CN101231466A - Photosensitive composition, alignment film and method for forming optical compensation film - Google Patents

Abstract

The present invention provides a photosensitive composition, which comprises a photosensitive polymer, a photosensitive monomer, and a photoinitiator compound, and can be used as an alignment film or an optical compensation film of a liquid crystal display, and the formation method is ultraviolet curing. The repeating unit of the photosensitive polymer has two olefinic double bonds, the first olefinic double bond can be polymerized to form a main chain, and the second olefinic double bond can be subjected to two-stage ultraviolet treatment to form an alignment film. In addition, the photosensitive monomer contains more than two olefinic double bonds, which can improve photosensitivity and reduce ultraviolet exposure.

Description

Method for forming photosensitive composition, alignment film and optical compensation film

technical field

The present invention relates to a photosensitive composition (photosensitive composition), more specifically, relates to a method for forming an alignment film (photoalignment film) or an optical compensation film (compensation film) from a photosensitive composition.

Background technique

As the display area of the display becomes larger and the thickness becomes thinner, how to further align the liquid crystal molecules has always been an important issue in the development of the liquid crystal display. In this field of research, in addition to the research and development of liquid crystal molecules, the design of alignment films and optical compensation films is also a focus. In the prior art, the alignment film is usually formed by forming a polymer film on a substrate, and aligning it by directional rubbing. Although this method is simple and has stable alignment, there are many problems as follows: (1) Dust pollution, static electricity residue, and scratches generated by brushing. (2) A single direction will result in a narrow viewing angle, which does not conform to the trend of wide viewing angles. Therefore, how to perform alignment in a non-contact manner is an opportunity to improve the above shortcomings. There are currently several methods of non-contact alignment, including optical alignment, plasma (plasma) beam alignment, and ion beam alignment. Photoalignment is to use polarized ultraviolet light to irradiate the alignment film in a specific direction to cause optical anisotropy, so that the polymers on the surface of the film undergo non-uniform photopolymerization, isomerization, or photocleavage reactions, so that the surface of the film has a special Directionality, and further induce liquid crystal molecules to align in a straight direction. Examples are as follows:

(1) Photo-induced crosslinking type (photo-induced crosslinking):

In the following formula, the branched chain of the polymer has an ethylenic double bond, which can undergo a [2+2] ring closure reaction. This kind of material uses aromatic groups with diamine groups (such as biphenyl with diamine groups) to react with phthalic anhydride (phthalic anhydride) to produce polymerization, form polymers and then form films, and finally use polarized ultraviolet rays The branched ethylenic double bond undergoes a ring closure reaction. This design is mainly to apply two different polymerization forms (main chain is amidation reaction, branch chain is ethylenic double bond ring closure) to avoid consuming the functional groups of the second cross-linking reaction in the first polymerization process . The disadvantage is that the functional groups of phthalic anhydrides have color, which will affect the light transmittance.

(2) Photo-induced isomerization type (photo-induced isomerization):

In the following formula, the azo group changes from trans to cis after light exposure. Since the polymerization of the main chain is the amidation reaction of the amino group and the acid group, it does not affect the azo group. After the main chain is polymerized to form a film, the branched azo group is isomerized with polarized ultraviolet light, so that it has the effect of an alignment film. However, this isomerization is not an irreversible reaction, especially after heating, its configuration will change from cis to trans, and the alignment effect will be lost. Therefore, the lack of thermal stability is an obstacle for the application of this material in alignment films.

(3) Photo-induced decomposition type (photo-induced decomposition)

In the following formula, after the main chain is polymerized to form a film, the tetracyclic functional group is cracked with polarized ultraviolet rays to have an alignment effect. This cleavage occurs in the main chain, so the physical properties of the cleaved film will change. This characteristic will cause problems for subsequent fine-tuning (type, number of substituents, degree of polymerisation, molecular weight, etc. of the polymer).

