JP6200988B2 - Liquid crystal display device and alignment film used therefor - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a liquid crystal display panel in which an alignment film is provided with an alignment control ability by irradiation of light.

  In a liquid crystal display device, there are a TFT substrate in which pixel electrodes and thin film transistors (TFTs) are formed in a matrix, and a counter substrate in which color filters are formed at locations corresponding to the pixel electrodes of the TFT substrate, facing the TFT substrate. The liquid crystal is sandwiched between the TFT substrate and the counter substrate. An image is formed by controlling the light transmittance of the liquid crystal molecules for each pixel.

  Since the liquid crystal display device is flat and lightweight, the application is expanding in various fields such as a large display device such as a TV, a mobile phone, and a DSC (Digital Still Camera). On the other hand, viewing angle characteristics are a problem in liquid crystal display devices. The viewing angle characteristic is a phenomenon in which luminance changes or chromaticity changes when the screen is viewed from the front and when viewed from an oblique direction. The viewing angle characteristic is excellent in an IPS (In Plane Switching) system in which liquid crystal molecules are operated by a horizontal electric field.

  As a method for imparting an alignment treatment, that is, an alignment control ability, to an alignment film used in a liquid crystal display device, there is a conventional method of rubbing. The alignment treatment by rubbing is performed by rubbing the alignment film with a cloth. On the other hand, there is a technique called a photo-alignment method that imparts alignment control capability to an alignment film in a non-contact manner. Since the IPS method does not require a pretilt angle, a photo-alignment method can be applied.

  “Patent Document 1” discloses a photo-decomposition-type photo-alignment process by irradiation with light typified by ultraviolet rays. According to this, in photo-decomposition-type photo-alignment process, (1) a complicated step in a pixel portion is disclosed. Uniform alignment control by reducing alignment disturbance due to structure, and (2) solving defective display caused by damage of thin film transistor due to static electricity in alignment processing by rubbing, disturbance of hair tip of rubbing cloth and alignment disturbance due to dust It is described that the complexity of the process due to frequent replacement of the rubbing cloth required to obtain the performance is solved.

  In “Patent Document 2”, the upper layer of the alignment film is a film having a large molecular weight and capable of efficiently performing photo-alignment, and the lower layer is formed of a film having a low molecular weight having photoconductivity to reduce an afterimage. The configuration is described.

JP 2004-206091 A JP 2010-72011 A

  However, it is known that the optical alignment treatment generally has lower alignment stability than the rubbing treatment in terms of imparting alignment control ability to the alignment film. If the alignment stability is low, the initial alignment direction varies, causing display defects. In particular, in a liquid crystal display device using a horizontal electric field type liquid crystal display panel that requires high alignment stability, a display defect symbolized by an afterimage tends to occur due to low alignment stability.

  In the photo-alignment process, there is no step in the LCD process, such as a rubbing process, in which the main chain of the polymer is stretched and linearized. Therefore, in the photo-alignment treatment, a synthetic polymer alignment film represented by polyimide irradiated with polarized light is given uniaxiality by cutting the main chain in a direction orthogonal to the polarization direction. The liquid crystal molecules are not cut and are aligned along the long main chain direction that remains on the straight line, but if the length of this main chain is shortened, the uniaxiality decreases and the interaction with the liquid crystal weakens. Since the orientation deteriorates, the above-mentioned afterimage is likely to occur.

  Therefore, in order to improve the uniaxiality of the alignment film and improve the alignment stability, it is necessary to increase the molecular weight of the alignment film. A photo-alignment film material can be used. According to this, the polyamic acid alkyl ester material does not involve a decomposition reaction into a diamine and an acid anhydride at the time of the imidation reaction that occurs in the conventional polyamic acid material, and can maintain a large molecular weight even after imidization. Orientation stability equivalent to that of rubbing treatment can be obtained.

  In addition, since the polyamic acid alkyl ester material does not contain a carboxylic acid in its chemical structure, the voltage holding ratio of the LCD is higher than that of the polyamic acid material, and improvement in long-term reliability can be ensured.

  In order to obtain the alignment stability and long-term reliability of the photo-alignment film, it is effective to apply a polyamic acid alkyl ester material, but this material generally has a higher specific resistance of the alignment film than the polyamic acid material. Therefore, when a DC voltage is superimposed on a signal waveform for driving liquid crystal molecules to form a residual DC, the time constant until the residual DC is relaxed is large, and it is likely to cause image sticking (DC afterimage).

