JPH01257918A - Liquid crystal element and liquid crystal display device using same - Google Patents

Abstract

PURPOSE:To obtain the bright liquid crystal display element which has a high contrast ratio by forming two liquid crystal layers and making the wavelength dispersion of the refractive index anisotropy of liquid crystal charged in a 2nd liquid crystal cell smaller than the wavelength dispersion of the refractive index anisotropy of liquid crystal charged in a 1st liquid crystal cell. CONSTITUTION:The 1st liquid crystal cell 4 is formed by sandwiching the nematic liquid crystal of positive dielectric anisotropy which contains a rotary polarizing material between a couple of transparent electrode substrates and the twist angle of liquid crystal molecules between both electrodes when no voltage is applied is 160-300 deg.. In this case, the 2nd liquid crystal cell 3 is laminated adjacently to the 1st liquid crystal cell, but the 2nd liquid crystal cell 3 has nearly the same twist angle with the 1st liquid crystal cell 4 and is opposite in spiral direction, and the wavelength dispersion of refractive index anisotropy DELTAn2 of the liquid crystal is made smaller than the wavelength dispersion of refractive index anisotropy DELTAn1 of the 1st liquid crystal cell. Consequently, the color at the time of turn-on/turn-off operation is as close to black and white as possible and the bright liquid crystal display element which has the high contrast ratio is obtained.

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, both? ! ! The super twist element (T, J, 5chefferand Nehri
ng, Appl, Phys, Lett.
45 (10) 1021-1023 (1984))
was known.

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 (Japanese Patent Application Laid-Open No. 60-10
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 0.5 μm, thereby obtaining a nearly black and white display. . (M, 5hadtet al, Appl
, Phys, Lett, 50(5), 19
(87°p, 236) However, when this method is used, the display is dark, the maximum contrast is not very high, and the display is bluish, resulting in a lack of clarity.

In addition, in order to improve this problem, a second liquid crystal cell with the same liquid crystal, almost the same twist angle, and an opposite helical direction was stacked on top of the first liquid crystal cell with a large twist angle. It has been proposed that a negative display that is black in the off state and white in the on state can be realized by arranging the liquid crystal cells so that the alignment directions of adjacent liquid crystal molecular axes are substantially orthogonal to each other. However, this method has the disadvantage that it has a slightly bluish tinge in the off state and a slightly yellowish tinge in the on state.

1. Problems to be Solved by the Invention 1. The purpose of the present invention is to eliminate the disadvantage of the above-mentioned characteristic color that the prior art had, and to realize a display that is closer to black and white, and which is bright and has a high contrast ratio. The purpose is to obtain a liquid crystal display element.

Furthermore, by forming a fine color filter inside or outside the cell, it is possible to realize a mono-color or multi-color display as previously achieved with a normal twisted nematic (TN) element with a 90° twist. It is.

[Means for Solving the Problems 1] The present invention has been made to solve the above-mentioned problems, and includes an optically active substance between a pair of transparent electrode substrates arranged approximately parallel to each other, and the voltage Between a first liquid crystal cell sandwiching a nematic liquid crystal with positive dielectric anisotropy with a twist angle of liquid crystal molecules between both electrodes of 160 to 300 degrees when no voltage is applied, and a pair of substrates arranged almost parallel to each other. On the outside, a nematic liquid crystal containing an optically active substance and having a twist angle of the liquid crystal molecules between the two electrodes when no voltage is applied is approximately the same as that of the first liquid crystal cell, and the helical direction is opposite. In a liquid crystal display element in which a sandwiched second liquid crystal cell is laminated and a pair of polarizing plates are installed on the outside thereof, the wavelength dispersion of the refractive index anisotropy Δn of the liquid crystal sealed in the second liquid crystal cell is Refractive index anisotropy Δ of the liquid crystal sealed in the liquid crystal cell No. 1
A liquid crystal display element characterized in that the wavelength dispersion is smaller than the wavelength dispersion of n1, and in the liquid crystal display element, the alignment directions of adjacent liquid crystal molecules of a first liquid crystal cell and a second liquid crystal cell are substantially perpendicular to each other. a liquid crystal display element arranged, and
One transparent electrode of the first liquid crystal cell of those liquid crystal display elements is arranged in a plurality of rows, and the other transparent electrode is arranged in a plurality of columns so as to be substantially perpendicular to the row. The present invention provides a liquid crystal display device that is connected to a group drive circuit and a column electrode group drive circuit, and is driven by applying voltage only to a first liquid crystal cell.

