JP2007256811A - Liquid crystal display - Google Patents

Abstract

A VA mode liquid crystal display device with excellent display quality is provided.
A liquid crystal display device according to the present invention includes a vertical alignment type liquid crystal layer, a first electrode provided on a liquid crystal layer side of a first substrate, and a first electrode provided on a liquid crystal layer side of a second substrate. It has two electrodes 12 and at least one alignment film provided so as to be in contact with the liquid crystal layer. The pixel region has liquid crystal domains A and B in which the tilt directions (t1, t2) of liquid crystal molecules near the center in the layer plane and in the thickness direction of the liquid crystal layer when a voltage is applied differ from each other by about 180 °, and The liquid crystal domains A and B are adjacent to each other.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a wide viewing angle characteristic.

  The display characteristics of liquid crystal display devices have been improved, and use in television receivers and the like is progressing. Although the viewing angle characteristics of liquid crystal display devices have been improved, further improvements are desired. In particular, there is a strong demand for improving the viewing angle characteristics of a liquid crystal display device (also referred to as a VA mode liquid crystal display device) using a vertically aligned liquid crystal layer.

  Currently, VA mode liquid crystal display devices used in large display devices such as televisions employ an alignment division structure in which a plurality of liquid crystal domains are formed in one pixel region in order to improve viewing angle characteristics. . As a method of forming the alignment division structure, the MVA mode is the mainstream. In the MVA mode, by providing an alignment regulating structure on the liquid crystal layer side of a pair of substrates facing each other with a vertical alignment type liquid crystal layer interposed therebetween, a plurality of domains (typically the alignment direction is different) 4 types). As the alignment regulating structure, slits (openings) or ribs (projection structure) provided on the electrodes are used, and the alignment regulating force is exhibited from both sides of the liquid crystal layer.

However, when slits and ribs are used, unlike the case where the pretilt direction is defined by the alignment film used in the conventional TN, the slits and ribs are linear, so that the alignment regulating force on the liquid crystal molecules is within the pixel region. For example, there is a problem that a distribution occurs in the response speed. In addition, since the light transmittance of the region where the slits and ribs are provided is lowered, there is also a problem that display luminance is lowered.
JP-A-11-133429 JP-A-11-352486

  In order to avoid the above-described problem, it is preferable to form the alignment division structure in the VA mode liquid crystal display device by defining the pretilt direction with the alignment film. Therefore, the present inventor conducted various studies and found that a disorder in alignment peculiar to a VA mode liquid crystal display device having an alignment division structure using an alignment film occurs, which adversely affects display quality.

  The present invention has been made in view of the above-described points, and an object thereof is to provide a VA mode liquid crystal display device excellent in display quality.

  The liquid crystal display device of the present invention includes a vertical alignment type liquid crystal layer, a first substrate and a second substrate facing each other through the liquid crystal layer, and a first electrode provided on the liquid crystal layer side of the first substrate. And the second electrode provided on the liquid crystal layer side of the second substrate, at least one alignment film provided so as to be in contact with the liquid crystal layer, and the pixel region when the voltage is applied to the liquid crystal layer A plurality of liquid crystal domains in which the tilt directions of liquid crystal molecules near the center in the layer surface and in the thickness direction are different from each other, and the plurality of liquid crystal domains are in the layer surface and the thickness of the liquid crystal layer when a voltage is applied. A first liquid crystal domain in which the tilt direction of the liquid crystal molecules near the center in the direction is the first direction, and a second liquid crystal domain in the second direction that is approximately 180 ° different from the first direction, and the first liquid crystal domain The second liquid Characterized in that the domains are adjacent.

  In one embodiment, the plurality of liquid crystal domains include a third direction in which a tilt direction of liquid crystal molecules in the layer plane of the liquid crystal layer and in the vicinity of the center in the thickness direction when a voltage is applied differs from the first direction by about 90 °. A third liquid crystal domain that is a direction, and a fourth liquid crystal domain that is a fourth direction that is approximately 90 ° different from the second direction.

  In one embodiment, the three liquid crystal domains and the fourth liquid crystal domain are adjacent to each other.

  In one embodiment, the liquid crystal layer further includes a pair of polarizing plates facing each other with the transmission axes orthogonal to each other, and the first direction is the transmission axis of the pair of polarizing plates. And an angle of about 45 °.

  In one embodiment, the vertical alignment liquid crystal layer includes a liquid crystal material having negative dielectric anisotropy, and the at least one alignment film is a pair of alignment films provided on both sides of the liquid crystal layer, The pretilt direction defined by one alignment film and the pretilt direction defined by the other alignment film differ from each other by approximately 90 °.

  In one embodiment, the at least one alignment film is a pair of alignment films provided on both sides of the liquid crystal layer, the pretilt angle defined by the one alignment film and the pretilt defined by the other alignment film. The corners are substantially equal to each other.

  In one embodiment, the at least one alignment film is formed of a photo-alignment film.

  According to the present invention, the display quality of a VA mode liquid crystal display device can be improved. In particular, the transmittance loss of a liquid crystal display device in which an alignment division structure is formed using an alignment film can be reduced.

  Hereinafter, the configuration of a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment.

