OPTICAL FILM COMPRISING BIREFRINGENT NAPHTHALATE COPOLYESTER HAVING BRANCHED OR CYCLIC C4-C10 ALKYL UNITS

• US 20090273836A1
• Filed: 05/02/2008
• Published: 11/05/2009
• Est. Priority Date: 05/02/2008
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Johnson, Stephen A., Yust, David T., Derks, Kristopher J.
• Granted Patent: US 8,012,571 B2
• Time in Patent Office: Days
• US Class Current: 359/494
• CPC Class Codes: B32B 2250/24 All layers being polymeric
• CPC Class Codes: B32B 2307/30 having particular thermal properties
• CPC Class Codes: B32B 2307/308 Heat stability
• CPC Class Codes: B32B 2307/40 having particular optical properties
• CPC Class Codes: B32B 2307/416 Reflective
• CPC Class Codes: B32B 2307/418 Refractive
• CPC Class Codes: B32B 2307/42 Polarizing, birefringent, filtering
• CPC Class Codes: B32B 2307/50 having particular mechanical properties
• CPC Class Codes: B32B 2307/718 Weight, e.g. weight per square meter
• CPC Class Codes: B32B 2457/202 LCD, i.e. liquid crystal displays
• CPC Class Codes: B32B 2551/00 Optical elements
• CPC Class Codes: B32B 2551/08 Mirrors
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/285 comprising polyethers
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: B32B 7/023 Optical properties
• CPC Class Codes: C08G 63/189 containing a naphthalene ring
• CPC Class Codes: C08L 67/02 Polyesters derived from dicarboxylic acids and dihydroxy compounds C08L67/06 takes precedence
• CPC Class Codes: G02B 1/04 made of organic materials, e.g. plastics G02B1/08 takes precedence
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: Y10T 428/24942 : including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/31786 : Of polyester [e.g., alkyd, etc.]

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 isophthtalate ionomer.

Claims

1. A multilayer optical film comprising:

at least one first birefringent optical layer 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; and

at least one second optical layer having a lower birefringence than the first optical layer.

2. The multilayer optical film of claim 1 wherein the copolyester comprises carboxylate subunits and glycol subunits and 80-100 mol % of the carboxylate subunits comprise the naphthalate subunits, 70 to 98 mol % of the glycol subunits are derived from ethylene glycol, and 2-16 mol % of the glycol subunits are derived from one or more branched or cyclic C4-C10 alkyl glycols.

3. The multilayer optical film of claim 1 wherein the first birefringent optical layer has an in-plane birefringence of at least 0.10 at 632.8 nm after the multilayer film is formed.

4. The multilayer optical film of claim 1 wherein the second optical layer has an in-plane birefringence of less than 0.040 at 632.8 nm after the multilayer film is formed.

5. The multilayer optical film of claim 1 wherein the first birefringent optical layer has an in-plane birefringence of at least 0.20 at 632.8 nm after the multilayer film is formed.

6. The multilayer optical film of claim 5 wherein the multilayer optical film is a polarizer.

7. The multilayer optical film of claim 1 wherein the first birefringent optical layer has an out-of-plane birefringence of at least 0.10 at 632.8 nm after the multilayer film is formed.

8. The multilayer optical film of claim 1 wherein the first birefringent optical layer has an out-of-plane birefringence of at least 0.16 at 632.8 nm after the multilayer film is formed.

9. The multilayer optical film of claim 8 wherein the multilayer optical film is a mirror.

10. The multilayer optical film of claim 1 wherein the copolyester has a glass transition temperature of at least 105°

C.

11. The multilayer film of claim 1 wherein the first optical layer has a ratio of birefringence to off-axis index mismatch as defined by (n_x1−

n_y1)/(n_y1−

n_z1) of at least 2.5.

12. The multilayer film of claim 1 wherein the first optical layer has a ratio of birefringence to off-axis index mismatch as defined by (n_x1−

n_y1)/(n_y1−

n_z1) of at least 2.7.

13. The multilayer optical film of claim 1 wherein the copolyester exhibits a second scan heat of fusion of less than 2 J/g according to differential scanning calorimetry when heated at a rate of 20°

C. minutes.

14. The multilayer optical film of claim 1 wherein the copolyester is has a melting temperature ranging from 225°

C. to 260°

C.

15. The multilayer optical film of claim 1 wherein the copolyester comprises 2 to 4 mol % of branched C4-C10 alkyl units.

16. The multilayer optical film of claim 15 wherein the copolyester comprises 2 to 4 mol % of neopentyl glycol units.

17. The multilayer optical film of claim 1 wherein the copolyester comprises 2 to 8 mol % of cyclic C4-C10 alkyl units.

18. The multilayer optical film of claim 17 wherein the copolyester comprises 2 to 8 mol % of cyclohexane dimethanol units.

19. The multilayer optical film of claim 1 wherein the copolyester further comprises up to 8 mol % of terephthalate units.

20. The multilayer optical film of claim 1 wherein the copolyester further comprises up to 1.0 mol % of units of dimethyl sulfosodium isophthalate ionomer.

21. The multilayer optical film of claim 1 wherein the multilayer comprises a plurality a first optical layers alternating with a plurality of second optical layers.

22. The multilayer optical film of claim 1 wherein the combination of the at least one first optical layer and the at least one second optical layer exhibits a change in viscosity of less than 15% as measured at a shear rate of 100s⁻

1 after 1 hour under nitrogen at a temperature of 250°

C.

23. A multilayer film comprising

at least one first optical layer having a ratio of birefringence to off-axis index mismatch as defined by (n_x1−

n_y1)/(n_y1−

n_z1) of at least 2.5, wherein the first optical layer comprises a copolyester that exhibits a second scan heat of fusion of less than 2 J/g according to differential scanning calorimetry when heated at a rate of 20°

C. minutes; and

at least one second optical layer having a lower birefringence than the first optical layer.

24. A multilayer film comprising

at least one first optical layer having a ratio of birefringence to off-axis index mismatch as defined by (n_x1−

n_y1)/(n_y1−

n_z1) of at least 2.5, wherein the first optical layer comprises a copolyester having a melting temperature ranging from 225°

C. to 260°

C.; and

at least one second optical layer having a lower birefringence than the first optical layer.

25. A birefringent copolyester film comprising:

40 to 50 mol % naphthalate units,

to 49 mol % ethylene units, and

1 to 8 mol % of branched or cyclic C4-C10 alkyl units;

wherein the copolyester film has an in-plane birefringence of at least 0.10 at 632.8 nm.

26. A copolyester polymeric material comprisingto 50 mol % naphthalate units,to 48.95 mol % ethylene units, and

1 to 8 mol % of branched or cyclic C4-C10 alkyl units;

0.05 to 1 mol % of units of dimethyl sulfosodium isophthalate ionomer.

27. The copolyester polymeric material of claim 26 where the copolyester has a melting temperature ranging from 225°

C. to 260°

C.

28. The copolyester polymeric material of claim 26 wherein the copolyester exhibits a change in viscosity of less than 15% after 1 hour under nitrogen as measured at a shear rate of 100s⁻

1 at a temperature up to 50°

C. above the melt temperature of the copolyester.