Polystyrene foam made with only carbon dioxide as a blowing agent and a process for making the same

Claim 2

A thermoplastic foam comprising: (a) a styrenic polymer; and (b) a blowing agent characterised in that the blowing agent consists essentially of carbon dioxide. wherein the thermoplastic foam has tensile elongation values greater than or equal to about five percent under ambient conditions in both a machine and a cross direction.

Claim 3

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam has substantially constant tensile elongation values under ambient conditions in both a machine and a cross direction after an initial aging period.

Claim 4

A thermoplastic foam, as recited in Claim 2, wherein the substantially constant tensile elongation values in either machine and a cross direction under ambient conditions vary by no more than about fifteen percent after an initial aging period of 20 hours.

Claim 5

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam has corrugation less than about fifteen percent.

Claim 6

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam is in sheet form.

Claim 7

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam has a density of 2 to 10 pounds per cubic foot.

Claim 8

A thermoplastic foam, as recited in Claim 6, wherein the thermoplastic foam has a density of 3 to 6 pounds per cubic foot.

Claim 9

A thermoplastic foam, as recited in Claim 5, wherein the thermoplastic foam has a thickness less than about 0.5 inch.

Claim 10

A thermoplastic foam, as recited in Claim 8, wherein the thermoplastic foam has a thickness less than about 0.25 inch.

Claim 11

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam has a cell size. in any direction, of less than about one millimeter.

Claim 12

A thermoplastic foam, as recited in Claim 10, wherein the thermoplastic foam has a cell size, in any direction of less than about 0.5 millimeter.

Claim 13

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam has a blow-up ratio of at least 2.0:1.

Claim 14

A thermoplastic foam, as recited in Claim 1; wherein the thermoplastic foam expands 20 50 percent upon heating prior to thermoforming.

Claim 15

A thermoplastic foam, as recited in Claim 1, wherein the thermoplastic foam has carbon dioxide present in an amount of 0.5 to 6 weight percent per weight of styrenic polymer immediately after being extruded from a die and foamed.

Claim 16

A foamable mixture comprising: (a) a molten styrenic polymer; and (b) a blowing agent consisting essentially of carbon dioxide.

Claim 17

A foamable mixture comprising: (a) a molten styrenic polymer; and (b) a blowing agent consisting essentially of carbon dioxide.

Claim 18

A foamable mixture, as recited in Claim 15, wherein the foamable mixture includes a nucleating agent.

Claim 19

A foamable mixture, as recited in Claim 16, wherein the foamable mixture has carbon dioxide present in an amount of 0.5 to 6 weight percent per weight of styrenic polymer.

Claim 20

A process for producing a thermoplastic foam comprising the following steps: (a) melting a styrenic polymer; (b) continuously directly introducing into the melted styrenic polymer a blowing agent consisting essentially of carbon dioxide; (c) mixing intimately the styrenic polymer and the carbon dioxide; and (d) extruding and foaming the mixture at a die temperature below about 150°C into a region of lower pressure to form thermoplastic foam.

Claim 21

A process for producing a thermoplastic foam comprising the following steps: (a) melting a styrenic polymer; (b) continuously directly introducing into the melted styrenic polymer a blowing agent consisting essentially of carbon dioxide; (c) mixing intimately the styrenic polymer and the carbon dioxide; and (d) extruding and foaming the mixture at a die temperature below about 150°C into a region of lower pressure to form thermoplastic foam.

Claim 22

The process for producing a thermoplastic foam, as recited in Claim 18, wherein the carbon dioxide is introduced in the polymer melt as a liquid.

Claim 23

The process for producing a thermoplastic foam, as recited in Claim 19, wherein the carbon dioxide is continuously and directly introduced into the polymer melt as a liquid in an amount of 0.5 to 6 weight percent by weight of the polymer.

Claim 24

The process for producing a thermoplastic foam, as recited in any one of Claims 18 to 20, including the step of thermoforming the thermoplastic foam into articles.

Claim 25

The process for producing a thermoplastic foam, as recited in any one of Claims 18 to 21, including the step of passing the thermoplastic foam over a forming mandrel having a blow up ratio of greater than about 2.0:1 immediately after step (d).

Claim 26

The process for producing a thermoplastic foam, as recited in any one of Claims 18 to 22, including the step of aging the thermoplastic foam, after step (d) and prior to thermoforming, until the thermoplastic foam has substantially constant tensile elongation values over an extended period of time under ambient conditions in both a machine and a cross direction after an initial aging period and the tensile elongation values are greater than or equal to about five percent over an extended period of time under ambient conditions in both a machine and a cross direction.

Claim 27

The process for producing a thermoplastic foam, as recited in any one of Claims 18 to 23, wherein the styrenic polymer is polystyrene.

Claim 28

The process for producing a thermoplastic foam, as recited in any one of Claims 18 to 24, wherein the die temperature in step (d) is from 130° to 145°C.