JP5511340B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a multiplex-driven vertical alignment type liquid crystal display device.

  Liquid crystal display devices are widely used as information display units in, for example, various consumer and in-vehicle electronic devices. A general liquid crystal display device is configured by disposing a liquid crystal layer made of a liquid crystal material between two substrates arranged to face each other with a gap of about several μm. A vertical alignment type liquid crystal display device is known as one of such liquid crystal display devices. A vertical alignment type liquid crystal display device includes a VA mode liquid crystal cell in which liquid crystal molecules in a liquid crystal layer disposed between two substrates are aligned substantially perpendicularly to the surface of each substrate, and the liquid crystal cell A polarizing plate provided outside is provided as a main configuration. Each polarizing plate is often in a crossed Nicol arrangement. In this way, since the transmittance of the liquid crystal display device when no voltage is applied becomes very low, a high contrast can be realized relatively easily.

  In order to realize a VA mode liquid crystal cell, it is important to control the alignment of liquid crystal molecules in the liquid crystal layer by applying a predetermined alignment treatment to the substrate surface. As the alignment treatment, for example, a metal oxide such as SiOx is vapor-deposited from a direction inclined with respect to the substrate normal, thereby forming a thin film having a saw-shaped surface on the substrate surface (so-called oblique vapor deposition method), After the organic alignment film material such as polyimide is formed on the substrate surface, a process of irradiating ultraviolet light from a specific direction (so-called photo-alignment processing method) or a vertical alignment film having specific surface free energy is formed on the substrate surface In addition, an alignment process or the like in which a rubbing process is performed is mainly known. According to these alignment treatments, an alignment in which liquid crystal molecules in the liquid crystal layer are aligned in one direction when no voltage is applied (so-called monodomain alignment) can be obtained.

  In the vertical alignment type liquid crystal display device with monodomain alignment as described above, the setting of the pretilt angle in the liquid crystal layer has a great influence on the display characteristics. Specifically, considering the steepness in the electro-optical characteristics, the best results are obtained when the liquid crystal molecules are aligned in the normal direction of the substrate when no voltage is applied, that is, when the pretilt angle is 90 °. In particular, when the liquid crystal display device is driven by a multiplex driving method, it is an effective means to increase the pretilt angle in order to increase the display capacity (that is, increase the duty). However, if the pretilt angle is set to 90 °, the alignment uniformity of the liquid crystal molecules at the time of voltage application cannot be obtained, so that it is necessary to perform the above-described alignment treatment in practice.

  Japanese Patent Laid-Open No. 2005-234254 (Patent Document 1) discloses that in a vertical alignment type liquid crystal display device, when the pretilt angle is larger than 89.5 ° (particularly when larger than 89.7 °), It has been pointed out that the maximum transmittance tends to decrease following the size. In addition, regarding this, Japanese Patent Laid-Open No. 2008-281752 (Patent Document 2) causes a dark region to appear in a part of the display portion under a driving condition with a relatively low frame frequency, resulting in non-uniform display. It is pointed out that it is one of these. As a method for improving such display non-uniformity, the above-mentioned Patent Document 2 describes the setting of the pretilt angle of the vertical alignment type liquid crystal display device and the corresponding method for each of various multiplex drive waveforms. A frame frequency setting method is disclosed. Specifically, in Patent Document 2, display uniformity is improved by increasing the frame frequency as the pretilt angle approaches 90 °, or by using a 1/2 line inversion drive waveform containing a lot of high frequency components. It has been shown to be feasible.

  By the way, when the technique disclosed in Patent Document 2 described above is applied to a vertically aligned liquid crystal display device having a relatively large number of scanning lines (that is, having a large duty), the internal impedance of the liquid crystal display device is reduced. The drive current increases due to the decrease. When the required drive current exceeds the current drive capability of the driver (drive device) that drives the liquid crystal display device, a voltage drop occurs in the middle of the transparent electrode that becomes a scanning line or the like, thereby applying a voltage to each pixel. Becomes non-uniform and display unevenness appears remarkably. For example, in a dot matrix type liquid crystal display device in which strip-shaped transparent electrodes are crossed and a liquid crystal layer is provided between them, streaky display unevenness along the extending direction of one transparent electrode may occur. , Variation in brightness and contrast may occur along the extending direction of the other transparent electrode. In order to eliminate such display unevenness, it is effective to increase the current drive capability of the driver, to reduce the frame frequency, or to use a drive waveform (frame inversion waveform) that does not contain a lot of high frequency components. However, increasing the current driving capability of the driver is not a preferable solution because it increases costs.

JP 2005-234254 A JP 2008-281752 A

  A specific aspect according to the present invention is a technique capable of reducing the frame frequency while maintaining display uniformity when a vertically aligned liquid crystal display device having a pretilt angle close to 90 ° is driven in multiplex. Is one of the purposes.

