JP2004355032A - Vertical alignment type ECB mode liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve display quality such as steepness of electro-optical characteristics, contrast and transmittance in a vertical alignment type ECB mode liquid crystal display device.
SOLUTION: A vertical alignment type ECB mode liquid crystal display element has electrodes and an alignment-treated vertical alignment film formed on a surface thereof, and a pair of substrates arranged to face each other at a predetermined interval, and disposed between the pair of substrates. A liquid crystal cell having a liquid crystal layer and a pair of polarizers arranged in a crossed Nicol arrangement disposed outside the liquid crystal cell, wherein the alignment treatment imparts an alignment direction to the liquid crystal in contact with the substrate, The direction that bisects the angle between the alignment directions on the pair of substrates is along one of the polarization directions of the pair of polarizers or the direction that bisects the angle between the polarization directions of the crossed Nicols arrangement. The pretilt angle of liquid crystal molecules existing at the interface between the substrate and the liquid crystal layer is set in a range of 85 ° to 60 ° with respect to the substrate surface.
[Selection] Fig. 10

Description

  The present invention relates to a liquid crystal display device, and more particularly, to a vertical alignment type ECB mode liquid crystal display device having excellent steepness of electro-optical characteristics and excellent light transmittance, contrast characteristics, and responsiveness (response).

  FIG. 1 shows a vertical alignment type ECB (Electrically Controlled Birefringence) mode liquid crystal display device (LCD). As shown in FIG. 1A, the liquid crystal molecules 6 are vertically aligned with respect to the upper and lower substrates 3 when no voltage is applied. Therefore, there is no optical anisotropy in the in-plane direction of the substrate. By combining with the polarizing plate 1 having the orthogonal Nicols arrangement, the black level of the orthogonal polarizing plate can be obtained as it is, and high contrast can be easily obtained. The optical anisotropy with the optical axis in the direction normal to the substrate is indicated by the arrangement of liquid crystal molecules. For this reason, it exhibits optical anisotropy with respect to obliquely incident light. By using an optical compensator (NOC film) 2 having a negative (uniaxial) refractive index anisotropy, the optical anisotropy of the liquid crystal layer 5 is compensated for, so that the viewing angle of black display can be compensated and a good visual field can be obtained. Easy to obtain angular characteristics. In FIG. 1, reference numeral 4 denotes a transparent electrode and a vertical alignment film.

  As shown in FIG. 1B, in this ECB mode, when a voltage is applied, the liquid crystal molecules in the central portion between the upper and lower substrates of the cell begin to fall, and at the same time, the retardation of the liquid crystal layer changes and the transmittance gradually increases. It has the electro-optical characteristics of

  FIG. 2 shows the electro-optical characteristics of the vertical alignment ECB-LCD. The horizontal axis indicates the applied voltage in V, and the vertical axis indicates the transmitted light intensity in arbitrary units. For reference, the electro-optical characteristics of a super twisted nematic (STN) LCD, which is the most common simple matrix LCD, are also shown. The electro-optical characteristics of the STN-LCD show that the transmitted light intensity does not become 0 even in a low applied voltage region, indicating that black display is difficult. However, the rise of the transmitted light intensity of the STN-LCD is steep, indicating that the transmitted light intensity changes rapidly with a change in voltage. It shows that the transmitted light intensity in the bright state is also high, and that relatively good contrast characteristics can be obtained with a high transmittance. However, STN cells have difficulty in displaying black, and can only display blue-white or yellow-black. In order to enable black-and-white display, two cells having different twist directions of the liquid crystal are stacked, and a two-layer STN-LCD method for driving one of the cells, or one or more positive uniaxial films in the liquid crystal cell are used. A method is adopted in which the sheets are stacked and a film compensation STN-LCD is used.

  However, in the two-layer STN-LCD method, since two liquid crystal cells are used, the thickness and the weight increase. Further, in the film compensation STN, a black level is hardly generated, and even if a black level is possible inside the electrode, the black level rises outside the electrode. In such a case, it is difficult to increase the contrast.

