JP7689890B2 - Styrenic resin composition, extruded sheet and molded article - Google Patents

Description

The present invention relates to a styrene-based resin composition, an extruded sheet molded using the styrene-based resin composition, and a molded product obtained by secondary molding of the extruded sheet.

Styrene-unsaturated carboxylic acid resins, such as styrene-methacrylic acid copolymer resins, are excellent in heat resistance, transparency, and rigidity, and are inexpensive, so they are widely used in food packaging materials for lunch boxes and prepared foods, foam boards for residential insulation, and diffusion panels for LCD televisions that contain diffusion agents. In particular, with the recent spread of high-power microwave ovens for commercial use in convenience stores and other places, they are used as container and lid materials that do not deform due to heat even at the temperatures used for cooking in high-power microwave ovens. On the other hand, as the heat resistance of styrene-unsaturated carboxylic acid resins improves, their viscosity increases and moldability deteriorates in the same molding temperature range as general styrene resins, so the molding temperature must be increased.

The rise in molding temperature promotes the volatilization or bleed-out of high-boiling oligomer components that are produced as by-products during the polymerization of styrene-unsaturated carboxylic acid resins and as a result of thermal decomposition during molding. The volatilized high-boiling oligomer components quickly aggregate on the take-up roll, and dirt caused by the high-boiling components accumulates on the take-up roll. When a large amount of dirt accumulates on the take-up roll, the dirt is transferred to the transparent sheet, causing surface opacity and leading to a decrease in the quality of the transparent sheet. Therefore, since it is necessary to remove dirt from the take-up roll at regular intervals, especially when producing transparent sheets, a method has been sought to suppress oligomer formation during the polymerization and molding of styrene-unsaturated carboxylic acid resins.

For example, Patent Document 1 discloses a method for suppressing oligomer formation during polymerization by producing a styrene-methacrylic acid resin through suspension polymerization in water at relatively low temperatures.

JP 2003-12734 A

The method of Patent Document 1 suppresses the oligomers produced during polymerization, but does not suppress the oligomers produced during molding, and as a result, is insufficient to suppress cloudiness of the resulting transparent sheet. In addition, excessive suppression of the oligomer components during polymerization reduces the plasticizing effect of the oligomers, and molding temperatures tend to become higher. Furthermore, high molding temperatures can cause problems such as yellowing of transparent sheets used for coverings for food containers, impairing their appearance.

Therefore, the problem to be solved by the present invention is to provide a styrene-based resin composition having excellent heat resistance, appearance and moldability, an extruded sheet using the composition, and a molded product obtained by secondary molding of the extruded sheet.

The present inventors have conducted intensive research in view of the above problems, and as a result, have succeeded in realizing a styrene resin composition excellent in heat resistance, appearance and moldability, an extruded sheet using the same, and a molded article (e.g., a container) obtained by subjecting the extruded sheet to secondary molding by adding a radical scavenger in a specific ratio to a styrene-unsaturated carboxylic acid resin in the latter half of polymerization to suppress oligomer formation during polymerization, and further suppressing oligomer formation during molding by setting the content of the radical scavenger in the resin composition within a specific range, thereby completing the present invention.
That is, the present invention is as follows.

[1] A styrene-based resin composition comprising: (A) a styrene copolymer having an unsaturated carboxylic acid monomer unit and a styrene-based monomer unit; (B) a styrene oligomer having a styrene-based monomer unit; and (C) a radical scavenger,
A styrene-based resin composition, characterized in that, relative to 100 parts by mass of the styrene copolymer (A), a content of an unsaturated carboxylic acid monomer unit contained in the styrene copolymer (A) is 2 to 15 parts by mass, a content of the styrene oligomer (B) is 0.05 to 0.4 parts by mass, and a content of the radical scavenger (C) is 0.001 to 0.1 parts by mass.

[2] The styrene-based resin composition according to [1], further comprising 0.001 to 0.08 parts by mass of ethylbenzene per 100 parts by mass of the styrene copolymer (A).

（上記一般式（１）中、Ｒ^１は、水素原子又はメチル基を表し、Ｒ^２はエステル置換基であり、炭素原子数６～１２のアルキル基を表す。）で表される（メタ）アクリル酸単量体単位を、前記スチレン共重合体（Ａ）１００質量部に対して０．０５質量部以上さらに有する、［１］又は［２］に記載のスチレン系樹脂組成物。 [3] The styrene copolymer (A) is represented by the following general formula (1):

(in the above general formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² is an ester substituent and represents an alkyl group having 6 to 12 carbon atoms), in an amount of 0.05 part by mass or more relative to 100 parts by mass of the styrene copolymer (A).

[4] The styrene-based resin composition according to any one of [1] to [3], further comprising 0.001 to 1 part by mass of a monohydric alcohol having 16 or more carbon atoms per 100 parts by mass of the styrene copolymer (A).

（上記一般式（２）中、Ｘ^１及びＸ^２は、それぞれ独立して、水素原子、ハロゲン原子又は置換若しくは非置換の芳香族環を表し、Ｌ^１及びＬ^２は、それぞれ独立して、単結合又は炭素原子数１～２３個のアルキレン基を表し、当該アルキレン基中の１以上のメチレン基は、互いに隣接しないよう－ＣＨ＝ＣＨ－に置換されてもよい。）で表される、［１］～［４］のいずれか１項に記載のスチレン系樹脂組成物。 [5] The radical scavenger (C) is represented by the following general formula (2):

(In the above general formula (2), ^X1 and ^X2 each independently represent a hydrogen atom, a halogen atom, or a substituted or unsubstituted aromatic ring; ^L1 and ^L2 each independently represent a single bond or an alkylene group having 1 to 23 carbon atoms, and one or more methylene groups in the alkylene group may be substituted with -CH=CH- so that they are not adjacent to each other.) The styrene-based resin composition according to any one of items [1] to [4].

[6] The styrene-based resin composition according to any one of [1] to [5], containing 0.5 to 5 parts by mass of rubber-modified polystyrene (D) per 100 parts by mass of the styrene copolymer (A).

[7] The styrene-based resin composition according to any one of [1] to [6], containing 0 to 0.6 parts by mass of conjugated diene monomer units per 100 parts by mass of the styrene copolymer (A).

[8] The styrene-based resin composition according to any one of [1] to [7], further comprising 0.001 to 0.5 parts by mass of liquid paraffin (E) per 100 parts by mass of the styrene copolymer (A).

[9] A non-foamed extruded sheet having the styrene-based resin composition described in any one of [1] to [8].

[10] A foamed extruded sheet having the styrene-based resin composition described in any one of [1] to [8].

[11] A molded product formed using the non-foamed extruded sheet described in [9] or the foamed extruded sheet described in [10].

According to the present invention, a styrene-based resin composition excellent in heat resistance, appearance and moldability can be provided.
According to the present invention, it is possible to provide an extruded sheet having excellent heat resistance, appearance and impact resistance, and a lid material for a lunch box container that can be cooked in a microwave oven.

The following provides a detailed description of the embodiment of the present invention (hereinafter, "the present embodiment"). Note that the present invention is not limited to the following embodiment, and can be modified in various ways within the scope of the gist of the invention.

