Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1981-07-30
1983-12-06
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 455, 521 54, 521134, 521138, 521139, C08J 922
Patent
active
044194595
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to processes of producing transparent foamed plastics materials, particularly foamed polymethacrylates, which may specifically be in the form of sheets, panels, molded articles and laminates having a foamed core.
DESCRIPTION OF PRIOR ART
It is known to make foamed materials from plastics, e.g. from polyurethane. Basically, two processes may be used. In the first process, the starting mixture of monomers and blowing agent is polymerized with simultaneous foaming in a one-shot process. This process will yield useful products only if the monomers polymerize quickly and thus form a mechanically strong product, which may be foamed by the gases or vapours of the blowing agent whereby stable cells are formed.
In the second known process the starting monomer is initially polymerized with the added blowing agent without foaming, whereupon in a second stage the polymer is brought into a plastic or free-flowing condition by the application of heat and at the same time the blowing agent is evaporated or decomposed so that gas bubbles will result within the plastics material and a foamed material will be formed.
None of these known processes will achieve the desired result in the case of polymethacrylates. When the first-mentioned process is used, the bubbles (cells) cannot be kept stable during polymerization of the acrylic foam. As a result of the polymerization the surface tension of the bubles will increase, causing the same to burst and to combine so that the foam will collapse prior to curing.
In the case of polymethacrylate, the known two-stage process also will not lead to the desired result. In accordance with the British Patent Specification No. 1,448,621 and the French Patent Specification No. 1,423,844 a polymethacrylate is to be foamed by initially polymerizing a methacrylate, to which a blowing agent is added, under conditions which prevent the blowing agent from becoming effective. In a second stage the hardened polymethacrylate is then heated to a softening temperature at which the blowing agent will become active. However, as a result of the high internal pressure the foamed material substantially contains only small bubbles. Experiments have shown, moreover, that during foaming the polymethacrylate composition will be blown into every direction so that a foam is obtained which has a wavy and warped surface. Furthermore, this process does not permit production of foamed articles having a continuously smooth and non-porous surface. In addition, the obtained products have little transparency and permit only a diffuse transmission of light, because the light will be reflected by the numerous small bubbles.
There is a demand for a clear, transparent foamed plastics material of high transparency and, at the same time, good mechanical strength, with a high degree of protection against loss of heat and a smooth surface structure. Such a foamed plastics material cannot be made with any of the processes known so far and also differs basically from any known transparent extruded laminate panels of plastics material which have either webs or closely adjacent tubes in their interior.
DESCRIPTION OF THE INVENTION
It is the object of the present invention to provide a process of producing transparent foamed plastics materials, which will result in a foamed plastics having closed, large, plane cells of controlled size, shape and density, a controlled mechanical strength as well as a smooth, non-porous surface; also, the process is to permit the manufacture of molded articles and laminate articles.
The above-specified object is solved by the process according to the present invention of producing a transparent foamed plastics, in which into a reaction resin containing the components required for curing, there are introduced (a) solid beads consisting of a mixture of at least one transparent polymer and blowing agent, and/or (b) solid beads consisting of at least one transparent polymer having microcapsules included therein which contain blowing agent, and in whic
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August Hohnholz KG
Foelak Morton
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