A liquid crystal alignment agent, its preparation method and application

Abstract

This invention provides a liquid crystal alignment agent, its preparation method, and its application, belonging to the field of liquid crystal technology. The method includes the following steps: mixing a diamine solution with tetracarboxylic dianhydride to obtain a polyamic acid solution; adding an auxiliary agent system to the polyamic acid solution to obtain the liquid crystal alignment agent; the auxiliary agent system includes a polar aprotic solvent, a leveling agent, and a stabilizer. The liquid crystal alignment agent obtained by this invention increases the anchoring ability of the alignment film to the liquid crystal, resulting in a highly stable alignment effect without defects, excellent pretilt angle stability, and good reliability. When applied to liquid crystal films, it can be effectively used in various devices, such as timers, calculators, clocks, word processors, laptops, automotive central control systems, portable digital devices, mobile phones, various monitors, various LCD TVs, information displays, and non-display type liquid crystal panels with special functions.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal technology, and in particular to a liquid crystal alignment agent, its preparation method, and its application. Background Technology

[0002] The display characteristics of liquid crystal display elements are affected by liquid crystal alignment, pretilt angle, stability, and electrical properties. Therefore, the liquid crystal material and liquid crystal alignment film used are very important in order to improve the display characteristics of liquid crystal display elements.

[0003] Liquid crystal alignment film materials are fundamental to liquid crystal molecule alignment technology and a crucial guarantee for realizing new LCD display methods. Common display modes include TN (Twisted Nematic), IPS (In-Plane Switching), VA (Vertical Alignment), and OCB (Optically Compensated Bending Alignment). In existing LCD panel manufacturing processes (first-generation G1 to eleventh-generation G11 production lines), PI (polyimide) material is primarily used as the alignment film. After treatment, anisotropy of molecular orientation is generated on its surface, inducing liquid crystal molecules to be "anchored" and subsequently oriented under the influence of an electric field. Polyimide, as a liquid crystal alignment agent, has the following advantages: the film itself has the function of orienting liquid crystal molecules; it has good alignment effects on all liquid crystal materials, exhibiting better applicability than other alignment materials; it is simple to process, allowing for rotation, rolling, spraying, and gravure coating according to the substrate size, simplifying the production process; it does not chemically react with liquid crystal molecules; it has strong adhesion to the substrate; and it is highly hydrophobic. Summary of the Invention

[0004] The purpose of this invention is to provide a liquid crystal alignment agent, its preparation method, and its application.

[0005] The present invention has the following beneficial effects:

[0006] The present invention provides a method for preparing a liquid crystal alignment agent, comprising the following steps: mixing a diamine solution with a tetracarboxylic acid dianhydride to obtain a polyamic acid solution; adding an auxiliary agent system to the polyamic acid solution to obtain the liquid crystal alignment agent; wherein the auxiliary agent system comprises a polar aprotic solvent, a leveling agent, and a stabilizer. The liquid crystal alignment agent obtained by the method of the present invention effectively increases the anchoring ability of the alignment film to the liquid crystal, resulting in a highly stable alignment effect of the alignment film, free from defects, and exhibiting excellent pretilt angle stability and good reliability.

[0007] The liquid crystal alignment agent obtained by the preparation method of the present invention is applied to the liquid crystal film, and the liquid crystal film can be effectively used in various devices, such as timers, calculators, clocks, word processors, laptops, automotive central control systems, portable digital devices, mobile phones, mobile phones, various monitors, various LCD TVs, information displays, and non-display type liquid crystal panels with special functions (liquid crystal panels with light phase adjustment, light refraction adjustment functions, etc.). Detailed Implementation

[0008] The present invention provides a method for preparing a liquid crystal alignment agent, comprising the following steps: (1) mixing a diamine solution with a tetracarboxylic acid dianhydride to obtain a polyamic acid solution; (2) adding an auxiliary agent system to the polyamic acid solution to obtain the liquid crystal alignment agent; wherein the auxiliary agent system comprises a polar aprotic solvent, a leveling agent and a stabilizer.

[0009] In this invention, the solvent in the diamine solution in step (1) is preferably N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, m-cresol or tetrahydrofuran.

[0010] In this invention, the molar ratio of diamine to solvent in the diamine solution is preferably 0.1:0.6 to 1.2, more preferably 0.1:0.7 to 1.1, and even more preferably 0.1:0.8 to 1.0.

