JP2009187043A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display panel that prevents display irregularities and has excellent viewing angle characteristics. <P>SOLUTION: The liquid crystal display device includes: first and second opposed substrates; liquid crystal held between the first and second substrates; a plurality of pixel electrodes, a bus line, and an alignment film provided to the inner surface side of the first substrate; and a common electrode and an alignment film provided to the inner surface side of the second substrate. At least one of the alignment films on the first and second substrates is subjected to processing for aligning the liquid crystal in a predetermined direction, and the alignment film on the second substrate is provided with a bank structure of 0.1 to 0.15 μm at a position corresponding to the bus line on the first substrate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device in which an alignment film is irradiated with ultraviolet rays or a bank structure is provided on the alignment film in order to control the alignment of liquid crystal. The present invention also relates to an aligner exposure apparatus and alignment film processing method for liquid crystal display devices.

  In a liquid crystal display device, a liquid crystal is sandwiched between a pair of substrates, and an electrode for applying an electric field to the liquid crystal and an alignment film for controlling the alignment of the liquid crystal are provided on the inner surface side of each substrate. The alignment film is subjected to an alignment treatment in order to align liquid crystal molecules in a predetermined direction. Typically, the alignment film is rubbed with a fiber material such as rayon, and the liquid crystal molecules are aligned in the rubbing direction. However, if the alignment film is rubbed with a fiber material, the fiber material may scatter and the liquid crystal panel may be contaminated. Therefore, there is a demand for a technique for controlling the alignment of liquid crystal without rubbing the alignment film.

  For example, Patent Document 1 discloses a technique for controlling the alignment of liquid crystal by irradiating an alignment film with ultraviolet rays obliquely. In the invention described in this publication, ultraviolet rays are applied to the alignment film from an oblique direction through a mask having slits while moving the alignment film.

  Patent Document 2 discloses a technique for controlling the alignment of liquid crystal by providing a bank structure (protruding pattern) on an alignment film. In this case, a vertical alignment film is used, and the liquid crystal molecules are aligned perpendicular to the alignment film. At a position where there is a bank structure (projection-like pattern), the liquid crystal molecules are aligned perpendicular to the side surface of the bank structure (projection-like pattern) and generally obliquely with respect to the substrate surface. . The bank structure (protruding pattern) has side surfaces on both sides, and the alignment direction of the liquid crystal molecules aligned perpendicular to one side of the bank structure (protruding pattern) is the bank structure (protruding pattern). This is opposite to the alignment direction of the liquid crystal molecules aligned perpendicular to the opposite side surface of the pattern. Thereby, the alignment division is achieved.

  The alignment division is to provide a plurality of regions having different liquid crystal alignments in one pixel. Taking rubbing as an example, the area of one pixel of the alignment film is divided into two regions, the first region is rubbed in one direction, and the second region is rubbed in the opposite direction. Then, the liquid crystal molecules in contact with the first region are pretilted in one direction, and the liquid crystal molecules in contact with the second region are pretilted in the opposite direction. It is known that the viewing angle characteristic is improved in the liquid crystal display device in which the alignment is divided.

  When a liquid crystal having negative dielectric anisotropy and an alignment film having vertical alignment are used, alignment division can be easily realized.

  When an alignment film having vertical alignment properties is irradiated with ultraviolet rays from an oblique direction, the alkyl side chain of the alignment film existing in a plane perpendicular to the irradiation direction of ultraviolet rays is cut by absorbing the ultraviolet rays, and a plane parallel to the irradiation direction of the ultraviolet rays. The alkyl side chain of the alignment film existing inside remains without absorbing ultraviolet rays, and the liquid crystal molecules are aligned according to the remaining alkyl side chain. In order to perform the alignment division, one region of the alignment film is irradiated with ultraviolet rays from one oblique direction, and the other region of the alignment film is irradiated with ultraviolet rays from the opposite oblique direction. In this case, a mask is disposed between the ultraviolet light source and the alignment film, and the one region and the other region are selectively irradiated with ultraviolet rays.

  Various materials are used as the alignment film. For example, Patent Document 3 discloses a TN type liquid crystal display device using an alignment film made of a mixture of polyamic acid and polyimide. However, in this publication, a mixture of polyamic acid and polyimide constitutes a TN liquid crystal cell.

  Further, when the alignment film having vertical alignment properties is irradiated with ultraviolet rays from an oblique direction, the liquid crystal is aligned in a direction parallel to the irradiation direction of the ultraviolet rays when used as a liquid crystal display device. On the other hand, the substrate is provided with electrodes along with the alignment film. One substrate is a TFT substrate and has a plurality of pixel electrodes and bus lines. The other substrate is a color filter substrate and has a common electrode. The alignment treatment of the alignment film is performed so that the alignment direction of the liquid crystal is parallel to the bus line. In this case, there is a problem that a horizontal electric field acts between the pixel electrode and the bus line, and the alignment of the liquid crystal is disturbed by the horizontal electric field at the boundary between the pixel electrode and the bus line.

JP-A-11-202336 Japanese Patent Laid-Open No. 11-352489 JP-A 64-004720

  When the alignment film is irradiated with ultraviolet rays obliquely, the ultraviolet light source is disposed at an angle with respect to the alignment film. In such an angled arrangement, the distance (optical path length) between the ultraviolet light source and the alignment film varies depending on the position of the alignment film. For this reason, the intensity of the ultraviolet rays applied to the alignment film may fluctuate, and the pretilt angle realized thereby may fluctuate. As a result, stable alignment cannot be obtained, and a good display can be obtained due to the appearance of domains. There was a problem of disappearing.

  In the alignment control technique using ultraviolet irradiation, an exposure apparatus including an ultraviolet light source and a mask is used to achieve alignment division. The mask is disposed between the ultraviolet light source and the alignment film, so that the ultraviolet rays are selectively irradiated onto the alignment film portion. In the first method of orientation division, the area of the opening of the mask is reduced so that ultraviolet light having scattering properties is transmitted through the opening of the mask. However, this method has a problem that the utilization efficiency of ultraviolet rays is low and the irradiation time of ultraviolet rays must be lengthened.

  In the second method of alignment division, the area of the opening of the mask is set to a size suitable for irradiating half of the pixels, and an ultraviolet light source is arranged obliquely with the mask to irradiate half of each pixel of the alignment film. Then, an ultraviolet light source is arranged obliquely in the reverse direction with the mask, and the other half of each pixel of the alignment film is irradiated with ultraviolet rays. However, in this case, as the pixels become smaller, it becomes difficult to align the mask and the alignment film. In proximity exposure, the mask and the alignment film are aligned with a gap between the mask and the alignment film. However, as the pixels become smaller, it is necessary to reduce the distance between the mask and the alignment film, but the distance between the mask and the alignment film cannot be made smaller than the allowable value.

  An object of the present invention is to provide a liquid crystal display device capable of realizing stable alignment of liquid crystals and thereby obtaining a good display.

  An object of the present invention is to provide an alignment film exposure apparatus that can realize stable alignment of liquid crystals with high utilization efficiency of ultraviolet rays.

  An object of the present invention is to provide a method for treating an alignment film, in which alignment of the mask and the alignment film can be easily performed when the alignment film is subjected to alignment treatment by ultraviolet irradiation.

