Nestable foam cup with improved heat retention and the process for its manufacture

Claim 2

A thermoplastic foam container consisting essentially of oriented styrenic polymer having a deep drawn wall of polymer foam, said foam characterized by containing flat, elongated, pancake-shaped, interleaved, gas-containing cells, uniformly distributed generally parallel to the codirectional wall surfaces; said styrenic polymer having a Vicat softening point of at least 100° C.; said wall further characterized by having an average specific gravity of less than 0.15 prior to any thermally caused increase in wall thickness; and said container capable of undergoing an excess of 10% increase in wall thickness when subjected to a temperature between about 82° C. and about 100° C.

Claim 3

The container of claim 1 wherein the styrenic polymer consists essentially of paramethyl styrene polymer.

Claim 4

A container according to claim 1 having a wall thickness increase for contained 100° C. water substantially within the shaded area of the dwell time-percent increase plot of FIG. 5.

Claim 5

The container of claim 1 wherein the foam stock material from which the container is deep drawn has an average specific gravity of from about 0.16 to about 0.20.

Claim 6

The container of claim 4 having a generally frustro-conical nestable shape with depth exceeding width and substantially uniform wall thickness.

Claim 7

The container of claim 3 wherein the container wall has improved crush resistance as compared to bead-formed polystyrene.

Claim 8

A nestable thermofoamed styrenic polymer foam cup comprising a thermally-expandable foam which expands in thickness at least 10% upon contact with hot fluid at between about 82° C. to about 100° C. for a predetermined dwell time to provide improved heat retention; the foam structure comprising flat, elongated, pancake-shaped, interleaved, gas-containing cells, uniformly distributed generally parallel to the codirectional wall surfaces of the cup wall.

Claim 9

A nestable thermofoamed styrenic polymer foam cup comprising a thermally-expandable foam which expands in thickness at least 10% upon contact with hot fluid at between about 82° C. to about 100° C. for a predetermined dwell time to provide improved heat retention; the foam structure comprising flat, elongated, pancake-shaped, interleaved, gas-containing cells, uniformly distributed generally parallel to the codirectional wall surfaces of the cup wall.

Claim 10

A nestable foam cup according to claim 7 wherein the foam comprises oriented styrene homopolymer having a Vicat softening point greater than 100° C.

Claim 11

A nestable foam cup according to claim 8 wherein the cup is thermoformed by uniformly deep drawing a pre-heated thermoplastic foam sheet having an average specific gravity of from about 0.16 to about 0.20 thereby forming said foam structure.

Claim 12

A nestable foam cup according to claim 9 wherein the styrenic foam is biaxially oriented during deep drawing to produce a low density cup.

Claim 13

In a thermoformed polymeric foam article with substantially uniform wall thickness comprising linear styrenic polymer having a thermal expansion capacity, the improvement which comprises: a cellular foam wall comprising a polymeric matrix and closed gas cells dispersed therein, the cells of the cellular foam wall comprising flat, elongated, pancake-shaped, interleaved, gas-containing cells, uniformly distributed generally parallel to the codirectional wall surfaces of the article wall; and the polymeric matrix having significant stretch orientation.

Claim 14

In a thermoformed polymeric foam article with substantially uniform wall thickness comprising linear styrenic polymer having a thermal expansion capacity, the improvement which comprises: a cellular foam wall comprising a polymeric matrix and closed gas cells dispersed therein, the cells of the cellular foam wall comprising flat, elongated, pancake-shaped, interleaved, gas-containing cells, uniformly distributed generally parallel to the codirectional wall surfaces of the article wall; and the polymeric matrix having significant stretch orientation.

Claim 15

A thermoformed foam article according to claim 11 wherein the elongated and flattened cell configuration is induced by thermoforming pre-oriented thermoplastic foam sheet.

Claim 16

A thermoformed foam article according to claim 11 where said foam has an average specific gravity of less than 0.15.

Claim 19

The method of claim 14 wherein the container is made by hot extruding a foam sheet from an extrusion mass containing molten polymer and alkane blowing agent, biaxially orienting the extruded foam sheet, aging the foam sheet to obtain a thermoformable sheet stock material consisting essentially of a polymeric matrix and closed gas cells; preheating the thermoplastic foam sheet stock; clamping the preheated stock material between cooled male and female molds; partially deforming the preheated sheet stock toward the female mold by extending a plug member from the male mold; and completely forming the container by drawing the partially formed preheated sheet stock and closing the male and female molds.

Claim 20

The method of claim 15 wherein a plug member deforms the preheated sheet stock with a dwell period of about 0.4 to one second before employing a vacuum or pressure differential.

Claim 21

The method of claim 14 wherein the container wall displays essentially linear growth substantially as shown in FIG. 6.