JPH02291519A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To allow the sharp display of a positive or negative type with a high display grade by disposing a double refractive plate having the uniaxiality to attain nx=nz>ny when nx and ny among three main refractive indices are designated as the refractive indices in the intra-surface direction of the double refractive plate and nz is designated as the refractive index in the thickness direction on one side between a liquid crystal layer and a polarizing plate. CONSTITUTION:The product DELTAn1.d1 of the refractive index anisotropy DELTAn1 of the liquid crystal in the liquid crystal layer 3 of the liquid crystal display element disposed with the double refractive plate 4 on one side between the liquid crystal 3 and the polarizing layers 1, 2 and the thickness d1 of the liquid crystal layer 3 is specified to 0.4 to 1.5mum. The double refractive plate 4 having such uniaxiality as to attain nx=nz>ny when the three main refractive indices of the double refractive plate 4 are designated as nx, ny and nz, nx, ny as the refractive indices in the intra-surface direction of the double refractive plate and (nx>nz), nz as the refractive indices in the thickness direction of the double refractive plate is disposed. The black and white display element which is good in contrast, bright and is wide in an angle of field is produced at a good yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display element suitable for high-density display.

[Conventional technology] Conventionally, by increasing the twist angle of liquid crystal molecules between both electrodes,
A super twist element (T
．． J. Schefferand J. Nehr
ing, Appl. , Phys. , Lett.
45(10) 1021-1023 (1984)
) was known.

However, in this method, the value of the product Δn-d of the birefringence 8n of the liquid product 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 (particularly 1986-10
No. 720), good contrast was obtained only with specific combinations of display colors, such as yellow-green and dark blue, bluish-violet and light yellow.

As described above, since this liquid crystal display element could not perform black and white display, it had the disadvantage that it could not perform multicolor or full color display when combined with a microcolor filter.

On the other hand, a method has been proposed that uses a similar method and sets the product Δn-d of the liquid crystal's birefringence and thickness to a small value of around 0.6 μm, thereby obtaining a nearly black and white display. There is. (M. Schadt et al, Ap
pl. Phys. Lett. 50(5),
19B? , p. 236) However, when this method was used, the display was dark, the maximum contrast was not very thick, and the display had a bluish tinge, resulting in a lack of clarity. In addition, as a liquid crystal display element with black and white display and high contrast, there is a method in which two layers of liquid crystal cells with opposite spirals are stacked, a voltage is applied to only one cell, and the other cell is used simply as an optical compensation plate. Proposed. (Hoga Okumura, Television Society Technical Report, 11(27), p.7
9, (1987)) However, in this method, the matching of Δn-d in a two-layer cell is very strict, making it difficult to improve yield, and since two layers of liquid crystal cells are required, the thinness of the liquid crystal cell
The drawback was that it sacrificed its lightness. In addition, a film-stacked liquid crystal display element has been proposed in which one of the two-layer cells described above is replaced with a uniaxial birefringent film to enable black-and-white display (Japanese Patent Laid-Open No. 63-2714).
No. 15, etc.).

[Problems to be Solved by the Invention I] Such a normal uniaxial birefringent film has three principal refractive indices of nm. ny. Let n* be n. ．． When n is the refractive index in the in-plane direction of the birefringent plate (n.>ny), and n is the refractive index in the thickness direction of the birefringent plate, nx> n
It has the property that y = nx. In a film-stacked liquid crystal display device using such a uniaxial birefringent film, compensation for the liquid crystal cell is performed by the uniaxial birefringent film as described above, so although it looks good in the vertical direction, However, it had the disadvantage that when viewed from an angle, it would appear colored or the black and white would be reversed.

For this reason, it has been difficult to produce liquid crystal display elements that are bright, have good black and white, and have a wide viewing angle with a high yield. Bright 《Black and white display elements with a wide viewing angle are not only easy to see without any distinctive coloring, but also have a color filter formed inside or outside the cell, making it possible to use conventional twisted nematic (TN) elements with a 90° twist. It is expected that the market will expand dramatically as it will be able to realize mono-color, multi-color, or full-color displays, and will exhibit its characteristics of being thin, light, and low power consumption.

