JP2007264226A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element whose display defect can be prevented while viewing angle characteristics are improved. <P>SOLUTION: The liquid crystal display element has a pair of substrates which are arranged opposite each other in parallel, transparent electrodes which are formed on the pair of substrates and have predetermined patterns formed for display, a liquid crystal layer sandwiched between the pair of substrates, and rectangular slits formed in the transparent electrodes. Here, first slits provided to one transparent substrate and second slits provided to the other transparent electrode are arranged alternately along the width, and also different in number of divisions of the first slits and the second slits. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element that prevents display defects.

  In recent years, a method using a slit has been proposed in order to improve the viewing angle characteristics of a liquid crystal display element. When a slit is formed in one of the upper and lower counter electrodes arranged across the liquid crystal layer, the lines of electric force generated from the portion facing the slit of the other electrode must be terminated at the electrodes on both sides of the slit and tilted. A fringe electric field is generated. When slits are alternately formed on the upper and lower electrodes, uniform alignment of liquid crystal molecules can be realized in the region between the upper and lower slits. The following patent document discloses a liquid crystal display element using a slit.

Japanese Patent No. 3108768 JP 2004-252298 A JP 2005-43696 A

  In the method disclosed in Japanese Patent No. 3108768, it is necessary to connect the areas divided by the slits outside the display area.

  In the method disclosed in Japanese Patent Application Laid-Open No. 2004-252298, since the areas divided by the slits are connected in the display area, the pattern design is simplified. However, the use of slits that are divided in the longitudinal direction tends to cause display defects.

  In the method disclosed in Japanese Patent Application Laid-Open No. 2005-43696, the slits provided in the upper and lower transparent electrodes are alternately arranged in the direction perpendicular to the longitudinal direction, and the upper and lower slits are shifted by a half pitch in the longitudinal direction, It is intended to prevent display defects. However, this method also causes some display defects.

  The objective of this invention is providing the liquid crystal display element which can prevent a display defect, utilizing the advantage of a slit structure.

  According to one aspect of the present invention, a pair of substrates opposed to each other in parallel, a transparent electrode formed on the pair of substrates and having a predetermined pattern for display, and sandwiched between the pair of substrates A liquid crystal layer, a rectangular slit formed in the transparent electrode, a first slit provided in one transparent electrode, and a second slit provided in the other transparent electrode, Provided is a liquid crystal display element having alternatingly arranged in the short direction of the slits, and slits having a structure in which the number of divisions per unit length of the first slits and the second slits are different.

  According to another aspect of the present invention, a pair of substrates opposed in parallel, a transparent electrode formed on the pair of substrates and having a predetermined pattern for display, and the pair of substrates A liquid crystal layer to be sandwiched, a rectangular slit formed in the transparent electrode, a first slit provided in one transparent electrode, and a second slit provided in the other transparent electrode A liquid crystal display element having alternatingly arranged in the short direction of the slits, and having a structure in which the number of divisions per unit length of one of the first slits and the second slits is zero. Provided.

  By having an electrode having the slit structure as described above, it is possible to prevent the occurrence of display defects while maintaining the effect of improving the viewing angle characteristics.

  First, Example 1 of the present invention will be described in detail while comparing with Comparative Example 1. In Comparative Example 1 and Example 1, a case of a segment display 2-domain TN-LCD (twisted nematic liquid crystal display) will be described.

(Comparative Example 1)
FIG. 1 shows an example of a two-domain TN-LCD having a segment structure. The TN-LCD shown in FIG. 1A has a structure in which an upper segment electrode 1 representing the number “1” and a lower common electrode 2 sandwich a liquid crystal as a pair of electrodes. The segment electrode 1 and the common electrode 2 are provided with rectangular slits 1s and 2s from which a part has been removed. As shown in FIG. 1B, slits 1s provided in the segment electrode 1 and slits 2s having the same shape as the slit 1s provided in the common electrode 2 are alternately arranged in the short direction of the slit. Has been.

