JP2819602B2 - Liquid crystal display device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display element suitable for high-density display.

[Prior art] Conventionally, as a method of increasing the twist angle of liquid crystal molecules between both electrodes to cause a sharp voltage-transmittance change and display a high-density dot matrix, a super twist element (TJ Scheffer and J. J. Nehring, Appl., Phys., Lett. 45
(10) 1021-1023 (1984)).

However, in this method, the value of the product Δn · d of the birefringent plate Δn of the liquid crystal of the liquid crystal display element used and the thickness d of the liquid crystal layer is substantially between 0.8 and 1.2 μm. 10720
No.), good contrast was obtained only with a combination of specific hues such as yellow-green and dark blue, and blue-violet and pale yellow as display colors.

As described above, since the liquid crystal display element cannot perform black-and-white display, there is a disadvantage that multicolor or full-color display cannot be performed in combination with a micro color filter.

On the other hand, there has been proposed a method in which a display substantially close to white and black can be obtained by using a similar method and setting the product Δn · d of the birefringence and the thickness of the liquid crystal as small as about 0.6 μm. (M. Schadt et al, Appl. Phys. Lett. 50 (5), 198
However, in the case of using this method, the display is dark, the maximum contrast is not so large, and the image is bluish.

In addition, as a liquid crystal display device having a black-and-white display and a high contrast, a method is used in which two layers of liquid crystal cells having mutually opposite spirals are stacked, a voltage is applied to only one cell, and the other cell is simply used as an optical compensator. Proposed. (Okumura et al., The Institute of Television Engineers of Japan, 11 (27), p.79, (19
87)) However, in this method, the matching of Δn · d in a two-layer cell is very severe, and it is difficult to improve the yield. In addition, since two liquid crystal cells are required, the thin and light liquid crystal cell is sacrificed. There were drawbacks.

[Problems to be Solved by the Invention] In the conventional method, it is difficult to produce a liquid crystal display device having a high brightness and a good black-and-white degree with a high yield.

The bright black-and-white display element is not only easy to see without a distinctive coloration, but also has a color filter formed inside or outside the cell, which was realized by a conventional 90 ° twisted nematic (TN) element. It can realize a mono-color, multi-color or full-color display, and is thin, light and has low power consumption.
The market is expected to expand dramatically.

For this reason, there has been a demand for a liquid crystal display element which is a bright black-and-white display element having good contrast and which can be produced with high yield.

Means for Solving the Problems The present invention has been made to solve the above-mentioned problems, and has an optical rotation pinched between a pair of substrates having a pair of transparent electrodes, which are arranged substantially in parallel and have an orientation control film. Twist angle of 160 due to nematic liquid crystal with positive dielectric anisotropy containing conductive material
A liquid crystal display element having a liquid crystal layer of about 300 ° and driving means for applying a voltage between the transparent electrodes of the upper and lower substrates sandwiching the liquid crystal layer, and a pair of polarizing plates provided outside the liquid crystal layer. , the product [Delta] n ₁ · d ₁ between the thickness d ₁ of the refractive index anisotropy [Delta] n ₁ and the liquid crystal layer of the liquid crystal in the liquid crystal layer is a 0.4 to 1.5 .mu.m, almost identical to the one between the liquid crystal layer and the polarizing plate Δn ₂・ d ₂ and the total Δn ₂・ d ₂ is 0.7 × Δn ₁・ d ₁ <Δn ₂・ d ₂ <1.1 × Δn ₁・
Two uniaxial birefringent plates of d ₁ were arranged, and the optical axis direction of the upper (polarizing plate side) birefringent plate viewed from the major axis direction of the liquid crystal molecules above the liquid crystal layer was measured clockwise. Θ ₂₁ , and the optical axis direction of the birefringent plate on the lower side (liquid crystal layer side) viewed from the long axis direction of the liquid crystal molecules on the upper side of the liquid crystal layer is measured clockwise as θ.
_{Assuming 22} , 40 ° ≦ θ ₂₁ ≦ 200 ° and 40 ° ≦ θ ₂₂ ≦ 1
An object of the present invention is to provide a liquid crystal display device characterized by satisfying 40 ° and θ ₂₂ ≦ θ ₂₁ .

