JP2768977B2 - Liquid crystal element and device using the same - 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 birefringence 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 (JP-A-60-10720).
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, when this method is used, the display is dark, the maximum contrast is not so large, and the display has a bluish color.

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.

Further, a film-laminated liquid crystal display device in which one of the above-described two-layer cells is replaced with a uniaxial birefringent film to enable monochrome display has been proposed (Japanese Patent Application Laid-Open No. 63-271415).

[Problems to be Solved by the Invention] In such a uniaxial birefringent film-type film-laminated liquid crystal display element, since the compensation of the liquid crystal cell is performed by the uniaxial birefringent film, It looks good, but has the drawback that when viewed from an oblique direction, it becomes colored and black and white are reversed. For this reason, it has been difficult to produce a liquid crystal display device that is bright, has good black-and-white degree, and has a wide viewing angle with a high yield.

The black and white display device with a wide viewing angle is not only easy to see without unique coloring, but also realized with a conventional 90 ° twisted nematic (TN) device with a color filter formed inside or outside the cell. As described above, it is possible to realize a mono-color, multi-color or full-color display, exhibit features such as thinness, light weight and low power consumption.

Therefore, a liquid crystal display device capable of producing a black-and-white display device having good contrast, brightness, and a wide viewing angle at a high yield has been desired.

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 layer having a thickness of about 300 mm and driving means for applying a voltage between the transparent electrodes of the upper and lower substrates sandwiching the liquid crystal layer, a pair of polarizing plates are provided outside the liquid crystal layer, and the liquid crystal layer and In a liquid crystal display device in which a plurality of birefringent plates are stacked and arranged on one side between a polarizing plate and a 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, the plurality of birefringent plates, a positive uniaxial birefringent plate whose optical axis is in the plane, and a positive uniaxial birefringent plate whose optical axis is in the film thickness direction using each one or more, the plurality of the principal refractive index n _xs total pressure average of three directions in consideration of the thickness of the birefringent plate, n _ys, and n _zs, n _xs, refractive index n _ys-plane direction And (n _xs > n _ys ), n
_{When zs} is the refractive index in the thickness direction of the birefringent plate, n _xs > n _zs
An object of the present invention is to provide a liquid crystal display device characterized by arranging a birefringent plate such that> _nys .

In the present invention, a positive uniaxial birefringent plate having an in-plane optical axis and a positive uniaxial birefringent plate having an optical axis in a film thickness direction are provided on one side between the liquid crystal layer and the polarizing plate. At least one or more sheets are stacked and used. The principal refractive index of the total pressure average of three directions in consideration of the plurality of the thickness of the birefringent plate n _xs, n _ys, and n _zs,
Let _nxs and _nys be the refractive index in the in-plane direction of the birefringent plate ( _nxs >
n _ys ) and _nzs are the refractive indices in the thickness direction of the birefringent plate,
A birefringent plate having a relationship such that n _xs > n _zs > _nys is arranged.

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. Further, as compared with the case where only one uniaxial birefringent plate is used, the display quality is less deteriorated when viewed from an oblique direction, and a monochrome liquid crystal display element having a wide viewing angle can be easily formed. can get.

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.
It should be 160-300mm. This is because there is little improvement in contrast when performing high-duty time-division driving, which requires a sharp change in transmittance at less than 160 mm, and conversely, when it exceeds 300 mm, hysteresis and domains that scatter light are generated. 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,
Display colors tend to have a bluish tint, and when the thickness exceeds 1.5 μm, the hue at the time of on changes from yellow to red, making it 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. Due to extreme 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 -Sn
A film of polyimide, polyamide or the like is provided on the surface of a substrate such as plastic or glass provided with a transparent electrode such as O ₂ ) or SnO ₂ and an alignment control film is formed by rubbing the surface or obliquely depositing SiO or the like. Prepare a substrate with a transparent electrode on which a liquid crystal layer having a dielectric anisotropy of 160 to 300 ° twisted by a positive nematic liquid crystal is sandwiched between the substrates with a 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. The polarizing plate itself is generally disposed outside the substrate constituting the cell, but if performance permits, the substrate itself may be formed of a polarizing plate and a birefringent plate, or a birefringent plate may be disposed between the substrate and the electrode. It may be provided as a refraction layer and a polarizing layer.