  Regarding the electro-optical characteristics of the vertical alignment ECB-LCD, good blocking of transmitted light is obtained under a low applied voltage state, and a good black display is obtained. However, the transmitted light intensity increases relatively slowly with an increase in the applied voltage, and it is difficult to obtain a sharp increase in the transmitted light intensity with a voltage change. In order to obtain a high contrast, it is necessary to significantly reduce the transmittance during bright display. Further, since the steepness of the electro-optical characteristics is moderate, it is difficult to increase the number of scanning lines, that is, the duty ratio.

  Increasing the thickness of the liquid crystal cell can improve the steepness of the electro-optical characteristics. However, the steepness of the electro-optical characteristics is improved, but at the same time, the response to voltage application tends to be significantly reduced.

  In the vertical alignment ECB-LCD, there is a trade-off relationship between light transmittance, contrast, and response, and it is difficult to improve all of them at the same time.

  An object of the present invention is to provide a vertical alignment ECB-LCD having excellent steepness in electro-optical characteristics, high contrast, and high light transmittance in a bright state.

  It is another object of the present invention to provide a vertical alignment ECB-LCD which can be driven at a high duty ratio and has high display quality.

  A vertical alignment type ECB mode liquid crystal display device according to one aspect of the present invention includes a pair of substrates formed with electrodes and an alignment-treated vertical alignment film on a surface thereof, and a pair of substrates arranged to face each other at a predetermined interval. A liquid crystal cell having a liquid crystal layer disposed thereon, and a pair of polarizers in a crossed Nicols arrangement disposed outside the liquid crystal cell, wherein the alignment treatment imparts an alignment direction to the liquid crystal in contact with the substrate. The direction that bisects the angle between the alignment directions on the pair of substrates is one of the polarization directions of the pair of polarizers, or the direction that bisects the angle between the polarization directions of the crossed Nicols arrangement. The pretilt angle of the liquid crystal molecules existing at the interface between the substrate and the liquid crystal layer is set in the range of 85 ° to 60 ° with respect to the substrate surface.

In the vertical alignment type ECB mode liquid crystal display device, the elastic free energy of the liquid crystal can be increased by setting the pretilt angle to a small value (in the direction in which the inclination of the liquid crystal molecules from the substrate normal increases). The steepness of the electro-optical characteristics can be enhanced, and a liquid crystal display device having good display quality in both contrast and transmittance can be obtained.

The vertical alignment type ECB mode liquid crystal display device shown in FIG. 1 increases the steepness of the change in the alignment of the liquid crystal molecules by bringing the inclination angle (pretilt angle θ _p ) of the liquid crystal molecules on the substrate surface to the substrate surface as close as possible to 90 °. The contrast is set to be high at the time of multiplex driving. However, in order to control the tilting direction the liquid crystal molecules when a voltage is applied, pretilt angle theta _p is set to less than 90 degrees.

FIG. 3 shows the tilt angle θ _z and the azimuth φ _z of the director n of the liquid crystal molecules. The upper and lower substrates 3 are arranged in parallel and define an xy plane. The normal to the substrate surface defines the z-direction. The angle between the director n of the liquid crystal molecules 6 and the xy plane is θ _z , and the angle between the projection of the director n onto the xy plane and the x axis is the azimuth φ _z . These angles θ _z and φ _z both change according to the thickness position z in the liquid crystal layer.

FIG. 4 shows the pretilt angle θ _p of the liquid crystal molecules. In the position the liquid crystal layer 5 is in contact with the upper and lower substrates, the director n is the substrate surface and the plane parallel to the angle of the liquid crystal molecules are pre-tilt angle theta _p. Liquid crystal molecules 6, at a position in contact with the substrate surface are aligned at the pretilt angle theta _p. Note that the director of the liquid crystal molecules on the liquid crystal layer center plane 12 is n _mid .

Figure 5 shows a polarizer when viewed LCD from the substrate normal direction, the analyzer, the liquid crystal layer upper and lower surfaces of the alignment easy axis, the relationship between n _mid. An angle is defined in a counterclockwise direction from the x-axis with the x-axis as a reference direction. The azimuth of director n _{mid on} the liquid crystal layer center plane is φ _mid, and the direction of the easy alignment axis on the upper surface of the liquid crystal layer is φ _pc . The azimuth angle of the transmission axis of the analyzer and phi _A. The transmission axis of the polarizer is orthogonal to the transmission axis of the analyzer. Easy orientation axis of the liquid crystal layer lower surface forms a cross angle phi _c from easy orientation axis of the liquid crystal layer top surface.