In the present invention, two uniaxial birefringent plates are arranged on one side of the liquid crystal layer and between the liquid crystal layer and the polarizing plate.

For this reason, only one liquid crystal layer is required, which reduces productivity,
A bright black-and-white liquid crystal display element can be easily obtained without providing a second liquid crystal layer that easily causes color unevenness.

This liquid crystal layer is a liquid crystal layer having the same configuration as the liquid crystal layer of the conventional super-twisted liquid crystal display element, and the electrode groups are opposed to each other, whereby the on / off of each dot can be controlled. The twist angle of this liquid crystal layer is about 160 to 300 °.

Specifically, a nematic liquid crystal having a positive dielectric anisotropy containing a rotatory substance is sandwiched between a pair of transparent electrode substrates arranged substantially in parallel, and the twist angle of liquid crystal molecules between the two electrodes is determined.
The angle may be set to 160 to 300 °. This is because there is little improvement in contrast when performing time-division driving at high data that requires a sharp change in transmittance below 160 °, and conversely, when it exceeds 300 °, hysteresis and light scattering domains occur. This is because it is easy.

The product Δn ₁ · d ₁ of the refractive index anisotropy (Δn ₁ ) of the liquid crystal of the liquid crystal layer and the thickness (d ₁ ) of the liquid crystal layer is set to 0.4 to 1.5 μm.

This is because when it is less than 0.4 μm, the transmittance at the time of ON is low,
This is because the display color tends to have a bluish tint, and when it exceeds 1.5 μm, the hue at the time of on changes from yellow to red, and it is difficult to display black and white.

In particular, in applications in which achromatic display colors are strictly required, Δn ₁ · d ₁ of the liquid crystal layer is preferably 0.5 to 1.0 μm.

It is preferable that the range of Δn ₁ · d ₁ is satisfied within the operating temperature range of the liquid crystal display element, and a beautiful display is obtained within the operating temperature range. However, due to other performance requirements, only in part of the operating temperature range,
It may be possible to satisfy this relationship. In this case, in a temperature range in which the range of Δn ₁ · d ₁ is out of the above range, the display is colored or the viewing angle characteristics are deteriorated.

ITO (In ₂ O ₃ -SnO) patterned to the desired pattern
₂ ) A film of polyimide, polyamide or the like is provided on the surface of a plastic or glass substrate provided with a transparent electrode such as SnO ₂ or the like, and the alignment control film is formed by rubbing the surface or obliquely depositing SiO or the like. A substrate with the formed transparent electrode is prepared, and a liquid crystal layer having a twist of 160 to 300 ° made of a nematic liquid crystal having a positive dielectric anisotropy is sandwiched between the substrates with the transparent electrode. As a typical example, there is a dot matrix liquid crystal display element in which a large number of matrix-shaped electrodes are formed, and 640 stripe-shaped electrodes are formed on one substrate, and the other substrate is formed so as to be orthogonal thereto. 400 striped electrodes are formed on the
The display is like a dot. Furthermore, these 640 stripe-shaped electrodes can be set as a set of three to form 1920 stripe-shaped electrodes, and RGB color filters can be arranged to display 640 × 400 dots in full color.

In addition, an insulating film such as TiO ₂ , SiO ₂ , Al ₂ O ₃ is provided between the electrode and the orientation control film to prevent a short circuit between the substrates, or a low-resistance lead such as Al, Cr, Ti is provided on the transparent electrode. If you add electrodes,
A color filter may be laminated on or under the electrode.

