Liquid crystal alignment agent, liquid crystal alignment film, and method for producing same, and use thereof

Abstract

This application provides a liquid crystal alignment agent comprising a polyimide resin and a solvent. The polyimide resin backbone contains fluorine substituents and a triazine ring structure. The polyimide resin is obtained by polymerization of dianhydride and diamine monomers. The diamine monomers include at least one monomer containing fluorine atoms and at least one monomer containing a triazine ring structure. The molar ratio of the fluorine-containing monomer to the triazine ring-containing monomer is 1:1 to 5:1. This application introduces triazine rings and fluorine atoms into the polyimide backbone. Through the synergistic effect of the triazine rings and fluorine atoms, the technical contradiction between ultraviolet light stability and pretilt angle control is simultaneously resolved, providing a key material solution for high-end liquid crystal display devices with balanced performance.

Description

Technical Field

[0001] This application relates to the field of polyimide material technology, and more specifically, to a liquid crystal alignment agent, a liquid crystal alignment film, a preparation method thereof, and its application. Background Technology

[0002] Liquid crystal display (LCD) technology, as a core pillar of modern information display, has undergone decades of evolution and development. Its technological trajectory has gradually expanded from the initial twisted nematic (TN) mode to the current vertical alignment (VA) mode, continuously pursuing higher contrast, faster response times, and lower power consumption. Among them, PSVA (Polymer Stabilized Vertical Alignment) technology, as a key branch of the VA technology system, effectively stabilizes the vertical alignment of liquid crystal molecules by constructing a polymer network structure within the liquid crystal layer, thereby achieving superior display characteristics such as wide viewing angles, high contrast, and fast response.

[0003] In the implementation of PSVA display technology, the performance of the alignment agent material becomes a core factor determining the final performance of the display panel. Polyimide (PI), with its excellent thermal stability, chemical stability, and mechanical properties, has become the mainstream choice for liquid crystal alignment materials. However, as display technology continues to develop towards higher resolutions, higher refresh rates, and longer lifespans, traditional liquid crystal alignment agents are gradually revealing many technical limitations in PSVA process applications.

[0004] The primary challenge lies in the insufficient stability under ultraviolet light. In the PSVA process, 365nm wavelength ultraviolet light is used to cure the liquid crystal layer to form a stable polymer network structure. However, traditional polyimide materials are prone to photodegradation under long-term ultraviolet irradiation, leading to molecular chain breakage and performance degradation. This photodegradation process not only shortens the lifespan of the alignment film but also generates low-molecular-weight byproducts, exacerbating ion contamination of the liquid crystal cell, and consequently causing display defects such as decreased voltage retention and image retention. Secondly, the accuracy and stability of pretilt angle control are also key factors affecting display quality. PSVA technology requires liquid crystal molecules to have a high pretilt angle (typically between 88° and 89.5°) to achieve optimal electro-optical performance. However, the pretilt angle of traditional liquid crystal alignment agents is easily affected by multiple factors such as environmental factors, process parameters, and material aging, causing fluctuations in the contrast and response speed of the display panel.

[0005] Furthermore, traditional liquid crystal alignment agents suffer from high hygroscopicity, difficulty in controlling surface morphology, and poor compatibility with liquid crystal materials. These shortcomings, to some extent, limit the application and expansion of PSVA display technology in high-end display products, especially in the field of display panels requiring large size, high resolution, and long lifespan.

[0006] In conclusion, there is an urgent need for a liquid crystal alignment agent to solve the problems of ultraviolet light stability and the accuracy and stability of pretilt angle control. Summary of the Invention

[0007] To address the shortcomings of the prior art, the first aspect of this application provides a liquid crystal alignment agent comprising a polyimide resin and a solvent, wherein the polyimide resin backbone contains fluorine substituents and a triazine ring structure.

[0008] Furthermore, the polyimide resin is obtained by polymerization of dianhydride and diamine monomers, wherein the diamine monomers include at least one monomer containing a fluorine atom and at least one monomer containing a triazine ring structure; Alternatively, the polyimide backbone contains a 1,3,5-triazine ring structure.

[0009] Furthermore, the fluorinated diamine monomer is selected from one or more of 2,2'-bis(trifluoromethyl)benzidine, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, and 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene; Or, the triazine diamine monomer is selected from one or more of 2,4-diamino-6-phenyl-1,3,5-triazine, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine, and 2,4-diamino-6-(4-amino-3-methylphenyl)-1,3,5-triazine; Or, the tetracarboxylic dianhydride monomer is selected from one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride.