  An object of the present invention is to provide a liquid crystal display device in which the orientation of liquid crystal is prevented from being disturbed by a lateral electric field at a boundary portion between a pixel electrode and a bus line.

  A liquid crystal display device according to the present invention includes a pair of substrates, a liquid crystal sandwiched between the pair of substrates, and an alignment film provided on the inner surface side of the substrate, and the alignment film includes a diamine component. It consists of a mixture of a polyamic acid and a polyimide containing a diamine component different from the diamine component of the polyamic acid, and the alignment film is characterized by being subjected to alignment treatment by ultraviolet irradiation.

  In this configuration, the pretilt angle realized with polyamic acid does not change even when the amount of ultraviolet irradiation changes, and the pretilt angle realized with polyimide changes greatly when the amount of ultraviolet irradiation changes. When both are mixed, when a certain time has elapsed since the start of ultraviolet irradiation, a pretilt angle corresponding to the mixing ratio of polyimide and polyamic acid is stably realized without depending on the amount of ultraviolet irradiation. However, if the diamine component used for the polyamic acid and the polyimide is the same, the polyamic acid and the polyimide are easily mixed uniformly, and the effect of changing the orientation state of the polyimide is reduced, so that the properties of the polyamic acid are close. End up. For this reason, it is better that the diamine component used for the polyamic acid is different from the diamine component used for the polyimide.

  An alignment film exposure apparatus according to the present invention includes an ultraviolet light source, a slit through which ultraviolet light emitted from the ultraviolet light source passes and a reflecting plate having a reflecting surface on the opposite side of the ultraviolet light source, and ultraviolet light emitted from the slit of the reflecting plate. It is characterized by comprising a photomask having an opening to pass through and a reflecting surface on the reflecting plate side.

  According to the exposure apparatus, the use efficiency of ultraviolet rays is high, and stable alignment of liquid crystals can be realized.

The alignment film processing method according to the present invention is a method for forming an alignment film in which an alignment film having a plurality of pixel regions is irradiated with ultraviolet rays to align the alignment film. A photomask is disposed above the alignment film. The photomask is aligned with the alignment film so that the center of the first opening of the photomask is aligned with the center of the first pixel region of the alignment film, and the ultraviolet light source is positioned above the photomask. An ultraviolet light source, a photomask, and an alignment film are arranged, and the number of ultraviolet rays that have passed through the first opening of the photomask is n (n is an integer of 0 or more) away from the first pixel region of the alignment film. The width of the opening of the photomask is a (μm), the distance between the photomask and the alignment film is d (μm), and the angle of the ultraviolet rays incident on the alignment film Θ (rad), the pixel area pixel When the switch and g ([mu] m), ultraviolet light, photomask, and an alignment layer is disposed so as to satisfy the following relationship:
(G / 2-20) ≦ a ≦ (g / 2 + 20) (1)

そして、紫外線光源から紫外線を照射して配向膜に配向処理を行うことを特徴とする。

Then, the alignment film is subjected to alignment treatment by irradiating ultraviolet rays from an ultraviolet light source.

  According to the above processing method, alignment between the mask and the alignment film can be easily performed, and the alignment film can be aligned by irradiation with ultraviolet rays.

  A liquid crystal display device according to the present invention includes a first and second opposing substrates, a liquid crystal sandwiched between the first and second substrates, and a plurality of liquid crystals provided on the inner surface side of the first substrate. A pixel electrode, a bus line, and an alignment film; and a common electrode and an alignment film provided on the inner surface side of the second substrate. A liquid crystal is applied to at least one alignment film of the first and second substrates. The alignment film of the second substrate is provided with a bank structure having a thickness of 0.1 to 0.15 μm at a position corresponding to the bus line of the first substrate. It is characterized by.

  In this configuration, the bank structure prevents the alignment of the liquid crystal from being disturbed by a lateral electric field at the boundary portion between the pixel electrode and the bus line.

  According to the present invention, it is possible to obtain a liquid crystal display device capable of realizing stable alignment of liquid crystals and thereby obtaining a good display.

It is a figure which shows the liquid crystal display device of 1st Example of this invention. It is a figure which shows the example which irradiates an ultraviolet-ray to the alignment film of FIG. It is a figure which shows the example which a liquid crystal molecule aligns when using the alignment film of FIG. It is a figure which shows the modification of the liquid crystal display device of FIG. It is a figure which shows the example which irradiates an ultraviolet-ray to the alignment film of FIG. It is a figure which shows the relationship between the irradiation amount of an ultraviolet-ray when a polyamic acid and a polyimide are each made into an alignment film independently, and a pretilt angle. It is a figure which shows the relationship between the irradiation amount of an ultraviolet-ray when a polyamic acid and a polyimide are mixed and it is set as an alignment film, and a pretilt angle. It is a figure which shows the relationship between the irradiation amount of the ultraviolet-ray of the alignment film when apply | coating two types of resin to a board | substrate independently, and the alignment film when it mixes, and surface energy. It is a figure which shows the irradiation amount and voltage holding rate of the ultraviolet-ray of the orientation film when apply | coating two types of resin to a board | substrate independently, and the orientation film when mixed. It is a figure which shows the aligner exposure apparatus by 2nd Example of this invention. It is a figure which shows the detail of the photomask of FIG. It is a figure which shows the modification of the exposure apparatus of the alignment film of FIG. It is a figure which shows the 1st exposure step of the exposure method of the alignment film by 3rd Example of this invention. It is a figure which shows the 2nd exposure step after the 1st exposure step of FIG. It is a figure which shows the board | substrate which has the orientation film processed by the exposure method of FIG.13 and FIG.14. It is a figure which shows the modification of the processing method of the alignment film of FIG.13 and FIG.14. It is a figure which shows the width | variety and alignment state of the non-exposure area | region of the liquid crystal display device which divided | segmented one pixel area | region by exposure twice. It is a figure which shows the width | variety and orientation state of the overlap exposure area | region of the liquid crystal display device which divided | segmented one pixel area | region by exposure twice. It is a figure which shows the exposure state of 1 pixel area | region at the time of changing the magnitude | size of the opening part of a photomask. It is a figure which shows the exposure state of 1 pixel area | region at the time of changing the space | interval between a photomask and alignment film. It is a figure explaining the problem at the time of changing a pixel pitch. It is a figure which shows the liquid crystal display device of 4th Example of this invention. It is an enlarged view which shows a part of color filter board | substrate of FIG. It is a top view which shows the color filter board | substrate of FIG. It is a top view which shows the TFT substrate in which the bank structure of the color filter substrate was additionally shown. It is a figure which shows the example of the liquid crystal display device for demonstrating that the orientation of a liquid crystal is disturb | confused by a horizontal electric field in the boundary part of a pixel electrode and a bus line. It is a figure which shows the basic example which prevents that the orientation of a liquid crystal is disturbed. It is a figure which shows the relationship between the overlap of a bank structure and a pixel electrode, and a luminance ratio. It is a figure which shows the relationship between the overlap of a bank structure and a pixel electrode, and a luminance ratio. It is a figure which shows the relationship between the overlap of a bank structure and a pixel electrode, and a luminance ratio.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a liquid crystal display device according to a first embodiment of the present invention. The liquid crystal display device 10 includes a pair of transparent substrates 12 and 14, a liquid crystal 16 sandwiched between the pair of substrates 12 and 14, and alignment films 18 and 20 provided on the inner surfaces of the substrates 12 and 14. . Electrodes 22 and 24 are provided under the alignment films 18 and 20, respectively. One electrode is provided together with an active matrix including TFTs. The liquid crystal 16 is a liquid crystal having negative dielectric anisotropy, and the alignment films 18 and 20 are vertical alignment films. Therefore, as shown in FIG. 1, the liquid crystal 16 is aligned substantially perpendicularly to the substrates 12 and 14 and with a pretilt.

