JPH09297313A - Method for orienting liquid crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To orient a liq. crystal by an easy and industrially useful method excellent in productivity without rubbing a polyimide film ensuring high orientation stability of a liq. crystal and high reliability. SOLUTION: A thin polymer film formed on a substrate is irradiated with polarized UV or electron beams in a certain direction to the surface of the substrate and a liq. crystal is oriented using the substrate without rubbing the polymer film. The polymer film contains polyimide resin consisting of repeating units represented by the formula (where R<1> is a tetravalent org. group having an alicyclic structure and R<2> is a divalent org. group) and obtd. by bringing a precursor of polyimide having 0.05-3.0dl/g reduction viscosity (0.5g/dl concn. in N-methyl-2-pyrrolidone at 30 deg.C) into dehydration ring closure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal alignment treatment method, more specifically, without rubbing treatment.
The present invention relates to a method for aligning liquid crystal molecules by irradiating polarized light on the surface of a polyimide film, from a more practical viewpoint, to an alignment treatment method using a wide range of polyimide resins.

[0002]

2. Description of the Related Art A liquid crystal display element is a display element utilizing electro-optical change of liquid crystal, and is small and light in terms of a device.
Attention has been paid to characteristics such as low power consumption, and in recent years, display devices for various displays have been remarkably developed. Above all, using nematic liquid crystal having positive dielectric anisotropy, liquid crystal molecules are arranged parallel to the substrate at each interface of a pair of electrode substrates facing each other, and the orientation directions of the liquid crystal molecules are orthogonal to each other. A twisted nematic (TN type) field effect type liquid crystal display element combining both substrates is a typical example thereof.

In such a TN type liquid crystal display device, the major axis direction of the liquid crystal molecules is aligned uniformly parallel to the substrate surface, and the liquid crystal molecules are tilted at a constant tilt orientation angle (hereinafter, tilt) with respect to the substrate. It is important to orient with an angle. Conventionally, two methods are known as typical methods for aligning liquid crystal molecules. A first method is a method in which an inorganic substance such as silicon oxide is obliquely vapor-deposited on a substrate to form an inorganic film on the substrate, and liquid crystal molecules are aligned in a vapor deposition direction. in this way,
Although stable alignment having a constant tilt angle can be obtained, it is not industrially efficient. The second method is a method in which an organic coating is provided on the surface of the substrate, and the surface is rubbed with a cloth such as cotton, nylon or polyester in a certain direction to align the liquid crystal molecules in the rubbing direction. In this method, a stable orientation can be obtained relatively easily, and therefore, this method is exclusively used industrially. Examples of the organic film include polyvinyl alcohol, polyoxyethylene, polyamide, and polyimide. Among them, polyimide is most commonly used in terms of chemical stability, thermal stability, and the like. A typical example of polyimide used in such a liquid crystal alignment film is disclosed in JP-A-61-47932.

[0004]

The liquid crystal alignment treatment method of rubbing a polyimide is industrially useful because it is simple and excellent in productivity. However, demands for higher performance and higher definition of liquid crystal display elements have been increasing more and more, and various problems of the rubbing method have been pointed out with the development of new display methods corresponding thereto. For example, STN (Super Twisted Nematic) method in which the twist angle of TN type liquid crystal display is increased, AM (Active Matrix) method in which a switching element is formed on each electrode, FLC (ferroelectric) using ferroelectric liquid crystal and antiferroelectric liquid crystal. Electric), AFLC (anti-ferroelectric) method and the like. In the STN method, scratches on the surface of the alignment film caused by rubbing cause display defects due to high contrast, and in the AM method, mechanical force or static electricity due to rubbing results in destruction of the switching element or dust generation due to rubbing. Is a display defect, FL
Various problems of the rubbing method have been clarified, for example, in the C and AFLC methods, it is difficult to achieve both uniform alignment of smectic liquid crystal and high-speed response only by simple rubbing treatment.

