Claims
- 1. A process for the preparation of an expanded polymeric foam comprising the steps of:
- (a) melt processing under pressure an alkenyl aromatic polymer having a glass transition temperature of between about 60.degree. to about 100.degree. C. together with a volatile blowing agent to form a flowable admixture, said volatile blowing agent comprising a mixture of from about 40 to about 90% by weight of a primary blowing agent comprising dichlorodifluoromethane, and from about 10 to about 60% by weight of a secondary blowing agent comprising a halogenated hydrocarbon, a hydrocarbon, or an aliphatic alcohol containing from 1 to 4 carbon atoms, said halogenated hydrocarbon, hydrocarbon or aliphatic alcohol having a normal atmospheric boiling point of from about 0.degree. to about 100.degree. C.,
- (b) extruding said admixture through a die to a zone of lower pressure and activating said blowing agent to expand said alkenyl aromatic polymer to a cellular structure, and
- (c) exposing said cellular structure to steam at substantially atmospheric pressure to expand further said cellular structure to a foam of lower density.
- 2. The process of claim 1 in which said alkenyl aromatic polymer is polystyrene.
- 3. The process of claim 1 in which said alkenyl aromatic polymer is a copolymer of styrene and acrylonitrile.
- 4. The process of claim 1 in which said volatile blowing agent is present in an amount of from 10-30 parts per hundred of said alkenyl aromatic polymer.
- 5. The process of claim 1 in which said volatile blowing agent comprises from about 60 to about 80% by weight dichlorodifluoromethane and from about 20 to about 40% by weight trichloromonofluoromethane.
- 6. The process of claim 1 in which an azido functional silane crosslinking agent is added in step (a).
- 7. A process for the preparation of an expanded polymeric foam comprising the steps of:
- (a) impregnating a volatile blowing agent into a granular alkenyl aromatic polymer having a glass transition temperature of between about 60.degree. to about 100.degree. C., said volatile blowing agent comprising a mixture of from about 40 to about 90% by weight of a primary blowing agent comprising dichlorodifluoromethane and from about 10 to about 60% by weight of a secondary blowing agent comprising a halogenated hydrocarbon, hydrocarbon, or an aliphatic alcohol containing from 1 to 4 carbon atoms, said halogenated hydrocarbon, hydrocarbon, or aliphatic alcohol having a normal atmospheric boiling point of from about 0.degree. to about 100.degree. C.,
- (b) heating said granular alkenyl aromatic polymer to activate said volatile blowing agent and expand said granular alkenyl aromatic polymer to a cellular structure, and
- (c) exposing said cellular structure to steam at substantially atmospheric pressure to expand further said cellular structure to a foam of lower density.
- 8. The process of claim 7 in which steps (b) and (c) occur substantially simultaneously and said steam supplies the necessary heat to activate said volatile blowing agent.
- 9. The process of claim 7 in which said alkenyl aromatic polymer is polystyrene.
- 10. The process of claim 7 in which said alkenyl aromatic polymer is a copolymer of styrene and acrylonitrile.
- 11. A process of claim 7 in which said volatile blowing agent is present in an amount of from 10-30 parts per hundred of said alkenyl aromatic polymer.
- 12. The process of claim 7 in which said volatile blowing agent comprises from about 60 to about 80% by weight dichlorodifluoromethane and from about 20 to about 40% by weight trichloromonofluoromethane.
- 13. The process of claim 7 in which an azido functional silane crosslinking agent is added to said alkenyl aromatic polymer in step (a).
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser. No. 672,001, filed Nov. 16, 1984.
US Referenced Citations (6)
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
672001 |
Nov 1984 |
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