JP4477055B2 - Liquid crystal display element - Google Patents

Description

  The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element having a light shielding film.

  A segment display liquid crystal display element is used to perform numeric display by seven segments, mark display having a specific shape, and the like. For example, Patent Documents 1 to 3 disclose a technique for forming a black mask, which is a light shielding film, on the entire background of the segment display pattern. Patent Document 3 describes that a black mask is provided in the background of a dot display pattern even in the case of dot matrix display.

  As described in Patent Document 3, one of the effects of the black mask is that light leakage due to an oblique electric field generated near the edge of the display pattern can be suppressed. This light leakage is likely to occur particularly in a vertical alignment type liquid crystal display element.

JP-A-5-281559 JP 2000-250024 JP JP-A-5-2161

  However, when a black mask is formed on the entire background, even if the display pattern is black, the display pattern appears to be displayed slightly (this is called crosstalk due to the black mask). Occur).

  Crosstalk due to the black mask can be achieved by changing the transmittance of the display pattern regardless of the display mode such as twisted nematic (TN), super twisted nematic (STN), and vertical alignment (VA). This happens because the transmittance cannot be as low as the rate. Note that this difference in transmittance becomes more prominent when the viewing angle is tilted.

  A schematic example of crosstalk caused by the black mask will be described with reference to FIG. FIG. 8 is a schematic plan view showing a display state of a 3-digit 7-segment display unit. The background of the 3-digit 7-segment display section is a black background with a black matrix formed on the entire surface, and the 3-digit 7-segment display section displays white as “321”. Of the 7-segment display portion, the black-displayed segment (shown by diagonal lines) has a higher transmittance than the background black mask formation region and appears to be displayed slightly.

  An object of the present invention is to provide a liquid crystal display element in which crosstalk caused by a light shielding film such as a black mask is suppressed.

According to one aspect of the present invention, a first transparent substrate, a second transparent substrate that faces the first transparent substrate, and a surface of the first transparent substrate that faces the second transparent substrate. A first transparent electrode disposed on the first transparent electrode having a first planar shape and a second transparent substrate disposed on a surface facing the first transparent substrate and having a second planar shape. and second transparent electrode, the first and second transparent substrates a liquid crystal layer sandwiched between, and a display pattern defined as overlapping portions of the in the display surface and the first and second transparent electrodes, wherein Only one of the strip-shaped light shielding film along the edge of the display pattern and the first and second transparent electrodes exists in the display surface, and the liquid crystal layer is exposed without being covered by the light shielding film. None of the first and second transparent electrodes exist in the background and the display surface, and the light shielding film A background that exposes the liquid crystal layer without being covered, and the light shielding film overlaps both an inner region and an outer region from an edge of the display pattern in the display surface, and the light shielding film However, the width that overlaps the inner area from the edge of the display pattern in the display surface, or the width that the light shielding film overlaps the outer area from the edge of the display pattern in the display surface is 5 μm or more. In the display surface, a liquid crystal display element in which the total width of the light shielding film is 50 μm or less is provided.

  By using a band-shaped light shielding film along the edge of the display pattern, the transmittance difference between the background and the black display pattern can be reduced as compared with the case where the light shielding film is formed on the entire background of the display pattern. .

  First, a liquid crystal display device according to a first embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view of the liquid crystal display element of the first embodiment. A segment electrode 3 and a black mask 4 are formed on the lower transparent substrate 2, and a lower alignment film 5 is formed so as to cover the segment electrode 3 and the black mask 4.

  A common electrode 8 is formed on the upper transparent substrate 9, and an upper alignment film 7 is formed so as to cover the common electrode 8. As the upper and lower alignment films 7 and 5, for example, a vertical alignment film SE-1211 manufactured by Nissan Chemical Industries, Ltd. is used.

  By rubbing the upper and lower alignment films 7 and 5 with a rayon-made rubbing cloth, a pretilt angle θ can be given to the liquid crystal molecules M so as to fall in the rubbing direction D as shown in FIG. . Here, the pretilt angle θ is defined by the inclination from the normal direction of the transparent substrate below the alignment film.

