Scrapless forming of plastic articles

DETAILED DESCRIPTION What is claimed is: 1.
A process for forming a foam thermoplastic article having dense surfaces and a porous less dense inner structure comprising the steps of: (a) dry blending a mixture of a thermoplastic powder and a chemical blowing agent in sufficient quantity to make said article; (b) compressing said blend into a briquette having green strength; (c) heating said briquette to a temperature in the range from about the alpha transition temperature to less than the melt forming temperature of said powder and the activation temperature of said blowing agent; (d) maintaining said temperature for a period sufficient to soften and sinter said briquette; and (e) forging said briquette within said temperature range with sufficient heat to activate said blowing agent, and with substantial plug flow deformation to obtain substantial fusion of the powder forming said article while providing said dense surfaces.
2.
The process of claim 1 wherein the blowing agent is selected so as to be activated at a temperature greater than that experienced in steps (c) and (d).
3.
The process of claim 1 wherein the blowing agent is selected so as to be activated at a temperature less than melt forming temperature of said powder.
4.
The process of claim 3 wherein the blowing agent is selected so as to be activated at about the forging temperature necessary to obtain substantial fusion of said powder as set forth in step (e).




Description:
DESCRIPTION OF THE INVENTION There has been a need for a fast, substantially solid phase, essentially scrap-free process for forming articles, such as containers, directly from powdered thermoplastic resin materials.
Such powder formed parts can be made at a lesser expense than a comparable part made by either an injection molding technique or a conventional vacuum forming process.
The reasons for the favorable economics of powder formed parts are elimination of a pelletizing step, the process is essentially scrapless, a reduced cooling cycle and more efficient material utilization