JP2616463C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission type liquid crystal display device having a wide viewing angle with improved viewing angle dependency. 2. Description of the Related Art FIG. 5 shows a structure of a liquid crystal panel of a conventional thin film transistor (TFT) active matrix liquid crystal display device, and FIG. 5A schematically shows a rubbing state of each alignment film. FIG. 3B is a cross-sectional view illustrating a configuration of the liquid crystal panel. This liquid crystal panel is roughly divided into a color filter substrate, a TFT substrate, and a TN (twisted nematic) liquid crystal layer 56 sandwiched between these substrates. The color filter substrate has a color filter 52 on a glass substrate 51a.
, A common electrode 53, and an alignment film 54a are sequentially stacked. The TFT substrate has a configuration in which a pixel electrode 55 and an alignment film 54b are sequentially stacked on a glass substrate 51b. T
The N liquid crystal layer 56 is in contact with both alignment films 54a and 54b. Then, polarizing plates 57a and 57b are attached to the back surfaces of the glass substrates 51a and 51b, respectively. Actually, the color filter substrate is provided with a black matrix, etc.
Although a thin film transistor or the like is formed on the T substrate, it is omitted here for simplicity. An alignment film 54a on a color filter substrate and an alignment film 54 on a TFT substrate
b is rubbed in the direction of the arrow shown in FIG. That is, the alignment film 54a has an upper right direction as indicated by a dotted line, and the alignment film 54b has
As shown by the solid line, rubbing is performed in one direction in the lower right direction, and the two rubbing directions are substantially orthogonal. Thereby, these alignment films 54a, 54b
The TN liquid crystal layer 56 sandwiched between them is twisted by 90 °. In the transmission type liquid crystal display device in the state where no voltage is applied to each electrode, light incident from below in the drawing is converted into linearly polarized light parallel to the rubbing direction of the alignment film 54b by the polarizing plate 57b on the TFT substrate side. After passing through the TN liquid crystal layer 56, the light is rotated by 90 °, and then enters the polarizing plate 57a on the glass filter substrate side. When the polarization direction of the polarizing plate 57a matches the rubbing direction of the alignment film 54a (
In a normally white mode, light is transmitted to form a white display, and a polarizing plate 57 is used.
When the polarization direction of “a” is orthogonal to the rubbing direction of the alignment film 54a (normally black mode), light is cut off, and black display is performed. [0005] When observing the liquid crystal panel configured as described above, the original display content based on the above-described principle can be visually recognized by observing from the front of the liquid crystal panel. However, when observed from a direction deviated from the normal line of the surface of the liquid crystal panel, display contents different from those observed from the front are observed due to the birefringence of the liquid crystal. For example, if each of the alignment films 54a and 54b is rubbed in a direction as shown in FIG. 5A, when viewed from a direction 30 ° above the normal, the display moves in a white direction as a whole. And it becomes a halftone, and black becomes whitish display (
On the other hand, when observed from the lower 30 ° direction, the display moves in the black direction as a whole, and the gradation is reversed. As described above, the conventional liquid crystal display device has a problem that the angle range in which the original display content can be visually recognized, that is, the viewing angle is narrow. Several proposals have been made to improve the narrow viewing angle of a liquid crystal display device. For example, Japanese Patent Application Laid-Open No. 54-5754 discloses a technique in which two liquid crystal alignment sections having different twist directions of liquid crystal molecules are formed in each minute unit area of a liquid crystal panel to reduce the viewing angle dependency. I have. Further, Japanese Patent Publication No. 58-43723 discloses a TN liquid crystal display device in which a liquid crystal is sandwiched between a pair of electrode plates. By applying slits at a minute pitch,
A technique for widening the viewing angle has been disclosed. The orientation performance is provided to the electrode plate surface by a polishing method, an oblique evaporation method, or the like. The polishing directions are orthogonal to each other between the electrode plates, and there are four combinations of the polishing directions as shown in FIGS. 6 (a) to 6 (d). In FIG. 6, a dotted arrow indicates a polishing direction on the front electrode plate as viewed from the front side of the display device, and a solid arrow indicates a polishing direction on the rear electrode plate. The technique described in Japanese Patent Publication No. 58-43723 utilizes the fact that the range in which a good display can be obtained varies depending on the combination of polishing directions as shown in FIGS. 6 (a) to 6 (d). It is intended to obtain a display with a wide viewing angle that does not depend on the viewing angle. The pitch of the reverse orientation performance is almost equal, and the area ratio between the two is 3: 2 to 3
