JPH1124066A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the driving voltage of the liquid crystal display device and to improve the field angle dependency. SOLUTION: The liquid crystal, display device is assembled by using a couple of upper and lower substrates 1 and 2 which are joined together across a specific gap. Polarizing plates 6 and 7 are arranged while joined to the substrates 1 and 2. Optical compensating plates 8 and 9 are interposed between the polarizing plates 6 and 7 and a liquid crystal layer 5, and compensate their field angle dependency of their optical characteristics. The liquid crystal layer 5 is formed of liquid crystal molecule having positive uniaxiality and positive dielectric anisotropy, and is arranged in the prescribed oriented direction when no voltage is applied nearly in parallel to the substrates 1 and 2. The layer 5, on the other hand, is arranged so that the tolting angle is continuously varies to the normals of the substrates 1, 2 when voltage applied. The optical compensating plates 8, 9 are composed of birefringent materials having negative uniaxiality and the tilt angles of their optical axes vary continuously to the normals of the substrates 1 and 2 along the thickness. The tilt directions of the optical axes deviate from the orientation direction of the liquid crystal 5 within a range of <=10 deg.. The optical compensating plate 8 is formed of a laminate of the birefringent material 8a and a base film 8b. The base film 8b has biaxiality or positive uniaxiality along the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a technology for improving a viewing angle of a liquid crystal display device and a technology for reducing a driving voltage.

[0002]

2. Description of the Related Art The principle of operation of a liquid crystal display device using a twisted nematic liquid crystal (TN mode) will be briefly described with reference to FIG. (A) shows a state where no signal voltage is applied, and (B) shows a state where a signal voltage is applied. The TN mode is most widely used among various operation modes because a display having characteristics such as low voltage, low power consumption, and long life can be created. A TN mode liquid crystal cell basically has a long axis of liquid crystal molecules sandwiching a nematic liquid crystal 205 having positive dielectric anisotropy between two glass substrates 203 and 204 on which transparent electrodes 201 and 202 are formed. Are aligned parallel to the glass substrate surface and continuously twisted by 90 ° between the upper and lower substrates, that is, twisted. In the state where no signal voltage is applied as shown in FIG. 3A, the linearly polarized light incident through the polarizing plate 206 changes its polarization direction by 90 ° due to the optical rotation of the liquid crystal cell, and exits from the liquid crystal cell. As shown in (B), when a sufficiently high signal voltage equal to or higher than the threshold is applied, the major axis of the liquid crystal molecules changes direction in the electric field, and the optical rotation of the liquid crystal cell almost disappears along the electrode surface. . In the illustrated structure, two polarizing plates 206,
207 is arranged such that the polarization axis coincides with the alignment direction of the liquid crystal molecules on the incident light side. When no signal voltage is applied, the light whose polarization direction has been changed by 90 ° becomes opaque because it is orthogonal to the polarization axis of the polarizing plate 207 on the emission side. When the signal voltage is applied, the polarization direction of the light does not change, so that the light passes through the output side polarizing plate 207 and becomes transparent. If the polarization axes of the upper and lower polarizing plates 206 and 207 are changed from parallel to orthogonal (crossed Nicols), the above-described light and dark state (black and white state) can be reversed, and a so-called normally white mode can be obtained.

[0003]

Since the above-mentioned TN mode uses a nematic liquid crystal which is twist-oriented, there is a viewing angle dependency such that a display color and a display contrast change depending on a viewing direction in principle of a display method. C
It does not exceed the display performance of RT. In order to solve this problem, a structure using an optical compensator has been proposed, which is disclosed in, for example, JP-A-6-214116. In this conventional example, an optical compensator having negative uniaxiality and having a structure in which the tilt direction of the optical axis with respect to the substrate normal is continuously changed is used. Hereinafter, the principle of the optical compensation will be briefly described. Generally, a nematic liquid crystal is a birefringent material having a positive uniaxial property. That is, the extraordinary light refractive index is larger than the ordinary light refractive index. The contrast changes depending on the viewing angle due to the birefringence, and the viewing angle dependence peculiar to the liquid crystal cell occurs. To compensate for this viewing angle dependence, a birefringent material having the same optical axis, the same refractive index anisotropy, and a negative uniaxiality is required. This birefringent material is joined to a liquid crystal cell as an optical compensator to improve the viewing angle dependency.

