A self-photo-initiating, high-reliability liquid crystal alignment agent

Abstract

This invention discloses a photosensitive resin composition for use as an alignment agent, the composition comprising: (A) a dianhydride monomer containing a photosensitive group, wherein the photosensitive group is selected from at least one of cinnamate, chalcone, anthracene, coumarin, or benzophenone; (B) a hydrogen donor diamine monomer; and (C) an aliphatic diamine monomer. This invention uses a self-initiating photosensitive resin composition to replace formulation systems relying on exogenous photoinitiators, introducing long alkyl chains into the polyimide molecular chain, which are complementary to the liquid crystal molecular structure, enhancing the interfacial anchoring energy, stabilizing the liquid crystal pretilt angle, and thus maintaining a stable display response time.

Description

Technical Field

[0001] This invention relates to the field of display, and more specifically to a photosensitive resin composition for an alignment agent, a polyimide resin and a method for preparing the same, a polyamic acid alignment agent and a method for preparing the same, a polyimide film prepared therefrom, a display device containing the polyimide film, and a display module. Background Technology

[0002] Polymer Stabilized-Vertical Alignment (PSVA) technology, with its advantages of high contrast, wide viewing angle, and fast response speed, has become the mainstream alignment technology for high-end LCD displays, and is widely used in display scenarios requiring long-term operation, such as automotive displays and outdoor displays. These applications require the display to maintain stable optoelectronic performance over a wide temperature range of 40℃ to 85℃ or even higher. As a key carrier for the orientation and alignment of liquid crystal molecules, the performance of the PSVA alignment film directly determines the stability and reliability of the display.

[0003] Currently, widely used PSVA alignment films mostly use polyimide (PI) as the substrate and achieve polymerization by adding exogenous photoinitiators. However, when used in high-temperature environments, this system still faces the following technical challenges: ① Traditional polyimide alignment films have insufficient thermal stability. After long-term aging in high-temperature environments exceeding 80°C, the movement of PI molecular chain segments intensifies, the activity of polar groups on the PI film surface decreases, and the anchoring energy decreases, leading to poor alignment stability of liquid crystal molecules. This, in turn, causes the liquid crystal pretilt angle to drift, resulting in display defects such as light leakage and decreased contrast. Patent CN101663347B describes a solvent-soluble, ultra-heat-resistant PI formed from pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, biphenyltetracarboxylic acid dianhydride, and 2,4-diaminotoluene. This PI exhibits a glass transition temperature (Tg) of 420°C and a pyrolysis initiation temperature (Tm) of over 500°C. The polyimide backbone structure described in this patent does not contain any photopolymerizable functional groups. Therefore, if applied to liquid crystal alignment processes requiring UV curing, a small-molecule photoinitiator must be added. ② Reliability issues arising from residual exogenous photoinitiators. Patent CN116520639A discloses a photosensitive polyimide resin prepared from 4,4'-hexafluoroisopropylphthalic anhydride (6FDA), pyromellitic dianhydride (PMDA), and 4,4'-diaminodiphenyl ether (ODA), and also includes appropriate amounts of photosensitive additives and organic solvents. This approach relies on external photoinitiators. Unreacted photoinitiators remaining in the system are easily converted into impurity ions, which not only reduce the resistivity of the alignment film but also exacerbate ion migration at high temperatures, leading to reliability issues such as image retention. Simultaneously, under high-temperature conditions, the interfacial anchoring effect between the polyimide surface and liquid crystal molecules weakens, and the liquid crystal molecule arrangement is easily disordered, affecting the display's response speed and image uniformity.

[0004] To improve the heat resistance of polyimide alignment films and address the reliability issues caused by residual exogenous photoinitiators, researchers have made numerous attempts. For example, some studies have found that nanoparticle doping with polyamic acid (PAA) can enhance the performance of PI films, including their heat resistance. As described in patent CN111533911B, sulfur atoms and specific functional groups are introduced into the dimethylmaleimide monomer to obtain a bismaleimide matrix material. Then, metal oxides are introduced into the bismaleimide matrix material, binding inorganic particles to the polymer backbone. The resulting PI material exhibits advantages such as high refractive index, high thermal stability, and high transmittance. However, during the inorganic reinforcing particle doping process, the introduced nanoparticles are prone to agglomeration in the polyimide matrix, making uniform dispersion difficult and hindering their ability to fully enhance the high-temperature resistance of the film. Furthermore, these agglomerates may become sources of alignment defects, negatively impacting display performance. Therefore, this approach does not completely solve the existing problems of polyimide alignment films.

[0005] Therefore, there is an urgent need for an orientation film material with strong thermal stability, high photoinitiation efficiency, good interfacial compatibility, and high reliability. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems and provide an orientation film material with good heat resistance and high reliability.

[0007] To achieve the above objectives, the technical method adopted by the present invention is as follows: A photosensitive resin composition for use as an orientation agent, the composition comprising: (A) A dianhydride monomer containing a photosensitive group, wherein the photosensitive group is selected from at least one of cinnamate group, chalcone group, anthracene group, coumarin group or benzophenone group; (B) Hydrogen donor diamine monomer; (C) Aliphatic diamine monomers; Preferably, the dianhydride monomer containing the photosensitive group in (A) includes at least one of the following dianhydrides: 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride, 2,2′,3,3′-benzophenone tetracarboxylic acid dianhydride as a dianhydride monomer, bis(4-carboxycinnamic acid) ester dianhydride, 4,4′-bis(cinnamoyloxy) diphenyl ether dianhydride, 4,4′-bis(4-azidophenoxy) diphenyltetracarboxylic acid dianhydride, and azido-substituted pyromellitic dianhydride; Preferably, the (B) hydrogen donor diamine monomer comprises at least one of the following diamines: 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, isophorone diamine, 4,4′-methylenebis(2-methylcyclohexylamine), and polyoxyethylene diamine; Preferably, the alkyl chain length of the (C) aliphatic diamine monomer ranges from 8 to 12 carbon atoms in the main chain; more preferably, the (C) aliphatic diamine monomer includes at least one of the following diamines: 1,8-diaminooctane, 1,10-diaminodecane, and 1,12-diaminododecane. Preferably, the molar ratio of (A) the dianhydride monomer containing a photosensitive group, (B) the hydrogen donor diamine monomer, and (C) the aliphatic diamine monomer is 1:(0.5~0.7):(0.3~0.5).