A pair of polarizing plates is arranged on both outer sides of the liquid crystal layer. It is general that the polarizing plate itself is also arranged outside the substrate constituting the cell, but if performance permits, the substrate itself may be formed of a polarizing plate or provided as a polarizing layer between the substrate and the electrode. Is also good.

In the present invention, two birefringent plates are stacked adjacent to one surface of the liquid crystal layer. The birefringent plate may be provided on one side of the liquid crystal layer between the liquid crystal layer and the polarizing plate.For example, the birefringent plate may be provided in a layer between the liquid crystal layer and the electrode, a layer between the electrode and the substrate, A polarizing plate that is itself a birefringent plate, provided in a layered manner between a substrate and a polarizing plate, or laminated and integrated with a polarizing plate and a birefringent plate so that the birefringent plate is on the liquid crystal layer side. They may be used or provided in combination.

As the birefringent plate, any uniaxial transparent plate showing birefringence can be used, and a plastic film, an inorganic crystal plate, or the like can be used. In order to obtain a desired birefringence effect, Δn ₂ · d ₂ is used after being adjusted.

In order to perform good black-and-white display, the size of Δn ₂・ d ₂ of the uniaxial birefringent plate and the optical axis of the liquid crystal layer having a specific twist angle and Δn ₁・ d ₁ It is important to optimize the direction and the direction of the polarization axis of the pair of polarizing plates.

The size of the total Δn ₂・ d ₂ of the birefringent plates arranged on one side is approximately equal to the size of the Δn ₁・ d ₁ of the liquid crystal layer, or good black and white if it is set slightly smaller than that. Easy to get indication. That is, the total Δn ₂ · d ₂ of the _two birefringent plates is 0.7 ×
Δn ₁ · d ₁ <Δn ₂ · d ₂ <1.1 × Δn ₁ · d ₁

When the total Δn ₂・ d ₂ of the birefringent plate is smaller than 0.7 × Δn ₁・ d ₁ , the transmittance at the on is lowered, the display becomes darker, and conversely, larger than 1.1 × Δn ₁・ d ₁ When this happens, the transmittance in the off state increases, and the contrast ratio decreases, so that the above range is set.

Specifically, when two birefringent plates are stacked and used, the magnitude of Δn ₂ · d ₂ is almost equal, so that the magnitude is approximately half of the magnitude of Δn ₁ · d ₁ of the liquid crystal layer. Set equal or slightly less than half.

It is said.

Further, the birefringent plate has a high main refractive index in a specific direction in the plane,
Since the main refractive index in the plane and the direction perpendicular thereto is low, and the main refractive index in the direction perpendicular to the plane is almost the same as the lower main refractive index in the plane, the optical axis is high. Direction with the rate.

 Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a perspective view schematically showing a liquid crystal display device according to the present invention. FIGS. 2 (A) and 2 (B) show the polarization axis direction of the upper polarizing plate, the optical axis direction of the two birefringent plates, and the long axis of the liquid crystal molecules above the liquid crystal layer, respectively, as viewed from above. FIG. 3 is a plan view showing directions, a polarization axis direction of a lower polarizing plate, and a relative position in a major axis direction of liquid crystal molecules below a liquid crystal layer.

In FIG. 1, reference numerals 1 and 2 denote a pair of polarizing plates, and 3 denotes a twist angle of a nematic liquid crystal having a Δn ₁ · d ₁ of 0.4 to 1.5 μm and a positive dielectric anisotropy of 160 to 1.5 for displaying characters and figures. 300 °
Liquid crystal layer, 4A and 4B are two birefringent plates laminated on the liquid crystal layer, 5 is the polarization axis of the upper polarizing plate, 6 is the polarization axis of the lower polarizing plate, and 7 is the upper side of the liquid crystal layer. The long axis direction of the liquid crystal molecules, 8 is the long axis direction of the liquid crystal molecules below the liquid crystal layer, 9A is the optical axis direction of the upper birefringent plate laminated, and 9B is the direction of the lower birefringent plate laminated. The optical axis direction is shown.