  In “Patent Document 2”, in order to solve this, a polyamic acid is used as a precursor in a lower layer, a polyimide having photoconductivity is formed, and a polyamic acid ester having excellent photoalignment characteristics as described above is formed in an upper layer. The structure which forms the polyimide used as a precursor is disclosed.

  The lower-layer photoconductive polyimide obtains photoconductivity by light from the backlight. However, in the liquid crystal display panel, there is a region where wiring or the like is present and the backlight is not irradiated, and the resistance value of this region remains high. Therefore, there is a problem that the afterimage characteristics are deteriorated as a whole due to the existence of the region where the photoconductivity cannot be obtained.

  An object of the present invention is to improve the afterimage characteristics of the entire liquid crystal display panel by facilitating movement of accumulated charges or reducing the resistance of an alignment film even in a region where backlight light is not irradiated. Is to realize.

  The present invention overcomes the above problems, and the main specific means are as follows.

  (1) Pixels in a region surrounded by scanning lines extending in the first direction and arranged in the second direction and video signal lines extending in the second direction and arranged in the first direction A liquid crystal display panel in which liquid crystal is sandwiched between a TFT substrate on which electrodes are formed, a counter substrate having a color filter corresponding to the pixel, and a backlight disposed on the back of the liquid crystal display panel. An alignment film is formed to cover the scanning line, the video signal line, and the pixel electrode, the alignment film has undergone a photo-alignment treatment, and the alignment film has photoconductive properties; A liquid crystal display device, wherein a photoresist is disposed under the alignment film covering the scanning lines.

(2) Pixels in a region surrounded by scanning lines extending in the first direction and arranged in the second direction and video signal lines extending in the second direction and arranged in the first direction A liquid crystal display panel in which liquid crystal is sandwiched between a TFT substrate on which electrodes are formed, a counter substrate having a color filter corresponding to the pixel, and a backlight disposed on the back of the liquid crystal display panel. An alignment film is formed to cover the scanning line, the video signal line, and the pixel electrode, the alignment film has undergone a photo-alignment treatment, and the alignment film has photoconductive properties; A liquid crystal display device, wherein a specific resistance of the alignment film covering the scanning line in a state where a backlight is turned off is smaller than a specific resistance of the alignment film covering the pixel electrode.
(3) Pixels in a region surrounded by scanning lines extending in the first direction and arranged in the second direction and video signal lines extending in the second direction and arranged in the first direction A liquid crystal display panel in which liquid crystal is sandwiched between a TFT substrate on which electrodes are formed, a counter substrate having a color filter corresponding to the pixel, and a liquid crystal display device in which a backlight is disposed on the back of the liquid crystal display panel A manufacturing method, the step of coating an alignment film covering the scanning lines, the video signal lines, and the pixel electrodes, the step of drying the alignment film, and the step of baking and imidizing the alignment film Irradiating polarized ultraviolet light to the alignment film to perform photo-alignment; heating the polarized ultraviolet light after irradiation; and heating only the alignment film to the alignment film covering the scanning line It has the process of irradiating with ultraviolet rays. Method of manufacturing a liquid crystal display device.

  According to the present invention, in the region where the backlight is not irradiated, charges are easily moved or the resistance of the alignment film is reduced, so that the afterimage characteristics can be improved as a whole display region. Therefore, a liquid crystal display device with excellent image quality can be realized.

It is sectional drawing which shows the 1st Example of this invention. It is a top view which shows the 1st Example of this invention. It is a cross-sectional schematic diagram for demonstrating the mechanism of this invention. It is sectional drawing which shows the form following FIG. It is sectional drawing which shows the form following FIG. It is a cross-sectional schematic diagram which shows a prior art example. It is a simulation which shows the afterimage characteristic of a prior art example. It is a simulation which shows the afterimage characteristic of this invention. FIG. 6 is a schematic cross-sectional view showing another embodiment of Example 1. FIG. 3 is a diagram showing a manufacturing process of Example 1. 6 is a cross-sectional view showing a configuration of Example 2. FIG. 6 is a plan view showing a configuration of Example 2. FIG. It is sectional drawing which shows the other form of Example 2. 6 is a diagram illustrating manufacturing steps of Example 2. FIG. This is a pattern for evaluating afterimages. It is a graph which shows the comparison of the afterimage characteristic in this invention and a prior art example. 1 is a cross-sectional view of an IPS liquid crystal display device to which the present invention is applied. It is a top view which shows the example of a pixel electrode and a common electrode. It is an example of a two-layer alignment film.

