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US 8,263,731 B2Granted
Optical film comprising birefringent naphthalate copolyester having branched or cyclic C4-C10 alkyl units
Assignee3M Innovative Properties Company
InventorsYufeng R. Liu, David T. Yust, Stephen A. Johnson, Kristopher J. Derks
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Abstract
The present invention relates to multilayer optical films and birefringent copolyester films. The birefringent copolyester optical layer or birefringent copolyester film comprises a major amount of naphthalate units, ethylene units, and a minor amount of branched or cyclic C4 to C10 alkyl units. Also described are certain copolyester polymeric materials further comprising subunits of a phthalate ionomer such as dimethyl sulfosodium isophthalate ionomer.
Claims15
A birefringent copolyester film comprising:
- comprising a copolyester comprising:
- 40 to 50 mol % naphthalate units,
- 35 to 49 mol % ethylene units, and
- 1 to 8 mol % of branched or cyclic C4-C10 alkyl units;
- wherein the copolyester film has an out of plane birefringence of at least 0.10 at 632.8 nm after the film is formed.
2 more elements
Dependencies are inferred from the claim text.