[0010] Furthermore, the molar ratio of the fluorinated monomer to the triazine ring monomer is 1:1 to 5:1.

[0011] A second aspect of this application provides a method for preparing a liquid crystal alignment agent, characterized by comprising the following steps: S1. Copolymerization reaction: Fluorine-containing monomers and triazine-containing monomers undergo a polycondensation reaction in a polar aprotic solvent to generate a polyamic acid solution; S2, Imidification treatment: The polyamic acid solution is subjected to imidization treatment to obtain polyimide resin; S3. Solution adjustment and filtration: Take the polyimide resin from S2, add solvent to adjust the concentration and viscosity, filter to remove gel and impurities, and obtain a liquid crystal alignment agent with a solid content of 3%-10%.

[0012] Furthermore, the imidization treatment in step S2 is either chemical imidization or thermal imidization. Furthermore, after stirring the reaction at room temperature, the reaction was then heated to continue. Alternatively, thermal imidization involves coating a polyamic acid solution onto a substrate to form a thin film, drying it, and then gradually heating it to a high temperature and holding it therefor a period of time.

[0013] Furthermore, in the chemical imidization treatment, the dehydrating agent is selected from aliphatic or aromatic acids, and the catalyst is selected from one or more of quinoline, triethylamine, 1,4-diazabicyclo(2.2.2)octane and pyridine, including but not limited to quinoline, triethylamine, 1,4-diazabicyclo(2.2.2)octane and pyridine.

[0014] Furthermore, the amount of dehydrating agent is 2 to 4 times the molar amount of polyamic acid, and the amount of catalyst is 1 to 3 times the molar amount of polyamic acid.

[0015] In a third aspect, this application provides a liquid crystal alignment film, which is prepared by coating, curing and aligning the liquid crystal alignment agent or the alignment agent obtained by the above-described preparation method.

[0016] In a fourth aspect, this application provides a liquid crystal display panel element in which the above-mentioned liquid crystal alignment film is used.

[0017] This application provides a liquid crystal alignment agent by introducing triazine rings and fluorine atoms into the polyimide backbone through molecular structure design. This technology, through the synergistic effect of triazine rings and fluorine atoms, simultaneously resolves the technical contradiction between ultraviolet light stability and pretilt angle control, providing a key material solution for high-end liquid crystal display devices with balanced performance, and achieving the following significant technical effects: 1. Significantly improved UV stability: The photodegradation rate of the material under 365nm UV light irradiation is reduced by about 40% compared with traditional liquid crystal alignment agents, effectively extending the service life of the display panel, while reducing low molecular weight byproducts generated by photodegradation and reducing the risk of liquid crystal cell ion contamination.

[0018] 2. Pretilt Angle Control Precision and Stability Optimization: Through precise control of the surface polarity component, the pretilt angle of the liquid crystal molecules is stably controlled within the optimal range of 88°-89° (test value reaches 88.7°), meeting the stringent requirements of PSVA technology for high pretilt angles and significantly improving the contrast ratio of the display panel (up to 16000:1).

[0019] 3. Improved surface morphology and roughness: The surface roughness of the alignment film is maintained within the ideal range of 4.8-5.2nm, ensuring the uniformity and consistency of liquid crystal molecule arrangement, providing a structural basis for high-resolution displays.

[0020] 4. Comprehensive upgrade in display performance: The LCD response speed has been significantly improved to below 5ms, and the image persistence time has been reduced by more than 40% (minimum 0.6 seconds), maintaining excellent dynamic display effects even in 4K / 120Hz high refresh rate scenarios.

[0021] 5. Enhanced reliability and durability: The material's moisture absorption rate is significantly reduced, and it can still maintain stable performance in high temperature and high humidity environments of 85℃ / 85%RH. The uniformity error of the film thickness is controlled within ±5%, which is suitable for the large-scale production needs of high-generation LCD panels. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0023] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] The present application will now be described in detail with reference to the embodiments.

[0026] This application provides a liquid crystal alignment agent comprising a polyimide resin and a solvent. The polyimide resin is prepared by copolymerization of a dianhydride monomer and a diamine monomer, wherein the diamine monomer includes a fluorinated diamine monomer and a diamine monomer containing a triazine ring structure.

