JP7619906B2 - Flame-retardant styrene-based resin composition and molded article - Google Patents

Description

The present invention relates to a flame-retardant styrene-based resin composition and a molded article.

Styrene-based resins are used in a wide range of applications due to their excellent moldability, dimensional stability, and impact resistance. Among them, polystyrene-based resin compositions imparted with flame retardancy are used in a wide range of applications, including home appliances and office automation equipment, and there is currently a demand for thinner products in order to reduce or lighten the weight of these products.
Conventionally, various flame retardants have been proposed for the purpose of imparting flame retardancy to polystyrene-based resin compositions. Among them, bromine-based flame retardants, which are inexpensive and have a good balance of physical properties, are widely used. However, in recent years, due to the movement to regulate halogen-containing organic compounds, mainly in Europe, there is an increasing demand for flame-retardant resins and flame-retardant resin compositions that do not contain bromine elements. Furthermore, from the viewpoint of carbon neutrality, there is an increasing need to contain bio-based materials.

As an alternative flame retardant to such bromine-based flame retardants, for example, Patent Document 1 discloses a technique of adding a phosphinate to a thermoplastic polymer.
Moreover, Patent Document 2 discloses a technique for improving flame retardancy by adding a flame retardant and cellulose nanofibers to a thermoplastic resin.

Japanese Patent Application Publication No. 11-124466 International Publication No. 2017/169494

Although the above-mentioned Patent Document 1 describes that it is possible to impart flame retardancy to a polystyrene-based resin composition, the flame retardant described in Patent Document 1 has poor dispersibility in polystyrene, insufficient flame retardancy, and generates black smoke during combustion, which are problems. In addition, in the technology of Patent Document 2, the flame retardancy is improved by blending the specific flame retardant and cellulose nanofiber described in Patent Document 2 into a polystyrene-based resin composition, but it is not possible to prevent black smoke from being generated during combustion of polystyrene. In addition, since composite products combining molded products of polystyrene-based resin compositions with internal mechanism parts or metals, etc., require dimensional accuracy of the material, if the linear expansion coefficient of a molded product of a polystyrene-based resin composition containing cellulose nanofibers as described in Patent Document 2 shows a large anisotropy between the MD direction and the TD direction, the adhesion to dissimilar materials such as metals may be adversely affected. Furthermore, when the polystyrene-based resin composition is processed, it turns brown, which is difficult to color it white.

Therefore, the present invention aims to provide a flame-retardant styrene-based resin composition that reduces the environmental impact and has low smoke generation, excellent flame retardancy, dimensional accuracy, and color tone.

As a result of intensive research to solve the above problems, the inventors have surprisingly found that a resin composition in which a flame retardant (B) and a specific cellulose polysaccharide (C) are added to a styrene resin in a specific ratio reduces the environmental load and has very high flame retardancy, low smoke generation, dimensional accuracy, and excellent color tone, leading to the completion of the present invention. That is, the present invention is as follows.

［上記式（ｉ）中、Ｒ^ｉ１及びＲ^ｉ２は、各々独立して、無置換又は１以上の水素原子が置換基Ｒ^ｉ３により置換されてもよい、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基、炭素原子数６～１０のアリール基又は炭素原子数６～１４のアラルキル基であり、
前記置換基Ｒ^ｉ３は、下記式（ｉｉ）：

「上記式（ｉｉ）中、Ｒ^ｉｉ１は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、＊は他の原子との結合を表す。」で表され、
Ｍ^ｉは、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり、ｐ^＋はＭ^ｉのイオン価を表し、１～３の正の整数であり、ｍ^ｉ１は、１～３の正の整数であり、ｎ^－は、－１、－２又は－３の負の整数を表し、ｒは１～３の正の整数を表し、｜ｐ^＋×ｒ｜＝｜ｎ^－×ｍ^ｉ１｜である。］で表されるホスフィン酸塩化合物（ｂ）を含む難燃剤（Ｂ）５～３０質量％と、
短軸ｄ_１或いは長軸ｄ_２の平均長さの少なくとも一方が１０～８０μｍであるセルロース系多糖類（Ｃ）３～３０質量％と、を含有することを特徴とする、難燃性スチレン系樹脂組成物である。
［２］本実施形態において、前記ホスフィン酸化合物（ｂ）は、下記一般式（１）で表されるホスフィン酸塩及び下記一般式（２）で表されるジホスフィン酸塩からなる群から選択される少なくとも１種又は２種以上であることが好ましい。

［上記式（１）中、Ｒ^１１及びＲ^１２は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、Ｍ^１は、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり、ａ^＋はＭ^１のイオン価を表し、１～３の正の整数であり、ｍ^１は、１～３の正の整数であり、ａ＝ｍ^１である。］
下記式（２）：

［上記式（２）中、Ｒ^２１及びＲ^２２は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、Ｌ^２３は、直鎖状若しくは分岐状の炭素原子数１～１０のアルキレン基、炭素原子数６～１０のアリーレン基、炭素原子数６～１４のアルキルアリーレン基又は炭素原子数６～１４のアリールアルキレン基であり；Ｍ^２は、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり、ｂ^＋はＭ^２のイオン価を表し、１～３の正の整数であり、ｍ^２は、１～３の正の整数であり、ｑは、１又は２の正の整数であり、ｂ×ｑ＝２ｍ^２である。］
［３］本実施形態において、前記スチレン系樹脂（Ａ）が、スチレン系単量体単位及び不飽和カルボン酸系単量体単位を含むことが好ましい。
［４］本実施形態において、前記セルロース系多糖類（Ｃ）が、リグニンを２０質量％以下含有することが好ましい。
［５］本実施形態において、前記セルロース系多糖類（Ｃ）のヘミセルロース量が１％以上であることが好ましい。
［６］本実施形態は、［１］～［５］のいずれか１項に記載の前記難燃性スチレン系樹脂組成物を含む成形品であることが好ましい。 [1] The present invention relates to a styrene-based resin (A) of 40 to 92% by mass,
The following general formula (i):

[In the above formula (i), R ⁱ¹ and R ⁱ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 6 to 14 carbon atoms, which may be unsubstituted or one or more hydrogen atoms may be substituted with a substituent R ⁱ³ ;
The substituent R ⁱ³ is represented by the following formula (ii):

In the above formula (ii), each R ⁱⁱ¹ is independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, and * represents a bond to another atom.
wherein M ⁱ is at least one selected from the group consisting of calcium ion, magnesium ion, aluminum ion, zinc ion, bismuth ion, manganese ion, sodium ion, potassium ion, and protonated nitrogen base, p ⁺ represents an ion valence of M ⁱ and is a positive integer of 1 to 3, m ⁱ¹ is a positive integer of 1 to 3, n ^- represents a negative integer of -1, -2, or -3, r represents a positive integer of 1 to 3, and |p ⁺ ×r|=|n ^- ×m ⁱ¹ |;
and 3 to 30 mass % of a cellulose-based polysaccharide (C) having an average length of at least one of the minor axis _d1 and the major axis _d2 of 10 to 80 μm.
[2] In the present embodiment, the phosphinic acid compound (b) is preferably at least one or more selected from the group consisting of a phosphinic acid salt represented by the following general formula (1) and a diphosphinic acid salt represented by the following general formula (2):

[In the above formula (1), R ¹¹ and R ¹² are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, M ¹ is at least one selected from the group consisting of calcium ion, magnesium ion, aluminum ion, zinc ion, bismuth ion, manganese ion, sodium ion, potassium ion, and protonated nitrogen base, a ⁺ represents the ionic valence of M ¹ and is a positive integer of 1 to 3, m ¹ is a positive integer of 1 to 3, and a=m ^1. ]
The following formula (2):

[In the above formula (2), R ²¹ and R ²² are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, L ²³ is a linear or branched alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 10 carbon atoms, an alkylarylene group having 6 to 14 carbon atoms, or an arylalkylene group having 6 to 14 carbon atoms; M ² is at least one selected from the group consisting of calcium ions, magnesium ions, aluminum ions, zinc ions, bismuth ions, manganese ions, sodium ions, potassium ions, and protonated nitrogen bases, b ⁺ represents the ionic valence of M ² and is a positive integer of 1 to 3, m ² is a positive integer of 1 to 3, q is a positive integer of 1 or 2, and b×q=2m ^2. ]
[3] In this embodiment, the styrene-based resin (A) preferably contains a styrene-based monomer unit and an unsaturated carboxylic acid-based monomer unit.
[4] In this embodiment, the cellulose polysaccharide (C) preferably contains 20% by mass or less of lignin.
[5] In this embodiment, the hemicellulose content of the cellulose polysaccharide (C) is preferably 1% or more.
[6] The present embodiment is preferably a molded article comprising the flame-retardant styrene-based resin composition according to any one of [1] to [5].

The present invention provides a flame-retardant styrene-based resin composition that reduces the environmental impact and has low smoke generation, excellent flame retardancy, dimensional accuracy, and color tone.

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

［上記式（ｉ）中、Ｒ^ｉ１及びＲ^ｉ２は、各々独立して、無置換又は１以上の水素原子が置換基Ｒ^ｉ３により置換されてもよい、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基、炭素原子数６～１０のアリール基又は炭素原子数６～１４のアラルキル基であり、
前記置換基Ｒ^ｉ３は、下記式（ｉｉ）：

「上記式（ｉｉ）中、Ｒ^ｉｉ１は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、＊は他の原子との結合を表す。」で表され、
Ｍ^ｉは、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり；ｐ^＋はＭ^ｉのイオン価を表し、１～３の正の整数であり；ｍ^ｉ１は、１～３の正の整数であり、ｎ^－は、－１、－２又は－３の負の整数を表し、｜ｐ^＋×ｒ｜＝｜ｎ^－×ｍ^ｉ１｜である。］で表される。
これにより、低発煙性、難燃性、寸法精度及び色調に優れた難燃性スチレン系樹脂組成物を提供できる。
以下、難燃性スチレン系樹脂組成物に含まれる各成分について説明する。 [Flame-retardant styrene-based resin composition]
The flame-retardant styrene-based resin composition of the present embodiment contains 40 to 92 mass% of a styrene-based resin (A) (hereinafter also referred to as component (A)), 5 to 30 mass% of a flame retardant (B) (hereinafter also referred to as component (B)) containing a phosphinate compound (b), and ₃ to 30 mass% of a cellulose-based polysaccharide (C) (hereinafter also referred to as component (C)) having an average length of at least one of the minor axis d1 and the major axis _d2 of 10 to 80 μm.
The phosphinate compound (b) is represented by the following general formula (i):

[In the above formula (i), R ⁱ¹ and R ⁱ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 6 to 14 carbon atoms, which may be unsubstituted or one or more hydrogen atoms may be substituted with a substituent R ⁱ³ ;
The substituent R ⁱ³ is represented by the following formula (ii):

In the above formula (ii), each R ⁱⁱ¹ is independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, and * represents a bond to another atom.
M ⁱ is at least one selected from the group consisting of a calcium ion, a magnesium ion, an aluminum ion, a zinc ion, a bismuth ion, a manganese ion, a sodium ion, a potassium ion, and a protonated nitrogen base; p ⁺ represents the ionic valence of M ⁱ and is a positive integer of 1 to 3; m ⁱ¹ is a positive integer of 1 to 3, n ⁻ represents a negative integer of −1, −2, or −3, and |p ⁺ ×r|=|n ⁻ ×m ⁱ¹ |.
This makes it possible to provide a flame-retardant styrene-based resin composition that is excellent in low smoke generation, flame retardancy, dimensional accuracy and color tone.
Each component contained in the flame-retardant styrene-based resin composition will be described below.

