JPH09222601A - Liquid crystal display element and optically anisotropic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to improve the dependence of a liquid crystal display element in visual angles by adding a phase difference plate which lessens the optical rotatory power in an upper position and to induce the optical rotatory power in a lower position. SOLUTION: The inclination of the major axis of an ellipse changes continuously from the electrode 3d of a lower substrate toward the electrode 3c of an upper substrate. The optical axis OL is nearly perpendicular to the substrate surface near the lower substrate 3d and is nearly parallel near the upper substrate electrode 3c. When the arrangement of Fig. (a) is observed diagonally from the z-axis, the arrangement is twisted toward the left viewed from the progressing direction according to the progression from below to above in Fig. (c) and is twisted rightward conversely therefrom in fig. (d). The characteristic that the rotating direction of the polarized light is reverse between the upper position and the lower position is embodied by the phase difference plate arranged diagonally in such a manner. The phase difference plate may be regarded as the structure obtd. by optically laminating optically anisotropic material layer units in its thickness direction. The phase difference plate consists of the constitution in which the respective layer units have the optical axes and that the inclination of the optical axes change continuously and stepwise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display element and an optical anisotropic element, and more particularly to an optical anisotropic element and an arrangement in which the contrast ratio of a liquid crystal display element and the viewing angle dependence of display color are improved.

[0002]

2. Description of the Related Art Since liquid crystal display elements have the great advantages of being thin and lightweight and of low power consumption, they are positively used not only as displays for wrist watches, calculators, Japanese word processors, personal computers, etc., but also as liquid crystal display elements. It is also used in products with new concepts that were used. In particular, liquid crystal display elements used in personal computers and the like have become large-area and large-capacity displays, and the size of the display surface has become 10 inches diagonal and 640 × 480 pixels have become mainstream. The display methods used for liquid crystal display elements of this class can be roughly classified into two types.
One is a simple matrix method and the other is an active matrix method.

The simple matrix system has a simple structure in which a liquid crystal is sandwiched between two glass substrates having comb-shaped transparent electrodes. Therefore, in the simple matrix system, high performance is required for the liquid crystal. Before describing the performance required of the liquid crystal, the display principle of the liquid crystal display element will be described.

The display of the liquid crystal display element is performed by changing the voltage applied to the liquid crystal to change the orientation of the liquid crystal molecules. Generally, a large voltage difference is required to obtain a large contrast ratio. However, in order to realize the display of 640 × 480 pixels, the voltage difference between dark and bright is as small as about 1V,
A large state change of liquid crystal molecules is required only by the difference of 1V.
To achieve this, it was studied by many researchers for a long time, and in 1985, it was done by the research group of Schaefer et al. According to their research, by increasing the twist angle of the alignment of liquid crystal molecules, the alignment changes sensitively to voltage, and in order to obtain a stable alignment with a large twist angle, We found that the molecule needs to have a certain degree of inclination. Since this research report, alignment technology for realizing this has been actively carried out and successfully put into practical use.

Generally, a twist angle of 180 ° or more is required to realize a display with an array of 640 × 480 pixels.
Due to such a large twist angle, this liquid crystal is called super twist nematic (STN). However, the initial STN display had a different background such as a yellow background and green characters, and was not a black and white display. This is because the twist angle is large, and as a means for eliminating such display coloration, a second liquid crystal cell in which the liquid crystal layer is twisted in the opposite direction is arranged between the polarizing plate and the liquid crystal cell. It has been reported in Japanese Patent Publication No. 63-53528 that black and white display can be realized.

The principle of black and white is that the light, which is transmitted through the first liquid crystal cell in which the liquid crystal molecules are arranged in a twisted arrangement and causes optical rotatory dispersion, is transmitted to the first liquid crystal cell and the second liquid crystal cell of the target structure. By doing so, the optical rotatory dispersion was resolved. As a result, coloring due to optical rotation dispersion of light is eliminated, and black and white display can be realized. In order to perform such conversion accurately, the second liquid crystal cell, which is an optical compensator, has substantially the same retardation value as the first liquid crystal cell, and the twist directions are opposite to each other. Need to be configured such that the alignment directions of the liquid crystal molecules closest to each other are orthogonal to each other.

As other means, various methods using an optically anisotropic film instead of the above-mentioned second liquid crystal cell have been proposed. This is a method in which several optically anisotropic films are laminated on a liquid crystal cell to have almost the same function as the second liquid crystal cell.

The optical compensation described above enables black-and-white display even on an STN display, and by combining it with a color filter, color display with a higher added value can be realized. However, since the simple matrix method is based on the principle of time division driving based on the voltage averaging method, if the number of scanning lines is increased in order to perform high definition display,
There is an essential problem that the voltage difference when blocking light and the voltage difference when transmitting light are significantly reduced, resulting in a small contrast ratio and a slow response speed of liquid crystal. In addition, such a conventional technology is observed as a phenomenon that the display image looks reversed depending on the azimuth and the angle when the liquid crystal display element is viewed, the display image disappears at all, or the display becomes colored, and the display quality is further improved. This is a serious problem when a liquid crystal display device with high cost is realized.

