| 摘要 |
A process of forming a sheet of thermoplastic polymer foam comprises extruding a hot sheet of a foamable thermoplastic polymer composition, rapidly chilling the principal surfaces only of the sheet to prevent expansion thereof and to form outer skins while permitting the still warm core of the sheet to expand, the chilling being controlled to form a sheet consisting of a foam polymer core having a density of at least 18 lbs. per cu. ft., and a non-porous, smooth, tough polymer skin on either side of the core, the core comprising between 50% and 94% of the total thickness of the sheet and being integrally united to the skins, which have a substantially higher density than the core. The preferred thermoplastic polymer is a styrene polymer containing more than 50% styrene. Other suitable polymers listed are cellulose ethers and esters, homopolymers and interpolymers of monomeric compounds containing the CH2=CH< group, e.g. olefins, vinyl halides, vinyl esters of carboxylic acids, vinyl ethers, unsaturated carboxylic acids and their derivatives and interpolymers of the above with a ,b -unsaturated polycarboxylic acids and their derivatives. Polycarbonates, polyurethanes, polyethylene terephthalate or nylon may also be used. Suitable foaming agents are volatile liquids boiling below 100 DEG C. The surfaces may be chilled by mixed air and water blasts, by air alone or by other inert gases, e.g. nitrogen, argon, carbon dioxide and helium at a temperature and a velocity sufficient to cool only the skin. The invention is of particular importance in the manufacture of cups, but food trays, buckets, plates and face masks may also be prepared. |
