Air bag housing cover

Abstract

The present invention relates to an air bag housing cover comprising (A) an olefin-based thermoplastic elastomer comprising (A1) a propylene homopolymer having an isotactic index of not less than 90%, and (A2) a copolymer of propylene and a C 2 to C 8 α-olefin other than propylene, said propylene homopolymer (A1) and said copolymer (A2) being present in amounts of 30 to 60% by weight and 70 to 40% by weight, respectively, based on a total amount of the components (A1) and (A2), and said copolymer having propylene unit and ethylene unit as essential constituting units, said olefin-based thermoplastic elastomer (A) being obtained by producing the component (A2) by polymerization subsequent to the production of the component (A1) by polymerization, and having a 0° C. eluate content of 30 to 60% by weight based on a total eluate content as measured at a temperature between 0° C. and 140° C. by a temperature rising elution fractionation using o-dichlorobenzene as a solvent.

What is claimed is:  
     
         1 . An air bag housing cover comprising (A) an olefin-based thermoplastic elastomer comprising (A1) a propylene homopolymer having an isotactic index of not less than 90%, and (A2) a copolymer of propylene and a C 2  to C 8  α-olefin other than propylene, said propylene homopolymer (A1) and said copolymer (A2) being present in amounts of 30 to 60% by weight and 70 to 40% by weight, respectively, based on a total amount of the components (A1) and (A2), and said copolymer having propylene unit and ethylene unit as essential constituting units, 
 said olefin-based thermoplastic elastomer (A) being obtained by producing the component (A2) by polymerization subsequent to the production of the component (A1) by polymerization, and having a 0° C. eluate content of 30 to 60% by weight based on a total eluate content as measured at a temperature between 0° C. and 140° C. by a temperature rising elution fractionation using o-dichlorobenzene as a solvent.  
 
     
     
         2 . An air bag housing cover according to  claim 1 , wherein said olefin-based thermoplastic elastomer (A) has an eluate content of 1 to 6% by weight in a temperature range of 80 to 100° C. as measured by the temperature rising elution fractionation.  
     
     
         3 . An air bag housing cover according to  claim 1 , wherein said olefin-based thermoplastic elastomer (A) contains a room-temperature xylene-soluble having weight-average molecular weight of 200,000 to 800,000.  
     
     
         4 . An air bag housing cover according to  claim 1 , further comprising (B) a propylene-based polymer in an amount of 10 to 150 parts by weight based on 100 parts by weight of the olefin-based thermoplastic elastomer (A).  
     
     
         5 . An air bag housing cover according to  claim 4 , wherein the content of the propylene-based polymer (B) is 10 to 200 parts by weight based on 100 parts by weight of the olefin-based thermoplastic elastomer (A).  
     
     
         6 . An air bag housing cover according to  claim 4 , wherein said propylene-based polymer (B) is a propylene-ethylene block copolymer having an ethylene content of 1 to 10% by weight.  
     
     
         7 . An air bag housing cover according to  claim 1 , further comprising (C) a softening agent for hydrocarbon-based rubbers in an amount of 1 to 30 parts by weight based on 100 parts by weight of the olefin-based thermoplastic elastomer (A).  
     
     
         8 . An air bag housing cover according to  claim 5 , further comprising (D) an ethylene-α-olefin copolymer in an amount of 15 to 180 parts by weight based on 100 parts by weight of the olefin-based thermoplastic elastomer (A).  
     
     
         9 . An air bag housing cover according to  claim 8  which is a destruction type air bag housing cover.  
     
     
         10 . An air bag housing cover according to  claim 8 , wherein a bending modulus thereof is 150 to 500 MPa.  
     
     
         11 . An air bag housing cover according to  claim 8 , wherein said olefin-based thermoplastic elastomer (A) contains an ethylene content of 30 to 55% by weight, and a room-temperature xylene-soluble having weight-average molecular weight of 200,000 to 800,000.  
     
     
         12 . An air bag housing cover according to  claim 8 , wherein said ethylene-α-olefin copolymer (D) has a density of 0.85 to 0.88 g/cm 3 , and a melt flow rate of 0.01 to 20 g/10 minutes as measured at 230° C. under a load of 21.18N.  
     