On the other hand, the active matrix type has a switching element composed of a thin film transistor and a diode for each display pixel, so that an arbitrary voltage ratio can be set in the liquid crystal layer of each pixel regardless of the number of scanning lines. Therefore, the liquid crystal is not required to have special performance as in the case of the simple matrix system. The twist angle does not need to be as large as STN, and is set to 90 °.

Liquid crystal cell (TN) having a twist angle of 90 °
Has a small twist angle and thus has no optical rotatory dispersion, and an achromatic and high-contrast display can be obtained. Also, the response to voltage is faster than STN. Active matrix method and TN
By combining and, it is possible to realize a liquid crystal display device having a large display capacity, a high contrast ratio, and a fast response speed. In addition, since there is a switching element for each pixel, an intermediate voltage can be applied, which enables halftone display. Furthermore, full color display can be easily realized by combining with a color filter.

However, even in the case of the active matrix system, although not so much in the case of the binary display, the display image looks inverted depending on the viewing direction when the halftone is displayed, or the display image is completely visible. It is observed as a phenomenon that the display disappears or the display is colored, which is a serious problem in realizing a liquid crystal display device with higher display quality.

As a means for reducing the viewing angle dependence of such a display, British Patent No. 1462978 discloses that a liquid crystal cell and a polymer film whose optical anisotropy is negative in the thickness direction are provided between two polarizing plates. Disposing a refraction layer is disclosed. On the other hand, in JP-A-3-67219,
It is disclosed that a birefringent layer made of a liquid crystal compound (or polymer liquid crystal) showing a cholesteric liquid crystal phase having a product of a helical pitch length and a refractive index of 400 nm or less is arranged on a liquid crystal cell. These two proposals are considered only in the case of a liquid crystal cell in which vertical alignment (liquid crystal molecules are aligned vertically with respect to an alignment substrate), and a liquid crystal cell in a twisted alignment such as a TN method or an STN method is considered. If not considered. Also, there is a proposal in Japanese Patent Laid-Open No. 4-349424 to control the viewing angle of a liquid crystal display element by an optical compensation element having a tilt angle in an array with a twist angle of 360 ° or more. The effect of angular expansion is not yet sufficient.

[0013]

The basic display principle of the liquid crystal display device described above is that the direction of liquid crystal molecules is changed by the voltage applied to the liquid crystal, thereby causing an optical change in the liquid crystal cell. .

Therefore, when the liquid crystal display element is tilted, the orientation of the liquid crystal molecules appears to change, and particularly when displaying a delicate halftone, the degree of tilt of the liquid crystal molecules is finely changed, which is more remarkable.

Due to such viewing angle dependence of the appearance of the arrangement of the liquid crystal molecules, it is observed as a phenomenon that the display image appears to be reversed or cannot be discriminated at all. Especially, in combination with a color filter, full color display is performed. When this is done, the reproducibility of the displayed image is significantly reduced, which is a serious problem.

The present invention solves the above-mentioned inconveniences and provides a liquid crystal display device having improved contrast ratio and viewing angle dependence of display color, and an optical anisotropic element used for the same.

[0017]

SUMMARY OF THE INVENTION The present invention resides in a liquid crystal display device having the following features.

At least one polarizer, a driving liquid crystal cell in which a liquid crystal layer is sandwiched between two substrates, and a polarizer and the driving liquid crystal cell are arranged, and the optical anisotropy is a negative sign. The first optical anisotropic layer in which the optical axis continuously changes in the layer thickness direction from a direction substantially perpendicular to the layer surface to a direction parallel to the layer surface and the optical anisotropy is a negative sign, and the optical axis is the layer surface. Is disposed adjacent to a second optical anisotropic layer that is substantially perpendicular to the second optical anisotropic layer, and the layer side that forms an optical axis that is substantially perpendicular to the first optical anisotropic layer is the second optical anisotropic layer. An optical anisotropic element adjacent to the layer,
A liquid crystal display device comprising:

The average optical axis of the driving liquid crystal cell and the average optical axis synthesized from the first optically anisotropic layer and the second optically anisotropic layer are substantially parallel to each other. Liquid crystal display device.

A liquid crystal display device characterized in that the display system of the driving liquid crystal cell is an optical rotation mode.

A liquid crystal display device characterized in that the display system of the driving liquid crystal cell is a birefringence mode.

A liquid crystal display device characterized in that the first optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal.

A crystal display device characterized in that the first optically anisotropic layer comprises a liquid crystal cell.

A liquid crystal display device, wherein the second optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal.

A liquid crystal display device, wherein the first optically anisotropic layer is formed inside a driving liquid crystal cell.

A liquid crystal display device, wherein the second optically anisotropic layer is formed inside a driving liquid crystal cell.

The present invention further resides in a liquid crystal display device having the following features.

The optical anisotropy of the optical anisotropy unit is a negative sign, and the optical axis is an array which is continuously changed in the thickness direction of the layer within a plane consisting of the thickness axis and the axis in a certain direction of the layer surface, A first optically anisotropic layer having the optical axis substantially perpendicular to the layer surface on one layer surface and the optical axis substantially parallel to the layer surface on the other layer surface; Second, almost perpendicular to
And the optical axis of the optical anisotropic unit closest to the second optical anisotropic layer of the first optical anisotropic layer, An optical anisotropic element characterized in that the optical axis of the optically anisotropic layer is substantially parallel.