  A liquid crystal display device according to an embodiment of the present invention is a VA mode liquid crystal display device having an alignment division structure using at least one alignment film, wherein the pixel region is within the plane of the liquid crystal layer when a voltage is applied and The liquid crystal molecules near the center in the thickness direction have a plurality of liquid crystal domains whose tilt directions are different from each other, and the plurality of liquid crystal domains are liquid crystals in the layer plane of the liquid crystal layer when a voltage is applied and near the center in the thickness direction. A first liquid crystal domain having a first tilt direction of molecules and a second liquid crystal domain having a second direction different from the first direction by about 180 °; and the first liquid crystal domain and the second liquid crystal domain are adjacent to each other. It is characterized by having. That is, in the pixel region having the alignment division structure, one or more boundary lines are formed between the adjacent liquid crystal domains. However, the liquid crystal display device according to the embodiment of the present invention has a configuration in which a voltage is applied. A boundary line or boundary region formed between liquid crystal domains in which the tilt directions of the liquid crystal molecules in the liquid crystal layer and in the thickness direction near the center are different from each other by about 180 ° (hereinafter referred to as “180 ° boundary line” for simplicity) Is divided so as to form. In the case of the bipartite alignment structure, the two liquid crystal domains are liquid crystal domains in which the tilt directions of the liquid crystal molecules near the center in the layer plane and in the thickness direction of the liquid crystal layer when a voltage is applied differ from each other by about 180 °. . In the case of a three-divided alignment structure, the alignment is divided so that at least one of the plurality of boundary lines is the above 180 ° boundary line.

  In this specification, the “vertical alignment type liquid crystal layer” refers to a liquid crystal layer in which a liquid crystal molecular axis (also referred to as “axis orientation”) is aligned at an angle of about 85 ° or more with respect to the surface of the vertical alignment film. . Liquid crystal molecules have negative dielectric anisotropy, and display in a normally black mode in combination with polarizing plates arranged in a crossed Nicol arrangement. The alignment film may be provided on at least one side, but is preferably provided on both sides from the viewpoint of alignment stability. In the following embodiments, an example in which vertical alignment films are provided on both sides will be described.

  In this specification, “pixel” refers to the smallest unit that expresses a specific gradation in display, and corresponds to a unit that expresses each gradation of R, G, and B in color display, for example. It is also called a dot. A combination of the R pixel, the G pixel, and the B pixel constitutes one color display pixel. The “pixel region” refers to a region of the liquid crystal display device corresponding to the “pixel” of display. The “pretilt direction” is an alignment direction of liquid crystal molecules regulated by the alignment film, and indicates an azimuth direction in the display surface. Further, the angle formed by the liquid crystal molecules with the surface of the alignment film at this time is called a pretilt angle. The pretilt direction is defined by performing a rubbing process or an optical alignment process on the alignment film. A four-divided structure can be formed by changing the combination of the pretilt directions of a pair of alignment films facing each other through the liquid crystal layer. The pixel region divided into four has four liquid crystal domains (sometimes simply referred to as “domains”). Each liquid crystal domain is characterized by the tilt direction (also referred to as “reference alignment direction”) of the liquid crystal molecules in the layer plane of the liquid crystal layer when the voltage is applied to the liquid crystal layer and near the center in the thickness direction. The tilt direction (reference orientation direction) has a dominant influence on the viewing angle dependency of each domain. The tilt direction is also the azimuth direction. The reference for the azimuth direction is the horizontal direction of the display, and is positive in the counterclockwise direction (when the display surface is compared to a clock face, the 3 o'clock direction is azimuth angle 0 ° and the counterclockwise direction is positive). The tilt directions of the four liquid crystal domains are four directions (for example, 12 o'clock direction, 9 o'clock direction, 6 o'clock direction, and 3 o'clock direction) in which the difference between any two directions is approximately equal to an integral multiple of 90 °. By setting to, the viewing angle characteristics are averaged and a good display can be obtained. Further, from the viewpoint of uniformity of viewing angle characteristics, it is preferable that the areas occupied by the four liquid crystal domains in the pixel region are equal to each other. The quadrant alignment structure is most preferable from the viewpoint of viewing angle characteristics, but the number of alignment divisions is not particularly limited.

  The vertical alignment type liquid crystal layer exemplified in the following embodiment includes a nematic liquid crystal material having negative dielectric anisotropy, and has a pretilt direction defined by one alignment film of a pair of alignment films provided on both sides of the liquid crystal layer. The pretilt direction defined by the other alignment film differs by approximately 90 ° from each other, and the tilt angle (reference alignment direction) is defined in the middle of these two pretilt directions. No chiral agent is added, and when a voltage is applied to the liquid crystal layer, the liquid crystal molecules in the vicinity of the alignment film are twisted according to the alignment regulating force of the alignment film. You may add a chiral agent as needed. As described above, the VA mode in which the liquid crystal molecules are twisted by using the vertical alignment films whose pretilt directions (alignment processing directions) defined by the pair of alignment films are orthogonal to each other is a VATN (Vertical Alignment Twisted Nematic) mode. Or it may be called RTN (Reverse Twisted Nematic) mode (for example, patent document 2).

