JP2000171836A - Liquid crystal display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve display failure due to surface pressing failure and obtain high definition and high display quality. SOLUTION: In a liquid crystal display device in which a liquid crystal 14 is oriented and sealed between a pair of transparent substrates 1 and 2 and a large number of pixels are arranged in a row and a column direction, the surface pressure resistance is Y (Kgf / c).
m ² ), pixel pitch d (μm), pretilt angle x
(°), where e is the natural logarithm, and the pixel pitch d and the pretilt angle x are within a range in which the surface pressure resistance Y represented by Y = 0.22e ^{(0.011d) x} is larger than a predetermined value. Is set, and when the pixel pitch d is 100 μm or less, the pretilt angle x is set to 2 ° to 6 °. As the pretilt angle increases, the surface pressure resistance increases, so the pixel pitch d
Has a pretilt angle x
Is 2 ° to 6 °, sufficient surface pressure resistance can be ensured, thereby improving display defects such as poor surface pressing and disclination, widening the viewing angle with low power consumption,
High contrast and high display quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element is formed by forming a transparent electrode on an opposing surface of a pair of transparent substrates with an alignment film, and aligning the liquid crystal between the pair of transparent substrates by each alignment film. Sealing is performed, whereby pixels are formed in portions where the electrodes face each other, and a large number of these pixels are arranged in the row and column directions. In this case, a black matrix for preventing light leakage from between the pixels is provided between the pixels. In such a liquid crystal display device, high definition is demanded, and accordingly, the number of pixels is increased and the pixel pitch is also reduced.

[0003]

However, in such a high-definition liquid crystal display device, when the transparent substrate is pressed from the outside in a black display state, the alignment of the liquid crystal molecules at the pressed position is disturbed. There occurs a bright spot where light leaks from a portion where the orientation is disturbed, and a defect occurs that the disorder of the orientation of the bright spot remains as a bright spot without returning to the original state. This is because the transparent substrate deforms when the transparent substrate is pressed, causing the liquid crystal to flow and move into the pixel area, where the poorly aligned part such as reverse tilt hidden in the black matrix is fixed, and this is fixed. It is a phenomenon that occurs.
This is referred to as surface pressing failure. This phenomenon becomes more conspicuous as the definition increases, and occurs even when a slight pressure is applied to the transparent substrate. For this reason, in an information device that requires high definition, when a load is applied to the transparent substrate by a touch panel, a pen input, or the like, there is a problem that a display defect due to a surface pressing defect is likely to occur.

An object of the present invention is to improve the occurrence of display defects due to poor orientation such as poor surface pressing, and to obtain a liquid crystal display device with high definition and high display quality.

[0005]

According to the present invention, there is provided a liquid crystal display device in which a liquid crystal is aligned and sealed between a pair of transparent electrode substrates, and a large number of pixels are arranged in a row and column direction. The surface pressure resistance at which no bright spot defect occurs when pressed from the outside is Y (Kgf / cm ² ), and the pixel pitch is d (μ).
m), when the pretilt angle of the liquid crystal molecules is x (°) and the natural logarithm is e, the surface pressing pressure Y represented by Y = 0.22e ^{(0.011d) x} is larger than a predetermined value. The pixel pitch d and the pretilt angle x are set.

According to the present invention, as the pretilt angle increases, the surface pressure resistance at which no bright spot failure occurs increases exponentially, and the smaller the pixel pitch, the smaller the surface pressure resistance at the same pretilt angle. By setting the pixel pitch d and the pretilt angle x so that the surface pressing withstand voltage Y represented by the above relational expression is larger than a predetermined value, the pixel pitch d is reduced to achieve higher definition. However, as the pretilt angle increases, the surface pressure resistance increases, so that the occurrence of display defects due to poor surface pressing can be improved, and a liquid crystal display device with high definition and high display quality can be obtained.