  In this embodiment, the alignment films 18 and 20 are formed of a material containing polyimide containing a diamine component. Preferably, the alignment films 18 and 20 are made of a mixture of a polyamic acid containing a diamine component and a polyimide containing a diamine component, and the diamine component of the polyamic acid and the diamine component of the polyimide are different from each other. The polyimide diamine component includes a diamine component that does not substantially contribute to vertical alignment and a diamine component that substantially contributes to vertical alignment, and contributes to the substantially vertical alignment with respect to the entire diamine component. The proportion of the diamine component is 30% or more.

  FIG. 2 is a diagram showing an example in which the alignment film 18 (20) is irradiated with ultraviolet rays. The diamine component that contributes substantially to the vertical alignment of the alignment film 18 (20) has the alkyl side chains 18a and 18b shown exaggeratedly. The alkyl side chains 18a and 18b protrude in various directions with respect to the surface of the alignment film 18 (20). The alkyl side chain 18a exists in a plane substantially parallel to the incident direction of ultraviolet rays, and the alkyl side chain 18b exists in a plane substantially perpendicular to the incident direction of ultraviolet rays. When the alignment film 18 (20) is irradiated with non-polarized or polarized ultraviolet rays obliquely, the alkyl side chain 18b existing in a plane substantially perpendicular to the irradiation direction of the ultraviolet rays is absorbed and cut. The alkyl side chain 18a existing in a plane substantially parallel to the incident direction of the light does not absorb ultraviolet rays and is not cut. Therefore, the alkyl side chain 18a remains uncut.

  FIG. 3 is a diagram showing an example in which liquid crystal molecules are aligned when the alignment film 18 (20) of FIG. 2 is used. When the liquid crystal display device including the alignment films 18 and 20 thus processed is assembled as shown in FIG. 1 and the liquid crystal 16 is inserted, the molecules of the liquid crystal 16 are pretilted according to the remaining alkyl side chains 18a without being cut. It becomes like this. Accordingly, the molecules of the liquid crystal 16 are aligned substantially perpendicular to the substrates 12 and 14 due to the vertical alignment of the alignment films 18 and 20, but are pretilted by a predetermined pretilt angle according to the alkyl side chain 18a.

  FIG. 4 is a view showing a modification of the liquid crystal display device of FIG. In FIG. 4, the liquid crystal 16 is aligned substantially perpendicularly to the substrates 12 and 14 and with a pretilt. However, the molecules 16a of the liquid crystal 16 in some regions are aligned (pretilt) in a direction different from the molecules 16b of the liquid crystals 16 in other regions. It is known that when there are a plurality of regions having different orientations within one pixel (alignment division), the viewing angle characteristics of the liquid crystal display device are improved.

  FIG. 5 is a diagram showing an example in which the alignment film 18 (20) of FIG. 4 is irradiated with ultraviolet rays. In order to align the molecules 16a of the liquid crystal 16 in a partial region, the ultraviolet ray UV1 is irradiated from one oblique direction. In order to align the molecules 16b of the liquid crystal 16 in another part of the region, the ultraviolet ray UV2 is irradiated from an oblique direction opposite to the above. The mask 26 is used when the ultraviolet rays UV1 and UV2 are irradiated.

  As described above, when ultraviolet rays are irradiated obliquely, the optical path length between the ultraviolet radiation source and the alignment film 18 (20) varies depending on the position, the intensity of the irradiated ultraviolet rays varies depending on the position, and the pretilt angle varies. Thus, there is a problem that a stable orientation cannot be obtained. Therefore, in the present invention, such a problem is improved by configuring the material of the alignment film 18 (20) as described above.

  FIG. 6 is a diagram showing the relationship between the irradiation amount of ultraviolet rays and the pretilt angle when polyamic acid and polyimide are each independently used as an alignment film. Curves A, B, and C are diagrams showing the relationship between the irradiation amount of ultraviolet rays and the pretilt angle for polyamic acids A, B, and C having different contents of diamine components that contribute to vertical alignment. For convenience, the type of resin and the corresponding curve are indicated by the same symbol. When the alignment film is made of polyamic acid alone, the realized pretilt angle hardly changes even if the content of the diamine component is different.

  Curves D, E, F, G, H, and I represent the relationship between the amount of UV irradiation and the pretilt angle for polyimides D, E, F, G, H, and I having different diamine component contents that contribute to vertical alignment. FIG. For convenience, the type of resin and the corresponding curve are indicated by the same symbol. The ratio of the diamine component that contributes to the vertical alignment of polyimides D, E, F, G, H, and I is 20, 40, 50, 60, 90, and 100%. When polyimide is used alone as an alignment film, the pretilt angle realized by ultraviolet irradiation changes greatly. However, when the alignment film is made of polyimide alone, the pretilt angle realized changes considerably when the irradiation amount of ultraviolet rays changes.

  FIG. 7 is a diagram showing the relationship between the amount of UV irradiation and the pretilt angle when polyamic acid and polyimide are mixed to form an alignment film. Curves DA, EA, CA, GB, HA, and IA are obtained by mixing the polyamic acids A, B, and C and the polyimides D, E, F, G, H, and I described above, respectively. Show the case. In the curve DA indicating a mixture containing polyimide with a small content (20%) of the diamine component that contributes to the vertical alignment, the pretilt angle that is realized changes greatly as the amount of ultraviolet irradiation changes. In the curve IA for a mixture containing polyimide with a high content of diamine component that contributes to vertical alignment (90 or 100%), the change in pretilt angle achieved is relatively high even when the amount of UV irradiation increases. Small. In the curves EA, FC, GB, and HA relating to a mixture containing polyimide with an appropriate content (30% or more) of a diamine component that contributes to vertical alignment, it is realized even though the irradiation amount of ultraviolet rays changes. The change in the pretilt angle is very small.

  In short, polyamic acid has a very small change in pretilt angle realized even when the amount of ultraviolet irradiation is large, and polyimide has a relatively large change in pretilt angle as the amount of ultraviolet irradiation increases. When both are mixed, the characteristics of polyimide and polyamic acid are averaged, and after a certain period of time from the start of UV irradiation, the mixing ratio of polyimide and polyamic acid does not depend on the amount of UV irradiation thereafter. Thus, the pretilt angle corresponding to is maintained stably. That is, in the range of the ultraviolet irradiation amount of 2000 mJ to 3000 mJ, the pretilt angle hardly changes in the curves EA, FC, GG, HA even if the ultraviolet irradiation amount changes. Therefore, even if the amount of ultraviolet rays actually irradiated varies, the realized pretilt angle is almost constant.

