JP2856466B2 - Liquid crystal display device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to an improvement of a DAP type liquid crystal display device.
The present invention relates to a P-type liquid crystal display device.

[Conventional technology]

As a liquid crystal display element, a TN type liquid crystal display element, an STN type liquid crystal display element, and a DAP type liquid crystal display element have been conventionally known.

Among them, TN type liquid crystal display elements are widely used mainly for display parts of watches and calculators because they are black and white display and have a simple configuration. There is a drawback that a large-capacity display cannot be used without a switching element such as a transistor.

Further, the STN-type liquid crystal display element has excellent steepness in voltage transmittance characteristics and is capable of large-capacity display, but has a problem in that the display is colored. For this reason, a black-and-white display method using a compensator has also been developed. However, this method has a problem that the configuration is complicated and the cost is high, and the accuracy of the cell thickness is strict, resulting in poor productivity.

In contrast, the DAP (Deformation of Vertically Ali
gned Phase) type liquid crystal display device is a display method that has been known for a long time, has excellent steepness in voltage transmittance characteristics, is capable of large-capacity display, and has a monochrome display or a color display depending on the setting of cell conditions. It has the feature that multicolor display is possible without using a filter.

Hereinafter, the configuration and principle of the DAP type liquid crystal display device will be described in the first.
This will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of the basic configuration of a DAP type liquid crystal display element. As shown in FIG. 1, a pair of light-transmitting substrates 11 and 2 having transparent electrodes 12 and 22 such as glass and plastic are provided.
A liquid crystal layer 3 made of a liquid crystal composition having a negative dielectric anisotropy is formed between them, and the outer periphery thereof is sealed with seals 14 and 24 to form a liquid crystal cell of a DAP type liquid crystal display device.
On the sides of the cell where the substrates 11 and 21 and the transparent electrodes 12 and 22 are in contact with the liquid crystal, alignment films 15 and 25 are formed so as to align the liquid crystal vertically to the substrates 11 and 21. A pair of polarizing plates 16 and 26 are provided outside the cell, and the cell and the pair of polarizing plates constitute a DAP type liquid crystal display device.

In a DAP-type liquid crystal display device having such a configuration, when no voltage is applied, the liquid crystal is oriented perpendicular to the substrates 11 and 21.
When the polarization axes of 16, 26 are orthogonal to each other, a black display is obtained. When a voltage is applied between the upper and lower transparent electrodes, the liquid crystal molecules are inclined with respect to the substrates 11, 21 as shown in FIG. 2 (b), and the direction of the inclination is parallel to the transmission axis or the absorption axis of the polarizing plate. In cases other than orthogonal, birefringence occurs and light is transmitted.
The spectral spectrum of the transmitted light corresponds to the retardation, and white or colored display can be performed by adjusting the thickness of the liquid crystal layer 3, the birefringence of the liquid crystal, and the applied voltage.

[Problems to be solved by the invention]

By the way, the above-mentioned DAP type liquid crystal display element has a feature that large-capacity display is possible, and moreover, monochrome display or multi-color display is possible without using a color filter depending on the setting of cell conditions. However, there is a disadvantage that it is difficult to control the alignment of the liquid crystal.

That is, in the DAP type liquid crystal display device, in order to obtain a uniform display, it is necessary to control the direction in which the liquid crystal tilts when a voltage is applied. As shown in FIG. 2 (a), it is necessary to perform an alignment control tilted by θ ₀ from the vertical direction. However, when the tilt angle θ ₀ is small, the tilt direction of the liquid crystal when voltage is applied becomes non-uniform, There is a problem that uneven display is caused by an alignment defect called reverse tilt, and the contrast is reduced. When the tilt angle θ ₀ is increased, the above-mentioned alignment defects do not occur, but the viewing angle becomes narrower, the sharpness of the voltage transmittance characteristic deteriorates, and the contrast during simple matrix driving decreases. Is impaired.

Further, the conventional DAP type liquid crystal display element has a drawback in production.

That is, the conventionally preferred tilt angle θ ₀ is 1 °
However, the alignment may be controlled by applying a vertical alignment agent such as an alkoxysilane having a long-chain alkyl group onto the substrate and then subjecting the substrate to a lapping process. After the horizontal alignment treatment, the surface is treated with a vertical alignment agent, etc., but the tilt angle of the liquid crystal obtained by these methods is poor in reproducibility, and therefore, the yield decreases. There was a problem that it was easy to invite.

