THERMOPLASTIC ELASTOMER COMPOSITION AND POWDER AND MOLDED ARTICLE THEREOF

Abstract: A thermoplastic elastomer composition comprising (a) 100 wt. parts of a polyolefin resin, (b) 5 to 250 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units is at least 50 wt. %, and (c) 0 to 500 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units is less than 50 wt. %. This composition can provide a molded article which is hardly whitened when it is bent, and has good flexiblity.

Description: The present invention relates to a thermoplastic elastomer composition, and a powder and a molded article of the same. Sheet-form molded articles having complicated uneven decorations such as grains or stitches are used as skin materials of interior parts of automobiles. As such molded articles, molded articles of thermoplastic elastomers are proposed as substitutes for conventional molded articles of vinyl chloride resins (see, for example, JP-A-5-001183 and JP-A-5-005050) . EP-A-0 540 941 describes a multi-layer molded article comprising a skin layer and a thermoplastic resin layer, wherein said skin layer comprises a layer produced by powder molding a powder composition containing a certain thermoplastic elastomer (A) or a composite layer comprising said powder molded layer further backed with a foamed layer formed by powder molding, wherein (A) is a thermoplastic elastomer comprising a composition composed of an ethylene/α-olefin copolymer rubber and a polyolefin resin, or a thermoplastic elastomer comprising a partially crosslinked composition composed of an ethylene/α-olefin copolymer rubber and a polyolefin resin; said thermoplastic elastomer having a certain complex dynamic viscosity and a certain Newtonian viscosity index. EP-A-0 515 223 refers to an integrally molded composite article comprising (I) a nonfoam layer formed from (A) a thermoplastic elastomer powder composition and (II) a foamed layer formed from a foamable composition comprising (B) a thermoplastic synthetic resin powder, (C) a heat decomposable foaming agent, and optionally (D) a liquid coating agent, wherein (A) is a thermoplastic elastomer powder composition comprising an ethylene-α-olefin copolymer rubber and a polyolefin resin, which composition may be partially crosslinked and has a certain complex dynamic viscosity and a certain Newtonian viscosity index. The published PCT application WO-A-93/01236 discloses a thermoplastic elastomer composition comprising certain amounts of a) an olefinic thermoplastic elastomer comprising an α-monoolefin copolymer rubber and a crystalline polyolefin resin and b) an ethylene-α-olefin copolymer with a certain density and a certain Vicat softening point. However, the molded articles of thermoplastic elastomers have lower flexibility than those of vinyl chloride resins, and tend to be whitened when they are bent. Thus, the molded articles of the thermoplastic elastomers are easily whitened at bent portions when they are removed from a mold in the molding process for the production of molded articles or when they are preshaped before they are laminated onto substrates. Therefore, an object of the present invention is to provide molded articles of thermoplastic elastomers which are less whitened on bending. This object was achieved on the basis of the finding that a thermoplastic elastomer composition comprising a polyolefin resin and a specific ethylene-α-olefin copolymer rubber in a specific ratio can provide a molded article which is hardly whitened. According to a first aspect, the present invention provides a thermoplastic elastomer composition comprising (a) 100 wt. parts of a polyolefin resin, (b) 5 to 250 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 60 to 90 wt. %, and (c) 0 to 500 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 5 to 40 wt. %. According to a second aspect, the present invention provides a powder comprising the above thermoplastic elastomer composition and having a sphere-converted average particle size of 1.2 mm or less and a bulk specific gravity of at least 0.38. Such a powder is used in a powder molding method and can provide a molded article which has neither pinholes nor underfills and which has also good flexibility so that it is hardly whitened when it is bent. According to a third aspect, the present invention provides a molded article comprising the above thermoplastic elastomer composition. The molded article of the present invention is hardly whitened when it is bent. According to a forth aspect, the present invention provides a multilayer molded article comprising at least one layer formed from a thermoplastic elastomer composition of the invention. Preferably, the above multilayer molded article further comprises a core layer of a thermoplastic resin. Fig. 1 is a schematic view of a molding machine for powder molding, which comprises a container (2) for receiving the powder (3) of a thermoplastic elastomer composition, and a mold (1) for powder slush molding, Fig. 2 is a plane view on the mold surface side of a mold for powder slush molding, and Fig. 3 is a cross section of a molded article produced using the mold of Fig. 2. The thermoplastic elastomer composition of the present invention comprises (a) 100 wt. parts of a polyolefin resin, (b) 5 to 250 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 60 to 90 wt. %, and (c) 0 to 500 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 5 to 40 wt. %. The polyolefin resin (a) is at least one crystallizable resin selected from the group consisting of polymers and copolymers which comprise at least one olefin. Examples of the olefin are ones having 2 to 8 carbon atoms such as ethylene, propylene, 1-butene, 1-hexene, or 1-octene. Examples of the polyolefin resin are polyethylene, polypropylene, polybutene-1, copolymers of propylene and an α-olefin other than propylene (e.g. 1-butene). When the polyolefin resin (a) is a propylene-ethylene copolymer or a propylene-1-butene copolymer, the thermoplastic elastomer composition of the present invention can provide molded articles having excellent flexibility. Copolymers can be used, which are prepared by copolymerizing at least two monomers selected from the group consisting of ethylene and α-olefins having 3 to 8 carbon atoms in two or more polymerization steps. For example, a copolymer can be used, which is prepared by homopolymerizing propylene in the first step and copolymerizing propylene with ethylene or an α-olefin other than propylene in the second step. When a molded article is produced by a powder molding method using the powder of the thermoplastic elastomer composition of the present invention, the polyolefin resin (a) has a melt flow rate (MFR) of from 20 to 500 g/10 min., preferably from 50 to 300 g/10 min. when measured according to JIS K-7210 at 230°C under a load of 2.16 kgf, from the viewpoint of the strength of the produced molded articles. The ethylene-α-olefin copolymer rubber (b) is at least one rubber selected from ethylene-α-olefin copolymers in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 60 to 90 wt. %. Among them, amorphous ethylene-α-olefin copolymers are preferred. Examples of the α-olefin are those having 3 to 8 carbon atoms such as propylene, 1-butene, 1-hexene, or 1-octene . Among them, α-olefins having 4 to 8 carbon atoms, in particular, 4 to 6 carbon atoms are preferable. In a preferred embodiment, said ethylene-α-olefin copolymer rubber (b) is an ethylene-1-butene copolymer rubber or an ethylene-1-hexene copolymer rubber. The ethylene-α-olefin copolymer rubber (b) may further contain, as monomeric units, a non-conjugated diene having 5 to 12 carbon atoms such as dicyclopentadiene, 2-methyl-2,5-norbornadiene, 5-ethylidene-2-norbornene, 1,4-hexadiene, or 1,6-octadiene ; or aromatic vinyl compounds having 8 to 12 carbon atoms such as styrene, α-methylstyrene, 2,5-dimethylstyrene, or p-methylstyrene. The content of the α-olefin units can be calculated from absorbances at peaks assigned to the α-olefin units (for example, a peak due to the symmetric deformation vibration of terminal methyl groups of short-chain branches, or a peak due to the rocking vibration of methylene groups in the branches) which are measured by an infrared spectrophotometry. This measurement of the α-olefin unit content is described in, for example, (1) "POLYMER ANALYSIS HANDBOOK" (KOUBUNSHI BUNSEKI HANDOBUKKU), Chapter 2, Section 2.2, pages 587-591 (1995) (edited by the Japan Analytical Chemistry Society, published by KINOKUNIYA SHOTEN), and (2) "CHEMISTRY DOMAIN" (KAGAKU NO RYOIKI), Extra Issue No. 140 "INFRARED, RAMAN AND VIBRATION [II] Present Situation and Future Prospects, pages 73-81 (1983) (edited by Naomichi Tsuboi, et al., published by NANKODO). The ethylene-α-olefin copolymer rubber (b) can be prepared by polymerizing ethylene, α-olefin and other optional monomer using a metal complex as an polymerization initiator in the presence of a co-catalyst, as disclosed in JP-A-3-163088 and JP-A-5-194641. Examples of a co-catalyst are aluminum compounds such as methylaluminoxane, aluminum halides, aluminumalkyl halides, or trialkylaluminums ; and Lewis acids having a boron atom such as tris(pentafluorophenyl)borane, or triphenylcarbenium-tetrakis(pentafluorophenyl)borane. The co-catalysts may be used singly or in a combination of two or more compounds. Examples of the metal complex are zirconium complexes such as (tert.-butylamide)dimethyl(η 5 -cyclopentadienyl)silane-zirconium dichloride; and titanium complexes such as (tert.