JP2768319B2 - Color liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a color liquid crystal display device suitable for high-density display.

[0002]

2. Description of the Related Art Conventionally, as a method of increasing the twist angle of liquid crystal molecules between two electrodes to cause a sharp change in voltage-transmittance and display a high-density dot matrix, a super twist element (TJ Scheffer and J . Nehring, Appl. Phy
s. Lett. 45 (10) 1021-1023 (1984)) was known.

However, this method uses a product Δn · multiplied by the birefringence Δn of the liquid crystal of the liquid crystal display element used and the thickness d of the liquid crystal layer.
The value of d is substantially between 0.8 and 1.2 μm (Japanese Patent Application Laid-Open No. 60-10720), and as a display color, a combination of specific hues such as yellow-green and dark blue and blue-violet and light yellow is used. only,
Good contrast was obtained. As described above, the liquid crystal display element cannot perform black-and-white display, and thus has a disadvantage in that multi-color or full-color display cannot be performed in combination with a micro color filter.

On the other hand, by using a similar method and setting the product Δn · d of the birefringence of the liquid crystal and the thickness to be as small as about 0.6 μm, a method in which a display almost similar to white and black is obtained is proposed. (M. Schadt et al, Appl. Phys. Let
t. 50 (5) 236 (1987)). However, when this method is used, the display is dark, the maximum contrast is not so large, and the display is bluish.

Further, as a liquid crystal display device having a black-and-white display and a high contrast, two layers of liquid crystal cells having mutually opposite spirals are laminated, and a voltage is applied to only one cell and the other cell is used as a mere optical compensator. (Okumura et al., The Institute of Television Engineers of Japan, 11 (27) 79 (1
987)). However, in this method, matching of Δn · d in a two-layer cell is extremely severe, and it is difficult to improve the yield.
Since two liquid crystal cells are required, there is a disadvantage that the thin and light liquid crystal cell is sacrificed.

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 a black-and-white display has been proposed (Japanese Patent Laid-Open No. Sho 63).
-271415).

[0007]

In such a uniaxial birefringent film type film-laminated liquid crystal display device,
Since the compensation of the liquid crystal cell is performed by a uniaxial birefringent film, the appearance is good in the vertical direction, but there is a drawback that when viewed from an oblique direction, the color is added and the 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.

A black-and-white display device having a bright and wide viewing angle is not only easy to see without a specific coloration but also has a color filter formed inside or outside the cell, so that a conventional 90 ° twisted twisted nematic (TN) is used. It is expected that the market can be dramatically expanded by realizing mono-color, multi-color or full-color display as realized by the device, exhibiting features such as thinness, lightness and low power consumption.

For this reason, the contrast is good, the brightness is high,
In addition, it has been desired to obtain a color liquid crystal display device having a wide viewing angle with a high yield.

[0010]

SUMMARY OF THE INVENTION 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 having alignment control films which are arranged substantially in parallel. A liquid crystal layer having a twist angle of 160 to 300 ° by a nematic liquid crystal having a positive dielectric anisotropy containing a conductive substance;
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 is provided outside the liquid crystal layer, and a pair of polarizing plates are provided on both outer sides of the liquid crystal layer. In a color liquid crystal display device in which a pair of birefringent plates are arranged inside a plate, a color filter is provided on the inner surface of the cell, and the product 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. Δn ₁ · d ₁ is 0.4 to 1.5 μm, and the birefringent plate is a birefringent plate having a different refractive index in three directions,
The main refractive indices are _nx , _ny , _nz , _nx , _ny are the indices of refraction in the in-plane direction of the birefringent plate ( _nx > _ny ), and _nz is the thickness in the thickness direction of the birefringent plate. In the case of a refractive index, _nx > _nz > n
to provide a color liquid crystal display device which is a _y.