The above three materials all require high exposure to form an alignment effect, which has a great impact on the yield. Therefore, how to provide a novel material that can overcome the above problems, and at the same time have a highly photosensitivity composition, and at low exposure Having an excellent alignment effect after being illuminated is an important goal of the present invention.

Contents of the invention

The present invention provides a photosensitive composition comprising: a. 80 to 90 parts by weight of a photosensitive polymer whose structural formula is as follows:

其中M₁为含有疏水性官能团R₁的单体，

Wherein _M is a monomer containing a hydrophobic functional group _R ,

其中R₂、R₃相异，为包含杂原子的链段，使具有R₄的烯键式双键的反应性高于具有R₅的烯键式双键；R₄、R₅各自独立地选自H或CH₃；Ar系芳香环；b.5至10重量份的感光性单体，包括甲基丙烯酸酯或M₂；以及c.2至10重量份的光引发剂(photoinitiator)。R ₁ is a C ₁ -C ₁₂ fluorinated alkyl group, a:b is between 0:100-99:1; the structure of M ₂ is as follows:

Wherein R ₂ and R ₃ are different and are chain segments containing heteroatoms, so that the reactivity of the ethylenic double bond with R ₄ is higher than that of the ethylenic double bond with R ₅ ; R ₄ and R ₅ are independently selected from H or CH ₃ ; Ar-based aromatic rings; b. 5 to 10 parts by weight of photosensitive monomers, including methacrylate or M ₂ ; and c. 2 to 10 parts by weight of photoinitiators.

The present invention also provides a method for forming an alignment film, which includes dissolving the photosensitive composition in a solvent to form a solution; coating the solution on a substrate; heating the substrate to remove the solvent; irradiating the substrate with polarized ultraviolet rays vertically; Polarized ultraviolet light irradiates the substrate at a non-perpendicular angle to form an alignment film.

The present invention also provides a method for forming an optical compensation film, comprising dissolving the photosensitive composition in a solvent to form a solution; coating the solution on a substrate; heating the substrate to remove the solvent; and irradiating the substrate with ultraviolet light to form an optical compensation film.

Description of drawings

FIG. 1 is a schematic diagram of an alignment film formed by two-stage ultraviolet rays.

Detailed ways

The invention provides a photosensitive composition, which comprises: a. photosensitive polymer, b. photosensitive monomer, and c. photoinitiator. The structural formula of the above-mentioned photosensitive polymer is as follows:

M ₁ is a monomer containing a hydrophobic functional group R ₁ , R ₁ is a C ₁ -C ₁₂ fluorinated alkyl group, and a:b is between 0:100-99:1. The arrangement of the photosensitive polymer includes block copolymer, alternate copolymer and random copolymer. The Mn of the photosensitive polymer is between 5000-3000 (preferably 20000-30000), the Mw is between 10000-60000 (preferably 30000-50000), and the Mw/Mn is 2. The polymer yield is between 5-40%, preferably between 10-25%, because an increase in the yield of the polymer will reduce the solubility of the polymer and increase the Mw/Mn. The method for forming the above-mentioned polymer includes light initiation method or heat initiation method, and the present invention is preferably heat initiation method, and its heat initiation agent includes but not limited to substituted or unsubstituted organic peroxide (substituted or unsubstituted organicperoxides), azo compounds (azo compounds), preferably azoisobisbutyronitrile (AIBN).

The structure of _M2 is as follows:

R₂、R₃相异，为包含杂原子的链段，使具有R₄的烯键式双键的反应性高于具有R₅的烯键式双键。R₄、R₅各自独立地选自H或CH₃。R₂、R₃包括下列结构：

-O-、-R-O-、

-O-R-O-、

其中R为C₁-C₁₂烷基。若R₂或R₃为

或

则有可能形成酰胺类(

)的官能团，该官能团可改进聚合物的热稳定性以及表面稳定性。

R ₂ and R ₃ are different and are chain segments containing heteroatoms, so that the reactivity of the ethylenic double bond with R ₄ is higher than that of the ethylenic double bond with R ₅ . R ₄ and R ₅ are each independently selected from H or CH ₃ . R ₂ and R ₃ include the following structures:

-O-, -RO-,

-ORO-,

Wherein R is a C ₁ -C ₁₂ alkyl group. If _R2 or _R3 is

or

Then it is possible to form amides (

), which can improve the thermal and surface stability of the polymer.

