Liquid crystal alignment agent, liquid crystal alignment film, liquid crystal display element and its preparation method

Abstract

This invention provides a liquid crystal alignment agent comprising the following components: soluble polyimide, additives, and solvent. The polyimide used to form a liquid crystal photoalignment film is prepared through the following steps: First, a polyamic acid solution with a specific molecular weight is prepared by reacting a diamine with a dianhydride; subsequently, the polyamic acid solution is esterified to obtain a polyamic acid ester with a certain esterification rate; finally, a chemical imidization reaction is carried out to obtain a soluble polyimide with a high imidization rate. This overcomes the drawbacks of traditional polyimide preparation at high temperatures (>200°C), avoiding a series of problems caused by high temperatures in the preparation process, such as stringent equipment requirements, increased energy consumption, and potential impact on material properties, thereby reducing preparation costs and broadening the applicability of the process.

Description

Technical Field

[0001] This invention relates to the field of polyimide material technology, and more specifically, to a liquid crystal alignment agent, a liquid crystal alignment film, a liquid crystal display element, and a method for preparing the same. Background Technology

[0002] The alignment layer is a crucial component of thin-film transistor-driven liquid crystal displays (TFT-LCDs). Its main function is to induce randomly arranged liquid crystal molecules to align in a specific direction, thereby enabling rapid response under an electric field and modulating light. Currently, the alignment layer used in TFT-LCD devices is primarily made of polyimide (PI), mainly because PI is an organic polymer material with a wide molecular design window, excellent film-forming properties, superior heat resistance and mechanical properties, excellent environmental stability, and resistance to abrasion treatment. With the continuous development of TFT-LCD panel application technology, the performance requirements for PI alignment layers are constantly increasing. Traditional PI alignment layer materials face numerous challenges in terms of liquid crystal molecule alignment stability and photoelectric properties. For example, mainstream wide-viewing-angle TFT-LCDs, such as in-plane switching (IPS) or edge field switching (FFS) TFT-LCDs, require the PI liquid crystal alignment film to have characteristics such as low moisture absorption, low temperature curing, high solubility, high voltage retention rate (VHR), low residual DC voltage (RDC), and the lowest possible pretilt angle (θp) for liquid crystal molecules, in order to give the display device good display effects, such as high contrast, low image retention, and low light leakage.

[0003] Currently, the curing temperature for PAA alignment agents is around 200-250℃. Resin films themselves have poor heat resistance; therefore, if the temperature during alignment layer formation is too high, the size or shape of the resin film will change, leading to a deviation in the alignment direction of the resulting alignment layer. This reduces the liquid crystal alignment capability and severely affects the quality of optical components or liquid crystal display components. Therefore, in practical applications, the curing temperature of PI alignment films must be below 230℃. Summary of the Invention

[0004] To address the shortcomings of the prior art, the first aspect of this application provides a liquid crystal alignment agent that can be cured at low temperatures and has good optical properties.

[0005] In a first aspect, this application provides a liquid crystal alignment agent comprising the following components: soluble polyimide, additives, and solvent; Polyimide has the following structure: (Equation 1) R1 is a tetravalent organic group derived from aliphatic or alicyclic acid dianhydrides, and R2 is a diamine residue. R1 is selected from at least one of the following structures: R 1-1 , R 1-2 , R 1-3 , R 1-4 , R 1-5 , R 1-6 ; R4 is independently one or a combination of hydrogen atom, halogen atom, alkyl group with 1-6 carbon atoms, alkenyl group with 2-6 carbon atoms, alkynyl group with 2-6 carbon atoms, and monovalent organic group phenyl group with 1-6 carbon atoms containing fluorine atom; R2 is selected from a diamine residue with an aromatic ring structure.

[0006] Furthermore, R2 includes at least one of the following structures: , , , , , , , , , , , , , , , , , , , , , , , , , , ; Furthermore, by mass percentage, it includes 2% to 10% soluble polyimide, 30% to 50% additives, and 50% to 65% solvent.

[0007] A second aspect of this application provides a method for preparing the above-mentioned polyimide liquid crystal photoalignment agent, comprising the following steps: Step 1: Preparation of polyamic acid. Diamine is dissolved in a solvent, dianhydride is added, and the reaction is carried out to obtain a polyamic acid solution. Step 2: Polyamic acid esterification. Take the polyamic acid solution from Step 1, add the alcohol source and the first catalyst, and react to obtain a polyamic acid ester solution. Step 3: Preparation of soluble polyimide. Take the polyamic acid ester solution from step 2, add the second catalyst and dehydrating agent to obtain soluble polyimide. Step 4: Preparation of liquid crystal photoalignment agent: Take the soluble polyimide from step 3, add solvent and additives, stir, filter to remove impurities, and obtain liquid crystal alignment agent.

[0008] Furthermore, at least one of the following conditions must be met in step 1: (1) The reaction atmosphere is a protective atmosphere; (2) The molar ratio of dianhydride to diamine is 0.9-1.1:1; (3) The solid content of the solute during the reaction stage is 10%-30%; (4) The reaction temperature is 40-70℃ and the reaction time is 2-10h.

[0009] Furthermore, at least one of the following conditions must be met in step 2: (1) The reaction atmosphere is a protective atmosphere; (2) The solid content of the polyamic acid solution is 4%~10%; (3) The alcohol source is selected from any one of methanol, ethanol, and propanol, including but not limited to methanol; (4) The first catalyst is selected from acidic catalysts and / or basic catalysts; (5) The acidic catalyst is selected from inorganic acids and / or organic acids; the inorganic acid is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, including but not limited to sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid; the organic acid is selected from at least one of formic acid and p-toluenesulfonic acid, including but not limited to formic acid and p-toluenesulfonic acid. (6) The alkaline catalyst is selected from at least one of alkaline metal salts and alkaline metal hydroxides; (7) The molar ratio of alcohol source to dianhydride is 0.8~1.4:1, and the molar ratio of catalyst to alcohol source is 1:1; (8) The reaction temperature is 50-90℃ and the reaction time is 10-15h; (9) The esterification rate of polyamide ester is 30%-60%.

