Stock material or miscellaneous articles – Structurally defined web or sheet – Physical dimension specified
Reexamination Certificate
1999-10-21
2001-07-31
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Structurally defined web or sheet
Physical dimension specified
C521S079000, C521S081000, C521S099000, C521S117000, C521S133000, C521S134000, C521S139000, C521S146000, C524S081000, C524S275000, C428S305500, C428S314800
Reexamination Certificate
active
06268046
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 polystyrene 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. These desirable aspects can be achieved while maximizing the amount of blowing agent soluble in the foamable mixtures.
In one embodiment, the present invention relates to a process for preparing a foam product including the steps of (A) forming a foamable mixture of (1) a major amount of a styrenic polymer having a low melt index, (2) a minor amount of a high melt index styrenic polymer, and (3) a blowing agent containing a major amount of carbon dioxide under a pressure sufficient to prevent prefoaming (the undesirable premature foaming of the foam mixtures before it reaches a region of reduced pressure) 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 major amount of a polystyrene having a weight average molecular weight of about 225,000 to about 400,000, (2) a minor amount of a polystyrene having a weight average molecular weight of about 50,000 to about 100,000, and (3) from about 1% to about 16% by weight of the polystyrenes, 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 a foam product.
In yet another embodiment, the present invention relates to a foam product comprising a major amount of a styrenic polymer having a low melt index, and a minor amount of a high melt index styrenic polymer, wherein the foam cells are free of halogen blowing agents.
DESCRIPTION OF PREFERRED EMBODIMENTS
The foamable mixtures which are extruded and foamed into foam products, such as foam board, foam sheet and other foam structures, in accordance with the inventive process contain two different styrenic polymers and a blowing agent. The foamable mixtures may contain other optional additives. One styrenic polymer has a high melt index and is a polymer of styrene or a copolymer of styrene and at least one copolymerizable monomer. The other styrenic polymer has a low melt index and is a polymer of styrene or a copolymer of styrene and at least one copolymerizable monomer. Neither, either or both of the two styrenic polymers may be further copolymerized with other monomers.
Both the high and low melt index styrenic polymers contain styrene monomers. A styrene monomer is an aromatic compound characterized by the general formula
Ar—CH═CH
2
(I)
wherein Ar represents an aromatic hydrocarbon group of the benzene series.
Both the high and low melt index styrenic polymers may be copolymers containing styrene monomers and copolymerizable monomers. A copolymerizable monomer is any monomer that can be polymerized with styrene monomers to form a styrene copolymer. Generally speaking, the copolymerizable monomer is a monomer containing an ethylenically unsaturated group. In one embodiment, the amount of copolymerizable monomer in the styrene copolymers is from about 0.1% to about 10%, and preferably from about 1% to about 5%.
In a preferred embodiment, the copolymerizable monomer containing an ethylenically unsaturated group is an aromatic compound of Formula II and may be represented by the following formula
wherein R
1
, R
3
, R
4
, R
5
and R
6
are each independently hydrogen, chlorine, bromine, or alkyl groups containing from 1 to about 8 carbon atoms, and R
2
is hydrogen or methyl, with the proviso that a total number of carbon atoms in the monomer does not exceed 20. In a preferred embodiment, at least one of R
4
, R
5
and R
6
are independently chlorine, bromine, or alkyl groups containing from 1 to about 8 carbon atoms. In another preferred embodiment, at least one of R
4
, R
5
and R
6
is an alkyl group containing from 1 to about 4 carbon atoms, such as a methyl group, ethyl group, propyl group, isopropyl group or butyl group. In a more preferred embodiment, one of R
4
, R
5
and R
6
is an alkyl group containing from 1 to about 4 carbon atoms and two of R
4
, R
5
and R
6
are hydrogen.
Examples of copolymerizable monomers according to Formula (II) include 3-methyl styrene, 4-methyl styrene, 2,4-dimethyl styrene, 2,5-dimethyl styrene, 4-chlorostyrene, 3-chlorostyrene, 4-chloromethyl styrene, 3-chloromethyl styrene, 4-bromostyrene, 3-bromostyrene, alpha-methyl styrene, alpha-2-dimethyl styrene, etc.
In another emb
Breindel Raymond Marshall
Cisar Thomas Earl
Miller Larry Michael
Weekley Mitchell Zane
Acquah Samuel A.
Barns Stephen W.
Eckert Inger H.
Owens Corning Fiberglas Technology Inc.
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