JP5213482B2 - Liquid crystal display element - Google Patents

Description

  The present invention relates to a liquid crystal display element.

  In a mono-domain vertical alignment liquid crystal display element driven in a multiplex manner, it is known that display quality is deteriorated due to a phenomenon called DMA (Dynamic Miss Alignment). As a measure against DMA, a liquid crystal display element is disclosed in which at least part of the edge of the display electrode has a zigzag pattern.

  This liquid crystal display element can prevent DMA. However, there is a problem that the zigzag shape is visually recognized, and an oblique electric field is generated at the edge portion due to the zigzag shape, and light leakage at the edge portion is increased.

  Japanese Patent Application Laid-Open No. 2000-250024 discloses a method of providing a black mask over the entire background portion to define a display pattern and preventing light leakage.

JP 2000-250024 JP

  According to Japanese Patent Laid-Open No. 2000-250024, although light leakage can be prevented, there is a difference in transmittance between a segment that does not display and the surrounding black mask portion (the transmittance of the black mask portion is almost 0%). It is almost completely black and darker than the display when no voltage is applied to the segment), and the display feels strange (a phenomenon similar to so-called crosstalk occurs).

  An object of the present invention is to provide a liquid crystal display element that improves display quality.

According to an aspect of the present invention, a pair of opposing substrates, a counter electrode pattern formed on each opposing surface of the pair of opposing substrates, and the counter electrode with respect to each of the pair of opposing substrates A vertical alignment film formed so as to cover the pattern, a vertical alignment liquid crystal layer sandwiched between the pair of opposing substrates, and a pair of polarizing plates disposed outside the pair of opposing substrates, An edge of the counter electrode pattern includes a zigzag pattern that is a set of sides in parallel or perpendicular to the in-plane direction of the liquid crystal director of the liquid crystal layer that is tilted by the alignment treatment, and is defined by the counter electrode pattern black mask covering the edge of the display pattern have a that, in a region deviated from the display pattern between the counter electrode pattern in which the black mask to cover the edge, Serial directly on the substrate, a liquid crystal display device wherein the vertical alignment film is formed is provided.

  According to the present invention, a liquid crystal display element with improved display quality can be provided.

  FIG. 1 is a schematic sectional view of a liquid crystal display element. The illustrated liquid crystal display element includes a glass back (lower) substrate 1a and a glass front (upper) substrate 1b opposed thereto, and a liquid crystal layer 2 is provided between the substrates 1a and 1b. ing.

  A rear transparent electrode 3a serving as a segment electrode is formed on the liquid crystal layer 2 side surface of the rear substrate 1a, and a front transparent electrode 3b serving as a common electrode is formed on the liquid crystal layer 2 side surface of the front substrate 1b.

  The transparent electrodes 3a and 3b overlap with each other with the liquid crystal layer 2 interposed therebetween, and a display region (display pattern) is formed in the overlapping portion.

  Further, vertical alignment films 4a and 4b are provided on the liquid crystal layer 2 side of the substrates 1a and 1b so as to cover the respective transparent electrodes. An insulating film may be provided between the vertical alignment film and the transparent electrode as necessary.

  A pair of polarizing plates 5a and 5b are formed on the outside in the normal direction of the upper and lower substrates 1a and 1b. The axial directions of the polarizing plates 5a and 5b are arranged so as to make 90 ° with each other. In addition, you may arrange | position the optical compensation board 6 between a board | substrate and a polarizing plate (for example, 1a and 5a) as needed.

  The vertical alignment films 4a and 4b are rubbed so that the liquid crystal molecule direction (liquid crystal director) that falls down by rubbing and the axial direction of the polarizing plate form an angle of 45 °.

  A sealing material 7 is formed to bond the substrates 1a and 1b together with the role of the wall enclosing the liquid crystal layer 2.

  In the display area, a black mask 8 is formed at the edge portion of the electrode. Here, it is formed on the lower substrate.

