| 摘要 |
The tendency of an article, produced by injection or extrusion moulding a thermoplastic synthetic resin, to contain sink marks or voids is substantially removed by the action of a blowing agent during moulding, the weight of the agent being less than 1% of that of the resin. In one example 6.8 grams of azodicarbonamide are mixed with 50 pounds of polystyrene pellets in a rotating drum and the mixture injected from apparatus at 218 DEG C. into shoe-heel moulds at 20 DEG C. The nitrogen released prevents sink marks or voids in the heels. The density of the finished heel is about 10% less than that of one formed from resin alone. The blowing agent may alternatively be a bicarbonate. Polyvinyl chloride, polythene or a copolymer of styrene with butadiene or acrylonitrile may also be moulded according to the invention. Specification 916,802 is referred to.
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