[0010] Furthermore, at least one of the following conditions must be met in step 3: (1) The reaction atmosphere is a protective atmosphere; (2) The solid content of the polyamic acid ester solution is 4%~10%; (3) The second 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; (4) The dehydrating agent is selected from aliphatic or aromatic organic acids or acid anhydrides; (5) The molar ratio of the second catalyst to the dianhydride is 1.6~2:1; the molar ratio of the dehydrating agent to the pyridine is 1:1; (6) The reaction temperature is 50-90℃ and the reaction time is 10-15h; (7) The imidization rate of soluble polyimide is 70%-90%.

[0011] Furthermore, the viscosity of polyamic acid is 800-1500 cp, and the weight-average molecular weight is 15000-30000 g / mol; Or, the aprotic polar solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0012] A third aspect of this application provides a liquid crystal alignment film, which is obtained by coating and curing using the liquid crystal alignment agent described above or a liquid crystal alignment agent prepared by the above preparation method.

[0013] In a fourth aspect, this application provides a liquid crystal display element that utilizes the aforementioned liquid crystal alignment film.

[0014] This application provides a polyimide liquid crystal photoalignment agent, wherein the polyimide contained in it for forming a liquid crystal photoalignment film is prepared by the following steps: First, a polyamic acid solution with a specific molecular weight is prepared by reacting a diamine with a dianhydride; subsequently, the polyamic acid solution is esterified to obtain a polyamic acid ester with a certain esterification rate; finally, a chemical imidization reaction is carried out to obtain a soluble polyimide with a high imidization rate. On the one hand, this overcomes the drawback of traditional polyimides requiring high-temperature (>200℃) preparation, avoiding a series of problems caused by high temperatures in the preparation process, such as stringent equipment requirements, increased energy consumption, and potential impact on material properties, thereby reducing preparation costs and broadening the applicability of the process; on the other hand, it improves the difficulty of dissolving soluble SPI at high imidization rates, making the material handling during preparation simpler and helping to improve the stability and controllability of the preparation process. Ultimately, the fabricated liquid crystal display element possesses excellent performance such as high voltage retention rate (VHR) and good contrast ratio, significantly improving the display quality of the liquid crystal display and better meeting the market demand for high-quality display products. Detailed Implementation

[0015] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0016] 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.

[0017] 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.

[0018] The present invention will now be described in detail with reference to the embodiments.

[0019] A liquid crystal alignment agent comprising the following components: soluble polyimide, additives, and solvent; Polyimide has the following structure: (Equation 1) R1 is a tetravalent organic group derived from the dianhydride of aliphatic or alicyclic acid, i.e., R1 is a dianhydride residue, and R2 is the divalent portion of a diamine after removing the diamine group, i.e., R2 is a diamine residue. R1 includes at least one of the following structures: R 1-1 , R 1-2 , R 1-3 , R 1-4 , R 1-5 , R 1-6 ; R4 is independently one or a combination of hydrogen atom, halogen atom, alkyl group with 1-6 carbon atoms, alkenyl group with 2-6 carbon atoms, alkynyl group with 2-6 carbon atoms, and monovalent organic group phenyl group with 1-6 carbon atoms containing fluorine atom; R2 is selected from a diamine residue having an aromatic ring structure, and preferably, R2 includes at least one of the following structures: , , , , , , , , , , , , , , , , , , , , , , , , , , ; The soluble polyimide resin, additives, and solvent in the liquid crystal photoalignment are, by mass percentage, 2%~10% soluble polyimide, 30%~50% additives, and 50%~65% solvent.

[0020] Specifically, by mass percentage, the soluble polyimide can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two values; the additives can be 30%, 35%, 40%, 45%, 50%, or any two values; and the solvent can be 50%, 52%, 55%, 58%, 60%, 65%, or any two values.

[0021] Specifically, the additives include a leveling agent selected from at least one of ethylene glycol monobutyl ether, diethylene glycol ethyl ether acetate, polyether-modified polydimethylsiloxane, and acrylate resins; specifically, the solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide. By precisely proportioning the mass fraction of each component, the coating adaptability and surface smoothness of the liquid crystal alignment film can be effectively improved. The synergistic effect of the three components results in a smooth, uniform, and orderly alignment of the coating, ultimately producing a high-performance liquid crystal alignment film that meets the requirements of high-precision liquid crystal display devices for the surface quality and optical properties of the alignment film.

[0022] A second aspect of this application provides a method for preparing a polyimide liquid crystal photoalignment agent, comprising the following steps: Step 1: Preparation of polyamic acid. Diamine is dissolved in a solvent, dianhydride is added, and the reaction is carried out to obtain a polyamic acid solution. Step 2: Polyamic acid esterification. Take the polyamic acid solution from Step 1, add alcohol and the first catalyst, and react to obtain a polyamic acid ester solution. Step 3: Preparation of soluble polyimide. Take the polyamic acid ester solution from step 2, add the second catalyst and dehydrating agent to obtain soluble polyimide. Step 4: Preparation of liquid crystal photoalignment agent: Take the soluble polyimide from step 3, add solvent and additives, stir, filter to remove impurities, and obtain liquid crystal alignment agent.

[0023] Specifically, the preparation of polyamic acid in step 1 includes the following steps: Under a protective gas atmosphere, a certain amount of diamine is weighed, and then a certain amount of solvent is added. After stirring and dissolving, dianhydride is added, and stirring is continued until dissolved. The mixture is then heated at 40-70℃ for 2-10 hours, after which heating is stopped. After cooling, the preparation is complete, yielding a polyamic acid solution. The solvent of the polyamic acid solution is adjusted to dilute it to a solid content of 4%~10%, and it is stored at -10~-30℃ for later use.

[0024] Specifically, the molar ratio of dianhydride to diamine is 0.9-1.1:1; preferably, the molar ratio of dianhydride to diamine can be 0.9-1.0:1.

[0025] The solvent is selected from aprotic polar solvents, specifically, the solvent is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC).

[0026] The viscosity of polyamic acid is 800-1500 cp, and the weight-average molecular weight is 15000-30000 g / mol.

[0027] In step 2, the polyamic acid is esterified: specifically, under a protective gas atmosphere, a certain amount of polyamic acid solution (solid content 4%~10%) is weighed, and then a certain amount of alcohol source and catalyst are added. The content of alcohol source and dianhydride is such that the molar ratio of hydroxyl to dianhydride is 0.8~1.4:1, and the molar ratio of catalyst to alcohol source is 0.8~1.2:1. After stirring evenly, the reaction is carried out at 50-90℃ for 10-15 hours. After cooling to room temperature, the reaction is stopped, and polyamic acid ester is obtained with an esterification rate of 30%-60%. The prepared polyamic acid ester solution is stored at -30 to -10℃ for later use.