In the present invention, there are two liquid crystal layers.

First, the first liquid crystal cell has the same structure as the liquid crystal cell of the conventional super twist liquid crystal display element, and the electric scratching groups are facing each other, so that it is possible to control on/off for each dot. Ru. The twist angle of this first liquid crystal layer is about 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 liquid crystal molecules between the two electrodes when no voltage is applied. The twist angle may be set to 160 to 300°.

In the present invention, the product Δn16 dl of the refractive index anisotropy Δn1 of the first liquid crystal layer and the thickness dl of the liquid crystal layer can be used within a fairly wide range, and approximately 0.5 to 2.0 μm can be used. In particular, when the thickness is about 0.6 to 1.4 μm, which is used in conventional super twist liquid crystal display elements, a bright display with a high contrast ratio can be easily obtained.

In the present invention, a second liquid crystal cell is stacked adjacent to the first liquid crystal cell. This second liquid crystal cell has almost the same twist angle as the first liquid crystal cell, the helical direction is opposite, and the wavelength dispersion of 〇2 due to the refractive index anisotropy of the liquid crystal is different from that of the first liquid crystal cell. The nematic liquid crystal cell may be a nematic liquid crystal cell whose wavelength dispersion is smaller than the wavelength dispersion of the refractive index anisotropy Δn+ of the liquid crystal sealed in the liquid crystal.

In this case, from the viewpoint of black-and-white display, it is preferable that the values of Δn1-dl of the first liquid crystal cell and Δn,·d2 of the second liquid crystal cell be approximately equal.

In addition, it is preferable that the alignment directions of adjacent liquid crystal molecules in both liquid crystal cells are arranged to be almost perpendicular to each other. In other words, when two liquid crystal cells are configured with three substrates, the alignment direction of the central substrate is In the case of configuring four substrates, it is sufficient that the alignment directions of the two intermediate substrates arranged in 11 layers are orthogonal to each other.

Since the nematic liquid crystal used in this second liquid crystal cell does not require electrical control of the molecular alignment direction, it can be used even if the dielectric anisotropy of the liquid crystal is not positive. Therefore, it is not necessary to form an electrode in the second liquid crystal cell.

In the present invention, the wavelength dispersion of the refractive index anisotropy Δn2 of the liquid crystal sealed in the second liquid crystal cell is made smaller than the wavelength dispersion of the refractive index anisotropy Δn of the liquid crystal sealed in the first liquid crystal cell. This is very important. This makes the colors closer to black and white when on and off.

This wavelength dispersion is the difference caused by the difference in Δn of the liquid crystal depending on the wavelength, and is usually the ratio of Δn400 at 400 nm, which is the edge of the visible light range, to Δn700 at 700 nm, Δn 400 / Δn7
It is sufficient to judge at °0.

In the present invention, the ratio of the wavelength dispersion of the refractive index anisotropy Δn of the liquid crystal sealed in the second liquid crystal cell is Δn240°/Δnll'.

0 is the refractive index anisotropy Δ of the liquid crystal sealed in the first liquid crystal cell
Ratio of wavelength dispersion of n, Δn, 400 /Δn, 700
be made smaller than

However, in the present invention, 0〈(Δn, 400/Δn
,? OO) (Δn, 400/Δn,
'') It is preferable that the difference be about <0.15. This is because if this difference is larger than 0.15, the transmittance of the black level during off time will increase, which is undesirable due to the large influence. If it is smaller than 0.03, it will be difficult to obtain a black and white display.In particular, it is preferable to set it to 0.03 or more because it will more closely approximate a black and white display.