[Styrene-based resin composition]
The styrene-based resin composition of the present embodiment is a styrene-based resin composition having a styrene copolymer (A) having an unsaturated carboxylic acid monomer unit and a styrene-based monomer unit, a styrene oligomer (B) having a styrene-based monomer unit, and a radical scavenger (C), characterized in that, when the total amount of the styrene copolymer (A) is 100 parts by mass, the content of the unsaturated carboxylic acid monomer unit contained in the styrene copolymer (A) is 2 to 15 parts by mass, the content of the styrene oligomer (B) is 0.05 to 0.4 parts by mass, and the content of the radical scavenger (C) is 0.001 to 0.1 parts by mass. (hereinafter, may be simply referred to as a resin composition)

<Styrene copolymer (A)>
In this embodiment, the styrene copolymer (A) is a copolymer (hereinafter also simply referred to as copolymer (A)) that contains a styrene-based monomer unit and an unsaturated carboxylic acid monomer unit as essential components and has a content of the unsaturated carboxylic acid monomer unit of 2 to 15 parts by mass when the total content of all monomer units constituting the styrene copolymer (A) (=total amount of the styrene copolymer (A)) is taken as 100 parts by mass. The styrene copolymer (A) has excellent heat resistance compared to a styrene homopolymer due to the introduction of the unsaturated carboxylic acid monomer unit into the polymer chain.
The styrene copolymer (A) in the present embodiment may contain other monomer units in addition to the styrene-based monomer units and the unsaturated carboxylic acid monomer units. As the other monomer units, (meth)acrylic acid ester monomer units are preferred.

<<Styrene-based monomers>>
In the above styrene copolymer (A), when the total content of all monomer units constituting the styrene copolymer (A) is taken as 100 parts by mass, the content of the styrene-based monomer unit is preferably 85 to 98 parts by mass, more preferably 80 to 96 parts by mass, and even more preferably 82 to 91 parts by mass. If the content is less than 70 parts by mass, the flowability is reduced, and if it is more than 98% by mass, it becomes difficult to contain a desired amount of an unsaturated carboxylic acid described below, and the effect of improving heat resistance by the unsaturated carboxylic acid cannot be sufficiently obtained.

The styrene monomer that forms the styrene monomer unit by polymerization is not particularly limited, but examples include styrene, α-methylstyrene, β-methylstyrene, paramethylstyrene, orthomethylstyrene, metamethylstyrene, chlorostyrene, bromostyrene, etc. From an industrial viewpoint, styrene and α-methylstyrene are particularly preferred, and styrene is more preferred. As the styrene monomer, these can be used alone or in a mixture of two or more kinds.

<<Unsaturated Carboxylic Acid Monomer>>
In the styrene copolymer (A), the unsaturated carboxylic acid monomer unit plays a role in improving heat resistance. When the total content of all monomer units constituting the styrene copolymer (A) is 100 parts by mass, the content of the unsaturated carboxylic acid monomer unit is 2 to 15 parts by mass, preferably 3 to 14 parts by mass, more preferably 4 to 13 parts by mass, even more preferably 5 to 12 parts by mass, and even more preferably 6 to 11 parts by mass. If the content is less than 2 parts by mass, the effect of improving heat resistance is insufficient. In addition, if the content of the unsaturated carboxylic acid monomer unit exceeds 15 parts by mass, the gelled matter in the resin increases, bubbles are generated during molding due to an increase in water absorption, and the viscosity becomes too high during production, which is not preferable.

Examples of the unsaturated carboxylic acid monomer in this embodiment include acrylic acid and methacrylic acid. From an industrial viewpoint, these may be used alone or in combination as the unsaturated carboxylic acid monomer. As the unsaturated carboxylic acid monomer, methacrylic acid is particularly preferred because of its large effect of improving heat resistance.

（上記一般式（１）中、Ｒ^１は、水素原子又はメチル基を表し、Ｒ^２はエステル置換基を表し、当該エステル置換基Ｒ^２は、炭素原子数６～１２のアルキル基を表す。＊は他の原子との結合を表す。） <<(Meth)acrylic acid ester monomer unit>>
In a preferred embodiment of this embodiment, the styrene copolymer (A) may contain a (meth)acrylic acid ester monomer unit in addition to the above-mentioned styrene-based monomer unit and unsaturated carboxylic acid monomer unit. The (meth)acrylic acid ester monomer unit is preferably a (meth)acrylic acid ester monomer unit having an ester substituent having 6 to 12 carbon atoms. This makes it possible to obtain a resin composition with excellent fluidity. Specifically, the (meth)acrylic acid ester monomer unit having an ester substituent having 6 to 12 carbon atoms is preferably a monomer unit represented by the following general formula (1).

(In the above general formula (1), ^R1 represents a hydrogen atom or a methyl group, ^R2 represents an ester substituent, and the ester substituent ^R2 represents an alkyl group having 6 to 12 carbon atoms. * represents a bond to another atom.)

The ester substituent having 6 to 12 carbon atoms refers to an alkyl group represented by ^R2 (a linear, branched or cyclic alkyl group having 6 to 12 carbon atoms). When the styrene copolymer (A) of the present embodiment is a ternary or higher copolymer, the content of the (meth)acrylic acid ester monomer unit having an ester substituent having 6 to 12 carbon atoms in the styrene copolymer (A) is preferably 0.05 parts by mass or more, more preferably 0.05 to 5 parts by mass, when the total amount of the monomer units contained in the styrene copolymer (A) is 100 parts by mass. If the content is less than 0.05 parts by mass, the effect of improving flowability cannot be sufficiently obtained, and if it exceeds 5 parts by mass, the heat resistance is significantly impaired.

<<Other Monomers>>
The styrene copolymer (A) according to the present invention may have a monomer unit other than the above-mentioned styrene-based monomer unit, unsaturated carboxylic acid monomer unit, and (meth)acrylic acid ester monomer unit having an ester substituent having 6 to 12 carbon atoms, which is an optional component. That is, in this embodiment, as long as it is copolymerizable with a styrene-based monomer and/or an unsaturated carboxylic acid monomer, it may be copolymerized with a monomer other than the two monomers shown above, without any particular limitation, within a range that does not impair the effects of the invention. Examples of the methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-octyl methacrylate, and 2-ethylhexyl methacrylate, acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and t-butyl acrylate, maleic anhydride, maleic acid, fumaric acid, itaconic acid, (meth)acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, maleimide, and nucleus-substituted maleimide. In particular, methyl methacrylate is preferred because it improves the transparency and strength of the resin by copolymerization.

The contents of the styrene-based monomer units, the unsaturated carboxylic acid monomer units, the optional (meth)acrylic acid ester monomer units having an ester substituent having 6 to 12 carbon atoms, and the other monomer units in the styrene copolymer (A) according to the present invention can be determined from the integral ratio of the spectrum measured by a proton nuclear magnetic resonance ( ^1H -NMR) measuring device.

The weight average molecular weight (Mw) of the styrene copolymer (A) according to the present invention is preferably 100,000 to 400,000, and more preferably 120,000 to 320,000. When the weight average molecular weight is 100,000 to 350,000, a resin having a practically excellent balance between impact strength and fluidity is obtained. The weight average molecular weight can be measured by gel permeation chromatography in terms of standard polystyrene.

The number average molecular weight (Mn) of the styrene copolymer (A) according to the present invention is preferably 30,000 to 200,000, and more preferably 40,000 to 170,000. When the number average molecular weight is 30,000 to 200,000, a resin having a practically excellent balance between impact strength and fluidity can be obtained. The number average molecular weight can be measured by gel permeation chromatography in terms of standard polystyrene.

<Production method of styrene copolymer (A)>
The method for producing the styrene copolymer (A) of the present embodiment will be described below. The method for producing the styrene copolymer (A) of the present invention preferably includes a step of mixing a styrene monomer, an unsaturated carboxylic acid monomer, a solvent, and optionally other monomers (such as (meth)acrylic acid ester monomer units having an ester substituent having 6 to 12 carbon atoms) and an initiator to prepare a mixed solution, a polymerization step of polymerizing the mixed solution, a step of adding a radical scavenger (C) described later, and a step of recovering the reaction product.
The polymerization method for the styrene copolymer (A) is not particularly limited, but for example, a radical polymerization method, among which a bulk polymerization method or a solution polymerization method can be preferably used.
Specifically, the polymerization method mainly comprises a polymerization step of polymerizing polymerization raw materials (monomer components) and a devolatilization step of removing volatile matters such as unreacted monomers and polymerization solvent from the polymerization product.

