Liquid crystal alignment agent, prepared liquid crystal alignment film and display element containing the alignment film

Abstract

The present invention discloses a liquid crystal alignment agent, a liquid crystal alignment film and a liquid crystal display element, wherein the liquid crystal alignment agent comprises a polymer obtained by reacting a tetracarboxylic dianhydride component a and a diamine component b, wherein the diamine component b comprises one or more of diamine compounds b-1 having a structure of the following formula 1; wherein R1 and R2 are each independently selected from a group of terminal amino groups. The liquid crystal display element obtained by the liquid crystal alignment agent of the present invention has the advantages of excellent light orientation performance, high imidization rate, good thermal stability and excellent residual image performance.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid crystal display, and in particular to a liquid crystal alignment agent, a prepared liquid crystal alignment film and a display element containing the alignment film. Background Art

[0002] In the 1980s, the production technology of thin-film transistor liquid crystal display was successfully developed and began to be mass-produced. It has now become the mainstream technology in the information display industry. Because of its high resolution, light weight, low energy consumption and flat display advantages, it has been widely used in various display areas, such as mobile phones, car displays, computer monitors, industrial display screens, etc. The working principle of liquid crystal display is that each pixel inside the screen has a TFT structure switch to control the voltage on and off, and control the application of an external electric field to the liquid crystal. The polar molecules of the liquid crystal twist under the action of the external electric field, changing the arrangement state of the liquid crystal molecules inside, so that the incident polarized light changes direction, and the use of polarizers can control whether the light passes through, thereby achieving the purpose of display. Liquid crystal display elements usually use an alignment film to control the initial arrangement state of the liquid crystal. The liquid crystal alignment film is an alignment film of a certain thickness prepared by coating a liquid crystal alignment agent on a display substrate and then baking and aligning treatment. The most mainstream method of alignment treatment is rubbing alignment treatment, that is, using cotton cloth or nylon to rub the liquid crystal alignment film on the electrode substrate in a single direction to produce grooves on the surface of the liquid crystal alignment film or to make the surface molecules of the alignment film orderly arranged along the rubbing direction, thereby inducing the arrangement of liquid crystal molecules on the surface of the alignment film. With the development and progress of society, people have higher and higher requirements for the quality of liquid crystal display. Various problems such as surface scratches, debris, static electricity and poor alignment of concave and convex parts in the surface caused by rubbing orientation can no longer meet the existing needs.

[0003] As a method to replace friction alignment, the use of linear polarized ultraviolet light to irradiate the surface of the liquid crystal alignment film to align the liquid crystal. The photo-orientation treatment can be divided into three types according to the mechanism, namely photodecomposition, photoisomerization and photocross-linking. Since photoisomerization has poor structural stability, most of the commercialized photo-orientation films currently use the photodecomposition method.

[0004] Liquid crystal boxes are divided into TN (twisted nematic), STN (super twisted), IPS (in-plane switching), FFS (fringe field switching), VA (vertical alignment) and other liquid crystal display elements according to the liquid crystal driving mode under the application of an external electric field. Among them, IPS (in-plane switching) and FFS (fringe field switching) display modes are widely used in high-end display areas such as mobile phones, home TVs and home computer displays due to their advantages such as high contrast and wide field of view. Compared with the existing friction orientation process, the above-mentioned optical orientation treatment method helps to improve the contrast and viewing angle of the two display modes of IPS and FFS, because the optical orientation treatment is more uniform than the friction orientation, and will not be affected by the uneven shape, scratches and static electricity of the substrate surface. However, compared with the friction orientation, the optical orientation treatment has the problem of weak liquid crystal anchoring ability, and afterimages will be generated after AC driving during long-brightness.

[0005] During the driving process of IPS and FFS type liquid crystal display elements TFT (thin film transistor), DC bias charge is generated. As the DC bias charge accumulates on the surface, an electric field of the bias charge is formed. When switching the screen, the accumulated charge cannot dissipate quickly, which will cause the electric field strength received by the liquid crystal to be inconsistent with the direction of the applied electric field strength, resulting in afterimages caused by the accumulation of DC charge. Summary of the invention

[0006] The purpose of the present invention is to provide a liquid crystal display element with excellent photo-orientation performance, high imidization rate, good thermal stability and excellent afterimage performance, in order to address the problems arising in liquid crystal display elements with IPS and FFS driving modes, such as afterimages caused by weak anchoring force of liquid crystal molecules and accumulation of DC charges.