Also,The birefringent plate is a biaxially stretched film
The color liquid crystal display device described above, wherein n _x > N
_z > N _y ≧ 1.5818, wherein
The refractive index of the color liquid crystal display element and the birefringent plate is (n _z -N
_y ) / (N _x -N _y ) ≧ 0.1
The above-mentioned color liquid crystal display element and the birefringent plate
Δn _Two = N _x -N _y , Thickness d _Two Then, a pair of bifurcations
Each Δn of folded plate _Two ・ D _Two Is Δn ₁ ・ D ₁ Almost half the size of
Minute value or slightly smaller
The above color liquid crystal display device is used in the transmissive type,
The background part other than is covered with a light shielding film.
The above color liquid crystal display element,And in those cells
A color filter is provided on the surface, and a transparent electrode is formed on it.
A color liquid crystal display element characterized by
And their color filters are red, blue, and green.
A color filter characterized by being a tripe-shaped color filter.
A color liquid crystal display device is provided.

[0012]

In DETAILED DESCRIPTION OF THE INVENTION The present invention, on both sides between the liquid crystal layer and the polarizing plate, and the three principal refractive indices n _x, n _y, and n _z,
n _x, the n _y and birefringent plate plane direction of the refractive index (n _x> n
_y ), where _nz is the refractive index in the thickness direction of the birefringent plate,
is obtained by placing a birefringent plate having n _x> n _z> n _y become such a relationship.

Therefore, a single liquid crystal layer may be used, and a clear color liquid crystal display device with a bright color can be easily obtained without reducing the productivity or providing a second liquid crystal layer which is liable to cause color unevenness. Further, as compared with the case where a uniaxial birefringent plate is used, the display quality when viewed from an oblique direction is less deteriorated, and a color liquid crystal display device having a wide viewing angle can be easily obtained.

This liquid crystal layer has the same structure as the liquid crystal layer of the conventional super twist 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 3
00 °.

More 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. May be set to 160 to 300 °. This is 1
When the angle is less than 60 °, the contrast is hardly improved when time-division driving is performed at a high duty that requires a steep transmittance change. Conversely, when the angle exceeds 300 °, a domain that scatters light and hysteresis is likely to occur. is there.

The refractive index anisotropy (Δn ₁ ) of the liquid crystal in the liquid crystal layer
And the product Δn ₁ · d _{1 of} the liquid crystal layer and the thickness (d ₁ ) of the liquid crystal layer is 0.1.
4 to 1.5 μm. If this is less than 0.4 μm,
When the transmittance is low, 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 where achromatic display colors are strictly required, Δn of the liquid crystal layer
₁ · d ₁ 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 can be obtained within the operating temperature range. Due to extreme performance requirements, it may be possible to satisfy this relationship only in part of the operating temperature range. 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.

IT patterned into a desired pattern
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 (In ₂ O ₃ -SnO ₂ ) or SnO ₂ , and the surface is rubbed or SiO is obliquely deposited. To prepare a substrate with a transparent electrode on which an orientation control film is formed, and between the substrate with the transparent electrode, a twisted liquid crystal layer having a dielectric anisotropy of 160 to 300 ° made of a positive nematic liquid crystal. To be held.

As a typical example, there is a dot matrix liquid crystal display device in which a large number of rows and columns of electrodes are formed. Stripe electrodes
640 in full color with RGB color filters
× 400 dots can be displayed. In the present invention, such a color filter is provided on the inner surface of the cell. This color filter is laminated on or under the electrode.

[0020] Incidentally, or an insulating film such as _{TiO 2, SiO 2, Al 2} O 3 in order to prevent inter-substrate short circuit between the electrode and the alignment layer, Al to the transparent electrode, Cr, such as Ti Low A resistance lead electrode may be provided.

A pair of polarizing plates are 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, a birefringent plate having a refractive index in the thickness direction different from that in the in-plane direction is laminated adjacent to both sides of the liquid crystal layer. This birefringent plate may be provided between the liquid crystal layer and the polarizing plate.

The birefringent plate may be provided between the liquid crystal layer and the polarizing plate. For example, the birefringent plate may be provided between the liquid crystal layer and the electrode in a layer, between the electrode and the substrate in a layer, What is necessary is just to provide a birefringent plate itself, to provide in a layer form between a board | substrate, and a polarizing plate, or to provide them in combination.

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

This birefringent plate has three main refractive indices n
_x, n _y, and n _z, n _x, the n _y and birefringent plate plane direction of the refractive index (n _x> n _y), when the n _z is the refractive index in the thickness direction of the birefringent plate, n a birefringent plate such that _x> n _z> n _y.

