JP4686260B2 - Liquid crystal display panel and driving method thereof - Google Patents

Description

  The present invention relates to an OCB (optically compensated bend) mode liquid crystal display panel and a driving method thereof.

  Liquid crystal display panels are widely used for screen display of personal computers, car navigation systems, monitors, TVs, and the like. As a liquid crystal display mode used for these liquid crystal displays, a TN mode and a STN mode using a nematic liquid crystal are often used. Furthermore, a liquid crystal display mode using a ferroelectric liquid crystal or the like that has a fast response speed and a wide viewing angle is also known, but improvement is required for shock resistance, temperature characteristics, and the like. On the other hand, as a mode with excellent high-speed response and a wide viewing angle, an optical compensation type in which liquid crystal molecules are aligned in parallel, that is, an OCB mode, is attracting attention and is actively developed for video equipment instead of twist alignment. It has been broken.

  In general, an active matrix liquid crystal display panel has a structure in which a liquid crystal layer is sandwiched between an array substrate and a counter substrate. The array substrate includes, for example, a plurality of pixel electrodes arranged in a substantially matrix, a plurality of scanning electrodes arranged along a row of the plurality of pixel electrodes, and a plurality of data signals arranged along a column of the plurality of pixel electrodes. A plurality of switching elements are disposed in the vicinity of the intersection positions of the electrodes, the plurality of scan electrodes, and the plurality of data signal electrodes. Each switching element is formed of, for example, a thin film transistor (TFT), and conducts when one scanning electrode is driven, and applies the potential of one data signal electrode to one pixel electrode. On the counter substrate, a counter electrode is provided to face the plurality of pixel electrodes arranged on the array substrate. The pair of pixel electrodes and the counter electrode constitute a pixel together with the pixel region of the liquid crystal layer, and the liquid crystal molecule arrangement in the pixel region is controlled by an electric field corresponding to a driving voltage held between the pixel electrode and the counter electrode.

  In the OCB mode liquid crystal display panel, liquid crystal molecules are splayed before power-on. This splay alignment is a state in which liquid crystal molecules are almost lying, and is obtained by alignment films that are rubbed in parallel on the pixel electrode and the counter electrode. The display operation of this liquid crystal display panel is initiated by applying a transition voltage to the liquid crystal layer when the power is turned on, and shifting the alignment state of the liquid crystal molecules from the splay alignment to the bend alignment by a relatively strong electric field corresponding to the transition voltage. Performed after processing. The alignment state of the liquid crystal molecules is maintained in the bend alignment during the display operation, and the high-speed response characteristic of the OCB mode is excellent and a display with a wide viewing angle is realized.

  In addition, the alignment state of the liquid crystal molecules reversely transitions from the bend alignment to the splay alignment again when a voltage application state below the level at which the splay alignment energy and the bend alignment energy antagonize or when no voltage is applied for a long period of time. . In the OCB mode liquid crystal display panel, a black insertion drive system is employed to prevent this reverse transition. In the black insertion drive, the reverse transition prevention voltage and the display voltage corresponding to the video signal are alternately applied to the liquid crystal layer as the drive voltage in the frame period to maintain the bend alignment. The OCB mode liquid crystal display panel is a normally white mode display panel, and the reverse transition prevention voltage corresponds to the black display voltage. Further, the ratio of the application period of the reverse transition prevention voltage to the total application period of the display voltage and the reverse transition prevention voltage is called a black insertion rate.

