JP2015179172A - Liquid crystal display device and driving method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving technology that is appropriate for maintaining display evenness when driving a vertical alignment type liquid crystal display device having a structure causing an electrode edge to be flexed into a polygonal line-shape at a driving voltage of an N line inverse waveform.SOLUTION: In a vertical alignment type liquid crystal display device with a pretilt angle less than 90°, a driving voltage of an N line inverse waveform is supplied as the driving voltage, and let a bias value of the driving voltage be B, a frame frequency thereof be f, and a duty number thereof be L, a value of the N is set so as to satisfy a condition of N≤(-0.0572×B+0.9998)×f×(64/L)+(-2.5×B-30.175).

Description

  The present invention relates to a liquid crystal display device and a driving technique thereof.

  For example, a liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 2011-99909 (Patent Document 1) is known as a prior art related to a vertical alignment type liquid crystal display device that operates by multiplex driving. The liquid crystal display device according to this prior art is a vertical alignment type liquid crystal display having a liquid crystal layer in which the pretilt angle given to the liquid crystal molecules is 89.8 ° or more and less than 90 ° and the alignment state is monodomain alignment. The apparatus is configured to perform multiplex driving under a driving condition in which the duty ratio is set to 1/16 or more and the bias value is set to be smaller than the optimum bias value. According to this configuration, a liquid crystal display device capable of lowering the frame frequency while maintaining display uniformity is provided.

  By the way, the above-mentioned patent document 1 discloses mainly suitable conditions when the driving voltage is a frame inversion waveform, and how to set the number N of inversion lines when the driving voltage is an N line inversion waveform. There is no particular disclosure as to whether or not is appropriate. In particular, as disclosed in Japanese Patent Application Laid-Open No. 2009-86214 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2012-93578 (Patent Document 3), the electrode edge has a bent line shape instead of a straight line shape. In a liquid crystal display device, there is no disclosure about a technique for appropriately setting the number N of inversion lines.

JP 2011-99909 A JP 2009-86214 A JP 2012-93578 A

  The specific embodiment according to the present invention is suitable for maintaining display uniformity when a vertical alignment type liquid crystal display device having a structure in which electrode edges are bent in a polygonal line is driven with a drive voltage having an N-line inversion waveform. One of the purposes is to provide a simple driving technique.

[1] A liquid crystal display device according to an aspect of the present invention includes (a) a first substrate and a second substrate that are disposed to face each other, and (b) provided on one surface side of the first substrate, along a first direction. (C) a plurality of second electrodes provided on one side of the second substrate and extending along a second direction intersecting the first direction; and (d) ) A liquid crystal layer provided between each surface of the first substrate and the second substrate and having a pretilt angle of less than 90 ° and substantially vertically aligned; and (e) the plurality of first electrodes and the plurality of second layers. Driving means for supplying a driving voltage for multiplex driving to the liquid crystal layer via the electrodes, and (f) a pixel region in each of the intersecting regions of the plurality of first electrodes and the plurality of second electrodes. And (g) each of the plurality of second electrodes has two electrode edges in plan view. And at least one of the electrode edges is a polygonal line formed by a line segment in which an angle formed by the second direction is greater than 0 ° and less than or equal to 15 °, and (h) the liquid crystal layer is substantially in the center in the layer thickness direction. The liquid crystal molecules are aligned so that the alignment direction of the liquid crystal molecules is oblique to the one electrode edge of the second electrode. (I) The driving means supplies a driving voltage having an N-line inversion waveform as the driving voltage. N ≦ (−0.0572 × B + 0.9998) × f × (64 / L) + (− 2.5 ×) where B is the bias value, f is the frame frequency, and L is the number of duties. B-30.175) is a liquid crystal display device in which the value of N is set so as to satisfy the condition.

[2] A liquid crystal display device according to one aspect of the present invention includes: (a) a first substrate and a second substrate that are disposed to face each other; (C) a plurality of second electrodes provided on one side of the second substrate and extending along a second direction intersecting the first direction; and (d) ) A liquid crystal layer provided between each surface of the first substrate and the second substrate and having a pretilt angle of less than 90 ° and substantially vertically aligned; and (e) the plurality of first electrodes and the plurality of second layers. Driving means for supplying a driving voltage for multiplex driving to the liquid crystal layer via the electrodes, and (f) a pixel region in each of the intersecting regions of the plurality of first electrodes and the plurality of second electrodes. And (g) each of the plurality of second electrodes has two electrode edges in plan view. Of these, at least one electrode edge is a polygonal line formed by connecting a plurality of line segments having the same length, and (h) the liquid crystal layer has an alignment direction of liquid crystal molecules at a substantially center in the layer thickness direction. (I) The drive means supplies a drive voltage having an N-line inversion waveform as the drive voltage, and the bias value is set to be oblique to the one electrode edge of the second electrode. The condition of N ≦ (−0.0025 × B + 0.6433) × f × (64 / L) + (− 8.4165 × B + 13.276), where B is the frame frequency and L is the duty number In the liquid crystal display device, the value of N is set so as to satisfy the above condition.

