Process for producing extruded foam products with higher...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...

Reexamination Certificate

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Details

C521S079000, C521S146000

Reexamination Certificate

active

06187831

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to processes for preparing extruded foam products and more particularly to a processes for producing such products having polymer blends with high levels of carbon dioxide as a blowing agent.
BACKGROUND OF THE INVENTION
Extruded synthetic resinous foams are useful materials for many applications including thermal insulation, decorative purposes, packaging and the like. Thermal insulation is one particularly important application for styrene polymer foams. In this application, it is desirable to maintain the insulating value of the foam for as long as possible. It is also desirable for the foam to have dimensional stability. The desirable characteristics can be achieved, in part, by providing foams having uniform cell size.
For a considerable period of time, styrene polymer foams were extruded using various halo-carbons, such as methyl chloride, ethyl chloride, chlorocarbons, fluorocarbons (including HFCs) and chlorofluorocarbons (CFCs) including dichlorodifluoromethane, fluorohydrocarbons or chlorofluorohydrocarbons (which, as the name implies, contain at least one hydrogen atom and have been referred to as “soft CFCs”, “HCFCs” and “HFCs”), as blowing agents. Examples of halo-carbons generally include (CFCs) such as CFC-11 which is chlorotrifluoromethane, CFC-12 which is dichlorodifluoromethane, and CFC-113 which is 1,2,2-trifluoro-1,1,2-tri-chloroethane, soft CFCs, HCFCs and HFCs, such as chlorodifluoromethane (F-22), 1,1-dichloro2,2,2-trifluoroethane (F-123), 1-chloro-1,1 -difluoroethane(F-142
b
), 1,1,1,2-tetrafluoroethane (F-134
a
), and 1,1-di-chloro-1-fluoroethane (F-141
b
).
Recently, the use of halo-carbons for applications including aerosols, refrigerants, foam-blowing agents and specialty solvents within the electronics and aerospace industries has been terminated by government regulation or is highly undesirable. This is because halo-carbons are believed to destroy the ozone layer in the stratosphere. Attempts have therefore been made to replace halo-carbons with hydrocarbons such as butane or inert gases such as carbon dioxide. However, there are a number of problems associated with using non-halo-carbon blowing agents including low solubility of the blowing agents in styrene polymers, low quality foam production and so on.
The general procedure utilized in the preparation of extruded synthetic resinous foam bodies generally involves the following steps. A resin, such as a polystyrene resin, is heat plastified and one or more fluid blowing agents is incorporated and thoroughly mixed into the plastified resin under conditions which permit thorough mixing of the blowing agent into the plastified resin and prevent foaming of the mixture. The mixture of resin, blowing agent and optional additives is cooled, and the pressure on the mixture is reduced resulting in foaming of the mixture and formation of the desired foam body. In other words, foam bodies are obtained by extruding the cooled plastified mixture of resin, blowing agent and optional additives into a region of lower pressure.
SUMMARY OF THE INVENTION
The present invention relates to polymer foams which are the so-called “extruded foams”. The extruded foams have fairly uniform, relatively small average cell size and are thus particularly useful for thermal insulation. The extruded foams also have a relatively low density and thus are even more particularly useful for thermal insulation. Another aspect of the extruded foams is that they possess a high level of dimensional stability. Finally, the extruded foams can be made without blowing agents such as CFCs, HCFCs, HFCs and soft CFCs.
In one embodiment, the present invention relates to a process for preparing a foam product involving the steps of (A) forming a foamable mixture of (1) a polymer comprising about 10% to about 90% monomers of at least one of meta-substituted styrene and para-substituted styrene and 0% to about 90% monomers of styrene, and (2) a blowing agent containing a major amount of carbon dioxide under a pressure sufficient to prevent prefoaming of the mixture and (B) foaming the mixture into a region of reduced pressure to form the foam product.
In another embodiment, the present invention relates to a process of preparing a foam product including the steps of (A) forming a foamable mixture of (1) a copolymer comprising about 1% to about 70% monomers of styrene and about 30% to about 99% monomers of at least one of meta-methylstyrene and para-methylstyrene, and (2) a blowing agent containing a major amount of carbon dioxide under a pressure sufficient to prevent prefoaming of the mixture and (B) foaming the mixture into a region of reduced pressure to form the foam product.
In yet another embodiment, the present invention relates to a foam product containing a copolymer of styrene and at least one of meta-substituted styrene and para-substituted styrene wherein the cells of the foam are free of halogen blowing agents.


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Copending U.S. application No. 09/154,067.
Copending U.S. application No. 09/154,367.

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