JPH01200329A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make a black-and-white display which has a wide field angle, superior visibility, and no color irregularity by forming a roughened surface which specifies the pitch of projections and recesses and the depth of the recesses on one electrode surface of an electrode substrate. CONSTITUTION:The roughened surface which has <=100mum projection-recess pitch and 0.2-1mum recessed depth based upon the projection parts is formed on the electrode surface 1 of at least one of the electrode substrates 1 and 2. The thickness (d) of a liquid crystal material layer 3 controlled by the elec trode substrates 1 and 2 varies according to the projections and recesses of the roughened surface. Then, when a recessed part of 1mum in depth and an adjacent recessed part are present at a <=100mum interval so that the pitch of the projections and recesses is much smaller than picture elements, various hues are represented by additive mixing, and consequently an observer recognizes the display screen in white. Consequently, the black-and-white display is made and the device which has the wide field angle is obtained.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a liquid crystal display device with improved display quality.

(Prior art) Liquid crystal display devices utilize optical changes in liquid crystal that occur when a voltage is applied through electrodes to a liquid crystal cell, which is made by sandwiching a liquid crystal material between two substrates equipped with electrodes. This method utilizes the phenomenon that the unique orientation (initial orientation) of liquid crystal molecules when no voltage is applied changes when a voltage is applied.

In display devices that utilize such electro-optical effects of liquid crystals, various display systems can be obtained by appropriately combining the alignment state of liquid crystal molecules when no voltage is applied and the type of liquid crystal material.

For example, in a liquid crystal cell using a twisted nematic (TN) method, the molecular axis of the nematic liquid crystal has a directionality that is horizontal to the substrate, and as it moves away from one substrate surface, it is continuously twisted little by little, and the molecular axis of the nematic liquid crystal is The substrate surface is arranged so as to be twisted at approximately 90° near the substrate surface. However, such a liquid crystal display device has a drawback that the viewing angle is narrow.

In recent years, there has been an increasing demand for increased display capacity and higher resolution for liquid crystal display devices, and in order to widen the viewing angle, a method in which the twist orientation angle of liquid crystal molecules is made larger (e.g. 270°) than in the conventional TN method is used. is being developed. As such a method, for example, Supertwisted
Birefrangence EHect (S BE
) or Supertwisted Ne
A method using matic EHect (STN) has been proposed.

(Problem to be Solved by the Invention) However, as described above, in the liquid crystal display device in which the viewing angle is widened by setting the twist angle of the liquid crystal molecules large, the optical path difference due to the birefringence effect is utilized. There is a problem in that a slight displacement of the image appears as a change in hue, and color unevenness tends to occur in the background. In other words, in a liquid crystal display device whose display principle is 1i refraction, the voltage is controlled by the retardation (R), that is, the product (Δn-d) of the double refractive index (Δn) of the liquid crystal material and the thickness (d) of the liquid crystal material. This is because the hue when no voltage is applied is determined. Here, Δn
is a value specific to the liquid crystal material. Therefore, if there are variations in the thickness (d) of the liquid crystal material, color unevenness is likely to occur in the background, making it difficult to distinguish between display and non-display areas depending on the background color. There was a problem that visibility deteriorated.

To deal with this problem, conventional liquid crystal display devices have taken measures such as polishing the surface of the substrate to make it smooth to make the thickness of the liquid crystal cell uniform. However, increasing the number of steps like this has the problem of deteriorating the yield during manufacturing and causing an increase in manufacturing costs.

Furthermore, since the SBE or STN system basically utilizes the interference phenomenon caused by birefringence, there is coloration, and it is difficult to achieve black and white display, which is considered the easiest to see on a light-receiving display.

The present invention was made to solve these problems, and has a wide viewing angle and excellent visibility, and can achieve black-and-white display without color unevenness even with slight variations in optical path difference, thereby increasing productivity. The purpose is to provide old liquid crystal display devices.

[Structure of the Invention] (Means for Solving the Problems) The liquid crystal display device of the present invention comprises two electrode substrates, at least one of which is transparent, a liquid crystal material sandwiched between the substrates, and a helical axis of liquid crystal molecules. The direction is approximately perpendicular to the electrode substrate and 18
means for twisting orienting at an angle in the range of 0 to 360°;
In a liquid crystal display device comprising a polarizing plate disposed on the outside of the transparent electrode substrate, at least one electrode surface of the electrode substrate has an unevenness pitch of 100 μm or less and a depth of the depressions based on the protrusions. It is characterized by a rough surface having a diameter in the range of 0.2 to 1 μm.

That is, the present invention makes the minimum depth of the concave portion of the unevenness formed on the electrode substrate larger than the depth of the concave portion (approximately 0.1 to 0.15 μm) existing on a normal glass surface. This is a characteristic feature. Note that if the maximum depth of the concave portion of the electrode substrate exceeds 1 μm based on the convex portion, the effect of making the background color uniform will not change, but on the contrary, the effect of making the background color white or black will change. This is not preferable because it causes a decrease in

The desired result can be obtained when there are three or more recesses per pixel on the surface of the rough substrate according to the present invention. Normally, in a liquid crystal display device, one pixel has a size of about 300 μm, so in the present invention, the pitch between adjacent recesses needs to be 100,741 or less.

As a method for forming irregularities on the electrode substrate, when the electrode substrate is a glass substrate, an etching method using hydrofluoric acid can be used. In this method, the depth and pitch of the unevenness can be adjusted by controlling the etching time.

