JPH05107563A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the element which has high transmittance and small dependency on visual sensation, is low in driving voltage and has a high response speed by putting the arrangement of a liquid crystal compsn. into a scattering state in microregions with the fine particles of liquid exclusive of the liquid crystal compsn. as nuclei and enabling controlling of this state. CONSTITUTION:The liquid exclusive of the liquid crystal is dispersed in the form of the fine particles 1 in a colloidal state into the liquid crystal 2. The cause for the perpendicular arrangement of the liquid crystal molecules 3 of the liquid crystal 2 on the surface of the fine particles 1 of the liquid lies in the boundary tension by the unbalance of the Van del Waals attraction force at the fine particle-liquid boundary. The shape of the particles is in principle perfectly speroidal and the liquid crystal molecules are arranged the boundary. The light scattering state by the disturbance of the liquid crystal molecule arrangement is, therefore, obtd. Namely, the fine particles exclusive of the liquid crystal compsn. are dispersed into the liquid crystal compsn. and liquid crystal molecules are perpendicularly adsorbed on the surfaces of the fine particles. The arrangement of the liquid crystal compsn. is put into the scattering state in the microregions with such fine particles as the nuclei. The display element having the high scattering characteristic, the low driving voltage and the highly bright contrast ratio is obtd. in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices (hereinafter abbreviated as LCD) have been widely used in word processors, personal computers, projection TVs, small TVs, and the like.

When these LCDs are classified from the viewpoint of light control, light and dark changes are caused by a combination of a polarization effect of liquid crystal molecules and a polarizer, and a phase transition of liquid crystals is used to cause light scattering and transmission. And a dye that is added to control the amount of visible light absorption of the dye to generate a color shade.

L, which is a combination of the former polarization effect and a polarizer
CD is a twisted nematic (TN) type liquid crystal having, for example, a 90 ° twisted molecular arrangement. In principle, polarization control can be performed at a low voltage, so that a high response ratio, low power consumption, and high contrast ratio It has been applied to a full color display liquid crystal TV and the like by using a calculator, a simple matrix drive, an active matrix drive having a switching element for each pixel, and a color filter in combination.

However, an LCD combining these polarization effects and a polarizer has a remarkably low transmittance of the element since a polarizing plate is used in principle, and the display color and the contrast ratio depend on the viewing angle / direction depending on the orientation of the molecular arrangement. Has a viewing angle dependency such as a large change in the display angle, and cannot completely exceed the display performance of a cathode ray tube (CRT).

On the other hand, the latter one utilizing the phase transition of liquid crystal and the LCD in which the visible light absorption amount of the dye is controlled, for example, from a cholesteric phase having a helical molecular arrangement to a homeotropic molecular nematic phase. A phase transition (PC) type liquid crystal that causes a phase transition by applying an electric field and a white-Taylor type guest host (GH) liquid crystal obtained by adding a dye to the phase transition (PC) type liquid crystal. In principle, a polarization effect is used without using a polarizer. Since it is not available, it is bright and has a wide viewing angle, and is applied to automobile equipment and projection-type displays.

However, in order to obtain sufficient light scattering, it is necessary to sufficiently thicken the liquid crystal phase and to increase the helical strength that causes scattering, which requires a high driving voltage and extremely slow response speed. Therefore, it is difficult to apply it to a display device having a large display amount (number of pixels). Further, it has been considered difficult to bring about gradation because the transmittance changes abruptly as the applied voltage increases.
Further, the applied voltage-transmittance characteristic has a hysteresis, and there is a practical problem that it is difficult to perform multiplex driving.

Further, as shown in FIG. 3, a microcapsule (NCA) in which a liquid crystal 16 is spherically held in an organic polymer 15 is used.
The P) -type LCD is a liquid crystal display element in a scattering mode and has no polarizing plate, so it is bright and has a wide viewing angle, and is applied to automobile devices, projection-type displays and the like. However, the voltage applied from the outside is divided into the organic polymer 15 and the liquid crystal 16, and only a part of the applied voltage is applied to the liquid crystal, which causes a problem that the operating voltage is increased practically. Further, in order to obtain sufficient light scattering, it is necessary to make the liquid crystal thickness sufficiently thick, and there is a problem that the response speed is extremely slow, so it is difficult to apply it to a display element with a large display amount (pixel number). Was there. Further, the applied voltage-transmittance characteristic has a hysteresis, and there is a practical problem that it is difficult to perform multiplex driving. The polymer-dispersed LCD in which liquid crystal is held in a network organic polymer that operates according to the same operation principle has the same problem.

