Polymer foam process
AssigneeMobil Oil Corporation
InventorsD. Emil Johnson, Charles M. Krutchen, G. Vincent Sharps, Jr.
Life of this patent
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Abstract
Thermoplastic foams of polystyrene, for example, are prepared with a blowing agent which is a mixture of an organic plasticizing blowing agent, such as pentane, and an atmospheric gas, such as carbon dioxide. Typically, such foams prepared with organic blowing agent alone were aged prior to thermoforming the foam into articles. Foams prepared with the mixed blowing agent of this invention exhibit the advantage of reduced atmospheric emissions on aging.
Claims28
A method for the formation of a thermoplastic foam which comprises
- introducing to a molten thermoplastic resin a blowing agent comprising at least one atmospheric gas and at least one volatile plasticizing blowing agent in amounts sufficient to plasticize said thermoplastic resin;
- extruding said thermoplastic in the form of a foam;
- and
- thermoforming said foam into articles;
- wherein the atmospheric gas is present in sufficient amounts to allow thermoforming immediately after the extrusion of the foam without substantial intermediate aging.
A method for the formation of a thermoplastic foam which comprises:
- (a) introducing to a molten thermoplastic resin a blowing agent comprising at least one atmospheric gas and at least one volatile plasticizing blowing agent in amounts sufficient to plasticize said thermoplastic resin;
- (b) extruding said thermoplastic in the form of a foam;
- and
- (c) thermoforming said foam into articles;
- wherein the atmospheric gas is present in sufficient amounts to substantially reduce emission of the organic blowing agents into the environs.
A continuous process for thermoplastic foam production comprising the steps of:
- (a) feeding a thermoplastic resin to a screw-type extruder and heating the thermoplastic resin to a first temperature substantially above melting temperature of the resin;
- (b) introducing volatile hydrocarbon and atmospheric gas blowing agent in liquid phase concurrently into the resin while mixing the resin at the first temperature;
- (c) cooling the mixture of molten resin and blowing agent to a second temperature below the first temperature and above the melting temperature;
- (d) extruding a foamed sheet of the thermoplastic resin by passing the molten mixture through an orifice into a zone of reduced pressure;
- and
- (e) thermoforming said extruded foam into articles.
A thermoplastic foam article containing in its porous interstices at least one atmospheric gas and at least one volatile plasticizing organic blowing agent, said organic blowing agent being present in an amount sufficient to allow thermoforming of said foam article without substantial aging as compared to thermoformed thermoplastic foam which does not contain said atmospheric gas within its porous interstices;
- said foam article emitting a reduced quantity of said organic blowing agent to the atmosphere during the formation of said foam article and thereafter thermoforming thereof.
Dependencies are inferred from the claim text.