JP6145479B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a vertical alignment type liquid crystal cell.

  The “vertical alignment” type liquid crystal display element, in which the liquid crystal molecular alignment in the liquid crystal layer of the liquid crystal cell is perpendicular to the substrate, has a very good black level when no voltage is applied. By introducing an optical compensator having a negative optical anisotropy having an appropriate parameter between the polarizing plates, a very good viewing angle characteristic is obtained.

  One type of vertical alignment type liquid crystal display element is a monodomain vertical alignment type liquid crystal display element. In the monodomain vertical alignment type element, the alignment is controlled so that the alignment state in the liquid crystal layer becomes uniform regardless of the presence or absence of voltage application. In order to prevent alignment defects when a voltage is applied, it is necessary to provide a pretilt angle so that the liquid crystal molecules are slightly inclined from the vertical to the substrate even when no voltage is applied.

  Such alignment control methods include “metal oxide oblique deposition method” in which a SiOx film is deposited on the alignment films disposed on the inner surfaces of the upper and lower substrates from an oblique direction of the substrate, and a polymer alignment film such as polyimide. A method of performing a rubbing process after coating on a substrate is conceivable. The rubbing process is advantageous in production. However, in the rubbing process similar to the manufacturing process of the TN liquid crystal display element, streak-like scratches are often generated in the rubbing direction, and there is a concern that the display quality is remarkably deteriorated.

  The inventors of the present application have proposed an alignment processing technique in which a scratch during rubbing is suppressed in Patent Document 1. By the method disclosed in this document, for example, it is possible to realize a monodomain vertical alignment type liquid crystal display element having a pretilt angle of 88.5 ° to 89.5 ° and in which defects are suppressed.

  Another type of vertical alignment type liquid crystal display element is a multi-domain vertical alignment type liquid crystal display element. In the multi-domain vertical alignment type element, a plurality of liquid crystal molecule alignment directions are given within one pixel, and the viewing angle characteristics of the display element when a voltage is applied can be improved.

  As a method for controlling the multi-domain alignment, for example, in Patent Document 2 and Patent Document 3, a rectangular opening is provided in a part of the electrodes on the inner surfaces of the upper and lower substrates constituting the pixel, and a voltage is applied in the vicinity of the opening. “An oblique electric field alignment control method” has been proposed in which the alignment direction of liquid crystal molecules is controlled by an oblique electric field.

  One of the driving methods for the vertical alignment type liquid crystal display element is a multiplex driving method. For the current (direct) multiplex drive method, an outline of the main specific method is described in, for example, the document “Electric drive method of LCD” (by Takashi Sugiyama, Keisuke Kobayashi, Magazine: Display and Imaging, 1994, Vol. 3, pp 117-131, published by Science Communications International).

  The most common driving method is the “optimal bias method”. In a liquid crystal display (LCD), the electro-optic response of an element is determined by the effective voltage, and AC driving (voltage average is 0) to prevent deterioration of the element performance is fundamental. As shown in FIG. 9A, “intra-frame inversion driving (or one-line inversion driving)” (hereinafter, this driving waveform is referred to as an A waveform) in which polarity inversion is performed during selection of one line, As shown in FIG. 9C, “frame inversion driving” (hereinafter referred to as “B waveform”) that performs polarity inversion for each frame as shown in FIG. “N-line inversion drive” (hereinafter referred to as this drive waveform) in which polarity inversion is performed every N lines in order to reduce the crosstalk (second-type crosstalk in the above-mentioned literature) to the display pattern that occurs during high-duty driving. Referred to as a waveform), and the like.

  9A to 9C show drive waveforms applied between the upper and lower electrodes of one pixel. In the current multiplex drive LCD, a B waveform that consumes the lowest power during driving is widely used.

  Further, as a method of reducing the “frame response” phenomenon that occurs when the response speed of the liquid crystal display element is high, an active addressing method in which a plurality of selection times are allocated within one frame, or one frame disclosed in, for example, Patent Document 4 is used. Among them, there is a “multiple line simultaneous selection method” (hereinafter, this drive waveform is referred to as an MLS waveform) in which N lines are simultaneously selected. In particular, this is often used for driving a high-speed response STN-LCD having a duty exceeding 1/32 (duty number greater than 32).

JP 2005-234254 A JP-A-3-259121 Japanese Patent No. 3834304 Japanese Patent No. 3119737

  In a monodomain vertical alignment type liquid crystal display element, in order to suppress alignment defects and obtain a good display state, the pretilt angle needs to be less than 90 °. Further, as shown in FIG. 10A, when the pretilt angle is larger than 89.5 °, particularly when it is larger than 89.7 °, the maximum transmittance Tmax in the electro-optical characteristics is directed toward the pretilt angle of 90 °. There is a tendency to decrease as the size increases.

  On the other hand, as shown in FIG. 10B, when the multiplex drive is performed, the contrast CR of the element tends to increase as the pretilt angle approaches 90 °. This is considered to be because the steepness near the threshold in the electro-optical characteristics is improved. Note that the data in FIGS. 10A and 10B is disclosed in Japanese Patent Application Laid-Open No. 2005-234254.