FIG. 13A shows birefringence due to liquid crystal, and FIG. 13B shows birefringence due to an optical compensator.
A liquid crystal having positive uniaxiality is represented by a refractive index ellipsoid whose major axis coincides with the optical axis. The optical axis substantially coincides with the normal direction of the substrate. When the refractive index in the optical axis direction is represented by nz, and the refractive index in the direction perpendicular to the optical axis is represented by nx and ny, nx = ny <n
z. As shown in (1), when light is incident parallel to the optical axis, no birefringence occurs. As shown in (2), when the light is obliquely incident, birefringence occurs. However, when the incident angle is small, the birefringence is also small. As shown in (3), the birefringence increases as the oblique incident angle increases.

On the other hand, as shown in FIG. 1B, an optical compensator having negative uniaxiality is represented by a refractive index ellipsoid whose minor axis coincides with the optical axis. Also in the optical compensator, the optical axis is set substantially perpendicular to the substrate normal. The optical compensator has a relationship of nx = ny> nz since it has negative uniaxiality. No birefringence occurs when light is incident parallel to the optical axis as shown in (1).
As shown in (2), when the oblique incident angle is relatively small, the birefringence is also small. As shown in (3), the birefringence increases as the oblique incident angle increases.

Incidentally, the TN in the normally white mode
In the case of a liquid crystal cell, the long axis (director) of the liquid crystal molecules is substantially aligned with the substrate in a black display state. But,
In practice, the director distribution of the liquid crystal molecules is not perfectly vertical alignment (homeotropic alignment), and the director is inclined from the normal direction closer to the substrate as shown in FIG. Therefore, to improve the viewing angle dependence of the liquid crystal,
The optical compensator also needs a structure in which the optical axis is continuously inclined with respect to the substrate normal. In FIG. 14, a state in which the optical axis of the optical compensator gradually changes is schematically represented by three refractive index ellipsoids. Similarly, the state in which the optical axis of the liquid crystal cell gradually changes is represented by six refractive index ellipsoids. The upper half of the liquid crystal cell is compensated by the upper optical compensator. The optical axis of the first refractive index ellipsoid from below the optical compensator and the optical axis of the first refractive index ellipsoid from above the liquid crystal cell correspond to each other, canceling out the birefringence. Similarly, the second refractive index ellipsoid from the bottom of the optical compensator corresponds to the second refractive index ellipse from the top of the liquid crystal cell, and the third refractive index ellipse from the bottom of the optical compensator and the liquid crystal cell And the third index ellipsoid from the top corresponds to each other.

