Foamed caps and closure seal comprising polyethylene foam
The invention is directed to foamed caps and closure seals comprising as one of the layers polyethylene foam. The polyethylene foam is obtained by foaming of low density polyethylene copolymer obtained by a high pressure polymerization process in the presence of 1,4-butanediol dimethacrylate.
1. Foamed caps and closure seal comprising as one of the layers polyethylene foam wherein the foam is obtained by foaming of low density polyethylene copolymer obtained by a high pressure polymerisation process in the presence of 1,4-butanediol dimethacrylate.
2. The foamed caps and closure seal according to claim 1 wherein low density polyethylene obtained by the high pressure polymerisation process in the presence of 1,4-butanediol dimethacrylate has a density between 910 kg/m 3 and 935 kg/m 3 (according to ISO 1183) and a melt index between 0.10 and 100 dg/minute (according to ASTM D1133).
3. The foamed caps and closure seal according to claim 1 , wherein the high pressure polymerisation process is a tubular polymerisation process.
4. The foamed caps and closure seal according to claim 1 , wherein the foam is obtained by physically foaming of low density polyethylene.
5. The foamed caps and closure seal according to claim 1 , comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.
6. The foamed caps and closure seal according to claim 2 , wherein the high pressure polymerisation process is a tubular polymerisation process.
7. The foamed caps and closure seal according to claim 2 , wherein the foam is obtained by physically foaming of low density polyethylene.
8. The foamed caps and closure seal according to claim 2 , comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.
9. The foamed caps and closure seal according to claim 3 , comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.
10. The foamed caps and closure seal according to claim 4 , comprising as one of the layers polyethylene foam with a foam structure wherein more than 50% of the cells have a cell diameter smaller than 70 micrometers and wherein more than 95% of the cells have a cell diameter smaller than 150 micrometers.
11. The foamed caps and closure seal according to claim 1 , wherein the foam consist essentially of closed cells.
12. The foamed caps and closure seal according to claim 1 , wherein at least 90% of the cells are closed.
13. The foamed caps and closure seal according to claim 1 , wherein the foam has an open cell content of 10% to 90% of all cells.
14. The foamed caps and closure seal according to claim 8 , wherein the foam consist essentially of closed cells.
15. The foamed caps and closure seal according to claim 8 , wherein at least 90% of the cells are closed.
16. The foamed caps and closure seal according to claim 8 , wherein the foam has an open cell content of 10% to 90% of all cells.