Optical film and reflective liquid-crystal display device

• US 20020054258A1
• Filed: 11/08/2001
• Published: 05/09/2002
• Est. Priority Date: 11/08/2000
• Status: Active Grant

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Umemoto, Seiji, Kondo, Hiroyuki, Ariyoshi, Toshihiko
• Granted Patent: US 6,665,029 B2
• Time in Patent Office: Days
• US Class Current: 349/113
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02F 1/133502 Antiglare, refractive index matching layers
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/133616 Front illuminating devices

Abstract

An optical film constituted by: a transparent film including a repetitive structure of a plurality of light exit means arranged at intervals of a regular pitch or intervals of irregular pitches in one of opposite surfaces of the transparent film, the repetitive structure of the plurality of light exit means having optical path changing slopes each inclined to the film surface at an inclination angle in a range of from 30 to 48 degrees in order to change an optical path of light from a direction of the film surface into a direction of thickness of the film; and an anti-reflection layer disposed on the film surface in which the plurality of light exit means are formed; wherein the optical film is light-transmissible in the direction of the thickness of the film. A reflective liquid-crystal display device constituted by: a reflective liquid-crystal display panel including at least one light source on one of side surfaces of the liquid-crystal display panel; and the optical film provided on a viewing side of the reflective liquid-crystal display panel so that a surface of the optical film in which a plurality of light exit means are formed faces outward.

Claims

1. An optical film comprising:

a transparent film including a repetitive structure of a plurality of light exit means arranged at intervals of a regular pitch or intervals of irregular pitches in one of opposite surfaces of said transparent film, said repetitive structure of said plurality of light exit means having optical path changing slopes each inclined to said film surface at an inclination angle in a range of from 30 to 48 degrees in order to change an optical path of light from a direction of said film surface into a direction of thickness of said film; and

an anti-reflection layer disposed on said film surface in which said plurality of light exit means are formed;

wherein said optical film is light-transmissible in said direction of the thickness of said film.

2. An optical film according to claim 1, further comprising an adhesive layer disposed on the other surface of said transparent film in which no light exit means are formed.

3. An optical film according to claim 2, wherein said adhesive layer is a pressure sensitive adhesive layer.

4. An optical film according to claim 1, wherein said anti-reflection layer exhibits a reflectance of not higher than 1.5% with respect to perpendicularly incident light with a wavelength of 550 nm.

5. An optical film according to claim 1, wherein said anti-reflection layer is made of a transparent dielectric thin film which is vapor-deposited on a surface of said transparent film.

6. An optical film according to claim 1, wherein said plurality of light exit means are constituted by continuous or discontinuous prism-like structures which are formed at intervals of a pitch in a range of from 50 μ

m to 1.5 mm and each of which has a combination of an optical path changing slope and a gentle slope, wherein each of said optical path changing slopes is inclined downward from one side of said film to an opposite side of said film and has a projected width of not larger than 40 μ

m on a film plane, wherein each of said gentle slopes is inclined to said film surface at an inclination angle in a range of from 0 (exclusive) to 10 degrees, wherein a difference in inclination angle between any two of said gentle slopes is not larger than 5 degrees while a difference in inclination angle between adjacent ones of said gentle slopes is not larger than 1 degree, and wherein a projected area of said gentle slopes on said film plane is not smaller than 8 times as large as a projected area of said optical path changing slopes on said film plane.

7. An optical film according to claim 6, wherein ridgelines of said prism-like structures are parallel with one side of said film or intersect one side of said film at an angle in a range of ±

35 degrees.

8. An optical film according to claim 1, wherein said plurality of light exit means are constituted by discontinuous grooves each of which has a combination of an optical path changing slope and an elevational face opposite to said optical path changing slope and each of is shaped substantially like a triangle in section;

wherein each of said elevational faces is inclined to said film surface at an inclination angle of not smaller than 48 degrees;

wherein each of said grooves has a length, a width and a depth, said length being not smaller than 5 times as large as said width, said depth ranging from 2 to 40 μ

m; and

wherein said plurality of light exit means are arranged irregularly while an area occupied by said plurality of light exit means is not larger than 15% of a whole area of said film surface.

9. A reflective liquid-crystal display device comprising:

a reflective liquid-crystal display panel including at least one light source on one of side surfaces of said liquid-crystal display panel; and

an optical film according to claim 1 and provided on a viewing side of said reflective liquid-crystal display panel so that a surface of said optical film in which a plurality of light exit means are formed faces outward.