  Although it is considered that the pretilt angle is preferably close to 90 ° from the viewpoint of improving the contrast, the transmittance at the time of bright display actually decreases as the pretilt angle approaches 90 °, so that the display quality is deteriorated.

  FIG. 11 shows an example of an appearance display state of a segment display type vertical alignment type liquid crystal display element in which a pretilt angle is set to 89.6 °. Note that the rubbing orientation of the upper substrate is downward in the drawing, and the rubbing orientation of the lower substrate is upward in the drawing. As a driving waveform, a B waveform was applied, and an operation was performed at a frame frequency of 80 Hz under 1/8 duty and 1/4 bias driving conditions. It was found that there was an area that was partially dark within the effective display area of the segment, and the display uniformity was significantly reduced. It is considered that the transmittance decrease in the electro-optical characteristics is due to such a phenomenon.

  On the other hand, in the vertical alignment type liquid crystal display element using the oblique electric field alignment control method as disclosed in Patent Document 3 (Japanese Patent No. 3834304), the display uniformity is reduced and the transmittance is reduced as in the monodomain type. May decrease.

  An object of the present invention is to provide a multiplex-driven multi-domain vertical alignment type liquid crystal display device, which is improved in display uniformity.

According to one aspect of the present invention, (i) A waveform that is 1 line inversion driving, (ii) B waveform that is frame inversion driving, and (iii) C waveform that is N line inversion driving, with a frame frequency of 30 Hz or less. (Iv) When an ON drive waveform, which is an MLS waveform, which is a multi-line simultaneous selection method, is applied, a linear shape parallel to the pixel edge, which is in a different state from the ON display, which is a bright display, in a part of one pixel Rather than a plane-shaped, flowing dark region, an oblique electric field alignment control multi-domain vertical alignment type liquid crystal cell, and a multiplex driving waveform applied to the liquid crystal cell to generate the planar dark region (I) the A waveform having a frame frequency of 60 Hz or more, (ii) the B waveform having a frame frequency of 300 Hz or more, and (iii) the number M of polarity inversion lines is 1. Above, the C waveform having a numerator of 1 or less of the denominator of the duty ratio expressed as 1, the frame frequency of 200 Hz or higher, and (iv) the number of polarity inversion lines M is 1 or higher, and the numerator is expressed as 1. Any one of the C waveform having a duty ratio less than or equal to the denominator and a frame frequency of 300 Hz or more, and (v) the number of simultaneously selected lines N being 2 to 4 and the frame frequency being 150 Hz or more. There is provided a liquid crystal display device having a driving device for applying a waveform to the liquid crystal cell.

  By applying an A waveform, for example, to the oblique electric field alignment control multi-domain vertical alignment type liquid crystal cell at a sufficiently high frame frequency, it is possible to suppress the occurrence of dark regions, thereby improving display uniformity.

FIG. 1 is a schematic sectional view showing a typical structure example of a monodomain vertical alignment type liquid crystal display device. FIG. 2 is a photomicrograph showing the results of the first experiment. FIG. 3 is a photomicrograph showing the results of the second experiment. FIG. 4 is a photomicrograph showing the results of the third experiment. FIG. 5 is a graph that summarizes the conditions under which stable display is possible with each drive waveform. FIG. 6 is a schematic cross-sectional view showing a typical structure example of a multi-domain vertical alignment type liquid crystal display device by oblique electric field alignment control. FIG. 7 is a plan view showing an arrangement example of the openings of the upper and lower electrodes, observed from the normal direction of the display element surface. FIG. 8 is a photomicrograph showing the results of the fourth experiment. 9A to 9C are graphs showing the A waveform, the B waveform, and the C waveform, respectively. FIG. 10A is a graph showing the relationship of the maximum transmittance Tmax to the pretilt angle, and FIG. 10B is a graph showing the relationship of the contrast CR to the pretilt angle. FIG. 11 is a photograph showing an example of a state in which display uniformity of a segment display type vertical alignment type liquid crystal display element is lowered.

  First, first to third experiments in which the display state of the monodomain vertical alignment type liquid crystal display device is examined will be described.

  FIG. 1 is a schematic sectional view showing a typical structure example of a monodomain vertical alignment type liquid crystal display device. Transparent electrodes 4 and 14, insulating films 5 and 15, and vertical alignment films 6 and 16 on which desired patterns are formed are formed on the inner surfaces of the upper glass substrate 3 and the lower glass substrate 13 facing each other from the substrate side, respectively. Is formed. A liquid crystal layer 7 made of a liquid crystal material having a dielectric anisotropy Δε <0 is sandwiched between the upper and lower vertical alignment films 6 and 16. If necessary, a structure in which one of the upper and lower insulating films 5 and 15 is omitted or a structure in which both of them are omitted may be employed.

