Thermoplastic elastomer composition and molded member

Abstract

To provide a thermoplastic elastomer composition in which physical properties are retained while glossiness is reduced to a matte finish.SOLUTION: The present invention provides a thermoplastic elastomer composition. Based on 100 pts.mass of a composition comprising (A) 14 to 43 mass% of styrene-butadiene rubber, (B) 30 to 45 mass% of a polypropylene-based polymer, (C) 0 to 43 mass% of a block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated product thereof, and (D) 2 to 32 mass% of a softener, the thermoplastic elastomer composition comprises (E) 0.04 to 0.15 pt.mass of a crosslinking agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermoplastic elastomer composition, and more particularly to a thermoplastic elastomer composition to be used after crosslinking, a crosslinked product thereof, and a molded part. [Background technology]

[0002] In recent years, elastomer compositions, which are soft materials with rubber elasticity and moldability similar to that of thermoplastic resins, have been widely used as alternatives to vulcanized rubber in various fields, including automotive parts, home appliance parts, wire coatings, medical parts, footwear, and miscellaneous goods. These elastomer compositions, such as dynamically crosslinked thermoplastic elastomers (TPVs), have attracted attention as potential alternatives to vulcanized rubber. Dynamically crosslinked thermoplastic elastomers are multiphase polymer materials with an island-in-a-sea structure in which crosslinked rubber particles are dispersed as domains within a thermoplastic resin matrix. These elastomers have advantages similar to those of thermoplastic resins, such as superior weather resistance and heat resistance compared to vulcanized rubber, as well as the ability to be colored to desired colors.

[0003] Because such dynamically crosslinked thermoplastic elastomers can be designed by arbitrarily combining thermoplastic resins and rubbers, various combinations of elastomers have been proposed. For example, various elastomers have been developed, such as polyolefin-based, polyurethane-based, polyester-based, polystyrene-based, and polyvinyl chloride-based elastomers. Among these, olefin-based TPV, which combines polypropylene resin (PP) and olefin-based rubber (EPDM), has attracted attention. For example, Patent Document 1 proposes a resin composition containing polypropylene resin, olefin-based rubber, polyethylene resin, and a resin modifier, as a resin composition with improved moldability without impairing the flexibility and other properties of olefin-based TPV. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-145364 Summary of the Invention [Problem to be solved by the invention]

[0005] However, olefin-based TPVs containing the above-mentioned olefin-based rubbers have a glossy surface after crosslinking, making them unsuitable for applications requiring a matte-like gloss. In particular, molded articles with reduced gloss are desired for applications requiring a durometer hardness (Type A) of approximately 80 to 95. To meet this demand, additives may be added to reduce the gloss, but the physical properties of the olefin-based TPV tend to deteriorate as the amount of additive added increases.

[0006] Therefore, an object of the present invention is to provide a thermoplastic elastomer composition that has reduced matte gloss while maintaining physical properties. [Means for solving the problem]

[0007]

[0006] In light of the above circumstances, the present inventors have conducted extensive research and have found that by using styrene-butadiene rubber instead of olefin-based rubber, which is the rubber component in a thermoplastic elastomer composition, it is possible to reduce the glossiness of the surface of a molded article after crosslinking while maintaining physical properties. The present invention is based on this finding. Specifically, the gist of the present invention is as follows.

[0008] [1] (A) 14 to 43 mass% of styrene butadiene rubber, (B) 30 to 45% by mass of a polypropylene-based polymer, (C) 0 to 43% by mass of a block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated copolymer thereof, and (D) 2 to 32 mass% of a softener For 100 parts by mass of a composition comprising (E) a crosslinking agent in an amount of 0.04 to 0.15 parts by mass; A thermoplastic elastomer composition comprising: [2] The thermoplastic elastomer composition according to [1], wherein the (E) crosslinking agent is an organic peroxide. [3] The thermoplastic elastomer composition according to [1] or [2], wherein the (B) polypropylene polymer contains two or more polypropylene polymers having different melt flow rates. [4] The thermoplastic elastomer composition according to any one of [1] to [3], wherein the block copolymer of an aromatic vinyl compound and a conjugated diene compound (C) is at least one selected from the group consisting of a styrene-ethylene-butene-styrene block copolymer (SEBS), a styrene-ethylene-propylene-styrene block copolymer (SEPS), and a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS). [5] A crosslinked product of the thermoplastic elastomer composition according to any one of [1] to [4]. [6] The crosslinked product according to [5], having a durometer hardness (type A) of 80 to 95 at 15 seconds as measured in accordance with JIS K 7215. [7] A molded article comprising the crosslinked product according to [5] or [6]. [Effects of the Invention]

