JPH04322224A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element which improved in visual characteristic and has excellent visibility. CONSTITUTION:The liquid crystal display element provided with two sheets of substrates having electrodes, a liquid crystal cell 3 for driving consisting of a liquid crystal which is crimped between these substrates and is twist- oriented at the time of non-impression of voltages, polarizing plates 1, 4 crimping this liquid crystal cell and a liquid crystal cell 2 for compensation having a liquid having a liquid crystal layer for compensation which is twist-oriented at the spiral axis nearly parallel with the normal of the above-mentioned substrates is so constituted that the average refractive index (n) and spiral pitch (p) of liquid crystal of the above-mentioned liquid crystal cell for compensation is 750nm<n.p or n.p<320 and that the retardation value RC of the liquid crystal cell for compensation is 2.(RLC-n.lambda)+m.lambda<¦RC¦<m.lambda at the time of n.lambda<RLC<n.lambda+lambda/2 and 2.(RLC-(1/2+n).lambda)+m.lambda<¦RC¦<lambda+m.lambda at the time of n.lambda+lambda/2<RLC<(n+1) when the effective retardation value of the liquid crystal cell for driving is designated as RLC, lambda as the wavelength of light and (n), (m) as integers.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which contrast ratio and viewing angle dependence of displayed colors are controlled.

0003

2. Description of the Related Art In recent years, liquid crystal display devices, which have the great advantages of being thin, lightweight, and low power consumption, have been actively used as display devices for personal office automation equipment such as Japanese word processors and desktop personal computers. Most liquid crystal display elements (hereinafter abbreviated as LCD) use twisted nematic liquid crystal, and the display method is as follows:
It can be roughly divided into two modes: birefringence mode and optical rotation mode.

[0004] LCDs with a birefringence mode display method using twisted nematic liquid crystals generally have a molecular arrangement twisted by more than 90 degrees (called the ST method) and have steep electro-optic characteristics, so switching is performed for each pixel. Even without any elements (thin film transistors or diodes), a large capacity display can be easily obtained by time-division driving even with a simple matrix-like electrode structure. However, since the ST method uses the birefringence effect, the display colors are yellow and dark blue (so-called yellow mode display) and white and blue (so-called blue mode display) due to light interference, resulting in black-and-white display and color display. It was impossible to display. It was reported in Japanese Patent Publication No. 63-53528 that as a means to eliminate such discoloration of the display, a black and white display could be achieved by placing a second liquid crystal cell twisted in the opposite direction between the polarizing plate and the liquid crystal cell. ing.

The principle of this black-and-white conversion is that the ordinary light component and the extraordinary light component, which have become elliptically polarized light in a display liquid crystal cell in which liquid crystal molecules are arranged in a twisted arrangement, are mutually exchanged by a second liquid crystal cell, which is an optical compensator. , and the elliptically polarized light is converted to linearly polarized light. As a result, coloring caused by light interference is eliminated, and black and white display can be realized. In order to convert elliptically polarized light into linearly polarized light as described above, the optical compensator must be arranged so that the retardation value is almost the same as that of the display liquid crystal cell, and the twist directions are opposite. The desired light conversion effect cannot be obtained unless the orientation directions of the liquid crystal molecules closest to each other are perpendicular to each other.

On the other hand, optically rotating mode LCDs have a molecular arrangement twisted at 90° and have a fast response time (several tens of milliseconds), exhibiting a high contrast ratio and good gradation display properties, and are therefore used in watches, calculators, and even other devices. Full-color LCD TVs that have a switching element for each pixel and are combined with color filters (TFT-LCD and MIM-LCD)
It is applied to.

Regarding color display, a CN liquid crystal cell that exhibits a certain hue using selective scattering when no voltage is applied is placed between a polarizing plate and a liquid crystal cell, and a combination of the CN liquid crystal cell and the presence or absence of voltage application to the liquid crystal cell Mol. Cryst. Liq. Cryst. ，
1977, VOL. 39, PP. 127-138.

However, since these liquid crystal display devices that utilize birefringence mode, optical rotation mode, or selective scattering use twisted nematic liquid crystals, they suffer from viewing angle dependence in which the displayed color and contrast ratio change depending on the viewing angle and direction. However, it has not reached the point where it completely exceeds the display performance of CRT.