: 2, preferably in the range of 9:11 to 11: 9. [0008] Similarly, Japanese Patent Application Laid-Open No. 63-106624 discloses a technique in which a plurality of regions having reversed orientations are formed in an orientation film corresponding to a pixel to increase the viewing angle. Further, Japanese Patent Application Laid-Open No. 5-173136 discloses that an alignment film corresponding to a pixel is formed with regions having directions opposite to each other, and a threshold voltage at which the alignment film corresponding to the pixel is exposed to liquid crystal. A technique has been disclosed in which the viewing angle is increased by further dividing the image into two different areas. Specifically, as shown in FIG. 7, the alignment process is changed in the A and B regions for the minute unit region corresponding to the pixel so that the threshold voltages are different in the X and Y regions. In FIG. 7, the alignment films 85 and 87 are indicated by arrows indicating their alignment directions. In order to make the threshold voltage for the liquid crystal different, a dielectric layer 88 is provided in the Y region. FIGS. 8A and 8B respectively show X
It is sectional drawing of this liquid crystal panel in an area | region and Y area | region. In both the X region and the Y region, an electrode 84 and an alignment film 85 are sequentially laminated on the substrate 81 on the lower side in the figure. In the substrate 82 on the upper side of the figure, an electrode 86 and an alignment film 87 are sequentially laminated in the X region, and a dielectric layer 88 is provided between the electrode 86 and the alignment film 87 in the Y region. Liquid crystal 8
3 is sealed between both alignment films 85 and 87. FIG. 9 shows the viewing angle characteristics (relationship of the transmittance T with respect to the applied voltage V) of the liquid crystal aligned in a single direction. The dashed line C indicates the characteristics when viewed from the front, and the broken lines L and U indicate the characteristics. This is a characteristic when viewed from obliquely below and obliquely above at an angle of 40 °. The solid line I is a characteristic obtained by averaging the broken line L and the broken line U. JP-A-5-173
In the liquid crystal display device disclosed in Japanese Patent Publication No. 136, by providing regions having different alignment directions in the pixel, the characteristic of oblique viewing becomes relatively bright (broken line L) and the characteristic of becoming black immediately (broken line). U) are averaged to obtain a characteristic represented by a solid line I, which is close to the characteristic (dash-dot line C) as viewed from the front, and the characteristic of the averaging (solid line I) is used to distinguish changes in gradation display. Ia
Is reduced by changing the threshold voltages of the X region and the Y region, thereby bringing the characteristics closer to the front. According to the technique disclosed in Japanese Patent Publication No. 58-43723, the alignment performance is reversed in substantially the same area to compensate for white spots and gradation inversion, and average the results. ing. One of the area divisions has an occupancy of 40 to 60%,
With this degree of occupancy, there is not much vertical asymmetry, and the averaging can be performed approximately.
As a result, a region where the gradation inversion does not occur is widened as a whole. However, when a liquid crystal panel is used in an OA device such as a notebook personal computer, it is desirable that the viewing angle be spread asymmetrically, particularly in the vertical direction, with respect to the surface of the liquid crystal panel. When a liquid crystal panel is used in an OA device, the liquid crystal panel is almost vertically or slightly inclined at the time of use. In such a state, it is almost impossible to look into the liquid crystal panel from the lower side. Often peeping from the side. Tokunosho 5
In the case of the technique disclosed in Japanese Patent Application Laid-Open No. 8-43723, there is a problem that a viewing angle is widened in a downward direction where a visual field is not so wide, and a grayscale inversion occurs in an upward direction where a wide visual field is desired. In the technique disclosed in Japanese Patent Application Laid-Open No. 5-173136, it is necessary to provide a dielectric layer, so that the number of steps is increased, and the viewing angle is widened in a specific viewing angle direction, for example, downward. If there is no need, there is a problem that it becomes unnecessary. An object of the present invention is to provide a transmissive liquid crystal display device capable of minimizing visual field inversion in a specific direction, for example, an upward direction. According to a first transmission type liquid crystal display device of the present invention, there is provided an active matrix substrate, a color filter substrate having a color filter formed thereon, and an active matrix substrate and a color filter substrate. TN liquid crystal injected between them,