-butylamide)dimethyl(tetrametyl-η 5 -cyclopentadienyl)-silanetitanium dichloride, or (anilide) (dimethyl) (tetramethyl-η 5 -cyclopentadienyl)-silanetitanium dichloride. The metal complexes may be supported on a carrier such as alumina, magnesium chloride, or silica. Ethylene and an α-olefin are copolymerized usually in a solvent. Examples of the solvent are hydrocarbons such as hexane, heptane, toluene, ethylbenzene, or xylene. The copolymerization may be carried out in the atmosphere of an inert gas such as nitrogen, argon, or hydrogen, under atmospheric pressure or reduced pressure. A polymerization temperature is usually from -30 to +250°C. The amount of the ethylene-α-olefin copolymer rubber (b) in the thermoplastic elastomer composition of the present invention is from 5 to 250 wt. parts, preferably from 20 to 250 wt. parts, more preferably from 50 to 250 wt. parts, in particular from 80 to 220 wt. parts, per 100 wt. parts of the polyolefin resin (a). When the amount of the ethylene-α-olefin copolymer rubber (b) is less than 5 wt. parts, the obtained molded articles lose flexibility and remarkably tend to be whitened when they are bent. When the amount of the copolymer rubber (b) exceeds 250 wt. parts, the surfaces of the obtained molded articles tend to have large tackiness. The thermoplastic elastomer composition of the present invention may contain up to 500 wt. parts of the ethylene-α-olefin copolymer rubber (c) per 100 wt. parts of the polyolefin resin (a). When the ethylene-α-olefin copolymer rubber (c) is contained in the thermoplastic elastomer composition, the cold resistance (low-temperature impact resistance) of molded articles produced from such a composition can be improved. In one embodiment of the thermoplastic elastomer composition of the invention, the ethylene-α-olefin copolymer rubber (c) is an ethylene-α-olefin copolymer rubber or an ethylene-α-olefin-non-conjugated diene copolymer rubber which has an α-olefin unit content as calculated from the infrared absorbances at peaks assigned to the α-olefin units of 5 to 40 wt.-%. In a preferred embodiment The ethylene-α-olefin copolymer rubber (c) is at least one copolymer selected from the group consisting of amorphous ethylene-α-olefin copolymers and amorphous ethylene-α-olefin-non-conjugated diene copolymers, which have an α-olefin unit content as calculated from the infrared absorbances at peaks assigned to the α-olefin units of 5 to 40 wt. %. Preferable examples of the α-olefin are ones having 3 to 10 carbon atoms such as propylene, 1-butene, 3-methyl-pentene-1, 1-octene, or 1-decene. In particular, propylene and 1-butene are preferable. Preferable examples of the non-conjugated diene are dicyclopentadiene, 2-methyl-2,5-norbornadiene, ethylidenenorbornene, 1,4-hexadiene, cyclooctadiene, methylenenorbornene, or 1,6-octadiene. In particular, ethylidenenorbornene is preferable. Examples of the ethylene-α-olefin copolymer rubber (c) include ethylene-propylene copolymer rubbers, ethylene-1-butene copolymer rubbers, and ethylene-propylene-ethylidenenorbornene copolymer rubbers (EPDM). The thermoplastic elastomer composition of the present invention comprising EPDM can provide molded articles having excellent heat resistance and tensile properties. The content of α-olefin units in the ethylene-α-olefin copolymer rubber (c) is from 5 to 40 wt. %, preferably from 10 to 35 wt. %, while the content of ethylene units is usually from 60 to 95 wt. %, preferably from 65 to 90 wt. %. The contents of the olefin and ethylene units are measured by infrared spectrophotometry. When molded articles are produced by a powder molding method from the powder of the thermoplastic elastomer composition of the present invention, the ethylene-α-olefin copolymer rubber (c) preferably has a Mooney viscosity (ML 1+4 (100°)) of from 10 to 350, more preferably from 15 to 300, when measured according to ASTM D-927-57T at 100°C, from the viewpoint of the strength of the obtained molded articles. The amount of the ethylene-α-olefin copolymer rubber (c) in the thermoplastic elastomer composition of the present invention is usually from 0 to 500 wt. parts per 100 wt. parts of the polyolefin resin (a). The amount of the ethylene-α-olefin copolymer rubber (c) is preferably from 5 to 400 wt. parts, more preferably from 10 to 250 wt. parts, from the viewpoint of the cold resistance (low-temperature impact resistance). In the thermoplastic elastomer composition of the present invention, the polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c) may be crosslinked intermolecularly and/or intramolecularly. That is, the polyolefin resin (a) may be intermolecularly and/or intramolecularly crosslinked, the ethylene-α-olefin copolymer rubber (b) may be intermolecularly and/or intramolecularly crosslinked, or the ethylene-α-olefin copolymer rubber (c) may be intermolecularly and/or intramolecularly crosslinked. Furthermore, the polyolefin resin (a) and the ethylene-α-olefin copolymer rubber (b), or the polyolefin resin (a) and the ethylene-α-olefin copolymer rubber (c), or the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c) may be intermolecularly crosslinked. For example, the polyolefin resin (a) and/or the ethylene-α-olefin copolymer rubber (c) can be crosslinked by kneading them, and further dynamic crosslinking the kneaded mixture. The dynamic crosslinking of the kneaded mixture can be carried out by kneading the mixture and a crosslinking agent while heating. As a crosslinking agent, usually an organic peroxide such as 2,5-dimethyl-2,5-di(tert.-butylperoxy)hexane, and dicumyl-peroxide. may be used. The crosslinking agent is used in an amount of 1 wt. part or less, preferably from 0.1 to 0.8 wt. parts, more preferably from 0.2 to 0.6 wt. parts, per 100 wt. parts of the total amount of the polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c). In the case of the use of an organic peroxide as a crosslinking agent, a thermoplastic elastomer composition, which provides molded articles having good heat resistance, can be obtained, when the dynamic crosslinking is carried out in the presence of a crosslinking aid such as a bismaleimide compound. In this case, the amount of the organic peroxide is usually 0.8 wt. parts or less, preferably from 0.2 to 0.8 wt. parts, more preferably from 0.4 to 0.6 wt. parts, per 100 wt. parts of the total amount of the polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c). The amount of the crosslinking aid is usually 1.5 wt. parts or less, preferably from 0.2 to 1 wt. parts, more preferably from 0.4 to 0.8 wt. parts, per 100 wt. parts of the total amount of the polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c). The crosslinking aid is added to the composition prior to the addition of the crosslinking agent. In general, the crosslinking aid is added when the components (a), (b) and (c) are kneaded. The polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c) can be crosslinked by kneading these components, a crosslinking agent and an optional crosslinking aid with a single- or twin-screw extruder while heating. The dynamic crosslinking under the above conditions preferentially crosslinks intermolecularly and/or intramolecularly the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c), while the polyolefin resin (a) may be intermolecularly and/or intramolecularly crosslinked, or the polyolefin resin (a) and the ethylene-α-olefin copolymer rubber (b) may be intermolecularly crosslinked, or the polyolefin resin (a) and the ethylene-α-olefin copolymer rubber (c) may be intermolecularly crosslinked, or the ethylene-α-olefin copolymer rubber (b) and the ethylene-α-olefin copolymer rubber (c) may be intermolecularly crosslinked. The thermoplastic elastomer composition of the present invention can contain any types of crosslinked materials. The thermoplastic elastomer composition of the present invention may contain any additives in addition to the above main components. Examples of the additives are mineral oil-based softening agents such as paraffinic process oils, phenol-based, sulfite-based, phenylalkane-based, phosphite-based, amine-based or amide-based heat stabilizers, age resistors (antioxidants) , weather stabilizers, antistatic agents, metal soaps, lubricants such as waxes, internal mold release agents such as methylpolysiloxane, pigments, fillers, foaming agents, foaming aids, and foam stabilizers. Among them, the mineral oil-based softening agents are preferable, since they can improve the melt flowability of the thermoplastic elastomer composition of the present invention, and the thermoplastic elastomer composition containing such a softening agent can provide molded articles having good flexibility. When a mixture of the above ethylene-α-olefin copolymer rubber (c) and the mineral oil-based softening agent, that is, an oil-extended ethylene-α-olefin copolymer rubber, is used in the production process of the thermoplastic elastomer composition of the present invention, good processability can be attained in the kneading and dynamic crosslinking processes. The content of the mineral oil-based softening agent in the oil-extended ethylene-α-olefin copolymer rubber is usually 120 wt. parts or less, preferably from 30 to 120 wt. parts, per 100 wt. parts of the ethylene-α-olefin copolymer rubber (c). In another preferred embodiment the thermoplastic elastomer composition of the invention further comprises a foaming agent. The thermoplastic elastomer composition of the present invention may contain other polymer, insofar as the effects of the present invention are not impaired, and examples of the other polymer are elastomeric polymers such as natural rubbers, butyl rubbers, cycloroprene rubbers, acrylonitrile-butandiene rubbers, hydrogenated acrylonitrile-butadiene rubbers, and epichlorohydrin rubbers, acrylic rubbers ; ethylene-acrylic acid copolymers; ethylene-vinyl