[0008] Another object of the present invention is to provide a polyimide resin for use as an orientation agent, said polyimide resin being formed from the above-described photosensitive resin composition by a polycondensation reaction or by a polycondensation and imidization reaction.

[0009] Another object of the present invention is to provide a method for preparing a polyimide resin, comprising the following steps: Step (1): Add the (A) dianhydride monomer containing a photosensitive group, the (B) hydrogen donor diamine monomer and the (C) aliphatic diamine monomer to an organic solvent to react and form a polyimide precursor; Step (2): The polyimide precursor obtained in step (1) is subjected to an imidization reaction to form a polyimide resin; Preferably, the reaction temperature in step (1) is 0-30℃ and the reaction time is 6-24h; Preferably, the imidization temperature in step (2) is 200-350℃ and the time is 120-180 min; Preferably, the imidization reaction is carried out under a nitrogen atmosphere; Preferably, step (2) before the imidization reaction further includes a drying step, and more preferably the drying temperature is 80-120℃ and the time is 10-20min; Preferably, the organic solvent includes at least one of the following solvents: N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, cyclopentanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether.

[0010] Another object of the present invention is to provide a polyamic acid orientation agent, said orientation agent comprising a polyamic acid resin formed by polycondensation reaction of the above-mentioned photosensitive resin composition; Preferably, the polyamic acid orientation agent further includes nanoparticles, and more preferably, the nanoparticles include at least one of the following nanoparticles: silica, alumina, titanium dioxide, zinc oxide, boron nitride, aluminum nitride, silsesquioxane, or organically modified montmorillonite. More preferably, the nanoparticles are nanoparticles with a silane coupling agent surface modified. More preferably, the nanoparticles have a particle size of 5-100 nm, and most preferably 10-20 nm.

[0011] The amount of the silane coupling agent used is 1 wt% to 10 wt% of the nanoparticles; Preferably, the silane coupling agent contains an amino group; more preferably, the silane coupling agent includes at least one of the following silane coupling agents: γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-cyclohexyl-aminopropyltrimethoxysilane, and dodecylaminopropyltrimethoxysilane.

[0012] Another object of the present invention is to provide a method for preparing a polyamic acid orientation agent, comprising the following steps: Step (1): Add the (A) dianhydride monomer containing a photosensitive group, the (B) hydrogen donor diamine monomer and the (C) aliphatic diamine monomer to an organic solvent to react and form a polyamic acid solution; Step (2): The nanoparticles are dispersed in a dispersion medium to form a dispersion. Step (3): The polyamic acid solution and the dispersion are mixed and reacted to obtain the polyamic acid orientation agent; Preferably, the reaction temperature in step (1) is 0-30℃ and the reaction time is 6-24h; Preferably, in step (1), the molar ratio of (A) the dianhydride monomer containing a photosensitive group, (B) the hydrogen donor diamine monomer, and (C) the aliphatic diamine monomer is 1:(0.5~0.7):(0.3~0.5). Preferably, step (2) further includes dispersing the silane coupling agent in a dispersion medium; Preferably, the dispersion medium includes at least one of the following solvents: N-methylpyrrolidone, ethylene glycol monobutyl ether, γ-butyrolactone, N,N-dimethylacetamide, propylene glycol monomethyl ether acetate, and cyclopentanone; more preferably, the dispersion medium is a mixed solvent of N-methylpyrrolidone and ethylene glycol monobutyl ether; and most preferably, the mass ratio of the two is 8:2-5:5. Preferably, the dispersion is performed by ultrasonic dispersion and / or mechanical stirring, more preferably the ultrasonic dispersion power is 250~350W and the time is 20~40min, and / or the mechanical stirring speed is 600~1000rpm and the time is 1~3h; Preferably, the reaction temperature in step (3) is 10-35°C and the time is 2-6 hours; more preferably, the reaction is carried out under a nitrogen atmosphere. Preferably, the mass ratio of the polyamic acid solution to the dispersion is 100:5~15; Preferably, the mass fraction of the nanoparticles in the solid component of the polyamic acid orientation agent is 0.1wt%-10wt%, more preferably 0.5wt% to 5wt%; the solid component includes polyamic acid resin, nanoparticles, and optional crosslinking agents or coupling agents, but does not include volatile solvents; Preferably, step (3) further includes a membrane filtration step after the reaction; More preferably, the membrane filtration is performed using a polytetrafluoroethylene microporous membrane, preferably with a pore size of 0.1-0.5 μm, and most preferably 0.2 μm.

[0013] Another object of the present invention is to provide a polyimide film, wherein the polyimide film is obtained by coating and imidization reaction of the polyamic acid orientation agent prepared by the above-mentioned polyamic acid orientation agent or the polyamic acid orientation agent prepared by the above-mentioned preparation method; Preferably, the thickness of the polyimide film is 80-120 nm; Preferably, the surface roughness of the polyimide film is <0.5 nm; Preferably, the imidization temperature is 200-350℃ and the time is 120-180 min; Preferably, the imidization reaction is carried out under a nitrogen atmosphere; Preferably, the imidization reaction further includes a drying step, and more preferably, the drying temperature is 80-120°C and the time is 10-20 min.

[0014] Another object of the present invention is to provide a display device comprising the above-described polyimide film; Preferably, the display device is a liquid crystal cell; More preferably, the liquid crystal cell further includes a substrate, a sealant layer, bead-shaped spacers, and a liquid crystal layer, wherein the sealant layer is preferably formed by curing an epoxy resin adhesive.