  In the manufacture of the liquid crystal display panel, after the array substrate 1 and the counter substrate 2 shown in FIG. 5A are separately formed, a rubbing process is performed on the alignment film on the array substrate 1 side and the alignment film on the counter substrate 2 side. The array substrate 1 and the counter substrate 2 are bonded to each other through the seal resin layer 3. The sealing resin layer 3 is applied so as to surround the liquid crystal injection space, leaving the injection port 4, and the injection port 4 is provided in the vicinity of the second side facing the first side of the array substrate 1 on which the driver circuit elements are arranged. It is done. The rubbing process of each alignment film is performed in the same direction from the second side to the first side so as not to electrostatically damage the driver circuit element. In FIG. 5A, RD1 represents the rubbing direction of the alignment film on the array substrate 1 side, and RD2 represents the rubbing direction of the alignment film on the counter substrate 2 side. The liquid crystal material is filled from the inlet 4 into the liquid crystal injection space as the liquid crystal layer LQ, and the inlet 4 is further sealed with the sealing material 5.

In the above manufacturing process, it is inevitable that impurity ions are mixed into the liquid crystal layer LQ. Specifically, the sealing material 5 releases the most impurity ions to the liquid crystal layer LQ. The impurity ions lower the insulation resistance of the liquid crystal and cause display characteristics to deteriorate due to a decrease in voltage holding ratio. Further, when the impurity ions move in the liquid crystal layer when the driving voltage is applied and the distribution of the impurity ions becomes nonuniform, display defects such as display unevenness occur. In order to prevent such non-uniform distribution of impurity ions, for example, a technique has been proposed in which an ion trap electrode is provided on a substrate and a high potential pulse is sequentially applied to a plurality of electrodes arranged in one direction (Patent Literature). 1). However, it is difficult to apply this technique in order to solve the problems caused in the OCB mode liquid crystal display panel.
JP-A-9-54325

  In the OCB mode liquid crystal display panel, liquid crystal molecules are bend-aligned in the liquid crystal layer LQ for display operation. The orientation angle of liquid crystal molecules changes greatly between a white display state in which a low voltage is applied to the liquid crystal layer LQ and a black display state in which a high voltage is applied to the liquid crystal layer LQ. Since the change in the orientation angle is accompanied by the displacement of the liquid crystal molecules, the liquid crystal molecules flow in the direction of the displacement in the liquid crystal layer LQ. The flow direction coincides with the rubbing direction of the alignment film that aligns the liquid crystal molecules in the OCB mode liquid crystal display panel. When the impurity ions move in the rubbing directions RD1 and RD2 shown in FIG. 5A, the impurity ions DF having a high concentration in the vicinity of the inlet 4 are diffused into the liquid crystal layer LQ as shown in FIG. 5B, and the black insertion driving is continued. As a result, display unevenness due to a partial decrease in charge retention occurs. This can be verified, for example, by continuously performing an operation of displaying the image of the evaluation pattern shown in FIG. 5C while performing black insertion driving, and thereafter displaying an image of a pattern that is entirely black. In this case, the whole is not black, but gray stripes as shown in FIG. 5D are observed as partial burn-in. Impurity ions flow from the white display area shown in FIG. 5C into the black display area and are concentrated during the black insertion drive. Gray streaks are generated by a decrease in charge retention due to concentrated impurity ions, that is, a loss of applied voltage.

  It is difficult to solve the image sticking problem that occurs in the OCB mode liquid crystal display panel only by applying a high potential pulse as in the above-mentioned document.

  An object of the present invention is to provide an OCB mode liquid crystal display panel that can suppress display unevenness caused by impurity ions that have entered a display region when black insertion driving is performed in a display operation, and a driving method thereof. To do.

  According to the present invention, a pair of electrode substrates, a liquid crystal layer that is sandwiched between the pair of electrode substrates and in which the alignment state of liquid crystal molecules is controlled by a driving voltage applied from these electrode substrates inside the display region, and the liquid crystal And a pair of alignment films arranged on a pair of electrode substrates adjacent to each other and parallel to each other in a rubbing direction. The display region includes a plurality of pixels arranged in a matrix, and the rubbing direction of the pair of alignment films is displayed. An OCB mode liquid crystal display panel is provided that is substantially opposite to a scanning direction in which a plurality of rows of pixels are sequentially selected to apply a driving voltage in operation.

