JP5067930B2 - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which can suppress a display defect such as display non-uniformity due to non-uniformity ions in a liquid crystal layer and has high display quality and high reliability. <P>SOLUTION: The liquid crystal display device includes a liquid crystal layer LQ which is held between a first substrate 12 and a second substrate 14, and has a display section 10A which is composed of a plurality of display pixels PX arrayed in a matrix and a peripheral section 10B which surrounds the display section 10A. The first substrate 12 includes pixel electrodes PE disposed in association with the plurality of display pixels PX. The second substrate 14 includes a counter electrode CE which is opposed to the plurality of pixel electrodes PE. The device includes a pair of alignment layers which are disposed on the plurality of pixel electrodes PE and on the counter electrode CE and control an alignment state of liquid crystal molecules included in the liquid crystal layer LQ by rubbing treatment. Dummy display pixels DPX in which a fixed voltage is applied to the liquid crystal layer LQ, are disposed at least on the terminal end side of the peripheral section 10B in the rubbing direction D1 of the alignment layer. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device.

  In general, a liquid crystal display device includes a liquid crystal display panel including a display unit on which an image is displayed. The liquid crystal display panel includes a pair of substrates facing each other. A liquid crystal layer is sandwiched between the pair of substrates.

  One substrate has a plurality of pixel electrodes arranged in a substantially matrix form. The other substrate includes a counter electrode facing the plurality of pixel electrodes. A pair of alignment films for aligning the liquid crystal is disposed on the plurality of pixel electrodes and the counter electrode. The alignment state of the liquid crystal can be obtained by controlling the alignment of liquid crystal molecules on the pair of alignment film surfaces. As a method for controlling the alignment of liquid crystal molecules, for example, there is a rubbing method. In the rubbing method, the alignment film is rubbed with a rubbing cloth. Then, the average direction of the major axis of the liquid crystal molecules is controlled by the rubbing process.

  In recent years, so-called black insertion driving that repeats black signal writing and video signal writing in one frame period has attracted attention in order to improve the video quality and improve the response speed in a liquid crystal display panel. In the operation of the liquid crystal display panel to which this driving method is applied, the orientation state of the liquid crystal molecules is periodically changed by periodically applying the black signal and the video signal. As a result, in the liquid crystal layer, a flow is generated in the same direction as the rubbing direction of the alignment film.

  Further, there are cases where ions are taken in in the assembly process of the liquid crystal display device, or that the material itself such as a glass substrate constituting the liquid crystal display device contains ions. Such ions move in the liquid crystal layer by the flow generated in the liquid crystal layer in the display unit. On the other hand, since no flow occurs in the liquid crystal layer in the peripheral portion, ions may aggregate near the boundary between the display portion and the peripheral portion. In the portion where the ions of the liquid crystal layer are aggregated, the transmittance-applied voltage characteristic is changed, which may be recognized as display unevenness.

Conventionally, in an OCB (Optically Compensated Birefringence) mode liquid crystal display device, an ion trap electrode provided in a peripheral portion surrounding the display portion with respect to a problem that spacers such as beads and impurity ions move due to a flow caused by a change in orientation of liquid crystal molecules. An invention has been proposed in which impurity ions are gathered together to provide a liquid crystal display device in which display defects such as display unevenness do not occur (see Patent Document 1).
JP-A-9-54325

  However, in the above invention, the rubbing direction of the alignment film is not taken into consideration, and it has been difficult to effectively suppress display defects due to ions moving in the rubbing direction. In addition, when a constant DC voltage that causes the liquid crystal molecules to bend in the peripheral portion is applied to the liquid crystal layer, the viscosity of the liquid crystal layer also increases. Therefore, diffusion of the liquid crystal layer is less likely to occur in the peripheral area, and impurity ions that have moved in one direction due to the flow of the liquid crystal layer do not move to the peripheral area, but aggregate in the vicinity of the boundary with the peripheral area of the display area. There was something to do.

  Therefore, when aggregation of ions occurs on the end side in the rubbing direction, the transmissivity-applied voltage characteristics of the liquid crystal layer change due to the ions, and in particular, the transmissivity-applied voltage characteristics of the liquid crystal layer change within the display portion, resulting in display unevenness. And so on.

  The present invention has been made in view of the above problems, and provides a liquid crystal display device that suppresses display defects such as display unevenness due to nonuniformity of ions in a liquid crystal layer, and has high display quality and reliability. The purpose is to do.