If the values of Δn,・d of the first liquid crystal cell and Δn2・d of the second liquid crystal cell are different, the polarization axes of the polarizing plates should be changed to each other as described later. Try moving it to the left and adjust it to get a clearer black and white display.

These two liquid crystal cells are sandwiched between separate substrates, and
Two substrates may be used to form two liquid crystal cells and these may be stacked and used, or three substrates may be used to form a cell having two liquid crystal layers.

In the present invention, there is no need to form electrodes in the second liquid crystal cell, so problems such as first alignment do not occur, so three substrates can be easily used to sandwich two liquid crystal layers. I can do it.

In the present invention, the twist angle of the liquid crystal is approximately 160 to 300 degrees. As a result, a liquid crystal display element with a high contrast ratio and fewer domains can be easily obtained.

In the present invention, a pair of polarizing plates are placed outside these two liquid crystal layers.

In order to obtain a display that is closer to black and white and has a high contrast ratio, it is preferable that the polarization axes of these pair of polarizing plates are arranged to be almost orthogonal in terms of -119.
For optimal adhesion, the corners should be Δn1 of the first and second liquid crystal cells.
Because it depends on the values of d,,Δn2・d, and their difference,
In reality, the angle of intersection of the polarization axes may be varied in the range of 60 to 120 @ for optimization.

Further, it is preferable that the polarizing axes of these polarizing plates are arranged in a direction that substantially equally divides the intersection angle of the liquid crystal molecule axes on the opposing substrate surfaces of the liquid crystal layer adjacent to the polarizing plate.

The relative positions of the liquid crystal molecular axis and the polarization axis of the polarizing plate in the liquid crystal display element of the present invention when no voltage is applied are shown in FIGS. 1 and 2.

FIG. 1 is a perspective view schematically showing a liquid crystal display element according to the present invention, and FIGS. 2(A) and 2(B) respectively show the upper second liquid crystal cell and the upper part of FIG. 1 when viewed from above. FIG. 3 is a plan view showing the relative position of the liquid crystal molecule axis direction of the lower first liquid crystal cell and the polarization axis of an adjacent polarizing plate.

In the figure, reference numerals 1 and 2 indicate polarizing plates to be pasted on the upper and lower sides, 3 a second liquid crystal cell to which no voltage is applied, and 4 a first liquid crystal cell that specifically displays characters and the like by applying a voltage. 5 is the polarization axis of the upper polarizing plate 1, 6 is the polarization axis of the lower polarizing plate 2, 7 is the upper liquid crystal molecule axis direction of the second liquid crystal cell, and 8 is the lower liquid crystal of the second liquid crystal cell. 9 indicates the direction of the liquid crystal molecule axis on the upper side of the first liquid crystal cell, and 10 indicates the direction of the liquid crystal molecule axis on the lower side of the first liquid crystal cell.

In the present invention, the adjacent liquid crystal molecular axes of both liquid crystal layers are substantially orthogonal, that is, the liquid crystal molecular axis direction 8 on the lower side of the second liquid crystal cell and the liquid crystal molecular axis direction 9 on the upper side of the first liquid crystal cell. Preferably, the angle ψ formed by the two is approximately 90''.

Further, as in this example, it is preferable that the polarizing axes 5.6 of the pair of polarizing plates are substantially perpendicular to each other. Furthermore, in this case, the polarizing axis 5 of the upper polarizing plate 1 is the same as that of the adjacent liquid crystal layer. It is preferable to arrange the liquid crystal molecule axis direction, that is, in a direction that almost equally divides the angle O3 formed by the upper liquid crystal molecule axis direction 7 and the lower liquid crystal molecule axis direction 8 of the upper second liquid crystal cell 3. Similarly, the polarization axis 6 of the lower polarizing plate 2 is the liquid crystal molecule axis direction of the adjacent liquid crystal layer, that is, the upper liquid crystal molecule axis direction 9 of the lower first liquid crystal cell 4 and the lower liquid crystal molecule axis direction. It is preferable that they be arranged in a direction that substantially equally divides the angle θ1 formed with the axial direction 10.