[0011] In this invention, the diamine in step (1) comprises a basic diamine and an orientation diamine;

[0012] The molar ratio of the basic diamine to the oriented diamine is preferably 0.01–100:0.01–50, more preferably 10–90:1–50, and even more preferably 40–60:20–30.

[0013] In this invention, the basic diamine is:

[0014]

[0015] X1 and X2 are independently hydrogen atoms, alkyl groups with 1 to 10 carbon atoms, alkenyl chains with 2 to 10 carbon atoms, and alkynyl chains with 2 to 10 carbon atoms. From the perspective of liquid crystal orientation, X1 and X2 are preferably hydrogen atoms or alkyl chains with 1 carbon atom.

[0016] The structure of Z1 is as follows:

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032] Among Z-25, Z-26, Z-27, Z-28, Z-92, Z-93 and Z-97, n independently ranges from 2 to 10;

[0033] Among Z-116, Z-118, Z-129, Z-131, Z-166, Z-182 and Z-185, n independently ranges from 1 to 20;

[0034] In Z-130, n ranges from 0 to 20;

[0035] In Z-156 and Z-161, n is independent and ranges from 1 to 5;

[0036] In Z-96, the number of R2 is 1 to 8, and R2 can be H, F, Cl, Br, I, CH3, CF3, CN or a benzene ring;

[0037] In Z-123, R3 can be F, Cl, Br, I, CH3, CF3, CN, or a benzene ring;

[0038] In Z-131, the number of R4 is 1 to 2, and the R4 can be F, Cl, Br, I, CH3, CF3 or CN, or a benzene ring.

[0039] In Z-138, the number of R5 is 1 to 2, and the R5 can be F, Cl, Br, I, CH3, CF3 or CN, or a benzene ring.

[0040] In Z-174, the number of R6 is 1 to 2, and R6 can be -COO, -OCO, -NHCO, -N(CH3)CO or a benzene ring.

[0041] The orientation diamine is:

[0042]

[0043] R7 represents one or more selected from -O-, -COO, -OCH2, -COOCH2, -CH2OCO, -CH2O, -NHCO, -CONH, -N(CH3)CO, alkenes, alkynes, benzene rings, cyclohexane, and imide rings;

[0044] R8 is an alkyl chain with 1 to 50 carbon atoms.

[0045] In this invention, the aligning diamine is preferably:

[0046]

[0047] In this invention, the basic diamine serves as the basis for synthesizing the polyimide material, and different structures can be selected to adjust the bulk resistance. The alignment diamine provides the orientation properties of the polyimide material. After photo-alignment, the synthesized polyimide material can be aligned with the liquid crystal, so that the liquid crystal cell has a certain pretilt angle.

[0048] In this invention, the basic diamine can be classified into high-resistance and low-resistance types according to its bulk resistance.

[0049] High resistance basic diamine structures include: Z-1~Z-10, Z-13~Z-19, Z-29~Z-30, Z-41~Z-42, Z-49~Z-50, Z-52~Z-57, Z-61~Z-62, Z-64~Z-72, Z-98~Z-105, Z-1 07~Z-109, Z-113~Z-115, Z-124~Z-128, Z-134~Z-135, Z-145~Z-150, Z-158~Z-160, Z-162~Z-163, Z-173~Z-174, Z-191~Z-193.

[0050] Low resistance basic diamine structures include: Z-11~Z-12, Z-20~Z-28, Z-31~Z-40, Z-43~Z-48, Z-51, Z-58~Z-60, Z-63, Z-73~Z-97, Z-106, Z -110~Z-112, Z-116~Z-123, Z-129~Z-133, Z-136~Z-144, Z-151~Z-157, Z-161, Z-164~Z-172, Z-175~Z-190.

[0051] In this invention, the tetracarboxylic acid dianhydride is:

[0052]

[0053]

[0054]

[0055] In G-3, the number of R9 is 1 to 2. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group.

[0056] In G-40, the number of R9 is 1 to 4. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group.

[0057] In G-41, the number of R9 is 1 to 5. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group.

[0058] In G-42, the number of R9 is 1 to 6. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group.

[0059] In G-43, the number of R9 is 1 to 6. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group.