  In order to solve the above-mentioned problems, the inventor of the present application diligently studied display nonuniformity that occurs when a vertically aligned liquid crystal display device having a pretilt angle close to 90 ° is driven in a multiplex manner. FIG. 9 is a photograph of external observation when a vertically aligned liquid crystal display device with a pretilt angle of 89.6 ° is multiplex driven under the conditions of a duty ratio of 1/8, a bias ratio of 1/5, and a frame frequency of 80 Hz. Show. As shown in the figure, a liquid crystal display device having a segment type display unit was used, and all the segments were turned on (bright display). The rubbing directions in this liquid crystal display device are the 12 o'clock direction and the 6 o'clock direction (anti-parallel), and the alignment direction of the liquid crystal molecules at the center of the liquid crystal layer is the 12 o'clock direction (the direction indicated by the arrow on the left side in the figure). . As shown in the figure, a dark region partially appears in each segment, and display uniformity is impaired. When this is observed in detail, there is a characteristic in the portion where the dark region appears. That is, a dark region is frequently generated in each segment near the edges of three segments having long sides in a direction substantially orthogonal to the rubbing direction. These dark regions can be eliminated by increasing the frame frequency, but this conflicts with the desire to lower the frame frequency. From the above observations, the generation of dark regions that degrade display uniformity is related to the state of oblique electric field generation near the edge of the electrode and the rubbing direction, that is, the alignment direction of the liquid crystal molecules in the center of the liquid crystal layer. It is considered. Therefore, the present inventor has reached the following invention based on the observation results as described above.

A liquid crystal display device according to one aspect of the present invention is a liquid crystal display device that operates by multiplex driving, and (a) a first substrate having a first electrode on one surface side, and (b) a second electrode on one surface side. A second substrate disposed opposite to the first substrate, and (c) a liquid crystal layer disposed between the first electrode of the first substrate and the second electrode of the second substrate, d) A pixel is defined in a region where the first electrode and the second electrode overlap each other. (e) The first electrode has a plurality of first openings arranged in a shape extending in the first direction and periodically arranged. (F) The liquid crystal layer has a pretilt angle set to 89.7 ° or more and less than 90 °, (g) the longitudinal direction of each of the plurality of first openings, and the liquid crystal layer This is a liquid crystal display device in which the angle formed by the alignment direction of liquid crystal molecules at the center of the liquid crystal is 0 ° or more and 45 ° or less .

  According to the above configuration, when a vertically aligned liquid crystal display device having a pretilt angle close to 90 ° is multiplex driven, the frame frequency can be lowered while maintaining display uniformity.

In the above liquid crystal display device, the angle formed between the longitudinal direction of each of the plurality of first openings and the alignment direction of the liquid crystal molecules in the center of the liquid crystal layer is preferably as close to 0 °, for example, approximately 45 ° or approximately 0 °. It is preferable that

  Thereby, the effect of lowering the frame frequency can be further enhanced. Further, by setting the angle to 0 ° or 45 °, it is also convenient in terms of the positional relationship with the absorption axis when a polarizing plate is provided outside each of the first substrate and the second substrate.

In the above liquid crystal display device, the plurality of first openings have a distance P between two first openings adjacent to each other in a second direction orthogonal to the first direction of 0.04 mm or more and less than 0.2 mm. It is also preferable that there is. Further, in the above liquid crystal display device, the plurality of first openings have a width in the second direction orthogonal to each first direction of 0.005 mm or more and 0.03 mm or less, and are adjacent in the first direction. it is also preferable distance between the two openings is less than twice the width in the second direction noted above. In the above liquid crystal display device, the first electrode has a plurality of second openings arranged periodically in the pixel, and each of the plurality of second openings has a plurality of first openings. It is also preferable that they are arranged so as to cross either one.

  This also makes it possible to increase the effect of reducing the frame frequency.

  A liquid crystal display device according to another aspect of the present invention is a liquid crystal display device that operates by multiplex driving, wherein (a) a first substrate having a first electrode on one surface side, and (b) a second substrate on one surface side. A second substrate having an electrode and disposed opposite to the first substrate, and (c) a liquid crystal layer disposed between the first electrode of the first substrate and the second electrode of the second substrate, (D) The first electrode has a cross shape formed by intersecting the first part extending in the first direction and the second part extending in the second direction, and has a plurality of periodically arranged openings. (E) the liquid crystal layer has a pretilt angle set to 89.7 ° or more and less than 90 °, and (f) the longitudinal direction of each of the first portion and the second portion of the plurality of openings, This is a liquid crystal display device in which the angle formed with the alignment direction of liquid crystal molecules at the center of the liquid crystal layer is 0 ° or more and less than 90 °.

  Also with the above configuration, in the case where a vertical alignment type liquid crystal display device having a pretilt angle close to 90 ° is driven in multiplex, the frame frequency can be lowered while maintaining display uniformity.

  In the liquid crystal display device described above, each of the plurality of openings has an angle formed by the first direction and the second direction of approximately 90 °, and each of the first direction and the second direction and the center of the liquid crystal layer. It is also preferable that the angle formed with the alignment direction of the liquid crystal molecules is approximately 45 °.

  Thereby, the effect of lowering the frame frequency can be further enhanced. It is also convenient in terms of the positional relationship with the absorption axis when a polarizing plate is provided outside each of the first substrate and the second substrate.