     
         13 . An air bag housing cover according to  claim 8 , further comprising (E) an inorganic filler in an amount of 1 to 50 parts by weight based on 100 parts by weight of the olefin-based thermoplastic elastomer (A).  
     
     
         14 . An air bag housing cover according to  claim 13 , wherein said inorganic filler (E) is talc having an average particle size of not more than 10 μm.  
     
     
         15 . An air bag housing cover according to  claim 8 , wherein the thermoplastic elastomer composition further comprises (F) a styrene-based thermoplastic elastomer in an amount of 1 to 50 parts by weight based on 100 parts by weight of a sum of the components (A), (B) and (D).  
     
     
         16 . An air bag housing cover according to  claim 8 , wherein the thermoplastic elastomer composition further comprises (C) a softening agent for hydrocarbon-based rubbers in an amount of 1 to 100 parts by weight based on 100 parts by weight of a sum of the components (A), (B) and (D).  
     
     
         17 . An air bag housing cover according to  claim 8 , wherein the thermoplastic elastomer composition has a −40° C. Izod impact strength of not less than 50 kJm 2 .  
     
     
         18 . An air bag housing cover according to  claim 8 , wherein said air bag housing cover has at least one groove portion for destruction, has a morphology of island-like phase of a rubber component dispersed in a matrix of polypropylene; the circle-corresponding diameter of the rubber component phase is not more than 2 μm; and the average acicularity of rubber component phase represented by a ratio a/b wherein a and b represent a major axis diameter and minor axis diameter, respectively, is 2 to 10.  
     
     
         19 . An air bag housing cover comprising: 
 (A) 100 parts by weight of an olefin-based thermoplastic elastomer comprising (A1) a propylene homopolymer having an isotactic index of not less than 90%, and (A2) a copolymer of propylene and a C 2  to C 8  α-olefin other than propylene, said propylene homopolymer (A1) and said copolymer (A2) being present in amounts of 30 to 60% by weight and 70 to 40% by weight, respectively, based on a total amount of the components (A1) and (A2), and said copolymer having propylene unit and ethylene unit as essential constituting units, 
 said olefin-based thermoplastic elastomer (A) being obtained by producing the component (A2) by polymerization subsequent to the production of the component (A1) by polymerization, and having a 0° C. eluate content of 30 to 60% by weight based on a total eluate content as measured at a temperature between 0° C. and 140° C. by a temperature rising elution fractionation using o-dichlorobenzene as a solvent;  
   (B) 10 to 150 parts by weight of a propylene-based polymer; and    (D) 15 to 180 parts by weight of an ethylene-α-olefin copolymer, 
 the composition comprising said components (A), (B) and (D) having a bending modulus of 150 to 500 MPa.  
   
     
     
         20 . An air bag housing cover comprising: 
 (A) 100 parts by weight of an olefin-based thermoplastic elastomer comprising (A1) a propylene homopolymer having an isotactic index of not less than 90%, and (A2) a copolymer of propylene and a C 2  to C 8  α-olefin other than propylene, said propylene homopolymer (A1) and said copolymer (A2) being present in amounts of 30 to 60% by weight and 70 to 40% by weight, respectively, based on a total amount of the components (A1) and (A2), and said copolymer having propylene unit and ethylene unit as essential constituting units, 
 said olefin-based thermoplastic elastomer (A) being obtained by producing the component (A2) by polymerization subsequent to the production of the component (A1) by polymerization, and having a 0° C. eluate content of 30 to 60% by weight based on a total eluate content as measured at a temperature between 0° C. and 140° C. by a temperature rising elution fractionation using o-dichlorobenzene as a solvent;  
   (B) 10 to 150 parts by weight of a propylene-based polymer; and    (D) 15 to 180 parts by weight of an ethylene-α-olefin copolymer, 
 the composition comprising said components (A), (B) and (D) having a bending modulus of 150 to 500 Mpa,  
 said air bag housing cover having at least one groove portion for destruction and having a morphology of island-like phase of a rubber component dispersed in a matrix of polypropylene;  
 the circle-corresponding diameter of the rubber component phase being not more than 2 μm; and  
 the average acicularity of rubber component phase represented by a ratio a/b wherein a and b represent a major axis diameter and minor axis diameter, respectively, being 2 to 10.