Furthermore, the wavelength dispersion of the refractive index anisotropy Δn2 of the liquid crystal of the second liquid crystal cell is different from the refractive index anisotropy Δn of the liquid crystal of the first liquid crystal cell.
+ wavelength dispersion, especially 0.03< (Δn
, 400/Δn,? 0O)-(Δn, 400/Δ
n, ”' ) <0.15 or so.

As a result, this liquid crystal display element can display a display that is closer to black and white.

In the present invention, the substrate constituting the liquid crystal cell may be an optically equisymmetric transparent substrate, and glass, plastic, etc. can be used.

Among these, electrodes are formed on the substrate constituting the first liquid crystal cell that displays specific content, and display is performed by turning the liquid crystal on and off by applying a voltage between the desired electrodes.
This electrode is usually ITO (IntOi-3no
w) A transparent electrode such as Snow or the like and a low resistance lead such as AI, Cr, Ti or the like combined therewith as required can be used to achieve the desired patterning. A typical example of this is a dot-to-matrix liquid crystal display device in which a large number of electrodes are formed in rows and columns, and 640 stripe-like electrodes are formed on one substrate and perpendicular to these electrodes on the other substrate. 400 striped electrodes are formed in this way, and a display like 640 x 400 dots is made.

As a treatment for aligning liquid crystal molecules, known rubbing methods, oblique evaporation methods, etc. can be used.
After forming a film of an inorganic material such as 10m, Ti1t, or AIJs and/or a film of an organic material such as polyimide or polyamide, alignment treatment may be performed.

Note that in the present invention, since a display close to a black and white display 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 achieved, 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.

Further, in the above description, the second liquid crystal cell to which no voltage is applied is placed at the top, but it may be placed at the bottom.

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

Since the liquid crystal display element of the present invention displays white on a black background, it usually has a negative type display and is often used as a transmissive type, but it can also be used as a reflective type. Further, in the case of a reflective type, the background part can be printed in a color close to white, and the driving can be performed in the opposite manner, such as applying a selection voltage to the part that is not desired to be displayed.

In the liquid crystal display element of the present invention, one transparent electrode of a first liquid crystal cell is arranged in a plurality of rows, and the other transparent electrode is arranged in a plurality of columns so as to be substantially perpendicular to the row. The electrode group and the column electrode group are connected to a row electrode group drive circuit and a column electrode group drive circuit, respectively, and a voltage is applied to only the first liquid crystal cell to drive the liquid crystal display device. It is particularly suitable for dot matrix type liquid crystal display devices.

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.

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

That is, in a state where no electric field is applied to the first liquid crystal cell, linearly polarized light that enters the first liquid crystal cell becomes elliptically polarized when it exits the first liquid crystal cell. When this elliptical polarized light enters the second liquid crystal cell and exits, it becomes substantially linearly polarized light and has a polarization axis in a direction substantially parallel to the polarization direction on the incident light side. When a polarization axis is provided perpendicular to this emitted light, light absorption occurs and the light becomes black.

In actual driving, a non-selective voltage is applied even when off, resulting in a deviation from a complete compensation state. Therefore, Δn of the first liquid crystal cell and the second liquid crystal cell
If the chromatic dispersion of the two is the same, the off-state color (I) will have a bluish tinge. Therefore, if a liquid crystal with small wavelength dispersion is used for the second liquid crystal cell, the compensation state at the blue wavelength will be different, and as a result, a black level closer to black can be realized.

