Multilayer stretch/shrink film

• US 5,272,016 A
• Filed: 02/19/1993
• Issued: 12/21/1993
• Est. Priority Date: 03/23/1992
• Status: Expired due to Term

• Current Assignee: Curwood Incorporated (Amcor Plc)
• Original Assignee: Viskase Corporation (Viskase Companies Incorporated)
• Inventors: Ralph, Donald J.
• Primary Examiner(s): Buffalow, Edith
• Application Number:
  US08/020,890
• Time in Patent Office: 305 Days
• Field of Search: 428/516, 428/34.9, 428/349, 428/910
• US Class Current: 428/516
• CPC Class Codes: B32B 27/32 comprising polyolefins comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30
• CPC Class Codes: B65D 75/004 with auxiliary packaging elements, e.g. protective pads or frames, trays
• CPC Class Codes: G02B 6/4476 with heat-shrinkable elements
• CPC Class Codes: Y10S 428/91 Product with molecular orientation
• CPC Class Codes: Y10T 428/1328 Shrinkable or shrunk [e.g., due to heat, solvent, volatile agent, restraint removal, etc.]
• CPC Class Codes: Y10T 428/2826 Synthetic resin or polymer
• CPC Class Codes: Y10T 428/31913 Monoolefin polymer

Abstract

A biaxially oriented heat shrinkable multilayer stretch film useful as a trayed poultry overwrap includes outer layers each comprising a blend of VLDPE (density below about 0.914 g/cm³ and an ethylene alpha-olefin plastomer (density below about 0.90 g/cm³).

Claims

1. A biaxially oriented heat-shrinkable multilayer stretch film comprising at least a first outer layer, a second outer layer, and a core layer between said first and second outer layers, said first and second outer layers each comprising a blend of between about 20 and about 35 weight % ethylene alpha-olefin plastomer copolymer of density below about 0.90 g/cm³, and between about 65 and about 80 weight % VLDPE of density at least 0.912 and below about 0.914 g/cm³, and said core layer comprising ethylene alpha-olefin copolymer having a higher melting point than the melting point(s) of either of said first and second outer layers.

2. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said ethylene alpha-olefin plastomer copolymer comprises between about 22 and about 30 weight % and said VLDPE comprises between about 70 and 78 weight % of the first and second outer layers blend.

3. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said VLDPE has higher crystallinity than said ethylene alpha-olefin plastomer copolymer.

4. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said ethylene alpha-olefin plastomer copolymer has a density of about 0.88 g/cm³, a melt index of 3.6 g/10 min., an Mw/Mn of about 2.35, and a Vicat softening point of about 54°

C.

5. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said ethylene alpha-olefin plastomer copolymer melts at between about 55°

C. and about 85°

C.

6. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said VLDPE has a crystalline melting point between about 117°

C. and about 125°

C.

7. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said VLDPE has a yield point and said ethylene alpha-olefin plastomer copolymer does not have a yield point.

8. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said VLDPE has a broader molecular weight distribution than said ethylene alpha-olefin plastomer.

9. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said VLDPE has Mw/Mn of at least about 5.

10. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said ethylene alpha-olefin plastomer has a Mw./Mn below about 2.5.

11. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said ethylene alpha-olefin copolymer plastomer has a Vicat softening point between about 50 °

C. and 65 °

C.

12. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said VLDPE has a Vicat softening point between about 78°

C. and about 100°

C.

13. A biaxially oriented shrinkable multilayer stretch film according to claim 1 wherein said alpha-olefin plastomer copolymer has density of about 0.88 g/cm³ and said VLDPE has density of about 0.905 g/cm³.

14. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said core layer is a polyolefin.

15. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said core layer is VLDPE.

16. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said core layer is LLDPE.

17. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said core layer is polypropylene.

18. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said core layer is a blend of two different ethylene alpha-olefins.

19. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said core layer is a blend of a lower density ethylene alpha-olefin and a higher density ethylene alpha-olefin.

20. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said film has at least about 30% shrinkage in both the machine and transverse directions.

21. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said film has at least about 40% shrinkage in both the machine and transverse directions.

22. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said film has a permanent deformation of less than about 7% in at least one of the machine and transverse directions.

23. A biaxially oriented heat-shrinkable multilayer stretch film according to claim 1 wherein said film has a permanent deformation of less than about 6% in both the machine and transverse directions.

24. A biaxially oriented heat shrinkable multilayer stretch film according to claim 1 wherein said film is an irradiated film.

25. A biaxially oriented heat shrinkable multilayer stretch film as in claim 1 comprising an intermediate layer between said core layer and each of said outer layers, said intermediate layer comprising a blend of the materials of said core layer and said first and second outer layers.

26. A biaxially oriented heat-shrinkable film according to claim 1 wherein said core layer comprises VLDPE of density about 0.912 g/cm³.

27. A biaxially oriented heat-shrinkable multilayer stretch film comprising at least a first outer layer, a second outer layer, and a core layer between said first and second outer layers, said first and second outer layers each comprising a blend of between about 20 and about 35 wt. % ethylene alpha-olefin plastomer copolymer of density below about 0.90 g/cm³, and between about 65 and about 80 wt. % VLDPE wherein said VLDPE comprises a blend of a first ethylene alpha olefin having a density of about 0.912 g/cm² and a second ethylene alpha olefin which is a butene comonomer having a density of about 0.900 g/cm², a melt index of about 3.5, a melting point of about 92°

C. and an Mw/Mn ratio of about 2 and said core layer comprises ethylene alpha-olefin copolymers having a high melting point than the melting point of either of each first and second outer layers.

28. A biaxially oriented heat-shrinkable multilayer film according to claim 27 wherein said first ethylene alpha olefin comprises between about 35 and about 40 wt. % and said second ethylene alpha olefin comprises between about 27 and about 32 wt. % of said blend.

29. A biaxially oriented heat-shrinkable multilayer film according to claim 27 wherein said second ethylene alpha olefin is Exact type 3010C/3027.