[0007] The present invention solves the above technical problems through the following technical means:

[0008] A liquid crystal alignment agent, comprising a polymer obtained by reacting a tetracarboxylic dianhydride component a and a diamine component b, wherein the diamine component b comprises one or more diamine compounds b-1 having a structure of the following formula (1);

[0009]

[0010] Wherein, R1 and R2 are each independently selected from a terminal amino group.

[0011] Preferably, the terminal amino group includes any one of amino and aromatic amino.

[0012] Preferably, the aromatic amine is one of -O-aromatic amine, amide aromatic amine, carbonyl aromatic amine, alkyl aromatic amine, and mercapto aromatic amine.

[0013] Preferably, the terminal amino group is any one of the following groups: -NH2,

[0014]

[0015] Preferably, the structural formula of the diamine compound b-1 is

[0016]

[0017]

[0018] Preferably, the tetracarboxylic dianhydride component a is a mixture of one or more of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, pyromellitic dianhydride, and 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride.

[0019] Preferably, the diamine component b further comprises p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 2,4'-diaminododecyloxybenzene, 1,3-bis(4-aminophenoxy)propane, 1,2-bis(4-aminophenoxy)ethane, N-methyl p-aminophenylethylamine, m-phenylenediamine, 3,5-diaminobenzoic acid, 1,3-bis(4-aminophenyl)urea, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, p-aminophenylethylamine, 4,4'-diaminodiphenylethane, 4,4'- A mixture of one or more of diaminobenzophenone, 1,3-bis(4-aminophenoxy)propane, N,N'-bis(4-aminophenyl)piperazine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,4-diaminooctadecyloxybenzene, 4,4'-diaminobenzamide, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2'-dimethyl-4,4'-diaminobiphenyl, and 4,4'-diaminodiphenylamine.

[0020] Preferably, the molar ratio of the diamine component b to the tetracarboxylic dianhydride component a is 100:80-120, more preferably 100:90-100.

[0021] Preferably, it also includes a solvent; the solvent is a mixture of one or more of N-methyl-2-pyrrolidone, N-ethylpyrrolidone, γ-butyrolactone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diacetone alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, and diethylene glycol methyl ether acetate.

[0022] In addition, the diamine component b and the tetracarboxylic dianhydride component a are polymerized in a reaction solvent, and the polymerization reaction temperature of the diamine component b and the tetracarboxylic dianhydride component a in the reaction solvent is preferably 0 to 150°C, more preferably 20 to 80°C, and the polymerization reaction time is preferably 0.5 to 24 hours, more preferably 2 to 6 hours. In addition, the reaction can be carried out at any concentration. If the reaction concentration is too low, it is difficult to obtain a high molecular weight degree of polymerization. If the reaction concentration is too high, the viscosity of the reaction liquid is large and is not conducive to sufficient stirring. The reaction concentration is preferably a solid content (the ratio of the sum of the weight of the diamine component b and the tetracarboxylic dianhydride component a used in the reaction to the weight of the reaction liquid) 2 to 50%, more preferably 5 to 30%.

[0023] There is no particular limitation on the solvent used for the polymerization reaction or the dilution of the polymer solid to prepare the liquid crystal alignment agent, as long as the polymer can be dissolved therein and the prepared liquid crystal alignment agent has excellent coating performance on the substrate. For example, there can be listed a mixture of one or more solvents selected from N-methylpyrrolidone, N-ethylpyrrolidone, γ-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, diacetone alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, and diethylene glycol methyl ether acetate.

[0024] The present invention also provides a liquid crystal alignment film, which is made of the liquid crystal alignment agent.

[0025] The present invention also provides a liquid crystal display element, comprising the liquid crystal alignment film.