By the way, as shown in FIG. 14, when the optical axis of the optical compensator having negative uniaxiality is continuously inclined along the normal direction of the substrate, the light incident on the substrate in a perpendicular direction is generally used. Also exhibits a birefringence effect. However, in a normal setting of the optical axis tilt type optical compensator, as shown in FIG. 15, the tilt direction of the optical axis of the optical compensator is arranged parallel or orthogonal to the absorption axis of the corresponding polarizing plate. For example, in the example of FIG. 15, the upper polarizing plate absorption axis is parallel to the tilt direction of the optical axis of the upper optical compensator. Similarly, the tilt direction of the absorption axis of the lower polarizing plate and the optical axis of the lower optical compensator are parallel.
The absorption axis of the upper polarizing plate is orthogonal to the absorption axis of the lower polarizing plate. Accordingly, the orientation of the upper substrate and the orientation of the lower substrate are orthogonal to each other, and the twist angle is 9 °.
0 °. With such a setting, the birefringence effect does not occur for the light beam that is perpendicularly incident on the substrate. Because of this,
Although the conventional optical compensator is effective in improving the viewing angle dependency, it has no effect on the contrast when viewed from the front. If the contrast increases, the image quality does not matter even if the drive voltage is reduced accordingly. In a liquid crystal display device, a reduction in drive voltage is strongly desired in the market. In particular, in a plasma address type liquid crystal display device using a plasma cell for addressing a liquid crystal cell, it is strongly desired to reduce the liquid crystal driving voltage due to restrictions on the withstand voltage of the driving circuit. To this end, approaches have been made based on the physical property values of liquid crystal materials, but the limit has been reached. Further, if the thickness of the liquid crystal layer is increased, the driving voltage can be reduced, but the viewing angle characteristic is contradictoryly deteriorated.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the liquid crystal display device according to the present invention has, as a basic configuration, a pair of substrates joined to each other via a predetermined gap and having at least one electrode formed thereon, and a pair of electrodes held in the gap and applied to the electrodes. A liquid crystal layer whose optical characteristics change according to the applied voltage, a polarizing plate bonded to each substrate, and an optical compensator interposed between each polarizing plate and the liquid crystal layer and compensating for viewing angle dependence of the optical characteristics. It has. The liquid crystal layer is composed of liquid crystal molecules having a positive uniaxial property and a positive dielectric anisotropy, and is oriented substantially parallel to the substrate along a predetermined orientation when no voltage is applied, while being perpendicular to the substrate when voltage is applied. On the other hand, they are aligned with the inclination angle continuously changed. The optical compensator is made of a birefringent material having negative uniaxiality, and has a structure in which the inclination angle of the optical axis changes continuously along the thickness direction with respect to the normal line of the substrate. As a characteristic feature, the tilt direction of the optical axis deviates from the alignment direction of the adjacent liquid crystal layer within a range of 10 ° or less. Preferably, the birefringent material changes continuously along the thickness direction in the range of 10 ° to 75 ° in the inclination angle of the optical axis. Preferably, the birefringent material has a retardation value represented by the product of refractive index anisotropy and thickness of 50 nm or more and 25 nm or more.
It is in the range of 0 nm or less.

According to another aspect of the present invention, the optical compensator comprises a laminate of the birefringent material and a base film.
The base film has a biaxial property or a positive uniaxial property in a plane direction. In the base film, the direction in which the refractive index becomes maximum is perpendicular to the absorption axis of the adjacent polarizing plate.
In the base film, when the refractive index in the direction in which the refractive index is maximized is nx, the refractive index in the direction perpendicular to this is ny, and the thickness is d, the value of (nx−ny) · d is larger than 0. Smaller than 150 nm.

