Multi-layered foamed polymeric objects and related methods
The invention disclosed herein relates to relates to foamed thermoplastic material objects and articles of manufacture having an internal layered cellular structure, as well as to methods of making the same. In one embodiment, the invention is directed to a multi-layer foamed polymeric article of manufacture, comprising: a non-laminated multi-layer thermoplastic material sheet, wherein the multi-layer thermoplastic material sheet has first and second discrete outer layers sandwiching a plurality of discrete inner foamed layers, and wherein the two outer layers and plurality discrete inner foamed layers are integral with one another. The thermoplastic material may be a semi-crystalline polymer such as, for example, PET (polyethylene terephthalate), PEEK (polyetheretherketone), PEN (polyethylene napthalate), PBT (polybutylene terephthalate), PMMA (polymethyl methacrylate), PLA (polyactide), polyhydroxy acid (PHA), thermoplastic urethane (TPU), or blends thereof. The two outer layers may be unfoamed skin layers having smooth outer surfaces, and the discrete inner foamed layers may be microcellular.
1. A multi-layer foamed polymeric article of manufacture, comprising:
a non-laminated multi-layer thermoplastic material sheet having a crystallinity gradient, and first and second discrete outer skin layers sandwiching a plurality of discrete inner foamed layers, wherein the two outer skin layers and plurality of discrete inner foamed layers are integral with one another, wherein the outer skin layers have a crystallinity, and wherein the plurality of discrete inner foamed layers includes at least:
(i) two substantially identical second inner foamed layers whose crystallinity is less than the crystallinity of the outer skin layers, and
(ii) a centrally positioned third inner foamed layer whose crystallinity is less than the crystallinity of the second inner foamed layers, the third inner foamed layer being positioned immediately adjacent to and interposed between the second inner foamed layers, wherein:
the three inner foamed layers are formed by foaming a single piece of the thermoplastic material and
the thickness of each of the two second inner foamed layers is greater than the thickness of the centrally positioned third inner foamed layer.
2. The multi-layer foamed polymeric article of manufacture according to claim 1 wherein the thermoplastic material is a semi-crystalline polymer.
3. The multi-layer foamed polymeric article of manufacture according to claim 2 wherein the semi-crystalline polymer is selected from the group consisting of PET (polyethylene terephthalate), PEEK (polyetheretherketone), PEN (polyethylene napthalate), PBT (polybutylene terphthalate), PMMA (polymethylmethacrylate), PLC (polyactide), polyhydroxy acid (PHA), thermoplastic urethane (TPU), and blends thereof.
4. The multi-layer foamed polymeric article of manufacture according to claim 2 wherein the semi-crystalline polymer is PET (polyethylene terphthalate).
5. The multi-layer foamed polymeric article of manufacture according to claim 1 wherein the two outer layers are unfoamed skin layers having smooth outer surfaces.
6. The multi-layer foamed polymeric article of manufacture according to claim 1 wherein each of the plurality of discrete inner foamed layers are microcellular.
7. The multi-layer foamed polymeric article of manufacture according to claim 1 wherein the second inner foamed layers each include a first plurality of closed cells wherein the first plurality of closed cells has an average cell diameter ranging from about 5 to about 10 microns.
8. The multi-layer foamed polymeric article of manufacture according to claim 7 wherein the centrally positioned third inner foamed layer includes second plurality of closed cells, wherein the second plurality of closed cells has an average cell diameter ranging from about 30 to about 50 microns.
9. The multi-layer foamed polymeric article of manufacture according to claim 1 wherein the thermoplastic material sheet is non-planar.
10. The multi-layer foamed polymeric article of manufacture according to claim 1 wherein the density of the multi-layer thermoplastic material sheet is graded across the sheet such that the outermost layers of the plurality of discreet inner foamed layers have the greatest density of the plurality of discrete inner foamed layers.