[0026] The beneficial effect of the present invention is that the liquid crystal alignment agent of the present invention is polymerized by a diamine monomer containing a benzimidazole cyclobutane benzimidazole fragment structure and a tetraacid dianhydride monomer. Because the unbonded n electrons of the N atom in the imidazole structure of the diamine monomer and the π electrons of N=C synergistically enhance the transition of the absorption of 254nm ultraviolet light energy to the excited state, the excited state electrons then return to the ground state and release energy to the cyclobutane to promote the cracking of the cyclobutane to form excellent alignment performance. The lone pair of electrons of the N atom in the benzimidazole structure forms a large π system conjugation with the benzene ring, which helps to quickly release the stored charge of the liquid crystal box, shorten the disappearance time of the residual image of the liquid crystal display element, and has good residual image performance.

[0027] The present invention selects a polyamic acid solution containing a specific structure to prepare a liquid crystal alignment agent, and the liquid crystal display element prepared therefrom has the advantages of excellent light alignment performance, high imidization rate, good thermal stability and excellent afterimage performance. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0030] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0031] The resistivity of the high-purity water used below is 18MΩ*cm.

[0032] Synthesis Example of Diamine Compound

[0033] (1) Synthesis of diamine compound b-1-1, the process is as follows:

[0034]

[0035] The specific steps include:

[0036] In a 1000ml three-necked flask, 4-nitro-o-phenylenediamine (84.226g, 0.55mol) was added to a mixture of 500g THF and triethylamine (50.595g, 0.5mol) to obtain solution A. A solution B was prepared by dissolving 1,3-dichlorocyclobutane (45.255g, 0.25mol) in 320g THF. Solution B was added dropwise to solution A under stirring, and the reaction temperature was controlled to be less than 25°C. After solution B was dripped in 2 hours, the reaction temperature was increased to 60-65°C and kept warm for one hour. No 4-nitro-o-phenylenediamine was found to remain after TLC tracking. After the reaction was completed, the temperature was lowered to room temperature, the slurry was poured into 3000ml high-purity water, and stirring was continued for 10 minutes. The filter cake was filtered to obtain a filter cake. The filter cake was then added with 1000ml high-purity water and slurried for 10 minutes, and filtered to obtain a filter cake. Add 500 g of ethanol to the filter cake, heat to 50-60°C and stir for 20 min. Filter and dry to obtain 87.206 g of yellow product b-1-1a with a yield of 84.24%.

[0037] Add sample b-1-1a (62.157 g, 0.15 mol) and 600 ml acetic acid into a 1000 ml three-necked flask, heat to reflux for 12 h, cool, filter and dry to obtain 54.342 g solid b-1-1b, with a yield of 95.75%.

[0038] In a 1000ml autoclave, b1-1-1b (37.835g, 0.1mol), 5% platinum carbon (3.7g, solid content of 30%) and 300g 1,4-dioxane were added, the autoclave was sealed, replaced with hydrogen three times, the hydrogen was pressurized to 0.8-1.0MPa, and the reaction was stirred at 80-90°C. After the reaction was completed, the catalyst was removed by filtration, 260g of solvent was removed from the filtrate, 120g of ethanol was added to the filtrate to precipitate solids and stirred for 30 minutes, and 28.457g of solid compound b-1-1 was obtained by filtration and drying, with a yield of 89.38%.

[0039] The high-resolution mass spectrum of the compound b-1-1, ESI source, positive ion mode, theoretical value 318.16, test value 318.18. Elemental analysis (C 18 H 18 N6), theoretical value C: 67.90, H: 5.70, N: 26.40; measured value C: 67.90, H: 5.71, N: 26.39, confirming that the substance is b-1-1.

[0040] (2) Preparation of diamine compound b-1-2, the process is as follows:

[0041]

[0042] The specific steps include:

[0043] b-1-1 (31.838 g, 0.1 mol), p-chloronitrobenzene (34.662 g, 0.22 mol), sodium hydroxide (8.8 g, 0.22 mol) and 400 g DMSO were added to a 1000 ml three-necked flask, and the reaction was heated to 110-120 ° C. After TLC tracking showed that there was no b-1-1 remaining, the temperature was kept for 1 hour; after the reaction was completed, the temperature was cooled to room temperature, the slurry was poured into 2000 ml of high-purity water, and the stirring was continued for 10 minutes, and the filter cake was filtered. The filter cake was then added with 1000 ml of high-purity water and slurried for 10 minutes, and the filter cake was filtered. 500 g of ethanol was added to the filter cake, heated to 50-60 ° C and stirred for 20 minutes, filtered, and dried to obtain 44.059 g of b-1-2a, with a yield of 78.65%.