A liquid crystal display device according to an aspect of the present invention includes an OCB mode liquid crystal layer sandwiched between a first substrate and a second substrate, and a display unit including a plurality of display pixels arranged in a matrix, and the display unit And a peripheral portion surrounding the display device, wherein the first substrate has pixel electrodes arranged corresponding to each of the plurality of display pixels, and the second substrate has the plurality of pixels. A pair of alignment films, each having a counter electrode facing the electrode, disposed on each of the plurality of pixel electrodes and the counter electrode, and controlling the alignment state of liquid crystal molecules contained in the liquid crystal layer by rubbing treatment; wherein at least the terminating side of the rubbing direction of the alignment film in the peripheral portion is arranged dummy display pixels reverse transition prevention signal is applied, the thickness of the liquid crystal layer in the dummy display pixels of the peripheral portion, the display It is formed smaller than the thickness of the liquid crystal layer in the display pixels.

  According to the present invention, it is possible to provide a liquid crystal display device with high display quality and reliability by suppressing display defects such as display unevenness due to non-uniformity of ions in the liquid crystal layer.

  Hereinafter, a liquid crystal display device according to a first embodiment of the present invention will be described with reference to the drawings. The liquid crystal display device according to this embodiment is an OCB mode liquid crystal display device, and is sandwiched between an array substrate 12 (shown in FIG. 7), a counter substrate 14 (shown in FIG. 7), and the array substrate and the counter substrate. The liquid crystal display panel 10 having the liquid crystal layer LQ is provided.

  As shown in FIGS. 1 and 3, the liquid crystal display panel 10 has a substantially rectangular shape, a display portion 10A composed of a plurality of display pixels PX arranged in a matrix, and a peripheral portion surrounding the periphery of the display portion 10A. 10B. In the color display type liquid crystal display device, various display pixels such as, for example, a red display pixel, a green display pixel, and a blue display pixel are arranged as the display pixel PX in the display unit 10A.

The array substrate 12 has a plurality of pixel electrodes PE arranged in a substantially matrix shape corresponding to each display pixel PX. The counter substrate 14 includes a counter electrode CE that faces a plurality of pixel electrodes PE.

  A pair of alignment films (not shown) for aligning the liquid crystal is disposed on the plurality of pixel electrodes PE and the counter electrode CE. The alignment state of the liquid crystal can be obtained by controlling the alignment of liquid crystal molecules on the pair of alignment film surfaces. In the liquid crystal display device according to the present embodiment, the pair of alignment films are rubbed in a predetermined direction to control the alignment state of the liquid crystal molecules included in the liquid crystal layer LQ.

  The liquid crystal molecules contained in the liquid crystal layer LQ are aligned so that their long axes generally follow the rubbing direction of the alignment film 16. In the liquid crystal display device according to the present embodiment, the alignment films of the array substrate 12 and the counter substrate 14 are rubbed in a direction D1 that is substantially parallel to each other.

  As shown in FIGS. 1 and 3, dummy display pixels DPX are arranged in the peripheral portion 10B along at least the display portion 10A on the end side in the rubbing direction D1. In the liquid crystal display device according to the present embodiment, the dummy display pixels DPX are arranged so as to surround the display unit 10A.

  The liquid crystal display device further includes a drive unit that drives the display pixel PX and the dummy display pixel DPX, and a controller CTRL that controls the drive unit. The drive unit has a scanning line drive circuit GD and a signal line drive circuit SD.

  In the array substrate 12, scanning lines GL extending along rows in which the display pixels PX are arranged and signal lines SL extending in columns in which the display pixels PX are arranged are arranged in the display unit DYP.

  The liquid crystal display device according to the present embodiment is, for example, a VGA (video graphics array) (horizontal 640 × 3 pixels, vertical 480 pixels), and the display unit 10A has 480 scanning lines (GL1 to GL480) and 1920 signals. Lines (SL1 to SL1920) are arranged. Further, in the peripheral portion 10B, a dummy scanning line DGL extending substantially parallel to the scanning line GL and a dummy signal line DSL extending substantially parallel to the signal line SL corresponding to a portion where the dummy display pixel DPX is disposed. Is arranged.

