Low-temperature impact-resistant polyamide-based stretch-oriented multilayer film
A stretch-oriented multilayer film suited for use as a freeze packaging material, a deep drawing packaging material, a vertical pillow packaging material, etc., is provided as a stretch-oriented multilayer film, comprising at least three layers including a surface layer (a) comprising a thermoplastic resin, an intermediate layer (b) comprising a polyamide resin and a surface layer (c) comprising a sealable resin, said multilayer film exhibiting an impact energy of at least 1.5 Joule at a conversion thickness of 50 μm at −10° C. The multilayer film is produced through an inflation process using water having a large capacity as a cooling and a heating medium and including a combination of a high degree of stretching and a high degree of relaxation heat treatment not exercised heretofore.
1. A stretch-oriented multilayer film, comprising at least three layers including a surface layer (a) comprising a thermoplastic resin, an intermediate layer (b) comprising a polyamide resin and a surface layer (c) comprising a sealable resin, said multilayer film exhibiting an impact energy of at least 1.5 Joule at a conversion thickness of 50 μm at −10° C.
2. A multilayer film according to claim 1 , exhibiting an actual impact energy at −10° C. of at least 1.6 Joule.
3. A multilayer film according to claim 1 , wherein the surface layer (a) has a larger heat resistance than the surface layer (c).
4. A multilayer film according to claim 1 , wherein the intermediate layer (b) has a larger thickness than the surface layer (a).
5. A multilayer film according to claim 1 , wherein the surface layer (a) comprises a stretch-oriented polyester resin.
6. A multilayer film according to claim 1 , having a heat-shrinkability.
7. A multilayer film according to claim 6 , having a hot-water shrinkability at 90° C. of below 20%.
8. A multilayer film according to claim 6 , having a hot-water shrinkability at 90° C. of below 15%.
9. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 1 .
10. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 1 .
11. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 1 .
12. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 1 .
13. A process for producing a stretch-oriented multilayer film, comprising the steps of:
co-extruding at least three species of melted thermoplastic resins to form a tubular product comprising at least three layers including an outer surface layer (a) comprising a thermoplastic resin other than polyamide resin, an intermediate layer (b) comprising a polyamide resin and an inner surface layer (c) comprising a sealable resin,
cooling with water the tubular product to a temperature below a lowest one of the melting points of the thermoplastic resin, the polyamide resin and the sealable resin constituting the layers (a), (b) and (c),
re-heating the tubular product to a temperature which is at most the lowest one of the melting points of the thermoplastic resin, the polyamide resin and the sealable resin constituting the layers (a), (b) and (c),
vertically pulling the tubular product while introducing a fluid into the tubular product to stretch the tubular product in the vertical direction and the circumferential direction, thereby providing a biaxially stretched tubular film,
folding the tubular film,
again introducing a fluid into the folded tubular film to form a tubular film,
heat-treating the tubular film from its outer surface layer (a) with steam or warm water until a relaxation ratio reaches at least 20% in at least one of the vertical direction and the circumferential direction, and
cooling the heat-treated tubular film to provide a stretch-oriented multilayer film exhibiting an impact energy of at least 1.5 Joule at a conversion thickness of 50 μm at −10° C.
14. A process according to claim 13 wherein the biaxially stretched tubular film is formed by stretching the tubular product at ratios of at least 2.9 times in a vertical direction and at least 3 times in a circumferential direction while vertically pulling the tubular product.
15. A process according to claim 13 , wherein the tubular film is heat-treated for the relaxation with steam or warm water at 75–95° C.
16. A multilayer film according to claim 2 , wherein the surface layer (a) has a larger heat resistance than the surface layer (c).
17. A multilayer film according to claim 2 , wherein the intermediate layer (b) has a larger thickness than the surface layer (a).
18. A multilayer film according to claim 3 , wherein the intermediate layer (b) has a larger thickness than the surface layer (a).
19. A multilayer film according to claim 2 , wherein the surface layer (a) comprises a stretch-oriented polyester resin.
20. A multilayer film according to claim 3 , wherein the surface layer (a) comprises a stretch-oriented polyester resin.
21. A multilayer film according to claim 4 , wherein the surface layer (a) comprises a stretch-oriented polyester resin.
22. A multilayer film according to claim 2 , having a heat-shrinkability.
23. A multilayer film according to claim 3 , having a heat-shrinkability.
24. A multilayer film according to claim 4 , having a heat-shrinkability.
25. A multilayer film according to claim 5 , having a heat-shrinkability.
26. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 2 .
27. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 3 .
28. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 4 .
29. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 5 .
30. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 6 .
31. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 7 .
32. A freeze-packaging material, comprising a stretch-oriented multilayer film according to claim 8 .
33. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 2 .
34. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 3 .
35. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 4 .
36. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 5 .
37. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 6 .
38. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 7 .
39. A vertical pillow-packaging material, comprising a stretch-oriented multilayer film according to claim 8 .
40. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 2 .
41. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 3 .
42. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 4 .
43. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 5 .
44. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 6 .
45. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 7 .
46. A deep drawing-packaging material, comprising a stretch-oriented multilayer film according to claim 8 .
47. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 2 .
48. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 3 .
49. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 4 .
50. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 5 .
51. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 6 .
52. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 7 .
53. A tray-packaging lid material, comprising a stretch-oriented multilayer film according to claim 8 .
54. A process according to claim 14 , wherein the tubular film is heat-treated for the relaxation with steam or warm water at 75–95° C.