JP2921589B2 - Color liquid crystal display device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal display device such as an ECB type or a DAP type which performs a multicolor display using a birefringent color of a liquid crystal layer.

[Problems to be solved by conventional technology and invention]

In a general color display device using a liquid crystal element (LCD), pixels are provided with red, green, and blue color filters, and color reproduction is performed by turning each color on and off. A wide range of color reproduction is possible by matching the optical characteristics of the light and the liquid crystal layer. However, such an LCD requires three steps of color filter dyeing,
In addition, if the light transmission characteristics of the color filter are not carefully designed, the color reproduction range becomes extremely narrow. Further, in such an LCD, since color display is performed by additive color mixing of colored light transmitted through red, green, and blue color filters, each pixel can emit only one of red, green, and blue, The pixel density is reduced to 1/3.

Another conventional color display method is the ECB type,
A method using a birefringent color of a liquid crystal layer, such as a HAN type or a DAP type, is known. In this method, an electric field is applied to the liquid crystal layer to change the state of alignment of liquid crystal molecules, thereby controlling the magnitude of birefringence of the liquid crystal layer, and performing display by birefringent color. In this method, it is not necessary to provide a color filter for each pixel, and the cell configuration and the cell manufacturing process are significantly simplified.

However, conventional LCDs that adopt a method of performing color display using birefringent colors include a color of about 400 to 450 nm (blue-violet to blue) when attempting to display red. Difficult to reproduce, because only the birefringent color is used, the color reproduction range is narrow (IEICE Transactions , J66-C , 169 ('83)), and black is displayed during time-division driving There is a problem that it is difficult.

The present invention has been made in view of the above-described problem in a liquid crystal display element of a type that performs color display using birefringent colors, can reproduce red with high color purity, has a wide color reproduction range, and has a black color reproduction range. Display is possible, and the pixel density is high,
An object of the present invention is to provide a color liquid crystal display element having excellent display characteristics.

[Means and actions for solving the problem]

In order to achieve the above object, according to the present invention, a liquid crystal layer sandwiched between a pair of substrates having electrodes, and a pair of polarizers arranged so as to sandwich these from the outside, By applying a voltage, the magnitude of the birefringence of the liquid crystal layer is changed, and in a color liquid crystal display element that performs a multicolor display by controlling the birefringence color accompanying the change in the birefringence, a pixel that does not perform a blue display. A color liquid crystal display element having a red or yellow color filter, a liquid crystal layer sandwiched between a pair of substrates having electrodes, and a pair of polarized light arranged to sandwich these from outside; A color liquid crystal display element configured to change the magnitude of birefringence of a liquid crystal layer by applying a voltage to the electrode and to control a birefringent color accompanying the change in birefringence to perform multicolor display. In red With arranging the color filters of cyan to the pixels not displayed, the color liquid crystal display device is provided, characterized in that arranged color filters yellow to a pixel is not performed blue display.

 Hereinafter, the color liquid crystal display device of the present invention will be described in detail.

The mode of a liquid crystal display device that can perform color display using birefringent color is an ECB that uses a liquid crystal cell in which liquid crystal molecules with positive dielectric anisotropy are aligned almost horizontally with respect to the substrate.
Type, a DAP type using a liquid crystal cell in which liquid crystal molecules with negative dielectric anisotropy are aligned substantially perpendicular to the substrate, and a HAN type combining a substantially horizontal alignment and a substantially vertical alignment on upper and lower substrates, etc. There is. However, at present, the range of colors that can be reproduced in any mode is narrowed due to poor color purity of red in particular. In addition, it is difficult to display black during time-division driving. The liquid crystal cell horizontally aligned in FIG. 1 is placed between two crossed Nicols polarizing plates.
The birefringence color when the orientation direction of the liquid crystal molecules and the transmission axis direction of the polarizing plate are arranged at 45 ° are shown. The trajectory shows the color change when the thickness of the liquid crystal layer is changed. In the drawing, the thickness d of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal are shown.
The thickness was indicated by the value of the product Δn · d (micron unit).
The data shown corresponds to the ECB type LCD, and in an actual cell, an electric field is applied to the liquid crystal layer to change the birefringence of the liquid crystal layer to perform color display, but here the thickness of the liquid crystal layer is This has been replaced by changes. R, G, and B in the figure indicate NTSC ternary colors, that is, red, green, and blue, respectively. Xy as in Figure 1
On the color coordinates, the color purity of blue appears to be high and the color purity of both green and red appears to be quite low. However, when actually observed visually, the color purity of green is good, and only red has low color purity. This is because the xy color coordinate system does not reflect the actual color sensation well. When redrawn on the 1960 UCS chromaticity diagram as shown in FIG. 2, colors other than red are close to ternary colors. You can see it. The trajectory of the color slightly changes due to the wavelength dispersion of Δn of the liquid crystal material, but does not approach the direction of R greatly (Transactions of the Institute of Electronics, Information and Communication Engineers, J66-C , 169 ('83)).
This can be understood from the Δn · d dependence of the transmission spectrum (see FIG. 3). When Δn · d is about 0.4 μm, the spectrum is too broad to transmit the wavelength range of only red (about 620 nm or more), and when it is about 1.0 μm, the interval between peaks becomes too narrow. Also shows a transmission peak. Δnd is 0.
Compared to transmitting only blue (400-500nm) at about 6 microns and almost green (500-600nm) at about 0.8 microns, it reproduces red with high color purity using only birefringent colors. It can now be seen that is impossible.

