Polystyrene foam extrusion into a foam assisting atmosphere

Claim 2

A process for preparing a thermoplastic resin thermoformable foam in sheet form comprising: (a) melting a thermoplastic resin; (b) introducing thereto, under pressure, a foaming agent in liquid form, said agent being a member selected from the group consisting of a low molecular weight aliphatic hydrocarbon, a low molecular weight halocarbon and mixtures thereof; and (c) extruding the combination in sheet form directly into a lower pressure atmosphere of a member selected from the group consisting of carbon dioxide, water vapor and mixtures thereof to cause foaming of said resin so as to expose both surfaces of said sheet to said lower pressure atmosphere.

Claim 3

The process of claim 1 wherein said lower pressure atmosphere is carbon dioxide.

Claim 4

The process of claim 1 wherein said lower pressure atmosphere is water vapor.

Claim 5

The process of claim 1 wherein said resin is a styrene polymer.

Claim 6

The process of claim 4 wherein said polymer is polystyrene.

Claim 7

The process of claim 4 wherein said polymer is poly-p-methylstyrene.

Claim 8

The process of claim 1 wherein a nucleating foam agent, in an amount effective for nucleating foam cells, is added to said resin prior to extrusion thereof.

Claim 9

The process of claim 7 wherein said nucleating agent is a mixture of citric acid and sodium bicarbonate.

Claim 10

The process of claim 1 wherein the extruded foam is thermoformed into articles without any substantial aging.

Claim 11

A continuous process for preparing a thermoplastic resin thermoformable foam in sheet form comprising: (a) feeding a thermoplastic resin to a screw-type extruder and heating the resin to a first temperature above the melting temperature of the resin; (b) introducing thereto, under pressure, a foaming agent in liquid form, while mixing the resin at said first temperature, said foaming agent being a member selected from the group consisting of a low molecular weight aliphatic hydrocarbon, a low molecular weight halocarbon and mixtures thereof; (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 sheet of said resin directly into a lower pressure atmosphere of a member selected from the group consisting of carbon dioxide, water vapor and mixtures thereof to cause foaming of said resin so as to expose both surfaces of said sheet to said lower pressure atmosphere.

Claim 12

A continuous process for preparing a thermoplastic resin thermoformable foam in sheet form comprising: (a) feeding a thermoplastic resin to a screw-type extruder and heating the resin to a first temperature above the melting temperature of the resin; (b) introducing thereto, under pressure, a foaming agent in liquid form, while mixing the resin at said first temperature, said foaming agent being a member selected from the group consisting of a low molecular weight aliphatic hydrocarbon, a low molecular weight halocarbon and mixtures thereof; (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 sheet of said resin directly into a lower pressure atmosphere of a member selected from the group consisting of carbon dioxide, water vapor and mixtures thereof to cause foaming of said resin so as to expose both surfaces of said sheet to said lower pressure atmosphere.

Claim 13

The process of claim 10 wherein said lower pressure atmosphere is carbon dioxide.

Claim 14

The process of claim 10 wherein said lower pressure atmosphere is water vapor.

Claim 15

The process of claim 10 wherein said resin is a styrene polymer.

Claim 16

The process of claim 13 wherein said foaming agent is a C 1 to C 10 hydrocarbon or a fluoro-chlorocarbon or mixtures thereof.

Claim 17

The process of claim 14 wherein said blowing agent is pentane.

Claim 18

The process of claim 15 wherein said resin is polystyrene.

Claim 19

The process of claim 15 wherein said resin is poly-p-methylstyrene.

Claim 20

The process of claim 16 wherein a nucleating agent, in an amount effective for nucleating foam cells, is added to said resin prior to extrusion thereof.

Claim 21

The process of claim 18 wherein said nucleating agent is a mixture of citric acid and sodium bicarbonate.