JPH01243021A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To substantially obviate the generation of domains, to easily obtain a uniform tilt angle and to substantially obviate the generation of unequal display by confining the difference in the tilt angles of orientation control films on both sides of a liquid crystal layer to 2-5 deg.. CONSTITUTION:This display has the liquid crystal layer which has 160-300 deg. twist angle by a nematic liquid crystal having positive dielectric anisotropy and a driving means for impressing voltages between transparent electrodes of upper and lower substrates sandwiching said liquid crystal layer. The difference of 2-5 deg. is given to the respective tilt angle of the orientation control films existing on both sides of the liquid crystal layer. The high tilt angle is thereby given to one orientation control film and, therefore, the domains are hardly generated even if the twist angle of the liquid crystal layer is 160-300 deg.. Since the tilt angle is low in the other orientation control film the uniform tilt angle is easily obtd. and the unequal display is hardly generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element suitable for high-density display.

[Conventional technology] Conventionally, by increasing the twist angle of liquid crystal molecules between both electrodes,
A super twist element (T,
J, 5chefferand J, Nehri
ng, Appl, Phys, Lett.
45(10) 1021-1023 (1984))
was known.

In such a liquid crystal display element, in order to realize a larger twisted spiral structure, it is necessary to increase the tilt angle of the alignment control film.

However, when the tilt angle is 8 degrees or more, it is difficult to obtain a uniform tilt angle for the alignment control film, and there is a problem in that display unevenness is likely to occur.

[Problems to be Solved by the Invention 1] Therefore, there has been a desire for a liquid crystal display element that is less likely to generate domains even when the twist angle is increased and is less likely to cause display unevenness.

[Means for Solving the Problems 1] The present invention has been made to solve the above-mentioned problems, and is directed to an optical rotation device sandwiched between a pair of substrates with transparent electrodes arranged substantially in parallel and having alignment control films. The twist angle of the nematic liquid crystal with positive dielectric anisotropy containing a polar substance is 160
In a liquid crystal display element having a liquid crystal layer with an angle of ~300° and a driving means for applying a voltage between transparent electrodes of upper and lower substrates sandwiching this liquid crystal layer, the difference in the tilt angle of the alignment system usM on both sides of the liquid crystal layer is A liquid crystal display element characterized by an angle of 2 to 6 degrees, and a dielectric anisotropy containing an optically active substance sandwiched between a pair of substrates with transparent electrodes arranged substantially in parallel and having an alignment control film. It has a liquid crystal layer made of positive nematic liquid crystal with a twist angle of 160 to 300'', and driving means for applying voltage between transparent electrodes of upper and lower substrates that sandwich this liquid crystal layer. A liquid crystal display element in which a polarizing film is installed in a birefringent mode, wherein the difference in tilt angle of the alignment control films on both sides of the liquid crystal layer is 2 to 5 degrees, and approximately A liquid crystal layer with a twist angle of 160 to 300@ made of nematic liquid crystal with positive dielectric anisotropy containing an optically active substance and sandwiched between a pair of substrates with transparent electrodes arranged in parallel and having alignment control films; In a liquid crystal display element that has a drive means that applies a voltage between transparent electrodes of upper and lower substrates that sandwich a liquid crystal layer, and a pair of polarizing films is installed outside the liquid crystal layer, there is a A liquid crystal display element, characterized in that a birefringence compensating layer for compensating birefringence in the liquid crystal layer is provided on at least one of the liquid crystal layers, and the difference in tilt angle between the alignment control films on both sides of the liquid crystal layer is 2 to 5 degrees. It provides:

In the present invention, the angles of the respective tilt angles (pretilt angles) of the alignment control films on both sides of the liquid crystal layer of the liquid crystal display element have two angles.
It makes a difference of ~5@. As a result, one alignment control film has a high tilt angle, making it difficult to generate domains even if the twist angle of the liquid crystal layer is 160 to 300°, and the other alignment control film has a low tilt angle, so it is uniform. It is easy to obtain a suitable tilt angle, and display unevenness is less likely to occur.

For this reason, specifically, the tilt angle of the alignment control film with a higher tilt angle is set to be 5° or more, and the tilt angle of the alignment control film 41m with a lower tilt angle is set to be 3° or more, so that the tilt angle of both is set to be 5° or more. The difference should just be 2 to 5 degrees.

Specifically, the orientation control film with a higher tilt angle may have a tilt angle of 5 to 15@, and the orientation control film with a lower tilt angle may have a tilt angle of approximately 3 to 10 degrees. The alignment control film with a higher angle has a tilt angle of 5 to 10 degrees, and the alignment control film with a lower tilt angle has a tilt angle of about 3 to 8 degrees.

