A method for improving water resistance and sprayability of polyimide alignment agents

Abstract

The application discloses a kind of water resistance of polyimide orientation agent improvement, the orientation agent is modified polyimide, which is at least one compound containing as polymer by diamine and tetracarboxylic dianhydride reaction obtained polyamide acid by imidization to obtain polyimide;The affinity or compatibility of the modified polyimide of the application to water has been significantly improved, and polyimide precipitation or hydrolysis is not easy to cause, which can effectively solve the problem that the spray machine is more likely to cause spraying disorder or hole blocking when switching PI liquid in tank or idle during mass production, so as to achieve the purpose of improving the effect of PI orientation agent Inkjet. It has practical application value.

Description

Technical Field

[0001] This invention relates to the field of materials science and technology, specifically to a method for improving the water resistance and spraying effect of polyimide orientation agents. Background Technology

[0002] Due to its superior performance, large-scale production capabilities, high degree of automation, and broad development prospects, TFT-LCD is the mainstream product in the display field. The TFT-LCD production process is complex. In the cell manufacturing process, a high-molecular organic thin film, called the alignment layer, is used to anchor the liquid crystal. Polyimide is the most widely used material for this alignment layer. The alignment layer is obtained by coating and baking a polyimide precursor such as polyamide acid (PAA) or a solution of soluble polyimide (PI) as the main component. Its function is to ensure that the liquid crystal molecules are aligned neatly in the designed direction. The main steps in the film formation process during TFT-LCD cell manufacturing are as follows: wet cleaning before printing, cleaning, drying, and cooling; dry cleaning before printing; PI film coating; PI pre-baking and curing; PI film printing quality inspection; substrate output; and cell assembly. PI film coating is the core process in PI film formation. Commonly known methods for forming liquid crystal alignment films include spin coating, dip coating, and flexographic printing. However, these methods are cumbersome, complex, and costly, making them unsuitable for large-scale production. Large-scale production utilizes PI inkjet equipment for PI film coating. The PI inkjet machine has a row of printing heads that directly spray PI liquid onto the substrate. This is achieved by the deformation of piezoelectric ceramics within the printhead, causing the PI liquid to be ejected from small orifices in the nozzles. The movement of the printhead or glass substrate stage forms a high-density array of PI droplets. Finally, under the influence of surface tension, the PI droplets diffuse and connect to form a film. Simply put, it's a method of adding fine droplets to the substrate and forming a film through the wetting and spreading of the liquid. By adjusting parameters such as machine voltage, frequency, and coating speed, PI alignment films of various thicknesses can be prepared. Spray coating not only eliminates the need for printing plates, simplifying the manufacturing process, but also allows for the free setting of printing patterns. Using PI spray coating has the advantage of less coating liquid waste, which can reduce the cost of LCD panels and improve production efficiency.

[0003] The nozzles of PI spray coating equipment are very small, allowing for precise droplet control down to the ng level. The tolerance of the PI liquid significantly affects the coating effect, primarily manifested in the PI's water resistance and the ease of solvent evaporation. Polyimide orientation agents are generally formed by the condensation of aromatic diamines with tetracarboxylic anhydrides to create five-membered imide rings, resulting in a rigid molecular chain with strong intermolecular forces. These characteristics make polyimides relatively difficult to dissolve. If PI is exposed to air for extended periods, it readily absorbs moisture and carbon dioxide, while the solvent evaporates, easily causing PI precipitation or hydrolysis. During mass production, spraying machine switching between PI liquids on the tank or during idle periods is more prone to causing spraying irregularities or clogging, thus affecting production capacity and yield. To improve this situation, we have invented a method to improve the water resistance and coating effect of polyimide orientation agents, thereby improving the performance of PI orientation agents (Inkjet). Summary of the Invention

[0004] In view of the deficiencies of the prior art, the purpose of this invention is to provide a method for improving the water resistance and spraying effect of polyimide orientation agents, so as to solve the problems mentioned in the background art.

[0005] The present invention solves the technical problem by adopting the following technical solution:

[0006] The present invention provides an improved water resistance of a polyimide orientation agent, wherein the orientation agent is a modified polyimide, which is a polyimide containing at least one compound that is an imide obtained by reacting a polyamic acid, which is a polymer, with a polyamic acid obtained by reacting a diamine and a tetracarboxylic dianhydride.

[0007] The method for improving the water resistance of the polyimide orientation agent includes the following steps:

[0008] S1. Preparation of polyimide acid (PAA) solution: The diamine monomer is first dissolved in a polar aprotic solvent, and then the dianhydride monomer is added to react and obtain a viscous transparent polyimide acid solution.