[0009]

It is generally known that liquid crystal molecules have different refractive indices in the major axis direction and the minor axis direction of the liquid crystal molecules. When polarized light enters a liquid crystal molecule exhibiting such anisotropy of refractive index, the polarization state of the polarized light changes depending on the angle of the liquid crystal molecule. The molecular arrangement of a twisted nematic liquid crystal cell has a structure in which the arrangement of liquid crystal molecules is twisted in the thickness direction of the liquid crystal cell, but the light that passes through the liquid crystal cell is transmitted through each of the liquid crystal molecules in this twisted arrangement. The light propagates while being sequentially polarized depending on the orientation of the liquid crystal molecules. Therefore, the polarization state of the light propagating through the liquid crystal cell is different depending on whether the light is incident perpendicularly to the liquid crystal cell or obliquely, and as a result, the display may vary depending on the direction or angle when viewing the liquid crystal display element. This appears as a phenomenon in which the displayed pattern appears reversed or the displayed pattern becomes completely invisible, which is undesirable from a practical standpoint.

The present invention solves the above-mentioned disadvantages.

[Configuration of the invention]

0012

[Means for Solving the Problems] The present invention provides a driving device that includes two polarizing plates and, between them, a liquid crystal that is sandwiched between two substrates having electrodes and arranged in a twisted manner when no voltage is applied. In a liquid crystal display element in which a liquid crystal cell for compensation and a liquid crystal cell for compensation including a liquid crystal arranged in a twisted arrangement with a helical axis substantially parallel to the normal line of the substrate of the liquid crystal cell for drive is arranged, the average of the liquid crystal of the liquid crystal for compensation cell is arranged. When the refractive index is n and the helical pitch is p, the product n・p is 750 nm<n・p or n・p<320 nm, and the retardation value R of the compensation liquid crystal cell is
C is the effective retardation value of the driving liquid crystal cell RL
When C and λ are optical wavelengths, when n・λ< RLC <n・λ+λ/2,
2・(RLC−n・λ)+m・λ < |RC
| <m・λn・λ+λ/2 < RLC <
When (n+1)・λ, 2・(RLC−(1/2
+n)・λ)+m・λ < |RC | <λ
+m・λ (n=0, ±1, ±2, ±3... integer) (m=
0, ±1, ±2, ±3...).

[0013]

[Operation] Generally, LCD using twisted nematic liquid crystal
There are two main types of arrangement of polarizing plates used in liquid crystal cells: a normally closed method in which light does not pass through when no voltage is applied to the liquid crystal cell, and a state in which light is transmitted when a voltage is applied; There is a normally open method in which light is transmitted when no voltage is applied to the liquid crystal cell, and light is blocked when voltage is applied.

FIG. 3 is a diagram showing contrast ratio dependence when the display surface is tilted from 0° to 60° from the normal to the left and right in the normally open and normally closed conventional TN systems. In the case of Mary Open (10.0
), and the normally closed case is indicated by (11.0). Comparing these, it can be seen that the contrast ratio is less dependent on viewing angle in the normally closed mode than in the normally open mode. The contrast ratio is a value obtained by dividing the brightness in a state where light is transmitted (bright state) by the brightness in a state in which light is blocked (dark state), and the contrast ratio greatly affects the brightness in the dark state. Therefore, when we measured the visual angle dependence of the brightness in the dark state in both the normally open and normally closed systems in the horizontal direction, we obtained the characteristics shown in FIG. 4. In the normally open case (10
．． The normally closed case in 1) is shown in (11.1). As is clear from the figure, the viewing angle dependence of the dark state is smaller in the normally closed mode than in the normally open mode, and as a result, the viewing angle characteristics of the contrast ratio are better in the normally closed mode than in the normally open mode.

Considering the difference between the normally open and normally closed dark states, in the normally open case a voltage is applied to the liquid crystal cell to block light, and in the normally closed case a voltage is applied to the liquid crystal cell to block light. A voltage is applied to the liquid crystal cell to transmit light. When calculating the molecular arrangement state when a voltage value that provides a dark state is applied to the liquid crystal cell in the normally open case, the state of molecular arrangement is shown in FIG. 5. Here, 7 and 8 in the figure are tilts, respectively.
angle and twist angle, and the tilt angle is defined as the long axis (5.
1L), and the twist angle is the tilt angle of liquid crystal molecules (5L).
．． 1) Axis (5.1xy) projected from the z-axis to the xy plane
This is the angle between the x-axis and the x-axis.

