Low Tg multilayer optical films

• US 20030072931A1
• Filed: 05/06/2002
• Published: 04/17/2003
• Est. Priority Date: 05/24/2001
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hebrink, Timothy J., Jonza, James M., Koneripalli, Nagraj
• Granted Patent: US 7,052,762 B2
• Time in Patent Office: Days
• US Class Current: 428/212
• CPC Class Codes: B32B 7/023 Optical properties
• CPC Class Codes: G02B 5/0841 comprising organic materials, e.g. polymers
• CPC Class Codes: G02B 5/287 comprising at least one layer of organic material
• 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

Abstract

Multilayer optical films are comprised of materials with glass transition temperatures below room temperature (<30° C.). The high refractive index polymers are unique in that they exhibit mechanical properties similar to other low Tg semi-crystalline polymers, yet have significant birefringence (>0.05) when strain induced oriented. Novel combinations of comonomers for thermoplastics control the rate of crystallinity for improved processability and flexibility, giving the films crease and crumple recovery advantages.

Claims

1. An optical film, comprising:

(a) a plurality of first optical layers, each first optical layer comprising high refractive index birefringent polymers, wherein such polymers have a Tg below room temperature; and

(b) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising low refractive index polymers, wherein such polymers have a Tg below room temperature.

2. The optical film according to claim 1, wherein the Tg of the high refractive birefringent index polymers and the Tg of the low refractive index polymers are in the range of −

100°

C. to 30°

C.

3. The optical film according to claim 2, wherein the high refractive index birefringent polymers of this invention are polyesters, strain induced oriented near their melting points to induce birefringence, and are not glassy at room temperature.

4. The optical film according to claim 2, further comprising one or more skin layers.

5. A method of using the optical film according to claim 1 as a bank note.

20. A bank note comprising the optical film according to claims 1 or 18.

21. The bank note according to claim 6 or 20 further comprising one or more covert security features and/or one or more overt security features.

22. The bank note according to claim 21, wherein one overt security feature is the addition of a color shifting film to at least one portion of the bank note.

23. The bank note according to claim 21, wherein one overt security feature is the inclusion of a security thread comprised of a color shifting film.

24. The bank note according claim 21, wherein any of the covert or overt security features are selected from the group consisting of one or more color shifting films, security threads, planchettes, polarizing films, color shifting inks, covert inks, magnetic inks, transparent windows containing color shifting film or ink, transparent windows containing opacifying coatings on one or both sides of the transparent window, or holographic embossing or hot stamping.

25. The optical film according to claim 1, wherein the high refractive index birefringent polymer comprises (i) carboxylate subunits derived from 90-100 mol % terephthalic or naphthalic acid or lower alkyl esters thereof and 0-10 mol % sebacic acid or lower alkyl esters thereof and (ii) glycol subunits derived from 90-100 mol % 1,6 hexane diol, 1-10 mol % triethylene glycol, and 0.01-10 mol % branching comonomer molecules.

26. The optical film according to claim 1, wherein the high refractive index birefringent polymer comprises (i) carboxylate subunits derived from 90-100 mol % terephthalic or naphthalic acid or lower alkyl esters thereof and 0-10 mol % sebacic acid or lower alkyl esters thereof:

and (ii) glycol subunits derived from 90-100 mol % 1,6 hexane diol, 1-10 mol % 2-butyl 2-ethyl 1,3 propanediol, and 0.01-10 mol % branching comonomer molecules.

27. The optical film according to claim 1, wherein the high refractive index birefringent polymer comprises (i) carboxylate subunits derived from 90-100 mol % terephthalic or naphthalic acid or lower alkyl esters thereof and 0-10 mol % sebacic acid or lower alkyl esters thereof:

and (ii) glycol subunits derived from 90-100 mol % 1,6 hexane diol, 1-10 mol % neopentyl glycol, and 0.01-10 mol % branching comonomer molecules.

28. The optical film according to claim 1, wherein the high refractive index birefringent polymer comprises (i) carboxylate subunits derived from 90-100 mol % terephthalic acid or lower alkyl esters thereof and 0-10 mol % sebacic acid or lower alkyl esters thereof:

and (ii) glycol subunits derived from 90-100 mol % 1,6 hexane diol, 1-10 mol % 2-butyl 2-ethyl 1,3 propanediol, 1-10 mol % TEG, and 0.01-10 mol % branching comonomer molecules.