[0009] According to the present invention, by using a thermoplastic elastomer composition containing, as essential components, styrene-butadiene rubber, a polypropylene-based polymer, a softener, and a crosslinking agent in predetermined proportions, it is possible to obtain a molded article in which the matte glossiness is reduced while maintaining physical properties. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Definition]

[0011] In this specification, the term "resin" is used to include a resin mixture containing two or more resins, and a resin composition containing components other than resin.

[0012] In this specification, the term "sheet" is used interchangeably or interchangeably with "film." The terms "film" and "sheet" are used to refer to materials that can be industrially wound into rolls.

[0013] In this specification, the term "more than or equal to" in relation to a numerical range means a certain number or more than a certain number. For example, 20% or more means 20% or more than 20%. The term "less than or equal to" in relation to a numerical range means a certain number or less than a certain number. For example, 20% or less means 20% or less than 20%. Furthermore, the symbol "to" in relation to a numerical range means a certain number, more than a certain number and less than another certain number, or another certain number. Here, another certain number is a number greater than the certain number. For example, 10 to 90% means 10%, more than 10% and less than 90%, or 90%. Furthermore, the upper and lower limits of a numerical range can be arbitrarily combined, and embodiments incorporating such combinations can be interpreted. For example, from a statement regarding the numerical range of a certain characteristic such as "usually 10% or more, preferably 20% or more. On the other hand, it is usually 40% or less, preferably 30% or less," or "usually 10 to 40%, preferably 20 to 30%," it can be read that the numerical range of the certain characteristic is 10 to 40%, 20 to 30%, 10 to 30%, or 20 to 40% in one embodiment.

[0014] Other than in the examples, or where otherwise specified, all numerical values ​​used in the specification and claims should be understood to be modified by the term "about." Without attempting to limit the application of the doctrine of equivalents to the claims, each numerical value should be construed in light of the number of significant digits and by applying ordinary rounding techniques.

[0015] [Thermoplastic elastomer composition] The thermoplastic elastomer composition of the present invention contains, as essential components, (A) styrene-butadiene rubber, (B) a polypropylene-based polymer, (D) a softener, and (E) a crosslinking agent, and optionally further contains (C) a block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated product thereof. The components constituting the present invention are described in detail below.

[0016] <(A) Styrene butadiene rubber> The thermoplastic elastomer composition according to the present invention contains (A) styrene-butadiene rubber as a rubber component. Conventionally, widely used olefin-based TPVs, which contain an olefin-based rubber and a polypropylene resin, produce glossy surfaces in crosslinked molded articles, and therefore are not suitable for applications where a matte or other less glossy surface is preferred. Surprisingly, the present invention has found that by using (A) styrene-butadiene rubber as the rubber component, it is possible to appropriately reduce the gloss while maintaining physical properties.

[0017] The styrene-butadiene rubber (A) used as the rubber component of the thermoplastic elastomer composition of the present invention is a copolymer of styrene units and butadiene units, and emulsion-polymerized styrene-butadiene rubber or solution-polymerized styrene-butadiene rubber can be used without limitation. Modified emulsion-polymerized styrene-butadiene rubber or solution-polymerized styrene-butadiene rubber can also be used. Since the molecular weight distribution (Mw / Mn) of solution-polymerized styrene-butadiene rubber is easier to control than that of emulsion-polymerized styrene-butadiene rubber, these styrene-butadiene rubbers may be used appropriately depending on the physical properties required for the molded article.

[0018] As the emulsion-polymerized styrene-butadiene rubber, a styrene-butadiene rubber having a butadiene component trans content of 50 to 85%, a cis content of 3 to 25%, a vinyl content of 10 to 25%, and a styrene content of 1 to 50% by mass is even more preferable, and a styrene-butadiene rubber having a trans content of 60 to 75%, a cis content of 10 to 20%, a vinyl content of 12 to 20%, and a styrene content of 20 to 40% is even more preferable.

[0019] As the emulsion-polymerized styrene-butadiene rubber described above, commercially available products may be used, such as "ESBR1502 (trade name)" manufactured by JSR Corporation and "Nipol1502 (trade name)" manufactured by Nippon Zeon Co., Ltd.