<Styrene-based resin (A): Component (A)>
In the flame-retardant styrene-based resin composition of this embodiment, the content of the styrene-based resin (A) is 40 to 92 mass%, preferably 50 to 90 mass%, and more preferably 60 to 85 mass%, based on 100 mass% of the total amount of the components (A), (B), and (C). If the content of the styrene-based resin (A) is less than 40 mass%, the moldability decreases, and if it exceeds 92 mass%, the flame retardancy decreases.

The styrene-based resin (A) that can be used in this embodiment is preferably a resin obtained by polymerizing a styrene-based monomer and, if necessary, one or more selected from other vinyl-based monomers copolymerizable with the styrene-based monomer and rubber-like polymer (a). In other words, the styrene-based resin (A) is preferably a polymer having a styrene-based monomer unit, and more preferably a polymer that essentially contains a styrene-based monomer unit and has, as an optional component, other vinyl-based monomers and/or monomer units of rubber-like polymer (a) that are copolymerizable with the styrene-based monomer unit.
The preferred form of the styrene-based resin (A) in this embodiment is not particularly limited, but specific examples include polystyrene, a rubber-modified styrene-based resin in which particles of a rubber-like polymer (a) are dispersed in a polymer matrix containing a polystyrene-based polymer (polystyrene and/or a polystyrene-unsaturated carboxylic acid-based polymer, etc.), and a styrene-based copolymer resin. A styrene-based polymer having a syndiotactic structure can also be used as the styrene-based resin (A).

<<Polystyrene>>
In this embodiment, polystyrene is a homopolymer obtained by polymerizing a styrene-based monomer, and generally available ones can be appropriately selected and used. As the styrene-based monomer constituting polystyrene, in addition to styrene, α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, or styrene derivatives such as bromostyrene and indene can be mentioned. Styrene is particularly preferable from an industrial viewpoint. One or more of these styrene-based monomers can be used. Although polystyrene does not exclude further inclusion of monomer units other than the above-mentioned styrene-based monomer units within a range that does not impair the effects of the present invention, it typically consists of styrene-based monomer units.

<<Rubber-modified styrene-based resin>>
In this embodiment, the rubber-modified styrene-based resin is a resin in which particles of a rubber-like polymer (a) (also referred to as rubber-like polymer (a) particles) are dispersed in a styrene-based resin as a matrix, and can be produced by polymerizing a styrene-based monomer in the presence of the rubber-like polymer (a).

In addition to styrene, examples of the styrene monomer constituting the rubber-modified styrene resin of this embodiment include α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, and t-butylstyrene, or styrene derivatives such as bromostyrene and indene. Styrene is particularly preferred. These styrene monomers can be used alone or in combination.

The rubber-like polymer (a) particles contained in the rubber-modified styrene-based resin of this embodiment may, for example, contain a resin containing a styrene monomer unit obtained from the above-mentioned styrene-based monomer inside the rubber-like polymer (a) particles, and/or may have a resin containing a styrene monomer unit grafted onto the surface of the rubber-like polymer (a) particles.

As the rubber-like polymer (a), for example, a rubber component such as polybutadiene, polyisoprene, natural rubber, polychloroprene, styrene-butadiene copolymer, or acrylonitrile-butadiene copolymer can be used. The rubber component may also include a form containing polystyrene and/or polystyrene-unsaturated carboxylic acid polymer. Among them, the rubber-like polymer (a) is preferably polybutadiene or styrene-butadiene copolymer. As the polybutadiene, both high-cis polybutadiene having a high cis content and low-cis polybutadiene having a low cis content can be used. In addition, both random structure and block structure can be used as the structure of the styrene-butadiene copolymer. One or more of these rubber-like polymers (a) can be used. In addition, saturated rubber obtained by hydrogenating butadiene rubber can also be used.

Examples of such rubber-modified styrene-based resins include HIPS (high impact polystyrene), ABS resin (acrylonitrile-butadiene-styrene copolymer), AAS resin (acrylonitrile-acrylic rubber-styrene copolymer), and AES resin (acrylonitrile-ethylene propylene rubber-styrene copolymer).

When the rubber-modified styrene resin is a HIPS resin, the particularly preferred rubber-like polymer (a) is a high-cis polybutadiene having 90 mol % or more of cis-1,4 bonds. In the high-cis polybutadiene, it is preferable that the vinyl 1,2 bonds are 6 mol % or less, and it is particularly preferable that the vinyl 1,2 bonds are 3 mol % or less.

The content of isomers having a cis-1,4 structure, a trans-1,4 structure, or a vinyl-1,2 structure as structural unit isomers of the above-mentioned isopolybutadiene can be measured using an infrared spectrophotometer and calculated by processing the data using the Morello method.

The high-cis polybutadiene can be easily obtained by known production methods, for example, by polymerizing 1,3-butadiene using a catalyst containing an organoaluminum compound and a cobalt or nickel compound.

The content of the rubber-like polymer (a) contained in the rubber-modified styrene-based resin (not including the styrene-based resin as a matrix incorporated in the rubber-like polymer (a) particles) is preferably 3 to 20 mass% and more preferably 5 to 15 mass% relative to 100 mass% of the total amount of the rubber-modified styrene-based resin. If the content of the rubber-like polymer (a) is less than 3 mass%, the impact resistance of the styrene-based resin may decrease. Also, if the content of the rubber-like polymer (a) exceeds 20 mass%, the flame retardancy may decrease.

In this disclosure, the content of rubber-like polymer (a) in the rubber-modified styrene-based resin is a value calculated using pyrolysis gas chromatography.

The average particle size of the rubber-like polymer (a) particles contained in the rubber-modified styrene-based resin is preferably 0.5 to 4.0 μm, and more preferably 0.8 to 3.5 μm, from the viewpoint of impact resistance and flame retardancy.

In the present disclosure, the average particle size of the rubber-like polymer (a) particles contained in the rubber-modified styrene-based resin can be measured by the following method.
A 75 nm thick ultrathin section is prepared from the rubber-modified styrene-based resin stained with osmium tetroxide, and a photograph is taken at a magnification of 10,000 times using an electron microscope. In the photograph, the particles stained black are rubber-like polymer (a) particles. From the photograph, the following formula (N1):
Average particle diameter = ΣniDri ³ /ΣniDri ² (N1)
(In the above formula (N1), ni is the number of rubber-like polymer (a) particles having a particle diameter Dri, and the particle diameter Dri is the particle diameter calculated as a circle-equivalent diameter from the area of the particle in the photograph.)
The area-average particle size is calculated from the above and is taken as the average particle size of the rubber-like polymer (a). This measurement is carried out by scanning a photograph at a resolution of 200 dpi with a scanner and using particle analysis software of an image analyzer IP-1000 (manufactured by Asahi Kasei Corporation).

The reduced viscosity of the rubber-modified styrene-based resin (which is an index of the molecular weight of the rubber-modified styrene-based resin) is preferably in the range of 0.50 to 0.85 dL/g, and more preferably in the range of 0.55 to 0.80 dL/g. If it is less than 0.50 dL/g, there is a risk that the impact strength will decrease, and if it exceeds 0.85 dL/g, there is a risk that moldability will decrease due to a decrease in fluidity.

In this disclosure, the reduced viscosity of the rubber-modified styrene-based resin is a value measured in a toluene solution at 30°C and a concentration of 0.5 g/dL.

The method for producing the rubber-modified styrene-based resin 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 the rubber-like polymer (a), or by bulk-suspension polymerization in which the reaction transitions to suspension polymerization during the course of the reaction, or by emulsion graft polymerization in which a styrene-based monomer is polymerized in the presence of the rubber-like polymer (a) latex. In bulk polymerization, the rubber-like polymer (a) can be produced by continuously supplying a mixed solution containing the rubber-like polymer (a) and the styrene-based monomer, and optionally 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 connected in series with multiple tank reactors.

<<Styrene-based copolymer resin>>
In this embodiment, the styrene-based copolymer resin is a resin containing a styrene-based monomer unit and another monomer (e.g., an unsaturated carboxylic acid-based monomer unit) copolymerizable with the styrene-based monomer. For example, when the other monomer is an unsaturated carboxylic acid-based monomer unit, the styrene-based copolymer resin according to the present invention has a styrene-based monomer unit content of preferably 69 to 98% by mass, more preferably 74 to 96% by mass, and even more preferably 77 to 92% by mass, when the total content of the styrene-based monomer unit and the unsaturated carboxylic acid-based monomer unit is taken as 100% by mass. By making the content 69% by mass or more, the flowability of the resin can be improved. On the other hand, by making the content of the styrene-based monomer unit 98% by mass or less, it becomes difficult to make the desired amount of the unsaturated carboxylic acid-based monomer unit described below, which is an example of the other monomer, present, and it becomes difficult to obtain the effects described below due to these monomer units.

In this embodiment, the unsaturated carboxylic acid monomer includes an unsaturated carboxylic acid monomer and an unsaturated carboxylic acid ester monomer.

In the preferred styrene-based copolymer resin of this embodiment, the unsaturated carboxylic acid monomer unit plays a role in improving heat resistance. When the total content of the styrene-based monomer unit, the unsaturated carboxylic acid monomer unit, and the unsaturated carboxylic acid ester monomer unit in the styrene-based copolymer resin is taken as 100% by mass, the content of the unsaturated carboxylic acid monomer unit is preferably 2 to 16% by mass, more preferably 4 to 14% by mass, and even more preferably 8 to 13% by mass. By making the content 2% by mass or more, the dispersibility of the (B) component is improved and the heat resistance can be further improved. On the other hand, by making the content 16% by mass or less, when the flame-retardant styrene-based resin composition of this embodiment is used as a master batch, excellent dispersibility in the styrene-based resin is exhibited, and the flame retardancy can be improved, and the molded appearance, the fluidity of the resin, and the mechanical properties are further improved.

