| 摘要 |
Known methods exist for recovering polyethene and polypropene and other polyolefins from salvage material by extracting with different solvents at relatively high temperatures and precipitating the polyolefin from the solution by lowering the temperature of the latter. However, the cooling of the solution is difficult to carry out since the precipitated polyolefin is sticky and gives rise to deposits and blockages in a normal heat exchanger. The present invention solves this problem by using water- insoluble solvents for the extraction and injecting the warm solution into cold water. Since the density of the solution differs substantially from that of the water, the solution either floats up to the surface of the water or sinks to the bottom of the water container where it is partitioned off from the water and then separated into solvent and a filter cake, which is dried to a powder or to a sintered cake of pure polyolefin by evaporation. Alternatively, the filter cake is reheated such that it once again forms a solution but one which is of a substantially higher concentration than was the original solution. This solution is then spread or sprayed out on a web of heated board or paper, whereupon remaining solvent is volatilized in a closed space, with the volatilized solvent being recovered. This results in a polyolefin-paper laminate which can be used for packing material, etc. In the same way, a polyolefin film can be produced if the web, consisting, for example, of steel belt or steel wire, is coated with teflon, for example, so that the film which is formed after volatilization of the solvent can be drawn free from the web and taken up on a reel. |