In a transmission type liquid crystal display device having a polarizing plate added to each of the substrates, the region is divided for each region corresponding to one pixel, and the region is divided in a vertical direction with respect to a display surface normal direction of the display device. In addition, two alignment regions having different alignment directions of the TN liquid crystal are formed and the ratio of the areas of the two alignment regions is in the range of 3: 7 to 2: 8. A second transmission type liquid crystal display device according to the present invention comprises an active matrix substrate having a polarizing plate and a first alignment film, and a color filter having a polarizing plate and a second alignment film and a color filter. In a transmission type liquid crystal display device having a substrate and a TN liquid crystal injected between the active matrix substrate and the color filter substrate, one of the alignment films is a unidirectional alignment film having a uniform rubbing direction. The other of the alignment films is a divided alignment film having two alignment regions having different rubbing directions for each range corresponding to one pixel, and the two alignment regions are in a region corresponding to the one pixel. In the vertical direction with respect to the normal direction of the display surface of the display device, the ratio of the areas of the two alignment regions in the divided alignment film is in the range of 3: 7 to 2: 8. That. In this case, the rubbing directions of the two alignment regions in the divided alignment film are opposite to each other, and the rubbing direction of the unidirectional alignment film is substantially perpendicular to each of the rubbing directions of the two alignment regions. Further, the pretilt angle of the TN liquid crystal can be set to be larger on the divided alignment film side than on the unidirectional alignment film side. In a liquid crystal display device in which two alignment regions having different alignment directions coexist within a range corresponding to one pixel, the ratio of the alignment regions in the divided alignment film is in the range of 2: 8 to 3: 7. By setting the angle within the range, the viewing angle including the desired direction can be expanded. Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a diagram illustrating a division state in a region corresponding to one pixel of a division alignment film in a liquid crystal panel according to an embodiment of the present invention, and FIG. 1B is a diagram illustrating the division alignment film and the unidirectional alignment film. FIG. 2 is a cross-sectional view illustrating a configuration of a liquid crystal panel of the present embodiment. This liquid crystal panel has a substantially rectangular shape and has pixels corresponding to R (red), G (green), and B (blue), and is capable of color display. Etc. are preferably used for OA equipment. In the following description, it is assumed that the liquid crystal panel is used in an almost upright state,
The terms ",""down,""left," and "right" are used in the up, down, left, and right directions in this use state. In this liquid crystal panel, as shown in FIG. 2, a TN liquid crystal layer 26 is provided between a color filter substrate on which a unidirectional alignment film 24a is formed and a TFT substrate on which a split alignment film 24b is formed. It has a sandwiched configuration. The color filter substrate is formed by sequentially forming a color filter 22, a common electrode 23, and a unidirectional alignment film 24a on a glass substrate 21a. The films 24b are sequentially formed. Then, polarizing plates 27a and 27b are attached to the back surfaces of the glass substrates 21a and 21b. Actually, a black matrix or the like is formed on the color filter substrate, and a thin film transistor or the like is formed on the TFT substrate, but these are omitted here for simplicity. In the divided alignment film 24b, as shown in FIG. 1 (a), two regions (regions A and B) whose rubbing directions are opposite to each other for each region of one pixel. The area ratio between the region A and the region B is selected from 2: 8 to 3: 7. In each pixel, the area A is arranged on the upper side in the use state of the liquid crystal panel, and the area B is arranged on the lower side. FIG. 1B shows the relationship between the rubbing direction in the unidirectional alignment film 24a and the rubbing direction in the split alignment film 24b. The rubbing direction of the unidirectional alignment film 24a is the upper right direction common to all pixels, as indicated by the dotted arrow. On the other hand, as shown by solid arrows, the rubbing direction of the divided alignment film 24b is, for each pixel, a lower right direction (region B) and an upper left direction (region A) within one pixel.
). The rubbing direction of the unidirectional alignment film 24a is substantially perpendicular to the rubbing directions in both the region A and the region B of the divided alignment film 24b. The TN liquid crystal layer 26 at the interface with each alignment film 24a, 24b
Each of the alignment films 24a and 24b is rubbed such that the tilt angle of the liquid crystal molecules is larger on the divided alignment film 24b side than on the unidirectional alignment film 24a side. In this embodiment, it is assumed that a stripe type pixel array structure is used. Here, the stripe type is one in which filters of each color of R, G, and B are formed on a straight line in the vertical direction, and one pixel is composed of three pixels of R, G, and B linearly arranged in the horizontal direction. Includes color. As shown in FIG. 1B, the pixels including these three colors are arranged in a straight line in the vertical and horizontal directions. FIGS. 3A and 3B show the twisted state of the liquid crystal molecules in the regions A and B in one pixel when each alignment film is rubbed as described above.