[0027] Specifically, the liquid crystal alignment agent of this application has the following structural features: In polyimide resins, the main chain contains fluorine substituents, preferably trifluoromethyl (-CF3) or hexafluoroisopropyl (-C(CF3)2-) structures.

[0028] Introducing fluorine atoms, especially fluorine-containing substituents, into polyimide resin can reduce the surface free energy of the polyimide alignment film, improve hydrophobicity, and significantly reduce the moisture absorption rate of the polyimide alignment film, thereby improving the reliability of the display panel in high temperature and high humidity environments. Fluorine substituents can absorb some ultraviolet light energy, reduce the damage of light to the molecular chain, reduce the photodegradation rate, and thus improve ultraviolet light stability, thereby extending the service life of the material.

[0029] Introducing a triazine ring structure into the main chain of polyimide resin, the triazine ring being a rigid planar structure, can enhance the regularity of the molecular chain in polyimide resin, thereby improving the material's thermal stability and UV absorption capacity.

[0030] Furthermore, in order to better coordinate ultraviolet light stability and pretilt angle control performance, this application adjusts the ratio of fluorine-containing monomers and triazine-containing monomers to achieve precise control of material properties.

[0031] The molar ratio of fluorinated monomer to triazine-containing monomer is between 1:1 and 5:1. If the proportion of fluorinated monomer is too low, the hydrophobicity of the alignment film may deteriorate, making it more susceptible to moisture corrosion and reducing its UV stability. If the proportion of triazine-containing monomer is too low, the heat resistance of the alignment film may be insufficient, posing a potential risk to its mechanical properties and affecting the material's mechanical strength. The molar ratio of fluorinated monomer to triazine-containing monomer can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, or any range of two of these values. More preferably, the molar ratio of fluorinated monomer to triazine-containing monomer is between 1:1 and 3:1.

[0032] This application introduces fluorine and triazine ring structures into the polyimide resin backbone. Through the synergistic effect of triazine ring and fluorine atoms, the stability of the material under 365nm ultraviolet light is significantly improved, and the photodegradation rate is reduced by about 40% compared with traditional liquid crystal alignment agents.

[0033] A second aspect of this application provides a method for preparing a liquid crystal alignment agent, comprising the following steps: S1. Copolymerization reaction: The dianhydride monomer and the diamine monomer are subjected to a polycondensation reaction in the first solvent to generate a polyamic acid solution; S2, Imidification treatment: The polyamic acid solution is imidized to convert it into a polyimide solution; S3. Solution adjustment: Adjust the concentration and viscosity of the polyimide solution to obtain an orientation agent composition with a solid content of 3%-10%.

[0034] Specifically, in step S1, the dianhydride monomer and the diamine monomer each independently include a fluorinated monomer and / or a monomer containing a triazine ring structure. As an example, the dianhydride monomer and the diamine monomer may be selected from the following options: 1. Dihydride monomers include fluorinated dianhydride monomers and dianhydride monomers containing triazine ring structures; diamine monomers include fluorinated diamine monomers and diamine monomers containing triazine ring structures. 2. Dianhydride monomers include fluorinated dianhydride monomers, and diamine monomers include diamine monomers containing a triazine ring structure; 3. Dianhydride monomers include dianhydride monomers containing a triazine ring structure, and diamine monomers include fluorinated diamine monomers; 4. Dihydride monomers include fluorinated dianhydride monomers and dianhydride monomers containing triazine ring structures; diamine monomers do not include fluorinated diamine monomers and diamine monomers containing triazine ring structures. 5. Diamine monomers include fluorinated diamine monomers and diamine monomers containing triazine ring structures, while dianhydride monomers do not include fluorinated dianhydride monomers and dianhydride monomers containing triazine ring structures.

[0035] Fluorine-containing monomers and / or monomers containing triazine ring structures can be selected from commercially available monomers or self-synthesized monomers.

[0036] The solvent is a polar aprotic solvent, selected from one or more of, but not limited to, N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), and sulfolane. The key to this application lies in the selection and combination of monomers, achieving the target performance through the rational design of monomer structures. The following are preferred monomers and their chemical structures: The fluorinated diamine monomer is selected from one or more of 2,2'-bis(trifluoromethyl)benzidine (TFMB), 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, and 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene.