  In the VATN mode, as described in Japanese Patent Application No. 2005-141846 by the applicant, it is preferable that the pretilt angles defined by each of the pair of alignment films are substantially equal to each other. By using an alignment film having substantially the same pretilt angle, there is an advantage that display luminance characteristics can be improved. In particular, when the difference in pretilt angle defined by the pair of alignment films is within 1 °, the tilt direction (reference alignment direction) of the liquid crystal molecules near the center of the liquid crystal layer can be stably controlled, and the display Luminance characteristics can be improved. This is because when the difference in pretilt angle exceeds 1 °, the tilt direction varies depending on the position in the liquid crystal layer, and as a result, the transmittance varies (that is, a region having a transmittance lower than the desired transmittance is formed). This is probably because

  As a method of defining the pretilt direction of the liquid crystal molecules in the alignment film, a method of performing a rubbing process, a method of performing a photo-alignment process, a fine structure is formed in advance on the base of the alignment film, and the fine structure is formed on the surface of the alignment film. Are reflected on the surface, or a method of forming an alignment film having a fine structure on the surface by obliquely depositing an inorganic substance such as SiO. From the viewpoint of mass productivity, rubbing treatment or light Orientation treatment is preferred. In particular, since the photo-alignment process can be performed without contact, there is no generation of static electricity due to friction unlike the rubbing process, and the yield can be improved. Further, as described in the above Japanese Patent Application No. 2005-141846, the variation in the pretilt angle can be controlled to 1 ° or less by using a photo-alignment film containing a photosensitive group. The photosensitive group preferably contains at least one photosensitive group selected from the group consisting of a 4-chalcone group, a 4'-chalcone group, a coumarin group, and a cinnamoyl group.

  In the following embodiments, a TFT type liquid crystal display device is shown as a typical example, but it goes without saying that the present invention can be applied to liquid crystal display devices of other driving systems.

  First, referring to FIGS. 1A to 1C and FIGS. 2A and 2B, the configuration of the liquid crystal domain in the pixel region of the liquid crystal display device according to the embodiment of the present invention and the alignment of the liquid crystal molecules And the transmittance will be described.

  FIGS. 1A to 1C are schematic views for explaining the configuration of the liquid crystal domain in the pixel region 10 of the liquid crystal display device according to the embodiment having a two-divided structure. FIG. FIG. 1B is a schematic diagram showing a relationship between tilt directions (reference alignment directions) t1 and t2 of liquid crystal domains A and B, and FIG. 1B shows pretilt directions PA1 and PA2 of an alignment film of a TFT substrate (lower substrate). FIG. 1C is a diagram schematically showing the pretilt directions PB1 and PB2 of the alignment film of the color filter (CF) substrate (upper substrate). These figures schematically show the orientation direction of the liquid crystal molecules when viewed from the observer side, and it is better for the observer to draw the end (elliptical part) of the liquid crystal molecules shown in a columnar shape. It shows that the liquid crystal molecules are tilted so as to approach. For the sake of simplicity, FIG. 1 shows a pixel region 10 formed corresponding to a substantially square pixel electrode, but the present invention is not limited to the shape of the pixel region. In the following drawings, alignment films provided on both sides of the liquid crystal layer 3 are omitted.

  As shown in FIG. 1A, the tilt directions (reference alignment directions) t1 and t2 of the two liquid crystal domains A and B included in the pixel region 10 are approximately 180 ° from each other. As shown in FIGS. 1B and 1C, the pixel region 10 can be formed by performing an alignment process. As shown in FIG. 1B, the pixel region on the TFT substrate side is divided into two, and alignment processing is performed so as to provide pretilt directions PA1 and PA2 that are antiparallel to the vertical alignment film. For example, the photo-alignment treatment is performed by obliquely irradiating ultraviolet rays using the photo-alignment film described in Japanese Patent Application No. 2005-141846. When ultraviolet rays are irradiated from a direction of about 40 ° with respect to the normal of the alignment film surface, pretilt can be performed in the ultraviolet irradiation direction. On the other hand, by the same method, as shown in FIG. 1C, the pixel region on the CF substrate side is divided into two, and alignment processing is performed so as to give pre-tilt directions PB1 and PB2 antiparallel to the vertical alignment film. . By bonding these substrates, an alignment division structure of the pixel region 10 can be obtained. The direction of light irradiation in the photo-alignment process is not limited to the above example. For example, the CF substrate side is irradiated from the direction inclined in the vertical direction (column direction), and the TFT substrate side is inclined in the horizontal direction (row direction). You may irradiate from the direction.

  With reference to FIG. 2A and FIG. 2B, the relationship between the alignment and transmittance of the liquid crystal molecules at the boundary line CL1 formed between the liquid crystal domains A and B shown in FIG. Will be explained.

  FIG. 2A is a cross-sectional view in a direction orthogonal to the boundary line CL1 of the pixel region 10, and shows equipotential lines of the electric field formed in the liquid crystal layer 3, the alignment direction of the liquid crystal molecules 3a, and the relative transmittance (front surface). ) Shows the result of the simulation. 2, 0, 50, and 100 on the right side indicate relative transmittances where the transmittance in the black display state is 0% and the maximum transmittance in the white display state is 100%. The thickness of the liquid crystal layer is about 3 μm, and the applied voltage is about 7V. The simulation was performed using an LCD MASTER manufactured by Shintech.