  The upper and lower vertical alignment films 6 and 16 are rubbed so that the rubbing direction 8 of the upper vertical alignment film 6 and the rubbing direction 18 of the lower vertical alignment film 16 are antiparallel. . By the rubbing treatment, the pretilt angle θp that is the tilt angle of the liquid crystal molecules at the interface between the alignment films 6 and 16 and the liquid crystal layer 7 is controlled. The pretilt angle θp is determined by the inclination from the surface of the alignment film. When there is no pretilt, θp is 90 °. By rubbing treatment, a desired pretilt angle θp in the range of 88.5 ° to 89.9 ° is given to form a liquid crystal cell of monodomain vertical alignment. It should be noted that monodomain alignment can also be achieved by rubbing only one side of the upper and lower alignment films.

  As the vertical alignment films 6 and 16, it is preferable to use a polymer material having a surface free energy of 35 N / m to 39 N / m. By using such a material as the vertical alignment film, rubbing scratches on the surface of the alignment film are suppressed. Such a rubbing treatment method is disclosed in the column “Best Mode for Carrying Out the Invention” in Japanese Patent Application Laid-Open No. 2005-234254.

  Polarizers 1 and 11 are bonded to the outside of the upper and lower glass substrates 3 and 13 via viewing angle compensation plates 2 and 12, respectively. The polarizing plates 1 and 11 are arranged in crossed Nicols so that the absorption axis is approximately 45 ° with respect to the rubbing direction in the display surface. In addition, if necessary, a structure in which one of the upper and lower viewing angle compensation plates 2 and 12 is omitted may be employed.

  A liquid crystal cell 21 is configured including the glass substrates 3 and 13, the transparent electrodes 4 and 14, the vertical alignment films 6 and 16, the liquid crystal layer 7, and the insulating films 5 and 15 as necessary. The driving device 31 applies a driving waveform to the transparent electrodes 4 and 14 of the liquid crystal cell 21 to control the display state.

  Next, the specific apparatus configuration used in the first to third experiments will be described. A segment display type was used as the display element. The insulating film is not provided between the transparent electrode and the vertical alignment film. The vertical alignment film was formed by flexographic printing using a vertical alignment film A manufactured by Chisso Petrochemical. For the rubbing treatment, a rubbing cloth made of cotton was used, and the rubbing strength was adjusted by appropriately changing the rubbing conditions, whereby the pretilt angle θp was set to a value of 88.5 ° to 89.9 °. The rubbing direction of the upper and lower substrates was antiparallel when the upper and lower substrates were bonded.

  The liquid crystal layer was adjusted to have a thickness of 4 μm, and the upper and lower substrates were bonded together to produce an empty cell. As a liquid crystal material, a material having a dielectric anisotropy Δ∈ <0 and a refractive index anisotropy Δn = 0.15 made by Merck was vacuum-injected into an empty cell. Thereafter, the inlet was sealed, and heat treatment was performed at a temperature equal to or higher than the isotropic phase temperature of the liquid crystal material for about 1 hour. The absorption axes of the upper and lower polarizing plates were arranged so as to be approximately 45 ° with respect to the liquid crystal molecule orientation direction in the center of the liquid crystal layer thickness direction.

  In the first to third experiments, it was examined how the dependence of the display state on the frame frequency changes when the duty ratio, drive waveform, and pretilt angle are changed. The drive waveform was applied between the upper and lower electrodes from the arbitrary waveform generator Biomation 2202A via an amplifier made by FLC. The waveform is such that the ON waveform is applied to all segments. About the upper half of the S-shaped segment was observed with a microscope. In addition, the measured value by the crystal rotation method is used as the pretilt angle.

  First, a first experiment in which the duty ratio is changed will be described. In the first experiment, a B waveform was applied to a liquid crystal cell having a pretilt angle of 89.6 ° while changing the duty ratio. The bias ratio is also changed according to the duty ratio.

  FIG. 2 shows the result of the first experiment. The micrographs of the upper half of the S-shaped segment are shown side by side for each frame frequency and duty ratio condition. In the photograph, the S-shape is reversed because the liquid crystal display element was observed from the back side.

  From the left side, the frame frequency is aligned with 30 Hz, 60 Hz, 100 Hz, 150 Hz, 200 H, and 300 Hz in the row direction, and from the upper side in the column direction, the duty ratio and the bias ratio are 1/4 bias with 1/4 duty, 1/4 bias at 1/8 duty, 1/5 bias at 1/16 duty, 1/6 bias at 1/32 duty, 1/9 bias at 1/64 duty, 1/11 bias at 1/120 duty Are lined up. Note that the larger the duty number, which is the denominator of the duty ratio (the larger the number of scanning lines), the higher the duty (or the higher the duty ratio).

  When the frame frequency is 30 Hz, a flowing dark region (a phenomenon in which a shadow generated in the segment display portion is flowing) is observed at a high duty of 1/16 duty or more, which cannot be identified in the photograph. However, a fixed dark region was observed at 1/4 duty and 1/8 duty. In observation at a frame frequency of 30 Hz, the area of the dark region was the widest at ¼ duty and seemed to become narrower as the duty became higher. However, any dark area causes display non-uniformity in appearance.

  By setting the frame frequency to 60 Hz, the dark region was fixed under all the duty conditions. Again, there was a tendency for the dark area to become smaller as the duty becomes higher.