Note that this tilt angle is an average value for each substrate, as long as there is no large variation, and it is sufficient that the average difference between the tilt angles of both alignment control films is 2 to 5 degrees.

In order to obtain such a difference in tilt angle, it is necessary to change the material such as polyimide or polyamide that becomes the alignment control film, change the curing conditions, change the rubbing conditions, or combine these to create the tilt angle as described above. Just make sure the corners are different.

As a liquid crystal display element to which the present invention is applied, a pair of ITO (In2
0j-3n02), 5n02, etc. between glass, plastic, etc. substrates with transparent electrodes, a nematic liquid crystal with positive dielectric anisotropy containing an optically active substance has a twist angle of 1.
A liquid crystal cell with a structure in which a liquid crystal layer is sandwiched between 60 and 300 degrees,
It has a driving means for applying a voltage between the transparent electrodes of the upper and lower substrates that sandwich the liquid crystal layer therebetween.

The liquid crystal layer used for display has the same structure as the liquid crystal layer of conventional super twist liquid crystal display elements,
The electrode groups face each other, which allows each dot to be turned on and off.

The twist angle of this liquid crystal layer is approximately 160 to 300". This is because if it is less than 160 degrees, there will be little improvement in contrast during time-division driving at a high date, which requires a steep change in transmittance. On the other hand, if it exceeds 300'', hysteresis or domains that scatter light tend to occur. In particular, a value of about 200 to 2606 is preferable in terms of contrast, domain, etc.

Note that the difference Δn-d between the refractive index anisotropy of the liquid crystal of the liquid crystal layer and the thickness of the liquid crystal layer may be about 0.4 to 1.5 μm.

In such a liquid crystal display element, by setting the difference in tilt angle of the alignment control films on both sides of the liquid crystal layer to 2 to 5'',
Even if the twist angle of the liquid crystal layer is 160 to 300 degrees, domains are less likely to occur and display unevenness is less likely to occur.

The present invention is particularly effective when the liquid crystal display element is used in birefringence mode. For use in this birefringence mode, a pair of polarizing films is placed outside the liquid crystal layer so as to be in the birefringence mode. in particular,
The polarizing film may be disposed with its polarization axis shifted by 20 to 70 degrees from the orientation treatment direction of the adjacent orientation control film. The light passing through the liquid crystal cell appears colored due to birefringence, and a display is created based on the color difference.

In a liquid crystal display element using such a birefringence mode, if there is any unevenness in alignment, the unevenness in alignment becomes extremely noticeable and appears as display unevenness, so that the present invention is highly effective.

Similarly, a birefringence compensating layer for compensating birefringence in the liquid crystal layer is provided between at least one of the liquid crystal layer and the polarizing film to provide a large effect on a liquid crystal display element that compensates for birefringence.

The birefringence compensation layer that compensates for this birefringence is approximately equal to the product Δn - d of the refractive index anisotropy (Δn) of the liquid crystal of the liquid crystal display element used for display and the thickness (d) of the liquid crystal layer. A similar liquid crystal cell or a uniaxial birefringent plate with a lower Δn-d, the same degree of twist angle with the opposite twist direction, or a 60 to 120' twist angle difference is used. used. These birefringence compensation I? ! m may be provided on one side of the liquid crystal layer or on both sides.

Even in a liquid crystal display element using such a birefringence compensation layer, if there is any unevenness in alignment, the unevenness in alignment becomes extremely noticeable and appears as display unevenness, so that the present invention is highly effective.

Taking as an example the case where the birefringence compensating layer is stacked with compensating liquid crystal cells having the opposite twist direction and the same twist angle as the liquid crystal display element used for display,
By appropriately disposing a pair of polarizing films on the outside of the stacked liquid crystal cells, the elliptically polarized light of the light that has passed through the two liquid crystal layers is compensated for and returns to almost linearly polarized light, thereby eliminating the characteristic coloration of birefringence. The image disappears and the display becomes almost black and white.

Even when liquid crystal cells with different twist angles of 60 to 120' are used as compensation liquid crystal cells, almost black and white display can be achieved by appropriately selecting parameters.

Even when a uniaxial birefringence plate such as a plastic film or an inorganic crystal plate is used as the birefringence compensation layer, substantially black and white display can be achieved in the same manner.

A typical example of the use of these liquid crystal display elements is a dot matrix liquid crystal display element in which many electrodes are formed in rows and columns, with 640 striped electrodes formed on one substrate and 400 striped electrodes are formed perpendicularly to the substrate, and 640×
Something like 400 dots will be displayed. Furthermore, this 64
0 striped electrodes each set as 3 electrodes 19
It is also possible to display 640 x 400 dots in full color by using 20 striped electrodes and arranging RGB color filters.