Hereinafter, polymerization of the styrene copolymer (A) according to this embodiment will be described.
In this embodiment, when the polymerization raw materials are polymerized to obtain the styrene copolymer (A), a polymerization initiator is typically contained in the polymerization raw material composition. Examples of the polymerization initiator include organic peroxides, for example, 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-butylperoxyacetate, 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 preferable.

When polymerizing the styrene copolymer (A), a chain transfer agent can be used as necessary. Examples of chain transfer agents include α-methylstyrene linear dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-octyl mercaptan.

As the polymerization method of the styrene copolymer (A), solution polymerization using a polymerization solvent can be adopted.As the polymerization solvent, aromatic solvents such as toluene, ethylbenzene, propylbenzene, butylbenzene, etc. are preferable, and a solvent system in which the solubility of the styrene copolymer (A) is adjusted by combining a polar solvent such as alcohols or ketones as necessary may be used.
In this embodiment, the polymerization solvent is preferably used in the range of 3 to 35 parts by mass, more preferably 5 to 30 parts by mass, relative to 100 parts by mass of the total of all monomers and solvent constituting the styrene copolymer (A). If the polymerization solvent exceeds 35 parts by mass, the polymerization rate decreases and the molecular weight of the resulting resin also decreases, so that the mechanical strength of the resin tends to decrease. In addition, if the polymerization solvent is less than 3 parts by mass, it may be difficult to control the heat removal during polymerization. It is preferable to add the polymerization solvent in a ratio of 3 to 35 parts by mass relative to 100 parts by mass of all monomers, because this makes it easier to uniformize the quality and also in terms of polymerization temperature control.
When a monohydric alcohol is used as a polymerization solvent, it is preferably added in an amount of 1 to 10 parts by mass per 100 parts by mass of the total of all monomers and the solvent.

The apparatus used in the polymerization step to obtain the styrene copolymer (A) according to the present invention is not particularly limited, and may be appropriately selected according to a general polymerization method for styrene-based resins. For example, in the case of bulk polymerization, a polymerization apparatus having one or more completely mixed reactors connected together may be used. There is also no particular limitation on the devolatilization step, and in the case of bulk polymerization, the polymerization is continued until the amount of unreacted monomer is preferably 50% by mass or less, more preferably 40% by mass or less.

When the monomers have been sufficiently polymerized, i.e., when the amount of unreacted monomer is 50 mass% or less, a radical scavenger (C) described below can be added to produce a styrene oligomer content within an appropriate range, described below.

To remove volatile matters such as unreacted monomers, a devolatilization process is carried out by a known method. For example, a conventional devolatilization device such as a flash drum, a twin-screw devolatilizer, a thin-film evaporator, or an extruder can be used, but a devolatilization device with a small retention area is preferred. The temperature for the devolatilization process is usually about 190 to 280°C, and from the viewpoint of suppressing decomposition, 190 to 260°C is more preferred. The pressure for the devolatilization process 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 devolatilization methods include, for example, a method of removing volatile matters by reducing pressure under heating, and a method of removing volatile matters through an extruder designed for the purpose of removing volatile matters.

<Styrene Oligomer (B)>
In this embodiment, the styrene oligomer (B) is a general term for a group of compounds consisting of styrene dimers and trimers produced by side reactions of styrene monomers or thermal decomposition of polymers when the styrene copolymer (A) is polymerized or melt processed, and a plasticizing effect of improving fluidity can be expected by moderately including it in the composition. When the plasticizing effect is improved, the molding temperature can be reduced, so that yellowing of the molded product can be suppressed and excellent appearance can be ensured. Therefore, the styrene oligomer (B) plays a major role in a styrene resin composition with improved heat resistance and reduced fluidity. On the other hand, if the styrene oligomer (B) is present in excess, the amount of volatilization during molding increases, causing staining of the die or mold and clouding of the transparent sheet. Therefore, in the present invention, it is important to include the styrene oligomer (B) in the composition in an appropriate range.

In this specification, the content of styrene oligomer (B) represents the sum of the contents of styrene dimer and trimer formed from styrene monomers. The content of styrene oligomer (B) in the styrene resin composition of the present invention is 0.05 to 0.4 parts by mass, preferably 0.08 to 0.3 parts by mass, more preferably 0.09 to 0.25 parts by mass, and even more preferably 0.1 to 0.2 parts by mass, when the content of the styrene copolymer (A) in the styrene resin composition is 100 parts by mass. If the content is less than 0.05 parts by mass, the composition is prone to yellowing due to a poor improvement effect in fluidity, and if the content exceeds 0.4 parts by mass, the die, mold, and sheet winding roll are contaminated during molding, and the heat resistance is also reduced. In particular, if the winding roll is contaminated during the production of a transparent sheet, the dirt derived from the styrene oligomer (B) on the roll is transferred to the transparent sheet, causing cloudiness. In particular, by setting the content of styrene oligomer (B) to 0.1 to 0.2 parts by mass, a styrene-based resin composition with an excellent balance of fluidity, low contamination, and heat resistance can be obtained.

Specific examples of the above styrene dimer and trimer compounds include dimers such as 2,4-diphenyl-1-butene, cis-1,2-diphenylcyclobutane, and trans-1,2-diphenylcyclobutane. Also, examples of trimers include 2,4,6-triphenyl-1-hexene, 1,3,5-triphenylcyclohexane, 1e-phenyl-4a-(2-phenylethyl)tetralin, and 1e-phenyl-4e-(1-phenylethyl)tetralin.

The amount of styrene oligomer (B) in the styrene resin composition of this embodiment can be determined by the gas chromatography method described below.

<<Radical Scavenger (C)>>
In the present embodiment, the radical scavenger (C) plays a role of appropriately adjusting the content of the styrene oligomer (B) in the styrene-based resin composition.

The content in the styrene-based resin composition is 0.001 to 0.1 parts by mass, preferably 0.003 to 0.08 parts by mass, more preferably 0.005 to 0.06 parts by mass, even more preferably 0.007 to 0.04 parts by mass, even more preferably 0.010 to 0.035 parts by mass, and most preferably 0.013 to 0.030 parts by mass, when the content of the styrene copolymer (A) is 100 parts by mass. If it is less than 0.001 parts by mass, the effect of reducing the styrene oligomer (B) is not sufficiently obtained, and if it exceeds 0.1 parts by mass, the oligomer reduction ability relative to the amount added is not sufficiently obtained, and in addition, the radical scavenger (C) itself causes contamination of the winding roll and clouding of the transparent sheet, so care must be taken. In particular, by setting the content of the radical scavenger (C) to 0.013 to 0.030 parts by mass, a resin composition with an excellent balance between the above-mentioned inhibition of oligomer generation and the inhibition of the appearance of the molded product due to the bleed-out of the radical scavenger (C) can be obtained.

Specific examples of the radical scavenger (C) include octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, ethylenebis(oxyethylene)bis[3-(5-t-butyl-4-hydroxyphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, 4-t-butylcatechol, 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis[(dodecylthio)methyl]-o-cresol, 2,4-dimethyl-6-(1-methylpentadecyl)phenol, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], DL-α-tocopherol, 2-t-butyl- Examples include 6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenyl acrylate, 4,4'-thiobis(6-t-butyl-3-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 4,4'-butylidenebis(3-methyl-6-t-butylphenol), bis-[3,3-bis-(4'-hydroxy-3'-t-butylphenyl)butanoic acid]-glycol ester, 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenzo[d,f][1,3,2]-dioxaphosphepine, 4-methoxyphenol, and 2-methoxyphenol.