An optical anisotropic element characterized in that the first optically anisotropic element is made of an organic material, an inorganic material or a polymer liquid crystal.

An optical anisotropic element characterized in that the first optically anisotropic layer comprises a liquid crystal cell.

An optical anisotropic element characterized in that the second optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention solves the problems as described above, and simultaneously reduces the contrast ratio of a liquid crystal display device, the brightness at the time of gradation display, and the viewing angle dependence of the display color, or It is intended to control the region of the display element where a specific contrast ratio is obtained to have a certain azimuth and viewing angle. The operation will be described below.

In a liquid crystal display element such as TN or STN, the polarization state of light propagating in the liquid crystal display element is different depending on whether the light is vertically incident on the display surface of the liquid crystal display element or obliquely. This difference in polarization state is directly reflected in the inversion phenomenon and the coloring phenomenon of the display image. Such a phenomenon is observed when the viewing angle of the display surface of the liquid crystal display element is greatly inclined from the normal to the display surface, and in particular, a liquid crystal cell of a liquid crystal cell (hereinafter referred to as a drive cell) having means for applying a voltage to the liquid crystal layer. It is noticeable in pixels where a voltage is applied to the layer.

FIGS. 17 (a) and 17 (b) show 0 ° to 60 ° in the left and right directions from the normal to the display surface of the conventional TN liquid crystal display element.
It is a figure which shows the angle dependence of the display brightness at the time of inclining.
1 to 8 levels are shown for each gradation number of gradation display, and the voltages applied to the liquid crystal cells are different in order. 0V for level 1 and 5V for level 8 are applied to the liquid crystal cell. For example, in the case of upward orientation (Fig. 17 (b)),
The brightness gradually increases as the angle (viewing angle) tilted from the normal to the display surface of the display increases from 0 ° (front) to 60 °. In the actual display, it is observed that the display color becomes whitish (white spots). On the other hand, regarding the lower position, when the viewing angle is tilted from the front (0 °) to 60 °, the brightness decreases contrary to the upward direction. This phenomenon is observed in the actual display image as the display color darkens (blackout). Also, on the front,
Brightest display level 1 and lower gradation level 2
The size relationship is reversed at the viewing angle of 35 ° in the upper direction, and is observed as an inverted display (reversal) like a negative of a photographic film in an actual display image. Ideally, the transmittance does not change even if the viewing angle changes for any gradation level. However, the actual viewing angle characteristics of TN are shown in FIG.
As shown in, the characteristic in the horizontal direction is relatively good, but the characteristic in the vertical direction is poor.

The reason why such a phenomenon occurs is that the viewing angle characteristics of the liquid crystal display element are caused by the fact that the polarization state varies depending on the incident angle of the light incident on the liquid crystal display element as described above. The TN will be described in detail as an example.

FIG. 3 shows the operating principle of the TN type liquid crystal display device. FIG. 3A shows TN when no voltage is applied to the electrodes 3c and 3d.
The alignment state of the liquid crystal molecules LM in the cell is shown. Voltage V
When no voltage is applied, the liquid crystal molecules are arranged in a continuously twisted arrangement in which the liquid crystal molecules are parallel to each other in the thickness direction of the liquid crystal layer (z-axis direction in the figure) substantially parallel to the substrate. . When the light Li polarized by the polarizer Pi is incident on the array of twisted molecules, the polarization plane rotates according to the twisted array of the liquid crystal molecules LM, and at the exit of the liquid crystal layer, the polarization plane is the same as before entering the liquid crystal layer. Rotate by the twist angle of the liquid crystal layer with respect to the plane of polarization. In this rotated direction, the transmission axis P of the analyzer Po
When ot is adjusted, transmitted light Lo is obtained.

FIG. 3B shows the alignment state of liquid crystal molecules in the TN cell when a voltage is applied. The liquid crystal molecule LM rises by the application of the voltage V, and the liquid crystal molecule L near the center of the cell
Mc is more inclined than the liquid crystal molecules LMs near the electrodes. Electrode 3
The reason why the inclination of the liquid crystal molecules LMs in the vicinity of c and 3d is small is that there is an alignment regulating force (necessary for aligning the liquid crystal) at the electrode-liquid crystal layer interface. The tilt of the liquid crystal molecules becomes large according to the magnitude of the voltage V, and at the same time, the twisted arrangement is also distorted, and when the voltage is further increased, the twist is finally released. When the polarized light Li enters in such a state, the polarization plane Lp does not rotate and travels through the liquid crystal layer because it is not in a twisted arrangement, and the polarization plane at the exit from the liquid crystal layer is the same as before the incidence on the liquid crystal layer. Therefore, the transmission axis Pot of the analyzer Po
Since is orthogonal to the plane of polarization Lp, it cannot transmit polarized light. In order to display halftones, the magnitude of the voltage applied to the liquid crystal layer is set smaller than this, a slight twist alignment is left in the liquid crystal layer, and the plane of polarization that exits the liquid crystal layer is rotated slightly to allow transmission of the intermediate transmitted light. To get Based on the above principle, the transmitted light is controlled by utilizing the distortion of the twisted arrangement.