[0016] When a voltage is applied, the liquid crystal molecules are tilted by nearly 90° near the center of the liquid crystal cell, but near the upper and lower substrate surfaces, the liquid crystal molecules are not tilted much due to the influence of the alignment regulating force of the substrate surfaces. . Further, the twist angle has an S-shaped distribution.

When the tilt angle of the liquid crystal molecules is constant in the cell thickness direction and the twist angle is linearly twisted, that is, when compared with the molecular arrangement state in the dark state in the normally closed case, the molecular arrangement state when voltage is applied is appears differently depending on the viewing angle and orientation of the liquid crystal cell, and as a result, differences in the appearance of the liquid crystal molecule arrangement state result in differences in the polarization state propagating through the liquid crystal cell, which is reflected in the viewing angle characteristics. Therefore, the reason why the viewing angle characteristics are better in the normally closed mode is that the difference in the appearance of the molecular arrangement state in the dark state depending on the viewing direction angle is smaller than in the normally open mode. Therefore, if some method can be devised so that the same molecular arrangement state can be seen from any direction, the viewing angle characteristics in the normally open dark state can be improved.

The place where the appearance of liquid crystal molecules changes the most depending on the viewing angle in the liquid crystal cell is at a location near the center of the liquid crystal cell where the liquid crystal molecules are largely tilted. Therefore, the viewing angle characteristics can be improved by reducing the change in appearance at this location.

The alignment state of liquid crystal can be simply represented by a three-dimensional refractive index ellipsoid. Figure 7 shows a state where liquid crystal molecules stand vertically using a refractive index ellipsoid. Since it is a phenomenon related to differences,
The refractive index body (6.4) in the two-dimensional plane when viewed from the z direction (that is, when the liquid crystal cell is viewed from the front) is a circle, and when viewed from the refractive index difference and the visual axis (6.1) It is different from the refractive index body (6.5). In the case of normally open (crossed Nicols), the refractive index difference when viewed from the z direction is 0.
Therefore, a dark state is obtained, but the two-dimensional surface when viewed from the visual axis (6.1) becomes an ellipse, resulting in a difference in refractive index, so a dark state is not obtained.

As the angle (6.3) at which the refractive index ellipsoid 6 is viewed increases, the ellipse (6.5) in the two-dimensional plane seen from the visual axis (6.1) increases in the length direction of n61. Therefore, more transmitted light is observed than when viewed from the visual axis (6.1). Therefore, in order to optically compensate for such a refractive index ellipsoid, as the angle (6.3) at which the refractive index ellipsoid is viewed increases, the refractive index in the longitudinal direction of n62 increases. , and an ellipse in a two-dimensional plane (6.5)
The visual axis (6.1
) If placed above, the index ellipsoid 6 can be optically compensated for.

Such optical compensation can be achieved by arranging a disk-shaped index ellipsoid on the liquid crystal cell as shown in FIG. The refractive index becomes substantially the same, and viewing angle characteristics are improved.

A refractive index ellipsoid as shown in FIG. 8 has so-called negative optical anisotropy, and cholesteric liquid crystal is used in this configuration.

Cholesteric liquid crystals were discovered in 1889 by Reinitzer. Cholesteric liquid crystal has a spirally twisted arrangement of liquid crystal molecules, and while ordinary liquid crystals have positive optical anisotropy, cholesteric liquid crystal has a negative optical anisotropy due to the spirally twisted arrangement. Show your gender.

When the wavelength of light is sufficiently larger than the helical pitch, the principal refractive indices no and ne of the cholesteric liquid crystal are given by the following equations.

[0025] no = [1/2・(E2 +D2)]1/2

(1.1) ne = D

(1.2
) E: refractive index D in the long axis direction of liquid crystal molecules
: Refractive index in the short axis direction of the liquid crystal molecule Even in the case of cholesteric liquid crystal, E>D, so Δn=ne-no
<0 (negative). Therefore, desired optical compensation can be obtained by combining a cholesteric liquid crystal cell under certain conditions with a driving liquid crystal cell.

