Styrenic resin composition and molded article thereof

Abstract

To provide a styrenic resin composition that uses biomass material for reduced environmental load, reduced die contamination during injection molding, and also high mechanical strength, and a molding thereof.SOLUTION: A styrenic resin composition contains 85.0-99.9 mass% of a rubber-modified styrenic resin (A), which contains a polymer matrix phase containing a styrenic polymer (A-1) and rubber-like polymer particles (A-2) dispersed in the polymer matrix phase, and 0.1-15 mass% of a biomass plasticizer (B) with a biomass carbon ratio (pMC%) of 10% or more. As measured under the conditions of 200°C and 49 N load, a melt mass flow rate is 10-80.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] Due to their moldability and mechanical strength, styrene-based resins are used for a wide range of purposes, including miscellaneous goods and home appliances. Furthermore, 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 progressing. For example, Patent Document 1 discloses a styrene-based resin composition containing rubber-modified polystyrene, polylactic acid, and a thermoplastic elastomer containing styrene monomer units.

[0003] In recent years, in the field of styrene-based resins, in the field of injection molding applications, there has been a demand for increasing the fluidity of resins and shortening the molding cycle time in order to improve productivity. Furthermore, increasing the fluidity of resins reduces the residual stress that occurs in molded products during cooling after injection molding, thereby reducing residual strain. It is known that reducing residual strain improves the mechanical strength of molded products, so increasing the fluidity of resins can also be expected to improve mechanical strength. Generally, a large amount of liquid paraffin is used as a plasticizer to increase the fluidity of resins, but this poses the problem of low-boiling-point components volatilizing during molding, causing staining of the mold and molded products. For example, Patent Document 2 discloses a method for producing a rubber-modified styrene-based resin that has an excellent balance of surface impact resistance, rigidity, and fluidity. Furthermore, methods for adjusting the molecular weight and molecular weight distribution of the resin have also been considered to increase the fluidity of the resin while preventing mold staining during molding. For example, Patent Document 3 discloses a method for producing a styrene-based resin that has high fluidity and produces little mold deposits by adjusting the molecular weight and molecular weight distribution without adding liquid paraffin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2016-199652 [Patent Document 2] Japanese Patent Application Publication No. 10-251355 [Patent Document 3] Japanese Patent Application Publication No. 2017-222770 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology of Patent Document 1 above considers a polymer alloy of styrene-based resin and polylactic acid, which has a relatively high melting point and toughness among plant-derived biodegradable polymers, but the compatibility of polylactic acid with styrene-based resin is very low, which makes it difficult to design products that satisfy the mechanical properties required in the market, such as impact resistance or elasticity.In addition, because polylactic acid is incompatible with styrene-based resin, there is also the problem that it is difficult to recycle waste materials.

[0006] The technology of Patent Document 2 above studies a method for producing a rubber-modified styrene-based resin that has an excellent balance of surface impact resistance, rigidity, and fluidity. However, the use of a large amount of liquid paraffin results in a large amount of volatile components during injection molding. As a result, it is thought that mold contamination during molding will worsen. Furthermore, the technology of Patent Document 3 above studies a styrene-based resin with high fluidity and little mold adhesion, but the low molecular weight of the resin makes it difficult to design a product without reducing the Charpy impact strength or the elasticity of the molded product. Furthermore, biomass raw materials, which have been attracting attention in recent years for their environmental impact reduction, are not used. Therefore, the techniques of Patent Documents 1 to 3 do not consider reducing mold fouling during molding and improving the efficiency of the molding cycle while maintaining a high level of mechanical strength. Therefore, an object of the present invention is to provide a styrene-based resin composition and a molded article thereof that use biomass raw materials to reduce the environmental load, cause less mold fouling during injection molding, have high mechanical strength, and are excellent in molding cycle. [Means for solving the problem]

