Thermoplastic elastomer composition and method for producing the same

Abstract

A thermoplastic elastomer composition of the invention, formed by dynamically crosslinking a polymer composition including a rubber and an olefinic resin and having an average particle size of rubber particles within a specific range, shows an excellent balance of mechanical properties such as flexibility and elastic recovery, and a moldability. Also an inclusion of a (meth)acrylate resin and a hydrogenated diene polymer provides a composition particularly excellent in scratch resistance. Also an inclusion of a maleimide compound provides a composition particularly excellent in injection fusibility. Also an inclusion of an undenatured organopolysiloxane of a specific viscosity and a denatured organopolysiloxane provides a composition particularly excellent in initial slidability and durable slidability.

1 . A thermoplastic elastomer composition prepared by a process which comprises:
 dynamically heat treating, in the presence of a crosslinking agent, a polymer composition comprising   a rubber and   an olefinic resin:   wherein the rubber, included in said thermoplastic elastomer composition, comprises rubber particles, has a gel fraction of 80% or higher, and the rubber particles contained in said thermoplastic elastomer composition have a number-averaged particle size (dn) equal to or less than 3 μm and a ratio (dv/dn) of a volume-averaged particle size (dv) to said number-averaged particle size (dn) equal to or less than 1.5.   
     
     
         2 . The thermoplastic elastomer composition according to  claim 1 , wherein said gel fraction is 95% or higher and said number-averaged particle size, dn, is 2 μm or less. 
     
     
         3 . The thermoplastic elastomer composition according to  claim 1 , wherein,
 for the sum of said rubber and said olefinic resin taken as 100 parts by mass,   said rubber is present at a level of 20 to 95 parts by mass,   said olefinic resin is present at a level of 5 to 80 parts by mass, and   said crosslinking agent is present at a level of 0.05 to 10 parts by mass.   
     
     
         4 . The thermoplastic elastomer composition according to  claim 1 , wherein said rubber is an ethylene.α-olefin copolymer rubber having a limiting viscosity [η] of 2.0 to 6.8 dl/g when measured at 135° C. in decaline as a solvent. 
     
     
         5 . A thermoplastic elastomer composition prepared by a process which comprises:
 dynamically heat treating, in the presence of a crosslinking agent, a polymer composition comprising   a rubber,   an olefinic resin,   a (meth)acrylate resin and   a hydrogenated diene polymer.   
     
     
         6 . The thermoplastic elastomer composition according to  claim 5 , wherein said hydrogenated diene polymer is formed by hydrogenation of a copolymer having a first polymer block principally formed by a vinyl aromatic unit and a second polymer block principally formed by a conjugate diene unit. 
     
     
         7 . The thermoplastic elastomer composition according to  claim 5 , wherein, for the sum of said rubber, said olefinic resin, said (meth)acrylate resin and said hydrogenated diene polymer taken as 100 mass %,
 said rubber is present at a level of 20 to 95 mass %,   said olefinic resin is present at a level of 3 to 70 mass %,   said (meth)acrylate resin is present at a level of 1 to 20 mass %, and   said hydrogenated diene polymer is present at a level of 1 to 10 mass %.   
     
     
         8 . The thermoplastic elastomer composition according to  claim 5 , wherein said rubber is an ethylene.α-olefin copolymer rubber having a limiting viscosity [η] of 2.0 to 6.8 dl/g when measured at 135° C. in decaline as a solvent. 
     
     
         9 . A thermoplastic elastomer composition prepared by a process which comprises:
 dynamically heat treating, in the presence of a crosslinking agent, a polymer composition comprising   a rubber,   an olefinic resin,   a softening agent and   a maleimide compound,   wherein, for the sum of said rubber, said olefinic resin and said softening agent taken as 100 mass %, said olefinic resin is present at a level of 5 to 36 mass %, and   for the sum of said rubber, said olefinic resin and said softening agent taken as 100 parts by mass, said maleimide compound is present at a level of 0.3 to 10 parts by mass.   
     
     
         10 . The thermoplastic elastomer composition according to  claim 9 , wherein, for the sum of said rubber, said olefinic resin and said softening agent taken as 100 mass %,
 said rubber is present at a level of 20 to 85 mass % and   said softening agent is present at a level of 10 to 75 mass %.   
     
     
         11 . A thermoplastic elastomer composition prepared by a process which comprises:
 dynamically heat treating, in the presence of a crosslinking agent, a polymer composition comprising   an ethylene.α-olefin copolymer rubber having a limiting viscosity [η] of 2.0 to 6.8 dl/g when measured at 135° C. in decaline as a solvent,   an olefinic resin,   a softening agent and   a maleimide compound,   wherein, for the sum of said rubber, said olefinic resin and said softening agent taken as 100 parts by mass, said maleimide compound is present at a level of 0.3 to 10 parts by mass.   
     
     
         12 . A thermoplastic elastomer composition prepared by a process which comprises:
 dynamically heat treating, in the presence of a crosslinking agent, a polymer composition comprising   a rubber,   an olefinic resin,   a softening agent,   a low-viscosity undenatured organopolysiloxane having a viscosity measured at 25° C. according to JIS K2283 less than 10,000 cSt,   a high-viscosity undenatured organopolysiloxane having a viscosity measured at 25° C. according to JIS K2283 equal to or higher than 10,000 cSt, and   a denatured organopolysiloxane.   
     