For this reason, there has been a desire for a liquid crystal display element that can produce a black and white display element with good contrast, brightness, and a wide viewing angle with a high yield.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems. The twist angle of nematic liquid crystal with positive dielectric anisotropy containing an optically active substance is 160
It has a liquid crystal layer of ~300° and a driving means that applies voltage between transparent electrodes of upper and lower substrates that sandwich this liquid crystal layer. A pair of polarizing plates is installed outside this liquid crystal layer, and the liquid crystal layer and In a liquid crystal display element in which a birefringent plate is arranged on one side between the polarizer and the polarizing plate, the product Δn1·d of the refractive index anisotropy Δn1 of the liquid crystal in the liquid crystal layer and the thickness d+ of the liquid crystal layer is 0.4 to 1. .5 μm, and the birefringent plate has three principal refractive indices of nm, ny.
Let nx be the refractive index in the in-plane direction of the birefringent plate (n yo > ny) * If nx is the refractive index in the thickness direction of the birefringent plate, then +1+1= nu > ny. The present invention provides a liquid crystal display element characterized by disposing a uniaxial birefringent plate.

In the present invention, each of the three principal refractive indices is n++. ny.
nl, nm. If ny is the refractive index in the in-plane direction of the birefringent plate (n.>n,) and nx is the refractive index in the thickness direction of the birefringent plate, then A birefringent plate is used, and this l-axis birefringent plate is placed on one side between the liquid crystal layer and the polarizing plate.

For this reason, the conventional n. >n,=n. Compared to the case of using a uniaxial birefringent plate with the following relationship, it has the same contrast ratio at the center and a wider viewing angle.
In particular, this has the advantage that the area where black and white are reversed becomes narrower.

This liquid crystal layer has the same structure as the liquid crystal layer of a conventional super twist liquid crystal display element, and has electrode groups facing each other, so that it is possible to control on/off for each dot. The twist angle of this liquid crystal layer is approximately 160 to 300'.

Specifically, a nematic liquid crystal with positive dielectric anisotropy containing an optically active substance is sandwiched between a pair of transparent electrode substrates arranged almost in parallel, and the twist angle of the liquid crystal molecules between the two electrodes is set to 1.
The angle may be 60 to 300°. This is because when the angle is less than 160°, there is little improvement in contrast when performing time-division driving at high duty rates, which requires a steep change in transmittance.On the other hand, when the angle exceeds 300°, hysteresis and a domain that disrupts the light occur. This is because it is easy to cause

In addition, the product Δn,·d, of the refractive index anisotropy (Δn+) of the liquid crystal in the liquid crystal layer and the thickness (a.) of the liquid crystal layer is 0.4 to 1.5.
It is assumed to be μm.

This is because when the thickness is less than 0.4 μm, the transmittance when turned on is low.
The display color tends to be bluish, and the thickness of 1.5 μm
If the value exceeds this value, the hue when turned on changes from yellow to red, and the display becomes black and white.

In particular, in applications where display colors are strictly required to be achromatic,
80,·d+ of the liquid crystal layer is preferably 0.5 to 1.0 μm. Note that this Δn1・d. It is preferable that the range 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, only in a portion of the operating temperature range,
It is possible that this relationship may be satisfied. In this case, in a temperature range where the range of Δn1·d1 deviates from the above range, the display will be colored or the viewing angle characteristics will deteriorate.

ITO (InaO) patterned into a desired pattern
a-Sn02), Sno2, etc. A film of polyimide, polyamide, etc. is provided on the surface of a substrate such as plastic or glass on which a transparent electrode is provided, and this surface is rubbed or SiO
A substrate with transparent electrodes on which an alignment control film is formed by obliquely vapor-depositing the above-mentioned nematic liquid crystal with positive dielectric anisotropy is placed between the substrates with transparent electrodes.
A liquid crystal layer with a twist of 0 to 300 degrees is sandwiched therebetween. A typical example of this is a dot matrix liquid crystal display device in which a large number of electrodes are formed in rows and columns, with 640 striped electrodes formed on one substrate, and 640 striped electrodes perpendicular to these electrodes on the other substrate. 400 strip-shaped electrodes are formed so that a display like 640 x 400 dots is made. Further, these 640 stripe-shaped electrodes can be made into a set of 3 each to make 1920 stripe-shaped electrodes, and RGB color filters can be arranged to display a full-color 640×400 dot display.

Note that an insulating film such as TiOz, SiO2, Al-Oa, etc. may be provided between the electrode and the alignment control film to prevent short circuit between the substrates, or an Al. Cr. A lead electrode of low resistance such as Ti may also be provided, or a color filter may be laminated above or below the electrode.