29. The optical film according to claim 1, wherein the high refractive index birefringent polymer comprises (i) carboxylate subunits derived from 50-100 mol % naphthalate subunits and 0-50 mol % adipate, azelate, sebacate, or longer chain dicarboxylate comonomers, and (ii) glycol subunits derived from 0-100 mol % 1,6 hexane diol, 0-100 mol % C7 and longer chain diols, 0-20 mol % TEG, 0-20 mol % neopentyl glycol, 0-20 mol % 2-butyl 2-ethyl 1,3 propanediol, and 0.01-10 mol % branching comonomers as glycol comonomer subunits.

30. The optical film according to claims 1 or 18, wherein the optical film has a crease recovery of at least 140°

after creasing under a 500 gm load over a 0.19 mm radius.

32. The optical film according to claims 1 or 18, wherein the optical film has a ratio of crumpled to uncrumpled height of less than 8, following 24 hour recovery under 969 gm load for a 67 mm square sample.

34. The optical film of claims 1 or 18, wherein the optical film has a normalized propagated tear resistance of greater than 8 N/mm.

36. The optical films of claim 1 or 18, wherein the films or a laminate comprising the films contains inner regions of white, black, opaque colored or transparent colored areas.

37. The film of claim 36, wherein embossing of the film brings out contrast to different regions of the film.

38. A document of value incorporating the film or thread of claims 36 and 37.

39. A document of value comprising at least one security thread using the film according to claim 1 or 18.

41. The multi-layer optical film of claim 36 where the opaque center core layer is a polymer filled with a pigment or dye.

42. The multi-layer optical film of claim 36 wherein the inner region is a coating such that the coating is between two laminated multi-layer optical films.

44. A bank note of claim 1, 6 or 18 wherein the change in stiffness due to the proximity of the glass transition(s) of the polymer(s) to human body, room and ice water temperatures allow for ready human or machine detection of the change in stiffness or sonic frequency of vibration.

6. A bank note, comprising:

(a) a plurality of first optical layers, each first optical layer comprising high refractive index birefringent polymers; and

(b) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising low refractive index polymers, wherein such low refractive index polymers have a T_gL below room temperature.

7. The bank note according to claim 6, wherein the high refractive index polymer is a polyester.

8. The bank note according to claim 6 or 7 further comprises one or more skin layers.

9. The bank note according to claim 8, wherein at least one of the skin layers is a polyolefin.

31. The bank note of claim 6, wherein the bank note has a crease recovery of at least 140°

after creasing under a 500 gm load over a 0.19 mm radius.

33. The bank note of claim 6, wherein the bank note has a ratio of crumpled to uncrumpled height of less than 8, following 24 hour recovery under 969 gm load for a 67 mm square sample.

35. The bank note of claim 6, wherein the bank note has a normalized propagated tear resistance of greater than 8 N/mm.

40. The document of value according to claim 31, wherein one or more security thread contains a holographic image, a printed image, a topographical feature or any combination thereof.

10. An optical film, comprising:

(a) a plurality of first optical layers, each first optical layer comprising high refractive index birefringent polymers, wherein such high refractive index birefringent polymers; and

(b) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising low refractive index polymers, with the proviso that T_gH is less than T_gL.

11. The optical film of claim 10 wherein the T_gH is less than room temperature.

12. The optical film of claim 10 wherein the T_gL is less than room temperature.

13. The optical film of claim 10, wherein the high refractive index polymer is a polyester.

14. The optical film of any of claims 10 to 13, further comprising one or more skin layers.

15. The optical film according to claim 14, wherein one or more skin layer is a polyolefin.

16. A bank note comprising the film of any of claims 10 to 13.

17. A method of processing a multi-layered optical film comprising, orienting a film at a temperature proximate to the T_mH, wherein the film is comprised of alternating layers wherein a first optical layer is comprised of high refractive index birefringent polymer having a T_mH and a T_gH, and a second optical layer is comprised of a low refractive index polymer, such that the T_gH is below room temperature and the T_mH is greater than T_gL.

18. An optical film obtained by orienting a multi-layered film, wherein the film is comprised of:

(a) a plurality of first optical layers, each first optical layer being oriented and comprising high refractive index birefringent polymers, wherein such polymers have a T_gH below room temperature; and

(b) a plurality of second optical layers disposed in a repeating sequence with the plurality of first optical layers, each second optical layer comprising low refractive index polymers, wherein such polymers have a T_gL below room temperature, with the proviso that T_gH is less than T_gL.

19. A method of using the optical film according to claim 18 as a bank note.

43. A multi-layer optical film with an opaque center core layer that is clear to reveal the color of the opaque center core layer, and upon embossing to specific optical layer thicknesses, reflects a range of light specified by the thickness of the embossed optical layers in the embossed area.