Thermoplastic elastomeric resin composition

Abstract: The invention provides a thermoplastic elastomeric resin composition comprising (a) 100 parts by weight of a block copolymer consisting of at least two polymeric blocks (A) composed mainly of a vinyl aromatic compound and at least one polymeric block (B) composed mainly of a conjugated diene compound, and/or a hydrogenated block copolymer obtained by hydrogenating said block copolymer, (c) 5 to 150 parts by weight of polyethylene or a copolymer composed mainly of ethylene, and (d) 5 to 80 parts by weight of polypropylene or a copolymer composed mainly of propylene, characterized in that component (c) is one which has been prepared using a single site catalyst. The composition is soft and excellent in heat deformation resistance and mechanical strength, moldability and processability and shows good results in the extraction tests.

Description: FIELD OF THE INVENTION The present invention relates to a thermoplastic elastomeric resin composition. PRIOR ART Thermoplastic elastomeric resins which are rubber-like materials, do not need a vulcanization process and have thermoplastic resin-like molding processability are attracting attention in the fields of auto parts, parts for electric appliances, electric wire insulation, footwears and general goods, and in the field of cap sealing materials. Various types of such thermoplastic elastomeric resins have been developed and put on sale, such as polyolefine type, polyurethane type, polyester type, polystyrene type and polyvinyl chloride type. Among those, polystyrene type thermoplastic elastomeric resins such as styrene-butadiene block copolymers (SBS) and styrene-isoprene block copolymers (SIS) and hydrogenated resins thereof have high softness and good rubber elasticity at normal temperature. Further, thermoplastic elastomeric resin compositions obtained from these show good processability. However, these block copolymer compositions are unsatisfactory in compression set at a high temperature, particularly at 100 °C and, moreover, tensile properties deteriorate considerably at 80 °C or more. Thus, such compositions do not meet the levels of properties required in the fields of vulcanized rubber. Meanwhile, the thermoplastic elastomers mentioned above are also attracting attention in the fields of cap sealing materials. Particularly, polyolefin type thermoplastic elastomers are used widely because of their high sanitary reliability and cheapness. However, these polyolefin type thermoplastic elastomers are poor in softness and, therefore, exhibit poor sealing property. Alternatively, polystyrene type thermoplastic elastomeric resins such as SBS and SIS and hydrogenated resins thereof have high softness and good rubber elasticity at normal temperature. Further, thermoplastic elastomeric resin compositions obtained from these show good processability. Accordingly, these are used widely as an alternate of vulcanized rubber. However, these polystyrene type thermoplastic elastomer compositions cannot meet the n-heptane extraction test of the tests of Notification No. 20 of the Japanese Welfare Ministry, because softening agents such as paraffinic oil are generally added to these compositions in order to control their hardness. Accordingly, it is hard to use them as a cap sealing. Alternatively, if the paraffinic oil is not used, the softness and moldability of them deteriorate. In order to solve such a drawback, there has been proposed a composition containing polybutene or polyisobutene as a softening agent. However, the composition disclosed are poor in heat resistance at 120 °C. Another resin compositions which comprise the block copolymer used as component (a) in the present invention has been proposed in Japanese Patent Application Laid-Open Nos. Sho-53-138451/1978, 53-138453/1978, 53-138454/1978, 53-138456/1978, 53-138458/1978, 53-138460/1978 and 53-138461/1978. However, heat resistance is poor. The composition disclosed in Japanese Patent Application Laid-Open No. 58-215446/1983 comprises isotactic polypropylene. This composition is excellent in mechanical strength and heat resistance. However, the hardness is in the D hardness area. Thus, it cannot be said that the composition is excellent in sealing property. SUMMARY OF THE INVENTION The purpose of the invention is to provide a thermoplastic elastomer composition which is soft and excellent in heat deformation resistance, mechanical strength, moldability and processability and used properly as a sealing material. Thus the present invention provides a thermoplastic elastomeric resin composition comprising (a) 100 parts by weight of a block copolymer consisting of at least two polymeric blocks (A) composed mainly of a vinyl aromatic compound and at least one polymeric block (B) composed mainly of a conjugated diene compound, and/or a hydrogenated block