  FIG. 2 is a plan view showing the electrode slit structure of the TN-LCD shown in FIG. The slit has a rectangular shape with a longitudinal dimension of 100 μm and a lateral dimension of 20 μm. The distance between the slits in the longitudinal direction is 20 μm, and the distance between the slits 1s and 2s adjacent to each other when viewed from above is 40 μm.

  The manufacturing procedure of such a TN-LCD is as follows. A low pretilt angle alignment film (SE-510 manufactured by Nissan Chemical Industries) is applied and fired on a substrate including an electrode having a predetermined slit pattern as shown in FIG. Thereafter, the substrate is rubbed with a rayon rubbing cloth. The twist direction of the liquid crystal is left-handed.

  FIG. 3 is a plan view showing the rubbing direction of the substrate. The solid arrow 3A is the rubbing direction of the upper substrate, and the dotted arrow 3B is the rubbing direction of the lower substrate. By making the rubbing direction shown in FIG. 3, the liquid crystal molecules are splay-aligned, and the tilt angle of the liquid crystal molecules at the center of the cell is 0 degree.

  The main sealing material is applied to the two substrates thus prepared, and after further spraying a gap control material having a diameter of 9 μm, the main sealing material is cured. A liquid crystal cell having a birefringence of 0.25 (including a chiral agent) manufactured by Dainippon Ink Co., Ltd. is injected into the completed empty cell. A polarizing plate is bonded to this liquid crystal cell.

  FIG. 4 shows the structure of the polarizing plate. The solid line arrow 4A is the absorption axis of the upper polarizing plate, and the dotted line arrow 4B is the absorption axis of the lower polarizing plate. In this way, a two-domain TN-LCD with normally black display can be manufactured.

  When a voltage was applied to the cell for display, a display failure occurred.

  5 and 6 show sketches of examples of display defects. Long slits 5s in the vertical direction are arranged in a matrix in the vertical and horizontal directions. The slits 5s arranged in the horizontal direction are alternately arranged on the upper and lower electrodes, and the region between the slits 5s is a region where the liquid crystal molecules should be uniformly oriented. The orientation is reversed on the left and right of the slit 5s. The disclination line 5 can be seen between the slits 5s arranged in the vertical direction, which is considered as a boundary between different orientations of the liquid crystal molecules. If the position is stable, there are few display problems. Display regions that are long in the vertical direction are arranged in the horizontal direction, and the two-domain alignment is formed by alternately changing the alignment. However, the disclination line 5 moves in a direction orthogonal to the longitudinal direction of the slit 5s in the portion surrounded by a circle in FIG. A display area that is long in the vertical direction is divided in the middle, and the position is not stable, so that a display defect occurs.

  Further, when the cell was continuously energized in an atmosphere at 85 ° C., the disclination line 5 moved in almost all places as shown in FIG. 6 after about 500 hours had elapsed, and the display became extremely difficult to see.

Example 1
FIG. 7 shows an example of a two-domain TN-LCD having a segment structure. The TN-LCD shown in FIG. 7 has a structure in which an upper segment electrode 6 representing the numbers “1” and “2” and a lower common electrode 7 sandwich a liquid crystal as a pair of electrodes. In this example, the conduction range of the segment electrode 6 is narrowed, and the conduction range of the common electrode 7 is widened.

  The segment electrode 6 and the common electrode 7 are provided with rectangular slits 6s and 7s from which a part is removed. And the slit 6s provided in the segment electrode and the slit 7s provided in the common electrode are alternately arranged in the short direction of the slit. In addition, the number of divisions per unit length is different between the slit provided in one electrode and the slit provided in the other electrode. Here, the number of divisions refers to the number of divisions in the longitudinal direction of the slit. When the number of divisions is 1, the number of slits is 2. Therefore, there are cases where the number of divisions is 0 (the number of slits is 1). In FIG. 7, the number of divisions per unit length of the slit 6s is increased, and the number of divisions per unit length of the slit 7s is set to zero. As a result, in the display area defined by the segment electrode 6 and the common electrode 7, the slit rows divided into several and the slit rows connected from end to end of the display area are alternately arranged in the slit short direction. It is the structure arranged in. Further, by leaving the electrode without providing the slit 7 s at the end of the common electrode 7, the common electrode 7 becomes one electrode that is electrically connected, so that design and connection are facilitated.