The present invention has been made in view of the above circumstances, has no alignment defects, has a wide viewing angle, does not generate alignment defects even at a small tilt angle, has high contrast, and is easy in alignment processing and has high productivity. An object of the present invention is to provide a DAP-type liquid crystal display device having high alignment stability and high time-division driving characteristics.

[Means for solving the problem]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises two substrates that have been subjected to vertical alignment processing with a slight inclination, a nematic liquid crystal sealed between the substrates, and an optically active substance (cholesteric liquid crystal or non-cholesteric liquid crystal). A liquid crystal composition having a negative dielectric anisotropy comprising a mixed composition of a liquid crystal optically active substance) and a pair of polarizing plates, wherein a twisted structure is induced in the liquid crystal by the optically active substance, and a voltage is applied. It is characterized in that the liquid crystal molecules are sometimes twisted in the angle range of 1 ° or more and less than 100 ° in the thickness direction.

[Action]

Here, the basic configuration of the device is the same as that shown in FIG. 1, but in the device of the present invention, the liquid crystal molecules take a twisted orientation in an angle range of 1 ° or more and less than 100 ° when a voltage is applied. It is configured as follows.

Such an alignment is, as a liquid crystal composition, for example, a mixed composition of a nematic liquid crystal and an optically active substance, having a negative dielectric anisotropy, specifically, a nematic liquid crystal having a negative dielectric anisotropy. A mixture of cholesteric liquid crystal or a mixture of a nematic liquid crystal having a negative dielectric anisotropy and a small amount of a non-liquid crystalline optically active substance. This is achieved by performing a process of tilting and orienting the substrate at a small angle.

Here, when the above liquid crystal composition is used, a twisted structure is induced in the liquid crystal by the optically active substance, and the induced natural pitch (the pitch when there is no alignment regulation) P ₀ and the thickness of the liquid crystal layer 3. There are favorable conditions for the relation of d. This relationship is represented by d / P ₀ , and preferably 0.005 ≦ d / P ₀ ≦ 0.5.

However, a more preferable range depends on the twist angle. For example, if the torsion angle during voltage application is 90 °, d /
P ₀ is preferably from 0.15 to 0.5. In the range of d / P ₀ that satisfies such conditions, alignment defects due to reverse tilt during voltage application can be reduced or eliminated very effectively.

When the torsion angle at the time of voltage application is smaller than 1 °,
Tilt disclination occurs and the display quality deteriorates.

Further, when the torsion angle at the time of applying a voltage is larger than 100 °, the sharpness of the voltage transmittance characteristic deteriorates, and at the time of high time division, the contrast decreases.

The amount of the optically active substance depends on the thickness d of the liquid crystal layer 3, the type of the nematic liquid crystal, and the type of the optically active substance.
% Range.

Next, as the alignment treatment, a vertical alignment treatment that is preferably slightly inclined is performed.

Examples of the aligning agent include alkoxysilanes having a long-chain alkyl group, alkoxytitanium, alkoxyzirconium,
Materials generally used for vertical alignment treatment, such as organometallic compounds such as chromium complexes of long-chain alkylcarboxylic acids or fluorine-substituted alkylcarboxylic acids, and fluorine-substituted polyalkylene resins can be used. It is preferable that the alignment film formed from the above material is subjected to rubbing treatment in one direction. Further, an oblique evaporation method of SiO can also be adopted. The preferred tilt angle obtained by this alignment treatment is in the range of 0.1 ° to 5 °, more preferably,
It is in the range of 0.1 ° to 3 °.

As described above, by using the present invention, cells can be manufactured without poor alignment even at a very small tilt angle, so that the range of use of the alignment agent can be greatly expanded. Also, if the cell was made with a small pretilt angle,
The viewing angle can be increased, and it has a very excellent display quality. The present invention does not limit the method of the alignment treatment.