copolymer obtained by hydrogenating said block copolymer, (c) 5 to 150 parts by weight of polyethylene or a copolymer composed mainly of ethylene, and (d) 5 to 80 parts by weight of polypropylene or a copolymer composed mainly of propylene, characterized in that component (c) is one which has been prepared using a single site catalyst. In a preferred embodiment, the composition further comprises (e) 0.01 to 100 parts by weight of an inorganic filler. PREFERRED EMBODIMENTS OF THE INVENTION Component (a), Block Copolymer Component (a) used in the invention is a block copolymer consisting of at least two polymeric blocks (A) composed mainly of a viny aromatic compound and at least one polymeric block (B) composed mainly of a conjugated diene compound, or a hydrogenated block copolymer obtained by hydrogenating said block copolymer, or a mixture thereof, such as vinyl aromatic compound-conjugated diene compound block copolymers having a structure, A-B-A, B-A-B-A or A-B-A-B-A, or those obtained by hydrogenating such. The block copolymer and/or the hydrogenated block copolymer (hereinafter referred to as (hydrogenated) block copolymer) contains 5 to 60 % by weight, preferably 20 to 50 % by weight, of a vinyl aromatic compound. Preferably, the polymeric block A composed mainly of a vinyl aromatic compound consists wholly of a vinyl aromatic compound or is a copolymeric block comprising more than 50 % by weight, preferably at least 70 % by weight, of a vinyl aromatic compound and an optional component such as a conjugated diene compound and/or a hydrogenated conjugated diene compound (hereinafter referred to as (hydrogenated) conjugated diene compound). Preferably, the polymeric block B composed mainly of a (hydrogenated) conjugated diene compound is composed solely of a (hydrogenated) conjugated diene compound or is a copolymeric block comprising more than 50 % by weight, preferably at least 70 % by weight, of a (hydrogenated) conjugated diene compound with an optional component such as a vinyl aromatic compound. The vinyl compound or the (hydrogenated) conjugated diene compound may be distributed at random, in a tapered manner (i.e., a monomer content increases or decreases along a molecular chain), in a form of partial block or mixture thereof in the polymeric block A composed mainly of a vinyl aromatic compound or the polymeric block B composed mainly of a (hydrogenated) conjugated diene compound, respectively. When two or more of the polymeric block A composed mainly of a vinyl aromatic compound or two or more of the polymeric block B composed mainly of a (hydrogenated) conjugated diene compound are present, they may be same with or different from each other in structure. The vinyl aromatic compound to compose the (hydrogenated) block copolymer may be one or more selected from, for instance, styrene, α-methyl styrene, vinyl toluene and p-tert.-butyl styrene, preferably styrene. The conjugated diene compound may be one or more selected from, for instance, butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene, preferably butadiene and/or isoprene. Any micro structure may be selected in the polymeric block B composed mainly of the conjugated diene compound. It is preferred that the butadiene block has 20 to 50 %, more preferably 25 to 45 %, of 1,2-micro structure. In the polyisoprene block, it is preferred that 70 to 100 % by weight of isoprene is in 1,4-micro structure and at lest 90 % of the aliphatic double bonds derived from isoprene is hydrogenated. A weight average molecular weight of the (hydrogenated) block copolymer with the aforesaid structure to be used in the invention is preferably 5,000 to 1,500,000, more preferably 10,000 to 550,000, further more preferably 100,000 to 550,000, particularly 100,000 to 400,000. A number average molecular weight is preferably 5,000 to 1,500,000, more preferably 10,000 to 550,000, particularly 100,000 to 400,000. A ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw/Mn, is preferably 10 or less, more preferably 5 or less, particularly 2 or less. Molecule structure of the (hydrogenated) block copolymer may be linear, branched, radial or any combination thereof. Many methods were proposed for the preparation of such block copolymers. As described, for instance, in JP Publication 40-23798/1965, block polymerization may be carried out using a lithium catalyst or a Ziegler catalyst in an inert solvent. The hydrogenated block copolymer may be obtained by hydrogenating the block copolymer thus obtained in the presence of a hydrogenation catalyst in an inert solvent. Examples of the (hydrogenated) block copolymer include SBS, SIS, SEBS and SEPS. A particularly preferred (hydrogenated) block copolymer in the invention is a hydrogenated block copolymer with a weight average molecular weight of 50,000 to 550,000 which is composed of polymeric block A composed mainly