Next, the phenomenon of oblique light will be described.

FIG. 4 is a diagram for explaining a state in which light obliquely enters the molecular arrangement state when displaying a halftone. FIG. 4A is a perspective view showing the relationship between the molecular alignment state LMint at the time of halftone display and the two directions L and U of incident light. To make it easier to understand, FIG. 4A is a view seen from the y-axis direction. 4 (b) and 4 (c). Here, the normal direction of the substrate of the driving liquid crystal cell is represented by the z axis, and the substrate surface is represented by the xy axes. The liquid crystal molecules LMs near the electrodes 3c and 3d on the upper and lower substrates are arranged with a slight inclination. This tilt is called a pretilt angle, and generally, the pretilt means a tilt of liquid crystal molecules at a substrate-liquid crystal interface, and the tilt angle is called a pretilt angle α0. When no voltage is applied, the upper and lower substrates 3
They are inclined at the same angle between a and 3b. If there is a predetermined inclination (pretilt) over the area to which the voltage V is applied, the inclination directions when the voltage is applied are aligned with the pretilt direction, and as a result, uniform display can be performed. If there is no pretilt, the liquid crystal molecules tilt in different directions when a voltage is applied, and a defect line is generated at the boundary between regions having different tilt directions, which causes a significant deterioration in display quality. Therefore, the pretilt is indispensable to obtain a uniform display, and the angle is generally 1 ° to 6 ° in the TN mode.

Therefore, as shown in FIGS. 4B and 4C, the arrangement state of the liquid crystal molecules is asymmetric with respect to the y-axis, particularly when displaying a halftone. Regarding the polarized light of L obliquely incident from the + x axis to the + z axis direction of FIG.
As shown by LM-L in FIG. 5, the alignment is in a state where the liquid crystal molecules LM are not tilted (as if they were aligned when no voltage is applied), and the plane of polarization can largely rotate. as a result,
The transmitted light is greater than the intensity of the emitted light with respect to the incident light (light parallel to the z axis) from the front. On the other hand, with respect to the polarized light U which is incident from the opposite azimuth of FIG. 4C (obliquely from the −x axis to the + z axis direction), the arrangement is as shown in LM-U of FIG. The liquid crystal molecules LM are largely tilted (as if they are aligned when a larger voltage is applied), and the plane of polarization cannot rotate. As a result, the transmitted light becomes smaller than the intensity of the emitted light with respect to the incident light (light parallel to the z axis) from the front. The correspondence with FIG. 2 is shown in FIG.
2 corresponds to the upper direction in FIG. 2, and the U direction in FIG. 4 corresponds to the lower direction in FIG.

As described above, the azimuth dependence of transmitted light in the halftone is due to the asymmetry of the alignment of liquid crystal molecules. The asymmetry of this arrangement causes the rotation (optical rotatory) angle of the polarization plane to differ depending on the direction in which light is incident, resulting in a change in transmittance. It can be said that the TN type liquid crystal display element tends to have optical rotatory power in the upper direction and reduce optical rotatory power in the lower position.
Therefore, in order to improve this, by adding a retardation plate in which the optical rotatory power is decreased in the upper direction and the optical rotatory property is generated in the lower position, the viewing angle dependency of the liquid crystal display element can be improved.

The present invention provides an optical anisotropic element having such characteristics and a liquid crystal display element equipped with this optical anisotropic element.

The retardation plate constituting the optical anisotropic element according to the present invention will be described.

First, to summarize the characteristics required for the retardation plate, the characteristic required for the retardation plate is that "the rotation direction of the optical rotation is opposite between the upper direction and the lower position". FIG.
FIG. 6 is a diagram showing an arrangement state of optical axes of the retardation plate of the present invention.
(A) is a cross-sectional view of a retardation plate of the present invention, and an ellipse in cross section shows an optical anisotropy unit L constituting the retardation plate.
D is shown, and the long axis normal of the ellipse in cross section of the three-dimensional disk body corresponds to the optical axis OL. The unit may be one molecule, or may be composed of a plurality of molecules that are stacked together. This unit was introduced to explain how the optical axis of a layer with negative optical anisotropy changes its slope continuously with respect to the thickness direction (z direction) within the layer. However, the negative optical anisotropic material layer is equivalently described.

The inclination of the ellipse major axis continuously changes from the electrode 3d on the lower substrate to the electrode 3c on the upper substrate, and the optical axis OL is substantially perpendicular to the substrate surface near the lower substrate 3d. It is almost parallel in the vicinity of the substrate electrode 3c (hybrid orientation). An example of this array viewed from above is shown in FIG. 6 (b). The arrow in the figure indicates the direction of the optical axis OL. FIG. 6C is an array diagram when observed obliquely from the z-axis. The tilt direction is indicated by the xyz axes in the figure. FIG. 6 (d) shows a view seen from the opposite diagonal direction. As can be seen from FIGS. 6 (c) and 6 (d), when the array of FIG. 6 (a) is observed obliquely from the z axis, in FIG. In d), the arrangement is twisted to the right and vice versa. With the retardation plates arranged obliquely in this way, the above-mentioned characteristic that "the rotation direction of the optical rotation is opposite between the upper azimuth and the lower azimuth" can be realized.