On the other hand, when an electric field is applied to the first liquid crystal cell, the arrangement of liquid crystal molecules in the first liquid crystal cell changes, and the output side of the second liquid crystal cell, to which no electric field is applied, always changes to the input side. The polarization axis is biased in a direction almost perpendicular to the polarization direction and passes through the polarizing plate placed on the output side as it is, so the electric field application section (electrically selected segment section) becomes white.
As a result, the display colors are white and black.

This white state has a yellowish tinge under normal conditions, but under the conditions of the present invention, a white level closer to white can be obtained.

As a result, while conventional super-twist liquid crystal display elements showed good contrast only in specific combinations of hues such as yellow-green and dark blue, bluish-purple and light yellow, the present invention provides clear black-and-white display with high contrast. Contrast ratio is possible.

In the present invention, the time division characteristics are comparable to those of the super twist liquid crystal display element, and as mentioned above, clear black and white display is possible, so fine color filters of the three primary colors of red, green, and blue are placed on the inner surface of the cell, etc. By doing so, it is also possible to obtain a high-density multicolor 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, including black and white display and color display.

[Example 1 Next, embodiments of the present invention will be described in detail using the drawings.

Example 1 A liquid crystal display element having the configuration shown in FIGS. 1 and 2 was produced.

ITO provided on a glass substrate as the first substrate
A substrate was used in which transparent electrodes were buttered into stripes, overcoated with polyimide, and rubbed to form an alignment layer.

For the second substrate, the ITO transparent electrodes provided on the first substrate and the glass substrate were patterned into stripes perpendicular to the first curtain plate, and overcoated with polyimide. A substrate was used in which an alignment layer was formed by rubbing, a polyimide overcoat was applied to the back side where no electrode was formed, and an alignment layer was formed by rubbing this in a direction perpendicular to the front side.

As the third substrate, we used a simple glass substrate with no electrodes formed on it, and overcoated it with polyimide.
A substrate on which an alignment layer was formed by rubbing this was used.

The peripheries of these three substrates were sealed with a sealant to form two layers into which liquid crystal was injected. This first liquid crystal layer is filled with a mixed liquid crystal r ZLI-3329J manufactured by Merck & Co., Ltd.
The second liquid crystal layer is a mixed liquid crystal r ZLI- manufactured by Merck & Co.
3276J was enclosed.

The wavelength dispersion ratio Δn, 400/Δn, too of the mixed liquid crystal r ZLI-3329J of this first liquid crystal layer is 1.
23, and the mixed liquid crystal r of the second liquid crystal layer ZLI-32
Ratio of chromatic dispersion of 76J Δn, 400/Δn1°0
was 1.16. That is, (Δn1→00/Δn, y
oo) The value of (Δn, 400/Δn, yoo) is 0
．． It was 07.

The twist angles of both of these liquid crystal layers are both 2401, and the twist angles are opposite to each other, and Δn,・d, and Δn,・d,
Both values were set to 0.8 μm.

Polarizing plates were placed on both sides of this liquid crystal cell, respectively, in a direction that equally divided the intersection angles of the liquid crystal molecular axes of the adjacent and opposing substrates. Thereby, the polarization axes of the pair of polarizing plates were set to be perpendicular to each other.

A backlight with a cold cathode discharge frame was disposed on the back side of this liquid crystal display element, and it was driven at a duty of 1/200 and a bias of 1/15.

As a comparative example, a mixed liquid crystal r ZLI-3329J manufactured by Merck & Co. was sealed in both liquid crystal layers, and the values of Δnl・dl and Δno・d were both 0.8 μm, but the same as in Example 1. A liquid crystal display element was manufactured. The liquid crystal display element of this comparative example was also driven under the same conditions as the example.

FIG. 3 is a diagram showing the state of display colors during driving in these examples and comparative examples, and rOJ indicates the on state of this example.
"•" indicates the off state of this example, "mouth" indicates the on state of the comparative example, and "■" indicates the off state of the comparative example.

