JPH0748094B2 - Color liquid crystal display - Google Patents

Description

The present invention relates to a color liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device capable of full-color display including black, which is suitable for a matrix drive color liquid crystal display device such as a color liquid crystal television.

(B) Conventional Technology Conventionally, as a color liquid crystal display device having a bright display and a good display contrast, various proposals have been made for two liquid crystal layers arranged in layers and a combination of a color polarizer for each of these liquid crystal layers. There is. In addition, the present inventors have added two pixels to each of the two liquid crystal layers in terms of further increasing the number of picture elements contributing to display and further improving the display contrast.
First, a color liquid crystal display device was proposed in which a large number of pairs of color polarizers whose absorption axis directions are orthogonal to each other and have a complementary color relationship to each other are patterned and stacked (Japanese Patent Application No. 62-99322).
No.), and a color liquid crystal display device in which these color polarizer pairs are composed of a combination of the same color over the entire surface without patterning for each picture element is being developed.

Such a liquid crystal display device uses a liquid crystal as a switch to switch the direction of linearly polarized light, and absorbs it in the color polarizer pair in either the upper layer or the lower layer of the liquid crystal, so that red, green, and blue in all picture elements can be respectively absorbed. It has the feature that it can display a single color.

(C) Problems to be Solved by the Invention However, since the above-mentioned liquid crystal display device uses two liquid crystal layers stacked, the twist direction of the first liquid crystal layer and the second liquid crystal layer is the forward direction (the first liquid crystal layer). As shown in FIG. 5, the first and second liquid crystal layers 1
When the twist directions are 0 and 11 and both are twisted to the left), linearly polarized light enters the first liquid crystal layer 10 and becomes elliptically polarized light, and then enters the second liquid crystal layer 11 as elliptically polarized light, and the elliptically polarized light becomes It will be further doubled. Due to this, as shown in FIG. 6, when a voltage is applied, the transmittance characteristics differ depending on red, green, and blue. Especially, when the threshold voltage is applied, the transmittance of red and blue is high, and the voltage is applied. To display the color normally
In the case of the black type, coloring of the display surface due to light leakage when there is no electric field has been a problem.

The present invention has been made in view of the above-mentioned conventional problems, and particularly provides a liquid crystal display device which is bright in display, has excellent display contrast, and can perform color display without color leakage. With the goal.

(D) Means for Solving the Problems Thus, according to the present invention, it is possible to selectively set a state in which the incident polarization direction is rotated by 90 ° by the application or non-application of a voltage or a state in which the incident polarization is directly transmitted. First and second liquid crystal layers are laminated and arranged, and a pair of color polarizers whose absorption axis directions are orthogonal to each other and have a complementary color relationship are laminated and arranged in each of the first and second liquid crystal layers. And a neutral polarizer disposed on the incident light side of the liquid crystal layer, and the twist directions of the liquid crystal molecules of the first liquid crystal layer and the second liquid crystal layer are set to be opposite to each other. A liquid crystal display device is provided.

The color polarizer pair according to the present invention is laminated and arranged on each liquid crystal layer. Each of the color polarizer pairs may be patterned in a large number corresponding to each pixel,
It is preferable from the standpoint of brightness of single-color display and ease of manufacturing that the two color polarizer layers having complementary colors are laminated in a plane direction without patterning. At this time, the selection of the color polarizer pair in the first liquid crystal layer and the second liquid crystal layer is such that red, green, blue, or black is finally added to an arbitrary pixel depending on the combination of voltage application to each liquid crystal layer. It is performed as displayed, and a specific example thereof is shown in Examples and the like described later.

In order to set the twist directions of the liquid crystal molecules in the first and second liquid crystal layers to the opposite directions, the combination of the alignment directions of the alignment films of the liquid crystal substrate is usually set to the opposite and the twist directions of the first and second liquid crystal layers are set to the opposite directions. It is only necessary to add optically active substances having opposite optical properties to the liquid crystal (usually, nematic liquid crystal), and as the optically active substances, various right-handed and left-handed optical optics known in the art can be used. Active substances are applicable.

Further, it is necessary to adjust the product of the refractive index anisotropy Δn of the liquid crystal in the first liquid crystal layer and the second liquid crystal layer and the thickness d of each liquid crystal layer: Δn · d so that they have substantially the same value. Most preferred in terms.