  The upper transparent substrate 9 and the lower transparent substrate 2 that have been rubbed on the alignment film are overlapped with each other through the gap control material having a diameter of 4 μm so that the alignment films face each other so that the rubbing direction is antiparallel. 12 to produce an empty cell.

  A liquid crystal cell 13 is produced by injecting a liquid crystal layer 6 by injecting a liquid crystal material having a birefringence Δn of 0.09 and a negative dielectric anisotropy into an empty cell. As the liquid crystal material, for example, a product manufactured by Merck & Co., Inc. can be used. Since the dielectric anisotropy is negative, the liquid crystal molecules M fall down from the vertical alignment when a voltage is applied.

  The lower polarizing plate 1 and the upper polarizing plate 11 are disposed on the lower side and the upper side of the liquid crystal cell 13, respectively. The lower polarizing plate 1 and the upper polarizing plate 11 are arranged in crossed Nicols. The liquid crystal display element of this embodiment is a vertical alignment type liquid crystal display element that performs normally black display. A backlight 14 is disposed under the lower polarizing plate 1, and the backlight 14 causes light to enter the lower polarizing plate 1. The bright display is called white display and the dark display is called black display.

  A biaxial plate 10 is inserted as a viewing angle compensation plate between the liquid crystal cell 20 and the upper polarizing plate 11. The biaxial plate 10 has an in-plane retardation of 50 nm and a retardation in the thickness direction (thickness cross section) of 220 nm. The in-plane slow axis of the biaxial plate 10 is arranged so as to be orthogonal to the absorption axis of the upper polarizing plate 10 that is a neighboring polarizing plate. The viewing angle compensation plate can also be disposed between the liquid crystal cell 20 and the lower polarizing plate 1.

  The segment electrode 3 and the common electrode 8 are formed of a transparent conductive material such as indium tin oxide (ITO), for example. An overlapping portion of the segment electrode 3 and the common electrode 8 defines a display pattern within the display surface. Corresponding to the shape of the desired display pattern, the segment electrode 3 and the common electrode 8 are formed in respective planar shapes. In the example shown in FIG. 1, the common electrode 8 includes the segment electrode 3 in the display surface, and the edge of the segment electrode 3 defines the edge of the display pattern. The control device 15 drives the liquid crystal display element in a simple matrix.

  The black mask 4 is formed on the display surface so as to cover the edge of the display pattern (in the example shown in FIG. 1, so as to cover the edge of the segment electrode 3). For example, the black mask 4 is formed of a material such as resin or metal having a light shielding property (for example, transmittance of 2% or less), and shields light from the backlight 14. In addition, it is preferable that the upper surface of the black mask 4 does not reflect external light incident from above the liquid crystal display element.

  As shown in FIG. 3A, when the black mask 4 is formed of a conductive material, an insulating layer 50 is formed between the segment electrode 3 and the black mask 4.

  As shown in FIG. 3B, a black mask 4 is formed on the substrate 2 so as to cover the edges of the display pattern, and segments are formed on the substrate 2 so as to partially cover the black mask 4. The electrode 3 can also be formed. A planarizing film having the same height (thickness) as the black mask 4 is formed between the black masks 4, and the segment electrode 3 is formed on the layer composed of the black mask 4 and the planarizing film. Thus, the flatness of the segment electrode 3 can be improved.

  As shown in FIG. 3C, the black mask 4 can cover the edge of the display pattern even if it is arranged on the common electrode 8 side instead of the segment electrode 3 side. In the example shown in FIG. 3C, the black mask 4A is arranged on the common electrode 8 so as to cover the edge E of the display pattern defined by the edge of the segment electrode 3 in the display surface.

  Although the example in which the edge of the segment electrode 3 defines the edge of the display pattern is given, the edge of the common electrode 8 may define the edge of the display pattern depending on the design of the electrode pattern. When the edges of both the third electrode 3 and the common electrode 8 are coincident, the edges of both electrodes define the edge of the display pattern.

  If necessary, a black mask can be formed on the segment electrode 3 side for a certain part of the edge of the display pattern, and a black mask can be formed on the common electrode 8 side for the other part. .

