JP5159687B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a lateral electric field type liquid crystal display device.

  A liquid crystal display device includes a thin film transistor array substrate (hereinafter referred to as “TFT substrate”) in which a plurality of thin film transistors (abbreviation: TFT) are disposed on a transparent substrate, and a color filter (Color TFT) in which a color filter is disposed on the transparent substrate. A liquid crystal display panel in which liquid crystal is sealed between a substrate and a filter (hereinafter referred to as “CF substrate”).

  On the TFT substrate, switching elements and pixel electrodes for driving liquid crystals connected to the switching elements are formed in an array. In addition, the CF substrate has, as a color filter, a pixel including colored layers of each color of red (Red: R), green (Green: G), and blue (Blue: B), and black disposed between the colored layers of each color. A shielding material called a matrix (Black Matrix; abbreviation: BM) is disposed so as to correspond to each switching element.

  In the liquid crystal driving method, the direction of the electric field applied to the liquid crystal sealed between the TFT substrate and the CF substrate is set to a direction substantially perpendicular to the substrate interface, and the liquid crystal molecules that are aligned in the horizontal direction are made vertical by the electric field. A twisted nematic display system (hereinafter referred to as “TN system”), which operates by being oriented, has been conventionally employed. However, this TN system has a problem that when the liquid crystal molecules are aligned in the vertical direction by an electric field, it has an angle with respect to the substrate, so that the brightness varies depending on the viewing direction and the viewing angle cannot be widened. Yes.

  As a measure for solving the above problem, a lateral electric field type liquid crystal display device has been proposed in which the direction of the electric field applied to the liquid crystal is made substantially parallel to the substrate interface and the liquid crystal molecules are rotated in the horizontal direction by the electric field. The lateral electric field method is also called an in-plane switching (abbreviation: IPS) method because switching is performed in a plane substantially parallel to the substrate interface.

  In the IPS liquid crystal display device, the major axis of the liquid crystal molecules constituting the liquid crystal layer is substantially parallel to the substrate interface, and the liquid crystal molecules do not rise in a direction perpendicular to the substrate interface. The change in height is small and there is almost no so-called viewing angle dependency. Therefore, the IPS liquid crystal display device has attracted attention as a liquid crystal display device for a monitor application having a very wide viewing angle and an excellent display quality as compared with a TN liquid crystal display device which is a vertical electric field method.

  An IPS liquid crystal display device performs display by rotating liquid crystal molecules in a horizontal plane parallel to a substrate. In driving, an arbitrary potential is applied to the signal line on the TFT substrate, and the TFT is driven by a signal of the scanning line to apply a predetermined potential to the pixel electrode. Depending on the potential difference between the pixel electrode and the common electrode, the alignment angle of the liquid crystal molecules is changed to change the brightness of the display. Therefore, a predetermined potential is applied to each of the signal line, the scanning line, and the common electrode line for driving the liquid crystal on the TFT substrate.

  In contrast, the CF substrate is electrically insulated. In the CF substrate, a colored layer of each color is arranged in a light transmission portion from the light source, and part or all of the signal lines, TFTs, and scanning lines of the TFT substrate are shielded by the BM of the CF substrate. . The BM of the CF substrate is formed of a metal material or a resin material having a resistance lower than that of the colored layer. Therefore, when a potential is applied to the signal line of the TFT substrate, charges are accumulated mainly in the BM, and the BM It will have a potential. When a potential difference is generated between the BM and the pixel electrode and the common electrode of the TFT substrate, an electric field is generated between them, so that the orientation of the liquid crystal molecules is disturbed, and there is a problem that the display is affected.

  For example, Patent Document 1 discloses a technique for suppressing the influence of the potential from the TFT substrate to the CF substrate in such an IPS liquid crystal display device. In the liquid crystal display device disclosed in Patent Document 1, in order to reduce the influence of the electric field due to the scanning line, a shield electrode having the same potential as the common electrode line or the signal line is arranged on the scanning line, and the potential of the scanning line is increased. It is configured to reduce the influence on the BM layer.

  In addition, the IPS liquid crystal display device has a problem that the display quality at the start of display deteriorates. The optimum potential of the common electrode in the display device is determined by the relationship between the potential of the scanning line, the signal line, and the pixel electrode. However, in the IPS liquid crystal display device, the optimum potential of the common electrode is several tens at the start of display. There is a phenomenon that changes over time. This is considered to be because no voltage is applied to the CF substrate, but the voltage of the CF substrate gradually changes under the influence of the TFT substrate.

  A technique for solving this problem is disclosed in Patent Document 2, for example. The liquid crystal display device disclosed in Patent Document 2 is configured to control a voltage signal supplied to a counter electrode corresponding to a common electrode in consideration of a charge amount charged to the CF substrate.

  In addition to the above-described problem, there is a problem that the BM and the colored layer of the color filter inside the display device are charged by the influence of static electricity from the outside and affect the display. For example, Patent Document 3 discloses a technique for preventing the influence of static electricity from the outside. In the liquid crystal display device disclosed in Patent Document 3, a conductive film is formed on a CF substrate, and a constant potential or the like having the same potential as the common electrode is applied to the conductive film so that the CF substrate is not charged by external static electricity or the like. It is configured as follows.

JP 2001-183699 A JP 2003-302648 A JP 2004-004754 A

  As described above, the IPS liquid crystal display device has a problem in that the display quality is deteriorated due to the influence of the charging of the CF substrate.