  According to the present invention, a pair of electrode substrates, a liquid crystal layer that is sandwiched between the pair of electrode substrates and in which the alignment state of liquid crystal molecules is controlled by a driving voltage applied from these electrode substrates inside the display region, and the liquid crystal A driving method of a liquid crystal display panel including a plurality of pixels arranged on a pair of electrode substrates adjacent to a layer and having a pair of alignment films parallel to each other in a rubbing direction, the display region being arranged in a matrix, A driving method comprising: sequentially selecting a plurality of pixel rows for a display operation in a scanning direction substantially opposite to the rubbing direction; and applying a driving voltage to the pixels in the selected row. Provided.

  In this liquid crystal display panel and driving method, the rubbing direction of the pair of alignment films is substantially opposite to the scanning direction. As a result, even if impurity ion drift occurs in the rubbing direction with black insertion driving, the scanning direction is opposite to the rubbing direction, so that the flow of impurity ions does not move continuously. Therefore, even when the liquid crystal display panel is driven for a long time, display unevenness caused by impurity ions entering the display region can be suppressed.

  Hereinafter, an OCB mode liquid crystal display panel LCD according to an embodiment of the present invention will be described with reference to the drawings. 1 shows a planar structure of a liquid crystal display panel LCD, FIG. 2 shows a circuit structure of the liquid crystal display panel LCD, and FIGS. 3A to 3C show cross-sectional structures of the liquid crystal display panel LCD. As shown in FIG. 1, the liquid crystal display panel LCD includes an array substrate 1, a counter substrate 2, and a liquid crystal layer LQ held between the substrates 1 and 2. The array substrate 1 and the counter substrate 2 are a pair of electrode substrates, and are bonded together via a seal resin layer 3 applied so as to surround the liquid crystal injection space leaving the injection port 4 in the gap between the substrates 1 and 2. . The liquid crystal layer LQ is obtained, for example, by filling a liquid crystal injection space with a nematic liquid crystal material from the injection port 4 and sealing the injection port 4 with a sealing material 5.

  In the liquid crystal display panel LCD, the display screen includes a plurality of pixels 11 shown in FIG. The array substrate 1 includes a plurality of pixel electrodes 23 arranged in a matrix in a display area 10 corresponding to a display screen, a plurality of scanning electrodes 12 arranged along a row of the pixel electrodes 23, and the pixel electrodes 23. A plurality of thin film transistors (TFTs) 17 arranged as switching elements in the vicinity of intersections of the plurality of data signal electrodes 13, the plurality of scanning electrodes 12, and the plurality of data signal electrodes 13 arranged along the column, and a plurality of pixels at one end A storage capacitor 20 connected to each of the electrodes 23, a scanning circuit 14 connected to the plurality of scanning electrodes 12, and a data signal circuit 15 connected to the plurality of data signal electrodes 13 are provided. Each scanning electrode 12 is connected to the gate of the thin film transistor 17 in the corresponding row, and each data signal electrode 13 is connected to the drain of the thin film transistor 17 in the corresponding column. Each pixel electrode 23 is connected to the source of the corresponding thin film transistor 17. The plurality of auxiliary capacitors 20 are connected to the common wiring 16 at the other end. Here, each thin film transistor 17 is formed as an n-channel MOS transistor. The counter substrate 2 includes a counter electrode 27 that faces the plurality of pixel electrodes 23. Each pixel 11 includes a pixel electrode 23, a counter electrode 27, and a part of the liquid crystal layer LQ disposed between the electrodes 23 and 27, and holds a drive voltage corresponding to a potential difference between the pixel electrode 23 and the counter electrode 27. Configure the liquid crystal capacitance. The auxiliary capacitor 20 is provided in parallel with the liquid crystal capacitor in order to stably maintain the drive voltage.