  In the liquid crystal display device described above, the plurality of openings are preferably arranged such that the distance P between the center points where the first and second portions overlap each other is 0.1 mm or more and 0.3 mm or less.

  This also makes it possible to increase the effect of reducing the frame frequency.

It is typical sectional drawing which shows the structure of the liquid crystal display device of one Embodiment. It is a schematic plan view for demonstrating the structure of each opening part provided in the 1st electrode. 6 is a diagram showing a microscope observation image of a pixel portion of the liquid crystal display device according to Example 1. FIG. It is a figure which shows the result of having observed the pretilt angle dependence of the frame frequency and the bias ratio dependence in a multiplex drive condition which can obtain display uniformity by external appearance observation. It is a figure which shows the result of having observed the frame frequency from which the display uniformity is obtained on the external appearance using the sample which changed the arrangement pitch P of each opening part. It is a figure which shows the result of having observed the pretilt angle dependence of the frame frequency and the bias ratio dependence in a multiplex drive condition from which display uniformity is obtained by external appearance observation. It is a figure which shows the result of having observed the frame frequency from which the display uniformity is obtained on the external appearance using the sample which changed the arrangement pitch P of each opening part. It is a schematic cross section explaining an effect in the case where an opening is a cross slit. It is a figure which shows the external appearance observation photograph at the time of carrying out the multiplex drive on the conditions with a duty ratio of 1/8, a bias ratio of 1/5, and a frame frequency of 80 Hz with a vertical alignment type liquid crystal display device with a pretilt angle of 89.6 °. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing the structure of a liquid crystal display device (liquid crystal panel) according to an embodiment. The liquid crystal display device according to the present embodiment shown in FIG. 1 mainly includes a first substrate 1 and a second substrate 2 that are disposed to face each other, and a liquid crystal layer 3 that is disposed between the two substrates. A first polarizing plate 4 is disposed outside the first substrate 1, and a second polarizing plate 5 is disposed outside the second substrate 2. A first viewing angle compensation plate 6 is disposed between the first substrate 1 and the first polarizing plate 4, and a second viewing angle compensation plate 7 is disposed between the second substrate 2 and the second polarizing plate 5. The periphery of the liquid crystal layer 3 is sealed with a sealing material 8. Hereinafter, the structure of the liquid crystal display device will be described in more detail.

  The first substrate 1 and the second substrate 2 are transparent substrates such as a glass substrate and a plastic substrate, respectively. Spacers (granular bodies) 10 are dispersed and arranged between the first substrate 1 and the second substrate 2. With these spacers 10, the gap between the first substrate 1 and the second substrate 2 is maintained at a predetermined distance (in the present embodiment, about 3.6 to 3.8 μm).

  The liquid crystal layer 3 is provided between the first electrode 11 of the first substrate 1 and the second electrode 12 of the second substrate 2. In the present embodiment, the liquid crystal layer 3 is configured using a liquid crystal material (nematic liquid crystal material) having a negative dielectric anisotropy Δε (Δε <0). The bold line shown in the liquid crystal layer 3 schematically shows the alignment direction of the liquid crystal molecules when no voltage is applied. As shown in the figure, in the liquid crystal display device of the present embodiment, the alignment state of the liquid crystal molecules in the liquid crystal layer 3 is restricted to monodomain alignment. The pretilt angle of the liquid crystal layer 3 in this embodiment is set to approximately 89.7 ° to 89.9 °. The retardation of the liquid crystal layer 3 is approximately 800 to 870 nm.

  The first electrode 11 is provided on one surface of the first substrate 1. In the present embodiment, the plurality of first electrodes 11 are arranged to face the second electrodes 12 respectively. The shape of each first electrode 11 is, for example, a rectangular shape (in the case of a dot matrix type), or a shape corresponding to an arbitrary display pattern (in the case of a segment display type). Each first electrode 11 is configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. Each first electrode 11 is provided with a plurality of openings (slits) 15. Details of each opening 15 will be described later.

  The second electrode 12 is provided on one surface of the second substrate 2. The second electrode 12 is configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. In the liquid crystal display device of this embodiment, each of the portions where the first electrode 11 and the second electrode 12 overlap in a plan view is a display unit.

  The alignment film 13 is provided on one surface side of the first substrate 1 so as to cover the first electrode 11. Similarly, the alignment film 14 is provided on one surface side of the second substrate 2 so as to cover the second electrode 12. In the present embodiment, as the alignment film 13 and the alignment film 14, a film (vertical alignment film) that regulates the alignment state in the initial state (when no voltage is applied) of the liquid crystal layer 3 to the vertical alignment state is used. More specifically, each of the alignment films 13 and 14 can give a pretilt angle of an angle extremely close to 90 ° (about 89.7 ° to 89.9 °) with respect to the liquid crystal molecules of the liquid crystal layer 3. Used.