Generally, styrene-methacrylic acid-based resins including styrene-methacrylic acid-methyl methacrylate copolymer resins, which are one form of the styrene-based copolymer resins of the present invention, are produced on an industrial scale in most cases by radical polymerization. However, in this embodiment, in order to suppress the gelling reaction in the devolatilization step, various alcohols can be added to the polymerization system to carry out the polymerization.

Unsaturated carboxylic acid ester monomers can be used to suppress the dehydration reaction of unsaturated carboxylic acid monomers through intermolecular interactions with the unsaturated carboxylic acid monomers, and to improve the mechanical strength of the resin. Furthermore, unsaturated carboxylic acid ester monomers also contribute to improving resin properties such as weather resistance and surface hardness.

In this embodiment, when the total content of the styrene monomer unit, the unsaturated carboxylic acid monomer unit, and the unsaturated carboxylic acid ester monomer unit is taken as 100% by mass, the content of the unsaturated carboxylic acid ester monomer unit is preferably 0 to 15% by mass, more preferably 1 to 12% by mass, and even more preferably 2 to 10% by mass. By setting the content to 15% by mass or less, the fluidity of the resin can be improved and water absorption can be suppressed. In addition, by setting the lower limit of the content of the unsaturated carboxylic acid ester monomer unit to 0% by mass, it is possible to improve heat resistance and reduce costs, but from the above viewpoint, the content of the unsaturated carboxylic acid ester monomer unit can also be set to more than 0% by mass.

When unsaturated carboxylic acid monomers and unsaturated carboxylic acid ester monomer units are bonded side by side, using a high-temperature, high-vacuum devolatilizer may cause a dealcoholization reaction under certain conditions, resulting in the formation of a six-membered cyclic acid anhydride. The styrene-based copolymer resin of this embodiment may contain this six-membered cyclic acid anhydride, but since this reduces fluidity, it is preferable that as little six-membered cyclic acid anhydride is produced as possible.

In the present embodiment, the contents of the styrene monomer unit (e.g., styrene monomer unit), the unsaturated carboxylic acid monomer unit (e.g., methacrylic acid monomer unit), and the unsaturated carboxylic acid ester monomer unit (e.g., methyl methacrylate monomer unit) in the styrene copolymer resin can be determined from the integral ratio of the spectrum measured by a proton nuclear magnetic resonance ( ^1H -NMR) measurement device.

In this embodiment, the styrene-based copolymer resin does not exclude further monomer units other than the styrene-based monomer units and unsaturated carboxylic acid-based monomer units (e.g., unsaturated carboxylic acid monomer units and unsaturated carboxylic acid ester monomer units), which are examples of other monomers, within a range that does not impair the effects of the present invention. However, it is preferable that the styrene-based copolymer resin in the present invention is typically composed of styrene-based monomer units, unsaturated carboxylic acid monomer units, and/or unsaturated carboxylic acid ester monomer units.

The styrene-based monomer constituting the styrene-based copolymer resin of this embodiment is not particularly limited, but examples thereof include styrene, α-methylstyrene, α-methyl-p-methylstyrene, ο-methylstyrene, m-methylstyrene, p-methylstyrene, vinyltoluene, ethylstyrene, isobutylstyrene, t-butylstyrene, bromostyrene, indene, and other styrene derivatives. From an industrial viewpoint, styrene is preferred as the styrene-based monomer. These styrene-based monomers can be used alone or in combination of two or more.

The unsaturated carboxylic acid monomer constituting the styrene-based copolymer resin of this embodiment is not particularly limited, but examples thereof include methacrylic acid, acrylic acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, and the like. As the unsaturated carboxylic acid monomer, methacrylic acid is preferred because it has a large effect of improving heat resistance, is liquid at room temperature, and has excellent handleability. These unsaturated carboxylic acid monomers can be used alone or in combination of two or more.

The unsaturated carboxylic acid ester monomer constituting the styrene-based copolymer resin of this embodiment is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, and cyclohexyl (meth)acrylate. As the (meth)acrylic acid ester monomer, methyl (meth)acrylate is preferred because it has little effect on the decrease in heat resistance. These unsaturated carboxylic acid ester monomers can be used alone or in combination of two or more.

Suitable styrene-based copolymer resins for this embodiment include styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-methacrylic acid-methyl methacrylate copolymer, styrene-acrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-acrylic acid-methyl acrylate copolymer, styrene-methyl methacrylate-butyl methacrylate copolymer, styrene-butyl methacrylate copolymer, and styrene-maleic anhydride copolymer.

In this embodiment, the weight average molecular weight (Mw) of the styrene copolymer resin is preferably 100,000 to 350,000, more preferably 120,000 to 300,000, and even more preferably 140,000 to 240,000. When the weight average molecular weight (Mw) is 100,000 to 350,000, a resin with a better balance between mechanical strength and fluidity is obtained, and there is also little gel contamination. The weight average molecular weight (Mw) is a value obtained by using gel permeation chromatography and converting it into standard polystyrene.

In this embodiment, the polymerization method for the styrene-based polymer resin is not particularly limited, but for example, a bulk polymerization method or a solution polymerization method can be suitably adopted as a radical polymerization method. The polymerization method mainly includes a polymerization process for polymerizing the polymerization raw materials (monomer components) and a devolatilization process for removing volatile matters such as unreacted monomers and polymerization solvents from the polymerization product.

Hereinafter, an example of a polymerization method for a styrene-based copolymer resin that can be used in this embodiment will be described.

When polymerizing the polymerization raw materials to obtain a styrene-based copolymer resin, a polymerization initiator and a chain transfer agent are typically included in the polymerization raw material composition.

Polymerization initiators used in the polymerization of styrene-based copolymer resins include 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-butylperoxyacetate; ketone peroxides such as acetylacetone peroxide; and hydroperoxides such as t-butyl hydroperoxide. From the viewpoints of decomposition rate and polymerization rate, 1,1-bis(t-butylperoxy)cyclohexane is particularly preferred.

Examples of chain transfer agents used in the polymerization of styrene-based copolymer resins include α-methylstyrene linear dimer, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-octyl mercaptan.

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

In this embodiment, the apparatus used in the polymerization step for obtaining the styrene-based copolymer resin is not particularly limited, and may be appropriately selected according to the polymerization method of the styrene-based resin. For example, when bulk polymerization is employed, a polymerization apparatus having one or more completely mixed reactors connected together can be used. There is also no particular limit to the devolatilization step. When bulk polymerization is employed, polymerization is continued until the final amount of unreacted monomer is preferably 50% by mass or less, more preferably 40% by mass or less, and devolatilization is performed by a known method to remove volatile matters such as unreacted monomer. More specifically, for example, a normal devolatilization apparatus such as a flash drum, a twin-screw devolatilizer, a thin film evaporator, or an extruder can be used, but a devolatilization apparatus with a small retention portion is preferred. The temperature of the devolatilization treatment is usually about 190 to 280°C, and 190 to 260°C is more preferred from the viewpoint of suppressing the formation of a six-membered ring acid anhydride due to the adjacent unsaturated carboxylic acid monomer (e.g., methacrylic acid) and an unsaturated carboxylic acid ester monomer (e.g., methyl methacrylate). 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 volatiles by reducing pressure under heating, and a method of removing volatiles through an extruder or the like designed for the purpose of removing volatiles.

［上記式（ｉ）中、Ｒ^ｉ１及びＲ^ｉ２は、各々独立して、無置換又は１以上の水素原子が置換基Ｒ^ｉ３により置換されてもよい、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基、炭素原子数６～１０のアリール基又は炭素原子数６～１４のアラルキル基であり、
前記置換基Ｒ^ｉ３は、下記式（ｉｉ）：

「上記式（ｉｉ）中、Ｒ^ｉｉ１は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、＊は他の原子との結合を表す。」で表され、
Ｍ^ｉは、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり、ｐ^＋はＭ^ｉのイオン価を表し、１～３の正の整数であり、ｍ^ｉ１は、１～３の正の整数であり、ｎ^－は、－１、－２又は－３の負の整数を表し、ｒは、１～３の正の整数であり、｜ｐ^＋×ｒ｜＝｜ｎ^－×ｍ^ｉ１｜である。また、Ｒ^ｉ１及びＲ^ｉｉ１がそれぞれ複数存在する場合は、それぞれのＲ^ｉ１及びＲ^ｉｉ１が同一であってもあるいは異なっていてもよい。］
そのため、本実施形態におけるホスフィン酸塩化合物（ｂ）としては、一般式（ｉ）で表されるホスフィン酸塩類以外の公知の難燃剤を、当該ホスフィン酸塩化合物（ｂ）全体（１００質量％）に対して３０質量％以下含んでもよい。
上記式（ｉ）中、Ｍ^ｉのイオン価を表す「ｐ^＋」と「ｒ」との積の絶対値が、「ｎ^－」と「ｍ^ｉ１」との積の絶対値に等しい。
上記（ｉ）中、ｐ^＋は、１又は２が好ましい。ｍ^ｉ１は、１又は２が好ましい。ｎ^－は、－１又は－２が好ましい。ｒは、１又は２が好ましい <Flame retardant (B): component (B)>
The flame-retardant styrene-based resin composition of the present embodiment contains 5 to 30 mass% of the flame retardant (B) relative to 100 mass% of the flame-retardant styrene-based resin composition, preferably 8 to 29 mass%, more preferably 10 to 28 mass%, and even more preferably 15 to 25 mass%.
In the present embodiment, the content of the phosphinate compound (b) is preferably 70% by mass or more relative to 100% by mass of the total amount of the flame retardant (B). Therefore, the flame retardant (B) may contain 30% by mass or less of a known flame retardant other than the phosphinate compound (b) and/or an optional added component (such as an antioxidant or an ultraviolet ray inhibitor) described later relative to 100% by mass of the total amount of the entire flame retardant (B).
In the present embodiment, the phosphinate compound (b) is represented by the following general formula (i) and preferably contains at least one phosphinate selected from a phosphinate and a diphosphinate, and more preferably the phosphinate accounts for 70 mass% or more of the entire phosphinate compound (b) (100 mass%).
The following general formula (i):

[In the above formula (i), R ⁱ¹ and R ⁱ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 6 to 14 carbon atoms, which may be unsubstituted or one or more hydrogen atoms may be substituted with a substituent R ⁱ³ ;
The substituent R ⁱ³ is represented by the following formula (ii):

In the above formula (ii), each R ⁱⁱ¹ is independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, and * represents a bond to another atom.
M ⁱ is at least one selected from the group consisting of calcium ion, magnesium ion, aluminum ion, zinc ion, bismuth ion, manganese ion, sodium ion, potassium ion, and protonated nitrogen base, p ⁺ represents the ionic valence of M ⁱ and is a positive integer of 1 to 3, m ⁱ¹ is a positive integer of 1 to 3, n ^- represents a negative integer of -1, -2, or -3, r is a positive integer of 1 to 3, and |p ⁺ ×r|=|n ^- ×m ⁱ¹ |. In addition, when there are a plurality of R ⁱ¹ and R ⁱⁱ¹ , each R ⁱ¹ and R ⁱⁱ¹ may be the same or different.]
Therefore, the phosphinate compound (b) in this embodiment may contain a known flame retardant other than the phosphinate represented by the general formula (i) in an amount of 30 mass% or less relative to the entire phosphinate compound (b) (100 mass%).
In the above formula (i), the absolute value of the product of "p ⁺ " representing the ionic valence of M ⁱ and "r" is equal to the absolute value of the product of "n ^- " and "m ⁱ¹ ".
In the above (i), p ⁺ is preferably 1 or 2. ^{m i1} is preferably 1 or 2. ^n- is preferably -1 or -2. r is preferably 1 or 2.