  2A shows an example of a display pattern and electrodes, and FIG. 2B shows an example of the arrangement of a black mask covering the electrodes. In FIG. 2A, the upward slanting line indicates the lower electrode 3a, and the downward sloping line indicates the upper electrode 3b. A cross hatch portion where the two substrates overlap is a display pattern.

  In the display pattern, the portion of the side that is not parallel to the vertical direction and the horizontal direction in the figure has a zigzag shape. This is a structure for preventing DMA. The zigzag shape was a pattern composed of sides of the 0 o'clock-6 o'clock direction and the 3 o'clock-9 o'clock direction when the upper direction in the figure was 0 o'clock. The size of the zigzag shape is about 40 μm in width (portion having the zigzag shape).

  The fine cross hatch portion shown in FIG. 2B is a black mask 8. The black mask 8 has a width of about 50 μm so as to cover the zigzag portion. If the black mask is too large, it will be visually recognized, so the upper limit is 200 μm. Note that the black mask width of the portion other than the zigzag shape portion may be narrower (for example, about 20 μm). The lower limit is 10 μm.

  A method for manufacturing the liquid crystal display element will be described. Here, a vertical alignment type liquid crystal display element will be described.

  In FIG. 1, first, transparent electrodes 3a and 3b are formed on both substrates 1a and 1b mainly using indium tin oxide ITO. Thereafter, a zigzag pattern is formed on the edge portion of the segment electrode 3a by patterning. Patterning is performed by applying a photoresist on ITO, exposing the photoresist, etching the ITO using the photoresist as a mask, and then removing the photoresist.

  Note that a zigzag shape may be formed in a portion corresponding to the display pattern in the common electrode.

  Next, as described above, the black mask 8 is formed on the edge portion of the display pattern. Here, it forms in the edge part of the segment electrode 3a. The black mask may be made of resin or metal. As a black mask, for example, a pigment dispersion resist or a carbon dispersion resist is used in the case of a resin, and chromium or molybdenum is used in the case of a metal. However, when a conductive material is used, an insulating layer is required between the black mask 8 and the transparent electrode 3a.

  Also, the thickness of the black mask is not particularly limited. For example, when using a film with a thickness of 3 μm or more, which is too thick for the liquid crystal layer, an edge shape is used to prevent liquid crystal alignment disorder at the black mask edge. Needs to be tapered or provided with a flat layer.

  Further, the positional relationship between the black mask 8 and the segment electrode 3 a may be reversed upside down, that is, the segment electrode 3 a may be disposed on the black mask 8.

  The vertical alignment films 4a and 4b are applied and baked so as to cover the transparent electrodes 3a and 3b and the black mask 8, respectively. SE1211 manufactured by Nissan Chemical Industries is used as the vertical alignment film material.

  The vertical alignment film is rubbed to give a pretilt of 89.5 ° when the substrate normal direction is 90 °. The rubbing is performed so that the upper and lower substrates are antiparallel in any direction of 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock shown in FIGS. 2A and 2B. Control of the tilt direction of liquid crystal molecules (alignment treatment) may be performed by slit alignment, protrusion alignment, ultraviolet light alignment, or the like.

  Next, a main sealing material is applied to each of the substrates 1a and 1b, and further, a gap control material (4 μm in this case) having a predetermined diameter is dispersed, and then both substrates 1a and 1b are overlapped with the electrode sides facing each other. The sealing material is cured to form an empty cell.

  Liquid crystal is injected into the formed empty cell to form the liquid crystal layer 2. A liquid crystal material having a negative dielectric anisotropy Δε and a birefringence Δn of about 0.09 is used. The liquid crystal molecules 2m of the liquid crystal layer 2 are aligned substantially vertically by the action of the vertical alignment film. If the liquid crystal material has a negative dielectric anisotropy, there are no particular restrictions on other physical property values or cell thickness.

  Thereafter, the optical compensation plate 6 and the rear polarizing plate 5a are bonded to the outer side (lower side in the drawing) of the rear substrate 1a, and the front polarizing plate 5b is bonded to the outer side (upper side in the drawing) of the front substrate 1b. Polatechno SHC-125U is used as the polarizing plate. The axial direction of the polarizing plate is crossed nicols with one axial direction of 1:30 to 7:30 and the other axial direction of 4:30 to 10:30.