of styrene and polymeric block B which is composed mainly of isoprene and in which 70 to 100 % by weight of isoprene has 1,4-micro structure and 90 % of the aliphatic double bonds derived from isoprene is hydrogenated. More preferably, 90 to 100 % by weight of isoprene has 1,4-micro structure in the aforesaid hydrogenated block copolymer. Component (c), Polyethylene or a Copolymer Composed Mainly of Ethylene Which Is Prepared Using a Single Site Catalyst As the polyethylene or a copolymer composed mainly of ethylene which is prepared using a single site catalyst, use may be made of one or more substances selected from polyethylene, for instance, high density polyethylene (polyethylene prepared in a low pressure method), low density polyethylene (polyethylene prepared in a high pressure method), linear low density polyethylene (copolymers of ethylene with a smaller amount, preferably 1 to 10 molar % of α-olefin such as butene-1, hexene -1 or octene-1); and olefinic copolymers such as ethylene-propylene copolymer, ethylene-vinyl acetate copolymer and ethylene-acrylate copolymer. Particularly preferable substances are ethylene-octene copolymer having a polymer density of at most 0.90 g/cm 3 or ethylene-hexene copolymer having a polymer density of at least 0.90 g/cm 3 which are prepared using a metallocene catalyst (single site catalyst). When Tm of these copolymer is not higher than 100 °C, it is necessary to add and crosslink them by the time of crosslinking at the latest. Tm disappears by the crosslinking and, therefore, fusion of octene or hexene does not occur. If the addition of them is carried out after the crosslinking, fusion at 30 to 60 °C of octene or hexene remains and, therefore, the heat resistance is decreased. The (co)polymer used as component (c) includes olefinic polymers which are prepared using a catalyst for olefine polymerization which is prepared in accordance with the method described in Japanese Patent Application Laid-Open Sho-61-296008/1986 and which is composed of a carrier and a reaction product of metallocene having at least one metal selected from the 4b group, 5b group and 6b group in the periodic table with alumoxane, the reaction product being formed in the presence of the carrier. Another example of component (c) is an olefinic polymer prepared using a metal coordinated complex described in Japanese Patent Application Laid-Open Hei-3-163008, which metal coordinated complex contains a metal selected from the group 3 (except scandium), groups 4 to 10 and the lanthanoid group and a delocalized π -bonding part substituted by a constrained inducing part, and is characterized in that said complex has a constrained geometrical form around said metal atom, and a metal angle between a center of the delocalized substituted π-bonding part and a center of at least one remaining substituted part is less than that in a comparative complex which is different from it only in that a constrained inducing substituted part is substituted with a hydrogen, and wherein in each complex having further at least one delocalized substituted π-bonding part, only one, per metal atom, of the delocalized substituted π-bonding parts is cyclic. The (co)polymer used as component (c) has an MFR determined at 190 °C and a load of 2.16 kg of preferably 0.1 to 10.0 g/10 min., more preferably 0.3 to 5.0 g/10 min. In the present composition, MFR of 0.3 to 2.0 g/10 min. is particularly preferred. In the present composition, component (c) is contained in an amount of at most 150 parts by weight, preferably at most 130 parts by weight, and at least 5 parts by weight, more preferably at least 70 parts by weight, per 100 parts by weight of component (a). If the amount is below the lower limit; softness is lost. If the amount exceeds the upper limit, the heat resistance of the elastomer composition deteriorates. Component (d), Polypropylene or a Copolymer Composed Mainly of Propylene The polypropylene or a copolymer composed mainly of propylene attains an effect of improving dispersion of the rubber in the composition obtained so as to improve appearance of a molded article. Further, the heat resistance may be also improved. The component is an olefinic (co)polymer which is pyrolyzed by the heat treatment in the presence of peroxide to decrease its molecular weight and, therefore, its melting flowability increases. Examples of such include isotactic polypropylenes, and copolymers of propylene with other α-olefine such as ethylene, 1-butene, 1-hexene or 4-methyl-1-pentene. Preferably, component (d) has Tm of 150 to 167 °C and ΔHm of 25 to 83 mJ/mg, as determined by DSC (differential scanning calorimetry) on its homopolymeric part. Crystallinity may be estimated from Tm and ΔHm. If Tm and ΔHm are out of the aforesaid ranges, rubber elasticity at 100 °C or higher of the elastomer composition obtained is not improved. In