JP2569585B2 - Color liquid crystal display device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color liquid crystal display device.

[Conventional technology]

A liquid crystal display device using a new twisted nematic mode (hereinafter referred to as NTN mode), which is an improvement on the conventional super twisted nematic mode, is disclosed in Japanese Patent Application No. 62-121.
By providing at least one layer of optically anisotropic material between a pair of polarizing plates as in Japanese Patent No. 701, the coloring of the appearance of the element was eliminated, and white display on a black background or black display on a white background was made possible.

Therefore, in a liquid crystal display element using the NTN mode, colorization can be easily realized by providing a color filter for each pixel.

The reason why the color liquid crystal display device using the NTN mode is superior to the color liquid crystal display device using the conventional twisted nematic mode (hereinafter referred to as TN mode) is that the threshold value of the electro-optical characteristics is steep. Therefore, a large display capacity can be achieved by time-division driving.

FIG. 4 is a cross-sectional view of a conventional color liquid crystal display device using the NTN mode, and FIG. 2 is a diagram showing the relationship between each axis.
In FIG. 4, reference numeral 1 denotes an upper polarizing plate, 2 denotes a liquid crystal cell for displaying (hereinafter referred to as a display cell), 3 denotes an optically anisotropic body, and 4 denotes a lower polarizing plate. Although a liquid crystal cell (hereinafter referred to as a compensation cell) is used here as the optically anisotropic member of No. 3, a polymer film or the like can be used. In the display cell and the compensation cell, the same liquid crystal SS-4008 (manufactured by Chisso) was added with a chiral dopant to adjust the twist angle, and the twist angle 23 of the liquid crystal of the display cell in FIG. 2 was set to 240 degrees to the right. . The angles 20 and 24 in FIG. 2 were both 45 degrees, and the angle 22 was 90 degrees. The thickness d of the liquid crystal layer was 6.0 μm, and Δn × d =
The thickness was set to 0.9 μm.

[Problems to be solved by the invention]

However, in the color liquid crystal display device using the NTN mode, since the threshold voltage of the electro-optical characteristics differs depending on the color, it is difficult to perform color display with good color balance.

FIG. 5 shows the electro-optical characteristics of the conventional color liquid crystal display device using the NTN mode for each color. 28 in the figure is red, 29
Is the voltage transmission curve of green and 30 is the voltage transmission curve of blue.
The light was represented by 650 nm, 550 nm, and 450 nm light. However, the transmittance was expressed assuming that the amount of transmitted light of the two polarizing plates bonded together with their polarization axis directions aligned was 100%.

When comparing the threshold voltage for each color, red is the highest 2.
At 17V, next is green at 2.15V, and blue is the lowest at 2.13V. Although this difference is not a large value, when the number of divisions of the time division driving increases, the difference in transmittance due to the color becomes remarkable, and the color balance is lost.

The present invention solves such a problem, and an object of the present invention is to provide a color liquid crystal display device having good color bunras.

[Means for solving the problem]

The color liquid crystal display element of the present invention has a liquid crystal cell in which a spacially nematic liquid crystal is sandwiched between a pair of substrates having electrodes on the inner surface of the substrate, and at least one optically anisotropic body disposed between the pair of polarizing plates. The optically anisotropic material is obtained by removing coloring of the liquid crystal cell, and a color filter composed of a plurality of color elements is arranged on one substrate of the liquid crystal cell, and a voltage transmission characteristic for each color element is provided. Are characterized in that the thickness of the liquid crystal layer corresponding to each of the color elements is varied so that the threshold voltages of the above-mentioned are substantially matched.

Further, the color liquid crystal display element of the present invention has a layer thickness (d _R ) of a liquid crystal layer corresponding to a red color element and a green That the thickness of the liquid crystal layer corresponding to the color element (d _G ) and the thickness of the liquid crystal layer corresponding to the blue color element (d _B ) are set to have a relationship of d _R <d _G <d _B Features.

Hereinafter, the present invention will be described in detail with reference to examples of the present invention.

〔Example〕

1 and 2 are a cross-sectional view of a color liquid crystal display device according to an embodiment of the present invention and a diagram showing a relationship between respective axes. In FIG. 1, 1 is an upper polarizer, 2 is a liquid crystal cell (display cell) for displaying, 3 is a liquid crystal cell (compensation cell) as an optically anisotropic body, and 4 is a lower polarizer. The twist angle was adjusted by adding a chiral dopant to the same liquid crystal SS-4008 for both the display cell and the compensation cell, and the twist angle 21 of the liquid crystal of the display cell in FIG. Was set to 240 degrees to the right. Also, the angles 20 and 24 in FIG. 2 were both 45 degrees, and the angle 22 was 90 degrees.

The color filter 9 of the display cell was prepared by a method in which a gelatin film was impregnated with a dye, and the thickness of the filter was changed for each color by using the swelling accompanying the dye impregnation. This red, green, thickness d _R of the liquid crystal layer corresponding to the color filters of each color of blue, d _G, and d _B respectively 5.95μm, 6.00μm, 6.05μ
m. Note that the liquid crystal layer thickness of the compensation cell is 6.0 μm and Δ
nxd = 0.9.

