Multilayer Thermoplastic Sheet Materials And Thermoformed Articles Prepared Therefrom
The present invention provides multilayer sheet structures especially suited for thermoforming applications such as refrigerator cabinet and door liners comprising a surface non-foamed layer A and a surface foamed layer B having a total sheet thickness of from about 0.5 to about 20 millimeters (“mm”). Improvements in thermoformability, including cycle time reduction and polymer and energy savings, are provided. Preferably the non-foamed thermoplastic polymer surface layer (A) has a thickness of from about 0.25 to about 6 millimeters and the foamed thermoplastic polymer surface layer (B) together with any other foamed polymer layers have a total density reduction of at least about five (5) weight percent and have a total thickness greater than the total thickness of the non-foamed layer A together with any other non-foamed layers. Also provided are improvements in the thermoforming process, thermoformed articles, processes for providing thermally insulating articles and thermally insulating articles.
1 . A multilayer sheet having two surface layers and optionally one or more interior layers, said multilayer sheet comprising a non-foamed thermoplastic polymer surface layer A, a foamed thermoplastic polymer layer B and an optional nonfoamed thermoplastic polymer surface layer (C) and having a total sheet thickness of from about 0.5 to about 20 millimeters (“mm”) and a foam to solid ratio of greater than 1 and wherein:
(a) the non-foamed thermoplastic polymer surface layer (A) has a thickness in the range of from about 0.25 to about 6 millimeters (“mm”) and (b) the foamed thermoplastic polymer layer (B) has a total density reduction of at least about five (5) weight percent and, in the absence of optional surface layer (C), is a surface layer.
2 . A multilayer sheet according to claim 1 wherein the thickness of the non-foamed surface layer A is at least 0.5 mm.
3 . A multilayer sheet according to claim 1 wherein the thickness of the non-foamed surface layer A is at least 0.75 mm.
4 . A multilayer sheet according to claim 1 wherein the foam to solid ratio is at least 1.86.
5 . A multilayer sheet according to claim 1 wherein the foam to solid ratio is at least 2.33.
6 . A multilayer sheet according to claim 1 having a density reduction of at least about ten (10) weight percent.
7 . A multilayer sheet according to claim 1 having a density reduction of at least about twenty (20) weight percent.
8 . A multilayer sheet according to claim 1 having a total sheet thickness of from about 1 to about 10 mm.
9 . A multilayer sheet according to claim 1 having a total sheet thickness of from about 2 to about 5 millimeters.
10 . A multilayer sheet according to claim 1 wherein layer B comprises a foamed monovinylidene aromatic polymer resin selected from the group of HIPS, GPPS, ABS, blends of two or more of these, and blends of one or more of these with one or more additional polymer.
11 . A multilayer sheet according to claim 1 wherein layers A and B are coextruded.
12 . A multilayer sheet according to claim 1 wherein layer A is film laminated or extrusion coated onto layer B.
13 . A multilayer sheet according to claim 1 wherein layer B is foamed using a physical blowing agent or a combination of physical blowing agent and chemical blowing agent nucleating agent or only chemical blowing agent.
14 . A thermoformed article prepared from a multilayer sheet according to any one of claims claim 1 .
15 . A thermoforming process comprising:
A. heating a multilayer sheet according to claim 1 to a heat softened, heat-plastified thermoformable state;
B. applying gas, vacuum and/or physical pressure to the heat softened, heat-plastified, thermoformable sheet and stretching the sheet to nearly the final part size;
C. conforming the sheet by vacuum or pressure to a mold shape; and
D. separating the thermoformed part from the mold.
16 . A process for preparing a thermally insulating molded part comprising: providing a thermally insulated foam layer to the thermoformed part produced according to claim 15 .
17 . A process for preparing a thermally insulating molded part according to claim 16 wherein the thermally insulating foam layer is a polyurethane foam.
18 . A process for preparing a thermally insulating molded part according to claim 17 wherein the thermally insulating layer is provided in a cavity or space that has been provided between the thermoformed part foam surface layer and an exterior casing or enclosure structure.
19 . A process for preparing a thermally insulating molded part according to claim 18 wherein the exterior casing or enclosure structure is a refrigerator cabinet or door.
20 . A thermally insulating molded part prepared according to claim 15 .