  According to the configuration of 1 or 2, in order to maintain display uniformity when a vertical alignment type liquid crystal display device having a structure in which electrode edges are bent in a polygonal line is driven with a drive voltage having an N-line inversion waveform. A liquid crystal display device that operates under appropriate driving conditions can be obtained.

[3] In the liquid crystal display device according to 1 or 2, it is also preferable that when the optimum value of the bias value is defined by √L + 1, the bias value B is set to a value smaller than the optimum value.

  Thereby, the effect of reducing the frame frequency can be obtained while maintaining the display uniformity.

[4] In the liquid crystal display device of 1, 2, or 3, the N line inversion waveform is forcibly reversed in polarity to positive or negative after the end of one frame, and the polarity is reversed at the start line of two consecutive frames. It is also preferable that

[5] A driving method of a liquid crystal display device according to one aspect of the present invention includes: (a) a first substrate and a second substrate which are arranged to face each other; (b) a first substrate provided on one surface side of the first substrate; A plurality of first electrodes extending along a direction; and (c) a plurality of second electrodes provided on one surface side of the second substrate and extending along a second direction intersecting the first direction; (D) a liquid crystal layer provided between each surface of the first substrate and the second substrate and having a pretilt angle of less than 90 ° and substantially vertically aligned; and (e) the plurality of first electrodes and the plurality of the plurality of first electrodes. Driving means for supplying a multiplex driving voltage to the liquid crystal layer via the second electrode, and (f) in each of the intersecting regions of the plurality of first electrodes and the plurality of second electrodes A pixel region is defined; (g) each of the plurality of second electrodes includes two regions in plan view; And (h) the liquid crystal layer is formed in a layer thickness direction, and is formed by a line segment in which at least one of the polar edges forms an angle with the second direction that is greater than 0 ° and less than or equal to 15 °. The liquid crystal display device is driven so that the alignment direction of the liquid crystal molecules at substantially the center of the second electrode is oblique to the one electrode edge of the second electrode, and (i) the drive means includes When a drive voltage having an N-line inversion waveform is supplied as a drive voltage, the bias value is B, the frame frequency is f, and the duty number is L, N ≦ (−0.0572 × B + 0.9998) × f In the liquid crystal display device driving method, the value of N is set so as to satisfy a condition of × (64 / L) + (− 2.5 × B−30.175).

[6] A driving method of a liquid crystal display device according to one aspect of the present invention includes: (a) a first substrate and a second substrate arranged to face each other; (b) provided on one surface side of the first substrate; A plurality of first electrodes extending along a direction; and (c) a plurality of second electrodes provided on one surface side of the second substrate and extending along a second direction intersecting the first direction; (D) a liquid crystal layer provided between each surface of the first substrate and the second substrate and having a pretilt angle of less than 90 ° and substantially vertically aligned; and (e) the plurality of first electrodes and the plurality of the plurality of first electrodes. Driving means for supplying a multiplex driving voltage to the liquid crystal layer via the second electrode, and (f) in each of the intersecting regions of the plurality of first electrodes and the plurality of second electrodes A pixel region is defined; (g) each of the plurality of second electrodes includes two regions in plan view; At least one electrode edge of the pole edges is a polygonal line formed by connecting a plurality of line segments having the same length, and (h) the liquid crystal layer has liquid crystal molecules at substantially the center in the layer thickness direction. A method for driving a liquid crystal display device, wherein the alignment direction is obliquely crossed with the one electrode edge of the second electrode, wherein (i) the driving means uses an N-line inversion waveform as the driving voltage. N ≦ (−0.0025 × B + 0.6433) × f × (64 / L) + where B is the bias value, f is the frame frequency, and L is the number of duties. In the liquid crystal display device driving method, the value of N is set so as to satisfy the condition (−8.4165 × B + 13.276).

  According to the configuration of 5 or 6, in order to maintain display uniformity when a vertical alignment type liquid crystal display device having a structure in which the electrode edge is bent in a polygonal line is driven with a drive voltage having an N-line inversion waveform. A method of driving a liquid crystal display device that can be operated under appropriate driving conditions is obtained.