[0037] The 2,2'-bis(trifluoromethyl)benzidine (TFMB) monomer contains two trifluoromethyl side groups, which significantly reduces the surface free energy of polyimide and improves its hydrophobicity. The 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl monomer exhibits greater molecular rigidity, which is beneficial for improving the thermal stability of the material. The 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene monomer is linked by ether bonds, possessing a certain degree of flexibility, which is beneficial for improving solution processing performance.

[0038] The triazine diamine monomer is selected from one or more of the following, including but not limited to 2,4-diamino-6-phenyl-1,3,5-triazine, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine, and 2,4-diamino-6-(4-amino-3-methylphenyl)-1,3,5-triazine.

[0039] The monomer 2,4-diamino-6-phenyl-1,3,5-triazine possesses a planar rigid structure, which enhances the regularity and UV absorption capacity of polyimides. 2,4-Diamino-6-(4-aminophenyl)-1,3,5-triazine contains additional amino groups, increasing reactivity and intermolecular interactions. 2,4-Diamino-6-(4-amino-3-methylphenyl)-1,3,5-triazine improves solubility by adjusting steric hindrance through methyl substitution.

[0040] In addition to fluorinated monomers and / or triazine-containing monomers, diamine monomers may also be selected from one or more of the following: 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PPD), m-phenylenediamine (MPD), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 3,3'-dimethyl-4,4'-diaminobiphenyl (DMBZ), 1,3-bis(4-aminophenoxy)benzene (TPER), 1,4-bis(4-aminophenoxy)benzene (APB), 4,4'-diaminodiphenylmethane (MDA), isophorone diamine (IPDA), 4,4'-diaminodicyclohexylmethane (PACM), and 1,6-hexanediamine (HMDA).

[0041] Furthermore, in the diamine monomer, the molar ratio of fluorine-containing monomers and triazine-containing monomers to all monomers is not less than 50%.

[0042] The dianhydride monomer is selected from one or more of the following, including but not limited to 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 4,4'-oxobisphthalic anhydride (ODPA), and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA).

[0043] 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride (BPDA): This monomer possesses a rigid biphenyl structure, which is beneficial for improving the thermal stability and mechanical properties of polyimides. 4,4'-Oxybisphthalic anhydride (ODPA): This monomer is linked by ether bonds, exhibiting a degree of flexibility, which is beneficial for improving the flexibility and adhesion of films. 2,2'-Bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA): This monomer contains both fluorine atoms and a rigid structure, which synergistically enhances the overall performance of the material.

[0044] Preferably, the diamine monomer in the comonomer includes fluorinated diamine monomers and diamine monomers containing triazine ring structures, and the dianhydride monomer does not include fluorinated dianhydride monomers and dianhydride monomers containing triazine ring structures.

[0045] As a specific implementation, step S1 includes step S1.1 monomer synthesis, which involves synthesizing fluorine-containing diamine monomers and / or dianhydride monomers, and diamine monomers and / or dianhydride monomers containing triazine rings.

[0046] The detailed steps of the preparation method are as follows: Step S1.1: Monomer Synthesis Synthesis of triazine cyclodiamine monomer: Taking 2,4-diamino-6-phenyl-1,3,5-triazine as an example, the cyanuric chloride method was used for synthesis: Cyanuric chloride (1.0 mol) was dissolved in anhydrous tetrahydrofuran and cooled to -10°C under nitrogen protection. A tetrahydrofuran solution of phenylboronic acid (1.1 mol) was slowly added dropwise over a period of 1 hour. After the addition was complete, the reaction temperature was raised to room temperature, and the reaction was stirred for another 24 hours. After the reaction was completed, the reaction mixture was washed with dilute hydrochloric acid to separate the organic phase. The organic phase was dried over anhydrous magnesium sulfate and the solvent was removed by vacuum distillation. The residue was recrystallized from ethanol to obtain white crystalline 2,4-dichloro-6-phenyl-1,3,5-triazine. The above product (1.0 mol) was refluxed with excess ammonia (25%) in an ethanol solution for 12 hours. After cooling to room temperature, the precipitate was collected by filtration and washed with water until neutral. Vacuum drying yielded the target product 2,4-diamino-6-phenyl-1,3,5-triazine, with a yield of over 85%.