  The liquid crystal display device is formed on a transparent substrate (for example, a glass substrate) 1a and a TFT substrate 1 including a pixel electrode 11 formed on the transparent substrate 1a, and on a transparent substrate (for example, a glass substrate) 2a and the transparent substrate 2a. A CF substrate 2 having a counter electrode 12 and a vertical alignment type liquid crystal layer 3 provided between the TFT substrate 1 and the CF substrate 2 are provided. A vertical alignment film (not shown) is provided on the surface of the TFT substrate 1 and the CF substrate 2 on the liquid crystal layer 3 side, and the alignment treatment is performed as shown in FIGS. 1B and 1C, respectively.

  FIG. 2B shows the orientation direction of the liquid crystal molecules 3a in the region including the boundary line CL1 between the liquid crystal domains A and B, and the center in the thickness direction of the liquid crystal layer 3 shown in FIG. The orientation direction of liquid crystal molecules in the vicinity is shown. FIG. 2B shows the directions of the polarization axes (transmission axes) of a pair of polarizing plates arranged to face each other with the TFT substrate 1 and the CF substrate 2 interposed therebetween.

  As can be seen from FIG. 2A, the transmittance has a minimum value, a maximum value, and a minimum value in a region where the tilt direction of the liquid crystal molecules changes by about 180 ° in the boundary region between the liquid crystal domain A and the liquid crystal domain B. Has changed. Here, the orientation direction of the liquid crystal molecules 3a at the position where the transmittance takes the maximum value is about 45 ° with respect to the polarization axes of the pair of polarizing plates arranged in crossed Nicols, as shown in FIG. 2 (b). . Thus, in the boundary region formed between the liquid crystal domains whose tilt directions (reference alignment directions) differ by about 180 °, the alignment is performed in the 45 ° direction with respect to the polarization axes of the pair of polarizing plates arranged in crossed Nicols. Since liquid crystal molecules are present, the transmittance has a maximum value in the vicinity thereof. The liquid crystal display device according to the embodiment of the present invention uses this phenomenon to reduce the loss of transmittance. In this way, a 180 ° boundary line formed between liquid crystal domains whose tilt directions are different from each other by about 180 ° is represented by a broken line CL1.

  For comparison, referring to FIGS. 3A to 3C and FIGS. 4A and 4B, a two-divided structure in which the difference in tilt angle of liquid crystal molecules between adjacent liquid crystal domains is about 90 °. The relationship between the orientation of the liquid crystal molecules in the pixel region 92 and the transmittance will be described. 3A to 3C correspond to FIGS. 1A to 1C, and FIGS. 4A and 4B correspond to FIGS. 2A and 2B, respectively.

  FIG. 3A is a schematic diagram showing the relationship between the tilt directions (reference alignment directions) t2 and t4 of the two liquid crystal domains B and D, and FIG. 3B shows the pretilt direction PA1 of the alignment film of the TFT substrate and FIG. 3C is a schematic diagram showing PA2, and FIG. 3C is a diagram schematically showing the pretilt direction PB1 of the alignment film of the CF substrate. By bonding the alignment-treated substrates as shown in FIGS. 3B and 3C, the alignment division structure of the pixel region 92 shown in FIG. 3A can be obtained.

  FIG. 4A is a cross-sectional view in a direction perpendicular to the boundary line CL2 of the pixel region 92. The equipotential lines of the electric field formed in the liquid crystal layer 3, the alignment direction of the liquid crystal molecules 3a, and the relative transmittance (front). ) Shows the result of the simulation. 4, 0, 50, and 100 on the right side indicate relative transmittances where the transmittance in the black display state is 0% and the maximum transmittance in the white display state is 100%. The simulation conditions are the same as in the case of FIG.

  FIG. 4B shows the orientation direction of the liquid crystal molecules 3a in the region including the boundary line CL2 between the liquid crystal domains B and D, and the center in the thickness direction of the liquid crystal layer 3 shown in FIG. The orientation direction of liquid crystal molecules in the vicinity is shown. FIG. 4B shows the directions of the polarization axes (transmission axes) of a pair of polarizing plates arranged so as to face each other with the TFT substrate 1 and the CF substrate 2 interposed therebetween.

  As can be seen from FIG. 4 (a), in the boundary region between the liquid crystal domain B and the liquid crystal domain D, the transmittance changes so as to take the only minimum value in the region where the tilt direction of the liquid crystal molecules changes by about 90 °. ing. Here, the orientation direction of the liquid crystal molecules 3a at the position where the transmittance takes a minimum value is perpendicular (or parallel) to the polarization axes of the pair of polarizing plates arranged in crossed Nicols, as shown in FIG. 4B. It is. As described above, in the boundary region formed between the liquid crystal domains whose tilt directions (reference alignment directions) are different by about 90 °, the alignment is performed in the direction of 45 ° with respect to the polarization axes of the pair of polarizing plates arranged in crossed Nicols. Since no liquid crystal molecules are present, the only minimum value is taken at the boundary line CL2. In this manner, a boundary line or boundary region formed between liquid crystal domains having tilt directions different from each other by about 90 ° is referred to as a 90 ° boundary line for the sake of simplicity and is represented by a solid line CL2.