For the purpose of solving these problems, a so-called "rubbingless" alignment method for aligning a liquid crystal without rubbing has been studied and various methods have been proposed. For example,
A method in which photochromic molecules are introduced into the surface of the alignment film and the molecules on the surface of the alignment film are aligned by light (JP-A-4-28).
44), LB film (Langmuir Blodgett film)
Method for orienting the molecular chains constituting the alignment film (Kobayashi et al., Japanese Journal of Applied Physics, Vol. 27, page 475 (1988) (S.
Kobayashi et al., Jpn.J.Appl.Phys., 27,475 (1988))
), A method of pressure-bonding an alignment film on a substrate which has been subjected to an alignment treatment in advance to transfer the alignment (Japanese Patent Laid-Open No. 6-43458).
However, in consideration of industrial productivity, it cannot be said to be a substitute for the rubbing method.

On the other hand, various methods have been proposed in which periodic irregularities are artificially formed on the surface of the alignment film and the liquid crystal molecules are aligned along the irregularities. The simplest method is a method in which a replica having periodic unevenness is prepared in advance, a thermoplastic film is thermocompression bonded thereon, and the unevenness is transferred onto the film (JP-A-4-172320). Japanese Patent Laid-Open No. Hei 4
-296820, JP-A-4-311926, etc.). Although it is possible with this method to efficiently form a film having periodic unevenness on the surface, it was not possible to obtain the practical reliability as much as the polyimide film used in the rubbing method. . On the other hand, high-energy light such as an electron beam (Japanese Unexamined Patent Publication No. 4-97130) and α-ray (Japanese Unexamined Patent Publication No. 2-198) are formed on a highly reliable polyimide film.
No. 36), X-rays (JP-A-2-2515), excimer lasers (JP-A-5-53513), and the like are proposed to form periodic unevenness on the film surface. However, the use of these high-energy light sources is not an efficient alignment treatment method, considering the industrial productivity of continuously performing alignment treatment uniformly over the entire surface of a large substrate. there were.

On the other hand, there is a photolithography method as an efficient method for forming periodic unevenness on the surface of a highly reliable polyimide film. Polyimide is used as an insulating film for semiconductors due to its high insulating property and excellent electrical characteristics.In recent years, a so-called photosensitive polyimide having photo-curing property in polyimide itself has been developed. This is an attempt to form periodic unevenness by a lithography method. Although it is possible to form irregularities on the surface of the polyimide film by this method, photo-curable polyimide was originally developed as an insulating film. Therefore, the property for aligning the liquid crystal becomes insufficient, and it becomes necessary to further coat the buffer layer (JP-A-4-24522).
No. 4), resulting in a complicated process, and in view of industrial productivity, it could not be an efficient alignment treatment method that could be a substitute for the rubbing method.

As a new alignment treatment method found recently, a method of irradiating polarized ultraviolet rays or the like on the surface of a polymer film to align liquid crystal molecules without rubbing treatment has been proposed. The following reports are examples of this. Gibbons et al., Nature, 351, p. 49 (199
1 year) (WMGibbons et al., Nature, 351, 49 (199
1)), Kawanishi et al., Molecular Crystal and Liquidus Questal, Volume 218, p.153 (199).
2 years) (Y. Kawanishi et al., Mol. Cryst. Liq. Crys
t., 218, 153 (1992)), Chat et al., Japanese Journal of Applied Physics, Vol. 31, 2
Page 155 (1992) (M. Shadt at al., Jpn.
J. Appl. Phys. 31, 2155 (1992)), Iimura et al., Japanese Journal of Applied Physics,
Volume 32, Page L93 (1993) (Y. Iimura et a
Lpn., Jpn. J. Appl. Phys. 32, L93 (1993)) These methods do not require the conventional rubbing treatment and are characterized by aligning liquid crystals in a certain direction by polarized light irradiation. According to this method, there are no problems such as scratches and static electricity on the film surface due to the rubbing method, and it is advantageous that the manufacturing process is simpler in consideration of industrial production.