acetate copolymers and their saponified products; ethylene-methyl methacrylate copolymers; or ethylene-glycidyl methacrylate-vinyl acetate copolymers. The viscolasticity of the thermoplastic elastomer composition of the present invention may vary in a wide range in accordance with the molding conditions of the composition. When the thermoplastic elastomer composition of the present invention is used to prepare a powder which is used in the powder molding method and produced by a freeze-grinding method which will be explained below, the complex dynamic viscosity η*(1) of the composition measured at a frequency ω of 1 radian/sec. at 250°C is preferably 1.5 x 10 4 Pa.s (1.5 x 10 5 poises) or less, more preferably 5 x 10 2 Pa.s (5 x 10 3 poises) or less, in particular 3 x 10 2 Pa·s (3 x 10 3 poises) or less from the viewpoint of the molding processability of the composition. The lower limit of η* (1) of the composition is usually 10 Pa.s (1 x 10 2 poises) preferably 30 Pa.s (3 x 10 2 poises) more preferably 50 Pa.s (5 x 10 2 poises). Herein, a complex dynamic viscosity η*(ω) measured at a frequency ω and at 250°C is calculated from a storage viscoelasticity G' (ω) and a loss viscoelasticity G" (ω) according to the following formula (1): η*(ω) = (1/ω) [(G'(ω)) 2 + (G" (ω)) 2 ] 1/2 When η*(1) exceeds 1.5x10 4 Pa·S (1.5 x 10 5 poises), the thermoplastic elastomer composition has insufficient melt flowability, and the processability of the composition in the powder molding method tends to deteriorate. A Newtonian viscosity index n is 0.67 or less, preferably from 0.01 to 0.35, more preferably from 0.03 to 0.25 from the viewpoint of the mechanical strength of the molded articles. Here, a Newtonian viscosity index n is calculated from the above complex dynamic viscosity η*(1) and a complex dynamic viscosity η*(100) measured at a frequency ω of 100 radian/sec. at 250°C according to the following formula (2): n = [logη*(1) - logη*(100)]/2 When a thermoplastic elastomer composition is used in the production of a powder by a solvent-treating method, a strand cutting method or a die-face cutting method, which will be explained below, the complex dynamic viscosity η*(1) of the composition is preferably 5 x 10 4 poises or less, more preferably from 1 x 10 2 to 3 x 10 3 poises, in particular from 3 x 10 2 to 2 x 10 3 poises from the viewpoint of the processability of the thermoplastic elastomer composition. The Newtonian viscosity index n of such a thermoplastic elastomer composition is preferably 0.28 or less, more preferably from 0.01 to 0.25, in particular from 0.03 to 0.20, from the viewpoint of the mechanical strength of the produced molded articles. The thermoplastic elastomer composition of the present invention can be prepared by kneading the polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) and optionally the ethylene-α-olefin copolymer rubber (c). When the ethylene-α-olefin copolymer rubber (c) is used, firstly the polyolefin resin (a) and the ethylene-α-olefin copolymer rubber (c) are kneaded, and then the ethylene-α-olefin copolymer rubber (b) is added and further kneaded. Furthermore, the thermoplastic elastomer composition of the present invention, in which the polyolefin resin (a) and/or the ethylene-α-olefin copolymer rubber (c) are intermolecularly and/or intramolecularly crosslinked, is usually prepared by dynamic crosslinking the polyolefin resin (a) and the ethylene-α-olefin copolymer rubber (c), and then adding the ethylene-α-olefin copolymer rubber (b), followed by further kneading. Here, a single- or twin-screw extruder can be used to knead the ethylene-α-olefin copolymer rubber (b). Alternatively, the thermoplastic elastomer composition of the present invention can be prepared by dynamic crosslinking the mixture of the polyolefin resin (a), ethylene-α-olefin copolymer rubber (b) and ethylene-α-olefin copolymer rubber (c). The above methods provide the thermoplastic elastomer composition of the present invention in the form of a molten mixture. The optional additives can be compounded by the use of the polyolefin resin (a), the ethylene-α-olefin copolymer rubber (b) or the ethylene-α-olefin copolymer rubber (c) which contains such additives, or by compounding such additives to the mixture of the components (a), (b) and (c) in the course of kneading or dynamic crosslinking. The thermoplastic elastomer composition of the present invention can be processed in the form of molded articles having various sizes and forms by a variety of molding methods. Molded articles produced from the thermoplastic elastomer composition of the present invention is characterized in that they are hardly whitened when they are bent. For example, the thermoplastic elastomer composition of the present invention can be molded in various types of molded articles by press molding, injection molding or extrusion molding a melt, for example, the above molten mixture of the composition. The forms and sizes of molded articles are not limited. The thermoplastic elastomer composition of the present invention can be processed to obtain powders having various sizes and shapes, and such powders are used to produce molded articles such as sheets or films by powder molding methods. The above-described sphere-converted average particle size is preferably 1.2 mm or less, more preferably from 0.15 to 1.0 mm from the viewpoint of the easiness of fusion bonding of particles in the powder molding. When the particles are insufficiently fusion bonded, the molded articles are apt to have pinholes or underfills. The bulk specific gravity of the powder is preferably at least 0.38, more preferably from 0.38 to 0.65, in particular from 0.42 to 0.65 from the viewpoint of the easiness of adhesion of the powder to mold surfaces in the powder molding. When the powder is insufficiently adhered to the mold surfaces, the molded articles are apt to have pinholes or underfills. Herein, a sphere-converted average particle size means a diameter of a sphere having the same volume as the average volume of powder particles. The average volume (V) of powder particles is defined by the following formula: V = W/D in which W is the total weight of randomly sampled 100 particles of a thermoplastic elastomer composition powder, and D is a density of the thermoplastic elastomer composition. The bulk specific gravity of a powder is defined and measured according to JIS K-6721. In a preferred embodiment of the above described powder of the invention an α-olefin in the ethylene-α-olefin copolymer (b) contained in said thermoplastic elastomer composition is an α-olefin having 4 to 8 carbon atoms. More preferably, in the powder of the invention said ethylene-α-olefin copolymer rubber (b) contained in said thermoplastic elastomer composition is an ethylene-1-butene copolymer rubber or an ethylene-1-hexene copolymer rubber. Such a powder can be produced by various methods, which will be explained below. Freeze-grinding method: A thermoplastic elastomer composition is cooled to a temperature lower than its glass transition temperature (usually - 70°C or less, preferably -90°C or less) and then ground. Solvent-treating method: The powder of a thermoplastic elastomer composition, which is produced by the above freeze-grinding method, is stirred in a solvent having a low compatibility with the thermoplastic elastomer composition in the presence of a dispersant and an emulsifier at a temperature higher than the melting point of the thermoplastic elastomer composition, preferably a temperature 30 to 50°C higher than the melting point, and then cooled (see, for example, JP-A-62-280226). This method produces spherical particles. Strand cutting method: A molten thermoplastic elastomer composition is extruded through a die into an air to form strands, and then the strands are cooled and cut (see, for example, JP-A-50-149747). Die-face cutting method: A molten thermoplastic elastomer composition is extruded from a die into water, and cut. In the above solvent treating method, ethylene glycol, polyethylene glycol, or polypropylene glycol is used as a solvent in an amount of from 300 to 1,000 wt. parts, preferably from 400 to 800 wt. parts, per 100 wt. parts of the thermoplastic elastomer composition. As a dispersant, an ethylene-acrylic acid copolymer, anhydrous silicic acid, or titanium oxide is used in an amount of usually from 5 to 20 wt. parts, preferably from 10 to 15 wt. parts, per 100 wt. parts of the thermoplastic elastomer composition. As an emulsifier, polyoxyethylene sorbitan monolaurate, polyethylene glycol monolaurate, or sorbitan tristearate is used in an amount of usually from 3 to 15 wt. parts, preferably from 5 to 10 wt. parts, per 100 wt. parts of the thermoplastic elastomer composition. In the strand cutting method, a die opening has a diameter of usually from 0.1 to 3 mm, preferably from 0.2 to 2 mm. The discharged amount of the thermoplastic elastomer composition from each die opening is usually from 0.1 to 5 kg/hr., preferably from 0.5 to 3 kg/hr. The haul-off rate of a strand is usually from 1 to 100 m/min., preferably from 5 to 50 m/min. The cooled strand is cut in a length of usually 1.4 mm or less, preferably from 0.3 to 1.2 mm. In the die-face cutting method, a die opening has a diameter of usually from 0.1 to 3 mm, preferably from 0.2 to 2 mm. The discharged amount of the thermoplastic elastomer composition from each die opening is usually from 0.1 to 5 kg/hr., preferably from 0.5 to 3 kg/hr. The temperature of water is usually from 30 to 70°C, preferably from 40 to 60°C. The powder of the invention is preferably obtainable by a solvent-treating method, a strand cutting method or a die-face cutting method. The