  FIG. 2 is a schematic plan view for explaining the structure of each opening provided in the first electrode. Each of the openings 15 shown in FIGS. 2A to 2C has a shape (substantially rectangular) extending in one direction. Each opening 15 shown in FIG. 2D has a shape (cross shape) obtained by intersecting two substantially rectangular openings. In each figure, W indicates the distance between the adjacent openings 15 in the short direction (distance between long side edges), L indicates the length in the longitudinal direction of each opening 15, and Ls indicates each adjacent opening. The mutual distance (short-side edge distance) in the longitudinal direction of the openings 15 is indicated, and S indicates the length (width) in the short direction of each opening 15. Further, in FIGS. 2A to 2C, P indicates a distance (arrangement pitch) between the openings 15 in the short direction. In FIG. 2D, P indicates the distance between the center points in the cross-shaped opening 15.

  Each opening 15 shown in FIG. 2A has a longitudinal direction (long side direction) substantially parallel to the alignment direction 16 (indicated by an arrow in the upper left in the figure) of the liquid crystal molecules in the central portion of the liquid crystal layer 3. It is arranged to be. That is, each opening 15 is arranged such that an angle formed between each longitudinal direction and the alignment direction of liquid crystal molecules in the center of the liquid crystal layer is approximately 0 °. The openings 15 arranged in this way may be hereinafter referred to as “vertical slits”. About each parameter mentioned above, it can be set as P = 0.1mm, S = 0.01mm, W = 0.09mm, Ls = 0.01mm, L = 0.09mm, for example.

  Each opening 15 shown in FIG. 2B is arranged so that the longitudinal direction thereof is substantially orthogonal to the alignment direction 16 (indicated by an arrow in the upper left in the drawing) of the liquid crystal molecules in the central portion of the liquid crystal layer 3. Yes. That is, each opening 15 is arranged such that an angle formed between each longitudinal direction and the alignment direction of the liquid crystal molecules at the center of the liquid crystal layer is approximately 90 °. The openings 15 arranged in this way may be referred to as “lateral slits” hereinafter. About each parameter mentioned above, it can be set as P = 0.1mm, S = 0.01mm, W = 0.09mm, Ls = 0.01mm, L = 0.09mm, for example.

  Each opening 15 shown in FIG. 2C has a longitudinal direction of 0 ° or more and less than 90 ° with respect to the alignment direction 16 (indicated by an arrow in the upper left in the drawing) of the liquid crystal molecules in the central portion of the liquid crystal layer 3. Are arranged so as to intersect at a predetermined angle. In this example, the case where the longitudinal direction of each opening 15 and the alignment direction of the liquid crystal molecules have an angle of 45 ° is shown. Each opening 15 arranged in this way may be hereinafter referred to as an “oblique slit”. About each parameter mentioned above, it can be set as P = 0.1mm, S = 0.01mm, W = 0.09mm, Ls = 0.01mm, L = 0.09mm, for example.

  Each opening 15 shown in FIG. 2D has a cross shape formed by intersecting two rectangular parts (first part and second part). In each opening 15, an angle formed by the longitudinal direction (first direction) of one rectangle and the longitudinal direction (second direction) of the other rectangle is set to approximately 90 °. Each opening 15 has an angle (in this example, the first direction and the second direction) with respect to the alignment direction of liquid crystal molecules in the center of the liquid crystal layer 3 (indicated by an arrow in the upper left in the figure). They are arranged so as to intersect each other at 45 °. The openings 15 arranged in this way may be hereinafter referred to as “cross slits”. About each parameter mentioned above, it can be set as S = 0.01mm, Ls = 0.014mm, L = 0.0628mm, for example.

  In any opening 15 shown in FIGS. 2A to 2D, the four corners are rounded. This depends on the formation conditions (etching conditions) when patterning the first electrode 11, and the four corners are sharpened by slowing the etching rate by changing the etching solution and temperature. It is also possible to do. According to the inventor of the present application, it has been confirmed that there is no influence due to the difference in the shape of the four corners of each opening 15.

  Next, an example of a manufacturing method of the liquid crystal display device will be described in detail.

First, a substrate having a transparent electrode on one surface is prepared. As the substrate, for example, a glass substrate in which one surface is polished, SiO ₂ is coated on the surface, and a transparent conductive film made of ITO (indium tin oxide) is formed thereon can be used. By performing a known photolithography process and etching process on this substrate, the first substrate 1 having the first electrode 11 and the second substrate 2 having the second electrode 12 are formed. If necessary, an insulating layer made of SiO ₂ or the like may be further formed on a part of the surface of the first electrode 11 or the second electrode 12.

  Next, an alignment film 13 is formed on one surface of the first substrate 1, and an alignment film 14 is formed on one surface of the second substrate 2. Specifically, after each substrate is washed with an alkali solution or the like, the material liquid of the vertical alignment film is applied onto one surface of the first substrate 1 and one surface of the second substrate 2 by a method such as flexographic printing. Is baked in a clean oven (for example, 180 ° C. for 30 minutes). Thereafter, the alignment films 13 and 14 are rubbed.