Ar of _M2 is an aromatic ring such as phenyl, naphthyl, anthracenyl, or a heterocyclic aromatic ring. When the aromatic ring is a phenyl ring, the substitution positions of R ₁ and R ₂ on the benzene ring include ortho, meta, and para, preferably para. And the aromatic ring may contain more than one substituent, and the ethylenic double bond with _R4 and the ethylenic double bond with _R5 have different reactivity through steric hindrance or electronic effect. These substituents include C _1-6 alkyl, functional groups that generate hydrogen bonds with N and H of R ₂ or R ₃ , such as ester groups, acid groups (hydrogen bond acceptors), or hydroxyl, amine groups (hydrogen bond donors). body). Adding hydrogen bond acceptor or donor substituents is to increase the steric hindrance of _R2 or _R3 , thereby affecting the reactivity of polymerization. But for the convenience of synthesis, it is preferably C _1-6 alkyl. The above additional substituents, the relative substitution positions of R ₂ and R 3 , and the types of R ₂ and R ₃ are all to make the reactivity of the ethylenic double bond with R ₄ or R ₅ different. It is worth noting that the difference in reactivity of the ethylenic double bond with _R4 or _R5 comes from _R1 and _R2 , not from _R4 and _R5 . In this way, upon polymerization, the more reactive ethylenic double bond (with _R substituent) will form the backbone _of the polymer, while the less reactive ethylenic double bond (with R substituent) will The remaining branched chains of the polymer are subjected to ultraviolet light or plasma treatment (plasma) after the film is formed to form an alignment film or an optical compensation film. Briefly, the monomers of the present invention have two ethylenic double bonds, one for polymer formation and one for UV alignment.

R ₂ and R ₃ connected to Ar do not connect Ar with O at the same time, this is to avoid Fries rearrangement reaction. When R ₂ or R ₃ of Ar is linked with O to produce Fries rearrangement, the other one can still undergo polymerization without being affected, and continue to polymerize to form a polymer. When there is a possibility of Fries rearrangement, the reactivity of the ethylenic double bond of the substituent that will generate Fries rearrangement (the substituent that connects Ar with O) is more preferred than the reaction of the substituent that will not generate Fries rearrangement Sex is low. A preferred design includes making the activation energy of the polymerization reaction lower than that of the rearrangement reaction, and avoiding the rearrangement reaction with temperature and reagents; a more preferable design is to avoid the use of substituents that will cause rearrangement reactions.

In the present invention, in order to further increase the polymerization speed of the photosensitive composition, a photosensitive monomer such as methacrylate or the above-mentioned _M2 and a photoinitiator are added to the composition. If the _M2 monomer is used, the complexity of the polymerization product of the photosensitive monomer and the photosensitive polymer can be reduced. However, the _M2 monomer has only two ethylenic double bonds. In order to increase the degree of crosslinking, methacrylates with multiple ethylenic double bonds can be used, such as dipentylthritol hexaacrylate containing six double bonds. (dipenthaerythiritol hexacrylate, DPHA,), dipentaerythritol pentaacrylate (dipentaerythritolpentacrylate, DPEPA) containing five double bonds, pentaerythritol tetraacrylate (PETIA) containing four double bonds, containing three Trimethylolpropane Triacrylate (TMPTA) or Pentaerythritol Triacrylate (PETA) with double bonds. These photosensitive monomers can increase the photocuring speed of the photosensitive composition.