[0009]

As described above, at present, liquid crystal display elements have the problems of low transmittance, viewing angle dependency, high driving voltage, and slow response speed.

The present invention has been made to solve the above-mentioned inconvenience, and an object of the present invention is to provide a liquid crystal display element having a high transmittance, a small viewing angle dependency, a low driving voltage, and a fast response speed.

[0011]

According to the present invention, a liquid other than a liquid crystal composition is dispersed as fine particles in a liquid crystal composition, and the fine particles serve as nuclei to arrange the liquid crystal composition in a scattering state in a minute region. A liquid crystal display element whose state is controllable.

[0012]

In other words, a liquid other than the liquid crystal composition is dispersed in the liquid crystal composition as fine particles having a minute size, and the fine particles serve as nuclei to cause the liquid crystal composition to be scattered in a minute region. A state is formed, and an external force is applied to the liquid crystal composition by a voltage or a thermo-optical effect to form a second state in which liquid crystal molecules of the liquid crystal composition are arranged in a certain direction. It is characterized by utilizing the change in optical properties between the two.

The achievement principle and method will be described.
As described above, in the liquid crystal display element, when the polarization effect and the polarizer are used, the transmittance is lowered in principle, and the viewing angle dependency is caused. That is, since at least one polarizing plate is used, the amount of transmitted light is at least 50% or less, and a pretilt angle is provided for manufacturing and stabilization of orientation, which affects the viewing angle characteristics. In particular, the problem of low transmittance is a problem in principle, and is an unavoidable problem when a polarizer is used.

Further, when utilizing the phase transition of the liquid crystal, these problems such as low transmittance and viewing angle dependency do not occur, but in order to sufficiently scatter light, the liquid crystal phase thickness is made sufficiently thick and the helical strength is increased. You need to be strong. This is because the scattering of light is due to various liquid crystal molecule arrangements. That is, in order to sufficiently scatter light, for example, in the case of a cholesteric phase having a helical molecular arrangement as shown in FIG. 3, it is necessary to have a helical axis in every direction with respect to the incident light direction. As described above, in order to have the helical axes in many directions, the liquid crystal phase thickness must be increased.

Further, a means (generally referred to as a DS effect) for obtaining a scattering property by applying a high voltage at a low frequency using Nn liquid crystal in which a conductive substance such as an organic electrolyte is dissolved has been proposed. In order to obtain a sufficient scattering property, the above problems must be accompanied. Of course, the same applies when the phase transition is controlled by the thermo-optical effect. Further, as shown in FIGS. 3 and 4, an NCAP type or polymer dispersed type LCD
Has proposed an attempt to enhance the scattering property by using a capsule-shaped or fibrous polymer, but has not yet achieved a sufficiently low driving voltage and required characteristics. This is because there is a restriction on the formation of the polymer, that is, from the manufacturing method and the principle, the polymer and the liquid crystal layer are mixed and solidified, but there is a restriction on the mixing ratio, and it is sufficient to satisfy the required driving characteristics. This is because it is not possible to obtain excellent scattering properties.

Therefore, if a substance, a method and a structure which have no limitation in the manufacturing method as a means for scattering light and can obtain a sufficient light scattering effect even if the quantitative ratio to the liquid crystal layer is low, the above-mentioned problems are caused. Without causing a polarizing plate, a wide viewing angle with a high transmittance and a thin liquid crystal phase thickness can be achieved, and thus a low voltage drive is possible, and a liquid crystal display element with a fast response speed can be obtained.

In such a liquid crystal display device, fine particles other than the liquid crystal composition are dispersed in the liquid crystal composition, liquid crystal molecules are vertically adsorbed on the surfaces of the fine particles, and the alignment of the liquid crystal composition is made minute by using this as a core. This can be easily achieved by a structure in which the region is in a scattering state.

Such means is disclosed in, for example, Japanese Patent Laid-Open No. 63-9.
As fine particles as proposed in Japanese Patent No. 6629,
It has been shown to be achieved by incorporating transparent, solid particles into the liquid crystal composition.

However, when solid particles are used, it is necessary to perform a hydrophobic treatment in order to adsorb liquid crystal molecules on the surface, and these affect the characteristics of the liquid crystal material.
Practical difficulty is considered.