[0047] Synthesis of fluorinated diamine monomers: Taking 2,2'-bis(trifluoromethyl)benzidine (TFMB) as an example: 1.0 mol of 2,2'-dinitrobiphenyl was dissolved in glacial acetic acid. 3.0 mol of trifluoroacetic anhydride was slowly added, and the mixture was stirred at room temperature for 48 hours. After the reaction was complete, the mixture was poured into ice water, and a yellow precipitate formed. The precipitate was collected by filtration and washed with ice water until neutral. The obtained 2,2'-dinitro-4,4'-bis(trifluoromethyl)biphenyl was dissolved in ethanol. A palladium-on-carbon catalyst (10% Pd / C, 0.1 mol) was added, and catalytic reduction was carried out under a hydrogen atmosphere. After the reaction was complete, the catalyst was removed by filtration, and the solvent was removed by vacuum distillation. The residue was recrystallized from ethanol to obtain white crystalline TFMB with a yield of over 90%.

[0048] Step S1, the specific operation of the copolymerization reaction is as follows: Under a protective gas atmosphere, diamine monomers, including fluorinated diamine monomers and triazine-containing diamine monomers, are dissolved in a solvent and stirred until completely dissolved. Tetracarboxylic acid dianhydride monomers are added in batches to the solution under a water bath at 0-5°C, avoiding localized overheating. After the addition is complete, the reaction is continued at a low temperature with stirring for 1-4 hours, then moved to room temperature and reacted for another 12-36 hours to obtain a viscous polyamic acid solution. During the reaction, the solution viscosity is measured periodically; the reaction is stopped when the viscosity reaches 30-50 CP.

[0049] The molar ratio of fluorinated monomer to triazine-containing monomer is 1:1 to 5:1. If the proportion of fluorinated monomer is too low, the hydrophobicity of the alignment film may deteriorate, making it susceptible to moisture corrosion and reducing its UV stability. If the proportion of triazine-containing monomer is too low, the heat resistance of the alignment film may be insufficient, posing a potential risk to its mechanical properties and affecting the material's mechanical strength. More preferably, the molar ratio of fluorinated monomer to triazine-containing monomer is 1:1 to 3:1.

[0050] The specific steps of step S2, imidization treatment, are as follows: Chemical imidization method: A dehydrating agent and a catalyst are added to the above polyamic acid solution. The reaction is stirred at room temperature for 0.5-2 hours, and then continued at 60-90°C for 2-4 hours. After the reaction is complete, the solution is poured into a large amount of deionized water, and a polymer precipitate is formed. The precipitate is collected by filtration and repeatedly washed with deionized water until neutral. After vacuum drying, polyimide powder is obtained.

[0051] The dehydrating agent is selected from aliphatic or aromatic acids, including but not limited to acetic anhydride, and the catalyst is selected from one or more of quinoline, triethylamine, 1,4-diazabicyclo(2.2.2)octane (DABCO) and pyridine, preferably pyridine.

[0052] The amount of dehydrating agent used is 2 to 4 times the molar amount of polyamic acid, and the amount of catalyst used is 1 to 3 times the molar amount of polyamic acid. The calculations here are based on the theoretical ratio of 1 mol dianhydride and 1 mol diamine to synthesize 1 mol polyamic acid.

[0053] Thermal imidization: A polyamic acid solution is coated onto a glass substrate to form a uniform thin film. It is then dried at 60-100°C for 1-3 hours to remove most of the solvent. Next, under a nitrogen atmosphere, the temperature is gradually increased to 230-280°C at a rate of 1-5°C / min and held at this temperature for 1-3 hours. After cooling to room temperature, a polyimide film is obtained.

[0054] Step S3, solution conditioning and filtration, i.e., the specific operations for preparing the liquid crystal alignment agent are as follows: The obtained polyimide powder is redissolved in a second solvent to prepare a solution with a solid content of 5%-15% and a viscosity of 30-50 CP. The solution is then filtered through a microporous membrane to remove gel and impurity particles, yielding the final orientation agent composition for later use.

[0055] A third aspect of this application provides a liquid crystal alignment film, which is obtained by coating, curing, and aligning a liquid crystal alignment agent obtained through the above preparation onto a substrate.

[0056] Specifically, the preparation method of a liquid crystal alignment film is as follows: The ITO glass substrate is ultrasonically cleaned sequentially with detergent, deionized water, and acetone, and then dried with nitrogen. An alignment agent solution is coated onto the ITO glass surface using a spin coating method, with the spin speed controlled at 1000-3000 rpm for 30-60 seconds. After coating, it is pre-baked at 60-90℃ for 5-15 minutes to remove residual solvent. Then, it is hardened at 180-220℃ for 20-40 minutes to form an alignment film with a thickness of 50-100 nm. Optionally, the alignment film is subjected to ultraviolet light alignment treatment, using 365nm polarized ultraviolet light irradiation with a dose controlled at 100-500 mJ / cm².

