JP3267989B2 - Method for manufacturing liquid crystal alignment film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal alignment film, and more particularly to a method for manufacturing a liquid crystal alignment film provided with an alignment control mechanism for aligning liquid crystal on a polymer film.

[0002]

2. Description of the Related Art Liquid crystal display devices have excellent features such as thinness, light weight and low power consumption, and are expected to be a new display device from various fields.

[0003] In a conventional liquid crystal display device, the basic structure of a liquid crystal cell is generally common. That is, the liquid crystal cell has a structure in which a pair of substrates provided opposite to each other is provided with a spacer therebetween to maintain a predetermined gap, a peripheral portion of the substrate is sealed with a sealant, and liquid crystal is sealed between the substrates. I have. Also,
An electrode and a liquid crystal alignment film are formed on inner surfaces of the pair of substrates.

The liquid crystal alignment film formed on the inner surface of the substrate has a function of arranging liquid crystals in a certain direction. As a method of aligning the liquid crystal, a method of aligning the liquid crystal in a direction parallel to the substrate and a method of aligning the liquid crystal in a direction perpendicular to the substrate are known. Of these, a method of orienting in a direction parallel to the substrate is often used.

Conventionally, a rubbing method or an oblique deposition method has been used to manufacture a liquid crystal alignment film. The rubbing method is a method in which a polymer film such as polyimide or polyvinyl alcohol is formed on the surface of a substrate and rubbed with a cloth such as velvet so that the surface of the polymer film has directionality. The oblique vapor deposition method is a method in which a metal oxide such as SiO is vapor-deposited at a certain angle with respect to a substrate to give directionality to the surface. Among them, the rubbing method is a simple process, and can perform a large amount of processing in a short time, and is most frequently used.

However, this type of method has the following problems. That is, in the rubbing method, a large amount of static electricity is accumulated because the film is rubbed with a cloth, and this static electricity causes destruction of the thin film transistor and adhesion of dust. In addition, contamination of the substrate is unavoidable because the fabric is in direct contact with the substrate. For these reasons, it has been pointed out that there is a limit to the application to a large and precise liquid crystal display device. In addition, the oblique deposition method has a problem that a long time is required for a deposition process, a pretilt angle of a liquid crystal is large, and alignment control is weak. At present, it is hardly used.

[0007]

As described above, conventionally, a rubbing method is often used to manufacture a liquid crystal alignment film.
In this method, static electricity is generated and the substrate surface is contaminated, and it has been difficult to apply the method to a large and precise liquid crystal display device.

The present invention has been made in view of the above circumstances, and an object of the present invention is to manufacture an excellent liquid crystal alignment film in a short time without causing surface contamination or generation of static electricity. It is an object of the present invention to provide a method for manufacturing a liquid crystal alignment film which can be applied to a large and precise liquid crystal display device.

[0009]

The gist of the present invention is to form a stretched portion and a contracted portion on the surface of a polymer film.

[0010] The present invention provides a method of manufacturing a liquid crystal alignment film for controlling alignment of the liquid crystal, high is formed on the substrate
Rubbing the molecular film; and
An energy beam is applied to the poorly-aligned portions of the polymer film.
Irradiating to remove the orientation; and
Irradiate the irradiated area with an energy beam along a predetermined direction
The body of the irradiated, irradiated part and the non-irradiated part adjacent to the irradiated part
Using the product change, the polymer film stretches and shrinks
And a step of forming

[0011]

When the polymer film is irradiated with an energy beam as in the present invention, the irradiated portion is locally heated and its volume changes. Here, if a material that shrinks the irradiated portion of the energy beam is used as the polymer film, it is possible to form a contracted portion and an extended portion in the polymer film. Further, when the energy beam is irradiated in a stripe pattern (parallel at a constant interval), the contracted portion and the stretched portion are arranged along one direction, and the liquid crystal is aligned along these arrangement directions. .

In this case, unlike the rubbing method, it is not necessary to rub the surface of the substrate with a cloth, and the generation of static electricity and contamination of the surface can be prevented. In addition, to irradiate an energy beam, a laser beam, an electron beam or the like may be optically scanned, and stripe irradiation of the energy beam can be performed in a short time. Therefore, an excellent liquid crystal alignment film can be manufactured in a short time.

