45,100 x G in a centrifuge (manufactured by Sakuma Seisakusho Co., Ltd., SS-2050A rotor: 6B-N6L). The precipitation tube was slowly tilted at about 45 degrees, and the supernatant liquid was removed by decantation. The mass of the insolubles containing toluene was weighed out, followed by vacuum drying at 160°C and 3 kPa or less for 1 hour, and then cooling to room temperature in a desiccator, and the mass of the toluene insolubles was weighed out (this mass was designated as W2).
The toluene insoluble content (%) of the styrene-based resin composition was calculated using the following formula.
Toluene insoluble content of styrene resin composition (%) = W2 / W1 × 100

(5) Measurement method for biomass carbon ratio (pMC%) The biomass carbon ratio (pMC%) of biomass plasticizer (B) was calculated by the AMS method using the radiocarbon ( ¹⁴ C) measurement method in accordance with ASTM-D6866, using the following formula (1): ( ¹⁴ C plasticizer/ ¹² C plasticizer)/( ¹⁴ C standard material/ ¹² C standard material).
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 the standard substance.

(6) Quantitative 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) Preparation of calibration curve Vegetable oil (glycerin fatty acid ester) was dissolved in deuterated chloroform (containing 1% TMS) containing 2-dimethoxyethane as an internal standard substance, and ¹ H-NMR measurement was performed. When the peak of TMS is set as the reference of 0 ppm, a peak derived from a proton bonded to a carbon adjacent to an ester group of the vegetable oil is detected at δ4.0-4.4 ppm, and a peak derived from 1,2-dimethoxymethane is detected at 3.4-3.6 ppm. The peak area derived from the vegetable oil is calculated when the peak area derived from 1,2-dimethoxymethane is set as 1. This operation was performed while changing the concentration of the vegetable oil to prepare a calibration curve of the vegetable oil concentration.
(6-2) Quantitative Analysis The pellet-shaped styrene resin composition obtained in the Examples or Comparative Examples was dissolved in deuterated chloroform (containing 1% TMS) and subjected to ^1H -NMR measurement. Using the above-mentioned calibration curve, the vegetable oil content in the styrene resin composition was quantified.
In the above method, when other peaks overlap with the peak of the internal standard and quantitative determination is difficult, an appropriate substance may be used as the internal standard, as appropriate.
Moreover, vegetable oils can also be quantified by a peak derived from triglyceride detected at 5.0 to 5.5 ppm.
When the biomass plasticizer (B) is a mixed oil of vegetable oil and moldability adjusting compound, the content of the vegetable oil is determined by the above-mentioned method, and the content of the moldability adjusting compound is determined separately. The moldability adjusting compound can be identified, quantified, and its molecular weight measured by various analytical devices such as liquid chromatography, GC-MS, ^1H -NMR, or ^13C -NMR.

(7) Calculation of Modification Ratio For a styrene-based resin containing a modified vegetable oil, the modification ratio of the modified vegetable oil can be calculated by ¹ H-NMR using the following procedure.
1 g of the pellet-shaped 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. Then, the pellets were 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. Next, the insoluble portion was removed, and the solution portion was placed in a recovery flask, and the mixture was evacuated for 2 hours using an evaporator to volatilize the methyl ethyl ketone and methanol. Then, the liquid (vegetable oil) remaining in the recovery flask was added to deuterated chloroform (containing 1% TMS), and ¹ H-NMR measurement was performed. With TMS as the standard of 0 ppm, a peak derived from the epoxy group was observed at δ2.8 to 3.2 ppm, and a peak derived from the proton bonded to the carbon adjacent to the ester group of the vegetable oil was observed at δ4.0 to 4.4 ppm. The epoxy modification rate was calculated from the area ratio of the above two peaks.