FIG. 3 shows the electro-optical characteristics of the color liquid crystal display element according to the embodiment of the present invention for each color. In the figure, 25 is a red, 26 is green, and 27 is a blue voltage transmittance curve. The threshold voltage for each color could be substantially matched by the effect of adjusting the thickness of the liquid crystal layer for each color. This color liquid crystal display element,
OFF effective voltage 2.10V, ON effective voltage 2.21V, 40 divisions
When time-division driving of 0 was performed, the transmittance at the time of OFF was 1% for both red, green and blue, and the transmittance at the time of ON was 35% for red, 40% for green,
Blue was 44%. As described above, since the difference in transmittance between colors is reduced, a color display with a good color balance can be performed both when on and when off.

〔The invention's effect〕

As described above, according to the present invention, the thickness of the liquid crystal layer corresponding to each color element is made different so that the threshold voltage in the voltage transmission characteristics of each color element of the color filter substantially matches each other. A good color liquid crystal display device can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a color liquid crystal display device according to one embodiment of the present invention. FIG. 2 is a diagram showing the relationship between the axes of a color liquid crystal display device according to an embodiment of the present invention and the prior art. FIG. 3 is a diagram showing the electro-optical characteristics of the color liquid crystal display element according to one embodiment of the present invention for each color. FIG. 4 is a sectional view of a conventional color liquid crystal display device. FIG. 5 is a diagram showing, for each color, the electro-optical characteristics of a color liquid crystal display device according to the prior art. DESCRIPTION OF SYMBOLS 1 ... Upper polarizing plate 2 ... Liquid crystal cell (display cell) which performs a display 3 ... Liquid crystal cell (compensation cell) as an optically anisotropic body 4 ... Lower polarizing plate 5 ... Upper substrate of a display cell 6 ...... Transparent electrode 7 Alignment layer 8 Liquid crystal of display cell 9 Color filter 10 Lower substrate of display cell 11 Upper substrate of compensation cell 12 Liquid crystal of compensation cell 13 Compensation cell The lower substrate 14: the direction of the polarization axis (absorption axis) of the upper polarizer 1 15: the rubbing direction of the upper substrate 5 of the display cell 16: the rubbing direction of the lower substrate 10 of the display cell 17: the compensation cell The rubbing direction of the upper substrate 11 of the display cell 18 The rubbing direction of the lower substrate 13 of the compensation cell 19 The direction of the polarization axis (absorption axis) of the lower polarizer 4 20 The rubbing direction 15 of the upper substrate of the display cell Angle 21 with the direction 14 of the polarization axis of the upper polarizer 21 Twist angle of the liquid crystal 8 of the display cell 22 Display Angle between the rubbing direction 16 of the lower substrate of the lens and the rubbing direction 17 of the upper substrate of the compensation cell 23... Twist angle of the liquid crystal 12 of the compensation cell 24. The angle between the direction 19 of the polarization axis of the polarizing plate and the direction 25 25 The voltage transmittance curve of red light (650 nm) in the example 26 The voltage transmittance curve of green light (550 nm) 27 in the example 27 Voltage transmittance curve of blue light (450 nm) 28… Voltage transmittance curve of red light (650 nm) in the prior art 29… Voltage transmittance curve of green light (550 nm) in the prior art 30… Blue light in the prior art (450nm) voltage transmittance curve

Claims (4)

(57) [Claims] 1. A liquid crystal cell comprising a pair of substrates having electrodes on the inner surface of a substrate and a liquid crystal cell sandwiched between a pair of nematic liquid crystals and at least one optically anisotropic body disposed between a pair of polarizing plates. The anisotropic body is obtained by removing coloring of the liquid crystal cell, a color filter composed of a plurality of color elements is arranged on one substrate of the liquid crystal cell, and a threshold value in a voltage transmission characteristic for each color element is provided. A color liquid crystal display device, wherein the thickness of the liquid crystal layer corresponding to each of the color elements is varied so that the voltages are substantially matched. 2. The color liquid crystal display device according to claim 1, wherein the thickness of said color filter is different for each color element. 3. A liquid crystal cell comprising a pair of substrates having electrodes on the inner surface of a substrate and a liquid crystal cell sandwiched between a pair of nematic liquid crystals and at least one optically anisotropic body disposed between a pair of polarizing plates. The anisotropic body is obtained by removing coloring of the liquid crystal cell, and a color filter composed of red, green, and blue color elements is arranged on one substrate of the liquid crystal cell, and a voltage transmission characteristic for each color element is provided. , The thickness of the liquid crystal layer corresponding to the red color element (d _R ), the thickness of the liquid crystal layer corresponding to the green color element (d _G ), and the blue A color liquid crystal display device wherein the thickness (d _B ) of a liquid crystal layer corresponding to a color element is set in a relation of d _R <d _G <d _B. 4. A color liquid crystal display device according to claim 3, wherein the thickness of said color filter is different for each color element.