[0044] b1-1-2a (28.009 g, 0.05 mol), 5% platinum carbon (2.7 g, solid content 30%) and 200 g 1,4-dioxane were added to a 1L autoclave, the autoclave was sealed, and after replacing with hydrogen three times, the hydrogen was pressurized to 0.8-1.0 MPa, and the reaction was stirred at 80-90 ° C. After the reaction was completed, the catalyst was removed by filtration, 160 g of solvent was removed from the filtrate, and 100 g of ethanol was added to the filtrate to precipitate solids and stirred for 30 minutes. After filtration and drying, 22.848 g of solid compound b-1-2 was obtained, with a yield of 91.35%.

[0045] The high-resolution mass spectrum of compound b-1-2, ESI source, positive ion mode, theoretical value 500.24, test value 500.23. Elemental analysis (C 30 H 28 N8), theoretical value C: 71.98, H: 5.64, N: 22.38; measured value C: 71.98, H: 5.65, N: 22.37, confirming that the substance is b-1-2.

[0046] (3) Preparation of diamine compound b-1-3, the process is as follows:

[0047]

[0048] The specific steps include:

[0049] b-1-1 (31.838 g, 0.1 mol), p-nitrobenzoyl chloride (37.113 g, 0.2 mol) and 400 g DMF were added to a 1000 ml three-necked flask, and triethylamine (20.238 g, 0.2 mol) was added dropwise through a dropping funnel. The reaction temperature was controlled to be less than 25 ° C. After the triethylamine was added in 1 hour, the mixture was heated to 60-65 ° C. After TLC tracking showed that there was no b-1-1 remaining, the mixture was kept warm for 1 hour. After the reaction was completed, the slurry was poured into 2000 ml of high-purity water, stirred for 10 minutes, and filtered to obtain a filter cake. The filter cake was then added with 1000 ml of high-purity water and beaten for 10 minutes, and filtered to obtain a filter cake. The filter cake was then added with 500 g of ethanol, heated to 50-60 ° C and stirred for 20 minutes, filtered, and dried to obtain 52.111 g of b-1-3a, with a yield of 84.57%.

[0050] b1-1-3a (28.009 g, 0.05 mol), 5% platinum carbon (2.7 g, solid content 30%) and 200 g 1,4-dioxane were added to a 1L autoclave, the autoclave was sealed, replaced with hydrogen three times, the hydrogen was pressurized to 0.8-1.0 MPa, and the reaction was stirred at 80-90 ° C. After the reaction was completed, the catalyst was removed by filtration, 160 g of solvent was removed from the filtrate, 100 g of ethanol was added to the filtrate to precipitate solids and stirred for 30 minutes, and 25.943 g of solid compound b-1-3 was obtained by filtration and drying, with a yield of 93.28%.

[0051] The high-resolution mass spectrum of compound b-1-3, ESI source, positive ion mode, theoretical value 556.23, test value 556.25. Elemental analysis (C 32 H 28 N8O2), theoretical value C: 69.05, H: 5.07, N: 20.13, O: 5.75; measured value C: 69.05, H: 5.08, N: 20.12, O: 5.75; it was determined that the substance was b-1-3.