[0009] S2. Preparation of polyimide (PI) solution:

[0010] S21. First, synthesize the polyimide acid solution according to step S1;

[0011] S22. Add a dehydrating agent and a catalyst to the polyimide solution obtained in S21, and carry out the imidization reaction using chemical imidization. The imidization rate of polyimide can be controlled by adjusting the amount of catalyst, reaction temperature, and reaction time. Then, remove the dehydrating agent and catalyst by rotary evaporation, add an appropriate amount of polar aprotic solvent, and remove most of the solvent by rotary evaporation. Repeat the above operation three times to obtain a polyimide solution. Control the final solid content to be greater than 20%, and finally dilute to 5% wt with a diluent. The base solvent system should be consistent with that of S21.

[0012] S3. Mixing with PI and PAA solutions: Mix the PI and PAA solutions obtained in S1 and S2 in a certain proportion, controlling the proportion of PI solution to 10-50%, and then ripen at 60-80℃ for 0.5-4 hours to obtain a mixed (PI / PAA) orientation agent.

[0013] S4. Modification method: The orientation agent synthesized by S1 or S2 or through S1, S2 or S3 is reacted with the modifier. Under nitrogen protection, the modifier is gradually added to the polyamic acid solution. The reaction time is 0.5-4h and the reaction temperature is 0℃-80℃.

[0014] Preferably, the molar ratio of diamine to dianhydride in S1 is 100:(85-100), the reaction process of S1 is a reaction temperature of -15℃ to 100℃, a reaction time of 0.5-48h, and the reaction solid content of the polyimide solution is 5-50%.

[0015] Preferably, the diamine is one or more of alicyclic diamines, aromatic diamines, heterocyclic diamines, and aliphatic diamines.

[0016] Preferably, the solvent in S1 is one or more of γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide, and dimethyl sulfone.

[0017] Preferably, S1 further contains 1-30% wt of a leveling agent, wherein the leveling agent is one or more of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol diethyl ether.

[0018] Preferably, in S22, the proportion of dehydrating agent used is 1-20 times the molar amount of dianhydride, the proportion of catalyst used is 1-10 times the molar amount of dianhydride, the reaction temperature of chemical imidization is -20℃ to 200℃, and the reaction time is 0.5-48h.

[0019] Preferably, the dehydrating agent in S22 is one or more of acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, the catalyst is one or more of pyridine, trimethylpyridine, dimethylpyridine, and triethylamine, and the imidization rate of the polyimide contained in the liquid crystal alignment agent in S22 is above 40%.

[0020] Preferably, the modifier in S4 has the following characteristics and its structure is as follows:

[0021]

[0022] In the above formula, Ra and Rb are independently alkyl groups with 1-6 carbon atoms or hydroxyalkyl groups with 1-6 carbon atoms, or Ra and Rb can combine to form a monocycle. Ra and Rb can be independent of each other, and their number and type can be different. In the above formula, Rc is an alkyl group with 1-6 carbon atoms.

[0023] The specific structure of the above-mentioned general formula is as follows:

[0024]

[0025] Preferably, the modifier in S4 reacts with the polyimide as follows:

[0026]

[0027] In the above formula, Ra and Rb are independently alkyl groups with 1-6 carbon atoms or hydroxyalkyl groups with 1-6 carbon atoms, or Ra and Rb can combine to form a monocycle. Ra and Rb can be independent of each other, and their number and type can be different. In the formula, Rc is an alkyl group with 1-6 carbon atoms.

[0028] The present invention also provides a method for improving the spraying effect of polyimide orientation agent water resistance, comprising the following steps:

[0029] a1. Filter the synthetic polyimide solution orientation agent through a microporous membrane;

[0030] a2. The alignment agent solution in a1 is sprayed onto the ITO glass, and then the ITO glass substrate is pre-baked at 70-110℃ for 10-20 min, and then imidized at 200-250℃ for 30-60 min.

[0031] a3. Use a friction machine to rub the polyimide film on the ITO glass substrate in a2 at a friction angle of 45°.

[0032] a4. Two ITO glass substrates coated with liquid crystal alignment film obtained in a3 are bonded together with their friction surfaces facing each other and their friction directions orthogonal using a thermosetting adhesive containing 4µm spacer particles. Liquid crystal is then poured in, and the substrates are sealed with photocurable adhesive to obtain a liquid crystal cell.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The modified polyimide of this invention exhibits significantly improved affinity and compatibility with water, making it less prone to precipitation or hydrolysis. This effectively addresses the issue of spraying irregularities or clogging that often occur during mass production when switching PI liquids on the tank or during idle periods on the spraying machine. Therefore, it improves the performance of the PI orientation agent Inkjet and has practical application value. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the PI water resistance test evaluation of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Typical liquid crystal alignment agents are polymer resin solutions. Polyamic acid is prepared by polycondensation of at least one dianhydride and at least one diamine, while polyimide is prepared by dehydration and cyclization (i.e., imidization) of polyamic acid. Liquid crystal alignment agents can be classified into polyamic acid (PAA) resin solutions, polyimide (PI) resin solutions, or PI-PAA mixed resin solutions.