  When the frame frequency is further increased, the dark region can be removed at 100 Hz or higher at 1/120 duty, 150 Hz or higher at 1/32 duty and 1/64 duty, and 200 Hz or higher at 1/4 to 1/16 duty. .

  Thus, it was found that by setting the frame frequency sufficiently high at any duty ratio, the dark region is removed and a good stable display state can be obtained. The frame frequency from which the dark region is removed becomes lower as the duty becomes higher.

  Next, a second experiment in which the drive waveform is changed will be described. In the second experiment, a liquid crystal cell having a pretilt angle of 89.6 ° was applied to an A waveform, a B waveform, a C waveform, and a 1/16 duty condition MLS waveform with a 1/16 duty, 1/5 bias drive condition. Was applied. Note that the polarity of the C waveform is inverted when the number of polarity inversion lines is M = 7, and the number of simultaneously selected lines in the MLS waveform is N = 2.

  Here, the reason why the 1/16 duty is selected is that, in the first experiment, the dark region that causes the display non-uniformity is the largest when the 1/4 to 1/16 duty driving is performed. 1/16 duty was selected to represent / 16 duty.

  FIG. 3 shows the result of the second experiment. The micrographs of the upper half of the S-shaped segment are arranged in a matrix for each frame frequency and drive waveform condition. With respect to the row direction, the frame frequency is aligned with 30 Hz, 60 Hz, 100 Hz, 150 Hz, 200 Hz, and 300 Hz from the left side, and with respect to the column direction, the drive waveform is aligned with the A waveform, B waveform, C waveform, and MLS waveform from the upper side. Yes.

  When the frame frequency was 30 Hz, a flowing dark region was seen in all the waveforms, and it was observed that the brightness was constantly changing.

  When the frame frequency was 60 Hz, a clear difference appeared depending on the drive waveform. In the B waveform, the C waveform, and the MLS waveform, a fixed dark region was observed, but in the A waveform, no such dark region was observed. Even in the B waveform, the C waveform, and the MLS waveform, the location where the dark region appears is different for each waveform, and the dark region is most widely distributed in the B waveform, and is narrowed in the order of the C waveform and the MLS waveform.

  In the C waveform and the MLS waveform, when the frame frequency was set to 100 Hz, the dark region was hardly observed. For the B waveform, when the frame frequency was set to 200 Hz, it was possible to remove the dark region.

  In the frequency region above the frame frequency from which the dark region is removed, display uniformity is maintained. That is, when the A waveform has a frame frequency of 60 Hz or higher, the C waveform and MLS waveform have a frame frequency of 100 Hz or higher, and the B waveform has a frame frequency of 200 Hz or higher, the dark region is not observed. Is preserved.

  Similar experiments were performed under the conditions of 1/4 duty and 1/8 duty, but almost the same tendency as 1/16 duty was confirmed except that a fixed dark region was generated when the frame frequency was 30 Hz.

  It is considered that the dark region is generated because the liquid crystal molecule alignment direction in the liquid crystal layer is deviated from the direction defined by the rubbing direction in the display surface. It has been found that, in any driving waveform, by setting the frame frequency sufficiently high, a good display state in which no dark region is observed can be obtained. It was also found that the frame frequency necessary to avoid the dark region varies depending on the drive waveform, with the A waveform being the lowest, the C waveform and the MLS waveform being subsequently low, and the B waveform being the highest.

  It should be noted that the duty ratio also changes with the A waveform, C waveform (number of polarity inversion lines M = 7), and MLS waveform (number of simultaneously selected lines N = 2, but N = 4 for high duty over 1/64 duty). As a result of the same examination as the first experiment, it was found that even when the duty ratio was changed, the B waveform had the highest frame frequency necessary for display uniformity. The frame frequency required for display uniformity can be lowered in the order of the C waveform, MLS waveform, and A waveform, and the same result as in the second experiment was obtained.

  From the results of the first and second experiments described above, it is considered that the dark region tends to decrease as the high-frequency component of the drive waveform increases. Even at a low frame frequency, it is possible to make the display state uniform by using a drive waveform having a frequency component as high as possible. In particular, the A waveform, the C waveform, and the MLS waveform are considered preferable.

  Next, a third experiment in which the pretilt angle of the liquid crystal display element with antiparallel orientation is changed will be described. In the third experiment, a B waveform having a 1/16 duty and 1/5 bias drive condition was applied to each liquid crystal cell having a different pretilt angle.

  FIG. 4 shows the result of the third experiment. Similar to the first and second experiments, about the upper half of the S-shaped segment is shown side by side for each frame frequency and pretilt angle condition. From the left side in the row direction, the frame frequencies are 30 Hz, 60 Hz, 100 Hz, 150 Hz, 200 Hz, and 300 Hz, and in the column direction, the pretilt angles are 89.9 °, 89.6 °, and 89.3 from the top. It is aligned with °, 89.0 °, and 88.5 °.

  When the frame frequency was 30 Hz, a flowing dark region was observed at a pretilt angle of 89.0 ° to 89.9 ° as observed under the frame frequency of 30 Hz in the first and second experiments. However, in 88.5, no dark region was observed, and a uniform display state was obtained.