  The scanning circuit 14 sequentially outputs scanning signals for each horizontal scanning period to the plurality of scanning electrodes 12 along the scanning direction 7 shown in FIGS. 1 and 2, and the data signal circuit 15 drives each scanning electrode 12 by the scanning signal. During this period, the video signals for one row are converted into pixel voltages, and these pixel voltages are output to the plurality of data signal electrodes 13. These pixel voltages are applied to the pixel electrodes 23 in the corresponding rows through the thin film transistors 17 for one row that are turned on by the scanning signal. This pixel voltage is a voltage applied to the pixel electrode 23 with reference to the common voltage set for the counter electrode 27. For example, the polarity of the pixel voltage is inverted with respect to the common voltage every one frame period and one horizontal scanning period. The transmittance of each pixel 11 is controlled corresponding to the driving voltage between the pixel electrode 23 and the counter electrode 27. The scanning direction 7 is a direction in which rows of a plurality of pixels 11 are sequentially selected in order to apply a driving voltage in a display operation.

  As shown in FIG. 3A, in the array substrate 1, the pixel electrode 23 is formed on a transparent insulating substrate 22 such as a glass substrate and covered with an alignment film 24. In the counter substrate 2, the counter electrode 27 is formed on the color filter layer 26 that covers the transparent insulating substrate 25 such as a glass substrate, and is covered with an alignment film 28. The array substrate 2 and the counter substrate 2 are bonded so that the alignment films 24 and 28 are adjacent to the liquid crystal layer LQ. The liquid crystal display panel LCD further includes a pair of optical compensation phase difference plates 30, a pair of polarizing plates 31, and a light source backlight 32. The pair of retardation plates 30 are attached to the transparent insulating substrates 22 and 25 on the side opposite to the liquid crystal layer LQ, and the pair of polarizing plates 31 are attached to the pair of retardation plates 30. The light source backlight 32 is disposed adjacent to the polarizing plate 31 on the array substrate 1 side.

  In this liquid crystal display panel LCD, the alignment film 24 and the alignment film 28 are rubbed in directions parallel to each other. In FIG. 1, RD 1 represents the rubbing direction of the alignment film 24, and RD 2 represents the rubbing direction of the alignment film 28. As a result, the liquid crystal molecules of the liquid crystal layer LQ are splay aligned as shown in FIG. 3A as an initial state. In this initial state, the liquid crystal molecules in the liquid crystal layer 29 near the surfaces of the alignment films 24 and 28 have a high pretilt angle (5 ° to 12 °) with respect to the surfaces of the alignment films 24 and 28.

  The above rubbing process is performed as shown in FIG. 4, for example. In this rubbing process, as in the other liquid crystal display modes, the array substrate 1 and the counter substrate 2 coated with the alignment film material as the alignment films 24 and 28 are prepared. Each of the array substrate 1 and the counter substrate 2 is mounted on the stage with the long side parallel to the axis of the rubbing roller 33, and moves in the direction of arrow X across the rubbing roller 33 together with the stage. A rubbing cloth 34 is wound around the rubbing roller 33. The rubbing cloth 34 rotates together with the rubbing roller 33 while being in contact with the alignment film 28. Thereby, each of the array substrate 1 and the counter substrate 2 is rubbed in the rotation direction of the rubbing roller 33, that is, in the direction of the arrow Y orthogonal to the rotation axis of the rubbing roller 33.

  In this liquid crystal display panel LCD, the scanning circuit 14 and the data signal circuit 15 apply a transition voltage different from the display voltage as a drive voltage to all the pixels 11 in units of rows as the power is turned on, and the alignment state of the liquid crystal molecules is sprayed. Initialization for transition from the orientation to the bend orientation shown in FIGS. 3B and 3C is performed. FIG. 3B shows the bend orientation obtained when the white display voltage is applied, and FIG. 3C shows the bend orientation obtained when the black display voltage is applied. The white display voltage is zero or a small value close to zero, and the pixel 11 is set to a high luminance state that transmits the backlight 32 light with high transmittance. The black display voltage is larger than the white display voltage, and the pixel 11 is set in a low luminance state that transmits the backlight 32 light with low transmittance. The luminance of each pixel 11 varies in the range of the luminance for white display and the luminance for black display in order to display an image.