［上記式（１）中、Ｒ^１１及びＲ^１２は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、Ｍ^１は、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり、ａ^＋はＭ^１のイオン価を表し、１～３の整数であり、ｍ^１は、１～３の整数であり、ａ＝ｍ^１である。Ｒ^１１及びＲ^１２がそれぞれ複数存在する場合は、それぞれのＲ^１１及びＲ^１２が同一であってもあるいは異なっていてもよい。］ In this embodiment, a preferred phosphinate is represented by the following general formula (1).

[In the above formula (1), R ¹¹ and R ¹² are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, M ¹ is at least one selected from the group consisting of calcium ion, magnesium ion, aluminum ion, zinc ion, bismuth ion, manganese ion, sodium ion, potassium ion, and protonated nitrogen base, a ⁺ represents the ionic valence of M ¹ and is an integer of 1 to 3, m ¹ is an integer of 1 to 3, and a=m ^1. When there are a plurality of ^{R 11} and R ¹² , each R ¹¹ and R ¹² may be the same or different.]

［上記式（２）中、Ｒ^２１及びＲ^２２は、各々独立して、直鎖状若しくは分岐状の炭素原子数１～６のアルキル基又は炭素原子数６～１０のアリール基であり、Ｌ^２３は、直鎖状若しくは分岐状の炭素原子数１～１０のアルキレン基、炭素原子数６～１０のアリーレン基、炭素原子数６～１４のアルキルアリーレン基又は炭素原子数６～１４のアリールアルキレン基であり、Ｍ^２は、カルシウムイオン、マグネシウムイオン、アルミニウムイオン、亜鉛イオン、ビスマスイオン、マンガンイオン、ナトリウムイオン、カリウムイオン及びプロトン化された窒素塩基からなる群より選ばれる少なくとも１種であり、ｂ^＋はＭ^２のイオン価を表し、１～３の整数であり、ｍ^２は、１～３の整数であり、ｑは、１又は２の整数であり、ｂ×ｑ＝２ｍ^２である。Ｒ^２１及びＲ^１２がそれぞれ複数存在する場合は、それぞれのＲ^２１及びＲ^２２が同一であってもあるいは異なっていてもよい。］からなる群より選ばれる少なくとも１種が挙げられる。 In this embodiment, a preferred diphosphinate is represented by the following general formula (2).

[In the above formula (2), R ²¹ and R ²² are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, L ²³ is a linear or branched alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 10 carbon atoms, an alkylarylene group having 6 to 14 carbon atoms, or an arylalkylene group having 6 to 14 carbon atoms, M ² is at least one selected from the group consisting of calcium ions, magnesium ions, aluminum ions, zinc ions, bismuth ions, manganese ions, sodium ions, potassium ions, and protonated nitrogen bases, b ⁺ represents the ionic valence of M ² and is an integer of 1 to 3, m ² is an integer of 1 to 3, q is an integer of 1 or 2, and b × q = 2m ^2. When there are a plurality of ^{R 21} and R ¹² , each R ²¹ and R ²² may be the same or different. At least one selected from the group consisting of:

In the above formulas (i), (ii), (1) and (2), examples of the linear or branched alkyl group having 1 to 6 carbon atoms include linear alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, an amyl group or a hexyl group, and branched alkyl groups such as an isopropyl group, an isobutyl group, a s-butyl group, a t-butyl group, an isoamyl group or a t-amyl group.
In the above formulas (i), (ii), (1) and (2), the aryl group having 6 to 10 carbon atoms may have a monocyclic or condensed ring structure, such as a phenyl group or a naphthyl group.
In the above formula (2), examples of the linear or branched alkylene group having 1 to 10 carbon atoms include groups in which one hydrogen atom has been removed from the above linear or branched alkyl group having 1 to 6 carbon atoms.
In the above formula (2), examples of the arylene group having 6 to 10 carbon atoms include groups in which one hydrogen atom has been removed from the above aryl group having 6 to 10 carbon atoms.
In the above formula (i), examples of the aralkyl group having 6 to 14 carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, a phenylbutyl group, a methylphenyl group, an ethylphenyl group, a propylphenyl group, a butylphenyl group, a methylnaphthyl group, an ethylnaphthyl group, and a tert-butylnaphthyl group.
In the above formula (2), examples of the alkylarylene group having 6 to 14 carbon atoms include a methylphenylene group, an ethylphenylene group, a tert-butylphenylene group, a methylnaphthylene group, an ethylnaphthylene group, and a tert-butylnaphthylene group.
In the above formula (2), examples of the arylalkylene group having 6 to 14 carbon atoms include a phenylmethylene group, a phenylethylene group, a phenylpropylene group, and a phenylbutylene group.
In the above formula (1), it is preferable that R ¹¹ and R ¹² are each independently a linear alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms.
In the above formula (1), ^M1 is preferably calcium, magnesium, aluminum, or zinc. Also, a represents the ionic valence of ^M1 and is 2 or 3.
In the above formula (2), it is preferable that R ²¹ and R ²² are each independently a linear alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms.
In the above formula (2), it is preferable that each L ²³ is independently a linear alkylene group having 1 to 6 carbon atoms or an arylene group having 6 to 10 carbon atoms.
In the above formula (2), ^M2 is preferably calcium, magnesium, aluminum, or zinc. Also, b represents the ionic valence of ^M2 and is 2 or 3.
The phosphinic acid salt compound (b) has excellent electrical properties and is therefore suitable for flame-retardant materials that require insulation. It also has excellent hydrolysis properties and can be used in applications under high temperature and high humidity conditions. It also has excellent recyclability.

The phosphinic acid salt (b) used in this embodiment is produced in an aqueous solution using, among others, phosphinic acid and a metal carbonate, metal hydroxide or metal oxide, and is essentially a monomeric compound, but depending on the reaction conditions and circumstances, it also includes polymeric phosphinic acid salts with a degree of condensation of 1 to 3.

Such phosphinate (b) is not particularly limited, and examples thereof include calcium dimethylphosphinate, magnesium dimethylphosphinate, aluminum dimethylphosphinate, zinc dimethylphosphinate, calcium ethylmethylphosphinate, magnesium ethylmethylphosphinate, aluminum ethylmethylphosphinate, zinc ethylmethylphosphinate, calcium diethylphosphinate, magnesium diethylphosphinate, aluminum diethylphosphinate, zinc diethylphosphinate, calcium methyl-n-propylphosphinate, magnesium methyl-n-propylphosphinate, aluminum methyl-n-propylphosphinate, zinc methyl-n-propylphosphinate, calcium methane di(methylphosphinate), magnesium methane di(methylphosphinate), aluminum methane di(methylphosphinate), zinc methane di(methylphosphinate), calcium benzene-1,4-(dimethylphosphinate), benzene-1,4 benzene-1,4-(dimethylphosphinate)magnesium, benzene-1,4-(dimethylphosphinate)aluminum, benzene-1,4-(dimethylphosphinate)zinc, calcium methylphenylphosphinate, magnesium methylphenylphosphinate, aluminum methylphenylphosphinate, zinc methylphenylphosphinate, calcium diphenylphosphinate, magnesium diphenylphosphinate, aluminum diphenylphosphinate, and zinc diphenylphosphinate are preferred, including calcium dimethylphosphinate, aluminum dimethylphosphinate, zinc dimethylphosphinate, calcium ethylmethylphosphinate, aluminum ethylmethylphosphinate, aluminum ethylbutylphosphinate, aluminum dibutylphosphinate, zinc ethylmethylphosphinate, calcium diethylphosphinate, aluminum diethylphosphinate, and zinc diethylphosphinate, with aluminum diethylphosphinate being more preferred.
Commercially available phosphinate compounds (b) are not particularly limited, and examples thereof include Exolit (registered trademark) OP1230, OP1240, OP1311, OP1312, OP930, and OP935 manufactured by Clariant Japan KK

In this embodiment, the phosphinate compound (b) is preferably granular. When the phosphinate compound (b) is granular, the average particle size of the phosphinate compound (b) is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less, from the viewpoint of improving the mechanical strength and appearance of the molded article obtained by molding the flame-retardant resin composition of this embodiment, and it is preferable to use the powder of the phosphinate compound (b) pulverized to this particle size. It is preferably more than 0.5 μm and 20 μm, more preferably more than 1 μm and 20 μm or less. When a powder with a preferred particle size is used, not only high flame retardancy is exhibited, but also impact strength is remarkably increased, so it is particularly preferable.
The average particle size of the granular phosphinate compound (b) is measured based on the volumetric particle size measured using a laser diffraction/scattering particle size distribution measuring device. The value is measured using a 3% isopropanol aqueous solution as the dispersion medium of the phosphinate compound (b). Specifically, the average particle size can be determined by performing a blank measurement using a laser diffraction/scattering particle size distribution measuring device LA-910 (manufactured by Horiba, Ltd.) with a dispersion medium of 3% isopropanol aqueous solution, and then putting a measurement sample so that the measurement sample has a specified transmittance (95% to 70%). The sample is dispersed in the dispersion medium by irradiating it with ultrasonic waves for 1 minute.

<Cellulose-based polysaccharides (C) (hereinafter also referred to as component (C))>
The content of the cellulose polysaccharides (C) in this embodiment is 3 to 30% by mass, preferably 5 to 28% by mass, and more preferably 10 to 25% by mass, based on 100% by mass of the flame-retardant styrene-based resin composition. By making the content of the cellulose polysaccharides (C) 3% by mass or more, it is possible to improve low smoke generation, flame retardancy, and dimensional accuracy. On the other hand, if the content is too much more than 30% by mass, the flame retardancy is reduced and the moldability is significantly reduced due to reduced fluidity. The content of the cellulose polysaccharides (C) in the composition can be found by dissolving the composition in a solvent that dissolves the styrene-based resin, removing the undissolved matter, and measuring the mass of the product dried at 120°C for 4 hours.

