Optical compensation film and liquid crystal display

• US 20050162592A1
• Filed: 03/24/2005
• Published: 07/28/2005
• Est. Priority Date: 03/31/2003
• Status: Active Grant

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Mori, Hiroyuki, Toyooka, Kentaro, Hirakata, Junichi
• Granted Patent: US 7,847,897 B2
• Time in Patent Office: Days
• US Class Current: 349/119
• CPC Class Codes: G02F 1/133632 with refractive index ellipsoid inclined relative to the LC-layer surface

Abstract

To provide a liquid crystal display, particularly TN type liquid crystal display capable of remarkably improving brightness inversion resistance at a high contrast with a simple configuration and an optical compensation film which realizes the aforementioned properties, the liquid crystal display includes a pair of polarizing plates, each of the polarizing plates being disposed on an outer side of a liquid crystal layer having a twisted structure, the liquid crystal layer being disposed between substrates facing to each other, at least one of the substrates having an electrode, each of the polarizing plates including a polarizing film, a protective film, and an optical compensation film, wherein the optical compensation film includes a compound having a discotic structure unit, and the compound having a discotic structure unit is aligned such that the average alignment direction of the molecular major axis of the discotic structure unit at each side of the upper and lower optical compensation films facing to the polarizing film cross each other at an angle of not greater than the crossing angle of absorption axes of the pair of polarizing plates.

Claims

1. A liquid crystal display comprising:

a pair of a upper polarizing plate and a lower polarizing plate; and

a liquid crystal cell between the upper and lower polarizing plates, the liquid crystal cell comprising;

a pair of substrates facing to each other, at least one of the pair of the substrates having an electrode; and

a liquid crystal layer between the pair of the substrates, the liquid crystal layer having a twisted structure of a liquid crystal,

wherein

the upper polarizing plate comprises an upper optical compensation film;

an upper polarizing film; and

a protective film in this order, the upper optical compensation film being between the upper polarizing film and the liquid crystal cell;

the lower polarizing plate comprises a lower optical compensation film;

a lower polarizing film; and

a protective film in this order, the lower optical compensation film being between the lower polarizing film and the liquid crystal cell;

each of the upper and lower optical compensation films comprises a compound having a discotic structure unit; and

the compound is aligned such that

the upper optical compensation film has an average alignment direction of a molecular major axis of the discotic structure unit,

the lower optical compensation film has another average alignment direction of the molecular major axis of the discotic structure unit, and

the alignment direction of the upper optical compensation film at a side of the upper optical compensation film facing to the upper polarizing film and the alignment direction of the lower optical compensation film at a side of the lower optical compensation facing to the lower polarizing film cross each other at an angle of not greater than a crossing angle of absorption axes of the upper and lower polarizing plates.

2. The liquid crystal display according to claim 1, which has a crossing angle of the alignment directions of the upper and lower optical compensation films, the crossing angle being not greater than a twist angle of the twisted structure.

3. The liquid crystal display according to claim 1, wherein at least one of the upper and lower optical compensation films has average alignment directions of the molecular major axis of the discotic structure unit, the alignment directions differing between at a side of the at least one of the upper and lower optical compensation films facing to the liquid crystal cell and at a side of the at least one of the upper and lower optical compensation films facing to the polarizing film.

4. The liquid crystal display according to claim 1, wherein each of the upper and lower optical compensation films comprises:

a first optical anisotropic layer; and

a second optical anisotropic layer, each of the first and second optical anisotropic layers comprising a liquid crystalline compound; and

the first optical anisotropic layer has an alignment direction of the liquid crystalline compound, the second optical anisotropic layer has another alignment direction of the liquid crystalline, and the alignment directrions of the first and second optical anisotropic layer differ from each other.

7. An optical compensation film as defined in claim 1.

5. A liquid crystal display comprising:

a pair of polarizing films;

a liquid crystal cell between the pair of the polarizing films, the liquid crystal cell comprising;

a pair of substrates facing to each other, at least one of the pair of the substrates having an electrode; and

a liquid crystal layer between the pair of the substrates; and

at least one optical compensation film between the pair of the polarizing films,

wherein

when the at least one optical compensation film is removed from the liquid crystal display leaving the other constitutions unchanged, the liquid crystal display has a ratio of T2(Vw) to T2(Vb) of less than 100;

1, wherein T2(Vw) represents a transmittance from an anterior view in a white display state at an applied voltage Vw, Vw represents an applied voltage so as to provide the white diplay state, T2(Vb) represents a transmittance from an anterior view in a black display state at an applied voltage Vb, and Vb represents an applied voltage so as to provide the black diplay state;

the optical compensation film satisfies a condition that when the optical compensation film is interposed between a pair of polarizing elements arranged in cross nicol configuration to provide a layer product, and the optical compensation film is rotated on a direction normal to a surface of the optical compensation film as a rotary axis, the layered product has a light transmittance of more than zero at all angles of rotation;

the liquid crystal display has a ratio of T1(Vw) to T1(Vb) of 100;

1 or more, wherein T1(Vw) represents a transmittance from an anterior view in the white display state at the applied voltage Vw, and T1(Vb) represents a transmittance from an anterior view in the black display state at the applied voltage Vb; and

the liquid crystal display has a ratio of a maximum value of the transmittance in the black display state to T1 (Vw) of 10% or less at an azimuth angle of 60°

from a direction normal to the substrates.

6. The liquid crystal display according to claim 5, wherein the optical compensation film comprises:

a first optical anisotropic layer; and

a second optical anisotropic layer, each of the first and second optical anisotropic layers comprising a liquid crystalline compound; and

the first optical anisotropic layer has an alignment direction of the liquid crystalline compound, the second optical anisotropic layer has another alignment direction of the liquid crystalline, and the alignment directrions of the first and second optical anisotropic layer differ from each other.

8. An optical compensation film as defined in claim 6.