  By setting the frame frequency to 60 Hz, the dark region was all fixed. It was found that the area of the dark region is wider when the pretilt angle is close to 90 °. At a frame frequency of 100 Hz, the dark region was removed at a pretilt angle of 89.0 °, and the dark region was gradually narrowed at other pretilt angles.

  At pretilt angles of 89.3 ° and 89.6 °, dark regions were removed at a frame frequency of 200 Hz. However, at a pretilt angle of 89.9 °, the dark region could not be removed even at a frame frequency of 300 Hz.

  Thus, it has been found that as the pretilt angle is larger, dark regions are more likely to occur, and the frame frequency at which dark regions can be removed tends to increase.

  In addition, we conducted experiments with different pretilt angles for other drive waveforms, and combined the results of the above experiments, and examined the conditions for stable display without observing the dark region of the monodomain vertical alignment type liquid crystal display device. .

  As described above, when the pretilt angle of the B waveform was 89.9 °, the dark region could not be removed even at a frame frequency of 300 Hz. However, it was found that the dark region could be removed if the frequency was 380 Hz or higher.

  FIG. 5 is a graph that summarizes the conditions under which stable display is possible with each drive waveform. This graph shows A waveform, B waveform, and C waveform (number of polarity inversion lines M = 7) with 1/16 duty and 1/5 bias, and 1/16 duty MLS waveform (number of simultaneously selected lines N = The result of 2) is shown. The horizontal axis represents the pretilt angle θp in degrees, and the vertical axis represents the frame frequency in Hz. The pretilt angle θp on the horizontal axis is displayed so as to decrease toward the right.

  The upper side of the graph (boundary line) shown for each of the A waveform, the B waveform, the C waveform, and the MLS waveform is an area where display can be performed while suppressing the occurrence of a dark area.

  As described above, a fluid dark region is likely to occur at a frame frequency of about 30 Hz, and the dark region tends to be fixed by setting the frame frequency to 60 Hz or higher. In order to suppress the occurrence of a fluid dark region, it is generally considered that the frame frequency is preferably 60 Hz or more. That is, it is considered that the lower limit of the frame frequency should be 60 Hz for all of the A waveform, B waveform, C waveform, and MLS waveform.

  In driving a normal liquid crystal display element, the drive frequency is rarely set to 50 Hz or less, and often set to 60 Hz or more. From this point of view, it is considered appropriate to set the lower limit of the frame frequency to 60 Hz.

  As described above, the dark region does not occur when the pretilt angle is sufficiently small as about 88.5 °, but is observed when the pretilt angle becomes larger than a certain angle (closer to 90 °). Although the dark region can be removed by sufficiently increasing the frame frequency, the frame frequency necessary for dark region removal increases as the pretilt angle increases.

  Therefore, the frame frequency that becomes the boundary of the region where good display can be performed is 60 Hz in the range of the pretilt angle where the dark region does not occur, and increases from 60 Hz according to the increase in the pretilt angle in the range of the pretilt angle where the dark region occurs. Do it. The pretilt angle at which the dark region starts to occur (the pretilt angle at which the frame frequency rises from 60 Hz in the graph of FIG. 5) and the gradient for increasing the frame frequency are different for each drive waveform.

  From the viewpoint that a dark region hardly occurs up to a large pretilt angle and the frame frequency for removing the dark region can be kept low, the A waveform is most preferable, and then the MLS waveform (the number of simultaneously selected lines N = 2). , C waveform (number of polarity inversion lines M = 7) and B waveform are preferable in this order.

  The graph of each drive waveform shown in FIG. 5 is for 1/16 duty. However, as shown in the first and second experiments, the frame frequency dependency is substantially the same even at 1/4 duty and 1/8 duty. It has also been confirmed that the dependence on the pretilt angle is equivalent. As described above, the dark area is more easily suppressed as the duty becomes higher. Therefore, the gradient of the frame frequency that increases as the pretilt angle increases to suppress the dark area can be reduced.

  Next, the conditions under which each drive waveform can be displayed uniformly while suppressing dark region generation will be described. First, the A waveform will be described. At 1/4 duty or more (particularly at 1/4 to 1/31 duty), when 88.5 ° ≦ θp <89.6 °, uniform display is obtained at a frame frequency of approximately 60 Hz or more, and 89.6 When ° ≦ θp ≦ 89.9 °, uniform display can be obtained at a frame frequency of approximately [120 × (θp−89.6) +60] Hz or more.

  For 89.6 ° ≦ θp ≦ 89.9 °, at 1/32 duty or more (particularly at 1/32 to 1/119 duty), approximately [60 × (θp−89.6) +60] Hz or more. Uniform display is obtained at a frame frequency of 1, and at 1/120 duty or more, uniform display is obtained at a frame frequency of approximately 60 Hz or more.

  Next, the B waveform will be described. At 1/4 duty or more (particularly at 1/4 to 1/31 duty), when 88.5 ° ≦ θp <88.8 °, uniform display is obtained at a frame frequency of approximately 60 Hz or more, and 88.8 When ° ≦ θp ≦ 89.9 °, uniform display can be obtained at a frame frequency of approximately [312 × (θp−88.8) +60] Hz or more.