  Techniques for solving this problem are disclosed in Patent Documents 1 to 3 described above. In the liquid crystal display device disclosed in Patent Document 1, the shield electrode is the same as the common electrode line or the signal line. Since it is necessary to apply a potential, power consumption is increased.

  Further, the liquid crystal display device disclosed in Patent Document 2 requires a complicated control circuit for controlling the voltage signal supplied to the counter electrode, resulting in an increase in cost.

  Further, in the liquid crystal display device disclosed in Patent Document 3, since a constant potential or the like that is the same potential as the common electrode is applied to the conductive film formed on the CF substrate, power consumption is increased.

  An object of the present invention is to provide a liquid crystal display device that can easily prevent a display defect after starting display with low power consumption.

  The liquid crystal display device of the present invention includes a pair of substrates disposed opposite to each other and a liquid crystal layer sandwiched between the pair of substrates, and one of the pair of substrates on the liquid crystal layer side. A liquid crystal display device that performs display by generating an electric field between a pixel electrode and a common electrode provided on a surface to control an orientation direction of liquid crystal molecules constituting the liquid crystal layer, the liquid crystal display device including: Among them, a counter electrode provided on the surface of the other substrate on the liquid crystal layer side and facing the one substrate, a counter electrode applying means for applying a voltage to the counter electrode, and the display at the start of the display The application of the voltage to the counter electrode is started, and when a predetermined voltage application time has elapsed from the start of display, the application of the voltage to the counter electrode is stopped and the counter electrode is set in a floating state. Control application means for counter electrode And a controlling means for.

  According to the liquid crystal display device of the present invention, an electric field is generated between the pixel electrode and the common electrode provided on the liquid crystal layer side surface of one of the pair of substrates sandwiching the liquid crystal layer, thereby liquid crystal Display is performed by controlling the alignment direction of the liquid crystal molecules constituting the layer. Along with the start of this display, the counter electrode applying means is controlled by the control means, and voltage application to the counter electrode provided on the liquid crystal layer side surface of the other substrate is started. The When a predetermined voltage application time elapses from the start of display, the application of the voltage to the counter electrode by the counter electrode applying unit is stopped by the control unit, and the counter electrode enters a floating state.

  Thus, a voltage is applied to the counter electrode until a predetermined voltage application time elapses from the time when display is started. As a result, the optimum value of the voltage applied to the common electrode in order to generate an electric field with the pixel electrode (hereinafter sometimes referred to as “optimum voltage”) is increased with the passage of time from the start of display. Thus, it is possible to suppress the time variation of the optimum voltage of the common electrode, which is a phenomenon that fluctuates. Accordingly, display defects after the start of display can be prevented, and display quality can be improved.

  Further, when a predetermined voltage application time elapses from the time when display is started, the application of the voltage by the application means for the counter electrode is stopped and the counter electrode enters a floating state, so that an increase in power consumption can be prevented. Therefore, it is possible to easily prevent a display defect after the start of display with low power consumption.

  Also, the control of the counter electrode applying means by the control means is a simple control in which the application of voltage to the counter electrode is started at the start of display and the voltage application to the counter electrode is stopped when the voltage application time elapses. Therefore, the control means can be realized with a simple configuration. This can prevent an increase in cost. Therefore, it is possible to realize a liquid crystal display device that can easily prevent a display defect after the start of display with low power consumption without causing an increase in cost.

It is sectional drawing which shows the structure of the liquid crystal display panel 1 of the liquid crystal display device used as the premise of this invention. It is a block diagram which shows the electrical constitution of the liquid crystal display device 100 which is the 1st Embodiment of this invention. 4 is a cross-sectional view illustrating a configuration of a liquid crystal display panel 40 in the liquid crystal display device 100. FIG. 4 is a plan view showing a configuration of a TFT substrate 60 in the liquid crystal display panel 40. FIG. 4 is a diagram showing an electrical equivalent circuit of one pixel in the liquid crystal display panel 40. FIG. It is a graph which shows the example of a measurement of the time fluctuation of the optimal voltage of a common electrode from the display start time. It is sectional drawing which shows liquid crystal display panel 40A of the other example. It is sectional drawing which shows the liquid crystal display panel 40B of another example. It is a top view which shows TFT substrate 60B in the liquid crystal display panel 40B. It is a figure which shows the polarity of the voltage applied to the pixel electrode of the odd-numbered flame | frame in a dot inversion drive system. It is a figure which shows the polarity of the voltage applied to the pixel electrode of the even number frame in a dot inversion drive system. It is a figure which shows the polarity of the voltage applied to the pixel electrode of the odd-numbered flame | frame in line common inversion drive. It is a figure which shows the polarity of the voltage applied to the pixel electrode of the even number frame in line common inversion drive. It is sectional drawing which shows 40C of liquid crystal display panels provided with the counter electrode 85 of another example. It is sectional drawing which shows liquid crystal display panel 40D provided with the counter electrode 86 of another example. It is sectional drawing which shows the structure of the liquid crystal display panel 90 in the liquid crystal display device which is the 2nd Embodiment of this invention.

<Prerequisite technology>
Before describing the liquid crystal display device of the present invention, the liquid crystal display device which is the premise of the present invention will be described. FIG. 1 is a cross-sectional view showing a configuration of a liquid crystal display panel 1 of a liquid crystal display device as a premise of the present invention. In FIG. 1, illustration of a TFT element, a scanning line, a signal line, an auxiliary capacitor, a polarizing plate, a light source, and the like is omitted for easy understanding.