In the present invention, it is desirable that the polymer film constituting the liquid crystal alignment film has sufficient strength and does not dissolve in the liquid crystal. As the polymer film constituting the liquid crystal alignment film, for example, a thermoplastic resin or a thermosetting resin can be used.

As the alignment film used in the conventional rubbing method, a thermoplastic resin such as polyimide or polyvinyl alcohol has been mainly used. These polymer films are excellent in film formation, mechanical strength, adhesion, heat resistance, etc.
It has already been used as an alignment film. When these polymer films are irradiated with an energy beam, the irradiated portions are locally heated and expanded. However, the irradiated portion shrinks due to the cooling process after stopping the irradiation of the energy beam. As a result, it becomes possible to form a contraction site and an extension site adjacent to the contraction site in the polymer film.

On the other hand, a thermosetting resin undergoes a curing reaction by heat, and shrinks at that time. When the polymer film is irradiated with the energy beam, the irradiated portion undergoes curing shrinkage, and as a result, it becomes possible to form a contracted portion on the alignment film and a stretched portion adjacent to the contracted portion. In addition, thermosetting resin may cause problems in terms of mechanical strength, adhesion, etc. In such a case, mixing the thermosetting resin into a thermoplastic resin such as polyimide will increase the mechanical strength. ,
It is possible to cause curing shrinkage while maintaining adhesion.

The liquid crystal alignment film of the present invention may have a multilayer structure. In this case, a structure in which the lower layer is made of a material having high flexibility such as silicone rubber or natural rubber and the upper layer is made of the above-described polymer film is desirable. In such a structure, the degree of shrinkage and stretching of the upper layer can be enhanced by the lower layer.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. (Example 1)

FIG. 1 is a sectional view showing the steps of manufacturing a liquid crystal alignment film according to the first embodiment of the present invention. First, as shown in FIG. 1A, a polymer solution is applied to the surface of the substrate 1 on which the electrodes are formed. The coating method of the polymer solution may be any of a spinner method and a printing method. Thereafter, the polymer solution is dried to form a polymer film (liquid crystal alignment film) 2 on the substrate 1.

Next, as shown in FIG.
Is irradiated from above. Further, the energy beam 3 may be irradiated from the back surface of the substrate 1. The energy beam 3 scans in a stripe pattern in parallel along a predetermined direction. Note that a plurality of energy beams may be irradiated simultaneously.

The portion of the polymer film 2 irradiated with the energy beam 3 contracts as described above, and as shown in FIG.
As shown in FIG. In the portion of the polymer film 2 to which the energy beam 3 has not been irradiated, stress acts in the direction indicated by the arrow in FIG. Is formed. Thus, a liquid crystal alignment film having a contraction site and an extension site is formed.

When the liquid crystal molecules 6 come into contact with the liquid crystal alignment film composed of the polymer film 2 thus formed as shown in FIG. 1D, the liquid crystal molecules 6 move in the contracting direction and the stretching direction of the polymer film 2. Oriented along. Further, as a result, the surface of the contracted portion 4 is depressed and the surface of the polymer film 2 is uneven, so that
The liquid crystal molecules 6 are more easily aligned along the irregularities on the surface of the polymer film 2 by the effect of the shape anisotropy.

FIG. 2 is a sectional view showing a schematic configuration of a liquid crystal display device prepared using the above-mentioned liquid crystal alignment film. This liquid crystal display element is manufactured as follows. First, on the surface of the substrate 1 on which the electrodes 9 are formed, a liquid crystal alignment film composed of the polymer film 2 in which the contracted portion and the stretched portion are formed in a striped manner by the method described above. A substrate 1 'similar to this is prepared, and a pair of substrates 1 and 1' are placed in a state where the surfaces on which the polymer films 2 and 2 'are formed face each other and a predetermined distance is maintained by a spacer 7, and , 1 ′ are adhered with a sealant 8. Then, after the liquid crystal is sealed between the pair of substrates 1 and 1 'from the injection port, the injection port is closed.

As described above, in the method of this embodiment, the polymer film 2
Can be manufactured very easily, and the disadvantages of the rubbing method, such as destruction of the thin film transistor due to accumulation of static electricity, adhesion of dust, and contamination of the substrate, can be avoided. Therefore, it can be applied to a large and precise liquid crystal display device, and its usefulness is enormous.