[0015] Another object of the present invention is to provide a method for manufacturing a display device, comprising the steps of: Step (1): The alignment agent is coated on the substrate, dried, and imidized to obtain substrate-alignment film laminate 1; Step (2): Bead-shaped spacers are distributed on the alignment film side of the substrate-alignment film laminate 1, and a sealant is printed on the bead-shaped spacers to form the laminate 2. Step (3): The substrate-alignment film laminate 1 and the laminate 2 are bonded together with the substrate as the outer side, and then the sealant is cured to obtain an empty box; Step (4): A liquid crystal mixture containing reactive monomers is injected into the empty cell to obtain a liquid crystal cell; Step (5): Apply an electric field and ultraviolet light to the liquid crystal cell to obtain the display device; Preferably, the diameter of the bead-like spacers is 3-6 μm; Preferably, the mass of the reactive monomer is 0.5 wt% to 1.0 wt% of the liquid crystal mixture. Preferably, the voltage of the electric field is 5-30V, and / or the wavelength of the ultraviolet light is 300-400nm, and the intensity is 1000-5000J / cm2.

[0016] Another object of the present invention is to provide a display module, the display module including the above-described display device; Preferably, when the display module is used in a temperature range of 40℃ to 85℃, the pretilt angle change is <0.15° and the voltage retention rate is >97%.

[0017] The beneficial effects of the technical solution of the present invention include: A self-initiating photosensitive resin composition was used to replace the formulation system relying on exogenous photoinitiators. Long alkyl chains were introduced into the polyimide molecular chain, which are complementary to the liquid crystal molecular structure, enhancing the interfacial anchoring energy. Through optimized design, nanoparticles were added to improve heat resistance. The resulting alignment film possesses high-temperature resistance, self-photoinitiating capability, interfacial compatibility, and dispersion stability. Display devices based on this film exhibit good high-temperature resistance, high reliability, and excellent display performance. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of fabricating a display device in one implementation of this application. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be further described in detail below with reference to specific embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the ordinary meaning that can be understood by one of skill in the art.

[0021] As analyzed in the background section, in existing technologies, the PSVA process is generally achieved by adding an exogenous photoinitiator to initiate the polymerization reaction. This system directly leads to a difficult-to-overcome problem: exogenous photoinitiator residue. Unreacted photoinitiator residue in the system easily transforms into impurity ions, which not only reduces the resistivity of the alignment film but also exacerbates ion migration at high temperatures, resulting in reliability issues such as image retention. Furthermore, mainstream polyimide alignment films lack the ability to maintain stable photoelectric performance over a wide temperature range of 40°C to 85°C or even higher. Generally, after prolonged aging in high-temperature environments exceeding 80°C, problems such as liquid crystal pretilt angle shift occur, leading to defects such as light leakage or decreased contrast. To solve the above problems, this invention innovates from the source of system design, using a self-initiating photosensitive resin composition to replace the formulation system relying on exogenous photoinitiators. In addition, long alkyl chains are introduced into the polyimide molecular chain, which are complementary to the liquid crystal molecule structure, improving the interface anchoring energy, stabilizing the liquid crystal pretilt angle, ensuring orderly alignment of liquid crystal molecules at high temperatures, and maintaining stable display response time. Furthermore, by optimizing the design, nanoparticles are added to improve heat resistance; even further, in order to solve the problem of nanoparticle dispersion, the present invention also modifies the surface of the nanoparticles.

[0022] The object of this invention is to provide a photosensitive resin composition for use as an orientation agent, the composition comprising: (A) A dianhydride monomer containing a photosensitive group, wherein the photosensitive group is selected from at least one of cinnamate group, chalcone group, anthracene group, coumarin group or benzophenone group; (B) Hydrogen donor diamine monomer; (C) Aliphatic diamine monomers; The above-mentioned (A) dianhydride monomers containing photosensitive groups provide photosensitive groups, which can abstract hydrogen atoms to generate free radicals under ultraviolet light; (B) the hydrogen donor diamine monomers are rich in carbonyl groups (such as benzophenone structures) that are easily excited by photo, or have amino groups with high functionality, which can abstract hydrogen atoms from adjacent molecular chains under ultraviolet light excitation to generate free radicals, thereby initiating the polymerization or cross-linking reaction of unsaturated photosensitive groups, or they themselves participate in the energy transfer process as photosensitive chromophores; (B) the hydrogen donor diamine monomers enhance photoinitiation efficiency as hydrogen donors; the benzophenone groups in the dianhydride monomers containing photosensitive groups in (A) work synergistically with the hydrogen donor diamine monomers in (B), which can efficiently initiate the polymerization of reactive monomers in liquid crystal mixtures without the need for external photoinitiators, avoiding ion contamination caused by residual photoinitiators, increasing the resistivity of the alignment film, and reducing ion mobility at high temperatures. By introducing long alkyl chain functional groups into polyimide using (C) aliphatic diamine monomers, the long alkyl chains complement the liquid crystal molecule structure, enhancing the interface anchoring energy. At high temperatures, the liquid crystal molecules are arranged neatly, and the display response time remains stable.

[0023] Preferably, the dianhydride monomer containing the photosensitive group in (A) has a rigid aromatic or alicyclic skeleton, which can serve as a structural unit of the polymer backbone and endow the polymer chain with photoreactivity to initiate photocrosslinking; preferably, the dianhydride monomer containing the photosensitive group in (A) includes at least one of the following dianhydrides: 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride, 2,2′,3,3′-benzophenone tetracarboxylic acid dianhydride as a dianhydride monomer, bis(4-carboxycinnamic acid) ester dianhydride, 4,4′-bis(cinnamoyloxy) diphenyl ether dianhydride, 4,4′-bis(4-azidophenoxy) diphenyltetracarboxylic acid dianhydride, and azido-substituted pyromellitic dianhydride; Preferably, the hydrogen donor diamine monomer (B) includes at least one of the following diamines: 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, and aliphatic or alicyclic diamines (such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, isophorone diamine, 4,4′-methylenebis(2-methylcyclohexylamine) or polyoxyethylene diamine) whose molecular backbone or side chain contains an easily abstracted αα-hydrogen atom. Such monomers are characterized by having a hydrogen atom attached to the carbon atom adjacent to the amino group, which can undergo a hydrogen abstraction reaction under the action of the photoexcited benzophenone group to generate free radicals, thereby acting as a co-initiator to efficiently drive the photocrosslinking and curing of the system; Preferably, the alkyl chain length of the (C) aliphatic diamine monomer ranges from 8 to 12 carbon atoms in the main chain; more preferably, the (C) aliphatic diamine monomer includes at least one of the following diamines: 1,8-diaminooctane, 1,10-diaminodecane, and 1,12-diaminododecane. Preferably, the molar ratio of (A) the dianhydride monomer containing a photosensitive group, (B) the hydrogen donor diamine monomer, and (C) the aliphatic diamine monomer is 1:(0.5~0.7):(0.3~0.5).

