TW201437261A - Liquid crystal alignment agent, liquid crystal alignment film, and liquid crystal display device having thereof - Google Patents

Abstract

A liquid crystal alignment agent including a polyamide acid derivative (A) is disclosed. The liquid crystal alignment agent can be employed to form a liquid crystal alignment film with stable pretilt angle and excellent film formability.

Description

Liquid crystal alignment agent, liquid crystal alignment film and liquid crystal display element thereof

The present invention relates to a liquid crystal alignment agent and a liquid crystal alignment film and liquid crystal display element produced thereby.

In order to improve the image quality of the liquid crystal display element, the liquid crystal alignment film should have the following properties: (1) Good electrical characteristics: no image sticking, high voltage holding ratio, and the like. (2) Stable pretilt angle: The liquid crystal molecules and the liquid crystal alignment film surface must be inclined at an angle, so that the liquid crystal molecules can be rotated in a fixed direction after being driven by the electric field to achieve a uniform alignment effect, and the tilt angle is the pretilt angle (Pretilt Angle) ), the stability of the pretilt angle affects the reaction time and alignment uniformity of the liquid crystal display element, thereby affecting the image quality. (3) Excellent brush film property: When the liquid crystal alignment film is coated on the substrate, no rubbing brush marks and cutting debris are generated.

With the popularization of liquid crystal display elements, consumers are increasingly demanding the imaging quality of liquid crystal display elements, and how to further improve the imaging quality of liquid crystal display elements is a goal of related companies.

Accordingly, it is an object of the present invention to provide a liquid crystal alignment agent which can provide a stable pretilt angle by using a liquid crystal alignment film, which contributes to shortening the reaction time of the liquid crystal display element and improving the alignment uniformity thereof. , thereby improving its image quality.

Another object of the present invention is to provide a liquid crystal alignment agent which has excellent film properties.

According to one embodiment of the present invention, there is provided a liquid crystal alignment agent comprising a poly-proline derivative (A) having a structure as shown in the formula (I), in the formula (I), A1 and A2 Each is an independent tetravalent organic group, and each of A3 and A4 is an independent divalent organic group, and R is a monovalent organic group, k+p=1, and 0.01 k:

According to the liquid crystal alignment agent described above, a polyimine, a polyaminic acid or a quinone imine-proline copolymer may be further included.

According to the foregoing liquid crystal alignment agent, wherein R may be an organic group represented by formula (III), formula (IV) or formula (V):

In the formulae (III) to (V), R1 may be an alkyl group having 1 to 20 carbon atoms, an alicyclic group having 4 to 22 carbon atoms, an organic group represented by the formula (VI) or a formula (VII). Organic base:

In the formula (VI) and the formula (VII), R2 may be benzene, cyclohexane, an alkyl group having 1 to 20 carbon atoms or an alicyclic group having 4 to 22 carbon atoms, and R3 is hydrogen and has a carbon number of 1 to An alkyl group of 20 or an alicyclic group having a carbon number of 4 to 22.

According to the liquid crystal alignment agent described above, the reactant in the formation reaction of one of the polyamic acid derivatives (A) may comprise tetracarboxylic dianhydride (a-1), diamine (a-2) and monoamine (a- 3).

According to another embodiment of the present invention, there is provided a liquid crystal alignment agent comprising a poly-proline derivative (B) having a structure represented by formula (II), wherein each of A1 and A2 is Independent tetravalent organic group, A3 and A4 are each independent divalent organic group, R is a monovalent organic group, k+m1+m2=1, 0 M1,0<m2, and 0.01 k:

According to another embodiment of the present invention, there is provided a liquid crystal alignment film formed using the liquid crystal alignment agent of any of the above.

According to still another embodiment of the present invention, there is provided a liquid crystal display element comprising the liquid crystal alignment film described above.

The liquid crystal alignment film formed by the liquid crystal alignment agent can provide a stable pretilt angle and excellent brush film property, and thus the liquid crystal display element made of the liquid crystal alignment film can satisfy the market demand.

Polyproline derivatives (A)

Poly-proline derivative (A) having the structure shown in formula (I): In formula (I), each of A1 and A2 is an independent tetravalent organic group, and each of A3 and A4 is an independent divalent organic group, and R is a monovalent organic group, k+p=1, and 0.01. k. Preferably, 0.05 k 0.7; more preferably, 0.05 k 0.4.