  In addition, although the example of the liquid crystal cell which formed the segment electrode in the lower substrate side and formed the common electrode in the upper electrode side is given, the segment electrode is formed in the upper substrate side as needed, and the lower substrate A liquid crystal cell in which a common electrode is formed on the side can also be used.

  The thickness of the black mask is not particularly limited. However, when the thickness is very large, for example, 3 μm or more, for example, the edge shape is tapered to suppress liquid crystal alignment disorder caused by the edge of the black mask. It may be preferable to provide a flattening layer that covers the black mask and flattens the surface.

  The arrangement of the black mask 4 will be further described with reference to FIG. FIG. 4 is a schematic plan view showing an example of the display surface of the liquid crystal display element. A one-digit 7-segment display portion in the display surface 20 is shown. The 7-segment display unit is composed of seven segment display patterns 21a to 21g. Band-shaped black masks 22a to 22g are formed along the edges so as to cover the edges of the segment display patterns 21a to 21g, respectively. The black masks 22a to 22g are indicated by oblique lines. In this example, the width of each black mask 22a-22g is 20 micrometers.

  For example, the black mask 22a is formed so as to overlap by 10 μm on the inner side of the segment display pattern 21a from the edge of the segment display pattern 21a in the width direction, and on the outer side of the segment display pattern 21a by 10 μm. Has been. The other black masks 22b to 22g are also formed so as to overlap by 10 μm from the edges of the segment display patterns 22a to 21g to the inner and outer regions, respectively.

  FIG. 5 is a schematic plan view showing a display state of a display portion in which seven-segment display portions on which such a black mask is formed are arranged in three digits. An example of the display state described with reference to FIG. 8 in the “background art” column will be referred to as a first comparative example. Similarly to the first comparative example, the display state of the present example is also a black background and a three-digit 7-segment display unit displaying white as “321”.

  In this embodiment, the black mask 22 is formed only near the edge of each segment display pattern. The black mask is not formed on the other background, and the liquid crystal layer is exposed. The transmittance of the black background (shown by diagonal lines) is not the transmittance of the black mask but the transmittance of the liquid crystal layer.

  Accordingly, the transmittance of the black display segment (shown by hatching) is substantially equal to the transmittance of the background. As a result, the phenomenon that the black display segment appears to be displayed slightly is suppressed as compared with the first comparative example in which the black mask is formed on the entire background. That is, crosstalk due to the black mask is suppressed.

  In order to eliminate the crosstalk caused by the black mask, a method may be considered in which a black mask having a transmittance similar to that of the segment display pattern for black display is formed on the entire background. However, since the transmittance of the display pattern changes according to the change in viewing angle, it is difficult to suppress the transmittance difference between the display pattern and the background in a wide viewing angle range.

  In this embodiment, a black mask is formed only near the edge of the segment display pattern, and the liquid crystal layer is exposed on the other backgrounds in the same manner as the display pattern. For this reason, as compared with the case where a black mask is formed on the entire background, the transmittance of the display pattern and the background changes in the same manner even if the viewing angle changes. Therefore, the transmittance difference between the display pattern and the background is suppressed in a wide viewing angle range.

  Since the black display portion of the vertical alignment type liquid crystal display element can generally maintain a low transmittance over a wide viewing angle range, the liquid crystal display element of the present embodiment keeps the black display pattern and the background transmittance low over a wide viewing angle range. However, the difference in transmittance between the black display pattern and the background can be suppressed.

  Furthermore, in the liquid crystal display element of the present embodiment, light omission near the edges is suppressed by the black mask formed near the edges of the segment display pattern.

  Consider a liquid crystal display element of a second comparative example in which the black mask is omitted from the liquid crystal display element of the first embodiment. Light leakage near the edge that occurs in the liquid crystal display element of the second comparative example will be described. When a normally black liquid crystal display element is driven in a simple matrix and a display pattern is displayed in black, an off voltage lower than an on voltage for performing white display is applied to the display pattern.

  FIG. 6C is a schematic cross-sectional view of the liquid crystal display element of the second comparative example showing the direction of the electric field when the off voltage is applied. A broken line indicates the direction of the electric field between the segment electrode 3 and the common electrode 8. The common electrode 8 is wide so as to include the segment electrode 3 in the display surface, and the edges of the segment electrode 3 and the common electrode 8 do not coincide with each other. An edge 30 of the segment electrode 3 defines an edge E of the display pattern.