The optical properties of cholesteric liquid crystals have been investigated in detail by J.L. Ferguson (J.L. Ferguson, Mole
cular Crystals. 1, 293 (1966
)), selective scattering occurs when light enters a cholesteric liquid crystal cell at a certain angle, and the wavelength λ indicating the maximum value of selective scattering at that time is given by the following equation.

λ=n・p・[cos{(1/2)・{sin−
1 (1/n・sin φi)+sin-1(1/n・s
in φs)}}]

…
(2.1) p: Helical pitch n: Average refractive index φi: Incident angle of light φs: Scattering angle of light In the above equation, when the wavelength λ that indicates the maximum value of selective scattering enters the visible range, a coloring phenomenon occurs and is displayed. Because of the color change, λ must be removed from the visible wavelength range. Here (2-
1) If the formula is λ=n·p·f(θ), then f(θ) takes the minimum value at θ=0. Therefore, n of the compensation liquid crystal cell
- The conditions for p are 750 nm<n.p, n.p<320 nm.

By the way, the transmitted light intensity I of the birefringence mode observed under crossed Nicols can be expressed by the following equation from the conditions of interference between ordinary light and extraordinary light. I== A・sin2 (π・R/λ)

...(3) Here, when no voltage is applied to the driving liquid crystal cell, R = Δn・d

...(4) A: proportionality constant Δn: refractive index anisotropy of liquid crystal d: thickness of liquid crystal layer λ: light source wavelength R is the birefringence Δn of the material through which light passes by an amount called retardation and the thickness d of the medium It is the product of That is, it shows the phase difference between ordinary light and extraordinary light. When a voltage is applied to a liquid crystal cell with positive dielectric anisotropy that is twisted horizontally to the substrate, the liquid crystal molecules are tilted with respect to the substrate, and the effective retardation value of the liquid crystal cell becomes small. For example, n
When voltage is applied to the liquid crystal cell with e = 1.5 and no = 1.4, the effective retardation value of the liquid crystal cell is shown in Figure 9.
Changes as shown in . Optical compensation changes the above R, so the retardation value of the compensation liquid crystal cell is R.
C. Letting RLC be the effective retardation value of the driving liquid crystal cell when the maximum voltage is applied during display, the R value after optical compensation is as follows.

R=RLC+RC

...(5) In the above equation (3), if R = 0 in any viewing angle direction, that is, RC = -RLC, then I = 0, which improves the characteristics in the dark state and improves the performance in a wide viewing angle range. This leads to high contrast. Equation (3) is illustrated in FIG. 10. Visual characteristics are improved by making the transmitted light intensity I after compensation smaller than the transmitted light intensity ILC before optical compensation. Therefore, the value of R is divided into two cases depending on the value of RLC, and R
The range of is as shown in the formula below.

[0030]n・λ<RLC<n・λ+λ/2
When 2・(RLC−n・λ)+m・λ <
|RC | <m・λn・λ+λ/2 <
When RLC < (n+1)・λ, 2・(RL
C-(1/2 +n)・λ)+m・λ < |RC
| <λ+m・λ
(n=0, ±1, ±2
, ±3…)
(m=
0, ±1, ±2, ±3…)


...(6) becomes. Therefore, the retardation value RC of the compensation liquid crystal cell depends on the effective retardation value RLC of the driving liquid crystal cell. Further, as described above, from equations (1.1) and (1.2), the retardation RC of the compensation liquid crystal cell is given by the following equation.

RC=Δnc・dc=(ne−
no) ・dc = (D-1/2 ・(E2 +D2)1/2
)・dcE: The refractive index in the long axis direction of the liquid crystal molecules used in the compensation liquid crystal cell D: The refractive index in the short axis direction of the liquid crystal molecules used in the compensation liquid crystal cell dc: The thickness or more of the liquid crystal layer of the compensation liquid crystal cell Although the explanation has been made by taking a TN liquid crystal cell as an example, similar effects can be obtained not only in the TN type but also in the ST type and the LCD in a display type with a small twist angle of 90° or less.

[0032]

EXAMPLES Examples of the liquid crystal display element of the present invention will be described in detail below.