(E) Action When each liquid crystal layer is in a twisted state, the linearly polarized light that has entered the first liquid crystal layer becomes elliptically polarized light and enters the second liquid crystal layer.
Since the second liquid crystal layer is twisted in the opposite direction with respect to the first liquid crystal layer, the amount of deviation to elliptically polarized light by the first liquid crystal layer is corrected by the second liquid crystal layer and returned to substantially linearly polarized light. Therefore, the display failure due to the elliptically polarized light when no electric field is applied is improved.

(F) Embodiment FIG. 4 is a diagram showing the construction of the liquid crystal display device of the present invention. In the figure, 1 is a glass substrate, 2 and 3 ₁₁ ... 3 ₁₄ , 3 ₂₁ ... 3 ₂₄ are
A large number of transparent electrodes such as ITO, 4 and 5 are a pair of color polarizers of red and cyan in the first liquid crystal layer, and 6 and 7 are a pair of magenta and green in the second liquid crystal layer. It is a polarizer. An organic or inorganic liquid crystal molecule alignment film is formed on each transparent electrode. Further, 8 is a liquid crystal molecule, 9 is a neutral polarizer, 10 is a first liquid crystal layer, and 11 is a second liquid crystal layer.
In the figure, 12 indicates the polarization direction of the neutral polarizer 9, 13,1
Reference numerals 4, 15 and 16 respectively indicate the absorption axis directions of the red color polarizer 4, the cyan color polarizer 5, the magenta color polarizer 6 and the green color polarizer 7. In this way, the absorption axis directions of the respective color polarizer pairs are configured to be orthogonal to each other.

FIG. 1 shows the twist directions of the first and second liquid crystal layers in the above cell structure. Here, the liquid crystal layer is twisted to the right, and as an optically active substance, Merck CB-15; Is used, while the second liquid crystal layer is twisted to the left, and nematic liquid crystal added with cholesteryl nonanoate (S-811 manufactured by Merck & Co., Inc.) as an optically active substance is used. Here, the first liquid crystal layer 10
And the twist angles of the second liquid crystal layer 11 are each 90 °, the transmittance in the state where no voltage is applied and Δn · d of the first and second liquid crystal layers.
The relationship is shown in FIG. As shown in FIG. 3, the first
It was found that when the values of Δn · dn of the second liquid crystal layer were made equal, the transmittance became the lowest, and high contrast liquid crystal display was possible.

Next, the operating principle of the color liquid crystal display device will be described with reference to FIG. Becomes linearly polarized light parallel to the paper surface by a neutral polarizer 9, the linearly polarized light is incident on the first liquid crystal layer 10, linearly polarized light in a portion of the transparent electrode 3 ₁₁ 90 ° twisted for a second-layer red color and polarization It is colored by the child 4 and passes through the first liquid crystal layer 10. Since the absorption axis of the color polarizer 5 and the polarization direction do not coincide with each other, the colored light passes through the polarizer 5 as it is, and the second liquid crystal layer 11 is twisted by 90 ° in the same manner, and the first color green polarizer 7 ( All the light except green is absorbed), so the red light is cut off and the display becomes black. If monochrome display of red, is colored with the second red color polarizer 4 of the first liquid crystal layer 10, but similarly incident on the second liquid crystal layer, transparent electrodes 3 of the second liquid crystal layer 11 ₂₂ When a voltage is applied to the liquid crystal molecules 8, the liquid crystal molecules 8 are aligned vertically and the red light passes through the magenta color polarizer 6 (passes red and green) of the second layer as it is, so that red display can be performed (in the figure). reference). At this time, the polarizer 7
Does not work because the absorption axis and the polarization direction do not match. Next, the monochromatic display of green will be described. First and second transparent electrodes 3 of the liquid crystal layer _13, 3 by applying a voltage to _23, likewise the first layer is colored in cyan color polarizer 5 of the cyan first layer green color polarizing The blue component is absorbed by the child to display green (see the figure). In the case of blue display, the first
By applying a voltage to the transparent electrode 3 ₁₄ of the liquid crystal layer of,
The incident polarized light is colored by the cyan color polarizer 5, and the green component is absorbed by the magenta color polarizer 6 in the second liquid crystal layer, and finally blue light is emitted. (See figure). The red, green, and blue single-color displays have been described above, but it is possible to freely display cyan, magenta, yellow, or white by selecting red, green, and blue for each pixel. Is possible.