[0038] The specific preparation method involves first dissolving the diamine monomer in a polar aprotic solvent, then adding the tetracarboxylic dianhydride monomer to react and obtain a viscous, transparent polyimide acid solution. Alternatively, the diamine component can be added to a solution obtained by dispersing or dissolving the tetracarboxylic dianhydride component in an organic solvent, or by alternately adding the tetracarboxylic dianhydride component and the diamine component. This yields the PAA precursor solution. To prepare a PI type, it undergoes appropriate thermal or chemical treatment (imidization or cyclization dehydration) to convert it into a polyimide solution. In the laboratory stage, chemical imidization is usually used, and the imidization rate must be carefully controlled, typically below 60%. Poor control can lead to problems such as decreased solubility, gelation, and residue during application. The schematic diagram of the imidization process is as follows:

[0039]

[0040] In the above general formula, Represents dianhydride residues; represents a diamine residue; n represents the number of repeating units.

[0041] Regardless of whether it is a polyamic acid (PAA) resin solution, a polyimide (PI) resin solution, or a PI-PAA mixed resin solution, the alignment agent will not be 100% imidized. Even when the alignment film is printed and cured at about 230°C during LCD production, the imidization rate is only 30% to 80%. Therefore, there are a large number of unimidized carboxylic acid groups in the polymer resin of the alignment film. Taking advantage of this property, we can modify polyimide alignment agents by chemical modification.

[0042] This embodiment of the present invention provides an improved water resistance of a polyimide orientation agent, wherein the orientation agent is a modified polyimide, which is a polyimide containing at least one compound that is an imide obtained by reacting a polyamic acid, which is a polymer, with a polyamic acid obtained by reacting a diamine and a tetracarboxylic dianhydride.

[0043] Methods for improving the water resistance of polyimide orientation agents include the following steps:

[0044] S1. Preparation of polyimide acid (PAA) solution:

[0045] The diamine monomer is first dissolved in a polar aprotic solvent, and then a dianhydride monomer is added to react and obtain a viscous, transparent polyimide acid solution. The molar ratio of diamine to dianhydride is 100:(85-100), where the molar ratio of dianhydride is used as a parameter to adjust the viscosity of the system. The reaction temperature is -15℃ to 100℃, preferably 0℃ to 80℃, and optimally 20℃ to 60℃. The reaction time is 0.5-48 h, preferably 1-24 h, and optimally 2-12 h. For the polyimide acid solution or polyimide solution used in this invention, the reaction solids content is 5-50%, preferably 8-40%, and optimally 10-30%. Initially, the reaction is carried out at a high concentration, and then an organic solvent is added. After the reaction is completed, the solution is diluted to 1-5% wt with a solvent content of 95-99% wt. When the solvent content in the spray coating exceeds 99% wt, the thickness of the liquid crystal alignment film after drying becomes too small, making it impossible to obtain a good liquid crystal alignment film. When the solvent content is below 95% wt, the nozzle's ejection performance deteriorates. From a spray coating perspective, the viscosity is preferably 5-16 mPa·s, and more preferably 6-10 mPa·s.

[0046] S2. Preparation of polyimide (PI) solution:

[0047] S21. First, synthesize the polyimide acid solution according to step S1;

[0048] S22. A dehydrating agent and catalyst are added to the polyimide solution obtained in reaction S1, and an imidization reaction is carried out using chemical imidization. The imidization rate of the polyimide can be controlled by adjusting the amount of catalyst, reaction temperature, and reaction time. The dehydrating agent and catalyst used are not limited to acetic anhydride and pyridine. The proportion of dehydrating agent used is 1-20 times the molar amount of dianhydride, and the proportion of catalyst used is 1-10 times the molar amount of dianhydride, but the proportions are not limited to 1-10 times. The reaction temperature for chemical imidization is -20℃ to 200℃, preferably 60℃ to 120℃, and most preferably 20℃ to 100℃. The reaction time is 0.5-48 h. For the dehydrating agent, anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride can be used, with acetic anhydride being preferred. The amount of dehydrating agent used depends on the desired imidization rate. Additionally, tertiary amines such as pyridine, trimethylpyridine, dimethylpyridine, and triethylamine can be used as dehydration ring-closing catalysts, with pyridine being preferred. The imidization rate of the polyimide contained in the liquid crystal alignment agent of the present invention is not particularly limited, but considering the electrical properties, it is preferably 40% or more, and more preferably 50% or more in order to obtain a higher voltage retention rate;

[0049] The polyimide solution obtained by chemical imidization reaction in S22 is subjected to rotary evaporation to remove most of the solvent, pyridine, and acetic acid. Then, an appropriate amount of the aprotic solvent used in step I is added, and rotary evaporation is repeated to remove most of the solvent. This cycle is repeated three times to remove the vast majority of pyridine and acetic acid, yielding the polyimide solution with a final solid content greater than 20%. After the reaction, the solution is diluted to 5% wt with a diluent, maintaining the same base solvent system as in S1, thus obtaining the chemically imidized polyimide solution.

