JPH0786621B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device, and more particularly, to a substrate in which a first transparent electrode and a plurality of color filters are laminated and a second transparent electrode are formed. The present invention relates to a liquid crystal display device in which a transparent substrate is disposed so that both transparent electrodes face each other, and liquid crystal is filled between both substrates.

[Prior Art] A liquid crystal display element has advantages that it is thin, can be driven at a low voltage, has low power consumption, and can be directly driven by an IC, so that the device can be easily downsized and thinned. Especially, TN type liquid crystal is excellent in low voltage and low power consumption,
Widely used in calculators, etc.

In recent years, portable small-sized televisions using TN type liquid crystals have become widespread, and research and development of wall-mounted televisions have also progressed. In these applications, colorization is desired due to compatibility with CRTs.

FIG. 4 is a partial cross-sectional view showing one structural example of a conventional matrix type TN type color liquid crystal display element.

In the figure, on the glass substrate 5a, transparent electrodes 6a patterned in rows (here, the transparent electrodes are three rows of 6a ₁ , 6a ₂ and 6a ₃ for simplification) are formed. Then, the alignment film 18a is further formed. On the glass substrate 5b, a red color filter 1, a green color filter 2, a blue color filter 3 and a black mask 4 are formed, and further transparent electrodes 6b and an alignment film 18b patterned in rows are formed.
The TN type liquid crystal 19 is filled between the glass substrate 5a and the glass substrate 5b with a constant distance maintained. Polarizing plates 20a and 20b are provided on the other surfaces of the glass substrate 5a and the glass substrate 5b, respectively.

[Object of the Invention] The above TN type color liquid crystal display device is difficult to manufacture a large-area display because it is sensitive to the thickness of the liquid crystal layer, and the contrast generally depends on the sharpness of the voltage-luminance characteristic, but the red, By the optical characteristics for each color of green and blue,
Due to the difference in the voltage-luminance characteristic, the contrast may differ for each color.

In recent years, the development of liquid crystals for use in display devices having a large area has progressed, and in recent years, polymer dispersed liquid crystals in which small spheres of liquid crystals are dispersed in a polymer matrix, such as NCAP (Nemati
c Curvilinear Aligned Pnase (nematic curvilinear aligned phase) A new liquid crystal technology called liquid crystal has been developed, and the thickness of the liquid crystal layer can be easily controlled to enable a large area, fast response time, and no need for a polarizing plate. Since it has features such as a wide viewing angle, it is expected to be suitably used for a display device having a relatively large area.

The object of the present invention is to provide a polymer-dispersed liquid crystal with voltage-contrast characteristics and voltage-depending on the size of the liquid crystal capsule.
An object of the present invention is to provide a liquid crystal display device in which the variation in contrast due to the difference in optical characteristics for each color of red, green and blue is improved by utilizing the property that the luminance characteristics change.

[Summary of the Invention] In a liquid crystal display device of the present invention, both transparent electrodes face a substrate in which a first transparent electrode and a plurality of color filters are laminated and a substrate in which a second transparent electrode is formed. A liquid crystal display device in which a liquid crystal is filled between both substrates, the liquid crystal is a polymer-dispersed liquid crystal, and a polymer corresponding to each color is used to correct the difference in optical characteristics for red, green, and blue light. The feature is that the size of the liquid crystal capsule of the dispersed liquid crystal is changed.

Here, the size of the liquid crystal capsule refers to the size of the liquid crystal body dispersed in the polymer.

[Operation] As described above, the contrast generally depends on the sharpness of the voltage-luminance characteristic, but the color filter and the dichroic dye used, the wavelength dependence of the scattering in the liquid crystal layer, or the dichroic dye. Due to improper combination, quantity ratio, etc. (in many cases, the dichroic ratio of a dichroic dye having an absorption maximum at a short wavelength is not very good), etc., there is a difference in voltage-luminance characteristics. When the screen is viewed through the green and blue color filters, the contrast may differ depending on each color, or a specific color may be emphasized.

According to the present invention, the polymer-dispersed liquid crystal has a structure as shown in FIG.
Utilizing the fact that the large force of the liquid crystal capsule shows the characteristic that the contrast rises at a low voltage, and the smaller the size of the liquid crystal capsule shows the characteristic that the contrast becomes larger when a voltage is applied (in FIG. The capsule is a sphere, the broken line has a particle size of about 1 μm, and the solid line has a particle size of about 5 μm.
Shows the case. ), The size of the liquid crystal capsule is controlled according to the difference in the optical characteristics for red, green, and blue light, and red,
It is intended to improve the voltage-contrast characteristic for each green and blue light.

EXAMPLES Examples of the present invention will be described in detail below with reference to the drawings. In the following examples, a case where NCAP liquid crystal is selected as an example of polymer dispersed liquid crystal will be described.

