Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1990-05-03
1991-06-25
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 88, 521 98, 521149, C08J 910
Patent
active
050267388
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the production of rigid foam comprising acrylic and/or methacrylic polymers by polymerization and foaming of acrylic acid and/or methacrylic acid compounds at elevated temperature in a mold and removal of the foamed plastics from the mold.
FR-A-1 423 844 sets forth a process for the production of foams from polyalkyl acrylates and polyalkyl methacrylates. According to this prior art process, the monomers are polymerized in a first step in the presence of a small amount of azobisisobutyronitrile at a low temperature of about 40.degree. to 45.degree. C. in the course of 6 to 15 hours to give a bubble-free product. In a second step the resulting polymerization product is heated at a temperature within the range of from 170.degree. to 190.degree. C. under vacuum. This known two-step process has the disadvantage that two separated steps have to be carried out and that no continuous production of the foam is possible.
The "Kunststoffberater" 4/76, pages 146, 148 and 150 in general sets forth expanding and foaming agents for foaming plastics. It is stated that there exists no universal expanding agent for all thermoplastics, thermosets and elastomers and that for the production of foamed plastics three different foaming processes exist, which are founded on either chemical, physical or mechanical basis.
U.S. Pat. No. 3,950,314 sets forth the production of bubble-free polymethyl methacrylates. In order to obtain bubble-free products, metal salts are added to the monomeric mixtures. If the use of the metal salts is dispensed with, no foams but solid glass containing undesired individual bubbles will be obtained.
In JP 52-117 987, cited in Hochmolekularbericht 1979, H. 4821/79 and in CPI Profile Booklet 1978, 81851Y/46, the polymerization of a mixture comprising methyl methacrylate and a methyl methacrylate prepolymer is described. The production of foams is not mentioned in this reference.
Furthermore, processes for the production of articles made of foamed polymethyl methacrylate have been known, according to which in a first step a mixture of monomeric methyl methacrylate, a foaming agent which cannot be evaporated at the polymerization temperature and at least one polymerization catalyst is polymerized at a pressure above the evaporation pressure of the foaming agent at the polymerization temperature to give an especially plate-like body. The resulting body is then foamed in a second step by heating to a sufficiently high temperature (cf. DE-PS 3 124 980). In this case, easily volatile fluorocarbons, such as trichlorofluoromethane and trichlorotrifluoroethane are used as liquid inert foaming agents. The use of easily volatile fluorocarbons as the foaming agent increasingly meets with objections and resistance for reasons of environmental protection. Foams result, which have a low weight per unit volume and no smooth surface and thus when used for external insulations require covering for the protection from climate and weather.
DE-PS 3 001 205 sets forth a process for the production foams comprising methacrylic ester. This process has the disadvantage that it also proceeds in two steps and requires several hours.
DE-OS 3 412 142 sets forth a process for the production of hardly inflammable products made of acrylic polymers. According to this process it is operated with excess pressure, both foamed and non-foamed products being producible. The foamed products obtained in this process have no smooth surfaces.
Foams comprising acrylic and/or methacrylic polymers are of growing interest as building materials, since they are transparent, i.e. pervious to light, but not transparent to heat. They are especially well suited as plates, e.g. for glass-houses. When using such foams it is essential that the foams have a smooth surface, so that it is no longer required to cover them with glass or plastics plates. If the foams do not have a smooth surface, dirt and moisture may easily penetrate, and the plates turn unsightly in a short time already. Furthermore, it is of advantage when
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Foelak Morton
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
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