JPS63274926A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a natural, easily visible, and black and white display by specifying the angle of torsion of a liq. crystal molecule, product of the anisotropy of the refractive index and the thickness, and deviation angles between the polarization axes of upper and lower polarizing plates and the liq. crystal molecule arrangement. CONSTITUTION:The angle of torsion PSI of the liq. crystal molecule between both electrodes when a voltage is not impressed is controlled to 250 deg., and the product of the anisotropy (DELTAn) of the refractive index of the liq. crystal and the thickness (d) of the liq. crystal layer is adjusted to 0.5-0.7mum. In addition, the deviation angle alpha between the arrangement direction of the liq. crystal molecule major axis on the surface of the electrode on the this side of an observer and the polarization axis of the adjacent polarizing plate is controlled to 40-60 deg.. The same deviation angle beta of the liq. crystal molecule on the opposite side of observer is adjusted to 30-50 deg.. A white display can be obtained by such a liq. crystal device when a voltage is not impressed, a black display is obtained when a voltage is impressed, and a natural, easily visible, and black and white display can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element used in display terminals such as personal computers, word processors, and data terminals.

[Conventional technology] Conventionally, by increasing the twist angle of liquid crystal molecules between both electrodes,
A super twist element (T
, J., 5chefferand Nehring
, Appl, , Phys, , Lett,
45 (lot1021-1023 (+911
4) ) was known.

However, this method is not suitable for the liquid crystal display element used.
The value is substantially between 0.8 and 1.2 μm (Japanese Unexamined Patent Publication No. 60-10720), and as a display color.

Good contrast was obtained only with specific combinations of hues, such as yellow-green and dark blue, bluish-purple and pale yellow.

As described above, since this liquid crystal display element could not perform black and white display, it had the disadvantage that it could not perform multicolor or full color display when combined with a microcolor filter.

[Problems to be Solved by the Invention J] The purpose of the present invention is to eliminate the above-mentioned drawback of the prior art having characteristic colors, to realize a display close to black and white, and to provide a display using a fine color filter. It is intended to be formed inside or outside the cell to realize a monochrome or multicolor display as conventionally achieved with TN elements.

1. Means for Solving Problem 1 The present invention has been made to solve the above-mentioned problem. A transparent electrode is formed in a predetermined shape, and the long axis of liquid crystal molecules has an inclination on the surface of the transparent electrode. A nematic liquid crystal with positive dielectric anisotropy containing an optically active substance is sealed between a pair of transparent electrode substrates that have been treated to align in a certain direction, and both electrode substrates are adhered almost parallel to each other. In a liquid crystal display element in which a peripheral sealing material for encapsulation and at least one or more polarizing plates are installed on the outside of both electrode substrates, the twist angle of liquid crystal molecules between both electrodes when no voltage is applied is 250 degrees. and the anisotropy of the refractive index of the liquid crystal (Δn)
The product of the thickness (d) of the liquid crystal layer is between 0.5 and 0.7 μm in the operating temperature range including room temperature, and the liquid crystal molecules on the electrode surface nearer to the viewer are When the angle between the alignment direction of the long axis and the polarization axis or absorption axis of the adjacent polarizing plate is a plane parallel to the electrode plane, the polarization axis or absorption axis is from the alignment direction of the liquid crystal molecules. It forms an angle of 40 to 60 degrees in the opposite direction to the twist direction of the molecules, and the long axis of the liquid crystal molecules on the electrode surface on the opposite side and the polarization axis or absorption axis of the adjacent polarizer plate are shown to the observer. The present invention provides a liquid crystal display element characterized in that the angle formed by the liquid crystal molecules is an angle of 30 degrees to 50 degrees in a direction opposite to the twist direction of the liquid crystal molecules.

In the present invention, the twist angle of the liquid crystal is approximately 250°. As a result, a liquid crystal display element that is excellent in contrast ratio and viewing angle and has relatively few domains can be easily obtained. If this twist angle deviates from 2506, the characteristics will deteriorate, but if it is around ±5°, it can be used.

FIG. 1 shows the relative positions of the liquid crystal molecular axes and the polarization axis or absorption axis of the polarizing plate when no voltage is applied to the elements other than the light source of the present invention.

FIG. 1 is a layout diagram of each component when a liquid crystal display element according to the present invention is viewed from above.