[0057] This application provides a liquid crystal alignment agent containing a triazine-fluorine copolymer structure. Through the synergistic effect of the triazine ring and fluorine atoms, the material's stability under 365nm ultraviolet light is significantly improved, and the photodegradation rate is reduced by approximately 40% compared to traditional liquid crystal alignment agents, effectively extending the lifespan of the display panel. The surface polarity component is precisely controlled, and the pretilt angle can be stably controlled within the optimal range of 88°-89°, meeting the stringent requirements of PSVA technology for high pretilt angles and significantly improving the contrast of the display panel. The film surface roughness is maintained within the ideal range of 4.8-5.2nm, ensuring the uniformity and consistency of liquid crystal molecule arrangement and improving display quality. The liquid crystal response speed is increased to below 5ms, and the image persistence duration is shortened by more than 40%, significantly improving display performance. The film thickness uniformity is excellent, with thickness error controlled within ±5%, suitable for large-scale production of high-generation liquid crystal panels. The material's moisture absorption rate is significantly reduced, improving the reliability of the display panel in high-temperature and high-humidity environments. Through molecular structure design, the synergistic optimization of ultraviolet light stability and pretilt angle control performance is achieved, overcoming the technical challenge of traditional materials requiring trade-offs between different properties.

[0058] Specifically, the following examples will further illustrate this.

[0059] Example 1: Raw material ratio: Diamine monomers: 2,2'-bis(trifluoromethyl)benzidine (TFMB): 0.3 mol; 2,4-diamino-6-phenyl-1,3,5-triazine: 0.1 mol Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.4 mol Solvent: N-methylpyrrolidone (NMP) Preparation steps: S1. Under nitrogen protection, TFMB and the triazine cyclodiamine monomer were dissolved in NMP solvent and stirred until completely dissolved. BPDA powder was added in batches to the solution under ice-water bath conditions (0-5℃). After the addition was complete, the reaction was continued at low temperature for 3 hours, then moved to room temperature and reacted for another 24 hours to obtain a viscous polyamic acid solution.

[0060] S2. Add acetic anhydride and pyridine to the above solution as dehydrating agent and catalyst, respectively. The amount of dehydrating agent is 3 times the molar amount of polyamic acid, and the amount of catalyst is 2 times the molar amount of polyamic acid. React at 120°C for 5 hours to carry out chemical imidization. After the reaction is completed, precipitate the polymer with acetone, wash and dry to obtain polyimide powder for later use.

[0061] S3. Take the polyimide powder obtained in step S2, redissolve it in NMP, and prepare an alignment agent solution with a solid content of 8%. Filter the solution through a 0.45μm microporous membrane to obtain the finished liquid crystal alignment agent A1.

[0062] Preparation of liquid crystal alignment film: Alignment film coating: On a clean ITO glass substrate, the alignment agent solution (solid content 8%) prepared in Example 1 was coated by spin coating at a speed of 2000 rpm for 45 seconds to form a uniform alignment film layer with a thickness of 80 nm.

[0063] Pre-baking and hardening: After coating, pre-baking is performed on an 80°C hot plate for 10 minutes to remove residual solvent, followed by hardening at 200°C for 30 minutes to ensure that the orientation film is fully cured and has a stable molecular arrangement structure.

[0064] Ultraviolet alignment treatment: The surface of the alignment film is irradiated with 365 nm polarized ultraviolet light, and the light dose is controlled at 300 mJ / cm² to precisely adjust the pretilt angle of the liquid crystal molecules to 88.7°, thus obtaining liquid crystal alignment film B1.

[0065] Liquid crystal cell assembly: The processed alignment film substrate is aligned and assembled with the opposing ITO glass substrate (also coated with alignment agent), the cell thickness is controlled by 5 μm glass spacers, and the liquid crystal cell is formed by sealing with sealant.

[0066] Liquid crystal injection and sealing: Nematic liquid crystal material (such as 5CB or commercial PSVA liquid crystal mixture) is injected into the liquid crystal cell under vacuum environment, and then sealed with UV curing adhesive to ensure no air bubbles remain.