The pretilt direction of the liquid crystal molecules on the substrate surface is determined by the rubbing direction in the rubbing method, and is determined by the evaporation direction in the oblique evaporation method. As shown in FIG. 3, in the present invention, the liquid crystal takes a torsional orientation with a tilt angle when a voltage is applied. At this time, it is not preferable that the liquid crystal takes a splay orientation, and the reverse tilt suppressing effect is reduced. Would. Therefore, in the present invention, it is preferable to control the direction of the pretilt. Therefore, the angle α between the pretilt directions of the upper and lower substrates defined in FIG. 4 (projection of liquid crystal molecules on the substrate onto the substrate surface) is the direction of the twist determined by the optically active material.
It must be in the same direction as the natural torsion angle determined by d / P ₀ (= d / P ₀ × 360 °), and must be within 1 ° to 100 °, and within 2 times the natural torsion angle Is preferred.

Note that the transmission axes of the polarizing plates 16 and 26 disposed above and below are substantially the same as the directions of the pretilt of the liquid crystal molecules on the adjacent substrates.
It is preferable to provide an angle of 30 ° to 60 °.

〔Example〕

 Hereinafter, specific examples of the present invention will be described.

The basic configuration of the liquid crystal display device is the same as that shown in FIG.

Example 1. One of glass substrates 11 and 21 having transparent electrodes 12 and 22 made of ITO (Indium Tin Oxide) was coated with a silane-based vertical alignment agent (for example, ODS-E manufactured by Chisso Corporation) and dried at 120 ° C. Rubbing in one direction with a cotton cloth. Then, the same processing is performed on the other substrate, and the two substrates 11 and 21 are bonded via a spacer such that the alignment film surfaces face each other and the rubbing directions are orthogonal to each other. A mixed liquid crystal composition of a liquid crystal composition EN37 having a negative dielectric anisotropy and a cholesteric liquid crystal S811 manufactured by Merck was injected into a gap between the two substrates to produce a liquid crystal cell.

The pitch of the liquid crystal used here is 30 μm, and the liquid crystal layer 3
Has a thickness d of 7.5 μm. The pretilt angle is 0.2
°.

Next, a pair of neutral gray linear polarizers 16 and 26 are arranged above and below the liquid crystal cell manufactured as described above such that their polarization axes are orthogonal to each other and form an angle of 45 ° with the rubbing direction. Thus, a liquid crystal display device was formed.

The liquid crystal display element shown in Example 1 was black when no voltage was applied, and became colorless when a voltage of 2.8 V was applied.
Also, no alignment defects such as tilt disclination were observed at all, and a very uniform display was obtained. Also,
The steepness expressed by the ratio of the voltage at which the transmittance changes by 10% to the voltage at which the transmittance changes by 50% was 1.13, and it was confirmed that the device had excellent time-division driving characteristics.

Example 2. Glass substrates 11 and 21 subjected to the same orientation treatment as in Example 1.
With the rubbing direction 45
Paste through the spacer so as to form an angle of °,
A mixed liquid crystal composition of a liquid crystal composition EN37 having a negative dielectric anisotropy and a cholesteric liquid crystal S811 manufactured by Merck was injected into a gap between the two substrates to produce a liquid crystal cell. The pitch of the liquid crystal used here was 70 μm. The thickness d of the liquid crystal layer 3 is 7.5 μm.

Next, a pair of neutral gray linear polarizers 16 and 26 are arranged above and below the liquid crystal cell manufactured as described above such that the polarization axis forms an angle of 45 ° with the rubbing direction to form a liquid crystal display element. Formed.

The liquid crystal display element shown in Example 2 was black when no voltage was applied, and became colorless when a voltage of 2.8 V was applied.
Also, no alignment defects such as tilt disclination were observed at all, and a very uniform display was obtained. Also,
The steepness was 1.12, and it was confirmed that the device had excellent time-division driving characteristics.

Next, as a comparative example, a liquid crystal display device having the following configuration was manufactured and compared.

Comparative example 1.

One of glass substrates 11 and 21 having transparent electrodes 12 and 22 made of ITO (Indium Tin Oxide) is coated with a silane-based vertical alignment agent ODS-E manufactured by Chisso, dried at 120 ° C., and then unidirectionally with a cotton cloth. A rubbing treatment is performed. Then, the same processing is performed on the other substrate, and the substrates 11 and 21 are bonded together via a spacer such that the alignment film surfaces face each other and the rubbing directions are antiparallel. Then, a liquid crystal composition EN37 manufactured by Chisso Corporation having a negative dielectric anisotropy was injected into a gap between the two substrates to produce a liquid crystal cell. The thickness d of the liquid crystal layer 3 of this liquid crystal cell is 7.5 μm.