  For 88.8 ° ≦ θp ≦ 89.9 °, a uniform display can be obtained at a frame frequency of approximately [160 × (θp−88.8) +60] Hz or more at 1/32 duty or more.

  Since the B waveform is most prone to dark regions compared to other waveforms, the lower limit of the frame frequency may be set higher than 60 Hz, for example, 100 Hz. When the lower limit of the frame frequency is set to 100 Hz, the frame frequency is about 100 Hz or more when 88.5 ° ≦ θp <89.0 ° at 1/4 duty or more (particularly at 1/4 to 1/31 duty). Is a condition for obtaining a uniform display. When 89.0 ° ≦ θp ≦ 89.9 °, a frame frequency of approximately [312 × (θp−89.0) +100] Hz or more is a condition for obtaining a uniform display.

  Further, for 89.0 ° ≦ θp ≦ 89.9 °, at 1/32 duty or more (particularly at 1/32 to 1/119 duty), approximately [160 × (θp−89.0) +100] Hz or more. The frame frequency is a condition for obtaining a uniform display. When the duty is 1/120 or more, a frame frequency of approximately 100 Hz or more is a condition for obtaining a uniform display.

  Next, the C waveform will be described. Assuming that the number of polarity inversion lines M = 1 in the C waveform, display uniformity can be realized under substantially the same conditions as the A waveform, and if the number of polarity inversion lines M is 16, which is equal to the number of duties (number of scanning lines), It was found that display uniformity can be realized under the same conditions as the B waveform. Although it is impossible in practice, the case where the number of polarity inversion lines M = 1/2 can be set is equal to the A waveform.

  Further, it was found that when the number M of polarity inversion lines is ½ of the duty number, an intermediate characteristic between the A waveform and the B waveform can be obtained. The smaller the polarity inversion line number M, the closer to the A waveform, the larger the pretilt angle at which the dark region begins to occur, and the lower the frame frequency required for dark region suppression.

  The conditions for obtaining uniform display when the number of polarity inversion lines M = 7 will be described. At 1/4 duty or more (particularly at 1/4 to 1/31 duty), when 88.5 ° ≦ θp <89.2 °, uniform display is obtained at a frame frequency of approximately 60 Hz or more, and 89.2 When ° ≦ θp ≦ 89.9 °, uniform display can be obtained at a frame frequency of approximately [216 × (θp−89.2) +60] Hz or more.

  Further, for 89.2 ° ≦ θp ≦ 89.9 °, at 1/32 duty or more (particularly at 1/32 to 1/119 duty), approximately [110 × (θp−89.2) +60] Hz or more. Uniform display is obtained at a frame frequency of 1, and at 1/120 duty or more, uniform display is obtained at a frame frequency of approximately 60 Hz or more.

  When the number M of polarity inversion lines is large, the condition for obtaining uniform display becomes stricter than when the number M of polarity inversion lines is small. Therefore, uniform display can be obtained even if 1 ≦ M ≦ 6 under the condition that uniform display can be obtained with the number of polarity inversion lines M = 7. Here, since the duty number is 16, the condition described for the case of the polarity inversion line number M = 7 is that the uniform display is obtained when the polarity inversion line number M is ½ or less of the duty number. You can think of it.

  Further, under the condition that a uniform display can be obtained with the B waveform, a uniform display can be obtained even with a C waveform having a polarity inversion line number of 1 or more and a duty number or less.

  Next, the MLS waveform will be described. In the MLS waveform, the number of simultaneously selected lines N = 2 at 1/4 to 1/63 duty, and the number of simultaneously selected lines N = 4 at 1/64 duty or more.

  At 1/4 duty or more (particularly at 1/4 to 1/31 duty), when 88.5 ° ≦ θp <89.3 °, uniform display is obtained at a frame frequency of approximately 60 Hz or more, and 89.3 When ° ≦ θp ≦ 89.9 °, uniform display can be obtained at a frame frequency of approximately [150 × (θp−89.3) +60] Hz or more.

  Further, for 89.3 ° ≦ θp ≦ 89.9 °, at 1/32 duty or more (particularly at 1/32 to 1/63 duty), approximately [75 × (θp−89.3) +60] Hz or more. A uniform display is obtained at a frame frequency of 1 Hz, and a uniform display is obtained at a frame frequency of approximately 60 Hz or more at 1/64 duty or more.

  It can be considered that the higher the number of simultaneously selected lines, the higher the high frequency component. Even when the number of simultaneously selected lines N is set to 3 or 4 at 1/4 to 1/63 duty, a uniform display can be obtained under the above conditions.

  As described above, in the monodomain vertical alignment type liquid crystal display element, conditions for obtaining uniform display can be estimated for each driving waveform. It is possible to improve the problem that the display uniformity is lowered and the transmittance is lowered at a large pretilt angle. In particular, it is effective for suppressing a decrease in transmittance at a pretilt angle of 89.5 ° or more, and particularly at a pretilt angle of 89.7 ° or more. From the viewpoint of realizing uniform display at a low frame frequency, it is preferable to use an A waveform, an MLS waveform, and a C waveform.