（上記一般式（２）中、Ｘ^１及びＸ^２は、それぞれ独立して、水素原子、ハロゲン原子又は置換若しくは非置換の芳香族環（例えば、１価の芳香族基（フェニル基、ジフェニルアルカン又はジフェニルアルケンから水素原子を１つ取り除いた基））を表し、Ｘ^１及びＸ^２は、それぞれ独立して、単結合又は炭素原子数１～２３個のアルキレン基を表し、当該アルキレン基中の１以上のメチレン基は、互いに隣接しないよう－ＣＨ＝ＣＨ－に置換されてもよい。）
上記一般式（２）において、Ｘ^１及びＸ^２はそれぞれ独立して、水素原子、以下の式（２－１）又は式（２－２）で表される基であることが好ましい。

（上記式（２－１）又は式（２－２）において、Ｒ^３～Ｒ^６はそれぞれ独立して、炭素原子数１～８の直鎖状又は分岐状のアルキル基を表し、Ｌ^３は炭素原子数１～５のアルキレン基を表す。） In particular, when the radical scavenger (C) has an ester-type chemical structure represented by the following general formula (2), the effect of reducing the amount of oligomers is high. Particularly preferred is 2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenyl acrylate.

(In the above general formula (2), ^X1 and ^X2 each independently represent a hydrogen atom, a halogen atom, or a substituted or unsubstituted aromatic ring (for example, a monovalent aromatic group (a group obtained by removing one hydrogen atom from a phenyl group, a diphenylalkane, or a diphenylalkene)), and ^X1 and ^X2 each independently represent a single bond or an alkylene group having 1 to 23 carbon atoms, and one or more methylene groups in the alkylene group may be substituted with -CH=CH- so as not to be adjacent to each other.)
In the above general formula (2), it is preferable that X ¹ and X ² each independently represent a hydrogen atom or a group represented by the following formula (2-1) or formula (2-2).

(In the above formula (2-1) or formula (2-2), R ³ to R ⁶ each independently represent a linear or branched alkyl group having 1 to 8 carbon atoms, and L ³ represents an alkylene group having 1 to 5 carbon atoms.)

The amount of radical scavenger (C) in the composition can be determined by the gas chromatography method described below.

<Rubber-modified polystyrene (D)>
In a preferred embodiment of the present invention, the styrene-based resin composition preferably contains a rubber-modified polystyrene (D). When importance is placed on impact resistance, the styrene-based resin composition of the present invention may further contain a rubber-modified polystyrene (D).

In this specification, rubber-modified polystyrene (D) refers to a resin consisting of rubber-like polymer particles having graft chains, which are dispersed by graft polymerization of a styrene monomer or other monomer onto a rubber-like polymer containing conjugated diene monomer units such as polybutadiene, while applying shear with an agitator or the like, and a matrix resin.

Rubber-modified polystyrene (D) improves the strength of the styrene resin composition as a whole, and in particular prevents cracking when the sheet is rolled up. In addition, the rubber-like polymer particles impart a suitable surface roughness, which helps prevent blocking between sheets.

The content of the rubber-modified polystyrene (D) in the resin composition is preferably 0.5 to 5.0 parts by mass, more preferably 0.7 to 4.5 parts by mass, and even more preferably 1.0 to 3.5 parts by mass, when the content of the styrene copolymer (A) is taken as 100 parts by mass. By making it 0.5 parts by mass or more, the strength of the resin composition can be improved, while if it is 5.0 parts by mass or more, transparency will be impaired.

The method of adding the rubber-modified polystyrene (D) is not particularly limited, but is preferably melt-kneaded in an extruder. The melt-kneading may be performed by dry blending the rubber-modified polystyrene (D) with the styrene copolymer (A) at the time of molding, or by melt-kneading the rubber-modified polystyrene (D) in advance in an extruder separate from the molding machine.

- Rubber-like polymer -
As the rubber-like polymer in the rubber-modified polystyrene (D), polybutadiene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, etc. can be used, but from an industrial point of view, polybutadiene and styrene-butadiene copolymer are preferred. As the polybutadiene, high-cis polybutadiene having a high cis content, low-cis polybutadiene having a low cis content, or both of these can be used. The structure of the styrene-butadiene copolymer may be a random structure, a block structure, or a combination of these. These rubber-like polymers may be used alone or in combination of two or more. Saturated rubber obtained by hydrogenating butadiene rubber can also be used.
In particular, when importance is attached to the appearance (suppression of yellowing), the total content of (meth)acrylonitrile monomer units in the styrene-based resin composition of the present invention can be preferably 2 mass% or less, more preferably 1.5 mass% or less, even more preferably 0.6 mass% or less, still more preferably 0.5 mass% or less, and even more preferably 0.4 mass% or less, relative to the total amount (100 mass%) of the styrene-based resin composition.

- Conjugated diene monomer unit -
In the present specification, the conjugated diene monomer unit is a diolefin having a pair of conjugated double bonds among the monomer units constituting the rubber-like polymer, and examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, etc. The content of the conjugated diene monomer unit in the rubber-modified polystyrene (D) and the resin composition can be measured by the procedure described in the Examples section below, or a method equivalent thereto.

The content of conjugated diene monomer units in the rubber-modified polystyrene (D) is preferably 2 to 15 mass%, more preferably 3 to 14 mass%, and even more preferably 4 to 13 mass%, based on the total amount of the rubber-modified polystyrene (D).

The total content of the conjugated diene monomer units in the styrene-based resin composition of the present invention is preferably 0 to 1.0 part by mass, more preferably more than 0 and not more than 1.0 part by mass, even more preferably 0.005 to 0.8 parts by mass, still more preferably 0.010 to 0.6 parts by mass, and most preferably 0.030 to 0.4 parts by mass, relative to 100 parts by mass of the content of the styrene copolymer (A) in the styrene-based resin composition.
In particular, by making the total content of the conjugated diene monomer units 0.01 parts by mass or more, the strength improving effect and blocking prevention effect due to the addition of the rubber-modified polystyrene (D) and other additives can be highly obtained, and by making it 0.6 parts by mass or less, a resin composition with excellent transparency can be obtained.
In particular, when the objective is to provide a styrene-based resin composition having excellent heat resistance, appearance, transparency and moldability, or when the objective is to provide an extruded sheet and a lid material for a lunch box container that can be cooked in a microwave oven having excellent heat resistance, appearance, transparency and impact resistance, it is particularly preferable that the total content of conjugated diene monomer units in the styrene-based resin composition of the present invention is 0.4 parts by mass or less per 100 parts by mass of the content of styrene copolymer (A) in the styrene-based resin composition.
The total content of the conjugated diene monomer units refers to the total amount of conjugated diene monomer units including not only the conjugated diene monomer units that can be contained in the essential components, styrene copolymer (A) and styrene oligomer (B), but also all the conjugated diene monomer units that can be contained in other additives, such as the optional components, rubber-modified polystyrene (D) and/or MBS rubber.

- Rubber particle size -
The rubber-like polymer in the rubber-modified polystyrene (D) is preferably present as rubber particles in the styrene-based resin composition. In this case, the average particle size of the rubber-like polymer particles (hereinafter also referred to as rubber particle size) is preferably 0.3 to 9.0 μm, more preferably 0.4 to 6.0 μm, and even more preferably 0.5 to 3.0 μm. When the rubber particle size is 0.3 μm or more, the mechanical strength of the resin composition is good. Also, when the rubber particle size is 9.0 μm or less, the transparency and appearance of the resin composition are good. The rubber-modified polystyrene system (D) is obtained by polymerizing a styrene-based monomer in a reactor equipped with a stirrer in the presence of a rubber-like polymer, and the rubber particle size can be adjusted by the number of revolutions of the stirrer, the molecular weight of the rubber-like polymer used, etc.
In the present specification, the average particle size of the rubber-like polymer is a value measured from a cross-sectional image observed by a transmission electron microscope.

