JPH05323287A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal element which is free from dispersion in electrooptical characteristics and has excellent durability by limiting the average diameters of transparent solid materials to a specific value or below. CONSTITUTION:This liquid crystal panel is constituted by dispersing liquid crystal materials 8 and the tubular transparent solid materials 9 via spacers 7 between transparent glass substrates 1 and 2 having transparent electrodes 3, 4. Sealing materials, 5, 6 are provided in order to shut off the liquid crystal layer from the outside world and a driving circuit 10 is connected to the transparent electrodes 3, 4. The liquid crystal panel attains a transparent state when a voltage is impressed thereto when the refractive index of the tubular transparent solid materials 9 and the ordinary light refractive index of the liquid crystal materials 8 are equalized to each other. On the other hand, the liquid crystal molecules arrange along the internal hollow parts of the tubular transparent solid materials 9 and the wall surfaces on the outer side thereof when the voltage is impressed to the cell and, therefore, a differences is in the refractive index between both arises and the liquid crystal molecules cloud and scatter. The diameters of the transparent solid materials 9 are preferably set in a 0.5 to 2mum range. The lengths of the transparent solid materials 9 are not particularly limited.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a structure of a transmission / scattering type liquid crystal display element having high durability and stable electro-optical characteristics.

[0002]

2. Description of the Related Art A conventional liquid crystal display element is of a so-called TN (twisted nematic) type in which a liquid crystal layer is sandwiched between two glass substrates with transparent electrodes and polarizing plates are arranged on both outer sides of the glass substrates. It has been used mainly.

However, since such a liquid crystal display device has a polarizing plate, the brightness of the device is not sufficient.
Even if the aperture ratio is assumed to be 100%, there is a drawback that only a transmittance of about 40% can be obtained. Further, the viewing angle of the display element is not sufficient, and there is a drawback that the contrast is lowered and the visibility is deteriorated when viewed from the left, right, top and bottom, for example, from a direction exceeding 50 degrees.

For such a TN type liquid crystal display element, there has been proposed a method which does not require a polarizing plate and electrically controls the apparent birefringence of the liquid crystal to create a cloudy state or a transparent state.

In the first type of this system, the ordinary refractive index of liquid crystal molecules and the refractive index of the transparent solid substance are matched,
It utilizes the fact that when a voltage is applied and the alignment of the liquid crystal molecules is aligned, the liquid crystal molecules become transparent, and when no voltage is applied, the liquid crystal molecules become disordered and the liquid crystal molecules become clouded and opaque.

[0006] A typical example of this method is a method called NCAP or PDLC, which is a method of dispersing capsule type liquid crystal microdroplets in a polymer. In this method, the capsule-type liquid crystal microdroplets are completely and independently enclosed in the polymer, so they do not flow and can be formed into a film, and the durability is relatively stable, so that a large screen is possible. The display element can be easily manufactured (described in JP-A-58-501631).

The second type is called PNLC, which cures a curing reaction by irradiating ultraviolet rays to a solution obtained by dissolving an uncured resin such as an acrylic or epoxy ultraviolet curable resin and a liquid crystal material. As the resin progresses, the resin has a structure in which it spreads in a continuous phase of liquid crystal in a three-dimensional network form (JP-A-1-198725, etc.).

In the second type, the liquid crystal component in the liquid crystal layer is
Since the continuous phase is as high as 60% or more, there is no influence of the voltage drop due to the polymer, so that the driving voltage can be lowered. In addition, this method has an advantage that a wide range of liquid crystal materials and polymer materials can be selected because sufficient transparency can be achieved by applying a voltage without approximating the refractive index of the liquid crystal and the refractive index of the polymer. It is becoming mainstream for displays.

However, these methods have a problem that it is difficult to control the capsule diameter and the voids of the network, and the capsule diameter and the voids of the network vary from element to element, resulting in variations in driving voltage and optical characteristics. .. Further, in the second method, since ultraviolet rays are used for phase separation, there is a problem in the TFT type cell that the liquid crystal molecules decomposed by ultraviolet rays or unreacted monomers lower the voltage holding ratio and deteriorate the durability.

[0010]

SUMMARY OF THE INVENTION The present invention solves the problems of these conventional techniques, and provides an excellent liquid crystal display element having no variations in electro-optical characteristics and having durability. The purpose is to do.

[0011]

The present invention has been made to solve the above-mentioned problems, and has two electrode substrates, at least one of which is transparent, and a liquid crystal layer sandwiched therebetween. In a liquid crystal display device comprising a liquid crystal material in which the liquid crystal layer has a positive dielectric anisotropy and a transparent solid substance, the average diameter of the transparent solid substance is 1/2 of the cell gap.
A liquid crystal display device having the following diameter is provided.

The substrate used is glass, metal, ceramic, plastic or the like, but when two substrates are opposed to each other to form a liquid crystal display element with a spacer for holding a gap therebetween, two substrates are used. At least one of them must be transparent so that the liquid crystal layer between them can be seen from the outside.

The liquid crystal material may be one kind or a mixture of two or more kinds of liquid crystals and has a positive dielectric anisotropy, and nematic liquid crystals, smectic liquid crystals and cholesteric liquid crystals are preferable. In addition, a dichroic dye material can be used in the liquid crystal material in order to supplement the shielding property of the cloudy scattering state when no voltage is applied. In the present invention, since the curing step by ultraviolet rays is not included, the dichroic dye material is not decomposed by ultraviolet ray irradiation.

Transparent solid materials include glass, ceramics,
Inorganic crystals, plastics, and other almost transparent materials may be used. However, it is necessary to match the refractive index of the transparent solid substance with the ordinary refractive index of the liquid crystal material. As a result, when the refractive index of the transparent solid substance and the refractive index of the liquid crystal material match, the light passes, and when they do not match, the light is clouded and scattered.