  In the structure of the vertically aligned LCD shown in FIG. 1, the azimuthal direction (in-plane direction aligned with the substrate) of the molecule at the center in the thickness direction of the liquid crystal layer 5 corresponds to the transmission axis (arrow) of the polarizing plate 1 in the crossed Nicols arrangement. On the other hand, the transmitted light intensity T in the 45 ° direction is defined by the following equation (1).

Here, n _e, n _o each represents an extraordinary light and tropism rate of ordinary LCD, theta _av represents the average inclination angle of the liquid crystal layer molecules. d indicates the cell thickness, λ indicates the incident wavelength, and I indicates the incident light intensity. θ _av changes depending on the applied voltage. The effective retardation Δn _eff d is the effective retardation when the vertically aligned LCD is viewed from the normal direction of the substrate, and is 0 when the pretilt angle θ _p is close to 90 degrees when no voltage is applied. When a voltage is applied between the substrates, the liquid crystal molecules tilt, and the effective retardation Δn _eff d increases. At this time, the average tilt angle θ _av of the molecules in the liquid crystal layer decreases.

In order to increase the steepness in the electro-optical characteristics, it is better that the change in the effective retardation Δn _eff d with a small potential difference is large. Therefore, to increase the steepness of electrooptical characteristics, 1) the retardation _{Δnd (Δn = n e -n o} ) the increase 2) Two methods for a steep orientation change of the liquid crystal molecules are contemplated.

  The first method 1) can be realized by increasing the cell thickness d, but the response of the change in the liquid crystal alignment is slowed down in proportion to the square of the cell thickness d. This is a difficult method to maintain the response and increase the steepness. As the remaining method, attention is paid to the second method 2).

  In order to increase the steepness of the liquid crystal alignment change, it is effective to increase the elastic free energy in the liquid crystal layer in the initial alignment state. In the x, y, z coordinate system of FIG. 3, when the thickness d of the liquid crystal layer is taken in the z-axis direction, the elastic free energy F per unit area in the liquid crystal layer can be defined by the following equation (2).

Here, θ _z : tilt angle φ _z at position z in the liquid crystal layer thickness direction: twist angles k ₁₁ , k ₂₂ , k ₃₃ at position z in the liquid crystal layer thickness direction: elastic constant P ₀ : natural pitch.

By rearranging f _d , it can be expressed by the following equation (3).

In the case of the vertical alignment ECB-LCD having the structure of FIG. 1, the liquid crystal molecules 6 do not change in the azimuthal direction φ along the z-axis, so that the second and third terms of the equation (3) become 0, The elastic free energy is low. Regarding the third term, since the liquid crystal has no chirality and the natural pitch P ₀ is infinite, it becomes double zero.

When a structure in which the axis of easy alignment of liquid crystal is twisted by rubbing treatment or the like between the upper and lower substrates of the vertical alignment ECB-LCD is introduced, the azimuthal angle φ _z of the liquid crystal molecules changes in the z-axis direction, and the second term is finite. Value. Furthermore, by adding a chiral agent to the liquid crystal layer and setting the natural pitch to a finite value, the third term also takes a finite value and the elastic free energy in the liquid crystal layer can be increased. By increasing the elastic free energy in the liquid crystal layer, a sharp change in alignment of liquid crystal molecules can be expected.

However, the second term of equation (3), the third term also cos ² theta _z is a function of the tilt angle theta _z of the liquid crystal contains. proportional to cos ² θ _z, shows that the elastic free energy increases. In a vertically aligned LCD in which θ _z in the initial alignment is close to 90 degrees, cos ² θ _z is close to 0, so that even if a chiral agent is added to the liquid crystal, a large change in energy cannot be expected.

For horizontal alignment LCD typified by STN-LCD, theta because _z is close to 0, the elastic free energy increases, steep orientation change is thought to be obtained. The present inventors propose to change the tilt angle from 90 degrees to a lower value in order to increase the elastic free energy in the vertical alignment LCD and realize a steeper alignment change. That is, it is expected that the elastic free energy can be increased by increasing cos ² θ _z and increasing the values of the second and third terms in equation (3). Furthermore, the elastic free energy is further increased by increasing the torsion angle of the easy alignment axis (rubbing direction) between the substrates and increasing the change of the liquid crystal director along the z-axis in the azimuthal direction by adding a chiral agent. Is expected to provide steep electro-optical characteristics.