(8) Measurement of thickness of biaxially stretched sheet From the styrene-based resin composition produced in the examples and comparative examples, a sheet having a thickness of 0.95 to 1.05 mm was produced using a 25 mmφ single-screw sheet extruder manufactured by Soken Co., Ltd. A sheet having a size of 8 cm x 8 cm was cut out from the produced sheet. The cut out sheet was subjected to simultaneous biaxial stretching under the following conditions using a biaxial stretching device (EX6-S1) manufactured by Toyo Seiki Co., Ltd., to produce a biaxially stretched sheet. The sheet thickness after stretching was measured using a microgauge.
Stretching temperature: Vicat softening temperature +20℃
Stretching speed: 170%
Stretching ratio: 2.0 times

(9) Measurement of Impact Strength (kgf·cm) of Biaxially Stretched Sheet The impact strength of the sheet produced by the method described in (8) above was measured using a film impact tester (A121807502) manufactured by Toyo Seiki Seisakusho.

(10) Appearance Evaluation of Sheet A sheet having a thickness of 0.3 mm was produced using a 25 mmφ single-screw sheet extruder manufactured by Soken Co., Ltd., and the number of foreign bodies, air bubbles, and transparent or opaque deposits having an average diameter of 1 mm or more (major axis + minor axis)/2 within 5 m of the sheet was counted.

(11) Releasability of biaxially oriented sheet The biaxially oriented sheet was cut into 3 cm x 3 cm pieces, sandwiched between two 5 mm metal sheets made of prehardened steel, and fixed with clips to prepare 20 pieces. After heating for 5 minutes in an oven at 130°C, the sheet was peeled off from the metal sheets. At that time, the number of sheet samples that did not separate from the metal sheets was used as an index of releasability. As a result of this evaluation, the fewer the number of samples that did not separate from the metal sheets, the better the releasability.

(12) Thickness Uniformity of Biaxially Stretched Sheet As one index of moldability into a biaxially oriented sheet, the thickness uniformity of the biaxially oriented sheet was evaluated by the following method.
On the sheet produced by the method described in (8) above, three straight lines were drawn in a grid pattern at intervals of 5 cm 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 points out of the total of 27 points where the thickness was outside the range of 0.23 to 0.27 mm.

(13) Demoldability of Injection Molded Article Demoldability was evaluated based on the degree of damage caused by the magnitude of demold resistance inside the molded article when the molded article was removed during injection molding. Specifically, a box-shaped molded article with an external dimension of 50 mm length, 90 mm width, 40 mm depth, and 2 mm thickness and a mold having two ribs with a thickness of 1 mm spaced 30 mm apart on the horizontal position was used. Injection molding was performed using a molding machine J100E-P (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, dot-like scratches can be seen on the corners inside the molded product.
Δ: Slight linear scratches of 2 mm or less were observed in the corners inside the molded product.
×: Linear scratches larger than 2 mm were observed in the corners inside the molded product.

(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)".

(15) Measurement of total light transmittance and YI (I) Preparation conditions of test pieces The styrene-based resin composition obtained under the following conditions was injection molded using a mold for plate molding to prepare a plate having a thickness of 2 mm, and a sheet body was prepared.
Molding machine: Toshiba Machine Co., Ltd. EC60N
Cylinder temperature: 220°C
Injection pressure: 45 MPa, injection time: 10 seconds, cooling time: 15 seconds, mold temperature: 45°C
(II) Conditions for Measuring Total Light Transmittance The total light transmittance (%) of the test piece sheet prepared above was measured in accordance with JIS K7361-1.
(III) Conditions for Measuring YI (Yellow Index) Using the test piece sheet prepared above, YI (Yellow Index) was measured in accordance with JIS K7105.

The materials used in the examples and comparative examples are as follows.
(Modified vegetable oil)
[Biomass plasticizer (B)]
Epoxidized soybean oil (product name "Newsizer 510R" (manufactured by 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, 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, and represents 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 ))

[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°C
(Polylactic acid)
Polylactic acid, product name "LX175" (manufactured by 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" (manufactured by Kao Corporation)
Zinc stearate, product name "Daiwax ZP" (manufactured by Dainichi Chemical Industry Co., Ltd.)