-Swelling index-
In the present invention, the swelling index of the toluene insoluble portion of the rubber-modified polystyrene (D) is preferably 8.0 to 14.0, and the mass ratio of the toluene insoluble portion to the rubber content in the toluene insoluble portion (toluene insoluble portion/rubber content in the toluene insoluble portion) is preferably 1.5 to 4.0. This swelling index is more preferably 9.0 to 13.0, even more preferably 9.5 to 12.5, and the ratio of the toluene insoluble portion/rubber content in the toluene insoluble portion is more preferably 2.0 to 3.5, even more preferably 2.5 to 3.5. When the swelling index of the toluene insoluble portion of the rubber-modified styrene-based resin (b) is 8.0 to 14.0, and the ratio of the toluene insoluble portion/rubber content in the toluene insoluble portion is 1.5 to 4.0, a resin having excellent mechanical strength is obtained. In this disclosure, the swelling index of the toluene insolubles and the ratio of toluene insolubles/rubber content in the toluene insolubles are values measured by the procedures described in the Examples section or procedures that will be understood by those skilled in the art to be equivalent thereto.

The melt flow rate of the rubber-modified polystyrene (D) at 200°C is preferably 0.5 to 20.0, more preferably 1.0 to 18.0, and even more preferably 2.0 to 16.0. If the melt flow rate is in the range of 0.5 to 20.0, the polystyrene has good mixability with the styrene copolymer (A) and good mechanical strength. In this disclosure, the melt flow rate is a value measured at 200°C and a load of 49 N in accordance with ISO 1133.

-Method for producing rubber-modified polystyrene (D)-
The method for producing the rubber-modified polystyrene (D) is not particularly limited, but it can be produced by 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 is changed to suspension polymerization during the course of 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, it can be produced by continuously supplying a mixed solution containing a rubber-like polymer, a styrene-based monomer, and, if necessary, an organic solvent, an organic peroxide, and/or a chain transfer agent to a polymerization apparatus consisting of a complete mixing reactor or a tank reactor and a plurality of tank reactors connected in series.

<Liquid Paraffin (E)>
In a preferred aspect of this embodiment, the styrene-based resin composition preferably further contains liquid paraffin (E). The styrene-based resin composition containing liquid paraffin (E) exhibits an effect of improving flowability and strength of a sheet molded product, and an effect of reducing cracks during winding.

The content of liquid paraffin (E) in the styrene resin composition is preferably 0.005 to 0.5 parts by mass, more preferably 0.010 to 0.4 parts by mass, and even more preferably 0.015 to 0.3 parts by mass, based on 100 parts by mass of styrene copolymer (A). If it is less than 0.005 parts by mass, the effect of improving fluidity cannot be obtained, and if it is more than 0.5 parts by mass, heat resistance will be reduced.

The liquid paraffin (E) used in the present invention may be called liquid paraffin, white mineral oil, mineral oil, MO, white mineral oil, etc., depending on the degree of refinement and commercial practice.

Liquid paraffin (E) is preferably one having a naphthene content ratio of 20% or more, more preferably 30% or more, as determined by n-d-M ring analysis, since it has excellent compatibility with the styrene copolymer (A). n-d-M ring analysis is a composition test method for high-boiling petroleum fractions, and is a method (ASTM D3238) for determining the aromatic ring ratio (%Ca), naphthene ring ratio (%Cn), and paraffin chain ratio (%Cp) in the oil by determining the refractive index (n), density (d), and molecular weight (M). From the viewpoint of product color, the polycyclic aromatic components in white mineral oil must be 3% or less, and preferably 0.5% or less. Liquid paraffin usually has 0% aromatic rings.

The low boiling point components in liquid paraffin (E) are effective in avoiding problems with volatile matter during extrusion molding. It is preferable that the 5% distillation temperature, calculated at normal pressure from the reduced pressure distillation method or gas chromatography method of JIS K2254, is 400°C or higher.

The kinetic viscosity of the liquid paraffin (E) is preferably in a range in which the above-mentioned low boiling point components are small, the Vicat softening temperature is effectively lowered, and handling is easy. The range of 40 mm2/s to 120 ^mm2 /s at 40°C is preferably, and more preferably, 60 to 80 mm2/s.

The method of adding the liquid paraffin (E) is not particularly limited, and examples thereof include a method of adding the liquid paraffin (E) in the polymerization step, a method of kneading the liquid paraffin (E) using a known kneader such as a single screw extruder, a twin screw extruder, a Banbury mixer, etc. In particular, it is preferable to add the liquid paraffin (E) during the production of the styrene copolymer (A) since this improves the dispersibility.
The quantity and identification of the liquid paraffin (E) in this embodiment can be easily confirmed by a person skilled in the art using a general method.
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 added dropwise in small amounts to precipitate the matrix resin and the rubber-like polymer. Thereafter, the filtrate is filtered through a glass filter, evaporated to dryness, and then adjusted to a constant volume with n-hexane. After passing through a polytetrafluoroethylene membrane filter, the mixture is 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.

<Monohydric alcohols having 16 or more carbon atoms>
In a preferred aspect of this embodiment, the styrene-based resin composition preferably contains a monohydric alcohol having 16 or more carbon atoms. Alcohols having 15 or less carbon atoms are highly volatile, and the alcohol generates an odor during molding, etc., reducing workability. However, it has been confirmed that by increasing the number of carbon atoms to 16 or more, the volatility is reduced and the unpleasant odor during molding, etc. is suppressed.
In this embodiment, by containing a monohydric alcohol having 16 or more carbon atoms, the formation of gelled matter during molding at around 250 ° C. is suppressed, and a molded product with excellent appearance can be obtained. The monohydric alcohol is an alcohol having 16 or more carbon atoms and containing one hydroxyl group, and may contain heteroatoms such as oxygen or nitrogen in the carbon chain, and may contain bonds other than single bonds, such as double bonds, triple bonds, ester bonds, and amide bonds in the carbon chain. The number of carbon atoms is preferably 16 or more, more preferably 17 or more, and even more preferably 18 to 50. The monohydric alcohol may be contained in the styrene-based resin composition. Therefore, by making the monohydric alcohol present (or adding) in the polymerization solution used for polymerizing the styrene copolymer (A), the monohydric alcohol may remain in the styrene-based resin composition, which is the final product, or may be contained by mixing in an extruder or solvent after polymerization of the styrene copolymer (A).
In this embodiment, when molding at around 200° C. or when emphasis is placed on suppressing turbidity, it is preferable to select an alcohol having 5 to 13 carbon atoms, and when molding at around 250° C. or when emphasis is placed on suppressing odor, it is preferable to select an alcohol having 16 or more carbon atoms.

The boiling point of the monohydric alcohol having 16 or more carbon atoms is preferably 260°C or higher, more preferably 270°C or higher, and even more preferably 290°C or higher. If the boiling point of the monohydric alcohol is less than 260°C, it becomes highly volatile and tends to produce an unpleasant odor during molding, etc.

The content of the monohydric alcohol having 16 or more carbon atoms in the styrene-based resin composition according to the present invention is preferably 0.001 to 1.0 part by mass, more preferably 0.03 to 1.0 part by mass, even more preferably 0.05 to 0.7 parts by mass, and even more preferably 0.08 to 0.4 parts by mass, based on 100 parts by mass of the styrene copolymer (A). If the content is less than 0.001 part by mass, the gel suppression effect during molding at around 250°C decreases, and if it exceeds 1.0 part by mass, the amount remaining in the resin increases, causing an unpleasant odor or a significant decrease in heat resistance, and the effect of increasing heat resistance due to methacrylic acid modification becomes poor.

Examples of monohydric alcohols having 16 or more carbon atoms include, but are not limited to, 1-hexadecanol, isohexadecanol, 1-octadecanol, 5,7,7-trimethyl-2-(1,3,3-trimethylbutyl)-1-octanol, isooctadecanol, 1-isoisoeicosanol, 8-methyl-2-(4-methylhexyl)-1-decanol, 2-heptyl-1-undecanol, 2-heptyl-4-methyl-1-decanol, 2-(1,5-dimethylhexyl)-(5,9-dimethyl)-1-decanol, and polyoxyethylene alkyl ethers.