In FIG. 2, the direction of the polarization axis 5 of the upper polarizer viewed clockwise from the major axis direction 7 of the liquid crystal molecules above the liquid crystal layer is θ ₁ , and the major axis of the liquid crystal molecules above the liquid crystal layer. Optical axis direction 9A of birefringent plate 4A on the upper side (polarizer side) viewed from direction 7
Is measured clockwise to θ ₂₁ , and the lower (liquid crystal layer side) birefringent plate 4B as viewed from the major axis direction 7 of the liquid crystal molecules above the liquid crystal layer.
Is the optical axis direction 9B measured clockwise, θ ₂₂ , and the clockwise direction of the polarization axis 6 of the lower polarizing plate viewed from the major axis direction 8 of the liquid crystal molecules below the liquid crystal layer is θ22. and θ _3.

In the present invention, θ ₁ , θ ₂₁ , θ ₂₂ , and θ ₃ may be optimized so as to provide a monochrome display.

When the liquid crystal display element of the present invention is used in a negative display, for example, the twist angle of the liquid crystal layer is set to about 240 °, Δn ₁ · d _{1 is set} to about 0.8 μm, and two uniaxial axes arranged on one surface thereof are used. When Δn ₂ · d ₂ of each of the birefringent plates is about 0.4 μm, it is preferable that the polarizing axes of the pair of polarizing plates are arranged so as to intersect at an angle of about 60 to 120 °.

When the same liquid crystal layer and a uniaxial birefringent plate are used and the display is used in a positive type display, the polarizing axes of the pair of polarizing plates should be arranged so as to intersect at an angle of about ± 30 °. Is preferred. As a result, this liquid crystal display device can perform monochrome display with excellent viewing angle characteristics and high contrast.

In this case, especially for the negative display, 60 ° ≦ θ ₂₁ ≦ 18
0 °, 50 ° ≦ θ ₂₂ ≦ 130 °, and θ ₂₂ ≦ θ ₂₁ is preferable because a display having a sufficient contrast with a low OFF transmittance and a high ON transmittance can be realized.

Further, similarly for the positive display, 40 ° ≦ θ ₂₁ ≦ 20
0 °, 40 ° ≦ θ ₂₂ ≦ 140 °, and θ ₂₂ ≦ θ ₂₁ is preferable because a sufficient contrast ratio can be obtained.

Further, in the above example, the liquid crystal layer is a left helix. However, even when the helix is reversed, that is, in the case of a right helix, the major axis direction of the liquid crystal molecules of the liquid crystal layer, the direction of the polarization axis of the polarizing plate, and the optical axis of the birefringent plate. The relationship with the direction θ ₁ , θ ₂₁ , θ ₂₂ , θ ₃ is made counterclockwise,
By appropriately selecting the same range, a black-and-white display can be easily obtained as in the case of the left spiral.

In the present invention, the crossing angle between the polarization axes of the pair of polarizing plates is set to approximately 90.
When the angle is set to ± 30 °, a negative type display is obtained. When the angle is set to 0 ° ± 30 °, a positive type display is obtained. However, a negative type display provided with a backlight is preferable in appearance.

In the present invention, since a display similar to a black and white display is obtained, a colorful display can be achieved by using a color filter in combination. In particular, since a high contrast ratio can be obtained even in high-duty driving, full-color gradation display is possible, and the liquid crystal television can be used.

By forming the color filter on the inner surface of the cell, a more accurate color display can be achieved without causing a shift due to a viewing angle. Specifically, it may be formed below the electrode, or may be formed above the electrode.

If it is necessary to make the color more completely black and white, use a color filter for color correction, a color polarizer, add a dye to the liquid crystal, or adjust the specific wavelength distribution. May be used.

According to the present invention, the liquid crystal cell having such a configuration is connected to driving means for applying a voltage to the electrode, and is driven.

