JPH11218765A - Method for aligning polymer thin film and liquid crystal display - Google Patents

Abstract

(57) [Object] To provide a liquid crystal alignment film which can be sufficiently applied to a liquid crystal display device by an alignment method of irradiating linearly polarized light. SOLUTION: A polymer thin film 5 having a portion which can be oriented by linearly polarized light and having a glass transition temperature of 200 ° C. or more is irradiated with linearly polarized light in a state where the orientable portion can be easily moved to be oriented. In order to easily move the orientable portion of the polymer thin film to a state where the polymer thin film can be easily moved, the polymer thin film is heated to a glass transition temperature of −150 ° C. or more and a glass transition temperature or less, or is brought into contact with a solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for aligning a polymer thin film and its application to a liquid crystal display.

[0002]

2. Description of the Related Art In a liquid crystal display device, a liquid crystal alignment film for aligning liquid crystal plays an important role. Conventionally, as a liquid crystal alignment film, a film obtained by mechanically rubbing a polyimide thin film with a roll or the like has been mainly used. However, this method is not preferable in terms of quality control because dust is generated in the friction step and dust adheres to the substrate due to generation of static electricity.

The performance of a liquid crystal display device is
It is described in Japanese Patent Application Laid-Open No. 2686661 and Japanese Patent Application Laid-Open No. Hei 2-2 that a pixel defect due to a short circuit between FTs and a display defect due to a defective orientation due to a scratch during rubbing are caused.
It is described in detail in, for example, Japanese Patent Publication No. 77025. As a method for solving these problems, Japanese Patent No. 2608661 and Japanese Patent Application Laid-Open No. 2-277025 disclose a method of aligning an alignment film by irradiating the alignment film with linearly polarized light.

[0004]

According to the above method,
By irradiating the alignment film material containing the absorption anisotropic molecules with linearly polarized light, an alignment film can be obtained without using the friction method. However, the properties of the alignment films aligned by these methods are not sufficient, and they cannot be used for liquid crystal display devices.

The present invention has been made in view of such a current situation of an alignment film used for a liquid crystal display element, and has improved an alignment method of irradiating an alignment film material containing anisotropic molecules with linearly polarized light. It is an object of the present invention to obtain a liquid crystal alignment film that can be sufficiently applied to a liquid crystal display device, and to provide a liquid crystal display element using the alignment film thus obtained.

[0006]

In a horizontal electric field type liquid crystal display device, an afterimage occurs when the voltage of a display portion changes from an on state to an off state, and the technical problem to be solved to eliminate the afterimage phenomenon is as follows. It is one. The present inventors have conducted studies to reduce the afterimage, and as a result, it has become clear that the afterimage decreases as the glass transition temperature of the polymer used increases.
It became clear that the afterimage phenomenon did not substantially appear above 0 ° C.

Next, based on this result, the present inventors,
Experiments were conducted on the alignment of these polymer thin films by linearly polarized light. As a result, the orientation of the polymer thin film by linearly polarized light is insufficient when irradiated with linearly polarized light at room temperature, and a sufficient contrast cannot be obtained when a liquid crystal display device is used. By irradiating linearly polarized light in a state of being heated from a temperature 150 ° C. lower than the glass transition temperature to a temperature equal to or lower than the glass transition temperature,
It has been clarified that efficient alignment can be realized and high contrast can be obtained when a liquid crystal display device is used. This effect is achieved by setting the heating temperature to the glass transition temperature of 100 ° C.
It was more remarkable when the temperature was changed from a low temperature to a glass transition temperature or lower. When the heating temperature was lower than the glass transition temperature of 150 ° C. or higher, the effect of the efficient orientation was not recognized.

Further, when polyimide is used as a polymer thin film, imidization proceeds very little, taking advantage of the fact that polyamide acid or polyamic acid ester, which is a precursor of polyimide, has a lower glass transition temperature than the corresponding polyimide. It has been clarified that an alignment film having excellent characteristics can be obtained by performing photo-alignment in a state where it is not in the above-mentioned state and then further performing imidization.

The present invention has been made based on such a study. That is, in the method for aligning a polymer thin film according to the present invention, a polymer thin film having a portion that can be oriented by linearly polarized light and having a glass transition temperature of 200 ° C. or higher is irradiated with linearly polarized light in a state where the orientable portion can move easily. It is characterized by the following. As a method for making the orientable portion of the polymer thin film easily movable, a method using heating or a method using a solvent can be adopted. In the case where the orientable portion can be easily moved by heating, the polymer thin film may be heated to a glass transition temperature of −150 ° C. or more and a glass transition temperature or less, preferably, the glass transition temperature of the polymer thin film −100 ° C. What is necessary is just to heat below the glass transition temperature.

