Post-formable multilayer optical films and methods of forming

• US 20020154406A1
• Filed: 04/03/2002
• Published: 10/24/2002
• Est. Priority Date: 01/13/1998
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Weber, Michael F., Ouderkirk, Andrew J., Benson, Olester Jr., Jonza, James M., Merrill, William W., Stumo, Roger J., Keller, Janet T.
• Granted Patent: US 6,788,463 B2
• Time in Patent Office: Days
• US Class Current: 359/498
• CPC Class Codes: B32B 2307/418 Refractive
• CPC Class Codes: B32B 2307/42 Polarizing, birefringent, filtering
• CPC Class Codes: B32B 27/08 of synthetic resin
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: B32B 3/28 characterised by a layer comprising a deformed thin sheet , i.e. the layer having its entire thickness deformed out of the plane, e.g. corrugated, crumpled B32B29/08 takes precedence
• CPC Class Codes: B32B 7/023 Optical properties
• CPC Class Codes: B41M 3/14 Security printing securities B42D25/29
• CPC Class Codes: B42D 25/29 Securities; Bank notes
• CPC Class Codes: B44F 1/14 Iridescent effects
• 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 5/3033 in the form of a thin sheet or foil, e.g. Polaroid
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• 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: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: Y10S 428/91 Product with molecular orientation
• CPC Class Codes: Y10T 428/24479 including variation in thickness
• CPC Class Codes: Y10T 428/24612 Composite web or sheet
• CPC Class Codes: Y10T 428/24628 Nonplanar uniform thickness material
• CPC Class Codes: Y10T 428/24694 Parallel corrugations
• CPC Class Codes: Y10T 428/31504 : Composite [nonstructural laminate]
• CPC Class Codes: Y10T 428/31855 : Of addition polymer from unsaturated monomers

Abstract

Articles including post-formed multilayer optical films with layers of at least one strain-induced birefringent material, methods of manufacturing such articles by post-forming multilayer optical films, and multilayer optical films that are particularly well-suited to post-forming operations are disclosed. The articles, methods and multilayer optical films of the present invention allow for post-forming of multilayer optical films including strain-induced index of refraction differentials while retaining the desired optical properties of the multilayer optical films.

Claims

1. An article comprising multilayer optical film comprising an optical stack comprising a plurality of layers, the layers comprising at least one birefringent polymer and at least one second polymer, wherein the optical stack comprises a strain-induced index of refraction differential between layers in the optical stack along a first in-plane axis, and further wherein the optical stack defines first and second major surfaces, the first major surface including at least one depressed area formed therein.

2. The article of claim 1, wherein the depth of the depressed area relative to the first surface is at least about 0.1 millimeter or more, and further wherein the second major surface includes at least one raised area formed thereon.

3. The article of claim 2, wherein each of the depressed areas formed in the first surface is located opposite one of the raised areas on the second surface.

4. The article of claim 2, wherein the optical stack further comprises a strain-induced index of refraction differential along a second in-plane axis that is perpendicular to the first in-plane axis.

5. The article of claim 1, wherein the depth of the depressed area relative to the first surface is at least about 1 millimeter or more.

6. The article of claim 5, wherein the second major surface comprises at least one raised area formed thereon.

7. The article of claim 6, wherein each of the depressed areas formed in the first surface is located opposite one of the raised areas on the second surface.

8. The article of claim 6, wherein the optical stack further comprises a strain-induced index of refraction differential along a second in-plane axis that is perpendicular to the first in-plane axis.

9. The article of claim 1, wherein the optical stack has a corrugated configuration.

10. The article of claim 1, wherein the optical stack includes one or more deformed portions whose thickness differs from remaining portions of the optical stack by at least about 10%.

11. The article of claim 10, wherein the one or more deformed portions are selected from the group consisting of embossed portions and thermoformed portions.

12. The article of claim 10, wherein the deformed portions define indicia.

13. The article of claim 10, wherein a thickness ratio of the optical stack between the deformed portions and the remaining portions is up to a factor of 3.

14. The article of claim 1, further comprising a rigid substrate attached to the multilayer optical film.

15. The article of claim 1, wherein the optical film has been underdrawn to achieve a crystallinity of the birefringent polymer of from about 3% to about 18%.

16. The article of claim 1, wherein the birefringent polymer has associated therewith a draw ratio Regime II over which the crystallinity of the birefringent polymer is at least about 3% and over which a refractive index difference of the birefringent polymer increases at a faster rate than over larger draw ratios, and wherein the optical film has been underdrawn such that the birefringent polymer has been stretched to a draw ratio in Regime II.

18. The article of claim 17, wherein the wavelength range of interest comprises 400 to 700 nanometers.

19. The article of claim 17, wherein the second reflective portion is thinned by a factor of at least 2 relative to the first reflective portion.

20. The article of claim 17, wherein the first wavelength range comprises at least 400 to 1800 nanometers.

21. The article of claim 17, wherein the second wavelength range comprises at least 400 to 900 nanometers.

22. The article of claim 17, wherein the second reflective portion is selected from the group consisting of an embossed portion and a thermoformed portion of the multilayer optical film.

23. The article of claim 17, wherein the optical stack comprises a strain-induced index of refraction differential between layers in the optical stack along a first in-plane axis, and further wherein the optical stack defines first and second major surfaces, the first major surface including a depressed area formed therein at the second reflective portion.

24. The article of claim 23, wherein the depth of the depressed area relative to the first surface is at least about 1 millimeter or more.

25. The article of claim 23, wherein the depth of the depressed area relative to the first surface is at least about 0.1 millimeter or more, and further wherein the second major surface includes at least one raised area formed thereon.

17. An article comprising a multilayer optical film comprising an optical stack comprising a plurality of layers, the layers comprising at least one birefringent polymer and at least one second polymer, the multilayer optical film comprising at least a first and second reflective portion wherein the second reflective portion is thinned relative to the first reflective portion, wherein the first and second reflective portions reflect normally incident light in a first and second wavelength range respectively that differ from each other but that overlap at least in a wavelength range of interest.