powders produced by the above solvent-treating method, strand-cutting method and die-face cutting method may be called "pellets". The powder of the thermoplastic elastomer composition can be used in various powder molding methods such as a powder slush molding method, a fluidized bed dipping method, an electrostatic coating method, a powder spray coating method, or a rotational powder molding. For example, the powder slush molding is carried out as follows: The powder of a thermoplastic elastomer composition is supplied on the mold surface of a mold which is heated at a temperature higher than the melt temperature of the thermoplastic elastomer composition, usually from 160 to 300°C, preferably from 210 to 270°C. The powder is heated on the mold surface for a certain period of time, and powder particles, at least the surfaces of which are molten, are allowed to fuse together. After the certain period of time, non-fused powder particles are recovered. If necessary, the mold carrying the fused thermoplastic elastomer composition is further heated. After that, the mold is cooled, and a formed sheet is removed from the mold. In such a method, the mold is heated by any method such as a gas heating furnace method, a heat transfer medium-circulation method, a dipping method in a heat transfer medium or hot fluidizing sand, or a radiofrequency induction heating method. A heating time to fuse together the particles of the thermoplastic elastomer composition is fitly selected according to the sizes, thickness and the like of desired molded articles. The molded articles of the present invention, which are produced from the thermoplastic elastomer composition of the present invention, have characteristics that they have good flexibility and are hardly whitened when they are bent. In one embodiment the above molded article is produced by press molding. In a another embodiment the molded article is obtainable by powder slush molding a powder of the invention. In a further embodiment the molded article is a foamed molded article. Foamed molded articles with good flexibility can be produced using the thermoplastic elastomer composition of the present invention which contains a foaming agent by various molding methods such as a powder molding method, a press molding method, an extrusion molding method, or an injection molding method. A foaming agent may be any conventional heat-decomposable foaming agent. Examples of such a heat-decomposable foaming agent are azo compounds such as azodicarbonamide, 2,2'-azobisisobutyronitrile, diazodiaminobenzene ; sulfonylhydrazide compounds such as benzenesulfonylhydrazide, benzene-1,3-sulfonylhydrazide, p-toluenesulfonylhydrazide; nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, N,N'-dinitroso-N,N'-dimethylterephthalamide ; azide compounds such as terephthalazide ; or carbonates such as sodium hydrogencarbonate, ammonium hydrogencarbonate, or ammonium carbonate. Among them, azodicarbonamide is preferably used. A foaming agent is compounded in the composition at a temperature of lower than the decomposition temperature of the foaming agent. The thermoplastic elastomer composition of the present invention may contain a foaming aid or a foam stabilizer together with a foaming agent. Alternatively, a foamed article can be produced by powder molding a mixture of a foaming agent and the powder of the thermoplastic elastomer composition of the present invention containing no foaming agent. A molded article produced from the thermoplastic elastomer composition of the present invention may be, for example, a two-layer molded article wherein a foamed layer is laminated. Such a two-layer molded article can be produced by a powder molding method which is disclosed in, for example, JP-A-5-473, or bonding a molded article of the thermoplastic elastomer composition of the present invention and a foamed molded article, which are separately produced, with an adhesive. In the case of the production by a powder molding method, the layer of the thermoplastic elastomer composition of the present invention containing no foaming agent is formed on a mold surface of a mold for powder molding according to the above-described method. Then, the powder of a composition containing a foaming agent and a thermoplastic resin (or a thermoplastic elastomer) on the layer of the thermoplastic elastomer composition, and the powder particles are fused together to form a new layer. After that, the layer of the composition containing the foaming agent is foamed to obtain a two-layer molded article. A composite molded article having a structure consisting of a non-foamed layer, a foamed layer and a non-foamed layer can be produced by an analogous method to the above method. In this case, two non-foamed layers may be the same or different. Foaming agents used in the production of such two-ply molded articles and composite molded articles may be the same heat-decomposable foaming agents as those used in the above. Examples of a thermoplastic resin or elastomer to be contained in the composition which contains a foaming agent are vinyl chloride resins, polyolefin resins, or olefinic thermoplastic elastomers. A polyethylene-based foamable composition, which is disclosed in JP-A-7-228720, may be used as the above-described composition containing a foaming agent. The above foamed layer may comprise a polyurethane foam. In this case, it is preferable to increase adhesion properties between the layer of the thermoplastic elastomer composition of the present invention and the polyurethane layer by pretreating the surface of the thermoplastic elastomer composition of the present invention with a primer such as chlorinated polyethylene, since the adhesion properties between the thermoplastic elastomer composition of the present invention and polyurethane are usually not good. The layer of a polyurethane foam can be formed by, for example, supplying a mixed liquid of a polyol, a polyisocyanate and a foaming agent between the molded article of the thermoplastic elastomer composition of the present invention and a resin core material which will be explained below, and foaming the mixed liquid. The molded article consisting of the thermoplastic elastomer composition of the present invention, or the composite molded article comprising the layer of the thermoplastic elastomer composition of the present invention and the foam layer can be used as a skin material for a resin molded article (a resin core material) to produce a multilayer molded article. For example, the sheet of the thermoplastic elastomer composition of the present invention (a skin material) is laminated on the resin core material to form a two-layer molded article. Furthermore, the two-layer molded article consisting of the layer of the thermoplastic elastomer composition of the present invention and the foam layer (a two-layer skin material) is laminated on a core material with the foam layer facing the core material to form a three-layer molded article. Examples of the resins which constitute the core materials are thermoplastic resins such as polyolefin (e.g. polyethylene, and polypropylene.), and ABS resins (e.g. acrylonitrile-butadiene-styrene copolymer resins). Among them, polyolefin resins such as polypropylene are preferable. The multilayer molded articles can be produced by supplying a molten resin on one side of a skin material and pressurizing them. The pressurization may be started after the completion of the resin supply. Alternatively, the pressurization may be started before the completion of the resin supply and continued after the completion of the resin supply. The pressurization may be effected by closing molds of a molding machine, or the supplying pressure of the resin. For the production of multilayer molded articles, molding methods such as injection molding, lowpressure injection molding, and low pressure compression molding, can be employed. For example, a molding machine comprising a pair of first and second molds which freely move between an open position and closed position relatively is used, and a skin material comprising the layer of the thermoplastic elastomer composition of the present invention is supplied into between the first and second molds which are in the open position. Then, a molten resin is supplied in-between the skin material and one of the molds. After or during the supply of the resin, the first and second molds are relatively moved to pressurize the skin material and resin to produce a multilayer molded article. When a skin material comprising the layer of the thermoplastic elastomer composition of the present invention and a foam layer is used in the above production method, a molten resin is supplied in-between the foam layer of the skin material and the mold which faces the foam layer. In the above production method, a molten resin can be supplied through a resin conduit which is provided in the wall of one mold. Alternatively, a resin supplying nozzle of a resin supplying apparatus, which is placed outside a molding machine, is inserted in a skin material and one mold, and a molten resin is supplied through the nozzle. Then, the nozzle is pulled back from the molds. The moving directions of the first and second molds are not limited. They can be moved vertically or horizontally. The above-described methods are more preferable than an injection molding method in which a molten thermoplastic resin is supplied in-between the first and second molds which are in the closed position, since the former methods can prevent the displacement of a skin material and also avoid the damage of a skin material in comparison with the injection molding method. When a skin material which is