JP5038858B2 - Liquid crystal display element - Google Patents

Description

  The present invention relates to a liquid crystal display device in which an electrode pattern is devised.

  In a liquid crystal display element (LCD), it is required to further improve display quality. In order to obtain a good display quality, it is required to control the alignment of liquid crystal molecules. A method of rubbing a substrate for orientation control is known. In the case of a liquid crystal display element subjected to rubbing treatment, the alignment direction of the liquid crystal layer central molecule is the same in-plane direction (monodomain alignment). In the case of monodomain orientation, a good display can be obtained from one direction, but there is a problem in viewing angle characteristics that a display cannot be said to be good from another direction.

  A method of performing so-called multi-domain alignment control in a segment type, a dot matrix type or a liquid crystal display device of a combination type of a segment and a dot matrix has been disclosed or proposed. There are several types of multi-domain orientation control. In the method using a slit, a slit-like opening is provided in the electrode part inside the device, and an oblique electric field is generated between the upper and lower electrodes of the display part in the vicinity of the opening. A plurality of orientation directions are used. Thereby, it is intended to improve the viewing angle characteristics.

  Among them, a so-called two-domain alignment liquid crystal display element has been proposed in which liquid crystal molecules are aligned in one of two directions different from each other by 180 ° within one pixel or one segment.

  A TN (twisted nematic) -LCD is disclosed in Japanese Patent No. 3108768, and a vertical alignment LCD is proposed in Japanese Patent Application Laid-Open No. 2004-252298. According to these patent documents, two types of oblique electric fields are generated in the short side direction of the slit-shaped opening when a voltage is applied, and a two-domain alignment is obtained in which liquid crystal molecules are tilted in accordance with one of the two kinds of oblique electric fields. It is done.

Patent 3108768 JP 2004-252298 A

  There is a demand for further improvement in display quality such as improvement in viewing angle characteristics and suppression of display unevenness. An object of the present invention is to provide a liquid crystal display element with improved display quality.

  According to one aspect of the present invention, a pair of substrates disposed opposite to each other, a pair of transparent electrodes that are provided on both substrates and overlap each other with a liquid crystal layer interposed therebetween, and a pair of the transparent electrodes A slit group comprising a plurality of rectangular slits provided in each of the slit groups, wherein the slit group includes a plurality of first slits provided in one of the pair of transparent electrodes and a plurality of slits provided in the other. Including a second slit, wherein the first slit and the second slit are arranged alternately in the short (column) direction of the slit within the display surface defined by the pair of transparent electrodes, In each of the slit groups, a liquid crystal display element is provided in which the interval between adjacent slits in the longitudinal direction of the display surface is shorter than the slit width.

  The display quality of the multi-domain liquid crystal display element is improved.

  FIG. 1A is a schematic cross-sectional view showing a structure common to a liquid crystal display element according to an embodiment described below and a liquid crystal display element according to a reference example. 1B and 1C are schematic cross-sectional views showing structures common to TN type and vertical alignment type liquid crystal display elements among the liquid crystal display elements according to Examples and Reference Examples, respectively.

  Reference is made to FIG. 1A. The liquid crystal display element includes an upper substrate 1, a lower substrate 2 disposed substantially parallel to the upper substrate 1, and a liquid crystal layer 3 sandwiched between the substrates 1 and 2. The upper substrate 1 is, for example, an upper transparent substrate 1a, which is a transparent glass substrate, on the upper transparent substrate 1a so as to cover the upper transparent electrode 1b, the upper transparent electrode 1b formed of ITO (indium tin oxide), for example. An upper alignment film 1d formed on the transparent substrate 1a is included. The upper transparent electrode 1b includes a slit 1c that is long in one direction (in the drawing, from the front to the back of the drawing).

  The same applies to the lower substrate 2. The lower substrate 2 includes a lower transparent substrate 2a, a lower transparent electrode 2b formed on the lower transparent substrate 2a, and a lower side formed on the lower transparent substrate 2a so as to cover the lower transparent electrode 2b. It includes an alignment film 2d. Corresponding components of the upper substrate 1 and the lower substrate 2 are formed of the same material. The lower transparent electrode 2b also includes a slit 2c that is long in one direction.

  The upper transparent electrode 1b and the lower transparent electrode 2b overlap each other with the liquid crystal layer 3 interposed therebetween, thereby defining a display area.

  By providing the slits 1c and 2c in the upper and lower transparent electrodes 1b and 2b, respectively, as described above, an oblique electric field (electric field whose electric field direction is inclined from the substrate normal direction) is applied to the slit portion when a voltage is applied. As it occurs, the direction of the oblique electric field is reversed on both sides of the slit. In the display region defined by the pair of electrodes, when a voltage is applied, small regions (for example, regions R and S or regions T and U in the figure) in which the rising directions of the liquid crystal molecules are opposite to each other are formed at the same time. The viewing angle dependency of the small area is complemented, and the viewing angle dependency is reduced as a whole display area, the visibility is improved, and the display quality is improved.