  The liquid crystal display panel 1 of the liquid crystal display device includes a color filter (abbreviation: CF) substrate 10, a thin film transistor (abbreviation: TFT) substrate 20, and a liquid crystal layer 30 sandwiched between the CF substrate 10 and the TFT substrate 20. It is prepared for.

  The CF substrate 10 includes a glass substrate 11, a black matrix (abbreviation: BM) 12 and a colored layer 13 disposed on the surface portion of the glass substrate 11 on the liquid crystal layer 30 side, and an overcoat film 14 that covers the BM 12 and the colored layer 13. And an alignment film 15 that covers the overcoat film 14.

  The TFT substrate 20 is disposed to face the CF substrate 10, and includes a glass substrate 21, a common electrode 23 and a pixel electrode 24 disposed on the surface portion of the glass substrate 21 on the liquid crystal layer 30 side, a common electrode 23, and a pixel electrode. And an alignment film 22 covering 24. Although not shown, the TFT substrate 20 includes a TFT element connected to the pixel electrode 24, and a signal line and a scanning line for driving the TFT element.

  The liquid crystal display device 1 is an IPS liquid crystal display device. In the liquid crystal display device 1, the TFT element of the TFT substrate 20 is driven to apply a voltage between the pixel electrode 24 and the common electrode 23, thereby generating an electric field E 0 between the pixel electrode 24 and the common electrode 23. Then, the alignment direction of the liquid crystal molecules constituting the liquid crystal layer 30 is controlled to control the brightness of the display. Therefore, in the TFT substrate 20, a predetermined potential is applied to the signal line and the scanning line in order to drive the TFT element. A predetermined potential is also applied to the common electrode 23.

  On the other hand, the CF substrate 10 does not have a member to which a potential is applied, and is electrically insulated. However, since the BM 12 of the CF substrate 10 is formed of a metal material or a resin material having a resistance lower than that of the colored layer 13, when a potential is applied to the signal line of the TFT substrate 20, the BM 12 is mainly charged. Will accumulate and the BM 12 will be charged.

  As a result, when a potential difference is generated between the BM 12 and the pixel electrode 24 and between the BM 12 and the common electrode 23, an electric field is generated between the CF substrate 10 and the TFT substrate 20, so that the orientation of the liquid crystal molecules is disturbed. The problem of affecting the display arises.

  Therefore, in the liquid crystal display device of the present invention, the configuration of the embodiment described below is adopted in order to solve the above problem.

<First Embodiment>
FIG. 2 is a block diagram showing an electrical configuration of the liquid crystal display device 100 according to the first embodiment of the present invention. The liquid crystal display device 100 of this embodiment is an IPS liquid crystal display device. The liquid crystal display device 100 includes a control unit 101, a display drive unit 102, an ON / OFF switch unit 103, a power supply unit 104, and a liquid crystal display panel 40. The control unit 101 includes a time measuring unit 105. The liquid crystal display panel 40 includes a counter electrode 52, a common electrode 63, and a pixel electrode 64.

  The control unit 101 is electrically connected to hardware resources including the display drive unit 102, the ON / OFF switch unit 103, and the power supply unit 104 that constitute the liquid crystal display device 100, and is configured to be able to transmit signals and information to each other. Is done. The control unit 101 is a processing circuit that comprehensively controls the hardware resources described above based on a control program stored therein. In the present embodiment, the control unit 101 is realized by a central processing unit (abbreviation: CPU).

  The ON / OFF switch unit 103 is realized by an operation start switch that is an ON switch and an operation end switch that is an OFF switch. The ON / OFF switch unit 103 gives an operation start command to the control unit 101 by operating the operation start switch. The control unit 101 gives a power supply command to the power supply unit 104 when the operation start command is given. The power supply unit 104 supplies power to the control unit 101 and the display drive unit 102 when a power supply command is given. The control unit 101 starts an image display operation using the power supplied from the power supply unit 104 when an operation start command is given.

  The ON / OFF switch unit 103 gives an operation end command to the control unit 101 by operating the operation end switch. The control unit 101 gives a power supply stop command to the power supply unit 104 when the operation end command is given. The power supply unit 104 stops supplying power to the control unit 101 and the display driving unit 102 when a power supply stop command is given. The control unit 101 ends the image display operation when an operation end command is given.

  The time measuring unit 105 measures the relative elapsed time and counts the elapsed time from the start of display. The control unit 101 determines whether a predetermined voltage application time has elapsed based on the elapsed time counted by the time measuring unit 105.

  In order to display the display image on the liquid crystal display panel 40, the display driving unit 102 applies a liquid crystal driving signal corresponding to the display image to the electrode circuit including the pixel electrode 64 and the common electrode 63. Specifically, the display driving unit 102 applies a voltage to the pixel electrode 64 and the common electrode 63 using the power supplied from the power supply unit 104. The display driving unit 102 applies a voltage to the counter electrode 52 using the power supplied from the power supply unit 104. The display drive unit 102 functions as a counter electrode application unit and a common electrode application unit.