FIG. 1 is a schematic cross-sectional view showing the structure of the liquid crystal display device (liquid crystal panel) of the first embodiment. FIG. 2 is a diagram illustrating a more detailed configuration example of the liquid crystal display device. FIG. 3 is a plan view for explaining a detailed structure of the first electrode and the second electrode of the first embodiment. FIG. 4 is a diagram showing an alignment structure during bright display of the liquid crystal display device of Example 1. FIG. 5 is a table showing the number N of inverted lines that can provide display uniformity at each value of the bias value B and the frame frequency f. FIG. 6 is a graph showing the data shown in FIG. 5 for each bias value B with the horizontal axis representing the frame frequency f and the vertical axis representing the number N of inverted lines. FIG. 7 is a table showing the slope a and the intercept b for each bias value in the linear model equation shown in FIG. FIG. 8 is a graph plotting the bias value dependence of the slope a and the intercept b shown in FIG. FIG. 9 is a graph plotting the bias value dependency of the slope a and the intercept b shown in FIG. FIG. 10 is a graph in which the approximate value obtained by the mathematical formula and the plot of the actually measured value shown in FIG. 6 are superimposed. FIG. 11 is a plan view for explaining a detailed structure of the first electrode and the second electrode of the second embodiment. FIG. 12 is a diagram showing an alignment structure during bright display of the liquid crystal display device of Example 2. FIG. 13 is a table showing the number N of inversion lines that can provide display uniformity at each value of the bias value B and the frame frequency f. FIG. 14 is a graph showing the data shown in FIG. 13 for each bias value B with the horizontal axis representing the frame frequency f and the vertical axis representing the number N of inverted lines. FIG. 15 is a table showing the slope a and the intercept b for each bias value in the linear model equation shown in FIG. FIG. 16 is a graph plotting the bias value dependence of the slope a and the intercept b shown in FIG. FIG. 17 is a graph plotting the bias value dependency of the slope a and the intercept b shown in FIG. FIG. 18 is a graph in which the approximate value obtained by the mathematical formula and the plot of the actually measured value shown in FIG. 6 are superimposed.

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

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing the structure of the liquid crystal display device (liquid crystal panel) of the first 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. 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. Between the first substrate 1 and the second substrate 2, spacers (granular bodies) are arranged in a dispersed manner. By these spacers, the gap between the first substrate 1 and the second substrate 2 is maintained at a predetermined value (for example, about 5 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 thick line shown in the liquid crystal layer 3 schematically shows the orientation direction of the liquid crystal molecules when no voltage is applied. As illustrated, in the liquid crystal display device of this embodiment, the alignment state of the liquid crystal molecules in the liquid crystal layer 3 is monodomain alignment.

  The first electrode 11 has a plurality of strip electrodes extending along a first direction (in this example, a direction orthogonal to the paper surface), and is provided on one surface of the first substrate 1. The second electrode 12 has a plurality of strip electrodes extending along a second direction (in this example, the left-right direction of the paper surface) intersecting the first direction, and is provided on one surface of the second substrate 2. It has been. The first electrode 11 and the second electrode 12 are configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. The liquid crystal display device of the present embodiment is a dot matrix type liquid crystal display device in which each of the locations where the first electrode 11 and the second electrode 12 intersect each other serves as a pixel region.

  The alignment film 8 is provided on one surface side of the first substrate 1 so as to cover the first electrode 11. Similarly, the alignment film 9 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 8 and the alignment film 9, a film (vertical alignment film) that restricts 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 8 and 9 can provide a pretilt angle of an angle very close to 90 ° (about 89.8 ° to 89.95 °) with respect to the liquid crystal molecules of the liquid crystal layer 3. Used. Details of the pretilt angle will be described later.

  FIG. 2 is a diagram illustrating a more detailed configuration example of the liquid crystal display device. The liquid crystal display device shown in FIG. 2 includes a liquid crystal panel 101, a backlight unit 102, a liquid crystal panel drive circuit 103, a backlight unit drive circuit 104, a control device 105, and a temperature sensor 106. It is configured. The liquid crystal panel 101 has the same configuration as the liquid crystal display device shown in FIG. The backlight unit 102 includes a light source such as a white LED and is disposed on the back surface of the liquid crystal panel 101. The liquid crystal panel drive circuit 103 is connected to the liquid crystal panel 101 and supplies a drive voltage (drive power) to the liquid crystal panel 101. The backlight unit drive circuit 104 performs operation control of the backlight unit 102, specifically, lighting / extinguishing, brightness adjustment, and the like. The control device 105 is connected to each of the liquid crystal panel drive circuit 103 and the backlight unit drive circuit 104, and performs operation control thereof. The temperature sensor 106 is set inside or on the surface of the liquid crystal panel 101, the backlight unit 102, or the like, and outputs an electrical signal corresponding to the temperature. A plurality of temperature sensors 106 may be provided. The liquid crystal panel driving circuit 103 and the control device 105 correspond to “driving means”.