Wherein R may be an organic group represented by formula (III), formula (IV) or formula (V):

In the formulae (III) to (V), R1 may be an alkyl group having 1 to 20 carbon atoms, an alicyclic group having 4 to 22 carbon atoms, an organic group represented by the formula (VI) or a formula (VII). Organic base:

In the formula (VI) and the formula (VII), R2 may be benzene, cyclohexane, an alkyl group having 1 to 20 carbon atoms or an alicyclic group having 4 to 22 carbon atoms, and R3 is hydrogen and has a carbon number of 1 to An alkyl group of 20 or an alicyclic group having a carbon number of 4 to 22.

The formation reaction of the polyproline derivative (A) can be carried out in an organic solvent by using tetracarboxylic dianhydride (a-1), diamine (a-2) and monoamine (a-3) as reactants. The reaction comes.

Polyproline derivatives (B)

Poly-proline derivative (B), the structure of which is represented by formula (II). In formula (II), each of A1 and A2 is an independent tetravalent organic group, and each of A3 and A4 is an independent divalent organic group. Base, R is a monovalent organic group, k+m1+m2=1,0 M1,0<m2, and 0.01 k; preferably, 0.05 k 0.7; more preferably, 0.05 k 0.4:

The polyglycine derivative (B) can be obtained by subjecting the polyproline derivative (A) to a dehydration ring-closure reaction, and when m1>0, it means that the polyamine can be obtained. The acid derivative (A) undergoes a partial dehydration ring closure reaction, and when m1 = 0, it indicates that the polyproline derivative (A) is subjected to a complete dehydration ring closure reaction.

Tetracarboxylic dianhydride (a-1)

The tetracarboxylic dianhydride (a-1) may be, but not limited to, the structure represented by the formula (a-1-1), the formula (a-1-2) or the formula (a-1-3):

The above tetracarboxylic dianhydride (a-1) may be used singly or in combination of two or more. The tetracarboxylic dianhydride (a-1) can also be used together with other tetracarboxylic dianhydrides without affecting the performance of the liquid crystal alignment film.

Diamine (a-2)

The diamine (a-2) may be, but not limited to, the structure represented by the formula (a-2-1) or the formula (a-2-2): The above diamines (a-2) may be used singly or in combination. The diamine (a-2) can also be used together with other diamines without affecting the performance of the liquid crystal alignment film.

Monoamine (a-3)

The monoamine (a-3) may be, but not limited to, the structure represented by the formula (a-3-1) or the formula (a-3-2): The above monoamines (a-3) may be used singly or in combination. The monoamine (a-3) can also be used together with other monoamines without affecting the performance of the liquid crystal alignment film.

Method for synthesizing polyaminic acid derivative (A)

The tetracarboxylic dianhydride (a-1), the diamine (a-2), and the monoamine (a-3) are used as a reactant, and polymerization is carried out in an organic solvent (a-4) to obtain a polyfluorene. A solution of the amino acid derivative (A).

Specifically, first, the first-stage reaction is carried out in the organic solvent (a-4) with the tetracarboxylic dianhydride (a-1) and the monoamine (a-3), and the temperature is from room temperature to 100 ° C to 1 to 5 hours, in this stage of the reaction, the equivalent ratio of the amine group of the monoamine (a-3) to the acid anhydride group of the tetracarboxylic dianhydride (a-1) may be 1:1 to 3:1, preferably, It is 1:1.

Thereafter, a chlorinating agent such as thionyl chloride is added to the product of the first-stage reaction to carry out the second-stage reaction (ie, chlorination reaction), and is carried out at room temperature for 1 to 5 hours. The equivalent ratio of the chlorinating agent to the acid anhydride group of the tetracarboxylic dianhydride (a-1) may be from 1:1 to 3:1, preferably from 1:1.

Next, a diamine (a-2) and a tetracarboxylic dianhydride (a-1) are added to the product of the second-stage reaction for a third-stage reaction, and the temperature is from room temperature to 60 ° C for 1 to 10 hours. A solution containing the polyamine derivative (A) is obtained. In this stage of the reaction, the equivalent ratio of the amine group of the diamine (a-2) to the acid anhydride group of the tetracarboxylic dianhydride (a-1) may be 0.5: From 1 to 2:1, preferably from 0.7:1 to 1.5:1.