In this case, when the pixel pitch d is 100 μm or less, the pretilt angle x is set in the range of 2 ° to 6 °, so that the pixel pitch d is 100 μm or less. Even if the resolution is improved, the pretilt angle x is 2 ° to 6 °, so that a sufficient surface pressure resistance can be secured, thereby improving display defects such as poor surface pressing and disclination, and low power consumption. The viewing angle is also increased by power, and a high-contrast display with high display quality can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a liquid crystal display device according to the present invention will be described below with reference to FIGS.
FIG. 1 is a front view of a liquid crystal display element, FIG. 2 is an enlarged view showing one pixel of FIG. 1, and FIG. 3 is an enlarged sectional view of AA in FIG. This liquid crystal display device includes a pair of upper and lower transparent substrates 1 and 2 made of transparent glass or a transparent film. As shown in FIGS. 2 and 3, pixel electrodes 3 made of a transparent conductive material such as ITO are arranged on the upper surface of the lower transparent substrate 1 in a row and column direction with a half pixel pitch shift. . As shown in FIG. 2, a TFT (thin film transistor) 4 is disposed at one corner of each of the pixel electrodes 3, and is electrically connected to each of the pixel electrodes 3.

Around each pixel electrode 3, an auxiliary capacitance electrode 5 for forming an auxiliary capacitance is interposed between the pixel electrode 3 and the insulating film 8 except for one side on which the TFT 4 is formed. The storage capacitor 5 is formed so as to partially overlap, and a storage capacitor is formed by the storage capacitor electrode 5 and a part of the pixel electrode 3 opposed to each other via the insulating film 8. A gate line 6 extending in the row direction is arranged between the pixel electrodes 3, and a part protruding from the gate line 6 constitutes a gate electrode of the TFT 4. A drain line 7 extending zigzag in the column direction is formed between the pixel electrodes 3, and portions protruding from the drain line 7 constitute drain electrodes of the TFT 4. Further, an insulating protective film 8a is formed so as to cover the auxiliary capacitance electrode 5, the gate line 6, and the drain line 7 located between the pixel electrodes 3, and on the insulating protective film 8a and the pixel electrodes 3, An alignment film 9 is formed over the entire area.

On the other hand, on the lower surface of the upper transparent substrate 2, FIG.
As shown in FIG. 1, a black matrix 10 is formed at a position where light is shielded between the pixel electrodes 3 on the lower transparent substrate 1, and a color filter 11 is formed so as to overlap a part of the black matrix 10. I have. A common electrode 12 made of a transparent conductive material such as ITO is formed on the entire lower surface of the color filter 11, and an alignment film 13 is formed on the entire lower surface of the common electrode 12.

Further, between the pair of upper and lower transparent substrates 1 and 2,
As shown in FIG. 3, the liquid crystal 14 is used as the sealing material 15 shown in FIG.
Is sealed. In this case, the lower alignment film 9 is
As shown in FIG. 4, rubbing is performed in a direction (rubbing direction) 9a from the upper left to the lower right, and the upper alignment film 1 is formed.
3 is the direction from the lower left to the upper right (rubbing direction) 13
The rubbing process is performed on a, and the rubbing directions 9a and 13a cross each other at 90 °. Thereby, as shown in FIG. 5, the liquid crystal 14 is aligned by twisting the liquid crystal molecules 16 by 90 ° by the upper and lower alignment films 9 and 13. Each of the liquid crystal molecules 16 adjacent to the upper and lower alignment films 9 and 13 is, as shown in FIG.
Are aligned at a predetermined pretilt angle x (only the lower liquid crystal molecules 16 are shown in the figure).

In this case, as shown in FIG. 3, the liquid crystal region corresponding to each pixel electrode 3 is a normal alignment region E1 in which the liquid crystal molecules 16 are normally aligned because each pixel electrode 3 is flat.
And a liquid crystal region between the pixel electrodes 3 includes a TFT 4, an auxiliary capacitance electrode 5, a gate line 6, and a drain line 7.
As a result, an electric field is generated between these electrodes, so that the liquid crystal molecules 16 form an abnormal alignment region E2 in which the liquid crystal molecules 16 are not normally aligned. These alignment regions E1, E2
Form a boundary region 17, and this boundary region forms a disclination line. The black matrix 10 is formed to block light leakage between pixels, but also covers the disclination line generated in the boundary area 17. Each pixel has an opening in a region corresponding to each pixel electrode 3 excluding the black matrix 10, and a gate line and a portion bent in the row direction of the drain line 7 are arranged so as to overlap each other. The liquid crystal display device having a high aperture ratio can be formed.