  That is, in the liquid crystal display device according to the present embodiment, the dummy display pixels DPX are arranged one row at the top and bottom of the display unit, and one column at the left side and the right side of the display unit. Accordingly, a dummy scanning line DGL1 extending substantially parallel to the scanning line GL is disposed above the display portion 10A, and a dummy scanning line DGL2 extending substantially parallel to the scanning line GL is disposed below the display portion DYP. Yes. A dummy signal line DSL1 extending substantially parallel to the signal line SL is disposed on the left side of the display unit 10A, and a dummy signal line DSL2 extending substantially parallel to the signal line SL is disposed on the right side of the display unit 10A.

  As shown in FIG. 2, a pixel switch SW is disposed in the vicinity of the intersection between the scanning line GL or the dummy scanning line DGL and the signal line SL or the dummy signal line DSL. The pixel switch SW has a thin film transistor (TFT) as a switching element, for example.

  The gate electrode of the pixel switch SW is electrically connected to the corresponding scanning line GL or dummy scanning line DGL. The source electrode of the pixel switch SW is electrically connected to the corresponding signal line SL or dummy signal line DSL. The drain electrode of the pixel switch SW is electrically connected to the pixel electrode PE disposed in each of the display pixel PX or the dummy display pixel DPX.

  The scanning line GL and the dummy scanning lines DGL1, DGL2 are electrically connected to the scanning line driving circuit GD. The signal line SL and the dummy signal lines DSL1 and DSL2 are electrically connected to the signal line driver circuit SD.

  The scanning line driving circuit GD and the signal line driving circuit SD are controlled by the controller CTRL to periodically apply the video signal and the reverse transition prevention signal to the liquid crystal layer LQ in the display pixel PX, and in the liquid crystal layer in the dummy display pixel DPX. A reverse transition prevention signal is periodically applied to LQ. In the liquid crystal display device according to the present embodiment, the voltage Vb corresponding to black display is applied to the display pixel PX and the dummy display pixel DPX as a reverse transition prevention signal.

  That is, the scanning lines GL are sequentially selected by the scanning line driving circuit GD, and a signal output from the signal line driving circuit SD is applied to the pixel electrode PE via the pixel switch SW connected to the selected scanning line GL. The A counter voltage is applied to the counter electrode CE by a counter electrode driver (not shown).

  In the liquid crystal display device according to this embodiment, a reverse transition prevention signal is periodically applied to the liquid crystal layer in order to prevent reverse transition of liquid crystal molecules. The liquid crystal display device according to the present embodiment employs black insertion driving in which a black display signal Vb corresponding to black display is applied as a reverse transition prevention signal. When the black insertion drive is applied to the liquid crystal display device, the display pixel PX displays an image alternately within one frame based on the video signal and the reverse transition prevention signal, thereby preventing the reverse transition of the liquid crystal molecules and the display. The quality can be improved.

  That is, as shown in FIG. 4, the scanning line driving circuit GD sequentially drives the scanning lines GL in each of the black insertion period and the video display period within one frame period. The signal line driver circuit SD applies a signal Vb corresponding to black display to the signal line SL during the black insertion period, and applies a video signal Vs corresponding to each of the signal lines SL during the video display period.

  In the liquid crystal display device according to the present embodiment, a voltage corresponding to black display is applied to the pixel electrode PE of the dummy display pixel DPX throughout one frame period. That is, as shown in FIG. 4, the scanning line driving circuit GD scans the dummy scanning line DGL1 simultaneously with the scanning line GL1 and the dummy simultaneously with the scanning line GL480 in each of the black insertion period and the video display period of one frame period. The scanning line DGL2 is scanned. The signal line driving circuit SD applies a signal Vb corresponding to black display to the dummy signal lines DSL1 and DSL2 throughout one frame period.

  That is, at the timing of displaying an image, the liquid crystal molecules can be in an alignment state between white display and black display based on the video signal Vs applied to the pixel electrode PE. On the other hand, at the timing of black insertion, the liquid crystal molecules are aligned in the same manner as black display based on the reverse transition prevention signal periodically applied to the pixel electrode PE.

  As shown in FIG. 5, when only the video signal Vs is applied to the pixel electrode PE throughout the frame period, the alignment state of the liquid crystal molecules becomes an alignment state between black display and white display throughout the frame period. Small change in orientation state.