  In the present specification, about 90 ° and about 180 ° with respect to the angle formed by the tilt direction includes ± 5 ° as a process error. In the alignment division structure, as described above, in order to maximize the transmittance, the tilt direction of the liquid crystal domain is controlled so as to maximize the utilization efficiency of light in the 45 ° direction from the polarization axis (transmission axis). . Therefore, ideally, the four tilt directions are an integral multiple of 90 ° at any two of their angles. However, for process reasons, an error of about ± 5 ° occurs in the tilt direction in an actual liquid crystal display device. Further, the tilt direction of each liquid crystal domain is obtained as an average tilt direction in a minute region optically obtained using a polarizing microscope or the like.

  As is clear from a comparison between FIG. 2A and FIG. 4A, in FIG. 2A, the transmittance changes so as to have a maximum value in the boundary region between the liquid crystal domains A and B. The transmittance in the boundary region between the liquid crystal domains A and B is higher than that in the boundary region between the liquid crystal domains B and D shown in FIG. According to the simulation, the boundary line CL1 in the pixel region 10 shown in FIG. 1 is difficult to be seen, whereas the boundary line CL2 in the pixel region 92 shown in FIG. 3 is clearly seen as a dark line, resulting in loss of transmittance. Is big.

  Thus, in the case of forming an alignment division structure, the boundary line formed between adjacent liquid crystal domains is preferably a 180 ° boundary line, and the 90 ° boundary line is reduced (shortened). It can be seen that this is preferable in order to reduce the loss.

 Next, a pixel area having a quadrant structure will be described with reference to FIGS. The pixel region having a four-part structure illustrated below has four liquid crystal domains A, B, C, and D. When the respective tilt directions (reference alignment directions) are t1, t2, t3, and t4, Are four directions in which the difference between any two directions is approximately equal to an integral multiple of 90 °. The areas of the liquid crystal domains A, B, C, and D are substantially equal to each other, which is an example of the most preferable quadrant structure in view angle characteristics.

  5 to 7, four liquid crystal domains A to D are arranged in a matrix of 2 rows and 2 columns.

  The pixel region 20 shown in FIG. 5A has liquid crystal domains A to D. When the horizontal azimuth angle (3 o'clock direction) on the display surface is 0 °, the tilt direction t1 of the liquid crystal domain A is about 225. The tilt direction t2 of the liquid crystal domain B is about 45 °, the tilt direction t3 of the liquid crystal domain C is about 135 °, and the tilt direction t4 of the liquid crystal domain D is about 315 °. The liquid crystal domain A and the liquid crystal domain B have a tilt angle different by about 180 °, and the liquid crystal domain C and the liquid crystal domain D have a tilt angle different by about 180 °. The tilt directions t1 to t4 of the liquid crystal domains A to D are the same in the other divided structures exemplified below.

  As shown in FIG. 5A, in the pixel region 20, the boundary line between the liquid crystal region A and the liquid crystal region B and the boundary line between the liquid crystal region C and the liquid crystal region D are both 180 ° boundary lines CL1, These form one 180 ° boundary line CL1 connected in a straight line. The 180 ° boundary line CL1 extends along the vertical direction (column direction: vertical direction of the display surface), and divides the pixel region into two in the horizontal direction (row direction: horizontal direction of the display surface).

  On the other hand, in the pixel region 20, the boundary line between the liquid crystal region A and the liquid crystal region C and the boundary line between the liquid crystal region B and the liquid crystal region D are both 90 ° boundary lines CL2, and these are connected in a straight line. The 90 ° boundary line CL2 is formed. The 90 ° boundary line CL2 extends along the horizontal direction (row direction: horizontal direction of the display surface), and divides the pixel region into two in the vertical direction (column direction: vertical direction of the display surface). Since the 180 ° boundary line CL1 has higher transmittance than the 90 ° boundary line CL2, all of the cross-shaped boundary lines formed when the four liquid crystal domains are arranged in a matrix of 2 rows and 2 columns are 90 ° boundaries. A decrease in transmittance is suppressed as compared with the alignment division structure as a line (see FIGS. 10A and 10B described later). A general pixel is composed of three pixels (R pixel, G pixel, and B pixel) arranged in the row direction, and this color pixel is configured to be substantially square. The pixel region has a shape that is long in the column direction. Therefore, as shown in FIG. 5A, if the 180 ° boundary line CL1 is formed parallel to the column direction and the 90 ° boundary line CL2 is formed parallel to the row direction, the 180 ° boundary line is formed. Since the length of the line CL1 can be made larger than the length of the 90 ° boundary line CL2, the loss of transmittance can be more effectively reduced.

  For example, the pixel region 20 shown in FIG. 5A is subjected to alignment processing on the TFT substrate side as shown in FIG. 5B, and is subjected to alignment processing on the CF substrate side as shown in FIG. 5C. Then, these substrates can be obtained by bonding. Here, in the alignment processing on the CF substrate side, as shown in FIG. 5C, it is necessary to form four regions characterized by the pretilt directions PB1 to PB4, respectively, but the pretilt directions PB1 and PB3 are the same. Since the pretilt directions PB2 and PB4 are the same direction, four regions can be formed by two alignment treatment steps.

  Next, the configuration of another pixel region 30 having four liquid crystal domains A to D arranged in a matrix of 2 rows and 2 columns will be described with reference to FIG.

