Process for compacting polymeric powders
The invention relates to a process for compacting a polymeric powder in a press, wherein the polymeric powder is supported during compaction by a powder carrier, characterized in that said powder carrier comprises a layer of thickness (T), said layer comprising a material with a static coefficient of friction (COF), and wherein T×COF is at least 10 μm. The invention also relates to a compacted polymeric powder obtainable with the above process.
1. A process for compacting a polymeric powder in a press, wherein the process comprises supporting the polymeric powder during compaction in the press by a powder carrier, wherein the powder carrier comprises a layer of a thickness (T), wherein the layer comprises a material with a static coefficient of friction (COF), and wherein T×COF is at least 10 μm.
2. The process of claim 1 which further comprises compacting the polymeric powder in an isochoric or an isobaric press.
3. The process of claim 1 which further comprises a step of roll-pressing the compacted polymeric powder to form an undrawn polymeric tape.
4. The process of claim 1 wherein the polymeric powder comprises particles having an average particle size of up to 1000 μm.
5. The process of claim 1 wherein the polymeric powder has a bulk density determined in accordance with ASTM-D1895 of below 0.6 g/cm 3 .
6. The process of claim 1 wherein the polymeric powder is a powder of ultra high molecular weight polyethylene (UHMWPE).
7. The process of claim 6 wherein the UHMWPE powder is a powder of a polyethylene having a weight average molecular weight (Mw) of at least 100,000 g/mol.
8. The process of claim 1 which comprises forming a powder bed of the polymeric powder on the powder carrier, said powder bed having a thickness of at most 60 mm.
9. The process of claim 1 wherein the thickness (T) of the layer is at least 20 μm.
10. The process of claim 1 wherein the powder carrier has a length direction and a width direction, and wherein the powder carrier has a bending resistance as measured according to DIN 53121 in the length direction of at least 20 mN.
11. The process of claim 1 wherein the powder carrier has a bending resistance (BR) and a coefficient of friction (COF) such that BR×COF≧7 mN.
12. The process of claim 1 wherein the material comprising the layer forming the powder carrier is a cellulosic material.
13. The process of claim 3 , which further comprises a step of stretching the undrawn polymeric tape to form a drawn polymeric tape.
14. The process of claim 7 wherein the UHMWPE powder has a Mw/Mn ratio of at most 6.
15. The process of claim 12 wherein the cellulosic material is derived from wood or rags.
16. A compacted polymeric powder obtained by the process of claim 1 .
17. The compacted polymeric powder according to claim 16 which is further rolled and drawn.
18. A ballistic resistant article comprising the compacted polymeric powder of claim 17 .