A rubbing-processed polyimide film was formed as the alignment film, and the nematic liquid crystal ZLI-3281 was used as the liquid crystal material.
(Manufactured by Merck & Co., Inc.) as the optically active substance, 0.5 wt% of cholesteryl nonanoate is added to the first liquid crystal layer 10 and 0.15 wt% of CB-15 is added to the second liquid crystal layer 11 to obtain nematic liquid crystal molecules. A color liquid crystal display device as shown in FIG. 4 in which the first liquid crystal layer 10 is twisted in the left twist direction 17 and the second liquid crystal layer 11 is twisted in the right twist direction 18 is manufactured. Here, in order to obtain a uniform cell thickness, spacers made of glass particles were scattered over the entire surface of the liquid crystal layer. In order to suppress the transmittance when the voltage is off and make Δn · d of the first and second liquid crystal layers equal, spacers having a diameter of 5 μm are used for both the first and second liquid crystal layers in this embodiment. The method of distributing the spacers on the substrate was performed by a known drive process. The neutral polarizer 12 installed on the light source side is installed so as to be normally black.

FIG. 2 shows the voltage dependence of the transmittance in the liquid crystal display layer having the reverse twist structure. As shown in this figure, the transmittance characteristics of the two-layer cell having the reverse twist structure of the present invention, especially the transmittances of red, green, and blue below the threshold voltage, are compared with those of FIG. It was found that it was possible to perform a pure black display when the voltage was off, because it was low and all three were present.

(G) Effect of the Invention In the color liquid crystal display device of the present invention, the 90 ° twist directions of the liquid crystal molecules of the two liquid crystal layers are set in opposite directions, so that coloring due to elliptically polarized light in the absence of an electric field occurs. As a result, it is possible to perform a multicolor display in which the display is bright and the display contrast is excellent and the color reproducibility is good.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a twist structure of liquid crystal molecules in a liquid crystal display device of the present invention, FIG. 2 is a graph showing the relationship between the transmittance and an applied voltage, and FIG. 3 is a transmission when the electric field is off. FIG. 4 is a graph illustrating the relationship between the rate and Δn · d,
FIG. 5 is a diagram for explaining the structure of the liquid crystal display device of the present invention, FIG. 5 is a diagram corresponding to FIG. 1 of a conventional liquid crystal display device, and FIG. 6 is an example of the relationship between the transmittance and the applied voltage of the liquid crystal display of FIG. FIG. 1 ...... glass substrate, 2 and 3 _{11-3 24} ...... transparent electrode, 4 ...... red color polarizer, 5 ...... cyan color polarizer, 6 ......
Magenta color polarizer, 7 ... Green color polarizer, 8
... liquid crystal molecule, 9 ... neutral polarizer, 10 ... first liquid crystal layer, 11 ... second liquid crystal layer, 12 ... polarization direction, 13, 14, 15, 1
6 …… Absorption axis direction, 17,18 …… Twisting direction.

Claims (1)

[Claims] 1. A neutral polarizer, a first transparent substrate, a first counter electrode, a first liquid crystal layer, a first applying electrode, a red color polarizer, a cyan color polarizer, and a second transparent. The substrate, the second counter electrode, the second liquid crystal layer, the second applying electrode, the magenta color polarizer, the green color polarizer, and the third transparent substrate are laminated in this order, and the polarization direction of the neutral polarizer. On the other hand, the absorption axis directions of the red color polarizer and the magenta color polarizer are orthogonal to each other, and the absorption axes of the cyan color polarizer and the green color polarizer are arranged to be parallel to each other, and The twist directions of the liquid crystal molecules of the liquid crystal layer and the second liquid crystal layer are set to be opposite to each other, and the incident light from the outside of the neutral polarizer to the first and second liquid crystal layers applies or does not apply a voltage. 90 ° incident polarization direction when applied
It is selectively set to rotate or transmit incident polarized light as it is.When displaying black, it is a combination of red color polarizer and green color polarizer, and when displaying red, it is red color polarizer. A combination of magenta color polarizers, a combination of cyan color and green color polarizers for green display, and a combination of cyan and magenta color polarizers for blue display. A color liquid crystal display device characterized in that