A pair of neutral gray linear polarizers 16 and 26 are arranged above and below the liquid crystal cell manufactured in this way so that their polarization axes are orthogonal to each other and form an angle of 45 ° with the rubbing direction. An element was formed.

This liquid crystal display element is black when no voltage is applied,
Although it became colorless by the application of a voltage of 2.8 V, a large number of alignment defects such as tilt disclination occurred, and the display was extremely uneven.

Comparative Example 2. One of the glass substrates 11 and 21 having the transparent electrodes 12 and 22 made of ITO (Indium Tin Oxide) was coated with SiO from the substrate normal.
Obliquely vapor-deposited from the direction of 60 ° to a thickness of about 300 °, and then applied a silane vertical alignment agent ODS-E manufactured by Chisso Co.
And dried. Next, the same processing is performed on the other substrate,
The two substrates 11 and 21 are bonded together via a spacer such that the alignment film surfaces face each other and the deposition directions are antiparallel. Then, a liquid crystal composition EN37 manufactured by Chisso Corporation having a negative dielectric anisotropy was injected into a gap between the two substrates to produce a liquid crystal cell. The thickness d of the liquid crystal layer 3 of this liquid crystal cell is 7.5 μm. The pretilt angle was 2 °.

A pair of neutral gray linear polarizers 16 and 26 are arranged above and below the liquid crystal cell manufactured in this manner so that their polarization axes are orthogonal to each other and form an angle of 45 ° with the vapor deposition direction. Was formed.

This liquid crystal display element is black when no voltage is applied,
It becomes colorless by applying a voltage of 2.8V. Although a uniform display was obtained without occurrence of tilt disclination or the like, the viewing angle was narrower than the liquid crystal display elements of Examples 1 and 2.

〔The invention's effect〕

As described above, the present invention provides a nematic liquid crystal and an optically active substance (a cholesteric liquid crystal or a non-liquid crystal optically active substance) as a liquid crystal composition of a DAP type liquid crystal display device.
A liquid crystal composition having a negative dielectric anisotropy comprising a mixed composition of
By adopting a configuration in which the twisted orientation is set within an angle range of less than 100 °, the occurrence of alignment defects (reverse tilt) can be effectively suppressed, and as a result, a liquid crystal display having a uniform display without alignment defects. An element is obtained.

Further, according to the present invention, since the alignment defect does not occur even at a small pretilt angle, the contrast is high,
A liquid crystal display device having a wide viewing angle can be obtained. further,
Since the alignment treatment is easy, a liquid crystal display device having high productivity and excellent alignment stability can be easily provided.

Further, the liquid crystal display element according to the present invention has excellent steepness in the voltage transmittance characteristic, and thus has a high time-division driving characteristic.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the basic configuration of a DAP type liquid crystal display element, FIG. 2 is an explanatory view of the orientation direction of liquid crystal molecules of the DAP type liquid crystal display element, and FIG. FIG. 4 is an explanatory view of the orientation direction of molecules, and FIG. 4 is a projection view of liquid crystal molecules on the substrate onto the substrate surface. 3 ... liquid crystal layer, 11,21 ... substrate, 12,22 ... transparent electrode, 1
4,24 ... outer peripheral seal, 15,25 ... alignment film, 16,26 ... polarizing plate.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-192220 (JP, A) JP-A-55-57824 (JP, A) JP-A-3-85538 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G02F 1/137

Claims (1)

(57) [Claims] 1. A mixed composition of two substrates subjected to a slightly inclined vertical alignment treatment, a nematic liquid crystal and an optically active material (cholesteric liquid crystal or non-liquid crystalline optically active material) sealed between the substrates. A liquid crystal composition having a negative dielectric anisotropy, and a pair of polarizing plates, wherein a twisted structure is induced in the liquid crystal by the optically active substance, and when a voltage is applied, the liquid crystal molecules are 1 ° or more in a thickness direction. 100 °
A liquid crystal display device characterized in that the liquid crystal display device is configured to have a twist alignment in an angle range of less than.