[0020] The (A) styrene-butadiene rubber is contained in a proportion of 14 to 43% by mass of the entire composition, excluding the amount of (E) crosslinking agent added, which will be described later. If the blending proportion of (A) styrene-butadiene rubber is less than 14%, the resulting crosslinked molded article may have insufficient elongation, or the softener contained in the composition may bleed out. On the other hand, if the blending proportion of (A) styrene-butadiene rubber is more than 43% by mass, the proportions of other components such as components (B) to (D) become relatively low, making it difficult to maintain a good balance among mechanical properties such as tensile strength and tensile elongation, oil resistance, and suppression of softener bleed-out. The blending proportion of (A) styrene-butadiene rubber is preferably 20 to 30% by mass, more preferably 24 to 28% by mass.

[0021] <Component (B): Polypropylene-based polymer> The polypropylene polymer, which is one of the components constituting the thermoplastic elastomer composition of the present invention, is a polymer mainly containing structural units derived from propylene. Component (B) contributes to heat resistance and moldability. Here, "mainly containing structural units derived from propylene" means that the content of structural units derived from propylene is usually 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and typically 75 to 100% by mass.

[0022] Examples of the component (B) include propylene homopolymers, random copolymers of propylene with small amounts of other α-olefin comonomers, and block copolymers of propylene with α-olefin comonomers.

[0023] Examples of the α-olefin comonomer include ethylene, 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene, dimethyl Examples of the α-olefin comonomer include 1-pentene, ethyl-1-pentene, trimethyl-1-butene, methylethyl-1-butene, 1-octene, methyl-1-pentene, ethyl-1-hexene, dimethyl-1-hexene, propyl-1-heptene, methylethyl-1-heptene, trimethyl-1-pentene, propyl-1-pentene, diethyl-1-butene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene. The α-olefin comonomer may be one of these or a mixture of two or more of them.

[0024] Specific examples of the random copolymer of propylene with a small amount of another α-olefin comonomer include a propylene-ethylene random copolymer, a propylene-1-butene random copolymer, a propylene-1-hexene random copolymer, a propylene-1-octene random copolymer, a propylene-ethylene-1-butene random copolymer, a propylene-ethylene-1-hexene random copolymer, and a propylene-ethylene-1-octene random copolymer.

[0025] The block copolymer of propylene and an α-olefin comonomer is a copolymer composed of a crystalline polypropylene component and a copolymer rubber component of propylene and an α-olefin comonomer. The crystalline polypropylene component is composed of a propylene homopolymer or a random copolymer of propylene and a small amount of another α-olefin comonomer.

[0026] From the viewpoint of heat resistance, the above component (B) is preferably a propylene homopolymer or a block copolymer of propylene and an α-olefin comonomer in which the crystalline polypropylene component is a propylene homopolymer, and more preferably a propylene homopolymer.

[0027] Commercially available examples of the component (B) include propylene homopolymer "VS200A (trade name)" manufactured by SunAllomer Co., Ltd. and propylene homopolymer "PM900A (trade name)" manufactured by SunAllomer Co., Ltd.

[0028] From the viewpoint of moldability, the component (B) preferably has a melt mass flow rate (MFR) of 0.1 to 100 g / 10 min, more preferably 10 to 50 g / 10 min, as measured in accordance with JIS K 7210-1999 under conditions of 230°C and 21.18 N. In the present invention, from the viewpoint of moldability, etc., two or more polypropylene polymers having different MFRs may be mixed and used. For example, a polypropylene polymer having an MFR of 0.1 to 1 g / 10 min and a polypropylene polymer having an MFR of 10 to 100 g / 10 min may be mixed and used.

[0029] From the viewpoint of heat resistance, the melting point of the component (B) is preferably 150°C or higher, more preferably 160°C or higher. The melting point here refers to the peak-top melting point of the peak appearing on the highest temperature side in a second melting curve (a melting curve measured during the final heating process) measured using a Diamond DSC differential scanning calorimeter manufactured by PerkinElmer Japan Co., Ltd., according to a program that involves holding at 230°C for 5 minutes, cooling to -10°C at 10°C / min, holding at -10°C for 5 minutes, and heating to 230°C at 10°C / min. There is no particular upper limit to the peak-top melting point, but for polypropylene-based polymers, the highest is 167°C.