  The upper limit of the duty is, for example, about 1/240 duty. Further, the upper limit of the frame frequency is, for example, about 500 Hz.

  Next, a fourth experiment in which the display state of the multi-domain vertical alignment type liquid crystal display device by oblique electric field alignment control is examined will be described.

  FIG. 6 is a schematic cross-sectional view showing a typical structure example of a multi-domain vertical alignment type liquid crystal display device by oblique electric field alignment control. Transparent electrodes 104 and 114, insulating films 105 and 115, and vertical alignment films 106 and 116 on which desired patterns are formed on the inner surfaces of the upper glass substrate 103 and the lower glass substrate 113 facing each other, respectively, from the substrate side. Is formed. A liquid crystal layer 107 made of a liquid crystal material having a dielectric anisotropy Δε <0 is sandwiched between the upper and lower vertical alignment films 106 and 116. Note that, if necessary, a structure in which one of the upper and lower insulating films 105 and 115 is omitted or a structure in which both are omitted may be employed.

  As the vertical alignment films 106 and 116, a polymer material having a surface free energy of 35 N / m to 39 N / m is preferably used, and the vertical alignment films 106 and 116 are not subjected to alignment treatment. Therefore, the pretilt angle is 90 °.

  In the effective display areas of the upper and lower transparent electrodes 104 and 114, rectangular slit openings 108 and 118 are respectively provided in a part of the electrodes, and the opening 108 and the lower electrode 114 of the upper electrode 104 are provided in the display surface. The openings 118 are alternately arranged in one direction at regular intervals.

  FIG. 7 shows an arrangement example of the openings 108 and 118 of the upper and lower electrodes observed from the surface normal direction of the display element. The upper electrode opening 108 is indicated by a thick line, and the lower electrode opening 118 is indicated by a thin line. A plurality of openings 108 of the upper electrode are arranged in a certain cycle in the length direction (left and right direction on the paper surface) to form a row. A plurality of rows of openings 108 are arranged at a constant period in a direction (vertical direction on the paper surface) perpendicular to the length direction.

  The length of one opening 108 is, for example, 90 μm, and the gap between adjacent openings 108 in the row is, for example, 10 μm. The openings 108 are arranged in a row, for example, with a period of 100 μm. The width of one opening 108 is, for example, 20 μm, and the center distance between the rows of openings 108 is, for example, 120 μm. The arrangement of the opening 118 on the lower electrode is the same.

  In the display surface, the upper and lower openings 108 and 118 are arranged such that the upper openings 108 and the lower openings 118 are alternately arranged at regular intervals in a direction perpendicular to the length direction of the openings. Be placed. The center distance between the row of openings 108 and the row of openings 118 adjacent to each other is, for example, 60 μm. With respect to the length direction of the opening, for example, the center of the opening 118 is arranged at the center of the gap between the adjacent openings 108. In addition, about the length direction of an opening, you may connect adjacent openings.

  Thus, by forming openings in the upper and lower transparent electrodes, an electric field having an oblique direction relative to the normal direction of the substrate can be applied between the upper and lower substrates, and the alignment of liquid crystal molecules is controlled by the electric field having the oblique direction. can do.

  Returning to FIG. 6, the description will be continued. Polarizing plates 101 and 111 are bonded to the outside of the upper and lower glass substrates 103 and 113 via viewing angle compensation plates 102 and 112, respectively. The polarizing plates 101 and 111 are arranged in crossed Nicols so that the absorption axis is approximately 45 ° with respect to the length direction of the slit openings 108 and 118 in the display surface, respectively. If necessary, one of the upper and lower viewing angle compensation plates 102 and 112 may be omitted.

  A liquid crystal cell 121 is configured including glass substrates 103 and 113, transparent electrodes 104 and 114, vertical alignment films 106 and 116, a liquid crystal layer 107, and insulating films 105 and 115 as necessary. The drive device 131 applies a drive waveform to the transparent electrodes 104 and 114 of the liquid crystal cell 121 to control the display state.

  Next, a specific apparatus configuration used in the fourth experiment will be described. A segment display type was used as the display element. The insulating film is not provided between the transparent electrode and the vertical alignment film. The vertical alignment film was formed by flexographic printing using a vertical alignment film A manufactured by Chisso Petrochemical. The rubbing process is not performed. The arrangement of the openings on the transparent electrode was as shown in FIG.

  The liquid crystal layer was adjusted to have a thickness of 4 μm, and the upper and lower substrates were bonded together to produce an empty cell. As a liquid crystal material, a material having a dielectric anisotropy Δ∈ <0 and a refractive index anisotropy Δn = 0.15 made by Merck was vacuum-injected into an empty cell. Thereafter, the inlet was sealed, and heat treatment was performed at a temperature equal to or higher than the isotropic phase temperature of the liquid crystal material for about 1 hour. The absorption axis of the upper and lower polarizing plates was arranged to be approximately 45 ° with respect to the length direction of the slit-shaped opening.