However, in the present invention, as shown in FIG.
The structure for dispersing a liquid other than the liquid crystal in the liquid crystal 2 as the fine particles 1 provides a means for solving the above-mentioned problems. Here, the reason why the liquid crystal molecules 3 of the liquid crystal 2 are vertically aligned on the surface of the liquid fine particles 1 is due to the interfacial tension due to the imbalance of the van der Waals attraction at the fine particle-liquid crystal interface, and in principle the shape of the particles is a perfect sphere. Therefore, the liquid crystal molecules are aligned vertically at the interface. Therefore, in the present invention, the light scattering state due to the disorder of the liquid crystal molecule alignment as shown in FIG. 1 can be obtained in practical use, and the above-mentioned problem can be solved.

Further, since the fine particles are sufficiently small, they cannot be discerned by the naked eye, but the arrangement of liquid crystal molecules around the fine particles can be sufficiently used for display.
The diameter of the fine particles is about 0.5 μm to 2.5 μm.

Further, by mixing a large number of fine particles in the liquid crystal phase, a very optically disordered molecular arrangement can be easily obtained, and sufficient light scattering can be obtained with a thin liquid crystal phase thickness. In this way, the first state is obtained.

When a voltage having a positive dielectric anisotropy is used as the liquid crystal material and a voltage is applied as an external force to the liquid crystal between the electrodes, the liquid crystal molecules 3 are aligned in the voltage applying direction. Therefore, the light incident in that direction is not scattered but is transmitted. This state is shown in FIG. Also, for example, when a material having a negative dielectric anisotropy is used, the liquid crystal molecules are rearranged in a direction orthogonal to the voltage application when a voltage is applied,
The difference in optical property at this time can be used for display. At this time, if some alignment regulating force is applied in the direction orthogonal to the voltage application direction, the alignment direction of the liquid crystal molecules becomes constant, which is more effective. In this way, the second state is obtained, and the change in the optical property between the first state and the second state can be used for display. By doing so, it is possible to provide a liquid crystal display device having a high transmittance, a small viewing angle dependency, a low driving voltage, and a high response speed.

Further, when the thermo-optical effect is used as a means for transmitting light, the molecule can be an isotropic liquid. As described above, in the liquid crystal display device utilizing the light scattering effect, the present invention provides means for obtaining light scattering and transmission with a thin liquid crystal layer thickness and a low driving voltage and easily solving the above problems. It is a thing.

Further, by mixing two or more kinds of fine particles having different sizes or by mixing two or more kinds of fine particles of different materials, the molecular regulation force is intentionally made non-uniform, and the light scattering / transmission is reduced. Since it directly responds to the strength of the external force (for example, the potential) that gives a change, a good gradation display property is easily exhibited. Further, the applied voltage-transmittance characteristic hysteresis can be substantially eliminated.

It is generally known that when an oil phase and an aqueous phase are brought into contact with each other, a micellar colloid state and an emulsion are produced, and emulsification occurs under certain conditions. By mixing a certain liquid in the liquid crystal and adding an external force such as mechanical or ultrasonic vibration as necessary, the liquid is dispersed in the liquid crystal in the state of fine particles in a state close to the colloidal state. As a nucleus, a so-called scattering state in which the molecular alignment of liquid crystal is disturbed in a minute region is obtained.

At this time, it is desirable that the liquid crystal composition and the liquid have similar refractive index values because the liquid crystal does not reflect at the interface between the liquid crystal and the liquid in the second state and the transparency is improved. Moreover, a method in which the liquid crystal composition has a large refractive index anisotropy is preferable because the scattering in the first state becomes large.

In addition, when the liquid crystal composition has a spiral structure,
In this state, the scattering property is improved, and a larger effect can be obtained.

Further, in the present invention, the difference in optical characteristics between the first state in which the molecules are in the scattering state and the second state in which the molecules are in a constant array is used for display, and the simplest mode is used. In addition to the switching operation between scattering and transparency, the present invention can be applied to, for example, a guest-host type in which a dichroic dye is mixed with liquid crystal, or a display mode utilizing a birefringence effect in which one or two polarizing plates are combined.

Further, as the electrode substrate to be used, when the substrate on the back side viewed from the viewing direction is colored with, for example, a black dye, a good display of black on a white background can be obtained. It can also be applied to color display by combining with a red, blue, and green mosaic color filter.