  FIG. 3 is a plan view for explaining a detailed structure of the first electrode and the second electrode of the first embodiment. In each figure, the planar shape of each electrode in a plan view from the first substrate 1 side of the liquid crystal panel 101 is shown. As shown in FIG. 3, each 1st electrode 11 is formed in the stripe form extended in the up-down direction in the figure. Each second electrode 12 extends in the left-right direction in the figure, and is formed in a polygonal line shape in which both edges are periodically bent. In the illustrated example, each first electrode 11 is disposed on the front side and each second electrode 12 is disposed on the back side, and a region where each first electrode 11 and each second electrode 12 intersect corresponds to the pixel region 16.

  Both edges of each second electrode 12 are formed by connecting a plurality of line segments having different extending directions at their respective end portions, and a connecting portion between the line segments, that is, a bending point, is formed in each pixel region 16. There are two locations per edge. An angle θ formed by each line segment constituting the edge and the extending direction of each second electrode 12 is preferably greater than 0 ° and equal to or less than 15 °, and is 10 ° in the illustrated example. Further, in the illustrated example, the positions of the two bending points included in each of the upper edge and the lower edge of the pixel region 16 defined by both edges of each second electrode 12 are equal in the left-right direction. The positions of may be different.

  The alignment direction 17 of the liquid crystal molecules at substantially the center in the layer thickness direction of the liquid crystal layer 3 is substantially orthogonal to the extending direction of each second electrode 12 (the left-right direction in the figure). Oblique with electrode edges. The alignment direction 17 is defined by the alignment process direction (for example, the rubbing process direction) for the alignment films 8 and 9. For example, in the present embodiment, the direction of the rubbing process for the alignment film 8 is a direction substantially parallel to the extending direction of each first electrode 11, and the direction of the rubbing process for the alignment film 9 is the extending direction of each second electrode 12. The orientation direction 17 as shown is defined by making the directions substantially orthogonal. In addition, the absorption axes 13 and 14 of the polarizing plates 4 and 5 are arranged so that they are substantially orthogonal to each other and each form an angle of approximately 45 ° with respect to the extending direction of the second electrode 12.

  FIG. 4 is a diagram showing an alignment structure during bright display of the liquid crystal display device of Example 1. In the liquid crystal display device of Example 1, a liquid crystal layer is formed using a liquid crystal material having a negative dielectric anisotropy and a refractive index anisotropy of 0.18, and the layer thickness (cell thickness) is 5 μm. The pretilt angle was 89.8 °. The arrangement of the absorption axis of each polarizing plate is the same as above (see FIG. 3). The electrode width of each first electrode and each second electrode was 450 μm, and the distance between adjacent pixel regions was 30 μm. As shown in the figure, at the upper, left, and right edges of the pixel region, the alignment direction of the liquid crystal molecules due to the oblique electric field generated in the vicinity thereof when an electric field is applied is the alignment of the liquid crystal molecules at the approximate center in the layer thickness direction of the liquid crystal layer. Since it is different from the direction, a region including a dark line is observed. In particular, at the upper edge of the pixel region, two dark lines are observed in the vicinity of the edge, and a state in which these two dark lines intersect in the vicinity of the bending point of the upper edge is observed. Such an alignment structure is generated almost uniformly in a plurality of pixel regions.

  Next, driving conditions of the liquid crystal display device will be described. Here, the liquid crystal display device of Example 1 described above was operated with various driving conditions set. The size of the effective display portion of the liquid crystal display device of Example 1 is 120 mm × 35 mm, and the size of the cell outline is approximately 131 mm × 41.6 mm. Further, a driving voltage having an N-line inversion waveform when the number of scanning lines is 64 is supplied from the driving means, and the voltage value is set to a condition for obtaining the maximum contrast. Also, in consecutive frames, the polarity inversion is forcibly inverted to positive or negative after the end of one frame so that the polarity is reversed on the start line of two consecutive frames. This is to prevent burn-in by bringing the average voltage close to 0V. Appearance was observed only from the front of the liquid crystal display device, and the ambient temperature during observation was 60 ° C. Under these conditions, the bias value B (bias ratio 1 / B) is set to 7 to 9, the frame frequency f is set to 60 to 200 Hz, and the number N of inversion lines is set with the bias value B and the frequency f fixed. When changed, the maximum number N of inversion lines that can provide display uniformity was measured.

  FIG. 5 is a table showing the number N of inverted lines that can provide display uniformity at each value of the bias value B and the frame frequency f. FIG. 6 is a graph showing the data shown in FIG. 5 for each bias value B with the horizontal axis representing the frame frequency f and the vertical axis representing the number N of inverted lines. In the drawing of FIG. 6, a straight line obtained by fitting different plots at each bias value to an actual measurement value by a least square method using a linear model formula of N = a × f + b is also shown. FIG. 7 is a table showing the slope a and the intercept b for each bias value in the linear model equation shown in FIG.

