JPH02236589A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory liquid crystal display panel free from deterioration in characteristics, such as drop in display brightness, by maintaining the liquid crystal in the display area of a picture at a high resistivity. CONSTITUTION:A liquid module 1 is constituted in such a way that an area 4, in which the liquid crystal is injected hermetically, a horizontal scanning circuit 3, and a vertical scanning circuit 2 are connected by flexible cables; in a display part and a dummy part, the structures of their scanning lines are exactly the same, and the structures of their picture elements are also the same. And a liquid crystal display device is provided with a means for preventing the resistivity of a liquid crystal layer in the display area of a picture from falling below the resistivity of a liquid crystal layer in the periphery of the display area. It is preferable to set the resistivity of the liquid crystal layer in the display area equal to or greater than 10<11>OMEGA.cm. Thus, factors destabilizing the liquid crystal is removed, instability of the liquid crystal, resulting from change in the lapse of time, can be prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a liquid crystal display device applied to liquid crystal televisions, OA, information, terminal display devices, etc., and relates to a structure of a display device that is effective in preventing instability of liquid crystal. (Prior Art) Conventional liquid crystal display devices are described in the Technical Report of the TV Society (6).
3.8.26) Volume 12, No. 32. Pages 13 to 18
A typical example is a combination of TN liquid and TPT, as shown on the page. Even in such a display device, there is instability of the liquid crystal, and this is countered by providing a storage capacitor for each pixel (page 14 of the above-mentioned document). On the other hand, as a conventional technique aimed at preventing a decrease in resistance of a liquid crystal layer, Japanese Patent Application Laid-open No. 11724/1984 can be mentioned. This prior art discloses that the so-called VT characteristics are improved by adsorbing ionic substances eluted into the liquid crystal using an adsorbent.

[Problem to be solved by the invention]

The former of the above conventional techniques aims to increase the effective discharge time constant of the voltage applied to each pixel by providing a storage capacitor for each pixel. This was intended to make uneven brightness distribution caused by the instability of the liquid crystal less noticeable; in other words, it did not eliminate the instability of the liquid crystal. Further, although the latter of the above-mentioned conventional techniques is certainly effective in improving the initial characteristics of the liquid crystal layer, it cannot necessarily be said to be sufficient for preventing deterioration of characteristics due to changes over time. An object of the present invention is to eliminate factors that cause instability of liquid crystals and to prevent amorphousness of liquid crystals due to changes over time.

[Means to solve the problem]

In order to achieve the above object, the present invention includes means for preventing the resistivity of the liquid crystal layer in the display area of the liquid crystal display device from being lower than the resistivity of the liquid crystal layer in the peripheral area other than the display area. Features. The resistivity of the liquid crystal layer in the above display area is 1011
It is preferable that it is Ω·cm or more. As an example of a more specific means, it is characterized by having means for preventing a factor that reduces the resistivity of the liquid crystal latent in the peripheral area from reaching the display area; The method is to apply an electric field to the target. More specifically, as detailed in the example, dummy pixels or border lines are set around the liquid crystal panel, and the average amplitude of the AC voltage applied to the liquid crystal corresponding to these dummy pixels or border lines is displayed. The amplitude is set to be larger than the average amplitude of the AC voltage applied to the region. Since these instabilities are particularly noticeable in active matrix liquid crystal panels, that is, liquid crystal displays using A-film transistors, etc., the method of applying a high voltage to the dummy pixels or border lines is particularly effective. Furthermore, since instability is particularly likely to occur at the upper and lower sides of the liquid crystal panel, the above objective is achieved by using dummy scanning lines or horizontal intervening lines. The purpose can also be achieved by applying the above-mentioned high average voltage to the pixels on these dummy scanning lines or the liquid crystals on the horizontal border lines. Here, the dummy pixel refers to a pixel that is not used for image display. Similarly, dummy scanning lines refer to lines that are not used as scanning lines for image display, and are placed outside the group of original scanning lines for image display and approximately parallel to these original scanning lines. A border line is a conductor line that is not directly connected to a pixel on the panel.A horizontal border line is a border line that is arranged substantially parallel to the scanning line. In this case, the higher voltage does not necessarily have to be always high, it may be low momentarily, and it is sufficient if it is high on average. [Effect 1] The inventors of the present application have found that factors that reduce the resistivity of the liquid crystal layer mainly occur in the peripheral area of the liquid crystal layer in a liquid crystal display. Therefore, by providing a means for preventing the resistivity of the liquid crystal layer in the image display area