FIG. 3 is a cross-sectional view showing the configuration of the liquid crystal display panel 40 in the liquid crystal display device 100.
FIG. 4 is a plan view showing the configuration of the TFT substrate 60 in the liquid crystal display panel 40. The TFT substrate 60 shown in FIG. 3 shows a cross-sectional view taken along the section line III-III in FIG. FIG. 5 is a diagram showing an electrical equivalent circuit of one pixel in the liquid crystal display panel 40. In order to facilitate understanding, the polarizing plate and the light source are not shown in FIGS. In FIG. 3, the TFT element 65, the scanning line 66, the signal line 67, and the auxiliary capacitor 72 are not shown, and in FIG. 4, the auxiliary capacitor 72 is not shown.

  As shown in FIG. 3, the liquid crystal display panel 40 includes a CF substrate 50, a TFT substrate 60, and a liquid crystal layer 70 that is sandwiched between the CF substrate 50 and the TFT substrate 60. The CF substrate 50 and the TFT substrate 60 correspond to a pair of substrates, the TFT substrate 60 corresponds to one substrate, and the CF substrate 50 corresponds to the other substrate.

  The CF substrate 50 includes a CF side glass substrate 51, a counter electrode 52 provided on the surface of the CF side glass substrate 51 on the liquid crystal layer 70 side, a BM 53 and a colored layer 54 provided on the surface portion of the counter electrode 52, and BM 53. And an overcoat film 55 that covers the colored layer 54 and a CF-side alignment film 56 that covers the overcoat film 55.

  The BM 53 and the colored layer 54 function as a color filter. The colored layer 54 includes colored layers of each color of red (Red: R), green (Green: G), and blue (Blue: B). The BM 53 is disposed between the colored layers 54 of the respective colors, and ends of the BM 53 are covered with the colored layer 54. Although different from the present embodiment, instead of the CF side glass substrate 51, another light transmitting substrate, for example, a light transmitting plastic substrate may be used.

  In the present embodiment, the counter electrode 52 is formed on the entire display surface of the liquid crystal display panel 40, that is, the entire region used for display on the CF side glass substrate 51. Therefore, it is necessary to use a translucent material having translucency for the counter electrode 52. This is because, if a light-transmitting material is not used, light that has passed through the liquid crystal layer 70 is blocked by the counter electrode 52, and display cannot be performed.

  Since the counter electrode 52 is also required to have conductivity, a material having translucency and conductivity (hereinafter referred to as “translucent conductive material”) is used as the material of the counter electrode 52. For example, indium tin oxide (abbreviation: ITO) may be used as the light-transmitting conductive material. When using ITO, the thickness dimension of the counter electrode 52 formed of ITO may be, for example, not less than 50 nm and not more than 200 nm.

  The TFT substrate 60 is disposed so as to face the CF substrate 50, the TFT side glass substrate 61, the common electrode 63 and the pixel electrode 64 provided on the surface of the TFT side glass substrate 61 on the liquid crystal layer 70 side, and the common electrode 63. And a TFT side alignment film 62 covering the pixel electrode 64. Although different from the present embodiment, instead of the TFT side glass substrate 61, another light transmitting substrate such as a light transmitting plastic substrate may be used.

  As shown in FIGS. 4 and 5, the TFT substrate 60 includes a TFT element 65 connected to the pixel electrode 64, and a signal line 67 and a scanning line 66 for driving the TFT element 65.

  The pixel electrode 64 is connected to the drain electrode of the TFT element 65, and the source electrode of the TFT element 65 is connected to the signal line 67. The gate electrode of the TFT element 65 is connected to the scanning line 66.

  In the liquid crystal display panel 40, the scanning lines 66 and the signal lines 67 intersect on the same substrate 61 to form a matrix structure. The pixel electrode 64 and the TFT element 65 are disposed in each pixel region partitioned by the scanning line 66 and the signal line 67. The common electrode 63 is provided over the entire substrate on the same substrate 61 as the pixel electrode 64. A liquid crystal capacitor 71 is formed by the pixel electrode 64 and the common electrode 63.

  A storage capacitor electrode connected to the drain electrode of the TFT element 65 is formed on the same substrate 61 as the pixel electrode 64. The storage capacitor electrode and the common electrode 63 form an auxiliary capacitor 72 in parallel with the liquid crystal capacitor 71. Since the liquid crystal display device 100 of the present embodiment is an IPS liquid crystal display device, all the electrodes shown in FIG. 5 are formed on the TFT substrate 60 side.

  As shown in FIG. 4, each pixel electrode 64 has a rectangular portion extending from a connection portion with the drain electrode of the TFT element 65 arranged at the center of the pixel region. A rectangular portion of each pixel region 64 has one opening that is opened in a slit shape. In the common electrode 63, a plurality of strip portions extending in the row direction are arranged in the column direction. Each belt-like portion of the common electrode 63 is opened in a slit shape and has a plurality of openings arranged in the row direction. The pixel electrode 64 is arranged so that the opening thereof is deviated from the opening of the common electrode 63.

  Returning to FIG. 2, the display drive unit 102 applies voltage to the pixel electrode 64, the common electrode 63, and the counter electrode 52 using the power supplied from the power supply unit 104. The display driving unit 102 acquires display information representing a display image from a display information storage unit (not shown), and each of the liquid crystal display panels 40 formed on the liquid crystal display panel 40 so that the display image represented by the acquired display information can be displayed. A voltage is selectively applied to the pixel electrode 64. Specifically, a voltage is applied to the pixel electrode 64 via the scanning line 66 and the signal line 67.