[0067] Polymer network formation: A specific voltage (e.g., 5 Vrms, 1 kHz) is applied to the liquid crystal-injected panel, while irradiation with 365 nm ultraviolet light (intensity 500 mW / cm²) for 30 seconds induces monomer polymerization in the liquid crystal layer to form a stable polymer network structure, ultimately yielding liquid crystal cell Q1. After continuous irradiation under 365 nm ultraviolet light for 500 hours, the pretilt angle drift is less than 0.5°, and there is no significant degradation of the film layer.

[0068] Example 2 The main difference from Example 1 is: Raw material ratio: Diamine monomers: 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene: 0.25 mol, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine: 0.15 mol; Dihydride monomer: 4,4'-O-diphthalic anhydride (ODPA): 0.4 mol.

[0069] The finished liquid crystal alignment agent A2, liquid crystal alignment film B2, and liquid crystal cell Q2 are obtained.

[0070] Example 3 The main difference from Example 1 is: Raw material ratio: Diamine monomer: 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene: 0.2 mol, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine: 0.2 mol; Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.4 mol.

[0071] The finished liquid crystal alignment agent A3, liquid crystal alignment film B3, and liquid crystal cell Q3 are obtained.

[0072] Example 4 The main difference from Example 1 is: Raw material ratio: Diamine monomer: 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene: 0.1 mol, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine: 0.3 mol; Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.4 mol.

[0073] The finished liquid crystal alignment agent A4, liquid crystal alignment film B4, and liquid crystal cell Q4 are obtained.

[0074] Example 5 The main difference from Example 1 is: Raw material ratio: Diamine monomer: 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene: 0.5 mol, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine: 0.1 mol; Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.6 mol.

[0075] The finished liquid crystal alignment agent A5, liquid crystal alignment film B5, and liquid crystal cell Q5 are obtained.

[0076] Example 6 The main difference from Example 1 is: Raw material ratio: Diamine monomer: 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene: 0.3 mol, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine: 0.1 mol, 4,4'-diaminodiphenyl ether: 0.4 mol; Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.8 mol.

[0077] The finished liquid crystal alignment agent A6, liquid crystal alignment film B6, and liquid crystal cell Q6 are obtained.

[0078] Comparative Example 1: The main difference from Example 1 is: Diamine monomer: 2,2'-bis(trifluoromethyl)benzidine (TFMB): 0.4 mol; Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.4 mol The finished liquid crystal alignment agent A7, liquid crystal alignment film B7, and liquid crystal cell Q7 are obtained.

[0079] Comparative Example 2: The main difference from Example 1 is: Diamine monomer: 2,4-diamino-6-phenyl-1,3,5-triazine: 0.4 mol; Dianhydride monomer: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA): 0.4 mol The finished liquid crystal alignment agent A8, liquid crystal alignment film B8, and liquid crystal cell Q8 are obtained.

[0080] The liquid crystal alignment agents A1-A8, liquid crystal alignment films B1-B8, and liquid crystal cells Q1-Q8 prepared in Examples 1-6 and Comparative Examples 1-2 were tested. The performance testing methods are as follows: Pretilt Angle Test: The pretilt angle was determined using the crystal rotation method. The prepared alignment film substrate and a blank ITO glass substrate were assembled into a liquid crystal cell, with the cell thickness controlled at 5 μm. A standard nematic liquid crystal (e.g., 5CB) was injected. The optical texture of the liquid crystal cell was observed using a polarizing microscope. The crystal platform was rotated, and the angle of the extinction position was recorded to calculate the pretilt angle value.

[0081] UV stability test: The alignment film sample was irradiated under 365 nm UV light with an intensity of 500 mW / cm². Periodic sampling was performed to measure film thickness changes and surface morphology. Fourier transform infrared spectroscopy (FTIR) was used to monitor molecular structure changes. The photodegradation rate constant was calculated, with the data from Comparative Example 1 sample recorded as 100%. The percentage of comparative data from other examples compared to Comparative Example 1 sample data was recorded as the test results.

[0082] Surface roughness: The test method is as follows: Atomic force microscopy (AFM) was used for testing. The alignment agent solution was spin-coated onto a glass substrate, pre-baked at 80℃ for 10 minutes, and hardened at 200℃ for 30 minutes. The substrate was then scanned using an AFM at room temperature. The scanning range was 5 μm × 5 μm, and the scanning rate was 1 Hz. The arithmetic mean surface roughness Ra value was measured. Five different locations were randomly selected for measurement on each sample, and the average value was taken as the final result.