  Before describing specific embodiments of the present invention, the configuration of an IPS liquid crystal display device to which the present invention is applied will be described. FIG. 17 is a cross-sectional view showing a structure in a display region of an IPS liquid crystal display device. Various electrode structures of IPS liquid crystal display devices have been proposed and put into practical use. The structure shown in FIG. 17 is a structure that is widely used at present. To put it simply, a comb-like pixel electrode 110 is formed on a counter electrode 108 formed of a flat solid with an insulating film interposed therebetween. Yes. Then, an image is formed by controlling the light transmittance of the liquid crystal layer 300 for each pixel by rotating the liquid crystal molecules 301 by the voltage between the pixel electrode 110 and the counter electrode 108. The structure of FIG. 17 will be described in detail below. Note that the present invention will be described by taking the configuration of FIG. 17 as an example, but can also be applied to IPS type liquid crystal display devices other than FIG.

  In FIG. 17, a gate electrode 101 is formed on a TFT substrate 100 made of glass. The gate electrode 101 is formed in the same layer as the scanning line. The gate electrode 101 has a MoCr alloy laminated on an AlNd alloy.

  A gate insulating film 102 is formed of SiN so as to cover the gate electrode 101. A semiconductor layer 103 is formed of an a-Si film on the gate insulating film 102 at a position facing the gate electrode 101. The a-Si film is formed by plasma CVD. The a-Si film forms the channel portion of the TFT, and the source electrode 104 and the drain electrode 105 are formed on the a-Si film with the channel portion interposed therebetween. Note that an n + Si layer (not shown) is formed between the a-Si film and the source electrode 104 or the drain electrode 105. This is for making ohmic contact between the semiconductor layer and the source electrode 104 or the drain electrode 105.

  The source electrode 104 is also used as a video signal line, and the drain electrode 105 is connected to the pixel electrode 110. The source electrode 104 and the drain electrode 105 are simultaneously formed in the same layer. In this embodiment, the source electrode 104 or the drain electrode 105 is made of a MoCr alloy. In order to reduce the electrical resistance of the source electrode 104 or the drain electrode 105, for example, an electrode structure in which an AlNd alloy is sandwiched between MoCr alloys is used.

  An inorganic passivation film 106 is formed of SiN so as to cover the TFT. The inorganic passivation film 106 protects the TFT, particularly the channel portion, from the impurities 401. An organic passivation film 107 is formed on the inorganic passivation film 106. The organic passivation film 107 has a role of flattening the surface at the same time as protecting the TFT, and thus is formed thick. The thickness is 1 μm to 4 μm.

  A photosensitive acrylic resin, silicon resin, polyimide resin, or the like is used for the organic passivation film 107. In the organic passivation film 107, it is necessary to form a through hole 111 at a portion where the pixel electrode 110 and the drain electrode 105 are connected. However, since the organic passivation film 107 is photosensitive, the organic passivation film 107 is not used without using a photoresist. The through hole 111 can be formed by exposing and developing itself.

  A counter electrode 108 is formed on the organic passivation film 107. The counter electrode 108 is formed by sputtering ITO (Indium Tin Oxide), which is a transparent conductive film, over the entire display region. That is, the counter electrode 108 is formed in a planar shape. After the counter electrode 108 is formed on the entire surface by sputtering, the counter electrode 108 is removed by etching only in the through hole 111 portion for conducting the pixel electrode 110 and the drain electrode 105.

  An upper insulating film 109 is formed of SiN so as to cover the counter electrode 108. After the upper electrode is formed, a through hole 111 is formed by etching. The through hole 111 is formed by etching the inorganic passivation film 106 using the upper insulating film 109 as a resist. Thereafter, ITO that becomes the pixel electrode 110 covering the upper insulating film 109 and the through hole 111 is formed by sputtering. The pixel electrode 110 is formed by patterning the sputtered ITO. ITO serving as the pixel electrode 110 is also deposited on the through hole 111. In the through hole 111, the drain electrode 105 extending from the TFT and the pixel electrode 110 become conductive, and a video signal is supplied to the pixel electrode 110.

  FIG. 18 shows an example of the pixel electrode 110. The pixel electrode 110 is a comb-like electrode. A slit 112 is formed between the comb teeth. A planar counter electrode 108 is formed below the pixel electrode 110. When a video signal is applied to the pixel electrode 110, the liquid crystal molecules 301 are rotated by electric lines of force generated between the counter electrode 108 through the slit 112. As a result, light passing through the liquid crystal layer 300 is controlled to form an image.