As means for driving these liquid crystal display elements, simple multiplex drive and active matrix drive can be applied in addition to static drive. A transmissive type in which a light source is arranged on the back surface, a reflective type in which a reflection plate is arranged, or an intermediate display is also possible. Alternatively, it can be applied to a system provided with a projection lens and a zoom mechanism, and can be used for a projection type display. In this case, the advantage of the present invention of high transmittance can be effectively used.

[0032]

EXAMPLES Examples of the liquid crystal display device of the present invention will be described in detail below.

(Example 1) First, as shown in 1, two glass substrates 12 each having a transparent electrode 11 such as indium tin oxide coated on one surface thereof were made to face each other at regular intervals. Prepare what has been placed.

On the other hand, a nematic liquid crystal ZL having a large refractive index anisotropy is used as a nematic liquid crystal having a positive dielectric anisotropy.
I-3926 (manufactured by Merck Japan, Δn = 0.2030) was mixed with 1.2% of a surfactant Extran (manufactured by Merck Japan) containing water as a liquid insoluble in liquid crystal, and the mixture was mixed at 20 ° C. at 20 ° C.
By stirring with a stirrer for a minute, the fine liquid fine particles 1 covered with the surfactant were dispersed in the liquid crystal 2. The liquid crystal composition thus prepared was sealed between the transparent electrode-attached substrates 12 and the periphery of the substrate was sealed with an epoxy adhesive sealant 13 to prepare a liquid crystal display element 10. Reference numeral 3 denotes liquid crystal molecules, which are vertically aligned on the surface of the fine particles 2.

In order to obtain the transmittance-applied voltage curve, He-Ne laser light was made incident on the liquid crystal display element and the transmittance was measured. The spot diameter of the light was 2 mm, and the transmitted laser light was detected by a photodiode located at a distance of 20 cm from the liquid crystal display device. The prototype device showed a good scattering state with a transmittance of about 0.5% when no voltage was applied from the power supply 14. FIG. 4 shows a transmittance-applied voltage curve when the applied voltage (AC 70 Hz) is gradually increased from 0 V to 10 V and gradually decreased from 10 V to 0 V. When a voltage of 10 V is applied, the transmittance is about 80
% (Maximum transmittance), high contrast ratio 160: 1
It was possible to obtain a good display with high transmittance. Further, as the voltage was gradually increased, the transmittance also gradually increased. This is because the phase state of the liquid crystal gradually changes from the scattering state shown in FIG. 1 to the homeotropic state as shown in FIG.

That is, the liquid crystal molecules 3 are released from the constraint of the liquid fine particles 1 and aligned in the direction of the electrodes 11.

(Example 2) In the same constitution as in Example 1, as a liquid crystal composition, ZLI- having a small refractive index anisotropy was used.
A liquid crystal display device was prepared in the same manner as in Example 1 using 1565 (Merck Japan product) mixed with 1.3 wt% of a dichroic black dye (s-304 manufactured by Mitsui Toatsu Chemicals, Inc.). The prototype device showed a favorable black scattering state with a transmittance of about 0.3% when no voltage was applied.

Further, when a voltage of 10 V was applied, a transmittance of about 67% (maximum transmittance) was exhibited, and a good display of high transmittance could be obtained with a high contrast ratio of 223: 1.

[0039]

According to the present invention, it is possible to obtain a liquid crystal display device having a high scattering characteristic, a low driving voltage, a high brightness, a high contrast ratio and excellent gradation.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement of liquid crystal molecules in a liquid crystal display element of the present invention when no voltage is applied.

FIG. 2 is a diagram showing an example of an arrangement of liquid crystal molecules when a voltage is applied to the liquid crystal display element of the present invention.

FIG. 3 is a diagram showing a display principle of a conventional capsule-type polymer-dispersed liquid crystal display device.

FIG. 4 is a diagram showing a transmittance-applied voltage curve of the device of Example 1 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fine particles, 2 ... Liquid crystal value, 3 ... Liquid crystal molecule 10 ... Liquid crystal display element, 11 ... Transparent electrode 12 ... Glass substrate 13 ... Sealant, 14 ... Power supply

Claims (1)

[Claims] 1. A liquid crystal display in which a liquid other than the liquid crystal composition is dispersed as fine particles in the liquid crystal composition, and the fine particles serve as nuclei to cause the alignment of the liquid crystal composition in a scattered state in a minute region to control this state. element.