To obtain a desired birefringence effect, Δn ₂ · d
_{2 = (n x -n y)} · d 2 a will be adjusted to use, if that can not be adjusted in one plate may be used in combination plurality of the same birefringent plate or a different birefringent plate.

In order to perform a good color display, it is necessary to perform a good black-and-white display using the liquid crystal layer and the birefringent plate. For a liquid crystal layer having a specific twist angle and Δn ₁ · d ₁ , It is important to optimize the size of Δn ₂ · d ₂ of the birefringent plate 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 half the value of Δn ₁ · d ₁ of the liquid crystal layer because this birefringent plate is arranged on both sides of the liquid crystal layer. If it is set a little smaller than that, it is easy to obtain good black and white display. Specifically, it may be about 0.1 to 0.75 μm. When a plurality of such birefringent plates are used, the total value of Δn ₂ · d ₂ may be set in the above range.

Then, in order to improve the angle dependency, it is necessary to adjust _nz . In the present invention, ( _nz −n
the value of _{y) / (n x -n y} ) preferably be 0.1 or more. This is because if this value is less than 0.1, it is difficult to obtain a sufficient difference in effect from the uniaxial birefringent plate.

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. Figure 2 (A) (B) is, the polarization axis direction of the upper polarizing plate of Figure 1 viewed from above, respectively, the long axis direction of the upper side of the liquid crystal molecules in the direction and the liquid crystal layer of the principal refractive indices n _x of the birefringent plate and is a plan view showing the relative position of the longitudinal direction of the liquid crystal molecules of the lower surface of the lower polarization axis of the polarizing plate, the direction and the liquid crystal layer of the principal refractive indices n _x of the birefringent plate.

In FIG. 1, reference numerals 1 and 2 denote a pair of polarizing plates, 3
Is Δn ₁ · d ₁ for displaying characters and figures of 0.4 to
Left spiral (counterclockwise twist as viewed from above) liquid crystal layer with a twist angle of 160 to 300 ° by a 1.5 μm nematic liquid crystal having a positive dielectric anisotropy, 4A and 4B are birefringent layers stacked on top and bottom Plate, 5 is the polarization axis of the upper polarizer, 6 is the polarization axis of the lower polarizer, 7 is the upper liquid crystal molecule of the liquid crystal layer, 8 is the lower liquid crystal molecule of the liquid crystal layer, and 9A is the upper birefringence. direction of the principal refractive indices n _x of the plate, 9B indicate the main refractive indices n _x of the lower birefringent plate
The direction of is shown.

The definition of the main refractive index of the birefringent plate used in the present invention will be described with reference to FIG. The birefringent plate of the present invention has different refractive indexes in three directions of x, y and z. Therefore, the direction in which the refractive index is large in the in-plane direction of the birefringent plate is defined as x
An axial direction, a direction having a small refractive index is defined as a y-axis direction, and a thickness direction is defined as a z-axis direction. The refractive index in each direction is n
_x , _ny , and _nz . In this case, _nx > _ny , and
A Δn ₂ = n _x -n _y, in the present invention n _x> n _z> n
_y . Note that d is the thickness of the birefringent plate.

In FIG. 2, the liquid crystal molecules 7 on the upper side of the liquid crystal layer
When the direction of the polarization axis 5 of the upper polarizing plate viewed from the long axis direction is measured clockwise, θ ₁ , and the liquid crystal molecules 7 on the upper side of the liquid crystal layer are measured.
The long axis of the upper birefringent plate as seen from the direction principal refractive indices n _x a theta ₂ that measure the direction 9A to clockwise, the lower side of the polarization viewed from the long axis direction of the liquid crystal molecules 8 of the lower liquid crystal layer Plate polarization axis 6
That measure the theta ₃ that measure the direction clockwise, the direction 9B principal refractive indices n _x of the lower bottom of the birefringent plate when viewed from the longitudinal direction of the liquid crystal molecules 8 in the liquid crystal layer in the clockwise Is θ ₄ . In the present invention, θ ₁ , θ ₂ , θ ₃ , and θ ₄ may be optimized so that black and white display is obtained when the color filters are excluded.

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 °, its Δn ₁ · d ₁ is about 0.8 μm, and the liquid crystal layer is arranged above and below it. When Δn ₂ · d ₂ of each of the pair of birefringent plates is set to 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 °.