(Embodiment 1) FIGS. 1 and 2 show cell configurations in this embodiment. The liquid crystal display element includes two polarizing plates 1,
4, and a compensating liquid crystal cell 2 and a driving liquid crystal cell 3 are sandwiched therebetween. Polarizing plate 1 is transparent substrate 1a
A polarizing film 1b is attached to the inside of the transparent substrate 4a, and the polarizing plate 4 is similarly formed by attaching a polarizing film 4b to a transparent substrate 4a. Also, the light transmission axes (1.1), (4.1) of these polarizing plates 1 and 4
are arranged so that they are perpendicular to each other.

The compensating liquid crystal cell 2 consists of these polarizing plates 1 and 4.
It has a liquid crystal cell structure in which a liquid crystal 2c is interposed between transparent substrates 2a and 2b.

The driving liquid crystal cell 3 is arranged between the compensation liquid crystal cell 2 and the polarizing plate 4. The upper substrate 3a and the lower substrate 3b form transparent electrodes 3c and 3d, respectively, and are connected to a drive power source 3f. A twisted nematic liquid crystal is introduced between the substrates 3a and 3b with a twist angle of 90 degrees, and its state changes depending on the voltage applied from the drive power source 3f.

The optical axis of the liquid crystal of the driving liquid crystal cell 3 is twisted counterclockwise from the lower substrate 3b to the upper substrate 3a (
left-handed twist). (3.1) and (3.2) are the rubbing axes of the upper and lower substrates, respectively, and these are perpendicular to each other. The retardation value of the driving liquid crystal cell 3 is 450 nm
, the effective retardation value RLC when 5V is applied is 150 nm. The compensation liquid crystal cell 2 has an average refractive index n of 1.5, a helical pitch p of 0.56 μm (n·p=840 nm), and a retardation value RC of -200 nm (2.1), ( 2.2) are the rubbing axes of the upper and lower substrates 2a and 2b, respectively, and these are orthogonal to each other.

The transmission axis (1.1) of the polarizing plate 1 and the rubbing axes (2.1), (3.1) of the upper substrate are parallel, and the transmission axis (4.1) of the polarizing plate 4 and the rubbing axes (2.1), (3.1) of the upper substrate are parallel. Rubbing shaft (2
．． 2) and (3.2) are parallel. The dark state of the liquid crystal display element of this configuration (5V between the drive power supply 3f and the liquid crystal cell electrode)
An example of the visual angle dependence in the X-axis direction and the Y-axis direction (at the time of application) is shown in FIGS. 11 and 12, together with a conventional example.

FIG. 11 is a diagram showing the transmittance of the liquid crystal cell in the dark state when the measurement point is tilted from 0° to 60° in the x and -x directions from the z-axis of the liquid crystal cell in FIG. is Figure 2
FIG. 12 is a characteristic diagram similar to FIG. 11 in the y and −y directions of FIG. (11.1) and (12.1) show the viewing angle characteristics in this embodiment, and (11.2) and (12.2) show the viewing angle characteristics in the conventional example. Ideally, it would be desirable for the transmittance to be small and to remain constant no matter what angle the liquid crystal cell is viewed from. Compared to the conventional example, the change in the tilt angle of transmittance in this example is smaller in the -y direction, y direction, and -x direction, and a TFT-LCD with a diagonal screen size of 10 inches was created with this configuration. When displaying gradations, we were able to create a high-contrast LCD that can distinguish between 16 gradations even when the viewpoint changes. When viewing angle characteristics of the contrast ratio were measured, a contrast ratio of 45:1 or more was obtained at a 60° cone, and a good display was obtained without inversion of the display image or change in display color even at an incident angle of 60° or more.

(Comparative Example) The viewing angle characteristics of the liquid crystal display element in Example 1 in which the compensation liquid crystal cell 2 was not disposed between the driving liquid crystal cell 3 and the upper and lower polarizing plates 1 and 4 were measured. The measurement results are shown in Figures 11 and 12 (11.2) and (12.2).
) is shown. The dark state changes depending on the viewing angle, and the maximum contrast ratio is only 5:1 with a 60° cone.
When the angle of incidence exceeded 60 degrees, the displayed image was either reversed or completely invisible depending on the viewing direction.