The liquid crystal display element according to the present invention is characterized in that a polymer thin film having a portion which can be orientated by linearly polarized light is irradiated with linearly polarized light in a state where the orientable portion can easily move. A liquid crystal display device characterized by using: When the alignment film is used as a liquid crystal alignment film of a liquid crystal display device in which a display method is an in-plane switching method, a high quality liquid crystal display device that does not cause an afterimage phenomenon can be obtained.

Further, the polymer thin film according to the present invention has a glass transition temperature of 200, characterized in that the polymer thin film is oriented by irradiating it with linearly polarized light in a state where the orientable portion can easily move.
It is a polymer thin film of not less than ° C. As the polymer, a polymer containing a polyimide polymer and its precursor as main components can be used. In particular, the imidation ratio of the polyimide precursor is 60%.
By irradiating linearly polarized light in the following conditions, heating conditions can be relaxed.

A liquid crystal display device according to the present invention is a liquid crystal display device using the above-mentioned polymer thin film as a liquid crystal alignment film. When the display method is the horizontal electric field method, a high-quality liquid crystal display device that does not cause an afterimage phenomenon can be obtained. The polymer having a glass transition temperature of 200 ° C. or higher used in the present invention generally has a dichroic dye or a photo-amphibitable portion that isomerizes by absorbing specific light. In the case where the molecules themselves are arranged by light absorption, it is not necessary to particularly provide a dichroic dye or a portion capable of photoamplitude. Various types of dichroic dyes and structures capable of photoamplitude are known, and any of them can be used in the present invention. Examples thereof include azobenzene derivatives, stilbene derivatives, spiropyran derivatives,
a-aryl-b-keto acid ester derivatives, chalconic acid derivatives, cinnamic acid derivatives and the like.

The light source for irradiating linearly polarized light used in the present invention is not particularly limited as long as it generates ultraviolet rays, and a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a xenon lamp, or the like can be used. He-Ne laser,
Lasers such as an Ar-F laser and a Xe-Cl laser can also be used as the light source. The in-plane switching mode liquid crystal device manufactured using the alignment film formed by the method of the present invention has a higher image lag and contrast than the alignment film formed by the conventional method without heating or using a solvent when irradiating linearly polarized light. In both cases, significant improvements were seen. As described above, according to the present invention, it is possible to obtain a liquid crystal alignment film that can sufficiently withstand practical use by the linearly polarized light irradiation method. By completely solving the problem such as adhesion to the liquid crystal display, it is possible to obtain an in-plane switching mode liquid crystal display device having less afterimage and high contrast.

[0014]

Next, the present invention will be described specifically with reference to examples. [Example 1] p-phenylenediamine (0.04mo
l) and 4,4′-diaminostilbene (0.01 mol)
l) 3,3 ', 4,4' in N-methylpyrrolidone solution
-Biphenyltetracarboxylic dianhydride (0.05mo
l) was added and reacted at room temperature to obtain a polyamic acid (1) of 15% by weight. This polyamic acid was formed on a silicon substrate by a spin coating method and heated at 210 ° C. for 30 minutes to obtain a film having a thickness of 5 μm. The glass transition temperature determined from the result of measuring the dynamic viscoelastic behavior of this film was 250 ° C. The imidation ratio determined by an infrared absorption spectrum was 80%.

As a substrate, two transparent glass substrates having a thickness of 1.1 mm and a polished surface are used, and a thin film transistor and a wiring electrode to which a lateral electric field can be applied are formed on one of these substrates. An insulating protective film made of silicon nitride was formed on the outermost surface thereon. FIG. 1 shows the structure of a thin film transistor and various electrodes. FIG. 1A is a front view seen from a direction perpendicular to the substrate surface, and FIG.
Is a sectional view taken along the line AA of the front view, and FIG.
It is a sectional side view in B.

The thin film transistor element 14 comprises a pixel electrode (source electrode) 4, a signal electrode (drain electrode) 3, a scanning electrode (gate electrode) 12, and amorphous silicon 13. The common electrode 1 and the scanning electrode 12, and the signal electrode 3 and the pixel electrode 4 were each formed by patterning the same metal layer. The pixel electrodes 4 are arranged between the three common electrodes 1 in the front view.