produced by the above-mentioned powder molding method is used, a mold used in the powder molding method can be used as a mold for the production of a multilayer molded article. In such as case, a mold for powder molding, which carries a skin material formed by the powder molding method on the mold surface, is attached to the above first mold. Then, the same steps as those described above are carried out to produce a multilayer molded article. This method can produce multilayer molded articles without damaging decorations which have been formed on the surface of the skin material by the powder molding. The above pair of molds may be, for example, a pair of male and female mold halves which can move with the outer peripheral surface of the first mold half and the inner wall surface of the second mold half being in slidingly contact each other. In this case, when a clearance between the above outer peripheral surface and the above inner wall surface is substantially the same as the thickness of a skin material, a multilayer molded article having the marginal portion of the skin material around the article edges can be produced. When the marginal portion of the skin material is folded back onto the back side of the multilayer molded article, the molded article the edges of which are covered with the skin material can be obtained. The thermoplastic elastomer composition of the present invention can provide molded articles which have excellent flexibility and are not easily whitened when they are bent. EXAMPLES The present invention will be explained in more detail by the following examples, which do not limit the scope of the invention in any way. Evaluation methods [1] Complex dynamic viscosity η*(1) A storage viscoelasticity G'(1) and a loss viscoelasticity G"(1) of a sample were measured using a dynamic analyzer (RDS-7700 manufactured by Rheometrix) with a parallel plate mode, at an applied strain of 5 %, a sample temperature of 250°C and a frequency ω of 1 radian/sec., and η*(1) was calculated from the measured storage and loss viscoelasticities according to the above formula (1). [2] Newtonian viscosity index n η*(100) was measured with the same sample as that used in the measurement of η*(1) in the same manner as in the measurement of η*(1) except that a frequency ω applied in the measurement of storage and loss viscoelasticities was changed to 100 radian/sec. Then, a Newtonian viscosity index n was calculated from the calculated η*(1) and η*(100) according to the above formula (2). [3] Content of 1-butene units in ethylene-1-butene copolymers (1) Construction of a calibration curve Each of five mixtures of an ethylene-propylene copolymer (containing 73 wt. % of ethylene units) and polybutene-1 in given ratios was heat pressed at 150°C to form a film having a thickness of 0.05mm. With each film, an absorbance ratio of a peak assigned to the ethylene units (wave number of 720cm -1 ) to a peak assigned to the 1-butene units (wave number of 772cm -1 ) was measured using an infrared spectrometer, and ratios of the 1-butene unit content to the total content of the ethylene and 1-butene units of the five mixtures were plotted in a graph with such ratios on the abscissa and the absorbance ratios on the ordinate, and a calibration curve was drawn. The mixtures of the ethylene-propylene copolymer and polybutene-1 were prepared by dissolving both polymers in toluene in a single vessel, adding methanol to the solution to precipitate the polymers, recovering the precipitated polymer mixture and then drying it. (2) Measurement of a 1-butene unit content An ethylene-1-butene copolymer rubber was heated to a temperature higher than its melting point and pressed to form a film having a thickness of 0.05 mm. With this film, an absorbance ratio of a peak assigned to the ethylene units to a peak assigned to the 1-butene units was measured using an infrared spectrometer, and a 1-butene unit content in the ethylene-1-butene copolymer rubber was read from the calibration curve. [4] Content of 1-hexene units in an ethylene-1-hexene copolymer rubber An ethylene-1-hexene copolymer rubber was heat pressed at 150°C to form a film having a thickness of 0.05 mm. With this film, an absorbance at a peak assigned to the terminal methyl groups on the n-butyl branches in the 1-hexene units was measured using an infrared spectrometer, and then a ratio of the number of the terminal methyl groups on the n-butyl branches to the number of carbon atoms in the backbone of the ethylene-1-hexene copolymer rubber, that is, the degree of branching, was calculated. From this degree of branching, the number of branched monomer units and the number of unbranched monomer units were calculated, and then a 1-hexene unit content (wt. %) was calculated from these numbers. A degree of branching was calculated according to the following formula: Degree of branching (%) = [(f x A)/(t x d)] x 100 wherein f is a coefficient (0.070 cm 2 /g), A is an absorbance, t is a film thickness (cm), and d is the density (g/cm 3 ) of an ethylene-1-hexene copolymer rubber. The coefficient f is cited from Usami, Takayama, et al. op . cit . [5] Sphere-converted average particle size of a thermoplastic elastomer composition One hundred particles of a thermoplastic elastomer composition were randomly sampled and their total weight was weighed. Then, an average volume per one particle was calculated from the total weight and the specific gravity of the thermoplastic elastomer composition, and a diameter of a sphere having the same volume as the average volume was calculated, and used as the sphere-converted average particle size of the powder of the thermoplastic elastomer composition. [6] Bulk specific gravity of powder of a thermoplastic elastomer composition The bulk specific gravity of the powder of a thermoplastic elastomer composition was measured according to JIS K-6721. [7] Appearance of a molded article With an obtained molded article, the presence of pinholes and underfills was visually observed at edges of projections A (height: 7 mm, width: 5 mm), B (height: 11 mm, width: 25 mm) and C (height: 15 mm, width: 25 mm) shown in Fig. 3, and evaluated according to the following criteria: ++: Neither pinholes nor underfills were observed on any edges of the projections A, B and C. +: Neither pinholes nor underfills were observed on any edges of the projections A and B, but pinholes or underfills were observed on the edges of the projection C. -: Neither pinholes nor underfills were observed on any edges of the projection A, but pinholes or underfills were observed on the edges of the projections B and C. --: Pinholes or underfills were observed on all the edges of the projections A, B and C. [8] Whitening in the bending test of a molded article A molded article was bent along its center line, and a load of 4,90N (500 gf) or 9,81N (1 kgf) was applied to the bent article for one minute. Then, the load was removed, and the whitened state of the bent portion of the molded article was visually observed and evaluated according to the following criteria: +: Whitening was scarcely observed. : Whitening was slightly observed. --: Remarkable whitening was observed. [9] Hardness of a molded article A molded article was cut into pieces each having sizes of 1 cm x 5 cm, and ten pieces were laminated. Then, Shore A hardness of the laminate was measured with a durometer-Shore A hardness meter. Reference Example 1 An oil extended EPDM (ESPRENE® E670F manufactured by Sumitomo Chemical Co., Ltd.) (50 wt. parts), which comprises EPDM (content of propylene units = 28 wt. %; iodine value = 12; ML 1+4 (100°C) = 242) and a mineral oil-based softener (DIANA PROCESS PW-380 manufactured by IDEMITSU KOSAN Co., Ltd.) in a weight ratio of 1:1 and has ML 1+4 (100°C) of 53, a propylene-ethylene random copolymer resin (content of ethylene units = 5 wt. %; MFR = 90 g/10 min.) (50 wt. part), and a crosslinking aid (SUMIFINE® BM, a bismaleimide compound manufactured by Sumitomo Chemical Co., Ltd.) (0.4 wt. part) were kneaded with a Banbury mixer for 10 minutes, and pelletized with an extruder and a pelletizer to obtain pellets having a diameter of 3 mm and a length of 6 mm. The pellets (100 wt. parts) and 2,3-dimethyl-2,5-di(tert.-butylperoxyno)hexane (SUNPEROX APO manufactured by SANKEN KAKO KABUSHIKIKAISHA) (0.1 wt. part) were kneaded and dynamic crosslinked at 230°C with a twin-screw extruder to obtain a composition having η* (1) of 5.2 x 10 2 Pa·s (5.2 x 10 3 poises)and n of 0.31. Then, the composition was extruded from the twin-screw extruder and pelletized with a pelletizer to obtain pellets having a diameter of 3 mm and a length of 6 mm. Reference Example 2 Absolute toluene (1 liter) was charged in a 2 liter separable flask which had been filled with nitrogen gas. Then, the flask was heated to 30°C while supplying a mixed gas of ethylene and 1-butene into the flask at an ethylene supply rate of 9 NL/min. and a 1-butene supply rate of 2.5 NL/min. After that, triisobutyl aluminum (0.25 g, 1.25 mmol) was added at 30°C while supplying the above mixed gas and stirring, and then (tert.