In addition to the etching method, the rough surface can also be formed by a method of diagonally depositing a metal oxide such as silicon dioxide on a flattened substrate.

In addition to the glass substrate, a resin film substrate such as polyethylene terephthalate can also be used as the substrate. In this case as well, the surface can be roughened by spraying silicon dioxide or the like.

As the liquid crystal material, it is common to use a nematic liquid crystal to which a chiral substance is added in order to control the twist angle. Depending on the use, a dye or the like may be further added.

(Function) In the present invention, at least one electrode surface of two electrode substrates sandwiching a liquid crystal material has an uneven pitch of 10.
0 μm or less, and the depth of the concave part based on the convex part is 0.2 ~
Since a rough surface in the range of 1 μm steel is formed, the thickness d of the liquid crystal material layer regulated by this electrode substrate takes various values depending on the unevenness of the rough surface. Therefore, when no voltage is applied,
The hue of a local portion of the unevenness defined by the product R of the thickness d and the birefringence Δn, which is a value specific to the liquid crystal material, varies depending on the value of d in that portion. If the pitch of the concaves and convexes is sufficiently small compared to the pixel, and the interval between a concave part with a depth of 1 μm and an adjacent concave part is 100 μm or less, these various hues are mixed additively. As a result, the display surface is perceived as white by the viewer. In this case, by adjusting the angle of the polarizing plate placed in the optical path of the liquid crystal material layer, it is possible to display white or black when the light is off, and vice versa, to display black or white when the light is on, making it possible to display black and white. Become.

In addition, in the present invention, slight irregularities existing on a normal glass surface or foreign substances that may adhere to the surface of the electrode are formed on the electrode surface as irregularities (depth: 0.2 μ1 m to 1 μm) larger than the normal dimensions. , is absorbed into the large undulations of the unevenness formed on this electrode substrate, and does not cause any problem on the display.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

The figure schematically shows a longitudinal section of an embodiment of the present invention. Reference numeral 1 denotes an electrode substrate on which a rough surface is formed with a pitch of concave and convex portions of 100 μm or less and a depth of concave portions in the range of 0.2 to 1 μm based on the convex portions, and this rough electrode substrate and a normal electrode A layer made of liquid crystal material 3 is provided at a distance from substrate 2 . Furthermore, a polarizing plate 4 is placed on the top surface of the normal electrode substrate 2.
A reflective plate 4 is provided on the lower surface of the rough electrode substrate 1 to constitute the liquid crystal display device of the present invention.

Next, a method for manufacturing the liquid crystal display device of the present invention having such a configuration will be described.

First, by etching the cleaned soda lime substrate using fluorohydrohydric acid, the pitch of the unevenness was reduced to 20 μm.
Below, the depth of the four parts based on the convex surface is 0.05 to 0.5
A rough substrate was covered with μ fog. Silicon dioxide was applied onto the rough surface of this rough substrate, and an indium oxide film (ITO film) having a thickness of 1000 nm was deposited thereon to obtain a rough transparent electrode substrate 1. Furthermore, another electrode substrate 2 with a flat surface without etching treatment was prepared, and patterning was performed on these two electrode substrates to enable a display of 640×400 dots, thereby obtaining a substrate for a liquid crystal display device of the present invention. I got it.

A liquid crystal material 3 was sandwiched between the rain plates thus obtained by a conventional method to form a liquid crystal display cell.

At this time, the average thickness of the liquid crystal material 3 is 7 μ■, and the twist angle is 2
The spacer and alignment film were controlled in advance so that the angle was 00°. Then, a polarizing plate 4 was placed on the upper surface of the electrode substrate 2 of this cell, and a reflecting plate 5 was placed on the lower surface of the rough electrode substrate 1 to obtain a liquid crystal display device of the present invention.

When a voltage was applied to this liquid crystal display device to display a display, the display was white when not lit and black when lit, and a black-and-white display with good contrast, wide viewing angle, and good display quality was achieved.

In this embodiment, the liquid crystal display panel 1 having a single layer of liquid crystal material was used, but the present invention is of course applicable to a liquid crystal display device using multiple layers. In this case, it is sufficient that at least one surface of 1 WJ is a rough surface.

[Advantageous Effects of the Invention 1] As explained above, according to the present invention, by making at least one electrode substrate have a rough surface, whiteness can be improved.

A liquid crystal display device capable of displaying black and having a wide viewing angle can be provided. In addition, by making the surface appropriately rough, small irregularities and foreign matter on the surface of the electrode substrate will not pose a problem in display, making it possible to provide a liquid crystal display device with high productivity.

[Brief explanation of the drawing]

The drawing is a diagram schematically showing a longitudinal section of an embodiment of the present invention. 1...... Rough surface electrode substrate 2... Electrode substrate 3... Liquid crystal material 4... Polarizing plate 5・・・・・・Reflector

Claims (1)

[Claims] (1) Two electrode substrates, at least one of which is transparent, a liquid crystal material sandwiched between these substrates, and the helical axis of the liquid crystal molecules twisted at an angle approximately perpendicular to the electrode substrates and in the range of 180 to 360°. In a liquid crystal display device comprising an orienting means and a polarizing plate disposed on the outside of the transparent electrode substrate, at least one electrode surface of the electrode substrate is provided with unevenness having a pitch of 100 μm or less with respect to the convex portion. 1. A liquid crystal display device characterized in that a rough surface is formed in which the depth of the recessed portion is in the range of 0.2 to 1 μm.