  The pretilt angle of the liquid crystal layer 3 can be controlled by appropriately setting the conditions for the rubbing treatment in this step. Here, the pretilt angle refers to an angle formed between the substrate surface and the average alignment direction (director) of liquid crystal molecules. In addition, by appropriately setting the rubbing direction (direction in which the rubbing cloth is rotated) when the rubbing process is performed on the first substrate 1, the alignment direction of the liquid crystal molecules and each opening in the center of the liquid crystal layer 3 are set. The positional relationship with the longitudinal direction of the portion 15 (see FIG. 2 described above) can be defined.

  Next, the sealing material 8 is formed on one substrate (for example, on one surface of the first substrate 1). The sealing material 8 is formed, for example, by applying a mixture of rod-shaped glass spacers having a particle diameter of about 4 μm by a method such as screen printing. On the other substrate (for example, on one surface of the second substrate 2), for example, spacers 10 having a particle diameter of about 4 μm are dispersed. The spacer 10 is sprayed by, for example, a dry spray method.

  Next, the first substrate 1 and the second substrate 2 are bonded together so that their one surfaces face each other and the rubbing directions with respect to the alignment films 13 and 14 are antiparallel, and are fired in a constant pressure state. . Thereby, the sealing material 8 is cured, and the first substrate 1 and the second substrate 2 are fixed (an empty cell is completed).

  Next, a liquid crystal material (with a dielectric anisotropy Δε <0) is injected into the gap between the first substrate 1 and the second substrate 2 by a method such as vacuum injection, and the injection port used for the injection is sealed. Then, firing is performed (for example, 120 ° C. for 60 minutes). Thereby, the liquid crystal layer 3 is formed.

  Thereafter, the first polarizing plate 4 and the viewing angle compensation plate 6 are bonded to the outside of the first substrate 1, and the second polarizing plate 5 and the viewing angle compensation plate 7 are bonded to the outside of the second substrate 2. For example, each of the first polarizing plate 4 and the second polarizing plate 2 has an angle of about 45 ° with respect to the alignment direction of the liquid crystal molecules in the center of the liquid crystal layer 3 and is disposed so that they are crossed Nicols. Is done. The viewing angle compensation plates 6 and 7 are provided as necessary, and may be omitted. Finally, the liquid crystal display device shown in FIG. 1 is completed by appropriately attaching a lead frame or the like.

  Next, the effect | action by providing each opening part 15 is demonstrated based on some Examples.

Example 1
In the liquid crystal display device having the structure shown in FIGS. 1 and 2, the dot matrix type liquid crystal in which each first electrode 11 is a pixel electrode of approximately 0.42 mm square and the mutual interval (pixel interval) is 0.03 mm. A display device was produced. Each first electrode 11 is provided with openings 15 in any of the four patterns shown in FIG. That is, the alignment films 13 and 14 were rubbed, and the first substrate 1 and the second substrate 2 were bonded so that the rubbing direction was antiparallel. The orientation direction of the liquid crystal molecules at the center of the liquid crystal layer 3 was set to the upward direction (12 o'clock direction) on the paper surface as shown in FIG. A plurality of openings 15 are provided for each first electrode 11. For comparison, an electrode not provided with the openings 15 was also formed adjacent to the first electrode 11 provided with the plurality of openings 15. The pretilt angle of the liquid crystal layer 3 was 89.9 °. A voltage is applied between the first electrode 11 and the second electrode 12 by multiplex driving under the conditions of 1/64 duty, 1/9 bias, and frame frequency of 130 Hz for the liquid crystal display device thus manufactured. did. The multiplex waveform was a frame inversion waveform.

  FIG. 3 shows a microscope observation image of the pixel portion of the liquid crystal display device according to Example 1 described above. In any of FIGS. 3A to 3D, in a pixel formed by an electrode having no opening 15 (shown on the upper side in the drawing), a dark region is randomly observed even in the center of the pixel. . Such random dark areas reduce display uniformity in appearance observation. On the other hand, when the opening 15 is a “vertical slit” as shown in FIG. 3A and when the opening 15 is a “cross slit” as shown in FIG. It is observed that the dark regions are regularly generated corresponding to the arrangement of the openings 15 without being randomly generated. For this reason, display uniformity was very good also in appearance observation.

  When the opening 15 is an “oblique slit” as shown in FIG. 3C, the dark region is generated with a certain degree of regularity in correlation with the arrangement of the openings 15. Observed. Further, the area of the dark region is also smaller than when no opening 15 is provided. Therefore, from the viewpoint of display uniformity, it can be said that a certain effect can be obtained although it does not reach the case of “vertical slit” and “cross slit”. On the other hand, as shown in FIG. 3B, when the opening 15 is a “lateral slit”, the dark region is generated in a state where the regularity is insufficient and it is almost random. For this reason, even in appearance observation, display uniformity was insufficient.

  Next, in the case where each of the openings 15 is “vertical slit”, “horizontal slit”, “diagonal slit”, and “cross slit”, the pretilt angle dependence and multi-frequency dependency of the frame frequency at which display uniformity can be obtained by appearance observation The result of observing the bias ratio dependency in the plex driving condition will be described with reference to FIG. The pretilt angle of the liquid crystal display device was either 89.7 ° or 89.9 °. As drive conditions, the drive waveform was a frame inversion waveform and the duty ratio was 1/64. The driving voltage was set such that the maximum contrast was obtained under any conditions. The measurement temperature is about 40 ° C.