[0050] S3. Mixing with PI and PAA solutions: Mix the PI and PAA solutions obtained in S1 and S2 in a certain proportion, controlling the proportion of PI solution to 10-50%, preferably 30%, and then ripen at 60-80℃ for 0.5-4h, preferably 2-4h, with 2h being the optimal time, to obtain a mixed (PI / PAA) orientation agent.

[0051] S4. Modification Method: The alignment agent synthesized by S1 or S2, or through S1, S2, or S3, is further reacted with the modifier. Under nitrogen protection, the modifier is gradually added to the polyamic acid solution. The reaction time is 0.5-4 hours, and the reaction temperature is 0℃-80℃, preferably 10℃-50℃. All modifiers can be one or more of the above-mentioned general structural formulas. The modifier is added in a molar ratio, with the total molar amount of diamine and dianhydride in the formula being 100 parts. The amount added is 0%-5%, preferably 1%-2% of the total molar amount of diamine and dianhydride. The maximum amount added should ensure that the synthesized polyamic acid solution does not precipitate. After adding the modifier, a modified polyamic acid solution is finally obtained. The method for preparing the polyimide alignment agent of the present invention is based on the fact that the components, mainly polyimide, are in a uniform state in the liquid crystal alignment agent.

[0052] The diamine in this embodiment is one or more of alicyclic diamines, aromatic diamines, heterocyclic diamines, and aliphatic diamines. Specific examples are given below:

[0053] Diamine compounds:

[0054]

[0055] Dihydride compounds:

[0056]

[0057] In S1 of this embodiment, the solvent is one or more of γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide, and dimethyl sulfone, preferably γ-butyrolactone or N-methyl-2-pyrrolidone.

[0058] In S1 of this embodiment, a leveling agent containing 1-30% wt is also added. The leveling agent is one or more of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol diethyl ether.

[0059] The modifier in S4 of this embodiment has the following characteristics and its structure is as follows:

[0060]

[0061] In the above formula, Ra and Rb are independently alkyl groups with 1-6 carbon atoms or hydroxyalkyl groups with 1-6 carbon atoms, or Ra and Rb can combine to form a monocycle. Ra and Rb can be independent of each other, and their number and type can be different. In the above formula, Rc is an alkyl group with 1-6 carbon atoms.

[0062] The specific structure of the above general formula is as follows:

[0063]

[0064] In this embodiment, the modifier reacts with the polyimide in S4 as follows:

[0065]

[0066] In the above formula, Ra and Rb are independently alkyl groups with 1-6 carbon atoms or hydroxyalkyl groups with 1-6 carbon atoms, or Ra and Rb can combine to form a monocycle. Ra and Rb can be independent of each other, and their number and type can be different. In the formula, Rc is an alkyl group with 1-6 carbon atoms.

[0067] This embodiment provides a method for improving the spraying effect of polyimide orientation agents in terms of water resistance, comprising the following steps:

[0068] a1. Filter the synthetic polyimide solution orientation agent through a microporous membrane;

[0069] a2. The alignment agent solution in a1 is sprayed onto the ITO glass, and then the ITO glass substrate is pre-baked at 70-110℃ for 10-20 minutes, and then imidized at 200-250℃ for 30-60 minutes.

[0070] a3. Use a friction machine to rub the polyimide film on the ITO glass substrate in a2 at a friction angle of 45°.

[0071] a4. Two ITO glass substrates coated with liquid crystal alignment film obtained in a3 are bonded together with their friction surfaces facing each other and their friction directions orthogonal using a thermosetting adhesive containing 4µm spacer particles. Liquid crystal is then poured in, and the substrates are sealed with photocurable adhesive to obtain a liquid crystal cell.

[0072] The types and molar percentages of dianhydride and diamine compounds in the embodiments and comparative examples of this invention are listed in Table 1:

[0073] Table 1

[0074]

[0075]

[0076]

[0077] Example 1.

[0078] I. In a nitrogen-protected reactor at room temperature, 3.86 g (10 mmol) A-6, 3.18 g (15 mmol) A-5, 4.96 g (25 mmol) A-2, 2.16 g (20 mmol) A-1, 6.01 g (30 mmol) A-3, and 168.09 g NMP were added sequentially. The mixture was stirred at room temperature for 30 min to ensure complete dissolution. Then, 3.92 g (20 mmol) G-1 and 17.93 g (80 mmol) G-2 were added sequentially. The mixture was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 487.46 g NMP, 201.71 g GBL, and 151.18 g BC were added and diluted to 4.0 wt% to obtain a polyamic acid solution with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0079] II. Under nitrogen protection, modifier N-1 was gradually added dropwise to the polyamic acid solution at a rate of 0.1783 g, which is 1% of the total molar amount of diamine and dianhydride (0.2 mol). The reaction was stirred for 2 hours at a temperature of 60°C. The solution was then filtered through a microporous membrane, and the coating effect was tested. After coating, the solution underwent subsequent processes to manufacture the cell, and the tilt angle and electrical performance of the liquid crystal cell were then tested.