In the present invention, at least one positive uniaxial birefringent plate having an in-plane optical axis and one positive uniaxial birefringent plate having an optical axis in a film thickness direction are provided adjacent to one side of the liquid crystal layer. Laminate more than one. These birefringent plates may be provided between the liquid crystal layer and the polarizing plate. As a refraction plate, provided in a layer between the substrate and the polarizing plate,
They may be provided in combination. In addition, the order of laminating these birefringent plates may be any order on the liquid crystal layer side.

The birefringent plate of the present invention can be used as long as it is a transparent plate having birefringence described later, and a plastic film, an inorganic crystal plate, or the like can be used.

Among these birefringent plates, a positive uniaxial birefringent plate having an optical axis in the plane is defined as three main refractive indices _nx1 , _ny1 , _nz1, and n
_x1 and _ny1 are the indices of refraction in the in-plane direction of the birefringent plate ( _nx1 >
n _y1 ) and _nz1 are the refractive indices in the thickness direction of the birefringent plate,
The birefringent plate has an optical axis in the x-axis direction and _nx1 > _ny1 = _nz1 .

A positive uniaxial birefringent plate having an optical axis in the film thickness direction has three main refractive indices n _x2 , n _y2 , n _z2 , n _x2 , n _x2
The _y2 and birefringent plate plane direction of the refractive index _{(n x2 = n y2),} n x2
Is the refractive index in the thickness direction of the birefringent plate, _nz2 > _nx2 =
It is a birefringent plate that becomes n _y2 .

In the present invention, at least one positive uniaxial birefringent plate whose optical axis is in the plane and at least one positive uniaxial birefringent plate whose optical axis is in the film thickness direction are laminated and used. n _xs three directions of the main refractive index of the average obtained by integrating in consideration of, n _ys, and n _zs, n
Let _xs and _nys be the refractive index in the in-plane direction of the birefringent plate ( _nxs >
n _ys), the n _zs when the film thickness direction of the refractive index of the birefringent plate, laminating a plurality of birefringent plates such that _{n xs> n zs> n ys} .

Here, n _xs , n _ys , and n _zs will be described.

There are i positive uniaxial birefringent plates whose optical axes are in the in-plane x-axis direction, and the main refractive indices in each of the three directions are n _x1i , n _y1i , n
and _{z1i (n x1i> n y1i =} n z1i), the film thickness is l _1i. Similarly, there are j positive uniaxial birefringent plates whose optical axes are in the z-axis direction, which is the film thickness direction, and the main refractive index in each of the three directions is n.
_{x2j, n y2j, n z2j (} n z2j> n x2j = n y2j) and then, the film thickness l _2j
And In this case, the total pressure average n _xs three directions of refractive index in consideration of these thicknesses, n _ys, n _zs can be expressed as follows.

In order to obtain the desired birefringence effect, the retardation Δn ₂ · d ₂ of the birefringent plate is used after being adjusted. However, when it is not possible to adjust the birefringent plate one by one, the same as described above. Using a birefringent plate or different birefringent plates laminated,
Three directions of the main refractive index is used in combination plurality as each _{match, Δn 2 · d 2 = (} n xs -n ys) · d 8 may be set so as to satisfy the condition.

For good black and white display, with respect to a particular twist angle and a liquid crystal layer having a _{Δn 1 · d 1, Δn 2} · birefringent plate
It is important to optimize the size of d ₂ and the direction in which they are attached, and the direction of the polarization axis of the pair of polarizing plates.

The size of Δn ₂ · d ₂ of the birefringent plate is approximately equal to Δ of the liquid crystal layer because the birefringent plate is arranged on one side between the liquid crystal layer and the polarizing plate.
Good black-and-white display can be easily obtained by setting the value to be approximately the same as the size of n ₁ · d ₁ or slightly smaller. In particular,
It may be about 0.1-1.5 μm.

Then, in order to improve the angle dependency, it is necessary to adjust _nzs .

In the present invention, the value of _{(n zs -n ys) / (} n xs -n ys) 0.1
It is preferable to make the above. This is because if this value is less than 0.1, it is difficult to obtain a sufficient difference in effect from the case where only one uniaxial birefringent plate is used.

