Liquid crystal display with two positive tilted retardation films and two negative retardant films

• US 5,777,709 A
• Filed: 10/07/1996
• Issued: 07/07/1998
• 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): Parker, Kenneth
• Application Number:
  US08/726,654
• Time in Patent Office: 638 Days
• Field of Search: 349/119, 349/120, 349/117, 359/494
• US Class Current: 349/120
• 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 liquid crystal display comprising:

a liquid crystal layer;

a rear polarizer having a transmission axis;

a front polarizer disposed on the viewer side of the liquid crystal layer so that the liquid crystal layer is disposed between the front and rear polarizers;

first and second tilted retardation films on opposite sides of the liquid crystal layer, said first and second tilted retardation films being positively birefringent and uniaxial, and each having an optical axis tilted or at an oblique angle relative to a normal axis that is substantially perpendicular to a surface of one of said tilted retardation films;

first and second negative retarders located on opposite sides of the liquid crystal layer, said first and second negative retarders each having an optical axis substantially parallel to the normal axis; and

wherein said negative retarders and said tilted retardation films have retardation values and axis alignment such that the display exhibits a contrast ratio, when a 550 nm wavelength is used, of at least about 10;

1 over a horizontal angular span of at least about 120° and

over a vertical angular span of at least about 80°

.

2. The display of claim 1, wherein said front and rear polarizers are arranged relative to one another so as to define a normally white twisted nematic display.

3. The display of claim 2, wherein d.Δ

n of the liquid crystal layer is from about 380-550 nm.

4. The display of claim 1, wherein the contrast ratio at 550 nm is at least about 40 or 40:

1 at 0°

vertical, ±

60°

horizontal.

5. The display of claim 1, wherein said polarizer and retardation axes are oriented relative to one another so that when gray level voltages of from about 2.25 volts to 6.5 volts are applied across the liquid crystal there are substantially no inversion humps or rises at horizontal viewing angles of from about -60°

to +60° and

at vertical viewing angles of from about 40°

to +40°

.