In particular, in the present invention, since a bright display is possible, the present invention is applicable to both a transmission type and a reflection type, and its application range is wide.

When the transmission type is used, a light source is arranged on the back side. Of course, a light guide, a color filter, and the like may be used together.

Although the liquid crystal display device of the present invention is often used in a transmission type, it can be used in a reflection type because it is bright.

When used in a transmission type, a background portion other than pixels can be covered with a light-shielding film by printing or the like. In addition to using a light-shielding film, it is also possible to perform reverse driving so that a selection voltage is applied to a portion not to be displayed.

In addition, the present invention can apply various techniques used in ordinary liquid crystal display elements as long as the effects of the present invention are not impaired.

In the present invention, the time-division characteristics are comparable to those of the super-twisted liquid crystal display device, and as described above, since bright and clear monochrome display is possible, red, green and blue fine color filters of the three primary colors are applied to the inner surface of the cell and the like. By arranging them, a high-density multi-color liquid crystal display element can be obtained.

The liquid crystal display device of the present invention is suitable as a display device of a personal computer, a word processor, a workstation, and the like, but the outer liquid crystal television, a fish finder, a radar, an oscilloscope, a black and white display such as various consumer dot matrix display devices, and a color display device. It can be used for various purposes without displaying.

[Operation] Although the operation principle of the present invention is not necessarily clear, it can be estimated as follows.

FIG. 3 (A) is a schematic side view showing the configuration of a super twisted liquid crystal display element not using only a birefringent plate for comparison with the liquid crystal display element of the present invention, and has a twist angle of 160 to 300. In °, a liquid crystal layer 13 made of a nematic liquid crystal having a positive dielectric anisotropy of Δn ₁ · d ₁ of 0.4 to 1.5 μm, and a pair of polarizing plates 11 and 12 disposed above and below the liquid crystal layer 13 are shown.
In this example, the crossing angle between the polarization axes of the pair of polarizing plates 11 and 12 arranged vertically is 90 °.

In the case of a liquid crystal display element having such a configuration, in a state where no voltage is applied to the liquid crystal layer or a state where a low voltage such as a non-selection voltage is applied, the lower polarizing plate on the incident side is used.
When almost completely linearly polarized light passes through the liquid crystal layer 13, the light becomes elliptically polarized. The shape and direction of the elliptical polarization differs depending on the wavelength of the light, and the light is divided into three primary colors of red, green and blue, as shown in FIG. 3 (B). When the circularly polarized light passes through the upper polarizing plate 11 on the emission side, the intensity of the light passing therethrough differs depending on the red, green, and blue light, so that the light appears to be colored in a specific color. In FIG. 3B, reference numerals 15 and 16 indicate the polarization axes of the polarizing plates 11 and 12, respectively.

On the other hand, in the present invention, as shown in a schematic view from the side in FIG.
A liquid crystal layer 23 of nematic liquid crystal having a positive dielectric anisotropy of Δn ₁ · d ₁ of 0.4 to 1.5 μm, two uniaxial birefringent plates 24A and 24B laminated on one surface thereof, and arranged above and below And a pair of polarizing plates 21 and 22 shown in FIG.

In this example, the twist angle of the liquid crystal layer is 240 ° and Δn ₁ · d ₁ is
The crossing angle between the polarization axes of the pair of polarizing plates 21 and 22 arranged vertically is 90 °.

When this uniaxial birefringent plate itself is sandwiched between polarizing plates, incident linear polarized light can be changed to any elliptical or circular polarized light depending on the value of Δn ₂・ d ₂ of the uniaxial birefringent plate. Or it can return to linearly polarized light.
Therefore, by superposing a plurality of birefringent plates of appropriate Δn ₂ · d _{2 on} one side of the liquid crystal layer, the configuration shown in FIG. 4B can be obtained.