In the setting of a normal optical axis tilt type optical compensator,
The tilt direction is made parallel to the absorption axis of the polarizing plate and thus to the orientation direction of the substrate. For this reason, the birefringence effect does not occur for light that is perpendicularly incident on the substrate. In the first aspect of the present invention, the birefringence effect is generated by shifting the optical axis inclination direction of the uniaxial optical compensator from the substrate orientation direction. Thereby, the retardation of the liquid crystal apparently changes downward, and as a result, the driving voltage of the liquid crystal cell can be reduced. According to the second aspect of the present invention, a material having biaxiality or positive uniaxiality in a plane direction is used for the base film constituting the optical compensator. By making the direction in which the refractive index of the base film becomes maximum perpendicular to the absorption axis of the adjacent polarizing plate, the viewing angle dependency of the polarizing plate can be compensated. By utilizing the birefringence of the base film, the vibration direction of the incident light can be adjusted to the absorption axis of the polarizing plate. As described above, in the present invention, the low voltage driving of the liquid crystal cell and the improvement of the viewing angle dependency of the polarizing plate are simultaneously achieved by using the optical compensator.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1A schematically shows a cross-sectional structure of a liquid crystal display device according to the present invention, and FIG. 1B schematically shows a planar configuration. As shown in the drawing, the present liquid crystal display device is assembled using a pair of upper and lower substrates 1 and 2 joined to each other with a predetermined gap therebetween. The electrode 3 is formed on the inner surface of the substrate 1. The electrode 4 is also formed on the inner surface of the substrate 2. A liquid crystal layer 5 is held in the gap between the two substrates 1 and 2, and the optical characteristics change according to the voltage applied to the upper and lower electrodes 3 and 4. A polarizing plate 6 is bonded to the upper substrate 1 and a polarizing plate 7 is also bonded to the lower substrate 2. An optical compensator 8 is interposed between the upper polarizer 6 and the liquid crystal layer 5 to compensate for the viewing angle dependence of the optical characteristics of the liquid crystal layer 5. Similarly, an optical compensator 9 is also interposed between the lower polarizer 7 and the liquid crystal layer 5 to compensate for the viewing angle dependence of the optical characteristics of the liquid crystal layer 5. The liquid crystal layer 5 is composed of liquid crystal molecules having positive uniaxiality and positive dielectric anisotropy, and the operation is as described with reference to FIG. That is, when no voltage is applied, the liquid crystal molecules move along the predetermined orientation in the directions of the substrates 1 and 2.
Are oriented almost in parallel. When a voltage is applied, the liquid crystal molecules are aligned with the tilt angle continuously changed with respect to the normal to the substrates 1 and 2. On the other hand, each of the optical compensators 8 and 9 is made of a birefringent material having negative uniaxiality. It has a structure in which the inclination angle of the optical axis changes continuously along the thickness direction with respect to the normal line of the substrate. This is as described with reference to FIG. As a characteristic feature, the tilt direction of each of the optical compensators 8 and 9 deviates from the alignment direction of the adjacent liquid crystal layer 5 within a range of 10 ° or less. Preferably, the birefringent material changes continuously along the thickness direction in the range of 10 ° to 75 ° in the inclination angle of the optical axis. Preferably, the birefringent material has a retardation value represented by a product of refractive index anisotropy and thickness in a range of 50 nm or more and 250 nm or less. As another feature, the optical compensator 8 is formed by laminating the above-described birefringent material 8a and the base film 8b. Similarly, the optical compensator 9 is also formed by laminating a birefringent material 9a and a base film 9b. Each of the base films 8b and 9b has a biaxial property or a positive uniaxial property in a plane direction. The upper base film 8b has a relationship in which the azimuth at which the refractive index becomes maximum is orthogonal to the absorption axis of the adjacent polarizing plate 6. Similarly, the lower base film 9b also has a relationship in which the azimuth at which the refractive index becomes maximum is orthogonal to the absorption axis of the adjacent polarizing plate 7. In each of the base films 8b and 9b, the refractive index in the azimuth at which the refractive index becomes maximum is nx, and the refractive index in the azimuth perpendicular to this is n
Assuming that y is y and the thickness is d, the value of (nx−ny) · d is larger than 0 and smaller than 150 nm. In this liquid crystal display device, a light diffusing plate 10 is added to one substrate 1 side.

As shown in FIG. 1B, the inclination direction of the optical axis of the upper optical compensator 8 is 1 degree from the orientation direction of the upper substrate 1.
It is shifted within a range of 0 °. Similarly, the inclination azimuth of the optical axis of the lower optical compensator 9 is 1 degree from the orientation azimuth of the lower substrate 2.
It is shifted within a range of 0 °. Note that the orientation direction of the upper substrate 1 and the orientation direction of the lower substrate 2 are orthogonal to each other, and the twist angle of the liquid crystal layer 5 is exactly 90 °. Upper polarizer 6
Is coincident with the orientation direction of the upper substrate 1. Similarly, the absorption axis of the lower polarizing plate 7 matches the orientation direction of the lower substrate 2. Therefore, the pair of upper and lower polarizing plates 6 and 7 are arranged in crossed Nicols. As described above, when the inclination directions of the optical axes of the optical compensators 8 and 9 are shifted from the orientation directions of the substrates 1 and 2, that is, the absorption axes of the polarizers 6 and 7, the transmittance / application of light vertically incident on the substrates The voltage characteristics change, and low-voltage driving becomes possible. As another feature of the present invention, as described above, birefringent materials having biaxiality or positive uniaxiality are used as the base films 8b and 9b of the optical compensators 8 and 9 respectively. Generally, since the polarizing plates 6 and 7 have their own viewing angle dependence, contrast at a large viewing angle is reduced. In order to compensate for this, the configuration of the base film described above is effective. At this time, as shown in (B), it is necessary that the maximum azimuth of the refractive index of the upper base film 8b and the absorption axis of the upper polarizer 6 are orthogonal to each other. Similarly, it is necessary that the maximum azimuth of the refractive index of the lower base film 9b and the absorption axis of the lower polarizing plate 7 are orthogonal to each other. With this arrangement, the base film of the optical compensator can adjust the vibration direction of the obliquely incident light to the absorption axis of the corresponding polarizer, thereby compensating the viewing angle dependence of the polarizer to some extent. .