In order to polymerize the photosensitive monomer (b) and the photosensitive polymer (a), a photoinitiator is required. The photoinitiator applicable to the present invention can be general common photoinitiator, is preferably acetophenones, benzoin, diphenyl ketones, thioxanthones, anthraquinones, or the combination of above-mentioned substances, as 2 -Hydroxy-2-methyl-1-phenyl-propan-1-ketone (2-hydroxy-2-methyl-1-phenyl-propan-1-one), 4-benzoin-4-methyldiphenyl Sulfide, 2-benzyl-2-dimethylamino-1-[4-(methylthio)phenyl]-2-morpholinopropane-1-one, 2,2-diethoxy-2 - phenylacetophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone or 2,4-dimethylthioxanthone.

In a preferred embodiment of the present invention, the photosensitive polymer accounts for 80-90 parts by weight, the photosensitive monomer accounts for 5-10 parts by weight, and the photoinitiator accounts for 2-10 parts by weight.

In the present invention, the above-mentioned photosensitive composition is dissolved in a solvent to form a solution, the solution is applied on a substrate, and the substrate is heated to remove the solvent. Next, polarized or unpolarized ultraviolet rays are used to irradiate the substrate at a non-perpendicular angle, and then polarized ultraviolet rays are used to irradiate the substrate vertically or obliquely to form an alignment film. The solvent is preferably a polar aprotic solvent such as DMF. The method of coating the solution on the substrate is preferably a spin coating method. The coating method can be completed at one time, or the flow can be uniformed at a slow speed, and then the film thickness can be uniformed at a fast speed. The film thickness is preferably 0.1-20 mm. The method of heating the substrate is preferably two-stage heating. First, soft bake at a lower temperature (90-120°C) for a short time (<15 minutes), and then hard bake at a higher temperature (140-170°C) for a longer time (>25 minutes). Minutes), the film thickness after removing the solvent is between 0.05-10 mm. Types of substrates include glass substrates and flexible plastic substrates for liquid crystal displays. Unpolarized ultraviolet light is irradiated at a lower exposure (0-100 mJ/cm ² ), and the film is irradiated at a non-perpendicular angle (15-75 degrees, preferably 45 degrees). Polarized ultraviolet rays irradiate the film on the substrate at a vertical or non-perpendicular angle with a considerable exposure (50-500mJ/cm ² ), and the formed alignment film has good quality, which can make the liquid crystal molecules have a pre-tilt angle of 0-90 degrees. The size of the angle depends on the type of polymer forming the alignment film. The key to forming the above-mentioned alignment film by applying two-stage ultraviolet rays is whether the branched ethylenic double bonds participate in the polymerization during the polymerization process. If it is not involved in polymerization, the UV process can react the ethylenic double bonds retained on the branch chains to achieve the effect of alignment. In addition, the photosensitive monomer can accelerate the photohardening speed of the photosensitive polymer, reduce the exposure intensity and time of the ultraviolet light source, reduce the process cost and speed up the production speed.

The alignment film provided by the present invention has the following characteristics: uniform alignment uniformity, average anchoring energy (about 10 ^-5 erg/cm ² ), thermal stability (heated to 10°C above the clear point and After maintaining for more than 10 minutes, it still has uniform alignment, and the alignment will not be destroyed by heating), and has good solvent resistance, and the alignment will not be destroyed by the solvent in the photosensitive liquid crystal solution.

In addition, the alignment film attached to the inner side of the substrate directly contacts and aligns the liquid crystal molecules; and the optical compensation film attached to the outer side of the substrate prevents ambient light from causing reflection of the metal grid in the liquid crystal display. The polymers of the present invention serve both purposes. The method of forming an optical compensation film is as follows: the above photosensitive composition is dissolved in a solvent to form a solution and then coated on the substrate; then the substrate is heated to remove the solvent, and the substrate is irradiated with ultraviolet light to form an alignment film, and then the alignment film Coat the photoreactive liquid crystal on it, and irradiate the liquid crystal with non-polarized ultraviolet rays to form an optical compensation film.