[0080] Example 2.

[0081] I. In a nitrogen-protected reactor at room temperature, 3.86 g (10 mmol) A-6, 2.99 g (15 mmol) A-4, 5.95 g (30 mmol) A-2, 2.16 g (20 mmol) A-1, 5.01 g (25 mmol) A-3, and 144.46 g NMP were added sequentially. The mixture was stirred at room temperature for 30 min to confirm complete dissolution. Then, 4.36 g (20 mmol) G-4 and 15.69 g (80 mmol) G-1 were added sequentially. The mixture was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0082] II. Then add 10.2 g (100 mmol) of NMP and 15.82 g (200 mmol) of pyridine, followed by 30.24 g of NMP. The solid content is now 15 wt%. React at room temperature for 2 hours for chemical imidization. First, remove most of the pyridine and solvent by rotary evaporation at 100 °C. Then add 120 g of NMP solvent. Repeat this process three times to remove most of the pyridine and acetic acid, thus obtaining a polyimide solution. Control the final solid content to be greater than 20%. After the reaction, the solid content was determined to be 21.69% by hot plate method. Add 479.74 g of NMP, 201.71 g of GBL, and 151.18 g of BC and stir to dilute to 4.0% wt, obtaining a polyimide solution with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0083] III. Under nitrogen protection, modifier N-1 was gradually added dropwise to the polyamic acid solution at a rate of 0.1783 g, which is 1% of the total molar amount of diamine and dianhydride (0.2 mol). The reaction was stirred for 2 hours at a temperature of 60°C. The solution was then filtered through a microporous membrane, and the coating effect was tested. After coating, the solution underwent subsequent processes to manufacture the cell, and the tilt angle and electrical performance of the liquid crystal cell were then tested.

[0084] Example 3.

[0085] Steps I and II are the same as in Example 2.

[0086] III. Under nitrogen protection, modifier N-3 was gradually added dropwise to the polyamic acid solution at a rate of 0.2103 g, which is 1% of the total molar amount of diamine and dianhydride (0.2 mol). The reaction was stirred for 2 hours at a temperature of 60°C. The solution was then filtered through a microporous membrane, and the coating effect was tested. After coating, the solution underwent subsequent processes to manufacture the cell, and the tilt angle and electrical performance of the liquid crystal cell were then tested.

[0087] Example 4.

[0088] I. In a nitrogen-protected reactor at room temperature, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-4, and 147.50 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to confirm complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 427.74 g of NMP, 177.00 g of GBL, and 132.75 g of BC were added and stirred to dilute to 4.0 wt%, resulting in polyamic acid solution A with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0089] II. In a nitrogen-protected reactor at room temperature, 3.86 g (10 mmol) of A-6, 6.37 g (30 mmol) of A-5, 11.90 g (60 mmol) of A-2, and 178.14 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to ensure complete dissolution. Then, 22.42 g (100 mmol) of G-2 was added sequentially, and the mixture was stirred at room temperature for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. Next, 10.2 g (100 mmol) of pyridine and 15.82 g (200 mmol) of pyridine were added, followed by 48.21 g of NMP, bringing the solid content to 15 wt%. The mixture was then reacted at 60 °C for 2 h for chemical imidization. Most of the pyridine and solvent were removed by rotary evaporation at 100 °C, followed by the addition of 120 g of NMP as solvent. This cycle was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 22.38% by hot plate method. 540.29g of NMP, 213.77g of GBL, and 160.33g of BC were added and stirred to dilute to 4.0% wt, resulting in polyimide solution B with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0090] III. Take 800g of solution A and 200g of solution B obtained in the above two steps, and then stir and mature them at 60℃ for 1 hour to obtain a uniform mixture. Under nitrogen protection, add modifier N-1 dropwise to the polyamic acid solution at a rate of 0.1783g, which is 1% of the total molar amount of diamine and dianhydride (0.2mol). Stir and react for 2 hours at 60℃. Filter the solution through a microporous membrane and then test the coating effect. After coating, proceed with subsequent processes to manufacture the liquid crystal cell, and then test the tilt angle and electrical performance of the liquid crystal cell.

[0091] Example 5.