[0028] Since the ester group is neutral, it cannot provide protons to initiate and catalyze the imidization reaction, and the hydrogen bonds are destroyed after esterification, an excessively high esterification rate will lead to difficulties in imidization.

[0029] Specifically, the alcohol source is selected from monohydric alcohols, including but not limited to methanol, ethanol, and propanol; preferably, the alcohol source is methanol. The first catalyst is selected from acidic and / or basic catalysts; specifically, the acidic catalyst is selected from inorganic acids and organic acids; the inorganic acid is selected from at least one of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid; the organic acid is selected from at least one of formic acid and p-toluenesulfonic acid. The basic catalyst is selected from at least one of basic metal salts and basic metal hydroxides. Preferably, the first catalyst is p-toluenesulfonic acid. Preferably, the basic metal salt is selected from sodium carbonate, and the basic metal hydroxide is selected from sodium hydroxide.

[0030] In step 3, soluble polyimide (SPI) is prepared: under a protective atmosphere, a certain amount of polyamic acid ester (PAE) solution prepared in step 2 is weighed, a certain amount of the second catalyst and dehydrating agent are added, and after stirring evenly, the reaction is carried out at 50℃-90℃ for 10-15h. After cooling to room temperature, the reaction is stopped to obtain soluble polyimide resin.

[0031] Specifically, in step 3, the reaction atmosphere is a protective atmosphere, preferably a nitrogen atmosphere; the solid content of the selected polyamide ester solution is 4%~10%.

[0032] The second catalyst is selected from one or more of quinoline, triethylamine, 1,4-diazabicyclo(2.2.2)octane (DABCO), pyridine, etc.; the dehydrating agent is selected from aliphatic or aromatic organic acids or anhydrides, and the dehydrating agent is selected from at least one of acetic anhydride, trifluoroacetic anhydride and benzoic anhydride, including but not limited to acetic anhydride, trifluoroacetic anhydride and benzoic anhydride.

[0033] Specifically, the second catalyst is preferably pyridine, the dehydrating agent is preferably acetic anhydride, the molar ratio of the second catalyst to the dianhydride is 1.6~2:1, and the molar ratio of the dehydrating agent to the second catalyst is 0.8~1.2:1, so that the imidization rate of the soluble polyimide is 70%-90%.

[0034] The molar ratio of the second catalyst to the dianhydride can be 1.6, 1.7, 1.8, 1.9, 2, or any range of two values.

[0035] Step 4, Liquid crystal photoalignment agent: Weigh a certain amount of the soluble polyimide resin obtained in step 3, add solvent and additives to it, stir evenly to remove impurities, and obtain liquid crystal alignment agent.

[0036] The liquid crystal photoalignment agent provided in this application is a polyimide used to form a liquid crystal photoalignment film. The preparation steps are as follows: First, a polyamic acid solution with a certain molecular weight is prepared using diamine and dianhydride; then, the polyamic acid solution is esterified to obtain a polyamic acid ester with a certain esterification rate; finally, the polyamic acid ester is chemically imidized to obtain a soluble polyimide with a high imidization rate. This soluble polyimide is then formulated as a liquid crystal alignment agent. Using the technical solution of this application, when preparing the liquid crystal photoalignment agent into a thin film, it is only necessary to remove the solvent at 150°C, eliminating the need for further thermal imidization reactions above 200°C as in traditional methods. This effectively avoids the impact of high temperatures on the glass substrate, improves the stability and reliability of the glass substrate during the preparation process, and helps ensure the quality of subsequent products. Compared with traditional methods, this technical solution reduces the high-temperature thermal imidization step, simplifies the preparation process, saves preparation time and energy consumption to a certain extent, improves production efficiency, and reduces production costs.

[0037] A third aspect of this application provides a liquid crystal light alignment film.

[0038] Specifically, the liquid crystal alignment agent solution is coated onto an indium tin oxide glass substrate and dried to remove the solvent, thus obtaining a thin film.

[0039] Under N2 protection, the film was pre-baked at 80°C for 2 minutes to remove more than 80% of the solvent, followed by drying at 150°C for 30 minutes to remove residual solvent, catalyst (p-benzenesulfonic acid, pyridine), and dehydrating agent. By adjusting the coating parameters, a final film thickness of 100 nm was obtained. The prepared film was irradiated with linearly polarized ultraviolet (PUV) light at a wavelength of 254 nm, with an exposure dose typically ranging from 200 to 1000 mJ. This caused photodecomposition of the polyimide chains along the polarization direction and slight photosynthesis of the chains perpendicular to the polarization direction, thereby achieving good alignment of the liquid crystal. The photolysis products were then first removed by rinsing with deionized water (BOC) and further removed by high-temperature sublimation (PAO) at 180°C for 20 minutes.

[0040] The coating method can be achieved through processes such as relief printing (APR COATING), spin coating (SPIN COATING), and inkjet printing (INKJET PRINTING).

[0041] A fourth aspect of this application provides a liquid crystal display element, particularly an FFS / IPS liquid crystal display element.

[0042] Fabrication of the liquid crystal cell (FFS / IPS liquid crystal display element): The two substrates described above are grouped together. Using a dispensing machine, photocurable adhesive containing 3μm spacers is printed onto the edge of one glass substrate. The other substrate is then bonded together with their respective liquid crystal alignment films aligned at 0°. The bonded substrates are then pressed together and heated in a 150°C hot air circulating oven for 60 minutes to cure the sealant, creating a blank cell. Positive liquid crystal MLC-3019 (manufactured by Merck) is injected into this blank cell using a reduced-pressure injection method, and the injection port is sealed, thus obtaining the FFS-driven liquid crystal cell.

[0043] The liquid crystal alignment agent provided in this application is coated onto indium tin oxide glass using a coating process. After removing the solvent by heating, it is exposed to linearly polarized light at a wavelength of 254 nm to prepare a liquid crystal optical alignment film. Liquid crystal displays are fabricated using indium tin oxide glass spin-coated with the liquid crystal vertical alignment agent of this invention.