[0060] The monovalent organic group containing fluorine atoms with 1 to 6 carbon atoms is:

[0061]

[0062] The preferred molar ratio of diamine to tetracarboxylic acid dianhydride is 100:80-100, more preferably 100:90-100, and even more preferably 100:95-100.

[0063] In this invention, the reaction viscosity is controlled by adjusting the molar ratio of diamine to tetracarboxylic acid dianhydride.

[0064] In this invention, tetracarboxylic dianhydrides can be classified into high-resistance tetracarboxylic dianhydrides and low-resistance tetracarboxylic dianhydrides based on their bulk resistance.

[0065] In this invention, the high-resistivity tetracarboxylic dianhydride is G-1 to G-4, G-7 to G-13, G-22, or G-28;

[0066] The low-resistivity tetracarboxylic acid dianhydrides are G-5, G-6, G-14 to G-21, G-23 to G-27, G-29 to G-43.

[0067] In this invention, the mixing temperature in step (1) is preferably -15 to 100°C, more preferably 0 to 80°C, and even more preferably 20 to 60°C. The mixing time is preferably 0.5 to 48 hours, more preferably 1 to 24 hours, and even more preferably 2 to 12 hours.

[0068] In this invention, the solid content of the polyamic acid solution obtained in step (1) is preferably 10-50%, more preferably 12-40%, and even more preferably 15-30%.

[0069] In this invention, the polar aprotic solvent is preferably one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, m-cresol, and tetrahydrofuran.

[0070] The leveling agent is:

[0071]

[0072] Among them, R 13 R represents alkyl groups with 1 to 12 carbon atoms. 14 -OH and / or -O;

[0073] In this invention, the mass ratio of the polar aprotic solvent to the leveling agent is preferably 20-80:20-80, more preferably 40-60:40-60, and even more preferably 45-55:45-55.

[0074] In this invention, the leveling agent is preferably ethyl acetate, ethylene glycol monobutyl ether, diethylene glycol diethyl ether, diacetone alcohol, ethylene glycol butyl ether acetate, etc.

[0075] In this invention, the stabilizer is:

[0076]

[0077] R 10 It can be a benzene ring, cyclohexane, cyclopentane, piperazine, imidazoline, pyridine, imidazole, benzoxazole, benzothiazole, pyrimidine, pyrazine, or triazine;

[0078] R11 Selected from one or more of -O-, -CH2-, -CHCH3-, -CCH3CH3-, -COO, -OCH2, -COOCH2, -CH2OCO, -CH2O, -NHCO, -CONH, -N(CH3)CO, alkenes, alkynes, benzene rings, cyclohexane, or imide rings;

[0079] R 12 It is an alkyl chain with 1 to 50 carbon atoms.

[0080] In this invention, the stabilizer is preferably:

[0081] In this invention, the mass of the stabilizer is preferably 0.01-20% of the combined mass of the diamine and tetracarboxylic dianhydride, more preferably 5-15%, and even more preferably 8-12%.

[0082] In this invention, the solid content of the liquid crystal alignment agent is preferably 1 to 10%, more preferably 3 to 8%, and even more preferably 5 to 6%.

[0083] The present invention also provides a liquid crystal alignment agent obtained by the preparation method described above.

[0084] The liquid crystal alignment agent structure provided by this invention is as follows:

[0085]

[0086] n≥1; where n=10~500, preferably n=50~400, and more preferably n=100~300;

[0087] A represents dianhydride residues, B represents basic diamine residues, and C represents orientation diamine residues.

[0088] The aforementioned polyimide can be a fully imidized product obtained by completely dehydrating and ring-closing the amic acid structure of polyamic acid or the amic acid ester structure of polyamic acid, or a partially imidized product in which only a portion of the amic acid or amic acid ester structure is dehydrated and ring-closed, and the amic acid or amic acid ester structure coexists with the imide ring structure. For the polyimide used, the imidization rate is preferably 20% or more, and from the perspective of ensuring solubility relative to the solvent, it is preferably 90% or less, more preferably 60% or less. This imidization rate is a value expressed as a percentage of the total number of amic acid or amic acid ester structures and the total number of imide ring structures in the polyimide. Here, a portion of the imide ring may be an isoimide ring.

[0089] The present invention also provides the application of the liquid crystal alignment agent in liquid crystal films or liquid crystal cells.