[0007] 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 rubber-modified styrene-based resin composition in which a rubber-modified styrene-based resin (A) is mixed with a biomass plasticizer (B) having a high boiling point and high viscosity and a biomass carbon ratio (pMC%) of 10% or more in a specific ratio, thereby completing the present invention. The present invention provides a styrene-based resin composition having a melt mass flow rate of 10 to 80 measured under conditions of 200°C and a load of 49 N, which contains 85.0 to 99.9 mass% of a rubber-modified styrene-based resin (A) containing a polymer matrix phase containing a styrene-based polymer (A-1) and rubber-like polymer particles (A-2) dispersed in the polymer matrix phase, and 0.1 to 15 mass% of a biomass plasticizer (B) having a biomass carbon ratio (pMC%) of 10% or more. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a styrene-based resin composition which reduces the environmental load, has an excellent balance between high mechanical strength and an excellent molding cycle, and causes little mold contamination during injection molding, and an injection-molded article made of the styrene-based resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] [Styrene-based resin composition] The styrene-based resin composition of the present embodiment contains 85 to 99.9 mass% of a rubber-modified styrene-based resin (A) containing a polymer matrix phase containing a styrene-based polymer (A-1) and rubber-like polymer particles (A-2) dispersed in the polymer matrix phase, and 0.1 to 15 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 85 to 99.9 mass% of the rubber-modified styrene-based resin (A) and 0.1 to 15 mass% of the biomass plasticizer (B) relative to the entire styrene-based resin composition (100 mass%), and the rubber-modified styrene-based resin (A) contains a polymer matrix phase containing a styrene-based polymer (A-1) and rubber-like polymer particles (A-2). This makes it possible to provide a styrene-based resin composition which reduces the environmental load, has an excellent balance between high mechanical strength and an excellent molding cycle, and causes little mold contamination during injection molding.

[0011] <Rubber-Modified Styrene-Based Resin (A) (Hereinafter, also referred to as Component (A))> The styrene-based resin composition of the present embodiment contains a rubber-modified styrene-based resin (A). In the present embodiment, the content of the rubber-modified styrene-based resin (A) is 85.0 to 99.9 mass %, and preferably 90.0 to 99.0 mass %, relative to the total mass of the styrene-based resin composition (100 mass %).

[0012] In this embodiment, the rubber-modified styrene-based resin (A) is a polymer matrix phase in which rubber-like polymer particles (referred to as rubber-like polymer particles (A-2)) are dispersed, and can be produced by polymerizing a styrene-based monomer in the presence of the rubber-like polymer. -Polymer matrix phase- In this embodiment, the monomer constituting the styrene polymer (A-1) is preferably a styrene monomer (a) or a vinyl monomer (b) copolymerizable with a styrene compound. Of the monomers constituting the styrene polymer (A-1), 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 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. 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.

[0013] 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.

[0014] 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.

[0015] In this embodiment, the weight average molecular weight (Mw) of the styrene polymer (A-1) is preferably 100,000 to 300,000, more preferably 120,000 to 250,000, and even more preferably 140,000 to 200,000. When the weight average molecular weight (Mw) is 100,000 to 300,000, 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.

[0016] In this embodiment, it is preferable that the styrene polymer (A-1) 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).

[0017] -Rubber-like polymer- The rubbery polymer particles (A-2) contained in the rubber-modified styrene-based resin (A) of this embodiment may, for example, encapsulate a styrene-based polymer (A-1) inside and / or may have a styrene-based polymer (A-1) grafted to the outside. The rubbery polymer particles (A-2) of this embodiment include not only a core-shell structure composed of a styrene-based polymer (A-1) as a core and a rubbery polymer as a shell surrounding the core, but also a salami structure composed of a plurality of styrene-based polymers (A-1) as cores and a rubbery polymer as a shell surrounding the plurality of styrene-based polymers (A-1) as cores.

[0018] Examples of materials that can be used for the rubbery polymer or rubbery polymer particles (A-2) of this embodiment include polybutadiene, polybutadiene containing polystyrene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, and acrylonitrile-butadiene copolymer, with polybutadiene or styrene-butadiene copolymer being preferred. As polybutadiene, both high-cis polybutadiene with a high cis content and low-cis polybutadiene with a low cis content can be used. Furthermore, the structure of the styrene-butadiene copolymer can be either a random structure or a block structure. These rubbery polymers can be used alone or in combination. Saturated rubbers obtained by hydrogenating butadiene rubbers can also be used. Examples of such rubber-modified styrene resins (A) include HIPS (high impact polystyrene), ABS resin (acrylonitrile-butadiene-styrene copolymer), and AES (acrylonitrile-ethylene propylene rubber-styrene copolymer).

