Optical film and surface light source using it

• US 20070064294A1
• Filed: 05/21/2004
• Published: 03/22/2007
• Est. Priority Date: 05/22/2003
• Status: Active Grant

• Current Assignee: Hitachi Chemical Company Limited (Resonac Holdings Corp.)
• Original Assignee: Hitachi Chemical Company Limited (Resonac Holdings Corp.)
• Inventors: Hoshino, Tetsuya, Sugimoto, Yasushi, Dobashi, Tomo, Teshima, Teruo
• Granted Patent: US 7,672,051 B2
• Time in Patent Office: Days
• US Class Current: 359/237
• CPC Class Codes: G02B 5/0252 using holographic or diffractive means
• CPC Class Codes: G02B 5/0257 creating an anisotropic diffusion characteristic, i.e. distributing output differently in two perpendicular axes
• CPC Class Codes: G02B 5/0278 used in transmission
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects

Abstract

An optical film 10 has a transparent base film 11 made of polyethylene terephthalate (PET), a prism made of photo-curing resin such as acryl modified epoxy on an incident surface 12 that is one face of the base film 11, and a hologram similarly made of photo-curing resin on an exit surface 13 opposing the incident surface 12. The prism has grooves or ridges each having a substantially triangular cross section to totally reflect incident light so as to bend the light into a direction perpendicular to the exit surface 13. The hologram anisotropically diffuses light exiting from the exit surface 13, to improve brightness.

Claims

1. An optical film comprising:

an incident surface having a shape to bend incident light; and

an exit surface opposing the incident surface and having a diffuser to diffuse light only into a specific spatial range of angles,

the shape of the incident surface being made to bend incident light to the incident surface into a direction perpendicular to the exit surface.

2. The optical film as set forth in claim 1, wherein the incident light is white light and the shape of the incident surface is to bend the white light into a direction perpendicular to the exit surface.

3. The optical film as set forth in claim 1, wherein the shape of the incident surface includes grooves or ridges at average intervals of 200 μ

m or below.

4. The optical film as set forth in claim 3, wherein the grooves or ridges are formed as concentric circular arcs.

5. The optical film as set forth in claim 3, wherein the grooves or ridges form a hologram.

6. The optical film as set forth in claim 5, wherein the hologram is a transmissive diffraction grating that bends white light having an incident angle of 60°

±

15°

into a direction perpendicular to the exit surface and has a sawteeth shape with average intervals of m1×

(5.0±

1.0) μ

m and an average depth of m2×

(3.7±

1.0)/(n−

1) μ

m where n is the refractive index of an optical material and m1, m2=1, 2, 3, . . . , or the grooves are buried up to less than 50% of the depth thereof.

7. The optical film as set forth in claim 6, wherein the sawteeth shape is approximated with N levels (N=4, 5, 6, . . . ).

8. The optical film as set forth in claim 3, wherein the grooves or ridges each have a substantially triangular cross-sectional shape.

9. The optical film as set forth in claim 8, wherein the grooves or ridges utilize a principle that light causes total reflection in a triangle, to bend light.

10. The optical film as set forth in claim 1, wherein diffusion angles of the diffuser on the exit surface are 10 degrees or below in every direction.

11. The optical film as set forth in claim 1, wherein a haze value of the diffuser on the exit surface is 50% or below.

12. The optical film as set forth in claim 10, wherein the diffuser on the exit surface is formed by embossing.

13. The optical film as set forth in claim 12, wherein the embossing is transferring from an electroformed mold having a pattern of speckles.

14. The optical film as set forth in claim 12, wherein the embossing is transferring from a metal mold roll having microscopic irregularities.

15. A surface light source comprising a light guide and the optical film as set forth in claim 1 arranged on an exit surface of the light guide, the incident surface of the optical film where the shape to bend incident light is formed facing the light guide.

16. The surface light source as set forth in claim 15, wherein the exit surface of the light guide is integrally provided with a hologram diffuser having an anisotropic diffusing characteristic.

17. The surface light source as set forth in claim 15, wherein a film having a function of preventing polarization split, color separation, and reflection is arranged between the light guide and the optical film, or on the exit surface of the optical film.

18. The optical film as set forth in claim 11, wherein the diffuser on the exit surface is formed by embossing.

19. The optical film as set forth in claim 18, wherein the embossing is transferring from an electroformed mold having a pattern of speckles.

20. The optical film as set forth in claim 18, wherein the embossing is transferring from a metal mold roll having microscopic irregularities.