Since the rubbing directions of the divided alignment films 24b differ by 180 ° between the region A and the region B, the tilt directions in the respective regions differ. Here, the pretilt angle of the liquid crystal molecules in the unidirectional alignment film 24a is set smaller than that of the split alignment film 24b, and the alignment of the liquid crystal is generally defined by the alignment direction on the high pretilt angle side. The liquid crystal molecules are aligned by the rubbing state of the divided alignment film 24b. As a result, the pretilt angle of the liquid crystal in the unidirectional alignment film 24a is stabilized in a state where the directions of the regions A and B are opposite to each other. Next, the reason why the area ratio (a: b) between the region A and the region B in the divided alignment film 24b should be 2: 8 to 3: 7 when used for OA equipment will be described. I do. FIGS. 4A to 4F are tone characteristic curve diagrams each showing the relationship between the viewing angle and the luminance using the tone as a parameter. 4 (a) shows a conventional liquid crystal panel [see FIGS. 5 (a) and 5 (b)], that is, a case where the alignment film does not divide a region according to the alignment direction, and FIGS. ) Respectively correspond to the case where the area ratio a: b of the region in each alignment direction in the divided alignment film is 1: 9, 2: 8, 3: 7, 4: 6, 5: 5. Here, it is assumed that the display is performed in eight gradations in which the γ value at a viewing angle of 0 ° (corresponding to the case of viewing from the front) is 2.2. In the figure, each curve represents any one of the eight gradations, the lowest curve represents the 0th gradation at a viewing angle of 0 °, and the first gradation, In the second gradation, the uppermost curve indicates the seventh gradation. If the characteristic curves intersect with each other, it means that gradation inversion has occurred there. In the case of the conventional liquid crystal panel [FIG. 4 (a)], the viewing angle range where the gradation inversion does not occur is narrow, and particularly in the downward direction, the gradation inversion occurs from around 10 °. Even in appearance, it immediately turns black in the downward direction, causing discomfort. By the way, in the case of a liquid crystal panel used in OA equipment such as a notebook personal computer, as described in the section of "Problems to be Solved by the Invention", it is not necessary to have such a large visual field in the downward direction. In the downward direction, even if the gradation inversion occurs at an angle of 30 ° or more, it is acceptable. Referring to FIGS. 4B to 4F, when a: b = 1: 9, gradation inversion occurs below 30 ° and is not suitable for use in OA equipment, but a: b = 2:
In No. 8, no gradation inversion occurs at the lower 30 °. As is clear from these figures, by setting the ratio of the area of the region A to the whole to be 0.2 or more, it becomes possible to use the liquid crystal panel without feeling uncomfortable in the downward visual field. Next, the upward visual field will be examined. JP-A-5-173 mentioned above
In Japanese Patent No. 136, the area of the area A is made equal to the area of the area B, and a part of the area of each pixel is provided with a dielectric layer so that gradation can be distinguished. When the areas of the region A and the region B are equal to each other, the gradation cannot be distinguished as it is in a portion represented by Ib in FIG. In consideration of use for OA equipment, it is desirable that gradation can be distinguished at an upper angle of 40 ° (dotted line in the figure). Referring to FIGS. 4B to 4F, it is understood that the area ratio of the region A to the entire region is not more than 0.4 so that the gradation can be distinguished at the upper 40 degrees. Further, it is assumed that a satisfactory gradation can be obtained if more than half of all gradations can be obtained when viewed from above 50 ° (dashed line in the drawing). In the case where the area ratio a: b is 4: 6 (see FIG. 4E), the grayscale inversion occurs at the fourth grayscale or higher, and more than half of all grayscales can be obtained. It does not mean that. On the other hand, if the ratio of the area of the region A to the whole area is 0.3 or less, more than half of all the gradations can be obtained. From the above consideration, the area ratio of the region A is 0.3.
In the following cases, satisfactory gradation is obtained in the upward direction when used for OA.