The pixel pitch is in the horizontal direction (that is, the signal electrode 3).
Is 100 μm, in the vertical direction (that is, between the scanning electrodes 12).
Is 300 μm. As for the electrode width, a scanning electrode, a signal electrode, and a common electrode wiring portion (a portion extending in parallel with the scanning wiring electrode), which are wiring electrodes extending over a plurality of pixels, were widened to avoid line defects. Widths are 10 μm, 8 μm and 8 μm respectively
It is. On the other hand, in order to improve the aperture ratio, the widths of the pixel electrodes independently formed in pixel units and the portions of the common electrode extending in the longitudinal direction of the signal wiring electrodes are slightly reduced to 5 μm each.
m and 6 μm. By reducing the width of these electrodes, the possibility of disconnection due to the incorporation of foreign matter and the like increases, but in this case, only one pixel is partially missing and no line defect occurs.
The signal electrode 3 and the common electrode 1 were spaced apart by 2 μm via an insulating film. The number of pixels is 640 × 3 by 640 × 3 (R, G, B) signal wiring electrodes and 480 wiring electrodes.
× 480.

On this substrate, the above-mentioned polyamic acid (1) was diluted to 6% with N-methylpyrrolidone, and γ-aminopropyltriethoxysilane was added in a solid content of 0.3% by weight.
After the addition, printing and heat treatment at 210 ° C. for 30 minutes were performed to form a dense polyimide alignment film having a thickness of about 800 °. Next, while the substrate was heated to 100 ° C. on a hot plate, the substrate was irradiated with linearly polarized light using a Xe—Cl laser as a light source to impart liquid crystal alignment capability.

As shown in FIG. 2, the other substrate 18a
A color filter with a light-shielding layer (black matrix 16 and color filter 17) is formed thereon, and an overcoat film 15 made of epoxy resin having a thickness of about 1.5 μm is formed thereon. About 800
The polyimide alignment film 5a of Å was formed. Next, in the same manner as described above, the polyimide alignment film 5a was irradiated with linearly polarized light using a Xe-Cl laser as a light source while being heated to 100 ° C. on a hot plate to impart liquid crystal alignment ability.

Next, a sealing agent is applied to the peripheral portion of the two substrates with the surfaces having the liquid crystal alignment ability facing each other and a spacer made of dispersed spherical polymer beads interposed therebetween. The cell was assembled. FIG. 3 is a schematic diagram showing a side cross section of the liquid crystal cell according to the present invention assembled in this manner. The alignment directions of the alignment films 5 and 5a formed on the two substrates 18 and 18a are substantially parallel to each other, and the angle between the alignment films 5 and 5a and the direction of the applied lateral electric field is 75 °. In this cell, the dielectric anisotropy Δε is positive and the value is 10.2 (1 kHz).
z, 20 ° C.) and the refractive index anisotropy Δn is 0.075.
(Wavelength 590 nm, 20 ° C.), nematic-liquid crystal composition 20 having a nematic-isotropic phase transition temperature T (NI) of about 76 ° C. was injected in vacuum, and sealed with a sealing material made of an ultraviolet-curable resin. . Thus, the thickness (gap) of the liquid crystal layer 20
Manufactured a 4.8 μm liquid crystal panel. The retardation (Δn · d) of this liquid crystal panel is 0.36 μm.

This liquid crystal panel is sandwiched between two polarizing plates (G1220DU manufactured by Nitto Denko Corporation) 19 and 19a, and the polarization transmission axis of one of the polarizing plates is substantially parallel to the alignment direction of the alignment film, and the other is perpendicular to the same. I let it. Thereafter, a driving circuit, a backlight, and the like were connected to form a module, and an active matrix liquid crystal display device was obtained. In the present embodiment, the normally closed characteristic is such that dark display is performed at a low voltage and bright display is performed at a high voltage.

In order to quantitatively measure the image sticking, the afterimage, and the contrast of the image of the liquid crystal display device manufactured as described above, evaluation was performed using an oscilloscope combined with a photodiode. First, the window pattern is displayed on the screen at the maximum luminance for 30 minutes, and then the entire screen is switched so that the afterimage is most noticeable, in this case, the luminance is 10% of the maximum luminance. The time until disappears was evaluated as an afterimage time, and the magnitude ΔB / B (10%) of the luminance variation of the luminance B between the afterimage portion of the window and the peripheral halftone portion was evaluated as the afterimage intensity. That is, ΔB / B (10%) is 30 at the maximum luminance.
This is the luminance variation rate at a luminance of 10% of the maximum luminance before and after standing for a minute. Here, the afterimage intensity allowed as a display device is 3% or less.