  Refer to FIG. 1B. In the TN type liquid crystal display element, the liquid crystal layer is a nematic liquid crystal showing a twist, and the upper polarizing plate 4 is disposed outside the upper substrate 1 of the liquid crystal cell having the structure shown in FIG. A lower polarizing plate 5 is disposed. The upper and lower polarizing plates 4 and 5 each have a transmission axis in the in-plane direction of the polarizing plate, and transmit only light polarized in the transmission axis direction.

  Reference is made to FIG. 1C. In the vertical alignment type liquid crystal display element, the alignment direction of the liquid crystal molecules is vertical. A viewing angle compensation plate 6 is disposed between the upper substrate 1 having the structure shown in FIG. 1B and the upper polarizing plate 4. The viewing angle compensation plate 6 has a function of compensating for changes in visibility due to viewing angles.

  The inventors prepared a sample (reference example) in which a slit as shown in FIG. 2 was provided in the electrode in the liquid crystal display element having the above configuration, and examined the display state at that time. Here, a sample of a vertical alignment mode liquid crystal display element was manufactured. A liquid crystal material having a negative dielectric anisotropy was used as the liquid crystal material in the liquid crystal layer. The liquid crystal layer thickness is 4 μm.

  FIG. 2 is a plan view showing the slit arrangement of the manufactured sample. As shown in the figure, slits provided in the transparent electrode are arranged in a matrix. In the figure, the solid line portion is the common electrode side slit opening 1c, and the dotted line portion is the segment electrode side slit opening 2c. In the display plane defined by the common electrode and the segment electrode, the matrix direction corresponds to the horizontal direction when the liquid crystal display element is viewed in a normal state, and the column direction corresponds to the vertical direction.

  The slits 1c and 2c will be described. In the common electrode 1b, the slits 1c are arranged in the row direction in the display surface in a certain row, and the slits 2c in the segment electrode 2b in the row adjacent to the column direction in the display surface have a slit pitch in the row direction. They are lined up in the row direction with a shift of about ½. Here, the spacing in the row direction between the slits is the same in all rows. Further, the shortest distance between the slits in the row direction is the same.

  The dimension of the slit will be described. The length (width) in the short direction of the slit 1c in the common electrode is Cw, the length in the longitudinal direction is Cl, and the interval between the slits 1c is Cp. Further, the length (width) of the slit 2c in the segment electrode in the short direction is Sw, the length in the longitudinal direction is Sl, and the interval between the slits 2c is Sp. Let P be the shortest distance between adjacent slits 1c and 2c in the column direction (in-plane short direction). In this reference example, the sizes of the slits 1c and 2c are the same, and Cw = Sw = 10 μm, Cl = Sl = 100 μm, Cp = Sp = 10 μm, and P = 50 μm.

  The slit was formed by forming a photoresist pattern having the slit-shaped opening on the glass substrate and etching with an acid solution using the photoresist as an etching mask. Thereafter, the resist pattern was removed.

  The size per liquid crystal display element is, for example, 23 mm long × 110 mm wide. Sixteen liquid crystal display element samples were prepared by multi-chatting on a pair of glass substrates measuring 300 mm long and 200 mm wide.

  FIG. 3 is a partial image of the liquid crystal display element sample provided with the slits observed with a microscope. The polarizing plate has a crossed Nicol arrangement in which the absorption axis is approximately 45 ° with respect to the slit longitudinal direction. Of the 16 samples that can be fabricated from a pair of substrates, some samples felt rough in appearance display. The roughness was different for each sample or each production lot. Referring to the illustrated photograph, a dark portion (disclination) on the loop is observed in a gap 1g between the slits 1c (dark portions) and a gap 2g between the slits 2c (dark portions). Furthermore, it can be confirmed that there is an area in which a dark region extends around the disclination as a base point (alignment defect). It is thought that the roughness during observation is caused by this dark part.

  Inventors measured the slit size of the produced sample. Then, it turned out that there is variation in size for each slit. The slit widths Cw and Sw were 7 μm to 12 μm, and the slit longitudinal direction intervals Cp and Sp were 8 μm to 13 μm.

  This variation in the slit size is considered to be caused by in-plane unevenness of etching. Display defects due to variations in slit size are likely to occur when the slit width is 30 μm or less.

  Further, when the portion where the display defect occurred was further investigated, the tendency that the display defect appeared more prominently as the distance in the slit longitudinal direction became larger than the slit width.

Based on the above consideration, the inventors have determined the relationship between the slit widths Cw and Sw and the slit longitudinal intervals Cp and Sp.

Cw> Cp and Sw> Sp—Formula 1

The liquid crystal display element which reduces a display defect by setting is proposed.

  Then, the slit size was set to Cw = Sw = 20 μm, Cp = Sp = 15 μm or 10 μm, and 16 liquid crystal display element samples were produced for each of Cp = Sp = 15 μm and 10 μm. The shortest distance P between adjacent slits in the in-plane row direction was 40 μm.