from becoming lower than that in the peripheral area, characteristic deterioration due to liquid crystal instability can be prevented. In this way, regarding the resistivity of the liquid crystal layer, making the value different between the display region that affects the display characteristics and the peripheral region that does not affect the display characteristics is a new concept that has never existed before. Furthermore, according to the findings of the inventors of the present invention, the resistivity-reducing factor generated in the peripheral area moves toward the image display area with the passage of time. Therefore, by providing means for preventing the above factors from reaching the display area, it is possible to prevent the resistivity of the display area from decreasing over a long period of time. The above means may be, for example, means for applying an electric field to the above factors. It is effective to provide this means in the periphery of the display area of the display panel, particularly above and below the display area. Further, according to the above-described specific means using dummy pixels or border lines, the dummy pixels, dummy scanning lines, or border lines provided around the liquid crystal panel function to block the occurrence of liquid crystal instability. That is, by applying the above-mentioned high voltage to the liquid crystal in the dummy pixel portion or the liquid crystal on the border line, the movement of the liquid crystal can be restricted, so that the occurrence of the above-mentioned instability can be suppressed. Example 1 An example of the present invention will be described below with reference to FIG. FIG. 1 shows the configuration of a liquid crystal module according to the present invention. The liquid crystal module has area 4 where liquid crystal is sealed.
The horizontal scanning circuit 3 and the vertical scanning circuit 2 are connected by a flexible cable. Each scanning circuit has T
A B
(onding) connection was used. The diagonal size of the display section is 6.3 inches, and the number of pixels (display section) is 480 (V) x 64
0 (H). Although there were 480 vertical scanning lines, three dummy lines were provided above and below the dummy lines, resulting in a panel having a total of 486 vertical scanning lines. The scanning lines of the display section and the scanning lines of the dummy part had exactly the same configuration. The pixel configuration is also the same. A voltage is applied to the pixels corresponding to the three upper and lower dummy lines, but these parts are not part of the display area and are bordered so that they cannot be seen from the outside. A scanning voltage is sequentially applied to the gate line of the panel, and during the scanning period, a voltage is applied to the pixel electrode, that is, the pixel liquid crystal, connected to the gate line via a thin film transistor. The voltage applied to the liquid crystal is an alternating current voltage. A voltage corresponding to the image signal is applied to each pixel in the display area except for the three upper and lower scanning lines. Whether the panel is monochrome or color, it is basically the same: a monochrome signal is applied to a monochrome panel, and a color signal is applied to a color panel. The liquid crystal used is a twisted nematic type (TN type) liquid crystal, which is a so-called normally closed type, with a threshold voltage V th of 2V, and a voltage at which the brightness reaches 90% of the saturation value is 4V. The maximum applied voltage is 6.5μ. As mentioned above, the voltage applied to the liquid crystal is an alternating current voltage, and for example, the maximum applied voltage corresponds to a voltage application of ±6.5V. A signal voltage between ±2v and ±6.5v is applied to the panel display area to display a halftone image. On the other hand, the three scanning lines provided at the top and bottom of the panel always have ±
5. Apply a signal voltage of OV. ±5. Although the OV voltage is not the maximum voltage or maximum brightness, the orientation of the liquid crystal molecules changes from parallel to the electrode plane to perpendicular to it. The verticality of the liquid crystal molecules at 5V is lower than that at 6.5V, but on average the verticality of the liquid crystal molecules in the display area is lower than in the dummy part. Therefore, the part of the dummy sufficiently plays the role of suppressing the occurrence of instability of the liquid crystal. Another embodiment of the invention will now be described. As shown in FIG. 2, each pixel consists of a liquid crystal pixel 7 driven by a non-quality silicon thin film transistor. Opposite electrodes of the liquid crystal represented by capacitor 7 are commonly connected and usually grounded. The diagonal size of the panel display is 10 inches, which is a non-quality thin film transistor driven twisted nematic type liquid crystal display device. The panel had a normally white configuration. In other words, the panel has the highest brightness when the minimum voltage is applied and the lowest brightness when the maximum voltage is applied. Number of scanning lines on display: 4