 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. 2 (A) and 2 (B) show the polarization axis direction of the upper polarizer of FIG. 1 viewed from above, the optical axis direction of a positive uniaxial birefringent plate whose optical axis is in-plane, and FIG. 4 is a plan view showing a major axis direction of liquid crystal molecules on an upper side of a liquid crystal layer, and a relative position of a polarization axis direction of a lower polarizing plate and a major axis direction of liquid crystal molecules on a lower side of the 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 左 left helix (counterclockwise twist when viewed from above) liquid crystal layer,
4A is a positive uniaxial birefringent plate having an optical axis in an in-plane direction laminated thereon, 4B is a positive uniaxial birefringent plate having an optical axis in a film thickness direction, and 5 is an upper polarizing plate , 6 is the polarization axis of the lower polarizing plate, 7 is the liquid crystal molecule on the upper side of the liquid crystal layer, 8 is the liquid crystal molecule on the lower side of the liquid phase layer, and 9A is the positive uniaxial axis whose optical axis is in the in-plane direction. 9B indicates the direction of the optical axis of the birefringent plate 4A, and 9B indicates the direction of the optical axis of the biaxial birefringent plate 4B having a positive optical axis in the film thickness direction.

Regarding the definition of the refractive index of the birefringent plate used in the present invention,
This will be described with reference to the drawings.

First, coordinate axes are set as shown in FIG. In FIG.
4A is a positive uniaxial birefringent plate whose optical axis is in the in-plane direction. If the x-axis direction is the optical axis direction, its three main refractive indices
for _{n x1, n y1, n z1} , a relationship of _{n x1> n y1 = n z1} .

4B is a positive uniaxial birefringent plate whose optical axis is in the film thickness direction, and has a relationship of _nz2 > _nx2 = _ny2 .

Further, in the present invention, the total averaging of the refractive indices in three directions n _xs , n _ys and n _zs in consideration of the thickness of these birefringent plates, n _xs >
It is necessary to satisfy _nzs > _nys .

That is, in the case of FIG. It is necessary to have the relationship of

In FIG. 2, the clockwise direction of the direction of the polarization axis 5 of the upper polarizer viewed from the major axis direction of the liquid crystal molecules 7 above the liquid crystal layer is θ ₁ , and the length of the liquid crystal molecules 7 above the liquid crystal layer is Positive uniaxial birefringent plate whose optical axis is in-plane viewed from the axial direction
The direction 9A of the optical axis of 4A measured clockwise was θ ₂ , and the direction of the polarization axis 6 of the lower polarizing plate as viewed from the major axis direction of the liquid crystal molecules 8 below the liquid crystal layer was measured clockwise. things and θ _3. In the present invention, θ ₁ , θ ₂ , and θ ₃ may be optimized so as to provide a monochrome display. A positive uniaxial birefringent plate having an optical axis in the film thickness direction only needs to be inserted as a matter of course, and does not depend on the direction.

When the liquid crystal display element of the present invention is used for negative display, for example, the twist angle of the liquid crystal layer is about 240 °, Δn ₁ · d ₁ is about 0.87 μm, and the birefringent plate disposed thereon is If Δn ₂ · d ₂ is about 0.58 μm, it is preferable to arrange the polarizing axes of the pair of polarizing plates so as to intersect at an angle of about 0 to 60 °.

When the same liquid crystal layer and the birefringent plate are used and a positive display is used, it is preferable to arrange the polarizing plate on one side in a state where the polarization axis is rotated by about 90 °. This allows
This liquid crystal display element enables high-contrast monochrome display with excellent viewing angle characteristics.

In this case, especially for negative display, 40 ° ≦ θ ₂ ≦ 14
Setting the angle to 0 ° is preferable because a display having a sufficient contrast with a low OFF transmittance and a high ON transmittance can be realized.

In particular, setting 60 ° ≦ θ ₂ ≦ 120 ° is preferable because the OFF transmittance is low and a sufficient contrast ratio can be obtained.

In the above example, the liquid crystal layer is a left helix, but when the helix is reversed, the liquid crystal layer has a long axis direction of liquid crystal molecules, a direction of a polarization axis of a polarizing plate, and a positive direction in which an optical axis is in an in-plane direction. By setting the relationships θ ₁ , θ ₂ , and θ ₃ counterclockwise with respect to the direction of the optical axis of the uniaxial birefringent plate in the counterclockwise direction, a monochrome display can be easily obtained as in the above example.

When the birefringent plate is inserted below the liquid crystal cell, θ ₁ , θ ₂ , and θ ₃ may be selected so that the cell has the same relationship as described above when viewed from below.

The above description is the optimization obtained in the vertical direction of the liquid crystal display element, and is the same as the case where only the positive uniaxial birefringent plate whose optical axis is in the in-plane direction is used. However, when the compensation is made only with the uniaxial birefringent plate, even if the compensation is performed well in the vertical direction and a high-contrast black-and-white element can be obtained, the compensation is shifted in the oblique direction, and the black-and-white element is reversed. Sometimes.