That is, although the liquid crystal alignment method using polarized light irradiation proposed here is still in the basic research stage, it is attracting attention as a new liquid crystal alignment treatment method which does not use rubbing treatment in the future. Seen as As the polymer materials used in the reports so far, specific polymer materials such as polyvinyl cinnamate and polyimide in which an azo dye is dispersed are mainly used because it is necessary to obtain photochemical sensitivity to polarized light. It is described that liquid crystal molecules can be aligned in a certain direction by irradiating the surface of these polymer films with polarized light.

However, when the liquid crystal alignment using the polarized light irradiation is actually applied in the future, not only the function of the liquid crystal alignment but also various functions as a liquid crystal alignment film for achieving a more advanced liquid crystal display. Are needed at the same time. This means that the polymer material used as the liquid crystal alignment film is not limited to a particular material, and selection of a wider chemical structure becomes important.

From the viewpoint of the alignment stability and reliability of the liquid crystal molecules, it is considered preferable to use the conventionally used polyimide. That is, an object of the present invention is to apply a liquid crystal alignment by polarized light irradiation to an actual liquid crystal display device by using a polyimide resin having more uniform and high reliability, and using a polyimide material system having a wide range of structure selection. Another object of the present invention is to provide an alignment treatment method.

[0012]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a polymer thin film formed on a substrate is irradiated with polarized ultraviolet rays or electron beams in a certain direction with respect to the substrate surface, and the liquid crystal is aligned using the substrate without rubbing treatment. In the alignment treatment method, the polymer thin film has a reduced viscosity of 0.05 to 3.0 dl / g (at a temperature of 30
0.5 g / d in N-methyl-2-pyrrolidone at ℃
General formula [I] obtained by dehydration ring closure of the polyimide precursor of l)

[0013]

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(Wherein R ¹ represents a tetravalent organic group having an alicyclic structure, and R 2 represents a divalent organic group), and is a polyimide resin containing a repeating unit. The present invention relates to a characteristic liquid crystal alignment treatment method.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION According to the liquid crystal alignment treatment method of the present invention, a polyimide film represented by the general formula [I] is formed on a substrate with an electrode such as glass or a plastic film having a transparent electrode, and then, It is used as a liquid crystal alignment-treated substrate without rubbing treatment by irradiating polarized ultraviolet rays on the film surface.

It is essential that the polyimide resin used in the liquid crystal alignment treatment method of the present invention contains a repeating unit represented by the general formula [I]. By using such a polyimide resin, it becomes possible to orient the liquid crystal molecules uniformly and stably with respect to the polarization direction by irradiation with polarized ultraviolet rays. In the polyimide resin represented by the general formula [I] used in the liquid crystal alignment treatment method of the present invention, the tetracarboxylic acid component used is a tetracarboxylic acid component having an alicyclic structure in its structure. It is essential to contain. Preferably, in the general formula [I], R ¹ is a polyimide resin containing a structure selected from the following structural formulas.

[0017]

Embedded image

(Wherein R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen or an organic group having 1 to 4 carbon atoms, R ⁷ is hydrogen or fluorine or an organic group having 1 to 2 carbon atoms, R ⁸ represents hydrogen or fluorine or an organic group having 1 to 4 carbon atoms.) Specific examples of the tetracarboxylic acid component having the above structure include 1,2,3,4-cyclobutanetetracarboxylic acid,
1,2,3,4-cyclopentanetetracarboxylic acid,
2,3,4,5-tetrahydrofuran tetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, 3,4-dicarboxy-1-cyclohexyl succinic acid, 3,4-dicarboxy-1,2, Examples thereof include alicyclic tetracarboxylic acids such as 3,4-tetrahydro-1-naphthalene succinic acid, dianhydrides thereof, and dicarboxylic acid diacid halides thereof.

Particularly, in the general formula [I], R1 is a polyimide resin containing the following structure, tetracarboxylic acid component is 1,2,3,4-cyclobutanetetracarboxylic acid and its dianhydride, and its carboxylic acid dicarboxylic acid. Acid halides are preferred in terms of liquid crystal alignment.