By the way, in such a liquid crystal display device,
For example, with the lower transparent substrate 1 placed down,
When the upper surface of the upper transparent substrate 2 is pressed, the alignment of the liquid crystal molecules 16 at the pressed position is disturbed to become a bright spot, and the disordered orientation of the bright spot portion does not return to the original position and remains as a bright spot. In order to prevent surface pressing failure, the surface pressing voltage, pixel pitch, and pretilt angle are set in the following relationship. That is, when the upper surface of the upper transparent substrate 2 is pressed, the transparent substrate 2 is deformed and the liquid crystal 14 flows, and the reverse tilt alignment portion which is the abnormal alignment region E2 hidden in the black matrix 10 and the boundary. The liquid crystal molecules 16 in the region 17 move into the normal alignment region E1 and are immobilized to cause poor surface pressing. In order to prevent the liquid crystal molecules 16 from returning to the original state, it is possible to prevent a bright spot defect which is a surface pressing defect.
In order not to cause this bright spot defect, the surface pressure resistance is set to Y (Kgf /
cm ² ), pixel pitch d (μm), pretilt angle x
(°), where natural logarithm is e, Y = 0.22e ^{(0.011d) x} (1) The pixel pitch is set within a range in which the surface pressure resistance Y expressed by the following ^formula is larger than a predetermined value. d and the pretilt angle x are set. In other words, the pixel pitch d and the pretilt angle x are set such that the surface pressure resistance Y calculated by the above equation (1) is larger than the value of the surface pressure resistance required for each liquid crystal display element. Thereby, it is possible to prevent the occurrence of a bright spot defect which is a surface pressing defect.

The above equation (1) was derived as follows. That is, four types of liquid crystal display elements having different pretilt angles were prepared, and the pressure at which a bright spot defect did not occur, that is, the surface pressure resistance described later was measured for each of the liquid crystal display elements. In this case, a rubbing treatment is performed on the four types of alignment films A to D having different pretilt angles under the same conditions, and four types of liquid crystal display elements are prepared under the same conditions except for the pretilt angle. The pixel pitch at this time is 61 μm. The pixel pitch of a normal liquid crystal display element is 1
In this example, the thickness is about 100 μm, while the thickness is about 50 μm.
m and a fine pixel pitch of less than m. The measurement of each pretilt angle was performed by a crystal rotation method.

In the plurality of liquid crystal display elements thus prepared, each of the electrodes 3, 12 of the pair of transparent substrates 1, 2 is provided.
An electric field is applied between them to make the whole display black, and in this state, as shown in FIG.
8, a push-pull gauge 19 is pressed against the upper surface of the upper transparent substrate 2, and the pressure at that time is measured. At this time, after pressing with an arbitrary pressure, measure the time, measure the time when the bright spot disappears, or the number of pixels where the bright spot remains,
The pressure at which no bright spot failure occurred was measured as the surface pressure resistance. The measurement results are as follows. Type of alignment film Pretilt angle (°) Surface pressure resistance (Kg) A 1.40 0.40 B 2.70 2.10 C 3.70 3.00 D 4.80 6.10

According to the measurement result, the surface pressure resistance increases exponentially as the pretilt angle increases.
That is, as shown in FIG. 7, the surface pressure resistance is represented as an exponential function of the pretilt angle.
The relationship between the pretilt angle and the surface pressure resistance varies depending on the pixel pitch. As shown in FIG. 8, when the pixel pitch is reduced and the resolution is increased, the surface pressure resistance is reduced even at the same pretilt angle. As a result, the relationship between the surface pressure resistance, the pixel pitch, and the pretilt angle is as follows: the surface pressure resistance is Y (Kgf / cm ² ), the pixel pitch is d (μm), the pretilt angle is x (°), and the natural logarithm is e. Then, the relational expression of Y = 0.22e ^{(0.011d) x} (1) is established. Note that the coefficients of this relational expression are based on the case where the size of the liquid crystal display element and the aspect ratio of the pixel are the same, and slightly vary depending on the size of the liquid crystal display element, the aspect ratio of the pixel, and the like.