  FIG. 17 illustrates this state as a cross-sectional view. A slit 112 shown in FIG. 17 is formed between the comb-shaped electrode and the comb-shaped electrode. A constant voltage is applied to the counter electrode 108, and a voltage based on a video signal is applied to the pixel electrode 110. When a voltage is applied to the pixel electrode 110, electric lines of force are generated, and the liquid crystal molecules 301 are rotated in the direction of the electric lines of force to control the transmission of light from the backlight, as shown in FIG. Since transmission from the backlight is controlled for each pixel, an image is formed.

  In the example of FIG. 17, a counter electrode 108 formed in a planar shape is disposed on the organic passivation film 107, and a comb electrode 110 is disposed on the upper insulating film 109. However, conversely, the pixel electrode 110 formed in a planar shape may be disposed on the organic passivation film 107, and the comb-like counter electrode 108 may be disposed on the upper insulating film 109.

  An alignment film 113 for aligning liquid crystal molecules 301 is formed on the pixel electrode 110. In the present invention, as will be described later, an alignment film is formed on a metal wiring such as a scanning line and is not irradiated with a backlight, and an alignment of a region irradiated with a backlight, such as an opening. Although the configuration of the film is changed, FIG. 17 shows the same.

  In FIG. 17, the counter substrate 200 is installed with the liquid crystal layer 300 interposed therebetween. A color filter 201 is formed inside the counter substrate 200. The color filter 201 is formed with red, green, and blue color filters 201 for each pixel, and a color image is formed. A black matrix 202 is formed between the color filters 201 to improve the contrast of the image. Note that the black matrix 202 also has a role as a light shielding film of the TFT, and prevents a photocurrent from flowing through the TFT.

  An overcoat film 203 is formed to cover the color filter 201 and the black matrix 202. Since the surface of the color filter 201 and the black matrix 202 is uneven, the surface is flattened by the overcoat film 203.

  On the overcoat film 203, an alignment film 113 for determining the initial alignment of the liquid crystal is formed. Since the alignment film 113 on the counter substrate side does not significantly affect the afterimage characteristics, the configuration of the alignment film is not changed depending on the region, unlike the alignment film on the TFT substrate 100 side.

  Also in the present invention, as shown in FIG. 19, the alignment film 113 can be constituted by an upper alignment film 113U having excellent photoalignment characteristics and a lower alignment film 113L having photoconductivity. However, in this specification, the lower layer and the upper layer are not particularly distinguished from each other, and the entire alignment film is described as having photoconductivity. This is because if the lower layer has photoconductivity, the entire alignment film is considered to have photoconductivity. The contents of the present invention will be described in detail by the following examples.

  FIG. 1 is a cross-sectional view showing the configuration of the first embodiment of the present invention, and FIG. 2 is a plan view of the first embodiment. Before explaining FIG. 1 and FIG. 2, the mechanism in which an afterimage exists for a long time will be explained with reference to FIGS. There are two types of afterimages: a so-called DC afterimage in which the pattern is burned and disappears gradually when the same picture is given, and an afterimage caused by a decrease in the alignment performance of the alignment film, a so-called AC afterimage. The present invention takes measures against so-called DC afterimages.

  FIG. 3 shows a state in which charges are accumulated on the surface of the alignment film 113 immediately after displaying a predetermined pattern. 3, the scanning line 10 is formed on the TFT substrate 100, and the intermediate layer 150 including various insulating layers such as the gate insulating film and the inorganic passivation film described in FIG. 17 is formed on the scanning line 10. An alignment film 113 is formed on the intermediate layer 150.

  When the backlight is irradiated from the back surface of the TFT substrate 100, the resistance of the alignment film 113 in the opening 55, which is not shielded by the scanning line 10, decreases due to photoconductive characteristics. On the other hand, the portion of the alignment film 113 that is shielded by the scanning line 10 is not irradiated with the backlight, so that the resistance does not decrease.

  FIG. 4 is a diagram illustrating a state of accumulated charges on the alignment film 113 when a certain time t1 has elapsed after displaying a predetermined pattern. The opening 55 that is not shielded by the scanning line 10 has the resistance of the alignment film 113 reduced due to the photoconductive effect, so that the charge disappears quickly, but the charge accumulated in the part shielded by the scanning line 10 is not. Since it moves to the opening 55, accumulated charge exists in the opening 55.

  FIG. 5 is a diagram illustrating a state of accumulated charges on the alignment film 113 when a longer time t2 has elapsed after displaying a predetermined pattern. The resistance of the alignment film 113 in the opening 55 is reduced by the photoconductive effect, and the charge is supplied from the light-shielding portion even though the charge disappears early. Charges still exist and an afterimage phenomenon appears.