  In the pixel region 30 shown in FIG. 6A, the boundary line between the liquid crystal region A and the liquid crystal region B and the boundary line between the liquid crystal region C and the liquid crystal region D are both 180 ° boundary lines CL1. A single 180 ° boundary line CL1 connected in a straight line is formed. Unlike the pixel region 20 shown in FIG. 5A, the 180 ° boundary line CL1 extends along the horizontal direction (row direction: horizontal direction of the display surface), and the pixel region extends in the vertical direction (column direction: display surface). In the vertical direction).

  On the other hand, in the pixel region 30, the boundary line between the liquid crystal region A and the liquid crystal region D and the boundary line between the liquid crystal region B and the liquid crystal region C are both 90 ° boundary lines CL2, and these are connected in a straight line. The 90 ° boundary line CL2 is formed. Unlike the pixel region 20 shown in FIG. 5A, the 90 ° boundary line CL2 extends along the vertical direction (column direction: vertical direction of the display surface), and the pixel region extends in the horizontal direction (row direction: display surface). In the horizontal direction). Since the 180 ° boundary line CL1 has higher transmittance than the 90 ° boundary line CL2, all of the cross-shaped boundary lines formed when the four liquid crystal domains are arranged in a matrix of 2 rows and 2 columns are 90 ° boundaries. A decrease in transmittance is suppressed as compared with the alignment division structure as a line. When the pixel region has a shape that is long in the row direction, the length of the 180 ° boundary line CL1 can be made larger than the length of the 90 ° boundary line CL2, so that the loss of transmittance is more effectively reduced. Can do.

  For example, the pixel region 30 shown in FIG. 6A is subjected to alignment processing on the TFT substrate side as shown in FIG. 6B, and is subjected to alignment processing on the CF substrate side as shown in FIG. 6C. Then, these substrates can be obtained by bonding. Here, in the alignment processing on the TFT substrate side, as shown in FIG. 6B, it is necessary to form four regions characterized by the pretilt directions PA1 to PA4, respectively, but the pretilt directions PA1 and PA3 are the same. Since the pretilt directions PA2 and PA4 are the same direction, if a photo-alignment film is used, four regions can be formed in two exposure steps.

   Next, the configuration of still another pixel region 40 having four liquid crystal domains A to D arranged in a matrix of 2 rows and 2 columns will be described with reference to FIG.

  In the pixel region 40 shown in FIG. 7A, the boundary line between the liquid crystal region A and the liquid crystal region B and the boundary line between the liquid crystal region C and the liquid crystal region D are both 180 ° boundary lines CL1. A single 180 ° boundary line CL1 connected in a straight line is formed. Similarly to the pixel region 20 shown in FIG. 5A, the 180 ° boundary line CL1 extends along the vertical direction (column direction: vertical direction of the display surface), and the pixel region is displayed in the horizontal direction (row direction: display). (Horizontal direction of the surface).

  On the other hand, in the pixel region 40, the boundary line between the liquid crystal region A and the liquid crystal region D and the boundary line between the liquid crystal region B and the liquid crystal region C are both 90 ° boundary lines CL2, and these are connected in a straight line. The 90 ° boundary line CL2 is formed. Similarly to the pixel region 20 shown in FIG. 5A, the 90 ° boundary line CL2 extends along the horizontal direction (row direction: horizontal direction of the display surface), and the pixel region is arranged in the vertical direction (column direction: display). It is divided into two in the direction perpendicular to the surface. Since the 180 ° boundary line CL1 has higher transmittance than the 90 ° boundary line CL2, all of the cross-shaped boundary lines formed when the four liquid crystal domains are arranged in a matrix of 2 rows and 2 columns are 90 ° boundaries. A decrease in transmittance is suppressed as compared with the alignment division structure as a line. In addition, since a general pixel region has a vertically long shape, the alignment division structure shown in FIG. 7A has a 180 ° boundary similarly to the alignment division structure shown in FIG. Since the line CL1 can be made longer than the 90 ° boundary line CL2, there is an advantage that the loss of transmittance can be reduced more effectively.

  For example, the pixel region 40 shown in FIG. 7A is subjected to alignment processing on the TFT substrate side as shown in FIG. 7B, and is subjected to alignment processing on the CF substrate side as shown in FIG. 7C. Then, these substrates can be obtained by bonding. It can be formed by the same method as that for the pixel region 20 shown in FIG. 5A only by changing the pretilt direction applied by the alignment treatment.

  Next, with reference to FIGS. 8A to 8C and FIGS. 9A to 9C, an alignment division structure in which four liquid crystal domains A to D are arranged in a line in the column direction will be described. Three boundary lines formed between adjacent liquid crystal domains extend in any row direction, and divide the pixel region into four regions having the same area in the column direction.

  A pixel region 50 shown in FIG. 8A has liquid crystal domains A, C, D, and B in this order along the column direction.

  The boundary line between the liquid crystal domain A and the liquid crystal domain C and the boundary line between the liquid crystal domain D and the liquid crystal domain B are 90 ° boundary line CL2, and the boundary line between the liquid crystal domain C and the liquid crystal domain D is 180 ° boundary line CL1. is there. By arranging the liquid crystal domains in this way, a decrease in transmittance is suppressed as compared with an alignment division structure (see FIG. 10C described later) in which all three boundary lines are 90 ° boundary lines.