[Method of producing styrene-based resin composition]
[Example 1]
(Method for producing styrene-based resin composition (PS-1))
A polymerization liquid in which 93.05 mass% of styrene, 6.5 mass% of ethylbenzene, 0.4 mass% of Multiace 20 (S) (manufactured by Nisshin Oillio Group, Ltd.), and 0.05 mass% of liquid paraffin were mixed and dissolved 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 rotation speed of the stirrer was 80 rpm. The reaction rate at the reactor outlet was 30%.
The reaction liquid was then sent to a 1.5-liter laminar flow reactor-2 equipped with an agitator connected in series with the laminar flow reactor-1 and capable of temperature control in three zones. The agitator's stirring speed was set to 40 revolutions per minute, and the temperature was set to 133°C/135°C/137°C. The reaction liquid was then sent to a 1.5-liter laminar flow reactor-3 equipped with an agitator and capable of temperature control in three zones. The agitator's stirring speed was set to 10 revolutions per minute, and the temperature was set to 147°C/150°C/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 the styrene-based resin composition, and the pellets were 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). In addition, 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 performed on the obtained styrene-based resin composition of Example 1. The evaluation results are shown in Table 2-1.

[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), (PS-24) to (PS-35) were produced in the same manner as for the styrene-based resin composition (PS-1), except that the polymerization conditions were changed as shown in Tables 1-1 to 1-3 below. In addition, the styrene-based resin composition (PS-21) was produced by adding palm oil to the styrene-based resin composition (PS-16) (GPPS without plasticizer) so that it contained 1 mass%, further adding 0.05 mass% of liquid paraffin and 0.2 ppm of Plast Violet 8840, kneading and pelletizing with a twin-screw extruder, and then adding 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.) to the obtained pellets. Similarly, the styrene-based resin composition (PS-22) was prepared by adding palm oil to KIBISAN (registered trademark) PN-117C (CHI-MEI product) so that the content was 1% by mass, further adding 0.05% by mass of liquid paraffin and 0.2 ppm of Plast Violet 8840, kneading the mixture with a twin-screw extruder, and then adding 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.). The above-mentioned various evaluations were carried out on the obtained styrene-based resin compositions of Examples 2 to 17. The evaluation results are shown in Tables 2-1 to 2-3.

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-based 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, kneading with a twin-screw extruder, and then adding 100 ppm of Daiwax ZP (manufactured by Dainichi Chemical Industry Co., Ltd.). The composition was kneaded with a twin-screw extruder. The above-mentioned various evaluations were performed on the obtained styrene-based resin compositions of Comparative Examples 1 to 6. The evaluation results are shown in Table 2-4.

The present invention provides a highly transparent styrene-based resin composition that reduces the environmental impact by using biomass raw materials, maintains high mechanical strength, and has excellent moldability into a biaxially oriented sheet and sheet appearance, and a biaxially oriented sheet made of 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 (7)

Contains 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 content of the styrene-based polymer (A) is 95.0 to 99.9% by 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% by mass or more based on the total amount of the styrene-based polymer (A);
The biomass plasticizer (B) is a natural vegetable oil or a modified vegetable oil, which is any one of a hydrogenated oil, a modified epoxidized oil, and a modified aminated oil;
A styrene-based resin composition, characterized in that a total light transmittance of a 2 mm thick plate is 70% or more. The styrene-based resin composition according to claim 1, having a Vicat softening temperature of 85°C or higher. The styrene-based resin composition according to claim 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. The styrene-based resin composition according to claim 1 or 2, wherein the toluene-insoluble content of the styrene-based resin composition is 3% by mass or less. The biomass plasticizer (B) is a mixture of vegetable oil and a moldability adjusting compound for adjusting moldability, and the moldability adjusting compound is contained in an amount of 0.01 to 5% by mass based on the entire styrene-based resin composition (A);
3. The styrene-based resin composition according to claim 1, wherein the moldability adjusting compound is one or more compounds selected from the group consisting of liquid paraffin and fatty acid-based compounds. The styrene-based resin composition according to claim 1 or 2, which contains 0.001 ppm to 10 ppm of a bluing agent relative to the styrene-based resin composition (A). A molded article made of the styrene-based resin composition according to claim 1 or 2.