The energy beam for irradiating the polymer film 2 is a laser, for example, YAG, Ar,
CO _{2 and the} like are conceivable. However, it is not limited to a laser. Further, it is possible to simultaneously form a plurality of contracted parts by using a plurality of energy beams, thereby improving the throughput.

The width of the contracted portion and the stretched portion of the polymer film 2 constituting the liquid crystal alignment film is suitably 1 to 50 μm. 1
Below μm, it is difficult to draw a fine pattern on the polymer film 2 with an energy beam. If it exceeds 100 μm, a coarse pattern is formed, and the liquid crystal cannot be sufficiently oriented. The ratio of the stretched portion to the contracted portion is in the range of 1 to 100, preferably 5 to 10.

The thickness of the polymer film 2 constituting the liquid crystal alignment film is 10 to 1000 nm, preferably 10 to 100 nm.
It is. If it is less than 10 nm, the liquid crystal cannot be sufficiently oriented. If it exceeds 1000 nm, the resistance of the alignment film increases, which adversely affects the operation of the liquid crystal display element.

In the liquid crystal display device shown in FIG.
The electrode 9 formed on the substrate surface may be of a simple matrix type or an active matrix type. In the latter, a thin film transistor (TF) is provided for each pixel on the substrate.
Since T) is formed, display characteristics can be improved.

The liquid crystal used is not particularly limited, and any liquid crystal such as a twisted nematic (TN) liquid crystal, a super twisted nematic (STN) liquid crystal, and a ferroelectric liquid crystal (chiral smectic liquid crystal) may be used. However, although TN liquid crystals have been widely used,
The display method using this liquid crystal has problems such as insufficient response speed and crosstalk.Therefore, application to devices that require a fast response speed, such as large-screen displays for moving images, is difficult. Have difficulty. The STN liquid crystal has a twist angle of 250 to 360 degrees, which is advantageous for increasing the contrast as compared with a TN liquid crystal having a twist angle of 90 degrees. The device using ferroelectric liquid crystal generates spontaneous polarization by the interaction between the liquid crystal material and the alignment film, and the liquid crystal is driven by the interaction between the spontaneous polarization and the electric field, thereby improving the response speed. It is effective for Next, more specific embodiments of the present invention (second embodiment, third embodiment)
Example) will be described. Example 2 First, a polymer composition was prepared using the following raw materials. Thermoplastic resin: Polyimide resin (manufactured by Hitachi Chemical, trade name P
IX-5400) Solvent: γ-butyrolactone

The obtained polymer composition is washed with washed glass.
Coated on a substrate with a spinner,
Heated for 1 minute to disperse the solvent, forming a 1 μm thick polymer film.
Formed. From above this film, a CW-YAG laser was
The beam diameter is reduced to 2μm, and stripes are formed in a certain direction at 20μm intervals.
Irradiation. The power density at this time is 1 kW / cm^Two so
is there. As a result, the contraction site and the extension site adjacent thereto
Was formed.

Next, the two substrates obtained as described above are held at intervals of 5 μm via a spacer,
These peripheral portions were sealed with a sealant, and a nematic liquid crystal (ZLI-1370, manufactured by Merk) was sealed between the substrates to form a liquid crystal cell. Each cell was observed using a polarizing microscope, and the orientation of the liquid crystal was evaluated. As a result, it was confirmed that the orientation of the liquid crystal was good. No defects such as contamination and flaws on the surface of the liquid crystal alignment film were observed, and no generation of static electricity was observed. The optimum value of the power density of the laser changes depending on the material of the liquid crystal alignment film and the substrate. (Embodiment 3) FIG. 3 is a sectional view showing a schematic structure of a liquid crystal display device according to a third embodiment of the present invention. This device will be described according to a manufacturing method.

First, a 300 nm Mo-Ta alloy is formed on the cleaned glass substrate 1 by, for example, a sputtering method, and the gate electrode, the gate line 20 and the load capacitance line 17 are patterned. Next, the gate insulating film (SiO film) 10 is
A 50 nm-thick SiN film 11, a 100 nm-thick a-Si film 12, and a 100 nm-thick protective film (SiN film) 13 functioning as an etching stopper are continuously formed. continue,
The protective film 13 is patterned, and the SiN film 11 and the a-Si film 12 are patterned in stripes. Then I
After a TO film 18 is formed to a thickness of 100 nm, the TO film 18 is patterned into the shape of a pixel electrode, and n ⁺ doped with an impurity such as phosphorus which is an ohmic contact layer of source / drain regions. A 50-nm type a-Si film 14 is formed.

