JP2625851B2 - Liquid crystal display element and liquid crystal display device using the same - Google Patents

Description

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

[Prior Art] Conventionally, as a method of increasing the twist angle of liquid crystal molecules between both electrodes to cause a sharp voltage-transmittance change and to realize a high-density dot matrix display, a super twist element (TJ Scheffer and Nehring, Appl., Phys., Lett. 45 (1
0) 1021-1023 (1984)).

However, in this method, the value of the product Δn · d of the birefringence Δn of the liquid crystal of the liquid crystal display element used and the thickness d of the liquid crystal layer is substantially between 0.8 and 1.2 μm (JP-A-60-10720).
No.), good contrast was obtained only with a combination of specific hues such as yellow-green and dark blue, and blue-violet and pale yellow as display colors.

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

On the other hand, there has been proposed a method in which a display almost close to white and black can be obtained by setting the product Δn · d of the birefringence of the liquid crystal and the thickness as small as about 0.5 μm using the same method. (M. Shadt et al, Appl. Phys. Lett. 50 (5), 1987,
However, in the case of using this method, the display is dark, the maximum contrast is not so large, and the display is bluish.

For the purpose of improving this, a second liquid crystal cell having the same liquid crystal and substantially the same twist angle but having the opposite helical direction is superimposed on the first liquid crystal cell having a larger twist angle. It has been proposed that a negative display in which the liquid crystal cell is arranged so that the alignment directions of adjacent liquid crystal molecular axes are substantially orthogonal to each other can be black in an off state and white in an on state. However, this method has a drawback that it is slightly bluish in the off state and slightly yellowish in the on state.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned disadvantages of the related art having the above-mentioned specific color, realize a display closer to black and white, and provide a bright liquid crystal with a high contrast ratio. It is intended to obtain a display element.

In addition, a fine color filter is formed inside or outside the cell to realize a mono-color or multi-color display, which has been realized by a conventional 90-degree twisted nematic (TN) element. It is.

[Means for Solving the Problems] The present invention has been made to solve the above-described problems, and has a structure in which a pair of transparent electrode substrates arranged substantially parallel to each other is provided.
A first liquid crystal cell containing a nematic liquid crystal having an optically rotatory substance and having a dielectric anisotropy having a twist angle of 160 to 300 ° between the two electrodes when no voltage is applied between the two electrodes, and a substantially nematic liquid crystal interposed therebetween; On the outer side between a pair of substrates arranged in parallel, an optically rotatory substance is contained, and the twist angle of liquid crystal molecules between the two electrodes when no voltage is applied is substantially 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 nematic liquid crystals having opposite helical directions is laminated, and a pair of polarizing plates is provided outside the liquid crystal display element, the refractive index anisotropy of the liquid crystal sealed in the second liquid crystal cell is increased. The wavelength dispersion of the property Δn ₂ is the refractive index anisotropy Δn _{1 of} the liquid crystal sealed in the first liquid crystal cell.
And a liquid crystal display device characterized in that the liquid crystal molecules are arranged so that the alignment directions of adjacent liquid crystal molecules of the first liquid crystal cell and the second liquid crystal cell are substantially orthogonal to each other. Liquid crystal display elements, 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 electrodes are arranged in a plurality of columns so as to be substantially orthogonal to the row. A liquid crystal display device is provided, which is arranged and connected to a row electrode group drive circuit and a column electrode group drive circuit, respectively, and drives only the first liquid crystal cell by applying a voltage. .

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

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

Specifically, a nematic liquid crystal having a positive dielectric anisotropy containing an optical rotatory substance is sandwiched between a pair of transparent electrode substrates arranged substantially in parallel, and the liquid crystal molecules between the two electrodes when no voltage is applied. May be set to 160 to 300 °.

In the present invention, the product Δn ₁ · d ₁ of the refractive index anisotropy Δn _{1 of the first} liquid crystal layer and the thickness d _{1 of the} liquid crystal layer can be used in a considerably wide range, and about 0.5 to 2.0 μm is used. it can. In particular, 0.6-0.6
A display with a brightness of about 1.4 μm and 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. The second liquid crystal cell has substantially the same twist angle as the first liquid crystal cell, the helical direction is reversed, and the wavelength dispersion of the refractive index anisotropy Δn ₂ of the liquid crystal is the same as that of the first liquid crystal cell. The nematic liquid crystal cell may be made smaller than the wavelength dispersion of the refractive index anisotropy Δn ₁ of the enclosed liquid crystal.

