Volatile foaming agent composition

Abstract

It is an object of the present invention to provide volatile foaming agent compositions for thermoplastic resins capable of producing a thermoplastic resin foam without any shinkage or expansion after foaming. A volatile foaming agent composition for thermoplastic resin according to the present invention comprises 1,1,1,2-tetrafluoro-ethane. As the permeability of 1,1,1,2-tetrafluoro-ethane in thermoplastic resins is smaller than that of the air, volatile foaming agent composition containing 1,1,1,2-tetrafluoro-ethane and other kind of volatile foaming agent having permeability higher than that of the air can be regulated to have the permeability similar to that of the air. Accordingly, the permeating speed of volatile foaming agent from the inside of foam cells to the outside and the permeating speed of substituting air into the foam cells from outside can be balanced and any shrinkage or expansion after foaming can be avoided.

What is claimed is: 
     
       1. A method of blowing a thermoplastic polymer comprising mixing a volatile blowing agent into the molten polymer and blowing the polymer; wherein said blowing agent comprises a mixture of 1,1,1,2 tetrafluoroethane with other volatile blowing agents having a permeability higher than air in the thermoplastic polymer and where the ratio of the 1,1,1,2 tetrafluoroethane to the other volatile blowing agents is regulated so that the overall gas permeability of the volatile mixture in the thermoplastic polymer is comparable to that of air; and wherein the thermoplastic polymer is selected from polyethylene, .Iadd.or .Iaddend.polypropylene, .[.polybutadiene, or polystyrene.].. 
     
     
       2. A method of blowing a thermoplastic polymer according to claim 1, wherein the other volatile blowing agent is trichloro-monofluoro-methane. 
     
     
       3. A method of blowing a thermoplastic polymer according to claim 1, wherein the other volatile foaming agent is dichloro-difluoro-methane. 
     
     
       4. A method of blowing a thermoplastic polymer according to claim 1, wherein the other volatile foaming agent is 1,2-dichlorotetrafluoro-ethane.