Further, the retardation plate as the optical anisotropic element of the present invention can be regarded as a structure in which optically anisotropic substance layer units are laminated in multiple layers in the thickness direction. Each layer unit has an optical axis, and the inclination of these optical axes changes continuously or stepwise. Further, the optical axis arrangement having the minimum optical rotatory power in the thickness direction is adopted.

Next, it will be described how such a retardation plate is combined with a driving cell to obtain a good compensation effect.

7 (b), (d) and (f) are shown in FIG.
The driving cells shown in FIGS. 4 and 5 are shown by adding arrows as in FIG. 6, and the reference symbol Lip indicates the polarization axis of the incident light and the reference symbol Lop.
Represents the polarization axis of the emitted light. FIG. 7A is a diagram of the retardation plate, and FIG. 7B is a diagram of the drive cell (TN) to which a voltage corresponding to a halftone is applied, viewed from the z-axis. (C) is a diagram showing an arrangement of molecules of each optically anisotropic substance layer constituting the retardation plate when viewed from the z-axis toward the + x-axis side, and linearly polarized light is incident on the diagram. The optical rotation state is shown. In this direction, the retardation plate has the property of rotating the polarization plane of incident light to the left (left-handed optical power). (D) shows the arrangement state of the driving cells when viewed from the same direction as (c). The liquid crystal molecules are tilted obliquely because a voltage corresponding to a halftone (a voltage slightly higher than the critical voltage (threshold voltage) at which the liquid crystal operates) is applied. From this direction, the long axis of the liquid crystal molecules is seen. An oriented portion is generated in which the length in the direction and the length in the minor axis direction are almost the same. Therefore, the incident polarized light is transmitted with little rotation, and the direction of the polarization axis Lop of the emitted light is the polarization axis Li of the incident light.
It is almost the same as p. This is the cause of a display abnormality called "blackout" in which the display is dark, and in this case, if the polarized light is rotated to the left (increasing the optical rotatory power), this is improved. The retardation plate of the above-mentioned figure (c) is suitable for this. The retardation film of FIG. 3C has a left-handed optical rotation ability, and compensates for the insufficient optical rotation by the driving cell.

On the other hand, with respect to the opposite direction, FIG.
This will be described with reference to FIG. Figures (e) and (f) show the arrangement of the optical axes when the retardation plate of Figure (a) is observed from the z-axis direction from the -x axis. It has the property of turning to (right rotation). Figure (f) shows
As in the case of FIG. 6D, a halftone voltage is applied, and from this direction, it seems that the liquid crystal molecules are not tilted even though the liquid crystal molecules are actually tilted. Out. This causes a display abnormality called "white spot" in which the display becomes brighter than necessary, and by applying the right-handed optical rotation that suppresses the left-handed optical rotation, the "white spot" is improved. The retardation plate of FIG. 6 (e) has a right-handed rotatory power, and by combining this with a driving cell, the characteristics of the device can be improved. In order to improve the viewing angle dependency with higher accuracy, it is necessary to match the inclination of the average optical axis of the retardation plate with the average optical axis of the driving cell. By doing so, the refractive index of the entire liquid crystal display element can be brought closer to an optical medium having no three-dimensional anisotropy, that is, a refractive index sphere, and a display having no viewing angle dependence can be obtained.

Actually, as shown in FIG. 2, in the retardation plate 20 in which the negative optically anisotropic substance is hybrid-arranged, the inclination θc of the average axis (2.1) of the optical axes is TN liquid crystal display element 3. Is more inclined with respect to the normal direction z than the inclination θLC of the optical axis (3.0). This is due to manufacturing reasons.

Here, for explanation of the hybrid arrangement, it is assumed that the anisotropic material layer is formed by stacking a plurality of optically anisotropic units 2a in the layer direction, and its optical axis 2L extends from the layer lower surface 2B to the layer upper surface 2A. , The inclination is continuously changed from the direction parallel to the lower surface 2B to the direction substantially perpendicular to the upper surface 2A. Note that 3L indicates the long axis direction of liquid crystal molecules having positive dielectric anisotropy. V is a power source for applying a voltage to the liquid crystal layer.

In order to correct the inclination of the optical axis of this hybrid array in the direction of the normal line, it is effective to add a negative retardation plate (FIG. 16) (ECP-646829: Fuji Photo Film, 95). See the annual liquid crystal debate).

The present inventors have paid attention to the optical axis of the retardation plate in such a structure. In this case, in order to correct the optical rotatory power of the drive cell, it is preferable that the optical axis of the retardation plate changes continuously as much as possible.

That is, as shown in FIG. 1 and FIG.
To combine the hybrid orientation retardation plate 20 and the negative retardation plate 30, the optical axis of the optically anisotropic unit (2.
It is extremely important that 1) and 30L are complete.