The refractive index anisotropy Δn of the liquid crystal layer 5 is 0.067.
If the thickness d is 6.3 μm, the value of the retardation Δn · d of the liquid crystal layer 5 is 420 nm. On the other hand, the value of Δn · d of the birefringent material 8a constituting the optical compensator 8 is, for example, 160 nm. Similarly, the lower optical compensator 9
The value of Δn · d of the birefringent material 9a constituting
It is. Further, when the base film 8b constituting the optical compensator 8 has biaxiality, ｛(nx + ny) / 2−n
The value of z｝ · d is, for example, 50 nm. The value of the base film 9a constituting the lower optical compensator 9 is also 50 nm. In this case, the total retardation value of the two optical compensators 8 and 9 is (160 + 50) × 2 = 420, and
The retardation value of the liquid crystal layer 5 is equal to 420 nm,
The desired viewing angle dependence compensation is performed. Generally, it is preferable that the retardation value of the birefringent material 8a constituting the optical compensator 8 be set in a range of 50 nm or more and 250 nm or less. The value of the retardation is optimally set according to the value of the retardation of the liquid crystal layer 5. on the other hand,
The value of (nx-ny) · d of the biaxial base film 8b is set to 80 nm. With this setting, the viewing angle dependence of the polarizing plate 6 can be compensated. Similarly, (nx-ny) · d of the lower base film 9b
Is also set to 80 nm, and the viewing angle dependency of the lower polarizing plate 7 can be compensated. In general, (nx-
If the value of (ny) · d is set smaller than 150 nm, a desired compensation effect can be obtained. If the value becomes larger than this,
Conversely, adverse effects occur.

FIG. 2 is a graph showing an applied voltage / transmittance characteristic of the liquid crystal display device. A shows the applied voltage / transmittance characteristics of the conventional liquid crystal display device, and B shows the applied voltage / transmittance characteristics of the liquid crystal display device according to the present invention shown in FIG.
As is clear from the graph, when the tilt direction of the optical axis of the optical compensator is shifted from the absorption axis of the polarizing plate according to the present invention, the applied voltage / transmittance characteristic changes downward, and low voltage driving is possible. . In addition, the graph of FIG. 2 measures the applied voltage / transmittance characteristic with respect to the light perpendicularly incident on the substrate. In this comparison, measurement was performed using a plasma addressed liquid crystal display device as a sample. The tilt direction of the optical axis of the optical compensator is shifted by 5 ° from the absorption axis of the polarizing plate. The voltage of black display is lower than the normal setting.

FIG. 3A is a graph showing the relationship between retardation Δn · d and transmittance T in a liquid crystal display device. Compared with the conventional retardation indicated by A, the retardation of the present invention indicated by B changes downward.
Accordingly, the transmittance T also slightly changes downward. As described above, by slightly shifting the tilt direction of the optical axis of the optical compensator from the absorption axis of the polarizing plate, the retardation value of the liquid crystal apparently decreases. (2) is a graph showing the relationship between the applied voltage V and the transmittance T of the liquid crystal display device. A conventional characteristic is indicated by a curve A, and a characteristic of the present invention is indicated by B. (1)
As described above, in the present invention, since the transmittance T is slightly lowered, the applied voltage / transmittance characteristic changes downward. As a result, the applied voltage at the time of black display is effectively reduced, and low voltage driving can be achieved.