In Figure 1, 1.2 is the rubbing direction on the upper and lower substrates of the liquid crystal cell, 3.4 is the alignment direction of liquid crystal molecules in the vicinity of the upper and lower substrates arranged by rubbing, and 5.5 is the polarized light of the polarizing plates attached above and below the liquid crystal cell. It indicates the axial direction or absorption axis direction, and ψ is the twist angle of the liquid crystal molecules between the upper and lower substrates, and in the present invention, ψ is 250°.

This figure shows an example in which the twist direction of the liquid crystal molecules is counterclockwise when viewed from above (observer side).

In this case, the angle α by which the polarization axis of the upper polarizing plate deviates from the alignment direction of the liquid crystal molecules on the adjacent substrate is 4 in the clockwise direction, which is the opposite direction to the twist direction of the liquid crystal molecules.
It is assumed that the rotation is from 0 to 60''.

In addition, the angle β at which the polarization axis of the lower polarizing plate deviates from the alignment direction of the liquid crystal molecules on the adjacent substrate is 30 to
It is assumed that it has been rotated by 50 degrees.

The polarization axis and absorption axis of this polarizing plate may be either,
When the rotation angle of the upper polarizing plate is set based on the polarizing axis, it is preferable to set the lower polarizing plate based on the polarizing axis. Conversely, when the rotation angle of the upper polarizing plate is set based on the absorption axis, both substrates are set based on the absorption axis. It is preferable to set the value as .Thereby, this liquid crystal display element can display in positive type and in colors close to black and white.

That is, specifically, the polarization axis of the polarizing plate on the side nearer to the viewer is moved from the alignment direction of the long axes of liquid crystal molecules on the adjacent electrode surface to the direction opposite to the twist direction of the liquid crystal molecules. When the angle is 40 to 60'', the polarization axis of the polarizing plate on the opposite side is moved from the alignment direction of the long axes of liquid crystal molecules on the adjacent electrode surface to the direction opposite to the twist direction of the liquid crystal molecules. The angle should be between 30 and 50 degrees.

Conversely, if the absorption axis of the polarizing plate on the near side to the viewer is 40 degrees from the alignment direction of the long axes of liquid crystal molecules on the adjacent electrode surface, in the opposite direction to the twist direction of the liquid crystal molecules.
When the angle is ~60°, the absorption axis of the polarizing plate on the opposite side is aligned in the direction opposite to the twist direction of the liquid crystal molecules from the alignment direction of the long axes of the liquid crystal molecules on the adjacent electrode surface. The angle should be between 30 and 50'.

On the other hand, if one has this tilt on the polarization axis and the other has this tilt on the absorption axis, the display will be negative, but the display will be brownish instead of black and white, and the display quality will deteriorate. Therefore, it is not very desirable.

Here, Δn-d is selected to be 0.50 to 0.70 μm.0 Display contrast and brightness are preferably selected to be 0.55 to 0.65 μm in consideration of whiteness.

a is in the range of 40° to 60°, and as 5a increases, the yellow-green color becomes stronger, and as α decreases, the blue color becomes stronger. On the other hand, β is between 30' and 50'', and when β is large, the blue color becomes strong, and when β is small, the yellow-green color becomes strong.The transmittance in this state is 14 to 31%, and in the region where Δn-d is small, the display is It will be dark, so it is recommended to use a light source.

On the other hand, when a voltage is applied to this element, the spiral structure of the liquid crystal molecules is unraveled, and the liquid crystal molecules near the center of the liquid crystal layer are
They are arranged almost perpendicular to the plane of the figure, and the displayed color changes from dark blue to a hue that appears to be black.

The present invention performs display by utilizing these two changes in transmittance, and a hue change that appears to be approximately white and black can be obtained.

An example of use is a matrix display in which electrodes are arranged in stripes in an X-Y direction.

Depending on the combination of Δn-d, α, and β, there are some combinations that have some color, and it is possible to make them closer to white and black by considering the contrast and hue and adjusting the emission intensity distribution of the light source and color correction of the filter as necessary. It is valid. Furthermore, monochrome or multicolor elements can be created by arranging a single color filter or fine color filters of the three primary colors of red, green, and blue on the outside of the cell or on the inside of the cell in line with the intersection of the X-Y electrodes. I can't do it. By forming this color filter on the inner surface of the cell, more precise color display is possible without causing deviation due to viewing angle.