Therefore, the area ratio between the region A and the region B in the divided alignment film 24b in one pixel (
It can be seen that a: b) should be 2: 8-3: 7. As described above, the liquid crystal panel preferably used for OA equipment has been described as an embodiment of the present invention. However, the present invention is not limited to the above-described embodiment, and is not limited to the scope of the present invention. Various changes are possible. For example, when a wide field of view is required in the downward direction and the field of view need not be so large in the upward direction as in a wall-mounted display, the area ratio between the region A and the region B may be reversed from the above. . In the above-described embodiment, the rubbing direction is changed in one pixel by using the alignment film on the TFT substrate side as a divided alignment film, but the alignment film on the TFT substrate side is changed to a unidirectional alignment film on the color filter side. The alignment film may be a divided alignment film. Further, the pixel array structure for color display is not limited to the stripe type, but can be applied to various array structures such as a delta type and a mosaic type. As described above, according to the present invention, two alignment regions having different alignment directions coexist within a range corresponding to one pixel, and the ratio of the areas of the alignment regions is from 2: 8. By setting the ratio within the range of 3: 7, there is an effect that it is possible to enlarge the viewing angle including a desired direction and obtain good gradation characteristics. For example, O
In the case of use in A equipment, it is possible to widen the field of view in the downward direction within the required range, and to minimize the inversion of grayscale that occurs in the upward direction as much as possible. Display can be performed. In addition, there is an effect that a display excellent in gradation can be performed without providing a dielectric layer or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a view for explaining a division state in a region corresponding to one pixel of a division alignment film in a liquid crystal panel according to an embodiment of the present invention, and FIG. FIG. 3 is a diagram illustrating a rubbing state between a film and a unidirectional alignment film. FIG. 2 is a cross-sectional view illustrating a configuration of a liquid crystal panel according to one embodiment of the present invention. FIGS. 3A and 3B are diagrams illustrating the relationship between a rubbing direction in a divided alignment film and how liquid crystal molecules are twisted. 4A and 4B are gradation characteristic curve diagrams showing a relationship between a viewing angle and luminance in a liquid crystal panel, wherein FIG. 4A is a diagram of a conventional liquid crystal panel, and FIGS. It is a figure at the time of changing each area ratio. 5A and 5B are diagrams illustrating a configuration of a conventional typical liquid crystal panel, in which FIG. 5A is a diagram schematically illustrating a rubbing state of each alignment film, and FIG. 5B is a cross-sectional view of the liquid crystal panel. FIGS. 6A to 6D are diagrams illustrating a polishing direction of an alignment film. FIG. 7 is a diagram illustrating a conventional liquid crystal panel in which an alignment film corresponding to a pixel is divided by an alignment direction and a threshold voltage. 8 is a cross-sectional view showing the structure of the liquid crystal panel of FIG. 7, wherein (a) and (b) show X
It is sectional drawing in an area | region and a Y area. FIG. 9 is a characteristic diagram showing a relationship between a transmittance of the liquid crystal panel and a voltage. [Description of Signs] 21a, 21b, 51a, 51b Glass substrate 22, 52 Color filter 23, 53 Common electrode 24a Unidirectional alignment film 24b Divided alignment film 25, 55 Pixel electrode 26, 56 TN liquid crystal layers 27a, 27b, 57a, 57b Polarizing plates 54a, 54b, 85, 87 Alignment films 81, 82 Substrate 83 Liquid crystal 84, 86 Electrodes 88 Dielectric layer

Claims (1)

Claims: 1. An active matrix substrate having a first alignment film to which a polarizing plate is added, a color filter substrate having a second alignment film to which a polarizing plate is added, and a color filter; In a transmission type liquid crystal display device having a TN liquid crystal injected between a matrix substrate and a color filter substrate, one of the alignment films is a unidirectional alignment film having a uniform rubbing direction, and The other is a divided alignment film having two alignment regions having different rubbing directions for each region corresponding to one pixel, wherein the two alignment regions are arranged in a region corresponding to the one pixel. It is arranged vertically with respect to the normal direction of the display surface, and the split alignment film is characterized in that the ratio of the areas of the two alignment regions is in the range of 3: 7 to 2: 8. Transmission type liquid crystal display device. 2. The rubbing directions of the two alignment regions in the divided alignment film are opposite to each other, and the rubbing direction of the one-directional alignment film is substantially perpendicular to each of the rubbing directions of the two alignment regions. The transmissive liquid crystal display device according to claim 1 , wherein: Wherein the pretilt angle of the TN liquid crystal, a transmissive liquid crystal display device according to claim 1 or 2 larger than the one direction alignment film side by the split alignment film side.