[0019] In this embodiment, the content of the rubbery polymer contained in the rubber-modified styrene-based resin (A) (this is the content of the rubbery polymer (for example, a conjugated diene-based polymer such as polybutadiene) itself, and does not include the styrene-based polymer (A-1) encapsulated in the rubbery polymer particles (A-2)) is preferably 1.0 to 15 mass %, more preferably 1.2 to 12 mass %, and even more preferably 1.5 to 10 mass %, relative to the total amount (100 mass %) of the rubber-modified styrene-based resin (A). If the content of the rubbery polymer is less than 1.0 mass %, there is a risk that the impact resistance of the entire styrene-based resin composition will decrease. On the other hand, if the content of the rubbery polymer exceeds 15 mass %, there is a risk that the fluidity of the entire styrene-based resin composition will decrease. In the present disclosure, the content of the rubber-like polymer contained in the rubber-modified styrene-based resin (A) is a value calculated using the method described in the Examples section.

[0020] In this embodiment, the content of the rubber-like polymer particles (A-2) contained in the rubber-modified styrene-based resin (A) (including the content of the rubber-like polymer (e.g., a conjugated diene-based polymer such as polybutadiene) itself and the content of the styrene-based polymer (A-1) encapsulated in the rubber-like polymer particles (A-2)) is preferably 4 to 30 mass %, more preferably 6 to 20 mass %, and even more preferably 8 to 18 mass %, relative to the total amount (100 mass %) of the rubber-modified styrene-based resin (A). In the present disclosure, the content of the rubber-like polymer particles (A-2) contained in the rubber-modified styrene-based resin (A) is a value calculated using the method described in the Examples section.

[0021] In this embodiment, the average particle size of the rubber-like polymer particles (A-2) contained in the rubber-modified styrene-based resin (A) is 0.3 to 5.0 μm, and from the viewpoint of impact resistance, it is preferably 0.8 to 3.5 μm. In this disclosure, the average particle size of the rubber-like polymer particles (A-2) contained in the rubber-modified styrene-based resin (A) is a value calculated using the method described in the Examples section.

[0022] In this embodiment, the reduced viscosity (which is an index of the molecular weight of the styrene polymer (A-1)) of the styrene polymer (A-1) contained in the rubber-modified styrene resin (A) is preferably in the range of 0.50 to 0.85 dL / g, more preferably 0.55 to 0.80 dL / g. If the reduced viscosity of the styrene polymer (A-1) is less than 0.50 dL / g, the impact strength decreases, and if the reduced viscosity exceeds 0.85 dL / g, the fluidity decreases. In the present disclosure, the reduced viscosity of the styrene-based polymer (A-1) is a value measured in a toluene solution at 30° C. and a concentration of 0.5 g / dL.

[0023] -Method for producing rubber-modified styrene-based resin (A)- In this embodiment, the rubber-modified styrene-based resin (A) can be produced by, but is not limited to, bulk polymerization (or solution polymerization) in which a styrene-based monomer (and a solvent) is polymerized in the presence of a rubber-like polymer, or bulk-suspension polymerization in which the reaction transitions to suspension polymerization during the reaction, or emulsion graft polymerization in which a styrene-based monomer is polymerized in the presence of a rubber-like polymer latex. In bulk polymerization, the resin can be produced by continuously supplying a mixed solution containing a rubber-like polymer and a styrene-based monomer, and optionally an organic solvent, an organic peroxide, and / or a chain transfer agent, to a polymerization apparatus configured by a complete mixing reactor or a tank reactor and multiple tank reactors connected in series.

[0024] In this embodiment, the polymerization method for the styrene polymer (A-1) that is the polymer matrix phase of the rubber-modified styrene resin (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.

[0025] An example of a method for polymerizing the styrene-based polymer (A-1) that can be used in this embodiment will be described below. When the polymerization raw materials are polymerized to obtain the styrene-based polymer (A-1), a polymerization initiator and a chain transfer agent are typically contained in the polymerization raw material composition. The polymerization initiator used for the polymerization of the styrene polymer (A-1) can be exemplified by organic peroxides, such as peroxyketals such as 2,2-bis(t-butylperoxy)butane, 1,1-bis(t-butylperoxy)cyclohexane, 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 viewpoint of decomposition rate and polymerization rate, 1,1-bis(t-butylperoxy)cyclohexane is particularly 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-1) 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 monomer.

[0026] Solution polymerization using a polymerization solvent can be used as a polymerization method for the styrene polymer (A-1), 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. Other polymerization solvents, such as aliphatic hydrocarbons, can be added to the aromatic hydrocarbons as long as they do not impair 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 in an amount 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.

[0027] In this embodiment, the apparatus used in the polymerization step to obtain the styrene-based polymer (A-1) 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 carried out 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.