A pair of polarizing plates is placed on both sides of this liquid crystal layer. This polarizing plate itself is generally placed outside the substrate that constitutes the cell, but if performance permits, the substrate itself may be composed of a polarizing plate and a birefringent plate, or a birefringent plate may be placed between the substrate and the electrode. It may be provided as a refractive layer and a polarizing layer.

In the present invention, an l-axis birefringent plate whose principal refractive index satisfies Q,=ng>ny is disposed adjacent to one side of the liquid crystal layer.

In addition, this l-axis birefringent plate may be provided between the liquid crystal layer and the polarizing plate. Alternatively, the substrate itself may be a birefringent plate, a layer may be provided between the substrate and a polarizing plate, or a combination of these may be provided.

As the uniaxial birefringent plate of the present invention, any transparent plate exhibiting birefringence as described below can be used, and plastic films, inorganic crystal plates, etc. can be used.

This uniaxial birefringent plate has three principal refractive indices of n. ．． n
Y, n! and nm. Let ny be the refractive index in the in-plane direction of the birefringent plate (nm>ny). When n* is the refractive index in the thickness direction of the birefringent plate, n++ ” nz > ny
It is a uniaxial birefringent plate such that

To obtain the desired birefringence effect, Δn2・d2=(nx
ny) - Although d2 is adjusted and used, if it cannot be adjusted with a single plate, a combination of the same uniaxial birefringent plate or a plurality of different l-axis birefringent plates may be used.

In order to perform a good black and white display, the Δn of the birefringent plate must be
It is important to optimize the size of 2.d2 and the direction in which they are attached, as well as the direction of the polarization axes of the pair of polarizing plates.

Since this birefringent plate is placed on one side between the liquid crystal layer and the polarizing plate, the size of Δn2·d2 of the birefringent plate is approximately the same as Δn,·d2 of the liquid crystal layer. Good black and white display can be easily obtained by setting the value to be approximately the same as or slightly smaller than the size of . Specifically, it may be about 0.1 to 1.5 LLm. Also,
When a plurality of birefringent plates are used in a stacked manner, the total value of Δn2·d2 may be within the above range.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a perspective view schematically showing a liquid crystal display element according to the present invention. Figures 2 (A) and (B) show the polarization axis direction of the upper polarizing plate in Figure 1, the optical axis direction of the birefringent plate, the long axis direction of the liquid crystal molecules above the liquid crystal layer, and , is a plan view showing the relative positions of the polarization axis direction of the lower polarizing plate and the long sleeve direction of the liquid crystal molecules under the liquid crystal layer.

In FIG. 1, 1 and 2 are a pair of polarizing plates, and 3 is Δn. for displaying characters and figures.・d+ is 0.4 to 15 μm
The twist angle of the nematic liquid crystal with positive dielectric anisotropy is 1.
60-300° left-handed spiral (counterclockwise twist when viewed from above) liquid crystal layer, 4 is a birefringent plate laminated on top of it, 5 is the polarizing axis of the upper polarizing plate, 6 is the lower polarizing plate polarization axis,
Reference numeral 7 indicates liquid crystal molecules above the liquid crystal layer, 8 indicates liquid crystal molecules below the liquid crystal layer, and 9 indicates the optical axis direction of the birefringent plate.

The definition of the principal refractive index of the l-axis birefringent plate used in the present invention will be explained with reference to FIG.

In the uniaxial birefringent plate of the present invention, the direction of the larger refractive index in the in-plane direction of the birefringent plate is the X-axis direction, the direction of the smaller refractive index is the y-axis direction, and the thickness direction is the biaxial direction. do. The refractive index in each direction is assumed to be 08, ny, and nx. In this case, n. > n, and Δn2=: nX n, and in the present invention, nA02>n. At this time,
The optical axis direction of the birefringent plate is the y-axis direction. Note that d is the thickness of the birefringent plate.

In Figure 2, θ is the direction of the polarization axis 5 of the upper polarizing plate viewed from the long axis direction of the liquid crystal molecules 7 above the liquid crystal layer, and the length of the liquid crystal molecules 7 above the liquid crystal layer. 02 is the optical axis direction 9 of the birefringence slope measured clockwise when viewed from the axial direction, and clockwise is the direction of the polarization axis 6 of the lower polarizing plate when viewed from the long axis direction of the liquid crystal molecules 8 below the liquid crystal layer. Let the measured circumference be θ. In the present invention, it is sufficient to optimize these θθ2, θ so that a black and white display is achieved.

