Polarizing plate with optical compensation layer, method of producing the same, and liquid crystal panel, liquid crystal display, and image display including the same

• US 7,557,883 B2
• Filed: 07/12/2007
• Issued: 07/07/2009
• Est. Priority Date: 07/12/2006
• Status: Active Grant

• Current Assignee: Nitto Denko Corporation
• Original Assignee: Nitto Denko Corporation
• Inventors: Yonezawa, Hideyuki, Shutou, Shunsuke, Takahashi, Naoki, Kawamoto, Ikuo, Chiba, Tsuyoshi, Hada, Kazuya
• Primary Examiner(s): Font; Frank G
• Assistant Examiner(s): Mooney; Michael P
• Application Number:
  US11/776,637
• Publication Number:
  US 20080049179A1
• Time in Patent Office: 726 Days
• Field of Search: 349/12, 349/75, 349/96, 349/106, 349117-119, 349/123, 349/187, 349/191, 264/1.34, 359/499
• US Class Current: 349/119
• CPC Class Codes: B29D 11/0073 Optical laminates
• CPC Class Codes: C09K 19/3852 Poly(meth)acrylate derivatives
• 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 1/133634 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 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/133784 by rubbing
• CPC Class Codes: G02F 2413/13 Positive birefingence

Abstract

A polarizing plate with optical compensation layers that performs a wide viewing angle compensation with respect to a liquid crystal cell, allows circularly polarized light to be obtained over a wide range of light wavelengths, contributes to the reduction in thickness, prevents thermal irregularity from occurring, and can effectively prevent light leakage from occurring in a black display. The polarizing plate includes a polarizer, a first optical compensation layer, and a second optical compensation layer that are stacked together in this order. The first optical compensation layer is formed of a liquid crystal compound and has a relationship of nx>ny=nz and an in-plane retardation Re₁ of 100 to 170 nm. The second optical compensation layer has a relationship of nx=ny>nz and a thickness direction retardation Rth₂ of 30 to 400 nm. The angle formed between the absorption axis of the polarizer and the slow axis of the first optical compensation layer is in the range of “plus” or “minus” 25 to 65 degrees.

Claims

1. A polarizing plate with optical compensation layers, comprising:

a polarizer;

a first optical compensation layer; and

a second optical compensation layer,

the polarizer, the first optical compensation layer, and the second optical compensation layer being stacked together in this order,

wherein the first optical compensation layer is formed of a liquid crystal compound and has a relationship of nx>

ny=nz and an in-plane retardation Re₁ in a range of 100 to 170 nm,

the second optical compensation layer has a relationship of nx=ny>

nz and a thickness-direction retardation Rth₂ in a range of 30 to 400 nm, and,

an angle formed between an absorption axis of the polarizer and a slow axis of the first optical compensation layer is in a range of 25 to 65 degrees in a clockwise direction (−

) or in a counterclockwise direction (+) with respect to the absorption axis of the polarizer.

2. The polarizing plate with optical compensation layers according to claim 1, wherein the first optical compensation layer has a thickness in a range of 0.5 to 3 μ

m.

3. The polarizing plate with optical compensation layers according to claim 1, wherein the second optical compensation layer includes a cholesterically aligned and solidified layer with a selective reflection wavelength range of 350 nm or shorter.

4. The polarizing plate with optical compensation layers according to claim 1, wherein the second optical compensation layer has a thickness in a range of 1 to 20 μ

m.

5. The polarizing plate with optical compensation layers according to claim 1, wherein the second optical compensation layer includes a layer formed of a film containing a resin with an absolute value of photoelastic coefficient of 2×

10<sup>−

11</sup> m²/N or lower and a cholesterically aligned and solidified layer with a selective reflection wavelength range of 350 nm or shorter, and the layer formed of a film containing a resin has a relationship of nx=ny>

nz.

6. The polarizing plate with optical compensation layers according to claim 1, wherein the second optical compensation layer comprises a layer formed of a non-liquid crystal polymer.

7. The polarizing plate with optical compensation layers according to claim 6, wherein the non-liquid crystal polymer is at least one selected from the group consisting of polyamide, polyimide, polyester, polyetherketone, polyaryletherketone, polyamide imide, and polyesterimide.

8. The polarizing plate with optical compensation layers according to claim 1, which does not contain a λ

/2 plate.

9. A liquid crystal panel, comprising a polarizing plate with optical compensation layers according to claim 1 and a liquid crystal cell,

wherein a second optical compensation layer is disposed on a side closer to the liquid crystal cell and is disposed on a visible side of the liquid crystal cell.

10. The liquid crystal panel according to claim 9, wherein the liquid crystal cell is a VA mode or an ECB mode.

11. A liquid crystal display, comprising a liquid crystal panel according to claim 9.

12. An image display, comprising a polarizing plate with optical compensation layers according to claim 1.

13. A method of producing a polarizing plate with optical compensation layers according to claim 1, the method comprising:

producing a first optical compensation layer by applying a liquid crystal compound to a rubbing-treated surface of a long base film that has been subjected to a rubbing treatment to be treated to have alignment, and fixing the alignment,

wherein the rubbing treatment is carried out by a rubbing method (A) below;

in a rubbing treatment process where the surface of the long base film is rubbed with a rubbing roll, the long base film is supported and conveyed by a conveyer belt with a metal surface, while a plurality of backup rolls are provided to support a lower surface of the conveyer belt that supports the long base film and to oppose the rubbing roll, and a rubbing strength RS defined by Formula (1) below is set at 800 mm or higher,

RS=N·

M(1+2π

r·

nr/v) 

 

(1)

where N denotes the number of times of rubbing (the number of rubbing rolls) (dimensionless quantity), M indicates an indentation amount (mm) of the rubbing rolls, π

denotes a ratio of a circumference of a circle to its diameter, r indicates a radius (mm) of the rubbing roll, nr denotes a rotational speed (rpm) of the rubbing roll, and v indicates a rate of conveying the long base film (mm/sec).