  The light shielding portion does not affect image formation, and only the opening 55 is related to image formation. That is, the afterimage lasts for a long time because the charge of the light shielding portion moves to the opening 55 over time. FIG. 6 schematically shows this phenomenon. FIG. 6 is a cross-sectional view of the liquid crystal display panel, but the structure is the same as that described in FIG.

  In FIG. 6, a resistor R <b> 1 is formed between the alignment film 113 in the light shielding portion and the alignment film 113 in the opening 55. This resistance is mostly the resistance of the alignment film 113 in the light shielding portion. This is because the light shielding portion has a large resistance because there is no photoconductive effect. That is, when the resistance R1 is large, the movement of charges becomes slow, and the charges move from the alignment film 113 in the light shielding portion toward the alignment film 113 in the opening 55 over a long time. Therefore, the afterimage continues for a long time. In order to prevent this, the resistance from the alignment film 113 in the light shielding portion toward the alignment film 113 in the opening 55 may be reduced.

  In the first embodiment of the present invention shown in FIG. 1, in the light shielding portion, the photoresist 30 is disposed between the intermediate layer 150 and the alignment film 113, whereby the alignment film 113 in the light shielding portion is changed to the alignment film 113 in the opening 55. In this configuration, the flow of electric charge is accelerated. In FIG. 1, a resistor R <b> 2 between the photoresist 30 and the alignment film 113 in the opening 55 is arranged in parallel with the resistance R <b> 1 between the alignment film 113 in the light shielding part and the alignment film 113 in the opening 55. For example, since the photoresist 30 is as thick as about 1.5 μm, the resistance R2 is smaller than that of R1.

Incidentally, the thickness of the alignment film 113 is about 70 nm. The specific resistance of the alignment film 113 when there is no photoconductive effect is 10 ¹⁵ Ωcm, and the specific resistance of the photoresist 30 is the same. However, since the thickness of the photoresist 30 is 20 times or more that of the alignment film 113, the resistance R2 is 1/20 or less of the resistance R1. Therefore, the time for the charge accumulated in the light shielding portion to move to the opening 55 is also shortened. Even if the thickness of the photoresist 30 is 10 times or more the thickness of the alignment film 113, that is, the resistance R2 is about 1/10 or less of the resistance R1, the effect of the present invention can be exhibited. The specific resistance of the alignment film 113 in which the photoconductive effect has occurred is about 10 ¹³ Ωcm.

  FIG. 2 is a plan view showing a pixel configuration in the display area. In FIG. 2, the scanning lines 10 extend in the horizontal direction and are arranged in the vertical direction. The video signal lines 20 extend in the vertical direction and are arranged in the horizontal direction. A region surrounded by the scanning lines 10 and the video signal lines 20 is an opening 55, that is, a pixel portion having a pixel electrode. In FIG. 2, TFTs are omitted.

  In FIG. 2, a photoresist 30 is formed on the scanning line 10. The alignment film 113 is formed on the resist 30 formed on the opening 55, the video signal line 20, and the scanning line 10. The charge from the alignment film 113 in the portion shielded by the scanning line 10 quickly moves to the opening 55 due to the influence of the resist 30, and the afterimage time can be shortened.

  In FIG. 2, since the video signal line 20 is also a light-shielding portion, by forming a photoresist 30 on the video signal line 20, the effect of quickly moving the charge on the video signal line 20 to the pixel portion can be obtained. I can do it. However, the polarity of the video signal applied to the video signal line 20 changes line by line or frame by frame for AC driving. Therefore, charges are unlikely to accumulate on the video signal line 20. On the other hand, since the scanning signals applied to the scanning lines 10 are always of the same polarity, charges are likely to be accumulated. Therefore, the region where the photoresist 30 is formed is most effective on the scanning line 10.

  FIGS. 7 and 8 are graphs showing the results of simulation and comparison of afterimages between the conventional structure shown in FIG. 6 and the structure of the present invention shown in FIG. 7 corresponds to the conventional example of FIG. 6, and FIG. 8 corresponds to the present invention of FIG. The horizontal axis in FIGS. 7 and 8 is time, and the vertical axis is the intensity of the afterimage. The intensity of the afterimage is synonymous with the amount of residual charge in the opening. The unit in the simulation is arbitrary. The simulation is performed assuming that the areas of the light shielding portion and the opening portion are the same.