The liquid crystal display element of the present invention maintains this continuity, and the surface of the hybrid retardation film on the side of the vertical optical axis and the surface of the negative retardation film are adjacent to each other to allow light rays to be obliquely incident. On the other hand, it exerts a sufficient visual angle compensation effect.

Further, in FIG. 8, the optical axis 2Lb parallel to the surface of the hybrid alignment retardation plate 20 and the optical axis 3La of the liquid crystal molecule LM along one alignment treatment direction of the liquid crystal cell 3 are aligned.

Although the principle of expanding the field of view has been described above by taking the combination of the hybrid orientation retardation plate and the negative retardation plate as an example, the retardation plate twisted in the hybrid orientation or evenly tilted between the upper and lower substrates. The oriented retardation plate has similar characteristics to those of the hybrid orientation retardation plate, which can be selected according to the design specifications of the liquid crystal display device. Although the TN has been described as an example, the same principle can be applied to the STN having a twist angle of 90 degrees or more and the cells having other twist angles, that is, the driving liquid crystal cell for displaying by using the birefringence effect.

As a substance having a negative optical anisotropy used for a layer having a negative optical anisotropy, C18H6 (OCOC7H1) having an alkyl chain attached to the triphenylene nucleus by an ester bond is used.
5) 6 and C6 (OCOCm H2m + 1) 6 with benzene nucleus
And so on, these are called discotic liquid crystals. It is also possible to form a desired array in the temperature region showing a liquid crystal phase and use it in a crystal phase so that the array does not change. Further, if the temperature range showing the liquid crystal phase is set to the operating temperature range of the liquid crystal module and an optical anisotropic element is manufactured so that the array can be controlled by an electric field or the like, the viewing angle characteristics can be voltage-controlled.

The retardation plate is formed by stacking retardation films (retardation films) having optical anisotropy by stretching a polymer film, twisted liquid crystal cells, and polymer liquid crystals. It can be realized by a twist-arranged thin film. In this case, for example, because it can be obtained by applying this polymer layer to at least one of the substrates of the driving liquid crystal cell, it is easy to manufacture,
A more desirable liquid crystal display device can be obtained. For example, it is possible to use, for example, a polymer copolymer having polysiloxane as the main chain and having biphenylbenzoate and cholesteryl groups in the side chains at an appropriate ratio.

The embodiments of the liquid crystal display device of the present invention will be further described below.

(Embodiment 1) FIGS. 9 and 10 are sectional views of a liquid crystal display device according to the present embodiment. The liquid crystal display element 10 includes two polarizing plates 1 and 4 (LLC2-92-18: manufactured by SANRITZ), and an optical anisotropic element 5 and 6 having a configuration of FIG. Further, the driving liquid crystal cell 3 is sandwiched. One optical anisotropic element 5 is a laminate of a hybrid orientation retardation plate 5b and a negative retardation plate 5a, and the other optical anisotropic element 6 is also a hybrid retardation plate 6b and a negative retardation plate. It is a laminated body of 6a. The polarizing plate 1 is provided by sandwiching the polarizing film 1b inside the transparent substrate 1a, and the polarizing plate 4 is also formed by similarly attaching the polarizing film 4b on the transparent substrate 4a.

The optical anisotropic element 5 includes a hybrid orientation retardation plate 5b and a negative retardation plate 5a, and a hybrid orientation retardation plate 5b is an optical anisotropic unit which is closest to the negative retardation plate 5a. The negative retardation plate 5a was placed so that its axes were substantially parallel to each other, and the negative retardation plate 5a was adjacent to the polarizing plate 1. The hybrid retardation plate has a Δnd of −120 nm, and the negative retardation plate has a Δnd of −80 nm. Further, another optically anisotropic element 6 having the same structure is arranged between the polarizing plate 4 and the liquid crystal display cell 3 with the hybrid alignment retardation plate 6b on the liquid crystal display cell 3 side.

The driving liquid crystal cell 3 disposed between the optical anisotropic elements 5 and 6 has two upper substrates 3a and 3b, and transparent electrodes 3c and 3d are formed on the respective substrates. It is connected to the driving power supply 3f. A chiral material S is formed on a twisted nematic liquid crystal having a positive dielectric anisotropy between the substrates 3a and 3b.
811 (made by E. Merck) mixed liquid crystal layer 3e
However, the twist angle is introduced at 90 degrees, and the state changes according to the voltage applied from the driving power supply 3f. The twisted arrangement is maintained when no voltage is applied.

The Δn of the liquid crystal used for the driving liquid crystal cell 3 is 0.09, and the thickness of the liquid crystal layer is 5 μm. The liquid crystal molecules of the driving liquid crystal cell 3 are twisted counterclockwise from the lower substrate 3b to the upper substrate 3a (left twist). This cell 3 has 90
It operates as a TN cell with a twist angle and controls light by the optical rotation effect.