First, the structure and operation of the NCAP liquid crystal will be described prior to the description of the liquid crystal display device of the present invention (the following description
"Principles and Applications of New Liquid Crystal Displays" Electronic Materials 198
7, 12, P.67 to P.71, based on the patent application publication No. 58-501631).

5 (A), (B), and (C) are schematic configuration diagrams for explaining one configuration example of the NCAP liquid crystal, and FIG. 5 (A) is a configuration diagram of the liquid crystal configuration unit, and FIG. B) is a configuration diagram of the liquid crystal layer, the fifth
FIG. (C) shows a configuration diagram of the liquid crystal capsule.

The NCAP liquid crystal element has a structure in which an NCAP liquid crystal layer 12 is sandwiched between plastic films 14 as shown in FIG.
Etc. are coated with a transparent conductive layer. FIG. 5 (B) shows the structure of the part 13 of the NCAP liquid crystal layer 12, and FIG. 5 (C) shows the structure of the liquid crystal capsule portion 15 of the NCAP liquid crystal layer 12. As shown in FIGS. 5B and 5C, the NCAP liquid crystal layer 12 is a collection of encapsulated liquid crystal bodies 16 dispersed in a polymer matrix 17. Usually, the liquid crystal body 16 is often a sphere, but there is also a case where spherical liquid crystal bodies are combined to form a liquid crystal body.

Figures 6 (A) and (B) show NCAP using a black dichroic dye.
6A and 6B are schematic explanatory diagrams for showing the operation of the liquid crystal. FIG. 6A shows a non-voltage state and FIG. 6B shows a voltage application state.

As shown in FIG. 6A, the liquid crystal molecules 16b in the liquid crystal body 16 tend to line up along the outer wall of the capsule in the non-voltage state. In this case, due to the birefringence of the liquid crystal molecule 16b, the incident light is scattered on the surface and inside of the liquid crystal capsule, and the dichroic dye 16
absorbed by a. As a result, the film appears dark black.

As shown in FIG. 6 (B), in the voltage applied state, the liquid crystal molecules 16b rotate their axes so as to align in the direction of the electric field. Liquid crystal molecule 1
If the refractive index of the axis of 6b and the refractive index of the polymer are the same, the light goes straight without being scattered and becomes transparent. In this way, by adjusting the voltage, it is possible to continuously change the state from the completely scattered and absorbed state to the sufficiently transparent state to perform display.

The liquid crystal display device of the present invention using the above NCAP liquid crystal will be described below.

1 (A) and 1 (B) are explanatory views of the configuration of a first embodiment of a liquid crystal display device of the present invention, and FIG. 1 (A) is a schematic partial sectional view and FIG. 4) is a schematic partial plan view of one substrate.

As shown in FIG. 1 (A), transparent electrodes 6a patterned in rows of ITO or the like on the glass substrate 5a (here, transparent electrodes 6a ₁ , 6a ₂ , 6a ₃ are used for simplification. 3 rows) are formed at a constant pitch. On the glass substrate 5b,
A red color filter 1, a green color filter 2, a blue color filter 3 and a black mask 4 are formed, and further transparent electrodes 6b patterned in rows are formed. The glass substrate 5a and the glass substrate 5b are filled with the NCAP liquid crystal which is the above-mentioned polymer dispersion type liquid crystal while maintaining a constant distance.
The AP liquid crystal layer 7 is formed. The transparent electrodes 6a and the transparent electrodes 6b are arranged in a matrix.

Although a glass substrate or a PET substrate is often used as the substrate, the substrate is not particularly limited to these and other materials may be used.

As shown in FIG. 1B, the transparent electrodes 6a ₁ , 6a ₂ and 6a ₃ are connected to the signal line 9 by the varistor film 8. A varistor is an element in which a current flows rapidly when a voltage of a certain value or more is applied, and is provided to prevent crosstalk and the like. The varistor film is formed by printing varistor powder into a paste on a substrate using a thick film printing technique.

In this embodiment, in the structure of a normal liquid crystal display device,
Since the voltage-contrast characteristic of the contrast when the screen is viewed through the blue color filter 3 rises more slowly than the contrast characteristics when the screen is viewed through the red and green color filters 1 and 2, As shown in FIGS. 1A and 1B, the particle size of the liquid crystal body 16 of the liquid crystal capsule of the NCAP liquid crystal layer 7 corresponding to the blue color filter 3 is increased to adjust the voltage-contrast characteristic for blue light. The voltage-contrast characteristic for red and green light is almost the same.

As a method of controlling the particle size of the liquid crystal capsule of the NCAP liquid crystal layer 7 and forming it on the transparent electrodes 6a ₁ , 6a ₂ , 6a ₃ corresponding to each color filter, screen printing, printing using a metal mask, etc. Can be used.

Hereinafter, a method for manufacturing the NCAP liquid crystal layer 7 will be described.