  The scanning circuit 14 and the data signal circuit 15 further have a predetermined black insertion rate, for example, every frame period in the display operation after initialization in order to prevent the orientation state of the liquid crystal molecules from reversely transitioning from the bend orientation to the splay orientation. Black insertion driving is performed in which a reverse transition prevention voltage corresponding to the black display voltage is sequentially applied to all the pixels 11 (liquid crystal layer LQ) in the scanning direction 7 in units of rows.

In the manufacture of the liquid crystal display panel LCD, after performing the forming process for integrally forming the array substrate 1, the counter substrate 2, the liquid crystal layer LQ, the pair of alignment films 24 and 28, etc. as a display panel as described above, a white display is performed. A voltage and a black display voltage are alternately applied to the liquid crystal layer LQ in each frame period, and the operation of generating a flow of liquid crystal molecules along the rubbing direction is continued for a predetermined period, whereby the liquid crystal layer LQ is aligned along the rubbing direction. An aging process for moving the impurity ions contained in the outside of the display region 10 is performed. The black display voltage and black insertion rate for aging treatment are set independently of the black display voltage and black insertion rate for driving black insertion, which prevents the orientation state of liquid crystal molecules from reverse transition from bend alignment to splay alignment. . As a result of this aging treatment, the impurity ion concentration contained in the liquid crystal layer LQ located in the display region 10 is as low as about 1/2 to 1/5 of the impurity ion concentration contained in the liquid crystal layer LQ located outside the display region 10. Set to a value.

  The rubbing directions RD1 and RD2 of the pair of alignment films 24 and 28 coincide with the scanning direction for aging processing from the top to the bottom of the screen of the display panel LCD (the direction opposite to the scanning direction 7 shown in FIG. 1). In this case, drift of impurity ions occurs downward for the pixels 11 in each row due to periodic changes in the drive voltage corresponding to the white display voltage and the black display voltage, and also occurs in the subsequent pixels 11 that are sequentially scanned. Thus, the impurity ions continuously move to the lower end of the display area 10 in the rubbing directions RD1 and RD2, and are efficiently discharged as a whole to the outside of the display area 10. Therefore, by performing this aging process, display unevenness due to impurity ions that are unevenly concentrated in the display region 10 due to black insertion driving when an image is displayed on the liquid crystal display panel LCD can be reduced.

  In the liquid crystal display panel of the present embodiment, a scanning signal is sequentially applied to the plurality of scanning electrodes 12 in the scanning direction 7 opposite to the rubbing directions RD1 and RD2 in order for the scanning circuit 14 to perform a display operation. In this case, as shown in FIG. 5C, impurity ion drift accompanying black insertion driving occurs downward for each pixel 11 in one line, but such downward drift is opposite to the rubbing directions RD1 and RD2. In the scanning direction 7, the pixels sequentially occur in the subsequent lines up to the top of the screen. At this time, the impurity ions do not flow in a continuous manner in the rubbing directions RD1 and RD2 throughout the display region 10. That is, it is alleviated that such a flow causes a state in which impurity ions are unevenly distributed in a certain region. As a result, even if the liquid crystal display panel LCD is driven for a long period of time, display unevenness caused by impurity ions that have entered the display region 10 can be suppressed.

  If the rubbing directions RD1 and RD2 coincide with the scanning direction 7, the downward drift of the impurity ions generated in one line of pixels 11 sequentially continues from the upper part of the screen toward the lower part. For this reason, the flow of impurity ions is generated in the entire display region 10, thereby making it easy to generate a state in which impurity ions are unevenly distributed in a certain region.