FIG. 10 is an exploded perspective view showing the structure of the liquid crystal display element according to this embodiment. (1.1) and (4.1) are absorption axes of the two polarizing plates 1 and 4,
These are orthogonal to each other and (1.1) is arranged at 135 ° counterclockwise when viewed from the + z direction which is the normal direction of the substrate with respect to the y axis. (3.1) and (3.2) are rubbing axes of the upper substrate 3a and the lower substrate 3b of the driving liquid crystal cell 3, that is, the alignment treatment directions, which are orthogonal to each other and are rubbed with respect to the y axis (3. The angle formed with 1) is 45 ° counterclockwise when viewed from the + z direction. (5.1), (6.1)
Is the average optical axis of the two optical anisotropic elements 5 and 6,
(5.1) is arranged parallel to the rubbing axis (3.1) of the driving cell 3, and (6.1) is arranged parallel to (3.2). The polarizing plate 1 was arranged so that the transmission axis (1.1) was orthogonal to the rubbing axis (3.2) of the viewing angle compensating liquid crystal cell 2.

That is, in the present embodiment, the optical difference on the layer surface side of the phase difference plate of the hybrid orientation, that is, the first optical anisotropic layer, which is closest to the negative phase difference plate, that is, the second optical anisotropic layer. The optical anisotropic elements 5 and 6 in which the optical axis of the anisotropic unit is continuous with the optical axis of the negative retardation plate are combined with the liquid crystal cell 3. As a result, the hybrid retardation plate faces the liquid crystal cell 3.

The electro-optical characteristics of the liquid crystal display device having this structure were measured in the coordinate system shown in FIG. Voltage value during measurement (driving voltage 3
The voltage applied from f to the electrodes 3c-3d of the driving liquid crystal cell 3 was changed from 1V to 5V. The result is shown in FIG.
Shown in

FIG. 12 shows the applied voltage-transmittance characteristics in four directions of up, down, left and right, and shows the transmittance when the viewing angle is changed by 30 ° from the front to 60 °. The ideal is that the angle is the same as the transmittance curve at the front (viewing angle θ = 0 °). In the frontal direction, the transmissivity decreases with increasing voltage above a certain voltage.

As shown in FIG. 12, the characteristics in the lower position are almost unchanged, and the gradation display characteristics in the left-right direction and the upper direction are improved. In particular, compared with the case where the optical axis is discontinuous in the upward direction (FIG. 15 of Comparative Example 3), the improvement effect is large and good gradation display performance is obtained.

(Comparative Example 1) FIG. 13 shows a conventional TN-LCD in which the optically anisotropic layer is removed in the first embodiment.
FIG. 6 is a diagram of applied voltage-transmittance characteristic of FIG. The characteristic of the downward direction is that the transmittance decreases as the viewing angle increases. This corresponds to the occurrence of "blackout" when the gradation display is actually performed. Further, the re-increase of the transmittance in the vicinity of 3 V at the viewing angle of 60 ° corresponds to "reversal" in the actual display. Looking at the upper direction, the transmittance increases as the viewing angle increases from 0 ° to 60 ° at a voltage of 3V. This corresponds to "whiteout" in the actual display.

In this comparative example, depending on the angle, the display was white in the upper azimuth, and the display was black in the lower azimuth, and the gradation was reversed.

(Comparative Example 2) FIG. 14 is a comparative example in which only the retardation plate 20 of hybrid orientation is used without using the negative retardation plate 30. Compared with the conventional TN-LCD, the downward direction does not change, and the gray scale display characteristics in the left and right directions and the upward direction are improved, but it cannot be said that it is sufficient in the upward direction.

(Comparative Example 3) FIG. 15 shows a phase difference plate 40 of hybrid orientation as shown in FIG. 16 in which the optical axis 40L of the optical anisotropic unit closest to the negative phase difference plate is negative. 5
It is a comparative example of an optically anisotropic element which is discontinuous with the optical axis 50L of 0. Compared to the TN-LCD characteristics of the conventional technique shown in FIG. 13, the gray scale display characteristics in the left and right directions and the up direction are improved without changing in the down direction, but it cannot be said that the gray scale display characteristics in the up direction are sufficient.

(Embodiment 2) In Embodiment 1, a liquid crystal display element was produced under the same conditions except that the driving cell was twisted by 180 degrees and the thickness of the liquid crystal layer was 10 μm. When this liquid crystal display device was driven and the display quality was visually evaluated, good gradation display performance could be confirmed in all directions.

In the above embodiment, the present invention is applied to the optically active T.
Although the example applied to the N-type liquid crystal display element has been described, an element utilizing birefringence, an active matrix using an switching element such as TFT or MIM, and S
It goes without saying that even when applied to a simple matrix liquid crystal display device such as TN, excellent effects can be obtained.

