Claims
- 1. A uniaxially heat-shrinkable, biaxially oriented, multilayer film having a polypropylene-containing core layer, said core layer containing isotactic polypropylene and a sufficient amount of syndiotactic polypropylene to inhibit long-term uniaxial shrinkage at temperatures below about 50.degree. C.
- 2. The multilayer film of claim 1, wherein said core layer comprises syndiotactic polypropylene in an amount greater than 10 wt. %.
- 3. The multilayer film of claim 2, wherein said core layer comprises syndiotactic polypropylene in an amount in the range of 15 wt. % to 45 wt. %.
- 4. The multilayer film of claim 1, comprising at least one polyolefin-containing skin layer adjacent said core layer.
- 5. The multilayer film of claim 1, wherein said film is capable of greater than 15% shrinkage at 130.degree. C. or higher in a first direction with .+-.5% or less stability in a second direction substantially normal to said first direction.
- 6. The multilayer film of claim 1, wherein said core layer comprises a plurality of voids formed by cavitation about a solid cavitating agent.
- 7. The multilayer film of claim 1, wherein said core layer contains 4 to 8 wt. % polybutylene terephthalate (PBT) dispersed as particles of 0.2 to 2.0 microns diameter.
- 8. The multilayer film of claim 1 further comprising a polypropylene supporting layer containing 4 to 15 wt. % TiO.sub.2 adjacent to said core layer.
- 9. The multilayer film of claim 1, which is primarily oriented by biaxially orienting 3 to 6 times in the machine direction, and 5 to 10 times in the transverse direction, and secondarily oriented by reorienting an additional 10 to 40% in the machine direction.
- 10. The multilayer film of claim 4, wherein said skin layer is selected from at least one of the group consisting of polypropylene, ethylene-propylene copolymer, polyethylene, propylene-butylene copolymer, and ethylene-propylene-butylene terpolymer, said skin layer having a thickness of 0.5 to 1.0 micron.
- 11. The multilayer film of claim 4, wherein said skin layer contains a non-meltable silicone resin.
- 12. A uniaxially heat shrinkable, multilayer, biaxially oriented film composition, wherein said film has at temperatures below about 50.degree. C. a shrinkage in the machine direction of less than about 3%, after one week, and at temperatures above about 130.degree. C., a shrinkage in the machine direction of at least about 15%, after 7 minutes.
RELATED APPLICATIONS
This case is related by subject matter to U.S. application Ser. No. 08/427,785, filed Apr. 25, 1995, which is a continuation in part of U.S. Ser. No. 08/276,124, filed Jul. 15, 1994. This case is also related by subject matter to U.S. application Ser. No. 08/806,428, filed Feb. 26, 1997.
US Referenced Citations (22)
Foreign Referenced Citations (5)
Number |
Date |
Country |
0 204 843 |
Dec 1984 |
EPX |
0 299 750 |
Jul 1988 |
EPX |
0 321 964 |
Dec 1988 |
EPX |
0 477 742 A1 |
Sep 1991 |
EPX |
0 595 270 A1 |
Oct 1993 |
EPX |