     
         13 . The thermoplastic elastomer composition according to  claim 12 , wherein, for the sum of said rubber, said olefinic resin and said softening agent taken as 100 parts by mass,
 said rubber is present at a level of 20 to 69 parts by mass,   said olefinic resin is present at a level of 1 to 50 parts by mass, and   said softening agent is present at a level of 20 to 79 parts by mass.   
     
     
         14 . The thermoplastic elastomer composition according to  claim 12 , wherein, for the sum of said rubber, said olefinic resin and said softening agent taken as 100 parts by mass,
 said low-viscosity undenatured organopolysiloxane is present at a level of 1 to 10 parts by mass,   said high-viscosity undenatured organopolysiloxane is present at a level of 1 to 10 parts by mass,   and said denatured organopolysiloxane is present at a level of 0.2 to 20 parts by mass.   
     
     
         15 . A thermoplastic elastomer composition prepared by a process which comprises:
 dynamically heat treating, in the presence of a crosslinking agent, a polymer composition comprising   an oil-extended rubber, comprising a rubber and a softening agent, wherein, for the sum of said rubber and said softening agent taken as 100 mass %, said rubber is present at a level of 30 to 70 mass % and said softening agent is present at a level of 30 to 70 mass %,   an olefinic resin,   optionally a post-addition softening agent,   an undenatured organopolysiloxane having a viscosity measured at 25° C. according to JIS K2283 less than 10,000 cSt,   an undenatured organopolysiloxane having a viscosity measured at 25° C. according to JIS K2283 equal to or higher than 10,000 cSt, and   a denatured organopolysiloxane.   
     
     
         16 . The thermoplastic elastomer composition according to  claim 15 , wherein, for the sum of said oil-extended rubber, said olefinic resin and said post-addition softening agent taken as 100 parts by mass,
 said oil-extended rubber is present at a level of 30 to 99 parts by mass,   said olefinic resin is present at a level of 1 to 50 parts by mass,   and said post-addition softening agent is present at a level of 50 parts by mass or less (including 0 parts by mass).   
     
     
         17 . The thermoplastic elastomer composition according to  claim 15 , wherein, for the sum of said oil-extended rubber, said olefinic resin and said post-addition softening agent taken as 100 parts by mass,
 said low-viscosity undenatured organopolysiloxane is present at a level of 1 to 10 parts by mass,   said high-viscosity undenatured organopolysiloxane is present at a level of 1 to 10 parts by mass,   and said denatured organopolysiloxane is present at a level of 0.2 to 20 mass %.   
     
     
         18 . The thermoplastic elastomer composition according to  claim 12 , wherein said rubber is an ethylene.α-olefin copolymer rubber having a limiting viscosity [η] of 2.0 to 6.8 dl/g when measured at 135° C. in decaline as a solvent. 
     
     
         19 . A method for producing a thermoplastic elastomer composition which comprises:
 melt kneading in a closed kneader,   a polymer composition comprising
 a rubber, 
 an olefinic resin, and 
 other additives excluding a crosslinking agent, to obtain a melt blended 
 substance (A) or 
   a polymer composition comprising
 a rubber, 
 an olefinic resin, and 
 other additives excluding at least a part of a crosslinking agent and 
 a crosslinking agent, to obtain a melted blended substance (B), and 
   supplying said melted blended substance (B) or said melted blended substance (A), and an additive comprising at least a crosslinking agent, to a continuous extruder thereby dynamically heat-treating the polymer composition.   
     
     
         20 . A method for producing a thermoplastic elastomer composition which comprises:
 adding a crosslinking agent to a polymer composition comprising a rubber and an olefinic resin to produce a mixture, and then   supplying the mixture to a plurality of connected continuous kneaders thereby dynamically heat-treating the mixture.   
     
     
         21 . A method for producing a thermoplastic elastomer composition which comprises:
 supplying a polymer composition, comprising a rubber and an olefinic resin to an extrusion apparatus comprising a serial connection of an upstream continuous two-shaft kneader with different rotating directions and a downstream two-shaft extruder with a same rotating direction, from a raw material introducing part of said continuous two-shaft kneader with different rotating directions, thereby   kneading said polymer composition in said continuous two-shaft kneader with different rotating directions to produce a kneaded substance, and   supplying the kneaded substance to said two-shaft extruder with a same rotating direction, maintaining the temperature of the kneaded substance at 250° C. or less at the exit of said continuous two-shaft kneader with different rotating directions thereby   dynamically crosslinking the polymer composition.   
     
     
         22 . A method for producing a thermoplastic elastomer composition which comprises:
 supplying a polymer composition, comprising a rubber, an olefinic resin and an organic peroxide having a 1-minute half-period temperature T h  (° C.) within a range of T m ≦T h ≦T m +50 (° C.) wherein T m  is the melting point (° C.) of said olefinic resin, to an extrusion apparatus constituted of a serial connection of an upstream continuous two-shaft kneader with different rotating directions and a downstream two-shaft extruder with a same rotating direction, from a raw material introducing part of said continuous two-shaft kneader with different rotating directions,   kneading said polymer composition in said continuous two-shaft kneader with different rotating directions to produce a kneaded substance, and   supplying the kneaded substance to said two-shaft extruder with a same rotating direction, maintaining the temperature (t a ) of said kneaded substance within a range of T h −30≦t a ≦T h +30 (° C.) at the exit of said continuous two-shaft kneader with different rotating directions, thereby   dynamically crosslinking the polymer composition.   
     
     
         23 . The thermoplastic elastomer composition according to  claim 15 , wherein
 said rubber is an ethylene.α-olefin copolymer rubber having a limiting viscosity [η] of 2.0 to 6.8 dl/g when measured at 135° C. in decaline as a solvent.