  The results of the computer simulation are shown below. The simulator used was a liquid crystal display simulator “LCDMASTER” manufactured by Shintec.

As shown in FIG. 4, in the LCD structure, a pair of polarizing plates 1 arranged in an orthogonal Nicol arrangement are arranged on both sides of the liquid crystal layer 5. The inclination angle of the liquid crystal molecules 6 positioned on the upper surface 10 and the lower surface 11 of the liquid crystal layer with respect to the substrate plane, that is, the pretilt angle is defined as θ _p, and the director of the liquid crystal layer central surface 12 is defined as _nmid .

As shown in FIG. 5, each parameter when the cell structure of FIG. 4 is viewed from above the substrate, that is, the analyzer, the polarizer, the easy axis (orientation direction) of the lower surface of the liquid crystal layer, and the directional relationship of the director on the center surface of the liquid crystal layer. Is defined. The positive direction of the x-axis is set to an azimuth of 0 °, and this is set as a reference axis of the angle. The azimuth angle of the director on the center plane of the liquid crystal layer is φ _mid , the transmission axis direction of the analyzer is φ _A , the direction of the easy alignment axis on the top surface of the liquid crystal layer is φ _pc , the cross angle is φ _c , and the transmission axes of the polarizer and the analyzer are The angle formed is always 90 ° (cross Nicol arrangement).

FIG. 6 shows the ratio of the liquid crystal layer thickness d = 3.8 μm, Δn = 0.22, Δε = −1.6 to the natural pitch p of the liquid crystal material having the liquid crystal layer thickness d (the natural pitch P ₀ is hereinafter referred to as p). _Shows the cross angle φ _c dependence of the electro-optical characteristics when d / p = 0, θ _p = 80 °, φ _mid = 0 °, φ _A = φ _mid + 45 °, φ _pc = φ _mid + φ _c / 2. . Note that the cross angle phi _c, refers to the orientation axis of easy and forms azimuth angle of the alignment easy axis of the liquid crystal layer lower surface of the liquid crystal layer upper surface (also called the twist angle or the twist angle).

In FIG. 5, when φ _mid = 0, n _mids overlap in the reference axis direction. φ _pc = φ _mid + φ _c / 2 can be transformed into φ _pc −φ _mid = φ _c / 2, and the angle between the easy alignment axis on the upper surface of the liquid crystal layer and the azimuth axis of the director at the center of the liquid crystal layer is the cross angle. , Ie, the direction which divides the angle between the easy axis direction of the upper surface of the liquid crystal layer and the easy axis direction of the lower surface of the liquid crystal layer into two. φ _A = φ _mid + 45 ° indicates that the direction of the director azimuth axis at the center of the liquid crystal layer is a direction that bisects the angle formed by a pair of polarizers arranged in crossed Nicols.

It can be seen that as the cross angle φ _c increases, the threshold value increases, the steepness in electro-optical characteristics improves, and the minimum transmitted light intensity decreases. According cross angle phi _c is increased, the elastic free energy increases, the threshold increases, believed to be causing the steepness increased.

Figure 7 shows a cross-angle dependence of the polar angle component theta _m versus applied voltage characteristic of the director n _mid of the liquid crystal layer center plane 12. According cross angle phi _c is increased, since the theta _m when no voltage is applied approaches 90 °, minimum transmitted light intensity in the electro-optical characteristic is considered to decrease.

The cross angle dependence described above was performed by setting the pretilt angle to θ _p = 80 degrees. If the pretilt angle theta _p is close to 90 degrees, a large change in the elastic free energy as described above is considered to hard to expect.

8, the liquid crystal layer thickness d = 3.8μm, Δn = 0.22, Δε = -1.6, the ratio d / p = 0 of the liquid crystal layer thickness d and the natural pitch _{P 0,} θ _p = 89.9 ° , Φ _mid = 0 °, φ _A = φ _mid +45 degrees, and φ _pc = φ _mid + φ _c / 2, showing the cross angle φ _c dependence of the electro-optical characteristics. Even if the cross angle is changed, no change in the electro-optical characteristics is observed.