(Example 2) In Example 1, a polymer liquid crystal was used as the compensating liquid crystal cell 2, and the cells were arranged in the same manner as in Example 1. When the electro-optical characteristics were measured, the same characteristics as in Example 1 were obtained, and the T
When an FT-LCD was created with this configuration and displayed 16 gradations, a high-contrast LCD that could distinguish between the 16 gradations even when the viewpoint was changed was realized. When viewing angle characteristics were measured, a contrast ratio of 47:1 or more was obtained at a 60° cone, and good display was obtained without inversion of the display image or change in display color even at an incident angle of 60° or more.

(Example 3) In order to be normally closed in Example 1, the transmission axis (4.1) of the polarizing plate 4 is arranged to be parallel to the transmission axis (1.1) of the polarizing plate 1. did. With this configuration, a 10-inch TFT-LCD was created and 16
When displaying gradations, we were able to create a high-contrast LCD that can distinguish between 16 gradations even when the viewpoint changes. When viewing angle characteristics were measured, a contrast ratio of 50:1 or more was obtained at a 60° cone, and good display was obtained without inversion of the display image or change in display color even at an incident angle of 60° or more.

(Embodiment 4) FIG. 13 shows a cell configuration in this embodiment. 1 and 4 are polarizing plates (1.1), and the viewing angle direction (4.1) corresponds to the transmission axis of the polarizing plate. 3 is
This is a liquid crystal cell with a twist angle of 90°, which is equipped with a transparent electrode that applies voltage to the liquid crystal layer, and is twisted counterclockwise from the lower substrate to the upper substrate (left-handed twist). (3.1), (3
．． 2) are the rubbing axes of the upper and lower substrates, respectively, which are orthogonal to each other. The retardation value of the driving liquid crystal cell 3 is 450 nm, and the effective retardation value RLC when 5V is applied is 130 nm. 2 and 5 are
In the compensation liquid crystal cell, the average refractive index n of the liquid crystal is 1.
5, the helical pitch p is 0.58 μm (n・p=870 nm
), and the retardation value RC is -150 nm. (2.1) and (2.2) are the rubbing axes of the lower substrate, and (5.1) and (5.2) are the rubbing axes of the upper substrate, which are orthogonal to each other.

The transmission axis (1.1) and the rubbing axes (2.1), (3.1), (5.1) of the upper substrate are parallel, and the transmission axis (4.1) and the rubbing axis of the lower substrate axis (2.2),
(3.2) and (5.2) are parallel.

[0044] Actual TFT with diagonal screen size of 10 inches
-When an LCD was created with this configuration and displayed 16 gradations,
We have achieved a high-contrast LCD that can distinguish between 16 gray levels even when changing the viewpoint. When viewing angle characteristics were measured, a contrast ratio of 40:1 or more was obtained at a 60° cone, and good display was obtained without inversion of the display image or change in display color even at an incident angle of 60° or more.

(Example 5) In order to be normally closed in Example 4, the transmission axis (4.1) of polarizing plate 4 is arranged to be parallel to the transmission axis (1.1) of polarizing plate 1. did. This configuration is a TFT-LC with a diagonal screen size of 10 inches.
When we created D and displayed it in 16 gradations, we found that it was a high-contrast LCD that could distinguish between the 16 gradations even when changing the viewpoint.
was realized. When viewing angle characteristics were measured, a contrast ratio of 40:1 or more was obtained with a 60° cone, and an incident angle of 60:1 was obtained.
Good display without inversion of the display image or change in display color was obtained even at 0° or more.

(Embodiment 6) FIG. 14 shows a cell configuration in this embodiment. 1 and 4 are polarizing plates (1.1), and the viewing angle direction (4.1) corresponds to the absorption axis of the polarizing plate. 3 is
This is a liquid crystal cell with a twist angle of 240°, which is equipped with transparent electrodes that apply voltage to the liquid crystal layer, and is twisted counterclockwise from the lower substrate to the upper substrate (left-handed twist). (3.1), (
3.2) are the rubbing axes of the upper and lower substrates, respectively, and the angle between these axes is 120°. The retardation value of the driving liquid crystal cell 3 is 860 nm, and the effective retardation value RLC during multiplex driving is 200 nm.

