| 摘要 |
A film or board of foamed copolymer is obtained by copolymerizing a mixture of styrene and maleic anhydride while forcing the mixture forward, adding a blowing agent to the initial or polymerizing mixture or to the copolymer formed and extruding through a die. The mixture which is copolymerized may contain at least one other monomer in an amount from 0.1-35% by weight. Examples of the latter are straight chain olefins having 3-36 carbon atoms, e.g. propylene, n-octene and n-octadecene; aliphatic vinyl ethers having 6-18 carbon atoms, e.g. cetyl vinyl ether. Alternatively a "rubbery" polymer or copolymer of low molecular weight may be added in an amount from 0.1-25% by weight, e.g. polyisobutylene, atactic polypropylene, and copolymers from butadiene and styrene, isoprene, methyl methacrylate or acrylonitrile. The copolymerization may be catalysed by a peroxide or hydroperoxide with an accelerator, an azo compound or a soluble redox system. At least part of one of the monomers may be heated with a catalyst until homopolymerization has started and then added to the other components of the mixture. The blowing agent may be a gas, e.g. air, carbon dioxide or nitrogen or a low boiling liquid which is not a solvent for the copolymer e.g. pentane, acetone, ethylene dichloride, methyl ethyl ketone or a fluorohydrocarbon or a solid or mixture of solids which on heating produce a gas, e.g. malonic acid or sodium carbonate/citric acid mixture. A nucleating agent e.g. finely divided metals, may be used with a gaseous blowing agent. Fillers, e.g. mica, may be added in an amount up to 30% of the total weight of the film. The films or boards have at least 20% of their cells open to the surface. An apparatus for carrying out the process consists of a screw extruder into which styrene, nucleating agent, catalyst and filler are fed through one hopper and molten maleic anhydride through another hopper. The polymerization takes place in the second part of the extruder which is cooled. Compressed air is injected into the melt which is extruded through a slit die as a foamed sheet which is carried on a conveyer belt and cooled by jets of air. The cooled sheet is slit into three thinner sheets by knives and the thinner sheets are then compressed between rollers. Alternatively, the melt may be extruded through an annular die of a twin screw extruder. The extrudate passes over a hemispherical mandrel coated with polytetrafluoroethylene, air is supplied to the interior of the tubular film to inflate it and the foamed film is cooled. The foamed, inflated film is collapsed between rollers and slit through its thickness. The slit film is compressed in both cases by subjecting it to a pressure of from 10 p.s.i.-100,000 p.s.i. |
