JPH0452625A - Color liquid crystal display element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a liquid crystal display element such as an ECB type or a DAP type that performs multicolor display by utilizing the birefringent colors of a liquid crystal layer.

[Prior art and problems to be solved by the invention] In a general color display device using a liquid crystal device (LCD), red, green, and blue color filters are provided in pixels, and color reproduction is performed by turning each color on and off. Therefore, by matching the light transmission characteristics of each color filter with the optical characteristics of the backlight and liquid crystal layer, it is possible to reproduce a wide range of colors.

However, such an LCD requires three dyeing steps for the color filters, and if the light transmission characteristics of the color filters are not carefully designed, the color reproduction range will be significantly narrowed. In addition, in such LCDs, color display is performed by additive color mixing of colored light transmitted through red, green, and blue color filters, so each pixel can only produce one color among red, green, and blue. The pixel density becomes 1/3.

Another conventional color display method is known, such as the ECB type, HAN type, and DAP type, which utilizes the birefringent color of the liquid crystal layer. In this method, the magnitude of birefringence of the liquid crystal layer is controlled by applying an electric field to the liquid crystal layer to change the alignment state of liquid crystal molecules, and display is performed using birefringence colors. With this method, there is no need to provide a color filter for each pixel, and the cell configuration and cell manufacturing process are significantly simplified.

However, in conventional LCDs that use birefringent colors to display color, colors of about 400 to 450 nm (bluish-purple to blue) are mixed when attempting to display red, so red with high color purity cannot be displayed. difficult to reproduce,
The color reproduction range is narrow because only birefringent colors are used (Transactions of the Institute of Electronics and Communication Engineers, J66-C, 169 ('83));
There have been problems such as difficulty in displaying black during time-division driving.

The present invention was made in view of the above-mentioned problems in a type of liquid crystal display element that displays color using birefringence, and is capable of reproducing red with high color purity, wide color reproduction range, and black. An object of the present invention is to provide a color liquid crystal display element that is capable of displaying images, has a high pixel density, and has excellent display characteristics.

[Means and effects for solving the problem] In order to achieve the above object, the present invention provides a liquid crystal layer sandwiched between a pair of substrates having electrodes, and a pair of liquid crystal layers sandwiched between them from the outside. A color liquid crystal display that changes the magnitude of birefringence of the liquid crystal layer by applying a voltage to the electrodes, and controls the birefringence color accompanying this change in birefringence to display a multicolor display. A liquid crystal display element is provided which is characterized in that the element is provided with a color filter.

Further, according to the present invention, there is provided a color liquid crystal display element having the above-mentioned structure, characterized in that a red or yellow color filter is disposed in a pixel that does not display blue.

Furthermore, according to the present invention, in the above structure, a color liquid crystal is provided, in which a cyan color filter is disposed on pixels that do not display red color, and a yellow color filter is disposed on pixels that do not display blue color. A display element is provided.

The color liquid crystal display element of the present invention will be described in detail below.

The mode of a liquid crystal display element that can perform color display using birefringence is ECB, which uses a liquid crystal cell in which liquid crystal molecules with positive dielectric anisotropy are aligned approximately horizontally with respect to the substrate.
The DAP type uses a liquid crystal cell in which liquid crystal molecules with negative dielectric anisotropy are aligned approximately perpendicular to the substrate, and the HA type uses a combination of approximately horizontal alignment and approximately vertical alignment on the upper and lower substrates.
There are types such as N. However, the range of colors that can be reproduced in any mode is currently narrow because the color purity of red in particular is poor.6 Furthermore, it is difficult to display black during time-division driving. As shown in Figure 1, a horizontally oriented liquid crystal cell is placed between two crossed nicol polarizing plates to determine the alignment direction of liquid crystal molecules.

The birefringence color when the polarizing plate is arranged so that the transmission axis direction is 45° is shown. The trajectory shows how the color changes when the thickness of the liquid crystal layer is changed. The thickness was expressed in -d (in microns).

The data shown corresponds to ECB type LCI), and in actual cells, color display is performed by applying an electric field to the liquid crystal layer and changing the birefringence of the liquid crystal layer. This is replaced by a change in size. R, G, and B in the figure represent NTSC ternary colors, that is, red, green, and blue, respectively.

On the xy color coordinates as shown in Figure 1, the color purity of blue is high;
The color purity of both green and red appears to be quite low. However, when I actually visually observed it, the color purity of green was good.
Only red has low color purity. This is because the 17 color coordinate system does not reflect the actual color sense well, and when redrawn on the 1960 UC5 chromaticity diagram as shown in Figure 2,
It can be seen that colors other than red are close to ternary colors. The color trajectory changes slightly depending on the wavelength dispersion of Δn of the liquid crystal material, but it does not approach the H direction significantly (Transactions of the Institute of Electronics and Communication Engineers, J66-C1169 ('83)). This can be understood by looking at the 0-d dependence of the transmission spectrum (see Figure 3). When Δn-d is about 0.4 microns, the spectrum is too broad to transmit only the red wavelength range (approximately 620 nm or more), and on the other hand, when Δn-d is about 1.0 microns, the interval between the peaks becomes too large. becomes too narrow,
There is also a transmission peak in the blue region.