That is, in a state where no voltage is applied to the liquid crystal layer or a state where a low voltage such as a non-selection voltage is applied,
The light that has been almost completely linearly polarized through the lower polarizing plate 22 on the incident side is transmitted through the liquid crystal layer 23 and is in an elliptical polarization state. The elliptically polarized light is further converted to birefringent plates 24B and 24B.
By passing through 4A, elliptical polarized light may be returned to a state close to linear polarized light again depending on conditions.

Considering that light is divided into three primary colors of red, green and blue,
The result is as shown in FIG. As in this example, when the directions of the polarization axes of red, green, and blue are almost aligned and return to almost linear polarization, regardless of the direction of the polarization axis on the emission side, the wavelength dependence of the transmitted light intensity is reduced. Can be eliminated. That is, achromatic color can be obtained.

As in this example, a polarizing plate is installed so that its polarization axis intersects by 90 °, and if the polarization on the output side matches the absorption axis of the upper polarizing plate on the output side, the transmitted light The intensity will be the lowest and appear black. Thus, a negative display is obtained. In FIG. 4B, reference numerals 25 and 26 denote the polarization axes of the polarizing plates 21 and 22, respectively.

Conversely, if the polarization axis of the upper polarizing plate is substantially parallel to the polarization axis of the lower polarizing plate, these intensities will be large and appear white, resulting in a positive display.

The negative and positive of the display are the twist angle of the liquid crystal layer, Δn ₁ · d ₁ thereof, Δn ₂ · d ₂ of the uniaxial birefringent plate, and the angles θ ₁ , θ ₂₁ , θ ₂₂ between them and the polarizing plate. vary by changing the configuration requirements of the theta ₃ or the like.

On the other hand, when a sufficient voltage is applied to the liquid crystal layer in this configuration, the shape and direction of the elliptical polarization transmitted through the liquid crystal layer differ from those before voltage application.

For this reason, the state of the elliptical polarization after passing through the birefringent plate is also different, which changes the transmittance and enables display.

However, by inserting a birefringent plate, although the shape and direction of circularly polarized light were successfully aligned without applying a voltage and a black or white state was created, it is not always necessary that the state becomes white or black with a voltage applied Not necessarily. For this reason, it is possible to experimentally optimize the birefringent plate Δn ₂・ d ₂ , its optical axis direction, the polarizing axis direction of the polarizing plate, etc. by the parameters such as the twist angle of the liquid crystal layer and Δn ₁・ d _1. preferable.

However, it is preferable to prioritize white as to which one of white and black is important, since a white white state, which is a state of high transmittance, is bright and clear and is suitable for colorization.

[Example] Example 1 As a first substrate, an ITO transparent electrode provided on a glass substrate was patterned in a stripe shape, and was subjected to an evaporation method.
An insulating film for short circuit prevention by SiO ₂ was formed, and a polyimide overcoat was spin-coated and rubbed to form a substrate on which an alignment control film was formed.

As a second substrate, an ITO transparent electrode provided on a glass substrate is patterned in a stripe shape so as to be orthogonal to the first substrate, an SiO ₂ insulating film is formed, and a polyimide overcoat is formed. A substrate on which an orientation control film was formed by rubbing so as to have an angle of intersection of 60 ° with the rubbing direction of the first substrate was prepared.

The periphery of the two substrates is sealed with a sealing material to form a liquid crystal cell, and a nematic liquid crystal having a positive dielectric anisotropy is injected into the liquid crystal cell so that a liquid crystal layer having a twist of 240 ° is formed. The inlet was sealed. In this liquid crystal layer, Δn ₁・ d ₁ is 0.
It was 85 μm.

_Two uniaxial birefringent plates having Δn ₂ · d ₂ of 0.40 μm were laminated on one side of the liquid crystal cell, and a pair of polarizing plates was further laminated on the upper and lower sides.