  Since the duty number L is 64 as described above, the optimum value of the bias value B defined by √L + 1 is 9. In each bias value, it is apparent that the number of inversion lines N has the same tendency between the actually measured value and the fitting value with respect to the frame frequency f. It can also be seen that the number N of inversion lines tends to be set larger at a lower frame frequency f as the bias value decreases. That is, it is apparent that the frame frequency f can be set low even with the same number of inversion lines N by decreasing the bias value.

  Since each bias value is considered to have a correlation, the number N of inversion lines is expressed by a functional expression having the frame frequency f and the bias value B as variables. 8 and 9 are graphs plotting the bias value dependence of the slope a and the intercept b shown in FIG. In FIG. 8, it was found that when fitting was performed by the least square method using a linear model formula of a = c × B + d, approximation was possible with a straight line of a = 0.0572 × B + 0.9998. Moreover, in FIG. 9, when fitting by the least squares method with the linear model formula of b = e * B + g, it turned out that it can approximate with the straight line of b = -2.5 * B-30.175.

Using the above approximate expression of the inclination a and the intercept b, the maximum number N of inversion lines in which display unevenness is not observed can be expressed by the following expression.
N = (0.0572 × B + 0.9998) × f + (− 2.5 × B−30.175)
The graph of FIG. 10 shows the approximate value obtained by this mathematical formula and the plot of the actual measurement value shown in FIG. It can be seen that the measured value and the approximate value tend to be almost equal without depending on the bias value.

From the above analysis, it can be seen that the number N of inversion lines in which display unevenness during external observation is not observed is obtained by the following equation.
N ≦ (0.0572 × B + 0.9998) × f + (− 2.5 × B−30.175)

The above analysis result is considered to be because the substantial high-frequency component is increased and the frame frequency f is reduced by decreasing the number N of inversion lines. From this, it can be considered that an increase in the number of duties has the same effect. Considering that the high frequency component increases as the duty number increases, the above analysis result is for the case where the duty number is 64. For example, when the duty number becomes 128, the double high frequency component is included. Will be. Therefore, it is considered that the same effect can be obtained even if the frame frequency f is halved compared to the case where the duty number is 64. From this point of view, the number N of inversion lines can be expressed by the bias value B, the frame frequency f, and the duty number L as follows. However, the number N of inversion lines is greater than 1 and less than the duty number L.
N ≦ (0.0572 × B + 0.9998) × f × (64 / L) + (− 2.5 × B−30.175)

  The above analysis results are obtained when the ambient temperature is 60 ° C., and the number N of inversion lines can be set larger due to the temperature drop. Therefore, the bias value, the frame frequency, and the number N of inversion lines may be variably set according to the ambient temperature detected by the temperature sensor 106 connected to the driving unit. In addition, the above analysis result was a case where the angle θ formed between the extending direction of each second electrode 12 and the line segment constituting the electrode edge was set to 10 °. If an oriented structure where dark lines intersect is obtained, the same effect as described above can be obtained. This angle θ should be larger than 0 °, more preferably 5 ° or more. In addition, it is preferable to set the angle θ to 15 ° or less so that the bending of the electrode edge of each second electrode 12 is not visually recognized in appearance observation, that is, in order to be visually recognized equivalent to the case where a conventional striped electrode is used. .

(Second Embodiment)
Next, a second embodiment will be described. The basic structure of the liquid crystal display device (liquid crystal panel) is the same as that of the first embodiment (see FIGS. 1 and 2), and the description thereof is omitted here.

  FIG. 11 is a plan view for explaining a detailed structure of the first electrode and the second electrode of the second embodiment. In each figure, the planar shape of each electrode in a plan view from the first substrate 1 side of the liquid crystal panel 101 is shown. Each first electrode 11 extends in the vertical direction in the drawing as a whole, and is formed in a polygonal line shape in which both electrode edges are periodically bent. Similarly, each second electrode 12 extends in the left-right direction in the drawing as a whole, and is formed in a polygonal line shape in which both electrode edges are periodically bent. In the illustrated example, each first electrode 11 is disposed on the front side and each second electrode 12 is disposed on the back side, and a region where each first electrode 11 and each second electrode 12 intersect corresponds to the pixel region 16.