preferred embodiment

Example 1-1

Copolymer of 4-(methacrylamido)phenylmethacrylate and perfluorinated propyl methacrylate1

Take 0.5g (2mmol) of 4-(methacrylamide) phenyl methacrylate, 0.375g (1.4mmol) of perfluorinated propyl methacrylate (2,2,3,3-tetrafluoropropylmethacrylate) and 0.00875g of AIBN was dissolved in 10mL of DMF and isolated from the air. After reacting at 80°C for 20 minutes, the reactant was slowly dropped into diethyl ether (200mL) under stirring at room temperature. After filtration, 0.374 g (42.7% yield) of copolymer 1 was obtained. IR (KBr), cm ^-1 : Broad peaks (broad) 3430, 3350 (NH), 1750 (-OCO-), 1670 (amide), 1510, 1260, 962, 945, 879, 661 (aryl), others Signals such as 2940, 1410, 1390, 1320, 1200, 1170, 1130, 1100, 1002, 833, 525.

Copolymer of 4-(methacrylamido)phenyl methacrylate and perfluorinated propyl methacrylate 2

Take 0.91g (4mmol) of 4-(methacrylamido)phenyl methacrylate, 1g (5mmol) of perfluorinated propyl methacrylate and 0.0191g of AIBN, dissolve them in 24mL of DMF and mix with air After being isolated and reacted at 80°C for 40 minutes, the reactant was slowly dropped into diethyl ether (200 mL) under stirring at room temperature. After filtration, 0.24 g (12% yield) of copolymer 2 was obtained. IR (KBr), cm ^-1 : Broad peaks 3392 (NH), 1752 (-OCO-), 1668 (amide), 1508, 1253, 965, 904, 664 (aryl), other signals such as 2937, 1408, 1392 , 1170, 1156, 1128, 1016, 805, 712.

Copolymer of 4-(methacrylamido)phenyl methacrylate and perfluorinated propyl methacrylate 3

Take 0.399g (1.6mmol) of 4-(methacrylamido)phenyl methacrylate, 0.760g (3.8mmol) of perfluorinated propyl methacrylate and 0.0116g of AIBN, dissolve in 5mL of DMF After being isolated from the air, react at 80° C. for 50 minutes, and slowly drop the reactant into diethyl ether (100 mL) under stirring at room temperature. After filtration, 0.062 g (7% yield) of copolymer 3 was obtained.

Copolymer of 4-(methacrylamido)phenyl methacrylate and perfluorinated pentyl methacrylate4

Take 0.6g (2.4mmol) of 4-(methacrylamido) phenyl methacrylate, 0.072g (0.24mmol) of perfluorinated pentyl methacrylate (2,2,3,3,4, 4,5,5-octafluoropentyl-methacrylate) and 0.0067g of AIBN were dissolved in 10mL of DMF and isolated from the air. After reacting at 80°C for 165 minutes, the reactants were slowly dropped into diethyl ether (100mL ). After filtration, 0.2658 g (39% yield) of copolymer 4 was obtained. IR (KBr), cm ^-1 : Broad peaks 3440 (NH), 1750 (-OCO-), 1670 (amide), 1510, 1260, 964, 661 (aryl), other signals such as 2940, 1410, 1390, 1320 , 1200, 1170, 1130, 1100, 1002, 816, 714, 525.

Copolymer of 4-(methacrylamido)phenyl methacrylate and perfluorinated pentyl methacrylate 5

Take 0.4g (1.6mmol) of 4-(methacrylamido)phenyl methacrylate, 0.342g (1.1mmol) of perfluorinated pentyl methacrylate and 0.0074g of AIBN, dissolve in 7mL of DMF After being isolated from the air, react at 80°C for 35 minutes, and slowly drop the reactant into diethyl ether (100 mL) under stirring at room temperature. After filtration, 0.1985 g (26.8% yield) of copolymer 5 was obtained. IR (KBr), cm ^-1 : Broad peaks 3420 (NH), 1750 (-OCO-), 1670 (amide), 1510, 1260, 966, 663 (aryl), other signals such as 2940, 1410, 1390, 1320 , 1200, 1170, 1130, 1050, 1002, 810, 525.

