Thermoplastic elastomer composition and molded body thereof

Abstract

Provided is a styrene-based thermoplastic elastomer composition for forming a molded body (cushioning member) that achieves both high resilience and excellent flexibility.　The thermoplastic elastomer composition contains a styrene-based thermoplastic elastomer (A) and a softening agent (B). The styrene-based thermoplastic elastomer (A) is a block copolymer composed of at least a styrene block (a1) and a hydrogenated conjugated diene block (a2). The absolute weight average molecular weight Mw (A) of the styrene-based thermoplastic elastomer (A) is 20,000-200,000. The hydrogenated conjugated diene block (a2) constituting the styrene-based thermoplastic elastomer (A) has a plurality of branched side chains. The branching degree Bn per molecule constituting the styrene-based thermoplastic elastomer (A) calculated by formulae (1)-(3) is 420 or less. The blending ratio of the softening agent (B) to the styrene-based thermoplastic elastomer (A) in terms of mass ratio satisfies: B / (A + B) = 0.30-0.90.

Description

Thermoplastic elastomer composition and molded article thereof

[0001] The present invention relates to a thermoplastic elastomer composition and a molded article thereof, and more particularly to a styrene-based thermoplastic elastomer composition that is used for shock-absorbing members mounted on sports shoes, etc.

[0002] In shoe design for sports shoes and other shoes requiring functionality, a shock-absorbing material with excellent shock absorption properties is typically mounted on a sole member made of resin or the like. This type of shock-absorbing material is required to be lightweight for ease of handling and to avoid interfering with the user's movements. Furthermore, since the shock-absorbing material is incorporated into the sole member in a manner that is visible from the outside, which allows the functionality to be appealing to consumers, it is also required to have a high level of design, such as a transparent appearance. Therefore, various shock-absorbing materials made of styrene-based thermoplastic elastomers, which have low specific gravity (lightweight) and transparency, have been proposed.

[0003] In recent years, in the field of sports shoes, shoe design technology has made remarkable progress in order to improve running performance. For example, in the field of running shoes, so-called platform shoes, which have thicker soles than general sports shoes, have become mainstream. Platform shoes aim to improve running performance by converting the rebound force generated when the sole of the shoe lands into propulsion force, so it is desirable for the sole to be equipped with a shock-absorbing material with a high rebound elasticity. Therefore, there is a demand for materials that can be used to form shock-absorbing materials with high rebound properties.

[0004] In this regard, Patent Document 1 discloses that a styrene-based thermoplastic elastomer composition capable of forming a molded article with an improved rebound resilience can be obtained by mixing (a) a block copolymer consisting of at least two polymer blocks A mainly made of a vinyl aromatic compound and at least one polymer block B mainly made of a conjugated diene compound, and / or a block copolymer obtained by hydrogenating the same, with (b) a copolymer mainly made of polyethylene or ethylene and (c) a copolymer mainly made of polypropylene or propylene.

[0005] Patent No. 3160212

[0006] However, although the thermoplastic elastomer described in Patent Document 1 improves the rebound resilience, the blending of an olefin-based polymer with a styrene-based thermoplastic elastomer material (a block copolymer consisting of a styrene block and a conjugated diene block) results in a molded product with a high durometer A hardness (Shore A hardness) of 70 to 80 (corresponding to an Asker C hardness of approximately 85 to 95), resulting in poor flexibility. Thus, attempts to improve the resilience of a cushioning material typically result in a loss of flexibility and a decrease in cushioning properties. Furthermore, blending an olefin-based polymer with a styrene-based thermoplastic elastomer material results in cloudiness and reduced transparency, resulting in poor designability.

[0007] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a styrene-based thermoplastic elastomer composition that can be used to form a molded article (a cushioning member) that has both high resilience and excellent flexibility.

[0008] The present inventors have found that a styrene-based thermoplastic elastomer composition capable of forming a molded article (a shock absorber member) having both high resilience and excellent flexibility can be obtained by adjusting the branching degree per molecule Bn of a block copolymer comprising at least a styrene block and a hydrogenated conjugated diene block so as to fall within a predetermined range. Based on this finding, the present invention has been completed.

[0009] In order to achieve the above object, the thermoplastic elastomer composition of the present invention is a thermoplastic elastomer composition containing a styrene thermoplastic elastomer (A) and a softener (B), wherein the styrene thermoplastic elastomer (A) is a block copolymer constituted of at least a styrene block (a1) and a hydrogenated conjugated diene block (a2), the absolute weight average molecular weight Mw(A) of the styrene thermoplastic elastomer (A) is 20,000 to 200,000, the hydrogenated conjugated diene block (a2) constituting the styrene thermoplastic elastomer (A) has a plurality of branched side chains, the degree of branching Bn per molecule constituting the styrene thermoplastic elastomer (A), calculated by the following formulas (1) to (3), is 420 or less, and the blending ratio of the styrene thermoplastic elastomer (A) to the softener (B) is, in mass ratio, B / (A+B)=0.30 to 0.90. In the following formula (1), η(A) is the intrinsic viscosity of the styrene-based thermoplastic elastomer (A), and η ０ is the value of intrinsic viscosity of standard sample (S) at the same absolute weight average molecular weight as the absolute weight average molecular weight Mw(A) of styrene-based thermoplastic elastomer (A), as determined from the approximate curve of the Mark-Houwink plot of standard sample (S), which is obtained by plotting the logarithm of the absolute weight molecular weight of standard sample (S) on the horizontal axis and the logarithm of the intrinsic viscosity of standard sample (S) on the vertical axis, and standard sample (S) is a styrene-ethylene-butylene-styrene block copolymer (SEBS) having a styrene content of 25% to 35% by mass, an absolute weight average molecular weight Mw(S) of 24,000 to 26,000, and an intrinsic viscosity of 1.0 dL / g to 1.3 dL / g. In the present invention, the absolute weight average molecular weight Mw(A) of styrene-based thermoplastic elastomer (A) and the absolute weight average molecular weight Mw(S) of standard sample (S) are values ​​measured by gel permeation chromatography (GPC).