  FIG. 8 shows a slit pattern of electrodes of the liquid crystal display element shown in FIG. The shape of the slit is a rectangle. The longitudinal dimension of the slit 6s having a large number of divisions per unit length provided in the upper segment electrode 6 is, for example, 40 μm, and the lateral dimension is, for example, 20 μm. The distance between the slits in the longitudinal direction is 20 μm, and the distance between the slits 6s and 7s adjacent to each other when viewed from above is 40 μm.

  A low pretilt angle alignment film (SE-510, manufactured by Nissan Chemical Industries, Ltd.) is applied and baked on the substrate including the electrode having such a slit pattern. Thereafter, the substrate is rubbed with a rayon rubbing cloth. The twist direction of the liquid crystal is left-handed.

  By making the rubbing direction shown in FIG. 3, the liquid crystal molecules are splay-aligned, and the tilt angle of the liquid crystal molecules at the center of the cell is 0 degree.

  The main sealing material is applied to the two substrates thus prepared, and after further spraying a gap control material having a diameter of 9 μm, the main sealing material is cured. A liquid crystal cell having a birefringence of 0.25 (including a chiral agent) manufactured by Dainippon Ink Co., Ltd. is injected into the completed empty cell. A polarizing plate having a structure as shown in FIG. 4 is bonded to this liquid crystal cell. In this way, a two-domain TN-LCD with normally black display can be manufactured.

  When a voltage is applied to the liquid crystal cell for display, no movement of the disclination line 5 in the short side direction of the slit as seen in FIG. I didn't feel rough when I looked at the camera from an oblique direction. Furthermore, when this cell was continuously energized in an atmosphere at 85 ° C., no problem occurred in the display even after 1000 hours.

  As described above, the display defect occurs when the display area becomes unstable due to the movement of the disclination line between the slits. It is considered that the disclination line can be prevented from moving by reducing or reducing the number of slits formed in one electrode to 0 and display defects do not occur. For this reason, it is more preferable that the number of slits formed in one electrode is zero.

  It supplements about the size of the slit used in Example 1. FIG. When the width of the slit (length in the short direction of the slit) is larger than a certain value, the electric field at the center of the slit becomes extremely weak, and a region where the liquid crystal molecules do not react to voltage application occurs. Display defects occur in the area. Further, the area other than the slit, that is, the area of the liquid crystal molecules responding to the electric field is reduced, and the so-called aperture ratio is reduced, so that the transmittance during voltage application is reduced. Considering this, the slit width is preferably 30 μm or less. Conversely, if the width of the slit is too narrow, a sufficient oblique electric field is not generated, and the effect of viewing angle characteristics is reduced. Experiments were performed with various slit widths. As a result, it was found that when the slit width was 10 μm or more, preferably 20 μm or more, stable two-domain orientation was obtained, and good display was obtained. In Example 1, the gap between the electrodes sandwiching the liquid crystal is 9 μm, and when calculated from the above results, even when the gap between the electrodes is changed, about 1 to 3 times the gap. It is sufficient to provide a slit having a width of about 3 times.

  Although the length in the longitudinal direction of the slit has a large number of divisions per unit length, the display defect shown in FIG. It is preferable to reduce the number. However, the longer the slit is, the smaller the area of the transparent electrode between the slits is, and there is a disadvantage that display unevenness occurs due to an increase in the resistance value of that portion. As a result of experimenting with slits having various lengths, it was found that those having a length of about 20 μm to 300 μm are suitable. Therefore, when changing the gap between the electrodes, a slit having a length of about 2 to about 33 times the gap may be provided.