[0052] The abbreviations of the compounds used in the following examples and comparative examples are as follows:

[0053] NMP: N-methyl-2-pyrrolidone

[0054] BC: Ethylene glycol monobutyl ether

[0055] b-2-1: p-phenylenediamine

[0056] b-2-2: 4,4'-diaminodiphenylmethane

[0057] b-2-3: 4,4'-diaminodiphenyl ether

[0058] b-2-4: 2,4'-diaminododecyloxybenzene

[0059] b-2-5: 1,3-bis(4-aminophenoxy)propane

[0060] a-1: 1,2,3,4-cyclobutanetetracarboxylic dianhydride, structural formula:

[0061] a-2: 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, structural formula:

[0062] a-3: pyromellitic dianhydride, structural formula:

[0063] a-4: 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, structural formula:

[0064] Example 1

[0065] Synthesis of polyamic acid solution: comprises the following steps: under a nitrogen atmosphere, a 500 ml three-necked round-bottom flask is charged with compound b-1-1 (15.909 g, 50 mmol), compound b-2-1 (3.242 g, 30 mmol) and compound b-2-5 (5.162 g, 20 mmol) as diamines and 124.472 g of NMP, and compound a-1 (19.618 g, 100 mmol) as tetracarboxylic dianhydride and 124.472 g of NMP are added, and the mixture is reacted at 40°C for 8 hours to obtain a solution containing 15% by mass of polyamic acid (referred to as polymer (PA-1-1)).

[0066] Dilution: Take 100g of PA-1-1 polyamic acid solution, add 100g NMP and 50g BC, stir at room temperature for 2 hours, and then filter through a 0.1μm filter membrane to obtain liquid crystal alignment agent A-1-1. The mass concentration of the polymer in the above liquid crystal alignment agent is 6%, the mass content of the solvent BC is 20%, and the rest is NMP.

[0067] The preparation methods of Examples 2-12 are similar to those of Example 1, except that: in the synthesis process of the polyamic acid solution, the types and usage ratios of the diamine and dianhydride monomers used are changed; the monomers of each example are specifically described in Table 1 below: wherein the total molar number of the diamine is 100 mmol, and the total molar number of the dianhydride is 100 mmol;

[0068] Table 1

[0069] Serial number Liquid crystal alignment agent Diamine (mol%) Dianhydride (mol%) Example 1 A-1-1 b-1-1(50%), b-2-1(30%), b-2-5(20%) a-1(100％) Example 2 A-1-2 b-1-1(60%), b-2-1(20%), b-2-4(20%) a-3(100％) Example 3 A-1-3 b-1-1(50%), b-2-2(30%), b-2-3(20%) a-4(100％) Example 4 A-1-4 b-1-1(40%), b-2-3(40%), b-2-5(20%) a-2(100％) Example 5 A-1-5 b-1-2(55%), b-2-2(25%), b-2-4(20%) a-4(100％) Example 6 A-1-6 b-1-2(45%), b-2-1(35%), b-2-5(20%) a-1(100％) Example 7 A-1-7 b-1-2(50%), b-2-3(30%), b-2-5(20%) a-3(100％) Example 8 A-1-8 b-1-2(60%), b-2-1(20%), b-2-2(20%) a-3(50%)、a-4(50%) Example 9 A-1-9 b-1-3(50%), b-2-1(25%), b-2-5(25%) a-2(100％) Example 10 A-1-10 b-1-3(40%), b-2-1(40%), b-2-3(20%) a-1(50%)、a-2(50%) Embodiment 11 A-1-11 b-1-3(50%), b-2-3(30%), b-2-4(20%) a-4(100％) Example 12 A-1-12 b-1-3(60%), b-2-2(20%), b-2-5(20%) a-1(100％)

[0070] The preparation methods of Comparative Examples 1-6 are similar to those of Example 1, except that: in the synthesis process of the polyamic acid solution, the types and usage ratios of the diamine and dianhydride monomers used are changed; the monomers of each comparative example are specifically described in Table 2 below: wherein the total molar number of the diamine is 100 mmol, and the total molar number of the dianhydride is 100 mmol;

[0071] Table 2

[0072]

[0073] Prepare an IPS type liquid crystal display box according to the following method, prepare two glass substrates of 3cm×4cm and 0.5mm thickness, wherein the lower substrate has a comb-shaped ITO electrode with an electrode width of 10μm, and the spacing between adjacent comb-shaped electrodes is 10μm, and the pixel electrode and the common electrode are arranged in a cross pattern. The upper glass substrate has no electrode, and the prepared liquid crystal alignment agent is coated on the two substrates, and after pre-baking at 100℃ for 3 minutes and main curing (oven, 230℃, 30 minutes), a polyimide alignment film with a film thickness of 100nm is obtained.