[0028] <Biomass Plasticizer (B) (hereinafter also referred to as "Component (B)")> The styrene-based resin composition in this embodiment contains a biomass plasticizer (B). The biomass plasticizer (B) has a biomass carbon ratio (pMC%) of 10% or more. If the biomass carbon ratio (pMC%) is within the above range, the amount of fossil fuel used can be reduced, and therefore a styrene-based resin composition that can reduce the environmental load can be provided. In this embodiment, the lower limit of the biomass carbon ratio (pMC%) is preferably 10% or more, more preferably 25% or more, even more preferably 50% or more, and even more preferably 75% or more. In this embodiment, the content of the biomass plasticizer (B) is 0.1 to 15% by mass relative to the total amount (100% by mass) of the styrene-based resin composition. The lower limit of the content of the biomass plasticizer (B) is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more. The upper limit of the content of the biomass plasticizer (B) is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 9% by mass or less, and even more preferably 7% by mass or less. If the content of biomass plasticizer (B) is too high, the amount of volatile components increases, causing mold fouling. Furthermore, if the content of biomass plasticizer (B) exceeds 15%, it tends to bleed out. On the other hand, if the content of biomass plasticizer (B) is too low, fluidity decreases, causing the molding temperature to rise, resulting in longer cooling times and a tendency for productivity to decrease. The biomass plasticizer (B) is preferably uniformly dispersed in the styrene-based resin composition. More specifically, it is preferably not an external lubricant (e.g., a lubricant insoluble in a polymer melt) that forms a monolayer of the biomass plasticizer (B) on the surface of the styrene-based resin composition. Examples of methods for uniformly dispersing the biomass plasticizer (B) in the styrene-based resin composition include a method of kneading the rubber-modified styrene-based resin (A) and the biomass plasticizer (B) in an extruder, and a method of incorporating the biomass plasticizer (B) into the polymerization raw material composition when polymerizing the polymerization raw material.

[0029] 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.

[0030] 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.

[0031] The biomass plasticizer in this embodiment refers to a plasticizer that uses biomass material as part or all of the raw material and has a biomass carbon ratio (pMC%) of 10% or more. The biomass plasticizer in this embodiment uses plant-derived biomass material as at least part of the 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In this embodiment, the viscosity of the vegetable oil (including natural vegetable oil and modified vegetable oil) at 25°C is preferably 1000 mPa·s or less, more preferably 50 to 1000 mPa·s, and even more preferably 100 to 800 mPa·s.

[0036] 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.

[0037] In this embodiment, the SP value of the styrene-based polymer (A-1) 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-based polymer (A-1) and the SP value of the biomass plasticizer (B) is ±2.5 or more, the two become less compatible with each other. The SP value of the styrene polymer (A-1) 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 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.

[0038] 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.

[0039] <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 mold release agents, flame retardants, dispersants, antioxidants, weathering agents, antistatic agents, fillers, antiblocking agents, colorants, antiblooming agents, surface treatment agents, antibacterial agents, and eye discharge inhibitors (such as silicone oils, monoamide compounds of higher aliphatic carboxylic acids, and monoester compounds obtained by reacting higher aliphatic carboxylic acids with monohydric to trihydric alcohol compounds, as described in JP 2009-120717 A). 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.

[0040] 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. As the release agent, a fatty acid compound or a fatty acid metal salt may be used. Examples of the antioxidant include phenolic compounds, phosphorus compounds, and thioether compounds. The total content of the above-mentioned optional additive components may be 0.05 to 5% by mass based on the entire styrene-based resin composition.

[0041] 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.

[0042] 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.