The shape of the cellulose polysaccharide (C) in this embodiment is not particularly limited, and examples thereof include spherical, irregular, powdery, scaly, fibrous, and rod-like shapes. At least one of the average lengths of the minor axis _d1 and major axis _d2 of the cellulose polysaccharide (C) is 10 to 80 μm, preferably 15 to 70 μm, preferably 20 to 60 μm, and more preferably 30 to 50 μm. If the average lengths of the minor axis _d1 and major axis _d2 are outside the above range, the dimensional accuracy may not be fully exhibited, or the anisotropy may become large in the MD and TD directions. On the other hand, if the average lengths of the minor axis _d1 and major axis _d2 are within the above range, the aggregation of the cellulose polysaccharide (C) can be reduced, and the dispersibility in the styrene resin (A) is improved, improving the oil resistance and moldability.
In the cellulose polysaccharide (C) of this embodiment, the average length of the minor axis _d1 is preferably equal to or less than the average length of the major axis _d2 , and the average length of the minor axis _d1 is preferably less than the average length of the major axis _d2 . In the present invention, the average length of the minor axis _d1 of the cellulose polysaccharide (C) is obtained by measuring the minor axis length (minimum length) of 100 cellulose polysaccharides (C) by observation with a transmission electron microscope (magnified at 5000 times) and taking the arithmetic average. On the other hand, the average length of the major axis of the cellulose polysaccharide (C) is obtained by measuring the major axis length (maximum length) of 100 cellulose polysaccharides (C) by observation with a transmission electron microscope (magnified at 5000 times) and taking the arithmetic average. In addition, the average length of the minor axis of the cellulose polysaccharide (C) is obtained by measuring the minor axis length (minimum length) of the cellulose polysaccharide (C) and using the same method as the average length of the major axis. The short axis length (minimum length) of the cellulose polysaccharide (C) refers to the length of the thinnest (or shortest) point on the image, and the long axis length (maximum length) of the cellulose polysaccharide (C) refers to the length of the longest point on the image. The linear expansion is affected by the shape of the cellulose polysaccharide (C), and is affected by the short axis in the case of fibers and the average diameter of the long axis in the case of scale-like or granular shapes.
The aspect ratio ( _d1 / _d2 ) of the average length of the minor axis _d1 to the average length of the major axis _d2 of the cellulose polysaccharide (C) in the present invention is preferably 1 to 500, more preferably 1.2 to 300, even more preferably 1.5 to 200, and particularly preferably 2 to 100.

The cellulose polysaccharide (C) in the present invention refers to a polysaccharide having a β-1,4-glucan structure, and includes cellulose and hemicellulose. The material of the cellulose polysaccharide (C) is not particularly limited as long as the fibers constituting the cellulose polysaccharide (C) are formed from polysaccharides having a β-1,4-glucan structure, and examples of the cellulose polysaccharide include cellulose fibers derived from higher plants [e.g., natural cellulose fibers (pulp fibers) such as wood fibers (wood pulp of conifers, broad-leaved trees, etc.), bamboo fibers, sugarcane fibers, seed hair fibers (cotton linters, bombax cotton, kapok, etc.), ginseng bark fibers (e.g., hemp, paper mulberry, mitsumata, etc.), and leaf fibers (e.g., Manila hemp, New Zealand hemp, etc.), cellulose fibers derived from animals (such as sea squirt cellulose), cellulose fibers derived from bacteria, and chemically synthesized cellulose fibers [cellulose acetate (acetic acid) Examples of the fibers that constitute the cellulose polysaccharide (C) include organic acid esters such as cellulose propionate, cellulose butyrate, cellulose acetate propionate, and cellulose acetate butyrate; inorganic acid esters such as cellulose nitrate, cellulose sulfate, and cellulose phosphate; mixed acid esters such as cellulose acetate nitrate; hydroxyalkyl cellulose (e.g., hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, etc.); carboxyalkyl cellulose (carboxymethyl cellulose (CMC), carboxyethyl cellulose, etc.); alkyl cellulose (methyl cellulose, ethyl cellulose, etc.); and cellulose derivative fibers such as regenerated cellulose (rayon, cellophane, etc.). These fibers that constitute the cellulose polysaccharide (C) may be used alone or in combination of two or more.

Among the fibers constituting the above-mentioned cellulose polysaccharide (C), preferred are plant-derived cellulose fibers, for example, pulp-derived cellulose fibers such as wood fibers (wood pulp of coniferous trees, broad-leaved trees, bamboo, etc.) and seed hair fibers (cotton linter pulp, etc.), because they have high production efficiency in terms of dispersibility, rigidity, and impact resistance when the cellulose polysaccharide (C) is produced, and have appropriate fiber diameter and fiber length.
In this embodiment, the content of lignin in 100% by mass of the cellulose polysaccharide (C) is preferably 20% by mass or less, and more preferably 10% by mass or less. If the content of lignin in the cellulose polysaccharide (C) is more than 20% by mass, odor and coloring will increase during thermal processing, and lignin degradation products will turn into charcoal-like black spots, reducing the product value, and causing problems with white coloring.
Furthermore, in this embodiment, it is preferable that hemicellulose is contained in an amount of 1% by mass or more relative to 100% by mass of the cellulose polysaccharide (C). By containing hemicellulose, the dispersibility with the styrene resin (A) is improved, and the rigidity and molded appearance can be improved. In the present invention, it is preferable that these components are not completely removed in the manufacturing process of the cellulose polysaccharide (C) but are allowed to remain in a content within a suitable range. Hemicellulose is a polysaccharide composed of sugars such as mannan and xylan, and plays a role in connecting microfibrils by hydrogen bonding with cellulose. In addition, since the solubility parameter (SP value) of hemicellulose is on the hydrophobic side compared to cellulose, it is considered that hemicellulose has an effect of mitigating the SP value difference between the styrene resin (A) and the cellulose polysaccharide (C). In addition, by containing 1% or more of hemicellulose, the bubble diameter is reduced, and the compressive strength and heat resistance are improved. The amount of hemicellulose in the cellulosic polysaccharide (C) can be adjusted to a desired amount by subjecting natural wood raw materials with a high hemicellulose content to a purification treatment. For example, when a raw material with a low hemicellulose content is used, the amount can be adjusted to a desired amount by adding hemicellulose obtained by extraction treatment from another raw material. In this case, it does not matter if the structure of the terminals of the hemicellulose, etc., is partially different from that of the natural product due to the purification or extraction treatment.
In this embodiment, for the purpose of reducing the SP value difference between the styrene-based resin (A) and the cellulose-based polysaccharide (C), the hemicellulose is preferably contained in an amount of 1% by mass or more and 25% by mass or less, more preferably 2% by mass or more and 20% by mass or less, even more preferably 3% by mass or more and 20% by mass or less, even more preferably 5% by mass or more and 19.5% by mass or less, and particularly preferably 7% by mass or more and 19.3% by mass or less, relative to the cellulose-based polysaccharide (C) (100% by mass).

<Dispersant>
In this embodiment, a dispersant may be contained in the styrene resin composition or the styrene resin molded product for the purpose of improving the dispersibility of the flame retardant (B) and the cellulose polysaccharide (C). The dispersant may be added in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the total of the (A) component, the (B) component, and the (C) component. By adding the dispersant, it is possible to prevent scorching and eye discharge of the extruder when the flame retardant (B) and the cellulose polysaccharide (C) are compounded with the styrene resin (A), and to improve the appearance of the molded product. If the amount of the dispersant is less than the specified amount, such an effect is not obtained, and if the amount is more than the specified amount, the heat resistance is reduced. The effect is greater if the dispersant has excellent affinity with the styrene resin (A).

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, a fatty acid metal salt, etc. In particular, fatty acid ester compounds, polyethylene glycol compounds, terpene compounds, and rosin compounds are preferred.
Examples of aliphatic ester lubricants include methyl laurate, methyl myristate, methyl palmitate, methyl stearate, methyl oleate, methyl erucate, methyl behenate, butyl laurate, butyl stearate, isopropyl myristate, isopropyl palmitate, octyl palmitate, coconut fatty acid octyl ester, octyl stearate, tallow fatty acid octyl ester, lauryl laurate, stearyl stearate, behenyl behenate, cetyl myristate, esters of linear, unbranched, saturated monocarboxylic acid having 28 to 30 carbon atoms (hereinafter abbreviated as montanic acid) and ethylene glycol, esters of montanic acid and glycerin, montanic acid, glycerin ... Examples of the montanic acid include esters of montanic acid and butylene glycol, esters of montanic acid and trimethylolethane, esters of montanic acid and trimethylolpropane, esters of montanic acid and pentaerythritol, glycerin monostearate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, etc. These may be used in combination of two or more kinds.

The terpene resin generally refers to a resin obtained by copolymerizing a terpene monomer alone, or a terpene monomer and an aromatic monomer, or a terpene monomer and a phenol in an organic solvent in the presence of a Friedel-Crafts catalyst, but is not limited thereto. Alternatively, the terpene resin may be a hydrogenated terpene resin obtained by subjecting the obtained terpene resin to a hydrogenation treatment. Examples of the terpene resin include α-pinene resin, β-pinene resin, aromatic modified terpene resin, terpene phenol resin, and hydrogenated terpene resin. Examples of the terpene monomer include, but are not limited to, hemiterpenes having 5 carbon atoms such as isoprene, α-pinene, β-pinene, dipentene, d-limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, γ-terpineol, sabinene, paramentadienes, and carenes, sesquiterpenes having 15 carbon atoms such as caryophyllene and longifolene, and diterpenes having 20 carbon atoms. Among these compounds, α-pinene, β-pinene, dipentene, and d-limonene are particularly preferably used.
Examples of aromatic monomers include, but are not limited to, styrene, α-methylstyrene, vinyltoluene, isopropenyltoluene, etc. Examples of phenols include, but are not limited to, phenol, cresol, xylenol, bisphenol A, etc.

Examples of rosin-based resins include rosins such as gum rosin, wood rosin, and tall oil rosin, as well as stabilized rosins obtained by disproportionating or hydrogenating the rosins, polymerized rosins (typically dimers) that are polymers of the rosins, and modified rosins modified with unsaturated acids such as maleic acid, fumaric acid, and (meth)acrylic acid. Examples of rosin derivative resins include esters of the rosin-based resins, phenol-modified products, and esters thereof. The rosin-based resins or rosin derivative resins used in the present invention are not limited to these resins.