  In the display surface, the electric field is parallel to the normal direction of the substrate (upper substrate 9 or lower substrate 2) sufficiently inside the edge 30 of the segment electrode 3, but in the vicinity of the edge 30, the normal direction of the substrate An oblique electric field tilted from is generated.

  In a region where the off-voltage is applied, the liquid crystal molecules do not move in the initial vertical alignment in the region where the electric field is parallel to the normal direction of the substrate, but in the region 31 near the edge 30, the liquid crystal molecules are affected by the oblique electric field. Will move. As a result, light leakage occurs in the region 31 near the edge 30.

  FIG. 7C is a photograph at the time of black display of the liquid crystal display element of the second comparative example in which the black mask is not formed. Light leakage occurs along the edge of the display pattern.

  FIG. 6A is a schematic cross-sectional view of the liquid crystal display element of the first embodiment showing the direction of the electric field when an off voltage is applied. Similar to the second comparative example, an oblique electric field is generated near the edge 30 of the segment electrode 3. However, in the first embodiment, the black mask 4 is formed so as to cover the region 31 where light leakage near the edge 30 occurs in the display surface. Without the black mask 4, the light that passes through is blocked by the black mask 4.

  FIG. 7A is a photograph at the time of black display of the liquid crystal display element of the first embodiment in which a band-shaped black mask is formed along the edge so as to cover the edge of the display pattern. The black mask has a width of 20 μm and is formed so as to overlap by 10 μm from the edge of the display pattern to both the inside and outside of the display pattern. Little light leakage near the edge of the display pattern is observed.

  Next, a liquid crystal display device according to a second embodiment will be described. In the first embodiment, the black mask is formed so as to overlap both the inside and outside of the display pattern from the edge of the display pattern. In the second embodiment, the display pattern is aligned along the edge of the display pattern. A black mask is formed so as to have an overlap only in the region inside.

  FIG. 6B and FIG. 7B are a schematic cross-sectional view showing a direction of an electric field when an off voltage is applied and a photograph at the time of black display, respectively, of the liquid crystal display element of the second embodiment. As shown in FIG. 6B, in the second embodiment, a black mask 4B is formed on the inner side from the edge 30 of the display pattern with the edge 30 as a starting point. Within the display surface, the edge E of the display pattern and the end of the black mask 4B overlap (the edge E of the display pattern and the black mask 4B are in contact with each other within the display surface).

  In the example of the photograph in FIG. 7B, the width of the black mask is 10 μm. Compared with the first embodiment in which the black mask is formed inside and outside the display pattern, light leakage along the edge is observed to some extent. However, light leakage is greatly improved as compared with the second embodiment in which no black mask is formed.

  If light leakage occurs only from the edge to the inside of the display pattern, the photograph of FIG. 7A of the first embodiment is the same as the photograph of FIG. 7B of the second embodiment. As in the example, almost no light leakage is observed. Further, if light leakage occurs only from the edge to the outside of the display pattern, the example of the photograph of FIG. 7B of the second example also shows the photograph of FIG. 7C of the second comparative example. As with the example, all light leakage will be observed.

  In the example of the photograph of FIG. 7B of the second embodiment, light leakage is increased as compared with the example of the photograph of FIG. 7A of the first embodiment, and FIG. 7C of the second comparative example. From the result that the light omission is improved as compared with the example of the photograph, it is considered that the light omission occurs in both the inner region and the outer region from the edge of the display pattern.

  From the above, it can be seen that even if a black mask is formed only on the inner side or the outer side from the edge of the display pattern, light leakage near the edge is effectively shielded. Furthermore, if black masks are formed on both the inner side and the outer side from the edge of the display pattern, light leakage is more effectively shielded.

  When the width of the black mask overlapped from the edge of the display pattern to the inside or outside is 5 μm, the light shielding effect was not as good as when the width was 10 μm, but light leakage was clearly suppressed compared to the case without the black mask. It was done. Therefore, it is preferable that the width of the overlap of the black mask from the edge of the display pattern to the inner region or the outer region in the display surface is 5 μm or more. Even if the width of the black mask overlapping from the edge of the display pattern to the inside or outside is larger than 10 μm, the light shielding effect is about the same as that of the width of 10 μm.