  Both electrode edges of each first electrode 11 are configured by connecting a plurality of line segments having different extending directions at their respective end portions, and a connecting portion between the line segments, that is, a bending point, is formed in each first electrode. 11 are periodically arranged along the extending direction. The angle formed between each line segment and the extending direction of each first electrode 11 is approximately 45 °, the angle formed between the line segments joined at the bending point is approximately 90 °, and the length of each line segment is equal. The distance between adjacent bending points, that is, the arrangement pitch of the bending points is, for example, 150 μm.

  Similarly, both electrode edges of each second electrode 12 are configured by connecting a plurality of line segments having different extending directions at their respective end portions, and the connecting portions of the line segments, i.e., bending points, respectively. The second electrodes 12 are periodically arranged along the extending direction. The angle formed between each line segment and the extending direction of each second electrode 12 is approximately 45 °, the angle formed between the line segments coupled at the bending point is approximately 90 °, and the lengths of the line segments are equal. The distance between adjacent bending points, that is, the arrangement pitch of the bending points is, for example, 150 μm. The arrangement pitch of the bending points may be different between each first electrode 11 and each second electrode 12.

  The alignment direction 17 of the liquid crystal molecules at the approximate center in the layer thickness direction of the liquid crystal layer 3 is substantially orthogonal to the extending direction of each second electrode 12 (the horizontal direction in the drawing). The orientation direction 17 is oblique to the extending directions of the line segments that respectively constitute the electrode edges of the first electrodes 11 and the electrode edges of the second electrodes 12. The alignment direction 17 is defined by the alignment process direction (for example, the rubbing process direction) for the alignment films 8 and 9. For example, in the present embodiment, the direction of the rubbing process for the alignment film 8 is a direction substantially parallel to the extending direction of each first electrode 11, and the direction of the rubbing process for the alignment film 9 is the extending direction of each second electrode 12. The orientation direction 17 as shown is defined by making the directions substantially orthogonal. In addition, the absorption axes 13 and 14 of the polarizing plates 4 and 5 are arranged so that they are substantially orthogonal to each other and each form an angle of approximately 45 ° with respect to the extending direction of the second electrode 12.

  FIG. 12 is a diagram showing an alignment structure during bright display of the liquid crystal display device of Example 2. In the liquid crystal display device of Example 2, a liquid crystal layer is formed using a liquid crystal material having a negative dielectric anisotropy and a refractive index anisotropy of 0.18, and the layer thickness (cell thickness) is 5 μm. The pretilt angle was 89.8 °. The arrangement of the absorption axis of each polarizing plate is the same as above (see FIG. 11). The electrode width of each first electrode and each second electrode was 450 μm, and the distance between adjacent pixel regions was 30 μm. As shown in the drawing, dark lines are included in the vicinity of the edge where the angle between the alignment direction of the liquid crystal molecules due to the oblique electric field generated when the electric field is applied and the alignment direction of the liquid crystal molecules at the approximate center in the layer thickness direction is greater than 45 ° A region is observed. In particular, at the upper edge of the pixel area where the angle between them is 135 ° or more, two dark lines are observed in the vicinity of the edge, and it is observed that these two dark lines intersect near the bending point of the upper edge. The Such an alignment structure is generated almost uniformly in a plurality of pixel regions.

  Next, driving conditions of the liquid crystal display device will be described. Here, the liquid crystal display device of Example 2 described above was operated with various driving conditions set. Specific operating conditions are the same as in the case of the first embodiment described above, and a description thereof will be omitted here.

  FIG. 13 is a table showing the number N of inversion lines that can provide display uniformity at each value of the bias value B and the frame frequency f. FIG. 14 is a graph showing the data shown in FIG. 13 for each bias value B with the horizontal axis representing the frame frequency f and the vertical axis representing the number N of inverted lines. In the drawing of FIG. 14, a straight line obtained by fitting different plots at each bias value to the actual measurement value by the least square method using a linear model formula of N = a × f + b is also shown. FIG. 15 is a table showing the slope a and intercept b for each bias value in the linear model equation shown in FIG.

  Since the duty number L is 64 as described above, the optimum value of the bias value B defined by √L + 1 is 9. In each bias value, it is apparent that the number of inversion lines N has the same tendency between the actually measured value and the fitting value with respect to the frame frequency f. It can also be seen that the number N of inversion lines tends to be set larger at a lower frame frequency f as the bias value decreases. That is, it is apparent that the frame frequency f can be set low even with the same number of inversion lines N by decreasing the bias value.

  Since each bias value is considered to have a correlation, the number N of inversion lines is expressed by a functional expression having the frame frequency f and the bias value B as variables. 16 and 17 are graphs plotting the bias value dependence of the slope a and the intercept b shown in FIG. In FIG. 16, it was found that when fitting was performed by the method of least squares using a linear model formula of a = c × B + d, approximation was possible with a straight line of a = −0.0025 × B + 0.6433. Further, in FIG. 17, it was found that when fitting was performed by a least square method using a linear model formula of b = e × B + g, approximation was possible with a straight line of b = −8.4165 × B + 13.276.