When Δn-d is about 0.6 microns, almost only blue color (40
0 to 500 nm), and at around 0.8 microns, almost only green (500 to 600 nm) is transmitted, but compared to this, it is impossible to reproduce red with high color purity using only birefringence color. can be understood from now on.

Therefore, in the present invention, the above-mentioned disadvantages are solved by providing a color filter in a type of LCD that performs color display using birefringence colors.

Specifically, for example, a red or yellow color filter is used for pixels that do not display blue.

500-600n when using a red color filter
Visible light on the wavelength side shorter than m is cut, and 400 to 450n, which is mixed when trying to display red using only birefringence color, is cut.
rm colors (blue-violet to blue) can be removed, a red color with high monochromatic linearity can be obtained, and the color reproduction range can be widened. Further, in this case, only one step is required to produce the color filter, which significantly simplifies the process compared to the conventional color display system using color filters, which requires at least three steps. Using a yellow filter cuts visible light with wavelengths shorter than about 490 nm,
In addition to obtaining the same effect as using a red filter, it also has the following advantages: In other words, a pixel equipped with a yellow color filter can transmit light with a wavelength longer than about 50 onlK, so to explain the case of FIG.
(Green when it corresponds to 1.8 microns, yellow when it corresponds to about 0.9 microns, red when it corresponds to about 1-1.2 microns, and black when it corresponds to about 0.6 microns. In this way, it is possible to display black, green, yellow, and red only with pixels equipped with yellow color filters.

FIG. 4 shows an example of the transmission spectrum of the color filter as described above. In the example of a in FIG. 4, there is some transmission in the wavelength range of 400 to 450 nm, but this does not lead to a significant deterioration of the characteristics. There are many constituent materials for such color filters, and materials that do not penetrate the blue range at all can be easily adopted. The chromaticity when using a color filter having the characteristics shown in a of FIG. 4 is indicated by arrows in FIG. It can be seen from the figure that by using the above color filter, it is possible to reproduce colors very close to the NTSC red point H.

Furthermore, in the present invention, a cyan color filter can be used for pixels that do not display red, and a yellow color filter can be used for pixels that do not display blue.

When color filters are combined in this way, the yellow color filter provides the same effects as above, and the cyan color filter provides the following effects.

FIG. 5 shows an example of the transmission spectrum of a cyan color filter and an example of the transmission spectrum of a yellow color filter. A pixel with a cyan color filter transmits light with a wavelength of 400 to 570 mm, so if we explain using Figure 3 in the same way as above, the liquid crystal layer glue tarp -
A color value of 0.55 micron is blue, 0.7 micron is cyan, 0.8 micron is green, and 0.45 micron is black, making it possible to further expand the color reproduction range.

〔Example〕

The present invention will be described in detail below, but the present invention is not limited to these Examples.

(Example 1) Vertical alignment agent FC-805 manufactured by 3M was applied with a spinner onto the transparent electrode side surface of a glass substrate on which a transparent electrode had been patterned, and baked in an oven at 130° C. for 1 hour.

Next, the surface of the alignment agent was rubbed with a nylon nonwoven fabric. On the other substrate, a red filter having the characteristics of a in FIG. 4 was printed only on the portion corresponding to the red pixel, and then the same alignment treatment as above was performed. A substrate with a filter and a substrate without a filter were pasted together so that the rubbing directions were antiparallel to each other to form a cell. The cell thickness has an average diameter of 10.
This was controlled by scattering 0 micron glass fibers onto the substrate. In this cell, ZLI-36, a nematic liquid crystal with negative dielectric anisotropy manufactured by Merli Co., Ltd.
40 were enclosed.

When the cell filled with liquid crystal was observed using a polarizing microscope, it was confirmed that the liquid crystal molecules were almost vertically aligned and tilted by about 1° in the rubbing direction.

This cell is placed between two crossed nicol polarizing plates so that the transmission axis and the rubbing direction of the cell are 45 degrees to form an LCD, and a voltage is applied to the electrodes of this LCD to observe the color of the cell. did. As a result, when the voltage was low enough, all pixels were black, but when voltage was applied little by little, all pixels turned on, and the pixels with the red filter became red, and the others became white. When the voltage was increased further, the pixels in the red filter remained red, while the other pixels gradually changed from yellow to pink. If a higher voltage is applied,
The red filter pixels gradually darkened to black, and the other pixels changed from purple to blue to green. Table 1 shows these changes.