  On the other hand, as shown in FIG. 6, when the video signal Vs and the signal Vb corresponding to the black display are periodically applied in the frame period, the black signal is displayed when the video signal Vs is applied to the pixel electrode PE. When the signal Vb corresponding to is applied, the alignment state of the liquid crystal molecules changes more greatly than in the case of FIG.

  By repeating the change in the alignment state of the liquid crystal molecules, a flow is generated in the rubbing direction D1 in the liquid crystal layer LQ. Further, when impurities contained in, for example, a glass substrate exist as ions in the liquid crystal layer LQ, the ions move in the rubbing direction D1 according to the flow generated in the liquid crystal layer LQ.

  The ions that have moved according to the flow of the liquid crystal layer LQ move to the vicinity of the boundary between the display unit 10A and the peripheral unit 10B. Here, in the liquid crystal display device according to the present embodiment, a voltage corresponding to black display is applied to the liquid crystal layer LQ in the dummy display pixel DPX.

  In this case, by arranging the dummy display pixel DPX in the peripheral portion 10B, the flow of the liquid crystal layer LQ does not disappear near the boundary between the display portion 10A and the peripheral portion 10B, and the display portion 10A is not in the liquid crystal layer LQ. To the peripheral portion 10B side. Therefore, as shown in FIG. 7, ions existing in the liquid crystal layer LQ move to the peripheral portion 10B through the boundary between the display portion 10A and the peripheral portion 10B.

  That is, according to the above liquid crystal display device, as shown in FIG. 7, a portion A where ions are aggregated in the peripheral portion 10B occurs, and ions in the liquid crystal layer LQ do not aggregate in the display portion 10A. In the portion 10A, the ions in the liquid crystal layer LQ do not become non-uniform.

  Therefore, according to the liquid crystal display device according to the present embodiment, display defects such as display unevenness due to nonuniformity of ions in the liquid crystal layer can be suppressed, and a liquid crystal display device with high display quality and reliability can be provided.

  Next, a liquid crystal display device according to a second embodiment of the present invention will be described with reference to the drawings. In the following description, the same components as those of the liquid crystal display device according to the first embodiment described above are denoted by the same reference numerals, and description thereof is omitted.

  In the liquid crystal display device according to the present embodiment, the dummy display pixels DPX are arranged along at least the display unit 10A on the end side in the rubbing direction D1, as in the liquid crystal display device according to the first embodiment. In the case of the liquid crystal display device according to the present embodiment, the dummy display pixels DPX are arranged so as to surround the display unit 10A.

Further, as shown in FIG. 8, the thickness of the liquid crystal layer LQ in the dummy display pixel DPX is smaller than the thickness of the liquid crystal layer LQ in the display pixel PX. In the liquid crystal display device according to the present embodiment, the counter substrate 14 has a convex portion at a position corresponding to the dummy display pixel DPX. For example, as shown in FIG. 8, the convex portion is provided by disposing the color filter layer CF at a position corresponding to the dummy display pixel DPX of the counter substrate 14. The color filter layer CF reduces the thickness of the liquid crystal layer LQ in the dummy display pixel DPX. In the figure, BM indicates a black mask for shielding the peripheral portion.

  As described above, the thickness of the liquid crystal layer LQ in the dummy display pixel DPX is made smaller than the thickness of the liquid crystal layer LQ in the display pixel PX, so that the display portion 10A is near the boundary between the display portion 10A and the peripheral portion 10B. The flow rate of the liquid crystal layer LQ from the side toward the peripheral portion 10B increases. Therefore, ions that have moved to the vicinity of the boundary between the display unit 10A and the peripheral unit 10B due to the flow generated in the liquid crystal layer LQ quickly move from the display unit 10A to the peripheral unit 10B.

  That is, according to the liquid crystal display device according to the present embodiment, in the display unit 10A, the ions in the liquid crystal layer LQ quickly move to the peripheral part 10B, and as shown in FIG. A is produced. As a result, since the ions do not aggregate in the display unit 10A, it is possible to more effectively suppress the ions in the liquid crystal layer LQ from becoming non-uniform in the display unit 10A.

  Therefore, according to the liquid crystal display device according to the present embodiment, display defects such as display unevenness due to nonuniformity of ions in the liquid crystal layer can be suppressed, and a liquid crystal display device with high display quality and reliability can be provided.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, the liquid crystal display devices according to the first and second embodiments described above are OCB mode liquid crystal display devices. However, the present invention is not limited to this, and a driving method for applying a constant signal periodically, such as black insertion driving. If the present invention is applied to the liquid crystal display device adopting the above, the same effect as the liquid crystal display device according to the above-described embodiment can be obtained. For example, the present invention can be applied to a liquid crystal display device in a TN mode, a VA mode, or an IPS mode.