Examples of the aliphatic amide lubricants include stearic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, and ethylene bislauric acid amide.
These may be used in combination of two or more.

Specific examples of saturated fatty acids among fatty acids include lauric acid (dodecanoic acid), isodecanoic acid, tridecanoic acid, myristic acid (tetradecanoic acid), pentadecylic acid, palmitic acid (hexadecanoic acid), margaric acid (heptadecanoic acid), stearic acid (octadecanoic acid), isostearic acid, tuberculostearic acid (nonadecanoic acid), 2-hydroxystearic acid, arachidic acid (icosanoic acid), behenic acid (docosanoic acid), lignoceric acid (tetradocosanoic acid), cerotic acid (hexadocosanoic acid), montanic acid (octadocosanoic acid), and melissic acid, and in particular, lauric acid, palmitic acid, stearic acid, behenic acid, 12-hydroxystearic acid, and montanic acid.

Specific examples of unsaturated fatty acids in the fatty acid series include myristoleic acid (tetradecenoic acid), palmitoleic acid (hexadecenoic acid), oleic acid (cis-9-octadecenoic acid), elaidic acid (trans-9-octadecenoic acid), ricinoleic acid (octadecadienoic acid), vaccenic acid (cis-11-octadecenoic acid), linoleic acid (octadecadienoic acid), linolenic acid (9,11,13-octadecatrienoic acid), elestearic acid (9,11,13-octadecatrienoic acid), gadoleic acid (icosanoic acid), erucic acid (docosanoic acid), and nervonic acid (tetradocosanoic acid). Two or more of these may be used in combination.

Examples of the fatty acid metal salt lubricant include lithium salts, calcium salts, magnesium salts, zinc salts, and aluminum salts of the fatty acids of the above fatty acid lubricants.
These may be used in combination of two or more.

<Optionally Added Ingredients>
In this embodiment, in addition to the above components (A) to (C), the flame-retardant styrene-based resin composition may contain optional components such as conventionally known additives, processing aids, etc., as necessary, within the scope of not impairing the effects of the present invention. Examples of these optional components include antioxidants, weather resistance agents, antistatic agents, fillers, etc.

Examples of the antioxidants include phenolic compounds, phosphorus compounds, and thioether compounds.

Examples of the phenol-based antioxidants include 2,6-di-t-butyl-p-cresol, 2,6-diphenyl-4-octadecyloxyphenol, distearyl (3,5-di-t-butyl-4-hydroxybenzyl)phosphonate, 1,6-hexamethylenebis[(3,5-di-t-butyl-4-hydroxyphenyl)propionic acid amide], 4,4'-thiobis(6-t-butyl-m-cresol), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-butylidenebis(6-t-butyl-m-cresol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol ... -cresol), 2,2'-ethylidenebis(4,6-di-t-butylphenol), 2,2'-ethylidenebis(4-sec-butyl-6-t-butylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-tris(2,6-dimethyl-3-hydroxy-4-t-butylbenzyl)isocyanurate, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene, 2-t-butyl-4-methyl- 6-(2-acryloyloxy-3-t-butyl-5-methylbenzyl)phenol, stearyl [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)methylpropionate]methane, thiodiethylene glycol bis [(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,6-hexamethylene bis [(3,5-di-t-butyl-4-hydroxyphenyl)propionate], bis [3,3-bis (4-hydroxy-3-t-butylphenyl) butyric acid] glycol ester, bis[2-t-butyl-4-methyl-6-(2-hydroxy-3-t-butyl-5-methylbenzyl)phenyl]terephthalate, 1,3,5-tris[(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate, 3,9-bis[1,1-dimethyl-2-{(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, triethylene glycol bis[(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], and the like.
These may be used alone or in combination of two or more.

Examples of the phosphorus-based antioxidant include tris(2,4-di-t-butylphenyl)phosphite, trisnonylphenyl phosphite, tris[2-t-butyl-4-(3-t-butyl-4-hydroxy-5-methylphenylthio)-5-methylphenyl]phosphite, tridecyl phosphite, octyldiphenyl phosphite, di(decyl)monophenyl phosphite, di(tridecyl)pentaerythritol diphosphite, di(nonylphenyl)pentaerythritol diphosphite, and the like. tetra(tridecyl)isopropylidenediphenol diphosphite, tetra(tridecyl)-4,4'-dimethylphenyl diphosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, bis(2,4,6-tri-t-butylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, tetra(tridecyl)isopropylidenediphenol diphosphite, tetra(tridecyl)-4,4'-dimethylphenyl diphosphite, -n-butylidenebis(2-t-butyl-5-methylphenol)diphosphite, hexa(tridecyl)-1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane triphosphite, tetrakis(2,4-di-t-butylphenyl)biphenylene diphosphonite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2,2'-methylenebis(4,6-t-butylphenyl)-2-ethylhexylphosphite phosphite, 2,2'-methylenebis(4,6-t-butylphenyl)-octadecyl phosphite, 2,2'-ethylidenebis(4,6-di-t-butylphenyl)fluorophosphite, tris(2-[(2,4,8,10-tetrakis-t-butyldibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]ethyl)amine, and phosphite of 2-ethyl-2-butylpropylene glycol and 2,4,6-tri-t-butylphenol.
These may be used alone or in combination of two or more.

Examples of the thioether-based antioxidant include dialkyl thiodipropionates such as dilauryl thiodipropionate, dimyristyl thiodipropionate, and distearyl thiodipropionate, and pentaerythritol tetra(β-alkylmercaptopropionate esters.
These may be used alone or in combination of two or more.

As the weather resistance agent, an ultraviolet absorber, a hindered amine light stabilizer, etc. can be used.
Examples of the ultraviolet absorber include 2-hydroxybenzophenones such as 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 5,5'-methylenebis(2-hydroxy-4-methoxybenzophenone);2-(2'-hydroxy-5'-methylphenyl)benzotriazole,2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole,2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole, and the like. 2-(2'-hydroxyphenyl)benzotriazoles such as 2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-dicumylphenyl)benzotriazole, 2,2'-methylenebis(4-t-octyl-6-(benzotriazolyl)phenol), and 2-(2'-hydroxy-3'-t-butyl-5'-carboxyphenyl)benzotriazole; phenyl salicylate; benzoates such as 2-ethyl-2'-ethoxyoxanilide and 2-ethoxy-4'-dodecyloxanilide; ethyl-α-cyano-β,β-diphenylacrylate, methyl ... cyanoacrylates such as aryl-2-cyano-3-methyl-3-(p-methoxyphenyl)acrylate; and triaryltriazines such as 2-(2-hydroxy-4-octoxyphenyl)-4,6-bis(2,4-di-t-butylphenyl)-s-triazine, 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-s-triazine, and 2-(2-hydroxy-4-propoxy-5-methylphenyl)-4,6-bis(2,4-di-t-butylphenyl)-s-triazine.
These may be used alone or in combination of two or more.

Examples of the hindered amine-based light stabilizer include 2,2,6,6-tetramethyl-4-piperidyl stearate, 1,2,2,6,6-pentamethyl-4-piperidyl stearate, 2,2,6,6-tetramethyl-4-piperidyl benzoate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidyl)sebacate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarbo xylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate, bis(2,2,6,6-tetramethyl-4-piperidyl) di(tridecyl)-1,2,3,4-butane tetracarboxylate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) di(tridecyl)-1,2,3,4-butane tetracarboxylate, bis(1,2,2,4,4-pentamethyl-4-piperidyl)-2-butyl-2-(3,5-di-t-butyl-4-hydroxybenzyl)malonate, 1-(2-hydroxyethyl)-2,2 ,6,6-tetramethyl-4-piperidinol/diethyl succinate polycondensate, 1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/2,4-dichloro-6-morpholino-s-triazine polycondensate, 1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/2,4-dichloro-6-t-octylamino-s-triazine polycondensate, 1,5,8,12-tetrakis[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazin-6-yl]-1,5,8,12-tetraazadodecane, 1, Examples of hindered amine compounds include 5,8,12-tetrakis[2,4-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-s-triazin-6-yl]-1,5,8-12-tetraazadodecane, 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazin-6-yl]aminoundecane, and 1,6,11-tris[2,4-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-s-triazin-6-yl]aminoundecane.
These may be used alone or in combination of two or more.

As the antistatic agent, cationic, anionic, nonionic, amphoteric, fatty acid partial esters such as glycerin fatty acid monoesters, and the like can be used.
Specifically, alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium salts, benzalkonium salts, N,N-bis(2-hydroxyethyl)-N-(3-dodecyloxy-2-hydroxypropyl)methyl ammonium methosulfate, (3-lauryl amidopropyl)trimethyl ammonium methyl sulfate, stearamidopropyl dimethyl-2-hydroxyethyl ammonium nitrate, stearamidopropyl dimethyl-2-hydroxyethyl ammonium phosphate, cationic polymers, alkyl sulfonates, alkyl benzene sulfonates, sodium alkyl diphenyl ether disulfonate, alkyl nitrate ester salts, phosphorus Acid alkyl ester salts, alkyl phosphate amine salts, stearic acid monoglyceride, pentaerythritol fatty acid esters, sorbitan monopalmitate, sorbitan monostearate, diglycerin fatty acid esters, alkyldiethanolamines, alkyldiethanolamine fatty acid monoesters, alkyldiethanolamides, polyoxyethylene dodecyl ethers, polyoxyethylene alkylphenyl ethers, polyethylene glycol monolaurates, polyoxyethylene alkylamines, polyoxyethylene alkylamides, polyether block copolymers, cetyl betaine, and hydroxyethyl imidazoline sulfate.
These may be used alone or in combination of two or more.

Examples of fillers that can be used include talc, calcium carbonate, barium sulfate, carbon fiber, mica, wollastonite, whiskers, etc.

In the present embodiment, the flame-retardant styrene-based resin composition may contain, in addition to the above-mentioned optional additive components, optional additive components such as an antiblocking agent, a colorant, an antiblooming agent, a surface treatment agent, an antibacterial agent, and an anti-viscosity agent (anti-viscosity agents such as silicone oil described in JP 2009-120717 A, monoamide compounds of higher aliphatic carboxylic acids, and monoester compounds obtained by reacting higher aliphatic carboxylic acids with monohydric to trihydric alcohol compounds).
In this embodiment, the total content of the above-mentioned optional components may be 0.05 to 5% by mass in the flame-retardant styrene-based resin composition.