In the present invention, by a _{n xs> n zs> n ys} , it can be prevented with color when viewed from an oblique direction, thereby improving the appearance.

The n _zs can be greater than n _xs, be less than n _ys, the angular dependence is reduced, the appearance when viewed from an oblique direction is reduced. In _{particular, (n zs -n ys) /} (n xs -n ys) ≧ 0.
By setting it to 1, the appearance when viewed from an oblique direction is greatly improved.

As the birefringent plate in the present invention, two types of uniaxial birefringent plates are required. As the positive uniaxial birefringent plate having an in-plane optical axis, a normal uniaxially stretched film or crystal plate can be used. As the positive uniaxial birefringent plate having an optical axis in the film thickness direction, a polymer film by a special manufacturing method, for example, a polymer liquid crystal film, an LB film, or a crystal plate is used. Further, these birefringent plates can be used even if the refractive index in the thickness direction is not uniform, as long as the average refractive index in the thickness direction satisfies the conditions described above.

In the present invention, since a display with a wide viewing angle close to a monochrome display can be obtained, a colorful display can be performed by using a color filter in combination. In particular, even with high duty driving,
Since a high contrast ratio can be taken, gradation display by full curry is possible, and it can be used for a liquid crystal television.

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 a super twisted liquid crystal display element, and since bright and clear black-and-white display is possible as described above, 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.

First, consider the case where the liquid crystal display element is viewed from the vertical direction.

FIG. 4 (A) is a schematic side view showing the configuration of a super twisted liquid crystal display element that does not use a birefringent plate for comparison with the liquid crystal display element of the present invention.
160 to 300 °, Δn ₁・ d ₁ shows a liquid crystal layer 13 of nematic liquid crystal having a positive dielectric anisotropy 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. I have. 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. 4 (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. 4B, reference numerals 15 and 16 denote the polarization axes of the polarizing plates 11 and 12, respectively.

On the other hand, in the present invention, as shown in FIG. 5 (A), a schematic view from the side thereof shows that the torsion angle is 160 to 300 °,
A liquid crystal layer 23 of a nematic liquid crystal having a positive dielectric anisotropy of Δn ₁ · d ₁ of 0.4 to 1.5 μm, a positive uniaxial birefringent plate 24A having an in-plane optical axis disposed thereon, and a light The figure shows a positive uniaxial birefringent plate 24B whose axis is in the film thickness direction, and polarizing plates 21 and 22 arranged vertically.

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 30 °. Note that, in this example, two types of birefringent plates of the present invention are used by arranging them one by one on the upper surface of the liquid crystal cell for the sake of simplicity. They may be laminated and used so that the directions of the main refractive indexes coincide with each other.

When this birefringent plate is sandwiched between polarizing plates, when viewed from the vertical direction, depending on the value of Δn ₂・ d ₂ of the birefringent plate, incident linearly polarized light can be changed to any elliptical polarized light,
Circularly polarized light or linearly polarized light can be returned. Therefore, by overlaying a birefringent plate of an appropriate Δn ₂ · d _{2 on} the liquid crystal layer, the structure shown in FIG. 5B 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,
When 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, the light becomes an elliptical polarization state. This elliptically polarized light passes through the birefringent plate 24B, but since the optical axis of the birefringent plate is in the film thickness direction, the birefringent plate has no effect on light traveling in the vertical direction. next,
The elliptical polarized light passes through the birefringent plate 24A. Since the birefringent plate is a so-called ordinary uniaxial birefringent plate, the elliptical polarized light can be returned to a state close to the 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 substantially aligned and return to substantially linear polarization, the wavelength dependence of the transmitted light intensity is eliminated regardless of the direction of the polarization axis on the emission side. Can be. That is, achromatic color can be obtained.

As in this example, a polarizing plate is installed so that its polarization axis intersects by about 30 °, and if the polarization on the output side matches the absorption axis of the upper polarizing plate on the output side, the transmission The light intensity will be the lowest and appear black. Thus, a negative display is obtained. In FIG. 5B, reference numerals 25 and 26 denote polarization axes of the polarizing plates 21 and 22, respectively.

Conversely, if the polarization axis of the upper polarizing plate is rotated by 90 ° to make it almost parallel to the direction of the polarized light on the emission side, these intensities become large and appear white, resulting in a positive display.