[0024] Another object of the present invention is to provide a polyimide resin formed from the above-mentioned photosensitive resin composition by a polycondensation reaction or by a polycondensation and imidization reaction.

[0025] Another object of the present invention is to provide a method for preparing a polyimide resin for use as an orientation agent, comprising the following steps: Step (1): Add the (A) dianhydride monomer containing a photosensitive group, the (B) hydrogen donor diamine monomer and the (C) aliphatic diamine monomer to an organic solvent to react and form a polyimide precursor; Step (2): The polyimide precursor obtained in step (1) is subjected to an imidization reaction to form a polyimide resin; Preferably, the reaction temperature in step (1) is 0-30℃ and the reaction time is 6-24h; Preferably, the imidization temperature in step (2) is 200-350℃ and the time is 120-180 min; Preferably, the imidization reaction is carried out under a nitrogen atmosphere; Preferably, step (2) before the imidization reaction further includes a drying step, and more preferably the drying temperature is 80-120℃ and the time is 10-20min; Preferably, the organic solvent includes at least one of the following solvents: N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), cyclopentanone, and ethylene glycol monoalkyl ether solvents (such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, or propylene glycol monomethyl ether).

[0026] Another object of the present invention is to provide a polyamic acid orientation agent, said orientation agent comprising a polyamic acid resin formed by polycondensation reaction of the above-described photosensitive resin composition; Preferably, the polyamic acid orientation agent further includes nanoparticles, and more preferably, the nanoparticles include at least one of the following nanoparticles: silica, alumina, titanium dioxide, zinc oxide, boron nitride, aluminum nitride, silsesquioxane, or organically modified montmorillonite. More preferably, the nanoparticles are nanoparticles with a silane coupling agent surface modified. More preferably, the nanoparticles have a particle size of 5-100 nm, and most preferably 10-20 nm.

[0027] In a typical embodiment of this application, the amount of the silane coupling agent is 1 wt% to 10 wt% of the nanoparticles. Preferably, the silane coupling agent contains an amino group; more preferably, the silane coupling agent includes at least one of the following silane coupling agents: γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-cyclohexyl-aminopropyltrimethoxysilane, and dodecylaminopropyltrimethoxysilane.

[0028] Surface amino functionalization of nanoparticles using silane coupling agents creates active groups on the nanoparticle surface that are complementary to the PI molecular chain. This not only inhibits nanoparticle aggregation but also enables strong interactions (e.g., hydrogen bonds, covalent bonds) with the PI molecular chain, thereby improving dispersion stability and interfacial bonding.

[0029] Another object of the present invention is to provide a method for preparing the above-mentioned polyamic acid orientation agent, comprising the following steps: Step (1): Add the (A) dianhydride monomer containing a photosensitive group, the (B) hydrogen donor diamine monomer and the (C) aliphatic diamine monomer to an organic solvent to react and form a polyamic acid solution; Step (2): The nanoparticles are dispersed in a dispersion medium to form a dispersion. Step (3): The polyamic acid solution and the dispersion are mixed and reacted to obtain the polyamic acid orientation agent; Preferably, the reaction temperature in step (1) is 0-30℃ and the reaction time is 6-24h; Preferably, in step (1), the molar ratio of (A) the dianhydride monomer containing a photosensitive group, (B) the hydrogen donor diamine monomer, and (C) the aliphatic diamine monomer is 1:(0.5~0.7):(0.3~0.5). Preferably, step (2) further includes dispersing the silane coupling agent in a dispersion medium; Preferably, the dispersion medium comprises at least one of the following solvents: N-methylpyrrolidone, ethylene glycol monobutyl ether (BC), ethylene glycol monobutyl ether, γ-butyrolactone (GBL), N,N-dimethylacetamide (DMAc), propylene glycol monomethyl ether acetate (PGMEA), and cyclopentanone; more preferably, the dispersion medium is a mixed solvent of N-methylpyrrolidone and ethylene glycol monobutyl ether; and most preferably, the mass ratio of the two is 8:2-5:5. Preferably, the dispersion is performed by ultrasonic dispersion and / or mechanical stirring, more preferably the ultrasonic dispersion power is 250~350W and the time is 20~40min, and / or the mechanical stirring speed is 600~1000rpm and the time is 1~3h; the nano-dispersion prepared by the ultrasonic dispersion-mechanical stirring composite process is uniform and stable. Preferably, the reaction temperature in step (3) is 10-35°C and the time is 2-6 hours; more preferably, the reaction is carried out under a nitrogen atmosphere. Preferably, the mass ratio of the polyamic acid solution to the dispersion is 100:5~15; Preferably, the mass fraction of the nanoparticles in the solid component of the polyamic acid orientation agent is 0.1wt%-10wt%, more preferably 0.5wt% to 5wt%; the solid component includes polyamic acid resin, nanoparticles, and optional crosslinking agents or coupling agents, but does not include volatile solvents; Preferably, step (3) further includes a membrane filtration step after the reaction to remove impurities and possible agglomerates; More preferably, the membrane filtration is performed using a polytetrafluoroethylene microporous membrane, preferably with a pore size of 0.1-0.5 μm, and most preferably 0.2 μm.

[0030] Another object of the present invention is to provide a polyimide film, wherein the polyimide film is obtained by coating and imidization reaction of the polyamic acid orientation agent prepared by the above-mentioned polyamic acid orientation agent or the polyamic acid orientation agent prepared by the above-mentioned preparation method; Preferably, the thickness of the polyimide film is 80-120 nm; Preferably, the surface roughness of the polyimide film is <0.5 nm; Preferably, the imidization temperature is 200-350℃ and the time is 120-180 min; Preferably, the imidization reaction is carried out under a nitrogen atmosphere; Preferably, the imidization reaction further includes a drying step, and more preferably, the drying temperature is 80-120°C and the time is 10-20 min.