It is a figure which shows the planar structure of the liquid crystal display panel of OCB mode which concerns on one Embodiment of this invention. FIG. 2 is a diagram showing a circuit structure of the OCB mode liquid crystal display panel shown in FIG. 1. It is a figure which shows the cross-sectional structure and liquid crystal molecular orientation of the liquid crystal display panel of OCB mode shown in FIG. It is a figure which shows the cross-sectional structure and liquid crystal molecular orientation of the liquid crystal display panel of OCB mode shown in FIG. It is a figure which shows the cross-sectional structure and liquid crystal molecular orientation of the liquid crystal display panel of OCB mode shown in FIG. It is a figure which shows the rubbing process with respect to the alignment film shown to FIG. 3A-FIG. 3C. It is a top view for demonstrating the problem which generate | occur | produces in the liquid crystal display panel of OCB mode. It is a top view for demonstrating the problem which generate | occur | produces in the liquid crystal display panel of OCB mode. It is a top view for demonstrating the problem which generate | occur | produces in the liquid crystal display panel of OCB mode. It is a top view for demonstrating the problem which generate | occur | produces in the liquid crystal display panel of OCB mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Array substrate, 2 ... Counter substrate, 3 ... Sealing resin layer, 4 ... Injection port, 5 ... Sealing material, RD1, RD2 ... Rubbing direction, 7 ... Scanning direction, 10 ... Display area, 11 ... Pixel, 12 ... Scan electrode, 13 ... Data signal electrode, 14 ... Scan circuit, 15 ... Data signal circuit, 16 ... Common wiring, 17 ... Thin film transistor, 23 ... Pixel electrode, 24, 28 ... Alignment film, 26 ... Color filter layer, 27 ... Opposite Electrode, LQ ... liquid crystal layer, LCD ... liquid crystal display panel.

Claims (6)

A pair of electrode substrates, a liquid crystal layer sandwiched between the pair of electrode substrates and in which the alignment state of liquid crystal molecules is controlled by a driving voltage applied from these electrode substrates inside the display region, and adjacent to the liquid crystal layer A pair of alignment films disposed on the pair of electrode substrates and having rubbing directions parallel to each other,
The display area includes a plurality of pixels arranged in a matrix, the rubbing direction of the pair of alignment films, the sequentially selected scanning direction the rows of the plurality of pixels for applying a driving voltage in the display operation An OCB mode liquid crystal display panel characterized by being in the reverse direction. Rubbing directions of the two alignment films is in the aging process of moving the impurity ions contained in the liquid crystal layer outside the display area by a flow of the liquid crystal molecules, sequentially selects a row of the plurality of pixels for applying a driving voltage the liquid crystal display panel of claim 1, wherein the match in the scanning direction. 2. The driving circuit according to claim 1, further comprising: a driving circuit configured to periodically apply a reverse transition preventing voltage for maintaining the alignment state of the liquid crystal molecules to bend alignment as the driving voltage to the pixels in each row. LCD display panel. A pair of electrode substrates, a liquid crystal layer sandwiched between the pair of electrode substrates and in which the alignment state of liquid crystal molecules is controlled by a driving voltage applied from these electrode substrates inside the display region, and adjacent to the liquid crystal layer A driving method of a liquid crystal display panel including a plurality of pixels arranged on a pair of electrode substrates and having a pair of alignment films parallel to each other in a rubbing direction, wherein the display region is arranged in a matrix,
A drive comprising: sequentially selecting a plurality of pixel rows for a display operation in a scanning direction opposite to the rubbing direction; and applying a driving voltage to the pixels in the selected row. Method. The display area by a flow of the liquid crystal molecules impurity ions contained in the liquid crystal layer by applying a sequentially selected and the driving voltage to match the scanning direction to the rubbing direction of the plurality of alignment layer line of the pair of pixels The driving method according to claim 4, wherein an aging process of moving outward is performed. 5. The driving method according to claim 4, wherein a reverse transition prevention voltage for maintaining the alignment state of the liquid crystal molecules in the bend alignment is periodically applied to the pixels in each row as the driving voltage.

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