  However, if the diamine component used in the polyamic acid and the diamine component used in the polyimide are the same, the polyamic acid and the polyimide are easily mixed uniformly, and the effect of changing the orientation state of the polyimide is reduced. It becomes close to the nature of. For this reason, it is better that the diamine component used for the polyamic acid is different from the diamine component used for the polyimide.

  In addition, some diamines exhibit vertical alignment and others do not. If the diamine that expresses the vertical alignment used in the polyimide is too small, the change in pretilt when irradiated with ultraviolet rays becomes too large, making it difficult to control the pretilt when mixed with polyamic acid. For this reason, it is good that the ratio of the diamine component which has the vertical orientation with respect to the whole diamine component is 30% or more. More preferably, the ratio of the diamine component having vertical alignment is 40% or more and 90% or less.

  FIG. 8 is a diagram showing the relationship between the surface energy and the irradiation amount of the alignment film when two kinds of resins are individually applied to the substrate and the alignment film when they are mixed. Curve B relates to polyamic acid B similar to polyamic acid B described above, and curve G relates to polyimide G similar to polyimide G described above. Curve GB relates to a mixture of polyamic acid B and polyimide G. As in the case of the pretilt angle shown in FIGS. 6 and 7, a stable region in which the surface energy hardly changes at a certain irradiation amount by mixing a resin whose surface energy hardly changes by irradiation with ultraviolet rays and a resin that changes greatly. Appears. Thereby, a stable pretilt can be obtained.

  If the surface energy is different, it is convenient for the same reason as when the diamine component is different, and a certain degree of non-uniformity is produced when the resin is mixed. Therefore, it is preferable that the alignment films 18 and 20 formed on the substrates 12 and 14 are a mixture of resins having different surface energy values of 2 mN / m or more.

  Mixing resins with different amounts of change in surface energy with respect to ultraviolet rays corresponds to mixing resins with different pretilt angles, such as when polyamic acid and polyimide are mixed. Therefore, it is preferable that the alignment films 18 and 20 formed on the substrates 12 and 14 are formed by mixing at least two kinds of resins having different surface energy change amounts with respect to ultraviolet rays.

  FIG. 9 is a diagram showing the irradiation amount of ultraviolet rays and the voltage holding ratio of the alignment film when two kinds of resins are individually applied to the substrate and when the alignment film is mixed. Curve C relates to polyamic acid C similar to polyamic acid C described above, and curve F relates to polyimide F similar to polyimide F described above. Curve FC relates to a mixture of polyimide F and polyamic acid C. The voltage holding ratio of the alignment film of curve C is lowered by ultraviolet rays, and the voltage holding ratio of the alignment film of curve F is increased by ultraviolet rays. When both are mixed (curve FC), a decrease in the voltage holding ratio is suppressed as a result, and a good voltage holding ratio can be obtained even when irradiated with ultraviolet rays.

  Therefore, it is preferable that the alignment films 18 and 20 formed on the substrates 12 and 14 are formed by mixing at least two types of resins having different amounts of change in the voltage holding ratio with respect to ultraviolet rays.

  Next, a specific example will be described.

(Example 1)
Alignment films 18 and 20 were made from a mixture of polyamic acid A and polyimide H (content of the diamine component contributing to vertical alignment is 90%). The mixing ratio was polyamic acid A: polyimide H = 49: 1. The alignment film material containing this mixture was applied with a spinner and baked to form alignment films 18 and 20 on the substrates 12 and 14. The alignment films 18 and 20 were irradiated with ultraviolet rays from an oblique direction of 45 °. Several samples were prepared by changing the irradiation amount of ultraviolet rays. A thermosetting sealing material was applied to one substrate, and a 4 μm spacer was sprayed on the other substrate, and both substrates were bonded together. After vacuum packing, thermosetting was performed to create an empty cell. A liquid crystal having a negative dielectric anisotropy was injected into the empty cell in a vacuum to prepare a liquid crystal display panel. When the pretilt angle of the liquid crystal display panel thus prepared was measured, as shown by the curve HA in FIG. 7, the pretilt angle became the lowest at the ultraviolet irradiation amount 3J, and the change in the pretilt angle was around this minimum value. Pretty small. As a result, a stable pretilt angle could be obtained.

(Example 2)
Alignment films 18 and 20 were made from a mixture of polyamic acid B having a change in surface energy as shown in FIG. 8 and polyimide G (content of diamine component contributing to vertical alignment is 60%). The mixing ratio was polyamic acid B: polyimide G = 4: 1. A liquid crystal display panel was produced in the same manner as in Example 1 using the alignment film material containing this mixture. When the pretilt angle of the liquid crystal display panel thus prepared was measured, as shown by the curve GB in FIG. 7, the pretilt angle became the minimum at the ultraviolet irradiation amount 3J, and the change in the pretilt angle was around this minimum value. Pretty small. As a result, a stable pretilt angle could be obtained. Moreover, as shown in FIG. 8, the surface energy hardly changed.

(Example 3)
Alignment films 18 and 20 were formed from a mixture of polyamic acid C having a change in surface energy as shown in FIG. 9 and polyimide F (content of diamine component contributing to vertical alignment is 50%). The mixing ratio was polyamic acid C: polyimide F = 3: 1. A liquid crystal display panel was produced in the same manner as in Example 1 using the alignment film material containing this mixture. When the pretilt angle of the liquid crystal display panel thus prepared was measured, as shown by the curve FC in FIG. 7, the pretilt angle was about 88 ° at an ultraviolet irradiation amount of 2J to 3J, and there was almost no change in the pretilt angle. . As a result, a stable pretilt angle could be obtained. Further, as shown in FIG. 9, the change in the voltage holding ratio was small, and a good voltage holding ratio could be obtained.

(Comparative example)
Alignment films 18 and 20 were made from a mixture of polyamic acid A and polyimide D (content of the diamine component contributing to vertical alignment is 20%). The mixing ratio was polyamic acid C: polyimide F = 49: 1. A liquid crystal display panel was produced in the same manner as in Example 1 using the alignment film material containing this mixture. When the pretilt angle of the liquid crystal display panel thus prepared was measured, as shown by the curve DA in FIG. 7, the pretilt angle rapidly decreased as the amount of ultraviolet irradiation increased, and a stable pretilt angle was obtained. I couldn't.

  FIG. 10 is a view showing an alignment film exposure apparatus according to a second embodiment of the present invention. The alignment film exposure apparatus 30 performs, for example, alignment processing on the alignment film 18 (20) of the liquid crystal display device 10 shown in FIG. The exposure apparatus 30 directly reacts the ultraviolet light source 32, the reflecting plate 34 having a slit 34a through which ultraviolet light passes, and the ultraviolet light a that has passed through the slit 34a of the reflecting plate 34 and after passing through the slit 34a of the reflecting plate 34. The plate 34 includes a photomask 36 having an opening 36a through which ultraviolet light reflected by the surface opposite to the ultraviolet light source 32 of the plate 34 passes.