[0031] Another object of the present invention is to provide a display device comprising the above-described polyimide film; Preferably, the display device is a liquid crystal cell; More preferably, the liquid crystal cell further includes a substrate, a sealant layer, bead-shaped spacers, and a liquid crystal layer. The sealant layer is made from common sealing adhesives, and preferably, the sealant layer is formed by curing epoxy resin adhesive.

[0032] Another object of the present invention is to provide a method for manufacturing the above-mentioned display device, comprising the steps of: Step (1): The alignment agent is coated on the substrate, dried, and imidized to obtain substrate-alignment film laminate 1; Step (2): Bead-shaped spacers are distributed on the alignment film side of the substrate-alignment film laminate 1, and a sealant is printed on the bead-shaped spacers to form the laminate 2. Step (3): The substrate-alignment film laminate 1 and the laminate 2 are bonded together with the substrate as the outer side, and then the sealant is cured to obtain an empty box; Step (4): A liquid crystal mixture containing reactive monomers is injected into the empty cell to obtain a liquid crystal cell; Step (5): Apply an electric field and ultraviolet light to the liquid crystal cell to obtain the display device; Preferably, the diameter of the bead-like spacers is 3-6 μm; Preferably, the bead-like spacers are silica microspheres, resin microspheres, or composite spacers with acrylate monomers coated on their surface; Preferably, the liquid crystal mixture containing reactive monomers is a mixture comprising a negatively dielectric anisotropic liquid crystal substrate, a chiral dopant, and a photopolymerizable monomer containing acrylate groups or methacrylate groups; Preferably, the mass of the reactive monomer is 0.5 wt% to 1.0 wt% of the liquid crystal mixture. Preferably, the voltage of the electric field is 5-30V, and / or the wavelength of the ultraviolet light is 300-400nm, and the intensity is 1000-5000J / cm2.

[0033] Another object of the present invention is to provide a display module, the display module including the above-described display device; Preferably, when the display module is used in a temperature range of 40℃ to 85℃, the pretilt angle change is <0.15° and the voltage retention rate is >97%.

[0034] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0035] Example 1: Synthesis of photoinitiated modified PAA solution: In a 250 mL three-necked flask under nitrogen protection, 10 mmol of 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride, 6 mmol of 3,3′-dimethyl-4,4′-diaminodiphenylmethane, and 4 mmol of decyl chain-containing aliphatic diamine 1,10-diaminodecane (DAD) were added, along with 40 g of NMP solvent. The mixture was stirred at 25 °C for 6 h to obtain PAA solution. Preparation of nano-dispersion: Take 10g of SiO2 nanoparticles with a particle size of 10nm, add 0.8g of γ-aminopropyltriethoxysilane modifier, and ultrasonically disperse in NMP / BC mixed solvent for 30min, then stir under mechanical stirring at 800rpm for 2h to obtain nano-dispersion. Composite material preparation: 100g of modified PAA was mixed with 10g of nano-dispersion and stirred at 50℃ for 6h. The mixture was then filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material. The modified PAA solution was coated onto a glass substrate and then pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film. Alignment film forming and curing: The material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8 wt% RM monomer is injected to prepare the liquid crystal cell. A voltage of 15V is applied, and UV light passing through a filter with a wavelength cutoff below 325nm at 10J / cm² is irradiated from the outside of the liquid crystal cell. Polymerization is completed, forming a stable polymer network and fixing the liquid crystal pretilt angle.

[0036] Example 2: The self-photoinitiated modified PAA solution was synthesized according to Example 1; Preparation of nano-dispersion: consistent with Example 1 - take 10g of SiO2 nanoparticles with a particle size of 10nm, add 0.8g of γ-aminopropyltriethoxysilane modifier, ultrasonically disperse in NMP / BC mixed solvent for 30min, and then stir under mechanical stirring at 800rpm for 2h to obtain nano-dispersion; Composite material preparation: 100g of modified PAA was mixed with 3g of nano-dispersion (the content of nano-dispersion was reduced compared to 10g in Example 1), stirred at 50℃ for 6h, and filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material; the modified PAA solution was coated onto a glass substrate and pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film; Alignment film forming and curing: consistent with Example 1—the material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8wt% RM monomer is injected, and a 4V voltage is applied. The liquid crystal is irradiated with 365nm ultraviolet light (4mW / cm²) for 100s to form a stable polymer network and fix the liquid crystal pretilt angle.

[0037] Example 3: Synthesis of photoinitiated modified PAA solution: In a 250 mL three-necked flask under nitrogen protection, 10 mmol of 4,4'-oxobisphthalic anhydride monomer containing a photosensitive group, 6 mmol of 1,4-bis(4-aminophenoxy)benzene, and 4 mmol of 1,6-diaminohexane from an aliphatic diamine monomer were added, along with 40 g of NMP solvent. The mixture was stirred at 25 °C for 6 h to obtain a PAA solution. Preparation of nano-dispersion: The dispersion was prepared according to Example 1; Composite material preparation: 100g of modified PAA was mixed with 10g of nano-dispersion and stirred at 50℃ for 6h. The mixture was then filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material. The modified PAA solution was coated onto a glass substrate and then pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film. Alignment film forming and curing: The material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8 wt% RM monomer is injected to prepare the liquid crystal cell. A voltage of 15V is applied, and UV light passing through a filter with a wavelength cutoff below 325nm at 10J / cm² is irradiated from the outside of the liquid crystal cell. Polymerization is completed, forming a stable polymer network and fixing the liquid crystal pretilt angle.