  Since a constant voltage is applied to the common electrode 63, a potential difference is generated between the pixel electrode 64 and the common electrode 63 by selectively applying a voltage to the pixel electrode 64. In this manner, the electric field E1 is generated between the pixel electrode 64 and the common electrode 63, and the liquid crystal display panel 40 is driven by controlling the alignment direction of the liquid crystal molecules constituting the liquid crystal layer 70, thereby performing display.

  That is, the display driver 102 adjusts the light transmittance by changing the orientation direction of the liquid crystal molecules for each pixel region of the liquid crystal display panel 40 by selectively applying a voltage to each pixel electrode 64. As a result, the liquid crystal display panel 40 can change the state of light passing therethrough, so that light corresponding to the image to be displayed can be emitted from the display surface. The image displayed on the liquid crystal display panel 40 may be a moving image or a still image.

  FIG. 6 is a graph showing a measurement example of the time variation of the optimum voltage of the common electrode from the start of display. The horizontal axis of FIG. 6 represents the elapsed time (minutes) from the start of display, and the vertical axis represents the optimum voltage (V) of the common electrode 63. The optimum voltage of the common electrode 63 is obtained as a voltage at which the flicker is minimized when the voltage applied to the common electrode 63 is changed at predetermined time intervals and, for example, the occurrence of flicker is confirmed. In FIG. 6, a curve indicated by reference symbol L1 indicates the optimum voltage of the common electrode 63 in the liquid crystal display panel 40 of the present embodiment, and a curve indicated by reference symbol L2 indicates that of the base technology shown in FIG. The optimal voltage of the common electrode 23 in the liquid crystal display panel 1 is shown.

  As shown in FIG. 6, in the liquid crystal display panel 1 of the base technology shown in FIG. 1, the phenomenon that the optimum voltage of the common electrode 23 fluctuates at the start of display due to the influence of the electric field from the TFT substrate 20 to the CF substrate 10 is observed. It is done. The optimum voltage of the common electrode 23 fluctuates greatly until the initial stage of display start, specifically, 20 minutes elapses from the start of display, but becomes an almost constant value after 60 minutes elapses. That is, the optimum voltage of the common electrode 23 is stabilized after a certain time. This is because, among the CF substrates 10 on which no member to which voltage is applied is formed, the BM 12 having high conductivity is gradually charged due to the voltage applied to the common electrode 23 and the pixel electrode 24 of the TFT substrate 20. This is thought to be an effect of

  In the time when the fluctuation of the optimum voltage is large until several tens of minutes from the start of display, when the display screen of the liquid crystal display device is switched, the display quality is lowered such that an afterimage of the screen before switching is seen. This is because the voltage applied between the pixel electrode 24 and the common electrode 23 is deviated from the optimum value immediately after the display is started, so that the voltage applied to the liquid crystal has a constant DC component, thereby causing an afterimage phenomenon. It is thought that it is easy to get up. Therefore, suppressing the fluctuation of the optimum voltage of the common electrode 23 leads to improvement of display quality.

  The liquid crystal display panel 40 of the present embodiment shown in FIG. 3 is different from the liquid crystal display panel 1 of the base technology shown in FIG. 1 in that a counter electrode 52 is provided on a CF substrate 50. A voltage is applied to the counter electrode 52 by the display driving unit 102. Based on an instruction from the control unit 101, the display driving unit 102 starts applying a voltage to the counter electrode 52 with the start of display, and when a predetermined voltage application time has elapsed from the start of display, The application of voltage to the counter electrode 52 is stopped, and the counter electrode 52 is brought into a floating state.

  For example, in the present embodiment, a voltage of 4.90 (V) is applied to the counter electrode 52 only for one minute after the display is started, and then the application of the voltage is stopped to bring the common electrode 63 into a floating state. The time variation of the optimum voltage is as indicated by L1 in FIG. That is, the time variation of the optimum voltage of the common electrode 63 in the present embodiment differs from the time variation of the optimum voltage of the common electrode 23 in the base technology, and almost no variation of the optimum voltage is observed. Under this condition, it was confirmed whether or not an afterimage was generated on the liquid crystal display panel 40 for 60 minutes from the start of the display. When the display screen of the liquid crystal display panel 40 was switched, the afterimage of the screen before the switching was not seen, which was good. Display characteristics could be obtained.

  Next, the effect when the voltage applied to the counter electrode 52 is cut halfway to place the counter electrode 52 in a floating state will be described. In the ideal state, since the state does not change after the voltage of the counter electrode 52 becomes a constant value, no current flows through the counter electrode 52 and the power consumption is zero. Therefore, even if power is always supplied, the power consumption remains zero. However, in actual use, charges may be injected into the counter electrode 52 due to static electricity from the outside of the liquid crystal display panel 40. When the power is constantly supplied, the voltage of the counter electrode 52 is restored to the original state. A current flows through the counter electrode 52. Therefore, the power consumption is a value greater than zero.

  On the other hand, if the counter electrode 52 is left in a floating state without applying a voltage to the counter electrode 52, the power consumption remains zero regardless of the influence of static electricity. Therefore, by applying a voltage to the counter electrode 52 only at the start of display and switching the counter electrode 52 to a floating state in the middle, it is possible to achieve an effect that the display characteristics at the start of display can be improved with low power consumption.