When using the liquid crystal display element of the present invention in negative type display,
For example, if the twist angle of the liquid crystal layer is about 240°, the Δ
n1・d. If it is about 0.9 μm and Δn2・d2 of the birefringent plate placed above it is about 0.6 μm, then the pair of polarizing plates are arranged so that their polarization axes intersect at an angle of about 0 to 60 degrees. It is preferable to do so.

Furthermore, when used in a positive type display, it is preferable that the polarizing axis of one polarizing plate be rotated by approximately 90 degrees. As a result, this liquid crystal display element is capable of high-contrast black-and-white display with excellent viewing angle characteristics.

In this case, especially for negative display, -85°≦02≦
By setting the angle to 50°, it is possible to realize a display having sufficient contrast with low off-state transmittance and high on-state transmittance, which is preferable.

In particular, by setting -50°≦02≦50′, it is preferable to obtain a low off-state transmittance and a sufficient contrast ratio of 1.

In the above example, the liquid crystal layer is left-handed, but if the spiral is reversed, the direction of the long axis of the liquid crystal molecules in the liquid crystal layer, the direction of the polarization axis of the polarizing plate, and the optical axis direction of the birefringent plate may be changed. Relationship θ,, θ
2. By turning θ3 counterclockwise and choosing in the same way,
As in the above example, black and white display can be easily obtained.

Further, when this birefringence plate is inserted under the liquid crystal cell, 01, θ2, and θ3 may be selected so that the relationship is similar to the above-described relationship when the cell is viewed from below.

In the present invention, by setting n++=nx>n,
When viewed from an oblique direction, the area where black and white are reversed becomes narrower, making it possible to widen the viewing angle.

In addition, in the present invention, since a display close to black and white display with a wide viewing angle can be obtained, a colorful display can be achieved by using a color filter in combination. In particular, even with high-duty driving, a high contrast ratio can be obtained, so full-color gradation display is possible, and it can also be used in LCD televisions.

By forming this color filter on the inner surface of the cell, more precise color display is possible without causing deviation due to viewing angle. Specifically, it may be formed below the electrode or above the electrode.

Also, if you need to make the colors completely black and white,
A color filter for color correction or a color polarizing plate may also be used, a dye may be added to the liquid crystal, or illumination having a specific wavelength distribution may be used.

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

In particular, since the present invention enables bright display, it can be applied to either a transmissive type or a reflective type, and has a wide range of applications.

Note that when using a transmission type, a light source is placed on the back side. Of course, a light guide, a color filter, etc. may be used in combination with this.

The liquid crystal display element of the present invention is often used in a transmissive type, but since it is bright, it can also be used in a reflective type.

When using a transmissive type, the background portion other than the pixels can be covered with a light-shielding film by printing or the like. Further, in addition to using a light-shielding film, it is also possible to perform reverse driving such that a selection voltage is applied to the displayed portion.

In addition to this, the present invention includes, within the scope that does not impair the effects of the present invention,
Various techniques used in ordinary liquid crystal display elements can be applied.

In the present invention, the time division characteristics are on the same level as super twist liquid crystal display elements, and as mentioned above, bright and clear black and white display is possible. By arranging them, it is possible to obtain a high-density multi-color liquid crystal display element.

The liquid crystal display element of the present invention can be used for personal computers,
Suitable as a display element for word processors, workstations, etc., but also for LCD TVs, fish finders, etc.
It can be used for a variety of purposes, including radar, oscilloscope, and various consumer dot matrix display devices, regardless of black and white display or color display.

[Operation 1] Although the principle of operation of the present invention is not necessarily clear, it can be estimated as follows.

First, the case where the liquid crystal display element is viewed from the vertical direction will be considered.

FIG. 4(A) is a schematic side view showing the structure of a super-twist liquid crystal display element that does not use a birefringent plate in comparison with the liquid crystal display element of the present invention, and the twist angle is 1.
At 60~300°, Δnl'' dl is 0.4~1.5
A liquid crystal [13] made of a nematic liquid crystal having a positive dielectric anisotropy of μm, and a pair of polarizing plates 11 disposed above and below the liquid crystal [13].
In this example, the crossing angle of the polarization axes of the pair of polarizing plates 11 and 12 arranged above and below is 90°.