In this case, it is preferable that the values of Δn ₁ · d ₁ of the first liquid crystal cell and Δn ₂ · d ₂ of the _second liquid crystal cell be substantially equal from the viewpoint of monochrome display.

Further, it is preferable that the liquid crystal cells are arranged so that the alignment directions of the liquid crystal molecules adjacent to each other are substantially orthogonal to each other. That is, when two liquid crystal cells are formed of three substrates, the alignment direction of the central substrate may be set to be orthogonal on both surfaces. 4
In the case of using two substrates, it is only necessary that the orientation treatment directions of two intermediate substrates to be laminated are orthogonal to each other.

The nematic liquid crystal used in the second liquid crystal cell does not need to electrically control the molecular arrangement direction, so that it can be used even if the liquid crystal does not have a positive dielectric anisotropy. For this reason,
No electrode need be formed in the second liquid crystal cell.

In the present invention, the wavelength dispersion of the refractive index anisotropy Δn ₂ of the liquid crystal sealed in the second liquid crystal cell is made smaller than the wavelength dispersion of the refractive index anisotropy Δn ₁ of the liquid crystal sealed in the first liquid crystal cell. It is very important to. Thereby, the color at the time of on / off becomes a color closer to black and white.

The wavelength dispersion is a difference due to the difference in Δn of the liquid crystal depending on the wavelength, and is usually at the end of the visible light range. The determination may be made based on the ratio Δn ⁴⁰⁰ / Δn ⁷⁰⁰ when viewing Δn ^{400 at 400} nm and Δn ⁷⁰⁰ at ⁷⁰⁰ nm.

In the present invention, the second ratio Δn ₂ ⁴⁰⁰ / Δn ₂ ⁷⁰⁰ of the wavelength dispersion of the liquid crystal refractive index anisotropy [Delta] n ₂ which is sealed in the liquid crystal cell, the refractive index anisotropy of the liquid crystal sealed in the first liquid crystal cell It is smaller than the ratio Δn ₁ ⁴⁰⁰ / Δn ₁ ⁷⁰⁰ of the wavelength dispersion of [Delta] n _1.

However, in the present invention, 0 <(Δn ₁ ⁴⁰⁰ / Δ
^{_{n 1 700) - (Δn 2}} 400 / Δn 2 700) < is preferably set to about 0.15. When the difference is larger than 0.15, the transmittance of the black level at the time of off becomes high, and the influence is large, which is not preferable. On the other hand, when the value is smaller than 0, it becomes difficult to obtain a monochrome display. In particular, it is preferable to set the value to 0.03 or more because the display becomes closer to black and white display.

If the value of Δn ₁ · d ₁ of the first liquid crystal cell is different from the value of Δn ₂ · d ₂ of the _second liquid crystal cell, the direction of the polarization axis of the polarizing plate is changed as described later. Try to shift them from each other and adjust them so that a clearer black and white display is obtained.

These two liquid crystal cells are sandwiched between different substrates, respectively.
Two liquid crystal cells may be formed using four substrates and stacked, or a cell having two liquid crystal layers may be formed using three substrates.

In the present invention, since the second liquid crystal cell does not need to form an electrode, there is no problem of alignment or the like.
Two substrates can be used to sandwich two liquid crystal layers.

In the present invention, the twist angle of the liquid crystal is about 160 to 300 °. As a result, a liquid crystal display device having a high contrast ratio and less generation of domains can be easily obtained.

In the present invention, a pair of polarizing plates is disposed outside the 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 generally preferable that the polarizing axes of the pair of polarizing plates are arranged so as to be substantially orthogonal to each other. Δn ₁ · d _{1 of} the first and second liquid crystal cells,
Because it depends on the value of Δn ₂・ d ₂ and their difference, actually 60
The angle of intersection of the polarization axes may be changed in the range of up to 120 ° for optimization.

Furthermore, it is preferable that the polarizing axes of these polarizing plates are arranged in a direction that substantially divides the crossing angle of the liquid crystal molecular axis on the facing substrate surface of the liquid crystal layer adjacent to the polarizing plate.

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

FIG. 1 is a perspective view schematically showing a liquid crystal display device according to the present invention, and FIGS. 2 (A) and 2 (B) show a second liquid crystal cell and a lower liquid crystal cell shown in FIG. FIG. 5 is a plan view showing a relative position of a liquid crystal molecular axis direction of a first liquid crystal cell on the side and a polarization axis of an adjacent polarizing plate.

