Birefringent film with n.sub.x >n.sub.z >n.sub.y, process for producing the same, retardation film, elliptically polarizing plate, and liquid crystal display

• US 5,245,456 A
• Filed: 10/23/1991
• Issued: 09/14/1993
• Est. Priority Date: 10/24/1990
• Status: Expired due to Term

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Yoshimi, Hiroyuki, Nagatsuka, Tatsuki, Osuka, Tatsuya, Fujimura, Yasuo
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): GROSS, ANITA P
• Application Number:
  US07/780,938
• Time in Patent Office: 692 Days
• Field of Search: 359/73, 359/494, 359/500
• US Class Current: 349/118
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• 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
• CPC Class Codes: G02F 2413/13 Positive birefingence

Abstract

A birefringent film in which molecules oriented in a direction parallel to the film plane and molecules oriented in the direction of the thickness of the film are present in a mixed state. Also, a process for producing the birefringent film, which comprises laminating a resin film on one or both sides thereof with a shrinkable film, thereby preparing a laminate, and then heat stretching the laminate, thereby performing stretching treatment of the resin film while imparting to the resin film the ability to shrink in the direction crossing the stretching direction. A retardation film is formed by using at least one birefringent film and has refractive indexes, n_x and n_y, in two directions parallel to the plate plane and crossing each other at right angles and a refractive index, n_z, in the direction of the thickness of the plate, said refractive indexes n_x, n_y, and n_z satisfying the following equation:

0<(n.sub.x -n.sub.z)/(n.sub.x -n.sub.y)<1

provided that n_x >n_y. Also, an elliptically polarizing plate comprises a laminate of the retardation film with a polarizing plate. Additionally, a liquid crystal display comprises a liquid crystal cell and a polarizing plate disposed at least on one side of said liquid crystal cell through the retardation film.

Claims

1. A birefringent film formed of a single resin in which molecules oriented in a direction parallel to the film plane and molecules oriented in the direction of the thickness of the film are present in a mixed state, which birefringent film has refractive indexes, n_x and n_y, in two directions parallel to the film plane and crossing each other at right angles and a refractive index, n_z, in the direction of the thickness of the film, wherein n_x >

n_z >

n_y.

2. A birefringent film as claimed in claim 1, wherein the film is made of a resin which is positively birefringent.

3. A birefringent film as claimed in claim 2, wherein the resin which is positively birefringent is a polycarbonate, poly(vinyl alcohol), cellulose acetate, polyester, polyacrylate, polyimide or polyolefin.

4. A birefringent film as claimed in claim 1, wherein the film is made of a resin which is negatively birefringent.

5. A birefringent film as claimed in claim 4, wherein the resin which is negatively birefringent is polystyrene, a styrene-based copolymer, poly(methyl methacrylate) or a methyl methacrylate-based copolymer.

6. A retardation film which uses at least one birefringent film as claimed in claim 1 and has refractive indexes, n_x and n_y, in two directions parallel to the film plane and crossing each other at right angles and a refractive index, n_z, in the direction of the thickness of the film, said refractive indexes n_x, n_y, and n_z satisfying the following equation:

space="preserve" listing-type="equation">0<

(n.sub.x -n.sub.z)/(n.sub.x -n.sub.y)<

1

provided that n_x >

n_y.

7. A retardation film as claimed in claim 6, wherein said refractive indexes n_x and n_y satisfy the following equation:

space="preserve" listing-type="equation">100 nm<

(n.sub.x -n.sub.y)d<

1,000 nm

wherein d is the thickness of the plate.

8. An elliptically polarizing plate comprising a laminate of the retardation film as claimed in claim 6 with a polarizing plate.

9. A liquid crystal display comprising a liquid crystal cell and a polarizing plate disposed at least on one side of said liquid crystal cell through the retardation film as claimed in claim 6.

10. A process for producing a birefringent film, which process comprises laminating a resin film on one or both sides thereof with a shrinkable film, thereby preparing a laminate, and then heat stretching the laminate, thereby performing stretching treatment of the resin film while imparting to the resin film the ability to shrink in the direction crossing the stretching direction in which molecules oriented in a direction parallel to the film plane and molecules oriented in the direction of the thickness of the film are present in a mixed state.

11. A process as claimed in claim 10, wherein the degree of width-direction or lengthwise direction shrinkage of the shrinkable film is higher by at least 5% than that of the resin film.