[0010]

[0011] A styrene-based thermoplastic elastomer composition capable of forming a molded article (a shock absorber) exhibiting both high resilience and excellent flexibility can be obtained by adjusting the absolute weight-average molecular weight Mw(A) of the styrene-based thermoplastic elastomer (A) to 20,000 to 200,000, the degree of branching Bn per molecule constituting the styrene-based thermoplastic elastomer (A) to 420 or less, and the blending ratio of the styrene-based thermoplastic elastomer (A) to the softener (B) to a mass ratio of B / (A+B) = 0.30 to 0.90. Furthermore, by adjusting the absolute weight-average molecular weight Mw(A) and degree of branching Bn of the styrene-based thermoplastic elastomer (A) and the blending ratio of each component within the above-mentioned ranges, a molded article (a shock absorber) exhibiting both high resilience and excellent flexibility can be designed. These numerical ranges serve as indicators, facilitating the design of a shock absorber having the desired physical properties.

[0012] Furthermore, by using a styrene-ethylene-butylene-styrene block copolymer (SEBS) having a styrene content of 25% by mass to 35% by mass, an absolute weight average molecular weight Mw(S) of 24,000 to 26,000, and an intrinsic viscosity of 1.0 dL / g to 1.3 dL / g as the standard sample (S) used in determining the degree of branching Bn per molecule constituting the styrene thermoplastic elastomer (A) calculated by the formulas (1) to (3), the degree of branching Bn of the styrene thermoplastic elastomer (A), which is a block copolymer composed of at least a styrene block (a1) and a hydrogenated conjugated diene block (a2), can be suitably determined.

[0013] In the thermoplastic elastomer composition of the present invention, the styrene content of the styrene-based thermoplastic elastomer (A) is preferably 10% by mass to 55% by mass, thereby allowing a suitable range to be selected for the styrene content of the styrene-based thermoplastic elastomer (A) constituting the thermoplastic elastomer composition of the present invention.

[0014] In addition, the thermoplastic elastomer composition of the present invention preferably has a blending ratio of the styrene thermoplastic elastomer (A) to the softener (B) in a mass ratio of B / (A+B) of 0.60 to 0.85, thereby obtaining a styrene thermoplastic elastomer composition that can be used to form a molded article (a cushioning member) having both higher resilience and greater flexibility and excellent cushioning properties.

[0015] In the thermoplastic elastomer composition of the present invention, the styrene-based thermoplastic elastomer (A) is preferably at least one block copolymer selected from the group consisting of styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS). This allows a suitable block copolymer to be selected as the styrene-based thermoplastic elastomer (A) constituting the thermoplastic elastomer composition of the present invention.

[0016] In the thermoplastic elastomer composition of the present invention, the softener (B) is preferably a paraffinic oil having a molecular weight of 300 to 1500. This allows a compound suitable as the softener (B) to be selected.

[0017] The molded article according to the present invention is obtained by molding the above-mentioned thermoplastic elastomer composition, thereby forming a molded article to be used for a cushioning material or the like.

[0018] The molded article according to the present invention preferably has an Asker C hardness of 5 to 80 (SRIS 0101 standard, 23±2°C) and a rebound resilience of 44% or more (ASTM D2632 standard). A molded article of a thermoplastic elastomer composition having such physical properties combines high rebound and excellent flexibility, and is therefore suitable for use as a shock-absorbing material mounted in the sole of footwear such as sports shoes.

[0019] According to the present invention, it is possible to provide a styrene-based thermoplastic elastomer composition and a molded article thereof having the following excellent effects: (1) A molded article having both high resilience and excellent flexibility, and a styrene-based thermoplastic elastomer composition capable of forming such a molded article, can be obtained. (2) A molded article having excellent cushioning properties and transparency, and a styrene-based thermoplastic elastomer composition capable of forming such a molded article, can be obtained. (3) The composition is suitably used as a cushioning material to be mounted in the sole member of footwear, including sports shoes.

[0020] 1 is a diagram illustrating a method for a drop impact test for evaluating the shock-absorbing properties of molded articles prepared in Examples and Comparative Examples. 2 is a graph showing an approximate curve L1 based on a Mark-Houwink plot of a standard sample (S) and a plot of the absolute weight-average molecular weight Mw (A) and the intrinsic viscosity η (A) of a material related to the styrene-based thermoplastic elastomer (A) used in Examples and Comparative Examples.

[0021] The thermoplastic elastomer composition according to the present invention contains a styrene-based thermoplastic elastomer (A) and a softener (B). The styrene-based thermoplastic elastomer (A) is a block copolymer composed of at least a styrene block (a1) and a hydrogenated conjugated diene block (a2), and has an absolute weight-average molecular weight Mw(A) of 20,000 to 200,000. The hydrogenated conjugated diene block (a2) constituting the styrene-based thermoplastic elastomer (A) has a plurality of branched side chains, and the degree of branching Bn per molecule constituting the styrene-based thermoplastic elastomer (A), calculated by the formula described below, is 420 or less. The blending ratio of the styrene-based thermoplastic elastomer (A) to the softener (B) is, in mass ratio, B / (A+B) = 0.30 to 0.90.

[0022] First, the styrene-based thermoplastic elastomer (A) constituting the thermoplastic elastomer composition will be described. In the present invention, the styrene-based thermoplastic elastomer (A) refers to a styrene-based block copolymer (SBC), which is a block copolymer composed of at least a styrene block (a1) and a hydrogenated conjugated diene block (a2). Examples of the block copolymer according to the present invention include a styrene-ethylene-butylene-styrene block copolymer (hereinafter also referred to as SEBS), a styrene-ethylene-propylene-styrene block copolymer (hereinafter also referred to as SEPS), a styrene-ethylene-ethylene-propylene-styrene block copolymer (hereinafter also referred to as SEEPS), a styrene-ethylene-butylene block copolymer (hereinafter also referred to as SEB), a styrene-ethylene-propylene block copolymer (SEP), and a styrene-ethylene-ethylene-propylene block copolymer (SEEP). Among these, from the viewpoint of achieving the effects of the present invention, i.e., obtaining a molded article (buffer material) that combines high resilience and excellent flexibility, SEBS, SEPS, or SEEPS, and combinations thereof, are preferably used as the block copolymer for the styrene-based thermoplastic elastomer (A). Note that although the block copolymer used in the present invention has a hydrogenated conjugated diene block (a2), it is not required that all of the carbon-carbon double bonds of the conjugated diene block be converted to carbon-carbon single bonds by hydrogenation treatment, and some carbon-carbon double bonds may remain.