Using the above approximate expression of the inclination a and the intercept b, the maximum number N of inversion lines in which display unevenness is not observed can be expressed by the following expression.
N = (− 0.0025 × B + 0.6433) × f + (− 8.4165 × B + 13.276)
The graph of FIG. 18 shows the approximate value obtained by this mathematical formula and the plot of the actual measurement value shown in FIG. It can be seen that the measured value and the approximate value tend to be almost equal without depending on the bias value.

From the above analysis, it can be seen that the number N of inversion lines in which display unevenness during external observation is not observed is obtained by the following equation.
N ≦ (−0.0025 × B + 0.6433) × f + (− 8.4165 × B + 13.276)

The above analysis result is considered to be because the substantial high-frequency component is increased and the frame frequency f is reduced by decreasing the number N of inversion lines. From this, it can be considered that an increase in the number of duties has the same effect. Considering that the high frequency component increases as the duty number increases, the above analysis result is for the case where the duty number is 64. For example, when the duty number becomes 128, the double high frequency component is included. Will be. Therefore, it is considered that the same effect can be obtained even if the frame frequency f is halved compared to the case where the duty number is 64. From this point of view, the number N of inversion lines can be expressed by the bias value B, the frame frequency f, and the duty number L as follows. However, the number N of inversion lines is greater than 1 and less than the duty number L.
N ≦ (−0.0025 × B + 0.6433) × f × (64 / L) + (− 8.4165 × B + 13.276)

  The above analysis results are obtained when the ambient temperature is 60 ° C., and the number N of inversion lines can be set larger due to the temperature drop. Therefore, the bias value, the frame frequency, and the number N of inversion lines may be variably set according to the ambient temperature detected by the temperature sensor 106 connected to the driving unit. In addition, the above analysis result was a case where the arrangement pitch of the bending points in each electrode was 150 μm, but this is not the case. If an orientation structure in which two dark lines intersect at a bending point of the upper edge of the pixel region, that is, a position different from the orientation direction of 135 ° or more is obtained, the same effect as described above can be obtained. In order to obtain such an oriented structure, it is preferable that at least the arrangement pitch of the bending points is 100 μm or more. Further, since the orientation texture at the upper edge of the pixel region is important, it is sufficient that at least the electrode edge of each second electrode is bent in a polygonal line, and each first electrode 11 does not have a bent shape. A general stripe shape may be used.

  Further, in the above-described second embodiment, the extending direction of the line segment constituting each electrode edge and the absorption axis direction of each polarizing plate are parallel or orthogonal, but such an arrangement is not necessarily required. . As the orientation structure at the upper edge of the pixel region, it is only necessary to obtain an orientation structure in which dark lines intersect each other in the vicinity of the bending point. Therefore, the angle formed by the two line segments constituting the bending point may be smaller than 90 °. It can be big. Furthermore, even if the electrode edge has a recess in plan view, it is considered that the same effect as that obtained when a bending point is provided can be obtained.

  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 embodiment, the liquid crystal layer has been illustrated as being not twisted, but may be twisted.

1: First substrate 2: Second substrate 3: Liquid crystal layer 4: First polarizing plate 5: Second polarizing plate 6: First viewing angle compensation plate 7: Second viewing angle compensation plate 8, 9: Alignment film 11: First Electrode 12: Second electrode 13, 14: Absorption axis direction 16: Pixel region 17: Orientation direction of liquid crystal molecules at substantially the center in the layer thickness direction of the liquid crystal layer 101: Liquid crystal panel 102: Backlight unit 103: Drive circuit for liquid crystal panel 104: Drive circuit for backlight unit 105: Control device 106: Temperature sensor

Claims (6)