[0044] Since this application mainly focuses on the synthesis process, the molecular structure design will not be changed in theory. In theory, most polyamic acids can be used to prepare soluble polyimides through the above process, which has wide industrial applicability. The additives used in this application are all removable at low temperatures, which overcomes the problem of needing to clean them later (for example, if the additive is a metal salt, if it is not cleaned, the metal ions will affect the performance of the display element). If cleaning is required, it may lead to problems such as a decrease in molecular weight and deterioration. The soluble liquid crystal alignment agent prepared in this application only requires solvent removal at 150°C during the preparation of the alignment film, unlike the traditional method which requires solvent removal and further thermal imidization reaction at over 200°C. This avoids the impact of high temperature on the glass substrate to a certain extent. In the process described in this application, a polyamic acid ester with a certain esterification rate is first prepared, but not completely esterified. This improves solubility while avoiding the difficulty of further imidization reaction when the esterification rate is high.

[0045] The technical solution of this application overcomes the drawback of traditional polyimide liquid crystal alignment film preparation requiring high temperatures (>200℃), avoiding problems such as demanding equipment requirements, high energy consumption, and potential adverse effects on the properties of related materials caused by high-temperature preparation. This reduces preparation costs and broadens the applicability of the preparation process. It effectively improves the problem of difficult dissolution of soluble SPI at high imidization rates, making material handling more convenient during preparation and enhancing the stability and controllability of the preparation process. Based on these improvements, the final liquid crystal display element exhibits high voltage retention rate (VHR) and contrast ratio, improving the display quality of liquid crystal displays and meeting market demand for high-quality display products.

[0046] The technical solution of this application is further illustrated below through specific embodiments. In the following embodiments, the selected dianhydride is assumed to be R. 1-1 :1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA), the selected diamine is R by default. 2-19 4,4′-Diphenylamine (ODA), the default catalyst for the selected PAE is p-benzenesulfonic acid, and the default alcohol source is methanol; the default catalyst for the selected SPI is pyridine, and the default dehydrating agent is acetic anhydride. The default coating process is spin coating.

[0047] Example 1: S1, Synthetic polyamic acid (PAA): ODA (26.95 g, 0.1 mol) was dissolved in NMP (252.7 g) at a flow rate of 0.1 MPa and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. After stirring for about 30 minutes, a clear diamine solution was obtained. Then, CBDA (17.65 g, 0.09 mol) was added to the solution and the reaction was continued for 30 minutes. After all the CBDA was dissolved, the reaction was heated at 70 °C for 5 hours. After cooling to room temperature, a PAA solution with a solid content of 15% was obtained. Then, 446.03 g of NMP was added to dilute the PAA to a solid content of 6 wt%. The solution was then stored at -20 °C and labeled PAA-1.

[0048] S2, Preparation of polyamic acid ester (PAE): Weigh 743g of PAA-1 at a flow rate of 0.1MPa N2 and place it in a 1000mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 2.304g of methanol and 12.39g of p-benzenesulfonic acid to the flask. Stir for 30min, then heat at 70℃ for 10h. Cool to room temperature and then store in a -20℃ refrigerator. Label it PAE-1.

[0049] That is, the molar ratio of the first catalyst to the dianhydride is 0.8:1, and the molar ratio of the alcohol source to the first catalyst is 1:1.

[0050] S3. Preparation of soluble polyimide SPI: Weigh 757 g of PAE-1 at a flow rate of 0.1 MPa N2 and place it in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 11.39 g of pyridine and 14.70 g of acetic anhydride to the flask. Stir for 30 min, then heat at 70 °C for 10 h. Cool to room temperature and store in a -20 °C refrigerator. Label it SPI-1.

[0051] That is, the molar ratio of the second catalyst to the dianhydride is 1.6:1, and the molar ratio of the dehydrating agent to the second catalyst is 1:1.

[0052] S4. Preparation of liquid crystal photoalignment agent: Weigh 100g of SPI-1 at a flow rate of 0.1MPa N2 and place it in a 500mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 80g of BC and 20g of NMP and stir until homogeneous. Filter the mixture using a syringe filter to remove insoluble impurities to obtain a liquid crystal alignment agent (3wt%). Store the agent in a -20℃ refrigerator and label it Q-1.

[0053] Liquid crystal cell fabrication: The indium tin oxide (ITO) glass substrate was sequentially cleaned with alkaline solution, detergent solution, water, and isopropanol. After drying, the liquid crystal alignment agent solution was spin-coated onto the ITO glass substrate. Under N2 protection, the substrate was pre-baked at 80°C for 2 minutes to remove more than 80% of the solvent, followed by drying at 150°C for 30 minutes to remove residual solvent, catalysts (p-benzenesulfonic acid, pyridine), and dehydrating agents. By adjusting the coating parameters, a final film thickness of 100 nm was obtained. The prepared film was irradiated with linearly polarized ultraviolet (PUV) light at a wavelength of 254 nm and an exposure dose of 500 mJ. This caused photodecomposition of the polyimide chains along the polarization direction and slight photosynthesis of the chains perpendicular to the polarization direction, thus achieving good alignment of the liquid crystal. The photolysis products were first removed by deionized water rinsing (BOC) and then further removed by high-temperature sublimation (PAO) at 180°C for 20 minutes. Finally, the two indium tin oxide glass thin film substrates (film side facing inward) prepared above were bonded together in antiparallel fashion using a photocurable adhesive containing 3μm spacers. The isotropic liquid crystal was then poured into the liquid crystal cell using a capillary method, and subsequently sealed with photocurable adhesive. The liquid crystal cell Cell-1 was obtained.

[0054] Example 2: The main difference from Example 1 is: In S2, 2.88 g of methanol and 15.49 g of p-benzenesulfonic acid were added, that is, the molar ratio of the first catalyst to the dianhydride was 1:1, and the molar ratio of the alcohol source to the first catalyst was 1:1, to obtain polyamic acid ester designated PAE-2.

[0055] S3. Preparation of soluble polyimide: 760 g of PAE-2 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 11.39 g of pyridine and 14.70 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-2. A liquid crystal photoaligning agent designated Q-2 and a liquid crystal cell Cell-2 were also prepared.

[0056] Example 3: The main difference from Example 1 is: In S2, 3.456 g of methanol and 18.59 g of p-benzenesulfonic acid were added, that is, the molar ratio of the first catalyst to the dianhydride was 1.2:1, and the molar ratio of the alcohol source to the first catalyst was 1:1, to obtain polyamic acid ester numbered PAE-3.