[0023] In the present invention, the molecular weight of the styrene-based block copolymer constituting the styrene-based thermoplastic elastomer (A) is 20,000 to 200,000 in terms of absolute weight average molecular weight Mw(A). From the viewpoint of obtaining a molded article (buffer member) that combines high resilience and excellent flexibility, the absolute weight average molecular weight Mw(A) of the block copolymer is preferably 30,000 to 190,000, and more preferably 35,000 to 180,000. The absolute weight average molecular weight Mw(A) in the present invention refers to a value measured by gel permeation chromatography (GPC).

[0024] In the present invention, the hydrogenated conjugated diene block (a2) constituting the styrene-based thermoplastic elastomer (A) has a plurality of branched side chains. Specifically, for example, a styrene-ethylene-butylene-styrene block copolymer (SEBS) is a hydrogenated product of a styrene-butadiene-styrene copolymer (SBS). The conjugated diene block of SBS may contain, as structural units derived from butadiene, 1,2-bond units and 1,4-bond units, depending on the bonded carbon. Of these, the 1,2-bond units branch off from the main chain of the conjugated diene block and have a bulky carbon chain as a side chain. Therefore, the hydrogenated conjugated diene block (a2) of SEBS has ethyl groups derived from the 1,2-bond units as side chains branched off from the main chain. Furthermore, for example, styrene-ethylene-propylene-styrene block copolymer (SEPS) is a hydrogenated product of styrene-isoprene-styrene copolymer (SIS), and the conjugated diene block of SIS may contain, as structural units derived from isoprene, mainly 3,4-bond units and 1,4-bond units, depending on the carbon to which they are bonded. Of these, the 3,4-bond units branch off from the main chain of the conjugated diene block and have a particularly bulky carbon chain as a side chain. Therefore, the hydrogenated conjugated diene block (a2) of SEPS has an isopropyl group derived from the 3,4-bond unit as a side chain branched off from the main chain. Similarly, for example, in the case of a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), the hydrogenated conjugated diene block (a2) of SEEPS has an ethyl group derived from the 1,2-bond unit of butadiene and an isopropyl group derived from the 3,4-bond unit of isoprene as a side chain branched off from the main chain.

[0025] As described above, the styrene-based thermoplastic elastomer (A) used in the present invention has a plurality of branched side chains in its hydrogenated conjugated diene block (a2). In the present invention, it is important to adjust the branching degree Bn per molecule constituting the styrene-based thermoplastic elastomer (A) to 420 or less. The branching degree Bn is a value corresponding to the number of branched side chains per molecule of the polymer compound, and indicates the degree of branching structure of the polymer compound. In the present invention, by adjusting the branching degree Bn per molecule constituting the styrene-based thermoplastic elastomer (A) to 420 or less, a molded article (buffer member) that combines high resilience and excellent flexibility can be obtained.

[0026] The branching degree Bn of the styrene-based thermoplastic elastomer (A) in the present invention refers to a value calculated by the following formulas (1) to (3). In formula (1), η(A) is the intrinsic viscosity of the styrene-based thermoplastic elastomer (A). ０is the value of the intrinsic viscosity of the standard sample (S) at the same absolute weight average molecular weight as the absolute weight average molecular weight Mw(A) of the styrene-based thermoplastic elastomer (A), as determined from the approximate curve of the Mark-Houwink plot of the standard sample (S), which is obtained by plotting the logarithm of the absolute weight average molecular weight of the standard sample (S) on the horizontal axis and the logarithm of the intrinsic viscosity of the standard sample (S) on the vertical axis. Usually, when determining the degree of branching Bn of a polymer compound by the Mark-Houwink plot, linear polybutadiene is used as the standard sample. However, in the case of a styrene-based block copolymer composed of a styrene block (a1) and a hydrogenated conjugated diene block (a2) as used in the present invention, the intrinsic viscosity value is undesirably affected by the styrene block (a1). Furthermore, when polystyrene is used as the standard sample, its intrinsic viscosity η(A) becomes higher than that of polystyrene, making it impossible to calculate the degree of branching Bn using the following formulas (1) to (3). Therefore, in the present invention, instead of linear polybutadiene, SEBS, which has a small number of branches per molecule (i.e., a high intrinsic viscosity relative to the molecular weight) and a predetermined absolute weight-average molecular weight Mw and a predetermined intrinsic viscosity, is assumed to be a linear polymer and is used as the standard sample (S). Specifically, the standard sample (S) in the present invention is a styrene-ethylene-butylene-styrene block copolymer (SEBS) having a styrene content of 25% to 35% by mass, an absolute weight-average molecular weight Mw(S) of 24,000 to 26,000, and an intrinsic viscosity of 1.0 dL / g to 1.3 dL / g. By using the standard sample (S) having such a configuration, the branching degree Bn of the styrene-based thermoplastic elastomer (A) can be calculated.

[0027]

[0028] More specifically, the degree of branching Bn of the styrene-based thermoplastic elastomer (A) in the present invention is not particularly limited, but can be determined, for example, by the following procedure. First, the absolute weight-average molecular weight Mw(A) and its intrinsic viscosity η(A) of the styrene-based thermoplastic elastomer (A) are measured by GPC-LLS-RI-VIS analysis (gel permeation chromatography-laser light scattering-differential refractive index-viscosity analysis). On the other hand, the absolute weight-average molecular weight Mw and intrinsic viscosity η of a standard sample (S) are measured by GPC-LLS-RI-VIS analysis. A Mark-Houwink plot is then performed by plotting the logarithm of the absolute weight-average molecular weight Mw of the standard sample (S) on the horizontal axis and the logarithm of the intrinsic viscosity η at the absolute weight-average molecular weight Mw on the vertical axis to obtain an approximate curve represented by the approximate equation logη = logK + logMw, and the intercept logK and slope a of the approximate equation are determined. From this approximation, the absolute weight average molecular weight Mw(A) of the styrene-based thermoplastic elastomer (A) and the intrinsic viscosity η of the standard sample (S) at the same absolute weight average molecular weight can be calculated. ０ The obtained η(A) and η ０ The branching degree Bn of the styrene-based thermoplastic elastomer (A) is calculated from the formulas (1) to (3). In the present invention, it is particularly preferable that the standard sample (S) is an SEBS having an intercept of the approximation formula in the above-mentioned Mark-Houwink plot of -2.2 to -2.5 and a slope of 0.53 to 0.57.