As a result, the afterimage intensity ΔB, which is the luminance variation,
/ B (10%) was about 2%, and the time until the afterimage disappeared was about 50 milliseconds, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 milliseconds. In the image quality afterimage inspection by visual inspection, no image burn-in or display unevenness due to the afterimage was observed, and high display characteristics were obtained. As described above, by using the alignment film, it was possible to obtain a liquid crystal display device in which image sticking and after-image display defects were reduced. In addition, the contrast between the voltage application part and the non-application part was as high as 200. [Example 2] The substrate heating temperature during irradiation of linearly polarized light was 150 ° C.
The same examination as in Example 1 was performed. As a result, ΔB
/ B (10%) was about 1.5%, and the time until the afterimage disappeared was about 50 milliseconds, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 milliseconds. In addition, the contrast between the voltage application part and the non-application part was as high as 250. Example 3 The p-phenylenediamine of Example 1 was replaced with 2,
3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is added to 2-bis {4- (p-aminophenoxy) phenyl} propane to 3,3 ′, 4,4′-diphenylethertetracarboxylic dianhydride. Polyamic acid (2) was obtained in the same manner as in Example 1 except that the anhydride was changed to an anhydride. The same study as in Example 1 was conducted using this polyamic acid (2).

As a result, the glass transition temperature of the polyimide determined from the dynamic viscoelasticity measurement was 210 ° C. Also, Δ
B / B (10%) is about 1.7%, and the time until the afterimage disappears is about 50 ms, which is almost the same as the fall response time of the liquid crystal used here which is about 35 ms. Was. The contrast between the voltage application part and the non-application part is 23.
A high value of 0 was obtained. Comparative Example 1 A liquid crystal panel was manufactured in the same manner as in Example 1 except that the substrate temperature during irradiation with linearly polarized light was changed to 25 ° C. A liquid crystal display device was manufactured using this liquid crystal display panel, and the same examination as in Example 1 was performed. As a result, ΔB / B (10
%) Is about 4%, and the time until the afterimage disappears is about 7%.
0 ms. The contrast between the voltage applied portion and the non-applied portion was 70. [Comparative Example 2] A liquid crystal display device was prepared in the same manner as in Example 1 except that the polyamic acid (2) used in Example 3 was used and the heating temperature during irradiation of linearly polarized light without forming a color filter was 220 ° C. Was manufactured, and the same examination as in Example 1 was performed.

As a result, ΔB / B (10%) was about 10%, and the time until the afterimage disappeared was about 100%.
Milliseconds. The contrast between the voltage applied portion and the non-applied portion was 50. Example 4 A film of 15% by weight of polyamic acid (1) was formed on a silicon substrate by a spin coating method.
After heating for 0 minutes, a film having a thickness of 5 μm was obtained. The glass transition temperature determined from the result of measuring the dynamic viscoelastic behavior of this film was 140 ° C. The imidation ratio determined by an infrared absorption spectrum was 50%.

Polyamic acid (1) was diluted to 6% with N-methylpyrrolidone on the same substrate as in Example 1 on which a thin film transistor and a wiring electrode were formed, and γ-aminopropyltriethoxysilane was converted to a solid content. After the addition of 0.3% by weight, printing was performed, and heat treatment was performed at 120 ° C. for 30 minutes to form an alignment film of about 900 °. Next, the substrate is brought to room temperature (25
C), the liquid crystal alignment ability was imparted by irradiating linearly polarized light using a Xe-Cl laser as a light source.

On the other substrate, a color filter with a light-shielding layer was formed in the same manner as in Example 1, and an alignment film made of polyamic acid (1) was formed on the outermost surface by the same processing as described above. Similarly, a liquid crystal alignment ability was imparted by irradiating linearly polarized light using a Xe-Cl laser as a light source at room temperature. Next, a heat treatment was performed on these two substrates at 210 ° C. for 30 minutes. Subsequently, a liquid crystal display device was assembled using these two substrates in the same manner as in Example 1, and the characteristics were evaluated.