  For example, the pixel region 50 shown in FIG. 8A is subjected to alignment processing on the TFT substrate side as shown in FIG. 8B, and is subjected to alignment processing on the CF substrate side as shown in FIG. 8C. Then, these substrates can be obtained by bonding. Here, in the alignment processing on the CF substrate side, as shown in FIG. 8C, it is necessary to form four regions characterized by the pretilt directions PB1 to PB4, respectively, but the pretilt directions PB1 and PB3 are the same. Since the pretilt directions PB2 and PB4 are the same direction, four regions can be formed by two alignment treatment steps.

  A pixel region 60 shown in FIG. 9A has liquid crystal domains A, B, D, and C in this order along the column direction.

  Only the boundary line between the liquid crystal domain B and the liquid crystal domain D formed at the center of the pixel region is the 90 ° boundary line CL2, and the boundary line between the liquid crystal domain A and the liquid crystal domain B and the boundary between the liquid crystal domain D and the liquid crystal domain C. The line is a 180 ° boundary line CL1. By arranging the liquid crystal domains in this way, a decrease in transmittance is suppressed as compared with an alignment division structure (see FIG. 10C described later) in which all three boundary lines are 90 ° boundary lines. Moreover, since two of the three boundary lines can be 180 ° boundary lines, the effect of suppressing the decrease in transmittance is greater than that of the alignment division structure shown in FIG. Further, in the configuration in which the auxiliary capacitance wiring is provided in the pixel region, if the auxiliary capacitance wiring is provided so as to overlap with the 90 ° boundary line between the liquid crystal domains B and D, the reduction in the effective aperture ratio can be suppressed. it can.

  For example, the pixel region 60 shown in FIG. 9A is subjected to alignment processing on the TFT substrate side as shown in FIG. 9B, and is subjected to alignment processing on the CF substrate side as shown in FIG. 9C. Then, these substrates can be obtained by bonding. Here, in the alignment process on the CF substrate side, as shown in FIG. 9C, it is necessary to form four regions characterized by the pretilt directions PB1 to PB4, respectively, but the pretilt directions PB1 and PB3 are the same. Since the pretilt directions PB2 and PB4 are the same direction, four regions can be formed by two alignment treatment steps.

  8 and 9 show an example in which the pixel region is divided into a plurality of regions along the column direction. Needless to say, the pixel region may be divided along the row direction, and the dividing direction is not particularly limited. There is no particular limitation on the number of divisions.

  FIGS. 10A to 10C show an example in which all of the boundary lines of the pixel region are formed by 90 ° boundary lines CL2 for comparison.

  The pixel region 94 shown in FIG. 10A and the pixel region 96 shown in FIG. 10B are the pixel regions 20 to 40 shown in FIG. 5A, FIG. 6A, and FIG. Similarly to the above, the liquid crystal domains A to D are arranged in a matrix of 2 rows and 2 columns. However, since the tilt directions (reference alignment directions) of adjacent liquid crystal domains are all 90 °, the cross boundary line is the 90 ° boundary line CL2, and the loss of transmittance is large.

  Similar to the pixel region 50 shown in FIG. 8A and the pixel region 60 shown in FIG. 9A, the pixel region 96 shown in FIG. 10C has four pixel regions arranged in a line in the column direction. Although the liquid crystal domains A to D are included, the tilt directions (reference alignment directions) of the adjacent liquid crystal domains are all 90 °, and therefore all three boundary lines are 90 ° boundary lines CL2. The loss of transmittance is large.

  As is clear from the above description, in the alignment division structure, the loss of transmittance can be reduced by setting the boundary line (boundary region) formed between adjacent liquid crystal domains to a 180 ° boundary line. The structure of the alignment division is not limited to the exemplified one, and if at least one of the boundary lines (boundary regions) formed between adjacent liquid crystal domains is a 180 ° boundary line, the loss of transmittance can be suppressed. Can be obtained. If a 180 ° boundary line is formed in a region that contributes to display and a 90 ° boundary line is formed in a region that does not contribute to display (for example, a region where an auxiliary capacitance wiring is formed), a decrease in effective aperture ratio is suppressed. This is preferable.

  The liquid crystal display device according to the present invention is suitably used for applications that require high quality display such as television receivers.