[0030] The (B) polypropylene-based polymer is contained in a proportion of 30 to 45% by mass of the entire composition excluding the amount of the (E) crosslinking agent added, which will be described later. If the blending proportion of the (B) polypropylene-based polymer is less than 30% by mass, moldability may be insufficient and oil resistance may be poor. On the other hand, if the blending proportion of the (B) polypropylene-based polymer is more than 45% by mass, the molded article may be too hard. The blending proportion of the (B) polypropylene-based polymer is preferably 35 to 43% by mass.

[0031] <(C) Block Copolymer of Aromatic Vinyl Compound and Conjugated Diene Compound or Hydrogenated Product thereof> The thermoplastic elastomer composition of the present invention contains (C) a block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated product thereof in a proportion of 0 to 43% by mass, which contributes to imparting flexibility to the thermoplastic elastomer composition.

[0032] An aromatic vinyl compound is a polymerizable monomer having a polymerizable carbon-carbon double bond and an aromatic ring. Examples of aromatic vinyl compounds include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylstyrene, N,N-diethyl-p-aminoethylstyrene, vinyltoluene, and p-tert-butylstyrene. Among these, styrene is preferred. One or more of these can be used as the aromatic vinyl compound.

[0033] Conjugated dienes are polymerizable monomers having a structure in which two carbon-carbon double bonds are connected by one carbon-carbon single bond. Examples of conjugated dienes include 1,3-butadiene, isoprene (2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, and chloroprene (2-chloro-1,3-butadiene). Among these, 1,3-butadiene and isoprene are preferred. As the conjugated diene, one or more of these can be used.

[0034] (C) The block copolymer of an aromatic vinyl compound and a conjugated diene compound is a block copolymer consisting of one or more polymer blocks A, preferably two or more from the viewpoints of mechanical strength and moldability, mainly composed of an aromatic vinyl compound, and one or more polymer blocks B, mainly composed of a conjugated diene compound. Examples of block copolymers include block copolymers having structures such as AB, ABA, BABA, and ABABA.

[0035] The content of structural units derived from aromatic vinyl compounds is preferably 5 to 60% by mass, more preferably 20 to 50% by mass, from the viewpoint of flexibility and the like.

[0036] The polymer block A is a polymer block consisting of only an aromatic vinyl compound or a copolymer block of an aromatic vinyl compound and a conjugated diene compound. When the polymer block A is a copolymer block, the content of structural units derived from the aromatic vinyl compound in the polymer block A is usually 50% by mass or more, and from the viewpoint of heat resistance, it is preferably 70% by mass or more, and more preferably 90% by mass or more. The distribution of structural units derived from the conjugated diene compound in the polymer block A is not particularly limited and can be any distribution. When there are two or more polymer blocks A, they may have the same structure or different structures.

[0037] The polymer block B is a polymer block consisting of only a conjugated diene compound or a copolymer block of an aromatic vinyl compound and a conjugated diene compound. When the polymer block B is a copolymer block, the content of structural units derived from the conjugated diene compound in the polymer block B is usually 50% by mass or more, and from the viewpoint of flexibility, it is preferably 70% by mass or more, more preferably 90% by mass or more. The distribution of structural units derived from the aromatic vinyl compound in the polymer block is not particularly limited and can be any distribution. The bonding mode between the conjugated diene compounds (hereinafter sometimes abbreviated as microstructure) is not particularly limited and can be any distribution. When there are two or more polymer blocks B, they may have the same structure or different structures.

[0038] The hydrogenation rate of the block copolymer of an aromatic vinyl compound and a conjugated diene compound (the ratio of the number of carbon-carbon single bonds that have been formed by hydrogenation to the number of carbon-carbon double bonds in the block copolymer of an aromatic vinyl compound and a conjugated diene compound before hydrogenation) is not particularly limited, but from the viewpoint of heat resistance, it may be usually 50 mol % or more, preferably 70 mol % or more, and more preferably 90 mol % or more.

[0039] When the conjugated diene polymer block is a butadiene polymer block, the microstructure may have 1,2-bonds in an amount of preferably 20 to 50 mol %, more preferably 25 to 45 mol %, from the viewpoint of flexibility, and may have 1,2-bonds selectively hydrogenated from the viewpoint of heat resistance.