The compensation liquid crystal cell 2 has an average refractive index n of 1.5.
So, the helical pitch p is 0.56 μm (n・p=840 nm
), the retardation value RC is a liquid crystal cell of -250 nm, and (2.1) and (2.2) are the rubbing axes of the upper and lower substrates, respectively, which are orthogonal to each other.

The transmission axis (1.1) of polarizing plate 1 is 110° counterclockwise from the y-axis, and the transmission axis (4.1) of polarizing plate 4 is 110° counterclockwise from the y-axis.
It is 90 degrees counterclockwise from the axis.

[0049] When a 640 x 400 dot super twist type LCD was created using this configuration and 16 gray scales were displayed using the frame thinning method at a duty of 1/200, the contrast was high enough to distinguish between the 16 gray scales even when the viewpoint was changed. We were able to realize a LCD that When viewing angle characteristics were measured, 6
A contrast ratio of 7:1 or more was obtained with a 0° cone, and a good display was obtained without inversion of the display image or change in display color even at an incident angle of 60° or more.

[0050]

According to the present invention, the viewing angle characteristics of the liquid crystal display element are improved, and it is possible to provide a liquid crystal display element with high quality display and excellent visibility. Furthermore, it goes without saying that excellent effects can be obtained even when the present invention is applied to active matrix liquid crystal display elements using three-terminal or two-terminal elements such as TFTs and MIMs.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a liquid crystal display element of Example 1 of the present invention.

FIG. 2 is an exploded perspective view showing the configuration of a liquid crystal display element according to Example 1 of the present invention.

FIG. 3 is a diagram illustrating the viewing angle characteristics of the contrast ratio of the normally open and normally closed systems in the horizontal direction of a conventional TN type liquid crystal display element.

FIG. 4 is a diagram illustrating viewing angle characteristics of brightness in a dark state in a normally open and normally closed mode in the left and right direction of a conventional TN type liquid crystal display element.

FIG. 5 is a diagram showing the molecular arrangement in the thickness direction of the liquid crystal cell when a voltage is applied to the liquid crystal cell.

FIG. 6 is a diagram showing a coordinate system of the tilt angle and twist angle of the liquid crystal molecules in FIG. 5;

FIG. 7 is a diagram showing a three-dimensional refractive index ellipsoid in which liquid crystal molecules stand.

8 is a diagram illustrating a refractive index ellipsoid that optically compensates for the refractive index ellipsoid in FIG. 7. FIG.

FIG. 9 is a diagram illustrating the voltage dependence of the effective retardation value of a driving liquid crystal cell.

FIG. 10 is a diagram showing retardation value R vs. transmitted light intensity characteristics according to equation (3).

FIG. 11 is a diagram illustrating viewing angle characteristics in a dark state according to an embodiment of the present invention and a conventional example.

FIG. 12 is a diagram illustrating viewing angle characteristics in a dark state according to an embodiment of the present invention and a conventional example.

FIG. 13 is an exploded perspective view showing the configuration of a liquid crystal display element according to Example 4 of the present invention.

FIG. 14 is an exploded perspective view showing the configuration of a liquid crystal display element according to Example 6 of the present invention.

[Explanation of symbols]

1, 4...Polarizing plate 2...Compensation liquid crystal cell 3...Drive liquid crystal cell

Claims (1)

[Claims] 1. A driving liquid crystal cell comprising two polarizing plates, and a liquid crystal sandwiched between two substrates having electrodes between them and having a twisted arrangement when no voltage is applied, and the driving liquid crystal. In a liquid crystal display element in which a compensating liquid crystal cell including a liquid crystal arranged in a twisted manner with a helical axis substantially parallel to the normal line of the substrate of the cell is arranged, the average refractive index of the liquid crystal of the compensating liquid crystal cell is defined as n and the helical pitch. If p is the product n・p
is 750nm<n・p or n・p<320nm, and the retardation value R of the compensation liquid crystal cell
C is the effective retardation value of the driving liquid crystal cell RL
If C and λ are optical wavelengths, and n and m are integers, then n・λ<
When RLC <n・λ+λ/2, 2・(RL
C-n・λ)+m・λ < |RC | <m・
λn・λ+λ/2 < RLC <(n+1)・
When λ, 2・(RLC−(1/2 +n)・λ
)+m・λ < |RC | <λ+m・λ.