In the case of a liquid crystal display element having such a configuration, when no voltage is applied to the liquid crystal layer or when a low voltage such as a non-selection voltage is applied, the lower polarizing plate l on the incident side
When light that has been almost completely linearly polarized through 2 passes through this liquid crystal layer 13, it becomes elliptically polarized. The shape and direction of this elliptical polarization differ depending on the wavelength of the light, and it divides light into three colors: red, green, and blue.
If we consider the primary colors separately, we get something like Figure 4 (B). When these circularly polarized lights, which have different shapes and directions, pass through the upper polarizing plate 11 on the output side, the intensity of the passing light differs depending on the red, green, and blue light, so that it appears colored in a specific color. In addition, in FIG. 4(B), 15, l6
are respectively polarizing plates 11. 12 polarization axes are shown.

In contrast, in the present invention, the twist angle is 160 to 300 degrees, as shown in a schematic diagram seen from the side in FIG.
A liquid crystal layer 23 made of nematic liquid crystal having positive dielectric anisotropy with Δnl' dl of 0.4 to 1.5 μm, one l-axis birefringent plate 24 placed above it, and further above and below A pair of arranged polarizing plates 2L22 are shown.

In this example, the twist angle of the liquid crystal layer is 240°Δn1・d+
is 0.87 μm, and a pair of polarizing plates 2 are arranged above and below.
The crossing angle of the polarization axes of 1.22 is 30°. In addition,
In this example, in order to simplify the explanation, one uniaxial birefringent plate of the present invention is placed on the top surface of the liquid crystal cell.
Two or more birefringent plates may be used. When this birefringent plate is sandwiched between polarizing plates,
When viewed from the vertical direction, depending on the value of Δn2・d2 of this birefringent plate, the incident linearly polarized light can be made into arbitrary elliptical polarized light,
It has the property of being able to make circularly polarized light or return it to linearly polarized light. Therefore, by superimposing a birefringent plate with an appropriate value of Δn2·d2 on the liquid crystal layer, the structure shown in FIG. 5 (.B) can be obtained.

That is, in a state where no voltage is applied to the liquid crystal layer or a low voltage such as a non-selective voltage is applied, light that is almost completely linearly polarized through the lower polarizing plate 22 on the incident side passes through the liquid crystal layer. When the light passes through the layer 23, it becomes an elliptical polarized state. When this elliptical polarized light passes through the birefringent plate 24, the elliptical polarized light may be returned to a state close to linearly polarized light depending on the conditions.

If we consider that light is divided into the three primary colors of red, green, and blue, it becomes as shown in Figure 5 (B). As in this example, when the directions of the polarization axes of red, green, and blue are almost the same and the polarization returns to almost linear polarization, regardless of the direction of the polarization axis on the output side, the wavelength dependence of the intensity of the passing light is can be done. In other words, it is possible to make the color achromatic.

As in this example, if a polarizing plate is installed with the polarization axes intersecting 90 degrees and the polarized light on the output side matches the absorption axis of the upper polarizing plate on the output side, the transmitted light The intensity is the lowest and it appears black. This results in a negative display.

In addition, in FIG. 5(B), 25 and 26 are polarizing plates 2, respectively.
1. 22 polarization axes are shown.

On the other hand, if the polarization axis of the upper polarizing plate is rotated by approximately 90 degrees, the intensity of these will be large and the image will appear white, resulting in a blurred display.

Note that negative and positive display values are determined by the twist angle of the liquid crystal layer and its Δ
n,·d, Δn2·d2 of the birefringent plate, and the angle θ between them and the polarizing plate. , θ2, 08, etc. by changing the configuration requirements.

On the other hand, if a sufficient voltage is applied to the liquid crystal layer with this configuration, the shape and direction of the circularly polarized light transmitted through the liquid crystal layer will be different from before the voltage was applied.

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

However, although the insertion of a birefringent plate successfully aligns the shape and direction of the elliptical polarized light and creates a black or white state when no voltage is applied, this does not necessarily mean that the state becomes white or black when a voltage is applied. is not limited. For this reason, it is preferable to experimentally optimize Δn2·d2 of the birefringent plate, its front axis direction, the polarization axis direction of the polarizing plate, etc. using parameters such as the twist angle of the liquid crystal layer and Δn1·d1.