  For example, when the present invention is applied to a TN mode liquid crystal display device, the vector in the direction of rubbing the alignment film on the array substrate side and the vector in the direction of rubbing the alignment film on the counter substrate side are in the direction of the sum. At least dummy display pixels are arranged. Thus, the same effect as that of the present invention can be obtained.

  Further, in the liquid crystal display devices according to the first and second embodiments described above, the dummy display pixels DPX are arranged so as to surround the periphery of the display unit 10A, but the dummy display pixels DPX are at least on the end side in the rubbing direction. If they are arranged, the same effect as in the above embodiment can be obtained. Further, the dummy display pixels DPX of two rows or two columns or more may be arranged around the display unit 10A. Even in that case, the same effect as the above-described embodiment can be obtained.

  In the liquid crystal display device according to the second embodiment described above, the color filter layer CF is disposed on the counter substrate side, whereby the thickness of the liquid crystal layer LQ in the dummy display pixel DPX is changed to the thickness of the liquid crystal layer LQ in the display pixel PX. However, the present invention is not limited to this. For example, an insulating layer may be disposed on the array substrate 12 side, and an insulating layer may be disposed on both the array substrate 12 side and the counter substrate 14 side. Also good. Further, in the display unit 10A, the array substrate 12 or the counter substrate 14 may be provided with a recess. Even in this case, the same effects as those of the liquid crystal display devices according to the first and second embodiments described above can be obtained.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

The figure which shows schematically the structural example of the liquid crystal display panel of the liquid crystal display device which concerns on one Embodiment of this invention. FIG. 2 is a diagram schematically showing a configuration example of display pixels of the liquid crystal display panel shown in FIG. 1. FIG. 2 is a diagram for explaining a configuration example in the vicinity of a boundary between a display unit and a peripheral unit of the liquid crystal display panel shown in FIG. FIG. 3 is a diagram for explaining an example of a driving method of the liquid crystal display device illustrated in FIG. 1. The figure for demonstrating an example of the orientation state of a liquid crystal molecule at the time of applying only a video signal to a liquid-crystal layer in 1 frame period. The figure for demonstrating an example of the orientation state of a liquid crystal molecule at the time of applying a video signal and a reverse transition prevention signal to a liquid crystal layer periodically in one frame period. The figure which shows an example of the cross section of the liquid crystal display panel in line AA 'shown in FIG. The figure which shows the other example of the cross section of the liquid crystal display panel in line AA 'shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... Array substrate, 14 ... Counter substrate, LQ ... Liquid crystal layer, PX ... Display pixel, DPX ... Dummy display pixel, PE ... Pixel electrode, CE ... Counter electrode, 10A ... Display part, 10B ... Peripheral part, 16 ... Alignment film, D1 ... rubbing direction

Claims (4)

A liquid crystal display device comprising a display unit comprising a plurality of display pixels arranged in a matrix, and a peripheral part surrounding the display unit, the OCB mode liquid crystal layer sandwiched between the first substrate and the second substrate Because
The first substrate has a pixel electrode disposed corresponding to each of the plurality of display pixels,
The second substrate has a counter electrode facing the plurality of pixel electrodes,
A pair of alignment films disposed on the plurality of pixel electrodes and the counter electrode, respectively, for controlling an alignment state of liquid crystal molecules contained in the liquid crystal layer by rubbing treatment;
A dummy display pixel to which a reverse transition prevention signal is applied is arranged at least on the end side in the rubbing direction of the alignment film in the peripheral portion,
A liquid crystal display device , wherein a thickness of a liquid crystal layer in the dummy display pixel in the peripheral portion is formed smaller than a thickness of a liquid crystal layer in the display pixel in the display portion . 2. The liquid crystal display device according to claim 1, wherein at least one of the first and second substrates has a convex portion corresponding to the dummy display pixel. The liquid crystal display device according to claim 2, wherein the convex portion is formed of an insulating layer or a color filter layer. The liquid crystal display device according to claim 1, wherein the reverse transition prevention signal is a signal corresponding to black display.

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