[0020]

[Chemical 6]

Further, one or more of these tetracarboxylic acids and their derivatives can be used in combination. Further, other tetracarboxylic acid dianhydride may be used in combination as long as the obtained polyimide resin is in a range capable of irradiating ultraviolet rays and exhibiting the effect of the present invention. Specific examples thereof include pyromellitic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7-anthracene tetracarboxylic acid, 1,2,5,6-anthracene tetracarboxylic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3,3 ′, 4- Biphenyltetracarboxylic acid,
Bis (3,4-dicarboxyphenyl) ether, 3,
3 ', 4,4'-benzophenonetetracarboxylic acid, bis (3,4-dicarboxyphenyl) sulfone, bis (3,4-dicarboxyphenyl) methane, 2,2-bis (3,4-dicarboxyphenyl) ) Propane, 1,
1,1,3,3,3-hexafluoro-2,2-bis (3,4-dicarboxyphenyl) propane, bis (3,4-dicarboxyphenyl) dimethylsilane, bis (3,4-dicarboxy) Phenyl) diphenylsilane, 2,3,4,5, -pyridinetetracarboxylic acid,
Aromatic tetracarboxylic acids such as 2,6-bis (3,4-dicarboxyphenyl) pyridine and their dianhydrides and their dicarboxylic diacid halides;
Examples include aliphatic tetracarboxylic acids such as 2,3,4-butanetetracarboxylic acid, dianhydrides thereof, dicarboxylic diacid halides thereof, and the like.

Further, one or more of these tetracarboxylic acids and their derivatives may be mixed and used. Further, a specific example of the diamine component R ² in the general formula [1] of the present invention is a primary diamine generally used in polyimide synthesis and is not particularly limited. Specific examples thereof are p-phenylenediamine, m-phenylenediamine, 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4. '-Diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, diaminodiphenylmethane, diaminodiphenylether, 2,2'-diaminodiphenylpropane, bis (3,5-diethyl-4-aminophenyl) Methane, diaminodiphenyl sulfone, diaminobenzophenone, diaminonaphthalene, 1,4-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenyl) benzene, 9,10-bis (4-aminophenyl) anthracene , 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis ( 4-aminophenoxy) diphenyl sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis (4-aminophenyl) hexafluoropropane, 2,
Aromatic diamines such as 2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, bis (4-
Aminocyclohexyl) methane, bis (4-amino-3)
Alicyclic diamines such as -methylcyclohexyl) methane and aliphatic diamines such as tetramethylenediamine and hexamethylenediamine, and

[0023]

[Chemical 7]

Examples thereof include diaminosiloxanes (m is an integer of 1 to 10). Further, in order to increase the tilt angle, 4,4′-diamino-3-dodecyldiphenyl ether
A diamine having a long-chain alkyl group represented by ter, 1-dodecanoxy-2,4-diaminobenzene and the like can be used. These diamine components may be used alone or in combination of two or more. Furthermore, a composition comprising a polyimide precursor and a monoamine having a long-chain alkyl group, as disclosed in JP-A-62-297819, JP-B-6-25834 and JP-B-6.
It is also possible to use a diimide composition containing a long-chain alkyl group disclosed in Japanese Patent Publication No. 25835.

It is essential that the polyimide resin of the present invention contains the tetracarboxylic acid component having the alicyclic structure described above, but the manufacturing method thereof is not particularly limited. Generally, the molar ratio of tetracarboxylic acid or its derivative and diamine is 0.50 to 2.0, preferably 0.9 to 1.1.
In the range of 0, the reduced viscosity is 0.
05-3.0 dl / g (temperature of 30 ° C. N-methyl-2-
A method of obtaining a polyimide resin precursor having a concentration of 0.5 g / dl) in pyrrolidone and then subjecting it to dehydration ring closure to obtain a polyimide resin can be adopted.

In this case, the reaction polymerization temperature of the tetracarboxylic acid or its derivative and the diamine may be any temperature from -20 to 150 ° C, but especially from -5 to 100 ° C.
Is preferred. Further, as a polymerization method of the polyimide resin precursor, a solution method is usually suitable. Specific examples of the solvent used in the solution polymerization method include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethylsulfoxide, tetramethylurea, pyridine, Examples thereof include dimethyl sulfone, hexamethylphosphoramide, and butyl lactone. These alone,
Moreover, you may mix and use it. Further, even if the solvent does not dissolve the polyimide resin precursor, the solvent may be used in addition to the above solvent within a range where a uniform solution can be obtained.