[0057] S3. Preparation of soluble polyimide: 764 g of PAE-3 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 11.39 g of pyridine and 14.70 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-3. A liquid crystal photoaligning agent designated Q-3 and a liquid crystal cell Cell-3 were also prepared.

[0058] Example 4: The main difference from Example 1 is: In S2, 4.032 g of methanol and 21.69 g of p-benzenesulfonic acid were added, that is, the molar ratio of the first catalyst to the dianhydride was 1.4:1, and the molar ratio of the alcohol source to the first catalyst was 1:1, to obtain polyamic acid ester numbered PAE-4.

[0059] S3. Preparation of soluble polyimide: 768 g of PAE-4 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 11.39 g of pyridine and 14.70 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-4. A liquid crystal photoaligning agent designated Q-4 and a liquid crystal cell Cell-4 were also prepared.

[0060] Example 5: The main difference from Example 1 is: In S3, 12.1 g of pyridine and 15.62 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.7:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-5. A liquid crystal photoaligning agent designated Q-5 and a liquid crystal cell, Cell-5, were also prepared.

[0061] Example 6: The main difference from Example 1 is: In S3, 12.8 g of pyridine and 16.52 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.8:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-6. A liquid crystal photoaligning agent designated Q-6 and a liquid crystal cell, Cell-6, were also prepared.

[0062] Example 7: The main difference from Example 1 is: In S3, 13.53 g of pyridine and 17.44 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.9:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-7. A liquid crystal photoaligning agent designated Q-7 and a liquid crystal cell, Cell-7, were also prepared.

[0063] Example 8: The main difference from Example 2 is that: In S3, 12.1 g of pyridine and 15.62 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.7:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-8. A liquid crystal photoaligning agent designated Q-8 and a liquid crystal cell, Cell-8, were also prepared.

[0064] Example 9: The main difference from Example 2 is that: In S3, 12.8 g of pyridine and 16.52 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.8:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-9. A liquid crystal photoaligning agent, designated Q-9, and a liquid crystal cell, Cell-9, were also prepared.

[0065] Example 10: The main difference from Example 2 is that: In S3, 13.53 g of pyridine and 17.44 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.9:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-10. A liquid crystal photoaligning agent designated Q-10 and a liquid crystal cell, Cell-10, were also prepared.

[0066] Example 11: The main difference from Example 3 is: In S3, 12.1 g of pyridine and 15.62 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.7:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-11. A liquid crystal photoaligning agent designated Q-11 and a liquid crystal cell Cell-11 were also prepared.

[0067] Example 12: The main difference from Example 3 is: In S3, 12.8 g of pyridine and 16.52 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.8:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-12. A liquid crystal photoaligning agent designated Q-12 and a liquid crystal cell, Cell-12, were also prepared.

[0068] Example 13: The main difference from Example 3 is: In S3, 13.53 g of pyridine and 17.44 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.9:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-13. A liquid crystal photoaligning agent designated Q-13 and a liquid crystal cell, Cell-13, were also prepared.

[0069] Example 14: The main difference from Example 4 is that: In S3, 12.1 g of pyridine and 15.62 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.7:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-14. A liquid crystal photoaligning agent designated Q-14 and a liquid crystal cell Cell-14 were also prepared.

[0070] Example 15: The main difference from Example 4 is that: In S3, 12.8 g of pyridine and 16.52 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.8:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-15. A liquid crystal photoaligning agent designated Q-15 and a liquid crystal cell Cell-15 were also prepared.

[0071] Example 16: The main difference from Example 4 is that: In S3, 13.53 g of pyridine and 17.44 g of acetic anhydride were added, i.e., the molar ratio of the second catalyst to the acetic anhydride was 1.9:1, and the molar ratio of the dehydrating agent to the second catalyst was 1:1, to obtain a soluble polyimide resin, designated SPI-16. A liquid crystal photoaligning agent designated Q-16 and a liquid crystal cell, Cell-16, were also prepared.

[0072] Example 17: The main difference from Example 1 is: S1, Synthetic PAA: ODA (26.95 g, 0.1 mol) was dissolved in NMP (258.28 g) at a flow rate of 0.1 MPa and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. After stirring for about 30 minutes, a clear diamine solution was obtained. Then, CBDA (18.63 g, 0.095 mol) was added to the solution and the reaction was continued for 30 minutes. After all the CBDA was dissolved, the reaction was heated at 70 °C for 5 hours. After cooling to room temperature, a PAA solution with a solid content of 15% was obtained. Then, 455.9 g of NMP was added to dilute the PAA to a solid content of 6 wt%. The solution was then stored at -20 °C and labeled PAA-2.

[0073] S2, Preparation of polyamic acid ester: Weigh 759.7 g of PAA-2 at a flow rate of 0.1 MPa and place it in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 2.432 g of methanol and 13.08 g of p-benzenesulfonic acid to the flask. Stir for 30 min, then heat at 70 °C for 10 h. Cool to room temperature and store in a -20 °C refrigerator. Label it PAE-5.

[0074] S3. Preparation of soluble polyimide: 775 g of PAE-5 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 14.27 g of pyridine and 18.43 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-17. A liquid crystal cell, Cell-17, was thus prepared.

[0075] Example 18: The main difference from Example 17 is that: In step S2, 759.7 g of PAA-2 was weighed at a flow rate of 0.1 MPa N2 and placed into a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 3.04 g of methanol and 16.359 g of p-benzenesulfonic acid were added. After stirring for 30 min, the mixture was heated at 70 °C for 10 h, cooled to room temperature, and then stored in a -20 °C refrigerator as PAE-6.

[0076] S3. Preparation of soluble polyimide: 779 g of PAE-6 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 14.27 g of pyridine and 18.43 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-18. A liquid crystal photoaligning agent designated Q-18 and a liquid crystal cell, Cell-18, were also prepared.

[0077] Example 19: The main difference from Example 17 is that: In step S2, 759.7 g of PAA-2 was weighed at a flow rate of 0.1 MPa N2 and placed into a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 3.648 g of methanol and 19.63 g of p-benzenesulfonic acid were added. After stirring for 30 min, the mixture was heated at 70 °C for 10 h, cooled to room temperature, and then stored in a -20 °C refrigerator as PAE-7.