Further, using the same liquid crystal layer and the birefringent plate,
When used in a positive display, it is preferable to arrange the polarizing axes of the pair of polarizing plates so as to intersect at an angle of about ± 30 °. 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, 5 °
It is preferable to set ≦ θ ₂ ≦ 140 ° and 40 ° ≦ θ ₄ ≦ 170 ° because a display having a sufficient contrast with a low OFF transmittance and a high ON transmittance can be realized.

Further, regarding θ ₁ , θ ₂ , θ ₃ , and θ ₄ , it is preferable that θ ₃ <θ ₄ when θ ₁ <θ _2, and when θ ₁ > θ ₂ , It is preferable that θ ₃ > θ ₄ . As a result, this liquid crystal display device can perform monochrome display with excellent viewing angle characteristics and high contrast ratio.

In particular, 40 ° ≦ θ ₂ ≦ 140 ° and 40 °
° ≦ θ ₄ ≦ 140 ° or −20 ° ≦ θ ₂ ≦ 20 °
When -20 ° ≦ θ ₄ ≦ 20 °, off transmittance is low and a sufficient contrast ratio can be obtained, which is preferable.

In the above example, the liquid crystal layer is a left helix, but when the helix is reversed, 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 main refraction of the birefringent plate. Rate _nx
By setting the relationships θ ₁ , θ ₂ , θ ₃ , and θ ₄ counterclockwise and selecting similarly, a monochrome display can be easily obtained in the same manner as in the above example.

The above description is the optimization obtained in the vertical direction of the liquid crystal display element, and is similar to the case where a uniaxial birefringent plate is used. However, when compensation is made with a 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 coloring or black and white is reversed, resulting in a beautiful Color display may not be obtained.

[0041] In the present invention, by a _{n x> n z> n y} , can be prevented with color when viewed from an oblique direction, thereby improving the appearance. The n _z is even greater than n _x, be less than n _y, the angular dependence is reduced, appearance is lowered when viewed from an oblique direction. In particular, ( _nz
With _{-n y) / (n x -n} y) ≧ 0.1,
This effect is great.

As such a birefringent plate, a biaxially stretched film or a biaxial crystal such as mica, gypsum, and saltpeter may be used.

In the above description, for the sake of simplicity, it is assumed that the refractive index _{nz in} the thickness direction of the birefringent plate is uniform in the thickness direction, but it is not necessarily required to be uniform. It is sufficient that the average refractive index in the thickness direction satisfies the above-described condition, and the same effect is obtained even when _nz is not uniform in the thickness direction.

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 realized 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 the viewing angle. Specifically, it may be formed below the electrode, or may be formed above the electrode.

When it is necessary to make the color more completely black and white, a color filter for correcting the color, a color polarizing plate may be used in combination, or a dye may be added to the liquid crystal.
Alternatively, illumination having a 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 can be applied 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 the transmission type is used, a background portion other than the 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.

According to the present invention, the time-division characteristics are comparable to those of the super-twisted liquid crystal display device, and a bright and clear black-and-white display is possible as described above. By arranging them on the inner surface or the like, a high-density multi-color liquid crystal display device can be obtained.

The liquid crystal display device of the present invention is suitable as a display device for a personal computer, a word processor, a work station, or the like. However, a color display such as a liquid crystal television, a fish finder, a radar, an oscilloscope, and various dot matrix display devices for consumer use. Can be used for display.

Although the operating principle of the present invention is not necessarily clear, it can be estimated as follows. First,
Consider a case where the liquid crystal display element is viewed from the vertical direction. FIG. 4A is a schematic side view showing the configuration of a super-twisted liquid crystal display device that does not use a birefringent plate for comparison with the liquid crystal display device of the present invention, and has a twist angle of 160 to 300 °. , Δn ₁ · d ₁ is 0.4 to 1.5 μ
m, a liquid crystal layer 13 of a nematic liquid crystal having a positive dielectric anisotropy of m, and a pair of polarizing plates 11, 1
2 is 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 the liquid crystal display device having such a configuration, in a state where no voltage is applied to the liquid crystal layer or in a state where a low voltage such as a non-selection voltage is applied, the liquid crystal layer passes through the lower polarizing plate 12 on the incident side. When almost completely linearly polarized light passes through the liquid crystal layer 13, the light becomes an elliptical polarization state. The shape and direction of this elliptical polarization depends on the wavelength of light,
When the light is divided into the three primary colors of red, green and blue, it is as shown in FIG. 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 indicate the polarization axes of the polarizing plates 11 and 12, respectively.