Therefore, in the present invention, the above-mentioned inconvenience is solved by providing a color filter in a type of LCD that performs color display using a birefringent color. Specifically, for example, a red or yellow color filter is used for a pixel that does not perform blue display. If a red color filter is used, visible light on the shorter wavelength side than 500 to 600 nm will be cut off, and the color of about 400 to 450 nm (blue-purple to blue) that will be mixed when attempting to display red with only birefringent colors will be removed. As a result, red with high color purity can be obtained, and the color reproduction range can be widened. Further, in this case, the process of manufacturing the color filter only needs to be performed once, and the process can be significantly simplified as compared with the conventional color display system using the color filter which requires at least three processes. The use of a yellow filter cuts off visible light on the shorter wavelength side than about 490 nm, has the same effect as the use of a red filter, and has the following advantages. That is, since a pixel having a yellow color filter can transmit light having a wavelength longer than about 500 nm, the case of FIG. 3 will be described as an example, and the retardation value of the liquid crystal layer is 0.7 to 0.8.
Green corresponds to microns, yellow corresponds to about 0.9 microns, red corresponds to about 1-1.2 microns, and black corresponds to about 0.6 microns. Only pixels with yellow color filters in this way,
The display of black, green, yellow, and red becomes possible.

FIG. 4 shows an example of the transmission spectrum of the color filter as described above. In the example of FIG. 4A, there is a slight transmission in the wavelength range of 400 to 450 nm, but this does not lead to a significant decrease in characteristics. There are many constituent materials of such a color filter, and a material that does not completely pass through the blue region can be easily adopted. The chromaticity when a color filter having the characteristics shown in FIG. 4A is used is indicated by an arrow point in FIG.
From the figure, using the color filter as described above
It can be seen that a color very close to the red point R of NTSC can be reproduced.

Further, in the present invention, a cyan color filter can be used for a pixel that does not perform red display, and a yellow color filter can be used for a pixel that does not perform blue display.

When the color filters are combined in this manner, the same operation and effect as described above can be obtained by the yellow color filter, and the following operation and effect can be obtained by the cyan color filter.

FIG. 5 shows an example of a transmission spectrum of a cyan color filter and an example of a transmission spectrum of a yellow color filter. Pixels provided with a cyan color filter transmit light of 400 to 570 mm. Therefore, the description will be made with reference to FIG. 3 in the same manner as described above. It becomes green at 0.8 microns and black at 0.45 microns, further expanding the color reproduction range.

〔Example〕

Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.

(Example 1) A vertical alignment agent FC-805 manufactured by 3M Co. was spin-coated on a surface of a glass substrate on which a transparent electrode had been patterned, on a transparent electrode side, and baked at 130 ° C for 1 hour. Next, the alignment agent surface was rubbed with a nylon nonwoven fabric. A red filter having the characteristics shown in FIG. 4A was printed only on the portion corresponding to the red pixel on the other substrate, and then the same orientation treatment as described above was performed. A substrate with a filter and a substrate without a filter were stuck together so that the rubbing directions were antiparallel to form a cell. The cell thickness was controlled by spraying glass fibers with an average diameter of 10.0 microns on the substrate. ZLI-3640, a nematic liquid crystal manufactured by Merck and having a negative dielectric anisotropy, was sealed in the cell.

When the cell in which the liquid crystal was sealed was observed with a polarizing microscope, it was confirmed that the liquid crystal molecules were substantially vertically aligned and inclined about 1 ° in the rubbing direction.

This cell is crossed between two polarizing plates
An LCD was formed by arranging the transmission axis and the rubbing direction of the cell at 45 °, and a voltage was applied to electrodes of the LCD to observe the color of the cell. As a result, when the voltage was sufficiently low, all the pixels were black, but when the voltage was applied little by little, all the pixels turned on, the pixels with the red filter turned red, and the others turned white. When the voltage was further increased, the pixels of the red filter remained red, and the other pixels gradually changed from yellow to pink. When a higher voltage was applied, the pixels of the red filter gradually became darker and became black, and the other pixels changed from purple to blue to green. Table 1 shows these changes.
Shown in

If the entire voltage range used in this experiment is used, the pixel with the red filter has black and red, and the other pixels have black and the full chromaticity range shown in FIG. Therefore, the color range obtained by mixing these colors is considerably wide.

