JPH06160856A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a negative display system matrix liquid crystal display element capable of accomplishing a good display without the occurrence of irregularities in display and also having such the coloration that is close to be almost anchromatic in a dark part even in the case of using a polarizing plate of high polarization and also having a little variation in hue in the dark part due to a visible angle and a temperature. CONSTITUTION:At least the film surface of an oriented film 16 of either one substrate 12 is formed to an uneven surface having a corrugated section and having a pitch P < twice a picture element arrangement pitch PO, and the value of retardation of the liquid crystal display element; DELTAn.d, is made continuously different.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As a matrix liquid crystal display device for displaying an image, when a liquid crystal molecule is in a twist alignment state, transmitted light is blocked by a light emitting side polarizing plate in a direction of a transmission axis of a pair of polarizing plates arranged on both sides thereof. Then, there is a so-called negative display system in which the transmitted light is set to pass through the outgoing side polarizing plate and to be emitted when the liquid crystal molecules are vertically arranged by applying an electric field.

FIG. 3 is a sectional view of a part of a conventional matrix liquid crystal display device. In this liquid crystal display element, a pair of transparent substrates 1 and 2 made of glass or the like are adhered to each other via a frame-shaped sealing material (not shown) that surrounds a liquid crystal enclosing region at their peripheral portions. The liquid crystal 7 is enclosed in the area surrounded by the sealing material, and the transparent electrodes 3 and 4 are formed on the inner surfaces of the substrates 1 and 2 (the surfaces facing the liquid crystal layer), respectively, and the transparent electrodes 3 and 4 are formed on the transparent electrodes 3 and 4. Alignment films 5 and 6 are formed.

The liquid crystal display element shown in the figure is a simple matrix liquid crystal display element. The transparent electrode 3 on one substrate 1 is a scanning electrode, and the transparent electrode 4 on the other substrate 2 is a signal electrode orthogonal to the scanning electrode. Is.

Further, this liquid crystal display element is of TN type, the alignment films 5 and 6 of both substrates 1 and 2 are aligned in directions substantially orthogonal to each other, and the molecules of the liquid crystal 7 are in both substrates 1. , 2 is twisted with a twist angle of about 90 °.

A pair of polarizing plates 8 and 9 are arranged on both surfaces of the liquid crystal display element (outer surfaces of both substrates 1 and 2). In the negative display type TN type liquid crystal display element, the polarizing plate 8 is used. , 9 are arranged such that their transmission axes are substantially parallel to each other.

The above-mentioned liquid crystal display element is one in which display voltage is applied by applying a driving voltage between the electrodes 3 and 4 of the substrates 1 and 2, and the electrodes 3 and 4 of the substrates 1 and 2 are opposed to each other. The display of each pixel corresponding to the present portion is dark when the liquid crystal molecules are in the twist alignment state, and is bright when the liquid crystal molecules are risen and aligned by the application of the electric field.

In the conventional liquid crystal display device, in order to display a uniform image without unevenness, as shown in FIG. The layer thickness d of the layer is made substantially uniform over the entire display region (liquid crystal enclosed region), and the retardation of the liquid crystal display element (product of refractive index anisotropy Δn of liquid crystal and liquid crystal layer thickness d) Δn.
The value of d is made almost equal over the entire display area.

[0009]

However, in the above-mentioned conventional liquid crystal display element, when the polarizing plates 8 and 9 having a high degree of polarization are used in order to increase the contrast (brightness ratio) of the display image, the pixel in the dark state is obtained. Portion and a portion between pixels (electrode 3,
That is, the wavelength range of the leaked light in the area where there is no 4 is narrowed, and the dark portion (the pixel portion in the dark state and the portion between pixels) appears to have a vivid color with high purity, and the image quality of the display image deteriorates. I had a problem.

This is especially true in a color liquid crystal display device for displaying a multicolor image such as a full color image by providing red, green and blue color filters (omitted in FIG. 3) corresponding to each pixel. It's a big problem.