[0029] In the present invention, the styrene content of the styrene-based block copolymer constituting the styrene-based thermoplastic elastomer (A) is preferably in the range of 10% by mass to 55% by mass, more preferably in the range of 11% by mass to 54% by mass, and even more preferably in the range of 12% by mass to 53% by mass. This makes it possible to obtain a molded article (a buffer member) that combines high resilience and excellent flexibility and also has excellent shock-absorbing properties. The styrene content of the styrene-based thermoplastic elastomer (A) in the present invention is determined in accordance with JIS K 6239-1:2017 Raw rubber - Determination of microstructure of solution-polymerized SBR (quantitative) - Part 1: １ According to H-NMR and IR (cast film) methods １ The value is determined by the H-NMR method (absolute method).

[0030] Next, the softener (B) constituting the thermoplastic elastomer composition will be described. Examples of softeners (B) that can be used in the present invention include process oils such as paraffinic oil, naphthenic oil, or aromatic oil; synthetic resin softeners such as liquid polybutene or low-molecular-weight polybutadiene; and rosin. Among these, paraffinic oil (hydrogenated paraffin) is preferred as the softener (B) from the viewpoint of maintaining the transparency of the molded article's appearance. Furthermore, from the viewpoint of improving the flexibility, high resilience, and cushioning properties of the molded article, the softener (B) preferably has an absolute weight-average molecular weight Mw of 300 to 1500, more preferably 350 to 1300, and particularly preferably 350 to 500. The softener (B) may be used alone or in combination with multiple softeners having different physical properties such as components and viscosity (molecular weight).

[0031] In the present invention, the blending ratio of the styrene-based thermoplastic elastomer (A) to the softener (B) is B / (A+B) = 0.30 to 0.90 by mass. From the viewpoint of realizing a molded article that combines higher resilience and excellent flexibility, and that does not cause oil bleeding and has an excellent appearance and feel, the blending ratio "B / (A+B)" is more preferably 0.60 to 0.85 by mass, and particularly preferably 0.60 to 0.80.

[0032] The thermoplastic elastomer composition of the present invention may contain an antioxidant from the viewpoint of improving weather resistance. By containing an antioxidant, oxidation of the thermoplastic elastomer composition and its molded article can be prevented, thereby improving weather resistance. Examples of antioxidants include hindered amine-based antioxidants and hindered phenol-based antioxidants that function as chain terminators, and phosphite-based antioxidants and thioether-based antioxidants that function as peroxide decomposers.The hindered amine antioxidant can be appropriately selected from known antioxidants, and examples thereof include N,N',N",N'"-tetrakis-(4,6-bis(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine, dibutylamine / 1,3,5-triazine / N,N'-bis-(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine / N-(2,2,6,6-tetramethyl-4 polycondensation polymer of {6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, [bis(2,2,6,6-tetramethyl-1(octyloxy)-4-piperidine)decanedioate] lysyl) ester, reaction products of 1,1-dimethylethyl hydroperoxide with octane (70%)]-polypropylene (30%), bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) tert-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dione, and the like.

[0033] The hindered phenol-based antioxidant may be appropriately selected from known ones, and examples thereof include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexane-1,6-diylbis[3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide], 2,4-dimethyl-6-(1-methylpentadecyl)phenol, diethyl[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphate, 3,3',3'',5,5',5''-hexa-tert-butyl-a,a' , a''-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octylthiomethyl)-o-cresol, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di- tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, 2-[1-(2-hydroxy-3,5-di-t-phenylpentyl)ethyl]-4,6-di-t-phenylpentyl acrylate, and the like.

[0034] The phosphite antioxidant can be appropriately selected from known ones, and examples thereof include triphenyl phosphite, tris(nonylphenyl) phosphite, dilauryl hydrogen phosphite, triethyl phosphite, tridecyl phosphite, tris(2-ethylhexyl) phosphite, tris(tridecyl) phosphite, tristearyl phosphite, diphenyl monodecyl phosphite, monophenyl didecyl phosphite, diphenyl mono(tridecyl) phosphite, tetraphenyl dipropylene glycol diphosphite, tetraphenyl tetra(tridecyl) pentaerythritol tetraphosphite, and hydrogenated bisphenol A. Phenol phosphite polymer, diphenyl hydrogen phosphite, 4,4'-butylidene-bis(3-methyl-6-tert-butylphenyl di(tridecyl)phosphite)tetra(tridecyl)4,4'-isopropylidene diphenyl diphosphite, bis(tridecyl)pentaerythritol diphosphite, bis(nonylphenyl)pentaerythritol diphosphite, dilauryl pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, tris(4-tert-butylphenyl)phosphite, tris(2,4-di-tert-butylphenyl)phosphite, hydrogenated bisphenol A Examples of the diphosphite include pentaerythritol phosphite polymer, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, 2,2'-methylenebis(4,6-di-tert-butylphenyl)octyl phosphite, and bis(2,4-dicumylphenyl)pentaerythritol diphosphite.

[0035] The thioether-based antioxidant can be appropriately selected from known ones, and examples thereof include pentaerythritol tetrakis(3-dodecylthiopropionate), didodecylthiodipropionate, ditridecylthiodipropionate, ditetradecylthiodipropionate, dioctadecylthiodipropionate, 2-mercaptobenzimidazole, and 2,4-bis[(dodecylthio)methyl]-6-methylphenol.

[0036] The antioxidants listed above can be used alone or in combination of two or more. When combining two or more types, the same or different components may be combined. Preferred combinations of different components include a hindered phenol-based antioxidant, a phosphite-based antioxidant, and a thioether-based antioxidant. More specifically, a more preferred combination is 2,2'-methylenebis(4,6-di-tert-butylphenyl)octyl phosphite as the phosphite-based antioxidant, 2-[1-(2-hydroxy-3,5-di-t-phenylpentyl)ethyl]-4,6-di-t-phenylpentyl acrylate as the hindered phenol-based antioxidant, and 2,4-bis[(dodecylthio)methyl]-6-methylphenol as the thioether-based antioxidant. The antioxidant is preferably added in an amount of 0.1 to 2 parts by mass, more preferably 0.5 to 1.5 parts by mass, per 100 parts by mass of the styrene-based thermoplastic elastomer (A). When a plurality of antioxidants are combined, the total addition ratio of the antioxidants is preferably within the above-mentioned range, and the addition ratio of each antioxidant is set within that range.