[0043] [Physical properties of styrene-based resin composition] <Melt Mass Flow Rate (MFR)> The melt mass flow rate (measured under conditions of 200°C and a load of 49 N) of the styrene-based resin composition of this embodiment is 10 to 80 (g / 10 min), preferably 13 to 60 (g / 10 min), more preferably 15 to 50 (g / 10 min), and even more preferably 15 to 35 (g / 10 min). If the MFR of the styrene-based resin composition is lower than 10, the fluidity decreases, the appropriate molding temperature increases, and the cooling time tends to be longer. Increasing the MFR of the styrene-based resin composition to more than 80 requires a large amount of plasticizer, which reduces the heat resistance. If the heat resistance decreases, the solidification temperature decreases, and the cooling time tends to be longer. Note that if the molding temperature can be lowered, the cooling time is shortened and the molding cycle is improved. In the present disclosure, the melt mass flow rate was measured in accordance with ISO 1133. When the melt mass flow rate of the styrene-based resin composition of the present embodiment is within the above range, the fluidity of the entire composition can be maintained at a high level, thereby reducing mold contamination during molding. <Vicat softening temperature> The Vicat softening temperature of the styrene-based resin composition of this embodiment is preferably 50°C to 105°C, more preferably 65°C to 95°C, and even more preferably 75°C to 90°C. If the Vicat softening temperature of the styrene-based resin composition is higher than 105°C, the fluidity decreases, and the appropriate molding temperature increases, so the cooling time tends to be longer. Furthermore, if the Vicat softening temperature of the styrene-based resin composition is lower, the solidification temperature decreases, so the cooling time tends to be longer. In this disclosure, the Vicat softening temperature (°C) was measured in accordance with ISO 306 under a load of 49N.

[0044] <Swelling index> The swelling index of the styrene-based resin composition of the present invention is preferably 8.5 to 14 from the viewpoint of impact strength, and more preferably 9.0 to 13. The swelling index is an index representing the degree of crosslinking of rubber particles. By setting the swelling index within the above range, the styrene-based resin composition of the present invention will have excellent impact properties. In the present disclosure, the swelling index of the styrene-based resin composition is a value calculated using the method described in the Examples section.

[0045] [Injection molded products] A commonly known method can be used to produce an injection-molded article 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, whereas if it is lower than 150°C, the composition will not be moldable due to its high viscosity, which is also not preferred.

[0046] Molded articles, particularly injection-molded articles (including injection-compressed articles), containing the styrene-based resin composition of the present embodiment are suitable for use in office automation equipment such as copiers, fax machines, personal computers, printers, information terminals, refrigerators, vacuum cleaners, and microwave ovens, home appliances, housings and various parts for electric and electronic devices, interior and exterior components for automobiles, construction materials, foam insulation materials, insulating films, and the like. [Example]

[0047] 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.

[0048] <Measurement and evaluation methods> The physical properties of the resin compositions and injection-molded articles obtained in each of the Examples and Comparative Examples were measured and evaluated according to the following methods.

[0049] (1) Measurement of the weight average molecular weight of the styrene polymer (A-1) and the biomass plasticizer (B) in the rubber-modified styrene resin used in the examples and comparative examples The weight average molecular weights of the styrene polymer (A-1) 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.

[0050] (2) Melt mass flow rate (MFR) The melt mass flow rate (g / 10 min) of the styrene polymer (A-1) in the rubber-modified styrene resin used in the examples and comparative examples was measured in accordance with ISO 1133 (200°C, load 49 N).

[0051] (3) Measurement of Vicat softening temperature (℃) The Vicat softening temperatures (°C) of the rubber-modified styrene-based resins and styrene-based resin compositions used in the present examples and comparative examples were measured in accordance with ISO 306 under a load of 49N.

[0052] (4) Measurement of the content and swelling index of rubber-like polymer particles (A-2) The content (mass%) of rubber-like polymer particles (A-2) in the rubber-modified styrene-based resin or styrene-based resin composition and the swelling index were measured as follows. 1.00 g of the rubber-modified styrene-based resin or styrene-based resin composition was weighed out (this mass was designated W1) into a settling tube, 20 mL of toluene was added, and the mixture was shaken at 23°C for 2 hours. It was then centrifuged for 60 minutes in a centrifuge (manufactured by 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 matter containing toluene was weighed out (this mass was designated W2). The mixture was then vacuum-dried 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 matter was weighed out (this mass was designated W3). The content and swelling index of the rubber-like polymer particles (A-2) in the rubber-modified styrene-based resin or styrene-based resin composition, i.e., the content and swelling index of the rubber-like polymer particles (A-2) in the rubber-modified styrene-based resin or styrene-based resin composition, were calculated using the following formula. Content of rubber-like polymer particles (A-2) = W3 / W1 x 100 Swelling index of rubber-like polymer particles (A-2) = W2 / W3 In Example 6 described later, when toluene was used as the solvent, the gel component also flowed out during decantation, making it impossible to measure accurate values. Therefore, in Example 6 described later only, a methyl ethyl ketone / methanol=9 / 1 solution was used, and the same treatment was carried out to determine the content of rubbery polymer particles (A-2) and the swelling index of rubbery polymer particles (A-2).

