OPTICAL POLARIZING FILMS WITH DESIGNED COLOR SHIFTS

• US 20080003419A1
• Filed: 08/13/2007
• Published: 01/03/2008
• Est. Priority Date: 12/31/2002
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hebrink, Timothy, Ruff, Andrew, Gilbert, Laurence, Jonza, James
• Granted Patent: US 7,744,987 B2
• Time in Patent Office: Days
• US Class Current: 428/213
• CPC Class Codes: B32B 27/36 comprising polyesters
• CPC Class Codes: B32B 7/023 Optical properties
• CPC Class Codes: B42D 25/355 Security threads
• CPC Class Codes: B42D 25/45 Associating two or more layers
• CPC Class Codes: G02B 5/287 comprising at least one layer of organic material
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/2495 Thickness [relative or absolute]

Abstract

Multilayer films are provided that exhibit a colored appearance when viewed at an oblique angle as a result of one or more reflection bands in the visible region of the spectrum. The films however provide no substantial reflection bands in either the visible or near infrared regions for light normally incident on the film. The films can be made to shift from clear at normal incidence to an arbitrary designed color at an oblique angle without necessarily becoming cyan.

Claims

1. An optical film, comprising a plurality of layers that form a plurality of optical repeat units, at least some of the optical repeat units having optical thicknesses equal to half of a wavelength of visible light, and wherein the optical film has a clear appearance at normal incidence.

2. The film of claim 1, wherein the film has no reflection band of reflectivity greater than 20% for normally incident light.

3. The film of claim 1, wherein the film comprises alternating layers of a first and second thermoplastic polymer, and wherein the first polymer is substantially isotropic and the second polymer is birefringent.

4. The film of claim 3, wherein the second polymer has a refractive index along a thickness axis of the film that differs from a refractive index of the first polymer along the thickness axis of the film by at least 0.1.

5. The film of claim 3, wherein the first polymer has a refractive index of at least 1.65.

6. The film of claim 3, wherein the film has a first and second portion, and the alternating layers in the first portion have a different overall thickness than the alternating layers in the second portion.

7. The film of claim 1, wherein the film has a clear transmitted appearance at normal incidence.

8. An optical film whose transmitted appearance changes from substantially clear to a first color over an angular range of observation angles, and where the optical film does not appear cyan over such angular range.