  7 and 8, the alternate long and short dash line indicates the influence on the afterimage due to the charge accumulated only in the opening. Since the opening has the same configuration in FIG. 6 and FIG. 1, the afterimage time due to the charge accumulated only in the opening is the same. 7 and 8, the dotted line indicates the effect on the afterimage due to the influence of the charge accumulated only in the light shielding portion. In the conventional example shown in FIG. 7, since the charge accumulated only in the light-shielding portion moves to the display area over a long time, an afterimage is generated for a long time. On the other hand, in the present invention shown in FIG. 8, the charge accumulated only in the light-shielding part due to the influence of the photoresist in the light-shielding part quickly moves to the opening, so that the afterimage disappears quickly.

  7 and 8, the actual afterimage is a combination of the influence of the charge accumulated only in the opening and the charge accumulated only in the light shielding portion. The solid line in FIGS. 7 and 8 is a curve showing an actual afterimage. The actual afterimage in the present invention shown in FIG. 8 disappears more quickly than the afterimage of the conventional example shown in FIG. That is, in the effect of the present invention in FIG. 8, the actual afterimage can be lost early due to the influence of the photoresist formed in the light shielding portion.

  FIG. 9 is a cross-sectional view showing the periphery of the display area of the liquid crystal display panel according to the first embodiment. In FIG. 9, an intermediate layer 150 is formed on the TFT substrate 100, and an alignment film 113 is formed thereon. The TFT substrate 100 is bonded to the counter substrate 200 by a sealing material 60, and the liquid crystal layer 300 is sandwiched between the TFT substrate 100 and the counter substrate 200. On the outside of the display area 50, the lead lines of the scanning lines 10 and the video signal lines 20 are formed, which serves as a light shielding area for the light from the backlight. Therefore, the alignment film 113 in this portion cannot obtain a photoconductive effect, and thus has a high resistance. Then, the charge accumulated on the alignment film 113 formed outside the display region 50 moves to the display region 50 over a long time, causing an afterimage.

  In FIG. 9, the photoresist 30 is disposed on the intermediate layer 150 outside the display region 50, and the alignment film 113 is formed thereon. Since the photoresist 30 is formed as thick as about 1.5 μm, the resistance R2 between the alignment film 113 in the display region 50 and the photoresist 30 can be reduced. As a result, the charge accumulated outside the display region 50 can be reduced. Can quickly move to the display area 50, so that the afterimage time can be shortened. Therefore, according to the configuration of FIG. 9, the afterimage phenomenon around the display area can be mitigated.

  FIG. 10 is a diagram illustrating a process for realizing the configuration of the first embodiment. In FIG. 10, the process is the same as before until the pixel electrode is formed on the TFT substrate. After forming the pixel electrode, a resist is applied and patterning is performed. Since the resist is left only in the light shielding portion, the influence of transparency and the like does not matter. Accordingly, a relatively inexpensive resist such as a phenol novolac type can be used as the resist material. After patterning the resist to leave the resist only in the light shielding portion, baking is performed at 140 ° C. to 150 ° C. Thereafter, an alignment film is applied. Subsequent steps are the same as in the prior art.

  Since the influence on the afterimage is dominated by the state of the alignment film on the TFT substrate side, it is not always necessary to form a photoresist on the light shielding portion on the counter substrate in order to reduce the specific resistance of the alignment film.

  FIG. 11 is a cross-sectional view showing the configuration of the second embodiment of the present invention in the display area, and FIG. 12 is a plan view thereof. In the conventional example shown in FIG. 6, since the alignment film 113 in the light shielding portion cannot obtain a photoconductive effect, the resistance is large and the charge accumulated in the light shielding portion cannot be quickly moved to the opening. It is. This embodiment is characterized in that the resistance of the alignment film 113 in the light shielding portion is originally reduced even if the photoconductive effect cannot be obtained.

  In the configuration of Example 2 shown in FIG. 11, after forming the alignment film 113, the opening 55 is shielded using a photomask 80 and only the light shielding part is irradiated with ultraviolet rays. The TFT substrate 100 on which the alignment film 113 is formed is disposed on the hot plate 70, and the substrate is heated at 200 ° C. to 210 ° C. simultaneously with the irradiation of ultraviolet rays. In this way, by irradiating the alignment film 113 in the light shielding portion with ultraviolet rays while heating, the structure of the alignment film 113 in the light shielding portion changes, and the specific resistance of the alignment film can be reduced. On the other hand, since the alignment film 113 in the opening 55 is not irradiated with ultraviolet rays, the characteristics of the alignment film 113 do not change and the alignment ability does not change. Since the light-shielding portion is not a portion for displaying an image, even if the alignment film 113 is altered and the alignment ability is reduced, the image characteristics are not affected.