[0076]

According to the present invention, it is possible to provide a high-quality liquid crystal display device having improved visibility and viewing angle characteristics of display color and excellent visibility.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating the configuration of the present invention,

FIG. 2 is a view for explaining the operation of the first embodiment of the present invention,
A schematic diagram showing the inclination of the optical axis when an optical anisotropic element is combined with a liquid crystal cell,

3A and 3B are diagrams for explaining the operation principle of a TN type liquid crystal display device,

FIG. 4 is a diagram for explaining the principle of occurrence of viewing angle characteristics of a TN type liquid crystal display element,

FIG. 5 is a diagram for explaining the principle of occurrence of viewing angle characteristics of a TN type liquid crystal display element,

FIG. 6 is a diagram showing an array state of optically anisotropic units of an optically anisotropic element,

FIG. 7 is a diagram illustrating an optical compensation principle for a liquid crystal cell when an optical anisotropic element is used,

FIG. 8 is a schematic diagram illustrating the operation of the present invention,

FIG. 9 is a cross-sectional view showing an embodiment of the present invention,

FIG. 10 is a view for explaining the operation of one embodiment of the present invention,

FIG. 11 is a diagram illustrating a coordinate system for measuring electro-optical characteristics,

FIG. 12 is a curve diagram showing transmittance characteristics in the vertical and horizontal directions according to the embodiment of the present invention;

FIG. 13 is a curve diagram showing the transmittance characteristics in the vertical and horizontal directions of Comparative Example 1,

FIG. 14 is a curve diagram showing the transmittance characteristics in the vertical and horizontal directions of Comparative Example 2;

FIG. 15 is a curve diagram showing the transmittance characteristics in the vertical and horizontal directions of Comparative Example 3;

16 is a schematic cross-sectional view illustrating the configuration of Comparative Example 3,

FIG. 17 is a curve diagram showing a viewing angle-luminance characteristic of the related art, showing (a) a horizontal direction and (b) a vertical direction.

[Explanation of symbols]

1, 4: Polarizer 3: Driving liquid crystal cell 3L: Long axis of liquid crystal molecule 5, 6: Optical anisotropic element 20: Hybrid arrangement retardation plate (first optically anisotropic layer) 2a: Optical anisotropic Characteristic unit 2L: optical axis 30: negative retardation plate (second optically anisotropic layer) 30L: optical axis

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Hato 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company Toshiba Yokohama office

Claims (16)

[Claims] 1. At least one polarizer, a driving liquid crystal cell having a liquid crystal layer sandwiched between two substrates, and a polarizing liquid crystal cell disposed between the polarizer and the driving liquid crystal cell and having a negative optical anisotropy. The first optical anisotropic layer in which the optical axis continuously changes from the direction substantially perpendicular to the layer surface to the direction substantially parallel to the layer thickness direction and the optical anisotropy is a negative sign. Is disposed adjacent to a second optically anisotropic layer that is substantially perpendicular to the layer surface, and the layer side that forms an optical axis that is substantially perpendicular to the first optically anisotropic layer is the second optical anisotropic layer. A liquid crystal display device comprising an optically anisotropic element adjacent to the anisotropic layer. 2. The average optical axis of the driving liquid crystal cell and the average optical axis synthesized from the first optically anisotropic layer and the second optically anisotropic layer are substantially parallel to each other. Claim 1
Liquid crystal display device described in 3. The liquid crystal display element according to claim 1, wherein the display system of the driving liquid crystal cell is an optical rotation mode. 4. The liquid crystal display device according to claim 1, wherein the driving liquid crystal cell has a display system of a birefringence mode. 5. The first optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal, wherein
Alternatively, the liquid crystal display element described in 2. 6. The liquid crystal display device according to claim 1, wherein the first optically anisotropic layer comprises a liquid crystal cell. 7. The second optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal, and
Alternatively, the liquid crystal display element described in 2. 8. The method according to claim 1, wherein the first optically anisotropic layer is formed inside the driving liquid crystal cell.
3. The liquid crystal display device according to item 1. 9. The liquid crystal display element according to claim 8, wherein the second optically anisotropic layer is formed inside the driving liquid crystal cell. 10. The liquid crystal display element according to claim 1, wherein the first optically anisotropic layer side of the optically anisotropic element is disposed on the liquid crystal layer side. 11. The two optically anisotropic elements sandwich the driving liquid crystal cell, and the first optically anisotropic layer of the two optically anisotropic elements is arranged facing the driving liquid crystal cell side. The liquid crystal display device according to claim 1, wherein 12. The liquid crystal display device according to claim 11, wherein the two polarizers sandwich the two optically anisotropic elements and the driving liquid crystal cell. 13. An optical anisotropy is a negative sign, and the optical axis is continuously changed in the thickness axis direction of the layer within a plane consisting of the thickness axis and an axis in the direction of the layer surface, and the optical axis is the same as the layer surface. A first optical anisotropic layer having an optical axis substantially perpendicular to the layer surface and the optical axis being substantially parallel to the layer surface on the other layer surface, and an optical anisotropy having a negative sign and substantially perpendicular to the layer surface. The second optical anisotropic layer is disposed adjacent to the second optical anisotropic layer, and the optical axis of the first optical anisotropic layer closest to the second optical anisotropic layer and the second optical anisotropy. An optical anisotropic element characterized in that the optical axes of the layers are substantially parallel. 14. The optical anisotropic element according to claim 13, wherein the first optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal. 15. The optically anisotropic element according to claim 13, wherein the first optically anisotropic layer comprises a liquid crystal cell. 16. The optical anisotropic element according to claim 13, wherein the second optically anisotropic layer is made of an organic material, an inorganic material or a polymer liquid crystal.