Finally, the solution containing the poly-proline derivative (A) is poured into a solvent having a poor solubility to precipitate, thereby obtaining a precipitate, which is washed and then dried under reduced pressure to obtain a precipitate. Poly-proline derivative (A). The obtained polyglycine derivative (A) can be purified one or more times, and the purification step is as follows: the polyproline derivative (A) is dissolved in an organic solvent (a-4), and the solvent is poorly soluble. Precipitation was carried out to obtain a precipitate, and the precipitate was washed and dried under reduced pressure.

The aforementioned organic solvent (a-4), comprising a poly-proline derivative (A) An organic solvent (a-4-1) having a relatively good solubility and an organic solvent (a-4-2) having a poor solubility. The organic solvent (a-4-1) having a better solubility includes, but is not limited to, N-methyl-2-pyrrolidone (a-4-1-1), N,N-dimethylformamide, N,N. - dimethyl acetamide, N-methyl caprolactam, dimethyl hydrazine, tetramethyl urea, hexamethylphosphonium, γ-butyrolactone, pyridine, the above organic solvent with better solubility ( A-4-1) may be used singly or in combination of two or more.

The organic solvent (a-4-2) having a poor solubility may also be used in combination with the above-mentioned organic solvent (a-4-1) having a preferable solubility, provided that the polyamine derivative (A) is not precipitated. The poorly soluble organic solvent (a-4-2) includes but is not limited to: methanol, ethanol, isopropanol, n-butanol, cyclohexanol, ethylene glycol, ethylene glycol methyl ether, ethylene glycol monoethyl Ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethyl ether, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate , tetrahydrofuran, dichloromethane, chloroform, 1,2-dichloroethane, benzene, toluene, xylene, n-hexane, n-heptane, n-octane.

Method for synthesizing polyamine derivative (B)

In the method for synthesizing the poly-proline derivative (A), the solution containing the poly-proline derivative (A) obtained in the third-stage reaction is subjected to a dehydration ring-closure reaction to obtain a polyglycine derivative (B). The solution, the reaction conditions and the extraction method are the same as the conventional polyglycine dehydration ring closure to obtain a polyimine, which will not be described herein.

Liquid crystal alignment agent

The liquid crystal alignment agent of the present invention comprises a polyindoline derivative (A) or a polyindoline derivative (B), an organic solvent (C), and optionally an additive (D).

The liquid crystal alignment agent of the present invention may further comprise polyiminoimine (E), polylysine (F) or quinone imine-proline copolymer (G) to improve the properties of the liquid crystal alignment agent.

The polyphthalic acid derivative (A) or the polyproline derivative (B) is dissolved in an organic solvent (C) to form a liquid crystal alignment agent. The temperature at which the liquid crystal alignment agent is prepared is preferably from 0 ° C to 150 ° C, more preferably from 20 ° C to 50 ° C.

The liquid crystal alignment agent can adjust the solid content contained therein according to the viscosity and the volatility, and preferably contains a solid content of 1 wt% to 10 wt%. If the solid content is less than 1% by weight, the thickness of the liquid crystal alignment film after coating is too thin to lower the alignment property, and if the solid content is more than 10% by weight, the coating quality is affected.

The aforementioned organic solvent (C) includes, but is not limited to, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylcaprolactam , dimethyl hydrazine, γ-butyrolactone, γ-butyrolactam, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-propyl ether, ethylene glycol monobutyl The above organic solvent (C) may be used in combination of two or more kinds. In addition to the organic solvent (C) exemplified above, an organic solvent (C) can be used as long as it can dissolve the polyamic acid derivative (A) or the polyamic acid derivative (B).

The aforementioned additive (D) may be an organic oxime (oxy)alkyl compound (D-1) or an epoxy compound (D-2).

Liquid crystal alignment film

The method of forming a liquid crystal alignment film comprises the following steps:

First, the liquid crystal alignment agent of the present invention is applied onto a glass substrate having a patterned transparent conductive film to form a coating layer, and the coating method includes, but is not limited to, a roll coating method, a spin coating method, and a printing method, and coating. The method is conventional and will not be repeated here.

Next, the coating layer is baked by heating to form a coating layer of the liquid crystal alignment film. The purpose of the heat baking is to remove the organic solvent (C) in the liquid crystal alignment agent, and at the same time, the poly (proline) derivative (A) or the poly-proline derivative (B) can be subjected to a dehydration ring closure reaction. The heating and baking temperature may be 80 ° C to 300 ° C, more preferably 100 ° C to 240 ° C. The thickness of the liquid crystal alignment film formed is preferably 0.005 to 0.5 μm.