  The interval between the slits 6s and 7s in the slit short direction is preferably large in order to secure a sufficient display area. However, the two-domain pattern can be identified visually by ensuring the stability of two domains. Narrower is better for the purpose of preventing. As a result of experiments in which this interval was varied, it was found that the interval in the slit short direction is preferably 60 μm or less. The minimum value is preferably 10 μm or more than the width of the slit because a wider value is preferable considering the aperture ratio. Moreover, it turned out that about 10-50 micrometers is suitable for the slit space | interval of a slit longitudinal direction. Therefore, when changing the gap between the upper and lower electrodes, it is only necessary to provide a slit whose slit interval is about 1 to about 6.6 times in the short direction and about 1 to 5.5 times in the longitudinal direction.

  The length of the slit provided in the other electrode with a small number of divisions in the longitudinal direction is determined by the length of the display area and the shape of each transparent electrode.

  Next, the case of a two-domain display type two-domain vertical alignment type LCD will be described by comparing the comparative example 2 and the example 2.

(Comparative Example 2)
FIG. 9A shows a cross-sectional view of a vertical alignment type LCD according to Comparative Example 2. As shown in FIG. 9A, a vertical alignment film 11A (SE-1211 manufactured by Nissan Chemical Industries, Ltd.) is formed on each of the upper and lower substrates 10A including electrodes 8A and 9A having the same pattern and slits 8As and 9As as in Comparative Example 1. Is applied and fired. A main seal material is applied to the two substrates, and a gap control material having a diameter of 4 μm is sprayed thereon, and then superimposed to cure the main seal material. A liquid crystal cell having a birefringence of 0.15 (including a chiral agent) manufactured by Merck is injected into the completed empty cell. The liquid crystal molecules 12A are aligned perpendicular to the substrate plane. A viewing angle compensation plate 13A (VAC-180 film manufactured by Sumitomo Chemical Co., Ltd.) and a polarizing plate 14A are bonded to the liquid crystal cell with a structure as shown in FIG. In this way, a two-domain vertical alignment type LCD can be manufactured.

  When a voltage is applied to the cell for display, the display defect as shown in FIG. 5 is not as high as that of the TN-LCD of Comparative Example 1, and the display is somewhat rough when the liquid crystal cell is viewed from an oblique direction. It was.

(Example 2)
FIG. 9B shows a cross-sectional view of a vertical alignment type LCD according to the second embodiment. As shown in FIG. 9B, a vertical alignment film 11B (SE made by Nissan Chemical Industries, Ltd.) is formed on the upper and lower substrates 10B including the electrodes 8B and 9B having the patterns and slits 8Bs and 9Bs as shown in the first embodiment. -1211) is applied and fired. A main seal material is applied to the two substrates, and a gap control material having a diameter of 4 μm is sprayed thereon, and then superimposed to cure the main seal material. A liquid crystal cell having a birefringence of 0.15 (including a chiral agent) manufactured by Merck is injected into the completed empty cell. The liquid crystal molecules 12B are aligned perpendicular to the substrate plane. A viewing angle compensation plate 13B (VAC-180 film manufactured by Sumitomo Chemical Co., Ltd.) and a polarizing plate 14B are bonded to the liquid crystal cell with a structure as shown in FIG. In this way, a two-domain vertical alignment type LCD can be manufactured.

  When a voltage was applied to the cell for display, no display roughness was observed even when the liquid crystal cell was viewed from an oblique direction. Furthermore, when this cell was continuously energized in an atmosphere at 85 ° C., no display defect occurred even after 1000 hours.

(Example 3)
A case of a simple matrix type two-domain TN-LCD and a two-domain vertical alignment type LCD will be described with reference to FIG. FIG. 10 is a plan view of a simple matrix type liquid crystal display device according to the present invention.