[0037] The thermoplastic elastomer composition of the present invention may also contain a light stabilizer from the viewpoint of improving weather resistance. By including a light stabilizer, photooxidative degradation of the thermoplastic elastomer composition and its molded article can be prevented, thereby improving weather resistance. Examples of light stabilizers include hindered amine light stabilizers (HALS), which have the effect of capturing and detoxifying radicals generated by photodegradation, and benzotriazole ultraviolet absorbers, which function as light resistance stabilizers by absorbing ultraviolet light to suppress photoinduced reactions that lead to photodegradation of polymers. These may be used alone or in combination. As the hindered amine light stabilizer, it is preferable to use a tertiary amine-containing hindered amine light stabilizer in order to improve the storage stability of the composition. Examples of the tertiary amine-containing hindered amine light stabilizer include TINUVIN 622LD, TINUVIN 144, TINUVIN 765, and CHIMASSORC119FL (all manufactured by BASF); MARK LA-57, LA-62, LA-67, and LA-63 (all manufactured by Asahi Denka Kogyo Co., Ltd.); and SANOL LS-765, LS-292, LS-2626, LS-1114, and LS-744 (all manufactured by Sankyo Co., Ltd.). Examples of the ultraviolet absorber include ultraviolet absorbers such as benzotriazole-based, triazine-based, benzophenone-based, and benzoate-based compounds.The ultraviolet absorber may be appropriately selected from known ones, and examples thereof include 2,4-di-tert-butyl-6-(5-chlorobenzotriazol-2-yl)phenol, 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, the reaction product of methyl 3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionate / polyethylene glycol 300, and the like. Examples of suitable hindered amine light stabilizers include benzotriazole-based ultraviolet absorbers such as 2-(2H-benzotriazol-2-yl)-6-(linear and branched chain dodecyl)-4-methylphenol, triazine-based ultraviolet absorbers such as 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]phenol, benzophenone-based ultraviolet absorbers such as octabenzone, and benzoate-based ultraviolet absorbers that also have a radical scavenging function such as 2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate. The hindered amine light stabilizer and ultraviolet absorber may be used alone or in combination. When a hindered amine light stabilizer and an ultraviolet absorber are used in combination, a combination of a hindered amine light stabilizer and a benzophenone-based ultraviolet absorber is preferred. The addition ratio of the light stabilizer is preferably 0.1 to 1.0 part by mass, more preferably 0.3 to 0.7 part by mass, per 100 parts by mass of the styrene-based thermoplastic elastomer (A). When a hindered amine-based light stabilizer and an ultraviolet absorber are used in combination, they may be combined in an appropriate ratio within the above range.

[0038] Furthermore, as one embodiment of the present invention, other additives may be added to the thermoplastic elastomer composition as long as the effects of the present invention are not impaired. Examples of additives include pigments, colorants, fillers, lubricants, and mold release agents. These may be used alone or in combination.

[0039] The thermoplastic elastomer composition according to the present invention can be produced by a known method for producing a thermoplastic elastomer composition. Specifically, for example, a melt mixer such as a single-screw extruder, a twin-screw extruder, a kneader, a Banbury mixer, or a heated roll is used to add blending components such as a styrene-based thermoplastic elastomer (A) and a softener (B), or blending components such as a styrene-based thermoplastic elastomer (A), a softener (B), an antioxidant and / or a light stabilizer, and various other components added as needed, in predetermined proportions, and then the blending components are heated and uniformly kneaded in a molten state. Furthermore, in order to improve the dispersibility of the styrene-based thermoplastic elastomer (A) and the softener (B), at least a portion of the softener (B) may be absorbed into the styrene-based thermoplastic elastomer (A) before melt mixing.

[0040] The thermoplastic elastomer composition obtained as described above may be pelletized or filamentized as necessary, and then molded into a predetermined shape by a known method such as injection molding, extrusion molding, blow molding, compression molding, calendar molding, or 3D modeling using a 3D printer, to obtain a molded article of the thermoplastic elastomer composition according to the present invention. The molded article of the thermoplastic elastomer composition according to the present invention preferably has a rebound resilience (ASTM D2632 standard) of 44% or more, more preferably 50% or more. Furthermore, the molded article preferably has an Asker C hardness (SRIS 0101 standard, 23±2°C) of 5 to 80, more preferably 5 to 50. Therefore, as a molded article that combines high rebound and excellent flexibility, it can be suitably used as a cushioning material for sports shoes and the like.

[0041] Furthermore, the molded article of the thermoplastic elastomer composition according to the present invention preferably has an impact acceleration G value of 15.0 G or less, more preferably 10.0 G or less. This impact acceleration G value is measured by a drop impact test in which an EVA sheet is laminated on a test stand to form an EVA layer with a thickness of 9 mm, a molded article sheet is laminated on this EVA layer to form a molded article layer with a thickness of 21 mm, and a 10 kg weight is dropped vertically onto the upper surface of the molded article layer from a height of 50 mm from the upper surface of the molded article layer. This results in a molded article that exhibits excellent shock-absorbing properties in addition to high resilience and excellent flexibility.

[0042] Furthermore, from the viewpoint of enhancing the designability of the appearance, it is also preferable that the molded article of the thermoplastic elastomer composition according to the present invention has transparency. Specifically, the haze value (according to JIS K7136:2000) is preferably 40% or less, more preferably 30% or less, and particularly preferably 15% or less. This results in a molded article with high external transparency that is suitable as a cushioning material to be used in a position visible from the outside.

[0043] The present invention will be specifically described below with reference to examples, but the present invention is not particularly limited to these examples.

[0044] The methods for measuring and evaluating the physical properties of the thermoplastic elastomer compositions prepared in the examples and comparative examples are as follows.