-butylamide)dimethyl(tetramethyl-η 5 -cyclopentadienyl)silanetitanium dichloride (0.018 g, 0.005 mmol) , which had been prepared according to the disclosure of JP-A-3-163088, was added. The obtained mixture was stirred at 30°C for 15 minutes while supplying the above mixed gas, and then triphenylcarbenium-tetrakis(pentafluorophenyl)borane (0.0023 g, 0.025 mmol) was added, followed by further stirring at 30°C for 30 minutes while supplying the above mixed gas. Thereafter, methanol (20 ml) was added to terminate the polymerization, and the obtained mixture was poured into methanol (10 liters). The precipitate was collected by filtration and dried at 80°C for 12 hours under reduced pressure to obtain an ethylene-1-butene copolymer rubber (156 g). The results of the evaluation of this ethylene-1-butene copolymer rubber are shown in Table 1. Reference Examples 3-6 An ethylene-1-butene copolymer rubber was prepared in the same manner as in Reference Example 2 except that a supply rate of 1-butene gas, a polymerization temperature and a polymerization time were changed as shown in Table 1. The results of the evaluation of each ethylene-1-butene copolymer rubber are shown in Table 1. Reference Example 7 Absolute toluene (1 liter) was charged in a 2 liter separable flask which had been filled with nitrogen gas, and an ethylene gas under atmospheric pressure was supplied at a rate of 2 NL/min. while maintaining the content in the flask at 0°C. Then, 1-hexene (126.2 g, 1.5 mol) and triisobutyl aluminum (0.25 g, 1.25 mmol) were added to the mixture, and further (tert.-butylamide)dimethyl(tetramethyl-η 5 -cyclopentadienyl)silanetitanium dichloride (0.018 g, 0.005 mmol), which had been prepared according to the disclosure of JP-A-3-163088, was added, while stirring at 0°C. After that, triphenylcarbeniumtetrakis(pentafluorophenyl)borane (0.0023 g, 0.025 mmol) was added, followed by further stirring at 0°C for 5 minutes while supplying the ethylene gas. Thereafter, methanol (20 ml) was added to terminate the polymerization, and the obtained mixture was poured into methanol (10 liters). The precipitate was collected by filtration and dried at 80°C for 12 hours under reduced pressure to obtain an ethylene-1-hexene copolymer rubber (119 g). The results of the evaluation of this ethylene-1-butene copolymer rubber are shown in Table 1. Ref. Ex. 2 Ref. Ex. 3 Ref. Ex. 4 Ref. Ex. 5 Ref. Ex. 6 Ref. Ex. 7 Supply rate of 1-butene (NL/min.) 2.5 3.2 4.5 1.8 1.4 --- Polymerization temp. (°C) 30 28 24 36 36 0 Polymerization time (min.) 30 30 30 30 30 5 1-Butene unit content (wt. %) 60 71 88 40 46 0 1-Hexene unit content (wt. %) 0 0 0 0 0 70 η*(1) (poises) 1.2x10 4 2.2x10 3 1.3x10 3 7.4x10 3 5.1x10 3 2x10 2 n 0.30 0.20 0.20 0.30 0.22 0.05 (1 poise = 10 -1 Pa·s) Example 1 The composition prepared in Reference Example 1 (100 wt. parts) and the ethylene-1-butene copolymer rubber prepared in Reference Example 2 (5 wt. parts) were kneaded with a twin-screw kneader at 190°C to obtain the molten mixture of a thermoplastic elastomer composition. The molten mixture was press molded to obtain a sheet having a thickness of 1 mm. The results of the evaluation of the thermoplastic elastomer composition which was molded, and the produced sheet are shown in Table 2. Example 2 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 1 except that the amount of the ethylene-1-butene copolymer rubber was changed to 10 wt. parts. The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Example 3 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 1 except that the amount of the ethylene-1-butene copolymer rubber was changed to 20 wt. parts. The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Example 4 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 1 except that the ethylene-1-butene copolymer rubber prepared in Reference Example 3 (10 wt. parts) was used in place of the ethylene-1-butene copolymer rubber which was prepared in Reference Example 2 (5 wt. parts). The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Example 5 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 4 except that the amount of the ethylene-1-butene copolymer rubber prepared in Reference Example 3 was changed to 20 wt. parts. The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Example 6 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 1 except that the ethylene-1-butene copolymer rubber prepared in Reference Example 4 (10 wt. parts) was used in place of the ethylene-1-butene copolymer rubber which was prepared in Reference Example 2 (5 wt. parts). The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Example 7 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 6 except that the amount of the ethylene-1-butene copolymer rubber prepared in Reference Example 4 was changed to 20 wt. parts. The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Comparative Example 1 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 1 except that the ethylene-1-butene copolymer rubber prepared in Reference Example 5 (10 wt. parts) was used in place of the ethylene-1-butene copolymer rubber which was prepared in Reference Example 2 (5 wt. parts). The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Comparative Example 2 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 1 except that the ethylene-1-butene copolymer rubber prepared in Reference Example 6 (10 wt. parts) was used in place of the ethylene-1-butene copolymer rubber which was prepared in Reference Example 2 (5 wt. parts). The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Comparative Example 3 A thermoplastic elastomer composition and a sheet were produced in the same manner as in Example 6 except that the ethylene-1-butene copolymer rubber prepared in Reference Example 6 (20 wt. parts) was used. The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Example 8 A propylene-ethylene random copolymer resin (ethylene unit content = 4.5 wt. %, MFR = 228 g/10 min.) (66.7 wt. parts) and an ethylene-propylene copolymer rubber (ESPRENE® V0141 manufactured by Sumitomo Chemical Co., Ltd.; propylene unit content = 27 wt. %, MFR = 0.7 g/10 min.) (33.3 wt. parts) were kneaded with a twin-screw kneader at a shear rate of 1.2 x 10 3 sec. -1 at 220°C to obtain a composition having η*(1) of 1.8 x 10 2 Pa·s (1.8 x 10 3 poises) and n of 0.12. The obtained composition (100 wt. parts) and the ethylene-1-butene copolymer rubber prepared in Reference Example 3 (66.7 wt. parts) were kneaded with a twin-screw kneader at 190°C to obtain a molten thermoplastic elastomer composition. Then, the composition was press molded to obtain a sheet having a thickness of 1 mm. The results of the evaluation of the thermoplastic elastomer composition, and the produced sheet are shown in Table 2. Ethylene-1-butene copolymer rubber Thermoplastic elastomer composition Whitening in the bending test of molded article 1-Butene unit content (wt. %) Amount ) (wt. parts) η n 4.90 N 500 kgf 9.81 N 1 kgf Ex. 1 60 10 3.1x10 3 0.21 - + Ex. 2 60 20 3.0x10 3 0.21 - + Ex. 3 60 40 3.1x10 3 0.21 + + Ex. 4 71 20 4.3x10 3 0.27 + + Ex. 5 71 40 2.1x10 3 0.17 + + Ex. 6 88 20 3.0x10 3 0.24 + + Ex. 7 88 40 3.0x10 3 0.24 + + C. Ex. 1 40 20 1.3x10 4 0.45 -- -- C. Ex. 2 46 20 1.0x10 4 0.40 -- -- C. Ex. 3 46 40 1.2x10 4 0.45 -- -- Ex. 8 71 100 1.9x10 3 0.14 + + Example 9 A molten thermoplastic elastomer composition was prepared in the same manner as in Example 3, and pelletized with a pelletizer to obtain pellets having a diameter of 3 mm and a length of 6 mm. The pellets were cooled to -120°C and comminuted with a freeze-grinder to obtain the powder of the thermoplastic elastomer composition. The powder had a sphere-converted average particle size of 0.20 mm, and a bulk specific gravity of 0.32. A nickel-electroformed mold (30 mm x 30 mm, thickness of 3 mm) having a grain pattern on a mold surface was heated at 250°C, and the above powder (1 kg) was poured onto the mold surface. After 14 seconds, unfused powder was removed, and the mold carrying the fused thermoplastic elastomer composition was heated in a heating furnace kept at 250° for 60 seconds. Then, the mold was pulled out from the heater and cooled, and the shaped molded article was removed from the mold. The molded article had a uniform thickness and no pinholes. The results of the evaluation of the molded article are shown in Table 3. Example 10 A thermoplastic elastomer composition and a sheet were produced in the same manners as in Example 9 except that the etylene-1-hexene copolymer rubber prepared in Reference Example 7 was used in place of the ethylene-1-butene copolymer rubber prepared in Reference Example 2. The results of the evaluation of the thermoplastic elastomer composition and the sheet are shown in Table 3. The thermoplastic elastomer composition had η*(1) of 1.2 x 10 2 Pa·s (1.2 x 10 3 poises) and n of 0.15. Ethylene-α-olefin copolymer rubber Whitening in the bending test of molded article α-olefin α-olefin unit content (wt. %) Amount (wt. parts) 4.90 N 500 gf 9.81N 1 kgf Ex. 9 1-Butene 60 40 + + Ex. 10 1-Hexene 70 40 + + Example 11 A propylene-ethylene random copolymer resin (ethylene unit content = 4.5 wt. %, MFR = 228 g/10 min.) (100 wt. parts) and an ethylene-1-butene copolymer rubber (1-butene unit content = 71 wt. %, η*(1) = 2.2 x 10 2 Pa·s (2.2 x 10 3 poises), n = 0.2) (50 wt. parts) were kneaded with a twin-screw kneader at 190°C to obtain a thermoplastic elastomer composition having η*(1) or 1.4 x 10 2 Pa·s (1.4 x 10 3 poises) and n of 0.13. This composition was cooled to -100°C with liquid nitrogen, and comminuted with a freeze-grinder to obtain the powder of the thermoplastic elastomer composition. The powder had a sphere-converted average particle size of 0.20 mm, and a bulk specific gravity of 0.33. A nickel-electroformed mold (30 mm x 30 mm, thickness of 3 mm) having a grain pattern on a mold surface was heated at 250°C, and the above powder (1 kg) was poured onto the mold surface. After 14 seconds, unfused powder was removed, and the mold carrying the fused thermoplastic elastomer composition was heated in a heating furnace kept at 250° for 60 seconds. Then, the mold was pulled out from the heater and cooled, and the shaped molded article was removed from the mold. The results of the evaluation of the molded article