  The slits 34a of the reflecting plate 34 and the openings 36a of the photomask 36 extend in a stripe shape in a direction perpendicular to the paper surface of FIG. The width of the slit 34a of the reflecting plate 34 is about 5 mm, for example. The width of the openings 36a of the photomask 36 is, for example, about 20 μm, and the openings 36a are provided at a pitch of 220 μm. The distance between the reflecting plate 34 and the photomask 36 is 1 cm, and the distance between the photomask 36 and the alignment film 18 (20) is 100 μm.

  In the embodiment, the reflecting plate 34 is attached to a transparent scattering plate 38. A mask used in a conventional exposure apparatus is made of chrome or the like, but chrome or the like has a low reflectance. The reflector 34 and the photomask 36 of the present invention are made of a material having a high reflectance in the ultraviolet wavelength region. For example, the reflector 34 and the photomask 36 are made of aluminum or aluminum coated with a fluorine compound. Alternatively, the reflecting plate 34 and the photomask 36 are formed of a dielectric multilayer film.

  The ultraviolet light source 32 mainly emits ultraviolet light in the range of 220 nm to 260 nm. Ultraviolet rays in this wavelength range are suitable for cleaving the alkyl side chain of the alignment film by irradiation with ultraviolet light, and a satisfactory alignment film alignment process can be performed. Also, ultraviolet rays in this wavelength range are easy to handle because they can be distinguished from room light. Aluminum has a reflectivity for ultraviolet rays in the range of 220 nm to 260 nm of about 90 percent, and is therefore suitable as a material having a high reflectivity for ultraviolet rays.

While aluminum is used, the surface is oxidized, and the oxide protects the aluminum, but it causes a decrease in the reflectivity of ultraviolet rays. Therefore, by using aluminum whose surface is coated with a fluorine compound, it is possible to prevent the reflectance of ultraviolet rays from decreasing and to increase the reflectance. Examples of such a fluorine compound include magnesium fluoride and calcium fluoride. Examples of the dielectric multilayer film include SiO ₂ / MgF ₂ and LaF ₃ / MgF ₂ . The dielectric multilayer film is formed by alternately forming several tens of layers of two materials having different refractive indexes with a thickness of ¼ wavelength, and the reflectance is about 95%.

  The surface on the photomask 36 side of the reflecting plate 34 and the surface on the reflecting plate 34 side of the photomask 36 are reflecting surfaces. The ultraviolet light source 32 emits scattered light. Therefore, as indicated by the solid arrow, the ultraviolet light emitted from the ultraviolet light source 32 passes through the slit 34a of the reflector 34 and passes through the opening 36a of the photomask 36 to irradiate the alignment film 18 (20). To do. Further, as indicated by the dashed arrow, the ultraviolet light emitted from the ultraviolet light source 32 passes through the slit 34a of the reflecting plate 34, is reflected by the photomask 36, and is reflected by the reflecting plate 34, and is opened by the opening 36a of the photomask 36. Then, the alignment film 18 (20) is irradiated.

  As described above, the ultraviolet rays emitted from the slit 34a of the reflecting plate 34 directly and the ultraviolet rays emitted from the slit 34a of the reflecting plate 34 and reflected by the photomask 36 and the reflecting plate 34 enter the opening 36a of the photomask 36. Then, the alignment film 18 (20) is irradiated. Therefore, the amount of ultraviolet rays passing through the opening 36a of the photomask 36 is increased as compared with the case where there is no reflecting plate 34, and the alignment film 18 (which can realize stable alignment of liquid crystal with high use efficiency of ultraviolet rays can be realized. 20) can be obtained. When the scattering plate 38 is provided, the ultraviolet rays that have passed through the scattering plate 38 come out from the slits 34a of the reflecting plate 34, and the utilization efficiency of the ultraviolet rays is further improved.

  The ultraviolet light source 32 emits scattered light, and the ultraviolet light passing through the opening 36a of the photomask 36 mainly irradiates the alignment film 18 (20) obliquely. Ultraviolet rays (UV1) traveling obliquely from one direction strike a part of the alignment film 18 (20). Ultraviolet rays (UV1) traveling obliquely from the opposite direction hit another part of the alignment film 18 (20). The action of the alignment treatment of the alignment film 18 (20) by obliquely irradiating the alignment film 18 (20) with ultraviolet rays as described above is as described with reference to FIGS. The action of achieving alignment division by ultraviolet rays (UV1) traveling obliquely from one direction and ultraviolet rays (UV1) traveling obliquely from the opposite direction is as described with reference to FIGS. In this embodiment, the alignment division can be achieved by one alignment process.

  FIG. 11 is a diagram showing details of the photomask 36. The photomask 36 is formed by forming a material layer (aluminum) 36c having a high ultraviolet reflectance on a transparent substrate 36b and a material layer (titanium oxide) 36d that absorbs ultraviolet rays in a two-layer structure. The opening 36a is formed in the material layer 36c having a high ultraviolet reflectance. The material layer 36c having a high ultraviolet reflectance reflects the ultraviolet light emitted from the slit 34a of the reflecting plate 34, and further allows the ultraviolet light reflected by the reflecting plate 34 to pass through the opening 36a. The material layer 36d that absorbs ultraviolet rays is located on the alignment film 18 (20) side to be irradiated and absorbs ultraviolet rays reflected by the alignment film 18 (20). Thus, ultraviolet rays reflected by the alignment film 18 (20) are prevented from being reflected by the photomask 36 and entering the alignment film 18 (20) as stray light.

  A thermosetting sealing material (manufactured by Mitsui Chemicals) is applied to one of the substrates 12 and 14 having the alignment films (manufactured by JSR) 18 and 20 created by the exposure apparatus 30 of FIGS. 10 and 11, and 4 μm is applied to the other substrate. The spacers (manufactured by Sekisui Fine Chemical Co., Ltd.) were sprayed to bond both substrates together. An empty cell was prepared by vacuum packing and leaving in an oven at 135 ° C. for 90 minutes. A vertical alignment film (made by Merck) 16 having negative dielectric anisotropy was inserted into the empty cell to manufacture a liquid crystal display panel.

  FIG. 12 is a view showing a modification of the alignment film exposure apparatus of FIG. Similar to the example of FIG. 11, the alignment film exposure apparatus 30 includes an ultraviolet light source 32, a reflecting plate 34 having a slit 34 a through which ultraviolet rays pass, ultraviolet rays emitted from the slit 34 a of the reflecting plate 34, and ultraviolet rays of the reflecting plate 34. A photomask 36 having an opening 36a through which ultraviolet rays reflected by the surface opposite to the light source 32 pass is provided. The reflection plate 34 is attached to a transparent scattering plate 38.

  In FIG. 12, the ultraviolet light source 32 emits parallel ultraviolet light, and a condensing means 40 composed of a convex lens is provided between the ultraviolet light source 32 and the reflection plate 34. The condensing means 40 condenses the ultraviolet light emitted from the ultraviolet light source 32 through the slit 34 a of the reflecting plate 34, and the condensed ultraviolet light passes through the slit 34 a of the reflecting plate 34. Further, the light transmitted through the scattering plate 38 also passes through the slit 34 a of the reflecting plate 34. The width of the slit 34a of the reflecting plate 34 is about 5 mm, for example. The width of the openings 36a of the photomask 36 is, for example, about 20 μm, and the openings 36a are provided at a pitch of 220 μm. The distance between the condensing means 40 and the reflecting plate 34 is 2 cm, the distance between the reflecting plate 34 and the photomask 36 is 1 cm, and the distance between the photomask 36 and the alignment film 18 (20) is 100 μm. A liquid crystal display panel was prepared in the same manner as the previous example.