Example 2 A cell was prepared in the same manner as in Example 1 using a horizontal alignment agent HL-1100 manufactured by Hitachi Chemical Co., Ltd. as an alignment agent, and a liquid crystal manufactured by Merck and having a positive dielectric anisotropy was used. 2293 was sealed to give an ECB type cell. The cell thickness was about 8 microns. The operation of the cell was observed with the rubbing direction and the transmission axis direction interposed between two polarizing plates, each having a crossed Nicol configuration, at 45 °. 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. Then, as the voltage was applied, the color of the pixel with the red filter changed from red to black, and the other pixels changed from pink to yellow to green. When further voltage is applied, the pixels with the red filter light up again and turn red, but the other pixels turn blue → magenta →
The color changed from pink to yellow to white. Table 1 shows these changes.
It is shown in FIG.

When a sufficiently high voltage was applied, all the pixels gradually became darker. The color reproduction range was as wide as that of Example 1.

(Example 3) In Examples 1 and 2, instead of the red filter,
LCD using a yellow filter with the characteristics shown in Figure b
As a result, the pixel provided with the yellow filter can display colors in the range of orange-yellow-yellow-green-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, the cell in which the liquid crystal is sealed is placed between the two crossed Nicol polarizers so that the transmission axis of the polarizer and the rubbing direction of the substrate are at 45 °, and a voltage is applied to the electrodes to change the birefringent color. The voltage was changed from green to red. Next, when a color glass filter V-Y50 made by Toshiba (transmission spectrum is almost the same as the yellow filter in FIG. 5) was overlapped and the voltage was slightly increased or decreased, the color changed in the order of black → green → yellow → red. . Similarly, an experiment was performed using a cyan color filter, and it was confirmed that a desired effect was obtained. Therefore, a color liquid crystal display device of the present invention was formed by using these two color filters, the liquid crystal cell and the polarizing plate.

(Example 5) Example 4 using horizontal alignment agent HL-1100 manufactured by Hitachi Chemical Co., Ltd.
A liquid crystal cell is created in the same manner as described above, and ZLI-2293, which has a positive dielectric anisotropy and is filled with nematic liquid crystal manufactured by Merck, is used for ECB.
Type LCD, which is sandwiched between cross nicicle polarizing plates.
A voltage was applied to the electrode to develop a birefringent color, and an experiment was performed in the same manner as in Example 4 using each of yellow and cyan filters. The effect of the present invention was confirmed in the same manner as in Example 4. Then, a liquid crystal display device of the present invention was formed using these two color filters, the liquid crystal cell and the polarizing plate.

〔The invention's effect〕

According to the color liquid crystal display device of the present invention, the following effects can be obtained because the birefringent color and the color filter accompanying the retardation change of the liquid crystal layer are used.

Red color reproduction with high color purity and black color display, which were impossible with a conventional color liquid crystal display device using only birefringent colors, can be performed, and multicolor display with a wide color reproduction range can be performed.

 Image density is improved.

As compared with a conventional color liquid crystal display device using a color filter, the process of manufacturing the color filter can be shortened, and the cell configuration is simplified.

[Brief description of the drawings]

Fig. 1 shows birefringence when a horizontally aligned liquid crystal cell is arranged between two crossed Nicols polarizers so that the orientation direction of liquid crystal molecules and the transmission axis direction of the polarizers are at 45 °. FIG. 2 shows the colors, FIG. 2 shows the data of FIG. 1 rewritten on a 1960 UCS chromaticity diagram, and FIG. 3 shows the Δn · d of the transmission spectrum.
FIG. 4 shows an example of the transmission spectra of the red and yellow color filters used in the present invention. FIG. 5 shows the transmission spectra of the cyan and yellow color filters used in the present invention. It is a figure showing an example of a transmission spectrum.

Continuation of front page (72) Inventor Takamichi Enomoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-49-96749 (JP, A) (58) Fields investigated (Int.Cl. ⁶ , DB name) G02F 1/13

Claims (2)

(57) [Claims] 1. A liquid crystal layer sandwiched between a pair of substrates having electrodes, and a pair of polarizers arranged so as to sandwich them from outside, and a liquid crystal layer is formed by applying a voltage to the electrodes. In a color liquid crystal display device that performs a multicolor display by controlling the birefringence color according to the change in the birefringence of a color liquid crystal display element, a pixel that does not perform a blue display has a red or yellow color filter. A color liquid crystal display device comprising: 2. A liquid crystal layer sandwiched between a pair of substrates having electrodes, and a pair of polarizers arranged so as to sandwich them from outside, and a liquid crystal layer is formed by applying a voltage to the electrodes. In a color liquid crystal display device that performs multicolor display by controlling the birefringence color according to the change in birefringence, a cyan color filter is disposed in a pixel that does not perform red display. A color liquid crystal display device, wherein a yellow color filter is arranged in a pixel that does not perform blue display.