(A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 10 of the liquid crystal display device of embodiment by this invention, (a) is two liquid crystal domains A and B of FIG. FIG. 4B is a schematic diagram showing a relationship between tilt directions t1 and t2, FIG. 5B is a schematic diagram showing pretilt directions PA1 and PA2 of the alignment film of the TFT substrate, and FIG. 5C is a pretilt direction PB1 of the alignment film of the CF substrate. It is a figure which shows PB2 typically. (A) And (b) is a figure for demonstrating the relationship between the orientation of the liquid crystal molecule | numerator of 180 degree boundary line CL1 vicinity in the pixel area | region 10 shown to Fig.1 (a), and the transmittance | permeability. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 92 of the liquid crystal display device for a comparison, (a) is the tilt direction of two liquid crystal domains B and D FIG. 2B is a schematic diagram showing a relationship between t2 and t4, FIG. 3B is a schematic diagram showing pretilt directions PA1 and PA2 of the alignment film of the TFT substrate, and FIG. 2C is a schematic diagram showing a pretilt direction PB1 of the alignment film of the CF substrate. FIG. (A) And (b) is a figure for demonstrating the relationship between the orientation of the liquid crystal molecule | numerator of 90 degree boundary line CL2 vicinity in the pixel area | region 92 shown to Fig.3 (a), and the transmittance | permeability. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 20 of the liquid crystal display device of embodiment by this invention, (a) is four liquid crystal domains AD. It is a schematic diagram which shows the relationship between the tilt directions t1-t4, (b) is a schematic diagram which shows the pretilt directions PA1 and PA2 of the alignment film of a TFT substrate, (c) is the pretilt direction PB1 of the alignment film of a CF substrate. It is a figure which shows -PB4 typically. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 30 of the liquid crystal display device of embodiment by this invention, (a) is four liquid crystal domains AD. It is a schematic diagram which shows the relationship between the tilt directions t1-t4, (b) is a schematic diagram which shows the pretilt directions PA1-PA4 of the alignment film of a TFT substrate, (c) is the pretilt direction PB1 of the alignment film of a CF substrate. It is a figure which shows PB2 typically. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 40 of the liquid crystal display device of embodiment by this invention, (a) is four liquid crystal domains AD. It is a schematic diagram which shows the relationship between the tilt directions t1-t4, (b) is a schematic diagram which shows the pretilt directions PA1 and PA2 of the alignment film of a TFT substrate, (c) is the pretilt direction PB1 of the alignment film of a CF substrate. It is a figure which shows -PB4 typically. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 50 of the liquid crystal display device of embodiment by this invention, (a) is four liquid crystal domains AD. It is a schematic diagram which shows the relationship between the tilt directions t1-t4, (b) is a schematic diagram which shows the pretilt directions PA1 and PA2 of the alignment film of a TFT substrate, (c) is the pretilt direction PB1 of the alignment film of a CF substrate. It is a figure which shows -PB4 typically. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area 60 of the liquid crystal display device of embodiment by this invention, (a) is four liquid crystal domains AD. It is a schematic diagram which shows the relationship of the tilt directions t1-t4, (b) is a schematic diagram which shows the pretilt directions PA1-PA3 of the alignment film of a TFT substrate, (c) is the pretilt direction PB1 of the alignment film of a CF substrate. It is a figure which shows -PB4 typically. (A)-(c) is a schematic diagram for demonstrating the structure of the liquid crystal domain in the pixel area | region of the liquid crystal display device for a comparison.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 TFT substrate 1a Transparent substrate 2 CF substrate 2a Transparent substrate 3 Vertical alignment type liquid crystal layer 3a Liquid crystal molecule 11 Pixel electrode 12 Counter electrode A, B, C, D Liquid crystal domain t1-t4 Tilt direction (reference alignment direction)
CL1 180 ° boundary line CL2 90 ° boundary line

Claims (7)

A vertically aligned liquid crystal layer;
A first substrate and a second substrate facing each other through the liquid crystal layer;
A first electrode provided on the liquid crystal layer side of the first substrate and a second electrode provided on the liquid crystal layer side of the second substrate;
At least one alignment film provided in contact with the liquid crystal layer;
The pixel region has a plurality of liquid crystal domains in which the tilt directions of the liquid crystal molecules near the center in the layer plane and the thickness direction of the liquid crystal layer when a voltage is applied are different from each other,
The plurality of liquid crystal domains include a first liquid crystal domain in which a tilt direction of liquid crystal molecules in a layer plane of the liquid crystal layer and a center in a thickness direction when a voltage is applied is a first direction, and the first direction. A liquid crystal display device comprising: a second liquid crystal domain that is in a second direction different by about 180 °, wherein the first liquid crystal domain and the second liquid crystal domain are adjacent to each other.   The plurality of liquid crystal domains have a third direction in which the tilt direction of the liquid crystal molecules near the center in the layer surface and in the thickness direction of the liquid crystal layer when a voltage is applied differs from the first direction by about 90 °. A liquid crystal display device further comprising a liquid crystal domain and a fourth liquid crystal domain which is a fourth direction different from the second direction by about 90 °.   The liquid crystal display device according to claim 2, wherein the three liquid crystal domains and the fourth liquid crystal domain are adjacent to each other. Further comprising a pair of polarizing plates arranged to face each other through the liquid crystal layer and the transmission axes are orthogonal to each other,
4. The liquid crystal display device according to claim 1, wherein the first direction forms an angle of about 45 ° with the transmission axis of the pair of polarizing plates. 5. The vertical alignment type liquid crystal layer includes a liquid crystal material having negative dielectric anisotropy,
The at least one alignment film is a pair of alignment films provided on both sides of the liquid crystal layer, and the pretilt direction defined by one alignment film and the pretilt direction defined by the other alignment film are approximately 90 ° from each other. The liquid crystal display device according to claim 1, which is different. The at least one alignment film is a pair of alignment films provided on both sides of the liquid crystal layer,
6. The liquid crystal display device according to claim 1, wherein the pretilt angle defined by the one alignment film and the pretilt angle defined by the other alignment film are substantially equal to each other.   The liquid crystal display device according to claim 1, wherein the at least one alignment film is formed of a photo-alignment film.

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