On the other hand, in the present invention, FIG. 5A is a schematic diagram viewed from the side. FIG. 5 (A)
Is a liquid crystal layer 23 of a nematic liquid crystal having a twist angle of 160 to 300 ° and Δn ₁ · d ₁ of 0.4 to 1.5 μm and having a positive dielectric anisotropy, and one of the liquid crystal layers 23 disposed on both sides thereof. The figure shows biaxial birefringent plates 24A and 24B and a pair of polarizing plates 21 and 22 arranged above and below the birefringent plates. In the following description, a color filter is not shown in order to make color correction by the birefringent plate easy to understand.

In this example, the twist angle of the liquid crystal layer is set to 240
°, Δn ₁ · d ₁ is 0.82 μm, and the crossing angle between the polarization axes of the pair of polarizing plates 21 and 22 arranged vertically is 90 °. In this example, one birefringent plate of the present invention is disposed on both sides for simplicity of description, but two or more birefringent plates may be used on both sides.

When this birefringent plate is sandwiched between polarizing plates, when viewed from the vertical direction, the birefringent plate has a ΔΔ
Depending on the value of n ₂ · d ₂ , there is a property that incident linearly polarized light can be changed to arbitrary elliptically polarized light, circularly polarized light, or returned to linearly polarized light. Therefore, an appropriate Δn ₂ · d ₂
By superposing the birefringent plate 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, the light almost linearly polarized through the lower polarizing plate 22 on the incident side. However, an appropriate elliptical polarization is obtained by the birefringent plate 24B below. When this elliptical polarized light passes through the liquid crystal layer 23, it becomes another elliptical polarized state. By passing this elliptically polarized light further through the birefringent plate 24A,
Under some conditions, elliptical polarized light may be returned to a state close to linearly polarized light in some cases.

This is as shown in FIG. 5B when light is divided into three primary colors of red, green and blue. 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. If an achromatic color can be obtained with the liquid crystal layer and the birefringent plate as described above, a vivid color display can be realized by combining it with a color filter.

As shown in this example, when a polarizing plate is installed so that its polarization axis crosses 90 °, and the polarization on the output side coincides with the absorption axis of the upper polarizing plate on the output side. , The transmitted light intensity is minimized, and the image looks black. Thus, a negative display is obtained. Note that in FIG.
Reference numerals 5 and 26 indicate the polarization axes of the polarizing plates 21 and 22, respectively.

Conversely, if the polarization axis of the upper polarizing plate is made substantially parallel to the polarization axis of the lower polarizing plate, these intensities become 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, its Δn ₁ · d ₁ , the Δn ₂ · d ₂ of the birefringent plate, and the angles θ ₁ , θ ₂ , θ ₃ , θ ₄ between them and the polarizing plate. It changes by changing the constituent requirements such as.

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 the voltage is applied. 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 the birefringent plate, the shape and direction of the circularly polarized light were successfully adjusted in a state where no voltage was applied, and a black or white state was formed. It is not always the state. Therefore, it is possible to experimentally optimize the birefringent plate Δn ₂ · d ₂ , its optical axis direction, the polarization axis direction of the polarizing plate, and the like by parameters such as the twist angle of the liquid crystal layer and Δn ₁ · d _1. preferable.

As described above, when the liquid crystal display element is viewed from the vertical direction, even if a uniaxial birefringent plate is simply used as the birefringent plate, a good black-and-white display element can be obtained by optimizing the conditions. Obtainable. 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, although the liquid crystal molecules are originally uniaxial in nature, they have a helical structure in the liquid crystal cell as shown in FIG. When a voltage is applied, the liquid crystal molecules near the center rise, so that the medium can no longer be regarded as a uniaxial medium, but can be regarded as a pseudo biaxial medium.