The flame-retardant styrene-based resin composition of the present embodiment may consist essentially of only the components (A), (B), and (C).Also, the flame-retardant styrene-based resin composition may consist essentially of only the components (A), (B), and (C), a dispersant, and optional additional components.
The phrase "consisting essentially of only the component (A), the component (B), and the component (C)" means that the component (A), the component (B), and the component (C) account for 80 to 100 mass% (preferably 88 to 100 mass%) of the total amount (100 mass%) of the flame-retardant styrene-based resin composition.
The phrase "consisting essentially of only the component (A), the component (B), the component (C), the dispersant, and any optional additional components" means that the component (A), the component (B), the component (C), the dispersant, and any optional additional components account for 95 to 100 mass% (preferably 98 to 100 mass%) of the total amount (100 mass%) of the flame-retardant styrene-based resin composition.
The flame-retardant styrene-based resin composition of the present embodiment may contain inevitable impurities in addition to the components (A), (B), and (C), the dispersant, and any optional additional components, as long as the effects of the present invention are not impaired.

The flame-retardant styrene-based resin composition of this embodiment contains a styrene-based resin (A), a phosphinate compound (b), a cellulose-based polysaccharide (C) having at least one of the average lengths of the minor axis _d1 and the major axis _d2 of 10 to 80 μm, and a dispersant and/or an optional additional component, which are added as needed, in a predetermined amount. The materials or characteristics of the styrene-based resin (A), the phosphinate compound (b), the cellulose-based polysaccharide (C), and the dispersant and/or an optional additional component, which are added as needed, which are added to the styrene-based resin composition, are as described above. The amounts of the (A) component, the (B) component, the (C) component, the dispersant, and the optional additional components added can be appropriately adjusted and added so that the content in the flame-retardant styrene-based resin composition is within the above range.

<Method for producing flame-retardant styrene-based resin composition>
The flame-retardant styrene-based resin composition of the present embodiment can be produced by melt-kneading each component by any method. For example, a high-speed agitator 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 can be used alone or in combination. The heating temperature during kneading is usually selected in the range of 180 to 260°C.

[Physical properties of flame-retardant styrene-based resin composition]
<Flame retardancy>
The flame retardancy of the flame-retardant styrene-based resin composition of the present embodiment is preferably within the standard in the UL94 vertical flame test (UL94-V test), i.e., the flame retardancy class is preferably V-0 to V-2. In addition, it is preferable that the composition does not generate black smoke during combustion.
In the present disclosure, flame retardancy and black smoke can be evaluated by the method described in the section [Examples] below.

<Linear expansion coefficient>
The linear expansion coefficient of a molded article obtained from the flame-retardant styrene-based resin composition of this embodiment is preferably 6.5×10 ⁻⁵ /° C. or less, and more preferably 5×10 ⁻⁵ /° C. or less. In addition, the ratio of the linear expansion coefficient in the MD direction (flow direction during molding) to the TD direction (direction perpendicular to the MD direction) (TD/MD ratio) is preferably 0.8 to 1.2, and more preferably 0.9 to 1.1.
If the linear expansion coefficient is greater than 6×10 ⁻⁵ /° C., thermal expansion may cause defects in the product, or the metal may peel off in products that are bonded to metals or the like. If the TD/MD ratio is outside the range, the product may warp due to heat. In this disclosure, the linear expansion coefficient is a value measured in accordance with the TMA method of JIS K7197. The dimensional accuracy of the molded article produced using the flame-retardant styrene-based resin composition of this embodiment is evaluated by the value of the linear expansion coefficient.

<Yellow Index>
The yellow index of the flame-retardant styrene-based resin composition of the present embodiment is preferably equal to or less than 20, and more preferably equal to or less than 15. If it is greater than 20, coloring may become difficult.

[Molded products]
The flame-retardant 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 flame-retardant 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.

Molded articles containing the flame-retardant styrene-based resin composition of this embodiment, preferably injection molded articles (including injection compression), office automation equipment such as copiers, fax machines, televisions, radios, tape recorders, video decks, personal computers, printers, telephones, information terminals, refrigerators, and microwave ovens, home appliances, housings and various parts for electric and electronic equipment, foam insulation materials, insulating films, etc.

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.
<Measurement and evaluation methods>
The physical properties of the resin compositions obtained in each of the Examples and Comparative Examples were measured and evaluated according to the following methods.
(1) Evaluation of Flame Retardancy (i) Evaluation of Flame Grade and Evaluation of Burning Time Using a test piece (b) (size: 127 mm × 12.7 mm, thickness: 1.5 mm) prepared by the method described below, the flame retardancy was evaluated by a method conforming to the UL94 vertical flame test (UL94-V test) using a test flame of 50 W. The flame of a gas burner was applied to the test piece (b) to evaluate the degree of combustion.
The flame retardancy grade indicates the flame retardancy class as classified by the UL94-V test. The test was performed five times for each test piece and the evaluation was made. The classification method is as follows:
V-0: Total burning time of 5 burners is 50 seconds or less, maximum burning time is 10 seconds or less, cotton dripping does not ignite V-1: Total burning time of 5 burners is 250 seconds or less, maximum burning time is 30 seconds or less, cotton dripping does not ignite V-2: Total burning time of 5 burners is 250 seconds or less, maximum burning time is 30 seconds or less, cotton dripping ignites Not V: Not UL94 standard Furthermore, the generation of black smoke during combustion was judged visually, with x if black smoke was generated during combustion, △ if a small amount of smoke was generated, and ◯ if almost no smoke was generated.

(2) Linear expansion coefficient The linear expansion coefficient (/°C) was measured in the MD and TD directions by cutting the center of a test piece (a) prepared by the method described below into a size of 10 × 5 × 4 mm in the MD and TD directions in accordance with the TMA method (−30°C to 80°C) of JIS K7197.

(3) Yellow Index For the test piece (a) prepared by the method described below, the yellow index of the resin composition was measured in accordance with JIS K7105 using a color difference turbidity meter COH300A (product name) manufactured by Nippon Denshoku Co., Ltd. Considering the purpose of toning, a value of 5 or less was considered to pass.

(4) Contents of styrene monomer units, methacrylic acid monomer units, and methyl methacrylate monomer units in styrene-based resin (a) The resin composition was quantified from the integral ratio of the spectrum measured by a proton nuclear magnetic resonance ( ¹ H-NMR) spectrometer.
Sample preparation: 30 mg of resin pellets were dissolved in 0.75 mL of d ₆ -DMSO by heating at 60° C. for 4 to 6 hours.
・Measuring equipment: JNM ECA-500 manufactured by JEOL Ltd.
Measurement conditions: measurement temperature 25°C, observation nucleus ^1H , number of integrations 64, repetition time 11 seconds.

(Spectral assignment)
Regarding the attribution of the spectrum measured in dimethyl sulfoxide deuterated solvent, the peaks at 0.5 to 1.5 ppm are peaks derived from hydrogen of α-methyl group of methacrylic acid, methyl methacrylate, and six-membered cyclic acid anhydride, the peaks at 1.6 to 2.1 ppm are peaks derived from hydrogen of methylene group of polymer main chain, the peak at 3.5 ppm is peak derived from hydrogen of carboxylate ester (-COOCH ₃ ) of methyl methacrylate, and the peak at 12.4 ppm is peak derived from hydrogen of carboxylic acid of methacrylic acid. In addition, the peak at 6.5 to 7.5 ppm is peak derived from hydrogen of aromatic ring of styrene. Note that, since the content of six-membered cyclic acid anhydride is small in the resins of the present embodiment and the comparative example, quantification is usually difficult by this measurement method.

(5) Measurement of the average length of cellulose polysaccharides An ultrathin slice having a thickness of 75 nm was prepared from the pellets obtained from the kneaded product, and a photograph was taken at a magnification of 50,000 times using an electron microscope. The photograph was then scanned at a resolution of 200 dpi, and the minimum and maximum lengths of 100 cellulose polysaccharides (C) were measured using particle analysis software of an image analyzer IP-1000 (manufactured by Asahi Kasei Corporation), and the arithmetic averages were taken as the average minor axis length d ₁ and the average major axis length d _2. Similarly to the above, a photograph of the cellulose polysaccharide (C) alone was also taken at a magnification of 50,000 times using an electron microscope, and the arithmetic averages were taken as the average minor axis length d ₁ and the average major axis length d ₂ .

(6) Quantitative Analysis of Lignin Amount The quantitative analysis of lignin in the cellulosic polysaccharide (C) was carried out with reference to the TGA method described in Journal of the Society of Material Cycles and Waste Management, Vol. 22, No. 5, p. 293, 2011.
The thermogravimetric analyzer used was a Shimadzu Corporation DTG-60 model, and the temperature was raised from room temperature to 900°C at a heating rate of 10°C/min in an air atmosphere. The samples to be analyzed were dried at 70°C for 2 hours, and 3 to 5 mg were precisely weighed, and the weight change due to thermal decomposition was measured. The sample container used was a disc-shaped platinum dish with an inner diameter of 5 mm and a height of 2 mm, and all experiments were performed under fixed conditions.

(7) Measurement of Hemicellulose Amount Quantitative analysis of hemicellulose in cellulosic polysaccharide (C) is as follows.
The dispersion medium was removed from the dispersion of the cellulose polysaccharide (C) or from a redispersion of the cellulose polysaccharide (C) obtained by dissolving and removing the resin component from the styrene-based resin composition, and the cellulose residue was recovered and dried at 105°C to obtain a dry sample, and the mass of the dry sample was measured by the following method.
The dried cellulose residue was ground to obtain a ground sample, which was extracted with an alcohol (ethanol)/benzene mixed solvent in a Soxhlet extractor for 6 hours. Then, extraction was performed for another 4 hours with an alcohol (ethanol)/benzene mixed solvent to obtain a defatted sample. 150 mL of distilled water, 1.0 g of sodium chlorite, and 0.2 mL of acetic acid were added to 2.5 g of the defatted sample, and the mixture was heated at 70 to 80°C for 1 hour. Then, 1.0 g of sodium chlorite and 0.2 mL of acetic acid were added again, and the mixture was heated at 70 to 80°C for 1 hour. This operation was repeated 3 to 4 times until the sample was decolorized to white. The obtained sample was filtered, washed with water and acetone, and dried at 105°C to obtain a holocellulose fraction (the total amount of α-cellulose and hemicellulose). The mass of this holocellulose fraction was measured.
Next, 25 mL of 17.5% by mass aqueous sodium hydroxide was added to 1.0 g of the holocellulose fraction, and after 3 minutes, the mixture was lightly crushed with a glass rod until it became swollen. The mixture was then left to stand at 20°C, and 30 minutes after the addition of the aqueous sodium hydroxide solution, 25 mL of distilled water was added, stirred for exactly 1 minute, left to stand at 20°C for 5 minutes, filtered through a glass filter, and washed until the filtrate became neutral. Further, 40 mL of 10% by mass acetic acid was suction filtered, and then 1 L of boiling water was suction filtered and the washed sample was dried at 105°C until the mass was constant, to obtain an α-cellulose fraction. The mass of this α-cellulose fraction was measured.
The hemicellulose content was calculated from the masses of the holocellulose fraction and the α-cellulose fraction obtained as above, using the following formula.
Holocellulose (%)=Holocellulose fraction (g)/sample (dry basis) (g)×100
α-Cellulose (%)=α-Cellulose fraction (g)/sample (anhydrous basis) (g)×100
Hemicellulose (%) = Holocellulose (%) - (α-cellulose (%))

(8) Method for measuring the average particle size of the phosphinate compound (b) The method for measuring the average particle size of the granular phosphinate compound (b) is based on the volume-based particle size measured using a laser diffraction/scattering type particle size distribution measuring device. The value is measured using a 3% isopropanol aqueous solution as the dispersion medium of the phosphinate compound (b). Specifically, using a laser diffraction/scattering type particle size distribution measuring device LA-910 (manufactured by Horiba, Ltd.), a blank measurement was performed using a dispersion medium of 3% isopropanol aqueous solution, and then the measurement sample was placed so that the specified transmittance (95% to 70%) was obtained. The sample was dispersed in the dispersion medium by irradiating it with ultrasonic waves for 1 minute.