Compared to 80 gate lines, the total number of gate lines was 482, and one dummy line was provided at the top and one at the bottom. (#1 and #482 are dummy lines). The voltage applied to the pixels attached to the dummy line had a waveform as shown in FIG. 3 (maximum oscillation voltage ±6.5 V). These two dummy lines are shaded as in the previous embodiment. There is one dummy line on the top and one on the top, but since the maximum applied voltage is applied, the verticality of the liquid crystal molecules is high, and the instability of the liquid crystal is effectively blocked. In the above embodiment, a configuration was described in which dummy pixels were created only above and below the display area. In order to sufficiently block liquid crystal instability, it is also possible to provide dummy pixels on the left and right sides of the display area in addition to the top and bottom, and to drive these with high voltage. In this case, the image display section is framed by dummy pixels, and the spread of liquid crystal instability to the display section is more completely suppressed. However, in a normal liquid crystal panel, it is sufficient to provide dummy lines on the upper and lower sides. This is because, due to the alignment direction of the alignment film, the orientation of the liquid crystal molecules is perpendicular to the upper and lower sides (i.e., from the outside to the inside of the panel at panel surface C), which tends to cause instability. On the other hand, the orientation of the liquid crystal molecules on the left and right sides is parallel to the sides, and instability of the liquid crystal is unlikely to occur in such cases. Here, even though it is perpendicular or parallel, the TN liquid product has a twist angle of 90' in that direction. Vertical and parallel mean vertical and parallel on average. Moreover, it goes without saying that, contrary to the above embodiment, if the liquid crystal molecules are oriented perpendicularly to the left and right sides on average, it is first necessary to provide dummy pixels on the left and right sides. FIG. 4 shows another embodiment of the invention. First, border lines 9 are placed adjacent to the upper and lower sides of the display area. The line width is 100 μm, and the gap between adjacent gate lines and pixel electrodes is 15 μm. These are formed in the same process as gate line formation. Furthermore, border lines 10 are formed adjacent to the right and left sides of the display area. The line width was 50 μm and the gap was 10 μm. These all-round lines are formed when forming the drain line. The border lines 10 and 9 are connected through contact holes and further connected to a terminal 11. After panel fabrication, during actual panel operation, the terminal 11 is ±6.
We were able to block the instability of the liquid crystal by applying an AC voltage of 5V to the device. In this embodiment, the border lines are formed to frame the display section, but the same effect can be expected by using only the border lines touching the top and bottom sides. At this time, the border lines on the top and bottom sides do not necessarily need to be connected. Alternatively, they may be connected to separate terminals and an alternating current voltage may be applied. Furthermore, the border lines are not limited to those formed in the process of forming gate lines and drain lines. For example, the same effect can be obtained by maintaining insulation with the drain line and gate line on the pixel electrode substrate or TPT substrate, and providing a border line in the same shape as above on the protective film in a separate process. I can do it. Furthermore, although this embodiment has described the method of installing the border line on the pixel electrode substrate or TPT substrate side, it goes without saying that the border line may be provided on the opposite substrate, that is, the common electrode substrate side. Although the present invention has been described above based on examples, the gist of the present invention is not limited thereto. That is, although the configuration of the dummy line is assumed to be the same as that of the pixel portion or display area, it does not necessarily have to be the same. The scanning line pitch may be slightly different, and the pixel transistor,
The structural dimensions of the electrodes etc. may be different. The gap (distance in the plane direction of the substrate) may be slightly larger between the display portion and a portion of the dummy. Furthermore, although the liquid crystal is of the TN type, it is not limited to the TN type. The size of the liquid crystal panel is not limited to 10 inches diagonally, but is also effective for larger sizes. Further, although an active matrix using thin film transistors has been described, a diode type active matrix may also be used. Furthermore, in the above embodiment, a case was described in which a constant voltage was applied to the dummy pixel;
It does not necessarily have to be a constant voltage, and it is sufficient if a voltage with an average amplitude larger than that of the image display section is applied. Therefore, the voltage of the dummy portion may be lower than that of the image display portion momentarily. [Advantageous Effects of the Invention 1] According to the present invention, by keeping the resistivity of the liquid crystal in the image display area high, it is possible to obtain a good liquid crystal display panel without deterioration of characteristics such as a decrease in display brightness. Furthermore, the perpendicularity of liquid crystal molecules can be increased by means of preventing factors that reduce the resistivity in the liquid crystal layer from reaching the display area. Therefore, the flow of liquid crystal molecules can be suppressed, and instability of the liquid crystal that occurs around the panel can be blocked. Therefore, it is possible to reduce or eliminate the value of storage capacitance or holding capacitance that has been conventionally used. This makes it possible to reduce the gate line load and simplify the manufacturing process, which has great effects. This effect becomes even greater as the size of the panel increases.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a diagram showing another embodiment of the invention, and Fig. 3 is a dummy line (
FIG. 4 is a diagram showing still another embodiment of the present invention. Explanation of symbols 1...Liquid crystal module, 2...Vertical scanning circuit, 3.