At this time, as shown in FIG. 6, attention is paid to the liquid crystal molecules near the center of the liquid crystal cell, and the average principal refractive indices in this region are defined as n _Lx , n _Ly , n _Lz (where n _Lx is the center). The average refractive index in the direction of projection of the liquid crystal molecules onto the substrate, n _Ly is the average refractive index in the direction perpendicular to n _Lx within the substrate plane, n _Lz
Is the average refractive index in the thickness direction). In this region, the liquid crystal molecules have a slightly helical structure and rise, so that it is expected that n _Lx > n _Lz > n _Ly .

[0065] Therefore, in order to correct even such a liquid crystal cell from the oblique direction is preferably birefringent plate of similar _{characteristics, n x> n z> n} y become such birefringence of the present invention It will be preferred to use a plate.

[0066]

【Example】

Examples 1 and 2 First, in order to confirm the degree of black and white by the liquid crystal layer and the birefringent plate, a liquid crystal display element was prepared using a substrate on which a color filter was not formed.

As a first substrate, an ITO transparent electrode provided on a glass substrate is patterned in a stripe shape,
A short-circuit preventing insulating film of SiO ₂ was formed by a vapor deposition method, a polyimide overcoat was spin-coated, and this was 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 polyimide is overcoated. This was rubbed so as to have an angle of intersection of 60 ° with the rubbing direction of the first substrate to form a substrate on which an orientation control film was formed.

A 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 to form a liquid crystal layer having a twist of 240 °. And the inlet was sealed. In this liquid crystal layer, Δn ₁ · d ₁ was 0.82 μm.

Various birefringent plates having a refractive index as shown in Table 1 were adhered to both sides of the liquid crystal cell one by one, and the widths of the viewing angles were compared.

[0071]

[Table 1]

The major axis direction of the liquid crystal molecules of this liquid crystal display element,
Relative relationship between the direction of the principal refractive indices n _x polarization axis direction and the birefringent plate polarizing _{plate, θ 1 = 150 °, θ} 2 = 80 °,
θ ₃ = 115 ° and θ ₄ = 90 °. The evaluation is
Driving with a 1/200 duty and a 1/15 bias was performed with the contrast ratio in the ON state and the OFF state.

The results are shown in FIGS. 7 to 11 show what is called an isocontrast curve. When the observation direction of the cell is displayed in polar coordinates, and the angle is expressed as (θ, Ψ), the contrast ratio of the liquid crystal cell is expressed by (θ, Ψ). Are shown by changing θ from 0 to 50 ° and changing Ψ from 0 to 360 °. In addition, Ψ 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. Contrast ratio (CR ratio)
Curve shows only 1, 10, and 50.

FIGS. 9 and 10 show embodiments of the liquid crystal display device according to the present invention, and FIGS. 7, 8 and 11 show comparative examples. However, these are all measured in a configuration excluding the color filter for easy comparison.

In the present invention, as shown in Table 1, n _x > n
Because using a birefringent plate such that _z> n _y, in the conventional mere uniaxial birefringent plate (n _x> n _y = n
_{From z} , Comparative Example 2 and FIG. 8), the contrast ratio indicated by oblique lines is 1 or less, that is, the region where the contrast of black and white is reversed is very small. Further, the region with a high contrast ratio (10 or more) was also widened, and an element with a wide viewing angle and a high contrast ratio was made possible.

On the other hand, when a biaxial birefringent plate other than the present invention is used, that is, in Comparative Example 1 ( _nx > _ny > _nz ) and Comparative Example 3 ( _nz > _nx > _ny ) In this case, as shown in FIGS. 7 and 11, it was found that the viewing angle was narrower than that of the present invention, and the region having a high contrast ratio was narrower.

Embodiments 3 and 4 As one of the substrates provided with the electrodes of the liquid crystal display element of Embodiments 1 and 2, three color filter layers of red, green and blue are formed on the substrate in stripes. When a cell was formed by using a substrate with electrodes on which electrodes were formed, and the cell was driven, full-color gradation driving was possible.

[0078]

As described above, the present invention has a wider viewing angle and a better viewing angle than the conventional two-layer type super twisted liquid crystal display device or the super twisted liquid crystal display device having a uniaxial birefringent plate laminated thereon. 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.