FIG. 4 schematically shows the director distribution of liquid crystal molecules during black display. The horizontal axis of the graph represents the position in the thickness direction of the liquid crystal layer in units of optical distance nm,
The vertical axis shows the tilt angle of the director of the liquid crystal molecules. Note that the position in the thickness direction represents the distance in the thickness direction from the origin 0 near the center of the liquid crystal layer to the substrate side. As described above, when the drive voltage is reduced, the director distribution of the liquid crystal molecules changes. In the example shown in FIG.
It is distributed between 0 ° and 72 °. On the other hand, the inclination direction distribution of the optical axis of the conventional optical compensator does not match the curve LC as shown by A. Therefore, in the present invention, the inclination azimuth distribution of the optical axis of the optical compensator is adjusted as indicated by B, and the curve L
It almost matches C. In general, the birefringent material constituting the optical compensator changes continuously along the thickness direction in the range of 10 ° to 75 ° in the tilt angle of the optical axis in response to the low voltage driving of the liquid crystal display device. It can be set as follows.

FIG. 5 is a schematic view showing another embodiment of the liquid crystal display device according to the present invention. Parts corresponding to those of the previous embodiment shown in FIG. 1 are denoted by corresponding reference numerals to facilitate understanding. As shown in FIG. 1A, the present liquid crystal display device includes a transmissive panel 0, a directional backlight 20, and a light diffusing plate 10. The panel 0 has a configuration in which a pair of glass substrates are adhered to each other, and a liquid crystal is sealed in a gap between the two. A polarizing plate 6 is provided on the front side of the upper glass substrate.
And an optical compensator 8. Another polarizing plate 7 and another optical compensator 9 are also arranged on the rear side of the lower glass substrate. The upper and lower glass substrates have a refractive index of, for example, about 1.53. The directional backlight 20 is arranged on the rear surface side of the panel 0 and makes the illumination light nearly parallel to the liquid crystal panel 0 incident thereon. In this example, the backlight 20 includes a light source 21 and a prism sheet 22. The light source 21 is composed of a flat fluorescent tube or the like and emits non-directional light. The prism sheet 22 refracts the non-directional light emitted from the light source 21,
It is converted to almost parallel light. The prism sheet 22 performs collimation of the light from the light source, and allows the illumination light substantially perpendicular to the liquid crystal panel 0 to be entirely incident.

The light diffusing plate 10 is disposed on the front side, and diffuses and emits illumination light transmitted through the panel 0. This light diffusion plate 10
Is composed of fine particles 10a and filler 10b.
The fine particles 10 a are spread between the front surface of the panel 0 and the optical compensator 8. The filler 10b is transparent and fills the gap between the fine particles 10a. The fine particles 10a have a refractive index different from that of the glass substrate constituting the front surface of the panel 0, while the filler 10b has a refractive index close to that of the glass substrate. For example, the fine particles 10a are made of transparent microbeads, have an average particle size of about 30 μm, and have a refractive index of 1.9.
3. This is significantly different from the refractive index of glass substrates of 1.53, and has excellent light scattering properties. on the other hand,
The transparent filler 10b is made of, for example, an ultraviolet curing resin, and has a refractive index of 1.55, which is almost equal to the refractive index of the glass substrate. After passing through the panel 0, the illumination light emitted from the directional backlight 20 is emitted in a form scattered by the fine particles 10a. The larger the refractive index of the fine particles 10a, the more the diffusion occurs and the wider the viewing angle. As described above, by using the combination of the directional backlight 20 and the light diffusing plate 10 in addition to the optical compensators 8 and 9 capable of improving the viewing angle characteristics, the viewing angle characteristics of the liquid crystal display device are further improved. be able to.

FIG. 2B is a schematic sectional view showing an example of the panel 0 shown in FIG. The panel 0 has a flat structure in which a liquid crystal cell 111, a plasma cell 112, and a common intermediate plate 113 made of a dielectric sheet interposed therebetween are stacked. The liquid crystal cell 111 is configured using a glass substrate 114 on the front side, and a plurality of signal electrodes 115 made of a transparent conductive film are formed in parallel on the inner main surface. Glass substrate 114 is spacer 1
16 and is adhered to the intermediate plate 113 via a predetermined gap. The gap is filled with liquid crystal 117. On the other hand, the plasma cell 112 is configured using a glass substrate 118 on the rear surface side. A plurality of plasma electrodes 119 orthogonal to the signal electrodes 115 are formed on the inner main surface of the glass substrate 118, and the anodes 120 and the cathodes 1 are alternately formed.
21 as a pair. Striped partition walls 122 are formed on the inner surface of the glass substrate 118 to partition each electrode pair. The top of the partition wall 122 is in contact with the intermediate plate 113. The glass substrate 118 is joined to the intermediate plate 113 using a frit seal 123. A hermetically sealed discharge channel 124 is formed between the two. The discharge channels 124 are divided by the partition walls 122 and individually serve as scanning units. An ionizable gas is sealed inside the discharge channel 124. The gas type can be selected from, for example, helium, neon, argon, or a mixed gas thereof. The discharge channel 124 forming each scanning unit and the signal electrode 115 forming the driving unit are orthogonal to each other, and a matrix pixel is defined at the intersection.

