Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1987-09-21
1990-01-16
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 53, 264DIG5, 521134, 521143, 521149, 521910, C08J 914
Patent
active
048943959
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of olefin polymer foams and, in particular, to an extrusion foaming process for olefin polymers using a stability control additive in conjunction with a blowing agent mixture.
In addition, the present invention also relates to an expandable olefin polymer composition containing the indicated stability control additive and mixed blowing agent system admixed therein and to polyolefin foams prepared therefrom.
It is well known to prepare olefin polymer foams by heat plastifying a normally solid olefin polymer resin, admixing such heat plastified resin with a volatile blowing agent under heat and pressure to form a flowable gel and thereafter extruding the gel into a zone of lower pressure and temperature to expand and cool the gel to form the desired solid olefin foam product.
Until very recently, there had been used only one blowing agent (i.e., 1,2-dichlorotetrafluoroethane) providing sufficient dimensional stability during the curing period.
However, a problem frequently encountered in preparing foams especially of very low density employing 1,2-dichlorotetrafluoroethane as a blowing agent is a limitation on the cross-sectional size of foamed product having smooth skin. This problem occurs when the die opening is increased to provide foam having a larger cross-section because the decrease in hydrostatic pressure in the die causes prefoaming with the result that the extruded foam has a rough skin and/or is physically deformed.
More recently, certain technology has been developed in the area of stability control agents in an attempt to permit the obtention of commercially acceptable dimensional stability with a wider range of volatile halogenated hydrocarbon blowing agents. (See, for example, U.S. Pat No. 3,644,230 and U.S. Pat. No. 4,214,054). Unfortunately, these techniques, while generally providing low density ethylenic polymer foams having improved dimensional stability, are also somewhat limited in terms of the maximum cross-section of the foam articles that can be obtained therewith from a given type of extrusion apparatus. Accordingly, it would be highly desirable to provide an improved extrusion foaming process capable of producing low density olefin polymer foam articles having both relatively large cross-sectional areas (e.g., providing an increase in the maximum achievable foam cross-sectional area which can be obtained with a given extrusion apparatus) and good dimensional stability as well as other desirable foam properties such as closed cells of small cell size and the like.
SUMMARY OF THE INVENTION
In accordance with the present invention such a process for preparing closed-cell olefin polymer foam articles having increased maximum achievable cross-sectional areas on a given type or size of extrusion apparatus and having good dimensional stability and smooth skin is provided along with an expandable olefin polymer composition suitable for use therein. In such process,
(A) a normally solid olefin polymer resin is heat plastified and intimately admixed, under elevated temperature and pressure, about 95 weight percent, and from about 5 to about 50 weight percent of an aliphatic hydrocarbon, a halogenated hydrocarbon compound physical blowing agent, or mixture thereof having an atmospheric pressure boiling point which is greater than that of 1,2-dichlorotetrafluoroethane (i.e. about 3.55.degree. C.) to about 50.degree. C., or 1,2-dichlorotetrafluoroethane, from about 5 to about 85 percent of dichlorodifluoromethane and from about 5 to about 50 weight percent of an aliphatic hydrocarbon, a halogenated hydrocarbon compound physical blowing agent or mixture thereof having an atmospheric pressure boiling point of from about 0.degree. C. to about 50.degree. C.
(B) the resultant mixture is then extruded into a zone of lower pressure and cooled to thereby form an olefin polymer foam.
The aforementioned process is particularly well suited for the preparation of closed-cell olefin polymer foamed articles of rel
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Foelak Morton
The Dow Chemical Company
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