[0074] The upper and lower glass substrates with polyimide coating were irradiated with ultraviolet polarized light for photo-alignment treatment. The wavelength of the irradiated ultraviolet polarized light was 254nm and the light dose was 400mj / cm 2 , and then heated in an oven at 230℃ for 30min, the upper and lower glass substrates that had been oriented were spin-coated with spacer microspheres with a diameter of 4μm on one substrate, and the other substrate was cut with a sealant at the edge. The sealant was cut directly on the surface of the orientation agent film, and a liquid crystal injection port with a diameter of 2mm was left. Then, the upper and lower substrates were bonded together in a manner that the orientation films were face to face, the polarization axes of the light orientation treatment were parallel, and the upper and lower substrates overlapped with a width of 3cm. The sealant was irradiated with a 365nm ultraviolet lamp for 30s for pre-curing, and thermally cured at a temperature of 150℃ for 30min to prepare an empty liquid crystal box. IPS liquid crystal was injected into the empty box by vacuum crystal filling; the liquid crystal injection port was sealed with a sealant, and the sealant was irradiated with a 365nm ultraviolet lamp for 60s to complete the curing of the sealant. The corresponding liquid crystal display element was prepared.

[0075] Characterization of the imidization rate of liquid crystal alignment film:

[0076] 50 μl of the liquid crystal alignment agent corresponding to the embodiment of the present invention and the comparative example were dropped on two potassium bromide windows respectively. The curing temperature and time of the two liquid crystal alignment agent potassium bromide windows were as follows: potassium bromide 1: pre-baking at 100°C×3min, post-baking at 230°C×20min; potassium bromide 2: pre-baking at 100°C×3min, post-baking at 300°C×30min. Infrared absorption test (instrument model: IRAffinity-1S, manufacturer: Shimadzu) was performed to record the 1360cm -1 The intensity of the absorption peak of the CN bond at 1510 cm -1 The intensity of the benzene ring absorption peak is measured, and then the ratios of CN to benzene ring absorption peaks at 230℃ and 300℃ are calculated as A1 and A2 respectively. The potassium bromide 2 post-baked at 300℃ is taken as the reference value of 100% imidization rate, then the imidization rate IR of the oriented film post-baked at 230℃ = (A1 / A2) × 100%.

[0077] ◎: IR≥90%, excellent imidization rate of liquid crystal alignment film;

[0078] ○: 90%>IR≥80%, the imidization rate of the liquid crystal alignment film is good;

[0079] △: 80%>IR, the imidization rate of the liquid crystal alignment film is poor;

[0080] Thermal stability of liquid crystal alignment film:

[0081] The thermal stability of the liquid crystal alignment film can be evaluated by the voltage holding ratio of the liquid crystal display element (hereinafter referred to as VHR). More specifically, the method for detecting the voltage holding ratio is as follows.

[0082] The conditions for testing VHR are: load 5V voltage, disconnect the voltage after 60us, and measure the VHR 167ms after the voltage is disconnected (recorded as VHR0). Then place the liquid crystal display element in an environment of 60℃ for 24 hours, and measure the VHR at this time (recorded as VHR1) using the same method. Then calculate the change value of VHR (recorded as ΔVHR(%)) by the formula. The lower the ΔVHR(%), the better the thermal stability.

[0083]

[0084] ◎: ΔVHR (%) ≤ 5%, excellent thermal stability;

[0085] ○: 5%<ΔVHR(%)≤10%, good thermal stability;

[0086] △: 10%<ΔVHR(%), poor thermal stability;

[0087] Evaluation of residual image performance of liquid crystal alignment film:

[0088] The afterimage performance of the liquid crystal alignment film can be evaluated by the residual voltage of the liquid crystal display element (hereinafter referred to as RDC). More specifically, the residual voltage of the liquid crystal display element is detected as follows.