[0038] Example 4: Synthesis of photoinitiated modified PAA solution: In a 250 mL three-necked flask under nitrogen protection, 10 mmol of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride containing a photosensitive group (belonging to the benzophenone group), 6 mmol of hydrogen donor diamine mono-2,5-diaminobenzoic acid, and 4 mmol of aliphatic diamine monomer 1,12-diaminododecane were added, along with 40 g of NMP solvent. The mixture was stirred at 25 °C for 6 h to obtain the PAA solution. Preparation of nano-dispersion: The dispersion was prepared according to Example 1; Composite material preparation: 100g of modified PAA was mixed with 10g of nano-dispersion and stirred at 50℃ for 6h. The mixture was then filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material. The modified PAA solution was coated onto a glass substrate and then pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film. Alignment film forming and curing: The material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8 wt% RM monomer is injected to prepare the liquid crystal cell. A voltage of 15V is applied, and UV light passing through a filter with a wavelength cutoff below 325nm at 10J / cm² is irradiated from the outside of the liquid crystal cell. Polymerization is completed, forming a stable polymer network and fixing the liquid crystal pretilt angle.

[0039] Example 5: Synthesis of photoinitiated modified PAA solution: In a 250 mL three-necked flask under nitrogen protection, 10 mmol of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride containing a photosensitive group, 7 mmol of 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 3 mmol of 1,10-diaminodecane (the diamine monomer was selected) were added, along with 40 g of NMP solvent. The mixture was stirred at 25 °C for 6 h to obtain the PAA solution. Preparation of nano-dispersion: The dispersion was prepared according to Example 1; Composite material preparation: 100g of modified PAA was mixed with 10g of nano-dispersion and stirred at 50℃ for 6h. The mixture was then filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material. The modified PAA solution was coated onto a glass substrate and then pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film. Alignment film forming and curing: The material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8 wt% RM monomer is injected to prepare the liquid crystal cell. A voltage of 15V is applied, and UV light passing through a filter with a wavelength cutoff below 325nm at 10J / cm² is irradiated from the outside of the liquid crystal cell. Polymerization is completed, forming a stable polymer network and fixing the liquid crystal pretilt angle.

[0040] Example 6: Synthesis of photoinitiated modified PAA solution: In a 250 mL three-necked flask under nitrogen protection, 10 mmol of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride containing a photosensitive group, 3 mmol of 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 7 mmol of 1,10-diaminodecane (selected as the diamine monomer) were added, along with 40 g of NMP solvent. The mixture was stirred at 25 °C for 6 h to obtain the PAA solution. Preparation of nano-dispersion: The dispersion was prepared according to Example 1; Composite material preparation: 100g of modified PAA was mixed with 10g of nano-dispersion and stirred at 50℃ for 6h. The mixture was then filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material. The modified PAA solution was coated onto a glass substrate and then pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film. Alignment film forming and curing: The material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8 wt% RM monomer is injected to prepare the liquid crystal cell. A voltage of 15V is applied, and UV light passing through a filter with a wavelength cutoff below 325nm at 10J / cm² is irradiated from the outside of the liquid crystal cell. Polymerization is completed, forming a stable polymer network and fixing the liquid crystal pretilt angle.

[0041] Example 7: Synthesis of photoinitiated modified PAA solution: In a 250 mL three-necked flask under nitrogen protection, 10 mmol of 2,3,3',4'-biphenyltetracarboxylic acid dianhydride containing a photosensitive group, 5 mmol of 3,3'-dimethyl-4,4'-diaminodiphenylmethane, and 5 mmol of 1,10-diaminodecane (the diamine monomer was selected) were added, along with 40 g of NMP solvent. The mixture was stirred at 25 °C for 6 h to obtain the PAA solution. Preparation of nano-dispersion: The dispersion was prepared according to Example 1; Composite material preparation: 100g of modified PAA was mixed with 10g of nano-dispersion and stirred at 50℃ for 6h. The mixture was then filtered through a 0.2μm polytetrafluoroethylene filter membrane to obtain the target material. The modified PAA solution was coated onto a glass substrate and then pre-baked at 80℃ for 30min, baked at 180℃ for 60min, and cured at 230℃ for 120min in sequence to obtain a modified PI oriented film. Alignment film forming and curing: The material is spin-coated onto an ITO substrate, cured, and then assembled into a liquid crystal cell. Liquid crystal containing 0.8 wt% RM monomer is injected to prepare the liquid crystal cell. A voltage of 15V is applied, and UV light passing through a filter with a wavelength cutoff below 325nm at 10J / cm² is irradiated from the outside of the liquid crystal cell. Polymerization is completed, forming a stable polymer network and fixing the liquid crystal pretilt angle.

[0042] Comparative Example 1: Synthesis of unmodified PI: 10 mmol of a photosensitive dianhydride 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA), 6 mmol of 3,3′-dimethyl-4,4′-diaminodiphenylmethane (DMMDA), and 4 mmol of an aliphatic diamine containing a decyl chain, 1,10-diaminodecane (DAD), were used as PAA monomers. 40 g of N-methylpyrrolidone (NMP) was added as a solvent. The reaction system was placed in a 25°C constant temperature water bath and mechanically stirred at 300 rpm for 6 h until the monomers were completely dissolved, yielding a transparent unmodified PAA solution with a solid content of approximately 20 wt%. Preparation of unmodified nano-dispersion: Take 10g of SiO2 nanoparticles with a particle size of 10nm, add them directly to NMP / BC mixed solvent, and prepare nano-dispersion through the same dispersion process; Comparative material preparation: 100g of unmodified PI and 10g of unmodified nano-dispersion were mixed, and 0.3g of external photoinitiator (benzoin isopropyl ether) was added at the same time to prepare the comparative material according to the method of Example 1; Orientation film forming and curing: The orientation film was prepared and polymerized and cured under the same process conditions as in Example 1.

[0043] Comparative Example 2: The synthesis of unmodified PI was carried out according to Comparative Example 1; Preparation of nano-dispersion: consistent with Example 1 - take 10g of SiO2 nanoparticles with a particle size of 10nm, add 0.8g of γ-aminopropyltriethoxysilane modifier, ultrasonically disperse in NMP / BC mixed solvent for 30min, and then stir under mechanical stirring at 800rpm for 2h to obtain nano-dispersion; Comparative material preparation: 100g of unmodified PI was mixed with 10g of modified nano-dispersion, and 0.3g of external photoinitiator (benzoin isopropyl ether) was added at the same time to prepare the comparative material according to the method of Example 1; Orientation film forming and curing: The orientation film was prepared and polymerized and cured under the same process conditions as in Example 1.