[0053] (5) Measurement of average particle size The average particle size (μm) of the rubber-like polymer particles (A-2) in the rubber-modified styrene-based resin or styrene-based resin composition used in the examples and comparative examples was measured by the following method. Using a COULTER MULTISIZER III (trade name) manufactured by Beckman Coulter, Inc. equipped with a 30 μm diameter aperture tube, 0.05 g of rubber-modified styrene-based resin pellets or styrene-based resin composition pellets were placed in approximately 5 ml of dimethylformamide and left to stand for approximately 2 to 5 minutes. Next, the dimethylformamide soluble content was measured as an appropriate particle concentration, and the volume-based median diameter was determined. In Example 6 described later, when a COULTER MULTISIZER III was used, the average particle size of the rubber-like polymer particles (A-2) was below the lower limit of the measurement range, making it impossible to perform an appropriate measurement. Therefore, only in Example 6, the same treatment was carried out, and then the volume-based median diameter was determined using a laser analysis particle size distribution analyzer manufactured by Beckman Coulter, Inc.

[0054] (6) Determination of rubber polymer content 0.25 g of the rubber-modified styrene-based resin or styrene-based resin composition used in the Examples and Comparative Examples was dissolved in 50 mL of chloroform, and iodine monochloride was added to react with the double bonds in the rubber component. Potassium iodide was then added to convert the remaining iodine monochloride to iodine, and the solution was then back-titrated with sodium thiosulfate (iodine monochloride method). Using this method, the mass of the rubber contained in the rubber-modified styrene-based resin or styrene-based resin composition (referred to as W4) was measured, and the content (mass%) of the rubber-like polymer in the rubber-modified styrene-based resin or styrene-based resin composition was calculated using the following formula from this value and the mass of the rubber-modified styrene-based resin or styrene-based resin composition (referred to as W1). Content (mass%) of rubber-like polymer in rubber-modified styrene-based resin or styrene-based resin composition = W4 / W1 × 100

[0055] (7) 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.

[0056] (8) Calculation of denaturation rate Using vegetable oil before denaturation and denatured vegetable oil after denaturation, 1 The modification rate was calculated by H-NMR.

[0057] (9) Charpy impact test The styrene resin composition was injection molded at 220°C according to JIS K 7152 to prepare a specimen, and the Charpy impact strength was measured according to JIS K 7111-1.

[0058] (10) Cooling time during molding In the examples and comparative examples, the cooling time during molding was evaluated by measuring the cooling time required for ten 2 mm plates to be injection molded and solidify without deformation after molding. In these examples and comparative examples, molding was performed using an EC60N injection molding machine manufactured by Toshiba Machine Co., Ltd., at a mold temperature of 45°C. The injection pressure, injection time, and dwell pressure were kept constant, and the cylinder temperature was set for each example to a temperature at which the plates could be molded without short shot.

[0059] (11) Mold contamination during injection molding When a styrene resin composition was prepared into an injection-molded piece at 220°C in accordance with JIS K 7152, mold fouling was evaluated using the number of shots until deposits were observed on the mold after continuous molding as an index. If the number of shots until deposits were observed on the mold was less than 100, the mold would need to be cleaned more frequently, which would reduce productivity. Therefore, a number of 100 or more was considered acceptable.

[0060] (12) 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 "J. Appl. Polym. Sci., 12, 2359 (1968)".

[0061] 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 ) (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: 8.2 ((cal / cm 3 ) 1 / 2 ))

[0062] [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

[0063] [Method of producing styrene-based resin composition] [Example 1] (Method for producing styrene-based resin composition (PS-1)) A polymerization solution containing 83.4% by mass of styrene, 1.8% by mass of polybutadiene rubber (Diene 35 manufactured by Asahi Kasei Chemicals Corporation), 10% by mass of ethylbenzene, 4.8% by mass of Newcizer 510R (manufactured by NOF Corporation), 0.016% by mass of 1.1-bis(t-butylperoxy)cyclohexane, 0.10% by mass of α-methylstyrene dimer, and 0.1% by mass of antioxidant (Irganox 1076 manufactured by BASF Japan Ltd.) 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 110 ° C / 118 ° C / 124 ° C. The stirrer rotation speed was 200 rpm. The reaction rate at the reactor outlet was 31%. The reaction liquid was then sent to a 1.5-liter laminar flow reactor-2 equipped with an agitator connected in series to the laminar flow reactor-1 and capable of temperature control in three zones. The agitator's stirring speed was set to 40 rpm, and the temperatures were set to 129°C / 137°C / 147°C. In addition, 0.04% by mass of α-methylstyrene dimer was added from the upper part of the laminar flow reactor-2. 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 rpm, and the temperatures were set to 152°C / 156°C / 160°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, to produce a styrene-based resin composition (PS-1). The temperature of the extruder was set to 230°C. 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 obtained styrene-based resin composition (PS-1) was evaluated for the above items (1) to (11), and the results are shown in Table 3 below.