In the figures, reference numerals 1 and 2 denote polarizing plates attached to the top and bottom, 3 denotes a second liquid crystal cell to which no voltage is applied, and 4 denotes a first liquid crystal cell which specifically displays characters or 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 direction of the upper liquid crystal molecule axis of the second liquid crystal cell, and 8 is the lower liquid crystal molecule of the second liquid crystal cell. The axial direction, 9 indicates the liquid crystal molecular axis direction above the first liquid crystal cell, and 10 indicates the liquid crystal molecular axis direction below the first liquid crystal cell.

In the present invention, the adjacent liquid crystal molecular axes of the two 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. Is preferably about 90 °.

Further, as in this example, it is preferable that the polarization axes 5 and 6 of the pair of polarizing plates are substantially orthogonal to each other. Further, in this case, the polarization axis 5 of the upper polarizer 1 is aligned with the liquid crystal molecular axis direction of the adjacent liquid crystal layer, that is, the upper liquid crystal molecular axis direction 7 of the upper second liquid crystal cell 3 and the lower liquid crystal molecular axis. it is preferably disposed in a direction substantially equal to the angle theta ₂ between the direction 8. Similarly, the polarization axis 6 of the lower polarizing plate 2 is aligned with the liquid crystal molecular axis direction of the adjacent liquid crystal layer, that is, the upper liquid crystal molecular axis direction 9 of the lower first cell 4 and the lower liquid crystal molecular axis direction. preferably placed in a direction substantially equally dividing the angle theta ₁ with 10.

Further, the liquid crystal of the wavelength dispersion of the refractive index anisotropy [Delta] n ₂ of the second liquid crystal cell, the refractive index anisotropy [Delta] n ₁ of the liquid crystal molecules in the first liquid crystal cell
Smaller than the wavelength dispersion of, in particular, 0.03 <(Δn ₁ ⁴⁰⁰ / Δn _{1
^{700) - (Δn 2 400 -Δn}} 2 700) < is about 0.15.

As a result, the liquid crystal display element can perform display closer to black and white.

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

Among these, electrodes are formed on a substrate constituting a first liquid crystal cell for displaying specific contents, and a liquid crystal is turned on / off by applying a voltage between desired electrodes to perform display. This electrode is usually made of ITO (In ₂ O ₃ —SnO ₂ ), a transparent electrode such as SnO _{2 and the} like, and Al combined as necessary.
Low resistance leads such as Cr and Ti can be used, and desired patterning is performed. As a typical example, there is a dot matrix liquid crystal display element in which a large number of matrix-shaped electrodes are formed, and 640 stripe-shaped electrodes are formed on one substrate, and the other substrate is formed so as to be orthogonal thereto. In this case, 400 stripe-shaped electrodes are formed, and a display such as 640 × 400 dots is made.

For the treatment for aligning the liquid crystal molecules, a known rubbing method, an oblique deposition method, or the like can be used.
After forming a film of an inorganic material such as SiO ₂ , TiO ₂ , or Al ₂ O ₃ and / or a film of an organic material such as polyimide or polyamide, alignment treatment may be performed.

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

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

Further, in the above description, the second liquid crystal cell to which no voltage is applied is arranged above, but may be arranged below.

If the color needs to be completely converted to black and white, a color filter for correcting the color may be used in combination, or illumination having a specific wavelength analysis may be used.

Since the liquid crystal display element of the present invention is white display on a black background, it usually has a negative display and is often used in a transmission type, but can also be used in a reflection type. Also,
In the case of the reflective type, the background part is made to be a color close to white by printing, and a selection voltage is applied to the part that you do not want to display,
The reverse drive can also be performed.

In the liquid crystal display element of the present invention, one transparent electrode of the 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 orthogonal 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 are suitable for a liquid crystal display device of a type in which a voltage is applied to only the first liquid crystal cell to drive it. It is suitable for a dot matrix type liquid crystal display device.

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.

[Operation] Although the operation principle 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 has entered the first liquid crystal cell is converted into elliptically polarized light when exiting the first liquid crystal cell. When this elliptical polarized light enters and exits the second liquid crystal cell,
The light is substantially linearly polarized, and has a polarization axis in a direction substantially parallel to the polarization direction on the incident light side. If a polarization axis is provided orthogonal to the emitted light, the light is absorbed and blackened.