  Next, simulation calculations were performed for the case where a chiral agent was added to the liquid crystal.

FIG. 9 shows the liquid crystal layer thickness d = 3.8 μm, Δn = 0.22, Δε = −1.6, d / p = 0.7, φ _mid = 0 °, φ _A = φ _mid + 45 °, φ _pc 7 shows a simulation result of the dependence of the electro-optical characteristics on the pretilt angle θ _p when setting = φ _mid + φ _c / 2 and cross angle φ _c = 270 °. The pretilt angles were 89.9 degrees, 88 degrees, 85 degrees, 80 degrees, and 70 degrees. According pretilt angle theta _p decreases, it can be seen that the steepness is increased in the electro-optical properties. In particular, when θ _p ≦ 85 °, the steepness increases and the maximum transmitted light intensity also increases. A characteristic change is observed between 85 degrees and 88 degrees. At θ _p = 70 °, the transmitted light intensity slightly increases even below the threshold voltage, and there is a concern that the black level may deteriorate.

The phenomenon that the pretilt angle θ _p decreases and the black level increases can be solved by setting the polarizing plate arrangement to φ _A = φ _mid . That is, the direction of the transmission axis of one polarizing plate may be aligned with the direction (parallel) along the liquid crystal molecule azimuthal orientation direction of the liquid crystal layer center plane 12.

In FIG. 10, the liquid crystal layer thickness d = 3.8 μm, the optical anisotropy Δn of the liquid crystal Δn = 0.22, Δε = −1.6, φ _mid = 0 degree, φ _A = φ _mid , φ _pc = φ _mid + φ The calculation result of the dependence of the pre-tilt angle θ _p on the electro-optical characteristics when _c / 2 and the cross angle φ _c = 270 degrees are shown. The pretilt angles θ _p were set to 50 degrees, 60 degrees, 70 degrees, and 80 degrees. Incidentally, d / p value 0.7 at theta _p = 80 °, 0.63 theta _p = 70 °, was 0.48 at theta _p ≦ 60 degrees. theta _p is a property of 60 to 80 degrees have excellent black level is obtained. When θ _p is 50 degrees, the transmitted light intensity shows a substantially constant value irrespective of the applied voltage, indicating that no black level can be obtained. Similar results are expected when θ _p <50 degrees. Therefore, the pretilt angle theta _p is preferably set to about 60 degrees or more.

FIG. 11 shows the liquid crystal layer thickness d = 3.8 μm, Δn = 0.22, Δε = −1.6, d / p = 0.7, φ _mid = 0 °, φ _A = φ _mid + 45 °, φ _pc 7 shows a simulation result of the dependence of the electro-optical characteristics on the cross angle φ _c when = φ _mid + φ _c / 2 and θ _p = 85 °. As the cross angle φ _c increases, the black level decreases and the steepness of the electro-optical characteristics increases when a voltage of 2.5 V is applied. When φ _c > 270 degrees, hysteresis occurred in the electro-optical characteristics.

FIG. 12 shows the liquid crystal layer thickness d = 3.8 μm, Δn = 0.22, Δε = −1.6, φ _mid = 0 °, φ _A = φ _mid + 45 °, φ _pc = φ _mid + φ _c / 2, The simulation results of the d / p dependence of the electro-optical characteristics when φ _c = 240 ° and θ _p = 80 ° are shown. As the d / p value increases, the threshold value decreases and the steepness in electro-optical characteristics improves.

FIG. 13 shows the liquid crystal layer thickness d = 3.8 μm, Δε = −1.6, φ _mid = 0 °, φ _A = φ _mid + 45 °, φ _pc = φ _mid + φ _c / 2, φ _c = 270 °, The simulation result of the dependence of the electro-optical characteristics on the Δn of the liquid crystal when θ _p = 80 ° and d / p = 0.7 is shown. It can be seen that the steepness and the maximum transmitted light intensity improve as Δn increases.

  Considering the results of FIGS. 9 to 13 in addition, good results will be obtained if the pretilt angle is approximately 60 to 85 degrees.