  Similarly to the segment display, the liquid crystal cell used in Example 3 has a structure in which the upper segment electrode 15 and the lower common electrode 16 sandwich the liquid crystal as a pair of electrodes as shown in FIG. . The segment electrode 15 and the common electrode 16 are provided with rectangular slits 15s and 16s from which a part has been removed. And the slit 15s provided in the segment electrode 15 and the slit 16s provided in the common electrode 16 are alternately arranged in the short direction of the slit. In addition, the number of divisions per unit length of the slits provided in one electrode and the slits provided in the other electrode are different. Then, it is provided on the common electrode 16 side. As a result, the common electrode 16 can be provided with a slit 16s having a long dimension, and the design and manufacturing process can be simplified. Using this electrode, a 2-domain TN-LCD and a 2-domain vertical alignment type LCD were fabricated, and the roughness of the display was confirmed. The roughness of the display was greatly reduced by using the electrode structure of the present invention. .

  In FIG. 10, slits are provided at the intersections of the horizontal segment electrodes 15 and the vertical common electrodes 16, but slits 16s extending over a plurality of dots are provided on the common electrode 16 side. Is also possible. However, care should be taken not to provide slits at the ends of the electrodes in order to simplify the manufacturing process. Also, it should be noted that in each dot, slits at both ends in the slit short direction are provided on the side of the electrode (here, the segment electrode 15) parallel to the slit short direction. Thereby, in each dot, the direction of the fringe electric field at the end in the slit short direction becomes parallel.

  Preferable values of the dimension of the slit and the dimension of the slit interval are the same as those in Examples 1 and 2.

Example 4
The case of a TFT active matrix liquid crystal display device will be described with reference to FIG. FIG. 11 shows a view of several pixel regions of the TFT active matrix liquid crystal display device as seen from below. As shown in FIG. 11, a plurality of TFT elements 17 made of amorphous silicon or the like, a pixel electrode 18 made of indium tin oxide (ITO) or the like, and a source electrode and a gate electrode of the TFT element 17 on a transparent glass substrate, respectively. A source line (signal line) 19 and a gate line (scanning line) 20 to be connected are formed, and the pixel electrode 18 is driven by the TFT element 17 through the drain electrode. On the pixel electrode 18, a vertical alignment film or a horizontal alignment film subjected to a rubbing process is formed. On the glass substrate on which the pixel electrode 18 is formed, another glass substrate is disposed with a liquid crystal layer facing the substrate, and a common electrode is formed on the substrate. In addition, the surface of the common electrode in contact with the liquid crystal layer is also formed by subjecting the vertical alignment film or the horizontal alignment film to rubbing treatment.

  The pixel electrode 18 is formed with a plurality of slits 18s indicated by solid lines in FIG. Further, a row of elongated slits 21s connected from end to end of the display area corresponding to the pixel electrode 18 is formed on the common electrode facing the pixel electrode 18 as indicated by a broken line. The slits 18s and 21s on the upper and lower substrates are arranged alternately.

  It should be noted here that, in the same manner as in the simple matrix type liquid crystal display element of the third embodiment, in each dot, slits at both ends in the slit short direction are provided on the common electrode side. Thereby, in each dot, the direction of the fringe electric field at the end in the slit short direction becomes parallel. It is also possible to form a slit 21s extending over a plurality of dots on the common electrode side. However, as in Example 3, care should be taken not to provide slits at the ends of the electrodes.

  Preferable values of the dimension of the slit and the dimension of the slit interval are the same as those in Examples 1 to 3.

  The same effects as in the first to third embodiments can be obtained for the liquid crystal display device having the structure of the fourth embodiment.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, the present invention can be applied to various transparent electrode structures. As an example, a liquid crystal display element combining a segment type and a simple matrix type can be cited.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