Note that an insulating film such as TiO2, 5ift, Al201, etc. may be provided between the electrode and the alignment control film to prevent short circuit between the substrates, or A1. A lead electrode of low resistance such as Cr or Ti may also be provided, or a color filter or a light shielding film may be laminated on or below the electrode.

In particular, the present invention is suitable for a color liquid crystal display element in which a color filter is formed on the inner surface of one of the substrates. In other words, when a color filter is provided between the substrate and the electrode or on the electrode, the color filter or its protective coating tends to be sensitive to heat, and the substrate on which the color filter is formed should be treated at a low temperature or with a weak rubbing treatment. It is necessary to form an alignment control film.

For this reason, the alignment control film on the substrate side without color filters is subjected to high temperature or strong rubbing treatment to obtain a high tilt angle alignment control film, and the alignment control film on the substrate side with color filters is subjected to low temperature or weak rubbing treatment. Then, a liquid crystal display element may be formed as an alignment control film with a low tilt angle.

Thereby, it is possible to easily obtain a liquid crystal display element capable of color display while taking advantage of the above-mentioned advantages of the present invention.

Also, if you need to make the colors completely black and white,
A color filter for color correction or a color polarizing film may also be used, a dye may be added to the liquid crystal, or illumination having a specific wavelength distribution may be used.

In the present invention, a driving means for applying a voltage to the electrodes is connected to the liquid crystal cell having such a configuration, and the liquid crystal cell is driven.

Note that when using a transmission type, a light source is placed on the back side. Of course, a light guide, a color filter, etc. may be used in combination with this.

In addition to this, the present invention includes, within the scope that does not impair the effects of the present invention,
Various techniques used in ordinary liquid crystal display elements can be applied.

The liquid crystal display element of the present invention can be used for personal computers,
Suitable as a display element for word processors, workstations, etc., but also for LCD TVs, fish finders, etc.
It can be used for a variety of purposes, including radars, oscilloscopes, and various consumer dot matrix display devices, regardless of black and white display or color display.

[Effect 1] When a liquid crystal display element has a large twist angle and a small tilt angle, striped domains are likely to occur when a voltage is applied between the electrodes.

This striped domain is thought to be a phenomenon in which when a voltage is applied, the liquid crystal molecules do not stand up continuously and the helix falls sideways with the structure of helix #1, that is, the helical axis becomes parallel to the inner surface of the cell. .

These domains have a property that they are more likely to occur as the temperature increases, and in order to prevent domains from occurring within a practical temperature range, it is necessary to use an alignment control film that has a tilt angle commensurate with the twist angle.

In the present invention, the physical or chemical properties of a pair of alignment control films formed on a substrate with electrodes are changed respectively, and the tilt angles are made to differ by 2 to 5 degrees, thereby creating an asymmetrical tilt angle. It is the one that carries out the transformation.

By making the orientation control<n film asymmetrical, the location where the tilt angle of the liquid crystal molecules is minimum shifts from the center of the cell, which increases the tilt bias at the center of the cell when voltage is applied, and It is thought that liquid crystal molecules will stand up continuously without forming any structure.

As a result, the self-distribution f! of both boards is controlled. ! Domains are less likely to occur compared to a liquid crystal display element in which the tilt angles of the films are aligned and raised.

At the same time, since the other alignment control film may have a low tilt angle, it is easy to obtain a uniform tilt angle over the entire alignment control film, and display unevenness is less likely to occur.

[Example 1 Example 1 As a first substrate, an ITO transparent electrode provided on a glass substrate was patterned into a stripe shape, and an insulating film made of Sin to prevent short circuits was formed by vapor deposition, and an overcoat of polyimide was applied. was spin-coded and rubbed to create a substrate on which an alignment control film with a tilt angle of 4'' was formed.

As a second substrate, an ITO transparent electrode provided on a glass substrate is patterned into a stripe shape perpendicular to the first substrate, an insulating film of SiO□ is formed, and a polyimide film different from that of the first substrate is formed. An overcoat was applied, and this was rubbed at an intersection angle of 60'' with the rubbing direction of the first substrate, thereby creating a substrate on which an alignment control film with a tilt angle of 7@ was formed.

The peripheries of these two substrates are sealed with a sealing material to form a liquid crystal cell, and a nematic liquid crystal with positive dielectric anisotropy (ZLI-2293J manufactured by Merck & Co., Ltd.) is injected into the liquid crystal cell at 240°. Make it a twisted right-handed helical liquid crystal layer,
A liquid crystal cell was created by sealing the injection port.