  When the above samples were observed for appearance, no rough display was confirmed for any of the samples. Further, when a sample having Cp = Sp = 20 μm was produced, some roughness was confirmed, but less roughness than the sample according to the reference example.

  FIG. 4 is a partial image obtained by observing the appearance of a sample with Cp = Sp = 10 μm with a microscope. As shown in the figure, dark portions other than the slits were hardly seen. In particular, dark portions due to loop-like disclinations in the gaps 1g and 2g between the slits 1c and 2c were hardly confirmed.

  Thus, in the sample of the liquid crystal display element in which the slit width is larger than the longitudinal interval between the slits, display defects due to disclination did not occur. It is considered that disclination did not occur because the alignment of the liquid crystal molecules was stable.

  In manufacturing, it is considered that the slit size varies due to uneven etching. Therefore, when forming the opening of the resist pattern, if the opening width (length in the short direction) is set larger than the set size and the interval in the longitudinal direction of the opening is set shorter than the predetermined size, the slit width is surely set between the slits. It could be larger than the longitudinal spacing.

Further, the sizes of Cp and Sp are preferably closer to 0. As a result of the study, the relationship between Cw and Sw

Cw × 0.75 ≧ Cp and Sw × 0.75 ≧ Sp −Formula 2

It was found that satisfying the above is more preferable.

  As described above, the display quality can be improved by setting the distance between the slits in the longitudinal direction to be shorter than the slit width.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, Cw and Sw do not need to be equal and may be 10 μm to 30 μm. Further, the range of the shortest distance P between the slits 1c and 2c adjacent to each other in the column direction (in-plane short direction) is 10 μm to 60 μm from the viewpoint of display quality, and preferably the slit width is 60 μm.

  FIG. 5 shows another arrangement example 1 of the slits. As shown in the figure, in this slit arrangement example, the slits provided in the common electrode and the segment electrode are arranged in a matrix on the display surface.

  FIG. 6 shows another arrangement example 2 of the slits. As shown in the figure, in this slit arrangement example, in the slit arrangement shown in FIG. 5, the slit long side direction is arranged at approximately 45 ° with respect to the left-right or vertical direction of the liquid crystal display element.

  Further, the slit longitudinal interval of either the segment or the common may be 0, or a portion of Cp (Sp> 0 and a portion of Cp (Sp) = 0 may be mixed.

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

FIG. 1A is a schematic cross-sectional view showing a structure common to liquid crystal display elements according to examples and comparative example shown below, and FIGS. 1B and 1C are liquid crystal display elements according to examples and comparative examples. FIG. 3 is a schematic cross-sectional view showing a structure common to TN type and vertical alignment type liquid crystal display elements. FIG. 2 is a plan view showing a slit arrangement according to Comparative Example 1. FIG. FIG. 3 is a partial image obtained by observing the appearance of the liquid crystal display element according to Comparative Example 1 with a microscope. FIG. 4 is a partial image obtained by observing the appearance of the sample in the case of Cp = Sp = 10 μm with a microscope according to the first embodiment. FIG. 5 shows another arrangement example 1 of the slits. FIG. 6 shows another arrangement example 2 of the slits.

Explanation of symbols

1, 2 substrate 1a, 2a transparent substrate 1b, 2b transparent electrode 1c, 2c slit 1d, 2d alignment film 1g, 2g gap 3 liquid crystal layer 4, 5 polarizing plate 6 viewing angle compensation plate

Claims (5)

A pair of opposed substrates;
A pair of transparent electrodes provided on both substrates and overlapping each other with a liquid crystal layer therebetween to form a display region;
A slit group comprising a plurality of rectangular slits provided in each of the pair of transparent electrodes;
The slit group includes a plurality of first slits provided in one of the pair of transparent electrodes, and a plurality of second slits provided in the other, the first slit and the second slit Are arranged alternately in the short (column) direction of the slit in the display surface defined by the pair of transparent electrodes,
In each of the slit groups, a liquid crystal display element in which an interval between adjacent slits in the longitudinal direction in the display surface is shorter than a slit width. The pair of transparent electrodes are a common electrode and a segment electrode,
2. The liquid crystal display according to claim 1, wherein Cw and Sw are 10 μm or more and 30 μm or less, where Cw is a slit width of the slit provided on the common electrode side and Sw is a slit width of the slit provided on the segment electrode side. element.   When the interval between the slits adjacent in the longitudinal direction of the slit provided on the common electrode side is Cp, and the interval between the slits adjacent in the longitudinal direction of the slit provided on the segment electrode side is Sp, The liquid crystal display element according to claim 2, wherein Cw × 0.75 ≧ Cp and Sw × 0.75 ≧ Sp are satisfied.   4. The liquid crystal display element according to claim 1, wherein, in the slit group, a shortest distance P between slits adjacent to each other in the short side direction of the display surface of the slit is 10 μm to 60 μm.   The liquid crystal display element according to claim 1, wherein the shortest distance P is a slit width of 60 μm.