FIG. 1 is an example of a two-domain TN-LCD having a segment structure. FIG. 2 is a plan view showing a slit structure of the electrode of the TN-LCD shown in FIG. FIG. 3 is a plan view showing the rubbing direction of the substrate. FIG. 4 is a plan view showing the structure of the polarizing plate. FIG. 5 is a sketch of an example of display failure. FIG. 6 is a sketch of another example of display failure. FIG. 7 is an example of a two-domain TN-LCD having a segment structure according to the first embodiment of the present invention. FIG. 8 shows a slit pattern of electrodes of the liquid crystal display element shown in FIG. FIG. 9A is a cross-sectional view showing the structure of a vertical alignment LCD according to Comparative Example 2, and FIG. 9B is a cross-sectional view showing the structure of a vertical alignment LCD according to Example 2. FIG. 10 is a plan view of a simple matrix type liquid crystal display device according to the present invention. FIG. 11 is a diagram of several pixel regions viewed from below in a TFT active matrix liquid crystal display device according to Example 4 of the present invention.

Explanation of symbols

1, 6, 15 Segment electrode 2, 7, 16 Common electrode 5 Disclination line 17 TFT element 18 Pixel electrode 19 Source line 20 Gate line 1s, 2s, 5s, 6s, 7s, 8As, 8Bs, 9As, 9Bs, 15s , 16s, 18s, 21s Slit 3A, 3B Rubbing direction 4A, 4B Polarizing plate absorption axis 8A, 8B Upper electrode 9A, 9B Lower electrode 10A, 10B Substrate 11A, 11B Vertical alignment film 12A, 12B Liquid crystal molecules 13A, 13B Viewing angle Compensation plate 14A, 14B Polarizing plate

Claims (11)

A pair of substrates oppositely arranged in parallel;
A transparent electrode formed on the pair of substrates and having a predetermined pattern for display;
A liquid crystal layer sandwiched between the pair of substrates;
A rectangular slit formed in the transparent electrode, wherein a first slit provided in one transparent electrode and a second slit provided in the other transparent electrode are in the short direction of the slit A liquid crystal display element having alternatingly arranged slits having a structure in which the number of divisions per unit length of the first slit and the second slit is different. A pair of substrates oppositely arranged in parallel;
A transparent electrode formed on the pair of substrates and having a predetermined pattern for display;
A liquid crystal layer sandwiched between the pair of substrates;
A rectangular slit formed in the transparent electrode, wherein a first slit provided in one transparent electrode and a second slit provided in the other transparent electrode are in the short direction of the slit A liquid crystal display element having alternately arranged and slits having a structure in which the number of divisions per unit length of one of the first slits and the second slits is zero.   The dimension of the slit having a large number of divisions per unit length is about 2 to about 33 times in the longitudinal direction and about 1 to about 3.3 times in the lateral direction with respect to the gap between the transparent electrodes. Item 3. The liquid crystal display element according to item 1 or 2.   An interval in a longitudinal direction of the slit having a large number of divisions per unit length is about 1 to about 5.5 times a gap between the transparent electrodes, and the first slit and the second slit are spaced apart from each other. 4. The liquid crystal display element according to claim 1, wherein an interval in a slit short direction is about 1 to about 6.6 times the gap. 5.   The said transparent electrode is a segment type which consists of a common electrode with a wide conduction range formed on one of the pair of substrates and a segment electrode with a narrow conduction range formed on the other substrate. 2. A liquid crystal display element according to item 1.   The liquid crystal display element according to claim 1, wherein the transparent electrode is a simple matrix type.   The liquid crystal display element according to claim 6, wherein in the simple matrix type transparent electrode, a slit having a small number of divisions per unit length is provided on the transparent electrode side parallel to the slit longitudinal direction.   8. The liquid crystal display according to claim 6, wherein, in each dot in the simple matrix type transparent electrode, a slit at an endmost portion in a slit short direction is provided on a transparent electrode side parallel to the short direction of the slit. element.   The liquid crystal display element according to claim 1, wherein the transparent electrode is an active matrix type.   The liquid crystal display element according to claim 9, wherein in the active matrix type transparent electrode, a slit having a small number of divisions per unit length is provided on a common electrode side.   11. The liquid crystal display element according to claim 9, wherein, in each dot in the active matrix type transparent electrode, a slit at an end in the slit short direction is provided on the common electrode side.

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