  For example, a biaxial plate (in-plane retardation ΔR = 50 nm, thickness direction retardation Δth = 220 nm) is used as the optical compensation plate 6. The slow axis in the plane of the biaxial plate is arranged so as to be orthogonal to the absorption axis of the rear polarizing plate 5a. In addition to the biaxial plate, an A plate, a biaxial retardation plate or the like may be used as the optical compensation plate 6.

  When the liquid crystal display device prepared as described above was observed, DMA did not occur in the low frequency drive of 80 Hz, and a phenomenon similar to crosstalk was not visually recognized. The black mask was not visually observed due to its narrow width of 50 μm. For comparison, a liquid crystal display element having the same display pattern, having no zigzag shape on the electrode, and not forming a black mask (the same applies to others) was produced. When the liquid crystal display element was driven, DMA was generated and the display quality was poor.

  By making the edge of the electrode pattern zigzag, the direction in which the liquid crystal molecules collapse due to the alignment treatment and the direction of the oblique electric field generated at the electrode edge are parallel or perpendicular to each other, so that DMA can be prevented.

  However, light leakage occurs at the zigzag edge, and a large contrast ratio cannot be obtained.

  Therefore, in the embodiment, light leakage is cut by providing a black mask covering the display edge portion including the zigzag pattern. Since the width of the black mask is thin, a difference in black and white density with respect to the background and off-segment is hardly observed, and a liquid crystal display element with good display quality can be obtained.

  DMA tends to occur in low frequency driving. However, according to the embodiment, it is possible to prevent both DMA generation and light leakage even at a low frequency, and the display quality is improved. Conventionally, as a countermeasure against DMA, an A waveform or a C waveform having a high pulse frequency and inverting in a frame has been used. By enabling low-frequency driving, the driving waveform can be changed to a general so-called B waveform for frame inversion, which simplifies the driving circuit and leads to cost reduction. Furthermore, power consumption can be suppressed by enabling low-frequency driving.

  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 element. 2A is a plan view of a display pattern and an example of an electrode, and FIG. 2B is a plan view of an arrangement example of a black mask that covers the electrode.

Explanation of symbols

1a, 1b (transparent) substrate 2 liquid crystal layer 2m liquid crystal molecules 3a, 3b electrodes 4a, 4b vertical alignment films 5a, 5b polarizing plate 6 optical compensation plate 7 sealing material 8 black mask

Claims (5)

A pair of opposing substrates;
A counter electrode pattern formed on the opposing surface side of each of the pair of opposing substrates;
A vertical alignment film formed to cover the counter electrode pattern for each of the pair of opposing substrates;
A vertically aligned liquid crystal layer sandwiched between the pair of opposing substrates;
A pair of polarizing plates disposed outside the pair of opposed substrates,
An edge of the counter electrode pattern includes a zigzag pattern that is a set of sides in a direction parallel or perpendicular to the in-plane direction of the liquid crystal director of the liquid crystal layer that falls down due to the alignment treatment,
Have a black mask covering the edge of the display pattern defined by the counter electrode pattern,
The liquid crystal display element , wherein the vertical alignment film is formed directly on the substrate in a region where the black mask covers an edge and deviates from the display pattern between the counter electrode patterns .   The liquid crystal display element according to claim 1, wherein the black mask has a width of 10 to 200 μm.   3. The liquid crystal display element according to claim 1, wherein the zigzag pattern is composed of sides extending from 0 o'clock to 6 o'clock and from 3 o'clock to 9 o'clock when the vertical direction is set to 0 o'clock to 6 o'clock.   The polarizing plate is arranged in crossed Nicols, and one axial direction of the polarizing plate is 1: 30-7: 30, and the in-plane direction of the liquid crystal director direction is 0, 3, 3, 6 and 9 o'clock. The liquid crystal display element according to claim 1, which is in any direction.   The liquid crystal display element according to claim 1, wherein the counter electrode pattern includes a segment electrode representing a display pattern.

Images