In particular, in order to improve the degree of blackening when voltage is applied, it is effective to use a polarizing plate with a higher degree of polarization to improve display contrast.

[Effect 1] In the present invention, whereas conventional super twist elements showed good contrast only in specific hue combinations such as yellow-green and dark blue, bluish-purple and light yellow, the refractive index anisotropy of liquid crystal ( By reducing the product Δn-d of Δn) and cell gap (d) and changing the direction in which the polarizing plate is attached, it is possible to display black on a white background.

The reason for this is that when no voltage is applied, because Δn-d is small, wavelength dispersion is small even though it is in a birefringent mode, so a white color can be obtained. On the other hand, when a voltage is applied, the liquid crystal molecules near the center of the cell stand almost vertically, so birefringence disappears, and the angle at which the polarizing axes of the upper and lower polarizing plates are attached is close to crossed Nicols, resulting in a black display.

In addition, attempts have been made to combine conventional super twist elements with color polarizing plates and color filters to bring the background color closer to white, but due to the original background color being too dark, complete correction is not possible or complete correction is not possible. If a filter that corrects the color is used, there are drawbacks such as the fact that the voltage application state is affected by the color of the filter and the color does not become black.

However, in the present invention, the original background color is quite close to white, so by inserting a correction filter with a very light hue or slightly changing the emission intensity distribution of the light source, the background can be easily made white, and the upper and lower polarization Since the angle of the plates is close to crossed Nicols, there is an advantage that even with such correction, the displayed color can be made black when voltage is applied.

Furthermore, if it is just a black and white display, it is possible to use a conventional TN element, but since the TN element has inferior time division characteristics, it can only display l/I.
QOθ is the limit.

On the other hand, in the present invention, the time division characteristics are comparable to those of the super twist element, and as mentioned above, black and white display is possible. Accordingly, it is also possible to create a high-density multicolor element.

[Example 1 Next, embodiments of the present invention will be described in detail using the drawings.

A liquid crystal display element having a configuration as shown in FIG. 1 was produced.

l, 2 is the rubbing direction on the upper and lower substrates of the liquid crystal cell, 3
．． 4 is the alignment direction of the liquid crystal molecules near the upper and lower substrates arranged by rubbing, 5 and 6 are the polarization axis directions of the polarizing plates attached above and below the liquid crystal cell, and the twist angle ψ of the liquid crystal molecules between the upper and lower substrates is 250°. be.

Merck's liquid crystal ZLI2978 is used in a cell with such a configuration.
-000 and liquid crystals to which S-811 was added as an optically active substance were sealed in cells with different cell gaps, and optical measurements were performed. In addition, 80 at room temperature of this liquid crystal is 0.0
1117, and S so that d/p = 0.59
The amount of -811 added was controlled for each cell gap. Further, the experiment was conducted with the polarizing plates attached at angles α=50° and β=40°.

The twist angle ψ and twist direction of the liquid crystal molecules are determined by the rubbing direction between the upper and lower substrates, 1.2, and the type and concentration of the optically active substance added to the nematic liquid crystal injected into the cell. At this time, if the pitch of the liquid crystal induced by the addition of the optically active substance is p, and the cell gap of the liquid crystal is d, then ψ=
In order to achieve a twist angle of 250°, (250°
-901/360 <d/p < (250+901
/360 relationship.

On the other hand, even with d/p in this range, in regions where d/p is large, stripe-like domains are generated when voltage is applied, and these domains scatter light, making it difficult to obtain a good display.

Due to the occurrence of this domain, d/p can be used in the present invention.
The upper limit value of the pretilt angle (
The pretilt angle is closely related to the rising angle of liquid crystal molecules on the substrate surface, and when ψ=250''', the pretilt angle is preferably 5° or more.

Considering contrast, brightness, whiteness, etc., the angles α and β between the polarization direction 5.6 of the polarizing plates pasted on the top and bottom and the direction 3.4 of the liquid crystal molecules near the top and bottom substrates are the angles α and β of the liquid crystal molecules in this example. Since the twist direction is counterclockwise, α ranges from 40 to 60" clockwise from the upper rubbing direction 1, and β ranges from 30 to 5" clockwise from the lower rubbing direction 2.
0" range, especially a=45~55@, β=3
Preferably, the angle is 5 to 45 degrees.