The relative relationship between the major axis direction of the liquid crystal molecules of the liquid crystal display element, the polarization axis direction of the polarizing plate, and the optical axis direction of the birefringent plate is θ.
₁ = 160 °, θ ₂₁ = 120 °, θ ₂₂ = 85 °, and θ ₃ = 135 °.

As a result of applying a voltage to the liquid crystal display element and examining the change in transmittance, a good threshold voltage characteristic was obtained as shown by a solid line A in FIG. 5, and a good contrast was obtained when multiplex driving was performed. It was found that a ratio was obtained.

A backlight of a C light source was arranged on the back side of the liquid crystal display element, and driven at 1/200 duty and 1/15 bias, the hue in the on / off state was observed. The result is shown in FIG. As is apparent from these results, a good white level slightly yellowish green was obtained when the display was turned on, and a negative black-and-white display was obtained in which the display was sufficiently black because the transmittance was low when the display was off.

Contrast ratio of this liquid crystal display element (only pixel part)
Was about 50, and a much higher contrast was obtained compared to a conventional simple super twisted liquid crystal display device. In addition, the transmittance in the ON state was about 27%, which was brighter than that of the OMI element, so that it could be used sufficiently in the reflection type.

Comparative Examples 1 and 2 The birefringent plate of Example 1 having Δn ₂ · d ₂ of 0.28 μm was designated as Comparative Example 1, and the birefringent plate having 0.46 μm was designated as Comparative Example 2.
The change in transmittance was examined in the same manner as in Example 1. The result is shown in FIG.

The comparative example 1 is indicated by a broken line B, but the ON transmittance is only about half that of the example 1, and the display is dark. Further, Comparative Example 2 is shown by a dashed line C, but the off transmittance was three times or more higher than that of Example 1, and a sufficient contrast ratio could not be obtained.

Examples 2 to 5 In the liquid crystal display device of Example 1, Δn ₁ · d ₁ of the liquid crystal layer
A liquid crystal display device was prepared as shown in Table 1 by using Δn ₂ · d ₂ of each of the birefringent plates arranged on both surfaces.

When these liquid crystal display elements were driven at 1/200 duty and 1/15 bias in the same manner as in the first embodiment, a negative black-and-white display almost equivalent to that of the first embodiment was obtained, and the contrast ratio (pixel portion) Only) was also about 40.

Example 6 In the liquid crystal display device of Example 1, a liquid crystal display device was prepared by changing only the relative relationship between the major axis direction of the liquid crystal molecules, the polarization axis direction of the polarizing plate, and the optical axis direction of the birefringent plate. . That is, θ ₁ = 70 °, θ ₂₁ = 120 °, θ ₂₂ = 85 °, θ ₃ = 45
°.

When this liquid crystal display element was driven at 1/200 duty and 1/15 bias in the same manner as in Example 1, a negative black-and-white display almost equivalent to that of Example 1 was obtained, and the contrast ratio (only the pixel portion) was about It was 50.

Example 7 In the liquid crystal display device of Example 1, Δn ₁ · d ₁ of the liquid crystal layer was set to 0.88 μm, and Δn ₂ · d ₂ of the birefringent plate was set to 0.36 μm.
m, only the relative relationship between the major axis direction of the liquid crystal portion, the polarization axis direction of the polarizing plate and the optical axis direction of the birefringent plate,
A liquid crystal display device was created. That is, θ ₁ = 165 °, θ ₂₁ = 1
35 °, θ ₂₂ = 80 °, and θ ₃ = 30 °.

When this liquid crystal display element was driven at 1/200 duty and 1/15 bias in the same manner as in Example 1, a good white level slightly yellowish greenish was obtained when it was off, and the transmittance was low when it was on. A positive black-and-white display was obtained so as to be seen. When the contrast ratio (only the pixel portion) of this liquid crystal display element was measured, it was about 40.

Example 8 Three stripes were formed on the electrodes of the liquid crystal display element of Example 1.
When a color filter layer was formed and driven, full-color gradation driving was possible.