The time-division display characteristics and the viewing angle characteristics also have excellent effects such as being comparable to those of the conventional super-twisted liquid crystal display device. In addition, 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.
By arranging blue color filters for each pixel,
The effect that multi-color and full-color display can be realized is also recognized, and more diverse applications can be opened.

In particular, in the present invention, bright color display is possible despite vivid color display with high black-and-white degree, and not only transmission type display but also reflection type display is possible. It is wide.

Further, according to the present invention, a display having a high brightness and a high degree of black and white can be performed without providing the second liquid crystal layer simply by arranging the birefringent plate. It also has the advantage of being expensive.

The present invention can be variously applied in the future 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.

Figure 2 (A) (B), the long axis direction of liquid crystal molecules in the upper and lower as viewed from above, respectively, the direction of the relative position of the principal refractive indices n _x polarization axis direction and the birefringent plate of the polarizer FIG.

FIG. 3 is a perspective view showing a definition of a main refractive index of a birefringent plate.

FIGS. 4A and 4B are a schematic diagram showing a configuration of a mere super-twisted liquid crystal display element and a plan view for explaining a polarization state thereof.

FIGS. 5A and 5B are a schematic diagram showing a configuration of a liquid crystal display element of the present invention and a plan view for explaining a polarization state thereof.

FIG. 6 is a diagram showing a molecular arrangement of a liquid crystal cell.

FIG. 7 is a diagram showing an equal contrast curve of a liquid crystal display element.

FIG. 8 is a view showing an equal contrast curve of a liquid crystal display element.

FIG. 9 is a diagram showing an equal contrast curve of a liquid crystal display element.

FIG. 10 is a diagram showing an equal contrast curve of a liquid crystal display element.

FIG. 11 is a diagram showing an equal contrast curve of a liquid crystal display element.

[Explanation of symbols]

Polarizing plate: 1, 2, 11, 12,
21, 22 Liquid crystal layer: 3, 13, 23 Birefringent plate: 4A, 4B, 24A,
24B Polarization axis: 5, 6, 15, 16,
25 and 26 the long axis direction of liquid crystal molecules: 7,8 direction of the principal refractive indices n _x birefringent plate: 9A, 9B

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

Claims (6)

(57) [Claims] 1. A nematic liquid crystal having a positive dielectric anisotropy and containing a rotatory substance sandwiched between a pair of substrates having 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. A pair of polarizing plates is provided outside the liquid crystal layer, and a pair of polarizing plates is provided on both outer sides of the liquid crystal layer. In a color liquid crystal display device in which a pair of birefringent plates are disposed inside a pair of polarizing plates, a color filter is provided on the inner surface of the cell, the refractive index anisotropy Δn ₁ of the liquid crystal in the liquid crystal layer and the thickness of the liquid crystal layer. product [Delta] n ₁ · d ₁ and d ₁ is a 0.4 to 1.5 .mu.m, the birefringent plate is a birefringent plate having a refractive index different three directions, the three principal refractive indices n
_x, n _y, and n _z, n _x, the n _y and birefringent plate plane direction of the refractive index (n _x> n _y), when the n _z is the refractive index in the thickness direction of the birefringent plate, n color liquid crystal display device which is a _x> n _z> n _y. 2. The method according to claim 1, wherein the birefringent plate is a biaxially stretched film.
The color liquid crystal display device according to claim 1, wherein: Wherein _{n x> n z> n y} ≧ 1.5818 Dearuko
3. A color liquid crystal display according to claim 1, wherein:
element. Wherein the refractive index of the birefringent plate _{(n z -n y) / (} n
claim 1, characterized in that the _x -n _y) ≧ 0.1,
4. The color liquid crystal display device according to 2 or 3 . 5. The method according to claim 1, wherein the refractive index anisotropy of the birefringent plate is Δn ₂ = n _x −
Assuming that n _y is d ₂ and the thickness is d ₂ , each Δn ₂ of the pair of birefringent plates
· D ₂ Do almost half of the magnitude of Δn ₁ · d _1, it
Claim 1, characterized in that it is slightly smaller than
5. The color liquid crystal display device according to 2, 3, or 4. 6. A transmissive type, wherein a background portion other than a pixel is
3. The method according to claim 1, wherein the light-shielding film is covered with a light-shielding film .
6. The color liquid crystal display device according to 3, 4 or 5.