[0078] S3. Preparation of soluble polyimide: 783 g of PAE-7 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 14.27 g of pyridine and 18.43 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-19. A liquid crystal photoaligning agent designated Q-19 and a liquid crystal cell Cell-19 were also prepared.

[0079] Example 20: The main difference from Example 17 is that: In step S2, 759.7 g of PAA-2 was weighed at a flow rate of 0.1 MPa N2 and placed into a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 4.256 g of methanol and 22.90 g of p-benzenesulfonic acid were added, and the mixture was stirred for 30 min. After stirring, the mixture was heated at 70 °C for 10 h, cooled to room temperature, and then stored in a -20 °C refrigerator as PAE-8.

[0080] S3. Preparation of soluble polyimide: 786 g of PAE-9 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 14.27 g of pyridine and 18.43 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-20. A liquid crystal photoaligning agent designated Q-20 and a liquid crystal cell Cell-20 were also prepared.

[0081] Comparative Example 1: The main difference from Example 1 is: S1, Polyamic Acid (PAA) Synthesis: ODA (26.95 g, 0.1 mol) was dissolved in NMP (252.7 g) at a flow rate of 0.1 MPa and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. After stirring for about 30 minutes, a clear diamine solution was obtained. Then, CBDA (17.65 g, 0.09 mol) was added to the solution and the reaction was continued for 30 minutes. After all the CBDA was dissolved, the reaction was heated at 70 °C for 5 hours. After cooling to room temperature, a PAA solution with a solid content of 15% was obtained. Then, 446.03 g of NMP was added to dilute the PAA to a solid content of 6 wt%. The solution was then stored at -20 °C and labeled PAA-1.

[0082] S2. Preparation of soluble polyimide: Weigh 746 g of PAA-1 at a flow rate of 0.1 MPa N2 and place it in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 13.53 g of pyridine and 17.44 g of acetic anhydride to the flask. Stir for 30 min, then heat at 70 °C for 10 h. Cool to room temperature and store in a -20 °C refrigerator, labeled SPI-21.

[0083] S3. Preparation of liquid crystal photoalignment agent: Weigh 100g of SPI-21 at a flow rate of 0.1MPa N2 and place it in a 500mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 80g of BC and 20g of NMP and stir until homogeneous. Filter the mixture using a syringe filter to remove insoluble impurities to obtain a liquid crystal alignment agent (3wt%). Store the agent in a -20℃ refrigerator and label it Q-21.

[0084] Comparative Example 2: The main difference from Example 1 is: S1, Polyamic Acid (PAA) Synthesis: ODA (26.95 g, 0.1 mol) was dissolved in NMP (241.6 g) at a flow rate of 0.1 MPa and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. After stirring for about 30 minutes, a clear diamine solution was obtained. Then, CBDA (15.68 g, 0.08 mol) was added to the solution and the reaction was continued for 30 minutes. After all the CBDA was dissolved, the reaction was heated at 70 °C for 5 hours. After cooling to room temperature, a PAA solution with a solid content of 15% was obtained. Then, 426.3 g of NMP was added to dilute the PAA to a solid content of 6 wt%. The solution was then stored at -20 °C and labeled PAA-3.

[0085] S2, Preparation of polyamic acid ester: Weigh 710 g of PAA-3 at a flow rate of 0.1 MPa N2 and place it in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 2.048 g of methanol and 11.02 g of p-benzenesulfonic acid to the flask. Stir for 30 min, then heat at 70 °C for 10 h. Cool to room temperature and store in a -20 °C refrigerator. Label it PAE-9.

[0086] S3. Preparation of soluble polyimide: 723 g of PAE-10 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 15.18 g of pyridine and 15.50 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-22. A liquid crystal photoaligning agent designated Q-22 and a liquid crystal cell Cell-22 were also prepared.

[0087] Comparative Example 3: The main difference between this example and Comparative Example 2 is: S2, Preparation of polyamic acid ester: Weigh 710g of PAA-3 at a flow rate of 0.1MPa N2 and place it in a 1000mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 3.58g of methanol and 19.28g of p-benzenesulfonic acid to the flask. Stir for 30min, then heat at 70℃ for 10h. Cool to room temperature and then store in a -20℃ refrigerator. Label it PAE-10.

[0088] S3. Preparation of soluble polyimide: 733 g of PAE-10 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 15.18 g of pyridine and 15.50 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-23. A liquid crystal photoaligning agent designated Q-23 and a liquid crystal cell Cell-23 were also prepared.

[0089] Comparative Example 4: The main difference from Example 1 is: S2, Preparation of polyamic acid ester: Weigh 743 g of PAA-1 at a flow rate of 0.1 MPa N2 and place it in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 4.608 g of methanol and 24.79 g of p-benzenesulfonic acid to the flask. Stir for 30 min, then heat at 70 °C for 10 h. Cool to room temperature and then store in a -20 °C refrigerator. The flask is labeled PAE-11.

[0090] S3. Preparation of soluble polyimide: 781 g of PAE-11 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 13.53 g of pyridine and 17.44 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-24. A liquid crystal photoaligning agent designated Q-24 and a liquid crystal cell Cell-24 were also prepared.

[0091] Comparative Example 5: The main difference from Example 1 is: S2, Preparation of polyamic acid ester: Weigh 743g of PAA-1 at a flow rate of 0.1MPa N2 and place it in a 1000mL three-necked round-bottom flask equipped with a mechanical stirrer. Add 0.576g of methanol and 3.099g of p-benzenesulfonic acid to the flask. Stir for 30min, then heat at 70℃ for 10h. Cool to room temperature and then store in a -20℃ refrigerator. Label it PAE-12.

[0092] S3. Preparation of soluble polyimide: 746 g of PAE-12 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 6.01 g of pyridine and 7.75 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-25. A liquid crystal photoaligning agent designated Q-25 and a liquid crystal cell Cell-25 were also prepared.

[0093] Comparative Example 6: The main difference from Example 1 is: S3. Preparation of soluble polyimide: 757 g of PAE-1 was weighed at a flow rate of 0.1 MPa N2 and placed into a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 6.01 g of pyridine and 7.75 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-26. A liquid crystal photoaligning agent designated Q-26 and a liquid crystal cell, Cell-26, were also prepared.