[0045] (1) Flexibility (Asker C Hardness) Each thermoplastic elastomer composition in the Examples and Comparative Examples was molded into a size of 60 mm length x 60 mm width x 3 mm thickness, and four of these were laminated in the thickness direction to form a layer thickness of 12 mm to prepare each test specimen. The Asker C hardness of each test specimen was measured using an Asker C durometer (SRIS 0101 standard) conforming to JIS K6253. Flexibility was evaluated as follows: an Asker C hardness of 5 to 50 was rated as excellent (◎); less than 5 or more than 50 but not more than 80 was rated as fair (◯); and more than 80 was rated as poor (×).

[0046] (2) Rebound (Rebound Elasticity) Each test specimen in the Examples and Comparative Examples was prepared by molding each thermoplastic elastomer composition into a size of 80 mm length x 80 mm width x 3 mm thickness, and then laminating four of these in the thickness direction to a layer thickness of 12 mm. To obtain a value for the rebound elasticity excluding the surface tack of the test specimen, an anti-blocking agent powder (product number: AS-300, manufactured by Nikkarico Co., Ltd.) was applied to the outermost surface of the test specimen. The rebound elasticity of each test specimen was measured in accordance with ASTM D2632 using a vertical drop rebound elasticity tester (product number: GT-7042-V, manufactured by GOTECH testing machines). Specifically, a 28 g (±0.5 g) weight was attached to the top of the tester, and the weight was allowed to freely drop onto the top of the test specimen from a height of 400 mm above the top surface of the test specimen. The maximum height of the top end of the rebound weight was read, and the rebound elasticity (%) was calculated using the following formula: The measurement was performed three times, and the average value was used as the rebound resilience of the test piece. Rebound resilience (%) = [maximum height of the rebound weight (mm) / drop height (400 mm)] x 100. The rebound resilience was evaluated as follows: a rebound resilience of 50% or more was rated as excellent (◎), a rebound resilience of 44% or more but less than 50% was rated as fair (○), and a rebound resilience of less than 44% was rated as poor (×).

[0047] (3) Cushioning (Impact Acceleration G) A specific method for testing cushioning (G value) will be described using FIG. 1 . FIG. 1 schematically illustrates the configuration of a test piece 30, which was specifically prepared as follows. First, three EVA sheets 21 made of ethylene-vinyl acetate copolymer, each 100 mm long, 100 mm wide, and 3 mm thick, were laminated in the thickness direction on the upper surface of the test stand 3 of a drop impact tester 1 (product number: ACST-200, manufactured by Shinyei Technology Co., Ltd.), to prepare an EVA layer 20 with a layer thickness of 9 mm. The EVA sheet 21 was prepared by crosslinking and foaming EV560 (a product of Dow Mitsui Polychemical Co., Ltd.) with ADCA and peroxide, and had a VA content of 14% by mass, an Asker C hardness of 55, a specific gravity of 0.29, and a rebound resilience of 45%. Seven molded body sheets 11, each of which was formed into a sheet shape measuring 80 mm long x 80 mm wide x 3 mm thick, were laminated on the EVA layer 20 in the thickness direction to produce a molded body layer 10 with a layer thickness of 21 mm. This resulted in a test piece 30 according to the example or comparative example with a total thickness of 30 mm. A drop impact test was performed by dropping a 10 kg weight 2 onto the upper surface of the molded body layer 10 of this test piece 30 from a height of 50 cm from the upper surface of the molded body layer 10, and the impact acceleration G value applied to each test piece was measured. The shock absorption performance was evaluated as follows: an impact acceleration of 10.0 G or less was rated as excellent (◎); an impact acceleration of more than 10.0 G but less than 15.0 G was rated as fair (○); and an impact acceleration of more than 15.0 G was rated as poor (×).

[0048] Tables 1 and 2 show the specifications of the materials used as components of the thermoplastic elastomer compositions prepared in the following Examples and Comparative Examples.

[0049]

[0050]

[0051] Among the measured values ​​for each material in Table 1, the styrene content was determined in accordance with JIS K 6239-1:2017 Raw rubber - Determination of microstructure of solution polymerized SBR (quantitative) - Part 1: １ According to H-NMR and IR (cast film) methods １Measurements were performed by H-NMR (absolute method) using deuterated chloroform as the measurement solvent at a measurement concentration of 10 mg / 0.7 mL using a Bruker AVANCE NEO 700 nuclear magnetic resonance (NMR) spectrometer.

[0052] Among the measured values ​​for each material in Table 1, the absolute weight-average molecular weight Mw and intrinsic viscosity η were measured in accordance with JIS K 7252-1:2016, "Method for Determining the Average Molecular Weight and Molecular Weight Distribution of Polymers by Plastic Size Exclusion Chromatography," as follows. First, 10 mg of a sample of each material was weighed out and dissolved in 10 mL of chloroform. The solution was then filtered through a membrane filter with a pore size of 0.2 μm to obtain a sample solution with a sample concentration of 1.0 mg / mL. The absolute weight-average molecular weight Mw and intrinsic viscosity η of each material were measured using a GPC-LLS-RI-VIS analysis method (gel permeation chromatography-laser light scattering-differential refractive index-viscosity analysis) using a multi-detector GPC / SEC system (product name: OMNISEC RESOLVE & REVEAL, manufactured by Spectris Inc.). The measurement conditions were as follows: Measurement temperature: 40°C, solvent: chloroform, flow rate: 0.6 mL / min, column: TSKgel Super HM-M, 6.0 mm x 150 mm, particle size: 3 μm (manufactured by Tosoh Corporation), two columns connected in series, detector: light scattering detector (7 degrees), viscosity detector (Wheatstone bridge type).

[0053] The branching degrees Bn of materials (A-1) to (A-14) related to the styrene-based thermoplastic elastomer (A) shown in Table 1 were calculated as follows. First, the absolute weight-average molecular weight Mw and its intrinsic viscosity η of the SEBS (Tuftec H1041, Asahi Kasei Corporation) used as the standard sample (S) were measured using the above-mentioned multi-detector GPC / SEC system (product name: OMNISEC RESOLVE & REVEAL, manufactured by Spectris Inc.). Using the software on this system, a Mark-Houwink plot was performed with the horizontal axis representing the logarithm of the absolute weight-average molecular weight Mw and the vertical axis representing the logarithm of the intrinsic viscosity η, and linear approximation was performed to obtain an approximation curve L1 for the standard sample (S). The approximation curve L1 was expressed by the approximation equation log[η] = log K + log Mw = -2.4 + 0.56 log Mw. Using this approximation curve L1, the absolute weight average molecular weight Mw(A) of each material (A-1) to (A-14) and the intrinsic viscosity value of the standard sample (S) at the same absolute weight average molecular weight are calculated as η ０ The intrinsic viscosity η(A) of each of the materials (A-1) to (A-14) and the degree of branching Bn of each of the materials (A-1) to (A-14) were calculated from the following formulas (1), (2), and (3).