FIG. 14 shows Δn = 0.22, Δε = −1.6, φ _mid = 0 degree, φ _A = φ _mid +45 degrees, φ _pc = φ _mid + φ _pc / 2, φ _pc = 270 degrees, θ of the liquid crystal. ₉ shows dependence of electro-optical characteristics on retardation Δnd when _p = 80 degrees and d / p = 0.7. The retardation Δnd was 0.5 μm, 0.7 μm, 0.9 μm, 1.3 μm, and 1.5 μm. As the retardation Δnd increases, the maximum transmitted light intensity increases, but when Δnd becomes 1.5 μm, the transmitted light intensity decreases. Therefore, the value of the retardation is desirably about 1.3 μm or less. In order to maintain a transmittance of 10% or more, Δnd ≧ 0.7 will be required.

  FIG. 15 shows a simulation result of the dependence of the electro-optical characteristics on the dielectric anisotropy Δε when Δn is fixed at 0.22. It can be seen that the threshold value decreases as the absolute value of Δε increases.

As described above, it has been found that by increasing the pretilt angle θ _p , the cross angle φ _c , and the d / p, a steeper electro-optical characteristic can be obtained in a vertically aligned LCD. When performing multiplex driving, it is considered that the liquid crystal cell should be designed under the following conditions based on the simulation analysis results.

(1) Pretilt angle θ _p : 85 ° to 60 ° (more safely about 80 ° to 60 °)
(2) Cross angle φ _c : 180 ° to 270 °,
(3) d / p: 0 to 0.7,
(4) Retardation Δnd of liquid crystal: 0.7 to 1.3 μm,
(5) Dielectric anisotropy Δε: negative.

  In the above description, for example, a case of a transmission type liquid crystal display device in which light from a light source device provided on the back surface of a liquid crystal cell is used for display has been described, but external light as shown in FIG. The present invention can also be applied to a reflection type liquid crystal display device used as a device.

  In FIG. 16, the same reference numerals as those in FIG. 1 indicate the same elements. 9 is a light reflection plate. In the configuration shown in FIG. 16A, the number of polarizing plates is one, and a 波長 wavelength plate 8 is used. In this case, the light use efficiency is improved. FIG. 16B uses two polarizing plates 1 in a crossed Nicols arrangement. The light reflecting plate 9 (along with one of the polarizing plates if necessary) may be arranged inside the substrate.

  Next, the results of actually preparing a vertical alignment type liquid crystal cell and measuring its performance will be described.

(Control of Pretilt Angle) Conventionally, it has been considered that it is very difficult to perform an alignment treatment at a pretilt angle of 85 degrees or less. In general, after the formation of the different legal surface shape of the substrate surface by oblique evaporation or rotary oblique evaporation of SiO _x, it is known techniques for applying a vertical alignment film thereon.

  The present inventors have realized an alignment treatment at a pretilt angle of 85 degrees or less by performing a rubbing treatment on the vertical alignment film. As the alignment film to be used, the one having the lowest possible vertical alignment control force could be used for better alignment control. It is preferable that the liquid crystal used has weak vertical alignment. Specifically, this tendency is higher when the refractive index anisotropy Δn is large.

  A vertical alignment film JALS-688 (40 nm thick) manufactured by JSR was spin-coated on a glass substrate, and then rubbed with a cotton rubbing cloth. As a result of various attempts, it was found that the pretilt angle could be controlled by the rubbing strength during rubbing and the liquid crystal material.

  FIG. 17 shows an example. The horizontal axis indicates the rubbing strength, and the vertical axis indicates the pretilt angle. All of the liquid crystal materials used have negative dielectric anisotropy, and LC-A and LC-B have very large refractive index anisotropies of 0.2 and 0.22, which are almost 0.2. On the other hand, MLC-2012 manufactured by Merck and EN-38 manufactured by Chisso are liquid crystals having Δn of about 0.1. With MLC-2012 and EN-38 having a refractive index anisotropy Δn of about 0.1, a pretilt angle of 85 ° or less was not obtained even when the rubbing strength was changed. When a liquid crystal having a refractive index anisotropy of about 0.2 or more was used, the pretilt angle was reduced as the rubbing strength was increased, and a pretilt angle of 85 degrees or less could be obtained. From these results, it is expected that a liquid crystal material having a larger value of Δn can control the pretilt angle in a wider range. For example, by using LC-A and LC-B, a pretilt angle of 85 degrees or less can be realized.