  As described above, according to the present embodiment, of the pair of substrates 50 and 60 that sandwich the liquid crystal layer 70, the pixel electrode 64 and the common electrode 63 provided on the surface of the TFT substrate 60 on the liquid crystal layer 70 side. Display is performed by generating an electric field between them to control the alignment direction of the liquid crystal molecules constituting the liquid crystal layer 70. Along with the start of the display, the display drive unit 102 is controlled by the control unit 101, and application of a voltage to the counter electrode 52 provided on the surface of the CF substrate 50 on the liquid crystal layer 70 side is started. When a predetermined voltage application time elapses from the start of display, the control unit 101 stops the application of voltage to the counter electrode 52 by the display driving unit 102 and the counter electrode 52 enters a floating state.

  Thus, a voltage is applied to the counter electrode 52 until a predetermined voltage application time elapses from the time when display is started. Accordingly, it is possible to suppress the time variation of the optimum value of the voltage applied to the common electrode 63 in order to generate an electric field between the pixel electrode 64, that is, the optimum voltage of the common electrode 63. Accordingly, display defects after the start of display can be prevented, and display quality can be improved.

  Further, when a predetermined voltage application time elapses from the time when display is started, the counter electrode 52 is stopped from applying voltage by the display driving unit 102 and is in a floating state, so that an increase in power consumption can be prevented. Therefore, it is possible to easily prevent a display defect after the start of display with low power consumption.

  The control of the display drive unit 102 by the control unit 101 starts application of a voltage to the counter electrode 52 with the start of display, and stops applying voltage to the counter electrode 52 when the voltage application time elapses. Since the control is simple, the control unit 101 can be realized with a simple configuration. This can prevent an increase in cost. Therefore, it is possible to realize the liquid crystal display device 100 that can easily prevent a display defect after the start of display with low power consumption without causing an increase in cost.

  Next, a voltage application time that is a time for applying a voltage to the counter electrode 52 will be described. First, consider the minimum time of voltage applied to the counter electrode 52. For example, in the 10-inch diagonal liquid crystal display panel 40, the capacitance and resistance of the counter electrode 52 installed on the CF substrate 50 are about 1 [nF] and 1 [MΩ], respectively, when estimated to be large. If a voltage is applied for 0.005 seconds or more, which is a time obtained by further multiplying the time constant determined by the product of the resistance and the resistance, the voltage of the counter electrode 52 becomes a substantially constant value.

  Since the size of the liquid crystal display panel 40 has a width of several inches to several tens of inches, the product of the capacitance and the resistance is several to 100 times as large as the above estimate. Even when an increase in the time constant due to a large resistance component such as a contact resistance of the power feeding circuit portion is taken into consideration, it is sufficient that the time required for charging the counter electrode 52 is one second. If the minimum application time required for stabilizing the voltage of the counter electrode 52 is 1 second, the voltage of the counter electrode 52 can be stabilized in any IPS liquid crystal display device 100.

  Next, the maximum time of the voltage applied to the counter electrode 52 will be considered. As shown by the curve L2 in FIG. 6 described above, in the IPS liquid crystal display panel 1 of the base technology, it is actually measured that about 60 minutes at the maximum is necessary for the optimum voltage of the common electrode 23 to be stabilized. It is known from the value. Since the various electrodes 23 and 24 of the TFT substrate 20 and the CF substrate 10 are made of many highly conductive materials, it is considered that the time constant for stabilization is long.

  Therefore, when the counter electrode 52 is installed on the CF substrate 60 and a voltage is applied as in the present embodiment, the voltage of the counter electrode 52 is reliably stabilized by applying a voltage to the counter electrode 52 for 60 minutes. I think that.

  From the above points, it is preferable that the voltage application time, which is the time for applying the voltage to the counter electrode 52 from the start of display, is not less than 1 second and not more than 60 minutes. Since the voltage of the counter electrode 52 can be stabilized by setting the voltage application time to 1 second or more and 60 minutes or less, it is possible to reliably achieve improvement in display quality at the start of display.

  In the present embodiment described above, the pixel electrode 64 and the common electrode 63 for driving the liquid crystal are formed on the same plane, specifically, on the surface portion of the TFT side glass substrate 61. It is not limited to such a configuration.

  FIG. 7 is a cross-sectional view showing a liquid crystal display panel 40A of another example. FIG. 8 is a cross-sectional view showing a liquid crystal display panel 40B of still another example. FIG. 9 is a plan view showing the TFT substrate 60B in the liquid crystal display panel 40B. The TFT substrate 60B shown in FIG. 8 is a cross-sectional view seen from the section line VIII-VIII in FIG. As shown in FIG. 7, the pixel electrode 64 and the common electrode 63 provided on the TFT substrate 60 </ b> A may be formed of different layers with an insulating film 80 interposed therebetween.

  Further, as shown in FIGS. 8 and 9, one of the pixel electrode 64 and the common electrode 81 provided on the TFT substrate 60B is formed as a flat surface, and the other has an opening that is opened in a slit shape. Also good. In the example shown in FIGS. 8 and 9, the common electrode 81 is formed with a flat surface, and the pixel electrode 64 has an opening that is opened in a slit shape.

  FIG. 10 is a diagram illustrating the polarity of the voltage applied to the pixel electrode in the odd-numbered frame in the dot inversion driving method. FIG. 11 is a diagram illustrating the polarity of the voltage applied to the pixel electrode of the even frame in the dot inversion driving method. Since the liquid crystal molecules constituting the liquid crystal layer 70 deteriorate when a DC voltage is applied, the liquid crystal display panel 40 is driven by inverting the polarity of the voltage applied between the pixel electrode 64 and the common electrode 63 for each frame. .