[0064] [Examples 2 to 16, 18, and 19] <Production of styrene-based resin compositions (PS-2) to (PS-16)> Styrenic resin compositions (PS-2) to (PS-16), (PS-18), and (PS-19) 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 and 2. The above evaluations (1) to (11) were carried out, and the results are shown in Tables 3 and 4 below.

[0065] [Example 17] <Production of styrene-based resin composition (PS-17)> A rubber-modified styrenic resin (A-17) was 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 and 2. The rubber-modified styrenic resin (component (A)) and the biomass plasticizer (B) (component (B)) were dry-blended in the ratio shown in Table 4 below (100% by mass of the rubber-modified styrenic resin (A-17) with 6% by mass of epoxidized soybean oil (product name: Newcizer 510R, manufactured by NOF Corporation)). The dry-blended mixture was then extruded at a resin temperature of 220°C using a twin-screw kneading extruder (TEM-26SS-12, manufactured by Toshiba Machine Co., Ltd.) to produce the styrenic resin composition (PS-17). The above evaluations (1) to (11) were performed, and the results are shown in Table 4 below.

[0066] [Comparative Examples 1 to 2] <Preparation of Resin Compositions (PS-20) to (PS-21)> Styrenic resin compositions (PS-20) to (PS-21) 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 2. The above evaluations (1) to (11) were carried out, and the results are shown in Table 4 below.

[0067] Comparative Example 3 <Preparation of Resin Composition (PS-22)> Resin composition (PS-22) was produced by dry-blending 100% by mass of the rubber-modified styrene-based resin (A-17) produced in a laminar flow reactor with 6% by mass of polylactic acid (product name: LX175, manufactured by Total Corbinion PLA), and then extruding the mixture at a resin temperature of 220°C using a twin-screw kneading extruder (TEM-26SS-12, manufactured by Toshiba Machine Co., Ltd.). The above evaluations (1) to (11) were carried out, and the results are shown in Table 4 below.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] [Table 4] [Industrial Applicability]

[0072] The present invention provides a styrene-based resin composition that reduces environmental impact and has excellent mechanical strength, and an injection-molded article made from the styrene-based resin composition. The molded article obtained from the styrene-based resin composition can be suitably used for miscellaneous goods, toys, home appliance parts, industrial materials, etc.

Claims

1. 85.0 to 99.9% by mass of a rubber-modified styrene-based resin (A) containing a polymer matrix phase containing a styrene-based polymer (A-1) and rubber-like polymer particles (A-2) dispersed in the polymer matrix phase; and 0.1 to 15 mass% of a biomass plasticizer (B) having a biomass carbon ratio (pMC%) of 10% or more; the content of the rubber-like polymer particles (A-2) contained in the rubber-modified styrene-based resin (A) is 4 to 30% by mass relative to 100% by mass of the rubber-modified styrene-based resin (A), and the swelling index of the rubber-like polymer particles (A-2) represented by the following formula is 8.5 to 14, Swelling index = W2 / W3 (In the above formula, W2 represents the mass of the toluene-insoluble matter containing toluene produced when toluene is added to the styrene-based resin composition, and W3 represents the mass of the toluene-insoluble matter after vacuum drying for 1 hour under conditions of 160°C and 3 kPa or less.) A styrene-based resin composition characterized in that the melt mass flow rate measured under conditions of 200°C and a load of 49 N is 15 to 80.

2. The styrene-based resin composition according to claim 1, wherein the biomass plasticizer (B) is a vegetable oil or a mixture of a vegetable oil and liquid paraffin.

3. 3. The styrene-based resin composition according to claim 1, wherein the rubber-like polymer particles (A-2) have an average particle size of 0.3 μm to 5.0 μm.

4. A molded article obtained by injection molding the styrene-based resin composition according to any one of claims 1 to 3.

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