[0044] The following describes the evaluation method and evaluation results of the liquid crystal cell samples prepared in the embodiments and comparative examples.

[0045] The glass transition temperature (Tg), pretilt angle change after aging at 80℃ for 500h, voltage retention rate (VHR), and surface roughness of the alignment film were tested.

[0046] Glass transition temperature (Tg) 1) Standard basis: Refer to ASTM E1356-08 "Standard Test Assignment for the Nominal Glass Transition Temperature by Differential Scanning Calorimetry" or GB / T19466.2-2009 "Differential Scanning Calorimetry (DSC) for Plastics - Part 2: Determination of Glass Transition Temperature".

[0047] 2) Testing equipment: TA Instruments Q2000 differential scanning calorimeter (DSC) from the United States.

[0048] [Changes in pretilt angle after aging at 80℃ for 500 hours] 1) Test principle: The pretilt angle of the liquid crystal cell is measured using the Crystal Rotation Method.

[0049] 2) Testing equipment: Otsuka Electronics Model LCA-100 pretilt angle tester or Autronix pretilt angle testing system (Japan).

[0050] Voltage retention rate (VHR) 1) Standard basis: Refer to the test method recommended by the SID Display Metrology Committee or the test provisions on voltage holding rate in GB / T36517-2018 "Test Methods for Liquid Crystal Display Devices".

[0051] 2) Testing equipment: Toyo Corporation's Model 6254 LCD property evaluation system, equipped with a high-temperature testing chamber.

[0052] 3) Test conditions: 1. Environment: The test temperature is set to 80℃ (simulating a harsh working environment).

[0053] 2. Waveform: Apply a square wave voltage with a frequency of 60 Hz and an amplitude of 5 V (higher than the liquid crystal threshold voltage).

[0054] 3. Process: The charging time is 16.67 ms (1 frame). After power failure, the voltage decay is monitored, and the duration is usually 16.67 ms or longer.

[0055] Surface roughness 1) Standard basis: Refer to ISO 4287:1997 "Geometrical Product Specifications (GPS) - Surface texture: Profile method - Terms, definitions and surface texture parameters" or GB / T 3505-2009 "Geometrical Product Specifications (GPS) - Surface texture profile method - Terms, definitions and surface texture parameters".

[0056] 2) Testing equipment: Bruker Atomic Force Microscope (AFM), Model Dimension Icon.

[0057] 3) Test conditions: 1. Probe: Use tapping mode, probe model RTESP-300 (silicon probe, nominal radius of curvature <10 nm).

[0058] 2. Scanning range: Five different locations were randomly selected on the film surface, and the scanning area of ​​each location was 5 μm × 5 μm.

[0059] 3. Resolution: The number of scan points is set to 512 × 512.

[0060] 4. Data processing: The instrument’s built-in software (Nanoscope Analysis) was used to perform a first-level plane fitting on the acquired three-dimensional topography image to remove the sloping background, and the arithmetic mean roughness Ra value was calculated. The final result was the average of 5 points.

[0061] [Evaluation Results] The evaluation results of the examples and comparative examples are shown in Table 1.

[0062] Table 1 Evaluation results of liquid crystal cell samples prepared in the examples and comparative examples As shown in Table 1, the liquid crystal cell samples prepared in Examples 1-7 have advantages such as high glass transition temperature, small change in pretilt angle after aging at 80℃ for 500h, high voltage retention rate, and low surface roughness. Their overall performance is better than that of the comparative examples.

[0063] In summary, the present invention achieves synergistic optimization of the high-temperature resistance, self-photoinitiation capability, interfacial compatibility, and dispersion stability of the alignment film. Therefore, display devices based on the alignment agent of this invention exhibit good high-temperature resistance, high reliability, and excellent display performance.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A photosensitive resin composition for an orienting agent, characterized by comprising: The composition comprises: (A) A dianhydride monomer containing a photosensitive group, wherein the photosensitive group is selected from at least one of cinnamate group, chalcone group, anthracene group, coumarin group or benzophenone group; (B) Hydrogen donor diamine monomer; (C) Aliphatic diamine monomers; Preferably, the dianhydride monomer containing the photosensitive group in (A) includes at least one of the following dianhydrides: 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride, 2,2′,3,3′-benzophenone tetracarboxylic acid dianhydride as a dianhydride monomer, bis(4-carboxycinnamic acid) ester dianhydride, 4,4′-bis(cinnamoyloxy) diphenyl ether dianhydride, 4,4′-bis(4-azidophenoxy) diphenyltetracarboxylic acid dianhydride, and azido-substituted pyromellitic dianhydride; Preferably, the (B) hydrogen donor diamine monomer comprises at least one of the following diamines: 3,3′-dimethyl-4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, isophorone diamine, 4,4′-methylenebis(2-methylcyclohexylamine), and polyoxyethylene diamine; Preferably, the alkyl chain length of the (C) aliphatic diamine monomer ranges from 8 to 12 carbon atoms in the main chain; more preferably, the (C) aliphatic diamine monomer includes at least one of the following diamines: 1,8-diaminooctane, 1,10-diaminodecane, and 1,12-diaminododecane. Preferably, the molar ratio of (A) the dianhydride monomer containing a photosensitive group, (B) the hydrogen donor diamine monomer, and (C) the aliphatic diamine monomer is 1:(0.5~0.7):(0.3~0.5).

2. A polyimide resin for an orienting agent, characterized by, The polyimide resin is formed from the photosensitive resin composition of claim 1 by polycondensation reaction or by polycondensation and imidization reaction.