Next, the first electrode on the terminal portion of the gate electrode
The SiO film 10, which is the insulating film, is removed by etching. Thereafter, a film of Cr is formed to a thickness of 100 nm, and a film of Al is formed to a thickness of 400 nm to form a signal line, a drain electrode 15 and a source electrode 16. Subsequently, n ⁺ is formed using the drain electrode 15 and the source electrode 16 as a mask. The drain electrode 15 and the source electrode 16 are electrically separated by removing the mold a-Si film 14 by etching,
Thus, an active matrix substrate is formed. Finally, the SiN film 19 is formed as a passivation film by 150
is formed and patterned.

Next, an alignment treatment was applied to the liquid crystal alignment film and the counter substrate by a conventional rubbing method. The opposing substrate and the substrate shown in FIG. 3 are opposed to each other on the surface on which the liquid crystal alignment film is formed, and a predetermined distance is maintained by a spacer.
The periphery of the substrate was bonded with a sealing material. After the liquid crystal is sealed between the pair of substrates from the inlet, the inlet is closed.

By the way, it is generally known that in the rubbing method, there are irregularities on the active matrix substrate, and depending on the rubbing direction, there are places where the liquid crystal alignment film is not rubbed well with the rubbing cloth. This alignment defect is visually recognized as a bright spot in the liquid crystal display element. Since the bright spot defect is considerably conspicuous on the display, it is necessary to correct the defective orientation.

Therefore, in this embodiment, first, CW
-YAG laser was applied from the back surface of the active matrix substrate to a beam diameter of 20 μm and a power density of 0.1 kW / cm.
^Two Then, the entire surface inside the pixel was irradiated by focusing on the liquid crystal alignment film. As a result, the liquid crystal was no longer aligned on the active matrix substrate.

Thereafter, the beam diameter was reduced to 2 μm, and the beam diameter was reduced to 20 μm.
Irradiation was performed in stripes at intervals of m in a direction shifted by 90 degrees from the direction initially oriented from the back surface of the substrate. The energy density at this time is 1 kW / cm ² And As a result, the liquid crystal was oriented along a direction shifted by 90 ° from the direction of the laser beam irradiation, and the orientation could be controlled. No damage to the surrounding liquid crystal due to laser beam irradiation was observed. The optimum value of the power density of the laser beam varies depending on the material of the liquid crystal alignment film, the substrate, and the like.

[0037]

As described above, according to the present invention, the orientation of the liquid crystal can be controlled by forming the stretched portion and the contracted portion on the surface of the polymer film by irradiation with the energy beam. Therefore, an excellent liquid crystal alignment film can be manufactured in a short time without causing surface contamination and generation of static electricity, and application to a large and precise liquid crystal display device is also possible.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process of a liquid crystal alignment film according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a liquid crystal display device using the liquid crystal alignment film of the first embodiment.

FIG. 3 is a sectional view showing a schematic configuration of a liquid crystal display device according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... polymer film, 3 ... energy beam, 4 ... contraction part, 5 ... extension part, 6 ... liquid crystal molecule, 7 ... spacer, 8 ... sealant, 9 ... electrode.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1337

Claims (3)

(57) [Claims] 1. A step of rubbing a polymer film formed on a substrate, a step of irradiating an energy beam on a portion of the polymer film caused by the rubbing to cause a misalignment, and removing the orientation of the energy beam. By irradiating the irradiated portion with an energy beam along a predetermined direction, using the volume change of the irradiated portion and the non-irradiated portion adjacent to the irradiated portion,
Forming a stretched part and a contracted part in the polymer film. 2. The polymer film according to claim 1 , wherein the stretched portion and the contracted portion are provided on the polymer film.
Energy beam with a reduced beam diameter when forming
2. The liquid crystal alignment film according to claim 1, wherein
Manufacturing method. Wherein the polymer film, The method according to claim 1 or 2 liquid crystal alignment film, wherein the thermoplastic resin or thermosetting resin.