Copolymer of 4-(methacrylamido)phenyl methacrylate and perfluorinated pentyl methacrylate6

Take 0.74g (3mmol) of 4-(methacrylamido)phenyl methacrylate, 0.9g (3mmol) of perfluorinated pentyl methacrylate and 0.0164g of AIBN, dissolve them in 22mL of DMF and mix with Insulated from air, after reacting at 80°C for 100 minutes, the reactant was slowly dropped into diethyl ether (200 mL) which was stirring at room temperature. After filtration, 0.32 g (54% yield) of copolymer 6 was obtained. IR (KBr), cm ^-1 : Broad peaks 3392 (NH), 1752 (-OCO-), 1668 (amide), 1508, 1253, 965, 904, 664 (aryl), other signals such as 2937, 1408, 1392 , 1170, 1156, 1128, 1016, 805, 712.

Copolymers of 4-(methacrylamido)phenyl methacrylate and perfluorinated pentyl methacrylate7

Take 0.225g (0.9mmol) of 4-(methacrylamido)phenyl methacrylate, 0.646g (2.2mmol) of perfluorinated pentyl methacrylate and 0.0087g of AIBN, dissolve in 5mL of DMF After being isolated from the air, react at 80° C. for 45 minutes, and slowly drop the reactant into diethyl ether (100 mL) under stirring at room temperature. After filtration, 0.181 g (20.7% yield) of copolymer 7 was obtained.

Copolymer of 4-(methacrylamido)phenyl methacrylate and octyl methacrylate 8

Take 0.43g (1.7mmol) of 4-(methacrylamido)phenyl methacrylate, 0.17g (0.85mmol) of octylmethacrylate (octylmethacrylate) and 0.0060g of AIBN, dissolve them in 6mL of DMF Insulated from the air, reacted at 80°C for 60 minutes, then slowly added the reactant dropwise into diethyl ether (100 mL) under stirring at room temperature. After filtration, 0.0862 g (14.4% yield) of copolymer 8 was obtained.

Example 1-2

Preparation of Alignment Film

80 parts by weight of copolymer 1-8, 10 parts by weight of dipentylthritol hexaacrylate (DPHA), and 5 parts by weight of photoinitiator were respectively dissolved in DMF to form a photosensitive composition solution. Then, the above solution was spin-coated onto the glass containing the ITO electrode at a speed of 3500 rpm, and baked at 180° C. for 1.5 hours to remove DMF. Next, the substrate was taken out from the oven and returned to room temperature, and the photosensitive composition film on the substrate was irradiated with ultraviolet light generated by a high-pressure mercury lamp, as shown in FIG. 1 . First, the film was irradiated with polarized ultraviolet rays obliquely at 45 degrees (exposure amount about 50 mJ/cm ² ). Afterwards, a polarizing plate is added, and the film is irradiated vertically with unpolarized ultraviolet light (exposure amount is about 50 mJ/cm ² ), forming an alignment film. The above polarized and unpolarized ultraviolet rays have a single wavelength (254nm). In addition to forming an alignment film with a two-stage exposure process of a single wavelength, the present invention can also use an ultraviolet band (270-400nm) to perform a single exposure process, such as irradiating the film with a polarized ultraviolet band at an angle of 45 degrees to form an optical compensation film. The amount is less than 50mJ/cm ² .

comparative example

Dissolve copolymer 1-8 in DMF to form a photosensitive composition solution. Then, the above solution was spin-coated onto the glass containing the ITO electrode at a speed of 3500 rpm, and baked at 180° C. for 1.5 hours to remove DMF. Then the substrate is taken out from the oven and returned to room temperature, and the polymer or copolymer film on the substrate is irradiated with ultraviolet rays generated by a high-pressure mercury lamp. First, the film was irradiated with polarized ultraviolet rays obliquely at 45 degrees (exposure amount about 360 mJ/cm ² ). Afterwards, a polarizing plate was added, and the film was irradiated vertically with non-polarized ultraviolet light (the exposure amount was about 360mJ/cm ² ). Since the comparative example has no photosensitive monomer and photoinitiator to help harden, its exposure amount is much greater than that of the embodiment of the present invention.