3. A method of producing the polyimide resin according to claim 2, characterized by, Includes the following steps: Step (1): Add the (A) dianhydride monomer containing a photosensitive group, the (B) hydrogen donor diamine monomer and the (C) aliphatic diamine monomer to an organic solvent to react and form a polyimide precursor; Step (2): The polyimide precursor obtained in step (1) is subjected to an imidization reaction to form a polyimide resin; Preferably, the reaction temperature in step (1) is 0-30℃ and the reaction time is 6-24h; Preferably, the imidization temperature in step (2) is 200-350℃ and the time is 120-180 min; Preferably, the imidization reaction is carried out under a nitrogen atmosphere; Preferably, step (2) before the imidization reaction further includes a drying step, and more preferably the drying temperature is 80-120℃ and the time is 10-20min; Preferably, the organic solvent includes at least one of the following solvents: N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, cyclopentanone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether.

4. A polyamic acid orienting agent characterized by comprising: The orientation agent comprises a polyamic acid resin formed by polycondensation reaction of the photosensitive resin composition of claim 1; Preferably, the polyamic acid orientation agent further includes nanoparticles, and more preferably, the nanoparticles include at least one of the following nanoparticles: silica, alumina, titanium dioxide, zinc oxide, boron nitride, aluminum nitride, silsesquioxane, or organically modified montmorillonite. More preferably, the nanoparticles are nanoparticles with a silane coupling agent surface modified. More preferably, the nanoparticles have a particle size of 5-100 nm, and most preferably 10-20 nm.

5. The polyamic acid orienting agent according to claim 4, characterized by, The amount of the silane coupling agent used is 1 wt% to 10 wt% of the nanoparticles; Preferably, the silane coupling agent contains an amino group; more preferably, the silane coupling agent includes at least one of the following silane coupling agents: γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-cyclohexyl-aminopropyltrimethoxysilane, and dodecylaminopropyltrimethoxysilane.

6. A method for producing the polyamic acid orienting agent according to claim 4 or 5, characterized by, Includes the following steps: Step (1): Add the (A) dianhydride monomer containing a photosensitive group, the (B) hydrogen donor diamine monomer and the (C) aliphatic diamine monomer to an organic solvent to react and form a polyamic acid solution; Step (2): The nanoparticles are dispersed in a dispersion medium to form a dispersion. Step (3): The polyamic acid solution and the dispersion are mixed and reacted to obtain the polyamic acid orientation agent; Preferably, the reaction temperature in step (1) is 0-30℃ and the reaction time is 6-24h; Preferably, in step (1), the molar ratio of (A) the dianhydride monomer containing a photosensitive group, (B) the hydrogen donor diamine monomer, and (C) the aliphatic diamine monomer is 1:(0.5~0.7):(0.3~0.5). Preferably, step (2) further includes dispersing the silane coupling agent in a dispersion medium; Preferably, the dispersion medium includes at least one of the following solvents: N-methylpyrrolidone, ethylene glycol monobutyl ether, γ-butyrolactone, N,N-dimethylacetamide, propylene glycol monomethyl ether acetate, and cyclopentanone; more preferably, the dispersion medium is a mixed solvent of N-methylpyrrolidone and ethylene glycol monobutyl ether; and most preferably, the mass ratio of the two is 8:2-5:

5. Preferably, the dispersion is performed by ultrasonic dispersion and / or mechanical stirring, more preferably the ultrasonic dispersion power is 250~350W and the time is 20~40min, and / or the mechanical stirring speed is 600~1000rpm and the time is 1~3h; Preferably, the reaction temperature in step (3) is 10-35°C and the time is 2-6 hours; more preferably, the reaction is carried out under a nitrogen atmosphere. Preferably, the mass ratio of the polyamic acid solution to the dispersion is 100:5~15; Preferably, the mass fraction of the nanoparticles in the solid component of the polyamic acid orientation agent is 0.1wt%-10wt%, more preferably 0.5wt% to 5wt%; the solid component includes polyamic acid resin, nanoparticles, and optional crosslinking agents or coupling agents, but does not include volatile solvents; Preferably, step (3) further includes a membrane filtration step after the reaction; More preferably, the membrane filtration is performed using a polytetrafluoroethylene microporous membrane, preferably with a pore size of 0.1-0.5 μm, and most preferably 0.2 μm.

7. A polyimide film, characterized in that, The polyimide film is obtained by coating and imidization reaction of the polyamic acid orientation agent prepared by the polyamic acid orientation agent according to claim 4 or 5 or the preparation method according to claim 6. Preferably, the thickness of the polyimide film is 80-120 nm; Preferably, the surface roughness of the polyimide film is <0.5 nm; Preferably, the imidization temperature is 200-350℃ and the time is 120-180 min; Preferably, the imidization reaction is carried out under a nitrogen atmosphere; Preferably, the imidization reaction further includes a drying step, and more preferably, the drying temperature is 80-120°C and the time is 10-20 min.

8. A display device, characterized in that, The display device comprises the polyimide film according to claim 7; Preferably, the display device is a liquid crystal cell; More preferably, the liquid crystal cell further includes a substrate, a sealant layer, bead-shaped spacers, and a liquid crystal layer, wherein the sealant layer is preferably formed by curing an epoxy resin adhesive.

9. A method for manufacturing the display device according to claim 8, characterized in that, Including the following steps: Step (1): The alignment agent is coated on the substrate, dried, and imidized to obtain substrate-alignment film laminate 1; Step (2): Bead-shaped spacers are distributed on the alignment film side of the substrate-alignment film laminate 1, and a sealant is printed on the bead-shaped spacers to form the laminate 2. Step (3): The substrate-alignment film laminate 1 and the laminate 2 are bonded together with the substrate as the outer side, and then the sealant is cured to obtain an empty box; Step (4): A liquid crystal mixture containing reactive monomers is injected into the empty cell to obtain a liquid crystal cell; Step (5): Apply an electric field and ultraviolet light to the liquid crystal cell to obtain the display device; Preferably, the diameter of the bead-like spacers is 3-6 μm; Preferably, the mass of the reactive monomer is 0.5 wt% to 1.0 wt% of the liquid crystal mixture. Preferably, the voltage of the electric field is 5-30 V, and / or the wavelength of the ultraviolet is 300-400 nm, and the intensity is 1000-5000 J / cm 2 .

10. A display module, characterized in that, The display module includes the display device as described in claim 8; Preferably, when the display module is used in a temperature range of 40℃ to 85℃, the pretilt angle change is <0.15° and the voltage retention rate is >97%.

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