[0040] When the conjugated diene polymer block is a copolymer block of isoprene and butadiene, the microstructure may have a 1,2-bond content of preferably less than 50 mol %, more preferably less than 25 mol %, and even more preferably less than 15 mol %, from the viewpoint of heat resistance.

[0041] When the conjugated diene polymer block is a copolymer block of isoprene and butadiene, the microstructure may have a 1,2-bond content of preferably less than 50 mol %, more preferably less than 25 mol %, and even more preferably less than 15 mol %, from the viewpoint of heat resistance.

[0042] When the conjugated diene polymer block is an isoprene polymer block, the microstructure may preferably contain 70 to 100 mol % of 1,4-bonds from the viewpoint of flexibility, and the hydrogenation rate is preferably 90 mol % or more from the viewpoint of heat resistance.

[0043] When the conjugated diene polymer block is an isoprene polymer block, from the viewpoint of gas barrier properties, the sum of 1,2-bonds and 3,4-bonds in the microstructure may be 80 mol % or more, preferably 90 mol % or more, and more preferably 95 mol % or more. From the viewpoint of heat resistance, the hydrogenation rate is preferably 90 mol % or more. Such a copolymer is often called a styrene-vinyl(ethylene-propylene)-styrene copolymer (V-SEPS). The glass transition temperature of the styrene-vinyl(ethylene-propylene)-styrene copolymer (V-SEPS) is preferably -40 to 20°C. The glass transition temperature means the midpoint glass transition temperature calculated from the curve of the final heating process measured in accordance with JIS K7121-1987 using a Diamond DSC differential scanning calorimeter manufactured by PerkinElmer Japan Co., Ltd., using a program that involves holding at 150°C for 5 minutes, cooling to -100°C at 10°C / min, holding at -50°C for 3 minutes, and heating to 150°C at 10°C / min.

[0044] (C) Examples of block copolymers of aromatic vinyl compounds and conjugated diene compounds or hydrogenated products thereof include styrene-ethylene-butene block copolymers (SEB), styrene-ethylene-propylene block copolymers (SEP), styrene-ethylene-butene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS), and styrene-vinyl(ethylene-propylene)-styrene copolymers (V-SEPS). Among these, from the viewpoints of flexibility and compression set resistance in high-temperature environments, styrene-ethylene-butene-styrene block copolymers (SEBS), styrene-ethylene-propylene-styrene block copolymers (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS) are preferred.

[0045] In consideration of flexibility and production costs, the blending ratio of (C) the block copolymer of an aromatic vinyl compound and a conjugated diene compound or its hydrogenated product is preferably 0 to 24 mass% based on the total mass of the composition excluding the added amount of (E) the crosslinking agent.

[0046] <(D) Softener> The thermoplastic elastomer resin composition of the present invention contains a (D) softener in a proportion of 2 to 32 mass % based on the total composition, excluding the amount of (E) crosslinking agent (described below). The inclusion of a predetermined amount of (D) softener can impart flexibility. Examples of (D) softeners include non-aromatic rubber softeners, aromatic rubber softeners, and ester-based plasticizers. Among these, non-aromatic rubber softeners are preferred from the standpoint of ease of handling.

[0047] Non-aromatic rubber softeners are non-aromatic mineral oils (hydrocarbon compounds derived from petroleum, etc.) or synthetic oils (synthetic hydrocarbon compounds), and are usually liquid, gel-like, or gum-like at room temperature. Here, "non-aromatic" means that for mineral oils, they are not classified as aromatic in the classification below (the number of aromatic carbon atoms is less than 30%). For synthetic oils, this means that they do not contain aromatic monomers.

[0048] Mineral oils used as rubber softeners are mixtures of one or more of paraffin chains, naphthenic rings, and aromatic rings. They are classified as follows: those with 30 to 45% naphthenic ring carbon atoms are called naphthenic; those with 30% or more aromatic carbon atoms are called aromatic; and those that are neither naphthenic nor aromatic and have 50% or more paraffin chain carbon atoms are called paraffinic.

[0049] Examples of non-aromatic rubber softeners include paraffinic mineral oils such as linear saturated hydrocarbons, branched saturated hydrocarbons, and derivatives thereof; naphthenic mineral oils; and synthetic oils such as hydrogenated polyisobutylene, polyisobutylene, and polybutene.