[0094] Comparative Example 7: The main difference from Example 1 is: S3. Preparation of soluble polyimide: Preparation of soluble polyimide: 757 g of PAE-1 was weighed at a flow rate of 0.1 MPa N2 and placed in a 1000 mL three-necked round-bottom flask equipped with a mechanical stirrer. 24.04 g of pyridine and 31 g of acetic anhydride were added, and the mixture was stirred for 30 min. The mixture was then heated at 70 °C for 10 h, cooled to room temperature, and stored at -20 °C. This flask was designated SPI-27. A liquid crystal photoaligning agent designated Q-27 and a liquid crystal cell Cell-27 were also prepared.

[0095] Test method: 1. Viscosity test: Testing equipment: Rotational viscometer: NDJ-1B Test conditions: 25℃, 0.5ml sample, TE-52 model rotor test. 2. GPC Test: Testing equipment: Gel permeation chromatography (GPC) system (GPC-101), chromatographic column (KD-803, KD-805) Test conditions: Mobile phase: DMF (as additive, lithium bromide monohydrate (LiBr·H2O) 40 mmol / L, phosphoric acid / anhydrous crystals (o-phosphoric acid) 30 mmol / L, tetrahydrofuran (THF) 10 mL / L); Flow rate: 0.8 mL / min; Temperature: 50 °C Standard samples used for calibration curve preparation: TSK standard polyethylene oxide (molecular weight; approximately 900,000, 150,000, 100,000 and 30,000) and polystyrene (molecular weight; approximately 12,000, 4,000 and 1,000).

[0096] 3. Esterification rate test method: Test equipment: Leici ZDJ-4B automatic potentiometric titrator 1. Sample preparation: Prepare a PAA sample and dilute it to 0.1 wt% using NMP. 2. Instrument settings: - Use a pH electrode and potentiometric titration system, with NaOH titrant (0.1 mol / L).

[0097] - Set titration parameters: initial potential recording, titration rate 0.05 mL / min.

[0098] 3. Titration procedure: - Begin titration, monitoring potential changes in real time until a potential jump (endpoint).

[0099] - Record the volume of NaOH consumed (e.g., 0.5 mL).

[0100] 4. Acid value calculation -AV- Acid Value (mgNaOH / g) -VNaOH—Sample titration volume (mL) -Vblank—Blank titration volume (mL) -CNaOH—NaOH concentration (mol / L) -m—Sample mass (g) -40—Molar mass of NaOH (g / mol) 5. Esterification rate calculation: Esterification rate = (AV before esterification - AV after esterification) / AV before esterification 4. Imine content (ID%) test method: Test equipment: Thermo Fisher Scientific Nicoleti S5 Test method: The sample spin-coated onto the glass substrate was first heated at 80°C for 2 minutes, then heated at 300°C for 1 hour. This was considered to indicate that the film was 100% fully imidized, and this sample was used for subsequent calibration. FT was used. The infrared absorption spectra of the thin films under various conditions were measured using the ATR mode of IR, and the data were recorded at 1380 cm⁻¹. 1(lmideC N) and 1500cm The peak height of the absorbance near the hydrogen atom on the benzene ring (1) is used to calculate the imidization rate of the sample using the following formula.

[0101] 5. Solubility test method: Weigh 10g of sample into a clear glass bottle. Initially, the sample will be a clear solution. Then, while shaking, add n-hexane dropwise using a capillary tube, continuously shaking the solution until the solution becomes cloudy immediately after the addition of n-hexane, and the turbidity does not disappear after shaking. Record the amount of n-hexane used (g). (The larger the amount of n-hexane used, the better the solubility of the orientation agent.) n-hexane > 3.0g indicates good solubility, 2.5g < n-hexane < 3g indicates moderate solubility, and n-hexane < 2.5g indicates poor solubility.

[0102] 6. Characterization of the electrical properties (VHR) of the liquid crystal cell: Test equipment: 6254C VHR measurement conditions: voltage 5V, pulse width 60µs / frame, period 1667ms, measurement temperature 23℃ / 90℃ Test method: Prepare sample (prepared liquid crystal cell) → Set measurement conditions → Apply test voltage → Measure holding voltage → Calculate voltage holding rate. Calculation formula: VHR = (Vr / Vs) * 100%. Vr: Residual voltage across the liquid crystal cell at the end of the holding period; Vs: Effective voltage across the liquid crystal cell during the application period.

[0103] 7. Characterization of liquid crystal cell pretilt angle: Test equipment: Toyo Corporation Test wavelength: 589nm Test mode: IPS mode Test method: Prepare sample (prepared liquid crystal cell) → Set measurement conditions → Select tilt mode to start testing liquid crystal cell pretilt angle.

[0104] 8. Characterization of Contrast Ratio Testing Methods Test equipment: DMS Series Test conditions: DC wave, test voltage 0V-20V, 0.1V / s, frequency 30Hz, backlight brightness: 10000cd / m2, test temperature 25℃ Test process: By continuously applying power to the liquid crystal cell, the brightness of the liquid crystal cell at each voltage is recorded, and finally the voltage (V)-brightness (T) curve of brightness as a function of voltage is obtained.

[0105] Contrast ratio calculation: Record the voltage-brightness (T) (cd / m2) during the test. Contrast ratio = T (brightest) / T (darkest) 9. Evaluation of anti-residual image capability: This evaluation assesses image retention (also known as AC image retention) caused by the deterioration of the alignment properties of the liquid crystal alignment film during long-term AC driving.

[0106] For the fabricated driving liquid crystal cell, an AC voltage of ±8V at a frequency of 60Hz was applied for 168 hours under a high-brightness backlight (light source: LED, brightness: 20000cd / m2) with a surface temperature of 50℃. Then, the pixel electrodes and common electrode of the liquid crystal cell were short-circuited and left at room temperature (23℃) for one day. Using the Toyo Corporation-3sigma test mode, the 3sigma values ​​of the liquid crystal cell before and after the test were measured. The 3sigma value reflects the anisotropy of liquid crystal orientation (the larger the 3sigma value, the more disordered the orientation and the worse the orientation). The difference in 3sigma before and after the test, Δ, was calculated; the larger the Δ, the worse the ability to resist image retention. Δ < 0.1 indicates excellent, 0.1 < Δ < 0.2 is considered good, and Δ > 0.2 indicates poor.