Claims (15)

1. A photosensitive composition comprising: The photosensitive polymer of a.80 to 90 weight parts, its structural formula is as follows:

Wherein M ₁ is a monomer containing a hydrophobic functional group R ₁ , R ₁ is a C ₁ -C ₁₂ fluorinated alkyl group, and a:b is between 0:100-99:1; The structure of _M2 is as follows: Wherein R ₂ and R ₃ are different and are chain segments containing heteroatoms, so that the reactivity of the ethylenic double bond with R ₄ is higher than that of the ethylenic double bond with R ₅ ; R ₄ and R ₅ are each independently selected from H or CH ₃ ; Ar is an aromatic ring; b. 5 to 10 parts by weight of a photosensitive monomer including methacrylate or _M2 ; and c. 2 to 10 parts by weight of a photoinitiator. 2. The photosensitive composition as claimed in claim 1, wherein the methacrylate monomer comprises dipentylthritol hexaacrylate, dipentylthritol pentaacrylate, pentaerythritol tetraacrylate, trihydroxy Methylpropane Triacrylate, or Pentaerythritol Triacrylate. 3. The photosensitive composition as claimed in claim 1, wherein R ₂ and R ₃ are selected from the following structures:

Wherein R is a C ₁ -C ₁₂ alkyl group. 4. The photosensitive composition as claimed in claim 1, wherein Ar of M ₂ comprises phenyl, naphthyl, anthracenyl, or a heterocyclic aromatic ring. 5. The photosensitive composition as claimed in claim 4, wherein when the aromatic ring Ar is phenyl, the relative positions of R ₂ and R ₃ substituted on the benzene ring are para-position. 6 . The photosensitive composition as claimed in claim 4 , wherein the substituents of the aromatic ring Ar include more than one substituent in addition to R ₂ and R ₃ . 7. The photosensitive composition as claimed in claim 6, wherein the more than one substituent comprises a C ₁ -C ₆ alkyl group. 8. A method for forming an alignment film, comprising: Dissolving the photosensitive composition according to claim 1 in a solvent to form a solution; coating the solution on the substrate; heating the substrate to remove the solvent; irradiating polarized ultraviolet light perpendicularly to the substrate; and The substrate is irradiated with non-polarized ultraviolet light at a non-perpendicular angle to form an alignment film. 9. The method for forming an alignment film as claimed in claim 8, wherein the concentration of the photosensitive polymer in the solution is 0.5-5 wt%. 10. The method for forming an alignment film as claimed in claim 8, wherein the method of coating the solution on the substrate comprises a spin coating method. 11 . The method for forming an alignment film according to claim 8 , wherein the substrate comprises a thin film transistor gate multi-set substrate or a color filter substrate of a liquid crystal display. 12. The method for forming an alignment film as claimed in claim 8, wherein energy of the polarized ultraviolet rays is less than energy of the unpolarized ultraviolet rays. 13. The method for forming an alignment film as claimed in claim 8, wherein the non-perpendicular angle at which the unpolarized ultraviolet rays irradiate the substrate is between 15° and 75°. 14. A method for forming an optical compensation film, comprising: Dissolving the photosensitive composition according to claim 1 in a solvent to form a solution; coating the solution on the substrate; heating the substrate to remove the solvent; The substrate is irradiated with ultraviolet rays to form an optical compensation film. 15. The method for forming an optical compensation film as claimed in claim 14, wherein the ultraviolet rays comprise unpolarized ultraviolet rays or polarized ultraviolet rays.

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