Finally, the liquid crystal alignment film is directionally rubbed by a roller wound with a nylon or cotton fiber cloth, so that the liquid crystal alignment film has an alignment property with respect to the liquid crystal molecules.

Liquid crystal display element

The method of forming a liquid crystal display element comprises the following steps:

First, a sealant is applied onto a glass substrate having the liquid crystal alignment film, and a spacer is sprayed on another glass substrate having the liquid crystal alignment film.

Next, the two glass substrates having the liquid crystal alignment film described above are combined in such a manner that the brush directions of the films are perpendicular to each other or parallel to each other.

Finally, liquid crystal is injected into the gap between the two glass substrates, and the injection holes are sealed to form a liquid crystal display element.

Evaluation method of liquid crystal display element

(1) Pretilt angle stability: The liquid crystal display element which has been injected into the liquid crystal (ZLI-4792) is measured by the crystal rotation method, and the degree of variability of the pretilt angle is calculated based on the measurement result. Specifically, first, the pretilt angle measurement values of nine points in the liquid crystal display element are obtained by the crystal rotation method, and the difference between the maximum value and the minimum value among the nine pretilt angle measurement values is used as the variability of the pretilt angle, and the variation of the pretilt angle. The smaller the degree, the higher the stability of the pretilt angle. When the variability of the pretilt angle is less than 0.1, the stability of the pretilt angle is determined to be excellent. When the variability of the pretilt angle is 0.1 to 0.2, the stability of the pretilt angle is determined to be medium, and when the variability of the pretilt angle is greater than 0.2, the pretilt angle is determined. The stability is poor. The method for measuring the pretilt angle conventionally used in the above-described crystal rotation method is not described herein.

(2) High temperature pretilt angle variation: the liquid crystal alignment agent is coated on the substrate, and heated and baked at 210 ° C, 220 ° C and 230 ° C, respectively, and finally combined into a liquid crystal display element; measured at three temperatures by a crystal rotation method The pretilt angle, each liquid crystal display element measures 10 points and averages them, taking the difference between the maximum value and the minimum value as a criterion for evaluation, and the smaller the value, the better the property.

(3) Brush film property: The liquid crystal alignment agent is applied on a tin indium oxide (ITO) substrate by spin coating, and baked in an oven at a speed of 1000 rpm, and a platform moving speed of 60 mm/sec. The amount of the film was 0.4 μm, and the film was oriented 3 times. The liquid crystal after the brush film was visually observed by a polarizing microscope. On the surface of the alignment film, no brush marks and chip defects were observed to be excellent, and it was observed that the brush marks and chips were judged to be inferior.

(4) ¹ H-NMR: A sample was placed in an NMR tube, and the sample was dissolved in deuterated chloroform, and it was measured using an NMR analyzer manufactured by Bruker Corporation (Model: Waters 2487).

(5) Polymer molecular weight measurement: using a gel permeation chromatography (GPC) device manufactured by Waters Corporation (model: Bruker AVANCE 400 MHz), at a column temperature of 35 ° C, will contain Lithium bromide and dimethylformamide (DMF) of phosphoric acid were used as rinse liquids, and the weight average molecular weight and the number average molecular weight were obtained by converting the time of passage through polystyrene.

Example

(1) Synthesis of monoamine (a-3-1), polyproline derivatives (A-1) to (A-6), and quinone imine-proline copolymer (G-1):

Synthesis Example 1: Synthesis of monoamine (a-3-1):

The reaction formula for the synthesis of the monoamine (a-3-1) is as follows. First, the intermediate product (w) is synthesized, and then the intermediate product (w) is used to synthesize the monoamine (a-3-1): .

First, in a 2 liter reaction flask, 102 g (550 mM) of 4-nitrobenzoyl chloride, 1200 g of Toluene, and 75.9 g of Potassium carbonate were added. 550 mmol; stir at room temperature for 5 minutes. Further, 126 g (500 mmol) of 4-(4'-n-pentyl)-dicyclohexanol (4-(4'-pentyl)-dicyclohexylanol) was dissolved in 200 g of toluene, and slowly dropped into the aforementioned reaction bottle. After the completion of the whole dropwise addition, the mixture was further stirred at room temperature for 4 hours, extracted with pure water for 3 times, and the organic layer was dried over magnesium sulfate. The filtrate was collected by filtration and concentrated to dryness under reduced pressure to give intermediate product (w). 188.5 g (470 mmol) with a yield of 94%. The spectral data of the intermediate product (w) are: ¹ H NMR (400 MHz, CDCl3) δ 8.30~8.23 (2H), 8.15~8.20 (2H), 5.24~5.36 (0.6H), 4.85~4.95 (0.4H), 0.8~2.1 (30H)ppm.