In the actual driving, the non-selection voltage is applied even in the off state, so that the state is completely out of the compensation state. Therefore, the Δ of the first liquid crystal cell and the second liquid crystal cell
If the chromatic dispersion of n is the same, the color of the off-state becomes bluish. Therefore, when a liquid crystal with small wavelength dispersion is used for the second liquid crystal cell, the compensation state at the blue wavelength is different, and as a result, a black level closer to black can be realized.

On the other hand, in a state where an electric field is applied to the first liquid crystal cell, the arrangement of the liquid crystal molecules in the first liquid crystal cell changes, and the output side of the second liquid crystal cell to which the electric field is not always applied and the input side Since the polarization axis is deviated in a direction substantially orthogonal to the polarization direction and passes through the polarizing plate disposed on the emission side as it is, the electric field application part (electrically selected segment part) becomes white, and as a result, white and black Display color.

In this white state, it takes on a yellow tint under normal conditions, but under the conditions of the present invention, a white level closer to white can be obtained.

As a result, the conventional super-twisted liquid crystal display device showed good contrast only in a specific hue combination such as yellow-green and dark blue, and blue-violet and pale yellow, whereas the present invention provides a high-quality clear black-and-white display. A contrast ratio becomes possible.

In the present invention, the time-division characteristics are almost the same as those of the super-twisted liquid crystal display element, and since a clear black-and-white display is possible as described above, a fine color filter of three primary colors of red, green and blue is arranged on the inner surface of the cell or the like. By doing so, 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 of a personal computer, a word processor, a workstation, and the like, but the outer liquid crystal television, a fish finder, a radar, an oscilloscope, a black and white display such as various consumer dot matrix display devices, and a color display device. It can be used for various purposes without displaying.

Example Next, an example of the present invention will be described in detail with reference to the drawings.

Example 1 A liquid crystal display device having a configuration as shown in FIGS. 1 and 2 was prepared.

ITO provided on a glass substrate as the first substrate
A transparent electrode was patterned in a stripe pattern, overcoated with polyimide, and rubbed to form an alignment layer.

As the second substrate, ITO transparent electrodes provided on the first substrate and the glass substrate are patterned in a stripe shape so as to be orthogonal to the first substrate, overcoated with polyimide, and rubbed. In addition to forming an alignment layer, a backside on which no electrode was formed was also overcoated with polyimide, and rubbed in a direction perpendicular to the front side to form an alignment layer.

As a third substrate, a simple glass substrate on which no electrode was formed was used, and a substrate overcoated with polyimide and rubbed to form an alignment layer was used.

The periphery of the three substrates was sealed with a sealing material to form two layers into which liquid crystal was injected. In this first liquid crystal layer,
The mixed liquid crystal “ZLI-3329” manufactured by Merck was sealed, and the mixed liquid crystal “ZLI-3276” manufactured by Merck was sealed in the second liquid crystal layer.

The first ratio Δn ₁ ⁴⁰⁰ / Δn ₁ ⁷⁰⁰ of the wavelength dispersion of the mixed liquid crystal layer liquid crystal "ZLI-3329" is 1.23, the ratio [Delta] n wavelength dispersion of the mixed liquid crystal of the second liquid crystal layer "ZLI-3276" ₂ ⁴⁰⁰ / Δn ₂ ⁷⁰⁰
Was 1.16. ^{_{That, (Δn 1 400 / Δn 1}} 700) - (Δn 2
⁴⁰⁰ / Δn ₂ ⁷⁰⁰ ) was 0.07.

The twist angles of both of these liquid crystal layers were both 240 °, and the liquid crystal layers were twisted in opposite directions, and the values of Δn ₁ · d ₁ and Δn ₂ · d ₂ were both 0.8 μm.

Polarizing plates were disposed on both sides of the liquid crystal cell in directions in which the crossing angles of the liquid crystal molecular axes of the adjacent opposing substrates were equally divided. Thereby, the polarization axes of the pair of polarizing plates were set to be orthogonal.

This liquid crystal display element was driven at a 1/200 duty and a 1/15 bias with a backlight with a cold cathode discharge tube arranged on the back side.

Example 1 As a comparative example, a mixed liquid crystal “ZLI-3329” manufactured by Merck was encapsulated in both liquid crystal layers, and the values of Δn ₁ · d ₁ and Δn ₂ · d ₂ were both 0.8 μm. A liquid crystal display device was manufactured in the same manner as described above. The liquid crystal display device of this comparative example was driven under the same conditions as those of the example.