[0092] I. In a nitrogen-protected reactor at room temperature, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-4, and 147.50 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to confirm complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 427.74 g of NMP, 177.00 g of GBL, and 132.75 g of BC were added and stirred to dilute to 4.0 wt%, resulting in polyamic acid solution A with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0093] II. In a nitrogen-protected reactor at room temperature, 1.11 g (10 mmol) of A-7, 3.86 g (10 mmol) of A-6, 4.24 g (20 mmol) of A-2, 11.90 g (60 mmol) of A-2, and 174.09 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to ensure complete dissolution. Then, 22.42 g (100 mmol) of G-2 was added sequentially, and the mixture was stirred at room temperature for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. Then, 10.2 g (100 mmol) of pyridine and 15.82 g (200 mmol) of pyridine were added, followed by 46.52 g of NMP, bringing the solid content to 15 wt%. The mixture was then reacted at 60 °C for 2 h for chemical imidization. First, most of the pyridine and solvent were removed by rotary evaporation at 100℃. Then, 120g of NMP solvent was added. This process was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction, the solid content was determined to be 23.65% by hot plate method. 538.46g of NMP, 208.91g of GBL, and 156.69g of BC were added and diluted to 4.0% wt to obtain polyimide solution B with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0094] III. Take 700g of solution A and 300g of solution B obtained in the above two steps, and then stir and mature them at 60℃ for 1 hour to obtain a uniform mixture. Under nitrogen protection, add modifier N-1 dropwise to the polyamic acid solution at a rate of 0.1783g, which is 1% of the total molar amount of diamine and dianhydride (0.2mol). Stir and react for 2 hours at 60℃. Filter through a microporous membrane and then test the coating effect. After coating, proceed with subsequent processes to manufacture the cell, and then test the tilt angle and electrical performance of the liquid crystal cell.

[0095] Comparative Example 1.

[0096] I. In a nitrogen-protected reactor at room temperature, 3.86 g (10 mmol) A-6, 3.18 g (15 mmol) A-5, 4.96 g (25 mmol) A-2, 2.16 g (20 mmol) A-1, 6.01 g (30 mmol) A-3, and 168.09 g NMP were added sequentially. The mixture was stirred at room temperature for 30 min to ensure complete dissolution. Then, 3.92 g (20 mmol) G-1 and 17.93 g (80 mmol) G-2 were added sequentially. The mixture was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 487.46 g NMP, 201.71 g GBL, and 151.18 g BC were added and diluted to 4.0 wt% to obtain a polyamic acid solution with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15. The coating is filtered through a microporous membrane, and then the coating effect is tested. After coating, the liquid crystal cell undergoes subsequent processes to form a cell, and then the tilt angle and electrical performance are tested.

[0097] Comparative Example 2.

[0098] I. In a nitrogen-protected reactor at room temperature, 3.86 g (10 mmol) A-6, 2.99 g (15 mmol) A-4, 5.95 g (30 mmol) A-2, 2.16 g (20 mmol) A-1, 5.01 g (25 mmol) A-3, and 144.46 g NMP were added sequentially. The mixture was stirred at room temperature for 30 min to confirm complete dissolution. Then, 4.36 g (20 mmol) G-4 and 15.69 g (80 mmol) G-1 were added sequentially. The mixture was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%.

[0099] II. Then, add 10.2g (100mmol) of pyridine and 15.82g (200mmol) of pyridine, followed by 30.24g of NMP. The solid content is now 15wt%. Chemical imidization is performed at room temperature for 2 hours. Most of the pyridine and solvent are removed by rotary evaporation at 100℃. Then, 120g of NMP solvent is added. This cycle is repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction, the solid content is measured to be 21.69% using a hot plate method. 479.74g of NMP, 201.71g of GBL, and 151.18g of BC are added and diluted to 4.0wt% with stirring, resulting in a polyimide solution with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15. The solution is filtered through a microporous membrane and then tested for coating effectiveness. After coating, the solution undergoes subsequent cell fabrication processes, and the tilt angle and electrical properties of the liquid crystal cell are then tested.

[0100] Comparative Example 3.

[0101] I. In a nitrogen-protected reactor at room temperature, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-4, and 147.50 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to confirm complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 427.74 g of NMP, 177.00 g of GBL, and 132.75 g of BC were added and stirred to dilute to 4.0 wt%, resulting in polyamic acid solution A with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0102] II. In a nitrogen-protected reactor at room temperature, 3.86 g (10 mmol) of A-6, 6.37 g (30 mmol) of A-5, 11.90 g (60 mmol) of A-2, and 178.14 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to ensure complete dissolution. Then, 22.42 g (100 mmol) of G-2 was added sequentially, and the mixture was stirred at room temperature for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. Next, 10.2 g (100 mmol) of pyridine and 15.82 g (200 mmol) of pyridine were added, followed by 48.21 g of NMP, bringing the solid content to 15 wt%. The mixture was then reacted at 60 °C for 2 h for chemical imidization. Most of the pyridine and solvent were removed by rotary evaporation at 100 °C, followed by the addition of 120 g of NMP as solvent. This cycle was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction was completed, the solid content was determined to be 22.38% by hot plate method. 540.29g of NMP, 213.77g of GBL, and 160.33g of BC were added and stirred to dilute to 4.0% wt, resulting in polyimide solution B with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0103] III. Take 800g of liquid A and 200g of liquid B obtained in the above two steps, and then stir and mature them at 60℃ for 1 hour to obtain a uniform mixture. Filter the mixture through a microporous membrane and then test the coating effect. After coating, proceed with subsequent processes to manufacture the liquid crystal cell, and then test the tilt angle and electrical performance of the liquid crystal cell.