are shown in Table 4. Example 12 A thermoplastic elastomer composition having η*(1) of 5 x 10 2 Pa·s (5 x 10 3 poises) and n of 0.18 was prepared in the same manner as in Example 11 except that 200 wt. parts of the ethylene-1-butene copolymer rubber was used. The powder of this composition was prepared and then a molded article was produced in the same manners as in Example 11. The results of the evaluation of the molded article are shown in Table 4. Example 13 A thermoplastic elastomer composition having η*(1) of 3 x 10 2 Pa·s (3 x 10 3 poises) and n of 0.04 was prepared in the same manner as in Example 11 except that 100 wt. parts of an ethylene-1-hexene copolymer rubber (1-hexene unit content = 70 wt. %, η*(1) =20 Pa·s (2 x 10 2 poises), n = 0.03) was used. The powder of this composition was prepared and then a molded article was produced in the same manners as in Example 11. The results of the evaluation of the molded article are shown in Table 4. Comparative Example 4 An oil extended EPDM (ESPRENE® E670F manufactured by Sumitomo Chemical Co., Ltd.) (50 wt. parts), which comprises EPDM (content of propylene units = 28 wt. %; iodine value = 12; ML 1+4 (100°C) = 242) and a mineral oil-based softener (DIANAPROCESS PW-380 manufactured by IDEMITSU KOSAN Co., Ltd.) in a weight ratio of 1:1 and has ML 1+4 (100°C) of 53, a propylene-ethylene random copolymer resin (content of ethylene units = 4.5 wt. %; MFR = 90 g/10 min.) (50 wt. part), and a crosslinking aid (SUMIFINE® BM, a bismaleimide compound manufactured by Sumitomo Chemical Co., Ltd.) (0.6 wt. part) were kneaded with a Banbury mixer for 10 minutes, and pelletized with an extruder and a pelletizer to obtain pellets having a diameter of 3 mm and a length of 6 mm). The pellets (100 wt. parts) and 2,3-dimethyl-2,5-di(tert.-butylperoxyno)hexane (SUNPEROX APO manufactured by SANKEN KAKO KABUSHIKIKAISHA) (0.4 wt. part) were kneaded and dynamic crosslinked at 200°C and a shear rate of 1.2 x 10 3 sec. -1 with a twin-screw extruder to obtain a composition having η*(1) of 1.5x10 2 Pa·s (1.5 x 10 3 poises)and n of 0.25. Then, the composition was cooled to -120°C with liquid nitrogen, and comminuted with a freeze-grinder to obtain a powder having a sphere-converted average particle size of 0.20 mm and a bulk specific gravity of 0.30. A molded article was produced in the same manner as in Example 11 except that the above obtained powder was used. The results of the evaluation of the molded article are shown in Table 4. Whitening in the bending test of molded article Shore A hardness of molded article 500 gf 1 kgf Ex. 11 + + 90 Ex. 12 + + 81 Ex. 13 + + 81 C. Ex. 4 -- -- 92 Example 14 <Preparation of the powder of a thermoplastic elastomer composition> The pellets of a composition which was prepared in the same manner as in Comparative Example 4 (100 wt. parts) and an ethylene-1-butene copolymer rubber (1-butene unit content = 71 wt. %, η*(1) = 2.2 x 10 2 Pa·s (2.2 x 10 3 poises), n= 0.2) (10 wt. parts) were supplied in an extruder having a diameter of 30 mm and kneaded at 160°C. The formed thermoplastic elastomer composition was extruded through a die having a discharging opening diameter of 1.0 mm at a discharging rate of 1 kg/hr. per one discharging opening, and the extruded composition was hauled off at a rate of 32 m/min. and then cooled to obtain strands having a diameter of 0.8 mm. The strands were cut with a pelletizer to obtain a powder having a sphere-converted average particle size of 0.91 mm and a bulk specific gravity of 0.465. The thermoplastic elastomer composition obtained by kneading had η*(1) of 1.7 x 10 2 Pa·s (1.7 x 10 3 poises) and n of 0.21. <Production of a molded article by powder slush molding> The above obtained powder was power slush molded with a molding machine, the schematic view of which is shown in Fig. 1. Firstly, the powder (3) was supplied into a container (2). Next, the container (2) and a mold (1) were mated and fixed so that the peripheries of the openings of the container and mold were in close contact with each other. The mold (1) had, on its mold surface, three depressions as shown in Fig. 2, that is a depression "a" having a depth of 7 mm, a depression "b" having a depth of 11 mm, and a depression "c" having a depth of 15 mm. The opening of each depression was a square having a side length of 25 mm. The whole mold surface of the mold (1) had a grain pattern. The temperature of the mold (1) was 250°C. Immediately after fixing the container (2) and the mold (1), they were rotated with a single-axis rotating apparatus by 180 degrees around a rotation axis (4) to supply the powder (3) onto the mold surface of the mold (1). Then, the fixed container (2) and mold (1) were oscillated twice at an amplitude of 45 degrees around the rotation axis (4) over 15 seconds to melt the powder (3) and adhere the molten powder (3) to the mold surface of the mold (1). After that, the fixed container (2) and mold (1) were again rotated by 180 degrees so that they returned to the original position, and a portion of the powder (3) which was not adhered to the mold surface of the mold (1) was recovered to the container (2). Thereafter, the mold (1) to which the fused powder (3) was adhered was detached from the container (2), heated in an oven at 250°C for 2 minutes, and cooled. Then, the molded article (5) was removed from the mold (1). The obtained molded article (5) had a thickness of 1.2 mm and three projections, that is, the projection A having a height of 7 mm, the projection B having a height of 11 mm, and the projection C having a height of 15 mm. The root portion of each projection was a square having a side length of 25 mm. The grain pattern formed on the mold surface of the mold (1) was exactly transferred to the surface of the molded article which was in contact with the mold surface of the mold (1). The cross section of this molded article is shown in Fig. 3. The results of the evaluation of the powder and the molded article are shown in Table 5. Example 15 A molded article was produced in the same manner as in Example 14 except that, in the production of the powder of the thermoplastic elastomer composition, the discharging rate of the composition from the die was changed to 0.8 kg/hr., and the haul-off rate was changed to 35 m/min. The powder used for the production of the molded article had a sphere-converted average particle size of 0.94 mm, and a bulk specific gravity of 0.460. The results of the evaluation of the molded article are shown in Table 5. Example 16 A molded article was produced in the same manner as in Example 14 except that, in the production of the powder of the thermoplastic elastomer composition, the haul-off rate was changed to 14 m/min. The powder used for the production of the molded article had a sphere-converted average particle size of 1.25 mm, and a bulk specific gravity of 0.470. The results of the evaluation of the molded article are shown in Table 5. Example 17 A molded article was produced in the same manner as in Example 14 except that an ethylene-1-hexene copolymer rubber (1-hexene unit content = 70 wt. %, η*(1) = 10 Pa·s (1 x 10 2 poises), n = 0.03) was used. The powder used for the production of the molded article had a sphere-converted average particle size of 0.92 mm, and a bulk specific gravity of 0.460. The thermoplastic elastomer composition constituting the powder had η* of 1.2 x 10 2 Pa·s (1.2 x 10 3 poises) and n of 0.15. The results of the evaluation of the molded article are shown in Table 5. Example 18 The pellets of a kneaded mixture, which was prepared in the same manner as in Comparative Example 4 (100 wt. parts), and an ethylene-1-butene copolymer rubber (1-butene unit content = 71 wt. %, η*(1) = 2.2x10 2 Pa·s (2.2 x 10 3 poises), n= 0.2) (10 wt. parts) were supplied into a twin-screw extruder and kneaded at 200°C. Then, the formed thermoplastic elastomer composition was extruded from the extruder, and cut with a cutter to obtain pellets. The thermoplastic elastomer composition had η* (1) of 1.7 x 10 2 Pa·s (1.7 x 10 3 poises) and n of 0.21. The pellets of the thermoplastic elastomer composition were cooled to -100°C with liquid nitrogen, and comminuted to obtain a powder which passed through the 32 mesh (opening: 500 µm x 500 µm) of the Tyler standard sieve. The powder had a sphere-converted average particle size of 0.20 mm and a bulk specific gravity of 0.290. A molded article was produced in the same manner as in Example 14 except that the above powder was used. The results of the evaluation of the powder and the molded article are shown in Table 5. Example 19 A composition prepared in the same manner as in Example 8 (100 wt. parts), and an ethylene-1-butene copolymer rubber (1-butene unit content = 71 wt. %; η*(1) = 2.2 x 10 2 Pa·s (2.2 x 10 3 poises); n = 0.2) (66.7 wt. parts) were supplied into an extruder having a diameter of 30 mm and kneaded at 160°C. The formed thermoplastic elastomer composition was extruded through a die having a discharging opening diameter of 1.0 mm at a discharging rate of 0.8 kg/hr. per one discharging opening, and the extruded composition was hauled off at a rate of 35 m/min. and then cooled to obtain strands having a diameter of 0.8mm. The strands were cut with a pelletizer to obtain a powder having a sphere-converted average particle size of 0.88 mm and a bulk specific gravity of 0.460. The thermoplastic elastomer composition obtained by kneading had η*(1) of 2 x 10 2 Pa·s (2 x 10 3 poises)and n of 0.14. Then, a molded article was produced in the same manner as in Example 14 except that the above powder was used. The results of the evaluation of the powder and the molded article are shown in Table 5. Comparative