[0083] Electro-optical performance testing: Assemble a complete PSVA liquid crystal display panel. Measure the contrast ratio of the display panel using a spectrophotometer. Record the liquid crystal response time using an oscilloscope. Continuously display the standard test image for 24 hours and measure image retention.

[0084] The experimental data for Examples 1-6 and Comparative Examples 1-2 are shown in Table 1: Table 1 As can be seen from the test results of the examples and comparative examples in Table 1, the liquid crystal alignment agent containing a triazine-fluorine copolymer structure of this application exhibits significant advantages in both ultraviolet light stability and pretilt angle control. The alignment agent provided in this application achieves precise control of a high pretilt angle (88.7°) in a 55-inch 4K PSVA LCD TV panel, significantly improving the panel's contrast, response speed, and image stability. Simultaneously, its excellent ultraviolet light stability (38% reduction in photodegradation rate) ensures the panel's reliability during long-term use, making it particularly suitable for high-end display products requiring large size, high resolution, and long lifespan.

[0085] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A liquid crystal alignment agent, characterized in that, It includes a polyimide resin and a solvent, wherein the polyimide resin backbone contains fluorine substituents and a triazine ring structure.

2. The orientation agent according to claim 1, characterized in that, The polyimide resin is obtained by polymerization of dianhydride and diamine monomer, wherein the diamine monomer includes at least one monomer containing fluorine atoms and at least one monomer containing a triazine ring structure; Alternatively, the polyimide backbone contains a 1,3,5-triazine ring structure.

3. The orientation agent according to claim 2, characterized in that, The fluorinated diamine monomer is selected from one or more of 2,2'-bis(trifluoromethyl)benzidine, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, and 1,3-bis(3-amino-4-trifluoromethylphenoxy)benzene; Or, the triazine diamine monomer is selected from one or more of 2,4-diamino-6-phenyl-1,3,5-triazine, 2,4-diamino-6-(4-aminophenyl)-1,3,5-triazine, and 2,4-diamino-6-(4-amino-3-methylphenyl)-1,3,5-triazine; Or, the tetracarboxylic dianhydride monomer is selected from one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride.

4. The orientation agent according to claim 2, characterized in that, The molar ratio of the fluorinated monomer to the triazine ring monomer is 1:1 to 5:

1.

5. A method for using a liquid crystal alignment agent, characterized in that, Includes the following steps: S1. Copolymerization reaction: Fluorine-containing monomers and triazine-containing monomers undergo a polycondensation reaction in a polar aprotic solvent to generate a polyamic acid solution; S2, Imidification treatment: The polyamic acid solution is subjected to imidization treatment to obtain polyimide resin; S3. Solution adjustment and filtration: Take the polyimide resin from S2, add solvent to adjust the concentration and viscosity, filter to remove gel and impurities, and obtain a liquid crystal alignment agent with a solid content of 3%-10%.

6. The method according to claim 5, characterized in that, The imidization treatment in step S2 is either chemical imidization or thermal imidization. Or, the chemical imidization treatment includes adding a dehydrating agent and a catalyst to a polyamic acid solution, stirring the reaction at room temperature, and then heating to continue the reaction; Alternatively, the thermal imidization process includes coating a polyamic acid solution onto a substrate to form a thin film, drying it, and then gradually heating it to a high temperature and maintaining it for a period of time.

7. The method according to claim 6, characterized in that, In the chemical imidization treatment, the dehydrating agent is selected from aliphatic or aromatic acids, and the catalyst is selected from one or more of quinoline, triethylamine, 1,4-diazabicyclo(2.2.2)octane and pyridine.

8. The method according to claim 7, characterized in that, The amount of the dehydrating agent is 2 to 4 times the molar amount of polyamic acid, and the amount of the catalyst is 1 to 3 times the molar amount of polyamic acid.

9. A liquid crystal alignment film, characterized in that, The liquid crystal alignment film is prepared by coating, curing, and aligning an alignment agent obtained by any one of the liquid crystal alignment agents described in claims 1-4 or by any one of the preparation methods described in claims 5-8.

10. A liquid crystal display panel element, characterized in that, The element employs the liquid crystal alignment film layer as described in claim 9.

Images