  When a voltage having the same polarity is applied to all pixels in the surface of the liquid crystal display panel 40, a problem arises that flicker is recognized and display quality is impaired. In order to avoid the occurrence of such a problem, a method is employed in which the polarity of the applied voltage is reversed between adjacent pixels. In such a driving method, flicker is hardly recognized and display quality is not impaired.

  In the present embodiment, a dot inversion driving method is adopted in which the voltage applied to the common electrode 63 is fixed and the voltage applied to the pixel electrode 64 is alternately positive and negative between adjacent pixels as shown in FIGS. adopt. In the dot inversion driving method, among the pixels arranged in a matrix in the row direction X and the column direction Y, for example, the pixel electrode 64 of the pixel in the Y1 row of the X1 column has a positive (+) voltage in the odd frame. And a negative (−) voltage is applied in even frames. By adopting the dot inversion driving method, display with high display quality can be realized.

  When the dot inversion driving method is employed, a constant voltage is always applied to the common electrode 63. Therefore, in the present embodiment, a voltage equal to that of the common electrode 63 is applied to the counter electrode 52 shown in FIG. If the same voltage as that of the common electrode 63 is applied to the counter electrode 52 in this way, it is not necessary to generate a new voltage in the liquid crystal display panel 40, so that the display quality can be improved at low cost. can do.

  Specifically, the voltage applied to each part of the liquid crystal display panel 40 is generated by boosting the power supply voltage supplied from the power supply unit 104 by a charge pump circuit built in the display drive unit 102. Therefore, if the same voltage as that of the common electrode 63 is applied to the counter electrode 52 as described above, it is not necessary to generate a new voltage in the liquid crystal display panel 40, so that the display quality can be reduced at low cost. An improvement can be achieved.

  In the examples shown in FIGS. 10 and 11, the dot inversion driving method in which polarity inversion alternately occurs in adjacent pixels has been described as the dot inversion driving method. However, a driving method in which the polarity is inverted every two pixels is applied. However, the same effect can be obtained. The same effect can be obtained even when there are three or more. In addition, the same effect can be obtained in all driving methods in which the voltage applied to the common electrode 63 is always constant.

  The liquid crystal driving method in the liquid crystal display panel 40 is not limited to the dot inversion driving method described above. FIG. 12 is a diagram illustrating the polarity of the voltage applied to the pixel electrode in the odd-numbered frame in the line common inversion driving. FIG. 13 is a diagram illustrating the polarity of the voltage applied to the pixel electrode of the even frame in the line common inversion driving.

  As a liquid crystal driving method, as shown in FIGS. 12 and 13, line common inversion driving in which positive and negative polarities are inverted for each line may be adopted. In the line common inversion driving method, for example, a positive (+) voltage is applied to the pixels in the Y1th row, that is, the pixel electrodes 64 in the X1 to X6 columns, and a negative (−) voltage is applied to the even frames. Applied.

  That is, in the line common inversion driving method, the voltage applied to the common electrode 63 and the voltage applied to the pixel electrode 64 are inverted between the positive and negative for each line. As a result, the amplitude of the voltage applied to the pixel electrode 64 and the common electrode 63 can be almost halved compared to the case where the dot inversion driving method is adopted, leading to a reduction in power consumption.

  When the line common inversion driving method is employed, a voltage that is inverted every frame is applied to the common electrode 63. Since the counter electrode 52 has a large capacity, applying the same voltage as the common electrode 63, that is, a voltage that is inverted every frame, to the counter electrode 52 causes an increase in power consumption, which is not preferable.

  Considering that the voltage affecting the CF substrate 50 from the TFT substrate 60 is approximately equal to the time average value of the voltage applied to the common electrode 63 for both the pixel electrode 64 and the common electrode 63, the line common inversion driving method is adopted. In this case, it is preferable that the voltage applied to the counter electrode 52 by the display driving unit 102 is set to the time average value of the voltage applied to the common electrode 63. By setting the voltage applied to the counter electrode 52 to the time average value of the voltage applied to the common electrode 63, it is possible to suppress the time variation of the optimum value of the common electrode 63 at the start of display and increase the power consumption. And display quality can be improved.

  In the present embodiment described above, the counter electrode 52 is provided between the CF side glass substrate 51 and the BM 53 and between the CF side glass substrate 51 and the colored layer 54. The position of the counter electrode 52 is However, the present invention is not limited to this.

  FIG. 14 is a cross-sectional view showing a liquid crystal display panel 40 </ b> C including another example of the counter electrode 85. FIG. 15 is a cross-sectional view showing a liquid crystal display panel 40D including a counter electrode 86 of still another example.

  As shown in FIG. 14, the counter electrode 85 may be provided between the BM 53 and the colored layer 54. That is, the counter electrode 85 may be provided by being laminated on the surface portion of the BM 53 and the CF side glass substrate 51 in the thickness direction of the CF side glass substrate 51, specifically, between the BM 53 and the overcoat film 55. In addition, it may be provided between the CF side glass substrate 51 and the colored layer 54.

  As shown in FIG. 15, the counter electrode 86 may be provided by being laminated on the surface portion of the BM 53 and the colored layer 54 that are laminated on the surface portion of the CF-side glass substrate 51. It may be provided between the overcoat film 55 and between the colored layer 54 and the overcoat film 55.