As described above, the larger the pre-tilt angle is, the more advantageous the surface pressing pressure is, and a high surface pressing pressure is obtained. However, if the pretilt angle is too large, the response speed at the time of low-temperature operation decreases, and display unevenness due to the variation of the pretilt angle occurs.
When it is not more than μm, the pretilt angle x is desirably 2 ° to 6 °, and most desirably 3 ° to 5 °.

As described above, according to this liquid crystal display device,
Even if the pixel pitch d is set to 100 μm or less to achieve high definition, by setting the pretilt angle x to 2 ° to 6 °, a sufficient surface pressure resistance can be obtained. It is possible to prevent the occurrence of poor surface pressing, which makes it possible to obtain high definition and high display quality. In particular, when the pretilt angle x is 2 ° to 6 °, the contrast is increased, the viewing angle is enlarged, and the threshold voltage is also reduced. it can. When the pretilt angle x is 6 ° or less, it is possible to prevent a reduction in response speed during low-temperature operation and display unevenness due to a variation in pretilt angle.

[0019]

As described above, according to the present invention, as the pretilt angle x increases, the value of the surface pressure resistance Y increases exponentially, and when the pixel pitch d decreases, the same pretilt angle x can be obtained. The pixel pitch d and the pretilt angle x are set so that the surface pressing withstand voltage Y represented by Y = 0.22e ^{(0.011d) x} becomes larger than a predetermined value due to the relationship that the surface pressing withstand voltage Y decreases. By setting, even if the pixel pitch is reduced and higher definition is achieved, the larger the pretilt angle, the higher the surface pressure resistance, so that display defects due to surface pressing failure can be improved, and high definition and display quality can be achieved. Can be obtained. In this case, when the pixel pitch d is 100 μm or less, the pretilt angle x is set in the range of 2 ° to 6 °, so that even if the pixel pitch d is 100 μm or less, the pretilt angle x is 2 °. When the angle is up to 6 °, a sufficient surface pressure resistance can be secured, thereby improving display defects such as poor surface pressing and disclination. In addition, the viewing angle can be increased with low power consumption, and the display quality can be improved with high contrast. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a front view showing one embodiment of a liquid crystal display device of the present invention.

FIG. 2 is an enlarged view showing one pixel of FIG. 1;

FIG. 3 is an enlarged sectional view taken along the line AA of FIG. 2;

FIG. 4 is a diagram showing rubbing directions of upper and lower alignment films in FIG. 3;

FIG. 5 is a view showing an alignment state of liquid crystal molecules in FIG. 3;

FIG. 6 is a side view showing a state where a push-pull gauge is pressed against the liquid crystal display element of FIG. 1;

FIG. 7 is a diagram illustrating a relationship between a pretilt angle and a surface pressure resistance;

FIG. 8 is a diagram showing a relationship between a pretilt angle and a surface pressure resistance due to a change in pixel pitch.

[Explanation of symbols]

 1, 2 Transparent substrate 3 Pixel electrode 9, 13 Alignment film 12 Common electrode 14 Liquid crystal 16 Liquid crystal molecule x Pretilt angle

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H088 HA04 HA08 HA12 JA05 MA01 MA02 MA07 2H090 HA03 KA05 LA04 LA15 MA11 MB01

Claims (2)

[Claims] 1. A liquid crystal display device in which liquid crystal is oriented and sealed between a pair of transparent electrode substrates, and a large number of pixels are arranged in a row and column direction. Y (Kgf / cm ² ) and the pixel pitch d
( ^Μm) , when the pretilt angle of the liquid crystal molecules is x (°) and the natural logarithm is e, the surface pressing pressure Y represented by Y = 0.22e ^{(0.011d) x} is larger than a predetermined value. Wherein the pixel pitch d and the pretilt angle x are set. 2. The liquid crystal display device according to claim 1, wherein the pretilt angle x is set in a range of 2 ° to 6 ° when the pixel pitch d is 100 μm or less.