[0090] By using the aforementioned liquid crystal alignment agent, a liquid crystal alignment film can be manufactured. Furthermore, the liquid crystal display element of the present invention includes a liquid crystal alignment film formed using the aforementioned liquid crystal alignment agent. There are no particular limitations on the operating mode of the liquid crystal display element of the present invention; for example, it can be applied to various operating modes such as TN (Twisted Nematic) type, STN type, vertical alignment type (including VA-MVA type, VA-PVA type, etc.), in-plane switching type (IPS type), FFS (Fringe Field Switching) type, and optically compensated bending type (OCB type).

[0091] The liquid crystal display element of the present invention can be manufactured, for example, by a process comprising steps 1.1 to 1.5. In step 1.1, the substrate used varies depending on the desired operating mode. The operating modes in steps 1.2 to 1.5 are common.

[0092] 1.1 Coating

[0093] First, the liquid crystal alignment agent of this invention is coated onto a substrate, and then a coating film is formed on the substrate by heating the coated surface. The printing method is not limited to, but includes, letterpress coating, spin coating, and inkjet printing. Generally, materials such as glass, flexible PET film, and flexible PI film with etched patterns are used as the backing material for the PI liquid crystal alignment film. As the substrate, for example, float glass, soda-lime glass, and borosilicate glass can be used; or transparent substrates made of plastics such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polycarbonate, PET, and flexible PI film can be used. The transparent conductive film on the backing material can be indium tin oxide or other transparent metal oxide coatings. The baking equipment used includes, but is not limited to, high-temperature ovens, vacuum ovens, hot plate curing ovens, and infrared radiation curing ovens. The pattern is formed by photolithography.

[0094] 1.2 Pre-baking

[0095] After coating the liquid crystal alignment agent, the substrate with the film layer needs to be pre-baked to allow the solvent to evaporate and the film layer to change from a wet film to a dry film. The pre-baking temperature is preferably 30–200°C, more preferably 60–150°C, and even more preferably 60–120°C. The pre-baking time is preferably 0.25–30 minutes, more preferably 0.5–8 minutes.

[0096] 1.3 Curing Process

[0097] One purpose of curing is to completely remove the solvent; another is to thermally imidize the amyl acid structures present in the polymer. The preferred curing temperature for the first stage is 80–300°C, more preferably 100–300°C, and even more preferably 100–250°C. The preferred curing time for the first stage is 5–200 min, more preferably 10–100 min, and even more preferably 15–60 min. The baking equipment used is not limited to high-temperature ovens, vacuum ovens, hot plate curing ovens, infrared radiation curing ovens, etc.

[0098] The thickness of the coating after drying is preferably 50-200 nm, more preferably 80-150 nm, and even more preferably 80-120 nm.

[0099] 1.4 Orientation Process

[0100] When manufacturing TN, STN, IPS, OCB, or FFS type liquid crystal display elements, the coating film formed in step 1.3 above is subjected to a process that imparts liquid crystal alignment capability. This imparts alignment capability to the liquid crystal molecules, thus creating a liquid crystal alignment film. Examples of the process for imparting alignment capability include: winding a cloth made of fibers such as nylon, rayon, or cotton onto a roller and rubbing the coating film in a specific direction with the roller; or photoalignment treatment by irradiating the coating film with polarized or unpolarized radiation. On the other hand, when manufacturing VA type liquid crystal display elements, the coating film formed in step 1.3 above can be used directly as a liquid crystal alignment film, or an alignment capability process can be applied to the coating film. When imparting liquid crystal alignment capability to the coating film through photoalignment treatment, the radiation irradiating the coating film can be, for example, ultraviolet light or visible light containing wavelengths of 150–800 nm, preferably ultraviolet light of 200–400 nm. If the radiation is polarized light, it can be linearly polarized or partially polarized light. Furthermore, when the radiation used is linearly polarized or partially polarized light, it can be irradiated from a direction perpendicular to the substrate surface, from an oblique direction, or a combination thereof. When irradiating unpolarized radiation, the irradiation direction is set to oblique. Examples of light sources used include low-pressure mercury lamps, high-pressure mercury lamps, deuterium lamps, metal halide lamps, argon resonant lamps, xenon lamps, and excimer lasers. Ultraviolet light in the preferred wavelength range can be obtained by using the light source in conjunction with, for example, filters or diffraction gratings. The radiation dose is preferably 10–5000 mJ / cm². 2 More preferably 30–2000 mJ / cm 2Furthermore, to improve reactivity, the coating film can be heated while simultaneously being irradiated with light. The heating temperature is typically 30–250°C, preferably 40–200°C, and more preferably 50–150°C. Alternatively, when using ultraviolet light containing wavelengths of 150–800 nm, the light-irradiated film obtained in the above process can be directly used as a liquid crystal alignment film, but it can also be fired. The firing temperature in this case is preferably 80–300°C, more preferably 120–250°C. The firing time is preferably 5–200 minutes, more preferably 10–100 minutes. This light alignment treatment is equivalent to light irradiation treatment in a state where the light does not contact the liquid crystal layer. It should be noted that the liquid crystal alignment film after brushing can also be treated as follows: a portion of the liquid crystal alignment film is irradiated with ultraviolet light to change the pretilt angle of that region; or a resist film is formed on a portion of the liquid crystal alignment film surface, followed by brushing in a direction different from the previous brushing process, and then the resist film is removed, resulting in different liquid crystal alignment capabilities in different regions of the liquid crystal alignment film. In this case, the viewing characteristics of the resulting liquid crystal display element can be improved. A liquid crystal alignment film suitable for VA-type liquid crystal display elements can also be used for PSA (Polymer Sustained Alignment) type liquid crystal display elements.