  FIG. 13 is a view showing a first exposure step of the alignment film exposure method according to the third embodiment of the present invention. FIG. 14 shows the second exposure step after FIG. The substrate 14 is a TFT substrate similar to the substrate 14 of the liquid crystal display device 10 shown in FIG. The substrate 14 has a pixel electrode 24 and an alignment film 20.

  Each pixel electrode 24 is surrounded by a gate bus line 42 and a data bus line. 13 and 14 are cross-sectional views crossing the gate bus line 42. The pixel electrode 24 has a shape extending long in parallel with the data bus line, and the gate bus line 42 and the data bus line have a pixel area of 200 μm × 70 μm. Form. The gate bus line 42 and the data bus line have a width of 5 μm and are formed 3 μm apart from the pixel electrode 24. The counter substrate 12 includes a black matrix, a common electrode 22, and an alignment film 18. The black matrix forms a pixel area of 200 μm × 70 μm. The pixel pitch g is determined by two gate bus lines 42. In the case of the counter substrate 12, the pixel pitch g is determined in the same manner.

  The exposure device 44 includes an ultraviolet light source 46 that emits parallel ultraviolet light and a photomask 48. The photomask 48 is provided with a light shielding member (for example, metallic chrome) 48a on the surface of a transparent plate (for example, quartz), and the light shielding member 48a has an opening 48b. The size of the opening 48b of the photomask 48 is a (μm).

  The photomask 48 is disposed above the alignment film 20, and the distance between the photomask 48 (the surface of the light shielding member 48a) and the alignment film 20 is d (μm). The photomask 48 is formed on the alignment film 20 so that the center of one opening 48b of the photomask 48 is aligned with the center of one pixel region of the alignment film 20 (the center between two gate bus lines 42). Aligned with respect to.

  The ultraviolet light source 46 is disposed obliquely above the photomask 48. The ultraviolet light source 46 is disposed so that the angle of ultraviolet light incident on the photomask 48 and the alignment film 20 is θ (rad). As shown in FIG. 13, the ultraviolet light source 46 is first arranged obliquely above the photomask 48 at an angle θ, and the first exposure is performed. Then, as shown in FIG. On the other hand, it is symmetrically arranged at an angle θ, and the first exposure is performed.

  It is desirable that the size a (μm) of the opening 48b is approximately half of the pixel pitch g (μm). For example, the size a of the opening 48b is 100 μm, and the pixel pitch g is 200 μm. In this way, as shown in FIG. 13, the photomask 48 can be positioned on the alignment film 20 to perform the first exposure, and half of each pixel area of the alignment film 20 can be irradiated with ultraviolet rays. The second exposure is performed as shown in FIG. 14 while maintaining the relationship between the alignment layer 48 and the alignment layer 20 (without positioning again), and the remaining half of each pixel region of the alignment layer 20 is irradiated with ultraviolet rays. can do. That is, it is possible to perform exposure twice from different angles by performing the positioning operation of the troublesome photomask 48 and the alignment film 20 only once.

  FIG. 15 is a view showing the substrate 14 having the alignment film 20 processed by the exposure method of FIGS. 13 and 14. The molecules 16a of the liquid crystal 16 in some regions and the molecules 16b of the liquid crystal 16 in other regions are aligned in opposite directions. In this manner, an alignment-divided liquid crystal display device can be easily manufactured.

  FIG. 16 is a view showing a modified example of the processing method of the alignment film in FIGS. 13 and 14. In FIG. 16, the exposure apparatus 44 includes an ultraviolet light source 46 that emits parallel ultraviolet light, and a photomask 48. The pixel pitch is g (μm), and the size of the opening 48b is a (μm). The photomask 48 is disposed above the alignment film 20, and the distance between the photomask 48 and the alignment film 20 is d (μm). The ultraviolet light source 46 is disposed obliquely above the photomask 48. The ultraviolet light source 46 is disposed so that the angle of ultraviolet light incident on the photomask 48 and the alignment film 20 is θ (rad).

  The photomask 48 is disposed above the alignment film 20, and the distance between the photomask 48 and the alignment film 20 is d (μm). The photomask 48 is formed on the alignment film 20 so that the center of one opening 48b of the photomask 48 is aligned with the center of one pixel region of the alignment film 20 (the center between two gate bus lines 42). Aligned with respect to. The ultraviolet light source 46 in FIG. 16 is first arranged obliquely above the photomask 48 at an angle θ, and is subjected to the first exposure, and then symmetrically arranged obliquely at an angle θ with respect to the ultraviolet light source 46 initially arranged. A second exposure is performed. Thus, similar to the alignment film processing method of FIGS. 13 and 14, the alignment film processing method of FIG. 16 differs from the complicated photomask 48 and alignment film 20 by performing the positioning operation between the photomask 48 and the alignment film 20 only once. Can be exposed twice.

  In the basic feature of the third embodiment, the ultraviolet light source 46, the photomask 48, and the alignment film 20 are arranged such that the ultraviolet rays that have passed through one opening 48b of the photomask 48 are aligned with the one opening 48b (the It is arranged so as to irradiate n pixel areas (n is an integer of 0 or more) away from the pixel area of the alignment film 20 (just below one opening 48b).

  In FIG. 16, the ultraviolet rays that have passed through one opening 48b of the photomask 48 are separated from the pixel region of the alignment film 20 aligned with the one opening 48b (directly below the one opening 48b). It is arranged so as to irradiate the (adjacent) pixel area. The examples in FIGS. 13 and 14 correspond to the case where n is 0.

  The ultraviolet light source 46, the photomask 48, and the alignment film 20 are arranged so as to satisfy the following relationship.

      (G / 2-20) ≦ a ≦ (g / 2 + 20) (1)

このように、位置決めを行った後で、紫外線光源４６から紫外線を照射して配向膜２０に配向処理を行う。

As described above, after the positioning, the alignment film 20 is subjected to the alignment treatment by irradiating the ultraviolet light from the ultraviolet light source 46.

  Further, the distance d (μm) between the photomask 48 and the alignment film 20 satisfies the following relationship.

また、配向膜２０に入射する紫外線の角度θ（ｒａｄ）は次の関係を満足する。

Further, the angle θ (rad) of the ultraviolet light incident on the alignment film 20 satisfies the following relationship.

