JP4861642B2 - Manufacturing method of liquid crystal display panel - Google Patents

Description

  The present invention relates to an OCB (optically compensated bend) mode liquid crystal display panel and a method of manufacturing the same.

  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 injection port 4 diffuse into the liquid crystal layer LQ as shown in FIG. 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 when black insertion driving is performed in a display operation, and a method of manufacturing the same.

  According to the present invention, 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, A step of integrally forming a pair of alignment films that are arranged adjacent to each other on a pair of electrode substrates and whose rubbing directions are parallel to each other as a display panel, and preventing the reverse transition of the alignment state of liquid crystal molecules from bend alignment to splay alignment The operation of generating a flow of liquid crystal molecules along the rubbing direction by applying a drive voltage that periodically changes at a black insertion rate that is set independently of the black insertion rate for black insertion driving to the liquid crystal layer. And an aging process for moving impurity ions contained in the liquid crystal layer to the outside of the display region by continuing over a period of time, and a method of manufacturing an OCB mode liquid crystal display panel There is provided.

  In these OCB mode liquid crystal display panels and manufacturing methods thereof, as a result of the aging process in the manufacturing process, the impurity ion concentration contained in the liquid crystal layer located in the display region is the impurity ion concentration contained in the liquid crystal layer located outside the display region. It is possible to reduce the impurity ions concentrated in the display region when black insertion driving is performed in the display operation, and to suppress display unevenness due to the concentrated impurity ions. .

  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.

  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 to all the pixels 11 as a drive voltage when the power is turned on, and the alignment state of the liquid crystal molecules is illustrated from the splay alignment. It is configured to perform initialization for transition to the bend orientation shown in 3B and FIG. 3C. 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. When the black insertion drive is employed, 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. Further, the white display voltage when the black insertion drive is not employed is set to a low voltage (for example, around 1 to 2 volts) in a range in which the bend-aligned liquid crystal molecules do not return to the splay alignment. On the other hand, 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 a 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.

  As shown in FIG. 1, when the rubbing directions RD1 and RD2 coincide with the scanning direction 7 from the top to the bottom of the screen of the display panel LCD, the drift of the impurity ions is periodic corresponding to the white display voltage and the black display voltage. Due to the change in the driving voltage, the pixel 11 of each row is generated downward, and further occurs in the subsequent pixels 11 that are sequentially scanned. Thereby, the impurity ions continuously move to the lower end of the display area 10 in the direction of the arrow 8 and are efficiently discharged outside the display area 10 as a whole. Therefore, by performing this aging process, display unevenness due to impurity ions that are unevenly concentrated due to black insertion driving in the display region 10 when an image is displayed on the liquid crystal display panel can be reduced.

  If the rubbing directions RD1, RD2 and the scanning direction 7 are matched as described above as described above, it is possible to effectively move the impurity ions in the aging process. Even if the two are not opposite to each other, the impurity ions can be reliably discharged by appropriately setting the aging treatment conditions. For example, the black display voltage for aging processing is set to 6 V that is slightly larger than the black display voltage for black insertion drive (= 5 V). In this way, a large aging effect can be obtained by setting the aging voltage to, for example, 5 to 6 volts.

  Further, when the black insertion rate for aging processing, that is, the ratio of the black display voltage application period to the total application period (one frame period) of the white display voltage and the black display voltage is increased, the impurity ion discharge efficiency is improved. However, the aging process has an optimum black insertion rate of 50 to 80%. In this embodiment, a black insertion rate of 70% was adopted in the aging process, and good results were obtained.

  The higher the aging treatment temperature, the more effectively the impurity ions can be discharged. In the present embodiment, the aging treatment temperature was set to 60 ° C., which is higher than normal temperature, and good results were obtained. However, when the processing temperature exceeds the NI temperature, good results cannot be obtained. Further, since the polarizing plate 31 is damaged by increasing the aging treatment temperature, 70 ° C. is the upper limit of the aging treatment temperature. It was confirmed that the impurity ion discharge effect was obtained at an aging temperature of 40 ° C. or higher.

  The longer the aging treatment time, the more effectively the impurity ions can be discharged. The impurity ion discharge effect can be obtained by setting the aging treatment to 1 hour or more, but it is saturated when it is set over 12 hours. Therefore, it is appropriate that the aging processing time is set in the range of 1 hour to 12 hours. However, considering the relationship between the impurity ion discharge effect and the aging treatment time from the viewpoint of production efficiency, it is appropriate to set the aging treatment time in the range of 3 to 5 hours. In this embodiment, the aging processing time is set to 3 hours, and good results are obtained.

  Further, a dummy electrode is provided in an external region adjacent to the upper side or the lower side of one side of the display region 10 positioned on the end side in the rubbing direction, and a white display voltage is constantly applied to the dummy electrode, thereby terminating the end of the display region 10. The effect of transferring impurity ions to a position substantially away from the portion can be obtained.

  In the description of the problem of the present invention, the elimination of display unevenness that appears as line burn-in at the boundary between white and black has been described. However, the present invention is not limited to this, and the same effect can be obtained. For example, in some cases, due to the effect of thermal diffusion, display unevenness may occur at a location where the black area has entered about 2 mm. In the above example, the flow in the rubbing direction has been described. However, there is an example in which impurity ions drift even in the reverse direction. That is, depending on the difference in ion mobility, it is determined which flow drifts. In any case, if the impurity ions are discharged by the above-described aging treatment, display unevenness can be suppressed.

  In the above-described embodiment, the scanning circuit 14 and the data signal circuit 15 are configured by using a plurality of thin film transistors arranged on the array substrate 1 of the liquid crystal display panel LCD, but these are arranged outside the liquid crystal display panel LCD. It may be replaced by an integrated circuit (IC).

  Further, the present invention may be applied to an OCB mode liquid crystal display panel that does not perform black insertion driving.

In this case, if the white display voltage used in the aging process is set to zero (V), it becomes easy to reversely transition from the bend alignment to the splay alignment. Therefore, in order to prevent the reverse transition, a low voltage of about 1 to 2 volts is set. It is preferable.

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 (7)

A pair of electrode substrates, a liquid crystal layer sandwiched between the pair of electrode substrates and in which the orientation state of liquid crystal molecules is controlled by a driving voltage applied from these electrode substrates in the display region, and a pair of electrode substrates adjacent to the liquid crystal layer A step of integrally forming a pair of alignment films that are arranged and whose rubbing directions are parallel to each other as a display panel;
Applying a drive voltage to the liquid crystal layer that periodically changes with the black insertion rate set independently of the black insertion rate for black insertion driving, which prevents the orientation state of the liquid crystal molecules from reverse transition from bend alignment to splay alignment And performing an aging process of moving the impurity ions contained in the liquid crystal layer to the outside of the display region by continuing the operation of generating the flow of liquid crystal molecules along the rubbing direction over a predetermined period. A method of manufacturing an OCB mode liquid crystal display panel, which is characterized.   2. The manufacturing method according to claim 1, wherein the drive voltage for the aging process is a substantially black display voltage and a substantially white display voltage applied alternately in each frame period.   The manufacturing method according to claim 2, wherein the black insertion rate for the aging process is a value that exceeds the black insertion rate for black insertion driving.   The manufacturing method according to claim 3, wherein the black insertion rate for the aging treatment is 50% or more.   The manufacturing method according to claim 4, wherein a black insertion rate for the aging treatment is 50% to 80%.   The manufacturing method according to claim 2, wherein the black display voltage for the aging process is set larger than the black display voltage for the black insertion drive.   The manufacturing method according to claim 2, wherein a processing temperature of the aging processing is set higher than normal temperature.

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