Liquid crystal display with tilted retardation film

• US 5,638,200 A
• Filed: 02/03/1995
• Issued: 06/10/1997
• Est. Priority Date: 02/03/1995
• Status: Expired due to Term

• Current Assignee: Guardian Industries Corporation (KOCH Industries Incorporated)
• Original Assignee: OIS Optical Imaging Systems, Inc. (KOCH Industries Incorporated)
• Inventors: Xu, Gang
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MILLER, CHARLES LELAND
• Application Number:
  US08/383,200
• Time in Patent Office: 858 Days
• Field of Search: 359/73, 359/494
• US Class Current: 349/117
• CPC Class Codes: G02B 5/3016 involving passive liquid crystal elements optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528
• CPC Class Codes: G02F 1/133632 with refractive index ellipsoid inclined relative to the LC-layer surface
• CPC Class Codes: G02F 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis

Abstract

A liquid crystal display includes a tilted retarder. The tilted retarder has an optical axis which is aligned at an angle of from about 5° to 15° with respect to normal. Thus, because the optical axis of the liquid crystal layer is aligned at an angle to one side of normal and the optical axis of the tilted retarder(s) is at an angle to the other side of normal, the retardation effects substantially cancel one another out. Tilted retarder(s) may be used in combination with negatively birefringent retarders according to certain embodiments of this invention in twisted nematic normally white displays.

Claims

1. A normally white liquid crystal display comprising:

a twisted nematic liquid crystal layer wherein dxΔ

n is from about 380 to 550 nm;

a backlight for illuminating said liquid crystal layer;

a rear polarizer disposed between said backlight and said liquid crystal layer;

a front polarizer disposed on the viewer side of said liquid crystal layer; and

a first tilted uniaxial retarder having a positive birefringent value, said tilted retarder being substantially parallel to said rear and front polarizers and having an optical axis tilted Θ

°

from an axis perpendicular to a plane parallel to said polarizers, where Θ

is from about 5°

to 15°

.

2. The liquid crystal display of claim 1, wherein Θ

is from about 7°

to 10°

so as to reduce inversion in the positive vertical viewing zone whereby gray level performance is improved.

3. The liquid crystal display according to claim 1, further comprising a first negatively birefringent retardation film, said first tilted retardation film and said first negatively birefringent retardation film being located on the same side of said liquid crystal layer.

4. The liquid crystal display according to claim 3, further comprising:

a second tilted uniaxial retardation film having a positive birefringent value, said second tilted retardation film having an optical axis tilted Θ

°

from an axis perpendicular to a plane parallel to said polarizers where Θ

is from about 5°

to 15°

.

5. The liquid crystal display according to claim 4, further comprising a second negatively birefringent retardation film, wherein said first tilted retardation film and said first negatively birefringent retardation film are located between said liquid crystal layer and said rear polarizer, and said second tilted retardation film and said second negatively birefringent retardation film are located between said liquid crystal layer and said front polarizer.

6. The liquid crystal display according to claim 5, wherein Θ

of said first and second retardation films is from about 7°

to 10°

.

7. The liquid crystal display according to claim 1, wherein the liquid crystal molecules of said liquid crystal layer are tilted to one side of an axis perpendicular to a plane parallel to said polarizers when predetermined voltages are applied to said liquid crystal layer, and said optical axis of said first tilted retardation film is titled Θ

°

to the other side of an axis perpendicular to a plane parallel to said polarizers and whereby retardation effects from the liquid crystal layer and said first tilted retardation film substantially cancel one another out.

8. The liquid crystal display according to claim 1, wherein the transmission axis of said rear polarizer defines a first direction and the transmission axis of said front polarizer defines a second direction, and wherein said first and said directions define an angle of about 85°

to 95°

therebetween.

9. The liquid crystal display according to claim 8, further comprising first and second orientation films, said first orientation film being disposed on the rear side of said liquid crystal layer and being buffed in substantially said first direction, and said second orientation film being buffed in substantially said second direction.