A first substrate and a second substrate disposed opposite to each other;
A plurality of first electrodes provided on one surface side of the first substrate and extending along a first direction;
A plurality of second electrodes provided on one surface side of the second substrate and extending along a second direction intersecting the first direction;
A liquid crystal layer provided between each surface of the first substrate and the second substrate and having a pretilt angle of less than 90 ° and substantially vertically aligned;
Driving means for supplying a driving voltage for multiplex driving to the liquid crystal layer via the plurality of first electrodes and the plurality of second electrodes;
Including
A pixel region is defined in each of the intersecting regions of the plurality of first electrodes and the plurality of second electrodes;
Each of the plurality of second electrodes is configured by a line segment in which at least one of the two electrode edges in the plan view forms an angle with the second direction that is greater than 0 ° and less than or equal to 15 °. It is a polygonal line,
The liquid crystal layer is oriented so that the orientation direction of the liquid crystal molecules at substantially the center in the layer thickness direction is oblique to the one electrode edge of the second electrode,
The driving means supplies a driving voltage having an N-line inversion waveform as the driving voltage, and when the bias value is B, the frame frequency is f, and the duty number is L,
The value of N is set so as to satisfy the following condition: N ≦ (−0.0572 × B + 0.9998) × f × (64 / L) + (− 2.5 × B−30.175)
Liquid crystal display device. A first substrate and a second substrate disposed opposite to each other;
A plurality of first electrodes provided on one surface side of the first substrate and extending along a first direction;
A plurality of second electrodes provided on one surface side of the second substrate and extending along a second direction intersecting the first direction;
A liquid crystal layer provided between each surface of the first substrate and the second substrate and having a pretilt angle of less than 90 ° and substantially vertically aligned;
Driving means for supplying a driving voltage for multiplex driving to the liquid crystal layer via the plurality of first electrodes and the plurality of second electrodes;
Including
A pixel region is defined in each of the intersecting regions of the plurality of first electrodes and the plurality of second electrodes;
Each of the plurality of second electrodes is a polygonal line formed by combining a plurality of line segments in which at least one of the two electrode edges has the same length in plan view,
The liquid crystal layer is oriented so that the orientation direction of the liquid crystal molecules at substantially the center in the layer thickness direction is oblique to the one electrode edge of the second electrode,
The driving means supplies a driving voltage having an N-line inversion waveform as the driving voltage, and when the bias value is B, the frame frequency is f, and the duty number is L,
The value of N is set so as to satisfy the following condition: N ≦ (−0.0025 × B + 0.6433) × f × (64 / L) + (− 8.4165 × B + 13.276)
Liquid crystal display device. When the optimum value of the bias value is defined as √L + 1, the bias value B is set to a value smaller than the optimum value.
The liquid crystal display device according to claim 1. The N line inversion waveform forcibly inverts the polarity inversion to positive or negative after the end of one frame, and the polarity is reversed at the start line of two consecutive frames.
The liquid crystal display device according to claim 1. (A) a first substrate and a second substrate which are arranged opposite to each other; (b) a plurality of first electrodes provided on one surface side of the first substrate and extending along a first direction; A plurality of second electrodes provided on one surface side of the second substrate and extending along a second direction intersecting the first direction; and (d) between each surface of the first substrate and the second substrate. A liquid crystal layer having a pretilt angle of less than 90 ° and substantially vertically aligned; and (e) a drive voltage for multiplex driving to the liquid crystal layer via the plurality of first electrodes and the plurality of second electrodes. And (f) a pixel region is defined in each of intersecting regions of the plurality of first electrodes and the plurality of second electrodes, and (g) the plurality of second electrodes includes: , In plan view, at least one of the two electrode edges is the second edge. And (h) the liquid crystal layer has an alignment direction of liquid crystal molecules substantially at the center in the layer thickness direction, which is formed by a line segment having an angle with the direction of greater than 0 ° and less than or equal to 15 °. A method for driving a liquid crystal display device, wherein the liquid crystal display device is oriented obliquely with the one electrode edge of the electrode,
The driving means supplies a driving voltage having an N-line inversion waveform as the driving voltage, and when the bias value is B, the frame frequency is f, and the duty number is L, N ≦ (−0.0572 × B + 0.9998) × f × (64 / L) + (− 2.5 × B−30.175) is set so that the value of N is satisfied.
A driving method of a liquid crystal display device. (A) a first substrate and a second substrate which are arranged opposite to each other; (b) a plurality of first electrodes provided on one surface side of the first substrate and extending along a first direction; A plurality of second electrodes provided on one surface side of the second substrate and extending along a second direction intersecting the first direction; and (d) between each surface of the first substrate and the second substrate. A liquid crystal layer having a pretilt angle of less than 90 ° and substantially vertically aligned; and (e) a drive voltage for multiplex driving to the liquid crystal layer via the plurality of first electrodes and the plurality of second electrodes. And (f) a pixel region is defined in each of intersecting regions of the plurality of first electrodes and the plurality of second electrodes, and (g) the plurality of second electrodes includes: , In plan view, at least one of the two electrode edges is longer than each other. (H) the liquid crystal layer has an alignment direction of liquid crystal molecules at a substantially center in a layer thickness direction and the one electrode edge of the second electrode. A method of driving a liquid crystal display device, which is oriented obliquely,
The driving means supplies a driving voltage having an N-line inversion waveform as the driving voltage, and when the bias value is B, the frame frequency is f, and the duty number is L, N ≦ (−0.0025 × B + 0.6433) × f × (64 / L) + (− 8.4165 × B + 13.276)
A driving method of a liquid crystal display device.