Moreover, in the liquid crystal display element, the effective liquid crystal layer thickness (layer thickness of the liquid crystal layer on the light transmission path) changes depending on the viewing angle (display viewing direction), and when the temperature changes, the refractive index of the liquid crystal becomes anisotropic. Since the value of the property Δn changes, the retardation Δn · d has a viewing angle dependency and a temperature dependency. However, in the conventional liquid crystal display element, when the polarization degree of the polarizing plates 8 and 9 is increased, the retardation due to the viewing angle and the temperature is increased. Δn · d
Changes the wavelength of the leaked light, which causes a large change in the hue of the dark part depending on the viewing angle and the temperature.

The coloring of the dark portion and the change of the hue of the dark portion due to the viewing angle and the temperature can be reduced to some extent by lowering the polarization degree of the polarizing plates 8 and 9, but this lowers the contrast of the display image. I will end up.

An object of the present invention is to provide a negative display type matrix liquid crystal display device having no display unevenness and using a polarizing plate with a high degree of polarization. An object of the present invention is to provide an excellent display in which the hue change in the dark part is small.

[0014]

In a liquid crystal display device according to the present invention, the alignment film surface of at least one of a pair of substrates facing each other across a liquid crystal layer has a pitch less than twice the pixel arrangement pitch. It is characterized in that it has an uneven surface with a wavy cross section.

[0015]

That is, according to the present invention, the alignment film surface of at least one of the substrates is made into the corrugated surface having the corrugated cross-section as described above, thereby increasing or decreasing the layer thickness of the liquid crystal layer and thereby increasing the retardation Δn · d of the liquid crystal display element. The value of is continuously different, and in this way, since the wavelength of the leaked light in the dark part is different at each point within the unit area, the coloring of the dark part is the leaked light of each wavelength at each of the points. The color is almost an achromatic color that is a composite of the colors, and the change in hue in the dark part due to the viewing angle and temperature is also small.

Further, in the present invention, since the alignment film surface is an uneven surface having a pitch less than twice the pixel array pitch,
Portions with large retardation Δn · d and portions with small retardation Δn · d are evenly distributed at a high repetition density over the entire display region, and therefore the displayed image appears as a uniform image.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the present invention is applied to a simple matrix liquid crystal display device will be described below with reference to FIG.

In this liquid crystal display element, a pair of transparent substrates 11 and 12 made of glass or the like are adhered to each other via a frame-shaped sealing material (not shown) that surrounds a liquid crystal enclosing region at their peripheral portions, and both substrates 11 are bonded together. , 12 in which a liquid crystal 17 is enclosed in a region surrounded by the sealing material, and a scanning electrode 13 is formed on the inner surface of one substrate 11 and a signal electrode 13 is formed on the inner surface of the other substrate 11. And both boards 1
Alignment films 15 and 16 are formed on the electrode formation surfaces 1 and 12, respectively.
Are formed.

This liquid crystal display element is of the TN type, and the molecules of the liquid crystal 7 are substantially between the substrates 11 and 12.
Twisted at a twist angle of 90 °. Further, this liquid crystal display element is of a negative display type, and the transmission axes of the pair of polarizing plates 18 and 19 arranged on both sides thereof are substantially parallel to each other.

The electrode forming surface of one of the pair of substrates 11 and 12, for example, the lower substrate (hereinafter referred to as the lower substrate) 12 in the drawing, extends over the entire display region (liquid crystal sealing region). The cross section is an uneven surface having a substantially sinusoidal shape.

This uneven surface is formed by roughening the surface of the substrate into a matte surface by etching, and the repeating pitch P of the unevenness is the pixel arrangement pitch (the arrangement pitch of the scanning electrodes 13 and the signal electrodes 14). It is less than twice P0. The arrangement pitch of the pixels is 130 to 150 μm (pixel width is about 100 μm), and in this embodiment, the repeating pitch P of the irregularities is 200 μm or less.