]Example 1 Examples 1 to 3, Comparative Example 1 As a first substrate, an ITO transparent electrode provided on a glass substrate was patterned into stripes, and an insulating film for preventing short circuits due to Sins was formed by vapor deposition. Then, a polyimide overcoat was coated, and this was rubbed to create a substrate on which an alignment control film was formed. Is it provided on a glass substrate as a second substrate? The ITO transparent electrode was patterned in a stripe shape perpendicular to the first substrate, an SiO2 insulating film was formed, and a polyimide overcoat was applied. A substrate on which an alignment control film was formed was prepared by rubbing so that the following was obtained.

The peripheries of these two substrates are sealed with a sealing material to form a liquid crystal cell, and a nematic liquid crystal with positive dielectric anisotropy is injected into this liquid crystal cell to form a liquid crystal layer twisted at 240 degrees. The injection port was sealed. The 80,·d1 of the liquid crystal layer of Example 1 was 0.87 μm. Between the top surface of this liquid crystal cell and the upper polarizing plate, one each of various uniaxial birefringent plates having refractive indexes shown in Table 1 (Examples 1 to 3, Comparative Example 1) was installed. Pasted.

The relative relationships between the long axis direction of the liquid crystal molecules, the polarization axis direction of the polarizing plate, and the optical axis direction of the birefringent plate in the liquid crystal display elements of Examples 1 to 3 are as follows: θ1=45°, θ2=5°, θs =135
°.

Table 1 Note that in Comparative Example 1, the optical axis direction of the birefringent plate is in the X direction by definition, so it is deviated by 90 degrees from that in the example, so θ2=95 degrees.

As a result of applying a voltage to this liquid crystal display element and examining the change in transmittance, it was found that good threshold voltage characteristics were obtained as shown in Figure 6, and a good contrast ratio was obtained when multiplex driving was performed. I found out that it can be done.

A backlight of a C light source was placed on the back side of this liquid crystal display element, and the device was driven at a duty of 1/200 and a bias of 1/15, and the hue in the on state and off state was observed. The results are shown in FIG. As is clear from these results, a good white level with a slightly yellow-greenish color was obtained when the display was on, and because the transmittance was low when the display was off, a negative black and white display that appeared sufficiently black was obtained.

When the contrast ratio (pixel portion only) of the liquid crystal display element of Example 1 was measured, it was approximately 50, which was much higher than that of a conventional simple super twist liquid crystal display element. Furthermore, the transmittance in the ON state was about 27%, and since it was brighter than the OMI element, it was also possible to use it as a reflective type.

In addition, when the contrast ratio (pixel portion only) of the liquid crystal display elements of Example 2 and Example 3 was measured, both were 4.
It was 0 or more.

The isocontrast curves of Example 1 and Comparative Example 1 are shown in FIGS. 8 and 9. In these figures, if the observation direction of the cell is expressed in polar coordinates and the angle is expressed as (θ, A), how the contrast ratio of the liquid crystal cell changes depending on (θ, A) is shown. The figures are shown with θ changed from 0 to 50° and the instep changed from 0 to 360°.

Note that ψ was set at 0° in the main viewing angle direction (downward) of the figure, and ranged from 0 to 360° counterclockwise, and θ was set at 0° at the center, and ranged from 0 to 50° concentrically. The contrast ratio curve is 1, l
Only O, 50 was shown.

FIG. 8 shows Example 1 of the liquid crystal display element according to the present invention, and FIG. 9 shows Comparative Example 1.

In the present invention, as shown in Table 1, n*=n〉
Since we are using a birefringent plate such that ny, the contrast ratio shown by diagonal lines is 1 compared to the conventional uniaxial birefringent plate (nl) ny = nz, Comparative Example 1, Figure 9). In other words, the area where the black-and-white contrast is reversed has become smaller, and the viewing angle has become wider, making it possible to create a device with a high contrast ratio.

Example 4 A liquid crystal display element was created by changing only the relative relationship between the long axis direction of the liquid crystal molecules, the polarization axis direction of the polarizing plate, and the optical axis direction of the birefringent plate in the liquid crystal display element of Example 1. . That is, θ, = 135°θ. = 5”.θs =
It was set to 135°.