  If the width of the black mask is too wide, the black mask itself is visually recognized, which is not preferable. Examination of various widths revealed that the total width of the black mask in the display surface is preferably 50 μm or less.

  As described above, by using a strip-shaped light shielding film along the edge of the display pattern, for example, the transmittance of the black display pattern and the transmittance of the black background compared to the case where the light shielding film is formed on the entire background. Can be suppressed.

  Furthermore, light leakage occurring near the edge of the display pattern during black display can be shielded by the band-shaped light shielding film along the edge of the display pattern. By making the width of the light shielding film sufficiently thin (for example, about 20 μm), the light shielding film itself can be prevented from being visually observed.

  In addition, although the embodiment of the vertical alignment type liquid crystal display element has been described, even if it is a liquid crystal display element of another type such as a horizontal alignment type liquid crystal display element such as TN or STN, it is a normally black display and a simple matrix. The technique of the embodiment is effective for a liquid crystal display element that applies a voltage to a display pattern during black display, such as driving.

  That is, by replacing the light shielding film formed on the entire background with a band-shaped light shielding film along the edge of the display pattern, the transmittance difference between the background and the black display pattern is reduced. Further, light leakage near the edge of the black display pattern can be shielded by the band-shaped light shielding film along the edge of the display pattern. Note that even in TN, STN, or the like, light leakage may occur due to disorder in the alignment near the edge due to an oblique electric field.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the relationship between the rubbing direction and the pretilt angle. FIG. 3A to FIG. 3C are schematic cross-sectional views showing various examples of black mask arrangement methods. FIG. 4 is a schematic plan view showing a black mask arrangement of the liquid crystal display element of the first embodiment. FIG. 5 is a schematic plan view showing a display state of the liquid crystal display element of the first embodiment. FIGS. 6A to 6C are schematic cross-sectional views of the liquid crystal display elements of the first example, the second example, and the second comparative example, respectively, showing the direction of the electric field when the off voltage is applied. FIG. FIGS. 7A to 7C are photographs at the time of black display of the liquid crystal display elements of the first example, the second example, and the second comparative example, respectively. FIG. 8 is a schematic plan view showing a display state of the liquid crystal display element of the first comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower polarizing plate 2 Lower transparent substrate 3 Segment electrode 4 Black mask 5 Lower alignment film 6 Liquid crystal layer 7 Upper alignment film 8 Common electrode 9 Upper transparent substrate 10 Biaxial plate 11 Upper polarizing plate 12 Sealing material 13 Liquid crystal cell 14 Backlight 15 Control device 20 Display surfaces 21a to 21g Segment display patterns 22a to 22g, 22 Black mask

Claims (2)

A first transparent substrate;
A second transparent substrate facing the first transparent substrate;
A first transparent electrode disposed on a surface of the first transparent substrate facing the second transparent substrate and having a first planar shape;
A second transparent electrode disposed on a surface of the second transparent substrate facing the first transparent substrate and having a second planar shape;
A liquid crystal layer sandwiched between the first and second transparent substrates;
A display pattern defined as an overlapping portion of the first and second transparent electrodes in a display surface ;
A strip-shaped light shielding film along an edge of the display pattern ;
Only one of the first and second transparent electrodes is present in the display surface, and a background exposing the liquid crystal layer without being covered with the light shielding film;
None of the first and second transparent electrodes exists in the display surface, and has a background that exposes the liquid crystal layer without being covered with the light shielding film ,
The light shielding film has an overlap in both the inner region and the outer region from the edge of the display pattern in the display surface,
The light shielding film has a width that overlaps an inner region from the edge of the display pattern in the display surface, or a width that the light shielding film overlaps an outer region from the edge of the display pattern in the display surface. 5 μm or more,
A liquid crystal display element having a total width of 50 μm or less in the display surface. The liquid crystal display element according to claim 1, wherein the liquid crystal layer includes a liquid crystal material having a negative dielectric anisotropy and is of a vertical alignment type.