  Since the purpose of the ultraviolet ray to be used is to alter the alignment film 113, it is most effective to use deep-UV (wavelength of 300 nm or less) and unpolarized ultraviolet rays. However, in order to simplify the manufacturing apparatus, it is possible to use polarized ultraviolet rays used for photo-alignment. In other words, linearly polarized ultraviolet rays having a wavelength of 240 nm to 400 nm can be used. However, it is difficult to carry out simultaneously with photo-alignment. This is because the ultraviolet irradiation in this embodiment is essential to be performed together with the heating of the substrate. For example, when polarized UV light having a wavelength of 250 nm is used, the specific resistance of the alignment film decreases to 2/3 when the substrate is heated to 200 ° C., and the specific resistance of the alignment film decreases when heated at 230 ° C. It became 1/2.

  Whether or not UV irradiation has been performed twice can be determined by irradiating the alignment film with infrared light and evaluating its absorption spectrum. That is, the number of polyimide rings in the alignment film in the light-shielding part irradiated with ultraviolet rays twice is reduced. As a result, the infrared absorption spectrum is different.

  FIG. 12 is a plan view of the present embodiment. FIG. 12 is a plan view showing a state in which a photomask 80 is disposed on the TFT substrate 100 on which the alignment film 113 is formed. In FIG. 12, a photomask hole 85 is formed in a portion of the photomask 80 corresponding to the scanning line 10 of the TFT substrate 100. That is, the ultraviolet light is irradiated only on the alignment film 113 on the scanning line 10. Therefore, only the alignment film 113 on the scanning line 10 is altered, and the specific resistance is lowered.

  Although the photomask hole 85 is formed only on the scanning line 10 in FIG. 12, the photomask hole 85 may also be formed on the video signal line 20 to alter the alignment film 113 on the video signal line 20. Good. However, the effect of reducing the resistance of the alignment film 113 is greater when the resistance of the alignment film 113 on the scanning line 10 is reduced as described in the first embodiment.

  FIG. 13 is a cross-sectional view of the liquid crystal display panel according to the second embodiment. In FIG. 13, an alignment film 113 is formed on the intermediate layer 150 on the TFT substrate 100. The counter substrate 200 is bonded to the TFT substrate 100 by the sealing material 60. A liquid crystal 300 is sandwiched between the TFT substrate 100 and the counter substrate 200. In the display area 50, the alignment film 113 is lowered in resistance by receiving light from the backlight. However, outside of the display area 50, the alignment film 113 is shielded from the light shielding area due to the influence of the lead lines such as the scanning lines 10 or the video signal lines 20. This portion of the alignment film 113 has a high resistance because no photoconductive effect occurs.

  In this embodiment, the alignment film 113 outside the display region 50 is irradiated with ultraviolet rays while heating the substrate, thereby reducing the specific resistance and allowing the charge to move quickly from the light shielding region to the display region 50. . Thereby, the afterimage around the display area 50 can be eliminated early.

  FIG. 14 is a diagram illustrating a process for realizing the configuration of the present embodiment. In FIG. 14, an alignment film is applied to the TFT substrate formed up to the pixel electrode. Thereafter, the alignment film is dried and leveled to obtain a uniform film. Then, it baked at 230 degreeC and imidation is performed. Thereafter, photo-alignment is performed by irradiating linearly polarized ultraviolet rays having a wavelength of 230 nm to 400 nm. Thereafter, heating is performed at 230 ° C. to 240 ° C. to volatilize the phenylene bismaleimide monomer and the like, thereby improving the alignment characteristics. Thereafter, using a photomask, only the light shielding portion of the TFT substrate is irradiated with ultraviolet rays, and the specific resistance of the alignment film in this portion is lowered. The substrate is heated at 200 ° C. to 230 ° C. simultaneously with the ultraviolet irradiation. Thereafter, a liquid crystal display panel is formed in combination with the counter substrate. Since the influence on the afterimage is dominated by the state of the alignment film on the TFT substrate side, the opposing substrate does not necessarily require an ultraviolet irradiation process in order to reduce the specific resistance of the alignment film.

  The effect of the present invention on the DC afterimage can be achieved by using a black and white 8 × 8 checker flag pattern as shown in FIG. That is, an 8 × 8 checker flag pattern in black and white as shown in FIG. 15 is displayed for 12 hours, and then returned to a gray solid halftone. The halftone gradation is 64/256.

  FIG. 16 shows the evaluation result of the DC afterimage. In FIG. 16, the horizontal axis represents the time after returning to the gray solid halftone. The vertical axis represents the afterimage level. On the vertical axis, RR is a state in which the checker flag pattern is clearly visible when the tone is returned to the halftone, and is NG. R is a state in which the checker flag pattern is thin but visible when the tone is returned to the halftone. In FIG. 16, a curve A is a DC afterimage characteristic when the alignment film according to the present invention is used. A curve B is an afterimage characteristic when an alignment film having no photoconductive effect is used.

