Core material for an automobile bumper

Abstract

For use in an automobile bumper, a core material composed of a molded article of prefoamed polyolefin resin particles. The core material has a density of 0.05 to 0.15 g/cm 3 and the relation represented by the following expression E.sub.20/ρ ≧20 kg-cm/g wherein E 20 is the amount of energy absorption (kg-cm/cm 3 ) when the core material is compressed to 50% at 20° C., and ρ is the density (g/cm 3 ) of the core material.

What is claimed is: 
     
       1. A core material for use in automobile bumpers, said core material being composed of a molded article of prefoamed particles of a polyolefin resin, and having a density of 0.05 to 0.15 kg-g/cm 3  and the relation represented by the following expression   E.sub.20 /ρ≧20 kg-cm/g     wherein E 20  is the amount of energy absorption (kg-cm/cm 3 ) when the core material is compressed to 50% at 20° C., and ρ is the density (g/cm 3 ) of the core material. wherein said particles are nearly spherical in shape, have a particle diameter of 2 to 15 mm, a cell diameter of 0.10 to 2.00 mm and a proportion of closed cells of at least 90% and contain air filled within the cells.     
     
     
       2. The core material of claim 1 which has a density of 0.06 to 0.13 g/cm 3  and the relation represented by the following expression E 20  /ρ≧22 kg-cm/g. 
     
     
       3. In an automobile bumper which is composed of a core material and a surface covering material, the improvement wherein said core material is composed of a molded article of prefoamed particles of a polyolefin resin, and having a density of 0.05 to 0.15 g/cm 3  and the relation represented by the following expression   E.sub.20 /ρ≧20 kg-cm/g     wherein E 20  is the amount of energy absorption (kg-cm/cm 3 ) when the core material is compressed to 50% at 20° C., and ρ is the density (g/cm 3 ) of the core material, wherein said particles are nearly spherical in shape, have a particle diameter of 2 to 15 mm, a cell diameter of 0.10 to 2.00 mm and a proportion of closed cells of at least 90% and contain air filled within the cells.     
     
     
       4. The automobile bumper of claim 3 wherein the core material has a density of 0.06 to 0.13 kg-g/cm 3  and the relation represented by the following expression   E.sub.20 /ρ≧22 kg-cm/g.     
     
     
       5. The automobile bumper of claim 3 which has a bumper height of from 50 to 100 millimeters. 
     
     
       6. The automobile bumper of claim 3 wherein the polyolefin resin is selected from the group consisting of polypropylene, ethylene/propylene random copolymer and high-density polyethylene. 
     
     
       7. The automobile bumper of claim 3 wherein the polyolefin resin is an ethylene/propylene random copolymer. 
     
     
       8. The automobile bumper of claim 3 wherein the polyolefin resin is high-density polyethylene. .Iadd. 
     
     
       9.  The core material of claim 1, wherein the polyolefin resin is not cross linked. .Iaddend. .Iadd.10. The core material of claim 1, wherein the polyolefin resin is cross linked. .Iaddend. .Iadd.11. The automobile bumper of claim 3 wherein the core material is composed of a polyolefin resin that is not cross linked. .Iaddend. .Iadd.12. The automobile bumper of claim 3 wherein the core material is composed of a polyolefin resin that is cross linked. .Iaddend. .Iadd.13. The automobile bumper of claim 7 wherein said copolymer is not cross linked. .Iaddend. .Iadd.14. The automobile bumper of claim 7 wherein said copolymer is cross linked. .Iaddend.