The polyoxyethylene alkyl ether is preferably a compound represented by the following general formula (3):
R-O-( _CH2 - _CH2 -O) _X -H...(3)
(In the above general formula (3), R is an alkyl group having 12 to 20 carbon atoms, and X is the average number of ethylene oxides added and is an integer of 1 to 15.)
As a specific example of polyoxyethylene alkyl ether, Emulgen 109P manufactured by Kao Corporation is particularly preferred.

<<Ethylbenzene>>
In a preferred embodiment of the present invention, the styrene resin composition preferably further contains ethylbenzene. By containing an appropriate amount of ethylbenzene, a further improvement in fluidity is expected. When the content of the styrene copolymer (A) in the styrene resin composition is taken as 100 parts by mass, the content of ethylbenzene is preferably in the range of 0.001 to 0.08 parts by mass, and by making it 0.001 parts by mass or more, a fluidity improvement effect can be obtained, and by making it 0.08 parts by mass or less, odor can be prevented. As a method for adding ethylbenzene, a method of adding it during polymerization of each resin is preferable.

<<Other ingredients>>
In addition to the above, the styrenic acid resin composition of the present embodiment may contain various additives that are generally used in general styrene-based resins or polystyrene-containing compositions in order to achieve known effects. Examples of the various additives include stabilizers, antioxidants, ultraviolet absorbers, lubricants, release agents, plasticizers, antiblocking agents, antistatic agents, antifogging agents, mineral oils, etc. In addition, reinforcing materials such as styrene-butadiene block copolymers or MBS resins may also be added to the extent that the physical properties are not impaired. There are no particular restrictions on the method of blending, but examples include a method in which the additives are added during polymerization and polymerized, or a method in which the additives are mixed in advance in a blender before melt-kneading after polymerization, and then melt-kneaded in an extruder or Banbury mixer, etc.

In this embodiment, various additives can be added to the styrene-based resin composition as described above, but the content of the styrene-based resin in the styrene-based resin composition is not particularly limited, but is preferably 95% by mass or more, more preferably 97% by mass, and even more preferably 99% by mass or more.

[Physical properties of styrene-based resin composition]
The physical properties of the styrene-based composition in this embodiment will be described below.
In this embodiment, the Vicat softening temperature of the styrene-based resin composition is preferably 105° C. or higher, more preferably 115° C. or higher. By setting it to 105° C. or higher, a sheet or container applicable to cooking in a general microwave oven of about 500 W can be obtained, and by setting it to 115° C. or higher, it can withstand cooking in a high-power commercial microwave oven of 1000 W or higher that is placed in a convenience store, etc. The Vicat softening temperature can be measured in accordance with ISO306 under conditions of a load of 50 N and a heating rate of 50° C./h.

In this embodiment, the melt flow rate of the styrene-based resin composition at 200°C is preferably in the range of 0.5 to 5.0 g/10 min, more preferably 1.0 to 3.5 g/10 min, and even more preferably 1.5 to 2.5 g/10 min. By making the melt flow rate 0.5 g/10 min or more, good moldability can be obtained, and by making it 4.5 g/10 min or less, a resin with excellent strength can be obtained.

In this embodiment, the haze of the styrene-based resin composition, i.e., the haze on a 2 mm plate, is preferably 20% or less, more preferably 15%, and even more preferably 10% or less. In particular, by making it 10% or less, a molded product having very excellent transparency can be obtained when molded into a sheet or container.
In this embodiment, the method for producing a 2 mm plate used in the method for measuring the haze and the method for measuring the haze are as follows: a styrene-based resin composition is molded into a 2 mm plate by injection molding under the conditions described in the Examples section below.

[Method of producing styrene-based resin composition]
The styrene-based resin composition of the present embodiment can be produced by melt-kneading each component by any method. For example, a high-speed stirrer such as a Henschel mixer, a batch-type kneader such as a Banbury mixer, a single-screw or twin-screw continuous kneader, a roll mixer, or the like may be used alone or in combination. The heating temperature during kneading is usually selected in the range of 180 to 260°C. In addition, a radical scavenger and/or liquid paraffin may be added during the production of the styrene copolymer (A) or rubber-modified polystyrene.
[Molded product]
The styrene-based resin composition of the present embodiment can be used to produce a molded article by the above-mentioned melt kneading molding machine, or by using pellets of the obtained styrene-based resin composition as a raw material, through injection molding, injection compression molding, extrusion molding, blow molding, press molding, vacuum molding, foam molding, or the like.

[Extruded sheet]
Another aspect of the present invention provides an extruded sheet formed using the above-mentioned styrene-based resin composition of the present invention. The extruded sheet may be either non-foamed or foamed. A commonly known method can be used as a method for producing an extruded sheet. A method for producing a non-foamed extruded sheet can be a method using a single-screw or twin-screw extruder equipped with a T-die and a device for taking up a sheet with a uniaxial or biaxial stretching machine, and a method for producing a foamed extruded sheet can be a method using an extrusion foaming molding machine equipped with a T-die or circular die.

<Foam extrusion sheet>
When forming a foamed extrusion sheet, materials that are commonly used for foaming agents and foam nucleating agents during extrusion foaming can be used. Butane, pentane, fluorocarbons, carbon dioxide, water, etc. can be used as the foaming agent, with butane being preferred. Talc, etc. can also be used as the foam nucleating agent.

The foamed extruded sheet preferably has a thickness of 0.5 mm to 5.0 mm, an apparent density of 50 g/L to 300 g/L, and a basis weight of 80 g/m ² to 300 g/m ^2. The foamed extruded sheet of the present invention may be multi-layered, for example, by further laminating a film. The type of film used may be any type commonly used for polystyrene.

<Non-foamed extruded sheet>
The thickness of the non-foamed sheet is preferably, for example, about 0.1 to 1.0 mm in terms of rigidity and thermoforming cycle. The uniaxial sheet may be formed only by roll stretching at a normal low magnification, and the biaxially stretched sheet is preferably stretched about 1.3 to 7 times in the machine direction (MD) with a roll and then stretched about 1.3 to 7 times in the perpendicular direction (TD) with a tenter in terms of strength. The non-foamed sheet may be multi-layered with a known styrene-based resin such as polystyrene resin. It may also be multi-layered with a resin other than the styrene-based resin. Examples of resins other than the styrene-based resin include PET resin and nylon resin.

Another aspect of the present invention provides a molded product formed using the non-foamed extruded sheet or foamed extruded sheet of the present invention described above. The foamed extruded sheet or a multi-layer body containing the foamed extruded sheet can be molded, for example, by vacuum forming to produce a container such as a tray. The non-foamed extruded sheet can also be molded, for example, by vacuum forming to produce a lid for a lunch box or a container for storing side dishes, etc.

The present invention will now be described in detail with reference to examples and comparative examples, but the present invention is not limited to these examples. The methods for analyzing and evaluating the resins and extruded sheets in the examples and comparative examples are as follows.

[Evaluation of properties of each resin material and styrene-based resin composition used in the examples and comparative examples]
(1) Measurement of Weight Average Molecular Weight The weight average molecular weight (Mw) of each resin material and each resin composition used in the examples and comparative examples was measured by gel permeation chromatography (GPC) under the following conditions.
Measuring equipment: Tosoh HLC-8220
Separation column: Two Tosoh TSK gel Super HZM-H (inner diameter 4.6 mm) connected in series Guard column: Tosoh TSK guard column Super HZ-H
Measurement solvent: tetrahydrofuran (THF)
Sample concentration: 5 mg of a measurement sample was dissolved in 10 mL of a solvent and filtered through a 0.45 μm filter.
Injection volume: 10μL
Measurement temperature: 40℃
Flow rate: 0.35 mL/min Detector: Ultraviolet absorption detector (Tosoh UV-8020, wavelength 254 nm)
The calibration curve was created using 11 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. The calibration curve was created using a linear approximation equation.