As is clear from this figure, both in the on state and the off state, the element of the example shows a color closer to the C light source than the element of the comparative example, and this example shows a color closer to the C light source than the element of the comparative example. You can see that it's almost black and white.

In the device of this example, the segment corresponding to the non-selection voltage was black, the segment corresponding to the selection voltage was white, and the contrast ratio (pixel portion) was about 30.

Example 2 When three color filter layers were formed in stripes on the electrodes of the liquid crystal display element of Example 1 and the device was driven, full-color gradation driving with good color reproducibility even in intermediate tones was possible. there were.

[Effects of the Invention] As explained above, the present invention has a contrast ratio equal to or higher than that of conventional super-twist liquid crystal display elements, and enables display closer to black and white, resulting in clearer and higher display quality. A high display can be obtained.

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

In addition, since the display is close to black and white, it is possible to display colorful displays by combining it with color filters.In particular, by arranging red, green, and blue color filters for each pixel, multi-color and full-color displays can be achieved. It has also been recognized that the method can be used to realize even more diverse applications.

The present invention can be applied in various ways to known liquid crystal display elements within a range that does not impair the effects of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing a liquid crystal display element according to the present invention. 2(A) and 2(B) show the directions of the liquid crystal molecular axes of the upper second liquid crystal cell and the lower first liquid crystal cell of FIG. 1 as viewed from above, respectively, and the polarizing axes of the adjacent polarizing plates. FIG. 3 is a plan view showing relative positions. FIG. 3 is a chromaticity diagram showing display colors of Examples and Comparative Examples. ], 2 is a polarizing plate, 3 is a second liquid crystal cell to which no voltage is applied, 4 is a first Ura crystal cell to which a voltage is applied, 5 is a polarizing axis of the upper polarizing plate l, 6 is a lower polarizing plate 2 is the polarization axis, 7 is the upper liquid crystal molecule axis direction of the second liquid crystal cell, and 8 is the second polarization axis.
9 is the liquid crystal molecule axis direction on the upper side of the first liquid crystal cell, 10 is the liquid crystal molecule axis direction on the lower side of the first liquid crystal cell.

Claims (4)

[Claims] (1) Between a pair of transparent electrode substrates arranged almost parallel,
A first liquid crystal cell sandwiching a nematic liquid crystal containing an optically active substance and having a positive dielectric anisotropy with a twist angle of liquid crystal molecules between the two electrodes of 160 to 300 degrees when no voltage is applied; An optically active substance is contained on the outside between a pair of substrates arranged in parallel, and the twist angle of the liquid crystal molecules between the two electrodes when no voltage is applied is approximately the same as that of the first liquid crystal cell, and In a liquid crystal display element in which a second liquid crystal cell sandwiching a nematic liquid crystal having an opposite helical direction is laminated, and a pair of polarizing plates is installed on the outside of the second liquid crystal cell, the second
A liquid crystal display characterized in that the wavelength dispersion of the refractive index anisotropy Δn_2 of the liquid crystal sealed in the first liquid crystal cell is smaller than the wavelength dispersion of the refractive index anisotropy Δn_1 of the liquid crystal sealed in the first liquid crystal cell. element. (2) The liquid crystal display element according to claim 1, wherein the first liquid crystal cell and the second liquid crystal cell are arranged so that the alignment directions of adjacent liquid crystal molecules are substantially perpendicular to each other. (3) One transparent electrode of the first liquid crystal cell of the liquid crystal display element according to claim 1 or 2 is arranged in a plurality of rows, and the other transparent electrode is arranged in a plurality of columns substantially perpendicular to the row. A liquid crystal display device characterized in that the first liquid crystal cell is driven by applying a voltage to only the first liquid crystal cell by connecting the first liquid crystal cell to a row electrode group drive circuit and a column electrode group drive circuit, respectively. (4) Any of claims 1 to 3, wherein the polarizing axis of the polarizing plate is arranged in a direction that approximately equally divides the intersection angle of the liquid crystal molecule axes on the opposing substrate surfaces.