図１７は１つの画素領域を２回の露光により配向分割した液晶表示装置の非露光領域の幅と配向状態を示す図である。図１８は１つの画素領域を２回の露光により配向分割した液晶表示装置の重複露光領域の幅と配向状態を示す図である。非露光領域及び重複露光領域は図１９及び図２０を参照して説明される。１回目及び２回目に露光される領域がそれぞれ１画素領域の中心線の両側に丁度分布するならば、非露光領域及び重複露光領域は生じない。しかし、実際にはそのように理想的にはいかない。非露光領域及び重複露光領域が小さいならば、配向状態に影響を与えないが、非露光領域及び重複露光領域が大きいと、配向状態に影響を与える。

FIG. 17 is a diagram showing the width and alignment state of a non-exposed region of a liquid crystal display device in which one pixel region is aligned and divided by two exposures. FIG. 18 is a diagram showing the width and alignment state of an overlapped exposure region of a liquid crystal display device in which one pixel region is aligned and divided by two exposures. The non-exposure area and the overlapping exposure area will be described with reference to FIGS. 19 and 20. If the areas exposed for the first time and the second time are just distributed on both sides of the center line of the one pixel area, the non-exposure area and the overlapping exposure area do not occur. However, in reality, this is not ideal. If the non-exposure area and the overlapping exposure area are small, the alignment state is not affected. However, if the non-exposure area and the overlap exposure area are large, the alignment state is affected.

  FIG. 17 shows that when the width of the non-exposed region is 20 μm or less, a good alignment state can be maintained. FIG. 18 shows that when the width of the overlapping exposure region is 20 μm or less, a good alignment state can be maintained. The above relational expressions (1) and (2) are based on the examination results shown in FIGS.

  FIG. 19 is a diagram showing an exposure state of one pixel region when the size a (μm) of the opening 48b of the photomask 48 is changed. Reference numeral 50 denotes one pixel area, 50A denotes an area exposed by the first exposure, and 50B denotes an area exposed by the first exposure. The arrow indicates the pretilt direction. In FIG. 19A, the size a (μm) of the opening 48b is set so that the areas 50A and 50B exposed by the first exposure and the second exposure are each distributed on both sides of the center line of the one pixel area. This is the case. In this case, there are no non-exposed areas and overlapping exposed areas.

  FIG. 19B shows a case where the size a (μm) of the opening 48b is set smaller than that in the case of FIG. In this case, since the exposure areas 50A and 50B are both narrowed, a non-exposure area 50C is generated. FIG. 19C shows a case where the size a (μm) of the opening 48b is set larger than that in the case of FIG. In this case, since both the exposure areas 50A and 50B become wide, an overlapping exposure area 50D is generated.

  FIG. 20 is a diagram showing an exposure state of one pixel region when the distance d (μm) between the photomask 48 and the alignment film 20 is changed. FIG. 20A shows a case where the distance d is set so that the areas 50A and 50B exposed by the first and second exposures are each distributed on both sides of the center line of one pixel area. In this case, there are no non-exposed areas and overlapping exposed areas.

  FIG. 20B shows a case where the interval d is set smaller than that in the case of FIG. In this case, since the exposure areas 50A and 50B are shifted outward, a non-exposure area 50C is generated at the center of the pixel, and an overlapping exposure area 50D is generated at the end of the pixel. FIG. 20C shows a case where the interval d is set larger than in the case of (A). In this case, since the exposure areas 50A and 50B are shifted to the center side, an overlapping exposure area 50D is generated at the center of the pixel, and a non-exposure area 50C is generated at the end of the pixel.

  FIG. 21 is a diagram for explaining a problem when the pixel pitch g (μm) is changed. In the proximity exposure, the photomask 48 and the alignment film 20 are aligned with a gap d between the photomask 48 and the alignment film 20. However, as the pixels become smaller, it is necessary to reduce the distance d between the photomask 48 and the alignment film 20, but the distance d cannot be made smaller than the allowable value.

  FIG. 21A is a diagram showing a case where the pixel pitch g is sufficiently large and the distance d between the photomask 48 and the alignment film 20 is within an allowable range. FIG. 21B is a diagram showing a case where the pixel pitch g becomes smaller and the interval d needs to be smaller than the allowable range. However, in practice, since the distance d cannot take a value smaller than the allowable range, in order to be able to perform two exposures with one alignment, the distance d is allowed. There is a case where the angle θ of the ultraviolet ray incident on the alignment film 20 is changed to a value within the range. However, changing the angle θ of the ultraviolet light incident on the alignment film 20 is not preferable because the alignment processing ability due to the ultraviolet irradiation is reduced.

  In such a case, as described with reference to FIG. 16, the ultraviolet rays that have passed through one opening 48b of the photomask 48 are aligned with the one opening 48b (directly below the one opening 48b). It is preferable to irradiate a pixel region n (n is an integer of 0 or more) away from the pixel region of the alignment film 20. In this way, the interval d can be set to a value within the allowable range, and the angle θ of the ultraviolet light incident on the alignment film 20 can be set to an appropriate value. The third embodiment can provide this advantage.

  FIG. 22 is a diagram showing a liquid crystal display device according to a fourth embodiment of the present invention. The liquid crystal display device 10 includes a pair of transparent substrates 12 and 14, a liquid crystal 16 sandwiched between the pair of substrates 12 and 14, and alignment films 18 and 20 provided on the inner surfaces of the substrates 12 and 14. . Electrodes 22 and 24 are provided under the alignment films 18 and 20, respectively. One substrate 12 is a color filter substrate, and the electrode 22 is a common electrode. The other substrate 14 is a TFT substrate, and the electrode 24 is composed of a plurality of pixel electrodes provided together with an active matrix including TFTs.

  FIG. 24 is a plan view showing the inner surface of the color filter substrate 12 of FIG. The color filter substrate 12 has a black matrix 54. FIG. 25 is a plan view showing the inner surface of the TFT substrate 14 on which the bank structure of the color filter substrate 12 is additionally shown. The pixel electrode 24 is surrounded by the gate bus line 42 and the data bus line 52. In FIG. 22, the data bus line 52 is visible.

  The liquid crystal 16 is a liquid crystal having negative dielectric anisotropy, and the alignment films 18 and 20 are vertical alignment films. The alignment films 18 and 20 are aligned so that the liquid crystal molecules 16c are aligned in a direction perpendicular to the paper surface of FIG. 24 and 25, the alignment direction (pretilt direction) of the liquid crystal is indicated by an arrow. The alignment treatment can be performed by any means. For example, the alignment treatment can be performed by rubbing or ultraviolet irradiation described above.

  FIG. 23 is an enlarged view showing a part of the color filter substrate 12 of FIG. 22 and 23, the alignment film 18 of the color filter substrate 12 is provided with a bank structure 56 at a position corresponding to the data bus line 52 of the TFT substrate 14. A dielectric film 58 is formed on the common electrode 22 in a predetermined shape, and the bank structure 56 is formed as a convex portion where the alignment film 18 covers the dielectric film 58. The dielectric film 58 is very thin. For example, when the dielectric film 58 is formed with a resist pattern, the resist pattern is thinned by ozone ashing the formed resist pattern. Further, the resist is thinned with a diluent, spin-coated, and the resist pattern is thinned by removing the diluent. In the present invention, the thickness t of the bank structure 56 is in the range of 0.1 to 0.15 μm.