[0101] 1.5 Construction of LCD Display Components

[0102] After successfully fabricating a substrate with a PI liquid crystal alignment film, a SPACER is used as a support between the two substrates. The SPACER can be a PHOTOSPACER, a homogeneous silicon sphere of equal particle size, or a homogeneous plastic microsphere of equal particle size, etc. The particle size is preferably 3 to 20 μm, more preferably 4 to 15 μm, and even more preferably 5 to 10 μm.

[0103] The frame uses a sealant as the sealing material. The sealant can be thermosetting epoxy resin or UV-cured acrylic resin. The sealant generally contains supporting microspheres of appropriate size, such as homogeneous silicon microspheres or homogeneous plastic microspheres of equal particle size. The particle size is preferably 3–20 μm, more preferably 4–15 μm, and even more preferably 5–10 μm. Liquid crystal can be vacuum-filled between the two substrates using a crystal filling machine, directly added via ODF process, or directly sprayed using a spraying process. Different types of liquid crystals are used depending on the display mode, not limited to IPS, FFS, TN, STN, VA, OCB, etc., or liquid crystals with specific characteristics. Precision bonding equipment is used to bond the two substrates after the above processes. Bonding must be done with the PI alignment film side facing each other. The bonding angle is determined according to the display mode of the liquid crystal display, ensuring that the photo-alignment of the two substrates forms a specific angle according to the requirements of the display mode. For example, FFS and IPS can be bonded by using two pieces with the same or opposite alignment directions, while TN mode can be bonded by using two alignment directions with an angle of 90°.

[0104] After liquid crystal filling and frame sealant curing, a liquid crystal display with homogeneous cell thickness is formed. Post-baking and cutting of polarity pad substrates can be performed as needed.

[0105] The liquid crystal display of this invention may or may not require the application of a polarizing film, depending on the display mode. Examples of polarizing films include those made by sandwiching a polarizing film between two protective cellulose acetate films, wherein the polarizing film is a type of film called an "H-film," which is formed by stretching and orienting polyvinyl alcohol while allowing it to absorb iodine; or polarizing films made from the H-film itself.

[0106] Then, by binding ICs, FPCs, inserting PINs, directly connecting via pins, bonding with conductive materials, or soldering, it can be connected to relevant devices to obtain corresponding display content under the drive of electrical signals.

[0107] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0108] The structure used in the following embodiments is as follows:

[0109] Z-1: p-Phenylenediamine

[0110] Z-11: 3,5-Diaminobenzoic acid

[0111] S-4: 2,4-Diaminophenyloctadecyl ether

[0112] S-5: Dihydrocholesterol 3,5-diaminobenzoate

[0113]

[0114] S-6: 4,4'-(1,3-propanedioxy)diphenylamine

[0115]

[0116] G-28: CBDA

[0117] G-40: 1,2,3,4-Tetramethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride

[0118]

[0119] X-1:

[0120]

[0121] X-2:

[0122] X-3:

[0123] BC: Ethylene glycol monobutyl ether; CAS number is 111-76-2.