[0054]

[0055] FIG. 2 shows an approximate curve L1 obtained by a Mark-Houwink plot of the standard sample (S), and plots of the absolute weight-average molecular weight Mw(A) and the intrinsic viscosity η(A) of materials (A-1) to (A-14) used as the styrene-based thermoplastic elastomer (A). The approximate line L2 shown on the graph in FIG. 2 is an approximate curve obtained by a Mark-Houwink plot of polystyrene. Normally, when determining the branching degree Bn of a polymer compound using a Mark-Houwink plot, linear polybutadiene is used as the standard sample. However, in the case of the styrene-based thermoplastic elastomer (A), the intrinsic viscosity value is disadvantageously affected by the styrene blocks constituting the styrene-based thermoplastic elastomer (A). On the other hand, when polystyrene is used as the standard sample, the intrinsic viscosities η(A) of the polymer materials (A-1) to (A-14) related to the styrene-based thermoplastic elastomer (A) are found to be higher than those of polystyrene, as shown in the graph in FIG. 2. Therefore, in the present invention, instead of linear polybutadiene, SEBS (Tuftec H1041, Asahi Kasei Corporation), which has a small number of branches per molecule and a predetermined absolute weight-average molecular weight Mw and a predetermined intrinsic viscosity, is assumed to be a linear polymer and used as the standard sample (S). The method for calculating the branching degree Bn of the standard sample (S) shown in Table 1 is the same as the method for calculating the branching degree Bn of materials (A-1) to (A-14), and the value of the intrinsic viscosity of the standard sample (S) at the same absolute weight-average molecular weight as the absolute weight-average molecular weight Mw(S) of the standard sample (S) is expressed as η ０ The degree of branching Bn was calculated from the intrinsic viscosity η(S) of the standard sample (S) and the following formulas (1) to (3).

[0056] Example 1 A thermoplastic elastomer composition of this example was prepared according to the following procedure, and various physical properties were measured and evaluated as described above. The blending ratios of the components of the thermoplastic elastomer compositions in this example and in each of the examples and comparative examples described below are shown in Tables 3 to 11 below. In this Example 1, the materials for each component shown in Tables 1 and 2 were used. As shown in the Example 1 column in Table 3, 15 parts by mass of a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) (A-1) having an absolute weight-average molecular weight Mw(A) of 58,000, a styrene content of 30% by mass, and a branching degree Bn of 66.0 as the styrene-based thermoplastic elastomer (A), and 85 parts by mass of paraffin oil (B-1) as the softener (B) were weighed out. The two were mixed at room temperature and then heated at 100°C for 12 hours to absorb and disperse the paraffin oil in the styrene-based thermoplastic elastomer. The above mixture was kneaded for 15 minutes in a batch-type twin-screw kneader (TD3-10MDX, manufactured by Toshin Corporation) at 130 to 170°C and 40 rpm to obtain the thermoplastic elastomer composition of Example 1. This composition was injection molded at 170 to 190°C or press molded at 130 to 150°C to obtain a sheet molded article, which was then cut into the desired test piece shape to obtain molded articles of the desired test piece shape used in the various evaluation tests described above. The obtained thermoplastic elastomer composition and its molded article were used to perform the various evaluation tests described above and evaluate various physical properties. The results of Example 1 are shown in Table 3.

[0057] [Examples 2 to 61] Furthermore, the thermoplastic elastomer compositions of each Example were obtained in the same manner as in Example 1, except that the constituent components, materials, and blending ratios of the styrene-based thermoplastic elastomer (A) and the softener (B) were changed as shown in Tables 3 to 9. As in Example 1, the obtained thermoplastic elastomer compositions and molded articles thereof were subjected to the various evaluation tests described above, and various physical properties were evaluated. The results of Examples 2 to 5 are shown in Table 3, the results of Examples 6 to 16 in Table 4, the results of Examples 17 to 25 in Table 5, the results of Examples 26 to 32 in Table 6, the results of Examples 33 to 41 in Table 7, the results of Examples 42 to 52 in Table 8, and the results of Examples 53 to 61 in Table 9.

[0058] [Comparative Examples 1 to 18] Furthermore, thermoplastic elastomer compositions of each comparative example were obtained in the same manner as in Example 1, except that the constituent components, materials, and blending ratios of the styrene-based thermoplastic elastomer (A) and the softener (B) were changed as shown in Tables 10 and 11. As in Example 1, the obtained thermoplastic elastomer compositions and molded articles thereof were subjected to the various evaluation tests described above, and various physical properties were evaluated. Note that oil bleeding occurred in the molded articles obtained from the thermoplastic elastomer compositions prepared in Comparative Examples 7 to 9. The results of Comparative Examples 1 to 9 are shown in Table 10, and the results of Comparative Examples 10 to 18 are shown in Table 11.

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068] The results of Examples 1 to 61 shown in Tables 3 to 9 and the results of Comparative Examples 1 to 18 shown in Tables 10 and 11 demonstrate that the configuration according to the present invention can provide a thermoplastic elastomer composition that combines high resilience and excellent flexibility and that can form molded articles with excellent cushioning properties. Specifically, the results of Examples 1 to 61 demonstrate that a thermoplastic elastomer composition that combines high resilience and excellent flexibility and that can form molded articles with excellent cushioning properties can be obtained by at least setting the absolute weight-average molecular weight Mw(A) of the styrene-based thermoplastic elastomer (A) constituting the thermoplastic elastomer composition to 36,000 to 175,000 and the degree of branching Bn to 420 or less, and setting the blending ratio of this styrene-based thermoplastic elastomer (A) to the softener (B) to a mass ratio of B / (A+B) = 0.30 to 0.85. Furthermore, it was shown that the styrene content of the styrene-based thermoplastic elastomer (A) is preferably in the range of at least 11.6% by mass to 53.1% by mass, and that within this range, the molded article exhibits both high resilience and excellent flexibility and also excellent cushioning properties. It was also shown that SEBS, SEPS, or SEEPS is suitable as the styrene-based thermoplastic elastomer (A), and that paraffin oil can be used as the softener (B), with a weight-average molecular weight Mw(B) of 400 to 1,200 being preferably used.