[0050] The dynamic viscosity of the non-aromatic rubber softener at 37.8°C is preferably 20 to 50,000 cSt, more preferably 20 to 1,000 cSt, from the viewpoint of molding processability. The dynamic viscosity at 100°C is preferably 5 to 1,500 cSt, more preferably 5 to 100 cSt, from the viewpoint of bleed-out resistance and heat resistance. The pour point is preferably -10 to -25°C, from the viewpoint of handleability during composition production. The flash point (COC) is preferably 170 to 350°C, from the viewpoint of safety. The mass average molecular weight is preferably 100 to 2,000, from the viewpoint of bleed-out resistance.

[0051] Commercially available examples of non-aromatic rubber softeners include the isoparaffinic hydrocarbon oil "NA Solvent (trade name)" from Nippon Oil & Fats Corporation, n-paraffinic process oils "Diana Process Oil PW-100 (trade name)" and "Diana Process Oil PW-380 (trade name)" from Idemitsu Kosan Co., Ltd., synthetic isoparaffinic hydrocarbon "IP-Solvent 2835 (trade name)" from Idemitsu Petrochemical Co., Ltd., and n-paraffinic process oil "Neothiosol (trade name)" from Sanko Chemical Industry Co., Ltd. Among these, paraffinic mineral oils are preferred from the viewpoint of compatibility, and paraffinic mineral oils with a low number of aromatic carbon atoms are more preferred.

[0052] The blending ratio of the (D) softener is preferably 5 to 30 mass % based on the total amount of the composition excluding the (E) crosslinking agent.

[0053] <Component (E): Crosslinking agent> The thermoplastic elastomer composition of the present invention contains a crosslinking agent in a predetermined proportion for crosslinking the above-mentioned component (A). There are no particular limitations on the crosslinking agent, and conventionally known organic peroxides, phenolic resins, sulfur, hydrosilicone compounds, amino resins, quinones or their derivatives, amine compounds, azo compounds, epoxy compounds, isocyanates, etc. can be used. These crosslinking agents may be used alone or in combination of two or more.

[0054] In the present invention, the (D) crosslinking agent is preferably an organic peroxide. When crosslinking (A) styrene-butadiene rubber, organic peroxides have superior crosslinking efficiency compared to crosslinking agents such as phenolic resins, allowing for a relatively smaller amount of crosslinking agent to be added. Furthermore, when using a resin-based crosslinking agent such as phenolic resin, the crosslinked product may absorb moisture depending on the catalyst. However, when using an organic peroxide as a crosslinking agent, this problem does not occur. Organic peroxides are compounds in which one or two hydrogen atoms of hydrogen peroxide are substituted with organic free radicals. Because they contain peroxide bonds within their molecules, they generate radicals during melt-kneading, which then cause a chain reaction that crosslinks not only (A) styrene-butadiene rubber but also component (C) a block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated product thereof. Furthermore, they decompose (B) polypropylene-based polymers, thereby controlling the fluidity of the composition during melt-kneading and improving the dispersion of the rubber component.

[0055] Examples of organic peroxides include dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3, 1,3-bis(tert-butylperoxyisopropyl)benzene, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl peroxybenzoate, tert-butylperoxyisopropyl carbonate, diacetyl peroxide, lauroyl peroxide, and tert-butylcumyl peroxide, and these may be used alone or in combination of two or more. Among these, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane and 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexyne-3 are preferred from the viewpoints of odor, coloring, and scorch safety.

[0056] The thermoplastic elastomer composition of the present invention contains 0.04 to 0.15 parts by mass of (E) crosslinking agent per 100 parts by mass of the composition containing the above-mentioned components (A) to (D). If the blending ratio of (E) crosslinking agent is less than 0.04 parts by mass, crosslinking will be insufficient and the desired physical properties will not be obtained. On the other hand, if the blending ratio of (E) crosslinking agent is more than 0.15 parts by mass, the elongation of the molded article may be insufficient. The blending ratio of (E) crosslinking agent is preferably 0.07 to 0.12 parts by mass, and more preferably 0.09 to 0.11 parts by mass.

[0057] <Other optional ingredients> The thermoplastic elastomer composition of the present invention may further contain, as desired, inorganic fillers, antioxidants, antioxidants, hydrolysis inhibitors, light stabilizers, various weather resistance agents such as ultraviolet absorbers, lubricants, nucleating agents, antistatic agents, and various organic and inorganic flame retardants, to the extent that the addition does not interfere with the object of the present invention. Note that these additives are preferably highly compatible with the thermoplastic elastomer composition of the present invention in order to prevent problems such as bleed-out and blooming on the surface of molded articles.