  In FIG. 4, the horizontal axis indicates a slit pattern, and “X slit” means “cross slit”. The vertical axis indicates the frame frequency at which display uniformity can be obtained in appearance. Since there are two types of pretilt angles θp and the bias ratio in the multiplex drive condition is 1/9 bias which is the optimum bias and 1/7 bias which is smaller than that, there are 4 conditions as a whole. Overall, when the bias ratio is 1/9 under the condition of θp = 89.9 ° where the frame frequency becomes high, the case of “vertical slit” indicates the lowest frame frequency, “cross slit”, There is a tendency for the frame frequency to increase in the order of “oblique slit” and “lateral slit”. In addition, it was confirmed that there is almost no difference between the “lateral slit” and the case where the opening 15 is not provided. That is, it has been found that the effect of lowering the frame frequency cannot be obtained. Further, it has been found that when the pretilt angle θp is small, the frame frequency can be lowered in any slit, and the effect is particularly remarkable in cases other than the “lateral slit”. Even when the bias ratio is 1/7, it is possible to reduce the frame frequency as a whole, but it has been found that the effect of “lateral slit” is low. From the above, it was found that display uniformity can be realized at a low frame frequency for slits other than the “lateral slit”, and the “vertical slit” is particularly effective.

(Example 2)
Next, in the liquid crystal display device in which the openings 15 are the above-described “vertical slits”, a frame frequency at which display uniformity is obtained in appearance is observed using a sample in which the arrangement pitch P of each opening 15 is changed. A result is demonstrated based on FIG. The pretilt angle of each sample was 89.9 °. The driving conditions were multiplex driving with a duty ratio of 1/64 and a bias ratio of 1/7 or 1/9, and a frame inversion waveform was used as the driving waveform.

  As shown in FIG. 5, it can be seen that the frame frequency tends to rapidly increase when the arrangement pitch P is 0.2 mm or more regardless of the bias ratio, and the effect of providing the opening 15 is reduced. Therefore, it can be said that the arrangement pitch P is preferably less than 0.2 mm. Further, when the arrangement pitch was narrowed, a region where the frame frequency could be lowered most was observed from 0.15 mm to 0.1 mm, and when the arrangement pitch was set to 0.05 mm, a tendency to turn up again was observed. Therefore, it can be said that the arrangement pitch P is more preferably 0.1 mm or more and less than 0.2 mm.

  Although not shown, the case where the opening 15 is the above-described “cross slit” was also examined. As a result, the same effect can be obtained by setting the arrangement pitch P twice as compared with the case of the “vertical slit”. I understood that. That is, the setting of the arrangement pitch P is preferably 0.2 mm or more and less than 0.4 mm, and more preferably 0.2 mm to 0.3 mm.

(Example 3)
In the liquid crystal display device having the structure shown in FIGS. 1 and 2, a liquid crystal display device in which each first electrode 11 is a segment type pixel electrode was manufactured. Each first electrode 11 is a 7-segment pixel electrode as shown in FIG. Each first electrode 11 is provided with a plurality of openings 15 in any of the four patterns shown in FIG. Note that an opening 15 may be provided in the second electrode 12 corresponding to the common electrode in the segment type liquid crystal display device. The alignment treatment was the same as in Examples 1 and 2, and the pretilt angle of the liquid crystal layer 3 was 89.7 ° or 89.9 °. The liquid crystal display device thus manufactured has a duty ratio of 1/64, a bias ratio of 1/7 or 1/9, and a first electrode by multiplex driving that is set by appropriately changing the frame frequency. A voltage was applied between 11 and the second electrode 12. The multiplex waveform was a frame inversion waveform. The driving voltage was set such that the maximum contrast was obtained under any conditions. The measurement temperature is about 40 ° C.

  The measurement results are shown in FIG. In FIG. 6, the horizontal axis indicates a slit pattern, and “X slit” means “cross slit”. The vertical axis indicates the frame frequency at which display uniformity can be obtained in appearance. Since there are two types of pretilt angles θp and the bias ratio in the multiplex drive condition is 1/9 bias which is the optimum bias and 1/7 bias which is smaller than that, there are 4 conditions as a whole. As shown in FIG. 6, in the case of “vertical slit”, the frame frequency can be set to the lowest, and then the frame frequency tends to be set lower in the order of “cross slit”, “oblique slit”, and “lateral slit”. It can be seen. Also in this example, it was confirmed that the “lateral slit” has almost no difference from the case where the opening 15 is not provided. Further, the pretilt angle dependency is the same as that in the first and second embodiments (dot matrix type) with respect to the bias ratio dependency, but it is understood that the frame frequency at which display uniformity can be obtained is high overall. It was.