(2) Measurement of Melt Mass Flow Rate (MFR) The melt mass flow rate (g/10 min) of each of the resin compositions used in the Examples and Comparative Examples was measured at 200° C. and a load of 49 N in accordance with ISO 1133.

(3) Measurement of Vicat Softening Temperature The Vicat softening temperature of each resin and resin composition used in the examples and comparative examples was measured in accordance with ISO 306. The load was 50 N, and the heating rate was 50° C./h.

(4) Measurement of the Content of Alcohols in the Resin Composition The contents of monohydric alcohols having 16 or more carbon atoms and ethylbenzene were measured using gas chromatography under the following conditions.
Sample preparation: 1.0 g of resin material was dissolved in 5 mL of methyl ethyl ketone, and then 5 mL of hexane containing a standard substance (p-diethylbenzene) was added to reprecipitate the polymer component, and the supernatant was collected and used as the measurement solution.
Measurement equipment: Agilent 6850 series GC system Detector: FID
Column: HP-1 (100% dimethylpolysiloxane) 30 m,
Film thickness: 0.25 μm, 0.32 mm diameter
Injection volume: 1 μL (splitless)
Column temperature: 40°C for 2 minutes → heated to 320°C at 20°C/min →
Hold at 320°C for 15 minutes Injection port temperature: 250°C
Detector temperature: 280°C
Carrier gas: Helium

(5) Measurement of Content of Conjugated Diene Monomer Units The content of conjugated diene monomer units was measured by pyrolysis GC.
Sample preparation: A styrene-based resin composition was dissolved in chloroform at 5% by mass, and 20 μl of the solution was applied to Pyrofoil and vacuum dried at 80° C. for 24 hours.
Measurement conditions:
Py-GC
Equipment: Curie point injector manufactured by Japan Analytical Industry Co., Ltd. Pyrofoil temperature: 590°C
High frequency irradiation time: 10 seconds GC:
Equipment: Agilent Technologies HP-GC-6890
Column: HP-5MS
30m, film thickness 0.25mm, 0.25mmφ
Column temperature: held at 50° C. for 5 minutes, heated at 10° C./min, and then heated from 100° C. at 70° C./min, and held at 300° C. for 10 minutes.
Inlet temperature: 300℃
Detector temperature: 300°C
Split ratio: 1/20
Carrier gas: Helium Detection method: MSD

(6) Average particle size of rubber particles in rubber-modified polystyrene The average particle size (μm) of rubber particles in rubber-modified polystyrene (hereinafter, HIPS resin) was measured by observing the cross section of 200 rubber-like elastomer particles using a transmission electron microscope, and the average particle size was calculated using the following formula:
Average particle diameter = Σ(ni×Di ⁴ )/Σ(ni×Di ³ )
{In the formula, ni is the number of rubber-like elastomer particles having a particle diameter Di, and Di is the average value of the major axis and minor axis of the rubber-like elastomer particles.}
It was calculated by:

(7) Measurement of swelling index of toluene insoluble matter of HIPS resin 1 g of HIPS resin was precisely weighed in a precipitation tube (W1), 20 ml of toluene was added, and the mixture was shaken at 23°C for 2 hours, and then centrifuged at 10°C or less and 20,000 rpm for 60 minutes in a centrifuge (himac, CR-20 (rotor: R20A2) manufactured by Hitachi, Ltd.). The precipitation tube was slowly tilted at about 45 degrees, and the supernatant liquid was removed by decantation. The mass of the insoluble matter containing toluene was precisely weighed (W2), and the mixture was vacuum-dried for 1 hour under conditions of 160°C and 3 kPa or less. The dried toluene insoluble matter was cooled to room temperature in a desiccator, and then the mass was precisely weighed (W3).
The swelling index of the toluene insoluble matter and the toluene insoluble matter were calculated according to the following formulas.
Toluene insoluble matter (mass%)=((W3)/(W1))×100
Swelling index of toluene insoluble matter=(W2/W3)

(8) Measurement of Haze (Haze of 2 mm Plate) The resin compositions prepared in the Examples and Comparative Examples were molded into 2 mm plates by injection molding (EC60N manufactured by Toshiba Machine Co., Ltd.) under the following conditions, and the haze was measured using a haze meter (NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd.) and the n3 average was recorded as the value.
2mm plate molding conditions Molding machine: Toshiba Machine Co., Ltd. EC60N
Cylinder temperature: 220-240-220-200℃
Measurement: 45mm
Holding pressure switching: 10mm
Injection time: 10 seconds Cooling time: 15 seconds Injection speed: 23 mm/sec Pressure holding speed: 23 mm/sec Pressure holding time: 10 seconds Mold temperature: 45°C
The above molding conditions are merely an example, and the temperature, pressure holding and other conditions may be finely adjusted as necessary.

[Evaluation of properties of sheet molded product]
(8) Appearance Evaluation of Extruded Sheets Using the styrene-based resin compositions of the Examples and Comparative Examples, sheets were extruded continuously for 3 hours using a 30 mmφ short-axis sheet extruder, and then five sheets measuring 10 cm × 20 cm were cut out from the 0.3 mm thick sheet. The numbers of gels and air bubbles, which are foreign matter with an average diameter of (major axis + minor axis)/2 of 0.5 mm or more on the surfaces of the five sheets, were counted, and the yellowness was evaluated visually. The appearance was evaluated according to the following criteria.
○: No yellowing when visually observed, and gels and bubbles are 2 points or less. △: No yellowing when visually observed, and gels and bubbles are 3 to 9 points. ×: No yellowing when visually observed, and gels and bubbles are 10 points or more. Y: A level where yellowing is visible when visually observed.

(9) Film impact of batch biaxially stretched sheet A press plate having a thickness of 1.2 to 1.6 mm was produced from the styrene-based resin composition of the examples and comparative examples using a press molding machine. A sheet having a size of 10 cm x 10 cm was cut out from the produced plate. 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 having a thickness of about 0.2 mm.
Stretching temperature: Vicat softening temperature of resin composition + 20 to 30°C,
Stretching speed: 170%
Stretching ratio: 2.5 times The obtained sheet was cut into a size of 8 cm x 8 cm, and the film impact was measured using a film impact tester (No. 195) manufactured by Toyo Seiki Seisakusho Co., Ltd., and the n8 average was recorded as the value.

(10) Heat resistance of batch biaxially stretched sheet A press plate having a thickness of 1.2 to 1.6 mm was produced from the styrene-based resin composition of the examples and comparative examples using a press molding machine. A sheet having a size of 10 cm x 10 cm was cut out from the produced plate. 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 Seisakusho Co., Ltd., to produce a biaxially stretched sheet having a thickness of about 0.2 mm.
Stretching temperature: Vicat softening temperature of resin composition + 20 to 30°C,
Stretching speed: 170%
Stretching ratio: 2.5 times The stretched sheet obtained under the above molding conditions was placed in an oven set at 110° C. for 60 minutes, after which the deformation of the container was visually observed and the heat resistance was evaluated based on the thermal deformation as follows.
○: No deformation ×: Dimensional change (3% or more)

(11) Contamination of the winding roll (formability)
After continuously extruding a sheet of about 250 μm for 10 hours using a 30 mmφ single-screw sheet extruder, the stain on the take-up roll was visually confirmed, and the roll stain was evaluated according to the following criteria.
○: Not dirty at all.
△: It appears not to be dirty at first glance, but when the roll is wiped with a cloth, the wiping area becomes visible.
×: Obviously dirty.
In this specification, the staining of the winding roll is evaluated as an example of an index of formability.