[0124] Example 1

[0125] At 25°C and under a nitrogen atmosphere, 90 mol of Z-1, 10 mol of S-4 and NMP were added sequentially, and after stirring for 30 minutes, 100 mol of G-28 was added. The mixture was stirred at 25°C for 3 hours to obtain a polyamic acid solution with a solid content of 30%.

[0126] NMP, BC and X-1 were mixed to obtain an auxiliary agent system with a solid content of 6% (the mass ratio of NMP and BC was 50:50, and the amount of X-1 added was 5% of the total mass ratio of diamine and tetracarboxylic dianhydride solids).

[0127] The above polyamic acid solution was mixed with the additive system and stirred for 0.5 h to obtain a liquid crystal alignment agent with a solid content of 6%.

[0128] Examples 2-18, Comparative Examples 1-6

[0129] The reaction parameters of Examples 2-18 and Comparative Examples 1-6 are the same as those of Example 1. The only difference is the added reactants and the ratio between them, as shown in Tables 1 and 2.

[0130] Table 1. Molar ratios of diamine and polycarboxylic dianhydride in the examples and comparative examples.

[0131]

[0132]

[0133] Table 2. Mass percentage of each component in the examples and comparative examples

[0134]

[0135]

[0136] To verify the beneficial effects of the present invention, the photoelectric properties of the liquid crystal cells prepared in the experimental embodiments and comparative examples were tested.

[0137] Characterization of liquid crystal orientation:

[0138] The liquid crystal display elements obtained in the examples and comparative examples were observed using an optical microscope at 50x magnification to detect the presence or absence of abnormal areas in the brightness changes when a 5V voltage was applied / removed. Cases where no abnormal areas were observed were considered to have "good" liquid crystal alignment, while cases where abnormal areas were observed were considered to have "poor" liquid crystal alignment.

[0139] Characterization of the electrical properties of the liquid crystal cell:

[0140] Test equipment: 6254C; VHR measurement conditions: voltage 5V, pulse width 60us / frame, period 1667ms, measurement temperature 23℃ / 90℃.

[0141] Characterization of liquid crystal cell pretilt angle: Test equipment: Shintech Optitro-STD (3STN11); Test wavelength: 591.4nm; Test mode: TN / VA / IPS mode.

[0142] Characterization of liquid crystal cell stability:

[0143] AC aging equipment: signal generator; ±14VAC aging for 72 hours, 30Hz, square wave, room temperature + backlight; High temperature and high humidity aging equipment: constant temperature test chamber; 85℃ / 85%RH aging for 72 hours; Simulated sunlight aging equipment: 300W LED lamp; UVA band 320-390nm; UVB band 270-320nm; aging for 72 hours; UV aging equipment: 10W fisheye UV LED lamp; 325mW / cm² 2 UVA band 320-390nm; aging test 72 hours; testing equipment: Shintech OPTIPRO-micro (1S2N11)

[0144] Measurement method: The absolute value of the difference in pretilt angle before and after aging of the liquid crystal cell was measured using Shintech Optitro-STD (3S1N11).

[0145] The evaluation results of the pretilt angle stability are as follows:

[0146] T1: ΔPretiltAngle < 0.1°, good stability; T2: ΔPretiltAngle is between 0.1 and 0.5°, moderate stability; T3: ΔPretiltAngle > 0.5°, poor stability.

[0147] Characterization of the resistivity of liquid crystal alignment films:

[0148] Testing equipment: electrometer / high resistance meter (KEYSIGHT B2985A), sample thickness 5-50 micrometers, effective area 30-60 cm². 2 Test parameters: voltage measurement range 1μV-20V, measurement resolution 0.01fA, 2000 readings / s.

[0149] The specific test results are shown in Table 3:

[0150] Table 3. Performance test results of liquid crystal alignment agents prepared in the examples and comparative examples.