[Effects of the Invention] As described above, the present invention enables a black-and-white display having a superior contrast ratio as compared with a conventional super-twisted liquid crystal display element, and provides a clear and high-quality positive or negative display. The display is obtained.

In addition, time-division display characteristics and viewing angle characteristics also have excellent effects such as being comparable to those of the conventional super twist liquid crystal display device.

Also, since the display is close to black and white, colorful display is possible by combining with a color filter, especially multi-color and full color display by arranging red, green and blue color filters for each pixel. Is also realized, and more diverse applications can be opened.

In particular, according to the present invention, a bright display is possible in spite of a monochrome display, and not only a transmission type display but also a reflection type display is possible, and the application range is wide.

Further, according to the present invention, a bright black-and-white display can be achieved without providing the second liquid crystal layer simply by arranging two birefringent plates on one surface of the liquid crystal layer. Is also very high.

The present invention can be applied to various applications as long as the effects of the present invention are not impaired.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a liquid crystal display device according to the present invention. FIGS. 2 (A) and 2 (B) are plan views showing the relative positions of the upper and lower liquid crystal molecules viewed from above, the major axis direction, the polarizing axis direction of the polarizing plate, and the optical axis direction of the birefringent plate, respectively. It is. FIGS. 3 (A) and 3 (B) are a schematic diagram showing the configuration of a mere super twisted liquid crystal display device and a plan view for explaining the polarization state thereof. FIGS. 4A and 4B are a schematic diagram showing the configuration of the liquid crystal display device of the present invention and a plan view for explaining the polarization state thereof. FIG. 5 is a graph showing threshold voltage characteristics of Example 1 and Comparative Examples 1 and 2. FIG. 6 is a hue diagram showing the hue of the first embodiment in the on and off states. 1, 2, 11, 12, 21, and 22 are polarizing plates, 3, 13, and 23 are liquid crystal layers, 4A, 4B, 24A, and 24B are birefringent plates, and 5, 6, 15, 16, 25, and 26 are polarization axes. , 7, 8 are the major axis directions of the liquid crystal molecules, 9A, 9B are the optical axis directions of the birefringent plate

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1335 510 G02F 1/133 500

Claims (1)

(57) [Claims] 1. A twisting angle of 160 to 300 ° by a nematic liquid crystal having a positive dielectric anisotropy containing a rotatory substance sandwiched between a pair of substrates having a pair of transparent electrodes having alignment control films disposed substantially in parallel. Liquid crystal layer, and driving means for applying a voltage between the transparent electrodes of the upper and lower substrates sandwiching the liquid crystal layer,
In a liquid crystal display device having a pair of polarizing plates provided outside the liquid crystal layer, the product Δn ₁ · d ₁ of the refractive index anisotropy Δn ₁ of the liquid crystal in the liquid crystal layer and the thickness d _{1 of the} liquid crystal layer is 0.4 to 1.5. μm, having approximately the same Δn ₂・ d ₂ on one side between the liquid crystal layer and the polarizing plate,
The total Δn ₂・ d ₂ is 0.7 × Δn ₁・ d ₁ <Δn ₂・ d ₂ <1.1 × Δ
Two uniaxial birefringent plates of n ₁ and d ₁ are arranged, and the upper side of the liquid crystal molecules above the liquid crystal layer as viewed from the major axis direction (polarizer side)
The optical axis direction of the birefringent plate measured clockwise is θ ₂₁ ,
When those measure the optical axis direction of the birefringent plate of the lower side as viewed from the longitudinal direction of the liquid crystal molecules in the upper side of the liquid crystal layer (liquid crystal layer side) in a clockwise direction and _{θ 22, 40 ° ≦ θ 21} ≦ 200 °, And 40 ° ≦ θ ₂₂
A liquid crystal display device characterized by satisfying ≦ 140 ° and θ ₂₂ ≦ θ ₂₁ .