The materials used in the examples and comparative examples are as follows.
[Styrene-based resin (A)]
[GPPS-1]
Polystyrene with MFR 7.8 (GPPS, manufactured by PS Japan, HF77) was used.
[HIPS-1]
A rubber-modified polystyrene resin with an MFR of 3.0 (HIPS, manufactured by PS Japan, HT478) was used.

[Copolymer resin-1]
A polymerization raw material composition liquid consisting of 70.0 parts by mass of styrene (ST), 15.0 parts by mass of butyl methacrylate (BA), 15.0 parts by mass of ethylbenzene, and 0.025 parts by mass of 1,1-bis(t-butylperoxy)cyclohexane was continuously supplied at a rate of 1.1 L/hour to a complete mixing type reactor having a capacity of 4 L, then to a polymerization apparatus consisting of a laminar flow type reactor having a capacity of 2 L, and further to a devolatilizer connected to a single screw extruder for removing volatile matters such as unreacted monomers and polymerization solvent, in this order, to prepare copolymer resin-1, which is a styrene-based copolymer resin.
The polymerization reaction conditions in the polymerization step were a polymerization temperature of 122° C. in the complete mixing reactor and a polymerization temperature of 120 to 142° C. in the laminar flow reactor. The devolatilized unreacted gas was condensed in a condenser through which a coolant of −5° C. was passed, and recovered as an unreacted liquid.
The polymer content in the final polymerization solution was measured after drying the polymerization solution at 215° C. under a reduced pressure of 2.5 kPa for 30 minutes according to the formula [(mass of sample after drying/mass of sample before drying)×100%], and was found to be 65.6% by mass, and the MFR was 4.6.

[Blend 1]
The above HIPS-1 was blended with 5% by mass of styrene-maleic anhydride copolymer (XIBOND250, manufactured by POLYSCOPE), and the MFR was 3.2.

[Phosphinate compound (b)]
Aluminum phosphinate (also referred to as DEP-A in Tables 1 and 2) "Exolit OP1230 manufactured by Clariant Japan" Average particle size 20 μm
Aluminum phosphinate (also referred to as DEP-B in Tables 1 and 2) "Exolit OP930 manufactured by Clariant Japan" Average particle size: 3 μm
Aluminum phosphinate (also referred to as DEP-C in Tables 1 and 2) was produced with reference to the method described in JP-A-08-73720. Average particle size: 0.8 μm
Phosphate ester: resorcinol bis-dixylenyl phosphate [PX-200, manufactured by Daihachi Chemical Industry Co., Ltd., melting point 92°C]

[Cellulosic polysaccharides (C)]
Cellulose fiber-1 (manufactured by Celite, SW-10, d ₁ : 20 μm, d ₂ : 700 μm, lignin content 0.5%, hemicellulose content 11% by mass)
Cellulose fiber-2 (manufactured by Asahi Kasei Corporation, ST-02, d ₁ : 50 μm, d ₂ : 100 μm, lignin content 0%, hemicellulose content 0% by mass)
CNF: Cellulose nanofiber (manufactured by Chuetsu Pulp Industry Co., Ltd., CNF-10, d ₁ : 35 nm, d ₂ : about 1 μm, lignin content 0%, hemicellulose content 15% by mass)
Wood flour (manufactured by Naka Wood Co., Ltd., raw material: cedar, d ₁ : 120 μm, d ₂ : 180 μm, lignin content 23%, hemicellulose content 18% by mass)
- Hemicellulose (Wako Pure Chemical Industries, xylan)

[Examples 1 to 9]
To 100 parts by mass of the total amount of the styrene-based resin (A) and the cellulose-based polysaccharide (B) having the composition ratio shown in Table 1 below, 0.2 parts by mass each of Irganox 1076 and Irgafos 168 were added and premixed. The resulting premixes were mixed together and melt-extruded at 180°C to 220°C using a twin-screw extruder (TEM-26SS, manufactured by Toshiba Machine Co., Ltd.) to obtain pellets of the styrene-based resin composition as a kneaded product. At this time, the screw rotation speed was 150 rpm and the discharge rate was 10 kg/hr. The pellet-shaped flame-retardant styrene-based resin composition thus obtained was molded using an injection molding machine manufactured by Japan Steel Works, Ltd. equipped with ISO527-2 multipurpose test piece type 1A at a cylinder temperature of 220°C, a mold temperature of 50°C, an injection pressure (gauge pressure 40-60MPa), an injection speed (panel set value) of 50%, and an injection time/cooling time of 5 sec/20 sec to produce a test piece (a), and the physical properties were measured. In addition, a test piece (b) was produced under the same conditions as the test piece (a) using a flat die with both ends gated with dimensions of 127 mm x 12.7 mm x thickness 0.8 mm, and the flame retardancy was measured. The experimental results of Examples 1 to 9 are shown in Table 1.

[Comparative Examples 1 to 13]
In Comparative Examples 1 to 13, foamed extruded sheets were obtained in the same manner as in Examples, except that the compositions were changed as shown in Table 2. The results of the measurements and evaluations of the various physical properties are shown in Table 2.

As shown in Table 1 above, the flame-retardant styrene-based resin compositions obtained in Examples 1 to 9 were compositions that reduced the environmental impact and had excellent low smoke generation, flame retardancy, dimensional accuracy, and color tone. In particular, it was confirmed that the low smoke generation was improved when the composition contained an unsaturated carboxylic acid monomer and the amount of hemicellulose in the cellulose-based polysaccharide (b) was 1% by mass or more.

As shown in Table 2, low smoke generation, flame retardancy, and dimensional accuracy cannot be obtained with only the phosphinate compound (b). Furthermore, low smoke generation, flame retardancy, and dimensional accuracy cannot be obtained with only the cellulose polysaccharide (C), and discoloration due to cellulose is also significant. If the size of the cellulose polysaccharide (C) is small, dimensional accuracy cannot be obtained, and conversely, if it is too large, black smoke is generated. Furthermore, when the phosphinate compound (b) is changed to a phosphoric ester, the heat resistance is greatly reduced, and under the conditions in Table 2, it melts and the linear expansion coefficient cannot be obtained. Furthermore, if the content of the phosphinate compound (b) or the cellulose polysaccharide (C) is more than the specified amount, the fluidity is poor and molding is not possible.

The flame-retardant styrene-based resin composition of the present invention can be suitably used for building materials, electronic and electrical parts, automobiles, food container parts, foam parts, etc.

Claims (6)

40 to 92% by mass of a styrene-based resin (A);
The following general formula (i):

[In the above formula (i), R ⁱ¹ and R ⁱ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 6 to 14 carbon atoms, which may be unsubstituted or one or more hydrogen atoms may be substituted with a substituent R ⁱ³ ;
The substituent R ⁱ³ is represented by the following formula (ii):

In the above formula (ii), each R ⁱⁱ¹ is independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, and * represents a bond to another atom.
wherein M ⁱ is at least one selected from the group consisting of calcium ion, magnesium ion, aluminum ion, zinc ion, bismuth ion, manganese ion, sodium ion, potassium ion, and protonated nitrogen base , p represents an ionic valence of M ⁱ and is a positive integer of 1 to 3, m ⁱ¹ is a positive integer of 1 to 3, n represents a positive integer of 1, 2, or 3, r represents a positive integer of 1 to 3, and | p × r | = | n × m ⁱ¹ |; and
and 3 to 30% by mass of a cellulose-based polysaccharide (C) having an average length of the minor axis _d1 of 10 to 80 μm ;
The average length of the minor axis d1 _is an arithmetic average of the shortest lengths of 100 cellulose polysaccharides (C) measured by observation with a transmission electron microscope (magnification: 5000 times). The flame-retardant styrene-based resin composition according to claim 1, wherein the phosphinate compound (b) is at least one or more selected from the group consisting of a phosphinate represented by the following general formula (1) and a diphosphinate represented by the following general formula (2):

[In the above formula (1), R ¹¹ and R ¹² are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, M ¹ is at least one selected from the group consisting of a calcium ion, a magnesium ion, an aluminum ion, a zinc ion, a bismuth ion, a manganese ion, a sodium ion, a potassium ion, and a protonated nitrogen base; a represents the ionic valence of M ¹ and is a positive integer of 1 to 3; m ¹ is a positive integer of 1 to 3; and a=m ^1. ]
The following formula (2):

[In the above formula (2), R ²¹ and R ²² are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, L ²³ is a linear or branched alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 10 carbon atoms, an alkylarylene group having 6 to 14 carbon atoms, or an arylalkylene group having 6 to 14 carbon atoms; M ² is at least one selected from the group consisting of calcium ions, magnesium ions, aluminum ions, zinc ions, bismuth ions, manganese ions, sodium ions, potassium ions, and protonated nitrogen bases, b represents the ionic valence of M ² and is a positive integer of 1 to 3, m ² is a positive integer of 1 to 3, q is a positive integer of 1 or 2, and b×q=2m ^2. ] The flame-retardant styrene-based resin composition according to claim 1 or 2, wherein the styrene-based resin (A) contains a styrene-based monomer unit and an unsaturated carboxylic acid-based monomer unit. The flame-retardant styrene-based resin composition according to any one of claims 1 to 3, wherein the cellulose-based polysaccharide (C) is cellulose containing 20% by mass or less of lignin. The flame-retardant styrene-based resin composition according to any one of claims 1 to 4, characterized in that the hemicellulose content of the cellulose-based polysaccharide (C) is 1% or more. A molded article comprising the flame-retardant styrene-based resin composition according to any one of claims 1 to 5.