  Even if the afterimage level is R when the halftone is restored, it can be said that there is no practical problem if it disappears in a short time. In the case of the curve B, which is a case where an alignment film having no photoconductive effect is used as the alignment film, the level R when returning to the halftone continues for a long time, so that there remains a practical problem. On the other hand, according to the configuration of the alignment film according to the present invention, the DC afterimage rapidly decreases, and after returning to the halftone, the DC afterimage disappears completely in about 13 minutes.

  In FIG. 16, when comparing the level of the DC afterimage 10 minutes after returning to the halftone, which is a measure of the DC afterimage, the DC afterimage is 90% when the alignment film is only one layer. On the other hand, the DC afterimage in the present invention is 10% or less, indicating that the effect of the present invention is very large.

  DESCRIPTION OF SYMBOLS 10 ... Scanning line, 20 ... Video signal line, 30 ... Photoresist, 40 ... Accumulated electric charge, 50 ... Display area, 55 ... Opening part, 60 ... Sealing material, 70 ... Hot op plate, 80 ... Photomask 100 ... TFT substrate 101 ... Gate electrode, 102 ... Gate insulating film, 103 ... Semiconductor layer, 104 ... Source electrode, 105 ... Drain electrode, 106 ... Inorganic passivation film, 107 ... Organic passivation film, 108 ... Counter electrode, 109 ... Upper insulating film, DESCRIPTION OF SYMBOLS 110 ... Pixel electrode, 111 ... Through-hole, 112 ... Slit, 113 ... Orientation film, 150 ... Intermediate layer, 200 ... Opposite substrate, 201 ... Color filter, 202 ... Black matrix, 203 ... Overcoat film, 210 ... Surface conductive film 300 ... Liquid crystal layer 301 ... Liquid crystal molecule 1 3U ... upper alignment film, 113L ... lower alignment film, BL ... Backlight, R1 ... orientation film between resistors, R2 ... photoresist - between the alignment film resistor

Claims (6)

A pixel electrode is formed in a region surrounded by a scanning line extending in the first direction and arranged in the second direction and a video signal line extending in the second direction and arranged in the first direction A liquid crystal display panel in which a liquid crystal is sandwiched between a TFT substrate formed and a counter substrate having a color filter corresponding to the pixel, and a backlight disposed on the back of the liquid crystal display panel,
An alignment film is formed to cover the scanning line, the video signal line, and the pixel electrode,
The alignment film has undergone a photo-alignment treatment;
The alignment film has photoconductive properties;
The liquid crystal display device, wherein a specific resistance of the alignment film covering the scanning line in a state where the backlight is turned off is smaller than a specific resistance of the alignment film covering the pixel electrode.   The liquid crystal display device according to claim 1, wherein a density of the imide ring in the alignment film covering the scanning line is smaller than a density of the imide ring in the alignment film covering the pixel electrode. 2. The liquid crystal display device according to claim 1, wherein the alignment film has a specific resistance of 10 ¹⁵ Ωcm when there is no photoelectric effect, and a specific resistance when the alignment film has a photoelectric effect of 10 ¹³ Ωcm.   A liquid crystal is sandwiched between a TFT substrate on which a plurality of scanning lines, a plurality of video signal lines, and a plurality of pixel electrodes are formed, a counter substrate having a color filter, and the TFT substrate and a bona fide color filter substrate. An alignment film used for a liquid crystal display device in which a liquid crystal display panel to be configured and a backlight provided on the back of the liquid crystal display panel are arranged,
  The alignment film is formed between the scanning line, the video signal line, the pixel electrode, and the liquid crystal,
  The alignment film has undergone a photo-alignment treatment,
  The alignment film has photoconductive properties,
  An alignment film used in a liquid crystal display device, wherein a specific resistance of the alignment film covering the scanning line in a state where the backlight is turned off is smaller than a specific resistance of the alignment film covering the pixel electrode.   5. The alignment film used in the liquid crystal display device according to claim 4, wherein a density of the imide ring in the alignment film covering the scanning line is smaller than a density of the imide ring in the alignment film covering the pixel electrode. .   The specific resistance in the absence of the photoelectric effect of the alignment film is 10 ¹⁵ The specific resistance in the case of Ωcm and photoelectric effect is 10 ¹³ The alignment film used for the liquid crystal display device according to claim 4, wherein the alignment film is Ωcm.

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