The negative and positive of the display are the configuration of the twist angle of the liquid crystal layer, Δn ₁ · d ₁ , Δn ₂ · d ₂ of the birefringent plate, and the angles θ ₁ , θ ₂ , θ ₃ between them and the polarizing plate. By changing the requirements,
change.

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.

Thus, when the liquid crystal display element is viewed from the vertical direction, even if only the uniaxial birefringent plate whose optical axis is in the in-plane direction is used as the birefringent plate, if the conditions are optimized, A good black and white display element can be obtained.

However, when such a black-and-white display element is viewed from an oblique direction, the display may look colored or the black-and-white display may be reversed.

This is because the liquid crystal molecules are originally uniaxial, but have a helical structure in the liquid crystal cell as shown in FIG.
Further, when a selection voltage or a non-selection voltage is applied to the liquid crystal cell for multiplex driving, the liquid crystal molecules near the center rise, so that the medium cannot be regarded as a uniaxial medium anymore. This is because it can be regarded as an axial medium.

At this time, as shown in FIG. 6, attention is paid to liquid crystal molecules near the center of the liquid crystal cell, and the average main refractive index in this region is represented by n _Lx , n _Ly , n _Lz (where n _Lx is the central liquid crystal). The average refractive index in the direction in which molecules are projected onto the substrate, n _Ly is the average refractive index in the direction perpendicular to n _Lx within the substrate plane, and n _Lz is the average refractive index in the film thickness direction) Since the liquid crystal molecules have a slightly helical structure and stand up,
It is expected that n _Lx > n _Lz > n _Ly .

Therefore, in order to correct such a liquid crystal cell even in an oblique direction, a birefringent plate having similar characteristics is preferable,
It is preferable to use a birefringent plate that _satisfies n _xs > n _zs > n _{ys of the} present invention.

In the present invention, such characteristics are provided by the combination of the birefringent plates 24A and 24B shown in FIG. That is, as described above, since the birefringent plate 24B is a positive uniaxial birefringent plate whose optical axis is in the film thickness direction, it has no effect on light traveling in the vertical direction. However, birefringence occurs for light traveling obliquely to the liquid crystal cell. Therefore, by taking better matching between the birefringent plate 24A, it can be successfully corrected n _xs> n _zs> n _ys, and the two axes of the liquid crystal layer.

Examples Examples 1 to 6 As a first substrate, an ITO transparent electrode provided on a glass substrate was patterned in a stripe shape, and was formed by 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 87 μm.

As shown in Table 1 (Examples 1 to 3), Table 2 (Examples 4 to 6), and Table 3 (Comparative Examples 1 to 3), between the upper surface of the liquid crystal cell and the upper polarizing plate. A variety of birefringent plates having refractive indexes were respectively attached, and the widths of the viewing angles were compared.

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 positive uniaxial birefringent plate whose optical axis is in the plane is θ ₁ = 45 °, θ ₂ = 95
゜, θ ₃ = 135 °.

The evaluation was performed with the contrast ratio in the ON state and the OFF state driven by 1/200 duty and 1/15 bias.

The results are shown in FIG. 7 to FIG. FIGS. 7 to 15 are called isocontrast curves. When the observation direction of the cell is displayed in polar coordinates and the angle is represented by (θ, Ψ), the angle of the liquid crystal cell is expressed by (θ, Ψ). The change in the contrast ratio is shown by changing θ from 0 ° to 50 ° and changing ０〜 from 0 ° to 360 °. Note that ゜ is 0 ° in the main viewing angle direction (downward) in the figure, 0 to 360 ° counterclockwise, θ is 0 ° in the center, and 0 to 50 ° concentrically. The contrast ratio curves showed only 1, 10, and 50.

7 to 12 show examples of the liquid crystal display device according to the present invention, and FIGS. 13 to 15 show comparative examples.

In the present invention, as shown in Tables 1 and 2, n _xs > n _zs
> Because it uses birefringent plate such that n _ys, when only the conventional mere uniaxial birefringent plates (n _xs> n _ys =
_nzs (Comparative Example 1, FIG. 13), the contrast ratio indicated by oblique lines is 1 or less, that is, the region where the black and white contrast is reversed is very small. In addition, the region with a high contrast ratio (10 or more) was widened, and an element with a wide viewing angle and a high contrast ratio became possible.