Table 1 Using the entire voltage range used in this experiment, the pixel with the red filter becomes black and red, and the other pixels become black, making the entire chromaticity range shown in Figure 2. Therefore, the color range obtained by mixing these colors is quite wide.

(Example 2) Horizontal alignment agent HL-1100 manufactured by Hitachi Chemical Co., Ltd. as an alignment agent
A cell was prepared in the same manner as in Example 1, and ZLI-2293, a liquid crystal manufactured by Merck & Co., Ltd. with positive dielectric anisotropy, was sealed to form an ECB type cell. The cell thickness was approximately 8 microns. This cell is sandwiched between two crossed nicol polarizing plates so that the rubbing direction and the transmission axis direction are 45 degrees.
Cell movement 1! I guessed it. As a result, in this case, when no voltage was applied, the pixels of the red filter were red, and the other pixels were reddish-purple. As voltage was applied, the color of the pixels with the red filter changed from red to black, while the other pixels changed from pink to yellow to green. When further voltage was applied, the pixels with the red filter lit up again and became red, but the other pixels changed from blue to reddish-purple to pink to yellow to white. Table 2 shows these changes.

Table 2 When a sufficiently high voltage was applied, all pixels gradually became darker. The color reproduction range was as wide as in Example 1.

(Example 3) In Examples 1 and 2, the fourth filter was used instead of the red filter.
LC using a yellow filter with the characteristics shown in figure b.
When D was manufactured, the pixels provided with the yellow filter were able to display colors in the range of orange-yellow, yellow-green, and green in addition to red.

(Example 4) A liquid crystal cell was prepared in the same manner as in Example 1 except that the red filter was not printed, and the same liquid crystal as in Example 1 was sealed. Then, a cell filled with liquid crystal is placed between two crossed nicol polarizing plates so that the transmission axis of the polarizing plate and the rubbing direction of the substrate are at 45 degrees, and a voltage is applied to the electrodes to change the birefringence color. We looked for the voltage that would produce a green to red color. Next, Toshiba back color glass filter V-Y50 (
The transmission spectrum is almost the same as the yellow filter in Figure 5)
When I overlapped them and slightly raised and lowered the voltage, black → green → yellow →
The colors changed from red to red. In a similar experiment using a cyan color filter, it was confirmed that the desired effect could be obtained. Therefore, a color liquid crystal display element of the present invention was prepared by using these two color filters, the liquid crystal cell, and the polarizing plate.

(Example 5) A liquid crystal cell was created in the same manner as in Example 4 using horizontal alignment agent HL-1100 manufactured by Hitachi Chemical Co., Ltd., and ZLI-2293, which was a nematic liquid crystal manufactured by Merck and had positive dielectric anisotropy. Example 4
An experiment was conducted in the same manner as in Example 4, and the effects of the present invention were confirmed in the same manner as in Example 4. And these two color filters,
A liquid crystal display element of the present invention was prepared using the above liquid crystal cell and polarizing plate.

〔Effect of the invention〕

According to the color liquid crystal display element of the present invention, the following effects can be obtained since the birefringent color and the color filter accompanying the change in thickness of the liquid crystal layer are utilized.

■It is now possible to reproduce red and black with high color purity, which was not possible with conventional color liquid crystal display devices that utilize only birefringent colors, allowing for multicolor display with a wide color reproduction range.

■Image density is improved.

■Compared to conventional color liquid crystal display devices that use color filters, the process for producing color filters can be shortened and the cell configuration can be simplified.

[Brief explanation of the drawing]

Figure 1 shows the birefringence when a horizontally aligned liquid crystal cell is placed between two crossed nicol polarizing plates so that the alignment direction of the liquid crystal molecules and the transmission axis direction of the polarizing plates are 45°. Figure 2 shows the colors, data from Figure 1 is 1960UC5
A diagram redrawn on the chromaticity diagram, Figure 3 is a diagram showing the Δn-dn- property of the transmission spectrum, and Figure 4 shows an example of the transmission spectrum of the red and yellow color filters used in the present invention. 5 are diagrams showing examples of transmission spectra of cyan and yellow color filters used in the present invention. Patent applicant Rico Co., Ltd.

Claims (3)

[Claims] (1) Consisting of a liquid crystal layer sandwiched between a pair of substrates having electrodes, and a pair of polarizers placed between them from the outside, the birefringence of the liquid crystal layer can be adjusted by applying a voltage to the electrodes. 1. A color liquid crystal display element that performs multicolor display by changing the size of the birefringence and controlling the color of birefringence that accompanies the change in birefringence, the color liquid crystal display element being provided with a color filter. (2) The color liquid crystal display element according to claim 1, characterized in that a red or yellow color filter is disposed on a pixel that does not display blue. (3) The color liquid crystal display element according to claim 1, characterized in that a cyan color filter is disposed on pixels that do not display red color, and a yellow color filter is disposed on pixels that do not display blue color.