Thereafter, in another 2 liter reaction flask, an intermediate product (w) of 188.5 g (470 mmol), 1000 g of toluene, 10 g of a 10% palladium-on-carbon catalyst (10 g, and stirring 10) was added. minute. Further, 50 ml of 80% aqueous hydrate (80% Hydrazine hydrate) was slowly added dropwise to the above reaction flask, and the mixture was stirred for 4 hours. The reaction temperature was lowered to room temperature, suction filtered, and the filtrate was collected, and the solvent was concentrated under reduced pressure to give 174 g (yield: 470 m) of monoamine (a-3-1) in a yield of 100%. Spectral data of monoamine (a-3-1): ¹ H NMR (400 MHz, CDCl3) δ 7.80~7.86 (2H), 6.58~6.65 (2H), 5.15~5.20 (0.6H), 4.75~4.85 (0.4 H), 3.96~4.06 (2H), 0.8~2.1 (30H) ppm.

Synthesis Example 2: Synthesis of polyproline derivative (A-1):

In a reaction flask, 1.49 g (4 mmol) of monoamine (a-3-1) and 0.39 g (2 mmol) of tetracarboxylic dianhydride (a-1-1) were added to 30 g. N-methyl-2-pyrrolidone (a-4-1-1) was stirred at room temperature for 2 hours, then the product in the reaction flask was subjected to a chlorination reaction for 2 hours, and a diamine (a-2) was continuously added. -1) 7.37 g (20 mmol) was stirred for 2 hours, and finally 3.53 g (18 mmol) of tetracarboxylic dianhydride (a-1-1) was added and stirred at room temperature for additional 3 hours. The reaction solution was poured into deionized water to precipitate a polyamine derivative (A-1), which was collected, washed several times with methanol, and then dried under vacuum at 60 to 70 °C. The resulting polyamine derivative (A-1) had a number average molecular weight (Mn) of 12,000 and a weight average molecular weight of 31,000 (Mw).

Synthesis Example 3-7: Synthesis of Polyproline Derivatives (A-2) to (A-6):

When the polyproline derivatives (A-2) to (A-6) were replaced at each stage and the synthesis example 2 was replaced, the following Table 1 is listed, and the remaining synthesis steps and conditions are the same as in Synthesis Example 2.

Synthesis Example 8: Synthesis of quinone imine-proline copolymer (G-1):

In a reaction flask, tetracarboxylic dianhydride (a-1-1) 4.90 g (25 mmol) and tetracarboxylic dianhydride (a-1-2) 13.51 g (45 mmol) were sequentially placed. 4,5 g (25 mmol) of tetracarboxylic dianhydride (a-1-3) and 36.84 g (100 mmol) of diamine (a-2-1) were added to 243 g of N-methyl-2- In the pyrrolidone (a-4-1-1), a solution having a solid content of 20% by weight is prepared and reacted at a temperature of from 40 ° C to 50 ° C for from 4 hours to 5 hours to obtain a solution containing poly-proline. 14 g of pyridine and 8 g of acetic anhydride were added to the above polyamic acid solution, and dehydration ring-closure reaction was carried out at 100 ° C to 110 ° C for 3 to 4 hours. The obtained solution was poured into methanol to carry out precipitation to obtain a quinone imine-proline copolymer (G-1), and finally, the quinone imine-proline copolymer (G-1) was washed with methanol. Drying was carried out under reduced pressure. The resulting quinone imine-proline copolymer (G-1) had a number average molecular weight of 22,000 and a weight average molecular weight of 62,000.

(II) Preparation and Experimental Methods of Liquid Crystal Aligning Agents of Examples 1 to 12:

Poly-proline derivatives (A-1)~(A-6) and quinone imine-guanamine A polymer such as an acid copolymer (G-1) is dissolved in a mixed solvent of γ-butyrolactone and N-methyl-2-pyrrolidone according to the ratio shown in Table 2 to prepare a solution having a solid content of 6 wt%. And filtering with a filter having a diameter of 0.45 μm, the collected filtrate is the first to the twelfth embodiment of the liquid crystal alignment liquid of the present invention.