  As shown in FIGS. 22 to 25, the bank structure 56 is located immediately above the data bus line 52 and extends in parallel with the data bus line 52. The bank structure 56 is wider than the data bus line 52. Therefore, the bank structure 56 not only covers the data bus line 52 but also overlaps the end portion of the pixel electrode 24. The amount of overlap between the bank structure 56 and the pixel electrode 24 is indicated by O, and the amount of protrusion of the bank structure 56 from the black matrix 54 is indicated by P.

  FIG. 26 is a diagram showing an example of a liquid crystal display device for explaining that the orientation of the liquid crystal is disturbed by a lateral electric field at the boundary portion between the pixel electrode and the bus line. The alignment films 18 and 20 are omitted in FIG. The liquid crystal molecules 16c are aligned in a direction perpendicular to the paper surface of FIG. However, the liquid crystal molecules 16d located at the boundary portion between the pixel electrode 24 and the data bus line 52 are affected by a lateral electric field between the pixel electrode 24 and the data bus line 52, and as shown by the broken arrows in FIG. 26 in a direction parallel to the paper surface (in a direction from the end of the pixel electrode 24 toward the center). For this reason, the alignment of the liquid crystal is disturbed at the boundary between the pixel electrode 24 and the data bus line 52, and disclination occurs as shown by hatching. For example, in this portion, when white display is performed, the transmittance is lowered and the luminance is lowered.

  FIG. 27 is a diagram showing a basic example for preventing the alignment of the liquid crystal from being disturbed. A bank structure 60 having a considerable thickness is provided in parallel with the data bus line 52 immediately above the data bus line 52. The liquid crystal molecules 16 d in the vicinity of the bank structure 60 try to align perpendicularly to the surface of the bank structure 60. The alignment direction of the liquid crystal molecules 16d in the vicinity of the bank structure 60 is opposite to the alignment direction of the liquid crystal molecules 16d that are located at the boundary between the pixel electrode 24 and the data bus line 52 and receive the action of a lateral electric field. Thus, it is possible to prevent an inclination from occurring in a direction parallel to the paper surface of FIG. 27 (in a direction from the end of the pixel electrode 24 toward the center). Therefore, the occurrence of disclination can be suppressed.

  However, since the bank structure 60 is provided on the color filter substrate 12, it is necessary to consider misalignment when the color filter substrate 12 and the TFT substrate 14 are bonded together. Further, the amount of overlap between the bank structure 60 and the end of the pixel electrode 24 becomes a problem. When the overlap amount is small, the orientation regulating force of the bank structure 60 is small, and the occurrence of disclination due to the transverse electric field cannot be suppressed. If the amount of overlap is large, the orientation regulating force of the bank structure 60 increases, and conversely due to the bank structure 60 occurs.

  As a result of considering the relationship between the amount of overlap between the bank structure 60 and the end of the pixel electrode 24 and the disclination, the overlap between the bank structure 60 and the end of the pixel electrode 24 when the disclination is most reduced. It has been found that the amount of wrap varies depending on the thickness t of the bank structure 60. The greater the thickness t of the bank structure 60, the smaller the overlap amount when the disclination is reduced. Conversely, the smaller the thickness t of the bank structure 60 is, the more the disclination is reduced. The amount of overlap increases.

  In order to reduce the occurrence of disclination based on misalignment, it is desirable to make the bank structure 60 as thin as possible. In the present invention, the thickness t of the bank structure 56 is in the range of 0.1 μm or more and 0.15 μm or less. In this case, the overlap amount between the bank structure 56 and the end of the pixel electrode 24 when disclination is reduced is preferably in the range of 2 μm or more and 8 μm or less.

  In the embodiment, the pixel pitch in the direction of the gate bus line 42 is 80 μm, the width of the data bus line 52 is 5 μm, the interval between the pixel electrode 24 and the data bus line 52 is 3 μm, and the width of the pixel electrode 24 is 69 μm. . Further, the width of the black matrix 54 is 11 μm, and the pitch of the black matrix 54 is 80 μm. The bank structure 56 has a thickness of 0.12 μm, and the bank structure 56 has a width of 21 μm. Therefore, the overlap amount O between the bank structure 56 and the pixel electrode 24 is 5 μm, and the protrusion amount P of the bank structure 56 from the black matrix 54 is 5 μm.

  The color filter substrate 12 and the TFT substrate 14 were bonded so that the end of the black matrix 54 and the end of the pixel electrode 24 were aligned. Further, the alignment was performed such that the pretilt direction of the alignment film 18 of the color filter substrate 12 and the pretilt direction of the alignment film 20 of the TFT substrate 14 were opposite to each other. When the color filter substrate 12 and the TFT substrate 14 are bonded together, it is necessary to consider an alignment margin of about ± 3 μm. When the overlap amount O between the bank structure 56 and the pixel electrode 24 is 5 μm, the overlap amount O is within the range of 2 μm to 8 μm even when a positional shift occurs. If the overlap amount O is within this range, the occurrence of disclination can be suppressed.

  FIG. 28 is a diagram showing the relationship between the brightness ratio and the overlap O between the bank structure 56 and the pixel electrode 24 when the thickness of the bank structure 56 is 0.15 μm. The luminance ratio indicates the luminance at the end of the pixel electrode 24 when the center of the pixel electrode 24 is 1. When the overlap O is in the range of 2 to 8 μm, the luminance reduction is within 20%. Further, even when the overlap O is outside the range of 2 to 8 μm, the decrease in luminance is small.

  FIG. 29 is a diagram illustrating the relationship between the brightness ratio and the overlap O between the bank structure 56 and the pixel electrode 24 when the thickness of the bank structure 56 is 0.31 μm. If the overlap O is within a small range centered on 3 μm, the luminance drop is within 20%. When the overlap O is out of this range, the brightness is rapidly reduced.

  FIG. 30 is a diagram showing the relationship between the brightness ratio and the overlap O between the bank structure 56 and the pixel electrode 24 when the thickness of the bank structure 56 is 1.75 μm. If the overlap O is in the range of −1 μm to +3 μm, the luminance reduction is within 20%. When the overlap O is out of this range, the brightness is rapidly reduced. Note that the overlap O of −1 μm indicates that the space between the bank structure 56 and the pixel electrode 24 is open.

  According to the present invention, it is possible to obtain a liquid crystal display device capable of realizing stable alignment of liquid crystals and thereby obtaining a good display.

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12, 14 Substrate 16 Liquid crystal 18, 20 Alignment film 22, 24 Electrode 26 Mask 30 Exposure device 32 Ultraviolet light source 34 Reflector plate 36 Photomask 38 Scatter plate 40 Condensing means 42 Gate bus line 44 Exposure device 46 Ultraviolet light source 48 Photomask 50 Pixel area 52 Data bus line 54 Black matrix 56 Bank structure 58 Dielectric film 60 Bank structure

Claims (1)

  First and second opposing substrates, liquid crystal sandwiched between the first and second substrates, a plurality of pixel electrodes, bus lines and alignment films provided on the inner surface side of the first substrate And a common electrode and an alignment film provided on the inner surface side of the second substrate, and at least one alignment film of the first and second substrates is subjected to a treatment for aligning liquid crystals in a predetermined direction. The alignment film of the second substrate is provided with a bank structure having a thickness of 0.1 to 0.15 μm at a position corresponding to the bus line of the first substrate. Display device.

Images