By setting a and β within this range, a display with a high contrast ratio and a color tone fairly close to black and white was obtained.

If α is larger than this range, the background color becomes yellow-green,
When it is made smaller, it becomes blue.

On the other hand, if β is larger than this range, the background color becomes blue, and if it is smaller, the background color becomes yellow-green, both of which are undesirable.

Furthermore, in the above example, substantially the same effect was obtained even when a liquid crystal display element was created in which the polarization axis of the polarizing plate was replaced with the absorption axis.

Table 1 and FIG. 2 show the results of experiments in which the cell gap was varied.

The larger Δn-d, the brighter the background.

The contrast ratio at 1/Ion is Δn-d=0.55~
The maximum value existed near 0.60. Further, it is preferable that the background hue is closer to the white point, but the hue closest to white was around 80-d=0.65. From the above, the brightness of the background,
Considering whiteness, contrast, etc., the range of Δn-d in the present invention is 0.5 to 0.7, especially 0.
．． It has been found that a range of 55 to 0.65 is desirable.

In the above experiment, a white light source was used and a neutral polarizing plate was used, so the background hue was not yet completely white and shifted slightly to the blue side. However, the liquid crystal display element of the present invention By inserting a filter to correct the hue between the image and the light source or in front of the liquid crystal display element, the degree of whiteness was further increased and a more complete black and white display was possible.

FIG. 3(a) shows the spectral transmittance of the liquid crystal display element of the present invention at Δn-d=6.0. Since the transmittance on the short wavelength side is high, the color has a slightly blue hue. FIG. 3(b) shows the spectral transmittance of a filter for correcting this blue color, which is a faint orange filter that has absorption on the short wavelength side.

Figure 3 (C) shows the spectral transmittance measured by stacking this filter and the liquid crystal display element of the present invention.The spectral transmittance was considerably flat compared to (a), and the whiteness was increased. I understand. In the experiment, a color filter for correction was installed separately, but it is not necessarily necessary.You can directly dye the support layer of the polarizing plate, the protection plate of the liquid crystal display element, etc., or place the filter in the gap of the light source. It may be covered with or dyed.

Another method for whitening the background color is to correct it by changing the emission spectrum of the light source. FIG. 4 simultaneously shows the emission spectrum of a three-wavelength light source for this purpose (solid line) and that of a conventional three-wavelength light source (broken line). This new three-wavelength light source is designed so that the longer the wavelength, the stronger the emission intensity.
The red color is stronger than the green color, and when combined with the liquid crystal display element of the present invention, a background color with good whiteness can be achieved. Moreover, the same effect can be achieved by performing the same operation with a three-wavelength light source instead of the three-wavelength light source. Further, by simultaneously performing the above-described correction using the filter and correction using the light source, a hue with even better whiteness was obtained.

By performing these hue corrections, it is possible to display almost black and white, and as shown in Figure 2, the transmittance change with respect to voltage is steep, so the time division characteristics are excellent, so red,
By forming fine green and blue color filters corresponding to each electrode, it was possible to perform high-density multicolor display.

In the above example, the twist direction of the helical structure of the liquid crystal molecules was explained as being counterclockwise, but even if it is one clockwise,
Needless to say, if the directions of α and β are reversed, exactly the same effect can be obtained.

Table 1 [Effects of the Invention] As explained above, the present invention allows the background color to be made whiter than the conventional super twist element, so it is possible to provide the most natural and easy-to-see black and white display as well as time-division display. It has excellent effects such as characteristics and wide viewing angle comparable to conventional super twist elements, and in particular, by using color filters for color correction and correcting the emission spectrum of the light source, it can produce a fairly complete black and white image. Can be displayed.

Additionally, by arranging red, green, and blue color filters for each pixel, it is possible to achieve multicolor or full-color display.