  In the fourth experiment, the drive waveform applied to the oblique electric field orientation control type liquid crystal display element is A waveform, B waveform, C waveform (number of polarity inversion lines M = 7), 1/16 duty, 1/5 bias condition Then, the display state when the frame frequency at the on-voltage was changed was observed with a microscope.

  FIG. 8 is a photomicrograph showing the observation results of the fourth experiment. The micrographs are arranged in a matrix for each frame frequency and drive waveform condition. In the row direction, the frame frequencies are aligned with 30 Hz, 60 Hz, 100 Hz, 150 Hz, 200 Hz, and 300 Hz from the left side, and in the column direction, the drive waveforms are aligned with the A waveform, the B waveform, and the C waveform from the upper side.

  At a frame frequency of 30 Hz, a flowing dark region observed in the first experiment or the like was confirmed in all waveforms, and it was found that display uniformity was insufficient.

  At a frame frequency of 60 Hz, the display uniformity is improved by using the A waveform, and the dark region is almost only between the slit opening and the left and right azimuth slits. In this state, it was confirmed that there was no problem in display uniformity even visually. On the other hand, with regard to the B waveform and the C waveform, the flowing dark region was not observed, but it was found that the fixed dark region was observed at random, and the visual appearance was poor.

  When the B waveform was used, it was confirmed by microscopic observation and visual observation that the dark region was completely erased and a uniform display state was obtained by setting the frame frequency to 300 Hz or higher. In the C waveform, uniform display was realized when the frame frequency was 200 Hz or higher.

  As described above, it was found that the use of the A waveform is most effective for uniform display. In addition, when the MLS waveform (the number of simultaneously selected lines N = 2) was used, it was visually confirmed that uniform display could be realized at a frame frequency of 150 Hz or more.

  As in the case of the mono domain described above, the dark region will be suppressed when the high-frequency component of the drive waveform is large. The above condition for 1/16 duty is considered to be effective for higher duty. Further, as in the case of the mono domain, it has been confirmed that the frame frequency dependency is substantially the same at 1/4 to 1/16 duty.

  Regarding the C waveform, the above-described result can be considered to be a condition under which uniform display can be obtained when the number M of polarity inversion lines is ½ or less of the duty number, as in the case of the mono domain. In addition, it is considered that uniform display can be obtained even with a C waveform having a polarity inversion line number of 1 or more and a duty number or less as long as a uniform display is obtained with a B waveform. For the MLS waveform, even if the number N of simultaneously selected lines is 3 or 4, uniform display can be obtained under the above conditions.

  As described above, also in the multi-domain vertical alignment type liquid crystal display device by the oblique electric field alignment control, it is possible to obtain a good display by selecting an appropriate frame frequency according to the driving waveform. From the viewpoint of realizing uniform display at a low frame frequency, it is preferable to use an A waveform, an MLS waveform, and a C waveform.

  As described above, in the mono-domain vertical alignment type liquid crystal display device and the multi-domain vertical alignment type liquid crystal display device by the oblique electric field alignment control, the display uniformity is selected by selecting an appropriate frame frequency according to the driving waveform. Can be improved.

  Examples of liquid crystal display elements to which such technology can be applied include segment display simple matrix drive liquid crystal display elements, dot matrix display simple matrix drive liquid crystal display elements, and segment display simple matrix drive liquid crystal displays in one liquid crystal display element. Examples thereof include a liquid crystal display element including an element portion and a dot matrix display simple matrix driving liquid crystal display element portion.

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

DESCRIPTION OF SYMBOLS 1, 11 Polarizing plate 2, 12 Viewing angle compensator 3, 13 Glass substrate 4, 14 Transparent electrode 5, 15 Insulating film 6, 16 Vertical alignment film 7 Liquid crystal layer 8, 18 Rubbing direction θp Pretilt angle 21 Liquid crystal cell 31 Driving device

Claims (1)

(I) A waveform that is 1 line inversion drive, (ii) B waveform that is frame inversion drive, (iii) C waveform that is N line inversion drive, and (iv) Multiple line simultaneous selection method with a frame frequency of 30 Hz or less. When an on-drive waveform that is a certain MLS waveform is applied, a part of one pixel is generated in a surface shape, not a line shape parallel to the pixel edge, which is different from the on-display that is a bright display. An oblique electric field alignment control multi-domain vertical alignment type liquid crystal cell that generates a flowing dark region;
A drive device for applying a multiplex drive waveform to the liquid crystal cell to prevent the occurrence of the planar dark region, wherein (i) the A waveform having a frame frequency of 60 Hz or more, and (ii) a frame frequency of 300 Hz or more. (Iii) The C waveform having (iii) polarity inversion line number M of 1 or more, ½ or less of the denominator of the duty ratio expressed as 1 and the frame frequency of 200 Hz or more, (iv) polarity The number of inversion lines M is 1 or more, the denominator of the duty ratio expressed as numerator is 1, the C waveform having a frame frequency of 300 Hz or more, and (v) the number N of simultaneously selected lines is 2 or more and 4 or less. A liquid crystal display device comprising: a driving device that applies any one of the MLS waveforms having a frame frequency of 150 Hz or more to the liquid crystal cell.