Further, in order to convert the polyimide resin precursor into a polyimide resin, a method of dehydration ring closure by heating is adopted. The heating dehydration ring-closing temperature is 150 to 450.
Any temperature can be selected, which is in the range of 170 ° C, preferably 170-350 ° C. The time required for this dehydration ring closure depends on the reaction temperature, but is suitably 30 seconds to 10 hours, preferably 5 minutes to 5 hours.

The polyimide or polyimide precursor solution of the present invention obtained as described above is applied onto a substrate by a method such as spin coating or transfer printing, and heated and baked under the above conditions. Form a polyimide film. The thickness of the polyimide film at this time is not particularly limited, but when used as a normal liquid crystal alignment film,
0 nm to 300 nm is suitable.

Then, the surface of the polyimide film is irradiated with polarized ultraviolet rays from a certain direction through a polarizing plate with respect to the substrate. Generally, the wavelength of ultraviolet rays used is 10
Ultraviolet rays in the range of 0 nm to 400 nm can be used, but it is particularly preferable to select an appropriate wavelength through a filter or the like depending on the type of polyimide used.

The irradiation time of ultraviolet rays is generally in the range of several seconds to several hours, but can be appropriately selected depending on the polyimide used. After the two substrates thus irradiated with polarized ultraviolet rays are prepared, the liquid crystal molecules can be oriented by sandwiching the liquid crystal with the film surfaces facing each other.

[0031]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Example 1 41.0 g (0.1 mol) of 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1,2,3
4, -Cyclobutanetetracarboxylic acid dianhydride 19.2
g (0.98 mol) to N-methylpyrrolidone (hereinafter NM
The mixture was reacted at room temperature in 343.5 g for 10 hours to prepare a polyimide precursor (polyamic acid) solution. The reduced viscosity of the obtained polyimide precursor is 0.98.
dl / g (concentration 0.5 g / dl, 30 ° C. in NMP).

This solution was added with NMP to obtain a total solid content of 3% by weight.
After the dilution, the glass substrate was spin-coated at 3000 rpm at 3000 rpm, and then heat-treated at 80 ° C. for 5 minutes and 250 ° C. for 1 hour to form a 100 nm-thick polyimide resin film. Two glass substrates coated with the polyimide resin film thus obtained were prepared, and each polyimide resin film was irradiated with ultraviolet light from a high-pressure mercury lamp with an output of 500 W for 60 minutes through a polarizing plate.

Two substrates irradiated with polarized ultraviolet rays were made so that the polyimide surfaces faced inward and the directions of the irradiated polarized ultraviolet rays were parallel to each other, and a cell of 50 μm was sandwiched between them to form a cell, which was then placed under vacuum. Liquid crystal (ZLI-2293 manufactured by Merck) was injected. When this cell was rotated under the crossed Nicols of a polarizing microscope, it was confirmed that clear light and darkness were generated, no defects were observed, and the liquid crystal was uniformly aligned.

Example 2 15.8 g (0.1 mol) of 1,5-diaminonaphthalene
And 1,2,3,4-cyclobutanetetracarboxylic dianhydride 19.2 g (0.98 mol) of NMP343.5 g
A polyimide precursor (polyamic acid) solution was prepared by reacting at room temperature for 10 hours. The reduced viscosity of the obtained polyimide precursor solution was 0.85 dl / g (concentration: 0.5 g /
dl, 30 ° C. in NMP).

This solution was treated with NMP to obtain a total solid content of 5% by weight.
After diluting, the glass substrate was spin-coated at 3500 rpm and heat-treated at 80 ° C. for 5 minutes and at 250 ° C. for 1 hour to form a polyimide resin film having a thickness of 100 nm. Similar to the method of Example 1, a cell was prepared after irradiation with polarized ultraviolet light. When this cell was rotated under the crossed Nicols of a polarizing microscope, it was confirmed that clear light and darkness were generated, no defects were observed, and the liquid crystal was uniformly aligned.