As a result, the afterimage intensity ΔB, which is the luminance variation,
/ B (10%) was about 2%, and the time until the afterimage disappeared was about 45 milliseconds, which was almost the same as the fall response time of the liquid crystal used here, which was about 35 milliseconds. In the image quality afterimage inspection by visual inspection, no image burn-in or display unevenness due to the afterimage was observed, and high display characteristics were obtained. As described above, by using the alignment film according to the present invention, it was possible to obtain a liquid crystal display element in which image sticking and after-image display defects were reduced. In addition, the contrast between the voltage application part and the non-application part was as high as 250. Example 5 The polyamic acid (2) described in Example 3 was diluted to 6% with N-methylpyrrolidone, and γ-aminopropyltriethoxysilane was added in a solid content of 0.3% by weight.
After the addition, printing was performed on the same two substrates as in Example 1 to obtain 2
Heat treatment was performed at 10 ° C. for 30 minutes to form an alignment film of about 900 °. Next, the formed alignment film was brought into contact with N-methylpyrrolidone for 3 minutes, and immediately after removing N-methylpyrrolidone on the surface, irradiation with linearly polarized light was performed in the same manner as in Example 1 except that the substrate was not heated. Liquid crystal alignment ability. After irradiation with the deflection, the substrate was heated at 150 ° C./10 minutes. Using these two substrates, a liquid crystal display device was manufactured in the same manner as in Example 1, and its characteristics were evaluated. As a result, Δ
B / B (10%) was about 1.8%, and the time until the afterimage disappeared was about 45 milliseconds, which was almost the same as the fall response time of the liquid crystal used here of 35 milliseconds. In addition, the contrast between the voltage application part and the non-application part was as high as 220. Comparative Example 3 A liquid crystal display device was manufactured in the same manner as in Example 5 except that the formed alignment film was not brought into contact with N-methylpyrrolidone for 3 minutes, and its characteristics were evaluated. As a result, ΔB / B (10%) was about 5%, and the time until the afterimage disappeared was about 110 milliseconds. The contrast between the voltage applied portion and the non-applied portion was 30.

[0029]

According to the present invention, it is possible to obtain a liquid crystal alignment film that can sufficiently withstand practical use by a method using linearly polarized light,
Further, it is possible to obtain a horizontal electric field type liquid crystal display device having a small contrast and a high contrast.

[Brief description of the drawings]

1A and 1B are diagrams showing a wiring structure of an electrode of a thin film transistor of the present invention, wherein FIG. 1A is a front view, FIG. 1B is a cross-sectional view along AA, and FIG. 1C is a cross-sectional view along BB.

FIG. 2 is a schematic cross-sectional view of the other substrate constituting the liquid crystal cell.

FIG. 3 is a schematic sectional view of a liquid crystal cell according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Common electrode (common electrode), 2 ... Gate insulating film, 3 ...
Signal electrode (drain electrode), 4 ... pixel electrode (source electrode), 5 ... alignment film, 12 ... scanning electrode (gate electrode), 1
3: amorphous silicon, 14: thin film transistor element, 15: overcoat film, 16: black matrix, 17: color filter, 18: glass substrate, 19
... deflection film, 20 ... liquid crystal

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Katsumi Kondo 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (12)

[Claims] 1. A polymer, which irradiates a polymer thin film having a portion which can be oriented by linearly polarized light and has a glass transition temperature of 200 ° C. or higher with linearly polarized light in a state where the orientable portion can easily move. How to align the thin film. 2. The method for aligning a polymer thin film according to claim 1, wherein the orientable portion is easily moved by heating. 3. The method for aligning a polymer thin film according to claim 2, wherein the polymer thin film is heated to a glass transition temperature of −150 ° C. or higher and a glass transition temperature or lower. 4. The method for aligning a polymer thin film according to claim 2, wherein the polymer thin film is heated to a glass transition temperature of −100 ° C. or higher and a glass transition temperature or lower. 5. The method for aligning a polymer thin film according to claim 1, wherein the portion capable of being oriented is easily moved by a solvent. 6. A liquid crystal alignment film formed by irradiating a polymer thin film having a portion that can be oriented by linearly polarized light with linearly polarized light in a state where the orientable portion can easily move, and using the film as a liquid crystal alignment film. Liquid crystal display device. 7. A liquid crystal alignment film formed by irradiating a polymer thin film having a portion that can be oriented by linearly polarized light with linearly polarized light in a state where the orientable portion can easily move is used as a liquid crystal alignment film. A horizontal electric field type liquid crystal display device. 8. A polymer thin film having a glass transition temperature of 200 ° C. or higher, wherein the polymer thin film is oriented by irradiating it with linearly polarized light in a state where an orientable portion can easily move. 9. The polymer thin film according to claim 8, comprising a polyimide polymer and its precursor as main components. 10. The polymer thin film according to claim 9, wherein
A polymer thin film, which is irradiated with linearly polarized light in a state where the imidation ratio of the polyimide precursor is 60% or less. 11. A liquid crystal display device using the polymer thin film according to claim 8, 9 or 10 as a liquid crystal alignment film. 12. A liquid crystal display device of a horizontal electric field type, wherein the polymer thin film according to claim 8, 9 or 10 is used as a liquid crystal alignment film.