(Example 4)
Next, in the liquid crystal display device in which the above-described “vertical slit” openings 15 are provided in the segment-type first electrode 11 as in the second embodiment, the arrangement pitch P of each opening 15 is changed. The results of observing the frame frequency at which display uniformity can be obtained from the appearance using the prepared samples will be described. The pretilt angle of each sample was 89.7 ° or 89.9 °. The driving conditions were multiplex driving with a duty ratio of 1/64 and a bias ratio of 1/7 or 1/9, and a frame inversion waveform was used as the driving waveform.

  As shown in FIG. 7, in any pretilt angle and bias ratio, the frame frequency tended to decrease as the arrangement pitch P decreased. Further, it was found that the change in the frame frequency due to the change in the arrangement pitch P appears more markedly when the bias ratio is lowered. From this result, it can be said that when the opening 15 of the “vertical slit” is provided in the segment type first electrode 11, the arrangement pitch P is preferably less than 0.2 mm. As a result of appearance observation, the arrangement pitch P is preferably larger than 40 μm from the viewpoint of a decrease in transmittance due to a decrease in aperture ratio.

  Although not shown, the case where the opening 15 is the “cross slit” is also examined. As in the case of the “vertical slit”, the frame frequency at which display uniformity can be obtained as the arrangement pitch P decreases. Was confirmed to decrease. That is, the setting of the arrangement pitch P is preferably larger than 0.1 mm and smaller than 0.3 mm.

(Example 5)
In some liquid crystal display devices, a dot matrix type display unit and a segment type display unit are mixed. In this case, the dot matrix type display unit and the segment type display unit can be driven by separate driving circuits, but it is more advantageous to drive by a common driving circuit in terms of cost reduction. As described in the first to fourth embodiments, it is known that display uniformity can be obtained at a lower frame frequency when the dot matrix type display unit is used than when the segment type display unit is used. Therefore, when the opening 15 is introduced in a liquid crystal display device in which a dot matrix type display unit and a segment type display unit are mixed, it is possible to set a frame frequency at which display uniformity in the segment type display unit can be obtained. Necessary.

  On the other hand, since the dot matrix type display portion has a gap between the pixels, the effective aperture ratio is originally low, and the transmittance is lower than that of the segment type display portion. The aperture ratio is approximately 85% under the conditions described in the first and second embodiments, that is, the condition where one pixel is approximately 0.42 mm square and the pixel interval is 0.03 mm.

  Further, in the liquid crystal display device in which the dot matrix type display unit and the segment type display unit are mixed, a configuration in which the opening 15 is provided only in the segment display unit may be employed. Alternatively, by setting the arrangement pitch of the openings 15 in the segment type display unit to be relatively smaller than the arrangement pitch of the openings 15 in the dot matrix type display unit, the frame frequency at which the display uniformity in both display units can be obtained. A configuration of matching can also be adopted.

(About the effect of the difference in the shape of the opening)
According to the above-described embodiment and each example, in the case of multiplex driving of a vertical alignment type liquid crystal display device having a pretilt angle close to 90 °, in the longitudinal direction of each opening 15 and the center of the liquid crystal layer 3 It was shown that the frame frequency can be lowered while maintaining display uniformity by crossing the alignment direction of the liquid crystal molecules at an angle smaller than orthogonal (90 °). Next, a theoretical explanation will be given as to whether the difference in the shape of the opening 15 causes a difference in the effect of reducing the frame frequency while maintaining display uniformity.

  As shown in FIG. 9 described above, when a side (edge) in a direction orthogonal to the alignment direction (corresponding to the rubbing direction) of the liquid crystal molecules in the center of the liquid crystal layer is long in the electrode, darkening occurs near that side. A region appears and display uniformity (display quality) is degraded. In the vicinity of the edge, the rubbing direction on the substrate surface and the direction in which the liquid crystal molecules are controlled by an oblique electric field generated when a voltage is applied to the liquid crystal layer are 180 ° different from each other. The director rotates 180 °. It is considered that the orientation of the liquid crystal molecules becomes non-uniform due to factors such as the direction of rotation being not regular at this time, thereby producing a dark region and lowering the display uniformity. Further, it is considered that a dark region is generated in a wider area depending on the shape of the electrode.

  Therefore, it is considered effective to devise the electrode structure so that such an edge is as short as possible. According to this concept, it is considered effective to provide the electrode with the opening 15 (vertical slit) shown in FIG. 2A or the opening 15 (oblique slit) shown in FIG. That is, it is effective to regularly provide a plurality of openings 15 for each electrode so that there are many edges arranged at an angle smaller than orthogonal to the rubbing direction.

  On the other hand, in the case of the opening 15 (cross slit) shown in FIG. 2D described above, a lot of local regions surrounded by the electric field non-application region are formed in the electrode. Even if the alignment disorder of the liquid crystal molecules occurs, it is considered that the effect of isolating it from the liquid crystal molecules in the adjacent region can be obtained. This will be described in detail with reference to FIG.