Then, the signal electrode 14 on the lower substrate 12
And the alignment film 16 thereabove are formed to have a substantially uniform thickness over the entire surface thereof. Therefore, the film surface of the alignment film 16 on the lower substrate 12 is less than twice the pixel array pitch P0 (200 μm or less). ) Is a concave and convex surface with a sinusoidal cross section.

On the other hand, the other substrate, that is, the upper substrate (hereinafter referred to as the upper substrate) 11 in the figure is a flat substrate similar to the conventional liquid crystal display element. The film surface is almost flat.

In this liquid crystal display device, the film surface of the alignment film 16 on one of the substrates (lower substrate) 12 is arranged on the pixel array pitch P0.
By using an uneven surface having a sinusoidal cross-section with a pitch P less than twice the above, the thickness of the liquid crystal layer is increased or decreased to continuously change the value of the retardation Δn · d. Then, the minimum liquid crystal layer thickness d1 and the maximum liquid crystal layer thickness d2 are set according to the refractive index anisotropy Δn of the liquid crystal 19 used, and the minimum retardation (retardation of the minimum liquid crystal layer thickness d1 portion) Δn · d1 is calculated. The retardation values up to the maximum retardation (retardation of the maximum liquid crystal layer thickness d2 portion) .DELTA.n.multidot.d2 are continuously varied within the range of 1.00 to 1.50 .mu.m.

In this liquid crystal display element, since the value of the retardation Δn · d is continuously made different within the above range, the wavelength of the leaked light in the dark portion (the pixel portion in the dark state and the portion between the pixels). Is different at each point within the unit area, and therefore, the coloring of the dark part is almost an achromatic color obtained by combining the colors of the leaked light of each wavelength at each of the points, and the hue of the dark part depending on the viewing angle and temperature. The change will also be small.

That is, also in the liquid crystal display device of the above-mentioned embodiment, the leaked light at each point is colored in a color corresponding to the wavelength range, but the human eye must perceive the color at each point individually. Therefore, the color of the dark part looks almost an achromatic color in which the colors of each point within a certain area are combined. This is also the case when the value of the retardation Δn · d changes depending on the viewing angle and the temperature. In this case, the hue at each point changes, but the color perceived by the human eye is
The color of each point is a color that is almost an achromatic color that is synthesized. Then, if the coloring of the dark portion is close to the achromatic color, the color of the dark portion becomes closer to black, and the image quality of the display image is improved.

This effect is particularly due to the fact that red, green and blue color filters (not shown in FIG. 1) are provided corresponding to each pixel to display a multi-color image such as a full color image. This is remarkable in display devices.

In the liquid crystal display device, since the film surface of the alignment film 16 is an uneven surface having a pitch less than twice the pixel arrangement pitch (200 μm or less), there are a large retardation Δn · d portion and a small retardation Δn · d portion. Are evenly distributed at a high repetition density over the entire display area, so that the displayed image appears as a uniform image. The pitch P of the irregularities on the film surface of the alignment film 16 is preferably as small as possible, and the smaller the pitch P, the better the image quality of the display image.

Next, a second embodiment of the present invention will be described with reference to FIG. In addition, in FIG. 2, the same components as those shown in FIG. 1 are designated by the same reference numerals, and the duplicated description will be omitted.

In the liquid crystal display element of this embodiment, the electrode forming surfaces of the pair of substrates 11 and 12 are formed on the both surfaces of the substrates 11 and 12 by forming uneven surfaces having a substantially sinusoidal cross section over the entire display area. The film surface of the alignment films 15 and 16 is less than twice the pixel array pitch P0 (200 μm or less)
In this embodiment, the uneven surface having a sinusoidal cross section is formed. The height difference between the highest portion and the lowest portion of the film surfaces of both alignment films 15 and 16 is the same as in the first embodiment. The retardation value from the minimum retardation .DELTA.n.multidot.d1 to the maximum retardation .DELTA.n.multidot.d2 is continuously made different in the range of 1.00 to 1.50 .mu.m.