When this liquid crystal display element was driven at a duty of 1/200 and a bias of 1/15 in the same manner as in Example 1, a positive black and white display was obtained, and the contrast ratio (pixel portion only) was approximately 40.

Example 5 As the substrate with electrodes of the liquid crystal display element of Example 1, a substrate with electrodes in which color filter layers of three colors were formed in a stripe shape on the substrate and electrodes were formed on the substrate was used. When a cell was configured and driven, full color gradation driving was possible.

[Effects of the Invention] As explained above, the present invention has a wider viewing angle and a larger viewing angle than the conventional two-calendar type super-twist liquid crystal display element or the conventional super-twist liquid crystal display element in which -axial birefringent plates are laminated. A black-and-white display with a better contrast ratio is possible, and a clear, high-quality positive or negative display can be obtained.

In addition, it has excellent effects such as time division display characteristics and viewing angle characteristics comparable to those of conventional super twist liquid crystal display elements.

In addition, since the display is close to black and white and has a wide field of view, it is possible to create a colorful display by combining it with color filters. It has also been recognized that it can produce color or full-color displays, opening up more diverse applications.

In particular, although the present invention enables black-and-white display, bright display is possible, and not only transmissive type display but also reflective type display is possible, and its application range is wide.

Furthermore, in the present invention, by simply arranging the birefringent plate,
Even without providing a second liquid crystal layer, bright black and white display is possible, and the liquid crystal display element has the advantage of extremely high productivity.

The present invention can be applied in various ways in the future without detracting from the effects of the present invention.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a liquid crystal display element according to the present invention. Figures 2 (A) and (B) are plan views showing the relative positions of the long axis directions of the upper and lower liquid crystal molecules, the polarization axis direction of the polarizing plate, and the optical axis direction of the birefringent plate, respectively, when viewed from above. It is. FIG. 3 is a perspective view showing the definition of the principal refractive index of a birefringent plate. FIGS. 4(A) and 4(B) are schematic diagrams showing the structure of a simple super-twist liquid crystal display element, and plan views illustrating the state of polarization thereof. FIGS. 5(A) and 5(B) are schematic diagrams showing the structure of the liquid crystal display element of the present invention and plan views illustrating the state of polarization thereof. FIG. 6 is a graph showing the threshold voltage characteristics of Example 1. FIG. 7 is a hue diagram showing hues in the on and off states of Example 1. FIG. 8 and FIG. 9 are diagrams showing equal contrast curves of Example 1 and Comparative Example 1. ■, 2, 11. 12, 21. 22 is a polarizing plate, 3, 1
3, 23 are liquid crystal layers, 4, 24 are birefringent plates, 5, 6, l5, l6, 25, 26 are polarization axes, 7, 8 are long axis directions of liquid crystal molecules, 9 are optical axis directions of birefringent plates Figure X Figure 1.5 2.0 2.5 Applied voltage (V) 3.0 Figure

Claims (3)

[Claims] (1) A nematic liquid crystal with positive dielectric anisotropy containing an optically active substance sandwiched between a pair of substrates with transparent electrodes arranged almost in parallel and having an alignment control film has a twist angle of 16
It has a liquid crystal layer with an angle of 0 to 300 degrees, and a driving means for applying a voltage between transparent electrodes of upper and lower substrates that sandwich this liquid crystal layer,
In a liquid crystal display element in which a pair of polarizing plates is installed outside the liquid crystal layer and a birefringent plate is placed on one side between the liquid crystal layer and the polarizing plate, the refractive index anisotropy Δn_1 of the liquid crystal in the liquid crystal layer and the liquid crystal The product Δn_1·d_1 with the layer thickness d_1 is 0.4 to 1.
5 μm, and the birefringent plate has three principal refractive indices n_x
, n_y, n_z, n_x, n_y are the refractive indices in the in-plane direction of the birefringent plate (n_x>n_y), and n_x is the refractive index in the thickness direction of the birefringent plate, then n_x=n_z>n
A liquid crystal display element characterized in that a uniaxial birefringent plate is arranged so that _y. (2) In the liquid crystal display element according to claim 1, the intersection angle between the liquid crystal molecular axis and the optical axis of the birefringent plate is -50°≦θ_2≦5.
A liquid crystal display element characterized in that it is arranged at an angle of 0°. (3) In the liquid crystal display element according to claim 1 or 2,
A liquid crystal display element characterized by having a color filter formed on the inner surface of the cell.