Liquid crystal display device and inspection method for a transparent substrate

• US 20040008297A1
• Filed: 04/28/2003
• Published: 01/15/2004
• Est. Priority Date: 04/26/2002
• Status: Active Grant

• Current Assignee: Optrex Corporation (Kyocera Corporation), Optrex Europe GmbH (Kyocera Corporation)
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.), Optrex Corporation (Kyocera Corporation)
• Inventors: Ozeki, Masao, Lauenstein, Christian, Fertig, Werner
• Granted Patent: US 6,906,763 B2
• Time in Patent Office: Days
• US Class Current: 349/74
• CPC Class Codes: G01B 11/0675 using interferometry
• CPC Class Codes: G01N 2021/9513 Liquid crystal panels
• CPC Class Codes: G01N 21/896 Optical defects in or on transparent materials, e.g. distortion, surface flaws in conveyed flat sheet or rod for other objects G01N21/958
• CPC Class Codes: G02F 1/133636 with twisted orientation, e.g. comprising helically oriented LC-molecules or a plurality of twisted birefringent sublayers
• CPC Class Codes: G02F 2203/64 Normally black display, i.e. the off state being black

Abstract

A liquid display device of D-STN mode capable of suppressing a line-shaped ununiformity of brightness in displaying a dark appearance is presented.

A displaying cell 1 and a compensation cell 21 are formed so that there is a difference of thickness of at least 0.05 mm between the thickness of a glass substrate 2 at a front side of the displaying cell 1 and the thickness of a glass substrate at a rear side of the compensation cell 21. The displaying cell 1 and the compensation cell 21 are arranged between a first polarizing plate 32 and a second polarizing plate 33. A backlight 31 is of a type emitting light whose half value width with respect to the peak luminance is at least 5 nm.

Claims

1. A liquid crystal display device comprising:

a displaying liquid crystal cell having a liquid crystal layer sandwiched by a pair of transparent substrates with transparent electrodes so as to maintain a state of twisted alignment when a voltage applied to the liquid crystal layer is not more than the threshold voltage,

a compensation cell having a liquid crystal layer sandwiched by a pair of transparent substrates so as to maintain a state of twisted alignment in which the direction of twisting is opposite to that in the displaying liquid crystal cell and the twist angle is substantially the same as that of the displaying liquid crystal, the compensation cell having substantially the same retardation value as the displaying liquid crystal cell, wherein the displaying liquid crystal cell and the compensation cell are arranged so that directions of alignment of liquid crystal molecules at sides of adjacent transparent substrates are substantially perpendicular to each other, and

a pair of polarizing plates disposed to sandwich the displaying liquid crystal cell and the compensation cell so that their polarization axes are substantially perpendicular to each other, the liquid crystal display device being characterized in that;

a backlight is disposed to irradiate light whose half value width with respect to the peak luminance is at least 5 nm, and

there is a difference of thickness of at least 0.05 mm between the thickness of the transparent substrate of the displaying liquid crystal cell at a side of compensation cell and the thickness of the transparent substrate of the compensation cell at a side of displaying liquid crystal cell.

2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is an in-vehicle liquid crystal display device mounted on a vehicle or a displaying liquid crystal device for presenting information to public.

3. The liquid crystal display device according to claim 1, wherein there is an air space of at least 75 μ

m between the displaying liquid crystal cell and the compensation cell.

4. A liquid display device comprising:

a displaying liquid crystal cell having a liquid crystal layer sandwiched by a pair of transparent substrates with transparent electrodes so as to maintain a state of twisted alignment when a voltage applied to the liquid crystal layer is not more than the threshold voltage,

a compensation cell having a liquid crystal layer sandwiched by a pair of transparent-substrates so as to maintain a state of twisted alignment in which the direction of twisting is opposite to that in the displaying liquid crystal cell and the twist angle is substantially the same as that of the displaying liquid crystal cell, the compensation cell having substantially the same retardation value as the displaying liquid crystal, wherein the displaying liquid crystal cell and the compensation cell are arranged so that directions of alignment of liquid crystal molecules at sides of adjacent transparent substrates are substantially perpendicular to each other, and

a pair of polarizing plates arranged to sandwich the displaying liquid crystal cell and the compensation cell so that their polarization axes are substantially perpendicular to each other, the liquid crystal display is device being characterized in that;

a backlight is disposed to irradiate light whose half value width with respect to the peak luminance is at least 5 nm, and

the transparent substrate of the displaying liquid crystal cell at a side of compensation cell and the transparent substrate of the compensation cell at a side of displaying liquid crystal cell are provided with first transparent sheets of substantially same thickness, and

the first transparent sheet of either the transparent substrate of the displaying liquid crystal cell at a side of compensation cell or the transparent substrate of the compensation cell at a side of displaying liquid crystal cell is in optically close contact with a second transparent sheet having a thickness of at least 0.05 mm.

5. An inspection method for inspecting a distribution of thickness of a transparent substrate, characterized in that:

a first transparent substrate having a known distribution of thickness and a second transparent substrate to be inspected are prepared, wherein the difference of thickness in average between first and second transparent substrates is not more than 50 μ

m,

the first transparent substrate and the second transparent substrate are arranged so that light transmits through a first substrate and a second substrate,

a substrate gap of at least 0.1 mm is provided between the first substrate and the second substrate,

a light source for irradiating light whose half value width with respect to the peak luminance is at least 5 nm is prepared, and

the degree of distribution of thickness of the second transparent substrate is judged from an interference intensity distribution of light passing through the first transparent substrate and the second transparent substrate.

6. The inspection method for a transparent substrate according to claim 5, wherein the judgment to the interference intensity distribution generated in the second transparent substrate is made according to the number of interference fringes generated by interference of light passing through the first transparent substrate and the second transparent substrate.