[0104] Comparative Example 4.

[0105] I. In a nitrogen-protected reactor at room temperature, 3.24 g (30 mmol) of A-1, 14.02 g (70 mmol) of A-4, and 147.50 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to confirm complete dissolution. Then, 19.61 g (100 mmol) of G-1 was added sequentially. The reaction was stirred at room temperature for 4 h to obtain a viscous polyamic acid solution with a solid content of 20 wt%. After the reaction was completed, 427.74 g of NMP, 177.00 g of GBL, and 132.75 g of BC were added and stirred to dilute to 4.0 wt%, resulting in polyamic acid solution A with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0106] II. In a nitrogen-protected reactor at room temperature, 1.11 g (10 mmol) of A-7, 3.86 g (10 mmol) of A-6, 4.24 g (20 mmol) of A-2, 11.90 g (60 mmol) of A-2, and 174.09 g of NMP were added sequentially. The mixture was stirred at room temperature for 30 min to ensure complete dissolution. Then, 22.42 g (100 mmol) of G-2 was added sequentially, and the mixture was stirred at room temperature for 4 h to obtain a transparent, viscous polyamic acid solution with a solid content of 20 wt%. Then, 10.2 g (100 mmol) of pyridine and 15.82 g (200 mmol) of pyridine were added, followed by 46.52 g of NMP, bringing the solid content to 15 wt%. The mixture was then reacted at 60 °C for 2 h for chemical imidization. First, most of the pyridine and solvent were removed by rotary evaporation at 100℃. Then, 120g of NMP solvent was added. This process was repeated three times to remove most of the pyridine and acetic acid, yielding a polyimide solution with a final solid content greater than 20%. After the reaction, the solid content was determined to be 23.65% by hot plate method. 538.46g of NMP, 208.91g of GBL, and 156.69g of BC were added and diluted to 4.0% wt to obtain polyimide solution B with a solvent ratio of NMP / GBL / BC = 65 / 20 / 15.

[0107] III. Take 700g of liquid A and 300g of liquid B obtained in the above two steps, and then stir and mature them at 60℃ for 1 hour to obtain a uniform mixture. Filter the mixture through a microporous membrane and then test the coating effect. After coating, proceed with subsequent processes to manufacture the liquid crystal cell, and then test the tilt angle and electrical performance of the liquid crystal cell.

[0108] The following examples illustrate the evaluation methods for the polyimide solutions obtained and their performance after box fabrication:

[0109] (1) Water resistance test:

[0110] Evaluation method: Weigh 10g of PI sample using a precision analytical balance. Observe and record the amount of water added when turbidity appears in the PI sample by adding water dropwise. A schematic diagram is shown below to better illustrate this evaluation method. Figure 1 .

[0111] The results of the water resistance test are shown in Table 2.

[0112] Table 2

[0113]

[0114] (2) Evaluation of spraying effect

[0115] The synthesized polyimide solution was sprayed using a spray gun for testing.

[0116] Printing method: I nkjet

[0117] Equipment Model: I J-1011-A2FS-M0

[0118] Head size: 50μm

[0119] Ejection process: TC3 (20.77V), 128mm / s × 43.5ng / dot × 1 cycle

[0120] Droplet: Standard: 43.5 ng / dot

[0121] The evaluation results of the spraying effect are shown in Table 3.

[0122] Table 3

[0123]

[0124]

[0125] (3) Test conditions for liquid crystal cell pretilt angle:

[0126] LCD cell pretilt angle test conditions:

[0127] Test equipment: Shintech Optitro-STD (3STN11)

[0128] Test wavelength: 591.4nm

[0129] Test mode: TN mode

[0130] HAV parameters: The test results of the liquid crystal cell pretilt angle and pretilt angle stability under DC program 20V power supply, temperature 60℃, 313nm light illumination for 125s are shown in Table 4.

[0131] Table 4

[0132]

[0133]

[0134] (4) Test conditions for the electrical performance of the liquid crystal cell:

[0135] Test equipment: 6254CVHR; Measurement conditions: 5V voltage, 60µs / frame pulse width, 1667ms period, measurement temperature 23℃ / 90℃.

[0136] Ion Density measurement conditions: voltage 5V, pulse width 60µs / frame, period 1667ms, measurement temperature 23℃ / 90℃

[0137] The electrical performance test results are shown in Table 5.

[0138] Table 5

[0139]

[0140] The innovation of this invention lies in:

[0141] The modified polyimide of this invention exhibits significantly improved affinity and compatibility with water, making it less prone to precipitation or hydrolysis. This effectively addresses the issue of spraying irregularities or clogging that often occur during mass production when switching PI liquids on the tank or during idle periods on the spraying machine. Therefore, it improves the performance of the PI orientation agent Inkjet and has practical application value.