(Example 1) With the structure of the LCD shown in FIG. 1, the conditions shown in Table 1 below were set, and cells with cross angles φ _c = 0 °, 90 °, and 180 ° were formed, and their electro-optics were formed. The properties were measured.

FIG. 18 shows the results. Threshold rise of the simulation results and similar tendency by increasing the cross angle phi _c, and improvement of sharpness, the effect of reduction in the black level obtained.

  Example 2 An LCD having the structure shown in FIG. 1 was manufactured under the conditions shown in Table 2 below.

FIG. 19 shows the results of measuring their electro-optical characteristics. FIG. 19 also shows the electro-optical characteristics of a conventional cell having a pretilt θ _p = 89.9 ° and a cross angle φ _c = 0 °. Obviously, the cell of this embodiment has better steepness.

Table 3 shows a comparison between the transmittance T and the contrast CR _max at the time of the 1/120 duty optimal bias method multiplex driving in the embodiment shown in Table 2 and the conventional one having θ _p = 89.9 °. Obviously, the examples of Table 2 have high transmittance and good contrast. Good results have been obtained with a pretilt angle of 81 °. The pretilt angle will preferably be between about 60 degrees and 81 degrees.

  FIG. 20 shows the electro-optical characteristics of the cell when the cell thickness d is changed to 5 μm. It can be seen that a sharper electro-optical characteristic can be obtained by increasing Δnd as the cell thickness increases.

  FIG. 21 shows the electro-optical characteristics when d / p is changed to 0.6 in the conditions shown in Table 1. FIG. 21 also shows the characteristics of the cell under the conditions of Table 1 for comparison. As shown in the figure, as the value of d / p decreases, the threshold value increases and the steepness decreases.

  All of the above electro-optical characteristics are for a monochrome display. Black-and-white display was possible without performing any color compensation or the like performed by an STN-LCD or the like.

  It will be obvious to those skilled in the art that the above configuration can be applied to a vertical alignment type ECB mode liquid crystal display element in which a liquid crystal layer of a liquid crystal display device includes a liquid crystal material containing a dichroic dye.

  As described above, the present invention has been described in connection with the embodiments. However, the present invention is not limited to these embodiments. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

FIG. 3 is a perspective view for explaining an alignment state of liquid crystal molecules of a vertical alignment type ECB mode liquid crystal display device. FIG. 4 is a diagram comparing the electro-optical steepness characteristics of a vertical alignment type ECB mode LCD and an STN type LCD. These are coordinates indicating the relationship between the substrate surface and the orientation direction of the liquid crystal molecules. FIG. 2 is a perspective view showing a structure of a liquid crystal cell and liquid crystal molecules according to an example of the present invention. FIG. 3 is a diagram illustrating a directional relationship of each parameter in an azimuth direction of a liquid crystal cell. 5 is a graph showing the cross angle φ _c dependence of the electro-optical characteristics of the liquid crystal cell according to the example of the present invention. 4 is a graph showing cross-angle dependence of electro-optical characteristics of a liquid crystal cell according to an example of the present invention. 9 is a graph showing the cross angle dependence of the electro-optical characteristics when the pretilt angle is set almost perpendicular. 5 is a graph showing the dependence of the electro-optical characteristics of a liquid crystal cell according to an embodiment of the present invention on the pretilt angle θ _p . 4 is a graph showing the pretilt angle dependence of the electro-optical characteristics of a liquid crystal cell. 5 is a graph showing the cross angle φ _c dependence of the electro-optical characteristics of the liquid crystal cell according to the present embodiment. 4 is a graph showing d / p dependence of electro-optical characteristics of a liquid crystal cell according to an example of the present invention. 6 is a graph showing the Δn dependence of the light-emitting property of a liquid crystal cell according to an example of the present invention. 4 is a graph showing the retardation Δnd dependence of the electro-optical characteristics of a liquid crystal cell according to an example of the present invention. 5 is a graph showing the dielectric anisotropy Δε dependence of the electro-optical characteristics of a liquid crystal cell according to an example of the present invention. FIG. 3 is a perspective view illustrating a structure of a liquid crystal cell of a reflective liquid crystal display according to an embodiment of the present invention. 5 is a graph showing the relationship between pretilt angle and rubbing strength when various vertical alignment films are used. 5 is a graph showing electro-optical characteristics according to a difference in a cross angle of a liquid crystal cell according to an embodiment of the present invention. 4 is a graph illustrating electro-optical characteristics of a liquid crystal cell according to an embodiment of the present invention. 4 is a graph illustrating electro-optical characteristics of a liquid crystal cell according to an embodiment of the present invention. 4 is a graph illustrating electro-optical characteristics of a liquid crystal cell according to an embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Polarizer 2 Optical compensator 3 Substrate 4 Electrode and vertical film 5 Liquid crystal layer 6 Liquid crystal molecule 7 Reflector 8 1/4 wavelength plate