In the panel 0 having such a configuration, the discharge channel 124 where the plasma discharge is performed is switched line-sequentially for scanning, and an image signal is applied to the signal electrode 115 on the liquid crystal cell side in synchronization with this scanning. Display driving is performed. When a plasma discharge occurs in the discharge channel 124, the inside thereof becomes almost uniformly at the anode potential, and
Pixel selection for each line is performed. That is, discharge channel 1
24 functions as a sampling switch. When an image signal is applied to each pixel in a state where the plasma sampling switch is turned on, sampling is performed and lighting or extinguishing of the pixel can be controlled. Even after the plasma sampling switch is turned off, the image signal is held in the pixel as it is. In the plasma address type panel having such a configuration, a signal voltage is applied to the liquid crystal 117 via the intermediate plate 113. Therefore, the effective voltage applied to the liquid crystal 117 is determined by the capacitance ratio between the liquid crystal capacitance and the intermediate plate. For this reason, a larger driving voltage is required for a plasma addressed liquid crystal panel than for a normal liquid crystal panel. Therefore,
The reduction of the drive voltage using the optical compensator according to the present invention is as follows.
In particular, a great effect is obtained in the case of a plasma addressed liquid crystal panel.

FIG. 6 is a graph showing an equal contrast curve of the conventional plasma addressed display device. The right direction of the screen of the display device is set to 0 ° and the left direction is set to 180 °. For light in the incident direction inclined from the normal direction of the screen between the azimuths 0 ° and 360 °, the contrast ratio between when a voltage is applied and when no voltage is applied is plotted. The outer curve connects the points with a contrast ratio of 10,
The inner curve connects the points where the contrast ratio is 50. As is clear from the graph, the range of the contrast ratio 50 is considerably narrow.

FIG. 7 is a graph showing viewing angle / transmittance characteristics of a conventional plasma addressed liquid crystal display. (A) shows the viewing angle / transmittance characteristics cut along the horizontal direction of the screen. The horizontal axis shows the inclination angle from the substrate normal, and the vertical axis shows the transmittance. The applied voltage is used as a parameter. (B) is a graph showing viewing angle / transmittance characteristics of a conventional plasma addressed display device. (B) particularly shows the viewing angle / transmittance characteristics cut along the vertical direction of the screen.

FIG. 8 is a graph showing an equal contrast curve of the plasma addressed display device according to the present invention. That is,
The tilt direction of the optical axis of the optical compensator deviates from the alignment direction of the adjacent liquid crystal layer within a range of 5 °. FIGS. 9A and 9B show the viewing angle / transmittance characteristics measured along the horizontal and vertical directions of the screen, respectively. As is clear from comparison of the data of the present invention shown in FIGS. 8 and 9 with the conventional example shown in FIGS. 6 and 7, the viewing angle characteristic is improved in the present invention. However, the base film constituting the optical compensator uses a negative uniaxial material.

FIG. 10 shows an isocontrast curve when a positive uniaxial material or a biaxial material is used for the base film of the optical compensator. FIGS. 11A and 11B similarly show viewing angle / transmittance characteristics. As is clear from the comparison between the data of FIGS. 8 and 9 and the data of FIGS. 10 and 11, the use of a positive uniaxial material or a biaxial material as the base film of the optical compensator reduces the viewing angle characteristics. It has been further improved.

