Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1992-06-08
1994-04-05
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 73, 521 95, 521145, 521149, 521178, C08J 910, C08J 930
Patent
active
053005333
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a new method for production of crosslinked foamed plastics, based on a copolymer where the monomer composition mainly consists of vinyl chloride.
A relatively great part of the PVC comsumption is used for foamed products. To obtain a foamed product, a blowing agent is added to the composition. At high temperatures the blowing agent is decomposed giving gas as one of the products, which results in foaming of the product. The foaming can be carried out during the processing, for example gelling of paste or free foaming after extrusion.
The process also could be carried out in several stages. First the material can be processed below the decomposition temperature for the blowing agent, and then be decomposed in a separate stage. This often is done under pressure in an autoclave in such a way that the material is not foamed. After cooling the pressure can be reduced without occurrence of foaming.
The high viscosity of the material at low temperatures is the cause of this. The foaming can be regulated by heating the blowing agent to a suitable temperature where the wanted properties are obtained, for example density and cell structure.
Foamed products are interesting because of their low density. Based on volume this gives a cheaper product, because the material demanded simultaneously decreases. Rigid, foamed PVC products often are used for "sandwich" constructions in automobile-, boat- and air industry. Soft products can be used as acoustic insulation, vibration damper, insulation, sealings etc. Both rigid and soft products are used in buoyancy bodies.
If the mechanical stability for the PVC foam is improved, especially at high temperatures, the range of application will increase. This can be obtained by crosslinking the foamed product. Many methods are avaiable for crosslinking of foam, for example radiation, use of peroxide which results in the formation of free radicals, the addition of low molecular substances which can be crosslinked etc. Crosslinking during radiation is an expensive process which often results in disintegration of PVC during processing. The resulting product often will be a brittle material.
A method much in use for production of crosslinked PVC foam, is a process developed by the French company Kleber Colombes (French patent No. 1 366 979). By this method isocyanate is added both as plasticiser and crosslinking agent. The method gives a network which reinforces the PVC foam, but PVC is not a part of this network. There are several drawbacks with this system, but first of all it concerns the handling of isocyanate, which demands great care. In addition the resulting product can be brittle and can have a reduced resistance to solvents.
The object of the invention is to develop a new method for production of crosslinked polymer foam with good mechanical stability. It is essential to obtain a method which is environmental friendly, simple and cheap. It is an object to avoid extra process steps as crosslinking, for example by radiation.
These and other objects of the invention are obtained by the method as described below and the invention is characterized and defined by the accompanying patent claims.
By this invention one has found a new method for production of crosslinked vinyl chloride containing foam. It is simple, cheap, environmental friendly and does not demand irridation or extra addition of chemicals (compared to production of non-crosslinked foam). The method is based on, the surprising discovery that the decomposition products from the blowing agent which is added to the polymer, can be used as crosslinking agent, provided that the polymer contains a glycidyl compound. Therefore a copolymer is produced where vinyl chloride and a glycidyl (epoxy) containing monomer or eventually another monomer is used in the polymerisation. A blowing agent is added to the polymer where the decomposition products from the blowing agent or the decomposition products of the reaction products from the blowing agent are chemically reactive with the epoxy-groups or thei
REFERENCES:
Toray, Abstract for JP 71005221 (1971).
Ishida, Abstract for JP 71005220 (1971).
Otsuka, Abstract for JP 58021433 (1983).
Mitsubishi Electric, Abstract for JP 77010151 (1977).
Furukawa, Abstract for EP 0053190 (1982).
Mitsubishi Monsanto, Abstract for GB 1490912 (1977).
Boreng Raymond
Dahl Roger
Pedersen Steinar
Foelak Morton
Norsk Hydro a.s.
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