[0069] Furthermore, in this example and comparative examples, when the results of Examples 5, 11, 21, 24, 32, 35, 46, and 56, in which the blending ratio of the styrene-based thermoplastic elastomer (A) to the softener (B) "B / (A+B)" was 0.40, were compared with the results of Comparative Examples 12, 15, and 17, it was found that when a styrene-based thermoplastic elastomer (A) with a high branching degree Bn was used, the resilience was inferior. More specifically, when SIBS having a branching degree Bn of 474.8 or more and a highly branched structure was used as the styrene-based thermoplastic elastomer (A), the resilience of the molded article was reduced to less than 44%. On the other hand, it was revealed by the present invention that the use of a styrene-based thermoplastic elastomer (A) with a low branching degree Bn improved the resilience of the molded article, and a molded article that could achieve both high resilience and excellent flexibility could be obtained. Therefore, it has been found that it is preferable to select a styrene-based thermoplastic elastomer (A) having a branching degree Bn of 420 or less, more preferably a styrene-based thermoplastic elastomer having a branching degree Bn of 200 or less, and even more preferably a styrene-based thermoplastic elastomer having a branching degree Bn of 100 or less.

[0070] Furthermore, the results of Comparative Examples 1 to 6 show that when the blending ratio "B / (A+B)" of the styrene-based thermoplastic elastomer (A) to the softener (B) is 0.20 or less by mass, the rebound resilience is low at less than 44%, resulting in low rebound. In contrast, the results of Examples 41, 47, and 52 show that when the blending ratio "B / (A+B)" of the styrene-based thermoplastic elastomer (A) to the softener (B) is 0.30 or more, the rebound resilience is 44% or more and the Asker C hardness is 55 or less, thereby achieving both flexibility and rebound. On the other hand, the results of Comparative Examples 7 to 9 show that when the blending ratio "B / (A+B)" of the styrene-based thermoplastic elastomer (A) to the softener (B) is 0.92 or more by mass, the rebound resilience is low at less than 44%, resulting in low rebound, and oil bleeding occurred. In contrast, the results of Examples 17, 26 and 37 show that by setting the blending ratio "B / (A+B)" of the styrene thermoplastic elastomer (A) to the softener (B) at a mass ratio of 0.85 or less, the rebound resilience was 44% or more and the Asker C hardness was 10 or less, making it possible to achieve both flexibility and rebound properties. Note that none of the molded articles of the thermoplastic elastomer compositions according to the present invention in Examples 1 to 61 exhibited oil bleeding.

[0071] The present invention is not limited to the above-described embodiments or examples, and various modified design forms are also included in the technical scope within the scope that does not deviate from the gist of the invention described in the claims.

[0072] The thermoplastic elastomer composition of the present invention and a molded article thereof are mainly used as a shock-absorbing material mounted on the soles of footwear such as sports shoes, and are also useful in a wide range of fields in which high shock-absorbing properties are required since they combine flexibility and high resilience.

[0073] REFERENCE SIGNS LIST 1 Drop impact tester 2 Weight 3 Test stand 10 Molded body layer 11 Molded body sheet 20 EVA layer 21 EVA sheet 30 Test piece

Claims

1. A thermoplastic elastomer composition containing a styrene-based thermoplastic elastomer (A) and a softener (B), wherein the styrene-based thermoplastic elastomer (A) is a block copolymer composed of at least a styrene block (a1) and a hydrogenated conjugated diene block (a2), the absolute weight average molecular weight Mw(A) of the styrene-based thermoplastic elastomer (A) is 20,000 to 200,000, the hydrogenated conjugated diene block (a2) constituting the styrene-based thermoplastic elastomer (A) has a plurality of branched side chains, the degree of branching Bn per molecule constituting the styrene-based thermoplastic elastomer (A), calculated by the following formulas (1) to (3), is 420 or less, and the blending ratio of the styrene-based thermoplastic elastomer (A) to the softener (B) is, in mass ratio, B / (A+B) = 0.30 to 0.

90. (wherein, in formula (1), η(A) is the intrinsic viscosity of the styrene-based thermoplastic elastomer (A), and η ０ is the value of the intrinsic viscosity of the standard sample (S) at the same absolute weight average molecular weight as the absolute weight average molecular weight Mw(A) of the styrene-based thermoplastic elastomer (A), which is determined from an approximate curve of a Mark-Houwink plot of the standard sample (S), which is obtained by plotting the logarithm of the absolute weight average molecular weight of the standard sample (S) on the horizontal axis and the logarithm of the intrinsic viscosity of the standard sample (S) on the vertical axis, and the standard sample (S) is a styrene-ethylene-butylene-styrene block copolymer (SEBS) having a styrene content of 25% to 35% by mass, an absolute weight average molecular weight Mw(S) of 24,000 to 26,000, and an intrinsic viscosity of 1.0 dL / g to 1.3 dL / g.

2. The thermoplastic elastomer composition according to claim 1, characterized in that the styrene content of the styrene-based thermoplastic elastomer (A) is 10% by mass to 55% by mass.

3. The thermoplastic elastomer composition according to claim 1, characterized in that the blending ratio of the styrene-based thermoplastic elastomer (A) to the softener (B) is, in mass ratio, B / (A+B) = 0.60 to 0.

85.

4. The thermoplastic elastomer composition according to claim 1, wherein the styrene-based thermoplastic elastomer (A) is at least one block copolymer selected from the group consisting of styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

5. The thermoplastic elastomer composition according to claim 1, wherein the softener (B) is a paraffinic oil having a molecular weight of 300 to 1,500.

6. A molded article obtained by molding the thermoplastic elastomer composition according to any one of claims 1 to 5.

7. The molded article according to claim 6, characterized in that the molded article has a rebound resilience of 44% or more (ASTM D2632 standard) and an Asker C hardness of 5 to 80 (SRIS 0101 standard, 23±2°C).

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