[0025]

As described above, according to the present invention,
The driving voltage can be reduced by shifting the tilt direction of the optical axis of the optical compensator from the alignment direction of the adjacent liquid crystal layer. Further, the viewing angle dependency of the polarizing plate can be compensated by using a birefringent material having biaxiality or positive uniaxiality in the plane direction as a base film of the optical compensator.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a graph showing an applied voltage / transmittance characteristic of a liquid crystal display device.

FIG. 3 is a graph showing retardation / transmittance characteristics and applied voltage / transmittance characteristics of a liquid crystal display device.

FIG. 4 is a graph showing a tilt angle distribution of liquid crystal molecules.

FIG. 5 is a sectional view showing another embodiment of the liquid crystal display device according to the present invention.

FIG. 6 is a graph showing an equal contrast curve of a conventional liquid crystal display device.

FIG. 7 is a graph showing viewing angle / transmittance characteristics of a conventional liquid crystal display device.

FIG. 8 is a graph showing an equal contrast curve of the liquid crystal display device according to the present invention.

FIG. 9 is a graph showing viewing angle / transmittance characteristics of the liquid crystal display device according to the present invention.

FIG. 10 is a graph showing an equal contrast curve of the liquid crystal display device according to the present invention.

FIG. 11 is a graph showing viewing angle / transmittance characteristics of the liquid crystal display device according to the present invention.

FIG. 12 is a schematic diagram illustrating an example of a conventional liquid crystal display device.

FIG. 13 is a schematic diagram showing birefringence by a liquid crystal and birefringence by an optical compensator.

FIG. 14 is a schematic view showing a configuration of a conventional optical compensator.

FIG. 15 is a plan view showing a configuration of a conventional liquid crystal display device.

[Explanation of symbols]

1 ... substrate, 2 ... substrate, 3 ... electrode, 4 ...
Electrodes, 5: Liquid crystal layer, 6: Polarizer, 7: Polarizer, 8: Optical compensator, 9: Optical compensator, 10
..Light diffusion plates

Claims (7)

[Claims] 1. A pair of substrates joined to each other via a predetermined gap and having at least one electrode formed thereon, and a liquid crystal held in the gap and having optical characteristics changed according to a voltage applied to the electrode. A liquid crystal display device comprising a layer, a polarizing plate bonded to each substrate, and an optical compensator interposed between each polarizing plate and the liquid crystal layer and compensating for viewing angle dependence of optical characteristics of the liquid crystal display device. The layer is composed of liquid crystal molecules having a positive uniaxial property and a positive dielectric anisotropy, and is oriented substantially parallel to the substrate along a predetermined orientation when no voltage is applied, while being perpendicular to the substrate normal when voltage is applied. The optical compensator is made of a birefringent material having negative uniaxiality, and the tilt angle of the optical axis is continuously changed in the thickness direction with respect to the normal line of the substrate. Along the optical axis and the tilt direction of the optical axis is adjacent The liquid crystal display device, characterized in that the alignment direction of the crystal layer are offset in the range of 10 ° or less. 2. The liquid crystal display device according to claim 1, wherein the birefringent material has its optical axis continuously changing along the thickness direction within a range of 10 to 75 °. . 3. The liquid crystal display device according to claim 1, wherein the birefringent material has a retardation value represented by a product of a refractive index anisotropy and a thickness in a range of 50 nm or more and 250 nm or less. . 4. The optical compensator according to claim 1, wherein the optical compensator comprises a laminate of the birefringent material and a base film, and the base film has a biaxial property or a positive uniaxial property in a plane direction. Liquid crystal display. 5. The liquid crystal display device according to claim 4, wherein the orientation in which the refractive index of the base film is maximized is perpendicular to the absorption axis of an adjacent polarizing plate. 6. In the base film, assuming that the refractive index in the direction in which the refractive index is the maximum is nx, the refractive index in the direction perpendicular to the refractive index is ny, and the thickness is d, (nx−ny) ·
6. The liquid crystal display device according to claim 5, wherein the value of d is larger than 0 and smaller than 150 nm. 7. The liquid crystal display device according to claim 1, wherein a light diffusion plate is added to one of the substrates.