Cover for a vehicle air bag

Abstract

A cover for a vehicle air bag comprises an external surface layer injection-molded from a thermoplastic material having a JIS-A hardness of 20 to 90 and a core layer injection-molded from a thermoplastic material having a bending elastic modulus (JIS K 7203) of not less than about 1000 kg/cm 2 and a hardness greater than that of the surface layer. The core has weakened zones along which the cover breaks when the air bag is inflated.

We claim: 
     
       1. A .Iadd.unitary .Iaddend.cover for housing a folded vehicle air bag, the cover being made solely of polymeric materials, being adapted to be fastened to a retainer base in a position generally between the air bag and the vehicle component and having weakened zones that enable it to break easily when the air bag inflates, characterized in that it has an external surface layer .Iadd.and a core layer integrally molded together, said surface layer .Iaddend.formed of a thermoplastic polymeric material having a Type A hardness of from about 20 to about 90 as determined by Japanese Industrial Standard K6301-1975 and .[.a.]. .Iadd.said .Iaddend.core layer formed of a thermoplastic polymeric material having a modulus in elasticity in flexure of not less than about 1000 kg/cm 2  as determined in accordance with Japanese Industrial Standard K7203-1982 and a hardness greater than that of the surface layer, and in that the weakened zones are formed in the core layer. 
     
     
       2. An air bag cover according to claim 1 and further characterized in that the thermoplastic polymeric material of the external surface layer contains a predominant amount of a member of the group consisting of olefin-based elastomers, styrene-based elastomers, vinyl-chloride elastomers, soft polyvinyl chloride, and combinations thereof. 
     
     
       3. An air bag cover according to claim 2 and further characterized in that the olefin-based elastomer is selected from the group consisting of ethylene-propylene copolymer synthetic rubber, ethylene-propylene-diene terpolymer synthetic rubber, ethylene-butene-1 copolymer synthetic rubber, polypropylene, polyethylene, polyisobutylene, and combinations thereof. 
     
     
       4. An air bag cover according to claim 2 and further characterized in that the styrene-based elastomer is selected from the group consisting of block copolymers of monovinyl aromatic hydrocarbon polymer blocks and conjugate diene polymer blocks, hydrogenated derivatives of block copolymers of monovinyl aromatic hydrocarbon polymer blocks and conjugate diene polymer blocks, hydrogenated derivatives of block copolymers of styrene polymeric blocks and butadiene polymer blocks, and hydrogenated derivatives of block copolymers of styrene polymer blocks and isoprene polymer blocks. 
     
     
       5. An air bag cover according to claim 3 or claim 4 and further characterized in that the material of the external layer contains a hydrocarbon-based rubber softener in an amount of up to 30% by weight. 
     
     
       6. An air bag cover according to claim 1 and further characterized in that thermoplastic polymeric material of the core layer contains a predominant amount of a member of the group consisting of high-density polyethylene, polypropylene, block copolymers of propylene and ethylene, random copolymers of propylene and ethylene, olefin-based synthetic rubbers, and combinations thereof. 
     
     
       7. An air bag cover according to claim 6 and further characterized in that the material of the core layer contains an olefin-based synthetic rubber in an amount not exceeding 60% by weight. 
     
     
       8. An air bag cover according to claim 6 and further characterized in that the material of the core layer is a blend of a block copolymer of propylene and ethylene and an olefin-based synthetic rubber and in that the amount of the olefin-based synthetic rubber in the blend does not exceed 60% by weight. .Iadd. 
     
     
       9.  A cover for housing a folded vehicle air bag, the cover being made solely of polymeric materials, being adapted to be fastened to a retainer base in a position generally between the airbag and the vehicle component and having weakened zones that enable it to break easily when the airbag inflates, characterized in that it has an external surface layer formed of a thermoplastic polymeric material having a Type A hardness of from about 20 to about 90 as determined by Japanese Industrial Standard K6301-1975 and a core layer formed of a thermoplastic polymeric material having a modulus in elasticity in flexure of not less than about 1000 kg/cm 2  as determined in accordance with Japanese Industrial Standard K7203-1982 and a hardness greater than that of the surface layer, and in that the weakened zones are formed in the core layer. .Iaddend..Iadd.10. An airbag cover according to claim 9 and further characterized in that the thermoplastic polymeric material of the external surface layer contains a predominant amount of a member of the group consisting of olefin-based elastomers, styrene-based elastomers, vinyl-chloride elastomers, soft polyvinyl chloride, and combinations thereof. .Iaddend..Iadd.11. An airbag cover according to claim 10 and further characterized in that the olefin-based elastomer is selected from the group consisting of ethylene-propylene copolymer synthetic rubber, ethylene-propylene-diene terpolymer synthetic rubber, ethylene-butene-1 copolymer synthetic rubber, polypropylene, polyethylene, polyisobutylene, and combinations thereof. .Iaddend..Iadd.12. An air bag cover according to claim 10 and further characterized in that the styrene-based elastomer is selected from the group consisting of block copolymers of monovinyl aromatic hydrocarbon polymer blocks and conjugate diene polymer blocks, hydrogenated derivatives of block copolymers of monovinyl aromatic hydrocarbon polymer blocks and conjugate diene polymer blocks, hydrogenated derivatives of block copolymers of styrene polymeric blocks and butadiene polymer blocks, and hydrogenated derivatives of block copolymers of styrene polymer blocks 
     
     
        and isoprene polymer blocks. .Iaddend..Iadd.13.  An air bag cover according to claim 11 or claim 12 and further characterized in that the material of the external layer contains a hydrocarbon-based rubber softener in an amount of up to 30% by weight. .Iaddend..Iadd.14. An air bag cover according to claim 9 and further characterized in that thermoplastic polymeric material of the core layer contains a predominant amount of a member of the group consisting of high-density polyethylene, polypropylene, block copolymers of propylene and ethylene, random copolymers of propylene and ethylene, olefin-based synthetic rubbers, and combinations thereof. .Iaddend..Iadd.15. An air bag cover according to claim 14 and further characterized in that material of the core layer contains an olefin-based synthetic rubber in an amount not exceeding 60% by weight. .Iaddend..Iadd.16. An air bag cover according to claim 14 and further characterized in that the material of the core layer is a blend of a block copolymer of propylene and ethylene and a olefin-based synthetic rubber and in that the amount of the olefin-based synthetic rubber in the blend does not exceed 60% by weight. .Iaddend.