(Example) First, 15 g of liquid crystal E-44 (manufactured by BDH) containing dichroic dye M676 (manufactured by Mitsui Toatsu Dye Co., Ltd.) and PVA, KM-11 (Nippon Gosei Co., Ltd.) purified by ion exchange. 10% solution of Chemical Industry Co., Ltd.
Mix 40 g and emulsify. At this time, the stirring speed at the time of emulsification is changed so that the emulsion having a particle size of 1 to 4 μm and the particle size of 4
˜10 μm emulsion is prepared. Emulsions with a particle size of _{1 to} 4 μm are 4 to 10 on transparent electrodes 6a ₁ and 6a ₂ such as ITO of glass substrate 5a corresponding to red color filter 1 and green color filter 2
The emulsified liquid of μm is applied on the transparent electrode 6a ₃ such as ITO of the glass substrate 5a corresponding to the blue color filter 3 and then dried to form the NCAP liquid crystal layer 7. The layer thickness at this time is 15μ
It was m. After that, transparent electrode 6b, color filter 1
The NCAP liquid crystal layer 7 was sandwiched between the glass substrates 5b on which Nos. 3 to 3 were formed to manufacture a liquid crystal display device.

(Comparative Example) An emulsion having a particle size of 1 to 4 μm is prepared under the same conditions as in the above-described example. This emulsion is used as a glass substrate for red color filter 1, green color filter 2, and blue color filter 3.
The transparent electrode 6a ₁ , 6a ₂ , 6a ₃ such as ITO of 5a is coated. A liquid crystal display device is manufactured under the same other conditions.

As shown in FIG. 3 (A), the liquid crystal display device manufactured by applying the particles having a particle size of 1 to 4 μm has a voltage-contrast characteristic when the screen is viewed through the blue color filter 3 and the red and green colors are displayed. Although the rise is slower than the contrast characteristic when the screen is viewed through the filters 1 and 2, the particle size of the liquid crystal body 16 of the liquid crystal capsule of the NCAP liquid crystal layer 7 corresponding to the blue color filter 3 is increased according to the present invention. In such a liquid crystal display device, the contrast of each color is improved as shown in FIG. 3 (B), and the voltage-contrast characteristic of each color becomes substantially constant. That is, by adjusting the particle size of the liquid crystal capsule of the NCAP liquid crystal layer, the R, G, B contrast can be adjusted to such an extent that there is no practical problem.

[Effects of the Invention] As described in detail above, according to the liquid crystal display device of the present invention, the polymer-dispersed liquid crystal exhibits a characteristic that the force of the liquid crystal capsule having a large particle diameter causes the contrast to rise at a low voltage.
Taking advantage of the fact that the smaller the particle size of the liquid crystal capsule is, the larger the contrast is when a voltage is applied. By controlling the size of the liquid crystal capsule in accordance with the difference in the optical characteristics for red, green, and blue light, the red, By improving the voltage-contrast characteristic for each of green and blue light, a liquid crystal display device with more excellent visibility can be provided.

[Brief description of drawings]

FIGS. 1A and 1B are explanatory views of the configuration of the first embodiment of the liquid crystal display device of the present invention. FIG. 2 is a diagram showing a difference in voltage-contrast characteristic depending on the particle size of the liquid crystal capsule. FIG. 3 (A) is a diagram showing voltage-contrast characteristics for red, green, and blue lights, and FIG. 3 (B) is a liquid crystal display device of the present invention for red, green, and blue lights. Voltage against −
It is a figure which shows a contrast characteristic. FIG. 4 is a partial cross-sectional view showing one structural example of a conventional matrix type TN type color liquid crystal display element. 5 (A), (B) and (C) are schematic configuration diagrams for explaining the configuration of the NCAP liquid crystal. Figures 6 (A) and (B) show NCAP using a black dichroic dye.
FIG. 6 is a schematic explanatory diagram illustrating an operation of liquid crystal. 1: Red color filter, 2: Green color filter, 3: Blue color filter, 4: Black mask, 5a, 5b: Glass substrate, 6a
₁ , 6a ₂ , 6a ₃ , 6b: transparent electrode, 7, 12: NCAP liquid crystal layer, 8: varistor film, 9: signal line, 10, 11: electrode, 14: plastic film, 16: liquid crystal body, 17: polymer Matrix, 16a: dichroic dye, 16b: liquid crystal molecule.

Claims (1)

[Claims] 1. A substrate in which a first transparent electrode and a plurality of color filters are laminated and a substrate in which a second transparent electrode is formed are arranged so that both transparent electrodes face each other. In a liquid crystal display device in which liquid crystal is filled in, the liquid crystal is a polymer-dispersed liquid crystal, and the size of the liquid crystal capsule of the polymer-dispersed liquid crystal corresponding to each color is adjusted in order to correct the difference in optical characteristics for red, green, and blue light. The liquid crystal display device is characterized in that