[0142] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0143] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for improving water resistance and sprayability of a polyimide alignment agent, characterized by, The alignment agent is a modified polyimide, which is at least one compound containing a polyimide obtained by imidization of a polyamide acid as a polymer, which is obtained by reacting a diamine and a tetracarboxylic dianhydride; The method for improving the water resistance of the polyimide alignment agent comprises the following steps: S1, preparing a polyamide acid (PAA) solution: dissolving a diamine monomer in a polar aprotic solvent first, and then adding a dianhydride monomer to react to obtain a viscous transparent polyamide acid solution; S2, preparing a polyimide (PI) solution: S21, first synthesizing a polyamide acid solution according to the step S1; S22, adding a dehydrating agent and a catalyst to the polyamide acid solution obtained in S21, and performing an imidization reaction by using a chemical imidization method, the imidization rate of the polyimide can be controlled by adjusting the amount of catalyst, the reaction temperature and the reaction time, then removing the dehydrating agent and the catalyst by rotary evaporation, adding an appropriate amount of polar aprotic solvent, removing most of the solvent by rotary evaporation, repeating the above operation three times, and finally obtaining a polyimide solution with a solid content of more than 20%, and then diluting to 5% wt with a diluent, the base solvent system is consistent with S21; S3, mixing PI and PAA solutions: mixing the PI and PAA solutions obtained in S1 and S2 in a certain proportion, controlling the proportion of PI solution to be 10-50%, and then aging at 60-80℃ for 0.5-4h to obtain a mixed (PI / PAA) alignment agent; S4, modification method: continuing to react the polyamide acid solution synthesized in S1, the polyimide solution synthesized in S2 or the alignment agent synthesized in S3 with a modifier, gradually adding the modifier to the above solution under the protection of nitrogen, stirring for 0.5-4h, and the reaction temperature is 0℃-80℃; The modifier in S4 has the following characteristics, and its structure is as follows: In the above formula, Ra and Rb are independently alkyl groups with carbon number 1-6 or hydroxyalkyl groups with 1-6 carbon atoms, or Ra and Rb can combine with each other to form a monocyclic ring, Ra and Rb can be independent of each other in quantity and type, and the above formula R is an alkylene group with 1-6 carbon atoms.

2. The method for improving water resistance and spray effect of polyimide alignment agent according to claim 1, characterized by, The molar ratio of the diamine to the dianhydride in S1 is 100: (85-100), the reaction process of S1 is that the reaction temperature is -15℃-100℃, the reaction time is 0.5-48h, and the reaction solid content of the polyamide acid solution is 5-50%.

3. The method for improving water resistance and spray effect of polyimide alignment agent according to claim 1, wherein The diamine is one or more of alicyclic diamine, aromatic diamine, heterocyclic diamine and aliphatic diamine.

4. The method for improving water resistance and sprayability of a polyimide alignment agent according to claim 1, wherein The solvent in S1 is one or more of γ-butyrolactone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethyl sulfoxide and dimethyl sulfone.

5. The method for improving water resistance and sprayability of a polyimide alignment agent according to claim 1, wherein The leveling agent in S1 contains 1-30% wt, and the leveling agent is one or more of ethylene glycol monobutyl ether, diethylene glycol monomethyl ether and diethylene glycol diethyl ether.

6. The method for improving water resistance and sprayability of a polyimide alignment agent according to claim 1, wherein The dehydration agent is used in a proportion of 1-20 times the moles of dianhydride, the catalyst is used in a proportion of 1-10 times the moles of dianhydride, the reaction temperature of the chemical imidization is -20-200℃, and the reaction time is 0.5-48h.

7. The method for improving water resistance and sprayability of a polyimide alignment agent according to claim 1, wherein The dehydration agent in S22 is one or several of acetic anhydride, propionic anhydride and trifluoroacetic anhydride, the catalyst is one or several of pyridine, trimethylpyridine, dimethylpyridine and triethylamine, and the imidization rate of the polyimide contained in the liquid crystal alignment agent in S22 is above 40%.

8. The method of improving water resistance and spray effect of a polyimide alignment agent according to claim 1, wherein The method comprises the following steps: a1. filtering the polyimide solution alignment agent through a microporous filter membrane; a2. spraying the alignment agent solution in a1 on ITO glass, then sequentially placing the ITO glass substrate in a temperature of 70-110℃ for 10-20min, and then imidizing at a temperature of 200-250℃ for 30-60min; a3. rubbing the polyimide film on the ITO glass substrate in a2 using a rubbing machine at an angle of 45°; a4. bonding the two ITO glass substrates coated with the liquid crystal alignment film into a cell with the rubbing surfaces opposite to each other and the rubbing directions orthogonal by using a hot curing adhesive containing 4um spacer particles, filling in liquid crystal, and then sealing with light curing adhesive to obtain a liquid crystal cell.

Images