In the liquid crystal display device having such a structure, when a voltage is not applied, a scattering state (white turbid state) is exhibited due to a difference in refractive index between the liquid crystal material and the solid substance which are not aligned, and a voltage is applied. In some cases, the liquid crystal material is aligned and the ordinary state refractive index of the liquid crystal material and the refractive index of the solid substance are matched to each other to show a transparent state, so that a reversible dimming function can be obtained. Further, it is not necessary to completely match the refractive index of the transparent solid substance and the ordinary light refractive index of the liquid crystal material, and if the difference in refractive index is set to about 0.10 or less, light will be almost transmitted.

The shape of the transparent solid substance is preferably spherical, indeterminate-diameter granular or tubular fiber. Further, the average diameter of the transparent solid substance needs to be set so that the inner diameter is about 1 μm in the case of a gap between particles or a tubular shape in order to improve the scattering property in the cloudy scattering state when no voltage is applied.

Further, it is preferable that the transparent solid substances are adhered to each other with an adhesive so as to be firmly supported in the liquid crystal display device in consideration of vibration resistance.

[0018]

According to the above-mentioned means, a gap (domain) filled with liquid crystal of a stable size is always provided without using a means such as heat or ultraviolet rays which impairs the durability of the liquid crystal material.
It is possible to realize a liquid crystal display element which can form a transparent state when a voltage is applied and which exhibits a cloudy scattering state when no voltage is applied.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. It should be noted that the following (FIG. 1) is only shown schematically for easy understanding of the present invention, and a color filter, a thin film transistor and the like are omitted.

FIG. 1 is a sectional view of a liquid crystal display panel according to the present invention. Transparent glass substrate having transparent electrodes 3 and 4
The liquid crystal material 8 and the tube-shaped transparent solid substance 9 are dispersed between the 1 and 2 via the spacer 7, and the sealing materials 5 and 6 are present to shield the liquid crystal layer from the outside. To do. Further, the drive circuit 10 is connected to the transparent electrodes 3 and 4.

In FIG. 1, when the refractive index of the tube-shaped transparent solid substance 9 and the ordinary refractive index of the liquid crystal material 8 are matched, the liquid crystal molecules are aligned in an electric field when a voltage is applied. The refractive index of the transparent solid substance and the refractive index of the liquid crystal material are the same, and light passes therethrough to become a transparent state.

On the other hand, when no voltage is applied, the liquid crystal molecules are arranged along the inner hollow portion or the outer wall surface of the tube-shaped transparent solid substance 9. Therefore, the refractive index of the transparent solid substance and the refractive index of the liquid crystal material are A difference in refractive index is generated between and, resulting in white turbid scattering.

The diameter of the tube-shaped transparent solid substance 9 used is not particularly limited as long as it is in the range of 0.1 μm to 5 μm in view of the scattering property of visible light, but it is particularly provided for practical use. The tubular transparent solid material to be used preferably has a diameter in the range from 0.5 μm to 2 μm. In addition, there is no limitation on the length of the tube-shaped transparent solid substance.

In the liquid crystal display device constructed as described above, the diameter of the hollow portion inside the tube-shaped transparent solid substance 9 and the size of the gap between the transparent solid substances can be stably obtained, and thus stable. Electro-optical characteristics can be obtained.
Furthermore, since heat and ultraviolet rays are not used to generate such gaps, liquid crystal molecules or unreacted monomers are not decomposed, and a high voltage holding ratio can be expected in the TFT type liquid crystal display device, and durability is also improved. It is possible to realize an excellent liquid crystal display element.

[0025]

Since the present invention is constructed as described above, it has the following effects.

(1) Since heat and ultraviolet rays are not required to form the gap filled with the liquid crystal, liquid crystal molecules, unreacted monomers, oligomers, cured polymers, etc. are not decomposed, so that they are excellent in durability. ing. In particular, it is effective in improving heat resistance.

(2) Since it does not require heat or ultraviolet rays, liquid crystal molecules, unreacted monomers, oligomers, cured polymers, etc. are not decomposed to generate ionic decomposition products, and therefore are high in a TFT type liquid crystal display device. A voltage holding ratio is obtained.

(3) Since the size of the gap filled with the liquid crystal is constant, a liquid crystal display device having a constant drive voltage, contrast, response speed, temperature characteristics, etc. can be realized. Further, for the same reason, a liquid crystal display device with less unevenness can be obtained.

(4) Since the wettability between the liquid crystal material and the transparent solid substance can be lowered, a liquid crystal display device having a lower driving voltage than that of the conventional one can be obtained.

(5) Since the structure of the liquid crystal layer (the gap filled with the liquid crystal) does not depend on the liquid crystal material and the constituent material of the solid substance, the cell parameters such as the size of the gap filled with the liquid crystal can be freely changed. And easy to find the optimum structure.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display element according to an embodiment of the present invention.

[Explanation of symbols]

 1, 2 Transparent substrate 3, 4 Transparent electrode 5, 6 Sealing material 7 Spacer material 8 Liquid crystal material 9 Transparent solid substance

Claims (2)

[Claims] 1. A liquid crystal material having two electrode substrates, at least one of which is transparent, and a liquid crystal layer sandwiched therebetween, wherein the liquid crystal layer has a positive dielectric anisotropy, and a transparent solid. A liquid crystal display element made of a substance, wherein the average diameter of the transparent solid substance is not more than ½ of the cell gap. 2. The liquid crystal display device according to claim 1, wherein the transparent solid substance has a hollow tubular shape inside.