On the other hand, when a birefringent plate other than the present invention, i.e., Comparative Example _{2 (n xs> n ys>} n zs) and Comparative Example 3 (n _zs> n _xs>
In the case of n _ys ), as shown in FIGS. 14 and 15, respectively, it was also found that the viewing angle was narrower and the region having a high contrast ratio was narrower than that of the present invention.

Examples 7 to 12 As one of the substrates with electrodes of the liquid crystal display elements of Examples 1 to 6, three color filter layers were formed in stripes on the substrate, and electrodes were formed thereon. When the cell was formed using the substrate and driven, full-curve grayscale driving was possible.

[Effects of the Invention] As described above, the present invention has a wider viewing angle and a better viewing angle as compared with a conventional two-layer type super twisted liquid crystal display element or a super twisted liquid crystal display element in which a uniaxial birefringent plate is laminated. A black-and-white display having a contrast ratio is made possible, and a clear or high-quality positive or negative display can be 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 and has a wide field of view, colorful display is possible by combining with a color filter.In particular, by arranging red, green, and blue color filters for each pixel, The effect of realizing color and full-color display is also recognized, and more diverse applications can be opened.

In particular, in the present invention, a bright display is possible in spite of a monochrome display, and not only a transmissive display but also a reflective display is possible, and its application range is wide.

Furthermore, in the present invention, bright black-and-white display can be achieved without providing the second liquid crystal layer simply by arranging the birefringent plate, and has the advantage that the productivity of the liquid crystal display device is extremely 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. 2 (A) and 2 (B) show positive uniaxial birefringence in which the major axis direction of the upper and lower liquid crystal molecules viewed from above, the polarization axis direction of the polarizing plate, and the optical axis are in-plane directions, respectively. It is the top view which showed the relative position of the direction of the optical axis of a board. FIG. 3 is a perspective view showing the definition of the main refractive index of two types of birefringent plates used in the present invention. FIGS. 4 (A) and 4 (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. 5A and 5B are a schematic diagram showing the configuration of the liquid crystal display device of the present invention and a plan view illustrating the polarization state thereof. FIG. 6 is a diagram showing a molecular arrangement of a liquid crystal cell. FIG. 7 to FIG. 15 are diagrams showing equal contrast curves of the liquid crystal display device. 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 polarizing axes. , 7, 8 are the major axis directions of the liquid crystal molecules, 9A, 9B are the optical axis directions of the birefringent plate

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1335 G02F 1/133 500

Claims (5)

(57) [Claims] 1. A nematic liquid crystal having a positive dielectric anisotropy and containing a rotatory substance sandwiched between a pair of transparent electrodes having alignment control films disposed substantially in parallel and having a twist angle of 160 to 300 °. 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 in which a pair of polarizing plates is provided outside the liquid crystal layer and a plurality of birefringent plates are stacked on one side between the liquid crystal layer and the polarizing plate, the refractive index anisotropy of the liquid crystal in the liquid crystal layer. Δn ₁
The product Δn ₁ · d _{1 of the} liquid crystal layer and the thickness d ₁ is 0.4 to 1.5 μm, and the plurality of birefringent plates are a positive uniaxial birefringent plate whose optical axis is in the plane, and an optical axis Using at least one positive uniaxial birefringent plate in the film thickness direction, and calculating the total averaging main refractive index in three directions n _xs , n _ys , in consideration of the thicknesses of the plurality of birefringent plates.
Let n _zs be the refractive index in the in-plane direction, and let n _xs and n _{ys be} the refractive index in the in-plane direction (n _xs >
_nys ) and _nzs are the refractive indexes in the thickness direction of the birefringent plate,
The liquid crystal display element characterized n _xs> n _zs> to the arrangement of the birefringent plate such that n _ys. About wherein a plurality of main refractive index of the total pressure average of three directions in consideration of the thickness of the birefringent _{plate, (n zs -n ys) /} (n xs -n
_2. The liquid crystal display device according to claim 1, wherein _ys ) ≧ 0.1. 3. The liquid crystal display device according to claim 1, wherein a color filter is formed on the inner surface of the cell. 4. The liquid crystal layer according to claim 1, wherein said liquid crystal molecules are arranged in a longitudinal direction.
Claim, characterized in that the optical axis is 40 ° ≦ θ ₂ ≦ 140 ° when what the direction of the optical axis of the birefringent plate as measured in the clockwise direction and the theta ₂ in the plane direction 1 4. The liquid crystal display device according to 2 or 3. 5. A dot matrix display device comprising the liquid crystal display device according to claim 1, wherein display is performed by gradation driving.