[0107] 10. Evaluation of the adhesion between the alignment film and the frame adhesive Take the prepared alignment film substrate and cut it into two strips, each 50cm long and 10cm wide. Apply a 3cm radius sealant to the film surface of one substrate, then cross-fit the other alignment film substrate to it, forming an alignment film-sealant-alignment film cross shape. Heat in a 150℃ hot air circulating oven for 60 minutes to cure the sealant, obtaining a sample for evaluating the adhesion between the alignment film and the sealant. Evaluation is performed using a LSDWJ-10T universal testing machine: specifically, one square substrate of the cross-shaped sample is fixed, and the other square substrate is brought into contact through a fixed fixture. After starting the equipment, a downward force is continuously applied until the sealant separates from the film. The force (N) at this point is recorded. Peel strength (N / cm²) = peel force / sealant area. A higher peel strength indicates better adhesion between the sealant and the alignment film. A peel strength > 50 N / cm² indicates good adhesion; a peel strength < 50 N / cm² indicates average adhesion; and a peel strength < 30 N / cm² indicates poor adhesion.

[0108] The test results for the examples and comparative examples PAA, PAE, and SPI are shown in Table 1: Table 1 The evaluation results of the liquid crystal alignment film and liquid crystal display element in the embodiments and comparative examples are shown in Table 2: Table 2 As shown in Tables 1 and 2, the liquid crystal alignment film and liquid crystal display element prepared in the examples exhibit superior performance compared to the comparative examples. Therefore, compared to existing technologies, the liquid crystal alignment agent of this invention, in its synthesis process, first prepares PAA of a certain molecular weight, then esterifies it (esterification rate 30%-60%), and finally further chemically imidizes PAE to prepare a soluble, low-temperature curable liquid crystal alignment agent. This not only improves the poor solubility of SPI itself but also enhances the display performance of the liquid crystal display element.

[0109] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A liquid crystal alignment agent, characterized in that, The composition comprises: soluble polyimide, auxiliary agent and solvent; The polyimide has the following structure: (Formula 1) R1 is a four-valent organic group derived from aliphatic, alicyclic acid dianhydride, and R2 is a diamine residue, R1 is selected from at least one of the following structures: R 1-1 、 R 1-2 、 R 1-3 、 R 1-4 、 R 1-5 、 R 1-6 ; R4 is independently a hydrogen atom, a halogen atom, an alkyl group with a carbon atom number of 1-6, an alkenyl group with a carbon atom number of 2-6, an alkynyl group with a carbon atom number of 2-6, a monovalent organic group with a carbon atom number of 1-6 containing a fluorine atom, a phenyl group, or a combination thereof; The R2 is selected from a diamine residue with an aromatic ring structure.

2. The liquid crystal alignment agent according to claim 1, characterized in that, The R2 includes at least one of the following structures: , , , , , , , , , , , , , , , , , , , , , , , , , , .

3. The liquid crystal aligning agent according to claim 1, characterized by The composition comprises: soluble polyimide, auxiliary agent and solvent; 4. A method for producing the polyimide liquid crystal photo-alignment agent according to any one of claims 1 to 3, characterized by, The composition comprises: Step 1, preparation of polyamide acid, dissolving diamine in solvent, adding dianhydride, and obtaining polyamide acid solution by reaction; Step 2, esterification of polyamide acid, taking the polyamide acid solution in step 1, adding alcohol source and first catalyst, and obtaining polyamide acid ester solution by reaction; Step 3, preparation of soluble polyimide, taking the polyamide acid ester solution in step 2, adding second catalyst and dehydrating agent, and obtaining soluble polyimide; Step 4, preparation of liquid crystal photo-alignment agent: taking the soluble polyimide in step 3, adding solvent and auxiliary agent thereto, stirring, and filtering to remove impurities to obtain the liquid crystal alignment agent.

5. The preparation method according to claim 4, characterized in that, In step 1, at least one of the following conditions is met: (1) the reaction atmosphere is a protective atmosphere; (2) the molar ratio of dianhydride to diamine is 0.9-1.1:1; (3) the solute solid content in the reaction stage is 10%-30%; (4) the reaction temperature is 40-70℃, and the reaction time is 2-10h.

6. The preparation method according to claim 4, characterized in that, In step 2, at least one of the following conditions is met: (1) the reaction atmosphere is a protective atmosphere; (2) the solid content of the polyamide acid solution is 4%-10%; (3) the alcohol source is selected from any one of, but not limited to, methanol, ethanol, and propanol; (4) the first catalyst is selected from an acidic catalyst and / or an alkaline catalyst; (5) the acidic catalyst is selected from inorganic acid and / or organic acid; the inorganic acid is selected from at least one of, but not limited to, sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid; the organic acid is selected from at least one of, but not limited to, formic acid and p-toluenesulfonic acid; (6) the alkaline catalyst is selected from at least one of alkaline metal salt and alkaline metal hydroxide; (7) the molar ratio of alcohol source to dianhydride is 0.8-1.4:1, and the molar ratio of catalyst to alcohol source is 1:1; (8) the reaction temperature is 50-90℃, and the reaction time is 10-15h; (9) the esterification rate of polyamide acid ester is 30%-60%.

7. The preparation method according to claim 4, characterized in that, In step 3, at least one of the following conditions is met: (1) the reaction atmosphere is a protection atmosphere; (2) the solid content of the polyamide acid ester solution is 4%-10%; (3) the second catalyst is selected from one or more of, but not limited to, quinoline, triethylamine, 1,4-diazabicyclo(2.2.2)octane, pyridine; (4) the dehydrating agent is selected from aliphatic or aromatic organic acids or acid anhydrides; (5) the molar ratio of the second catalyst to dianhydride is 1.6-2:1; the molar ratio of the dehydrating agent to pyridine is 1:1; (6) the reaction temperature is 50-90℃, and the reaction time is 10-15h; (7) the imidization rate of the soluble polyimide is 70%-90%.

8. The preparation method according to claim 4, characterized in that, the viscosity of the polyamic acid is 800-1500cp, and the weight average molecular weight is 15000-30000g / mol; and / or the solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide.

9. A liquid crystal alignment film, characterized in that, The liquid crystal alignment agent prepared by using the liquid crystal alignment agent of any one of claims 1-3 or the preparation method of any one of claims 4-8 is coated and cured to obtain.

10. A liquid crystal display element using the liquid crystal alignment film of claim 9.

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