Example 3 4,2-bis [4- (4-aminophenoxy) phenyl] propane 41.0 g (0.1 mol) and 3,4-dicarboxy-1,2,3,4-tetrahydro- 29.4 g (0.98 mol) of 1-naphthalene succinic acid dianhydride was added to N
A polyimide precursor (polyamic acid) solution was prepared by reacting in MP343.5 g at room temperature for 10 hours. The reduced viscosity of the obtained polyimide precursor solution is 0.80 dl / g.
(Concentration 0.5 g / dl, 30 ° C. in NMP).

This solution was added with NMP to obtain a total solid content of 6% by weight.
After diluting, the mixture was spin-coated on a glass substrate at 3500 rpm and heat-treated at 80 ° C. for 5 minutes and 250 ° C. for 1 hour to form a polyimide resin film having a thickness of 100 nm. Similar to the method of Example 1, a cell was prepared after irradiation with polarized ultraviolet light. When this cell was rotated under the crossed Nicols of a polarizing microscope, it was confirmed that clear light and darkness were generated, no defects were observed, and the liquid crystal was uniformly aligned.

Comparative Example 1 2,2-bis [4- (4-aminophenoxy) phenyl] propane 41.0 g (0.1 mol) and pyromellitic dianhydride 21.2 g (0.97 mol) were added to NMP34.
The reaction was carried out at room temperature for 10 hours in 3.5 g to prepare a polyimide precursor (polyamic acid) solution. The reduced viscosity of the obtained polyimide precursor was 1.10 dl / g (concentration: 0.
5 g / dl, 30 ° C. in NMP).

This solution was diluted with NMP to a total solid content of 3% by weight, and then spin-coated on a glass substrate at 4500 rpm.
Then, heat treatment was performed at 80 ° C. for 5 minutes and at 250 ° C. for 1 hour to form a polyimide resin film having a thickness of 100 nm. Similar to the method of Example 1, a cell was prepared after irradiation with polarized ultraviolet light. When this cell was rotated under the crossed Nicols of a polarizing microscope, a number of defects were observed, although some light and dark were generated, and the liquid crystal was not uniformly aligned.

[0040]

EFFECTS OF THE INVENTION By using the polyimide resin of the present invention and irradiating polarized light on the film surface in a certain direction, liquid crystal molecules can be uniformly dispersed without rubbing treatment which is a conventional liquid crystal alignment treatment method. It can be stably oriented. In addition, in the liquid crystal alignment method using polarized light irradiation, a wider range of structural systems can be selected, and a practical liquid crystal alignment treatment method having more functions as a liquid crystal alignment film can be provided. It will be possible.

Claims (3)

[Claims] 1. An alignment for irradiating a polymer thin film formed on a substrate with polarized ultraviolet rays or electron beams in a certain direction with respect to the substrate surface, and using the substrate to align liquid crystals without rubbing treatment. In the treatment method, the polymer thin film is dehydrated and cyclized by a polyimide precursor having a reduced viscosity of 0.05 to 3.0 dl / g (concentration: 0.5 g / dl in N-methyl-2-pyrrolidone at a temperature of 30 ° C.). General formula [I] obtained by (Wherein R ¹ represents a tetravalent organic group having an alicyclic structure, and R ² represents a divalent organic group), which is a polyimide resin containing a repeating unit. Liquid crystal alignment treatment method. 2. In the general formula [I], R ¹ has the following structure: (Wherein R ³ , R ⁴ , R ⁵ and R ⁶ are hydrogen or an organic group having 1 to 4 carbon atoms, R ⁷ is hydrogen or fluorine or an organic group having 1 to 2 carbon atoms, and R ⁸ is The liquid crystal alignment treatment method according to claim 1, which is a polyimide containing a structure selected from hydrogen, fluorine or an organic group having 1 to 4 carbon atoms. 3. In the general formula [I], R ¹ has the following structure: The method for aligning liquid crystal according to claim [I], which is a polyimide containing.