[0058] [Method of producing thermoplastic elastomer composition] The thermoplastic elastomer composition of the present invention can be obtained by adding the above components (A), (B), (D), and (E), optionally the optional component (C), and other optional components simultaneously or in any order, and melt-kneading them using any kneader.

[0059] The melt-kneading is preferably carried out for 1 minute or more at a temperature of 180° C. or higher, and more preferably for 1 minute or more at a temperature of 190° C. or higher. The melt-kneading temperature may be usually 240° C. or lower, preferably 220° C. or lower, from the viewpoints of mechanical properties, manufacturability of the composition, and moldability.

[0060] Examples of melt kneaders include batch kneaders such as pressure kneaders and mixers; extrusion kneaders such as single-screw extruders, co-rotating twin-screw extruders, and counter-rotating twin-screw extruders; and calendar roll kneaders. These may be used in any combination. The resulting composition can be pelletized by any method and then molded into an article by any method.

[0061] The pelletization can be carried out by a method such as hot cutting, strand cutting, or underwater cutting.

[0062] [Crosslinked and molded articles] The crosslinked product of the present invention is obtained by crosslinking the above-mentioned thermoplastic elastomer composition. As described above, the crosslinked product is obtained in the process of melt-kneading the respective components. Furthermore, a molded article can be obtained by molding the crosslinked product into a desired shape by any molding method, such as blow molding, extrusion molding, injection molding, press molding, compression molding, or a method combining two or more of these.

[0063] The crosslinked products and molded articles obtained by crosslinking the thermoplastic elastomer composition of the present invention have a moderately matte surface, making them suitable for use in applications requiring a matte surface appearance (e.g., automobile parts such as mudguards). The crosslinked products and molded articles obtained by crosslinking the thermoplastic elastomer composition of the present invention have a surface roughness Sa of 0.5 to 10 μm. The surface roughness Sa can be calculated using a laser microscope for shape analysis in accordance with ISO 25178-2:2012.

[0064] Furthermore, the crosslinked product and molded article of the thermoplastic elastomer composition of the present invention can be suitably used for molded articles (for example, automobile parts such as dust covers) that require a durometer hardness (type A) of about 80 to 95. The durometer hardness refers to a value measured in accordance with JIS K 7215. [Example]

[0065] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0066] <Ingredients used> (A) Styrene butadiene rubber: (A-1) "SBR1502 (product name)" manufactured by JSR Corporation. Emulsion-polymerized styrene-butadiene rubber, styrene content 23.5%.

[0067] (A') Olefin-based TPV: (A'-1) "EQA9631P (product name)" manufactured by Riken Technos Corporation. An olefin-based TPV that combines PP and EPDM.

[0068] (B) Polypropylene-based polymer: (B-2) Polypropylene homopolymer "VS200A (product name)" manufactured by SunAllomer Co., Ltd. Melt mass flow rate: 0.45 (g / 10 min). (B-2) Polypropylene homopolymer "PM900A (product name)" manufactured by SunAllomer Co., Ltd. Melt mass flow rate: 30 (g / 10 min).

[0069] (C) A block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated product thereof: (C-1) Kuraray Co., Ltd.'s styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) "SEPTON 4055 (trade name)".

[0070] (D) Softener: (D-1) Idemitsu Kosan Co., Ltd. n-paraffinic process oil "PW-100 (product name)". Kinematic viscosity at 40°C measured in accordance with JIS K2283:2000: 99 mmHg 2 / s.

[0071] (E) Crosslinking agent (E-1) Organic peroxide crosslinking agent "Perhexa 25B (trade name)" manufactured by Nippon Oil & Fats Corporation (E-2) Alkylphenol formaldehyde resin crosslinking agent "LQA7706N (trade name)" manufactured by Riken Technos Corporation. Takkiroll (trade name, manufactured by Taoka Chemical Co., Ltd.) 40% masterbatch product.

[0072] <Measurement method> (1)Surface hardness Using the composition obtained below, an injection molding machine with a clamping pressure of 120 tons was used to produce an injection sheet measuring 13 cm long x 13 cm wide and 2 mm thick at a molding temperature of 220°C. A 6.3 mm thick press sheet was then produced using the obtained injection sheet. The durometer hardness (Type A) of the obtained press sheet was measured after 15 seconds according to JIS K 7215. (Judgment criteria) A surface hardness in the range of 80 to 95 was considered acceptable.