the present elastomer composition, component (d) is contained in an amount of 5 to 80 parts by weight, preferably 30 to 50 parts by weight, per 100 parts by weight of component (a). If the amount is below the lower limit, the moldability of the elastomer composition was poor. If the amount exceeds the upper limit, the softness and rubber elasticity of the elastomer composition deteriorate. Component (e), Inorganic Filler Inorganic fillers may be blended, if needed. The fillers improve some physical properties, such as compression set of a molded article, and further offer an economical advantage as an extender. Any conventional inorganic fillers may be used, such as calcium carbonate, talc, magnesium hydroxide, mica, clay, barium sulfate, natural silica, synthetic silica (white carbon), titanium oxide, and carbon black. Among those, calcium carbonate and talc are particularly preferred, which meet the test of Notification No. 20 of the Japanese Welfare Ministry. The inorganic filler may be blended in an mount of at most 100 parts by weight per 100 parts by weight of component (a). If the amount exceeds 100 parts by weight, mechanical strength of the elastomer composition obtained is very low and, further, its hardness is so high that its flexibility is lost and an article with rubber-like touch cannot be obtained. In addition, the moldability deteriorates. In the present invention, it is possible to blend various conventional additives such as anti-blocking agents, sealing property-improving agents, heat stabilizers, light stabilizers, UV absorbers, nucleating agents and colorants in addition to the aforesaid components, depending on the applications. The thermoplastic elastomeric resin composition of the present invention will be further explained hereinafter. The present elastomer composition comprises 100 parts by weight of composnent (a), 5 to 150 parts by weight of component (c) and 5 to 80 parts by weight of component (d). These components are described specifically hereinbefore. The present composition may contain any other components mentioned above, if needed. The present composition may be prepared by melt kneading the aforesaid components (a), (c) and (d) in any order or at the same time. EXAMPLES The present invention is further elucidated with reference to the following Examples and Comparison Examples, which is not intended to limit the invention. The evaluation methods used were as follows: 1) Hardness: determined in accordance with the Japanese Industrial Standards (JIS) K 7215. Pressed sheets having a thickness of 6.3 mm were used as test pieces. 2) Tensile strength: determined in accordance with JIS K 6301 using a test piece which was obtained by punching out a pressed sheet having a thickness of 1 mm by a No. 3 dumbbell die. The tensile speed was 500 mm / min. In Examples 1 to 5 and Comparison Examples 1 to 10, the test temperature was room temperature (23 °C), 60 °C or 80 °C. 3) Tensile elongation: determined in accordance with JIS K 6301 using a test piece which was obtained by punching out a pressed sheet having a thickness of 1 mm by a No. 3 dumbbell die. The tensile speed was 500 mm / min. 4) Stress at 100 % elongation: determined in accordance with JIS K 6301 using a test piece which was obtained by punching out a pressed sheet having a thickness of 1 mm by a No. 3 dumbbell die. The tensile speed was 500 mm / min. 5) Impact resilience: determined in accordance with BS903 using a pressed sheet having a thickness of 4 mm as a test piece. 6) Compression set: determined in accordance with JIS K 6262 using a pressed sheet having a thickness of 6.3 mm as a test piece. Conditions: 25% deformation at 100 °C x 70 hrs in Examples 1 to 5 and Comparison Examples 1 to 10, or at 125 °C x 1 hr in Examples 6 to 11 and Comparison Examples 11 to 17. 7) Tearing strength: determined in accordance with JIS K 6301 using a test piece which was obtained by punching out a pressed sheet having a thickness of 2.5 mm by a B type dumbbell die. The tensile speed was 500 mm / min. 8) Oil resistance: determined in accordance with JIS K 6301 using a test piece which was obtained by punching out a pressed sheet having a thickness of 1 mm by a No. 3 dumbbell die. ASTM No. 2 oil was used. Tensile strength retained and elongation retained were measured after dipping at100 °C x 24 hrs. The tensile speed was 500 mm / min. 9) Moldability: determined by molding a composition into a sheet of 12.5 x 13.5 x 1 mm on a 120 tons injection molding machine in the following conditions: molding temperature : 220 °C, mold temperature : 40 °C, injection rate : 55 mm/sec., injection pressure : 1400 kg /cm 2 , holding pressure : 400 kg /cm 2 , injection time : 6 seconds, cooling time : 45 seconds. It was observed whether delamination, deformation or flow marks which extremely deteriorated appearance was present or not. o ○ : very good ○ : good × : bad 10) Extraction tests. carried out according to the test of Notification No. 20 of the Japanese Welfare Ministry, using a pressed sheet having a thickness of 1.0 mm as a test piece. Test items : Oily foods elution test (eluting solution : n- heptane), Aqueous foods elution test (eluting solution : water), Alcohol elution test (eluting solution : 20 % ethanol), and Determination of the amount of potassium permanganate consumed by the eluted product. 