[Brief explanation of drawings]

FIG. 1 is a layout diagram of constituent elements in a liquid crystal display element according to the present invention. 1.2: Rubbing direction on the upper and lower substrates 3.4: Arrangement direction of liquid crystal molecules near the upper and lower substrates 5.6: Polarization axis direction or absorption axis direction of polarizing plates placed above and below the cell FIG. 2 shows the liquid crystal display of the present invention. Graph showing the voltage versus transmittance curve of the device. FIG. 3(a) shows the spectral transmittance of the liquid crystal display element of the present invention, (
(b) is a graph showing the spectral transmittance of the correction filter, and (c) is a graph showing the spectral transmittance when both are combined. FIG. 4 is a graph showing a comparison of the emission spectra of a three-wavelength light source for color correction and a conventional three-wavelength light source. 3 times, ri: Ibian de t1 ≦ and λIqtt nh) 惺+IZ Wavelength (h-) Procedural amendment May 14, 1988 2, Name of the invention Liquid crystal display element 3, Relationship to the case of the person making the amendment Patent applicant Address 2-1 Marunouchi, Chiyoda-ku, Tokyo Number 2 name
(004) Asahi Glass Co., Ltd. 4, Agent 6, Number of inventions increased by amendment None 7, Subject of amendment Detailed explanation of the invention in the specification column 8, Contents of amendment

Claims (8)

[Claims] (1) A dielectric material containing an optically active substance is formed between a pair of transparent electrode substrates on which a transparent electrode is formed into a predetermined shape and whose surface is treated so that the long axes of liquid crystal molecules are aligned in a certain direction with an inclination. A nematic liquid crystal with positive anisotropy is encapsulated, and both electrode substrates are adhered almost parallel to each other, and a peripheral sealing material for encapsulating the liquid crystal and at least one polarizing plate are installed on the outside of both electrode substrates. In this liquid crystal display element, the twist angle of the liquid crystal molecules between the two electrodes when no voltage is applied is 250 degrees, and the anisotropy of the refractive index of the liquid crystal (Δn
) and the thickness (d) of the liquid crystal layer is between 0.5 and 0.7 μm in the operating temperature range including room temperature, and the long axis of the liquid crystal molecule on the electrode surface on the near side to the observer The angle between the alignment direction of the liquid crystal molecules and the polarization axis or absorption axis of the adjacent polarizing plate is such that when the projection plane is a plane parallel to the electrode plane, the polarization axis or absorption axis is from the alignment direction of the liquid crystal molecules. Forms an angle of 40 to 60 degrees in the direction opposite to the twisting direction, and the relationship between the long axis of the liquid crystal molecules on the electrode surface on the opposite side to the observer and the polarization axis or absorption axis of the adjacent polarizing plate. A liquid crystal display element characterized in that the angle similarly forms an angle of 30 degrees to 50 degrees in a direction opposite to the twist direction of the liquid crystal molecules. (2) The polarization axis of the polarizing plate on the near side of the viewer is 40 to 60 degrees from the alignment direction of the long axes of liquid crystal molecules on the adjacent electrode surface in the opposite direction to the twist direction of the liquid crystal molecules. The polarizing axis of the polarizing plate on the opposite side of the viewer is located at an angle of The liquid crystal display element according to claim 1, which forms an angle of 30 degrees to 50 degrees in the direction. (3) The absorption axis of the polarizing plate in front of the viewer is 40 degrees to 60 degrees from the alignment direction of the long axes of liquid crystal molecules on the adjacent electrode surface in the opposite direction to the twist direction of the liquid crystal molecules. The absorption axis of the polarizing plate on the opposite side to the observer is located at an angle of 100° from the alignment direction of the long axes of the liquid crystal molecules on the adjacent electrode surface, which is also opposite to the twisting direction of the liquid crystal molecules. The liquid crystal display element according to claim 1, which forms an angle of 30 degrees to 50 degrees in the direction. (4) The scope of the patent claims that a filter is installed on one side of the polarizing plate to correct the emission spectrum of the light source and the absorption spectrum of the liquid crystal display element and adjust the spectral transmittance so as to obtain almost white and black colors. The liquid crystal display element according to any one of items 1 to 3. (5) Claims in which the spectral intensity ratio of the light source is made larger for green than blue and red than green, so that the light transmitted through the liquid crystal display element becomes closer to white and black in response to voltage application. The liquid crystal display element according to any one of items 1 to 3. (6) A liquid crystal display element according to any one of claims 1 to 5, in which a color filter is formed corresponding to each electrode, and color display is possible by selecting the applied voltage. (7) The liquid crystal display element according to claim 6, wherein the color filter is formed inside the cell. (8) The liquid crystal display element according to claim 6, in which the color filter is a red, green, and blue color layer, and provides multicolor display.