The liquid crystal alignment agent of each of the above examples was applied onto a glass substrate by a roller printer, and dried on a hot plate at 200 ° C for 20 minutes to form a film having a thickness of 0.08 μm. The film was subjected to directional rubbing at a roller rotation speed of 1000 rpm, a platform moving speed of 60 mm/sec, and a press-in amount of 0.4 μm.

The frame filler is coated on the glass substrate having the liquid crystal alignment film, and the spacer is sprayed on the glass substrate of the other liquid crystal alignment film, and the two glass substrates having the liquid crystal alignment film are mutually perpendicular to each other. The liquid crystal display element is formed by injecting liquid crystal (ZLI-4792) into the gap between the two glass substrates and sealing the injection hole.

The obtained liquid crystal display element was evaluated for pretilt angle, pretilt stability, and brushing property. The evaluation results are shown in Table 2.

It can be seen from Table 2 that the pretilt angle stability of Examples 1 to 12 is above medium and high, and the high temperature pretilt angle variation is only 0.24 at the maximum, and the brush film property is excellent. Therefore, the present invention is utilized by the liquid crystal alignment agent. The addition of the polyaminic acid derivative (A) allows the resulting liquid crystal alignment film to have a stable pretilt angle and excellent brush film properties.

In Table 2, except for the pretilt stability of Example 6 and Example 10, the pretilt stability of the other examples was excellent. As a matter of view, the contents of the polyamine derivatives (A) of Examples 1 to 5, Examples 7 to 9, and Examples 11 to 12 are higher than those of Examples 6 and 10, that is, polypyrene The amino acid derivative (A) can improve the stability of the pretilt angle of the liquid crystal alignment film.

According to the above embodiment, the liquid crystal alignment film prepared by the liquid crystal alignment agent has a stable pre-preparation by adding a poly-proline derivative (A) or a poly-proline derivative (B) to the liquid crystal alignment agent. The tilt angle and excellent brush film properties can improve the image quality of the liquid crystal display element to meet market demands.

Although the present invention has been disclosed above in the embodiments, it is not The scope of the present invention is defined by the scope of the appended claims, which are defined by the scope of the appended claims. quasi.

Claims (10)

A liquid crystal alignment agent comprising: a poly-proline derivative (A) having a structure as shown in formula (I): In formula (I), each of A1 and A2 is an independent tetravalent organic group, and each of A3 and A4 is an independent divalent organic group, and R is a monovalent organic group, k+p=1, and 0.01. k. The liquid crystal alignment agent of claim 1, further comprising: a polyimine, a polyaminic acid or a quinone imine-proline copolymer. The liquid crystal alignment agent of claim 1, wherein the R is an organic group represented by the formula (III), the formula (IV) or the formula (V): In the formulae (III) to (V), R1 is an alkyl group having 1 to 20 carbon atoms, an alicyclic group having 4 to 22 carbon atoms, an organic group represented by the formula (VI) or a formula (VII). Organic base: In the formula (VI) and the formula (VII), R2 is benzene, cyclohexane, an alkyl group having 1 to 20 carbon atoms or an alicyclic group having 4 to 22 carbon atoms, and R3 is hydrogen and having a carbon number of 1 to 20 The alkyl group or the alicyclic group having a carbon number of 4 to 22. The liquid crystal alignment agent of claim 1, wherein the reactant in the one of the polyamic acid derivatives (A) is a tetracarboxylic dianhydride (a-1), a diamine (a-2), and a single Amine (a-3). The liquid crystal alignment agent of claim 4, wherein the tetracarboxylic dianhydride (a-1) comprises the formula (a-1-1), the formula (a-1-2) or the formula (a-1-3) Structure: The liquid crystal alignment agent of claim 4, wherein the diamine (a-2) comprises a structure represented by the formula (a-2-1) or the formula (a-2-2): The liquid crystal alignment agent of claim 4, wherein the monoamine (a-3) comprises a structure represented by the formula (a-3-1) or the formula (a-3-2): A liquid crystal alignment agent comprising: a poly-proline derivative (B) having a structure as shown in formula (II): In formula (II), each of A1 and A2 is an independent tetravalent organic group, and each of A3 and A4 is an independent divalent organic group, and R is a monovalent organic group, and k+m1+m2=1,0 M1,0<m2, and 0.01 k. A liquid crystal alignment film formed of the liquid crystal alignment agent according to any one of claims 1 to 8. A liquid crystal display element comprising the liquid crystal alignment film of claim 9.