For comparison, the first substrate was also overcoated with the same polyimide as the second substrate, and this was rubbed to form an alignment control film with a tilt angle of 7''. A liquid crystal cell of a comparative example was prepared using the following methods. In this liquid crystal cell of a comparative example, the tilt angles of the alignment control films on both substrates were approximately 7''.

When the liquid crystal cell of this comparative example was compared with the liquid crystal cell of the example, the generation temperature of the domain when voltage was applied at d/p = 0.57 was compared with that of the liquid crystal cell of the comparative example. We were able to raise the temperature by 10°C.

A pair of polarizing films are arranged on both sides of the liquid crystal cell of this example, with their polarizing axes being shifted by 40'' from the adjacent alignment control direction (so that the polarizing axes of both polarizing films intersect at 50''), A yellow mode liquid crystal display device was created using birefringence mode.

This liquid crystal display element had uniform alignment and almost no display unevenness.

Example 2 A liquid crystal cell for birefringence compensation with a reverse twist and a twist angle of 150" was laminated on the liquid crystal cell of Example 1, and a pair of polarizing films was placed on both sides of the cell, and the polarization axis was set 50" from the adjacent alignment control direction. A birefringence-compensated black-and-white liquid crystal display element was produced by arranging the polarizing films so that they were shifted from each other (so that the polarization axes of both polarizing films intersect at 100").

This liquid crystal display element displayed almost black and white, had uniform alignment, and exhibited almost no display unevenness.

Example 3 Furthermore, uniaxial birefringence plates for birefringence compensation were fitJ'ff on both sides of this liquid crystal cell, and a pair of polarizing films were laminated above and below the plates.

This liquid crystal display element also displayed almost black and white, had uniform alignment, and exhibited almost no display unevenness.

Example 4.5 An RGBa color filter is formed in a stripe shape on the first substrate, a protective coating layer is formed on it to flatten the surface, and an ITO transparent electrode film is formed on it. A liquid crystal cell for display was manufactured in the same manner as in Example 1, except that .

Using this liquid crystal cell, a birefringence compensation layer was laminated in the same manner as in Example 2.3 to create a liquid crystal display element.

This liquid crystal display element was capable of displaying almost three colors of RGB, had uniform alignment, and exhibited almost no display unevenness.

[Effects of the Invention] As explained above, the present invention is less likely to generate domains than the conventional super twist liquid crystal display element.
Moreover, it is easier to obtain a uniform tilt angle, and display unevenness is less likely to occur.

In addition, it has excellent effects such as time division display characteristics and viewing angle characteristics comparable to those of conventional super twist liquid crystal display elements.

The present invention can be applied in various ways in the future without detracting from the effects of the present invention.

Claims (3)

[Claims] (1) A nematic liquid crystal with positive dielectric anisotropy containing an optically active substance sandwiched between a pair of substrates with transparent electrodes arranged almost in parallel and having an alignment control film has a twist angle of 16
In a liquid crystal display element having a liquid crystal layer with an angle of 0 to 300 degrees and a driving means for applying a voltage between transparent electrodes of upper and lower substrates sandwiching this liquid crystal layer, the difference in tilt angle of the alignment control films on both sides of the liquid crystal layer A liquid crystal display element characterized in that the angle is 2 to 5 degrees. (2) A twist angle of 16 by a nematic liquid crystal with positive dielectric anisotropy containing an optically active substance and sandwiched between a pair of substrates with transparent electrodes arranged almost in parallel and having alignment control films.
It has a liquid crystal layer of 0 to 300° and a driving means for applying a voltage between transparent electrodes of upper and lower substrates sandwiching this liquid crystal layer,
This liquid crystal display element has a pair of polarizing films installed outside the liquid crystal layer so as to be in a birefringent mode, and is characterized in that the difference in tilt angle between the alignment control films on both sides of the liquid crystal layer is 2 to 5 degrees. Liquid crystal display element. (3) A twist angle of 16 due to the nematic liquid crystal with positive dielectric anisotropy and containing an optically active substance sandwiched between a pair of substrates with transparent electrodes arranged almost in parallel and having alignment control films.
It has a liquid crystal layer of 0 to 300° and a driving means for applying a voltage between transparent electrodes of upper and lower substrates sandwiching this liquid crystal layer,
In a liquid crystal display element in which a pair of polarizing films is installed outside the liquid crystal layer, a birefringence compensation layer for compensating for birefringence in the liquid crystal layer is provided at least on one side between the liquid crystal layer and the polarizing film, and the liquid crystal layer The difference in tilt angle between the alignment control films on both sides of is 2.
A liquid crystal display element characterized in that the angle is 5°.