[0089] The conditions for testing RDC are: to the liquid crystal display element manufactured by the above operation, a DC voltage of 5V is applied for 1 hour at an ambient temperature of 60°C, and then the external voltage is removed, the pixel electrode and the common electrode are short-circuited for 1 second, and then the residual voltage between the two electrodes is immediately tested for 600 seconds.

[0090] The evaluation criteria for RDC are as follows:

[0091] ◎: RDC≤0.2V, excellent afterimage performance;

[0092] ○: 0.2V<RDC≤0.6, good afterimage performance

[0093] △: RDC>0.6V, poor afterimage performance

[0094] Liquid crystal orientation evaluation:

[0095] The prepared IPS liquid crystal display box was placed between the upper and lower polarizers, and the dark state of the liquid crystal display box was observed.

[0096] ◎: The dark state of the liquid crystal display cell is completely opaque and has good orientation performance;

[0097] △: There is light emitted in the dark state of the liquid crystal display cell, and the orientation performance is poor;

[0098] The performance of each embodiment is shown in Table 3 below:

[0099] Table 3

[0100] Serial number Liquid crystal alignment agent Orientation performance Imidization rate (%) Thermal stability (%) Afterimage performance (mV) Example 1 A-1-1 ◎ 91.2 3.13 106 Example 2 A-1-2 ◎ 94.5 2.18 94 Example 3 A-1-3 ◎ 92.3 3.39 82 Example 4 A-1-4 ◎ 91.8 3.84 74 Example 5 A-1-5 ◎ 93.5 4.12 88 Example 6 A-1-6 ◎ 94.8 2.89 123 Example 7 A-1-7 ◎ 93.9 3.67 109 Example 8 A-1-8 ◎ 92.7 1.81 114 Example 9 A-1-9 ◎ 95.3 1.67 98 Example 10 A-1-10 ◎ 94.7 2.02 104 Embodiment 11 A-1-11 ◎ 93.6 2.54 91 Example 12 A-1-12 ◎ 91.6 2.76 121

[0101] The performance of each comparative example is shown in Table 4 below:

[0102] Table 4

[0103]

[0104]

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid crystal alignment agent, characterized in that: The liquid crystal alignment agent comprises a polymer obtained by reacting a tetracarboxylic dianhydride component a and a diamine component b, wherein the diamine component b is one or more of a diamine compound b-1 having a structure of the following formula (1) and comprises p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 2,4'-diaminododecyloxybenzene, 1,3-bis(4-aminophenoxy)propane, 1,2-bis(4-aminophenoxy)ethane, m-phenylenediamine, 3,5-diaminobenzoic acid, 1,3-bis(4-aminophenyl)urea, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, p-amino A mixture of one or more of phenylethylamine, 4,4'-diaminodiphenylethane, 4,4'-diaminobenzophenone, 1,3-bis(4-aminophenoxy)propane, N,N'-bis(4-aminophenyl)piperazine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,4-diaminooctadecyloxybenzene, 4,4'-diaminobenzamide, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2'-dimethyl-4,4'-diaminobiphenyl, and 4,4'-diaminodiphenylamine; Wherein, R1 and R2 are each independently selected from a terminal amino group; the terminal amino group includes any one of an amino group and an aromatic amino group.

2. The liquid crystal alignment agent according to claim 1, characterized in that: The terminal amino group is any one of the following groups: -NH2, 3. The liquid crystal alignment agent according to claim 1, characterized in that: The structural formula of the diamine compound b-1 is 4. The liquid crystal alignment agent according to claim 1, characterized in that: The tetracarboxylic dianhydride component a is a mixture of one or more of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, pyromellitic dianhydride, and 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride.

5. The liquid crystal alignment agent according to any one of claims 1 to 4, characterized in that: It also includes a solvent; the solvent is a mixture of one or more of N-methyl-2-pyrrolidone, N-ethylpyrrolidone, γ-butyrolactone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diacetone alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, and diethylene glycol methyl ether acetate.

6. A liquid crystal alignment film, characterized in that: Made from the liquid crystal alignment agent described in any one of claims 1 to 5.

7. A liquid crystal display element, characterized in that: Comprising the liquid crystal alignment film as claimed in claim 6.

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