FIG. 3 is a diagram showing the state of display colors at the time of driving of these examples and the comparative example, where “○” indicates the on state of this example, “●” indicates the off state of this example, “□” indicates the ON state of the comparative example, and “Δ” indicates the OFF state of the comparative example.

As is clear from this figure, in each of 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 has a higher color than the comparative example. It turns out that it is close to black and white.

In the element 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 A stripe of 3 was formed on the electrode of the liquid crystal display element of Example 1.
When the color filter layer was formed and driven, full-color gradation driving with good color reproducibility was possible even in a halftone.

[Effects of the Invention] As described above, the present invention enables a display closer to black and white while having a contrast ratio equal to or higher than that of a conventional super-twisted liquid crystal display element, and provides clear display and display quality. Is high.

In addition, time-division display characteristics and a wide viewing angle also have excellent effects such as comparable to that of the conventional super twisted liquid crystal display device.

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

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

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a liquid crystal display device according to the present invention. FIGS. 2A and 2B show the polarization axes of the polarizers adjacent to the liquid crystal molecular axis directions of the upper second liquid crystal cell and the lower first liquid crystal cell of FIG. It is the top view which showed the relative position. FIG. 3 is a chromaticity diagram showing display colors of the example and the comparative example. Reference numerals 1 and 2 denote polarizing plates, 3 denotes a second liquid crystal cell to which no voltage is applied, 4 denotes a first liquid crystal cell to which a voltage is applied, 5 denotes a polarization axis of the upper polarizing plate 1, and 6 denotes a lower polarizing plate 2. 7 is a liquid crystal molecular axis direction above the second liquid crystal cell, 8 is a liquid crystal molecular axis direction below the second liquid crystal cell, 9 is a liquid crystal molecular axis direction above the first liquid crystal cell, 10 is the liquid crystal molecular axis direction below the first liquid crystal cell

Claims (5)

(57) [Claims] 1. A dielectric material comprising an optical rotatory substance between a pair of transparent electrode substrates arranged substantially in parallel, wherein the twist angle of liquid crystal molecules between the two electrodes when no voltage is applied is 160 to 300 °. An optically rotatory substance is contained between a first liquid crystal cell sandwiching a nematic liquid crystal having a positive anisotropy and a pair of substrates disposed substantially parallel to each other, and the optically active substance is formed between the two electrodes when no voltage is applied. A second liquid crystal cell sandwiching nematic liquid crystal having a twist angle of liquid crystal molecules substantially equal to that of the first liquid crystal cell and having a helical direction opposite to that of the first liquid crystal cell is laminated, and a pair of polarizing plates is installed outside the second liquid crystal cell. In the liquid crystal display device, the wavelength dispersion of the refractive index anisotropy Δn ₂ of the liquid crystal sealed in the second liquid crystal cell is larger than the wavelength dispersion of the refractive index anisotropy Δn ₁ of the liquid crystal sealed in the first liquid crystal cell. A liquid crystal display element characterized by being reduced in size. 2. The liquid crystal display device according to claim 1, wherein adjacent liquid crystal molecules of the first liquid crystal cell and the second liquid crystal cell are arranged so that their alignment directions are substantially orthogonal. 3. The liquid crystal display device according to claim 1, wherein the polarization axis of the polarizing plate is arranged in a direction that substantially divides the crossing angle of the liquid crystal molecular axis on the opposing substrate surface. In 4. 400nm and 700 nm, and the refractive index anisotropy [Delta] n ₂ of the liquid crystal molecules in the second liquid crystal cell, and the refractive index anisotropy [Delta] n ₁ of the liquid crystal molecules in the first liquid crystal cell satisfies the following relationship The liquid crystal display device according to claim 1, wherein: ^{_{0.03 <(Δn 1 400 / Δn}} 1 700) - (Δn 2 400 / Δn 2 700) <0.15 5. The liquid crystal display device according to claim 1, wherein one of the transparent electrodes of the first liquid crystal cell is arranged in a plurality of rows, and the other transparent electrode is substantially orthogonal to the rows. A liquid crystal display device, wherein a plurality of columns are arranged in a row, and these are connected to a row electrode group drive circuit and a column electrode group drive circuit, respectively, and drive is performed by applying a voltage only to the first liquid crystal cell. .