(12) 250 μm sheet haze (cloudiness) after 8 hours of extrusion
A transparent sheet of about 250 μm was extruded continuously for 8 hours using a 30 mmφ single-screw sheet extruder. At the end of the 8 hours, the haze of the transparent sheet at 250 μm was measured using a Nippon Denshoku Industries Co., Ltd. haze meter (NDH-2000), and the n3 average was recorded as the haze value.

Specific production examples will be described below with reference to Examples and Comparative Examples. In these Examples, compositions were produced using rubber-modified polystyrenes d-1 to d-3 having the properties shown below.

[Example 1]
A polymerization raw material composition liquid consisting of 73.0 parts by mass of styrene, 5.8 parts by mass of methacrylic acid, 17.2 parts by mass of ethylbenzene, 3.0 parts by mass of 2-ethyl-1-hexanol, Nissan Chemical Co., Ltd.'s Fine Oxocol 180 (monohydric alcohol having 18 carbon atoms) and 0.05 parts by mass of 1,1-bis(t-butylperoxy)cyclohexane was prepared and supplied to a completely mixed reactor for polymerization. At the outlet of the completely mixed reactor, Sumitomo Chemical Co., Ltd.'s Sumilizer GS was added in an amount of 0.1 parts by mass per 100 parts by mass of the polymerization reaction composition liquid, stirred, and then continuously supplied to a devolatilizer connected to a single-screw extruder for removing volatile components such as unreacted monomers and polymerization solvent. The temperature of the single-screw extruder was set to 200 to 250°C and the pressure to 10 torr, and volatile components such as unreacted monomers and polymerization solvent were devolatilized. The volatilized volatile components were condensed in a condenser through which a refrigerant at -5°C was passed and recovered as an unreacted liquid, and the styrene-based resin composition was recovered as resin pellets 1. The physical properties of the resin composition obtained by the above-mentioned analytical methods are shown in Table 2-1 below.
Next, the obtained resin pellet 1 and the rubber-modified polystyrene (D) pellets of d-1 having the composition shown in Table 1 were dry-blended to a mass ratio of 100/1.5, and the resin pellet 1/d-1 was continuously molded into a sheet using a short-axis sheet extruder for 10 hours to produce an extruded sheet (A). The extruded sheet (A) was then subjected to the evaluation of appearance, staining of the winding roll, and 250 μm sheet haze after 8 hours of extrusion according to the above-mentioned evaluation methods. The results are shown in Table 2-1 below.
Similarly, the resin pellets 1/rubber-modified polystyrene (D) (d-1) were dry-blended in a mass ratio of 100/1.5, melt-kneaded in a twin-screw extruder, and then press-molded, followed by batch biaxial stretching to produce an extruded sheet (B). The film impact and heat resistance of the extruded sheet (B) were evaluated according to the above-mentioned evaluation methods.

[Examples 2 to 19]
A styrene-based resin composition and extruded sheets (A) and (B) were obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 2-1 below.

[Comparative Example 1]
A resin composition was obtained in the same manner as in Example 1, except that the polymerization conditions were changed as shown in Table 2-2 below. When a styrene homopolymer was used instead of the styrene copolymer (A), the heat resistance of the extruded sheet was reduced.

[Comparative Example 2]
A resin composition was obtained in the same manner as in Example 1, except that the polymerization conditions were changed as shown in Table 2-2 below. When an excessive amount of Sumilizer GS was added as the radical scavenger (C), the staining of the take-up roll and the haze of the sheet after 10 hours of extrusion worsened.

[Comparative Example 3]
A resin composition was obtained in the same manner as in Example 1, except that the polymerization conditions were changed as shown in Table 2-2 below. When the radical scavenger (C) was not added, the amount of oligomer increased, and the staining of the take-up roll and the haze of the sheet after 10 hours of extrusion worsened.

[Comparative Example 4]
A resin composition was obtained in the same manner as in Example 1, except that the polymerization conditions were changed as shown in Table 2-2 below. The flowability was decreased due to the decrease in the amount of oligomer, as compared with Example 2. The decrease in the flowability of the entire composition increased the molding temperature of the extruded sheet (A), and the sheet appeared yellowish at a level that was visible to the naked eye.

In addition, in Tables 2-1 and 2-2, "out of reactor" in "Timing of radical scavenger addition" means that the radical scavenger was added after the polymerization process of styrene copolymer (A) was completed and the copolymer was discharged from the reactor, between the polymerization process and the devolatilization process, and "before reactor" means that the radical scavenger was added before the polymerization of styrene copolymer (A).

The styrene-based resin disclosed herein has excellent heat resistance, appearance, and moldability. Therefore, the styrene-based resin composition of the present invention can be widely used for non-foamed or foamed sheets produced by extrusion molding, food packaging containers using these, or molded products produced by injection molding (electrical appliance parts, toys, daily necessities, various industrial parts, containers), and plays a major role in the industrial world.

Claims (10)

A styrene-based resin composition comprising: (A) a styrene copolymer having an unsaturated carboxylic acid monomer unit and a styrene-based monomer unit; (B) a styrene oligomer having a styrene-based monomer unit; and (C) a radical scavenger,
The radical scavenger (C) is a compound represented by the following general formula (2):
(in the above general formula (2), X1 ^and X2 ^each independently represent a hydrogen atom, a halogen atom, or a substituted or unsubstituted aromatic ring; L1 ^and L2 ^each independently represent a single bond or an alkylene group having 1 to 23 carbon atoms, and one or more methylene groups in the alkylene group may be substituted with -CH=CH- so that they are not adjacent to each other),
When the styrene copolymer (A) is taken as 100 parts by mass, the content of the unsaturated carboxylic acid monomer unit contained in the styrene copolymer (A) is 2 to 15 parts by mass, the content of the styrene oligomer (B) is 0.05 to 0.4 parts by mass, and the content of the radical scavenger (C) is 0.001 to 0.1 parts by mass,
The styrene oligomer (B) is a styrene dimer or a styrene trimer which is any one of 2,4-diphenyl-1-butene, cis-1,2-diphenylcyclobutane, trans-1,2-diphenylcyclobutane, 2,4,6-triphenyl-1-hexene, 1,3,5-triphenylcyclohexane, 1e-phenyl-4a-(2-phenylethyl)tetralin, and 1e-phenyl-4e-(1-phenylethyl) tetralin. The styrene-based resin composition according to claim 1, further comprising 0.001 to 0.08 parts by mass of ethylbenzene per 100 parts by mass of the styrene copolymer (A). The styrene copolymer (A) is represented by the following general formula (1):

(In the above general formula (1), R ¹ represents a hydrogen atom or a methyl group, and R ² is an ester substituent and represents an alkyl group having 6 to 12 carbon atoms.) The styrene-based resin composition according to any one of claims 1 to 3, further comprising 0.001 to 1 part by mass of a monohydric alcohol having 16 or more carbon atoms per 100 parts by mass of the styrene copolymer (A). The styrene-based resin composition according to any one of claims 1 to 4 , further comprising 0.5 to 5 parts by mass of a rubber-modified polystyrene (D) based on 100 parts by mass of the styrene copolymer (A). The styrene-based resin composition according to any one of claims 1 to 5 , comprising 0 to 0.6 parts by mass of a conjugated diene monomer unit relative to 100 parts by mass of the styrene copolymer (A). The styrene-based resin composition according to any one of claims 1 to 6 , further comprising 0.001 to 0.5 parts by mass of liquid paraffin (E) based on 100 parts by mass of the styrene copolymer (A). A non-foamed extruded sheet comprising the styrene-based resin composition according to any one of claims 1 to 7 . A foamed extruded sheet comprising the styrene-based resin composition according to any one of claims 1 to 7 . A molded product formed using the non-foamed extruded sheet according to claim 8 or the foamed extruded sheet according to claim 9 .