In FIG. 2, the pair of substrates 11 and 12 are
Although the highest part and the lowest part of the respective alignment film surfaces are arranged so as to face each other, the positional relationship between the substrates 11 and 12 may be shifted to some extent.

Also in the liquid crystal display element of this example, since the value of the retardation Δn · d is continuously made different within the above range, the wavelength of the leaked light in the dark portion is different at each point within the unit area, Therefore, the coloring of the dark area is
The color of the leaked light of each wavelength at each point is almost an achromatic color, and the hue change in the dark part due to the viewing angle and temperature is small.

Also in this embodiment, the alignment film 15,
Since the film surface of 16 is a concavo-convex surface having a pitch less than twice the pixel array pitch (200 μm or less), a portion with a large retardation Δn · d and a portion with a small retardation Δn · d are evenly distributed at a high repetition density. Therefore, the displayed image appears as a uniform image.

The liquid crystal display elements of the first and second embodiments are simple matrix type, but the present invention is an active matrix type liquid crystal display element using a TFT (thin film transistor) or the like as an active element. Also in this case, if the film surface of the alignment film on at least one of the substrates is a concavo-convex surface having a sinusoidal cross section with a pitch less than twice the pixel array pitch (200 μm or less), It is possible to obtain the same effect as that of the above embodiment.

In the case of an active matrix liquid crystal display device, the retardation value from the minimum retardation to the maximum retardation is 0.50 to 0.85 μm.
It is desirable to set the minimum liquid crystal layer thickness and the maximum liquid crystal layer thickness so as to be continuously different in the range of m.

Further, in each of the above-mentioned embodiments, the surface of the alignment film is a concave and convex surface having a sinusoidal cross section, but the surface of the alignment film may be a concave and convex surface having a triangular wave cross section, and the repeating pitch of the concave and convex is extremely large. When it is made small, it may be an uneven surface having a rectangular wave shape in cross section.

Further, in the above-mentioned embodiment, the substrate surface is roughened and the film surface of the alignment film on it is made into a corrugated surface having a wavy cross section. However, the film thickness of this alignment film is continuously varied. The film surface may be an uneven surface, and in that case, the substrate may be a flat substrate.

[0038]

According to the liquid crystal display element of the present invention, the alignment film surface of at least one of the substrates is formed as a corrugated surface having a wavy cross section with a pitch less than twice the pixel arrangement pitch, so that the layer thickness of the liquid crystal layer is increased. Since the value of the retardation Δn · d of the liquid crystal display element is continuously changed by increasing or decreasing, there is no display unevenness, and even if a polarizing plate with a high degree of polarization is used, the coloring of the dark part is almost achromatic. It is possible to provide a matrix liquid crystal display element of a negative display system that can obtain a good display that is close to the above and has a small change in the hue of the dark part due to the viewing angle and temperature.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a liquid crystal display element showing a first embodiment of the present invention.

FIG. 2 is a sectional view of a part of a liquid crystal display element showing a second embodiment of the present invention.

FIG. 3 is a partial cross-sectional view of a conventional liquid crystal display element.

[Explanation of symbols]

 11, 12 ... Substrate 13, 14 ... Electrode 15, 16 ... Alignment film 17 ... Liquid crystal 18, 19 ... Polarizing plate P0 ... Pixel array pitch P ... Repeated pitch of unevenness of alignment film surface d1, d2 ... Liquid crystal layer thickness

Claims (1)

[Claims] 1. A negative display type matrix liquid crystal display element, wherein an alignment film surface of at least one of a pair of substrates facing each other across a liquid crystal layer has a pitch less than twice a pixel array pitch. A liquid crystal display device having a corrugated uneven surface with a cross section.