  The counter electrode can obtain the same effect in any arrangement described above. However, when the counter electrode approaches the liquid crystal layer 70, the orientation of the liquid crystal molecules is disturbed and the display quality is lowered. In order to prevent this, as in the present embodiment shown in FIG. 3, the position of the counter electrode 52 is set between the CF side glass substrate 51 and the BM 53 which are the farthest from the liquid crystal layer 70, and the CF side glass. What is necessary is just to put between the board | substrate 51 and the colored layer 54, and an effect can be achieved easily by this.

  As shown in FIG. 15, even when the position of the counter electrode 86 is between the colored layer 54 closest to the liquid crystal layer 70 and the overcoat film 55 and between the BM 53 and the overcoat film 55, the overcoat film 55. If the thickness is made sufficiently thick, the influence on the display can be reduced, and the same effect as this embodiment can be obtained.

<Second Embodiment>
FIG. 16 is a cross-sectional view showing a configuration of a liquid crystal display panel 90 in the liquid crystal display device according to the second embodiment of the present invention. The electrical configuration of the liquid crystal display device according to the present embodiment is the same as that of the liquid crystal display device 100 according to the first embodiment described above. The description common to the embodiment is omitted.

  In the first embodiment described above, the counter electrode 52 and the black matrix (BM) 53 are separate members, but a black matrix may be used as the counter electrode. In the present embodiment, the CF side substrate 91 is provided with a black matrix (BM) 92 that functions as a counter electrode.

  As the material of BM92, for example, a material selected from metal chromium (Cr) and its oxide is used. For example, BM92 is formed with a multilayer film of Cr and its oxide. Since the black matrix 92 formed of such a material has high conductivity, it can be used as a counter electrode.

  By using the black matrix 92 as the counter electrode in this way, there is no need to newly provide a counter electrode, so that there is an effect that it is not necessary to increase the number of steps. The cross-sectional structure is the same as that of the liquid crystal display panel 1 of the base technology, but the liquid crystal display panel 90 of the present embodiment differs from the black matrix 92 in the liquid crystal display panel 90 of the present embodiment, unlike the liquid crystal display device of the base technology. A mechanism for supplying power from the outside, specifically, a mechanism for applying a voltage from the display driving unit 102 is provided.

  Even when the black matrix 92 is used as a counter electrode as in the present embodiment, as in the case of the first embodiment using a transparent counter electrode that is a counter electrode made of a translucent material, the display is started. An improvement in display quality can be achieved.

  1, 40, 40A, 40B, 40C, 40D, 90 Liquid crystal display panel, 10, 50, 50A, 50B, 91 Color filter (CF) substrate, 12, 53, 92 Black matrix (BM), 13, 54 Colored layer, 20, 60, 60A, 60B Thin film transistor (TFT) substrate, 23, 81 common electrode, 24 pixel electrode, 30, 70 liquid crystal layer, 52, 85, 86 counter electrode, 65 TFT element, 66 scanning line, 67 signal line, 100 Liquid crystal display device, 101 control unit, 102 display drive unit, 103 ON / OFF switch unit, 104 power supply unit, 105 timing unit.

Claims (6)

A pixel electrode provided on a surface of one of the pair of substrates on the liquid crystal layer side, and a pair of substrates disposed opposite to each other, and a liquid crystal layer sandwiched between the pair of substrates. A liquid crystal display device that performs display by generating an electric field between a common electrode and controlling an alignment direction of liquid crystal molecules constituting the liquid crystal layer,
Of the pair of substrates, a counter electrode provided on the surface of the other substrate on the liquid crystal layer side and facing the one substrate;
A counter electrode applying means for applying a voltage to the counter electrode;
When the display starts, the application of voltage to the counter electrode is started, and when a predetermined voltage application time has elapsed from the start of display, the application of voltage to the counter electrode is stopped and the counter electrode is floated. A liquid crystal display device comprising: control means for controlling the counter electrode application means so as to be in a state. A common electrode applying means for applying a predetermined voltage to the common electrode;
The liquid crystal display device according to claim 1, wherein the counter electrode application unit applies a voltage equal to a voltage applied to the common electrode by the common electrode application unit to the counter electrode. The common electrode is provided with a common electrode applying means for applying a time-varying voltage,
2. The liquid crystal display according to claim 1, wherein the counter electrode application unit applies a voltage equal to a time average value of a voltage applied to the common electrode by the common electrode application unit to the counter electrode. apparatus. The other substrate comprises a translucent substrate, a black matrix and a colored layer provided on the surface of the translucent substrate, and an overcoat film covering the black matrix and the colored layer,
The counter electrode is
Formed of a translucent conductive material having translucency and conductivity,
Between the translucent substrate and the black matrix, between the translucent substrate and the colored layer, between the black matrix and the overcoat film, and between the translucent substrate and the colored layer. 2. It is provided in any one position between layers, and between the black matrix and the overcoat film and between the colored layer and the overcoat film. The liquid crystal display device according to any one of? The other substrate is provided on the surface on the liquid crystal layer side, and includes a black matrix formed of a material selected from metal chromium (Cr) and an oxide thereof,
The liquid crystal display device according to claim 1, wherein the black matrix functions as the counter electrode.   6. The liquid crystal display device according to claim 1, wherein the voltage application time is selected from 1 second to 60 minutes.

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