[0151]

[0152]

[0153] As can be seen from the above embodiments, the present invention provides a method for preparing a liquid crystal alignment agent, comprising the following steps: mixing a diamine solution with tetracarboxylic dianhydride to obtain a polyamic acid solution; adding an auxiliary agent system to the polyamic acid solution to obtain the liquid crystal alignment agent; the auxiliary agent system comprising a polar aprotic solvent, a leveling agent, and a stabilizer. The liquid crystal alignment agent obtained by the present invention effectively increases the anchoring ability of the alignment film to the liquid crystal, resulting in a very stable alignment effect of the alignment film, free from defects, and exhibiting excellent stability of the pretilt angle and good reliability.

[0154] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a liquid crystal alignment agent, characterized in that, Includes the following steps: (1) A polyamic acid solution is obtained by mixing a diamine solution with a tetracarboxylic acid dianhydride; (2) The liquid crystal alignment agent is obtained by adding an auxiliary agent system to a polyamic acid solution; The additive system includes a polar aprotic solvent, a leveling agent, and a stabilizer; The molar ratio of the diamine to the tetracarboxylic dianhydride is 100:80~100; The solid content of the polyamic acid solution is 10-50%; The mass ratio of the polar aprotic solvent to the leveling agent is 20~80:20~80; The stabilizer is: , or ; The mass of the stabilizer is 0.01~20% of the sum of the masses of the diamine and the tetracarboxylic dianhydride; The solid content of the liquid crystal alignment agent is 1-10%.

2. The preparation method according to claim 1, characterized in that, The solvent in the diamine solution in step (1) is N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, m-cresol or tetrahydrofuran.

3. The preparation method according to claim 2, characterized in that, The diamine mentioned in step (1) includes a basic diamine and an orientation diamine; The molar ratio of the basic diamine to the orientation diamine is 0.01~100:0.01~50.

4. The preparation method according to claim 3, characterized in that, The basic diamine is: ； X1 and X2 are independently hydrogen atoms, alkyl groups with 1 to 10 carbon atoms, alkenyl chains with 2 to 10 carbon atoms, and alkynyl chains with 2 to 10 carbon atoms; The structure of Z1 is as follows: ； Among Z-25, Z-26, Z-27, Z-28, Z-92, Z-93 and Z-97, n independently ranges from 2 to 10; In Z-116, Z-118, Z-129, Z-131, Z-166 and Z-185, n is independent and ranges from 1 to 20; In Z-130, n is 0~20; In Z-156 and Z-161, n is independently 1 to 5; In Z-96, the number of R2 is 1 to 8, and R2 can be H, F, Cl, Br, I, CH3, CF3, CN or a benzene ring; In Z-131, the number of R4 is 1 to 2, and the R4 can be F, Cl, Br, I, CH3, CF3 or CN, or a benzene ring. In Z-138, the number of R5 is 1 to 2, and the R5 can be F, Cl, Br, I, CH3, CF3 or CN, or a benzene ring. In Z-174, the number of R6 is 1 to 2, and R6 can be -COO, -OCO, -NHCO, -N(CH3)CO or a benzene ring. The structure of the orientation diamine is: 2,4-diaminophenyl octadecyl ether, dihydrocholesterol 3,5-diaminobenzoate, or 4,4'-(1,3-propanedioxy)diphenylamine.

5. The preparation method according to claim 3 or 4, characterized in that, The tetracarboxylic acid dianhydride is: ； In G-19, n is 0~20; In G-3, the number of R9 is 1 to 2. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group. In G-40, the number of R9 is 1 to 4. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group. In G-41, the number of R9 is 1 to 5. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group. In G-42, the number of R9 is 1 to 6. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group. In G-43, the number of R9 is 1 to 6. R9 can be a hydrogen atom, a halogen atom, an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, an alkynyl group with 2 to 6 carbon atoms, or a monovalent organic group with 1 to 6 carbon atoms containing a fluorine atom and a phenyl group.

6. The preparation method according to claim 5, characterized in that, The mixing temperature in step (1) is -15~100℃, and the mixing time is 0.5~48h.

7. The preparation method according to claim 1, characterized in that, The polar aprotic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, m-cresol, and tetrahydrofuran; The leveling agent is ethyl acetate, ethylene glycol monobutyl ether, diethylene glycol diethyl ether, diacetone alcohol, or ethylene glycol butyl ether acetate.

8. The liquid crystal alignment agent obtained by the preparation method according to any one of claims 1 to 7.

9. The application of the liquid crystal alignment agent according to claim 8 in a liquid crystal film or liquid crystal cell.

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