Example 5 A kneaded composition prepared in the same manner as in Comparative Example 4 (100 wt. parts) was supplied into an extruder having a diameter of 30 mm and kneaded at 160°C. Then, the composition was extruded through a die having a discharging opening diameter of 1.0 mm at a discharging rate of 1 kg/hr. per one discharging opening, and the extruded composition was hauled off at a rate of 32 m/min. and then cooled to obtain strands having a diameter of 0.8 mm. The strands were cut with a pelletizer to obtain a powder having a sphere-converted average particle size of 0.90 mm and a bulk specific gravity of 0.450. Then, a molded article was produced in the same manner as in Example 14 except that the above powder was used. The results of the evaluation of the powder and the molded article are shown in Table 5. Comparative Example 6 The pellets of a kneaded composition, which was prepared in the same manner as in Comparative Example 4, were cooled to -100°C with liquid nitrogen, and comminuted to obtain a powder which passed through the 32 mesh of the Tyler standard sieve. The powder had a sphere-converted average particle size of 0.18 mm and a bulk specific gravity of 0.293. A molded article was produced in the same manner as in Example 14 except that the above powder was used. The results of the evaluation of the powder and the molded article are shown in Table 5. Example 20 <Preparation of the powder of a thermoplastic elastomer composition> A propylene-ethylene random copolymer (ethylene unit content = 4.5 wt. %; MFR = 228 g/10 min.) (100 wt. parts) and an ethylene-1-butene copolymer rubber (1-butene unit content = 71 wt. %) (100 wt. parts) were supplied into an extruder having a diameter of 30 mm and kneaded at 160°C. The formed thermoplastic elastomer composition was extruded through a die having a discharging opening diameter of 1.0 mm at a discharging rate of 1 kg/hr. per one discharging opening, and the extruded composition was hauled off at a rate of 32 m/min. and then cooled to obtain strands having a diameter of 0.8 mm. The strands were cut with a pelletizer to obtain a powder having a sphere-converted average diameter of 0.91 mm and a bulk specific gravity of 0.460. The above thermoplastic elastomer composition had η* (1) of 1.4 x 10 2 Pa·s (1.4 x 10 3 ) poises and n of 0.13. <Production of a molded article by powder slush molding> A molded article was produced in the same manner as in Example 14 except that the above powder was used. The results of the evaluation of the molded article are shown in Table 6. Example 21 The powder of a thermoplastic elastomer composition was prepared in the same manner as in Example 20 except that the amount of the ethylene-1-butene copolymer rubber was changed to 200 wt. parts. This powder had a sphere-converted average particle size of 0.94 mm and a bulk specific gravity of 0.450. The thermoplastic elastomer composition had η*(1) of 1.8 x 10 2 Pa·s (1.8 x 10 3 poises) and n of 0.15. A molded article was produced in the same manner as in Example 20 except that the above powder was used. The results of the evaluation of the molded article are shown in Table 6. Example 22 A molded article was produced in the same manner as in Example 20 except that an ethylene-1-hexene copolymer rubber (1-hexene unit content = 70 wt. %; η*(1) = 20 Pa.s (2 x 10 2 poises); n = 0.03) was used in place of the ethylene-1-butene copolymer rubber. The powder used in the production of the molded article had a sphere-converted average particle size of 0.93 mm and a bulk specific gravity of 0.458, while the thermoplastic elastomer composition constituting the powder had η*(1) of 30 Pa·s (3 x 10 2 poises) and n of 0.04. The results of the evaluation of the molded article are shown in Table 6. Example 23 The powder of a thermoplastic elastomer composition was prepared in the same manner as in Example 20 except that the haul-off rate of the thermoplastic elastomer composition from the die was changed to 14 m/min. The powder has a sphere-converted average particle size of 1.25 mm and a bulk specific gravity of 0.450. A molded article was produced in the same manner as in Example 20 except that the above powder was used. The results of the evaluation of the molded article are shown in Table 6. Example 24 A propylene-ethylene random copolymer resin (ethylene unit content = 4.5 wt. %; MFR = 228 g/10 min.) (100 wt. parts) and an ethylene-1-butene copolymer rubber (1-butene unit content = 71 wt. %) (100 wt. parts) were supplied into a twin-screw extruder and kneaded at 200°C to obtain a thermoplastic elastomer composition having η*(1) of 1.4 x 10 2 Pa·s (1.4 x 10 3 poises) and n of 0.13. This composition was extruded from the same twin-screw extruder as used in the above step, and cut with a cutter to obtain pellets of the composition having a diameter of 3 mm and a length of 6 mm. Then, the pellets were cooled to -100°C with liquid nitrogen and comminuted to obtain a powder which passed through the 32 mesh of the Tyler standard sieve. The powder had a sphere-converted average particle size of 0.20 mm and a bulk specific gravity of 0.270. A molded article was produced in the same manner as in Example 20 except that the above powder was used. The results of the evaluation of the molded article are shown in Table 6. Comparative Example 7 The pellets of a thermoplastic elastomer composition having η* (1) of 1.5 x 10 2 Pa·s (1.5 x 10 3 poises) and n of 0.25 were prepared in the same manner as in Comparative Example 4. The pellets were supplied into an extruder having a diameter of 30 mm and kneaded at 160°C. The formed thermoplastic elastomer composition was extruded through a die having a discharging opening diameter of 1.0 mm at a discharging rate of 1 kg/hr. per one discharging opening, and the extruded composition was hauled off at a rate of 32 m/min. and then cooled to obtain strands having a diameter of 0.8 mm. The strands were cut with a pelletizer to obtain a powder having a sphere-converted average diameter of 0.91 mm and a bulk specific gravity of 0.450. A molded article was produced in the same manner as in Example 20 except that the above powder was used. The results of the evaluation of the molded article are shown in Table 6. Comparative Example 8 The pellets of a thermoplastic elastomer composition, which was prepared in the same manner as in Comparative Example 7, were cooled to -100°C and comminuted to obtain a powder which passed through the 32 mesh of the Tyler standard sieve. The powder had a sphere-converted average particle size of 0.18 mm and a bulk specific gravity of 0.293. A molded article was produced in the same manner as in Example 20 except that the above powder was used. The results of the evaluation of the molded article are shown in Table 6.

Claims: A thermoplastic elastomer composition comprising (a) 100 wt. parts of a polyolefin resin, (b). 5 to 250 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 60 to 90 wt. %, and (c) 0 to 500 wt. parts of an ethylene-α-olefin copolymer rubber in which the content of the α-olefin units as calculated from the infrared absorbances at peaks assigned to the α-olefin units is 5 to 40 wt. %. A thermoplastic elastomer composition according to claim 1, wherein an α-olefin in said ethylene-α-olefin copolymer (b) is an α-olefin having 4 to 8 carbon atoms. A thermoplastic elastomer composition according to claim 1, wherein said ethylene-α-olefin copolymer rubber (b) is an ethylene-1-butene copolymer rubber or an ethylene-1-hexene copolymer rubber. A thermoplastic elastomer composition according to claim 1, wherein said ethylene-α-olefin copolymer rubber (c) is an ethylene-α-olefin copolymer rubber or an ethylene-α-olefin-non-conjugated diene copolymer rubber. A thermoplastic elastomer composition according to claim 1, wherein at least one polymer selected from the group consisting of said polyolefin resin (a), said ethylene-α-olefin copolymer rubber (b) and said ethylene-α-olefin copolymer rubber (c) is intermolecularly and/or intramolecularly crosslinked. A thermoplastic elastomer composition according to claim 1, which further comprises a foaming agent. A powder comprising a thermoplastic elastomer composition as claimed in claim 1, which has a sphere-converted average particle size of 1.2 mm or less, and a bulk specific gravity of at least 0.38. A powder according to claim 7, wherein an α-olefin in the ethylene-α-olefin copolymer (b) contained in said thermoplastic elastomer composition is an α-olefin having 4 to 8 carbon atoms. A powder according to claim 7, wherein said ethylene-α-olefin copolymer rubber (b) contained in said thermoplastic elastomer composition is an ethylene-1-butene copolymer rubber or an ethylene-1-hexene copolymer rubber. A powder according to claim 7, which is obtainable by a solvent-treating method, a strand cutting method or a die-face cutting method. A molded article comprising a thermoplastic elastomer composition as claimed in claim 1. A molded article according to claim 11, which is obtainable by press molding. Amolded article according to claim 11, which is obtainable by powder slush molding a powder of claim 7. A molded article according to claim 11, which is a foamed molded article. A multilayer molded article comprising at least one layer formed from a thermoplastic elastomer composition as claimed in claim 1. A multilayer molded article according to claim 15, which further comprises a core layer of a thermoplastic resin.

Inventors: HOZUMI HIDETAKE, NAKATSUJI YOSHIHIRO, SUGIMOTO HIROYUKI, HOZUMI, HIDETAKE, NAKATSUJI, YOSHIHIRO, SUGIMOTO, HIROYUKI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1997
Main classification: C08L23
IPC codes: C08L23