Method of injection molding expanded thermoplastics and articles

Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making

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Details

264 455, 264 90, 264 93, 264316, 264328, 264DIG5, 264DIG14, 425DIG124, 428315, B29D 2700, B29C 104

Patent

active

040311767

ABSTRACT:
Typically, injection molded expandable thermoplastics exhibit imperfect surfaces in the form of mottled areas, visible flow lines, and pin holes; these imperfections are caused by the quick chilling of the surface of the expanded thermoplastic as it contacts the mold surface. This invention is a method of injection molding expanded thermoplastics free of these defects by injecting a short-shot of the expandable thermoplastic into an elastic membrane positioned within a cooled mold cavity, containing the short-shot within the membrane until a skin forms on the thermoplastic in contact with the membrane, and then permitting expansion of the thermoplastic in the cavity to form a smooth skin or surface on a substantial portion of the article.

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