Claims (11)

An electrode and an alignment-treated vertical alignment film are formed on the surface, a pair of substrates disposed to face each other at a predetermined interval, and a liquid crystal cell having a liquid crystal layer disposed between the pair of substrates,
A pair of polarizers in a crossed Nicol arrangement arranged outside the liquid crystal cell,
Wherein the alignment treatment imparts an alignment direction to the liquid crystal in contact with the substrate, and a direction that bisects an angle between the alignment directions on the pair of substrates is any one of the polarization directions of the pair of polarizers. Alternatively, along a direction that bisects the angle between the polarization directions of the crossed Nicols arrangement, the pretilt angle of the liquid crystal molecules existing at the interface between the substrate and the liquid crystal layer is 85 ° to 60 ° with respect to the substrate surface. A vertical alignment type ECB mode liquid crystal display device set in the range of °.   2. The vertical alignment type ECB mode liquid crystal display device according to claim 1, wherein the orientation direction of the pair of substrates defines an in-plane twist angle, and the twist angle is set in a range of 180 ° to 270 °.   2. The vertical alignment type ECB mode liquid crystal display device according to claim 1, wherein the retardation of the liquid crystal layer is set to 0.7 [mu] m to 1.3 [mu] m.   2. The vertical alignment type ECB mode liquid crystal display device according to claim 1, wherein the liquid crystal layer includes a liquid crystal material to which a chiral agent is added.   The liquid crystal layer is set so as to satisfy a relation of 0 ≦ d / p ≦ 0.7 when a chiral pitch of a liquid crystal material is p and the predetermined interval between the pair of substrates is d. 5. The vertical alignment type ECB mode liquid crystal display device according to item 4.   2. The vertical alignment type ECB mode liquid crystal display device according to claim 1, further comprising a light source for transmitting light passing through said liquid crystal layer disposed outside said pair of substrates.   7. The vertical alignment type ECB mode liquid crystal display device according to claim 6, further comprising a quarter-wave plate disposed between any one of the pair of polarizers and the liquid crystal cell.   The vertical alignment type ECB mode liquid crystal display device according to any one of claims 1 to 7, wherein the pretilt angle is in a range of 81 degrees to 60 degrees.   2. The vertical alignment type ECB mode liquid crystal display device according to claim 1, further comprising a reflector disposed between the pair of substrates or outside the pair of substrates to reflect light transmitted through the liquid crystal layer. The vertical alignment type ECB mode liquid crystal display device according to claim 1, wherein the liquid crystal layer includes a liquid crystal material containing a dichroic dye. An electrode and an alignment-treated vertical alignment film are formed on the surface, a pair of substrates disposed to face each other at a predetermined interval, and a liquid crystal cell having a liquid crystal layer disposed between the pair of substrates,
A polarizer disposed above the liquid crystal cell,
A reflector disposed below the liquid crystal cell,
A quarter-wave plate disposed between the liquid crystal cell and the reflector,
Wherein the direction that bisects the angle between the in-plane directions of the alignment treatment on the pair of substrates is any one of the transmission axis direction and the light shielding axis direction of the polarizer, or the angle between these directions. And a pre-tilt angle of liquid crystal molecules existing at an interface between the substrate and the liquid crystal layer is set in a range of 85 ° to 60 ° with respect to the substrate surface. Mode liquid crystal display element.

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