11) Bleed-out property: the molded sheet obtained from (9) was compressed by 50 % under the conditions of 100 °C x 22 hrs. It was observed whether bleeding or blooming of low molecular weight substances was visually observed or not, and whether stickiness was felt or not in tough by fingers. ○ : good × : bad 12) DSC, determined as follows : The aforesaid molded article was cut to obtain an about 20 mg piece. This was used as a sample for the determination of DSC. DSC was determined using a DSC220C, SII, ex Seiko Electronic Industries Ltd., in a range of -50 °C to 200 °C at a rate of 10°C/min. to obtain glass transition temperature, Tg 1 , melting point, Tm 1 and Tm 2 , and crystallization temperature, Tc 1 and Tc 2 , wherein Tm 1 and Tc 1 are attributed to polyethylene and Tm 2 and Tc 2 to polypropylene. 13) Gloss: determined in accordance with JIS Z 8741 on the aforesaid molded article. The larger the values are, the more smooth the surface is, and the smaller the values are, the more rough the surface is. Materials used: Component (a) : hydrogenated block copolymer, Septon 4077, ex. Kuraray Inc., styrene content : 30 % by weight, isoprene content : 70 % by weight, number average molecular weight : 260,000, weight average molecular weight: 320,000, molecular weight distribution : 1.23, and hydrogenation ratio : at least 90 %. Component (c) : ethylene-octene copolymer, Engage EG8150, trade mark, ex Dow Chemical Japan Inc., density : 0.868 g/cm 3 , melt index, determined at 190 °C and a load of 2.16 kg : 0.5 g/10 min. Component (d) : propylene homopolymer, PP CJ700, ex Mitsui Petrochemical Industries Inc., crystallization degree : Tm 166°C, ΔHm 82 mJ/mg, Component (e) : inorganic filler, calcium carbonate, RS400, trade mark, ex Sankyo Seihun Co., used in Examples 1 to 5 and Comparison Examples 1 to 10. talc, JA13R, ex Asada Seihun Co., used in Examples 6 to 11 and Comparison Examples 11 to 17. Examples 1 to 6 In Examples 1 to 6 , components (a), (c) and (d) and optionally (e) were charged all together into a twin-screw kneader, kneaded at a kneading temperature of 180 to 240 °C and a screw rotation speed of 100 rpm and pelletized. The pellets obtained were put in a predetermined mold and pressed in the conditions of 220 °C and 50 kg/cm 2 to prepare sheets for the aforesaid evaluation methods (1 ) to (6). The results are as shown in Table 1. Comparison Examples 1 to 2 The same procedures were repeated as in the aforesaid Examples, except that each of the following polyethylenes which had been polymerized without using a single site catalyst was used in place of component (c). Polyethylene for Comparison Example 1, V-0398CN, ex Idemitsu Petrochemical Co., type : HDPE (high density polyethylene) density : 0.907 g/cm 3 melt index, determined at 190 °C and a load of 2.16 kg : 3.3 g/10 min. Polyethylene for Comparison Example 2, 440M, ex Idemitsu Petrochemical Co., type : LLDPE (linear low density polyethylene) density : 0.954 g/cm 3 melt index, determined at 190 °C and a load of 2.16 kg : 1.0 g/10 min. The results are as shown in Table 1. Comparison Examples 3 to 7 The same procedures were repeated as in the aforesaid Examples, except that components (a), (c), (d) and (e) were used in an amount exceeding or below the range of the present invention. The results are as shown in Table 2.

Claims: A thermoplastic elastomeric resin composition comprising (a) 100 parts by weight of a block copolymer consisting of at least two polymeric blocks (A) composed mainly of a vinyl aromatic compound and at least one polymeric block (B) composed mainly of a conjugated diene compound, and/or a hydrogenated block copolymer obtained by hydrogenating said block copolymer, (c) 5 to 150 parts by weight of polyethylene or a copolymer composed mainly of ethylene, and (d) 5 to 80 parts by weight of polypropylene or a copolymer composed mainly of propylene, wherein component (c) is one which has been prepared using a single site catalyst, and wherein no softening agent is incorporated. The thermoplastic elastomeric resin composition as described in claim 1, wherein the composition further comprises (e) 0.01 to 100 parts by weight of an inorganic filler.

Inventors: TAMURA AKIHIRO, TASAKA MICHIHISA, TAMURA, AKIHIRO, TASAKA, MICHIHISA
Applicants: RIKEN TECHNOS CORP, RIKEN TECHNOS CORPORATION
Application year: 1997
Main classification: C08L53
IPC codes: C08L91, C08L23, C08L53