[0073] (2) Tensile test: Using a No. 3 dumbbell punched out from the 2 mm thick injection sheet obtained above as a test piece, the tensile strength and tensile elongation were measured at a tensile speed of 500 mm / min in accordance with JIS K 6251-2010. (Judgment criteria) A tensile strength of 8.0 MPa or more was considered acceptable. The higher the value, the better the mechanical properties. A tensile elongation of 340% or more was considered acceptable. The higher the value, the better the mechanical properties.

[0074] (3) Oil resistance: In accordance with JIS K 6258-2003, test pieces were punched out from the 2 mm thick injection sheet obtained above, and the volume swelling ratio was measured after immersion in IRM#903 oil at a temperature of 120°C for 22 hours. (Judgment criteria) Oil resistance was considered acceptable if it was 170% or less. The lower the value, the better the oil resistance.

[0075] (4) Surface roughness (Sa): Using the composition obtained below, an extruded sheet measuring 25 mm in length, 150 mm in width, and 2 mm in thickness was produced using a 20 mm diameter single-screw extruder at a molding temperature of 200° C. The surface of the resulting 2 mm-thick extruded sheet was observed with a shape analysis laser microscope, and the surface roughness Sa was calculated in accordance with ISO 25178-2:2012. (Judgment criteria) A surface roughness Sa of 4.0 μm or less was considered acceptable. The smaller the value, the smoother the surface.

[0076] (5) Bleed out A 2 mm thick injection sheet was left to stand at 23°C for 168 hours, and the surface was observed visually and by touch, and the amount of bleeding was evaluated using the following three levels. (Judgment criteria) Rating 1: Bleeding can be visually confirmed Rating 2: Difficult to see with the naked eye, but sticky to the touch Rating 3: Not sticky to the touch A rating of 2 or higher was considered acceptable. The higher the rating, the less bleeding there was.

[0077] (6) Surface gloss of molded products The surface gloss of the 2 mm thick injection sheet was measured in accordance with JIS Z8741 using a gloss meter (Gloss Checker IG-330, manufactured by Horiba, Ltd.) at a measurement angle of 60 degrees. (Judgment criteria) A gloss value of 20 or less was considered acceptable. The lower the value, the less glossy the surface.

[0078] <Examples 1 to 14 and Comparative Examples 1 to 11> The components in the amounts (parts by mass) shown in the table below were melt-kneaded using a Japan Steel Works, Ltd. twin-screw extruder with a diameter of 28 mm and an L / D ratio of 42 mm, equipped with a water-cooled strand-cutting granulator, at a screw speed of 600 rpm and an extruder outlet temperature of 200°C, to obtain pellets of the composition. Tests (1) to (6) above were carried out. The results are shown in Tables 1 and 2.

[0079] [Table 1]

[0080]

Table 2

Claims

1. (A) 14 to 43 mass% of styrene-butadiene rubber, (B) 30 to 45% by mass of a polypropylene-based polymer, (C) 0 to 43% by mass of a block copolymer of an aromatic vinyl compound and a conjugated diene compound or a hydrogenated product thereof, and (D) 2 to 32% by mass of a softener For 100 parts by mass of a composition comprising (E) a crosslinking agent in an amount of 0.04 to 0.15 parts by mass; A thermoplastic elastomer composition comprising:

2. The thermoplastic elastomer composition according to claim 1 , wherein the crosslinking agent (E) is an organic peroxide.

3. The thermoplastic elastomer composition according to claim 1 , wherein the polypropylene polymer (B) comprises two or more polypropylene polymers having different melt flow rates.

4. 2. The thermoplastic elastomer composition according to claim 1, wherein the block copolymer (C) of an aromatic vinyl compound and a conjugated diene compound is at least one selected from the group consisting of a styrene-ethylene-butene-styrene block copolymer (SEBS), a styrene-ethylene-propylene-styrene block copolymer (SEPS), and a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

5. A crosslinked product of the thermoplastic elastomer composition according to claim 1.

6. 6. The crosslinked product according to claim 5, wherein the 15-second value of durometer hardness (type A) measured in accordance with JIS K 7215 is 80 to 95.

7. A molded article comprising the crosslinked product of claim 6.

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