  FIG. 8A schematically shows the electrode and the liquid crystal molecules in the liquid crystal layer when the opening 15 is not provided. Here, it is assumed that a vertical alignment film is formed on each of the upper and lower electrodes 111 and 112, and the alignment process is performed in an anti-parallel manner in the horizontal direction of the drawing by rubbing them. When a voltage is applied between the electrodes 111 and 112, it is considered that liquid crystal molecules are uniformly reoriented horizontally around the center of the liquid crystal layer 3 as shown in the figure. However, if non-uniform orientation occurs in the in-plane direction with respect to the substrate surface, such as near the edge of the electrode, the non-uniform orientation propagates to the region that has been re-orientated in the horizontal orientation, and is displayed in a wide range Defects occur.

  FIG. 8B schematically shows the electrode and the liquid crystal molecules in the liquid crystal layer when the opening is provided. Here, it is assumed that a vertical alignment film is formed on each of the first electrode 11 and the second electrode 12, and the alignment process is performed in an antiparallel manner in the left-right direction on the paper surface by rubbing them. Further, it is assumed that a plurality of openings 15 are regularly provided only in the first electrode 11. When the illustrated configuration is used, the alignment of the liquid crystal molecules in the liquid crystal layer 3 can partially maintain the vertical alignment state corresponding to the arrangement of the openings 15. By locally surrounding the liquid crystal layer 3 with a region that maintains such a vertical alignment state, even if non-uniform alignment occurs, the region is shielded from the surroundings so that it does not propagate outside. Can do. Thereby, it is considered that the alignment uniformity of the liquid crystal layer 3 can be improved and the display uniformity can be ensured. However, the opening 15 in the case of a cross slit has higher alignment uniformity when the longitudinal direction is not perpendicular to the rubbing direction. Therefore, for example, as shown in FIG. 2D, it is considered effective to arrange the opening 15 so that the longitudinal direction thereof has an angle of 45 ° with respect to the rubbing direction.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously. For example, in the above-described embodiments and examples, a preferable numerical example of the length S in the short direction of each opening 15 is set to 0.01 mm, but the numerical value of S is not limited to this. The setting range of the length S is preferably 0.005 mm or more and 0.03 mm or less. The length L of each opening 15 in the longitudinal direction is not particularly limited, but it is preferable that the length L is twice or more the length S. Furthermore, although the distance between the adjacent openings 15 in the longitudinal direction (distance between the short edges) Ls is set equal to the length S in the above, the value of Ls is not limited to this. The mutual distance Ls may be 0 mm. That is, a plurality of openings may be connected in the longitudinal direction to form one opening. It is also preferable that the inter-distance Ls is not more than twice the length S. In addition, as an example of the case where each opening is a cross slit, a cross-shaped object in which the first part and the second part intersect each other at approximately 90 ° has been shown, but the first part and the second part The formed angle is not limited to 90 °.

  DESCRIPTION OF SYMBOLS 1 ... 1st board | substrate, 2 ... 2nd board | substrate, 3 ... Liquid crystal layer, 4 ... 1st polarizing plate, 5 ... 2nd polarizing plate, 6 ... 1st viewing angle compensation plate, 7 ... 2nd viewing angle compensation plate, 8 ... Seal Materials: 10 ... Spacer, 11 ... First electrode, 12 ... Second electrode, 13, 14 ... Alignment film, 15 ... Opening, 16 ... Orientation direction of liquid crystal molecules in the center of the liquid crystal layer

Claims (6)

A liquid crystal display device that operates by multiplex driving,
A first substrate having a first electrode on one side;
A second substrate having a second electrode on one side and disposed opposite to the first substrate;
A liquid crystal layer disposed between the first electrode of the first substrate and the second electrode of the second substrate;
Including
A pixel is defined in a region where the first electrode and the second electrode overlap,
The first electrode has a plurality of first openings in the pixel that extend in the first direction and are periodically arranged.
The liquid crystal layer has a pretilt angle set to 89.7 ° or more and less than 90 °,
The angle formed between the longitudinal direction of each of the plurality of first openings and the alignment direction of the liquid crystal molecules at the center of the liquid crystal layer was set to 0 ° to 45 ° .
Liquid crystal display device. The angle formed between the longitudinal direction of each of the plurality of first openings and the alignment direction of liquid crystal molecules at the center of the liquid crystal layer was set to approximately 0 °.
The liquid crystal display device according to claim 1. The longitudinal direction of each of the plurality of first openings, and a 4 5 ° the angle between the alignment direction of liquid crystal molecules in the center of the liquid crystal layer,
The liquid crystal display device according to claim 1. In the plurality of first openings, a distance P between two first openings adjacent in a second direction orthogonal to the first direction is 0.04 mm or more and less than 0.2 mm.
The liquid crystal display device according to claim 1. The plurality of first openings have a width in a second direction orthogonal to each of the first directions of 0.005 mm or more and 0.03 mm or less, and two first openings adjacent to each other in the first direction. The mutual distance is not more than twice the width in the second direction,
The liquid crystal display device according to claim 1.   The first electrode has a plurality of second openings arranged periodically in the pixel,
  Each of the plurality of second openings is arranged to intersect with any of the plurality of first openings.
  The liquid crystal display device according to claim 1.