...Horizontal scanning circuit, 4...Liquid crystal section, 5...Gate line, 6...Signal line, 7...Liquid crystal pixel, 8...Common electrode, 9.10...Edging line , 11... Border wire terminal. 1...Liquid crystal module 3...Horizontal scanning circuit 5...Gate line Fig. 1 2...Vertical scanning circuit 4...Liquid crystal section 6...Signal line Fig. 3 Fig. 2

Claims (1)

[Claims] 1. A display device using liquid crystal, in which the resistivity of the liquid crystal layer in the display area of the display device is not lower than the resistivity of the liquid crystal layer in the peripheral area other than the display area. A liquid crystal display device characterized by having the following means. 2. The resistivity of the liquid crystal layer in the above display area is 10^1^
2. The liquid crystal display device according to claim 1, wherein the resistance is 1 Ω·cm or more. 3. The liquid crystal display device according to claim 1 or 2, wherein the liquid crystal display device includes means for preventing a factor that reduces the resistivity of the liquid crystal layer in the peripheral area from reaching the display area. . 4. The liquid crystal display device according to claim 3, wherein said means is means for applying an electric field to said factor. 5. A liquid crystal display device having a plurality of scanning lines, in which a dummy pixel portion is provided outside the display area of the display device, and the average amplitude of the AC voltage applied to the liquid crystal corresponding to these dummy pixels is displayed as described above. A liquid crystal display device characterized in that the amplitude of an alternating current voltage applied to a region is larger than the average amplitude. 6. In a liquid crystal display device consisting of a plurality of scanning lines, a border line is provided outside the display area of the display device, and the average amplitude of the AC voltage applied to the border line is equal to the average amplitude of the AC voltage applied to the pixel portion of the display area. A liquid crystal display device characterized in that the amplitude is larger than the amplitude. 7. The liquid crystal display device according to claim 5 or 6, wherein the liquid crystal panel has a thin film transistor corresponding to each pixel, and the transistor switches the voltage applied to the liquid crystal. 8. The liquid crystal display device according to claim 5 or 7, wherein the dummy pixels are pixels corresponding to dummy scanning lines installed on the upper and lower sides of the display device. 9. The liquid crystal display device according to claim 8, wherein the number of dummy scanning lines is within three on both the upper and lower sides. 10, the number of dummy scanning lines is 1 each on the top and bottom sides
10. The liquid crystal display device according to claim 9, wherein the liquid crystal display device is a book. 11. The liquid crystal display device according to claim 6 or 7, wherein the border lines are provided on the upper and lower sides of the display area. 12. The liquid crystal display device according to claim 6, 7 or 11, wherein the width of the border line is 100 μm or less. 13. One of claims 5 to 12, wherein the liquid crystal operates in a twisted nematic display mode, and the voltage amplitude applied to the dummy pixels or the border line is 50% or more of the maximum signal voltage applied to the panel. The liquid crystal display device described in . 14. The liquid crystal display device according to claim 13, wherein the voltage applied to the dummy pixel liquid crystal or the border line is 80% or more of the maximum signal voltage applied to the panel. 15. The liquid crystal display device according to claim 13, wherein the voltage applied to the dummy pixel liquid crystal or the border line is equal to the maximum signal voltage applied to the panel. 16. A liquid crystal television using the display device according to claim 1. 17. A terminal device characterized by using the display device according to any one of claims 1 to 15. 18. A video playback device characterized by using the display device according to any one of claims 1 to 15.